Preface

Benzimidazole is an aromatic, heterocyclic molecule containing C, H, N, and S formed from the benzene and imidazole moieties. Benzimidazole derivatives have attracted much interest from researchers due to their biological activities and clinical applications. Benzimidazole nucleus is also a constituent of Vitamin B12. Benzimidazole derivatives act as promising bioactive compounds and exhibit a range of biological activities like anticancer, antimicrobial, antiviral, anticonvulsant, antiproliferative, antioxidant, and antiparasitic properties. The increased interest in benzimidazole compounds is due to their bioavailability, increased stability, significant biological activity, and so on.

A vast number of benzimidazole derivatives have been reported and studies on their mechanism of action, structural features, and pharmacological applications have been carried out to achieve more stable and active pharmaceutical drugs. Interesting features of benzimidazole derivatives include their N-donor ligands and the physical interaction of double bound with other ring systems.

This book examines aspects and newer mechanisms of benzimidazoles containing heterocyclic moiety. Chapters report on anticancer properties of benzimidazole derivatives, novel methods of synthesis of benzimidazoles, versatile nature of the benzimidazoles, spectral and theoretical studies of benzimidazole derivatives, and medicinal importance and pharmacological aspects of benzimidazole derivatives.

The editors are thankful to Lancashire University, UK, and the director of the Angadi Institute of Technology and Management for her support.

> **Dr. Pravin Kendrekar** Visiting Scientist, Lipid Nanostructure Laboratory, University of Central Lancashire, Preston, Preston, United Kingdom

**Dr. Vinayak Adimule** Professor and Dean R&D, Department of Chemistry, Angadi Institute of Technology and Management, Belagavi, India

Section 1

## Anticancer Properties of Benzimidazole

#### **Chapter 1**

## Advances of Benzimidazole Derivatives as Anticancer Agents: Bench to Bedside

*Kashif Haider and Mohammad Shahar Yar*

#### **Abstract**

Benzimidazole is one of the privileged nitrogen-containing scaffolds known for its versatile diversified role in insecticides, pesticides, dyes, pigments and pharmaceuticals. Due to its electron-rich environment, structural features and binding potency of various therapeutic targets, benzimidazole derivatives exhibit a broad spectrum of biological activity that majorly includes antimicrobial, antifungal, analgesics, anti-diabetic and anticancer agents. Several benzimidazole scaffolds bearing drugs are clinically approved; they are used for various indications. For example, Bilastine, Lerisetron, Maribavir and Nocodazole are the most widely used benzimidazolebased marketed drugs available as an antihistamine, antiviral and antimitotic agent, respectively. Another example is the recently approved anticancer drug Binimetinib and Selumetinib, which are indicated for BRAF mutated melanoma and plexiform neurofibromas. Not only this, many benzimidazole-based anticancer drugs are in late phases of clinical development. Due to the vast therapeutic potential of benzimidazole scaffold in cancer research, medicinal chemists have gained a lot of attraction to explore it more and develop novel, highly effective and target-specific benzimidazolebased potential anticancer drugs.

**Keywords:** benzimidazole, enzyme inhibitors, anticancer agents, hybrid derivatives

#### **1. Introduction**

Cancer is a complex, severe class of diseases that involves a group of cells that exhibit abnormal and uncontrolled division and proliferation. It is one of the primary health concerns which accounts for the second major cause of death globally. As per the recent statistics of the world health organization (WHO), in 2020, around 10 million people succumbed to death due to cancer. However, every year the number of incidences is increasing day by day. According to WHO, around 0.3 million new cases are diagnosed each year among the age group of 0–19 years. Cancer can affect a person of any age; however, with age, the risk increases. Globally, steady increases in cancer cases every year are taking a toll on the health care system [1–5]. To combat cancer, identification of potential drugs and potential drugs combination is essential. Potential research has been carried out to counter such problems

by addressing novel drug design and discovery approaches. In medicinal chemistry, heterocyclic rings have played a significant role in the search for potential therapeutic agents. Various drugs are currently in use and in development that widely addresses

*Advances of Benzimidazole Derivatives as Anticancer Agents: Bench to Bedside DOI: http://dx.doi.org/10.5772/intechopen.101702*

such problems. However, due to changes in cancer forms and mutations, current therapy faces challenges of poor selectivity and specificity towards certain types of cancer cells, which narrows down their effectiveness. Generally, cancer cells act by disrupting and disturbing the cell signaling pathways; therefore, it is crucial to design novel target-based heterocyclic anticancer compounds with high efficacy and fewer side effects, which will provide a solid backup to the present chemotherapeutic regime [6–10].

#### **2. Benzimidazole**

Benzimidazole is a bicyclic nitrogen bearing aromatic heterocyclic ring, structurally it consists of benzene ring fused with imidazole ring at the 4th and 5th position of the ring. Chemically it appears as white crystals, amphoteric in nature, resembles the structure of purine. It is synthesized by different reported methods. However, condensation of 1,2-diamino benzene with carbonyl compounds to give benzimidazole is the conventional method which was used widely for its preparation. In 1858, it was synthesized by Heinrich Debus, a German chemist from glyoxal, ammonia and formaldehyde, that's why it was also known as glyoxalin. Benzimidazole ring is one of bioactive heterocyclic scaffold exhibiting wide range of biological activities. The ▬NH group present at second position of the ring is both highly acidic and weak base in nature, it also has ability to form stable salts [11–16].

With time benzimidazole ring emerged as an important multifaceted heterocyclic system due to its wide range of pharmacological activity such as antibacterial [17], antiparasitic [18], antifungal [19], anti-inflammatory [20], analgesics [21], antiviral [22], antitubercular [23], anticoagulant [24], antihistaminic [25], antioxidant [26], antiulcer [27] and anticancer [28–31]. Some of the benzimidazole based marketed drugs are listed in with their indication and marketed name in **Figure 1**. Adding to this benzimidazole scaffold have also displayed a significant role in synthesis of organic intermediates. In light of the application of benzimidazole earlier various authors have reported many review articles. Due to the diverse therapeutic potential, benzimidazole have attracted lot of researchers to explore more in the field of drug discovery to synthesize novel and potent compounds with a broad spectrum of biological activities. Owing to this, with time efforts have been made to create libraries of these potent compounds. In cancer treatment benzimidazole based drugs played a significant role, various targeted therapies are designed and developed as Kinase inhibitors such as EGFR, VEGFR and PI3K inhibitors here, in this chapter we have included some potent benzimidazole based kinase inhibitors.

#### **3. Advances of benzimidazole based anticancer agents**

Benzimidazole based compounds have got much attention due to exhibiting significant cytotoxic activity. In last one decade a lot of benzimidazole based anticancer drugs have received status of US FDA global approval. Recently, Binimetinib, Selumetinib and Abemaciclib got approval for treatment of various mutated forms of cancer. Here, we have discussed some of benzimidazole based anticancer drugs which are recently approved, under development and in pipeline.

#### **3.1 Benzimidazole based marketed anticancer drugs**

#### *3.1.1 Binimetinib (***1***)*

Binimetinib (**1**) is chemically 5-((4-bromo-2-fluorophenyl)amino)-4-fluoro-N-(2-hydroxyethoxy)-1-methyl-1H-benzimidazole-6-carboxamide approved by US FDA recently in 2018. It is an orally available, potent selective inhibitor of mitogen activated protein kinase (MEK 1/2). Binimetinib is developed by Array Biopharma, commercially available by the name of Mektovi. It is indicated for patients having metastatic melanoma with BRAF mutation as combination therapy with BRAF inhibitors Encorafenib [32]. Presently, Binimetinib is in various phases of clinical development as monotherapy or in combination for conditions like KRAS mutated cancer, mutated non-small cell lung cancer [33, 34]. Structures of all the drugs are presented in **Figure 2**. More details of clinical trials are enlisted in **Table 1**.

#### *3.1.2 Bendamustine (***2***)*

Bendamustine (**2**) is chemically 4-(5-(bis(2-chloroethyl)amino)-1-methyl-1H-benzimidazol-2-yl)butanoic acid, it is an alkylating agent well known for its efficacy and tolerability in wide range of hematologic malignancies [35]. Bendamustine is indicated for the treatment of chronic lymphocytic leukemia and non-Hodgkin lymphoma [36]. Currently Bendamustine is further investigation as combination therapy along with Bcl-2 inhibitor Venetoclax and Rituximab for treatment of patient above 60 years of age with mantle cell lymphoma (NCT03834688).

**Figure 2.**

*Benzimidazole based clinically approved anticancer agents.*


*Advances of Benzimidazole Derivatives as Anticancer Agents: Bench to Bedside DOI: http://dx.doi.org/10.5772/intechopen.101702*


#### **Table 1.**

*Benzimidazole based anticancer drugs in clinical development.*

#### *3.1.3 Selumetinib (***3***)*

Selumetinib (**3**) is chemically 5-((4-bromo-2-chlorophenyl)amino)-4-fluoro-N- (2-hydroxyethoxy)-1-methyl-1H-benzimidazole-6-carboxamide recently approved by US FDA in on April 10, 2020 for the treatment of plexiform neurofibromas and neurofibromatosis in pediatric patients [37, 38]. Selumetinib is an orally available MEK 1/2 kinase inhibitor developed by AstraZeneca commercially available by the name of Koselugo. It is also received status of orphan drug in USA as adjuvant drug for treatment of thyroid cancer [39, 40].

#### *3.1.4 Abemaciclib (***4***)*

Abemaciclib (**4**) is chemically N-(5-((4-ethylpiperazin-1-yl)methyl)pyridin-2-yl)-5-fluoro-4-(4-fluoro-1-isopropyl-2-methyl-1H-benzimidazol-6-yl) pyrimidin-2-amine, approved by US FDA on 28 September 2017, for the treatment of patients with hormone receptor (HR) positive, human epidermal growth factor receptor (HER-2) advanced/negative metastatic breast cancer as a combination therapy with estrogen receptor antagonist fulvestrant in female patients and as monotherapy in adult patient with diseases progression following chemotherapy. Abemaciclib is commercially available by the name of Verzenio, developed by Eli Lilly as cyclin dependent kinase-4 (CDK4) and CDK6 inhibitor [41]. Furthermore, Abemaciclib is currently in various phase of clinical development as monotherapy or in combination therapy for treatment of various types of cancer and mutated forms [42, 43].

*Advances of Benzimidazole Derivatives as Anticancer Agents: Bench to Bedside DOI: http://dx.doi.org/10.5772/intechopen.101702*

#### *3.1.5 Veliparib (***5***)*

Veliparib (**5**) is chemically (R)-2-(2-methylpyrrolidin-2-yl)-1H-benzimidazole-4-carboxamide, it is an oral PARP inhibitor. Veliparib is investigational drug showed promising results in preclinical and clinical studies when treated for ovarian cancer and for mutated form BRCA-mutated ovarian cancer [44]. Further development of Veliparib is ongoing as monotherapy and combination therapy for treatment of different forms of ovarian cancer [45, 46].

#### *3.1.6 Dovitinib (***6***)*

Dovitinib (**6**) is chemically 4-amino-5-fluoro-3-(5-(4-methylpiperazin-1-yl)- 1H-benzoimidazol-2-yl) quinolin-2(1H)-one, it is a potent orally available pan tyrosine kinase inhibitor targeting VEGFR, FGFR) and other tyrosine kinases [47]. It is a pipeline drug under development, for treatment of gastrointestinal stromal tumor, metastatic breast cancer and renal cell carcinomas. Recently on April 2, 2021 Dovitinib has received acceptance from US FDA for premarket approval (PMA) which was filed by Allarity therapeutics (details can be found on Allarity therapeutics website). Dovitinib is also explored for different typed of mutated forms of cancer, currently it is under phase II clinical trial study for patient with castration resistant prostate cancer [48].

#### *3.1.7 Pracinostat (***7***)*

Pracinostat (7) is chemically (E)-3-(2-butyl-1-(2-(diethyl amino) ethyl)-1H-benzoimidazol-5-yl)-N-hydroxyacrylamide, it is orally available, investigational drug exhibiting potential antitumor activity [49, 50]. Pracinostat is a small molecule next generation histone diacetylases (HDAC) inhibitor indicated acute myeloid leukemia [51]. In some recent study Pracinostat was found to suppresses growth and metastasis of breast cancer by inactivating the IL-6/STAT3 signaling pathway [52].

#### *3.1.8 Galeterone (***8***)*

Galeterone (**8**) is chemically (3S,8R,9S,10R,13S,14S)-17-(1H-benzimidazol-1-yl)- 10,13-dimethyl-2,3,4,7,8,9,10,11,12,13,14,15-dodecahydro-1H-cyclopenta[a]phenanthren-3-ol, it is an orally available, small molecule investigational drug. Galeterone is developed by Tokai pharmaceutical as potent androgen receptor antagonist, indicated for treatment of prostate cancer [53]. Some in vivo studies revealed that Galeterone monotherapy inhibited breast cancer growth, also when administered in combination with cisplatin the results where promising and much better compare to monotherapy of cisplatin [54].

#### *3.1.9 Nazartinib (***9***)*

Nazartinib (**9**) is chemically (R,E)-N-(7-chloro-1-(1-(4-(dimethylamino) but-2-enoyl)azepan-3-yl)-1H-benzo[d]imidazol-2-yl)-2-methylisonicotinamide, it is an orally available third generation EGFR kinase inhibitor under development for treatment of conditions like non-small cell lung cancer (NSCLC) and EGFR mutated NSCLC [55]. Nazartinib have demonstrated favorable safety profile and efficacy in a Phase-I study when administered to adult patients with

EGFR mutated lung carcinoma [56]. However, clinical development of Nazartinib is progress for different forms of mutated carcinomas as monotherapy or in combination [57, 58].

#### **3.2 Benzimidazole based derivatives as potent kinase inhibitors**

Commonly the mechanism behind action of anticancer agents involve DNA intercalation, gene regulation, microtubule inhibition, transcription regulation, DNA synthesis inhibition, enzyme inhibition and so on. Nowadays in cancer treatment, target therapy emerged as one of the acknowledged strategies. Most of the available anticancer drugs acts by targeting structural proteins, tyrosine kinases, phosphoinositide 3 kinase and protein kinases for example Binimetinib acts by inhibiting mitogen activated kinase as discussed in earlier section. In this section we have included some recent examples of benzimidazole based enzyme inhibitors as potent anticancer agents.

#### *3.2.1 EGFR inhibitors*

Akhter et al. have reported a novel series of benzimidazole based oxadiazole derivatives as potential EGFR inhibitors. The target compound **10** and **11** demonstrated significant binding to EGFR with an IC50 value of 0.081 and 0.098 μM respectively. Cytotoxicity of both derivatives against selected human cancer cell line A549, MDA-MB231, MCF7 and HepG2 was found promising. Compound **10** exhibited excellent inhibitory potency with an IC50 value of 15.2 μM, 5.0 μM, 14.5 μM and 12.5 μM whereas compound **11** have shown an IC50 value of 13.2 μM, 2.5 μM, 0.131 μM and 15.6 μM against cancer cell line A549, MCF7, MDA-MB231 and HepG2 respectively. Further findings of these derivatives showed that compound **10** cause cell cycle arrest of MCF7 cells in a dose dependent manner at G2/M phase. Docking analysis of target compound **10** and **11** showed that both the compound made strong interactions within the active site of protein kinase, the binding pattern of target compounds resembles as that of standard drug erlotinib, which is a potent EGFR inhibitor. In vivo acute toxicity of target compound showed that both compounds **10** and **11** are nontoxic and safe with oral LD50 value >500 < 2000 mg/kg which is recommended by OECD guidelines [59].

