**African Plants with Antiproliferative Properties**

Newman Osafo, Yaw Duah Boakye, Christian Agyare, Samuel Obeng, Judith Edem Foli and Prince Amankwaah Baffour Minkah

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68568

#### **Abstract**

Plant-derived compounds have been an integral component in man's quest to discover ideal anticancer agents. A number of new agents are currently in clinical development with promising selective activity against cancer cell lines and cancer-related molecular targets. This book chapter discusses 14 of such compounds isolated from African plants from 15 plant families. Also contained in this book chapter are compounds from African plants that hold prospect as potential anticancer agents as informed by their *in vitro* and *in vivo* preclinical studies. It is, therefore, worthwhile that researchers in the African continent and the world over should keep on working on identifying biomolecules with potential in cancer management.

**Keywords:** African plants, antiproliferation, clinical trials, preclinical studies, cancer

### **1. Introduction**

Plant-derived compounds have been an important source of several clinically useful antiproliferative agents in the past half century [1, 2]. Compounds of natural origin such as vinblastine, vincristine, topotecan and irinotecan, etoposide, and paclitaxel have been some of the chemotherapeutic agents still in clinical practice. A number of new agents are currently in clinical development with promising selective activity against cancer cell lines and cancerrelated molecular targets, while some agents that failed in earlier clinical studies are stimulating renewed interest.

The present chapter will consider plant-derived antineoplastic single chemical entities currently in clinical trials as oncology drugs. Lead compounds from plants showing promising

© 2017 The Author(s). Licensee InTech. 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.

*in vivo* antiproliferative activity will also be discussed in terms of their origin, possible mechanism of action, and their potential use in cancer management. Most importantly, natural products are generally believed to possess therapeutic potentials hence mostly pharmacologically relevant. This is coupled with the belief that they hold a significant advantage of them being the safer alternative to synthetic molecules [3–5].

Natural products hold a convincing prospect in the continual search for effective anticancer agents with tolerable side effect profile. These observations are well articulated in reviews that have unearthed the fact that about 47% of new anticancer agents that have been approved up to 2006 were either a natural product or their derivative [6]. Due to the labor-intensiveness of bioassay-guided isolation of natural products from crude extracts, more pharmaceutical firms tend to resort to a rapid high-throughput screening of molecular target-based pure compound chemical libraries. Nevertheless, the importance of identification of these bioactive molecules from natural origin is still very palpable in recent years with industries adopting screening procedures that maximize their output [7–9].

A substantial number of chemical moieties of plant origin are currently in various stages of clinical trials [10–12]. However, most of these plant-derived biomolecules are derived from the anticancer agents in clinical therapy which include paclitaxel [ABI-007, RPR-116278A, XRP9881 (RPR109881A)], camptothecin [exatecan mesylate, orathecin], vinblastine and vincristine (vinflunine ditartrate, vinorelbine, anhydrovinblastine, vincristine sulfate TCS), and epipodophyllotoxin (NK-611 and tafluposide 105) [10–12]. Such newer molecules based on the structures of these anticancer agents were not discussed in this book chapter. However, newly isolated compounds from African plants which show potential as possible anticancer agent based on their *in vivo* and *in vitro* studies were included in this book chapter.

### **2. Compounds of plant origins currently under clinical trial as potential anticancer drugs**

### **2.1. Betulin, β-sitosterol, and betulinic acid**

*Parinari curatellifolia* Planch. ex. Benth (Chrysobalanaceae) is a plant found widely distributed in Africa. Traditionally, it is used for the treatment of toothache (root infusion), pneumonia (hot fomentation of the bark), fevers (leaf decoction), and also as dressing agents for fractures, dislocations, wounds, sores, and cuts (crushed leaves) [13]. In Northern Nigeria, traditional healers use it for the treatment of cancer. Research has indicated that the bioactive constituents of the plant can decrease cancer risk through their antioxidant, antitumorigenic, and antimicrobial activity as well as their ability to directly suppress carcinogen bioactivation. Betulinic acid has been shown to be cytotoxic to neuroectodermal and brain tumor cells [14]. Its apoptotic property is through the regulation of the intrinsic pathway by changing mitochondrial membrane potential and activation of p38 MAPK and SAP/JNK by initiating reactive oxygen species (ROS) generation [15]. This compound can be semisynthesized by oxidation of betulin, which occurs more abundantly [16]. A betulinic acid-containing ointment is undergoing Phase I/II clinical evaluation for the treatment of dysplastic nevi with moderate to severe dysplasia [17]. Halilu et al. after preliminary investigations also revealed that betulin, β-sitosterol, and betulinic acid were toxic to the cervical epithelial carcinoma (HeLa) cell line used in the assay using the XTT colorimetric assay and cell proliferation Kit II [18].

### **2.2. Curcumin (diferuloylmethane)**

*in vivo* antiproliferative activity will also be discussed in terms of their origin, possible mechanism of action, and their potential use in cancer management. Most importantly, natural products are generally believed to possess therapeutic potentials hence mostly pharmacologically relevant. This is coupled with the belief that they hold a significant advantage of them

Natural products hold a convincing prospect in the continual search for effective anticancer agents with tolerable side effect profile. These observations are well articulated in reviews that have unearthed the fact that about 47% of new anticancer agents that have been approved up to 2006 were either a natural product or their derivative [6]. Due to the labor-intensiveness of bioassay-guided isolation of natural products from crude extracts, more pharmaceutical firms tend to resort to a rapid high-throughput screening of molecular target-based pure compound chemical libraries. Nevertheless, the importance of identification of these bioactive molecules from natural origin is still very palpable in recent years with industries adopting

A substantial number of chemical moieties of plant origin are currently in various stages of clinical trials [10–12]. However, most of these plant-derived biomolecules are derived from the anticancer agents in clinical therapy which include paclitaxel [ABI-007, RPR-116278A, XRP9881 (RPR109881A)], camptothecin [exatecan mesylate, orathecin], vinblastine and vincristine (vinflunine ditartrate, vinorelbine, anhydrovinblastine, vincristine sulfate TCS), and epipodophyllotoxin (NK-611 and tafluposide 105) [10–12]. Such newer molecules based on the structures of these anticancer agents were not discussed in this book chapter. However, newly isolated compounds from African plants which show potential as possible anticancer

agent based on their *in vivo* and *in vitro* studies were included in this book chapter.

**2. Compounds of plant origins currently under clinical trial as potential** 

*Parinari curatellifolia* Planch. ex. Benth (Chrysobalanaceae) is a plant found widely distributed in Africa. Traditionally, it is used for the treatment of toothache (root infusion), pneumonia (hot fomentation of the bark), fevers (leaf decoction), and also as dressing agents for fractures, dislocations, wounds, sores, and cuts (crushed leaves) [13]. In Northern Nigeria, traditional healers use it for the treatment of cancer. Research has indicated that the bioactive constituents of the plant can decrease cancer risk through their antioxidant, antitumorigenic, and antimicrobial activity as well as their ability to directly suppress carcinogen bioactivation. Betulinic acid has been shown to be cytotoxic to neuroectodermal and brain tumor cells [14]. Its apoptotic property is through the regulation of the intrinsic pathway by changing mitochondrial membrane potential and activation of p38 MAPK and SAP/JNK by initiating reactive oxygen species (ROS) generation [15]. This compound can be semisynthesized by oxidation of betulin, which occurs more abundantly [16]. A betulinic acid-containing ointment is undergoing

being the safer alternative to synthetic molecules [3–5].

4 Natural Products and Cancer Drug Discovery

screening procedures that maximize their output [7–9].

**anticancer drugs**

**2.1. Betulin, β-sitosterol, and betulinic acid**

Curcumin, a polyphenol obtained from turmeric (*Curcuma longa* L., Family: Zingiberaceae), has been associated with a wide range of activities including potential antitumor effect, antimicrobial, antioxidant, anti-inflammatory, and immunomodulatory effect [19]. Turmeric plant is very common in Asia and Africa [20]. The plant is employed in traditional medicine for treating a wide range of communicable and noncommunicable diseases such as skin infections, worm infestations, diabetes, liver diseases, and gallstones [21]. A phase II clinical trial of curcumin in patients with advanced pancreatic cancer showed a brief but significant tumor regression with no toxicities observed. Also, clinical studies of curcumin alone or in combination with other chemotherapeutic agents (gemcitabine, 5-fluorouracil, and oxaliplatin) have been carried out in the United States and Israel for patients with colorectal and pancreatic cancers [22]. The mechanism of action was shown to be possibly due to its ability to downregulate expression of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), cyclooxygenase-2 (COX-2), and phosphorylated signal transducer and activator of transcription 3 (STAT3) in peripheral blood mononuclear cells. However, absorption was observed to be poor [22].

### **2.3. Lycopene**

This compound is present in fruits and vegetables, notably *Solanum lycopersicum* L. (Solanaceae) and its processed products [23]. *Solanum lycopersicum* is widely distributed in Africa. It is used in folk medicine for treating burns, wounds, and toothaches. Nahum et al. reported that lycopene inhibits cell cycle progression via reduction of the cyclin D level and retention of p27 in cyclin E-cdk2, thus leading to inhibition of G1 CDK activities in breast and endometrial cancers [24]. Besides its antioxidant and anti-inflammatory activities, lycopene has been established to possess anticancer property in both *in vitro* and *in vivo* models. Its mechanism of action has been established to be via the activation of the electrophile/antioxidant response element (EpRE/ARE) transcription system, inducing the expression of phase II detoxifying enzymes, and arresting the cell cycle at the G0/G1 phase by regulating cyclin D1 and the PI3K/ Akt pathway [25]. Lycopene is currently in Phase II clinical trials in the United States for the prevention and treatment of prostate cancer [26].

