C-glycosyl flavone from Urginea indica inhibits proliferation & angiogenesis & induces apoptosis via cyclin-dependent kinase 6 in human breast, hepatic & colon cancer cell lines

BACKGROUND & OBJECTIVES: Search for novel compounds beneficial to the treatment of cancer attracts a great deal of attention. We earlier demonstrated the isolation of 5,7-dihydroxy-2-[4’-hydroxy-3’-(methoxymethyl)phenyl]-6-C-β-glucopyranosyl flavone, a novel C-glycosyl flavone from Urginea indica bulb. The present study was undertaken to investigate the effect of this novel compound on human normal epithelial and breast, hepatic and colon cancer cell lines. METHODS: The maximum non-toxic concentration (MNTC) and cytotoxicity of C-glycosyl flavone were assayed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Cell cycle was analyzed by flow cytometry. Docking studies were performed to predict possible targets. Levels of cyclin-dependent kinase 1 (CDK1) and CDK6, Bcl2 and BAX and cytochrome c were quantified by specific ELISA. Mitochondrial membrane potential was determined using JC-1 dye. Apoptosis was quantified by Annexin V ELISA method. RESULTS: Flow cytometry analysis demonstrated G0/G1 arrest. In silico docking studies predicted CDK1 and CDK6 as a possible target of C-glycosyl flavone. In vitro study confirmed CDK6 as the main target in C-glycosyl flavone-treated cancer cell lines. C-glycosyl flavone treatment also induced membrane blebbing, chromatin fragmentation and nucleosome formation. C-glycosyl flavone treatment caused marked loss of mitochondrial membrane potential, decrease in Bcl2/BAX ratio and activation of caspase-3 and release of caspase-9 and cytochrome c. In addition, C-glycosyl flavone inhibited the tumour-induced angiogenesis and reduced the vascular endothelial growth factor levels. Similarly, CDK6 inhibitor significantly inhibited proliferation and angiogenesis and induced apoptosis in tested cell lines. INTERPRETATION & CONCLUSIONS: The results indicate that C-glycosyl flavone may exert induction of apoptosis, cell cycle arrest and inhibition of angiogenesis via CDK6. Thus, targeting CDK6 using C-glycosyl flavone may serve as a novel therapeutic approach for the treatment of breast, hepatic and colon cancers.