Srour et al. have reported a novel series of thiazole benzimidazole derivatives as potent inhibitor of EGFR tyrosine kinase. Target compound **12** and **13** displayed significant activity against EGFR kinase with an IC50 value of 71.67 nM and 109.71 nM. Both target compounds are evaluated for cytotoxicity against MCF7 cancer cell lines, compound 4n displayed an IC50 value of 11.91 μM and compound 4a exhibited excellent inhibitory potency with an IC50 value of 6.30 μM against MCF7 cancer cell line respectively. Furthermore, both compound **12** and **13** have shown good inhibition when tested against normal hTERT-RPE1 normal cells with 65 and 11.9% inhibition. Due to balanced bioactivity of target compound **13**, it is further studied for cell cycle analysis against MCF7 cell line, it displayed the cell cycle arrest at G2/M phase. Compound **13** also displayed increase in the expression of p53, Bax/Bcl-2 and caspase-3 expression and remarkable decrease in levels of PARP-1 enzyme. Molecular docking analysis of compound **12** and **13** showed that both the compounds embedded tightly by hydrogen bond formed between the Nitrogen of benzimidazole with amino acid residue Lys721 and Phe699 respectively [60].

#### *Advances of Benzimidazole Derivatives as Anticancer Agents: Bench to Bedside DOI: http://dx.doi.org/10.5772/intechopen.101702*

Akhter et al. have reported as series of pyrazole benzimidazole derivatives as potential inhibitors of EGFR. Target compound **14** and **15** displayed potent activity against EGFR kinase with IC50 value of 0.97 μM and 1.7 μM respectively. In vitro cytotoxicity of both compound showed excellent inhibitory activity against selected cell line, compound **14** displayed an IC50 value of 0.97 μM, 2.2 μM and 11.9 μM and compound 5d displayed an IC50 value of 1.7 μM, 2.8 μM and 15.2 μM against MCF7, A549 and MDA-MB-231 cancer cell lines respectively. Target compound **14** also shown cell cycle arrest at G2/M phase of MCF7 cells by inducing apoptosis. Docking analysis of **14** displayed ability of the respective compound to fit into the active site of EGFR by forming strong hydrogen and hydrophobic within the domain (**Figure 3**) [61].

#### *3.2.2 VEGFR 2 inhibitors*

Abdullaziz et al. have reported a novel series of 2-furybenzimidazole derivatives as potent inhibitors of VEGFR-2 kinase. Target compound **16** and **17** displayed excellent

**Figure 3.** *Examples of benzimidazole derivatives as potent EGFR inhibitors.*

inhibitory activity with total percentage inhibition of 94% and 96% and IC50 value of 0.64 μM and 1.26 μM compared to standard drug Sorafenib (IC50 value 0.1 μM) against VEGFR-2 respectively. In vitro cytotoxicity study of compound **16** and **17** displayed potential inhibitory activity with IC50 range of 8.33–9.86 μM against HepG2 and MCF7 cancer cell lines respectively. Molecular docking analysis of target compound showed a strong binding interaction of 2-furylbenzimidazole moiety within the active site of VEGFR-2 by involving hydrogen bond formation with key amino acid residue Glu885 and Asp1046 [62].

Lien et al. have reported novel 2-aminobenzimidazole derivative **18** as potential inhibitor of VEGFR-2. Target compound **18** exhibited 30% inhibition of kinase activity of VEGFR-2 when treated at a concentration of 10 μM. **18** displayed inhibitions of VEGF-A angiogenic action along with it also suppress MDA-MB-231 cell lines when studied in vivo. Compound **18** displayed anti-angiogenic properties by targeting VEGFR-2 signaling. Target compound **18** also found to reduce lung metastasis of B16F10 melanoma cells in mice models. Molecular docking studies of target compound showed strong binding with in the active site of VEGFR-2 by forming hydrogen bond between nitrogen of benzimidazole with amino acid residue His1026 [63].

Recently Yuan et al. have designed and synthesized a new series of benzimidazole derivatives as potent and selective inhibitor of VEGFR-2 kinase. Target compound **19** displayed excellent inhibitory activity against with VEGFR-2 kinase with an IC50 value of 0.054 μM, it also displayed significant anti-angiogenesis activity. In vitro cytotoxicity study of compound **19** against HepG2 and A549 cancer cell line were found promising with an IC50 value of 2.57 μM and 73.81 μM respectively. Cell cycle analysis of target compound **19** shows that it arrests the HepG2 cells in G0/G1 phase in a dose dependent pattern. Molecular docking analysis of compound **19** demonstrated strong interactions within the ATP binding active site of VEGFR-2 kinase [64] (**Figure 4**).

#### *3.2.3 EGFR/VEGFR-2 dual inhibitors*

Meguid et al. have reported a novel series of benzimidazole derivatives as potent dual inhibitors of EGFR and VEGFR-2 kinases. Target compound **20** and **21** displayed strong inhibitory activity against EGFR kinases, however activity against VEGFR-2 is

**Figure 4.** *Examples of benzimidazole derivatives as potent VEGFR-2 inhibitors.*

#### *Advances of Benzimidazole Derivatives as Anticancer Agents: Bench to Bedside DOI: http://dx.doi.org/10.5772/intechopen.101702*

considerably good. Target compound **20** exhibited an IC50 value of 0.157 μM against EGFR and 123.27 μM against VEGFR-2 kinase. Target compound **21** displayed an IC50 value of 0.109 μM and 69.62 μM against EGFR and VEGFR-2 kinases respectively. Cytotoxicity activity of both compound **9** and **21** was also found excellent against HeLa cancer cell line with IC50 value of 1.62 μM and 1.44 μM compare to standard drug doxorubicin which displayed an IC50 value of 2.05 μM respectively. Cell cycle analysis study revealed that both compounds arrest cell cycle of HeLa cells at G0/ G1 phase. Furthermore, docking analysis showed that target compound **20** and **21** demonstrated strong binding within the active site of HER2 kinase with dock score of −9.4 and −9.7 kcal/mol respectively [65].

Kassab et al. have reported novel quinazoline bearing benzimidazole derivatives as potential inhibitors of EGFR and VEGFR-2 kinases. Target compound 22 displayed excellent inhibitory activity against EGFR kinase with an IC50 value of 127.4 μM, whereas it displayed an IC50 value of 185.7 μM against VEGFR-2 kinase. Further, cytotoxicity study of compound against MCF7 cancer cell line demonstrated good potency with IC50 value of 12.0 μM [66] (**Figure 5**).

#### *3.2.4 PI3K inhibitors*

GSK2636771 (**23**) is a novel, potent, orally available benzimidazole derivatives. It demonstrated selective PI3K beta inhibitor with antineoplastic activity. Preclinical study of GSK2636771 demonstrated selective inhibition of PTEN-deficient cancer cell growth along with inhibition of protein kinase B in a dose and time dependent manner. First in human trial study of GSK2636771 in patients of advanced solid tumors on oral administration as monotherapy demonstrated significant exposure, inhibition of target and excellent safety profile [67, 68].

Jin et al. have reported novel benzimidazole derivatives as potent PI3K inhibitor. Target compound 24 was found most potent against PI3Kα with 36% and 86% inhibition compare to reference drug Alpelisib, which showed an inhibition of 110% and 109% at 50 nM and 500 nM respectively. Further, molecular docking analysis of target compound 24 demonstrated strong binding with six strong hydrogen bond with GLN-859, SER-854 and VAL-851 amino acid residues. Further, HUMO-LUMO calculation which is studied by using Gaussian 09 software target compound 24 showed presence of thiazole core and amide bonds which played an important role in its biological activity [69].

#### **Figure 5.**

*Examples of benzimidazole derivatives as potent EGFR/VEGFR dual inhibitors.*

Recently a novel series of benzimidazole based dehydroabietic acid derivatives were reported Yang et al. as potent PI3Kα inhibitors. Target compound **25** have demonstrated excellent PI3K inhibitory activity with an IC50 value of 0.012 μM against PI3Kα which is 17-fold greater compare to PI3Kβ (IC50 value 0.21 μM) isoenzyme. Compound **25** is a selective PI3Kα inhibitor, it also displayed suppression of phosphorylated Akt level in HCT-116 cancer cells in a dose dependent pattern. In vitro cytotoxic activity of compound **25** showed its potent inhibitory activity against selected cancer cell line namely HCT-116, MCF-7, HeLa, HepG2 and Ges-1 cancer cell lines with an IC50 value of 0.18 μM, 0.43 μM, 0.71 μM, 0.63 μM and 21.95 μM respectively. Further cell apoptosis study of target compound **25** showed that it induces also apoptosis in HCT-116 when treated in a concentration dependent manner, Compound **25** comes out as potent PI3Kα inhibitor, it can be a promising agent for further development in discovery of novel anticancer agent [70].

Chanrasekhar et al*.* have reported a novel series of benzimidazole derivatives as potent PI3K inhibitors Target compound **26** was found to exhibit potential inhibitory activity against PI3Kβ inhibitor, it demonstrated excellent inhibitory potency with an IC50 value of 0.002 μM against PI3Kβ with good selectivity against all three isoforms of class I PI3Ks. Further pharmacokinetic profile of compound was evaluated in four different preclinical species (Sprague-Dawley rat, Beagle dog, Cynomolgus monkey, Rhesus monkey). Target compound **26** has shown low to intermediate clearance compare to hepatic flow of blood, whereas in rat model consistent high oral availability and high permeability was observed [71].

Wu et al. have reported a novel series of triazine substituted benzimidazole derivatives a potent dual inhibitor of PI3K and mTOR, most of the compounds from the series displayed potent inhibitory activity with IC50 below 33 nM. Target compound **27** was found most potent in the series, it exhibited strong inhibitory activity against both kinases with an IC50 value of 5.1 μM and 5.6 μM against PI3Kδ and mTOR, it exhibited PI3Kα and PI3Kβ at an IC50 of 7.3 nM and 21.3 nM respectively. Further, western blot analysis of compound **27** shown inhibition of phosphorylation of Akt and p70S6K, confirming dual inhibitory activity of the presenting compound. Target compound **27** displayed potent antiproliferative activity against selected cell lines, exhibited an IC50 of 0.4 μM, 0.9 μM, 1.5 μM, 7.3 μM and 7.7 μM against MCF-7, HCT116, MDA-MB-231, CNE2 and HeLa respectively. Compound **27** displayed promising PI3K/mTOR dual inhibitory activity, further development can add a potent dual inhibitor in the regimen of cancer therapy [72].

Shin et al. have reported a novel series of benzimidazole derivatives a potent inhibitor of PI3Kδ. Target compound **28** and **29** displayed an IC50 value of 0.016 μM and 0.019 μM against PI3Kδ and IC50 value of 1.78 μM and 2.33 μM PI3Kβ respectively. In vivo pharmacokinetic profile of target compound was found good with oral bioavailability of 45% and 41% respectively. In vivo studied of compound **28** and **29** suggested that both the compounds can inhibit KLH-specific antibodies [73].

He et al. has reported benzimidazole-isoquinolinone derivatives which inhibits the cell growth via inhibiting PI3K/mTOR/Akt pathway. Target compound **30** demonstrated excellent inhibitory activity against SW620 and HT29 cancer cell line with an GI50 value of 23.78 μM and 24.13 μM. Target compound **30** also decreases the levels of phosphorylated Akt and mTOR levels. Compound **30** also demonstrated cell cycle arrest of human colorectal cancer cells at G2/M phase by decreasing the levels of cyclin B1 and CDK1 [74].

Wu et al. have reported triazine bearing benzimidazole derivatives a potent inhibitor of PI3K and mTOR. Target compound **31** and **32** displayed potent activity with

and IC50 value of 2.3 nM and 13.0 nM against PI3Kδ, IC50 value of 14.6 and 20.1 nM against PI3Kα and IC50 value of 34.0 and 28.0 against PI3Kβ isoform respectively. Both the compound also displayed excellent inhibitory potency against mTOR with an IC50

**Figure 6.**

*Examples of benzimidazole derivatives as potent PI3K inhibitors.*

value of 12.9 nM and 15.4 nM respectively. Further, compound **32** was evaluated for antiproliferative activity where it demonstrated moderate activities against selected cancer cell line HCT116, HepG2, HeLa, MDA-MB-231 and MCF7 with an IC50 value of 0.3 μM, 1.3 μM, 2.4 μM, 4.8 μM and 4.9 μM respectively. Further western blot analysis study of compound **32** confirmed that it completely prevented the phosphorylation of Akt and p70S6K in HCT116 cells, thus target compound was determined as potential dual inhibitor of PI3K and mTOR kinase. Molecular docking analysis of compound **32** displayed that good binding interaction within the active site of PI3Kα [75] (**Figure 6**).

#### *3.2.5 CDK inhibitors*

Ibrahim et al. have reported a novel series of flavopiridol-benzimidazole as potent inhibitor potent inhibitor of CDK2 and CDK9 kinase. Target compound **33** exhibits potential inhibitory activity with an IC50 value of 0.064 and 1.725 μM against CDK2 and CDK9 kinases respectively. Furthermore, compound **33** also displayed potential antiproliferative activity against selected cancer cell line SKOV3, PC3 and K562 with an IC50 value of 94.0 μM, 85.0 μM and 50.8 μM respectively. Cell cycle analysis study of target compound revealed that it arrests the cell cycle of K562 cancer cell at G1 and G2 phase in a dose dependent manner [76] (**Figure 7**).

#### **3.3 Benzimidazole based hybrid derivatives as potent anticancer agents**

Pankaj et al. have reported a novel hybrid derivatives of benzimidazole-thiazolidinedione as potent cytotoxic agents. Target compound **34** demonstrated potent inhibitory activity against A549, DU-145, MDA-MB-231 and PC-3 cancer cell line with an IC50 value of 11.46 μM, 31.41 μM, 29.18 μM and 39.87 μM respectively. Compound **34** have shown cell cycle arrest in G2/M phase of A549 cells in a dose dependent manner. Furthermore, compound **34** also demonstrated cell shrinkage of A549 cells along with chromatin condensation and horse shoe shaped nuclei formation [77].

Sivaramakarthikeyan et al. have reported novel hybrid derivatives of benzimidazole and pyrazole as potent anticancer agents. Compound 35 and 36 have demonstrated potent anticancer activity against selected human pancreatic cancer cell lines namely SW1990 and AsPC1 with an IC50 value in range of 30.9–61.8 μM respectively. Molecular docking study of both compound showed significant binding with the active site of B-cell lymphoma [78].