### **2.4. Resveratrol**

Resveratrol (3,4,5-trihydrostilbene) is a phenolic compound found in several plants such as *Vitis vinifera* L. (Vitaceae), *Morus alba* L. (Moraceae), and *Arachis hypogaea* L. (Fabaceae). *A. hypogea* and *M. alba* are widely distributed in Africa. It is used in the treatment of infectious diseases. The cardioprotective property of red wine has been attributed to resveratrol [27, 28]. A number of studies have reported on the antioxidant, anti-inflammatory, anticancer, and anti-aging activities of resveratrol [27–29]. Its mechanism of action entails the enhancement of apoptosis by acting at multiple cellular targets, including activation of p53, inhibiting cyclooxygenase and cytochrome P450 enzymes, and activating AMP-activated kinase (AMPK) [27–29]. Also, it exhibits sensitization effects on drug-resistant tumor cells and results in a synergistic cytotoxicity when combined with established anticancer therapies [30]. This compound is now undergoing Phase I/II clinical trials for the prevention and treatment of colon cancer in the United States [31].

### **2.5. 2″-Oxovoruscharin and UNBS1450**

From *Calotropis procera* (Aiton) W.T. Aiton (Asclepiadaceae) is isolated the cardenolide, 2"-oxovoruscharin with a demonstrated *in vitro* antitumor and Na+/K+-ATPase inhibitory activities [32]. *Calotropis procera* is native to North Africa, Tropical Africa, Western Asia, South Asia, and Indochina [33]. Reduction of the formyl group in the 2"-oxovoruscharin molecule into a hydroxymethyl group yields UNBS1450 with an improved *in vitro* cytotoxicity profile when compared with the parent compound [34]. UNBS1450 has been established to induce the disruption of the actin cytoskeleton to affect multiple signaling pathways by binding to the sodium pump, and that leads to nonapoptotic cell death [35]. UNBS1450 has entered Phase I clinical studies in Europe for patients with solid tumors and lymphomas [36]. *Calotropis procera* is widely distributed in Africa and also employed in folkloric medicine as an abortifacient, hepatoprotective agent, anti-inflammatory agent as well as treating leprosy, syphilis, and cutaneous infections [37].

### **2.6. Combretastatin A1 and combretastatin A4**

Combretastatins isolated from the South African tree, *Combretum caffrum* Kuntze (Combretaceae) are simple stilbenoid compounds with a number of activities including anticancer activity. The A series combretastatin are cis-stilbenes with potent *in vitro* antiproliferative activity against the leukemic P388 and L1210 cell lines. Combretastatin A4, the most potent member of the group, in sodium phosphate prodrug form, has not long ago completed phase I clinical trials as an antiangiogenic tubulin-binding agent and in nonsmall cell lung cancer and cervix carcinoma, and is presently being assessed in a phase II trial with regards to ovarian, anaplastic thyroid, gastric, and other solid tumors [19, 38]. A propanamide derivative of combretastatin A4 exhibits even more potent antitumor effect than the phosphate by inducing an irreversible blockage of tumor blood flow and is now in phase I clinical studies in Europe and the United States [39, 40]. Again, a bisphosphate prodrug of combretastatin A1 has also been reported to be more potent than combretastatin A4 phosphate and is undergoing phase I anticancer clinical trials in the United Kingdom [40].

### **2.7. Perillyl alcohol**

The essential oils of *Lavandula X intermedia* (Lamiaceae) and *Prunus avium* L. (Rosaceae) are rich in perillyl alcohol, a monoterpenoid with a monocyclic carbon skeleton [41]. *Lavandula*  *X intermedia* and *Prunus avium* are plants which are widely distributed in South and North Africa, respectively. *In vitro* studies have established the cytotoxicity of perillyl alcohol to cell lines derived from lung cancer, pancreatic cancer, prostate cancer, breast cancer, and leukemia. *In vivo* studies also revealed the inhibitory effects of perillyl alcohol against UVB-induced skin carcinogenesis and DMBA-induced murine melanoma models [42, 43]. Its antiproliferative activity was shown to be due to its arrest of the G0/G1 phase, by modulating the protein levels of cyclin-dependent kinases and cyclin-dependent kinase inhibitors [44]. Currently, perillyl alcohol is undergoing phase I/II clinical trials in patients with breast cancer, ovarian cancer, and glioblastoma multiform [45].

### **2.8. Alvocidib (Flavopiridol)**

A number of studies have reported on the antioxidant, anti-inflammatory, anticancer, and anti-aging activities of resveratrol [27–29]. Its mechanism of action entails the enhancement of apoptosis by acting at multiple cellular targets, including activation of p53, inhibiting cyclooxygenase and cytochrome P450 enzymes, and activating AMP-activated kinase (AMPK) [27–29]. Also, it exhibits sensitization effects on drug-resistant tumor cells and results in a synergistic cytotoxicity when combined with established anticancer therapies [30]. This compound is now undergoing Phase I/II clinical trials for the prevention and treatment of colon

From *Calotropis procera* (Aiton) W.T. Aiton (Asclepiadaceae) is isolated the cardenolide, 2"-oxovoruscharin with a demonstrated *in vitro* antitumor and Na+/K+-ATPase inhibitory activities [32]. *Calotropis procera* is native to North Africa, Tropical Africa, Western Asia, South Asia, and Indochina [33]. Reduction of the formyl group in the 2"-oxovoruscharin molecule into a hydroxymethyl group yields UNBS1450 with an improved *in vitro* cytotoxicity profile when compared with the parent compound [34]. UNBS1450 has been established to induce the disruption of the actin cytoskeleton to affect multiple signaling pathways by binding to the sodium pump, and that leads to nonapoptotic cell death [35]. UNBS1450 has entered Phase I clinical studies in Europe for patients with solid tumors and lymphomas [36]. *Calotropis procera* is widely distributed in Africa and also employed in folkloric medicine as an abortifacient, hepatoprotective agent, anti-inflammatory agent as well as treating leprosy,

Combretastatins isolated from the South African tree, *Combretum caffrum* Kuntze (Combretaceae) are simple stilbenoid compounds with a number of activities including anticancer activity. The A series combretastatin are cis-stilbenes with potent *in vitro* antiproliferative activity against the leukemic P388 and L1210 cell lines. Combretastatin A4, the most potent member of the group, in sodium phosphate prodrug form, has not long ago completed phase I clinical trials as an antiangiogenic tubulin-binding agent and in nonsmall cell lung cancer and cervix carcinoma, and is presently being assessed in a phase II trial with regards to ovarian, anaplastic thyroid, gastric, and other solid tumors [19, 38]. A propanamide derivative of combretastatin A4 exhibits even more potent antitumor effect than the phosphate by inducing an irreversible blockage of tumor blood flow and is now in phase I clinical studies in Europe and the United States [39, 40]. Again, a bisphosphate prodrug of combretastatin A1 has also been reported to be more potent than combretastatin A4 phosphate and is undergoing phase I anticancer clinical trials in the United

The essential oils of *Lavandula X intermedia* (Lamiaceae) and *Prunus avium* L. (Rosaceae) are rich in perillyl alcohol, a monoterpenoid with a monocyclic carbon skeleton [41]. *Lavandula* 

cancer in the United States [31].

6 Natural Products and Cancer Drug Discovery

**2.5. 2″-Oxovoruscharin and UNBS1450**

syphilis, and cutaneous infections [37].

Kingdom [40].

**2.7. Perillyl alcohol**

**2.6. Combretastatin A1 and combretastatin A4**

Alvocidib, a semisynthetic rohitukine, is an N-methylpiperidine alkaloid first isolated from *Aphanamixis polystachya* (Roxb.) Wight & Arn. (Meliaceae) and later from the African plant *Schumanniophyton magnificum* (K.Schum.) Harms. (Rubiaceae) [46]. It is also present in the stem bark of *Dysoxylum binectariferum* Hiern (Meliaceae) from India and documented to have immunomodulatory and anti-inflammatory activity [46, 47]. Alvocidib has been established to exhibit cytotoxicity for a wide range of cancer cell lines and has demonstrated *in vivo* activity against prostate cancer, head and neck cancer, hematopoietic neoplasia, leukemia, and lymphoma xenograft murine models [48, 49]. Its mechanism has been established to involve inhibition of cyclin-dependent kinases (CDKs) by competing with adenosine triphosphate (ATP) at their nucleotide binding sites and causes cell cycle arrest at either the G1 or G1/M phases. Also, it exhibits apoptosis induction, and antiangiogenic and antiproliferative effects, by interacting at other target sites besides CDK [50, 51]. Alvocidib is the first cyclin-dependent kinase inhibitor in clinical trials for the treatment of patients with non-Hodgkin's lymphoma, renal, prostate, colon, and gastric cancers [50–53].

