Discovery of amentoflavone as a natural PDE4 inhibitor with anti-fibrotic effects

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease with high mortality rate but effective therapeutics are still lacking. Phosphodiesterase-4 (PDE4) inhibitors were reported to be promising anti-IPF agents. Herein, series of biflavonoids isolated from Selaginella uncinate were found to be PDE4 inhibitors and the most active amentoflavone gave a half maximal inhibitory concentration (IC50) of 12 nmol/L, which was further validated by isothermal titration calorimetry with Kd of 23 nmol/L. Besides, co-crystal structure of PDE4-amentoflavone was determined and gave a different binding pattern from roflumilast with multiple H-bonds between it and key residues such as Asn321/Thr333/Gln369/Gly371. So far, this was the first reported co-crystal structure of amentoflavone with its potential binding target in despite of the extensive investigations of this common natural biflavonoid. Furthermore, amentoflavone exhibited remarkable anti-IPF effects in vivo and in vitro, suggesting it as a novel anti-fibrotic agent by targeting PDE4.