**Figure 7.** *Examples of benzimidazole derivative as potent CDK inhibitor.*

*Advances of Benzimidazole Derivatives as Anticancer Agents: Bench to Bedside DOI: http://dx.doi.org/10.5772/intechopen.101702*

Mantu et al. have reported a novel series of benzimidazole-quinoline hybrid derivatives as potent anticancer agent. Target compound 37 exhibited potent antitumor activity against renal cancer cell line A498 and breast cancer cell line MDA-MB-468 with percentage growth inhibition of 52.92% and 56.54% respectively. Compound 37 also exhibited potent antitumor activity against leukemia cell line RPMI-8226 and non-small cell lung cancer cell line NCI-H23 with total growth inhibition of 35% [79].

Sharma et al. have reported benzimidazole-thiazolidinedione hybrid derivatives as potent anticancer agents. Target compound 38 and 39 displayed potent anticancer activity against cancer cell line with an IC50 value of in range of 0.13-10.24 μM against prostate cancer cell line PC-3, breast cancer (MDAMB-231), cervical cancer (HeLa), lung cancer (A549), and bone cancer (HT1080) cell lines. Both hybrid derivative 38 and 39 demonstrated significant inhibition of A549 cells migration

through disruption of F-actin assembly, further treatment with 38 and 39 also showed increase in level of ROS in A549 cells by collapsing the mitochondrial membrane potential [80].

Bistrovic et al. have reported novel hybrid derivatives of benzimidazole-1,2,3 triazole as potent anticancer agents. Target compound 40 and 41 demonstrated excellent inhibitory activity with IC50 value of 0.05 and 6.18 against A549 cancer cell line and an IC50 value of 17.53 and 8.80 against HeLa cancer cell line respectively. Furthermore, apoptosis detection study by annexin assay of compound **40** showed significant reduction of viable cell population by 70.59%, with increase in early necrotic cell population by 27.81% and late apoptotic cells by 40%. Similarly compound 41 also displayed markable decrease in cell population by 49.77%. Molecular docking analysis of compound 40 and 41 demonstrated that both the compound bind to the active site of p38 complex strongly [81] (**Figure 8**).

#### **4. Conclusion**

Many benzimidazole-containing compounds as anticancer agents are studied and available, involving various mechanisms in inhibiting mutated cancerous cells, in which kinases inhibitors play a significant role. However, in targeted therapy, benzimidazole-based derivatives are still widely explored. Due to the challenge of target specificity and poor selectivity, very few compounds have been approved to treat mutated cancers. The search for a novel benzimidazole-based next generation kinase inhibitor is going to subside such challenges. Benzimidazole-based target therapies such as enzyme inhibitors have gained a lot of attraction; owing to this, recently US FDA has approved EGFR inhibitor Abemaciclib and MEK inhibitor Binimetinib and Selumetinib as potent anticancer compounds against mutated forms of cancer. Apart from this, many benzimidazole-containing compounds are in the developmental phase as EGFR, VEGFR-2, CDK and PI3K inhibitors. However, some of the compounds demonstrated excellent kinase inhibitory activity but failed to provide a strong safety profile; these compounds will pave a path as lead compounds; further modifications, designing, and developing such compounds will give potent compounds with maximum efficiency and minimal side effects. The presented chapter mainly focuses on benzimidazole-based kinase inhibitors and their advances; the pivotal information catered here can be regarded as noteworthy and crucial by medicinal chemists for drug design, discovery and development of novel, potent and safe, target-based anticancer agents.

#### **Acknowledgements**

Authors wishes to acknowledge Jamia Hamdard (deemed-to-be-University) for providing support for conducting this study.

#### **Conflict of interest**

Authors declare "no conflict of interest."

*Advances of Benzimidazole Derivatives as Anticancer Agents: Bench to Bedside DOI: http://dx.doi.org/10.5772/intechopen.101702*

### **Author details**

Kashif Haider and Mohammad Shahar Yar\* Department of Pharmaceutical Chemistry, School of Pharmaceutical Education and Research (SPER), Jamia Hamdard, New Delhi, India

\*Address all correspondence to: msyar@jamiahamdard.ac.in

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

[1] Siegel RL, Miller KD, Fuchs HE, Jemal A. Cancer statistics, 2021. CA: A Cancer Journal for Clinicians. 2021; **71**(1):7-33

[2] Haider K, Rahaman S, Yar MS, Kamal A. Tubulin inhibitors as novel anticancer agents: An overview on patents (2013-2018). Expert Opinion on Therapeutic Patents. 2019;**29**(8): 623-641

[3] WHO report on cancer: Setting priorities, investing wisely and providing care for all. Geneva: World Health Organization; 2020. License: CC BY-NC-SA 3.0 IGO

[4] Haider K, Rehman S, Pathak A, Najmi AK, Yar MS. Advances in 2-substituted benzothiazole scaffoldbased chemotherapeutic agents. Archiv der Pharmazie. 2021;**354**:e2100246

[5] Kharb R, Haider K, Neha K, Yar MS. Aromatase inhibitors: Role in postmenopausal breast cancer. Archiv der Pharmazie. 2020;**353**(8):2000081

[6] Paul A, Singh P, Kuznetsov ML, Karmakar A, da Silva MF, Koch B, et al. Influence of anchoring moieties on new benzimidazole-based Schiff base copper (ii) complexes towards estrogen dependent breast cancer cells. Dalton Transactions. 2021;**50**(10):3701-3716

[7] Pathak A, Pandey V, Pokharel YR, Devaraji V, Ali A, Haider K, et al. Pharmacophore based drug design and synthesis of oxindole bearing hybrid as anticancer agents. Bioorganic Chemistry. 2021;**116**:105358

[8] Dandawate P, Ahmed K, Padhye S, Ahmad A, Biersack B. Anticancer active heterocyclic chalcones: Recent

developments. Anti-Cancer Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry-Anti-Cancer Agents). 2021;**21**(5):558-566

[9] Scattolin T, Piccin A, Mauceri M, Rizzolio F, Demitri N, Canzonieri V, et al. Synthesis, characterization and anticancer activity of palladium allyl complexes bearing benzimidazole-based N-heterocyclic carbene (NHC) ligands. Polyhedron. 2021;**207**:115381

[10] Gondru R, Li Y, Banothu J. Coumarin–benzimidazole hybrids: A review of developments in medicinal chemistry. European Journal of Medicinal Chemistry. 2021;**227**:113921

[11] Shrivastava N, Naim MJ, Alam MJ, Nawaz F, Ahmed S, Alam O. Benzimidazole scaffold as anticancer agent: Synthetic approaches and structure–activity relationship. Archiv der Pharmazie. 2017;**350**(6):e201700040

[12] Shaharyar M, Mazumder A. Benzimidazoles: A biologically active compounds. Arabian Journal of Chemistry. 2017;**10**:S157-S173

[13] Satija G, Sharma B, Madan A, Iqubal A, Shaquiquzzaman M, Akhter M, et al. Benzimidazole based derivatives as anticancer agents: Structure activity relationship analysis for various targets. Journal of Heterocyclic Chemistry. 2021

[14] Akhtar W, Khan MF, Verma G, Shaquiquzzaman M, Rizvi MA, Mehdi SH, et al. Therapeutic evolution of benzimidazole derivatives in the last quinquennial period. European Journal of Medicinal Chemistry. 2017;**126**:705-753

[15] Akhtar MJ, Yar MS, Sharma VK, Khan AA, Ali Z, Haider MD, et al. Recent progress of benzimidazole hybrids for

*Advances of Benzimidazole Derivatives as Anticancer Agents: Bench to Bedside DOI: http://dx.doi.org/10.5772/intechopen.101702*

anticancer potential. Current Medicinal Chemistry. 2020;**27**(35):5970-6014

[16] Gaba M, Mohan C. Development of drugs based on imidazole and benzimidazole bioactive heterocycles: Recent advances and future directions. Medicinal Chemistry Research. 2016;**25**(2):173-210

[17] Song D, Ma S. Recent development of benzimidazole-containing antibacterial agents. ChemMedChem. 2016;**11**(7): 646-659

[18] Farahat AA, Ismail MA, Kumar A, Wenzler T, Brun R, Paul A, et al. Indole and benzimidazole bichalcophenes: Synthesis, DNA binding and antiparasitic activity. European Journal of Medicinal Chemistry. 2018;**143**:1590-1596

[19] Morcoss MM, El Shimaa MN, Ibrahem RA, Abdel-Rahman HM, Abdel-Aziz M, Abou El-Ella DA. Design, synthesis, mechanistic studies and in silico ADME predictions of benzimidazole derivatives as novel antifungal agents. Bioorganic Chemistry. 2020;**101**: 103956

[20] Veerasamy R, Roy A, Karunakaran R, Rajak H. Structure–activity relationship analysis of benzimidazoles as emerging anti-inflammatory agents: An overview. Pharmaceuticals. 2021;**14**(7):663

[21] Eswayah A, Khaliel S, Saad S, Shebani N, Fhid O, Belaid A, et al. Synthesis and analgesic activity evaluation of some new benzimidazole derivatives. American Journal of Chemistry and Application. 2017;**4**(5): 30-35

[22] Kanwal A, Ahmad M, Aslam S, Naqvi SA, Saif MJ. Recent advances in antiviral benzimidazole derivatives: A mini review. Pharmaceutical Chemistry Journal. 2019;**53**(3):179-187

[23] Araujo DM, Maste MM, Alegaon S, Saxena A. Synthesis, antitubercular evaluation and docking studies of novel benzimidazole analogues. International Journal of Pharmaceutical Sciences and Research. 2018;**9**:3696-3704

[24] Matsubara Y, Matsumoto T, Yoshiya K, Yoshida A, Ikeda S, Furuyama T, et al. Budding uninhibited by benzimidazole-1 insufficiency prevents acute renal failure in severe sepsis by maintaining anticoagulant functions of vascular endothelial cells. Shock. 2019;**51**(3):364-371

[25] Wang XJ, Xi MY, Fu JH, Zhang FR, Cheng GF, You QD. Synthesis, biological evaluation and SAR studies of benzimidazole derivatives as H1-antihistamine agents. Chinese Chemical Letters. 2012;**23**(6):707-710

[26] Aroua LM, Almuhaylan HR, Alminderej FM, Messaoudi S, Chigurupati S, Al-Mahmoud S, et al. A facile approach synthesis of benzoylaryl benzimidazole as potential α-amylase and α-glucosidase inhibitor with antioxidant activity. Bioorganic Chemistry. 2021;**114**:105073

[27] Ganie AM, Dar AM, Khan FA, Dar BA. Benzimidazole derivatives as potential antimicrobial and antiulcer agents: A mini review. Mini Reviews in Medicinal Chemistry. 2019;**19**(16): 1292-1297

[28] Djemoui A, Naouri A, Ouahrani MR, Djemoui D, Lahcene S, Lahrech MB, et al. A step-by-step synthesis of triazolebenzimidazole-chalcone hybrids: Anticancer activity in human cells+. Journal of Molecular Structure. 2020; **1204**:127487

[29] Ren Y, Wang Y, Li G, Zhang Z, Ma L, Cheng B, et al. Discovery of novel benzimidazole and indazole analogues as tubulin polymerization inhibitors with potent anticancer activities. Journal of Medicinal Chemistry. 2021;**64**(8): 4498-4515

[30] Akhtar S, Abbas M, Naeem K, Faheem M, Nadeem H, Mehmood A. Benzimidazole derivative ameliorates opioid-mediated tolerance during anticancer-induced neuropathic pain in mice. Anti-Cancer Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry-Anti-Cancer Agents). 2021;**21**(3):365-371

[31] Choi HS, Ko YS, Jin H, Kang KM, Ha IB, Jeong H, et al. Anticancer effect of benzimidazole derivatives, especially mebendazole, on triple-negative breast cancer (TNBC) and radiotherapyresistant TNBC in vivo and in vitro. Molecules. 2021;**26**(17):5118

[32] Shirley M. Encorafenib and binimetinib: First global approvals. Drugs. 2018;**78**(12):1277-1284

[33] Kopetz S, Grothey A, Yaeger R, Van Cutsem E, Desai J, Yoshino T, et al. Encorafenib, binimetinib, and cetuximab in BRAF V600E–mutated colorectal cancer. New England Journal of Medicine. 2019;**381**(17):1632-1643

[34] Grothey A, Tabernero J, Taieb J, Yaeger R, Yoshino T, Maiello E, et al. LBA-5 ANCHOR CRC: A single-arm, phase 2 study of encorafenib, binimetinib plus cetuximab in previously untreated BRAF V600E-mutant metastatic colorectal cancer. Annals of Oncology. 2020;**31**:S242-S243

[35] Balfour JA, Goa KL. Bendamustine. Drugs. 2001;**61**(5):631-638

[36] Yamshon S, Martin P. Are novel agents ready to assume the mantle in the frontline treatment of mantle cell lymphoma? Clinical Advances in

Hematology & Oncology: H&O. 2021;**19**(6):376-382

[37] Markham A, Keam SJ. Selumetinib: First approval. Drugs. 2020;**80**:931-937

[38] Casey D, Demko S, Sinha A, Mishra-Kalyani PS, Shen YL, Khasar S, et al. FDA Approval Summary: Selumetinib for Plexiform Neurofibroma. Clinical Cancer Research. 2021

[39] Gross AM, Wolters PL, Dombi E, Baldwin A, Whitcomb P, Fisher MJ, et al. Selumetinib in children with inoperable plexiform neurofibromas. New England Journal of Medicine. 2020;**382**(15):1430-1442

[40] Mukhopadhyay S, Maitra A, Choudhury S. Selumetinib: The first ever approved drug for neurofibromatosis-1 related inoperable plexiform neurofibroma. Current Medical Research and Opinion. 2021;**37**(5):789-794

[41] Kim ES. Abemaciclib: First global approval. Drugs. 2017;**77**(18):2063-2070

[42] Cuyun Carter G, Sheffield KM, Gossai A, Huang YJ, Zhu YE, Bowman L, et al. Real-world treatment patterns and outcomes of abemaciclib for the treatment of HR+, HER2-metastatic breast cancer. Current Medical Research and Opinion. 2021;**1**:37

[43] Toi M, Inoue K, Masuda N, Iwata H, Sohn J, Park IH, et al. Abemaciclib in combination with endocrine therapy for East Asian patients with HR+, HER2− advanced breast cancer: MONARCH 2 & 3 trials. Cancer Science. 2021;**112**(6): 2381

[44] Ghisoni E, Giannone G, Tuninetti V, Genta S, Scotto G, Aglietta M, et al. Veliparib: A new therapeutic option in ovarian cancer? Future Oncology. 2019;**15**(17):1975-1987

*Advances of Benzimidazole Derivatives as Anticancer Agents: Bench to Bedside DOI: http://dx.doi.org/10.5772/intechopen.101702*

[45] Boussios S, Karihtala P, Moschetta M, Abson C, Karathanasi A, Zakynthinakis-Kyriakou N, et al. Veliparib in ovarian cancer: A new synthetically lethal therapeutic approach. Investigational New Drugs. 2020;**38**(1):181-193

