c-MET pathway in human malignancies and its targeting by natural compounds for cancer therapy.

BACKGROUND: c-MET is a receptor tyrosine kinase which is classically activated by HGF to activate its downstream signaling cascades such as MAPK, PI3K/Akt/mTOR, and STAT3. The c-MET modulates cell proliferation, epithelial-mesenchymal transition (EMT), immune response, morphogenesis, apoptosis, and angiogenesis. The c-MET has been shown to serve a prominent role in embryogenesis and early development. The c-MET pathway is deregulated in a broad range of malignancies, due to overexpression of ligands or receptors, genomic amplification, and MET mutations. The link between the deregulation of c-MET signaling and tumor progression has been well-documented. Overexpression or overactivation of c-MET is associated with dismal clinical outcomes and acquired resistance to targeted therapies. Since c-MET activation results in the triggering of oncogenic pathways, abrogating the c-MET pathway is considered to be a pivotal strategy in cancer therapeutics. Herein, an analysis of role of the c-MET pathway in human cancers and its relevance in bone metastasis and therapeutic resistance has been undertaken. Also, an attempt has been made to summarize the inhibitory activity of selected natural compounds towards c-MET signaling in cancers. METHODS: The publications related to c-MET pathway in malignancies and its natural compound modulators were obtained from databases such as PubMed, Scopus, and Google Scholar and summarized based on PRISMA guidelines. Some of the keywords used for extracting relevant literature are c-MET, natural compound inhibitors of c-MET, c-MET in liver cancer, c-MET in breast cancer, c-MET in lung cancer, c-MET in pancreatic cancer, c-MET in head and neck cancer, c-MET in bone metastasis, c-MET in therapeutic resistance, and combination of c-MET inhibitors and chemotherapeutic agents. The chemical structure of natural compounds was verified in PubChem database. RESULTS: The search yielded 3935 publications, of which 195 reference publications were used for our analysis. Clinical trials were referenced using ClinicalTrials.gov identifier. The c-MET pathway has been recognized as a prominent target to combat the growth, metastasis, and chemotherapeutic resistance in cancers. The key role of the c-MET in bone metastasis as well as therapeutic resistance has been elaborated. Also, suppressive effect of selected natural compounds on the c-MET pathway in clinical/preclinical studies has been discussed.

Ginkgolic Acids Confer Potential Anticancer Effects by Targeting Pro- Inflammatory and Oncogenic Signaling Molecules.

BACKGROUND: Medicinal plants and herbal preparations in the form of traditional medicines have been used in healthcare worldwide. The extracts of Ginkgo biloba L. seeds and leaves contain a complex mixture of numerous components, such as flavonol glycosides, terpene lactones, and a group of alkylphenols (anacardic or ginkgolic acids, cardanols and cardols) that have been a part of traditional Chinese medicine. These extracts are also sold as dietary supplements worldwide. G. biloba extract (EGb 761 and LI 1370) represent the standard form of G. biloba extract. Six different 6-alkylsalicylic acids (syn. ginkgolic acids) with alkyl substituents (C13:0, C15:0, C15:1, C17:0, C17:1, and C17:2) have been identified. OBJECTIVE: The aim of this review is to unravel scientific evidence on anti-inflammatory and anticancer activities of ginkgolic acids to understand its therapeutic potential against inflammatory and oncologic diseases. METHODS: A structured literature search was independently performed by the authors on PubMed, ScienceDirect, Scopus, and Web of Science. Accordingly, this review article critically analyses available scientific evidence on anti-inflammatory and anticancer activities of ginkgolic acids. Moreover, the review only included articles written in the English language. RESULTS: Several forms of ginkgolic acids, especially C13:0, C15:0 and C17:1, isolated from the leaves of G. biloba exhibited cytotoxic activity against a variety of human cancers by suppressing various pro-inflammatory signaling cascades and oncogenic transcription factors through multiple modes of action in various in vitro and in vivo preclinical models. Ginkgolic acids have also been reported to be potent post-translational small ubiquitin-related modifiers (SUMO)ylation inhibitors. CONCLUSION: In this review, we present updated information on the anti-inflammatory and anticancer properties of ginkgolic acids both in vitro and in vivo. Although ginkgolic acids show significant therapeutic potential in inflammatory and oncologic diseases, more investigations regarding the safety and efficacy of these natural agents are warranted before the clinical transition.

