Discovery of a Best-in-Class small molecule p53 Y220C reactivator: Breaking through the potency ceiling

The tumor suppressor p53 is inactivated in approximately 50% of human cancers. In about 1% of solid tumors, a specific Y220C point mutation induces p53 misfolding, leading to its inactivation. This mutation also creates a unique, druggable pocket on the protein's surface, making it a promising target for cancer therapy. The first-generation small molecule reactivator (PC14586, Rezatapopt), designed to bind to this pocket, to refold p53 and to restore its tumor-suppressive functions, has shown clinical efficacy in patients harboring the Y220C mutations. However, this first-generation compound is limited by modest potency, necessitating high dosing in patients. This high-dose requirement increases the risk of adverse events and narrows the therapeutic window, as monotherapy and even more so in combination regimens. As a result, this compound fails to deliver the drug pressure needed to reach full reactivation of this critical tumor suppressor. Thus, there is a clear need to discover and develop a highly potent p53 small molecule reactivator to fully unlock the therapeutic potential of this promising target. At Onco3R Therapeutics, our patient centric approach, integrating deep translational science with rational, structure-based and AI-augmented drug design, has led to the identification of best-in-class series of p53 Y220C reactivators. Our lead series exhibits more than 200-fold superior potency compared to the clinical compound PC14586 (Rezatapopt) across diverse preclinical assays, including biochemical p53 refolding, cellular p53 refolding, and cellular p21 induction. Importantly, our lead series, characterized by strong potency and long residence times in vitro, significantly sustains target engagement and P53 reactivation in cells. This profile enables robust activation of the pro-apoptotic protein PUMA and induces potent, selective cytotoxicity in p53 Y220C mutant cells and in an isogenic cell model. In line with their superior cellular activity and in combination with optimized key ADME, safety parameters, and favorable in vivo PK profiles across species, our leads reach similar efficacy in vivo as PC145586 at much lower exposure. In conclusion, we have identified unique p53 Y220C small molecule reactivators with clear best-in-class cellular potency and favorable drug-like properties. We are currently further profiling these leads as potential drug candidates to achieve superior efficacy at substantially lower doses, maximizing the safety window to ultimately deliver better outcomes to cancer patients with p53 Y220C mutations.