#### **2.9. Maytansinoids**

The parent nitrogen-containing macrocylic substance, maytansine, was first isolated by Kupchan and colleagues from the Ethiopian shrub *Maytenus serrata* (Hochst. ex A. Rich.) R. Wilczek (Celastraceae) [54]. Maytansinoids exhibits antimitotic activity due to tubulin binding hence resulting in inhibition of microtubule assembly [55, 56]. However, there is an overlap of maytansinoids with vincristine in their binding site activity [57, 58]. Maytansinoids has exhibited antiproliferative activity against Lewis lung carcinoma, B-16 melanocarcinoma, murine solid tumor test system, and antileukemic activity against P-388 lymphocytic leukemia, significantly over a 50–100 fold dosage range at the µg/kg level [54, 59]. Clinical trials with maytansine, both alone and as a monoclonal antibody conjugate, however, showed toxicity as well as low response rates in adults with advanced cancer [12, 31, 60]. This informed further metabolic studies involving maytansine to be undertaken to produce analogs with better clinical potential [61]. The extremely high *in vitro* potency of the maytansinoids has sustained interest in structure-activity relationship studies, analog development, total synthesis, and preclinical studies [62].

### **2.10. Indirubin and 1-methylisoindigo**

These are indole alkaloids isolated from the leaves and/or stems of several plants which include the African plant, *Indigofera tinctoria* L. (Fabaceae), as well as *Baphicacanthus cusia* (Nees) Bremek. (Acanthaceae), *Indigofera suffruticosa* Mill. (Fabaceae), *Isatis tinctoria* L. (Brassicaceae), and *Polygonum tinctorium* Ait. (Polygonaceae) [63, 64]. Indirubin has been demonstrated to exert its antileukemic effect by competing with ATP for binding to the catalytic subunit of cyclin-dependent kinase (CDK), via hydrogen bonding, leading to the inhibition of this enzyme [65]. 1-Methylisoindigo is a derivative developed to improve water solubility and other pharmaceutical properties of indirubin. 1-methylisoindigo exhibited significant anticancer activity through a multitargeting profile including inhibition of DNA biosynthesis and assembly of microtubules, induction of cell differentiation, and down-regulation of c-myb gene expression [65, 66]. 1-Methylisoindigo is under clinical trial in the People's Republic of China for chronic myelogenous leukemia (CML) [67].

### **3. Plant-derived compounds with potential anticancer activity but not yet in clinical trials**

#### **3.1. Fagaronine**

Fagaronine is a benzophenanthridine alkaloid isolated from *Fagara zanthoxyloides* Lam. (syn. *Zanthoxylum zanthoxyloides*) (Rutaceae), which is widely distributed in Uganda and some other African countries. The root bark extract of the plant is used in the treatment of elephantiasis, malaria, dysmenorrhoea, impotence, and abdominal pain. Fagaronine exhibits antitumor activity against P388 and L1210 murine leukemic cell lines. Its mechanism of action is via inhibition of DNA and RNA polymerase activities as well as inhibition of protein synthesis. This results in disruption of replication in rapidly dividing neoplastic cells. Again, there has been observed inhibition of reverse transcriptase by fagaronine (**Tables 1** and **2**) [68, 69].

### **3.2. Isofuranonaphthoquinone**

Isofuranonaphthoquinone is a phytochemical constituent that occurs in *Bulbine* species (Asphodelaceae) such as *Bulbine abyssinica* A. Rich., *Bulbine capitata* Poelln., and *Bulbine frutescens* (L.) Willd., which are found in Australia and southern Africa. Traditionally, *Bulbine frutescens* is used for a wide range of skin conditions including acne, burns, blisters, cold sores, cracked lips, fingers, nails and heels, insect bites, fever blisters, mouth sores, sunburn, and ringworm among others. It is used internally for coughs, cold, and arthritis. Cell viability assay was used to investigate the action of isofuranonaphthoquinone found in *Bulbine frutescens* on Jurkat T cells [70]. In this study, it was concluded that the effect of isofuranonaphthoquinone was comparable to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), an anticancer agent, and its effects were irreversible. The study showed that isofuranonaphthoquinone could be exerting its activity by generating reactive oxygen species which result in cell death and that it inhibits drug efflux pumps which have been implicated in drug resistance in cancer cells. A combination with BCNU

**2.10. Indirubin and 1-methylisoindigo**

8 Natural Products and Cancer Drug Discovery

**in clinical trials**

**3.2. Isofuranonaphthoquinone**

**3.1. Fagaronine**

These are indole alkaloids isolated from the leaves and/or stems of several plants which include the African plant, *Indigofera tinctoria* L. (Fabaceae), as well as *Baphicacanthus cusia* (Nees) Bremek. (Acanthaceae), *Indigofera suffruticosa* Mill. (Fabaceae), *Isatis tinctoria* L. (Brassicaceae), and *Polygonum tinctorium* Ait. (Polygonaceae) [63, 64]. Indirubin has been demonstrated to exert its antileukemic effect by competing with ATP for binding to the catalytic subunit of cyclin-dependent kinase (CDK), via hydrogen bonding, leading to the inhibition of this enzyme [65]. 1-Methylisoindigo is a derivative developed to improve water solubility and other pharmaceutical properties of indirubin. 1-methylisoindigo exhibited significant anticancer activity through a multitargeting profile including inhibition of DNA biosynthesis and assembly of microtubules, induction of cell differentiation, and down-regulation of c-myb gene expression [65, 66]. 1-Methylisoindigo is under clinical trial in the People's Republic of China for chronic myelogenous leukemia (CML) [67].

**3. Plant-derived compounds with potential anticancer activity but not yet** 

Fagaronine is a benzophenanthridine alkaloid isolated from *Fagara zanthoxyloides* Lam. (syn. *Zanthoxylum zanthoxyloides*) (Rutaceae), which is widely distributed in Uganda and some other African countries. The root bark extract of the plant is used in the treatment of elephantiasis, malaria, dysmenorrhoea, impotence, and abdominal pain. Fagaronine exhibits antitumor activity against P388 and L1210 murine leukemic cell lines. Its mechanism of action is via inhibition of DNA and RNA polymerase activities as well as inhibition of protein synthesis. This results in disruption of replication in rapidly dividing neoplastic cells. Again, there has been observed inhibition of reverse transcriptase by fagaronine (**Tables 1** and **2**) [68, 69].

Isofuranonaphthoquinone is a phytochemical constituent that occurs in *Bulbine* species (Asphodelaceae) such as *Bulbine abyssinica* A. Rich., *Bulbine capitata* Poelln., and *Bulbine frutescens* (L.) Willd., which are found in Australia and southern Africa. Traditionally, *Bulbine frutescens* is used for a wide range of skin conditions including acne, burns, blisters, cold sores, cracked lips, fingers, nails and heels, insect bites, fever blisters, mouth sores, sunburn, and ringworm among others. It is used internally for coughs, cold, and arthritis. Cell viability assay was used to investigate the action of isofuranonaphthoquinone found in *Bulbine frutescens* on Jurkat T cells [70]. In this study, it was concluded that the effect of isofuranonaphthoquinone was comparable to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), an anticancer agent, and its effects were irreversible. The study showed that isofuranonaphthoquinone could be exerting its activity by generating reactive oxygen species which result in cell death and that it inhibits drug efflux pumps which have been implicated in drug resistance in cancer cells. A combination with BCNU

**Class of compounds Structure References**

**[63–65]**

**[63–67]**

**[22]**

**[27–31]**

**[40]**

**[19, 38–40]**

**2. Alkaloids** – **Indole**

10 Natural Products and Cancer Drug Discovery

**3. Polyphenols**

– **Stilbenoid**

– **Diarylheptanoid**

**Table 1.** Plant-derived compounds currently under clinical trial as anti-cancer drugs.

showed greater toxicity effects on the Jurkat T cells than the individual compounds. Thus, this compound is a potential lead candidate for anticancer drug development and an adjunct compound in combination treatment regimens [70].

**Class of compounds Structure References**

**[72]**

**[76]**

**[68, 69]**

**[70]**

**1. Terpenoids**

– **Monoterpenes • Iridoid lactone**

12 Natural Products and Cancer Drug Discovery

– **Diterpenes • Kaurane**

**2. Alkaloids** – **Benzophenanthridine**

**3. Quinones**

**Table 2.** Plant-derived compounds with potential anti-cancer activity but not yet in clinical trials.

#### **3.3. Plumericin**

**Class of compounds Structure References**

**[75]**

**[75]**

**[75]**

**[75]**

**[75]**

**6.** 

**Crotophorbolanes**

14 Natural Products and Cancer Drug Discovery

*Momordica charantia* L., (Cucurbitaceae) is a plant commonly known as bitter gourd or bitter melon which is widely distributed in Asia and tropical Africa. Bitter gourd extracts have been shown to have antioxidant, antimicrobial, antiviral, antihepatotoxic, hypoglycemic, and antiulcerogenic properties [71]. It has also been shown to have anticancer properties. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide) assay was used in this experiment to investigate the antiproliferative activity of plumericin, isolated from this plant. The results indicated it to have high antiproliferative effect against leukemia (NB4 and K562), breast cancer (T47D) cell lines, and a moderate activity against liver cancer cell line (C3A) [72].

