Abstract 6588: Discovery of ASTX295, a potent, next-generation small molecule antagonist of MDM2 with differentiated pharmacokinetic profile

Abstract In response to cellular stress, the tumor suppressor p53 is activated to modulate cell cycle progression, DNA repair, and apoptosis. Inhibition of the MDM2-p53 interaction in tumors carrying wild-type p53 prevents its degradation and can reactivate p53 to elicit an anti-cancer effect. Targeting the p53-MDM2 interaction therefore remains a promising strategy for cancer therapy. However, development of first generation MDM2 antagonists has been challenged by dose-limiting, on-target bone marrow toxicities. Understanding of differential effects of p53 pathway activation in normal hematopoietic versus cancer cells (to be presented in a separate abstract) together with our expertise in structure-based drug design have led to the discovery of ASTX295, a potent MDM2 antagonist with differentiated pharmacokinetic profile aimed at sparing bone marrow toxicities and increasing the therapeutic index. Here, we present the first disclosure of the structure and pre-clinical characterisation of ASTX295. ASTX295 exhibits potent activity (IC501 nM) against MDM2 in an ELISA-based in vitro assay and induces significant growth reduction in p53 wild-type, MDM2-amplified SJSA-1 cells (GI50=27 nM). Antiproliferative activity of ASTX295 was further demonstrated in a panel of 219 p53 wild-type cell lines, with 143 cell lines showing GI50 values less than 1 μM and 50 showing values less than 0. 1 μM. Effects of ASTX295 are shown in cell lines carrying functional p53 as confirmed in three p53 wild-type and mutant cell line pairs (SJSA1 and SN40R2, A2780 and A2780CP, HCT116 and HCT116 p53−/−). In addition to inhibiting cell cycle progression and cell proliferation, ASTX295 also potently induces apoptosis following 24-48 hour treatment. Further in vitro analyses of ASTX295 demonstrated an increase in the levels of p53 (EC50=10 nM after 2 hours) and its transcriptional targets such as p21 and MDM2. In vivo, ASTX295 shows robust induction of p53 and its target genes at 3 and 6 hours after oral administration together with dose-dependent inhibition of tumour growth in the SJSA-1 xenograft model. Importantly, ASTX295 exhibits optimised pharmacokinetic and pharmacodynamic profiles with relatively short duration of pathway modulation and a desired predicted human half-life of 2-8 hours. Based on our pre-clinical hypothesis on differential time-dependent sensitivities of normal versus cancer cells to p53 activation, achieving such a profile while maintaining potency may increase the therapeutic index. These data highlight the therapeutic potential of ASTX295, which is currently being tested in a Phase 1/2 clinical trial in advanced solid tumors with wild-type p53 (NCT03975387). We plan to present preliminary clinical data in a separate abstract at this meeting. Citation Format: Maria Ahn, Luke Bevan, Ildiko Buck, Celine Cano, Juan Castro, Ben Cons, Jane Endicott, Lynsey Fazal, Nicola Ferrari, Ian Hardcastle, Keisha Hearn, Rhian Holvey, Steven Howard, Chris Johnson, Claire Jennings, Justyna Kucia-Tran, Suzanne Kyle, John Lunec, John Lyons, Duncan Miller, David Rees, Martin Noble, David R. Newell, Judith Reeks, Harpreet Saini, Jeffrey St. Denis, Emiliano Tamanini, Huw Thomas, Neil Thompson, Mladen Vinkovic, George Ward, Nicola Wallis, Hugh Walton, Stephen Wedge, Pamela Williams, Elaine Willmore, Nicola Wilshire, Yan Zhao, Gianni Chessari. Discovery of ASTX295, a potent, next-generation small molecule antagonist of MDM2 with differentiated pharmacokinetic profile 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 6588.