PKM2 Inhibitor Shikonin Overcomes the Cisplatin Resistance in Bladder Cancer by Inducing Necroptosis

Cisplatin-based chemotherapy often results in the development of chemo-resistance when used to treat bladder cancer (BC), which is difficult to overcome. Recent data indicate that pyruvate kinase M2 (PKM2), a glycolytic enzyme for Warburg effect, is strongly upregulated in BC, and contributes to the cisplatin resistance in BC. However, the underlying mechanisms remain unclear. In this study, we also found that the expression level of PKM2 is also higher in cisplatin resistant BC cells and tumors. Down-regulation of PKM2 by siRNA or inhibition of PKM2 by shikonin re-sensitized the cisplatin resistant T24 cells. Shikonin and cisplatin together exhibit significantly greater killing effects than when used alone. Interestingly, we found shikonin kills the T24 cisplatin resistant cells by inducing necroptosis, as the cell death could not inhibited by apoptosis inhibitor, z-VAD, but compromised by RIP3 inhibitor, GSK872, or RIP3 siRNA. In contrast, shikonin induced apoptosis in T24 parental cells. We further investigate the underlying mechanism, and found that the dysregulation of Bcl-2 family proteins, including Bcl-2, PUMA, Bax, play an important role in deciding that shikonin kills the BC cells by necroptosis or apoptosis. Collectively, our results suggested that inducing necroptosis is an alternative way to overcome the apoptosis resistant in BC therapy, and orchestrating the regulation of Bcl-2, PUMA, and Bax in BC cisplatin resistant cells may improve the therapy effect of cisplatin in BC tumor.