Abstract 1482: M4645 is a potent and highly selective inhibitor of disease relevant cKIT mutations for the treatment of metastatic or recurrent GIST

Abstract

Abstract Oncogenic mutations in cKIT in exons 9 and 11 are the main driver of gastrointestinal stromal tumors (GIST). Imatinib is standard of care in 1L in unresectable metastatic or recurrent GIST, yet secondary resistance mutations in exons 13/14 and 17/18 of the cKIT kinase domain frequently arise limiting efficacy. Currently approved 2L and 3L therapies sunitinib and regorafenib target these mutations only to some extent and show limited clinical benefit. Even with the recent approval of ripretinib as 4L treatment, a high unmet medical need remains for patients with imatinib resistance mutations in exon13/14. M4645 was designed to particularly inhibit the frequent V654A resistance mutation in exon 13 of cKIT. Based on cKIT inhibitor scaffolds identified within the Merck compound collection, a 3,5,6-substituted indazole-lead was discovered. Substituent optimization in the 5- and 6-positions of the core scaffold resulted in highly selective kinase inhibitors. Through variation at the 3-position, potency and physicochemical properties were optimized, resulting in the candidate molecule M4645 which combined potency, kinase selectivity, and solubility with a good safety profile. The excellent kinase selectivity could be rationalized by the crystal structure of cKIT V654A mutant kinase domain in complex with M4645. M4645 showed potent inhibition of cKIT autophosphorylation and of downstream P-ERK1/2 and P-AKT signaling in cell lines bearing activating and resistance mutations of cKIT. Dose-dependent inhibition of cKIT activation was demonstrated in a GIST xenograft model expressing the cKIT resistance mutation V654A in exon 13. Strong antitumor activity was observed in cell line and patient-derived GIST xenograft models with this imatinib resistance mutation. Compared to imatinib, M4645 induced prolonged anti-tumor response in a GIST model with a primary activating mutation of cKIT. In summary, the favorable profile and strong antitumor activity, particularly in GIST models expressing the V654A resistance mutation, suggests superiority of M4645 compared to currently available > 2L treatment options for unresectable metastatic or recurrent GIST patients. Citation Format: Nina Linde, Andreas Blum, Dieter Dorsch, Ulrich Graedler, Michael Busch, Nina Glaser, Carl Petersson, Aaron Ruff, Eva Sherbetjian, Christina Esdar. M4645 is a potent and highly selective inhibitor of disease relevant cKIT mutations for the treatment of metastatic or recurrent GIST [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1482.