Anthocyanins : Targeting of Signaling Networks in Cancer Cells

Research over the decades has gradually and sequentially shown that there is an organized interaction of cells with surrounding environment and cells respond to environmental clues accordingly via intracellular signal-transduction network. This well organized network is composed of hierarchy of upstream activators and downstream effectors which receive, transmit and interpret information. Due to substantial role in cellular physiology, intracellular signaling network and several of its subnetworks, have emerged as deeply studied molecular mechanisms underlying carcinogenesis. These transduction cascades are initiated by ligand-receptor interactions, and disrupt spatio-temporal behavior of the cell. Upregulation of oncogenes and suppression of tumor suppressor genes is an essential mechanism that is regulated by intracellular signaling cascades. These cascades have downstream effectors which are activated and thus stimulate or repress the expression of oncogenes and tumor suppressors respectively. NF-κB, AP-1, STAT-1 and OCT-1 are some of the transcription factors which are activated in colorectal cancer cells. Interestingly metabolites of anthocyanins particularly, trihydroxybenzaldehyde, gallic acid and methylgallic acid have also been studied for their potential in inducing apoptosis in colon cancer cells. Evidence suggested that cancer cell treated with these metabolites had notably


Introduction
Research over the decades has gradually and sequentially shown that there is an organized interaction of cells with surrounding environment and cells respond to environmental clues accordingly via intracellular signal-transduction network.This well organized network is composed of hierarchy of upstream activators and downstream effectors which receive, transmit and interpret information.Due to substantial role in cellular physiology, intracellular signaling network and several of its subnetworks, have emerged as deeply studied molecular mechanisms underlying carcinogenesis.These transduction cascades are initiated by ligand-receptor interactions, and disrupt spatio-temporal behavior of the cell.
Upregulation of oncogenes and suppression of tumor suppressor genes is an essential mechanism that is regulated by intracellular signaling cascades.These cascades have downstream effectors which are activated and thus stimulate or repress the expression of oncogenes and tumor suppressors respectively.NF-κB, AP-1, STAT-1 and OCT-1 are some of the transcription factors which are activated in colorectal cancer cells.Interestingly metabolites of anthocyanins particularly, trihydroxybenzaldehyde, gallic acid and methylgallic acid have also been studied for their potential in inducing apoptosis in colon cancer cells.Evidence suggested that cancer cell treated with these metabolites had notably reduced NF-κB, AP-1, STAT-1and OCT-1 (Forester et al., 2012).Anthocyanins have recently been shown to stimulate the expression of tumor suppressor genes via demethylation of promoters of CDKN2A, and SFRP2, SFRP5, and WIF1 (Wang et al., 2013).
Tumour-associated cell cycle defects are frequently triggered by dysregulated cyclin-dependent kinase (CDK) activity.There is considerable evidence that suggests that CDKs are involved in unscheduled proliferation as well as genomic and chromosomal instability.p21 and p27 negatively regulate CDKs and are well positioned to function as both a sensors and effectors of multiple signals that can converge to induce cell cycle arrest.It is interesting to note that anthocyanins and anthocyanidins extracted from purple-shoot tea effectively target cyclin E and cyclin D1 in colorectal carcinoma cells.In addition there was a notable activation of p21 and p27 (cyclindependent kinase inhibitors) and caspase-3 (Hsu et al., 2012).3-Deoxyanthocyanin isolated from red sorghum bran has been shown to stimulate the expression of p53 in breast cancer cells.Additionally, anti-apoptotic gene BCL-2 was remarkably suppressed (Suganyadevi et al., 2013).Anthocyanins have been shown to induce apoptosis in different cancer cells via a mitochondrial pathway (Banjerdpongchai et al., 2013) and human leukemia U937 cells via activation of caspase-3, -8 and -9.However, Bcl-2 overexpressing U937 cells did not show anthocyanin induced apoptosis (Lee et al, 2009).

