**Targeting the Cytoskeleton with Plant-Bioactive Compounds in Cancer Therapy**

Anca Hermenean and Aurel Ardelean

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/66911

#### **Abstract**

In this overview we describe the main plant-derived bioactive compounds used in cancer therapy which has the cell cytoskeleton as therapeutic target. Three major classes of these compounds are described: antimitotics with microtubule-destabilizing and—stabilizing effects, plant-bioactive compounds that interact with intermediate filaments/actin, and plant-bioactive compounds that interact with intermediate filaments like keratins and vimentin. We also focus on the molecular aspects of interactions with their cellular targets: microtubules, intermediate filaments, and microfilaments. Some critical aspects of cardiac side effects of cancer chemotherapy are also discussed, focusing on cardiac cytoskeleton and protective effect of plant-derived compounds. The application of plant bioactives in the treatment of cancer has resulted in increased therapeutic efficacy through targeting the cytoskeleton, respectively, prevention of the injury of cytoskeletal components elicited by chemotherapeutics.

**Keywords:** plant-derived compounds, cancer therapy, microtubules, intermediate filaments, microfilaments

### **1. Introduction**

Chemotherapy is routinely used for cancer treatment. Since tumor cells lose many of the regulatory pathways of the normal cells, they continue to divide without control. Chemotherapeutic drugs try to solve these abnormalities, but sometimes the toxicity of allopathic treatments creates a significant problem.

The cytoskeleton constitutes the supporting framework of the cell, and it is composed of three types of cytosolic filaments: microtubules, intermediate filaments, and microfilaments. The entire cytoskeletal network is a dynamic structure which regulates the cell structure, and it

is involved in many cellular functions such as movement, transport, or cell division [1]. The cytoskeleton is one of the main therapeutic targets in cancer cells [2].

Various cancer therapies use plant-derived bioactive products. There are four classes of plant-derived anticancer drugs currently used in oncotherapy: vinca alkaloids (vinblastine, vincristine), epipodophyllotoxins (etoposide and teniposide), taxanes (paclitaxel and docetaxel), and camptothecin derivatives (camptothecin and irinotecan) [3]. To date, new generations of vinca alkaloids, camptothecins, and epothilones as well as a novel class of taxanes have been developed. Some of these are in clinical use, others in clinical trials.

The major inconvenience in using antimicrotubule agents in oncotherapy is that these compounds cause significant side effects such as neutropenia and neurotoxicity and because of their limited efficacy as single agents [3].

This review describes the main natural compounds identified in the last year as potential anticancer agents, which have cell cytoskeleton as therapeutic target. We focus on the interactions of plant-derived anticancer drugs with all three types of cytosolic filaments: microtubules, intermediate filaments, and microfilaments. In addition, we summarize the most recent advances in the understanding of the molecular aspects of these interactions.

Some critical aspects of cardiac side effects of cancer chemotherapy are also discussed, focusing on cardiac cytoskeleton and protective effects of plant-derived compounds.

### **2. Microtubules as chemotherapeutic targets of plant-derived bioactives**

Microtubules are dynamic structures involved in different cellular processes including cell division, where they are the most important constituents of the mitotic spindle apparatus during the M phase of cell division [4]. They are polymers composed of α- and β-tubulin heterodimers, characterized by high dynamics of polymerization/depolymerization, resulting in the elongation or shrinkage of the filaments. Polymerization of microtubules occurs when α- and β-tubulin monomers bind to a GTP at the nucleotide exchangeable site (E-site) in β-tubulin and the non-exchangeable site (N-site) in α-tubulin. Once GTP is hydrolyzed, it becomes nonexchangeable, which matches the addition of the next tubulin dimer to the plus (+) end of the microtubule. Upon depolymerization, the GTP cap is detached, allowing the microtubules depolymerize releasing the α-/β-tubulin heterodimers into the cytoplasm. Subsequently, the GDP attached to another free β-tubulin and can exchange to GTP at the E-site, before another polymerization cycle begins [4, 5].

Dynamic instability is regulated by a number of microtubule-associated proteins (MAPs), which bind to stabilize the microtubules [6]. MAP phosphorylation induces its dissociation leading to microtubule instability. Some cytokines have a critical role in the regulation of MAPs and microtubule dynamics, such as controlling centromere localization Cdc2 kinases, mitogen-activated protein kinases ERK, controlling cell migration JNK, and the main serine/ threonine phosphatases, type 1 (PP1) and type 2A (PP2A) [7–10].

