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 TrkA^G595R and TrkA^G667C. The best Trk Inhibitor 5c had IC₅₀ values of 0.75 and 0.96 nM against TrkA^G595R and TrkA^G667C, 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 TrkA^{WT/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-TRKA^G667C 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.