Targeting of Pro-survival Signaling
Pro-survival signaling in cancer cells is an essential mechanism to overcome apoptosis inducing signals.NFKB inhibition is necessary to induce apoptosis.It is noteworthy that anthocyanins isolated from Vitis coignetiae Pulliat induced apoptosis in colon cancer HCT-116 cells.The results revealed that anthocyanins inhibited NFKB HCT-116 cells.Moreover, p38-MAPK was activated in HCT-116 cells treated with anthocyanins (Shin et al., 2009).Certain reports have provided evidence that metabolites of anthocyanins are more effective as anticancer agents.Metabolites of anthocyanins efficiently reduced proliferation of Caco-2 cells (Forester and Waterhouse, 2010).Anthocyanin rich-fraction considerably reduced B16-F10 melanoma murine cells proliferation (Bunea et al., 2013).Peonidin-3-glucoside and cyaniding-3-glucoside are anthocyanin pigments and remarkably effective against HER positive cancer cells.Results revealed that there was a reduced HER2 phosphorylation in anthocyanin pigments treated cancer cells.Moreover pAkt levels were also repressed suggesting that pigments substantially inhibited HER2 signaling axis (Liu et al., 2013).Anthocyanins induced apoptosis was noted in MCF-7 cells as evidenced by increase in amounts of oligonuceosomal-sized fragments (Devi et al., 2011).

Animal Model Studies
Anthocyanins have shown potential via exerting their inhibitory effects in prostatic hyperplasia-induced rat model.Mice were given anthocyanin for 4 weeks and it was noted that prostate weights were significantly lower in the group receiving oral doses of anthocyanin (Jang et al., 2010).Preneoplastic hepatic nodules in diethylnitrosamine-induced hepatocellular carcinogenesis in rats have also been noted to be reduced considerably.Additionally it was found that there was an increase in protein expression of Bax (Bishayee et al., 2011).On a similar note efficacy of anthocyanins has been tested in BALB/c nude mice inoculated with MDA-MB-453 cells and results revealed substantial regression of tumor growth (Hui et al., 2010).Colon cancer cells have also been studied to underscore regulation of mTOR signaling by anthocyanins and it was shown that cancer cells pretreated with anthocyanins displayed marked decrease in phosphorylated mTOR levels.Furthermore, mice xenografted with HT-29 colon cancer cells indicated decrease in tumor volumes (Lee et al., 2010).There was a notable reduction in intestinal adenoma development in mice fed with Red grape pomace extract (Cai et al., 2010).It is noteworthy that dietary anthocyanin suppressed azoxymethane-induced formation of aberrant crypt foci in the colons of CF-1 mice (Lim et al., 2013).Peonidin 3-glucoside has been shown to inhibit metastasizing potential of Lewis lung carcinoma cells in cancer bearing mice (Ho et al., 2010).Prostate cancer has also been noted to be inhibited in athymic nude mice xenografted with prostate cancer cells.This inhibitory effect was exerted through delphinidin via inhibition of NFKB and its DNA binding activity Hafeez et al. (2008).Anthocyanins are also found in sweet potato greens extract (SPGE) and effectively inhibited cancer progression in nude mice inoculated with prostate cancer cells (Karna et al., 2008).Metastasizing potential of B16-F1 cells in C57BL/6 mice was considerably reduced by mulberry anthocyanins mediated inhibitory effects on PI3K, Ras and NFKB (Huang et al., 2008).Pharmacokinetics of Cyanidin-3-glucoside (C3G) have been studied in C57BL6J and results revealed that after oral administration C3G accumulated in gastrointestinal mucosal tissues and liver (Marczylo et al., 2009).It has been experimentally shown that 12-O-tetradecanoylphorbol-13-acetate (TPA) induced epidermal hyperplasia in mice.Mechanistically it was noted that TPA induced activation of NFKB, IKK and inhibition of IKB.Moreover, TPA-induced phosphorylation of ERK1/2, p38 and JNK1/2.However, anthocyanins inhibited TPA induced hyperplasia via inhibition of NFKB, ERK, p38 MAPK and JNK (Afaq et al., 2005).TPA-induced neoplastic transformation in JB6 P+ cells and H-Ras-transformed JB6 P+ mouse epidermal cells. in vitro analysis revealed that Raf/MEK/ ERK signaling axis was activated in TPA treated cells.Delphinidin substantially inhibited NFKB activation and Raf/MEK/ERK signaling axis (Kang et al., 2008).Nitrosomethylbenzylamine (NMBA)-induced tumors in the rat esophagus were also considerably suppressed in anthocyanins fed rats.It was observed that anthocyanins induced apoptosis in preneoplastic esophageal tissues (Wang et al., 2009).

Conclusion
It is encouraging to note that evaluation of bilberry anthocyanins as chemopreventive agents in twenty-five colorectal cancer patients has opened anew window of opportunity in translating the findings from laboratory to clinic (Gu et al., 2013).