The dynamic ability of microtubules to polymerize and depolymerize is essential for cellular division and chromosome segregation during mitosis. Due to their crucial roles in dividing cells, microtubules have been considered a major target for cancer therapy. Microtubuleinteracting plant-derived biomolecules, namely, antimitotics, can be classified into two main groups based on their apparent mechanisms of action: microtubule-destabilizing agents act as tubulin polymerization inhibitors, and microtubule-stabilizing agents act as tubulin polymerization promoters [11].

#### **2.1. Microtubule-destabilizing agents**

is involved in many cellular functions such as movement, transport, or cell division [1]. The

Various cancer therapies use plant-derived bioactive products. There are four classes of plant-derived anticancer drugs currently used in oncotherapy: vinca alkaloids (vinblastine, vincristine), epipodophyllotoxins (etoposide and teniposide), taxanes (paclitaxel and docetaxel), and camptothecin derivatives (camptothecin and irinotecan) [3]. To date, new generations of vinca alkaloids, camptothecins, and epothilones as well as a novel class of taxanes have been developed. Some of these are in clinical use, others in clinical trials.

The major inconvenience in using antimicrotubule agents in oncotherapy is that these compounds cause significant side effects such as neutropenia and neurotoxicity and because of

This review describes the main natural compounds identified in the last year as potential anticancer agents, which have cell cytoskeleton as therapeutic target. We focus on the interactions of plant-derived anticancer drugs with all three types of cytosolic filaments: microtubules, intermediate filaments, and microfilaments. In addition, we summarize the most recent

Some critical aspects of cardiac side effects of cancer chemotherapy are also discussed, focusing

**2. Microtubules as chemotherapeutic targets of plant-derived bioactives**

Microtubules are dynamic structures involved in different cellular processes including cell division, where they are the most important constituents of the mitotic spindle apparatus during the M phase of cell division [4]. They are polymers composed of α- and β-tubulin heterodimers, characterized by high dynamics of polymerization/depolymerization, resulting in the elongation or shrinkage of the filaments. Polymerization of microtubules occurs when α- and β-tubulin monomers bind to a GTP at the nucleotide exchangeable site (E-site) in β-tubulin and the non-exchangeable site (N-site) in α-tubulin. Once GTP is hydrolyzed, it becomes nonexchangeable, which matches the addition of the next tubulin dimer to the plus (+) end of the microtubule. Upon depolymerization, the GTP cap is detached, allowing the microtubules depolymerize releasing the α-/β-tubulin heterodimers into the cytoplasm. Subsequently, the GDP attached to another free β-tubulin and can exchange to GTP at the E-site, before another

Dynamic instability is regulated by a number of microtubule-associated proteins (MAPs), which bind to stabilize the microtubules [6]. MAP phosphorylation induces its dissociation leading to microtubule instability. Some cytokines have a critical role in the regulation of MAPs and microtubule dynamics, such as controlling centromere localization Cdc2 kinases, mitogen-activated protein kinases ERK, controlling cell migration JNK, and the main serine/

threonine phosphatases, type 1 (PP1) and type 2A (PP2A) [7–10].

advances in the understanding of the molecular aspects of these interactions.

on cardiac cytoskeleton and protective effects of plant-derived compounds.

cytoskeleton is one of the main therapeutic targets in cancer cells [2].

their limited efficacy as single agents [3].

316 Cytoskeleton - Structure, Dynamics, Function and Disease

polymerization cycle begins [4, 5].

Vinca alkaloids and colchicines prevent the polymerization of tubulin and promote the depolymerization of microtubules.

Vinca alkaloids are a series of biologically active agents isolated from *Catharanthus roseus* (*Vinca rosea*) with a potent antitumor activity, related to their ability to inhibit the polymerization of microtubules and preventing cell division [12]. There are approximately 130 vinca alkaloids distributed in different vegetal tissues: vincristine, vinblastine, and yohimbine in the aerial parts; catharanthine and vindoline in leaves; and almalicine and reserpine in roots [13]. They have demonstrated clinical efficacy in a broad spectrum of cancers, both as single agents and in combination. Vincristine, vinblastine, and vindesine are the first vinca alkaloids used as antitumor drugs. Vinorelbine is the first new second-generation vinca alkaloid, while vinflunine, a bis-fluorinated vinorelbine derivative, was synthesized by superacid chemistry and studied in phase I–III clinical trials [14, 15].

