Abstract 2054: Characterization of TQB3823, a differentiated PARP inhibitor with anti-tumor activity in BRCA-deficiency cancer models

Objective: Homology-directed repair (HDR) pathway is the major DNA double-strand break repair pathway. BRCA-deficiency impairs this pathway, and combination with Poly(ADP-ribose) polymerase (PARP) inhibition results in cell death. This process is known as “synthetic lethality”. A proportion of breast cancer, ovarian cancer and other solid tumor patients carrying BRCA-mutated gene receive benefits from PARP inhibitors. In this study, we present in vitro activity and in vivo efficacy data of a novel small molecule PARP inhibitor, TQB3823 to support it as our clinical candidate. Method: Enzyme inhibition activities of TQB3823 were determined in PARP1/PARP2/Tankyrase 1 assays. Cellular anti-proliferative activity and selectivity were evaluated in MDA-MB-436 cell line with BRCA1 mutation and BRCA wild type MDA-MB-231 cell line. Antitumor efficacy of TQB3823 was investigated in BRCA1 mutated MDA-MB-436 breast cancer CDX model. Result: TQB3823 showed high potency and selectivity at both enzymatic and cellular level. IC50 of TQB3823 in PARP1/PARP2/Tankyrase 1 assays are 2.8/0.9/629.3 nM, respectively. It inhibited proliferation of BRCA1 mutant MDA-MB-436 cell with IC50 of 9.6 nM. In contrast, TQB3823 showed little anti-proliferative activity in BRCA-wild type MDA-MB-231 cell with IC50 >10 μM. TQB3823 demonstrated antitumor efficacy in dose dependent fashions with tumor regression was observed at 25 mg/kg in MDA-MB-436 CDX model. The level of antitumor effects was superior to niraparib at the same dose in the same study. DNA trapping experiments revealed similar potency to olaparib indicative of low toxicity. Conclusion: We have identified a novel, potent and selective PARP inhibitor TQB3823, which inhibits the proliferation of BRCA mutant cells but spares the wild type cells. In vivo study in a BRCA-deficiency tumor model confirms the high in vivo efficacy of this molecule. In conclusion, TQB3823 represents a promising differentiated clinical candidate for treating solid cancers with homology directed repair. Citation Format: Hu Yanbin, Zhang Xiquan, Yang Ling, Tian Xin, Li Gang, Hu Lihong, Charles Z. Ding, Xia Yuanfeng, Li Wei, Yin Shanshan, Chen Ying, Wu Songliang, Chen Shuhui. Characterization of TQB3823, a differentiated PARP inhibitor with anti-tumor activity in BRCA-deficiency cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2054.