Rational Optimization of Rho-Associated Coiled-Coil Containing Protein Kinase 2 Inhibitors via Disruption of Molecular Planarity for Pulmonary Fibrosis

Given the therapeutic potential of ROCK2 in pulmonary fibrosis (PF) and the significant efficacy of our previously identified lead compound 1, we initiated an optimization campaign focused on addressing physicochemical liabilities through disrupting molecular planarity. By implementing “sp3-rich” and “magic methyl” strategies, two series of ROCK2 inhibitors featuring 4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine or imidazo[1,2-b]pyridazine scaffolds were developed. A dedicated evaluation discovered the optimal compound 39, which exhibited potent ROCK2 inhibition (IC50 = 0.0081 μM), enhanced kinetic solubility (77 μg/mL in water), improved metabolic stability (t1/2 = 5.0 h for p.o), favorable kinase selectivity, and an acceptable safety profile. Notably, 39 effectively suppressed TGF-β1-induced fibroblast activation and migration, while significantly attenuating bleomycin-induced PF in vivo. Moreover, mechanistic studies revealed that the antifibrotic effects of 39 were mediated through inhibition of the TGF-β/Smad and ROCK2/STAT3 signaling pathways. Overall, these findings validate the proposed design strategy and deliver a novel candidate for ROCK2-targeted therapy in PF.