The vinca alkaloids are dimeric compounds consisting of two multi-ringed subunits, vindoline and catharanthine, linked by a carbon-carbon bridge [16]. They act by binding specifically to β-tubulin and block its ability to polymerize with α-tubulin into microtubules, thus disrupting the mitotic spindle. This blocks mitosis and kills actively dividing cells. The results indicate that vinorelbine and vinflunine affect microtubule dynamics differently from vinblastine and proved to be weak binders [17].

Vincristine is used in the treatment of hematological and lymphatic neoplasms, whereas vinblastine in breast cancer, testicular cancer, choriocarcinoma, and vindesine in non-small cell lung cancer or breast cancer. Vinorelbine is useful for the treatment of non-small-cell lung cancer, and vinflunine has been used in the treatment of bladder, non-small-cell lung, and breast cancers [17].

Similar to Vinca alkaloids, colchicine extracted from plants of the genus *Colchicum* (*autumn crocus*) is a microtubule-destabilizing agent at high concentrations and stabilizes microtubule dynamics at low concentrations [18]. It first binds to soluble tubulin, leading to a complex that copolymerizes into the ends of the microtubules and prevents the elongation of the microtubule polymer. It is severely toxic to normal tissues at high dose, which limits its use in cancer therapies [19]. Colchicine showed different antitumoral effects which include inhibition of metastatic potential [20] and angiogenesis [21], cell blebbing through a Rho/Rho effector kinase (ROCK)/ myosin light-chain kinase (MLCK) pathway [22], decrease of ATP influx into mitochondria [23].

Novel microtubule-destabilizing plant-bioactive compounds are summarized in **Table 1**.



**Table 1.** Potential plant-bioactive compounds that interact with microtubules as microtubule-destabilizing agents for cancer therapy.

#### **2.2. Microtubule-stabilizing agents**

**Active substance/herbal** 

Flavonoids isolated from *Tanacetum gracile*

Artelastin isolated from the wood bark of *Artocarpus elasticus*

318 Cytoskeleton - Structure, Dynamics, Function and Disease

Podoverine A isolated from *Podophyllum versipelle*

Plinabulin chemical probe

2′-Hydroxy-2,4,6-trimethoxy-5′,6′-naphthochalcone

KPU-244-B3

**Mechanism of action Therapeutic use References**

Breast cancer [24]

Breast cancer [25]

Fibrosarcoma [27]

Colon cancer [28]

Cancer therapy [30]

Lung cancer [31]

Breast cancer [32]

Cervical carcinoma Lung carcinoma

[26]

[29]

Renal cancer Breast cancer

—Modulate microtubule

the microtubule network —Kinetochores are not affected

spindle checkpoint

tubulin

transition

HeLa cells

and HeLa cells

bond with Gly 142

dependent manner

Safranal —Inhibition of tubulin assembly (IC50

Isochaihulactone —Inhibition of tubulin polymerization

Carnosol —Modulation of autophagic markers

cells

Aqueous extract of ginger —Disruption of interphase

depolymerization by activating mitotic

—Bind at α- β interfacial site of tubulin

—Radial structure disorganization of

—Mitotic arrest and inhibition of microtubule polymerization by targeting the vinca-binding site on

—Binds in the boundary region between α- and β-tubulin near the

—Induce tubulin depolymerization

microtubule network of A549 and

—Inhibition of temperaturedependent reassembly of cold-treated depolymerized microtubule of A549

was obtained at 72.19 µM) —Binds between α- and β-tubulin closer to alpha-tubulin and hydrogen

—Hydrophobic interactions play critical roles for safranal molecule stabilization in binding site

in a concentration-dependent manner in A549 non-small-cell lung cancer cells —Cause G2/M phase arrest and apoptosis in a time- and concentration-

microtubule- associated protein 1A/1B light-chain 3 I (LC3 I) to microtubuleassociated protein 1A/1B light-chain 3 II (LC3 II) and p62 in MDA-MB-231

—Disruption of microtubular networks by inhibition of tubulin polymerization —Failure of mitotic spindle formation and blocking mitosis at the prometaphase or metaphase-anaphase

colchicine-binding site

**formulation**

Taxanes are the main class of microtubule-stabilizing agents, which prevent the depolymerization of microtubules and promote the polymerization of tubulin to microtubules.

