Discovery of Potent Phosphodiesterase-9 Inhibitors for the Treatment of Hepatic Fibrosis.
Wu Y, Wang Q, Jiang MY, Huang YY, Zhu Z, Han C, Tian YJ, Zhang B, Luo HB.
Hepatic fibrosis commonly exists in chronic liver disease and would eventually develop to cirrhosis and liver cancer with high fatality. Phosphodiesterase-9 (PDE9) has attracted profound attention as a drug target because of its highest binding affinity among phosphodiesterases (PDEs) with cyclic guanosine monophosphate. However, no published study has reported PDE9 inhibitors as potential agents against hepatic fibrosis yet. Herein, structural modification from a starting hit <b>LL01</b> led to lead <b>4a</b>, which exhibited an IC<sub>50</sub> value of 7.3 nM against PDE9, excellent selectivity against other PDE subfamilies, and remarkable microsomal stability. The cocrystal structure of PDE9 with <b>4a</b> revealed an important residue, Phe441, capable of improving the selectivity of PDE9 inhibitors. Administration of <b>4a</b> exerted a significant antifibrotic effect in bile duct-ligation-induced rats with hepatic fibrosis and transforming growth factor-β-induced fibrogenesis. This therapeutic effect was indeed achieved by selectively inhibiting PDE9 rather than other PDE isoforms, identifying PDE9 inhibitors as potential agents against hepatic fibrosis.