Focus on Formononetin: Anticancer Potential and Molecular Targets.

Formononetin, an isoflavone, is extracted from various medicinal plants and herbs, including the red clover (Trifolium pratense) and Chinese medicinal plant Astragalus membranaceus. Formononetin's antioxidant and neuroprotective effects underscore its therapeutic use against Alzheimer's disease. Formononetin has been under intense investigation for the past decade as strong evidence on promoting apoptosis and against proliferation suggests for its use as an anticancer agent against diverse cancers. These anticancer properties are observed in multiple cancer cell models, including breast, colorectal, and prostate cancer. Formononetin also attenuates metastasis and tumor growth in various in vivo studies. The beneficial effects exuded by formononetin can be attributed to its antiproliferative and cell cycle arrest inducing properties. Formononetin regulates various transcription factors and growth-factor-mediated oncogenic pathways, consequently alleviating the possible causes of chronic inflammation that are linked to cancer survival of neoplastic cells and their resistance against chemotherapy. As such, this review summarizes and critically analyzes current evidence on the potential of formononetin for therapy of various malignancies with special emphasis on molecular targets.

Honokiol for cancer therapeutics: A traditional medicine that can modulate multiple oncogenic targets.

In spite of billions of dollars expended on cancer research every year, the incidence rate and the mortality rate due to this widespread disease has increased drastically over the last few decades. Recent reports from the World Health Organization advocate that overall global cancer burden and deaths due to cancer are expected to double by the next decade. Synthetic drugs developed as chemotherapeutics have repeatedly shown adverse side effects and development of chemoresistance. Cancer is basically a multifactorial disease that necessitates the modulation of multiple targets and oncogenic signaling pathways. Honokiol (C18H18O2) is a biphenolic natural compound isolated from the leaves and barks of Magnolia plant species and has been extensively studied for its beneficial effects against several chronic diseases. Honokiol is capable of efficiently preventing the growth of wide variety of tumors such as those of brain, breast, cervical, colon, liver, lung, prostate, skin, and hematological malignancies. Recent work has shown that this phytochemical can modulate various molecular targets such as activation of pro-apoptotic factors, suppression of anti-apoptotic proteins and different transcription factors, downregulation of various enzymes, chemokines, cell surface adhesion molecules, and cell cycle proteins, and inhibition of activity of protein tyrosine kinases and serine/threonine kinases. Because of its pharmacological safety, honokiol can either be used alone or in combination with other chemotherapeutic drugs for the prevention and treatment of cancer. The current review describes in detail the various reports supporting these anti-cancer studies documented with this promising agent.

Targeting autophagy using natural compounds for cancer prevention and therapy.

Autophagy, also known as macroautophagy, is a tightly regulated process involved in the stress responses, such as starvation. It is a vacuolar, lysosomal pathway for the degradation of damaged proteins and organelles in eukaryotic cells. Autophagy also plays a key role in various tissue processes and immune responses and in the regulation of inflammation. Over the past decade, three levels of autophagy regulation have been identified in mammalian cells: 1) signaling, 2) autophagosome formation, and 3) autophagosome maturation and lysosomal degradation. Any deregulation of the autophagy processes can lead to the development of diverse chronic diseases, such as diabetes, obesity, cardiovascular disease, neurodegenerative disease, and malignancies. However, the potential role of autophagy in cancer is rather complex and has been associated with both the induction and the inhibition of neoplasia. Several synthetic autophagy modulators have been identified as promising candidates for cancer therapy. In addition, diverse phytochemicals derived from natural sources, such as curcumin, ursolic acid, resveratrol, thymoquinone, and γ-tocotrienol, also have attracted attention as promising autophagy modulators with minimal side effects. In this review, the authors discuss the importance of autophagy regulators and various natural compounds that induce and/or inhibit autophagy in the prevention and therapy of cancer.

Pro-Apoptotic and Anti-Cancer Properties of Diosgenin: A Comprehensive and Critical Review.