One of the most important plant compounds in the fight against cancer was discovered in the bark of *Taxus brevifolia*—taxol, now named paclitaxel, which has become one of the most effective drugs against breast and ovarian cancer and has been approved for the clinical treatment of cancer patients. Since the first discovery of paclitaxel in the 1960s, a variety of other microtubule-stabilizing agents have been derived primarily from natural resources [37]. The molecular mechanism includes polymerization of tubulin to stable microtubules and also interacts directly with microtubules, stabilizing them against depolymerization and thereby blocks cells in the G2/M phase of the cell cycle [38]. The binding of taxol to β-tubulin in the polymer results in cold-stable microtubules even in the absence of exogenous GTP. Hydrogen/deuterium exchange (HDX) coupled to liquid chromatography-electrospray ionization MS demonstrated a marked reduction in deuterium incorporation in both β- and α-tubulin in the presence of taxol and contributed to increased rigidity in taxol microtubules and complementary to that due to GTP-induced polymerization [39].

Initially obtained from *Taxus brevifolia* bark, paclitaxel is now a semisynthetic product of 10-deacetylbaccatin III, which is extracted from the needles of the *Taxus baccata*. Similarly, docetaxel, a second-generation taxane, was directly obtained semisynthetically by esterification from the inactive taxane precursor 10-deacetylbaccatin III [40]. Paclitaxel and docetaxel bind to the specific binding sites of tubulin, which is different from the binding site of guanosine triphosphate, vinblastine, colchicine, and podophyllotoxin [41].

Docetaxel has a 1.9-fold higher affinity for the site than paclitaxel and induces tubulin polymerization at a 2.1-fold lower critical tubulin concentration. The effect on the cell cycle is different: paclitaxel inhibits the cell cycle traverse at the G2/M phase junction [42], while docetaxel produces its maximum cell-killing effect against cells in the S phase [43].

To decrease the toxicity and enhance delivery and distribution, new taxane formulations of micelles were investigated, including nanoparticles, emulsions, and liposomes [44]. Compounds such as Abraxane, CT-2103, and docosahexaenoic acid (DHA)-paclitaxel are examples of new taxanes with higher activity than paclitaxel in taxane-resistant cancers, as well as in tumors that have been unresponsive to paclitaxel [16].

Protopine is a benzylisoquinoline alkaloid isolated from *Opium poppy*, *Corydalis tubers*, and *Fumaria officinalis*. It stabilizes tubulin polymerization process but has no affinity to taxolbinding site. It induces a marked increase of tubulin polymerization in a dose-dependent manner in human hormone-refractory prostate cancer (PC-3 cells), similar to paclitaxel. It enhances microtubule assembly and formation of mitotic spindles in PC-3 cells [45].

Taccalonolides are plant steroids possessing a C2–C3 epoxide group and an enol-lactone isolated from *Tacca leontopetaloides*, *Tacca plantaginea*, *Tacca chantrieri*, *Tacca plantaginea*, *Tacca integrifolia*, etc. They act as microtubule stabilizers by binding to another microtubule site than taxol resulting in the formation of microtubule bundles and leading to cell cycle arrest and apoptosis. It is also reported that taccalonolides bind to β-tubulin near the lumen of microtubule, which is different from the taxol-binding site stabilizers which bind to α-tubulin protofilaments [46–49].

Recent study shows that the dietary flavonoid fisetin binds to tubulin and stabilizes microtubules with binding characteristics far superior than paclitaxel. It induces upregulation of microtubuleassociated protein (MAP)-2 and microtubule-associated protein (MAP)-4 and increases α-tubulin acetylation, an indicator of microtubule stabilization [50].

effective drugs against breast and ovarian cancer and has been approved for the clinical treatment of cancer patients. Since the first discovery of paclitaxel in the 1960s, a variety of other microtubule-stabilizing agents have been derived primarily from natural resources [37]. The molecular mechanism includes polymerization of tubulin to stable microtubules and also interacts directly with microtubules, stabilizing them against depolymerization and thereby blocks cells in the G2/M phase of the cell cycle [38]. The binding of taxol to β-tubulin in the polymer results in cold-stable microtubules even in the absence of exogenous GTP. Hydrogen/deuterium exchange (HDX) coupled to liquid chromatography-electrospray ionization MS demonstrated a marked reduction in deuterium incorporation in both β- and α-tubulin in the presence of taxol and contributed to increased rigidity in taxol microtubules and complementary to that

Initially obtained from *Taxus brevifolia* bark, paclitaxel is now a semisynthetic product of 10-deacetylbaccatin III, which is extracted from the needles of the *Taxus baccata*. Similarly, docetaxel, a second-generation taxane, was directly obtained semisynthetically by esterification from the inactive taxane precursor 10-deacetylbaccatin III [40]. Paclitaxel and docetaxel bind to the specific binding sites of tubulin, which is different from the binding site of guanosine

