Calmodulin antagonists promote TRA-8 therapy of resistant pancreatic cancer

// Kaiyu Yuan 1 , Sun Yong 1 , Fei Xu 1 , Tong Zhou 2 , Jay M McDonald 1, 3 , Yabing Chen 1, 3 1 Department of Pathology, University of Alabama at Birmingham, Alabama 35294, Birmingham, USA 2 Department of Medicine, University of Alabama at Birmingham, Alabama 35294, Birmingham, USA 3 Birmingham Veterans Affairs Medical Center, Alabama 35294, Birmingham, USA Correspondence to: Yabing Chen, e-mail: ybchen@uab.edu Keywords: death receptor 5, apoptosis, resistance, calmodulin antagonists, pancreatic cancer Received: April 06, 2015      Accepted: June 30, 2015      Published: July 11, 2015 ABSTRACT Pancreatic cancer is highly malignant with limited therapy and a poor prognosis. TRAIL-activating therapy has been promising, however, clinical trials have shown resistance and limited responses of pancreatic cancers. We investigated the effects of calmodulin(CaM) antagonists, trifluoperazine(TFP) and tamoxifen(TMX), on TRA-8-induced apoptosis and tumorigenesis of TRA-8-resistant pancreatic cancer cells, and underlying mechanisms. TFP or TMX alone did not induce apoptosis of resistant PANC-1 cells, while they dose-dependently enhanced TRA-8-induced apoptosis. TMX treatment enhanced efficacy of TRA-8 therapy on tumorigenesis in vivo . Analysis of TRA-8-induced death-inducing-signaling-complex (DISC) identified recruitment of survival signals, CaM/Src, into DR5-associated DISC, which was inhibited by TMX/TFP. In contrast, TMX/TFP increased TRA-8-induced DISC recruitment/activation of caspase-8. Consistently, caspase-8 inhibition blocked the effects of TFP/TMX on TRA-8-induced apoptosis. Moreover, TFP/TMX induced DR5 expression. With a series of deletion/point mutants, we identified CaM antagonist-responsive region in the putative Sp1-binding domain between -295 to -300 base pairs of DR5 gene. Altogether, we have demonstrated that CaM antagonists enhance TRA-8-induced apoptosis of TRA-8-resistant pancreatic cancer cells by increasing DR5 expression and enhancing recruitment of apoptotic signal while decreasing survival signals in DR5-associated DISC. Our studies support the use of these readily available CaM antagonists combined with TRAIL-activating agents for pancreatic cancer therapy.