[46] Ghisoni E, Giannone G, Tuninetti V, Genta S, Scotto G, Aglietta M, et al. Veliparib: A new therapeutic option in ovarian cancer? Future Oncology. 2019;**15**(17):1975-1987

[47] Nightingale J, Lum B, Ladwa R, Simpson F, Panizza B. Adenoid cystic carcinoma: A review of clinical features, treatment targets and advancement in improving the immune response to monoclonal antibody therapy. Biochimica et Biophysica Acta (BBA)- Reviews on Cancer. 2021;**1875**:188523

[48] Choi YJ, Kim HS, Park SH, Kim BS, Kim KH, Lee HJ, et al. Phase II study of dovitinib in patients with castrationresistant prostate cancer (KCSG-GU11-05). Cancer Research and Treatment: Official Journal of Korean Cancer Association. 2018;**50**(4):1252

[49] Gurnari C, Voso MT, Maciejewski JP, Visconte V. From bench to bedside and beyond: Therapeutic scenario in acute myeloid leukemia. Cancers. 2020;**12**(2):357

[50] Yu J, Jiang PY, Sun H, Zhang X, Jiang Z, Li Y, et al. Advances in targeted therapy for acute myeloid leukemia. Biomarker Research. 2020;**8**:1-1

[51] Chua CC, Wei AH. Future developments: Novel agents. In: Acute Myeloid Leukemia. Cham: Springer; 2021. pp. 293-315

[52] Chen J, Li N, Liu B, Ling J, Yang W, Pang X, et al. Pracinostat (SB939), a histone deacetylase inhibitor, suppresses breast cancer metastasis and growth by

inactivating the IL-6/STAT3 signalling pathways. Life Sciences. 2020;**248**:117469

[53] Njar VC, Brodie AM. Discovery and development of Galeterone (TOK-001 or VN/124-1) for the treatment of all stages of prostate cancer. Journal of Medicinal Chemistry. 2015;**58**(5): 2077-2087

[54] Xu Y, Liao S, Wang L, Wang Y, Wei W, Su K, et al. Galeterone sensitizes breast cancer to chemotherapy via targeting MNK/eIF4E and β-catenin. Cancer Chemotherapy and Pharmacology. 2021;**87**(1):85-93

[55] Cui J, Xiao Z, Zhang LL. Clinical efficacy and safety of nazartinib for epidermal growth factor receptor mutated non-small cell lung cancer: Study protocol for a prospective, multicenter, open-label. Medicine. 2021;**100**(21):e25992

[56] Tan DS, Leighl NB, Riely GJ, Yang JC, Sequist LV, Wolf J, et al. Safety and efficacy of nazartinib (EGF816) in adults with EGFR-mutant non-small-cell lung carcinoma: A multicentre, open-label, phase 1 study. The Lancet Respiratory Medicine. 2020;**8**(6):561-572

[57] Jassem J, Dziadziuszko R. Nazartinib in EGFR Thr790Met-mutant non-smallcell lung cancer. The Lancet Respiratory Medicine. 2020;**8**(6):528-529

[58] Liu C, Lu H, Wang H, Loo A, Zhang X, Yang G, et al. Combinations with allosteric SHP2 inhibitor TNO155 to block receptor tyrosine kinase signaling. Clinical Cancer Research. 2021;**27**(1):342-354

[59] Akhtar MJ, Siddiqui AA, Khan AA, Ali Z, Dewangan RP, Pasha S, et al. Design, synthesis, docking and QSAR study of substituted benzimidazole linked oxadiazole as cytotoxic agents,

EGFR and erbB2 receptor inhibitors. European Journal of Medicinal Chemistry. 2017;**126**:853-869

[60] Srour AM, Ahmed NS, Abd El-Karim SS, Anwar MM, El-Hallouty SM. Design, synthesis, biological evaluation, QSAR analysis and molecular modelling of new thiazol-benzimidazoles as EGFR inhibitors. Bioorganic & Medicinal Chemistry. 2020;**28**(18):115657

[61] Akhtar MJ, Khan AA, Ali Z, Dewangan RP, Rafi M, Hassan MQ, et al. Synthesis of stable benzimidazole derivatives bearing pyrazole as anticancer and EGFR receptor inhibitors. Bioorganic Chemistry. 2018;**78**:158-169

[62] Abdullaziz MA, Abdel-Mohsen HT, El Kerdawy AM, Ragab FA, Ali MM, Abu-Bakr SM, et al. Design, synthesis, molecular docking and cytotoxic evaluation of novel 2-furybenzimidazoles as VEGFR-2 inhibitors. European Journal of Medicinal Chemistry. 2017;**136**: 315-329

[63] Lien JC, Chung CL, Huang TF, Chang TC, Chen KC, Gao GY, et al. A novel 2-aminobenzimidazole-based compound Jzu 17 exhibits antiangiogenesis effects by targeting VEGFR-2 signalling. British Journal of Pharmacology. 2019;**176**(20):4034-4049

[64] Yuan X, Yang Q, Liu T, Li K, Liu Y, Zhu C, et al. Design, synthesis and in vitro evaluation of 6-amide-2-aryl benzoxazole/benzimidazole derivatives against tumor cells by inhibiting VEGFR-2 kinase. European Journal of Medicinal Chemistry. 2019;**179**:147-165

[65] Abd El-Meguid EA, El-Deen EM, Nael MA, Anwar MM. Novel benzimidazole derivatives as anti-cervical cancer agents of potential multi-targeting kinase inhibitory activity. Arabian Journal of Chemistry. 2020;**13**(12):9179-9195

[66] Kassab AE, Gedawy EM, El-Nassan HB. Synthesis of 4-heteroaryl– quinazoline derivatives as potential anti-breast cancer agents. Journal of Heterocyclic Chemistry. 2017;**54**(1): 624-633

[67] Mateo J, Ganji G, Burris HA, Han SW, Swales K, DeYoung P, et al. A first time in human trial of GSK2636771, a PI3Kβ selective inhibitor, in patients with advanced solid tumors

[68] Mateo J, Ganji G, Lemech C, Burris HA, Han SW, Swales K, et al. A first-time-in-human study of GSK2636771, a phosphoinositide 3 kinase beta-selective inhibitor, in patients with advanced solid tumors. Clinical Cancer Research. 2017;**23**(19):5981-5992

[69] Jin RY, Tang T, Zhou S, Long X, Guo H, Zhou J, et al. Design, synthesis, antitumor activity and theoretical calculation of novel PI3Ka inhibitors. Bioorganic Chemistry. 2020;**98**:103737

[70] Yang YQ, Chen H, Liu QS, Sun Y, Gu W. Synthesis and anticancer evaluation of novel 1H-benzo [d] imidazole derivatives of dehydroabietic acid as PI3Kα inhibitors. Bioorganic Chemistry. 2020;**100**:103845

[71] Chandrasekhar J, Dick R, Van Veldhuizen J, Koditek D, Lepist EI, McGrath ME, et al. Atropisomerism by design: Discovery of a selective and stable phosphoinositide 3-kinase (PI3K) β inhibitor. Journal of Medicinal Chemistry. 2018;**61**(15):6858-6868

[72] Wu TT, Guo QQ, Chen ZL, Wang LL, Du Y, Chen R, et al. Design, synthesis and bioevaluation of novel substituted triazines as potential dual PI3K/mTOR inhibitors. European Journal of Medicinal Chemistry. 2020;**204**:112637

[73] Shin Y, Suchomel J, Cardozo M, Duquette J, He X, Henne K, et al.

*Advances of Benzimidazole Derivatives as Anticancer Agents: Bench to Bedside DOI: http://dx.doi.org/10.5772/intechopen.101702*

Discovery, optimization, and in vivo evaluation of benzimidazole derivatives AM-8508 and AM-9635 as potent and selective PI3Kδ inhibitors. Journal of Medicinal Chemistry. 2016;**59**(1):431-447

[74] He LJ, Yang DL, Li SQ, Zhang YJ, Tang Y, Lei J, et al. Facile construction of fused benzimidazole-isoquinolinones that induce cell-cycle arrest and apoptosis in colorectal cancer cells. Bioorganic and Medicinal Chemistry. 2018;**26**(14):3899-3908

[75] Wu TT, Guo QQ, Chen ZL, Wang LL, Du Y, Chen R, et al. Design, synthesis and bioevaluation of novel substituted triazines as potential dual PI3K/mTOR inhibitors. European Journal of Medicinal Chemistry. 2020;**204**:112637

[76] Ibrahim N, Bonnet P, Brion JD, Peyrat JF, Bignon J, Levaique H, et al. Identification of a new series of flavopiridol-like structures as kinase inhibitors with high cytotoxic potency. European Journal of Medicinal Chemistry. 2020;**199**:112355

[77] Sharma P, Reddy TS, Thummuri D, Senwar KR, Kumar NP, Naidu VG, et al. Synthesis and biological evaluation of new benzimidazole-thiazolidinedione hybrids as potential cytotoxic and apoptosis inducing agents. European Journal of Medicinal Chemistry. 2016;**124**:608-621

[78] Sivaramakarthikeyan R, Iniyaval S, Saravanan V, Lim WM, Mai CW, Ramalingan C. Molecular hybrids integrated with benzimidazole and pyrazole structural motifs: Design, synthesis, biological evaluation, and molecular docking studies. ACS Omega. 2020;**5**(17):10089-10098

[79] Mantu D, Antoci V, Moldoveanu C, Zbancioc G, Mangalagiu II. Hybrid imidazole (benzimidazole)/pyridine

(quinoline) derivatives and evaluation of their anticancer and antimycobacterial activity. Journal of Enzyme Inhibition and Medicinal Chemistry. 2016;**31** (suppl. 2):96-103

[80] Sharma P, Reddy TS, Kumar NP, Senwar KR, Bhargava SK, Shankaraiah N. Conventional and microwave-assisted synthesis of new 1H-benzimidazolethiazolidinedione derivatives: A potential anticancer scaffold. European Journal of Medicinal Chemistry. 2017;**138**:234-245

[81] Bistrović A, Krstulović L, Harej A, Grbčić P, Sedić M, Koštrun S, et al. Design, synthesis and biological evaluation of novel benzimidazole amidines as potent multi-target inhibitors for the treatment of non-small cell lung cancer. European Journal of Medicinal Chemistry. 2018;**143**:1616-1634

### **Chapter 2**

## The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes

*Imran Ahmad Khan, Noor ul Amin Mohsin, Sana Aslam and Matloob Ahmad*

#### **Abstract**

Cancer is the most lethal ailment throughout the world in the present era. The development of new anticancer remedies with minor unhealthful effects and an alternate mechanism is crucial. Benzimidazole is a distinguished heterocyclic compound and is now recognized as the privileged scaffold for new drug discovery. This chapter deals with the anticancer capability of benzimidazolium salts and their metal complexes. The benzimidazolium derivatives have been prepared by the introduction of aliphatic and aromatic groups at two nitrogen atoms of the benzimidazole ring. Other modifications include hybridization with other pharmacophores and the preparation of metal complexes. The potent derivatives presented in this review can serve as novel drug candidates against cancer.

**Keywords:** benzimidazolium salts, Benzimidazole, metal complexes, salts, hybrid, silver, breast cancer (MCF-7) cell line, colon cancer (HCT-116) cell line

#### **1. Introduction**

Cancer is among the most dreadful diseases and a significant cause of assassinations all over the globe. In 2018, 9.6 million expirations were because of this malady [1]. Breast cancer is the paramount form of cancer in women all over the world. In 2018, 2.3 million victims and 627,000 fatalities were reported due to breast cancer. Prostate cancer is the second most common cancer in males and 1.3 million patients were reported in 2018 [1]. It has been deduced that more than 13 million people will die due to cancer in 2030 [2]. The major risk factors associated with cancer are chronic infections, inherited mutations in genes, overweight, no physical activity, exposure to ionizing radiation, and carcinogens such as polychlorinated biphenyls, chloroform, Dichlorodiphenyltrichloroethane (DDT), and formaldehyde [3]. Treatment patterns for cancer involve radiotherapy, surgery, and drug therapy. Drug therapy includes inorganic, organic, organometallic monomers, and polymers as well as nanoparticles [4]. Drug therapy is associated with severe adverse properties such as alopecia, anemia, and infertility. There is also the development of resistance against currently

**Figure 1.** *Anticancer drugs based on benzimidazole scaffold.*

available drugs [5]. Consequently, the development of new anticancer drugs affiliated with low toxicities is very significant.

Nitrogen-containing heterocycles are abundantly present in natural and synthetic drug molecules [6]. Benzimidazole is one of the most significant members of nitrogen-containing heterocycles. This heterocycle is a constituent of the structures of some natural compounds such as vitamin B12 [7]. Benzimidazole derivatives have antihypertensive [8], anti-inflammatory [9], antimicrobial [10], antiulcer [11], antiviral [12], antioxidant [13], antitumor [14], lipid modulator, and anticoagulant properties [15]. Benzimidazole derivatives have also the major therapeutic activities against cancer [16–18]. Benzimidazole is also the main pharmacophore of anticancer drugs (**Figure 1**) such as bendamustine (**1)**, selumetinib (**2)**, and galeterone (**3)** out of which bendamustine is approved for clinical use, while the other two are in clinical trial stages [19, 20]. The structural resemblance of benzimidazole with nucleotides makes them very vital from the biological point of view [21]. Benzimidazolium salts are 1,3-disubstituted benzimidazole derivatives and possess acidic hydrogen at position 2. Benzimidazole salts find application as a carbene precursor for the preparation of n-heterocyclic carbenes (NHC) with different metals [22]. These benzimidazolium salts and their complexes have displayed significant antimicrobial and anticancer properties [23]. This review deals with the anticancer activities of benzimidazolium salts and their metal complexes.

#### **2. Anticancer properties of benzimidazolium salts**

Benzimidazolium salts and their anticancer capabilities have been reviewed in the following sections.

#### **2.1 Hybrid molecules containing benzimidazolium salts**

Molecular hybridization has become an effective approach for new drug discovery. In molecular hybridization, two or more pharmacophores are linked to each other to produce the new molecules [24, 25]. Yang et al. synthesized hybrid molecules in which benzimidazolium salts were linked to trimethoxy phenyl chalcones. Compound **4** (**Figure 2**) demonstrated excellent anticancer potential against leukemia (HL-60), breast carcinoma (MCF-7), and colon carcinoma (SW480) cell lines presenting IC50 values of 0.83, 1.57, and 2.92 μM, respectively, which is 5–11-folds higher than the standard drug cisplatin. In compound **4**, 2-naphthylmethyl substituent is attached

*The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

**Figure 2.** *Hybrid molecules comprising benzimidazole salts and natural compounds.*

to benzimidazole nitrogen. The superior activity of these salts was related to the high solubility of benzimidazolium salts. Benzimidazole derivatives with substituents at positions 5, 6 showed greater activity as compared to unsubstituted benzimidazoles [26]. Karatas et al. reported a series of hybrid molecules in which coumarin was attached to the substituted benzimidazolium chlorides. Anticancer screening by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay showed that these compounds have the potential to discontinue the cell cycle for human prostate (PC-3) and ovarian (A2780) cancer cells. Specifically, compound **5** (IC50 = 44.5 μM) showed some inhibitory potential against PC-3 at the dose of 1 μM [27]. Next year, Wang et al. produced the 3-benzyl coumarin imidazolium salts using the hybrid molecular strategy. The anticancer activity evaluation showed that compound **6** is one of the most active derivatives having IC50 values ranging from 2.04 to 4.51 μM. The best activity was displayed *versus* the MCF-7 cell line having an IC50 value of 2.04 μM. The 5, 6-dimethyl-substituted benzimidazole hybrids exhibited prominent activity as compared to unsubstituted benzimidazoles or imidazoles. These molecules showed selectivity for MCF-7 and SW-480 cancer cell lines. Compound **6** also showed the apoptosis in liver carcinoma (SMMC-7721) cell line [28]. Deng et al. linked benzimidazolium salts with steroidal molecules such as cholesterol, dehydroepiandrosterone, and diosgenin. Anticancer activities were carried out against HL-60, A-549, SMMC-7721, SW480, and MCF-7 cancer cell lines. Diosgenin-imidazolium salts displayed higher activity, and compound **7** was the most effective having IC50 values from 0.44 to 0.79 μM against different cell lines.