### **3.4. Balanitin-6 and balanitin-7**

*Balanites aegyptiaca* Del (Balanitaceae) is a spiny evergreen tree found in the dry regions of the Middle East, Africa, and Southern Asia. [73]. Traditionally in Egypt, the fruits are used as antidiabetic agents. In Sudan, it is used in the treatment of jaundice and as an anthelminthic. Additionally, the extracts have been shown to show abortive and antiseptic characteristics [74]. A study was conducted to further characterize the anticancer activity of the steroidal saponins of *B. aegyptiaca* kernels, which contain a mixture of Balanitin-6 (28%) and balanitin-7 (72%). The mixture was found to display greater antiproliferative activity than oxaliplatin as well as etoposide against human cancer cell lines U373 glioblastoma and A549 nonsmall cell lung cancer, though it was less active compared to taxol. The results also showed that the balanitin-6, balanitin-7 mixture is more cytotoxic than it is cytostatic. Its antiproliferative activity does not appear to be by inducing apoptotic cell death and it does not appear to induce detergent-like effects on the cells tested in the study. Rather, its *in vitro* activities are indicated to be at least partially as a result of ATP depletion, the result of which is considerable disorganization of the actin cytoskeleton, finally leading to impaired cancer cell proliferation and migration. Additionally, the study showed that the mixture does not cause intracellular reactive oxygen species levels to increase, unlike a number of anticancer agents of natural origin. In *in vivo* studies, the extent of increase of survival time reported for vincristine was found to be the same for the mixture when tested on mice bearing murine L1210 leukemia grafts. The preliminary *in vivo* results obtained showed that new hemi synthetic derivatives of balanitin-6 and -7 which have enhanced *in vivo* and *in vitro* anticancer activity coupled with decreased toxicity could possibly be produced, which would markedly improve the therapeutic ratio of these compounds [74].

#### **3.5. Spirostanes and furostanes**

Another study used the MTT assay to evaluate the antiproliferative activity of furostane (KE-1046 and KE-1064) as well as spirostane (SAP-1016 and SAP-884) saponins isolated from *Balanites aegyptiaca* Del. Potent antiproliferative activity was observed for SAP-1016 against HT-29 human colon and MCF-7 human breast cancer cells. Additionally, for furostane saponins, there was considerable selectivity in growth inhibition between HFF normal cells and MCF-7 breast cancer cells. It was shown that SAP-1016 works by generation of reactive oxygen species in a time-dependent manner in both MCF-7 and HT-29 cancer cells. It also induced apoptosis through the activation of caspase-3 in HT-29 cells [73].

#### **3.6. Curcusones**

Found in Africa and Asia, *Jatropha curcas* L. (Euphorbiaceae) is a large drought-resistant shrub, which is used for multiple purposes. The seeds and the oil obtained from them are used for biodiesel production, as a cure for syphilis, and also as a purgative. Different forms of this plant are used in West Africa to treat ailments such as jaundice, mouth sores as well as sores due to guinea worm infestation, fever, and joint rheumatism. The crushed leaves and the latex show antiparasitic activity as well as antibacterial activity against Staphylococcus aureus. Extracts of the stem have been suggested to have anti-insect, anti-inflammatory, cytotoxic, and molluscicidal activities. The MTT method was used to determine the anticancer activity of curcusone A, B, C, and D, pure compounds obtained from the stem of this plant. Curcusone A and B were revealed to possess antiproliferative activity with curcusone B, additionally, suppressing the metastatic process effectively at nontoxic doses. Curcusone C and D were shown to be active against L5178y mouse lymphoma cells. 2-Epi-hydroxyisojatrogrossidion, 4Z-jatrogrossidentadion, 2-hydroxyisojatrogrossidion, 4E-jatrogrossidentadion, and Multidione, 15-epi-4Z-jatrogrossidentadion have also been reported to exhibit potent cytotoxic activity against HeLa human cervix carcinoma cells and L5178y mouse lymphoma cells but exhibited no or low activities against the neuronal cell, PC12 [75].

### **3.7. Kaurenoic acid**

been shown to have antioxidant, antimicrobial, antiviral, antihepatotoxic, hypoglycemic, and antiulcerogenic properties [71]. It has also been shown to have anticancer properties. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide) assay was used in this experiment to investigate the antiproliferative activity of plumericin, isolated from this plant. The results indicated it to have high antiproliferative effect against leukemia (NB4 and K562), breast cancer (T47D) cell lines, and a moderate activity against liver cancer cell line (C3A) [72].

*Balanites aegyptiaca* Del (Balanitaceae) is a spiny evergreen tree found in the dry regions of the Middle East, Africa, and Southern Asia. [73]. Traditionally in Egypt, the fruits are used as antidiabetic agents. In Sudan, it is used in the treatment of jaundice and as an anthelminthic. Additionally, the extracts have been shown to show abortive and antiseptic characteristics [74]. A study was conducted to further characterize the anticancer activity of the steroidal saponins of *B. aegyptiaca* kernels, which contain a mixture of Balanitin-6 (28%) and balanitin-7 (72%). The mixture was found to display greater antiproliferative activity than oxaliplatin as well as etoposide against human cancer cell lines U373 glioblastoma and A549 nonsmall cell lung cancer, though it was less active compared to taxol. The results also showed that the balanitin-6, balanitin-7 mixture is more cytotoxic than it is cytostatic. Its antiproliferative activity does not appear to be by inducing apoptotic cell death and it does not appear to induce detergent-like effects on the cells tested in the study. Rather, its *in vitro* activities are indicated to be at least partially as a result of ATP depletion, the result of which is considerable disorganization of the actin cytoskeleton, finally leading to impaired cancer cell proliferation and migration. Additionally, the study showed that the mixture does not cause intracellular reactive oxygen species levels to increase, unlike a number of anticancer agents of natural origin. In *in vivo* studies, the extent of increase of survival time reported for vincristine was found to be the same for the mixture when tested on mice bearing murine L1210 leukemia grafts. The preliminary *in vivo* results obtained showed that new hemi synthetic derivatives of balanitin-6 and -7 which have enhanced *in vivo* and *in vitro* anticancer activity coupled with decreased toxicity could possibly be produced, which would markedly improve the therapeutic ratio of these compounds [74].

Another study used the MTT assay to evaluate the antiproliferative activity of furostane (KE-1046 and KE-1064) as well as spirostane (SAP-1016 and SAP-884) saponins isolated from *Balanites aegyptiaca* Del. Potent antiproliferative activity was observed for SAP-1016 against HT-29 human colon and MCF-7 human breast cancer cells. Additionally, for furostane saponins, there was considerable selectivity in growth inhibition between HFF normal cells and MCF-7 breast cancer cells. It was shown that SAP-1016 works by generation of reactive oxygen species in a time-dependent manner in both MCF-7 and HT-29 cancer cells. It also induced

Found in Africa and Asia, *Jatropha curcas* L. (Euphorbiaceae) is a large drought-resistant shrub, which is used for multiple purposes. The seeds and the oil obtained from them are used for

apoptosis through the activation of caspase-3 in HT-29 cells [73].

**3.4. Balanitin-6 and balanitin-7**

16 Natural Products and Cancer Drug Discovery

**3.5. Spirostanes and furostanes**

**3.6. Curcusones**

*Annona senegalensis* Pers. (Annonaceae), (popular names: African custard apple or wild custard apple) has been reported to possess cytotoxic and anticancer effects. Kaurenoic acid, a diterpenoid, has been shown to have anticonvulsant, anti-inflammatory as well as antimicrobial properties. A cytotoxicity assay on Kaurenoic acid was performed using the MTT assay method against Henrietta Lack's cervical (HeLa) and pancreatic tumor (PANC-1) cell lines. Okoye et al. reported that kaurenoic acid exhibited better cytotoxic and antiproliferative activity against HeLa cells, than PANC-1 cells [76]. The anticancer effect of kaurenoic acid on breast, leukemia, and colon cancer cells has been documented, as well as activity on human glioblastoma, murine, and human melanoma cell lines. Terpenoids have been shown to exhibit antitumor activities by inducing apoptosis in various cancer cells by activating various pro-apoptotic signaling cascades and by the inhibition of metastatic progression and tumor-induced angiogenesis. Thus, kaurenoic acid, a terpenoid can potentially be further studied for its potential anticancer activity [76].

#### **3.8. Aloe emodin**

Aloe emodin is an anthraquinone compound found in many medicinal plants including the widely grown *Aloe vera* L. and *Rheum palmatum* L. (Rhei rhizome), used in traditional medicine in China and Africa. Previous studies report that aloe emodin has laxative, antibacterial, antiviral, antifungal, and hepatoprotective properties [77]. A recent study has shown that it possesses *in vivo* and *in vitro* antineuroectodermal tumor activity [78]. Another study indicated that aloe emodin showed inhibition of cell proliferation as well as induction of apoptosis in both Hep 3B and Hep G2 human liver cancer cell lines but through different antiproliferative mechanisms. p53 expression was induced in Hep G2 cells, along with a cell cycle arrest in the G1 phase. Added to this, there was a considerable increase in Bax and FAS/APO1 receptor expression. In the Hep 3B cells, the antiproliferative activity was in a p21-dependent manner which did not lead to cell cycle arrest or rise in Fas/APO1 receptor level. Rather, aloe emodin induced apoptosis was promoted through enhanced Bax expression. As a result, aloe emodin may be instrumental in preventing liver cancer [79].

### **4. Conclusion**

A sizeable number of plant-derived compounds are currently under clinical trial for the management of cancers though much needs to be identified. This goes a long way to affirm the therapeutic benefits plants hold. It is therefore prudent that scientist and researchers in Africa and the world as a whole to continue to work on identifying newer compounds of natural origin that would hold potential in the management of cancers.

