Structure-based Scaffold Hopping Reveals Strategies to Overcome Oncogenic KIT and PDGFRA Mutation-Driven Drug-Resistance in GIST

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. Current tyrosine kinase inhibitors (TKIs) targeting oncogenic KIT and PDGFRA have improved patient outcomes, yet off-target toxicities and drug resistance mutations remain major clinical challenges. Many approved TKIs, often repurposed from other cancer indications, harbor diverse hinge-binding motifs that limit activity against resistance mutations clustering in the ATP-binding pocket of the kinase domain. Here, we describe a structure-based scaffold-hopping strategy to design novel inhibitors with selectivity for mutant KIT/PDGFRA. Using structure-activity relationship (SAR) studies and 14 newly determined co-crystal structures, including the first structure of the PDGFRA-G680R solvent-front mutation, we define key molecular interactions underlying resistance and inhibitor selectivity. Our lead 6,7-quinazoline-based inhibitors show high potency against clinically relevant KIT/PDGFRA mutations and effectively suppress downstream signaling. These compounds provide selective chemical tools to interrogate resistance mechanisms, and the PDGFRA-G680R structure offers new insights for targeting solvent-front mutations across oncogenic kinases. *T. Schulz, M. Beerbaum, A. Scrima contributed equally.