Fragment-Based Discovery of a Dual pan-RET/VEGFR2 Kinase Inhibitor Optimized for Single-Agent Polypharmacology

Oncogenic conversion of the RET (rearranged during transfection) tyrosine kinase is associated with several cancers. A fragment-based chemical screen led to the identification of a novel RET inhibitor, Pz-1. Modeling and kinetic analysis identified Pz-1 as a typeII tyrosine kinase inhibitor that is able to bind the "DFG-out" conformation of the kinase. Importantly, from a single-agent polypharmacology standpoint, Pz-1 was shown to be active on VEGFR2, which can block the blood supply required for RET-stimulated growth. In cell-based assays, 1.0nM of Pz-1 strongly inhibited phosphorylation of all tested RET oncoproteins. At 1.0mg kg^-1 day^-1 per os, Pz-1 abrogated the formation of tumors induced by RET-mutant fibroblasts and blocked the phosphorylation of both RET and VEGFR2 in tumor tissue. Pz-1 featured no detectable toxicity at concentrations of up to 100.0mg kg^-1, which indicates a large therapeutic window. This study validates the effectiveness and usefulness of a medicinal chemistry/polypharmacology approach to obtain an inhibitor capable of targeting multiple oncogenic pathways. Dual inhibition: A kinase-directed fragment-based screen identified a novel active pharmacophore for the RET tyrosine kinase (RET=rearranged during transfection). In a medicinal chemistry/polypharmacology approach, Pz-1 was found to be a dual pan-RET/VEGFR2 inhibitor and able to simultaneously treat the parenchyma (RET) and stroma (VEGFR2) of RET-driven tumors in cell and xenograft models.