Antitumour Activity of Muricatacin Isomers and its Derivatives in Human Colorectal Carcinoma Cell HCT116

Background and Purpose: Colorectal cancer is one of the leading causes of cancer-related death in elderly people. The natural product muricatacin is an important member of the gamma-lactone family, and it has exhibited antitumour activity in multiple cancer cell lines; however, the antitumour activities of muricatacin stereoisomers and their derivatives in colorectal cancer cells have not yet been systematically explored. Methods: The colorectal carcinoma cell line HCT116 was investigated in this study. Cell proliferation was assessed by MTT assay or crystal violet staining. Cell cycle arrest and cell apoptosis were evaluated by flow cytometry assay. The expression levels of p53, p21, cyclin E, cyclin D1, caspase-3, cleaved caspase-3, caspase-9, cleaved caspase-9 and LC3B were measured using western blot analysis. Autophagy induced by M2 was monitored by immunofluorescence assay with an antibody against LC3B. Results: Cell proliferation assays showed that both naturally occurring muricatacin (M4) and its synthetic stereoisomer (M2) are potent cell growth inhibitors in HCT116 cells, with IC50 values of 79.43 and 83.17 mu M, respectively; these values are much lower than those of the other two isomers, M1 and M3, and those of the six-membered lactone analogues. The flow cytometry analysis revealed that M2 and M4 induced significant cell cycle arrest during G(0)/G(1) phase and caused relatively low apoptosis rates in HCT1 16 cells. Further analysis indicated that M2 caused p53-independent p21 induction and cyclin E/cyclin D1 downregulation. In addition, M2 also markedly induced autophagy in the early stage of administration. Conclusion: Our results suggested that muricatacins possess potent antitumour activity against the colorectal carcinoma cell tine HCT116 through inducing G(0)/G(1) phase cell cycle arrest and autophagy in the early stage of administration.