Docetaxel has a 1.9-fold higher affinity for the site than paclitaxel and induces tubulin polymerization at a 2.1-fold lower critical tubulin concentration. The effect on the cell cycle is different: paclitaxel inhibits the cell cycle traverse at the G2/M phase junction [42], while docetaxel produces

To decrease the toxicity and enhance delivery and distribution, new taxane formulations of micelles were investigated, including nanoparticles, emulsions, and liposomes [44]. Compounds such as Abraxane, CT-2103, and docosahexaenoic acid (DHA)-paclitaxel are examples of new taxanes with higher activity than paclitaxel in taxane-resistant cancers, as well as in

Protopine is a benzylisoquinoline alkaloid isolated from *Opium poppy*, *Corydalis tubers*, and *Fumaria officinalis*. It stabilizes tubulin polymerization process but has no affinity to taxolbinding site. It induces a marked increase of tubulin polymerization in a dose-dependent manner in human hormone-refractory prostate cancer (PC-3 cells), similar to paclitaxel. It

Taccalonolides are plant steroids possessing a C2–C3 epoxide group and an enol-lactone isolated from *Tacca leontopetaloides*, *Tacca plantaginea*, *Tacca chantrieri*, *Tacca plantaginea*, *Tacca integrifolia*, etc. They act as microtubule stabilizers by binding to another microtubule site than taxol resulting in the formation of microtubule bundles and leading to cell cycle arrest and apoptosis. It is also reported that taccalonolides bind to β-tubulin near the lumen of microtubule, which is different from the taxol-binding site stabilizers which bind to α-tubulin

enhances microtubule assembly and formation of mitotic spindles in PC-3 cells [45].

due to GTP-induced polymerization [39].

320 Cytoskeleton - Structure, Dynamics, Function and Disease

triphosphate, vinblastine, colchicine, and podophyllotoxin [41].

its maximum cell-killing effect against cells in the S phase [43].

tumors that have been unresponsive to paclitaxel [16].

protofilaments [46–49].

### **3. Microfilaments as chemotherapeutic targets of plant-derived bioactives**

Actin filaments are composed of globular actin (G-actin) which polymerizes into filamentous (F) actin and participates in many important cellular processes including cell division and cytokinesis, cell signaling, vesicle and organelle movement, cell junction establishment, and maintenance.

Like microtubules, actin microfilaments can change rapidly their structure in response to external stimuli. Actin polymerization is stimulated by nucleating factors such as the Arp2/3 complex, which mimics a G-actin dimer in order to stimulate actin polymerization [51]. Actin binds ATP to stabilize microfilament formation and hydrolysis [52]. The growth of microfilaments is regulated by thymosin, which binds G-actin to lead the polymerizing process, whereas profilin binds G-actin and catalyzes the exchange of ADP to ATP, promoting monomeric addition to the plus end of F-actin [53].

During cytokinesis, disruption of actin polymerization can effect cellular structure. Cytokinesis inhibitors such as cytochalasin B disrupt the actin cytoskeleton, and the cell is unable to divide [54] but is still able to initiate another mitotic event, continuing to form nuclei and eventually becoming enlarged and multinucleated [55, 56]. Cell lines derived from bladder, kidney, and prostate carcinomas become multinucleated when grown in cytochalasin B-supplemented medium, whereas cells from corresponding normal tissue remain monoor binucleate under comparable conditions [55]. These particular features make tumor cells ideal targets for chemotherapy, as they have reduced cytoskeletal integrity and multiple nucleation and increased mitochondrial activity [57].

Actin filaments are also of substantial importance to cancer cell migration. Cancer cell migration can convert between mesenchymal and amoeboid types. This latter can occur, e.g., when cells are exposed to protease inhibitors [58] and thereby mesenchymal cancer cell invasion is repressed by specific targeting of protease function. Inhibiting RhoA/ROCK signaling promotes the formation of multiple competing microfilament-derived lamellipodia that suppress amoeboid migration of tumor cells [59]. Tumor cells unable to move through amoeboid migration will switch to mesenchymal migration [60]. However, tumor cells exposed to protease inhibitors will move mainly through amoeboid migration. Using microfilament disrupting RhoA/ROCK inhibitors in combination with protease inhibitors would simultaneously block both types of cell migration.

