In previous work, the target of
asperphenamate as a natural product was successfully determined as
cathepsin by the natural product consensus pharmacophore strategy. In order to develop accurate SAR (structure-activity relationship) of
asperphenamate-type
cathepsin inhibitor, we chose several novel analogs with heterocyclic moiety to perform further study. The molecular simulation showed that 4-pyridyl derivative 3 with the greatest
cathepsin inhibitory activity presented new interaction modes with
protein utilizing its B-ring moiety. And then molecular dynamics (MD) simulation further revealed that 3 and
cathepsin kept stable interaction in the binding site, which validated the molecular docking results. In view that
cathepsins play an important role in
fibrosis and some
cathepsin inhibitors display the therapeutic ability for
fibrosis, we investigated the anti-fibrotic effect of 3in vitro and in vivo. The results indicated that 3 displayed the strongest inhibitory effect on the formation of α-SMA and
collagen I as the
protein markers of
fibrosis among all tested derivatives. Further in vivo assay confirmed that 3 indeed showed significant inhibitory ability against
pulmonary fibrosis by the method of H&E and Masson staining as well as immunohistochemical staining for characteristic α-SMA
proteins.