The Pan-RAF–MEK Nondegrading Molecular Glue NST-628 Is a Potent and Brain-Penetrant Inhibitor of the RAS–MAPK Pathway with Activity across Diverse RAS-and RAF-Driven Cancers

Abstract

Alterations in the RAS–MAPK signaling cascade are common across multiple solid tumor types and are a driver for many cancers. NST-628 is a potent pan-RAF–MEK molecular glue that prevents the phosphorylation and activation of MEK by RAF, overcoming the lim-itations of traditional RAS–MAPK inhibitors and leading to deep durable inhibition of the pathway. Cellular, biochemical, and structural analyses of RAF–MEK complexes show that NST-628 engages all isoforms of RAF and prevents the formation of BRAF–CRAF heterodimers, a differentiated mechanism from all current RAF inhibitors. With a potent and durable inhibition of the RAF–MEK signaling complex as well as high intrinsic permeability into the brain, NST-628 demonstrates broad efficacy in cellular and patient-derived tumor models harboring diverse MAPK pathway alterations, including orthotopic intra-cranial models. Given its functional and pharmacokinetic mechanisms that are differentiated from previ-ous therapies, NST-628 is positioned to make an impact clinically in areas of unmet patient need. Significance: This study introduces NST-628, a molecular glue having differentiated mechanism and drug-like properties. NST-628 treatment leads to broad efficacy with high tolerability and central ner-vous system activity across multiple RAS-and RAF-driven tumor models. NST-628 has the potential to provide transformative clinical benefits as both monotherapy and vertical combination anchor.