Phytomedicine developed actin-targeted potential drugs, designed for cancer therapy (**Table 2**).


**Table 2.** Plant-bioactive compounds which interact with actin for cancer therapy.

### **4. Intermediate filaments as chemotherapeutic targets of plant-derived bioactives**

Along with microfilaments and microtubules, intermediate filaments are the other component of the cytoskeleton that can be exploited in the clinical treatment of cancer. All intermediate filaments have a central alpha-helical domain that is composed of four protofibrils separated by three linker regions [72]. The N- and C-terminus segments of intermediate filaments are non-alpha-helical regions of polypeptide sequences, associated with head to tail into protofilaments that pair up laterally into protofibrils; four of these protofibrils form an intermediate filament.

Whereas microfilaments and microtubules are actin or tubulin polymers, intermediate filaments are composed of 50 different proteins classified into six types based on similarities in amino acid sequence [72]. In regard to potential chemotherapeutic targets, the most promising intermediate filaments are keratins, nestin, and vimentin.

### **4.1. Anti-keratin agents**

Keratin and cytokeratin are intermediate filaments found in the cytoskeleton of epithelial tissue. There are twenty different keratin polypeptides (K1–K20) identified and classified into type I (K9–K20) and type II (K1–K8) intermediate filaments [73]. Keratins of importance to cancer therapy are keratin 8 (K8) and keratin 18 (K18), the most common and characteristic members of intermediate filaments expressed in single-layer epithelial tissues [74, 75]. Oncogenes, which activate Ras signaling, stimulate expression of K18 through transcription factors [76]. However, aberrant K8 and K18 expression has been noticed in particularly invasive carcinomas [77, 78]. K18 was found to be a substrate of the cysteine-aspartic proteases during epithelial apoptosis [77].

Based on aberrant keratin expression found in many cancers, these intermediate filaments present a novel chemotherapeutic target that need to be investigated.

Crude acetone extract of *Bupleurum scorzonerifolium* (AE-BS) showed antiproliferative activity, induced cell arrest in G2/M phase, and apoptosis in A549 human lung cancer cells [79]. In a further study, Chen et al. [73] noticed K8 phosphorylation after AE-BS treatment of A549 cells. The association of ERK1/2 activation with K8 phosphorylation may be related to the apoptotic effect of AE-BS.

#### **4.2. Anti-vimentin agents**

**4. Intermediate filaments as chemotherapeutic targets of plant-derived** 

Along with microfilaments and microtubules, intermediate filaments are the other component of the cytoskeleton that can be exploited in the clinical treatment of cancer. All intermediate filaments have a central alpha-helical domain that is composed of four protofibrils separated

**Mechanism of action Therapeutic use References**

Breast cancer [61]

Sarcoma [62]

Liver cancer [63]

[64]

[65]

[68]

[71]

Lung metastasis of mammary adenocarcinoma

Prostate carcinoma

Myeloid leukemia

Melanoma cell line

B16–F10

95D lung cancer cells [66]

HeLa cells [67]

Cancer cells [69]

Bladder cancer cells [70]

cells

cells

**bioactives**

**Active substance/herbal** 

322 Cytoskeleton - Structure, Dynamics, Function and Disease

Alkaloid mixture derived from *Senna spectabilis* cassine and spectaline

Resveratrol —50 µM resveratrol decreases Rac and Cdc42

actin cytoskeleton

Oleuropein —Disrupt actin filaments in a dose-dependent manner

Deoxyelephantopin (DET) —Affects the actin cytoskeleton network and

proteomic profiling

Cucurbitacin E —Disruption of the F-actin cytoskeleton

Cucurbitacin E —Damaged F-actin without affecting beta-tubulin

Jasplakinolide (JAS) —Rearranged the actin cytoskeleton

*Ganoderma lucidum* extracts —Inhibits growth and induce actin polymerization

actin fraction

Cucurbitacin I —Induced the co-aggregation of actin with

Cucurbitacin B —Induced rapid and improper polymerization of the F-actin network

4-Hydroxycoumarin —Disorganized the actin cytoskeleton correlated

random motility

**Table 2.** Plant-bioactive compounds which interact with actin for cancer therapy.

—JAS has a phalloidin-like action

filaments

signaling to the actin cytoskeleton

several actin-associated proteins

—5 µM resveratrol increases Rac signaling to the

—Altered normal distribution pattern of F-actin

downregulates calpain-mediated proteolysis of

—Inhibition of proteolysis of actin cytoskeletonassociated proteins identified by differential

