WF-47-JS03 is a potent and selective RET kinase inhibitor with IC50s of 1.7 nM and 5.3 nM for KIF5B-RET transfected Ba/F3 cells and CCDC6-RET transfected LC-2/ad lung cancer cells, respectively. WF-47-JS03 demonstrates >500-fold selectivity against kinase insert domain receptor (KDR). Effective brain penetration.