14. The Novartis RET inhibitor, compound 1, demonstrated robust oral in vivo efficacy in RET-driven tumor xenografts at low doses (10 mpk QD). RET inhibitors (selpercatinib and pralsetinib) have recently been approved in RET+ cancers based on significant efficacy in selected patients. Compound 1 was advanced through preclinical studies including rat toxicology but does not appear to have progressed further. It possesses a significantly different structure from the approved RET inhibitors and has interesting bicyclooctane and aniline motifs. The aniline appears to make two critical hydrogen-bonding interactions deep into the active site [based on an analog’s X-ray crystal structure (PDB = 7RUN)] and would be non-trivial to replace.