Abstract 4102: Differing molecular mechanisms involved in the sensitization of human renal cancer cells to TRAIL-induced apoptosis

We have previously shown that the proteasome inhibitor bortezomib (Velcade/PS-341) specifically sensitized certain human renal carcinoma (RCC) lines to apoptosis induced by the TNF family-member TRAIL. A high-throughput screen conducted by the Molecular Targets Laboratory identified several promising new TRAIL sensitizers. One of these novel TRAIL sensitizers was the natural product withanolide E. Withanolide E, in contrast to bortezomib, had no activity as a proteasome inhibitor. Also withanolide E could sensitize some human RCC to TRAIL that were resistant to the effects of bortezomib. Furthermore sensitizing concentrations of bortezomib were also cytostatic to the RCC, whereas those of withanolide E were not. Bortezomib treatment of RCC resulted in the appearance of various proteins associated with a stress response, yet these proteins were not elevated by withanolide E treatment. By contrast the antioxidant n-acetyl cysteine completely blocked the TRAIL-sensitizing effects of withanolide E but not those of bortezomib. This suggests that changes in cellular redox are important for the sensitizing effects of withanolide E but not those of bortezomib. In order to study the molecular basis for increased TRAIL-mediated apoptosis, we investigated proximal apoptosis signaling events at the death-inducing signaling complex (DISC). Both bortezomib and withanolide E treatments resulted in an enhanced activation of the apoptosis signaling enzyme caspase-8 following exposure of the RCC to TRAIL. However, immunoprecipitation of the DISC revealed that bortezomib treatment resulted in a 4-5 fold increase in the amount of DISC formed. By contrast withanolide E treatment did not significantly alter the amount of the DISC, but reduced levels of the antiapoptotic DISC component c-FLIP. Therefore, both compounds amplified the apoptotic signal from the DISC via distinct molecular mechanisms of action. Funded in part by HHSN261200800001E Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4102. doi:10.1158/1538-7445.AM2011-4102