Abstract C130: Discovery and characterization of an MTA-cooperative and brain-penetrant PRMT5 inhibitor

Abstract Introduction: MTAP is homozygous deleted in ~50% in glioblastoma and many other cancers. PRMT5*MTA inhibition has been shown to be synthetic lethal with MTAP deletion. First generation PRMT5 inhibitors could not distinguish between PRMT5*MTA or PRMT5 alone, thus limited by their shallow therapeutic windows in clinical use. Development of selective PRMT5*MTA inhibitors may improve not only safety but also therapeutic efficacy. Leveraging advanced computation-aided structural analysis and medicinal chemistry design, we have discovered a potent and selective MTA-cooperative and brain-penetrable PRMT5 inhibitor ABK-PRMT5-1, which demonstrates strong anti-tumor activity and brain-penetrating activity in various preclinical models. Method: Isogenic cell line pairs (MTAP-/- and MTAP+/+) were used to determine the effects of ABSK-PRMT5-1 on cell proliferation and PRMT5-dependednt downstream signaling. Cancer cell line panel was also used to confirm its activity and selectivity. Its in vivo efficacy was evaluated in cell line derived xenograft (CDX) mouse models with tumors harboring MTAP gene deletion. Results: ABSK-PRMT5-1 strongly inhibits cell proliferation in MTAP-deleted cancer cell lines, with minimal effects on MTAP wildtype cell lines. Furthermore, it significantly reduces SDMA in MTAP-deleted cancer cell lines. Oral administration of ABSK-PRMT5-1 strongly inhibits tumor growth in MTAP-deleted xenograft tumor models. In addition, ABSK-PRMT5-1 demonstrates strong brain penetration with excellent Kp values in animals. DMPK and safety profiling shows good overall drug-like properties of ABK-PRMT5-1. Conclusion: ABK-PRMT5-1, presented here by Abbisko Therapeutics, is a highly selective MTA-cooperative and brain-penetrable PRMT5 inhibitor. Its superior profile supports fast-track preclinical development. Citation Format: Weiling Pan, Hui Wang, Fangfei Qi, Haibing Deng, Fei Yang, Hongping Yu, Yao-Chang Xu, Zhui Chen, Haiyan Ying. Discovery and characterization of an MTA-cooperative and brain-penetrant PRMT5 inhibitor [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C130.