p53 restoration can overcome cisplatin resistance through inhibition of Akt as well as induction of Bax

Cisplatin (CDDP) is a chemotherapeutic agent that is widely used to treat many cancers. However, initial resistance to CDDP is a serious problem in treating cancers. In this study, in order to develop an approach to overcome resistance to CDDP, we investigated the difference in apoptotic processes between CDDP-sensitive cells and CDDP-resistant cells. By screening with CDDP sensitivity tests, we chose SNU-16 cells which are relatively resistant to CDDP, and SNU-1 cells which are sensitive to CDDP. We compared the difference between the two cell lines focusing on apoptosis. CDDP-induced reactive oxygen species (ROS) generation significantly induced loss of mitochondrial membrane potential (MMP, Delta Psi(m)) in SNU-1 cells, but not in SNU-16 cells. In addition, the ratio of Bax to Bcl-2 was increased by CDDP treatment in SNU-1 cells, but not in SNU-16 cells. To augment the loss of MMP, Delta Psi(m) in SNU-16, we inhibited Akt activity of SNU-16 cells to suppress their anti-apoptotic activity. The inhibition of Akt activity led to suppression of the anti-apoptotic protein XIAP. Akt inhibition slightly enhanced CDDP-induced apoptosis in SNU-16 cells. In addition, we enhanced pro-apoptotic activity by transfecting the cells with the wild-type p53 gene. The induction of wild-type p53 can enhance CDDP-induced apoptosis not only by inducing Bax protein but also by suppressing anti-apoptotic proteins through inhibition of Akt. In conclusion, this study suggests that the primary contributor to resistance to CDDP in SNU-16 cells may well be a failure of induction of apoptosis due to a lack of induction of pro-apoptotic proteins rather than suppression of anti-apoptotic proteins, and that restoration of p53 function can overcome the resistance to CDDP not only by augmenting the pro-apoptotic drive through p53-mediated transcriptional activation but also by inhibiting the anti-apoptotic drive through inhibition of Akt activity.