Artificial Intelligence-Driven Discovery of Pyrazolo[1,5‑a]pyrimidine Derivatives as Novel Phosphodiesterase 4 Inhibitors for Treating Idiopathic Pulmonary Fibrosis

Phosphodiesterase 4 (PDE4) has been validated as a promising therapeutic target for idiopathic pulmonary fibrosis (IPF), a devastating interstitial lung disease lacking really effective therapeutic drugs, particularly exacerbated in the post-COVID-19 era. Herein, we reported the discovery of 13c, a novel pyrazolo[1,5-a]pyrimidine-based PDE4 inhibitor, via an innovative artificial intelligence (AI)-driven virtual screening approach integrated with structure-based design. The cocrystal analysis of PDE4-13c elucidated the structural basis of its high affinity, revealing that the unique “halogen-binding and metal-coordination” synergistic network significantly influenced PDE4 inhibitory activity, which resulted in a 268-fold potency enhancement (IC50 = 2.7 nM) over hit T3700 (IC50 = 725 nM). Notably, 13c exhibited remarkable hepatic microsomal stability (RLM1/2 = 141.4 min). Furthermore, 13c exhibited remarkable antifibrotic activity in vitro and significantly attenuated bleomycin-induced pulmonary fibrosis in vivo, highlighting its potential as a novel PDE4 inhibitor for IPF.