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Abstract 1751: BPI-23314: A novel orally bioavailable small molecular BET inhibitor with target protein degradation activity

The Bromo- and Extra-Terminal (BET) proteins, BRD2, BRD3, and especially BRD4, play important roles in transcriptional regulation of many oncogenes like MYC or BCL2, thus makes it an attractive drug target in multiple pathological settings, particularly in cancer. Earlier BET inhibitors, while effectively bind and inhibit the activity of BRD4, adversely induce compensatory accumulation of the target protein, that may account for their limited preclinical and clinical efficacy. Herein, we report BPI-23314, a potent, selective, and orally available small molecular BET bromodomain inhibitor, which possesses potent target inhibition activity as well as target protein degradation property. In vitro, BPI-23314 induced dose-dependent growth inhibition in a wide range of cancer cell lines, including those from AML, MM, DLBCL, NSCLC, TNBC, and CRPC, etc. Quantitative RT-PCR revealed that BPI-23314 markedly affected the transcription of genes encoding MYC, BCL2, and HEXIM1, thus induced G1 cell cycle arrest and apoptosis in MV-4-11 AML cell line. In vivo, oral administration of BPI-23314 led to tumor growth suppression or regression in multiple xenograft models of AML and MM. Transcriptional modulation of MYC, BCL2 and HEXIM1 were confirmed in BPI-23314-treated xenografts and in normal monkey, supporting their potential as pharmacodynamic biomarkers in clinical trials. Unlike previously described BET inhibitors that induced BRD4 accumulation, BPI-23314 serendipitously decreased BRD4 protein in MV-4-11 cells and in tumors from MV-4-11 xenografts. The feature of target-protein degradation differentiates BPI-23314 from the other BET inhibitors, renders it good in vivo efficacy, and suggests a lower risk of drug resistance in future clinical development. In conclusion, our study establishes BPI-23314 as a novel small molecular BET inhibitor with target BRD4 protein degradation property. BPI-23314 has obtained IND approval from Chinese regulatory authority and is planned to enter Phase 1 clinical development in hematologic malignancies in early 2020. Citation Format: Jing Guo, Yan Xu, Dan Yan, Bo Yu, Weiwei Yu, Haibo Chen, Xiaofeng Xu, Xiangyong Liu, Hong Lan, Lieming Ding, Jiabing Wang. BPI-23314: A novel orally bioavailable small molecular BET inhibitor with target protein degradation activity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1751.