Purpose: Apoptosis plays a central role in tumor development and it has been hypothesized that lack or failure of apoptosis leads to the development of tumors, including colon cancers. Anticancer drugs do not invariably cytotoxic to all cancer cells. Some resistant cells against anticancer drugs are resuming to proliferate after initial damage, whereas others undergo permanent growth arrest or death. The resistance of advanced colorectal cancers to chemotherapy s often reiated to mutations in p53 tumor suppressor gene.
Methods: To understand the molecular mechanism of lovastation-induced apoptosis, the relationship between p53 and p38 MAPK upon cytotoxicity by anticancer drug was investigated in colon cancer cell lines including HCT-116 (p53 wild type) and HT-29 (mutated p53). Doxorubicin (dox) or lovasxatin (lova) increased the cytotoxicity of colon cancer cells in a dose- and time-dependent manner.
Results: Cytotoxic effects of dox and lova was more prominent in HCT-116 than HT-29. The combined treatment of dox and lova further increased the cytotoxic effect on both cells. The cytotoxicity of dox and lova was resulted from apoptotic cell death, which was determined by genomic DNA fragmentation, PARP cleavage and activation of caspase-3 and -9. The Combined treatment of dox and lova synergistically increased the catalytic activity of caspase-3 and -9 in colon cancer cells, but not caspase-6 and -8. Anticancer drugs also induced the cytosolic release of cytochrome c from mitochondria. Dox also induced the accumulation and activation of p53 protein (phosphorylation of p53, ser15), which was suppressed by lova. p38 MAPK inhibitor, SB203580, significantly increased the apoptotic death of lova-treated cells. Furthermore, Lova significantly induced apoptotic death of MKK6 D/D stable transfectant compared to pcDNA3.1 transfectant of HT-29 cells, which was determined by MTT assay, DNA fragmentation, and caspase activation. Similarly to MKK6 D/D transfectant, Exip (alternative splicing p38 gene) transfectant showed the apoptogenic effect of dox with lova.
Conclusion: These results indicate that lova induces apoptosis in colon cancer cells via p38 MAPK-dependent and p53-independent mechanism
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