Compound **7** disrupted the cell cycle in G1/G0 stage and showed apoptosis in the SMMC-7721 cell line. Structure-activity relationship (SAR) studies showed that 5, 6-dimethyl-substituted benzimidazolium salts showed excellent anticancer activity. Attachment of 2-bromobenzyl with 2-naphthyl methyl at position 3 of benzimidazole also amplified the activity [29]. Brazilin is a natural compound and possesses extensive bioactivities such as anti-inflammatory, anticancer, and antioxidant [30]. Huang et al. connected aza-brazilin with imidazolium salts to produce hybrid molecules. Anticancer activity was evaluated against A549, SMMC-7721, MCF-7, and SW480 cell lines. Derivative **8** appeared as the most active (IC50 = 0.35 μM) against the MCF-7 cell line and displayed more potency as compared to cisplatin. Derivatives having a 5,6-dimethylbenzimidazole ring displayed prominent activity. The introduction of electron-withdrawing groups on the aza-brazilin nucleus produced more active derivatives. Derivatives having an alkyl chain as linker groups produce higher potency as compared to acyl chains [31]. Zhou et al. also used a hybrid molecular strategy to conjugate *N*-substituted tetrahydro-*β*-carbolines with imidazolium salts. Compound **9** exhibited prominent activity with IC50 values ranging from 2.61 to 17.13 μM against five different cancer cell lines. Most prominent activity was achieved against MCF-7 (IC50 = 2.79 μM) and SW-480 (IC50 = 9.46 μM) cancer cell lines. Compound **9** carries a naphthyl methyl scaffold at position 3 of benzimidazole. Compound **9** also showed the phenomenon of apoptosis in the MCF-7 cell line as well as inhibited the cell cycle in the G1 phase [32].

Xu et al. coupled a three-substituted indole ring with imidazolium salts to produce new hybrid molecules. Upon evaluation of anticancer activity, compound **10** (**Figure 3**) showed prominent performance against MCF-7 (IC50 = 3.19 μM), A549 (IC50 = 3.51 μM), SW480 (IC50 = 11.57 μM), and SMMC-7721 (IC50 = 3.60 μM) cancer cell lines. SAR studies showed that 5,6-dimethyl-substituted benzimidazole derivatives showed prominent activity as compared to unsubstituted benzimidazoles. Compound **10** carries a naphthyl acyl ring at position 3 of the benzimidazole nucleus. Further studies showed that compound **10** is capable of inducing apoptosis and caused cell cycle blockage in the *S* phase [33]. Li et al. synthesized carbazole and imidazolium salts using the molecular hybridization technique. Replacement of the imidazole ring by the benzimidazole increased the anticancer selectivity against a particular cell line. Among the benzimidazolium salts, derivative **11** showed excellent activity against the HeLa cell line (IC50 = 0.02 μM) as compared to standard drug cisplatin (IC50 = 13.61 μM) [34]. Wang et al. synthesized imidazolium salts and dibenzofuran comprising hybrid molecules. The estimation of anticancer activity against five cancer cell lines showed that 2-methylbenzimidazolium and dibenzofuran hybrid molecular salts are more active as compared to individual molecules. 2-Methyl-substituted benzimidazolium salts showed higher activity as compared to unsubstituted and 5,6-dimethylbenzimidazolium salts. Compound **12** expressed prominent activity (IC50 = 0.64–1.47 μM) against MCF-7, A549, SW480, HL-60, and SMMC-7721 cancer cell lines. Most prominent activity was observed against MCF-7 (IC50 = 0.64 μM) and SW-480 (IC50 = 0.88 μM) cell lines. Compound **12** carries a 4-methoxy phenacyl substituent at position 3 of the benzimidazole nucleus. Replacement of 4-methoxy phenacyl substituent by 2-naphthylacyl also produced potent derivatives [35]. Zhang and co-workers synthesized hybrid molecules comprising 2,3,6,7-tetrahydrobenzodifuran and imidazolium salts. Compound **13** appeared as the most active derivative against five cancer cell lines having an IC50 value less than 4.34 μM. Compound **13** showed selectivity for A549, SMMC-7721, and SW-480 cancer cell lines. Some derivatives of this series also exhibited the phenomenon of apoptosis and seized

*The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

**Figure 3.** *Hybrid molecules of benzimidazole salts with synthetic molecules.*

cell cycle in the G1 stage [36]. Zhou et al. manufactured hexahydropyrrolo[2,3b]indole-1*H*-imidazolium salts as anticancer agents. The nitrogen at position 3 of the benzimidazole ring was linked to 2-bromobenzyl and 2-naphthyl methyl scaffolds. Compound **14** emerged as the most active derivative against HL-60, MCF-7, SMMC-7721, A549, and SW-480 cell lines having an IC50 value less than 2.68 μM. The introduction of the *N*-benzyl group at the indole nitrogen also increased the activity [37].

#### **2.2 Benzimidazolium salts having aromatic and aliphatic substituents**

Akkoc et al. reported benzimidazolium salts screened for anticancer potential against human embryonic kidney (HEK-293 T), human colon epithelial colorectal adenocarcinoma (DLD-1), and human breast epithelial adenocarcinoma (MDA-MB-231) cancer cell lines by using MTT assay. Palladium (Pd) metal complexes were also prepared and found inactive against these cells lines having IC50 values over 100 μM. The naphthalen-1-yl-methyl incorporated benzimidazolium chloride **15** (**Figure 4**) (IC50 = 26.09 μM) showed most cytotoxicity against DLD-1 cell line [38]. In an additional study, Akkoc and his coworkers reported a

**Figure 4.** *Benzimidazole salts having aromatic substituents.*

novel series of benzimidazolium salts containing cyanobenzyl, nitrophenyl, and *N*-methylphthalimide substitutions. All salts were tested for their cytotoxicity against DLD-1 and human breast cancer (MDA-MB-231) cell lines. Compounds **16** and **17** demonstrated exceptional activity against MDA-MB-231 cell lines with IC50 values of 1.26 and 2.01 μM and were considerably better than cisplatin (IC50 = 5.77 μM). Derivatives **16** and **17** contain anthracene and naphthalene rings, respectively, attached with the nitrogen of benzimidazole. The N1 and N3 substituents produced a prominent effect on anticancer activity [39]. In 2019, Akkoc extended his previous finding of cytotoxicity of benzimidazolium salts. In this regard, 2-hydroxyethylcontaining benzimidazolium salts along with respective Pd-complexes were prepared and their anticancer capacity was noted against human cancer cell lines. Surprisingly, compound **18** exhibited notable activity against MDA-MB-231 (IC50 = 7.59 μM) and DLD-1 (IC50 = 39.51 μM) cell lines in comparison with their Pd-complexes [40].

Lin et al. synthesized 1,3-bis-naphthyl-substituted benzimidazolium bromides and estimated for activity against MDA-MB-468 as well as PC-3 cell lines. As compared to the standard drug tamoxifen (IC50 = 22.5 μM), compound **19** (**Figure 5**) was found as an active agent (IC50 = 9.7 μM) against MDA-MB-468. The presence of the naphthyl group was vital for the activity of these derivatives [41]. Wright et al. synthesized naphthalene-substituted imidazolium salts and evaluated the anticancer performance against non-small-cell lung cancer (NSCLC) cell lines. The anticancer activity was evaluated by the MTT assay. Compound **20**, the benzimidazolium salt, displayed IC50 values of 3, 4, and 5 μM against NCI-H460, NCI-H1975, and HCC-827, respectively. Compound **20** carries naphthyl rings at both nitrogens of benzimidazole [42]. Stromyer et al. synthesized benzimidazole

*The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

**Figure 5.** *Benzimidazole salts having naphthalene and quinoline rings.*

salts having triphenylphosphonium group. The nitrogen atoms of benzimidazole were linked with naphthyl methyl groups. Compound **21** revealed marvelous activity against bladder cancer cell lines RT4, RT112, UMUC3, and SW780. This compound also showed apoptosis by causing mitochondrial damage. The drug causes a rapid and irreversible effect against bladder cancer [43]. Shelton et al. synthesized *N,N*-bis-arylmethyl-substituted benzimidazolium salts *via* cyclization of *o*-phenylenediamine or 2-(2-(2-methoxy ethoxy)ethoxy)acetic acid with 2-(chloromethyl) quinolone or 2-(bromomethyl)-naphthalene followed by alkylation and quaternization. Various hydrophilic and hydrophobic groups were added at both nitrogen atoms of benzimidazole. Insight into *in vitro* cytotoxicity of synthesized salts, compound **22** showed adequate activity against NSCLC cancer cells having IC50 values ranging between 1 and 7 μM comparable to the standard drug, cisplatin. This compound bears quinoline and naphthalene rings to both nitrogen atoms of benzimidazole. The presence of ether linkage at position two increased the hydrophilicity of this compound [44].

Bansode et al. carried out the synthesis of ferrocene-linked ionic liquids by incorporating long alkyl chains. Anticancer activity was evaluated against MCF-7 by using sulforhodamine B assay. These ferrocene-quaternized azolium salts showed significant cytotoxic potential against MCF-7 and 1-(ferrocenylmethyl)-3-tetradecylbenzimidazolium bromide **23** (**Figure 6**) was found to be most potent (GI50 = 0.016 μM) as compared to standard drug doxorubicin (GI50 = 0.018 μM). Derivatives in this followed the Lipinski rule of five and showed excellent pharmacokinetic properties [45]. Kucukbay et al. synthesized *N, N*-disubstituted benzimidazolium bromides and evaluated anticancer activity against PC-3 and ovarian (A2780) cancer cell lines. Derivatives **24-26** presented prominent activity against PC-3 and A2780 cancer cell lines having IC50 values in micromolar concentration. These compounds bear a 4-methoxyphenyl ethyl group at the benzimidazole nitrogen [46]. Haque et al. prepared a collection of bis-benzimidazolium salts and evaluated against human colon cancer (HCT-116). All compounds showed superior activity than the reference

**Figure 6.** *Bis-benzimidazolium and ferrocene-linked benzimidazolium salts.*

drug, fluorouracil. Derivatives having *N*-methylene phenyl substituents presented prominent activities. The highest anticancer potential was observed in the case of derivative **27** (IC50 = 0.2 μM) remarkably better than reference drug, 5-fluorouracil (IC50 = 19.2 μM) [47]. Noor ul Huda et al. synthesized bis-NHC benzimidazolium salts and evaluated them as antimicrobial and anticancer agents. Compound **28** exhibited prominent activity against HCT-116 cancer cell lines showing 75% inhibition at 1 mg/ ml as determined by using sulforhodamine Β assay. Compound **28** contains a lipophilic alkyl chain and the lipophilicity of the alkyl chain was linked to the increased activity of this derivative [48].

#### **2.3 Benzimidazolium silver metal complexes**

Cisplatin is the first metal-based drug used for the cure of cancer [49]. The serendipitous discovery of cisplatin stimulated the search for new metal-based anticancer agents. Silver (Ag) salts have been used as antimicrobial agents for purification of drinking water and wound healing [50, 51]. Based on its antimicrobial property, silver has also been explored as an anticancer agent. *N*-Heterocyclic carbenes (NHC) are a prominent family of organometallic ligands.

#### *2.3.1 Bis-benzimidazolium silver metal complexes*

Iqbal and his coworkers performed a detailed study to reduce the risk of malignant neoplasm and reported novel binuclear benzimidazolium salt and corresponding Ag (I) NHC complex. Compound **29** (**Figure 7**)presented prominent activity (IC50 = 1.7 μM) against HCT-116 cell line. This compound also showed significant inhibition of inflammatory cytokines such as tumor necrosis factor-alpha and interleukin in human macrophages. Compound **29** showed apoptotic activity *via* inhibition of the caspase pathway. Photomicrographs of the cell treated with compound **29** showed deposition of silver in cells [52]. Gadhayeb et al. carried out the synthesis of mono- and bis-NHC complexes having palladium (Pd) and silver metals. The anticancer activity was evaluated out against HCT-116 cell line. Compounds

*The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

#### **Figure 7.**

*Mono and binuclear bis-benzimidazolium silver metal complexes.*

**30** and **31** exhibited prominent activities having IC50 values of 12.3 ± 1.2 μM and 10.6 ± 1.8 μM, respectively. The mono-NHC showed more activity as compared to bis-NHC. The increased activity of compound **31** could be due to the increased release of silver from the mono-NHC complex. These compounds contain a butyl chain at the benzimidazole nitrogen [53]. Following this principle, Sarhan et al. reported benzimidazolium-acridine-based salts and metal complexes with pronounced biological potential. Specifically, compound **32** can be considered an excellent *in vitro* anticancer agent against MCF-7 (IC50 = 21 μM) and selectivity index of 3.6. Therefore, Ag-NHC complexes demonstrated prominent activity [54]. A series of 5-methyl benzimidazole-based *n*-heterocyclic carbene (NHC) salts and their silver (I)-complexes were prepared by Habib et al. The Ag (I)-benzimidazolium complexes showed dominant activity against human breast cancer (MDA-MB-231) and colon cancer (HCT-116) as compared to NHC salts. Compound **33** showed promising activity against MDA-MB-231 (IC50 = 4.2 ± 0.24 μM, SI = 7.63) and HCT-116 (IC50 = 7.43 ± 0.23 μM SI = 4.33) as compared to reference drug (IC50 = 8.20 ± 0.14 μM and 5.5 ± 0.34 μM) against these cell lines respectively. Compound **33** carries pentyl chains at both nitrogen atoms of the benzimidazole core. Derivatives having a longer alkyl chain were found more active. These molecules showed dose-dependent cytotoxicities and apoptosis by mitochondrial pathways [55]. A range of substituted Ag(I)-benzimidazolium carbene complexes were reported by Atif et al. and *in vitro* anticancer studies were carried out against MCF-7, HCT 116, and erythromyeloblastoid leukemia (K-562)

cell lines. Promising anticancer activity was shown by **34** (IC50 = 0.31 μM) against the K-562 cell line. Compound **34** is a bis-benzimidazole silver complex and carries propyl groups at both nitrogen atoms of benzimidazole rings [56].

