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.In Vitro: WF-47-JS03 inhibits Tel-KDR transfected Ba/F3 cells and Ba/F3 wild-type cell lines with IC50s of 0.99 and 1.5 μM, respectively.In Vivo: WF-47-JS03 significantly inhibits tumor growth in RIE KIF5B-RET xenograft mice and is well tolerated at 1, 3, and 10 mg/kg in the 10 day study.