Discovery of new non-macrocyclic TRK inhibitors based on conformational flexibility and scaffold hopping to overcome clinical acquired resistance.

Targeted tropomyosin receptor kinase (TRK) inhibitors represent a therapeutic approach for cancers with NTRK gene fusions. However, the therapeutic efficacy of first-generation inhibitors is limited by the emergence of acquired drug resistance. Through the application of scaffold-hopping and conformational-flexibility design strategies, we identified a series of novel non-macrocyclic inhibitors, which showed enhanced activity against the TRKAG595R and TRKAG667C. The best TRK inhibitor 5c had IC50 values of 0.75 and 0.96 nM against TRKAG595R and TRKAG667C, showing better potency than drugs larotrectinib (approximately 87- and 46-fold improvement) and selitrectinib (approximately 10- and 13-fold improvement). 5c also strongly suppressed the proliferation of Ba/F3 cells transfected with TRKAWT/595R 667C with IC50 values of 3 - 41 nM. More importantly, 5c demonstrated favorable in vivo pharmacokinetic properties and antitumor efficacy (tumor growth inhibition (TGI) of 91% at 30 mg/kg and 115% at 60 mg/kg with 4 of 6 partial regression) in a BaF3-TMP3-TRKAG667C xenograft mouse model, which is greatly superior to that of selitrectinib (TGI of 2% at 30 mg/kg). Compound 5c exhibits significant potential to overcome clinical acquired multiple resistance to TRK inhibitors.