Novel and alternative options are being adopted to combat the initiation and progression of human cancers. One of the approaches is the use of molecules isolated from traditional medicinal herbs, edible dietary plants and seeds that play a pivotal role in the prevention/treatment of cancer, either alone or in combination with existing chemotherapeutic agents. Compounds that modulate these oncogenic processes are potential candidates for cancer therapy and may eventually make it to clinical applications. Diosgenin is a naturally occurring steroidal sapogenin and is one of the major bioactive compounds found in dietary fenugreek (Trigonella foenum-graecum) seeds. In addition to being a lactation aid, diosgenin has been shown to be hypocholesterolemic, gastro- and hepato-protective, anti-oxidant, anti-inflammatory, anti-diabetic, and anti-cancer. Diosgenin has a unique structural similarity to estrogen. Several preclinical studies have reported on the pro-apoptotic and anti-cancer properties of diosgenin against a variety of cancers, both in in vitro and in vivo. Diosgenin has also been reported to reverse multi-drug resistance in cancer cells and sensitize cancer cells to standard chemotherapy. Remarkably, diosgenin has also been reported to be used by pharmaceutical companies to synthesize steroidal drugs. Several novel diosgenin analogs and nano-formulations have been synthesized with improved anti-cancer efficacy and pharmacokinetic profile. In this review we discuss in detail the multifaceted anti-cancer properties of diosgenin that have found application in pharmaceutical, functional food, and cosmetic industries; and the various intracellular molecular targets modulated by diosgenin that abrogate the oncogenic process.

Potential role of genipin in cancer therapy.

Genipin, an aglycone derived from the iridoid glycoside, geniposide, is isolated and characterized from the extract of Gardenia jasminoides Ellis fruit (family Rubiaceae). It has long been used in traditional oriental medicine for the prevention and treatment of several inflammation driven diseases, including cancer. Genipin has been shown to have hepatoprotective activity acting as a potent antioxidant and inhibitor of mitochondrial uncoupling protein 2 (UCP2), and also reported to exert significant anticancer effects. It is an excellent crosslinking agent that helps to make novel sustained or delayed release nanoparticle formulations. In this review, we present the latest developments of genipin as an anticancer agent and briefly describe its diverse mechanism(s) of action. Several lines of evidence suggest that genipin is a potent inhibitor of UCP2, which functions as a tumor promoter in a variety of cancers, attenuates generation of reactive oxygen species and the expression of matrix metalloproteinase 2, as well as induces caspase-dependent apoptosis in vitro and in in vivo models. These finding suggests that genipin can serve as both a prominent anticancer agent as well as a potent crosslinking drug that may find useful application in several novel pharmaceutical formulations.

Potential Role of Natural Compounds as Anti-Angiogenic Agents in Cancer.

BACKGROUND: Neovascularization, also known as angiogenesis, is the process of capillary sprouting from pre-existing blood vessels. This physiological process is a hallmark event in normal embryonic development as blood vessels generally supply both oxygen and nutrients to the cells of the body. Any disruption in this process can lead to the development of various chronic diseases, including cancer. In cancer, aberrant angiogenesis plays a prominent role in maintaining sustained tumor growth to malignant phenotypes and promoting metastasis. The leakiness in the tumor microvasculature is attributed to the tumor cells migrating to distal site organs and forming colonies. METHODS: In this article, we briefly review the various mediators involved in the angiogenic process and the anti-angiogenic potential of selected natural compounds against various malignancies. RESULTS: Several growth factors and their receptors such as vascular endothelial growth factor and receptor (VEGF/VEGFR), basic fibroblast growth factor and receptor (bFGF/FGFR), angiopoietins, and hypoxia inducible factors facilitate the development of angiogenesis and are attractive anti-cancer targets. Natural products represent a rich diversity of compounds for drug discovery and are currently being actively exploited to target tumor angiogenesis. CONCLUSION: Agents such as curcumin, artemisinin, EGCG, resveratrol, emodin, celastrol, thymoquinone and tocotrienols all have shown prominent anti-angiogenic effects in the preclinical models of tumor angiogenesis. Several semi-synthetic derivatives and novel nano-formulations of these natural compounds have also exhibited excellent anti-angiogenic activity by increasing bioavailability and delivering the drugs to the sites of tumor angiogenesis.

Butein and Its Role in Chronic Diseases.

