Small molecule RL71 targets SERCA2 at a novel site in the treatment of human colorectal cancer.

// Baofang Yang 1,* , Minxia Zhang 1,* , Jian Gao 1 , Jiahuang Li 1 , Lu Fan 1 , Gang Xiang 1 , Xingqi Wang 1 , Xiaoning Wang 1 , Xuefeng Wu 1 , Yang Sun 1 , Xudong Wu 1 , Guang Liang 2 , Yan Shen 1 and Qiang Xu 1 1 State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, China 2 Bioorganic and Medicinal Chemistry Research Center, School of Pharmaceutical Sciences, Wenzhou Medical College, Wenzhou, China * These authors have contributed equally to this work Correspondence to: Qiang Xu, email: // Yan Shen, email: // Keywords : RL71, SERCA2, novel binding site, colorectal cancer, targeted agent Received : May 09, 2015 Accepted : September 26, 2015 Published : October 10, 2015 Abstract While targeted agents are an important part of the treatment arsenal for colorectal cancer, there is still a lack of efficient small-molecule targeted agents based on the understanding of pathogenic molecular mechanisms. In this study, curcumin analog RL71 displayed potent cytotoxicity towards human colon cancer cells with an IC 50 of 0.8 µM in SW480 cells and inhibited xenotransplanted tumor growth in a dose-dependent manner. Using affinity chromatography, we identified sarco/endoplasmic reticulum calcium-ATPase (SERCA) 2 as the binding target of RL71. Most notably, RL71 demonstrated special binding to SERCA2 at a novel site with the lowest estimated free energy -8.89 kcal mol -1 , and the SERCA2 residues critical for RL71 binding were identified. RL71 suppressed the Ca 2+ -ATPase activity of SERCA2 both in vitro and in vivo , accompanied by the induction of endoplasmic reticulum stress leading to apoptosis and G2/M cycle arrest in SW480 cells. In addition, RL71 showed synergistic cytotoxicity with the pan-SERCA inhibitor thapsigargin. These results suggest that RL71 could be a selective small-molecule inhibitor of SERCA2, and that it may serve as a lead compound for the study of targeted colorectal cancer therapy.