Achar et al. reported a novel series based on benzimidazolium salts linked with coumarin heterocycle, and their silver cationic bis-NHC and Ag neutral mono-NHC were synthesized. The anticancer activity was evaluated by sulforhodamine assay. Complex **35** (**Figure 8**) exhibited moderate activity against the A549 cell line having an IC50 value of 8.3 ± 0.40 μM. Compound **35** is the bis-NHC-coordinated Ag hexafluorophosphate (PF6) salt. The mono-NHC coordinates Ag acetate complexes showed inferior activity with IC50 values greater than 10 μM. Bis-NHC complexes also showed prominent antibacterial activity [57]. Yasar et al. also worked out to yield novel zwitterionic-sulfonated benzimidazolium salts and their Ag-(I) complexes by following a reported synthetic approach. Anticancer activity was assessed against human cervix carcinoma (HeLa), human adenocarcinoma (HT29), and mouse fibroblast (L929) cancer cell lines. Silver complexes were found most active as compared to their salts. Compound **36** (IC50 = 11 ± 1 μM) showed higher potency against HT29 cancer cell line as compared to cisplatin (IC50 = 42 ± 6 μM). Compound **36** was found to be the least toxic (IC50 = 126 ± 3 μM) against non-cancer L929 cell lines [58]. Karlık et al. prepared a series of aqua-bis-benzimidazole Ag (I) *p*-toluene sulfonate complexes *via* a multistep approach and investigated their anticancer properties against human colorectal (Caco-2) and MCF-7 cancer cell lines. Salts were found to be ineffective against these cell lines. Benzimidazolium Ag complex **37** (IC50 value of 9 ± 3 μM) showed excellent activity against the Caco-2 cell line but was inactive against the MCF-7 cell line. Derivatives **37** carries an *o*-chloro-substituted benzyl group attached with the nitrogen of benzimidazole and this substituent was found more effective at

*The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

this position as compared to *o-*methyl and *p*-methyl analogues [59]. Fatima et al. successfully explored the cytotoxic effect of different alkyl chains on benzimidazoliumbased Ag complexes. It was observed that compound **38** containing longer n-alkyl chains showed the best cytotoxic potential against HCT-116 (IC50 = 0.02 μM) as compared to 5-fluorouracil (IC50 = 10.2 μM) as a standard drug. The incorporation of silver ions and elongation of the alkyl chain amplified the anticancer activity [60].

Similarly, Haque et al. prepared Ag(I) complexes containing nitrile-functionalized benzimidazolium salt as an active agent against HCT-116. Among all synthesized complexes, compound **39** (IC50 = 14.9 ± 0.8 μM) showed the highest cytotoxicity as compared to fluorouracil (IC50 = 5.2 ± 0.3 μM). The activity was linked to the nitrile group (**Figure 9**) at the meta position of the benzyl group causing the weak electron-withdrawing effect [61]. Early on, Haque et al. also synthesized silver metal complexes containing benzimidazolium ligand. These silver-based benzimidazolium complexes are capable of slow release of the silver ion at the cancerous cell, affecting cell morphology. Complex **40** (IC50 = 1.20 ± 0.3 μM), a binuclear silver entity, expressed superior activity as compared to fluorouracil (IC50 = 5.2 ± 0.3 μM) against HCT-116. Complex **40** was found to be the least active (IC50 = 103 ± 2.3 μM) against the HT29 cell line. Therefore, the HT-29 cell line was found to be resistant to this complex [62]. Hussaini et al. successfully formulated silver (I)-benzimidazolium carbenes. A series of propylene-linked bis-benzimidazolium salts having different alkyl chains and respective binuclear silver complexes were prepared. Complexes showed dose-dependent cytotoxicities. Their cytotoxic studies against the MCF-7 cell line revealed compound **41** as the most active (IC50 = 7 ± 1 μM) complex as compared to tamoxifen (IC50 = 11 ± 2 μM). The presence of the propyl chain at the benzimidazole nucleus was found to be optimum for anticancer activity [63]. Later on, in 2018,

#### **Figure 9.**

*Bis-benzimidazolium silver metal complexes containing aliphatic nitriles, aromatic nitriles, benzyl and alkyl chains.*

Hussaini and his coworkers reported benzimidazolium salts having aliphatic nitrile group and their Ag (I)-benzimidazolium carbenes complexes. All of these NHC complexes showed good cytotoxicities with IC50 values in the range of 7.0–12.9 μM against the MCF-7 cell line. Compound **42** (IC50 = 7 ± 1.06 μM) was found to be the most potent and it carries a pentyl chain attached to the benzimidazole nitrogen. Cytotoxicities of these compounds increase as the alkyl chain length expands [64].

#### *2.3.2 Benzimidazolium silver and gold metal complexes*

Akkoc et al. reported a series of silver- and palladium-based metal complexes with benzimidazolium ligand. This attempt was made in search of the non-platinum antitumor drugs due to the observed side effects of cisplatin and nedaplatin. However, silver complex **43** (**Figure 10**) showed promising *in vitro* cytotoxic potential against DLD-1 (IC50 = 12.41 μM), MDA-MB-231 (IC50 = 11.98 μM) cancer cell lines, and HEK-239 (IC50 = 4.2 μM) non-cancer cell lines. Therefore, the silver complex was found more potent than the palladium complex [65]. Sahin et al. employed the conventional technique to synthesize *n*-allyl-substituted benzimidazolium-based carbene and corresponding Ag-(I) complexes. The first step was to obtain *n*-alkylated benzimidazole and later followed by salt formation. Silver dioxide was used to obtain the allyl-linked benzimidazolium Ag-(I) complex. Among all synthesized compounds, derivatives **44** (IC50 = 1.41 μM) and **45** (IC50 = 1.21 μM) showed the best *in vitro* anticancer potential against DU-145 and MCF-7, and MDA-MB-231 (IC50 < 1 μM) cancer cell lines. Derivatives **44** and **45** also exhibited some degree of selectivity [66]. Ozdemir et al. carried out the synthesis of silver and gold (Au) NHC-propyl sulfonate complexes. Silver complexes presented dominant activity as compared to gold salts. Compounds **46** (IC50 = 2.32 ± 0.089 μM) and **47** (IC50 = 9.31 ± 0.95 μM) presented prominent *in vitro* activities against adenocarcinoma (HEP3B) cancer cell lines. Complexes **46** and **47** are silver and gold complexes, respectively. These complexes

**Figure 10.** *Benzimidazolium silver and gold metal complexes.*

#### *The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

possess a dimethoxyethyl group at the benzimidazole nitrogen. Replacement of dimethoxyethyl group by diethoxyethyl group produced less active derivatives [67].

Similarly, the synthetic work of Cevik Yildiz and his coworkers resulted in the formation of novel benzimidazolium salt. These benzimidazolium salts were used as a ligand to obtain corresponding novel Ag (I)- benzimidazolium complexes. Cytotoxic studies of salts and complexes were carried out against MCF-7, MDA-MB-23, DU-145 by MTT assay. Compound **48** (**Figure 11**) displayed prominent activity (IC50 < 1 μM) against breast cancer MCF-7 and MDA-MB-23 cell lines. Compound **49** also showed prominent activity (IC50 < 1 μM) against the MCF-7 cell line than standard drug. These compounds showed concentration-dependent killing and also showed selectivity for cancer cell lines [68]. Aktas et al. carried out the synthesis of 2-morpholine ethyl-substituted benzimidazolium salts and their Ag-NHC complexes. Compounds **50** (IC50 = 6.59 μM) and **51** (IC50 = 6.56 μM) exhibited prominent activity against MCF-7 cell line. Ag-NHC complexes presented prominent activity as compared to benzimidazolium salts. Compounds **50** and **51** carry methyl and tetra-methyl benzyl groups at the benzimidazole nitrogen [69]. A series of di-isopropylamine ethyl benzimidazolium salts have been reported by Kızrak et al. These salts were further used as a precursor for the syntheses of corresponding silver and gold benzimidazolium carbene complexes. Resultant derivatives displayed prominent activity against the human brain (SHSY5Y) cell line and compounds **52, 53** were most prominent presenting IC50 values of 5.23 and 4.74 μM, respectively. Compounds **52** and **53** are

**Figure 11.** *Benzimidazolium silver metal complexes.*

silver and gold complexes, respectively. Therefore, the gold complex was found more potent than silver complexes. Compound **52** was also found significant against HEP3B (IC50 = 6.19 ± 1.09 μM) and HTC-116 (IC50 = 8.44 ± 1.07 μM) cancer cell line [70]. Sahin-Bolukbasi and Sahin synthesized two new benzimidazolium salts and reacted with silver dioxide (Ag2O) to obtain Ag-(I) benzimidazolium complexes. Evaluation of the anticancer potential of all these compounds reflected the higher cytotoxicity (IC50 < 1 μM) of **54** against DU-145, MCF-7, and MDA-MB-231. This compound carries 2-methyl propenyl and *p*-isopropyl benzyl substituents at the N1 and N3 positions of benzimidazole ring [71]. Early on, Sahin-Bolukbasi et al. synthesized unsymmetrical benzimidazolium salt and respective Ag-(I) complexes. All of the synthesized compounds were subjected to cytotoxic evaluation. Higher cytotoxicity was noted for benzimidazolium-based Ag complexes as compared to benzimidazolium salts, and particularly **55** and **56** were most active (IC50 < 1 μM) against MCF-7, MDA-MB-231 cancer cell lines. These compounds also demonstrated activity against DU-145 cell line having IC50 values of 6.02 ± 0.30 μM and 5.16 ± 0.33 μM, respectively. The *ortho*-substituted benzyl group proved more active as compared to *meta*- and *para*-substituted benzyl groups. And in *ortho*-substituted derivatives methyl group was found more potent as compared to the chlorine atom [72].

#### **2.4 Selenium-based benzimidazolium salts and complexes**

Selenium (Se) is very important for the human body and its deficiency can lead to cancer, diabetes, and cardiovascular diseases [73]. Selenium is present in some food and drinks in traces [74]. Recently, selenium has been incorporated in new anticancer agents due to its low toxicity. Kamal et al. applied a green synthetic approach to obtain novel benzimidazolium salts and Se-based benzimidazolium-heterocyclic carbenes. The *in vitro* anticancer potential was evaluated against RGC-5, Hela, MCF-7, and mouse melanoma (B16F10) cancer cell lines using fluorouracil as a standard drug. Prominent anticancer activity was observed against Hela and RCG cell lines. Among benzimidazolium salts (**Figure 12**), compounds **57** (IC50 = 0.04 ± 0.31 μM) and **58** (IC50 = 0.24 ± 0.22 μM) displayed prominent activity against Hela cell line.

**Figure 12.** *Benzimidazolium salts and selenium metal complexes.* *The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

The corresponding Se-NHC-adducts compounds **59** (IC50 = 0.11 ± 0.20 μM) and **60** (IC50 = 4.3 ± 0.11 μM) were found most active against Hela cell line. Compound **59** was also effective against RCG cell line (IC50 = 9.16 ± 0.27 μM). Molecular docking investigation of compounds **59** and **60** with epidermal growth factor (EGF), vascular endothelial growth factor (VEGF), and cyclooxygenase (COX-1) displayed strong interactions [75]. Similarly, green synthesis of benzimidazolium salts and di-Se-*N*-heterocyclic carbene complexes was carried out by Iqbal et al. The benzimidazolium salts **61** (IC50 = 3.94 μM) and respective Se-NHC **62** (IC50 = 3.49 μM) displayed prominent activity against HCT-116 cell line as compared to fluorouracil (IC50 = 4.9 μM). Both compounds possess benzyl groups at positions 1 and 3 of the benzimidazole nucleus. Compounds **61** and **62** also showed some degree of apoptosis by the mitochondrial pathway. Further pro-apoptotic evaluation for HCT-116 even at low concentration due to a strong release of selenium metal for DNA interaction was successfully reported [76].

#### **2.5 Ruthenium complexes based on benzimidazolium salts**

Organic compounds having ruthenium (Ru) metal are also being used as anticancer agents. Akkoc et al. synthesized methylpyridine-linked benzimidazolium salt and corresponding Ru (II) complexes containing benzimidazolium ligand. The antiproliferative assay revealed that **63** (**Figure 13**) showed DNA binding as well as the best cytotoxic potential against MCF-7 (IC50 = 23.8 μM), Caco-2 (IC50 = 18.0 μM) cell lines, respectively. Compound **63** carries a hexamethyl phenyl ring at position 2 of the benzimidazole ring. Compound **63** showed electrostatic and hydrophobic interaction with DNA and presented a binding affinity of −13.779 kcal/mol [77]. Omar et al. synthesized benzotriazole-functionalized palladium and ruthenium complexes. Comparison of cytotoxic studies revealed that ruthenium complexes are better than palladium complexes against MCF-7 and Caco-2 cancer cell lines. Although the activity displayed by these compounds

**Figure 13.** *Ruthenium complexes.*

was not prominent, these compounds were found inert for normal cell line L-929. Compound **64** (IC50 = 90 μM) is one member of this series [78]. Lam and his coworkers aimed for the novel benzimidazolium-based Ru complexes with halogen ligands for exploration of cytotoxic potential against HCT-116, SiHa, and NCI-H460 cell lines. Promising cytotoxic potential was observed in case of **65** against HCT-116 (IC50 = 6.2 ± 0.4 μM), SiHa (IC50 = 8.4 ± 0.2 μM), and NCI-H460 (IC50 = 7.8 ± 1.0 μM) cancer cell lines. Replacement of ruthenium by osmium (Os) also presented equal cytotoxicity against HCT-116 cell line [79].