### **Author details**

Newman Osafo1 \*, Yaw Duah Boakye2 , Christian Agyare2 , Samuel Obeng<sup>3</sup> , Judith Edem Foli<sup>2</sup> and Prince Amankwaah Baffour Minkah<sup>2</sup>

\*Address all correspondence to: nosafo.pharm@knust.edu.gh

1 Department of Pharmacology, Faculty of Pharmacy and Pharmaceutical Sciences, College of Health Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

2 Department of Pharmaceutics, Faculty of Pharmacy and Pharmaceutical Sciences, College of Health Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

3 Department of Medicinal Chemistry, Virginia Commonwealth University, Richmond, Virginia, USA

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**4. Conclusion**

18 Natural Products and Cancer Drug Discovery

**Author details**

Newman Osafo1

Virginia, USA

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A sizeable number of plant-derived compounds are currently under clinical trial for the management of cancers though much needs to be identified. This goes a long way to affirm the therapeutic benefits plants hold. It is therefore prudent that scientist and researchers in Africa and the world as a whole to continue to work on identifying newer compounds of natural

, Christian Agyare2

1 Department of Pharmacology, Faculty of Pharmacy and Pharmaceutical Sciences, College of Health Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana 2 Department of Pharmaceutics, Faculty of Pharmacy and Pharmaceutical Sciences, College of Health Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana 3 Department of Medicinal Chemistry, Virginia Commonwealth University, Richmond,

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## **Anticancer Effects of Some Medicinal Thai Plants**

Pongtip Sithisarn and Piyanuch Rojsanga

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67648

#### **Abstract**

[75] Aiyelaagbe OO, Hamid AA, Fattorusso E, Taglialatela-Scafati O, Schröder HC, Müller WEG. Cytotoxic activity of crude extracts as well as of pure components from jatropha species, plants used extensively in African traditional medicine. Evidence-Based Complementary and Alternative Medicine. 2011;1-7pp. ArticleID 134954,7 pages. DOI:

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HeLa cells. European Journal of Medicinal Plants. 2014;**4**(5):579-589

http://dx.doi.org/10.1155/2011/134954

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24 Natural Products and Cancer Drug Discovery

Ethanolic extracts from thirty Thai edible plants collected from Sa Keao province, Thailand, were screened for *in vitro* antiproliferative effect on HCT-116 human colon cancer cell line using cell titer 96 aqueous one solution cell proliferation assay. It was found that leaf extract of *Crateva adansnii*, fruit and leaf extracts of *Ardisia elliptica*, shoot extract of *Colocasia esculenta*, leaf extract of *Cratoxylum fomosum*, and leaf extract of *Millettia leucantha* exhibited antiproliferative activities. The fruit extract of *Ardisia elliptica* showed the highest antiproliferative activity. Ethanolic extract of the stems from *C. fenestratum* and its dichloromethane and aqueous fractions showed antiproliferative activity to human colorectal cancer cells (HCT-116) determined by cell growth assay. Berberine, one of the major alkaloid in the stems of *C. fenestratum*, also promoted antiproliferative effect. Extracts from the leaves of three *Azadirachta* species in Thailand, *A. indica*, *A. indica* var. *siamensis*, and *A. excelsa*, were reported to promote *in vitro* antioxidant effects determined by various methods. Ten *Russula* mushroom collected from northeastern part of Thailand were tested for *in vitro* antioxidant activities using photochemiluminescence assay for both lipid-soluble and water-soluble antioxidant capacities. *R. medullata* extract exhibited the highest antioxidant effects in both lipid-soluble and water-soluble models.

**Keywords:** anticancer, *Coscinium fenestratum*, berberine, *Azadirachta*, *Russula*

### **1. Introduction**

Cancer cells uncontrollably divide to form masses of tissue, which are called tumors. Tumors can grow and interfere with the functions of many bodily systems including the digestive, nervous, and cardiovascular systems. Cancer has been reported to be the first in the rank of causes of the death in the Thai population. Liver, colon, and lung cancers are the most prevalent cancers in Thai males, while breast, cervical, and colon cancers are the most prevalent cancers in Thai females [1].

© 2017 The Author(s). Licensee InTech. 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 development of cancer or carcinogenesis occurs through a multistep process involving the mutation, selection of cells with a progressive increasing capacity for proliferation, survival, invasion, and metastasis [2]. The first step in the process, tumor initiation, relates to the genetic alteration leading to the changes in normal cells. Then, in the promotion or development stage, the cells abnormally proliferate leading to the outgrowth of a population of clonally derived tumor cells [2]. This stage can be stimulated by carcinogens, which are a group of substances such as tobacco, asbestos, arsenic, radiation such as gamma and X-rays, sun light, polycyclic hydrocarbons, nitrosamines, and aflatoxins: these substances do not directly cause cancers but promote or aid the development of cancers [2, 3]. After that, tumor progression continues as additional mutations occur within the cells of the tumor population to further advantage the cancer cells, such as more rapid growth, which will allow them to become dominant within the late tumor population. The process is called clonal selection, since a new clone of tumor cells evolves on the basis of its increased growth rate or other properties such as survival, invasion, or metastasis. Clonal selection continues throughout tumor development, so tumors continuously become more rapid-growing and increasingly malignant [2].

### **2. Cancer therapy**

The modern treatments for cancers mainly are surgery, radiation, and chemotherapy. However, most of chemotherapeutic drugs are not specific to only cancer cells, but also cause damage to normal cells, especially bone marrow, mucous glands, mucous membranes, hair, and nails and can lead to the suppression of the immune system [3]. The success of chemotherapy depends on the number of cancer cells, the proliferation rate, the duration of the drug administration, and the therapeutic interval. To avoid drug resistance, polychemotherapy is always used instead of monochemothearpy [3]. The anticancer drugs can also cause some other side effects including nausea, vomiting, agranulocytosis, inhibition of spermatogenesis and ovulation, alopecia, inflammation of mucous membranes, and terratogenesis [3].

Some compounds separated from natural products are now being developed as modern medicines for the treatments of cancers including paclitaxel, catharanthus alkaloids, and derivatives of podophyllotoxin.

Paclitaxel was separated from the bark of *Taxus brevifolia* Nutt. (Pacific Yew), which is a tree in Taxaceae. Paclitaxel will bind with b-tubulin and stimulate the aggregation of a tubulin subunit to become a nonphysiological microtubule composed of 12 proto-filaments, which cause the inhibition of cell cycles in mitosis and interphase (G2 -phase) and lead to cell apoptosis. This compound is normally used in an injection formulation as the adjuvant chemotherapy for the treatments of ovarian, breast, and bronchial cancers [3].

Some alkaloids are separated from the leaves of *Catharanthus roseus* (L.) G. Don., such as vincristine and vinblastine. Vincristine is used for the treatment of lymphatic leukemia, neuroblastoma, and Wilms tumor, while vinblastine is used to treat lymphogranuloma (Morbus Hodgin), lymphosarcoma, testicular carcinoma, and chorionic carcinoma [3].

Podophyllotoxin was separated from the rhizome of *Podophyllum peltatum* L. or American mandrake. Two derivatives of podophyllotoxin, etoposide and teniposide, are now being developed and used as anticancer drugs. Etoposide is used for the treatment of bronchial cancer, testicular carcinoma, and chorionic carcinoma, while tenoposide is used to treat brain or bladder cancers [3]. The chemical structures of some anticancer compounds from natural products are shown in **Figure 1**.

The development of cancer or carcinogenesis occurs through a multistep process involving the mutation, selection of cells with a progressive increasing capacity for proliferation, survival, invasion, and metastasis [2]. The first step in the process, tumor initiation, relates to the genetic alteration leading to the changes in normal cells. Then, in the promotion or development stage, the cells abnormally proliferate leading to the outgrowth of a population of clonally derived tumor cells [2]. This stage can be stimulated by carcinogens, which are a group of substances such as tobacco, asbestos, arsenic, radiation such as gamma and X-rays, sun light, polycyclic hydrocarbons, nitrosamines, and aflatoxins: these substances do not directly cause cancers but promote or aid the development of cancers [2, 3]. After that, tumor progression continues as additional mutations occur within the cells of the tumor population to further advantage the cancer cells, such as more rapid growth, which will allow them to become dominant within the late tumor population. The process is called clonal selection, since a new clone of tumor cells evolves on the basis of its increased growth rate or other properties such as survival, invasion, or metastasis. Clonal selection continues throughout tumor development, so tumors continuously become more rapid-growing and increasingly

The modern treatments for cancers mainly are surgery, radiation, and chemotherapy. However, most of chemotherapeutic drugs are not specific to only cancer cells, but also cause damage to normal cells, especially bone marrow, mucous glands, mucous membranes, hair, and nails and can lead to the suppression of the immune system [3]. The success of chemotherapy depends on the number of cancer cells, the proliferation rate, the duration of the drug administration, and the therapeutic interval. To avoid drug resistance, polychemotherapy is always used instead of monochemothearpy [3]. The anticancer drugs can also cause some other side effects including nausea, vomiting, agranulocytosis, inhibition of spermatogenesis and ovulation, alopecia, inflammation of mucous membranes, and

Some compounds separated from natural products are now being developed as modern medicines for the treatments of cancers including paclitaxel, catharanthus alkaloids, and deriva-

Paclitaxel was separated from the bark of *Taxus brevifolia* Nutt. (Pacific Yew), which is a tree in Taxaceae. Paclitaxel will bind with b-tubulin and stimulate the aggregation of a tubulin subunit to become a nonphysiological microtubule composed of 12 proto-filaments, which cause the

compound is normally used in an injection formulation as the adjuvant chemotherapy for the

Some alkaloids are separated from the leaves of *Catharanthus roseus* (L.) G. Don., such as vincristine and vinblastine. Vincristine is used for the treatment of lymphatic leukemia, neuroblastoma, and Wilms tumor, while vinblastine is used to treat lymphogranuloma (Morbus

Hodgin), lymphosarcoma, testicular carcinoma, and chorionic carcinoma [3].


malignant [2].

