Preclinical evaluation of TQB3728, a potent orally active IAP antagonist

Objectives: Evasion of apoptosis and avoidance of immune surveillance represent two key hallmarks of cancer. Members of the inhibitor of apoptosis (IAP) gene play important interconnecting roles in both of these characteristic pathways of tumorigenesis, providing a critical nexus in targeting of cancer. Small-molecule antagonists of the IAPs, known as Smac mimetic compounds (SMCs), are in quick clinical development for cancer therapy. We disclose here a novel IAP antagonist TQB3728 and its preclinical evaluation on tumor therapy. Methods: The biochemical activities of TQB3728 for cIAP1 BIR3, cIAP2 BIR3 and XIAP BIR3 were measured by the corresponding biochemical assays. The in vitro anti-proliferative activity was evaluated on MDA-MB-231 and EMT6 cell lines. The in vivo antitumor activity of TQB3728 was evaluated in two cell-derived xenograft (CDX) models of TNBC (MDA-MB-231) and lymphoma (Karpas 422), and one syngeneic model of TNBC (EMT6). PK/PD was assessed by western blot analysis of cIAP1 expression and cleaved caspase 3 level in the treated tumor tissues. Results: TQB3728 displayed potent biochemical activities for cIAP1 BIR3, cIAP2 BIR3 and XIAP BIR3 with IC50 of 0.7, 11.8 and 22.5 nM, respectively. The expected anti-proliferative activities were also observed in both tumor cell lines, with a IC50 of 14.3 Nm for MDA-MB-231, and IC50 of 149.5 nM for EMT6 in the presence of exogenous TNFα (1 ng/ml). TQB3728 showed in vivo antitumor activity in the MDA-MB-231 CDX model with 89.8% TGI @30 mpk QD, which is better than LCL-161 (71.9% TGI @30 mpk, QD). TQB3728 also showed good antitumor activity in vivo in the Karpas 422 lymphoma CDX model with 112.2% TGI @100 mpk Q3D. In EMT6 tumor-bearing mice, the combination of TQB3728 and anti-PD1 antibody significantly regressed the tumor growth (TGI = 106.3%), whereas monotherapies only displayed moderate activities ( 60.6% and 0.4% TGI for anti-PD1 and TQB3728, respectively). Western blot analysis of the tumor samples showed that TQB3728 promoted caspase 3 cleavage, indicating that the tumor growth inhibition could be mediated by cell apoptosis signaling. Conclusions: We have discovered a potent orally active IAP antagonist, TQB3728, which shows activity of cIAP1 inhibition and strong antitumor activity in both in vitro and in vivo preclinical tumor models. These results are highly promising and warrant moving the compound forward to clinical investigation. Citation Format: Yingchun Liu, Xiquan Zhang, Ling Yang, Xin Tian, Tiantian Dong, Charles Z. Ding, Lihong Hu, Zhaobing Xu, Yuanfeng Xia, Haijuan Tong, Wenxi Li, Lijuan Hou, Chichung Chan, Shuhui Chen. Preclinical evaluation of TQB3728, a potent orally active IAP antagonist [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 724.