Osthole induces accumulation of impaired autophagosome against pancreatic cancer cells

Pancreatic cancer (PC) is one of the most aggressive malignancies worldwide, and few effective therapeutics are available. Osthole (OST), a natural coumarin, has been proven to be a potential anticancer compound. In this study, we found that OST significantly inhibited PC growth both in vitro and in vivo. Notably, the anti-PC effect of OST is mediated by excessive autophagosome accumulation and consequent apoptosis in PC cells. Mechanistically, OST increased the number of autophagosomes via two pathways. First, OST induced autophagy initiation by suppressing the Akt/mTOR signaling pathway. Second, OST induced autophagic arrest by blocking autophagosome-lysosome fusion. Consistently, inhibition of autophagy initiation restored PC cell growth, whereas autophagic flux inhibitors exacerbated the antitumor effect of OST in PC cells, suggesting a cytotoxic role of OST-induced autophagosome accumulation. In addition, we found that OST upregulates the expression of activating transcription factor 3 (ATF3), resulting in inactivation of the Akt/mTOR signaling pathway and autophagy initiation in PC cells. ATF3 overexpression increased the activation of autophagy, and inhibition of ATF3 expression decreased autophagy. Taken together, our study provides new insights into the OST-induced growth inhibitory effect on PC cells, suggesting a promising potential therapeutic role of OST for PC treatment.