**2. Cancer therapy**

26 Natural Products and Cancer Drug Discovery

terratogenesis [3].

tives of podophyllotoxin.

inhibition of cell cycles in mitosis and interphase (G2

treatments of ovarian, breast, and bronchial cancers [3].

**Figure 1.** Chemical structures of some anticancer compounds from natural products. A = paclitaxel, B = vinblastine, C = vincristine, D = etoposide, E = teniposide.

### **3. Anticancer effects of medicinal plants and natural products**

Natural products from plants, animals, marine sources, and minerals have been used for the treatments of ailments and diseases for a long time. In Thai traditional medicine, the word "cancer" could refer to the symptom of chronic wound, abscess, emaciation, and weak [4]. Active phytochemicals in plants can be classified into two main groups of primary metabolites, which are the compounds necessary for plant growth and development such as carbohydrates, proteins, and fats. Another group is secondary metabolites, which promote the defense mechanisms or support the lives of the plants; they include polyphenolic compounds, flavonoids, terpenoids, and alkaloids [5]. Ethanolic extracts from thirty Thai local edible plants collected from Wang Nam Yen district, Sa Keao province, Thailand were screened for the *in vitro* anti-proliferative effect on HCT-116 human colon cancer cell lines using a cell titer 96 aqueous one solution cell proliferation assay. It was found that six ethanolic plant extracts, including a leaf extract of *Crateva adansnii*, fruit and leaf extracts of *Ardisia elliptica*, a shoot extract of *Colocasia esculenta*, a leaf extract of *Cratoxylum fomosum*, and a leaf extract of *Millettia leucantha* exhibited antiproliferative activities on the HCT-116 cell line. The fruit extract of *Ardisia elliptica* showed the highest antiproliferative activities with an IC50 value of 5.12 ± 0.54 μg/ml [6]. The mechanisms of the action of medicinal plants for anticancer effects have been reported as following [4]:

### **3.1. Inhibition of cell division in the cancer cell cycle**

Alpha-mangostin from mangosteen (*Garcinia mangostana*) fruit rind promoted inhibitory effects to breast cancer cell line (MDA-MB-231) by inhibition of cell division in G1 and S phases [7]. Methanol extract of *Morus alba* L. leaves inhibited liver cancer cell line Hep G2 by inhibition of cell division in G2/M phase [8]. Cucurbitacin B, a triterpenoid from *Trichosanthes cucumerina* L., also inhibited breast cancer cell division in G2/M phase [9].

### **3.2. Induction of cancer cell apoptosis**

This mechanism includes some minor mechanisms which stimulate anticancer genes, induction of caspase enzymes, induction of free radical formation, inhibition or induction of enzymes relating to histone protein, and the formation of spingosine or ceramide [4]. Dehydrocostus lactone from the root of *Saussurea lappa* induced the apoptosis of liver cancer cells Hep G2 and PLC/PRF/5 via p53 protein [10]. Water extract of the seed from *Sapindus rarak* Candolle. induced lung cancer cells A549 apoptosis through the induction of the caspase enzyme [11], while methanol extract of *Derris scandens* Benth. induced apoptosis of colon cancer cells SE480 by increased caspase-3 activity and down-regulated Bcl-2 and upregulated Bax protein of SW480 cells; it also significantly induced cell necrosis determined by the release of LDH [12]. Alpha-mangostin separated from the fruit rind of mangosteen also upregulated Bax and down-regulated Bcl-2 proteins in rat liver tissue [13]. Methanol extract from stem bark of *Myristica fragrans* Houtt. promoted the apoptosis of lymphoblast Jurkat by controlling the SIRT1 gene [14]. G1 b, a glycospingolipid from *Murdannia loriformis* (Hassk.) R.S.Rao & Kammathy, inhibited breast, lung, colon, and liver cell lines [15].

#### **3.3. Immune stimulation**

Methanol extract from the leaves of *Moringa oleifera* Lam. exhibited immune stimulation effect both cell-mediated immunity and humoral immunity by induction of neutrophile production and stimulation of macrophages in animals damaged by the toxicity of anticancer drugs [16].

In Thai traditional medicine, there are some medicinal formulas compose of several plants in different ratios. These formulas are traditionally used for a long time usually for the treatments of cancers in patient with the late stage cancers, patients who cannot improve after treatment with chemotherapy, radiation or surgery, patients with cancers in several organs or patients with incurrent diseases [4]. The sources of anticancer herbal formulas usually come from local traditional doctors or priests in the temples (in Thai, temple is called as "Wat"), with the normal method of preparation being the decoction of plant materials with water [4]. A herbal remedy from Wat Tha-it (Tha-it temple), Ang Thong province, Thailand, composed of several plant materials including *Gelonium multiflorum* A. Juss., *Erycibe elliptilimba* Merrill & Chun, *Balanophora abbreviate* Blume, *Smilax china* L., *Smilax glabra* Wall. ex Roxb., and *Millingtonia hortensis* Linn. was reported to significantly promote synergistic effects on doxorubicin in the treatment of A549 cancer cells by the inhibition of cell divisions in the G2/M phase [4, 17]. Another herbal remedy is from a Thai herbal nursing home, Wat Khampramong, Sakon Nakhon province comprises of several plant materials such as *Rhinacanthus nasutus* (L.) Kurz, *Acanthus ebrateatus* Wall., *Smilax glabra* Wall. ex Roxb., *Artemisia annua* L., *Angelica sinensis* (Oliv.) Diels, *Salacia chinensis* L., and *Orthosiphon aristatus* Miq [18]. This herbal remedy can inhibit the growth of some cancer cell lines such as breast adenocarcinoma MDA-MB 231, synovial sarcoma SW982, hepatocellular carcinoma HepG2, cervical adenocarcinoma HeLa, and lung carcinoma A549 [18].

### **4. Some potential Thai medicinal plants with anticancer effects**

### **4.1.** *Coscinium fenestratum* **(Gaertn.) Colebr**

**3.1. Inhibition of cell division in the cancer cell cycle**

**3.2. Induction of cancer cell apoptosis**

28 Natural Products and Cancer Drug Discovery

**3.3. Immune stimulation**

Alpha-mangostin from mangosteen (*Garcinia mangostana*) fruit rind promoted inhibitory effects to breast cancer cell line (MDA-MB-231) by inhibition of cell division in G1 and S phases [7]. Methanol extract of *Morus alba* L. leaves inhibited liver cancer cell line Hep G2 by inhibition of cell division in G2/M phase [8]. Cucurbitacin B, a triterpenoid from *Trichosanthes* 

This mechanism includes some minor mechanisms which stimulate anticancer genes, induction of caspase enzymes, induction of free radical formation, inhibition or induction of enzymes relating to histone protein, and the formation of spingosine or ceramide [4]. Dehydrocostus lactone from the root of *Saussurea lappa* induced the apoptosis of liver cancer cells Hep G2 and PLC/PRF/5 via p53 protein [10]. Water extract of the seed from *Sapindus rarak* Candolle. induced lung cancer cells A549 apoptosis through the induction of the caspase enzyme [11], while methanol extract of *Derris scandens* Benth. induced apoptosis of colon cancer cells SE480 by increased caspase-3 activity and down-regulated Bcl-2 and upregulated Bax protein of SW480 cells; it also significantly induced cell necrosis determined by the release of LDH [12]. Alpha-mangostin separated from the fruit rind of mangosteen also upregulated Bax and down-regulated Bcl-2 proteins in rat liver tissue [13]. Methanol extract from stem bark of *Myristica fragrans* Houtt. promoted the apoptosis of lymphoblast Jurkat by controlling the SIRT1 gene [14]. G1 b, a glycospingolipid from *Murdannia loriformis* (Hassk.)

Methanol extract from the leaves of *Moringa oleifera* Lam. exhibited immune stimulation effect both cell-mediated immunity and humoral immunity by induction of neutrophile production and stimulation of macrophages in animals damaged by the toxicity of anticancer drugs [16]. In Thai traditional medicine, there are some medicinal formulas compose of several plants in different ratios. These formulas are traditionally used for a long time usually for the treatments of cancers in patient with the late stage cancers, patients who cannot improve after treatment with chemotherapy, radiation or surgery, patients with cancers in several organs or patients with incurrent diseases [4]. The sources of anticancer herbal formulas usually come from local traditional doctors or priests in the temples (in Thai, temple is called as "Wat"), with the normal method of preparation being the decoction of plant materials with water [4]. A herbal remedy from Wat Tha-it (Tha-it temple), Ang Thong province, Thailand, composed of several plant materials including *Gelonium multiflorum* A. Juss., *Erycibe elliptilimba* Merrill & Chun, *Balanophora abbreviate* Blume, *Smilax china* L., *Smilax glabra* Wall. ex Roxb., and *Millingtonia hortensis* Linn. was reported to significantly promote synergistic effects on doxorubicin in the treatment of A549 cancer cells by the inhibition of cell divisions in the G2/M phase [4, 17]. Another herbal remedy is from a Thai herbal nursing home, Wat Khampramong, Sakon Nakhon province comprises of several plant materials such as *Rhinacanthus nasutus* (L.) Kurz, *Acanthus ebrateatus* Wall., *Smilax glabra* Wall. ex Roxb.,

*cucumerina* L., also inhibited breast cancer cell division in G2/M phase [9].

R.S.Rao & Kammathy, inhibited breast, lung, colon, and liver cell lines [15].

