Abstract 4972: PDK inhibition sensitizes bladder tumors to cisplatin

Pyruvate Dehydrogenase Kinase-4 (PDK4) is a member of the PDK enzyme family. PDKs phosphorylate and inactivate the pyruvate dehydrogenase (PDH) complex, shunting pyruvate into the cytoplasm for oxidative metabolism, a phenomenon known as aerobic glycolysis or the Warburg Effect. This confers both growth advantages and resistance to chemotherapy. We previously noted that high grade human bladder tumors have substantial upregulation of PDK4, in the absence of other PDKs. We hypothesized PDK4 would be upregulated in bladder tumors, and inhibition of PDK4 would reduce bladder tumor growth and sensitize cells to cisplatin. We explored tested this hypothesis in cell culture and xenograft and carcinogen induced mouse models. Substantial overexpression of PDK4 (20-120 fold) was confirmed by qPCR in multiple bladder cancer cell lines as compared to UROtsa cells, a benign urothelial cell line. Treatment with dichloroacetate (DCA), a pan-specific PDK inhibitor, significantly increased PDH activity and reduced cellular proliferation in HTB-9 and HTB-5 cancer cells. In line with previous studies in other tumors, DCA also sensitized HTB-9 and HTB-5 cells to cisplatin induced cell death. Notably, this was not through enhanced apoptosis, as caspase activity did not increase, but rather co-treatment resulted in significant increases in LDH release, a marker of necrosis, and increased PI/Annexin V positive cells in DCA plus cisplatin treated cells compared to DCA or cisplatin alone. Inhibition of apoptosis with z-VAD-fmk confirmed the increased necrosis, as DCA plus cisplatin treated cells still had significant increases in cell death compared to DCA or cisplatin alone. Treatment of HTB-9 tumor xenografts with DCA or cisplatin did not reduce tumor volumes; however, co-treatment with both compounds resulted in significant reductions in viable tumor weights, along with increased TUNEL staining. As DCA is a pan-specific PDK inhibitor (PDK1-4), we also used the recently generated PS10 compound with equal specificity for PDK2 and PDK4. PS10 also significantly increased PDH activity, sensitized UM-UC3 cells to cisplatin and reduced cellular proliferation at concentrations at, and above 20µM. To further validate PDK inhibition as a therapeutic target, C57Bl/6J WT mice were treated with 0.05% BBN in the drinking water for 14 weeks to initiate tumorigenesis, and then treated with 70mg/kg PS10 daily +/- weekly[B1] ip cisplatin for 3 weeks. PS10 alone had no effect. While cisplatin reduced bladder weights, only PS10 plus cisplatin resulted in significant reduction in bladder tumor weight. Inhibition of PDKs sensitizes bladder cancers to cisplatin both in vitro and in vivo, as well as having direct anti-proliferative effects in vitro. PDK inhibition may be a useful and novel way to enhance cisplatin based therapies in bladder cancer. Citation Format: Sambantham Shanmugam, Erika Abbott, Justin Penticuff, Dharamainder Choudhary, Benjamin L. Woolbright, John A. Taylor. PDK inhibition sensitizes bladder tumors to cisplatin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4972.