### **2.6 Miscellaneous metal complexes**

As mentioned earlier, NHC-carbenes are highly reactive species depending upon the nature of the ligand and transition metal used; consequently, different transition metals have been coordinated with benzimidazolium ligand for a better cytotoxic effect. Troung et al. studied the cytotoxicity of rhodium (Rh)- and iridium (Ir)-based benzimidazolium complexes. A series of rhodium and iridium complexes were prepared and evaluated for anticancer potential against HCT-116, NCI-H460, SiHa, SW480 human cancer cell lines. Compounds **66** and **67** (**Figure 14**)

**Figure 14.** *Benzimidazole metal complexes with gold, rhodium, iridium, and palladium.*

#### *The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

advertised notable activity against HCT-116 (IC50 = 7.4 ± 0.5 μM, 11 ± 0.1 μM), NCI-H460 (IC50 = 11 ± 1 μM, 23 ± 3 μM), SiHa (IC50 = 10 ± 1 μM, 19 ± 1 μM), SW (IC50 = 5.8 ± 1 μM, 19 ± 1 μM) cancer cell lines. Compounds **66** and **67** are Ir and Rh metal complexes, respectively. These compounds contain benzyl groups at both nitrogen atoms of benzimidazole. Studies of the mode of action of rhodium complexes are based on the fact that instead of interaction with DNA, it accumulates in the cytoplasm [80]. Zhao et al. synthesized naphthyl NHC-Rh complexes by incorporating a hydroxy alkyl chain at benzimidazole nitrogen. Upon evaluation against MCF-7 cell line, compounds **68** (IC50 = 0.38 μM), **69** (IC50 = 0.45 μM), and **70** (IC50 = 0.72 μM) showed excellent activity as compared to standard drug paclitaxel (IC50 = 1.38 μM). Therefore, the introduction of the hydroxyl group and alkyl group at the benzimidazole nitrogen is beneficial for the activity [81]. Sanchez-Mora et al. reported the formation of two benzimidazolium-based Ir(I) complexes as new cytotoxic agents. The benzimidazole ring was substituted by benzyl and pentafluorobenzyl groups. The benzyl-substituted derivative presented prominent activity and compound **71** was found to be the strongest agent against PC-3 (IC50 = 10.6 ± 0.9 μM) and SKLU-7 (IC50 = 10.4 ± 1.5 μM) cell lines. This compound showed less toxicity for normal cell line COS-7 [82]. Choo et al. synthesized pyridine-functionalized Pd-based imidazolium and benzimidazolium carbenes. Imidazolium Pd complex showed prominent activity against cancer cell lines. Benzimidazolium Pd complex **72** is also an excellent candidate for anticancer studies. Generally, NHC-Pd complexes create covalent bonding with DNA resulting in cross-linking of guanine base [83]. Early on in 2012, Sivaram and his coworker were able to synthesize new gold (I) and gold (III) complexes bearing benzimidazolium ligand. These complexes were mono-, homo-bis-, and hetero-bis-benzimidazole NHC. The hetero-bis-benzimidazole complexes are nonclassical pyrazole-derived NHC. Complexes **73** (IC50 = 0.284 ± 0.11 μM) and **74** (IC50 = 0.24 ± 0.01 μM) exhibited prominent inhibitory action against NSCLC (NCI-H1666) cell line. These complexes are isopropyl-substituted homo-bis and hetero-bis NHC complexes, respectively [84]. Rehm et al. synthesized benzimidazole platinum complexes having different alkyl chains such as methyl, ethyl, butyl, and octyl chains. The bisphosphane complexes showed the excellent anticancer activity against seven cancer cell lines. Compound **75** appeared as the most effective against different cancer cell lines having IC50 values placing from 0.10 to 0.30 μM. Complex **75** displayed prominent activity (IC50 = 0.10 ± 0.01 μM) against multidrug-resistant strains of MCF-7. Cell cycle analysis of some complexes indicated that they produced cell blockage in the G1 stage [85].

#### **3. Conclusion**

The pharmacological properties of benzimidazolium salts have attracted the attention of medicinal chemists. The resemblance of benzimidazole scaffold with purine bases establishes it biologically significant. Benzimidazolium salts have demonstrated promising activities against various cancer cell lines. Benzimidazolium salts derivatives have been prepared by the functionalization of two nitrogen atoms in the imidazole ring along with the preparation of hybrid molecules, and metal complexes. The hybridization of benzimidazole salts with natural compounds such as chalcones and steroids exhibited prominent activities (IC50 < 1 μM) against various cancer cell lines. Some hybrids compounds also showed the phenomenon of apoptosis. Compounds

carrying alkyl chains and aromatic rings at benzimidazole nitrogen showed pronounced activity. The introduction of phenyl, naphthalene, anthracene, and quinoline rings at the benzimidazole nitrogens through methylene groups intensified the anticancer activity. The 5,6-dimethyl-substituted benzimidazole derivatives were also found more active as compared to unsubstituted benzimidazole rings. In the case of silver metal complexes, bis-benzimidazolium complexes exhibited exceptional activity against colon cancer (IC50 < 1 μM) cell line. But silver metal complexes presented less selectivity indices. Mono-benzimidazolium metal complexes proved more active against breast cancer (IC50 < 1 μM) cell lines. In some derivatives, the introduction of a long alkyl chain at the benzimidazole nitrogen is beneficial for the augmentation of anticancer activity. The activity of selenium metal complexes was almost equivalent to their respective salts. While the halogen-substituted ruthenium benzimidazole metal complexes showed moderate activity. Rhodium, platinum, and gold complexes have also shown encouraging anticancer activities and are excellent candidates for future investigations. The *in vivo* investigations of potent compounds mentioned in this chapter could lead to further developments in the field.

#### **Author details**

Imran Ahmad Khan1 , Noor ul Amin Mohsin2 , Sana Aslam3 and Matloob Ahmad1 \*

1 Department of Chemistry, Government College University, Faisalabad, Pakistan

2 Department of Pharmaceutical Chemistry, Faculty of Pharmaceutical Sciences, Government College University, Faisalabad, Pakistan

3 Department of Chemistry, Government College Women University Faisalabad, Pakistan

\*Address all correspondence to: matloob.ahmad@gcuf.edu.pk

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

### **References**

[1] Bray F, Ferlay J, Soerjomataram I. Global cancer statistics 2018: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA: A Cancer Journal for Clinicians. 2018;**68**(6):394-424. DOI: 10.3322/caac.21492

[2] Bray F, Jemal A, Grey N. Global cancer transitions according to the Human Development Index (2008-2030): A population-based study. The Lancet Oncology. 2012;**13**(8):790-801. DOI: 10.1016/S1470-2045(12)70211-5

[3] Danaei G, Vander Hoorn S, Lopez AD, Comparative Risk Assessment collaborating group (Cancers). Causes of cancer in the world: Comparative risk assessment of nine behavioural and environmental risk factors. The Lancet. 2005;**366**(9499):1784-1793. DOI: 10.1016/S0140-6736(05)67725-2

[4] Pucci C, Martinelli C, Ciofani G. Innovative approaches for cancer treatment: Current perspectives and new challenges. Ecancermedicalscience. 2019;**13**:961. DOI: 10.3332/ ecancer.2019.961

[5] Masoud V, Pages G. Targeted therapies in breast cancer: New challenges to fight against resistance. World Journal of Clinical Oncology. 2017;**8**(2):120-134. DOI: 10.5306%2Fwjco.v8.i2.120

[6] Vitaku E, Smith DT, Njardarson JT. Analysis of the structural diversity, substitution patterns, and frequency of nitrogen heterocycles among us FDA approved pharmaceuticals. Journal of Medicinal Chemistry. 2014;**57**(24): 10257-10274. DOI: 10.1021/jm501100b

[7] Barker HA, Smyth RD, Weissbach H. Isolation and properties of crystalline

cobamide coenzymes containing benzimidazole or 5, 6-dimethy lbenzimidazole. Journal of Biological Chemistry. 1960;**235**(2):480-488. DOI: 10.1016/s0021-9258(18)69550-x

[8] Khan MT, Razi MT, Jan SU. Synthesis, characterization, and antihypertensive activity of 2-phenyl substituted benzimidazoles. Pakistan Journal of Pharmaceutical Sciences. 2018;**31**(3):1067-1074. DOI: 10.36721/pjp s.2019.32.6.reg.2585-2597.1

[9] Kaur G, Silakari O. Benzimidazole scaffold-based hybrid molecules for various inflammatory targets: Synthesis and evaluation. Bioorganic Chemistry. 2018;**80**:24-35. DOI: 10.1016/j. bioorg.2018.05.014

[10] Al-Blewi FF, Almehmadi MA, Aouad MR. Design, synthesis, ADME prediction, and pharmacological evaluation of novel benzimidazole-1, 2, 3-triazole-sulfonamide hybrids as antimicrobial and antiproliferative agents. Chemistry Central Journal. 2018;**12**(1):1-14. DOI: 10.1186/ s13065-018-0479-1

[11] Scheinfeld N. Cimetidine: A review of the recent developments and reports in cutaneous medicine. Dermatology Online Journal. 2003;**9**(2):4. DOI: 10.5070/D33s15q645

[12] Vausselin T, Seron K, Lavie M. Identification of a new benzimidazole derivative as an antiviral against hepatitis C virus. Journal of Virology. 2016;**90**(19): 8422-8434. DOI: 10.1128/JVI.00404-16

[13] Ozil M, Parlak C, Baltas N. A simple and efficient synthesis of benzimidazoles containing piperazine or morpholine skeleton at C-6 position as glucosidase

inhibitors with antioxidant activity. Bioorganic Chemistry. 2018;**76**:468-477. DOI: 10.1016/j.bioorg.2017.12.019

[14] Hussain A, Alajmi MF, Rehman M. Evaluation of transition metal complexes of the benzimidazole-derived scaffold as promising anticancer chemotherapeutics. Molecules. 2018;**23**(5):1232-1250. DOI: 10.3390/molecules23051232

[15] Bharadwaj SS, Poojary B, Nandish SKM. Efficient synthesis and in silico studies of the benzimidazole hybrid scaffold with the quinolinyloxadiazole skeleton with potential α-glucosidase inhibitory, anticoagulant, and antiplatelet activities for type-II diabetes mellitus management and treating thrombotic disorders. ACS Omega. 2018;**3**(10):12562- 12574. DOI: 10.1021/acsomega.8b01476

[16] Wang YT, Shi TQ, Zhu HL. Synthesis, biological evaluation, and molecular docking of benzimidazole grafted benzsulfamide-containing pyrazole ring derivatives as novel tubulin polymerization inhibitors. Bioorganic & Medicinal Chemistry. 2019;**27**(3):502- 515. DOI: 10.1016/j.bmc.2018.12.031

[17] Ibrahim HS, Albakri ME, Mahmoud WR. Synthesis and biological evaluation of some novel thiobenzimidazole derivatives as anti-renal cancer agents through inhibition of c-MET kinase. Bioorganic Chemistry. 2019;**85**:337- 348. DOI: 10.1016/j.bioorg.2019.01.006

[18] Min R, Wu W, Wang M. Discovery of 2-(1-(3-(4-Chloroxyphenyl)-3-oxopropyl) pyrrolidine-3-yl)-1*H*-benzo [d] imidazole-4-carboxamide: A potent poly (ADP-ribose) polymerase (PARP) inhibitor for treatment of cancer. Molecules. 2019;**24**(10):1901. DOI: 10.3390/molecules24101901

[19] Gaba M, Mohan C. Development of drugs based on imidazole and

benzimidazole bioactive heterocycles: Recent advances and future directions. Medicinal Chemistry Research. 2016;**25**(2):173-210. DOI: 10.1007/ s00044-015-1495-5

[20] Purushottamachar P, Ramalingam S, Najar VC. Development of benzimidazole compounds for cancer therapy. In: Chemistry and Applications of Benzimidazole and its Derivatives. 2019. pp. 1-15. DOI: 10.5772/ intechopen.86691

[21] Narasimhan B, Sharma D, Kumar P. Benzimidazole: A medicinally important heterocyclic moiety. Medicinal Chemistry Research. 2012;**21**(3):269-283. DOI: 10.1007/s00044-010-9533-9

[22] Gupta S, Basu B, Das S. Benzimidazole-based palladium-*N*heterocyclic carbene: A useful catalyst for C-C cross-coupling reaction at ambient condition. Tetrahedron. 2013;**69**(1):122-128. DOI: 10.1016/j. tet.2012.10.055

[23] Medici S, Peana M, Crisponi G. Silver coordination compounds: A new horizon in medicine. Coordination Chemistry Reviews. 2016;**327**:349-359. DOI: 10.1016/j.ccr.2016.05.015

[24] Viegas-Junior C, Danuello A, da Silva Bolzani VDS. Molecular hybridization: A useful tool in the design of new drug prototypes. Current Medicinal Chemistry. 2007;**14**(17):1829- 1852. DOI: 10.2174/092986707781058805

[25] Singh A, Singh JV, Rana A. Monocarbonyl curcumin-based molecular hybrids as potent antibacterial agents. ACS Omega. 2019;**4**(7):11673- 11684. DOI: 10.1021/acsomega.9b01109

[26] Yang JL, Ma YH, Li YH. Design, synthesis, and anticancer activity of novel trimethoxyphenyl-derived chalcone-benzimidazolium salts. ACS *The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

Omega. 2019;**4**(23):20381-20393. DOI: 10.1021/acsomega.9b03077

[27] Karatas MO, Tekin S, Alici B. Cytotoxic effects of coumarin substituted benzimidazolium salts against human prostate and ovarian cancer cells. Journal of Chemical Sciences. 2019;**69**:131. DOI: 10.1007/s12039-019-1647-0

[28] Wang XQ, Chen XB, Ye PT. Synthesis and biological evaluation of novel 3-benzylcoumarin-imidazolium salts. Bioorganic & Medicinal Chemistry Letters. 2020;**30**(4):126896. DOI: 10.1016/j.bmcl.2019.126896

[29] Deng G, Zhou B, Wang J. Synthesis and antitumor activity of novel steroidal imidazolium salt derivatives. European Journal of Medicinal Chemistry. 2019; **168**:232-252. DOI: 10.1016/j.ejmech. 2019.02.025

[30] Nirmal NP, Rajput MS, Prasad RGSV. Brazilin from *Caesalpinia sappan* heartwood and its pharmacological activities: A review. Asian Pacific Journal of Tropical Medicine. 2015;**8**(6):421-430. DOI: 10.1016/j.apjtm.2015.05.014

[31] Huang M, Duan S, Ma X. Synthesis and antitumor activity of aza-brazilan derivatives containing imidazolium salt pharmacophores. MedChemComm. 2019;**10**(6):1027-1036. DOI: 10.1039/ C9MD00112C

[32] Zhou B, Liu ZF, Deng GG. Synthesis and antitumor activity of novel *N*-substituted tetrahydro-betacarboline-imidazolium salt derivatives. Organic & Biomolecular Chemistry. 2016;**14**(39):9423-9430. DOI: 10.1039/ C6OB01495J

[33] Xu XL, Wang J, Yu CL. Synthesis and cytotoxic activity of novel 1-((indol-3-yl)methyl)-1H-imidazolium salts. Bioorganic & Medicinal Chemistry

Letters. 2014;**24**(21):4926-4930. DOI: 10.1016/j.bmcl.2014.09.045

[34] Li YH, Zhou B, Shi YM. Novel 3-substituted *N*-methylcarbazoleimidazolium salt derivatives: Synthesis and cytotoxic activity. Chemical Biology & Drug Design. 2018;**92**(1):1206-1213. DOI: 10.1111/cbdd.13178

[35] Wang XQ, Ye PT, Bai MJ. Synthesis and biological activity of new bisbenzofuran-imidazolium salts. Bioorganic & Medicinal Chemistry Letters. 2020;**30**(13):127210. DOI: 10.1016/j.bmcl.2020.127210

[36] Zhang CB, Liu Y, Liu ZF. Synthesis and cytotoxic activity of novel tetrahydrobenzodifuran-imidazolium salt derivatives. Bioorganic & Medicinal Chemistry Letters. 2017;**27**(8):1808-1814. DOI: 10.1016/j.bmcl.2017.02.053

