Loss of p73 Induction in a Cisplatin-Resistant Bladder Cancer Cell Line

Background: Cisplatin (CDDP) plays an important role in the treatment of transitional-cell carcinoma (TCC), but resistance develops. The mechanism is not entirely understood. Methods: To assess acquired resistance to CDDP, we established a CDDP-resistant subclone, CL8-2, of T24, which is a bladder cancer cell line. We examined the changes in the various pathways leading to apoptosis in the parent line and CL8-2. Results: The drug caused apoptosis of T24 cells but not CL8-2 cells. The CL8-2 cells were 6.4 times more resistant to CDDP than was T24. In both cell lines, the mismatch repair genes hMLH-1 and hMSH-2 were expressed at high levels. The p53 protein was not detected in either cell line but p73 protein was induced by CDDP treatment in T24 cells, which was followed by activation of caspases 3, 8, and 9. This phenomenon was not observed in CL8-2 cells. Conclusion: These results suggest that loss of p73 induction may lead to CDDP resistance of TCC.