NAG-1 or nonsteroidal anti-inflammatory drug (NSAID)-activated gene was identified in COX-negative cells by PCR-based subtractive hybridization from an NSAID-induced library as a divergent member of the TGF-β superfamily [19]. The overexpression of NAG-1 in cancer cells results in growth arrest and an increase in apoptosis, suggesting that NAG-1 has antitumorigenic activity [20]. NAG-1 expression is also upregulated by a number of dietary compounds, medicinal plants, and anticancer drugs [21–25]. *Coscinium fenestratum* is one of the medicinal plants that promoted antiproliferative effects on colon cancer cell lines with mechanisms related to NAG-1 [20].

*Coscinium fenestratum* (Gaertn.) Colebr. is a large climber with yellow wood and sap, known in the Thai language as Hamm or Khamin khruea. The genus *Coscinium* belongs to the tribe Coscinieae of the family Menispermaceae. This genus comprises two species, which are *Coscinium blumeanum* Miers. and *C. fenestratum* (Gaertn.) Colebr. Both of them are stout woody climbers growing in the tropical rain forest regions of Asia [26]. *Coscinium* species are characterized by the axillary flowers, extra-axillary or cauliflorous in racemiform, or peduncled subumbellate aggregate, of 20–50 cm in length. The inflorescences are axillary or cauliflorous with 6–12 florets. Male flowers are sessile or with pedicels, up to 1 mm. Sepals are broadly elliptic to obovate with the inner 3–6 spreading, yellow, and 1.5–2 mm long. Stamens are 6 with 1 mm long. The Sepals of female flower are as in male flowers. Staminodes are 6 and claviform with 1 mm long. Drupes are subglobose, tomentellous, brown to orange or yellowish, 2.8–3 cm diameter. Pericarp is drying woody. Seeds are whitish and subglobose with the enveloping condyle. The leaves are subpeltate or ovate, large, hard-coriaceous, palmately nerved, reticulate, and densely hairy beneath [26]. Physical characteristic of the *Coscinium fenestratum* stem (cross section) is shown in **Figure 2**.

The stem decoction and maceration extracts of *Coscinium fenestratum* have been traditionally used in the Northeastern part of Thailand for the treatment of various diseases such as cancer, diabetes mellitus, and arthritis [27]. The ethanolic extract of the stems from *C. fenestratum* and its dichloromethane and aqueous fractions showed antiproliferative activity on human colorectal cancer cells (HCT-116) determined by a cell growth assay. Berberine, one of the major alkaloids in the stems of *C. fenestratum*, also promoted an antiproliferative effect [20]. The mechanisms of action of the extracts from *C. fenestratum* were reported as the activation of proapoptotic proteins and pparγ [20]. It was also reported that berberine facilitated the apoptosis of cancer cells, and the molecular targets for its activity are NAG-1 and AFT3 [24]. The chemical structure of Berberine is shown in **Figure 3**.

**Figure 2.** Physical characteristic of *Coscinium fenestratum* stem purchased from Nongkhai province, Thailand (cross section ×1).

**Figure 3.** Chemical structure of Berberine.

#### **4.2.** *Azadirachta* **plants**

Oxidative stress is considered to be of some importance for many ailments and pathologies; including cardiovascular diseases, cancers, rheumatoid arthritis, and Alzheimer's disease [28]. Polyphenolic compounds have been reported to have important anticancer and chemopreventive effects [29]. Phenolic acids such as gallic acid, ellagic acid, and ferulic acid induce apoptosis in cancer cells, activated caspase, prevented cancer formation, and suppress the angiogenesis of cancer [29–32]. Flavonoids such as quercertin and kaempferol also promote apoptosis, inhibit oncogenes, and generated cell cycle arrest [29, 33–35].

Suttajit et al. [36] studied the antioxidant activities of extracts from many Thai medicinal plants using a ABTS-metmyoglobin assay and reported some plants with high antioxidant activities; including *Uncaria gambier* Roxb., *Piper betle* Linn., *Camellia sinensis* (L.) Kuntze., *Azadirachta indica* A. Juss. var. *siamensis* Valeton., *Curcuma zedoaria* Roxb., *Syzygium aromaticum* (L.) Merr. & Perry and *Tamarindus indica* Linn. When focusing on Thai medicinal plants, the Siamese neem tree (*Azadirachta indica* A. Juss. var. *siamensis* Valeton.) is an interesting plant that showed high antioxidant activity in the screening test [36, 37]. Moreover, there are reports about its antioxidant potential based on the antioxidant content as the butylated hydroxyanisole (BHA) equivalent of Thai indigenous vegetable extracts. From this report, the Siamese neem tree leaf extract appeared to be a high potency antioxidant, containing more than 100 mg BHA equivalent in 100 g fresh weight.

*Azadirachta* plants comprise of three different plant species; *Azadirachta indica* A. Juss or *A. indica* A. Juss var. *indica* (neem), *Azadirachta indica* A. Juss. var. *siamensis* Valeton (Siamese neem tree), and *Azadirachta excela* (Jack) Jacobs. (marrango tree). The Siamese neem tree leaves are wider, longer, and thicker than the leaves of neem, while the marrango tree has the widest, longest, and thickest leaves. The margin of the leaflet of Siamese neem tree is crenate to entire, while the margin of neem is serrate and that of marrango tree is entire to undulate. The colors of the leaflet blade of the Siamese neem tree, neem, and marrango tree are green, light green, and dark shiny green, respectively [38, 39]. The physical characteristics of Siamese neem tree, neem, and marrango tree leaves are shown in **Figure 4**.

The leaves and flowers of Siamese neem tree and neem have been traditionally used as element tonics and antipyretic and gastric secretion stimulating agents, while the stem bark of all *Azadirachta* plants is used to treat amoebic dysentery and diarrhea [40, 41]. There also reports suggesting that polysaccharides and limonoids found in neem bark, leaves, and seed oil reduce tumors and cancers and showed effectiveness against lymphocytic leukemia [42–44]. Moreover, the young leaves and flowers of the Siamese neem tree are popularly consumed as vegetables [39].

**4.2.** *Azadirachta* **plants**

**Figure 3.** Chemical structure of Berberine.

30 Natural Products and Cancer Drug Discovery

section ×1).

Oxidative stress is considered to be of some importance for many ailments and pathologies; including cardiovascular diseases, cancers, rheumatoid arthritis, and Alzheimer's disease [28]. Polyphenolic compounds have been reported to have important anticancer and chemopreventive effects [29]. Phenolic acids such as gallic acid, ellagic acid, and ferulic acid induce apoptosis in cancer cells, activated caspase, prevented cancer formation, and suppress the angiogenesis of cancer [29–32]. Flavonoids such as quercertin and kaempferol also promote

**Figure 2.** Physical characteristic of *Coscinium fenestratum* stem purchased from Nongkhai province, Thailand (cross

apoptosis, inhibit oncogenes, and generated cell cycle arrest [29, 33–35].

**Figure 4.** Physical characteristics of *Azadirachta* plants; A = Siamese neem tree (*Azadirachta indica* var. *siamensis*), B = neem (*Azadirachta indica*), C = marrango tree (*Azadirachta excela*).

For the antioxidant effect, *Azadirachta* plants were reported to promote *in vitro* activities tested by various methods. Extracts from the leaves of *A. indica*, *A. indica* var. *siamensis*, and *A. excelsa* were reported to promote *in vitro* antioxidant effects determined by a DPPH scavenging assay, Fremy's salt assay, ESR detection of POBN spin adducts, and an oxygen consumption assay [45, 46]. The leaf's aqueous and flower ethanol extracts from the Siamese neem tree provide antioxidant activity on lipid peroxidation formation induced by UV-irradiation of a Chago K-1 bronchogenic cell culture at a concentration of 100 μg/ml determined by the thiobarbituric acid reactive substances (TBARS) method [47].

Cloning and expression analysis of genes involving flavonoid biosynthesis showed that Siamese neem tree leaves total RNA contained nucleotide sequences related to enzymes F3′H, FLS, DFR, and F3′5′H, which could be responsible for the biosynthesis of the antioxidant flavonoids [48]. Some flavonoids that were separated from Siamese neem tree and neem leaves and flowers are kaempferol, myricetin, quercetin, and rutin [39, 49–51]. The chemical structures of some flavonoids found in *Azadirachta* plants are shown in **Figure 5**.

**Figure 5.** Chemical structures of some flavonoids found in *Azadirachta* plants. A = kaempferol, B = myricetin, C = quercetin, D = rutin.

#### **4.3.** *Russula* **mushrooms**

It is well established that many compounds separated from mushrooms can be used as immuno-modulators or as biological response modifiers [52]. Several mushroom species in Basidiomycetes have been reported to possess anti-tumor activity [53, 54].

Many phytochemical compounds have been reported in various mushrooms, and they can be classified into two main groups: high molecular weight compounds such as beta-glucan and other polysaccharides [55] and low molecular weight compounds including polyphenolics, flavonoids, and terpenoids [52]. Polyphenolics such as caffeic acid, chlorogenic acid, ferulic acid, and gallic acid and flavonoids such as myricetin and catechin were found in *Agaricusbisporus*, *Boletus edulis*, *Calocybe gambosa*, and *Cantharellus cibarius* [56]. Triterpeniods were found in *Agaricus bisporus*, *Ganoderma lucidum*, and *Russula lepida*. Moreover, aristolane sesquiterpenoids were also found in *Russula lepida* [57]. Polysaccharides were found in *Agaricus bisporus*, *Agaricus brasiliensis, Ganoderma lucidum*, and *Phellinus linteus* [58]. Some polysaccharides such as beta-glucan are reported to promote immunomodulatory effects via CR3, the leukocytemembrane receptor for β-glucans [59]. The mechanisms of the action of the mushrooms to promote anticancer effects have been reported as NF-κB inhibitors, protein kinase inhibitors, protein and DNA alkylating agents, modulators of G1/S and G2/M phases, inhibitors of MAPK protein kinase signaling pathways, aromatase and sulfatase inhibitors, matrix metalloproteinases inhibitors, cyclooxygenase inhibitors, DNA topoisomerases, and DNA polymerase inhibitors and anti-angiogenic substances [52].