—Increases the filamentous or polymerized

phospho-myosin II by stimulation of the RhoA/ ROCK pathway and inhibition of LIM-kinase

—Distribution of actin filaments was different from that induced by cytochalasin D

with reductions in cell adhesion to four extracellular matrix proteins and inhibition of

**formulation**

Vimentin functions as a regulator in cancer cells undergoing epithelial-mesenchymal transition (EMT), an important change during tumor progression where cells detached from their original tissue become highly motile and invasive. Studies have shown that quercetin prevented epidermal growth factor (EGF)-induced EMT, migration, and invasion of prostate cancer cells by suppressing the expression of vimentin and N-cadherin [80]. Genistein, an isoflavone found in soybeans, fava beans, and lupine, has been shown to downregulate mesenchymal markers ZEB1, slug, and vimentin and therefore cause reversal of EMT in gemcitabine-resistant pancreatic cancer cells [81]. Similarly, this flavonoid was able to decrease protein expression of vimentin, cathepsin D, and MMP-2 and thus suppressed epithelialmesenchymal transition and migration capacity of BG-1 ovarian cancer cells [82]. Other natural compounds, like silibinin, induced the morphological reversal of mesenchymal phenotype to epithelial phenotype through downregulation of vimentin and MMP-2 and upregulation of cytokeratin-18 [83]. Moreover, silibinin meglumine, a water-soluble form of milk thistle silymarin, impedes the EMT in EGFR-mutant non-small-cell lung carcinoma cells by upregulation of the relative mRNA expression of CDH1 (E-cadherin) accompanied by downregulation of vimentin [84]. Berberine, a plant alkaloid present in various plants like *Berberis*, decreased the expression of the mesenchymal markers vimentin and fibronectin and restored the epithelial marker E-cadherin, thereby contributing to the reversal of EMT [85].

Piplartine, a biologically active component from *Piper* species (Piperaceae), also suppresses tumor progression and migration by disruption of the p120-ctn/vimentin/N-cadherin complex, which plays a critical role in tumor progression and invasion/metastasis [86].

Phenethyl isothiocyanate (PEITC), the main bioactive compound present in cruciferous vegetables, decreases breast and prostate tumor growth inhibition through vimentin suppression [87]. Cucurbitacin E induced disruption of vimentin cytoskeleton in prostate carcinoma cells, while microtubules were unaffected [65]. The natural product withaferin A (WFA) exhibits antitumor activity by binding to vimentin and covalently modifying its cysteine residue, which is present in the highly conserved helical coiled coil 2B domain [88]. Penduletin and casticin, flavonoids from the Brazilian plant *Croton betulaster*, induced changes in the pattern of expression of the cytoskeletal protein vimentin and thereby inhibit the growth of human glioblastoma cells [89].

### **5. Protective effect of plant-bioactive compounds on anthracycline-induced cardiac cytoskeletal toxicity**

Cardiotoxicity is the most serious side effect of antitumoral anthracyclines, which include adriamycin, doxorubicin, mitoxantrone, daunorubicin, or epirubicin [90]. The main cause of toxicity is their effect on the cardiac cytoskeleton, consisting of myofibrils disarray [91], including both structural and functional changes: troponin I and troponin C phosphorylation mediated by a doxorubicin-induced protein kinase C activation [92, 93] and decrease of troponin I, and changes of α-actin, creatine kinase, and myosin light-chain 2 expression [93]. In other studies, degradation of cardiac cytoskeletal proteins, including titin [94] and dystrophin [95], was observed. Recently, changes in the cardiac distribution of desmin have been detected, with areas of decreased expression in the cytoplasm and protein aggregation after mitoxantrone treatment [96, 97]. The use of plant bioactives might protect against the oxidative stress caused by anthracycline drugs, including cytoskeleton injuries. Our group recently demonstrated that the flavonoid chrysin inhibits mitoxantrone-triggered cardiomyocyte apoptosis via multiple pathways, including decrease of the Bax/Bcl-2 ratio and caspase-3 expression along with preservation of the desmin disarray [96].

### **6. Conclusions**

Plant-derived bioactive molecules constitute promising tools for the treatment of cancer. The application of plant bioactives in the treatment of cancer has resulted in increased therapeutic efficacy through targeting the cytoskeleton and prevention of cytoskeletal injuries due to chemotherapy side effects. Research results testify both the evolution of knowledge coming from pharmacognosy and the great possibilities of future progress by means of a rational approach of natural product-based drug discovery or new pharmaceutical formulations.

