Abstract 7275: GS-P-328, a brain-penetrant small molecule p53 Y220C reactivator for tumors harboring p53 Y220C mutation

Abstract As a tumor suppressor, p53 can prevent tumor development through multiple pathways. However, mutation of TP53 and the resultant inactivation of p53 allow evasion of tumor cell death and rapid tumor progression. The oncogenic Y220C mutation is the ninth most frequent p53 missense mutation in cancer. Y220C mutation creates a narrow, hydrophobic pocket on the surface of the p53 DBD that reduces its thermal stability. As a result, the Y220C mutation causes a rapidly unfold of the p53 protein under physiological conditions, abrogates p53 signaling and drives tumorigenesis. There are approximately 100, 000 new Y220C mutation cancer cases per year worldwide with limited treatment choices. The initial clinical evaluation of PC14586 that can restore missense-mutant p53 protein has seen efficacy in patients harboring p53 Y220C mutation even though there is still room for improvement. Here we report a brain-penetrable, highly potent p53 Y220C reactivator which has great in vitro activity as well as induce tumor shrinkage in multiple tumor models at a much lower systematic exposure comparing to PC14586. In vitro, GS-P-328 could bind to p53 Y220C protein with a single nM potency and potently induce cell death in a wide range of p53 Y220C tumor cells while have no anti-proliferative effects with p53 WT cells. GS-P-328 is also active in patient-derived cell (PDC) models in various tumor background including SCLC, gastric, ovarian and colon. In vivo, GS-P-328, at approximately 1/3 of systematic exposure comparing to a leading clinical reactivator, causes tumor shrinkage in multiple CDX models. GS-P-328 could induce MDM2/p21 upregulation in cell systems. In vivo, GS-P-328 could induce 2 fold and more increase in MDM2/p21 protein levels in tumor tissues at approximately 1/3 of plasma concentrations comparing to PC14586. More importantly, in a NUGC3-luc intracranial model, GS-P-328 could strongly inhibit growth of cancer cells in the mouse brain. GS-P-328 has a favorable ADME profile in rodents, dogs and NHPs, as well as a much better safety profile. GS-P-328 is now under IND-enabling study and P1 study is planned in early 2025. Citation Format: Meng Liu, Kaijun Geng, Biao Lu, Yuanfeng Xia, Fanglong Yang. GS-P-328, a brain-penetrant small molecule p53 Y220C reactivator for tumors harboring p53 Y220C mutation abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 7275.