The role of caspase family protease, caspase-3 on cisplatin-induced apoptosis in cisplatin-resistant A431 cell line

Purpose: Cisplatin (cis-diamminedichloro-platinum(II), CDDP) has been reported to induce apoptosis in cancer cells, the mechanism of the apoptosis in cancer cells induced by CDDP is still unclear. Recent studies have revealed that caspase family of cystine proteases play an important role in the regulation of several apoptotic processes. In this study, whether apoptosis induced by CDDP could be mediated by the activation of caspase-3, a caspase family protease, was investigated. Methods: The CDDP-resistant subline A431/CDDP2 from the previously established human epidermoid carcinoma cell line A431 was used. The parent A431 cells (A431/P) and the A431/CDDP2 were exposed to CDDP with or without a caspase family protease inhibitor (Z-Asp-CH₂-DCB), and cellular sensitivity to CDDP was determined. DNA fragmentation was then analyzed, and the caspase-3 protein levels determined by Western blotting following exposure of the cells to CDDP with or without Z-Asp-CH₂-DCB. Results: In the A431/P cells, the cytotoxicity of CDDP was clearly reduced by Z-Asp-CH₂-DCB compared with its cytotoxicity in A431/CDDP2 cells. Furthermore, quantitative analysis of DNA fragmentation revealed that Z-Asp-CH₂-DCB inhibited DNA fragmentation induced by CDDP in A431/P cells, but not in A431/CDDP2 cells. Western blotting analysis demonstrated a marked reduction in procaspase-3 protein levels in A431/P cells treated with Z-Asp-CH₂-DCB. In the A431/CDDP2 cells, procaspase-3 protein levels were no different with and without Z-Asp-CH₂-DCB. Conclusions: These findings suggest that caspase-3 may mediate apoptosis induced by CDDP, and its induction could represent a novel approach to the effective treatment of malignant tumors.