Targeted induction of apoptosis via TRAIL and cryoablation: A novel strategy for the treatment of prostate cancer

Adjuvant therapies contribute to the successful treatment of cancer. Our previous reports have shown that combining cryoablation with cytotoxic agents enhances cell death. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytotoxic agent that preferentially induces apoptosis in a variety of human cancer cells. Human prostate cancer cells (PC-3) are resistant to many cytodestructive agents, including cryoablation and TRAIL. Here, we evaluated the effects of TRAIL combined with cryoablation on PC-3 and normal prostate (RWPE-1) cell death. Exposure of PC-3 cells to freezing (-10°C) or TRAIL (500ng/ml) results in minimal cell death, whereas a complete loss of viability is observed with the simultaneous combination. The synergistic effect was found to be due to a marked increase in apoptosis. Western blot analysis revealed a significant level of caspase-8 and -3 cleavage between 12 and 24 h post-exposure. Caspase activation assays provided similar results and also indicated a role for caspase-9. Inhibitors to caspase-8 and -9 along with a pan-caspase inhibitor were incorporated to determine which pathway was necessary for the combined efficacy. Inhibition of caspase-8 significantly blocked the combination-induced cell death compared to cells that did not receive the inhibitor (63% compared to 10% viable). The addition of the caspase-9 inhibitor resulted in only a minimal protection. Importantly, the combination was not effective when applied to normal prostate cells. The results describe a novel therapeutic model for the treatment of prostate cancer and provide support for future in vivo studies.