Background and Purpose: Colorectal cancer is one of the leading causes of cancer deaths in elderly people. The natural product muricatacin is an important member of γ-lactones family, which has been shown to exhibit antitumor activity in multiple cancer cell lines, but the antitumor activities of muricatacin stereoisomers and their derivatives against colorectal cancer cells has not been systematically explored yet.
Methods: Colorectal carcinoma cell line HCT116 was applied 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. 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 antibody against LC3B.
Results: Cell proliferation detections showed that both naturally occurring muricatacin (M4) and its synthetic stereoisomer (M2) are the potent cell growth inhibitors against HCT116 cell line with IC50 79.43 and 83.17μM, respectively, much stronger than the other two isomers M1, M3 and the six-membered lactone analogs. The flow cytometry analysis revealed that M2 and M4 induced significant cell cycle arrest during G0/G1 phase and caused apoptosis in a relatively faint level in HCT116 cells. Further analysis indicated that M2 caused a p53-independent p21 induction and Cyclin-E/Cyclin-D1 down regulation. Meanwhile, M2 could also induce remarked autophagy in the early stagy of administration.
Conclusions: Our results suggested that muricatacins possessed potent antitumor activity against colorectal carcinoma cell line HCT116 through inducing cell cycle arrest in G0/G1 phase and autophagy in the early stagy of administration.