Abstract 4572: Discovery of SY-14556, a highly potent and selective small molecule reactivator of p53 Y220C mutant with differentiated preclinical profile

Abstract As a key tumor suppressor, p53 binds to DNA and transcriptionally activates target genes to regulate cell-cycle arrest, DNA damage repair, apoptosis, and multiple other antiproliferative processes. TP53 is the most frequently mutated gene in human cancer, and Y220C is one hot-spot mutation occurring in approximately 1% of solid tumors. Pharmacologic stabilization and reactivation of the Y220C mutant to a wild-type-like conformation is a validated therapeutic strategy, as demonstrated by the clinical activity of PC14586 (rezatapopt). Here, we characterize SY-14556 as a highly potent and selective p53 Y220C reactivator. In biochemical assay, SY-14556 induced p53 Y220C DNA binding with an EC50 < 5 nM. In luciferase reporter assay, SY-14556 activated wild-type p53 transcriptional activity with an EC50 < 50 nM. Across a panel of p53 Y220C-mutant cancer cell lines, SY-14556 inhibited proliferation (IC50 20-100 nM) with >100-fold selectivity over p53-WT cells. Consistent with high-fidelity p53 pathway reactivation, SY-14556 also dose-dependently activated p53 target genes expression including p21 and MDM2, inducing cell cycle arrest and apoptosis. In vivo, SY-14556 demonstrated robust anti-tumor activity in several p53 Y220C-mutant cell line-derived xenograft (CDX) models. Furthermore, SY-14556 displayed favorable PK properties and tolerability in preclinical studies. In conclusion, SY-14556 is a best-in class p53-Y220C reactivator with robust preclinical efficacy and safety. These data support its advancement into clinical trials for p53 Y220C-mutant solid tumors. Citation Format: Hongjuan Li, Zhenbang Lou, Xiaopeng Li, Chang Lu, Shikang Cheng, Bo Li, Xianxing Shang, Xiaofeng Zhai, Yan Zhu, Hong Luo, Yinghui Sun. Discovery of SY-14556, a highly potent and selective small molecule reactivator of p53 Y220C mutant with differentiated preclinical profile [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4572.