Identification of 3′,4′,5′-trihydroxyflavone as an mammalian target of rapamycin inhibitor and its suppressive effects on dextran sulfate sodium-induced ulcerative colitis

Flavone derivatives have been shown to possess anti-inflammatory properties in various inflammation model systems; however, their underlying molecular mechanisms remain elusive. In this study, a flavone derivative 3′,4′,5′-trihydroxyflavone (THF; NJK16003) was synthesized, and its anti-inflammatory effects and molecular targets were investigated using in vitro systems and an in vivo colitis model. NJK16003 showed potent anti-inflammatory activities in cell-based assays using macrophages. In vitro enzyme activity assays using various inflammation-related kinases revealed the mammalian target of rapamycin (mTOR) as a possible molecular target. Treatment of RAW264.7 cells with NJK16003 resulted in an increase in light chain 3B protein lipidation and a decrease in p62 protein levels and ribosomal S6 kinase phosphorylation, indicating that NJK16003 induces autophagy through mTOR inhibition. NJK16003 treatment resulted in significant induction of autophagy and suppression of inflammatory responses in intestinal epithelial cells. Autophagy induction has been shown to alleviate colitis by suppressing inflammatory responses and apoptotic cell death of intestinal epithelial cells. Indeed, inflammatory responses and intestinal epithelial cell death in our DSS-induced colitis mouse model were significantly suppressed by NJK16003 treatment. Our results indicate that NJK16003 could suppress inflammation by inducing autophagy through its mTOR inhibitory activity. These results suggest that NJK16003 could be a possible therapeutic agent for the treatment of inflammatory bowel diseases including colitis.