Abstract
PURPOSE: Ascofuranone is an antiviral antibiotic that is known to exert multiple anti-tumor effects, including cell cycle arrest, inhibition of mitochondrial respiration, and inhibition of angiogenesis. In this study, we investigated the molecular mechanisms underlying the anti-metastatic effects of ascofuranone in insulin-like growth factor-I (IGF-1)-responsive cancer cells. METHODS: The inhibitory effect of ascofuranone on cancer cell migration and invasion was assessed using scratch wound healing and Matrigel invasion assays, respectively. F-actin cytoskeleton organization was assessed using FITC conjugated phalloidin staining. Target gene expression was evaluated using Western blotting and gene silencing was performed using siRNA transfections. Finally, the anti-metastatic effect of ascofuranone was investigated in vivo. RESULTS: We found that ascofuranone suppressed IGF-1-induced cell migration, invasion and motility in multiple cancer cell lines. The effects of ascofuranone on actin cytoskeleton organization were found to be mediated by suppression of the mTOR/p70S6K/4EBP1 pathway. Ascofuranone inhibited IGF-1-induced mTOR phosphorylation and actin cytoskeleton organization via upregulation of AMPK and downregulation of Akt phosphorylation. It also selectively suppressed the IGF-1-induced mTOR complex (mTORC)1 by phosphorylation of Raptor, but did not affect mTORC2. Furthermore, we found that focal adhesion kinase (FAK) activation decreased in response to ascofuranone, rapamycin, compound C and wortmannin treatment. Finally, we found that ascofuranone suppressed phosphorylation of FAK and mTOR and dephosphorylation of Raptor in cancerous metastatic lung tissues in vivo. CONCLUSIONS: Our data indicate that ascofuranone suppresses IGF-1-induced cancer cell migration and invasion by blocking actin cytoskeleton organization and FAK activation through inhibition of the mTORC1 pathway, and reveal a novel anti-metastatic function of this compound.