Abstract 2953: Inhibition of calmodulin enhances TRA-8-induced apoptosis in pancreatic cancer cells .

Abstract

Abstract Current chemotherapy and radiotherapy are not curative for pancreatic cancer. Tumor necrosis factor-related apoptosis-inducing ligand or agonist antibodies for death receptor 4/5 have been shown to be a promising cancer therapy. TRA-8, a humanized activating antibody for the death receptor 5 (DR5), is a potent apoptosis-inducing reagent for cancer cells. However, several pancreatic cell lines are resistant to TRA-8-induced apoptosis. We have previously demonstrated that calmodulin (CaM) antagonists enhance the Fas death receptor-mediated apoptosis pathway. Therefore, we investigated whether inhibition of CaM might affect DR5-induced apoptotic signaling in pancreatic cancer cells. We found that CaM antagonists, trifluoperazine (TFP) and tamoxifen (TMX), dose dependently enhanced TRA-8-induced apoptosis of the TRA-8-resistant PANC-1 pancreatic cells. Consistently, TFP and TMX increased TRA-8-induced activation of caspase 8, caspase 9 and caspase 3. Pretreatment of PANC-1 with Z-IETD-FMK, the caspase-8 inhibitor, decreased TFP-enhanced apoptosis by 2 fold, and markedly decreased caspase 3 activation. Immunoprecipitation analysis of the DR5-induced death inducing signaling complex (DISC) identified the interaction of CaM with DR5. Activation of DR-5 by TRA-8 increased the recruitment of CaM into the DISC, which was inhibited by TFP. In addition, TFP decreased the recruitment of the adaptor protein, FADD, and other DISC proteins that regulate cell survival, including Src and the caspase-8 inhibitory protein FLIP. Collectively, these results support an important role for CaM in DR5-induced DISC formation, thus regulating DR5-mediated survival and apoptotic signaling in pancreatic cancer cells. In summary, we have demonstrated that CaM antagonists sensitize pancreatic cancer cell to TRA 8-induced apoptosis, and that CaM binding to DR5 regulates DR5-induced DISC formation. Defining the function of CaM in regulating DR5-induced signaling pathways may lead to novel therapeutic strategies including the use of CaM antagonists with TRA-8 as combination therapy for pancreatic cancer. Citation Format: Kaiyu Yuan, Tong Zhou, Jay McDonald, Yabing Chen. Inhibition of calmodulin enhances TRA-8-induced apoptosis in pancreatic cancer cells . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2953. doi:10.1158/1538-7445.AM2013-2953