### **Author details**

of milk thistle silymarin, impedes the EMT in EGFR-mutant non-small-cell lung carcinoma cells by upregulation of the relative mRNA expression of CDH1 (E-cadherin) accompanied by downregulation of vimentin [84]. Berberine, a plant alkaloid present in various plants like *Berberis*, decreased the expression of the mesenchymal markers vimentin and fibronectin and restored the epithelial marker E-cadherin, thereby contributing to the reversal of EMT [85]. Piplartine, a biologically active component from *Piper* species (Piperaceae), also suppresses tumor progression and migration by disruption of the p120-ctn/vimentin/N-cadherin complex,

Phenethyl isothiocyanate (PEITC), the main bioactive compound present in cruciferous vegetables, decreases breast and prostate tumor growth inhibition through vimentin suppression [87]. Cucurbitacin E induced disruption of vimentin cytoskeleton in prostate carcinoma cells, while microtubules were unaffected [65]. The natural product withaferin A (WFA) exhibits antitumor activity by binding to vimentin and covalently modifying its cysteine residue, which is present in the highly conserved helical coiled coil 2B domain [88]. Penduletin and casticin, flavonoids from the Brazilian plant *Croton betulaster*, induced changes in the pattern of expression of the cytoskeletal protein vimentin and thereby inhibit

**5. Protective effect of plant-bioactive compounds on anthracycline-induced** 

Cardiotoxicity is the most serious side effect of antitumoral anthracyclines, which include adriamycin, doxorubicin, mitoxantrone, daunorubicin, or epirubicin [90]. The main cause of toxicity is their effect on the cardiac cytoskeleton, consisting of myofibrils disarray [91], including both structural and functional changes: troponin I and troponin C phosphorylation mediated by a doxorubicin-induced protein kinase C activation [92, 93] and decrease of troponin I, and changes of α-actin, creatine kinase, and myosin light-chain 2 expression [93]. In other studies, degradation of cardiac cytoskeletal proteins, including titin [94] and dystrophin [95], was observed. Recently, changes in the cardiac distribution of desmin have been detected, with areas of decreased expression in the cytoplasm and protein aggregation after mitoxantrone treatment [96, 97]. The use of plant bioactives might protect against the oxidative stress caused by anthracycline drugs, including cytoskeleton injuries. Our group recently demonstrated that the flavonoid chrysin inhibits mitoxantrone-triggered cardiomyocyte apoptosis via multiple pathways, including decrease of the Bax/Bcl-2 ratio and caspase-3

Plant-derived bioactive molecules constitute promising tools for the treatment of cancer. The application of plant bioactives in the treatment of cancer has resulted in increased therapeutic

which plays a critical role in tumor progression and invasion/metastasis [86].

the growth of human glioblastoma cells [89].

324 Cytoskeleton - Structure, Dynamics, Function and Disease

expression along with preservation of the desmin disarray [96].

**cardiac cytoskeletal toxicity**

**6. Conclusions**

Anca Hermenean<sup>1</sup> \* and Aurel Ardelean<sup>2</sup>

\*Address all correspondence to: anca.hermenean@gmail.com

1 Department of Histology, Faculty of Medicine, Vasile Goldis Western University of Arad, Arad, Romania

2 Department of Cell and Molecular Biology, Faculty of Medicine, Vasile Goldis Western University of Arad, Arad, Romania

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### *Edited by Jose C. Jimenez-Lopez*

The cytoskeleton is a highly dynamic intracellular platform constituted by a threedimensional network of proteins responsible for key cellular roles as structure and shape, cell growth and development, and offering to the cell with "motility" that being the ability of the entire cell to move and for material to be moved within the cell in a regulated fashion (vesicle trafficking). The present edition of Cytoskeleton provides new insights into the structure-functional features, dynamics, and cytoskeleton's relationship to diseases. The authors' contribution in this book will be of substantial importance to a wide audience such as clinicians, researches, educators, and students interested in getting updated knowledge about molecular basis of cytoskeleton, such as regulation of cell vital processes by actin-binding proteins as cell morphogenesis, motility, their implications in cell signaling, as well as strategies for clinical trial and alternative therapies based in multitargeting molecules to tackle diseases, that is, cancer.

Cytoskeleton - Structure, Dynamics, Function and Disease

Cytoskeleton

Structure, Dynamics, Function and Disease

*Edited by Jose C. Jimenez-Lopez*

Photo by LV4260 / iStock