Natural compounds isolated from various plant sources have been used for therapeutic purpose for centuries. These compounds have been routinely used for the management of various chronic ailments and have gained considerable attention because of their significant efficacy and comparatively low side effects. Butein, a chacolnoid compound that has been isolated from various medicinal plants has exhibited a wide range of beneficial pharmacological effects, such as anti-inflammatory, anticancer, antioxidant, and anti-angiogenic in diverse disease models. This article briefly summarizes the past published literature related to the therapeutic and protective effects of butein, as demonstrated in various models of human chronic diseases. Further analysis of its important cellular targets, toxicity, and pharmacokinetic profile may further significantly expand its therapeutic application.

Cancer prevention and therapy through the modulation of transcription factors by bioactive natural compounds.

The association between chronic inflammation and cancer development has been well documented. One of the major obstacles in cancer treatment is the persistent autocrine and paracrine activation of pro-inflammatory transcription factors such as nuclear factor-κB, signal transducer and activator of transcription 3, activator protein 1, fork head box protein M1, and hypoxia-inducible factor 1α in a wide variety of tumor cell lines and patient specimens. This, in turn, leads to an accelerated production of cellular adhesion molecules, inflammatory cytokines, chemokines, anti-apoptotic molecules, and inducible nitric oxide synthase. Numerous medicinal plant-derived compounds have made a tremendous impact in drug discovery research endeavors, and have been reported to modulate the activation of diverse oncogenic transcription factors in various tumor models. Moreover, novel therapeutic combinations of standard chemotherapeutic drugs with these agents have significantly improved patient survival by making cancer cells more susceptible to chemotherapy and radiotherapy. In this review, we critically analyze the existing literature on the modulation of diverse transcription factors by various natural compounds and provide views on new directions for accelerating the discovery of novel drug candidates derived from Mother Nature.

Garcinol sensitizes human head and neck carcinoma to cisplatin in a xenograft mouse model despite downregulation of proliferative biomarkers.

Platinum compounds such as cisplatin and carboplatin are frequently used as the first-line chemotherapy for the treatment of the head and neck squamous cell carcinoma (HNSCC). In the present study, we investigated whether garcinol, a polyisoprenylated benzophenone can chemosensitize HNSCC to cisplatin. We found that garcinol inhibited the viability of a panel of diverse HNSCC cell lines, enhanced the apoptotic effect of cisplatin, suppressed constitutive as well as cisplatin-induced NF-κB activation, and downregulated the expression of various oncogenic gene products (cyclin D1, Bcl-2, survivin and VEGF). In vivo study showed that administration of garcinol alone (0.5 mg/kg body weight, i.p. five times/week) significantly suppressed the growth of the tumor, and this effect was further increased by cisplatin. Both the markers of proliferation index (Ki-67) and microvessel density (CD31) were downregulated in tumor tissues by the combination of cisplatin and garcinol. The pharmacokinetic results of garcinol indicated that good systemic exposure was achievable after i.p. administration of garcinol at 0.5 mg/kg and 2 mg/kg with mean peak concentration (Cmax) of 1825.4 and 6635.7 nM in the mouse serum, respectively. Overall, our results suggest that garcinol can indeed potentiate the effects of cisplatin by negative regulation of various inflammatory and proliferative biomarkers.

The multifaceted role of curcumin in cancer prevention and treatment.

Despite significant advances in treatment modalities over the last decade, neither the incidence of the disease nor the mortality due to cancer has altered in the last thirty years. Available anti-cancer drugs exhibit limited efficacy, associated with severe side effects, and are also expensive. Thus identification of pharmacological agents that do not have these disadvantages is required. Curcumin, a polyphenolic compound derived from turmeric (Curcumin longa), is one such agent that has been extensively studied over the last three to four decades for its potential anti-inflammatory and/or anti-cancer effects. Curcumin has been found to suppress initiation, progression, and metastasis of a variety of tumors. These anti-cancer effects are predominantly mediated through its negative regulation of various transcription factors, growth factors, inflammatory cytokines, protein kinases, and other oncogenic molecules. It also abrogates proliferation of cancer cells by arresting them at different phases of the cell cycle and/or by inducing their apoptosis. The current review focuses on the diverse molecular targets modulated by curcumin that contribute to its efficacy against various human cancers.

Oleanolic acid and its synthetic derivatives for the prevention and therapy of cancer: preclinical and clinical evidence.