[37] Zhou Y, Duan K, Zhu L. Synthesis and cytotoxic activity of novel hexahydropyrrolo[2,3-b]indole imidazolium salts. Bioorganic & Medicinal Chemistry Letters. 2016; **26**(2):460-465. DOI: 10.1016/j. bmcl.2015.11.092

[38] Akkoc S, Kayser V, Ilhan IO. New compounds based on a benzimidazole nucleus: Synthesis, characterization and cytotoxic activity against breast and colon cancer cell lines. Journal of Organometallic Chemistry. 2017;**839**: 98-107. DOI: 10.1016/j.jorganchem. 2017.03.037

[39] Akkoc S, Kayser V, Ilhan IO. Synthesis and *in vitro* anticancer evaluation of some benzimidazolium salts. Journal of Heterocyclic Chemistry. 2019;**56**(10):2934-2944. DOI: 10.1002/ jhet.3687.svg

[40] Akkoc S. Antiproliferative activities of 2-hydroxyethyl substituted

benzimidazolium salts and their palladium complexes against human cancerous cell lines. Synthetic Communications. 2019;**49**(21):1-12. DOI: 10.1080/00397911.2019.1650187

[41] Lin ZJ, Bies J, Johnson SS. Synthesis and anti-proliferative activity of *N, N*′-bis-substituted 1,2,4-triazolium salts against breast cancer and prostate cancer cell Lines. Journal of Heterocyclic Chemistry. 2018;**56**(2):533-538. DOI: 10.1002/jhet.3428

[42] Wright BD, Deblock MC, Wagers PO. Anti-tumor activity of lipophilic imidazolium salts on select NSCLC cell lines. Medicinal Chemistry Research. 2015;**24**:2838-2861. DOI: 10.1007/ s00044-015-1330-z

[43] Stromyer ML, Southerland MR, Satyal U. Synthesis, characterization, and biological activity of a triphenylphosphonium-containing imidazolium salt against select bladder cancer cell lines. European Journal of Medicinal Chemistry. 2020;**185**:111832. DOI: 10.1016/j.ejmech.2019.111832

[44] Shelton KL, Debord MA, Wagers PO. Synthesis, anti-proliferative activity, SAR study, and preliminary in vivo toxicity study of substituted *N,N'* bis(arylmethyl) benzimidazolium salts against a panel of non-small cell lung cancer cell lines. Bioorganic & Medicinal Chemistry. 2017;**25**(1):421-439. DOI: 10.1016/j.bmc.2016.11.009

[45] Bansode P, Patil P, Choudhari P. Anticancer activity and molecular docking studies of ferrocene tethered ionic liquids. Journal of Molecular Liquids. 2019;**290**:111182. DOI: 10.1016/ j.molliq.2019.111182

[46] KucuKbay H, Mumcu A, Tekin S. Synthesis and evaluation of novel *N, N'*-disubstituted benzimidazolium

bromides salts as antitumor agents. Turkish Journal of Chemistry. 2016;**40**(3):393-401. DOI: 10.3906/ kim-1510-15

[47] Haque RA, Iqbal MA, Ahamed MBK. Design, synthesis and structural studies of meta-xylyl linked bisbenzimidazolium salts: Potential anticancer agents against human colon cancer. Chemistry Central Journal. 2012;**6**(1):68. DOI: 10.1186/1752- 153x-6-68

[48] Huda NU, Islam S, Zia M. Anticancer, antimicrobial and antioxidant potential of sterically tuned bis-*N*-heterocyclic salts. Zeitschrift für Naturforschung - Section C Journal of Biosciences. 2018;**74**(1):17-23. DOI: 10.1515/znc-2018-0095

[49] Rosenberg B, Van Camp L, Krigas T. Inhibition of cell division in *Escherichia coli* by electrolysis products from a platinum electrode. Nature. 1965;**205**: 698-699. DOI: 10.1038/205698a0

[50] Da Silva B, Habibi M, Ognier S. Silver nanocluster catalytic microreactors for water purification. The European Physical Journal Special Topics. 2016;**225**:707-714. DOI: 10.1140/epjst/ e2015-50262-6

[51] Varaprasad K, Mohan YM, Vimala K. Synthesis and characterization of hydrogel-silver nanoparticle-curcumin composites for wound dressing and antibacterial application. Journal of Applied Polymer Science. 2011;**121**(2):784-796. DOI: 10.1002/app.33508

[52] Iqbal MA, Umar MI, Haque RA. Macrophage and colon tumor cells as targets for a binuclear silver(I) *N*-heterocyclic carbene complex, an anti-inflammatory and apoptosis mediator. Journal of Inorganic

*The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

Biochemistry. 2015;**146**:1-13. DOI: 10.1016/j.jinorgbio.2015.02.001

[53] Ghdhayeb MZ, Haque RA, Budagumpi S. Mono- and bis-*N*heterocyclic carbene silver(I) and palladium(II) complexes: Synthesis, characterization, crystal structure and *in vitro* anticancer studies. Polyhedron. 2017;**121**:222-230. DOI: 10.1016/j. poly.2016.09.065

[54] Sharhan O, Heidelberg T, Hashim NM. Benzimidazolium-acridinebased silver *N*-heterocyclic carbene complexes as potential anti-bacterial and anti-cancer drug. Inorganica Chimica Acta. 2020;**504**: 119462. DOI: 10.1016/j.ica.2020.119462

[55] Habib A, Nazari VM, Iqbal MA. Unsymmetrically substituted benzimidazolium based Silver(I)-*N*heterocyclic carbene complexes: Synthesis, characterization and in vitro anticancer study against human breast cancer and colon cancer. Journal of Saudi Chemical Society. 2019;**23**(7):795-808. DOI: 10.1016/j.jscs.2019.03.002

[56] Atif M, Bhatti HN, Haque RA. Synthesis, structure and anticancer activity of symmetrical and nonsymmetrical silver(I)-*N*-heterocyclic carbene complexes. Applied Biochemistry and Biotechnology. 2020;**191**:1171-1189. DOI: 10.1007/ s12010-019-03186-9

[57] Achar G, Shahini CR, Patil SA. Sterically modulated silver(I) complexes of coumarin substituted benzimidazol-2 ylidenes: Synthesis, crystal structures and evaluation of their antimicrobial and antilung cancer potentials. Journal of Inorganic Biochemistry. 2018;**183**:43-57. DOI: 10.1016/j.jinorgbio.2018.02.012

[58] Yasar S, Koprulu TK, Tekin S. Synthesis, characterisation and cytotoxic properties of *N* -heterocyclic carbene silver(I) complexes. Inorganica Chimica Acta. 2018;**479**:17-23. DOI: 10.1016/j.ica.2018.04.035

[59] Karlik O, Balcıoglu S, Karatas MO. Synthesis, structural characterization and cytotoxicity studies of T-shaped silver(I) complexes derived from 1-benzyl-3*H*-benzimidazolium *p*-toluenesulfonates. Polyhedron. 2018;**142**:63-70. DOI: 10.1016/j. poly.2017.12.033

[60] Fatima T, Haque RA, Razali MR. Effect of lipophilicity of wingtip groups on the anticancer potential of mono *N*-heterocyclic carbene silver(I) complexes: Synthesis, crystal structures and *in vitro* anticancer study. Applied Organometallic Chemistry. 2017;**31**(10): e3735. DOI: 10.1002/aoc.3735

[61] Haque RA, Choo SY, Budagumpi S. Synthesis, crystal structures, characterization and biological studies of nitrile-functionalized silver(I) *N*-heterocyclic carbene complexes. Inorganica Chimica Acta. 2015;**433**: 35-44. DOI: 10.1016/j.ica.2015.04.023

[62] Haque RA, Choo SY, Budagumpi S. Silver(I) complexes of mono- and bidentate *N*-heterocyclic carbene ligands: synthesis, crystal structures, and *in vitro* antibacterial and anticancer studies. European Journal of Medicinal Chemistry. 2015;**90**:82-92. DOI: 10.1016/ j.ejmech.2014.11.005

[63] Hussaini SY, Haque RA, Asekunowo PO. Synthesis, characterization and anti-proliferative activity of propylene linked bisbenzimidazolium salts and their respective dinuclear Silver(I)-*N*heterocyclic carbene complexes. Journal of Organometallic Chemistry. 2017;**840**:56-62. DOI: 10.1016/j. jorganchem.2017.04.011

[64] Hussaini SY, Haque RA, Fatima T. Nitrile functionalized silver(I) *N*-heterocyclic carbene complexes: DFT calculations and antitumor studies. Transition Metal Chemistry. 2018;**43**: 301-312. DOI: 10.1007/s11243-018-0216-6

[65] Akkoc S, Ozer Ilhan I, Gok Y. *In vitro* cytotoxic activities of new silver and PEPPSI palladium *N*-heterocyclic carbene complexes derived from benzimidazolium salts. Inorganica Chimica Acta. 2016;**449**:75-81. DOI: 10.1016/j.ica.2016.05.001

[66] Sahin N, Sahin-Bolukbasi S, Tahir MN. Synthesis, characterization and anticancer activity of allyl substituted *N*-Heterocyclic carbene silver (I) complexes. Journal of Molecular Structure. 2019;**1179**:92-99. DOI: 10.1016/j.molstruc.2018.10.094

[67] Ozdemir I, Ciftci O, Evren E. Synthesis, characterization and antitumor properties of novel silver(I) and gold(I) *N*-heterocyclic carbene complexes. Inorganica Chimica Acta. 2020;**506**:119530. DOI: 10.1016/j. ica.2020.119530

[68] Cevik-Yildiz E, Sahin N, Sahin-Bolukbasi S. Synthesis, characterization, and investigation of antiproliferative activity of novel Ag (I)-*N*-heterocyclic Carbene (NHC) compounds. Journal of Molecular Structure. 2020;**1199**:126987. DOI: 10.1016/j.molstruc.2019.126987

[69] Aktas A, Kelestemur U, Gok Y. 2-Morpholinoethyl-substituted *N*-heterocyclic carbene (NHC) precursors and their silver (I) NHC complexes: Synthesis, crystal structure and *in vitro* anticancer properties. Journal of the Iranian Chemical Society. 2018;**15**:131-139. DOI: 10.1007/ s13738-017-1216-8

[70] Kızrak U, Ciftci O, Ozdemir I. Amine-fnctionalized silver and gold *N*-heterocyclic carbene complexes: Synthesis, characterization and antitumor properties. Journal of Organometallic Chemistry. 2019;**882**: 26-32. DOI: 10.1016/j.jorganchem. 2018.12.018

[71] Sahin-Bolukbasi S, Sahin N. Novel Silver-NHC complexes: Synthesis and anticancer properties. Journal of Organometallic Chemistry. 2019;**891**: 78-84. DOI: 10.1016/j.jorganchem. 2019.04.018

[72] Sahin-Bolukbasi S, Sahin N, Tahir MN. Novel *N*-heterocyclic carbene silver(I) complexes: Synthesis, structural characterization, and anticancer activity. Inorganica Chimica Acta. 2019;**486**:711- 718. DOI: 10.1016/j.ica.2018.11.044

[73] Roman M, Jitaru P, Barbante C. Selenium biochemistry and its role for human health. Metallomics. 2014;**6**(1): 25-54. DOI: 10.1039/c3mt00185g

[74] Eiche E, Nothstein AK, Gottlicher J. The behaviour of irrigation induced Se in the groundwater-soil-plant system in Punjab, India. Environmental Science. Processes & Impacts. 2019;**21**(6):957- 969. DOI: 10.1039/C9EM00009G

[75] Kamal A, Nazari M, Yaseen M. Green synthesis of Selenium-*N*-heterocyclic carbene compounds: Evaluation of antimicrobial and anticancer potential. Bioorganic Chemistry. 2019;**90**:103042. DOI: 103042, 10.1016/j. bioorg.2019.103042

[76] Iqbal MA, Haque RA, Ng WC. Green synthesis of mono- and di-Selenium-*N*heterocyclic carbene adducts: Characterizations, crystal structures and pro-apoptotic activities against human colorectal cancer. Journal of

*The Anticancer Profile of Benzimidazolium Salts and Their Metal Complexes DOI: http://dx.doi.org/10.5772/intechopen.101729*

Organometallic Chemistry. 2016;**801**: 130-138. DOI: 10.1016/j.jorganchem. 2015.10.023

[77] Akkoc M, Balciolu S, Gurses C. Protonated water-soluble *N*-heterocyclic carbene ruthenium(II) complexes: Synthesis, cytotoxic and DNA binding properties and molecular docking study. Journal of Organometallic Chemistry. 2018;**869**:67-74. DOI: 10.1016/j. jorganchem.2018.06.003

[78] Onar G, Gurses C, Karatas MO. Palladium (II) and ruthenium (II) complexes of benzotriazole functionalized *N*-heterocyclic carbenes: Cytotoxicity, antimicrobial, and DNA interaction studies. Journal of Organometallic Chemistry. 2019;**886**: 48-56. DOI: 10.1016/j.jorganchem. 2019.02.013

[79] Lam NYS, Truong D, Burmeister H. From catalysis to cancer: Toward structure-activity relationships for benzimidazol-2-ylidene-derived *N*-heterocyclic-carbene complexes as anticancer Agents. Inorganic Chemistry. 2018;**57**(22):14427-14434. DOI: 10.1021/ acs.inorgchem.8b02634

[80] Truong D, Sullivan MP, Tong KKH. Potent inhibition of thioredoxin reductase by the Rh derivatives of anticancer M(arene/Cp\*) (NHC)Cl2 complexes. Inorganic Chemistry. 2020;**59**(3):3281-3289. DOI: 10.1021/acs. inorgchem.9b03640

[81] Zhao X, Shi L, He W. Synthesis of novel NHC–Rh complexes with antitumor activity against MCF-7 human breast cancer cells. ARKIVOC. 2020;**vi**:94-104. DOI: 10.24820/ ark.5550190.p011.129

[82] Sanchez-Mora A, Valdes H, Ramirez-Apan MT. NHC-Ir (I)

complexes derived from 5, 6-dinitrobenzimidazole. Synthesis, characterization and preliminary evaluation of their *in vitro* anticancer activity. Inorganica Chimica Acta. 2019;**496**:119061. DOI: 10.1016/j. ica.2019.119061

[83] Choo KB, Mah WL, Lee SM. Palladium complexes of bidentate pyridine *N*-heterocyclic carbenes: Optical resolution, antimicrobial and cytotoxicity studies. Applied Organometallic Chemistry. 2018;**32**: e4377. DOI: 10.1002/aoc.4377

[84] Sivaram H, Tan J, Huynh HV. Syntheses, characterizations, and a preliminary comparative cytotoxicity study of gold(I) and gold(III) complexes bearing benzimidazole- and pyrazolederived *N*-heterocyclic carbenes. Organometallics. 2012;**31**(16):5875-5883. DOI: 10.1021/om300444c

[85] Rehm T, Rothemund M, Bar A. *N, N*-dialkylbenzimidazol-2-ylidene platinum complexes - effects of alkyl residues and ancillary cis-ligands on anticancer activity. Dalton Transactions. 2018;**47**(48):17367-17381. DOI: 10.1039/ C8DT03360A

Section 2