For the antioxidant effect, *Azadirachta* plants were reported to promote *in vitro* activities tested by various methods. Extracts from the leaves of *A. indica*, *A. indica* var. *siamensis*, and *A. excelsa* were reported to promote *in vitro* antioxidant effects determined by a DPPH scavenging assay, Fremy's salt assay, ESR detection of POBN spin adducts, and an oxygen consumption assay [45, 46]. The leaf's aqueous and flower ethanol extracts from the Siamese neem tree provide antioxidant activity on lipid peroxidation formation induced by UV-irradiation of a Chago K-1 bronchogenic cell culture at a concentration of 100 μg/ml determined by the thiobarbitu-

Cloning and expression analysis of genes involving flavonoid biosynthesis showed that Siamese neem tree leaves total RNA contained nucleotide sequences related to enzymes F3′H, FLS, DFR, and F3′5′H, which could be responsible for the biosynthesis of the antioxidant flavonoids [48]. Some flavonoids that were separated from Siamese neem tree and neem leaves and flowers are kaempferol, myricetin, quercetin, and rutin [39, 49–51]. The chemical struc-

It is well established that many compounds separated from mushrooms can be used as immuno-modulators or as biological response modifiers [52]. Several mushroom species in

**Figure 5.** Chemical structures of some flavonoids found in *Azadirachta* plants. A = kaempferol, B = myricetin, C =

Many phytochemical compounds have been reported in various mushrooms, and they can be classified into two main groups: high molecular weight compounds such as beta-glucan and other polysaccharides [55] and low molecular weight compounds including polyphenolics, flavonoids, and terpenoids [52]. Polyphenolics such as caffeic acid, chlorogenic acid, ferulic acid, and gallic acid and flavonoids such as myricetin and catechin were found in *Agaricusbisporus*, *Boletus edulis*, *Calocybe gambosa*, and *Cantharellus cibarius* [56]. Triterpeniods

Basidiomycetes have been reported to possess anti-tumor activity [53, 54].

tures of some flavonoids found in *Azadirachta* plants are shown in **Figure 5**.

ric acid reactive substances (TBARS) method [47].

32 Natural Products and Cancer Drug Discovery

**4.3.** *Russula* **mushrooms**

quercetin, D = rutin.

A previous study reported the presence of 1147 mushroom species in the Northeast part of Thailand. They are composed of 647 consumed mushroom species, 222 trade mushroom species, and 400 poisonous mushroom species [60]. Thirty-seven species of these mushrooms are used in traditional medicine [60]. However, there are still some mushrooms in Thailand, especially in the Northeastern part of the country, that have never been studied for their biological properties and phytochemical compounds.

*The Russula* mushroom's shape resembles an umbrella. There have a clear cap and stem, with the gills underneath the cap. The cap is thin and has an underlying radius arranged around the center. The mushroom has no ring and no latex in the cap. The mushroom is fresh, soft, fragile, and perishable [61]. There are around 750 worldwide species of *Russula* [62, 63]. The distribution of the *Russula* species shows that they are present in several countries, including the United States of America, Sweden, France, Norway, Madagascar, Italy, Belgium, Taiwan, China, Japan, and Thailand [64]. In Thailand, *Russula* mushrooms have been found in 17 provinces in the Northeastern region of Thailand [65]. Numerous *Russula* mushrooms have been consumed as food such as *R. monspeliensis*, *R. virescens*, *R. alboareolata*, *R. medullata*, and *R. helios* [65, 66]. Various *Russula* mushrooms have been traditionally used for the treatments of various diseases such as *R. cyanoantha* and *R. nobilis*, which are used for the treatment of fever; *R. luteotacta*, which is used for wound healing; and *R. delica* and *R. parazurea*, which are used for the treatment of gastritis and high blood pressure, while *R. acrifolia* is used for treatments of skin cancer [36]. Moreover, some *Russula* mushrooms have also been traditionally used for tonic purposes such as *R. cyanoxantha*, *R. nobilis*, *R. delica*, *R. parazurea*, *R. acrifolia*, and *R. luteotacta* [67]. In addition, *Russula luteotacta* has been used as a sleep promoting agent [67]. Physical characteristics of some *Russula* mushrooms found in Thailand are shown in **Figure 6**.

Ten *Russula* mushroom collected from northeastern part of Thailand: *R. crustosa*, *R. delica*, *R. monspeliensis*, *R. velenovskyi*, *R. virescens*, *R. lepida*, *R. alboareolata*, *R. paludosa*, *R. medullata*, and *R. helios* were tested for their *in vitro* antioxidant activities using a photochemiluminescence assay for both lipid-soluble and water-soluble antioxidant capacities. *R. medullata* extract exhibited the highest antioxidant effects in both lipid-soluble and water-soluble models with antioxidant capacities of 1.1658 nmol of trolox equivalence and 1.323 nmol of ascorbic acid equivalence, respectively [68].

**Figure 6.** Physical characteristics of some Russula mushrooms found in Thailand; A = *Russula crustosa* Peck, B = *Russula delica* Fries, C = *Russula monspeliensis* Sarnari, D = *Russula velenovskyi* Melzer & Zvára, E = *Russula virescens* (Schaeff) Fries, F = *Russula alboareolata* Hongo.

Some chemical constituents have been reported from *Russula* mushrooms including phenolic acids such as ρ-hydroxy-benzoic acid, chlorogenic acid, ferulic acid, caffeic acid, protocatechuic acid, and coumaric acid and flavonoids such as quercetin, chrysin, and catechin [69–71]. Some terpeniods were also found in *Russula* mushrooms including aristolane and marasmane [57, 72]. The chemical structures of the constituents found in *Russula* mushrooms are shown in **Figure 7**.

**Figure 7.** Chemical structures of some flavonoids found in *Russula* mushrooms. A = ferulic acid, B = chrysin, C = aristolane.

#### **5. Conclusion**

Natural products have been main sources of drug discoveries including the development of active compounds or formulas for the treatment of cancers. Even though it has become difficult to discover or synthesize new active components, with the knowledge and intelligence regarding traditional medicine, there are still several ethnomedical herbal formulas and regional plants that could be studied and developed for further medicinal utilizations. Herbal remedies from Wat Tha-it and Wat Khampramong, Thailand, are examples of the efforts to develop anticancer therapies from traditional knowledge. Both remedies can inhibit the growth of various cancer cell lines. The stem extract and active compound, Berberine from the Thai medicinal plant *Coscinium fenestratum*, significantly promoted anti-proliferative activity on human colorectal cancer cells with the mechanism of action via NAG-1 and AFT3. Plants in the genus *Azadirachta* have been traditionally used as a tonic. They promote significant antioxidant activities, which could support the body's systems and prevent oxidative stress, which is one of the causes of carcinogenesis. *Russula* is the local mushroom species in the Northeastern part of Thailand. They promote significant antioxidant effects in both lipid-soluble and watersoluble models. These plants and natural products have the potential to be sources of anticancer compounds or active extracts for the treatments of cancer. However, standardization and quality control of the extract or active compounds should be performed before studying the toxicity, *in vivo* biological activity tests, and further clinical studies in the future.

### **Acknowledgements**

The authors acknowledge the Thailand Institute of Scientific and Technological Research for the support in supplying the photos of *Russula* mushrooms. The authors would like to thank Dr. Prapaipat Klungsupya for her valuable guidance and support about photochemiluminescence assays. The authors also thank Ms. Charinan Jaengklang for her assistance in the *Russula* mushrooms work.

### **Author details**

Some chemical constituents have been reported from *Russula* mushrooms including phenolic acids such as ρ-hydroxy-benzoic acid, chlorogenic acid, ferulic acid, caffeic acid, protocatechuic acid, and coumaric acid and flavonoids such as quercetin, chrysin, and catechin [69–71]. Some terpeniods were also found in *Russula* mushrooms including aristolane and marasmane [57, 72]. The chemical structures of the constituents found in *Russula* mushrooms are shown

**Figure 6.** Physical characteristics of some Russula mushrooms found in Thailand; A = *Russula crustosa* Peck, B = *Russula delica* Fries, C = *Russula monspeliensis* Sarnari, D = *Russula velenovskyi* Melzer & Zvára, E = *Russula virescens* (Schaeff) Fries,

Natural products have been main sources of drug discoveries including the development of active compounds or formulas for the treatment of cancers. Even though it has become

**Figure 7.** Chemical structures of some flavonoids found in *Russula* mushrooms. A = ferulic acid, B = chrysin, C =

in **Figure 7**.

F = *Russula alboareolata* Hongo.

34 Natural Products and Cancer Drug Discovery

**5. Conclusion**

aristolane.

Pongtip Sithisarn1 \* and Piyanuch Rojsanga<sup>2</sup>

\*Address all correspondence to: pongtip.sit@mahidol.ac.th

1 Department of Pharmacognosy, Faculty of Pharmacy, Mahidol University, Bangkok, Thailand

2 Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Mahidol University, Bangkok, Thailand

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**Nutrients and Herbal Anticancer Agents**