Oleanolic acid (OA, 3ß-hydroxyolean-12-en-28-oic acid) is a ubiquitous pentacyclic multifunctional triterpenoid, widely found in several dietary and medicinal plants. Natural and synthetic OA derivatives can modulate multiple signaling pathways including nuclear factor-κB, AKT, signal transducer and activator of transcription 3, mammalian target of rapamycin, caspases, intercellular adhesion molecule 1, vascular endothelial growth factor, and poly (ADP-ribose) polymerase in a variety of tumor cells. Importantly, synthetic derivative of OA, 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO), and its C-28 methyl ester (CDDO-Me) and C28 imidazole (CDDO-Im) have demonstrated potent antiangiogenic and antitumor activities in rodent cancer models. These agents are presently under evaluation in phase I studies in cancer patients. This review summarizes the diverse molecular targets of OA and its derivatives and also provides clear evidence on their promising potential in preclinical and clinical situations.

Garcinol, a polyisoprenylated benzophenone modulates multiple proinflammatory signaling cascades leading to the suppression of growth and survival of head and neck carcinoma.

Constitutive activation of proinflammatory transcription factors such as STAT3 and NF-κB plays a pivotal role in the proliferation and survival of squamous cell carcinoma of the head and neck (HNSCC). Thus, the agents that can modulate deregulated STAT3 and NF-κB activation have a great potential both for the prevention and treatment of HNSCC. In the present report, we investigated the potential effects of garcinol, an active component of Garcinia indica on various inflammatory mediators involved in HNSCC progression using cell lines and xenograft mouse model. We found that garcinol inhibited constitutively activated STAT3 in HNSCC cells in a time- and dose-dependent manner, which correlated with the suppression of the upstream kinases (c-Src, JAK1, and JAK2) in HNSCC cells. Also, we noticed that the generation of reactive oxygen species is involved in STAT3 inhibitory effect of garcinol. Furthermore, garcinol exhibited an inhibitory effect on the constitutive NF-κB activation, mediated through the suppression of TGF-ß-activated kinase 1 (TAK1) and inhibitor of IκB kinase (IKK) activation in HNSCC cells. Garcinol also downregulated the expression of various gene products involved in proliferation, survival, and angiogenesis that led to the reduction of cell viability and induction of apoptosis in HNSCC cells. When administered intraperitoneally, garcinol inhibited the growth of human HNSCC xenograft tumors in male athymic nu/nu mice. Overall, our results suggest for the first time that garcinol mediates its antitumor effects in HNSCC cells and mouse model through the suppression of multiple proinflammatory cascades.

Ursolic acid in cancer prevention and treatment: molecular targets, pharmacokinetics and clinical studies.

Discovery of bioactive molecules and elucidation of their molecular mechanisms open up an enormous opportunity for the development of improved therapy for different inflammatory diseases, including cancer. Triterpenoids isolated several decades ago from various medicinal plants now seem to have a prominent role in the prevention and therapy of a variety of ailments and some have already entered Phase I clinical trials. One such important and highly investigated pentacyclic triterpenoid, ursolic acid has attracted great attention of late for its potential as a chemopreventive and chemotherapeutic agent in various types of cancer. Ursolic acid has been shown to target multiple proinflammatory transcription factors, cell cycle proteins, growth factors, kinases, cytokines, chemokines, adhesion molecules, and inflammatory enzymes. These targets can potentially mediate the chemopreventive and therapeutic effects of ursolic acid by inhibiting the initiation, promotion and metastasis of cancer. This review not only summarizes the diverse molecular targets of ursolic acid, but also provides an insight into the various preclinical and clinical studies that have been performed in the last decade with this promising triterpenoid.

Key cell signaling pathways modulated by zerumbone: role in the prevention and treatment of cancer.

Phytochemicals and their synthetic derivatives are making a significant contribution in modern drug discovery programs by targeting several human diseases, including cancer. Most of these natural compounds are often multitargeted in nature, which is generally a very desirable property for cancer therapy, as carcinomas typically involve dysregulation of multiple genes and associated cell-signaling pathways at various stages of initiation, progression and metastasis. Additionally, these natural agents generally have lower side-effects, are readily available and hence are cost effective. One such natural compound is zerumbone, a cyclic eleven-membered sesquiterpene, isolated from the tropical plant Zingiber zerumbet Smith that has attracted great attention recently for its potent anticancer activities in several tumor models. This review summarizes the data based on various in vitro and in vivo studies related to the effects of zerumbone on numerous pivotal molecular targets in cancer and its reported chemopreventive/therapeutic effects in different models of cancer.

