Obacunone and obacunone glucoside inhibit human colon cancer (SW480) cells by the induction of apoptosis

• Published in: Food and chemical toxicology 2011-07, Vol.49 (7), p.1616-1625
• Main Authors: Chidambara Murthy, K.N., Jayaprakasha, G.K., Patil, Bhimanagouda S
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Antiproliferation; Apoptosis; bcl-2-Associated X Protein - genetics; bcl-2-Associated X Protein - metabolism; Benzoxepins - isolation & purification; Benzoxepins - pharmacology; Biological and medical sciences; Camptothecin - metabolism; Carcinogenesis, carcinogens and anticarcinogens; Caspase 3 - genetics; Caspase 3 - metabolism; Caspase 8 - genetics; Caspase 8 - metabolism; Caspase 9 - genetics; Caspase 9 - metabolism; caspase-3; caspase-9; Caspases; Cell Cycle; Cell Line, Tumor; cell proliferation; Chemical agents; Chromatography, High Pressure Liquid; Citrus paradisi - chemistry; Colon cancer cells; colorectal neoplasms; Cyclin-Dependent Kinase Inhibitor p21 - genetics; Cyclin-Dependent Kinase Inhibitor p21 - metabolism; cytochrome c; Cytochromes c - metabolism; cytosol; cytotoxicity; DNA fragmentation; DNA Fragmentation - drug effects; Down-Regulation; Gastroenterology. Liver. Pancreas. Abdomen; Glucosides - isolation & purification; Glucosides - pharmacology; grapefruits; high performance liquid chromatography; Humans; inhibitory concentration 50; Limonins - isolation & purification; Limonins - pharmacology; limonoids; Magnetic Resonance Spectroscopy; Medical sciences; Mice; Molecular Sequence Data; NIH 3T3 Cells; nuclear magnetic resonance spectroscopy; seeds; Seeds - chemistry; Stomach. Duodenum. Small intestine. Colon. Rectum. Anus; transcription (genetics); Triterpenes - isolation & purification; Triterpenes - pharmacology; Tumors; Up-Regulation
• ISSN: 0278-6915; 1873-6351
• DOI: 10.1016/j.fct.2011.04.014

► Isolated and Identified obacunone and obacunone glucoside from Marsh White grapefruits for the first time. ► Inhibition of human colon cancer cell (SW480) proliferation was reported for the first time. ► Possible mode of apoptosis induction by limonoids in human colon cancer cells. ► Combining limonoids with camptothecin demonstrated additive apoptosis was observed in colon cancer cells. Objectives: The study was aimed to purify obacunone and obacunone glucoside (OG) from seeds of Marsh White grapefruit and understand the mode of cytotoxicity of limonoids on colon cancer (SW480) cells. Methodology: Both limonoids were purified using chromatographic techniques. The structures and purity of limonoids were confirmed by NMR and HPLC analysis, respectively. Results: Obacunone and OG inhibited SW480 cell proliferation with IC50 values of 97 and 109.7μM respectively, at 24h. Sequence of events such as decreased ratio of bcl2/bax gene transcription, activation of caspase-3, fragmentation of DNA in cells treated with obacunone and OG demonstrated induction of apoptosis by limonoids. Additionally, higher induction of cytochrome-c in cytosol suggests the activation of intrinsic apoptosis by limonoids. Involvement of apoptosis was also confirmed through expression of bax, bcl2, pro-caspase-3 and caspase-9. Both the limonoids activated p21 and arrested cells at G1 and G2/M phase. Additive activity of proliferation inhibition and activation of caspase-3 by limonoids was observed when combined with camptothecin, demonstrating the induction of apoptosis. In conclusion, both limonoids induced apoptosis by activation of intrinsic apoptosis pathway and activation of p21 leading to arresting cells at G2/M phase of the cell cycle.