Targeted inhibition of tumor proliferation, survival, and metastasis by pentacyclic triterpenoids: potential role in prevention and therapy of cancer.

Over the last two decades, extensive research on plant-based medicinal compounds has revealed exciting and important pharmacological properties and activities of triterpenoids. Fruits, vegetables, cereals, pulses, herbs and medicinal plants are all considered to be biological sources of these triterpenoids, which have attracted great attention especially for their potent anti-inflammatory and anti-cancer activities. Published reports in the past have described the molecular mechanism(s) underlying the various biological activities of triterpenoids which range from inhibition of acute and chronic inflammation, inhibition of tumor cell proliferation, induction of apoptosis, suppression of angiogenesis and metastasis. However systematic analysis of various pharmacological properties of these important classes of compounds has not been done. In this review, we describe in detail the pre-clinical chemopreventive and therapeutic properties of selected triterpenoids that inhibit multiple intracellular signaling molecules and transcription factors involved in the initiation, progression and promotion of various cancers. Molecular targets modulated by these triterpenoids comprise, cytokines, chemokines, reactive oxygen intermediates, oncogenes, inflammatory enzymes such as COX-2, 5-LOX and MMPs, anti-apoptotic proteins, transcription factors such as NF-κB, STAT3, AP-1, CREB, and Nrf2 (nuclear factor erythroid 2-related factor) that regulate tumor cell proliferation, transformation, survival, invasion, angiogenesis, metastasis, chemoresistance and radioresistance. Finally, this review also analyzes the potential role of novel synthetic triterpenoids identified recently which mimic natural triterpenoids in physical and chemical properties and are moving rapidly from bench to bedside research.

Targeting cell signaling and apoptotic pathways by dietary agents: role in the prevention and treatment of cancer.

Cancer is one of the leading causes of death in the United States and around the world. Most modern drug-targeted therapies, besides being enormously expensive, are associated with serious side effects and morbidity. Still, the search continues for an ideal treatment that has minimal side effects and is cost-effective. Indeed, the design and development of chemopreventive agents that act on specific and/or multiple molecular and cellular targets is gaining support as a rational approach to prevent and treat cancer. We present evidence on numerous dietary agents identified from fruits and vegetables that act on multiple signal transduction and apoptotic cascades in various tumor cells and animal models. Some of the most interesting and well documented are turmeric (curcumin), resveratrol, silymarin, EGCG, and genistein. This review will provide an insight on the cellular and molecular mechanism(s) by which dietary agents modulate multiple signaling and apoptotic pathways in tumor cells and elucidate the role of these agents in both prevention and treatment of cancer.

Molecular targets of celastrol derived from Thunder of God Vine: potential role in the treatment of inflammatory disorders and cancer.

Identification of active constituents and their molecular targets from traditional medicine is an enormous opportunity for modern pharmacology. Celastrol is one such compound that was originally identified from traditional Chinese medicine (Thunder of God Vine) almost three decades ago and generally used for the treatment of inflammatory and auto-immune diseases. Celastrol has attracted great interest recently, especially for its potential anti-inflammatory and anti-cancer activities. The anti-inflammatory effects of this triterpene have been demonstrated in animal models of different inflammatory diseases, including arthritis, Alzheimer's disease, asthma, and systemic lupus erythematosus. This triterpene has also been found to inhibit the proliferation of a variety of tumor cells and suppress tumor initiation, promotion and metastasis in various cancer models in vivo. Celastrol's ability to modulate the expression of pro-inflammatory cytokines, MHC II, HO-1, iNOS, NF-κB, Notch-1, AKT/mTOR, CXCR4, TRAIL receptors DR4 and DR5, CHOP, JNK, VEGF, adhesion molecules, proteasome activity, topoisomerase II, potassium channels, and heat shock response has been reported. This review describes the various molecular targets of celastrol, cellular responses to celastrol, and animal studies with celastrol in cancer and other inflammatory disorders.