Sinomenine inhibits the growth of melanoma by enhancement of autophagy via PI3K/AKT/mTOR inhibition

Abstract

Background: Melanoma is a common skin tumor in adults with high metastasis and mortality rates. Thus, finding a better effective approach to treat melanoma has become very urgent. Sinomenine (SIN), the major active compound of Sinomenium acutum, has shown antitumori-genic activities in certain cancers. However, its role in melanoma remains unclear. Purpose: This study aimed to explore the effects of SIN on melanoma in vitro and in vivo, in addition to exploring the underlying mechanism. Methods: Mouse melanoma cell B16-F10 treated by SIN was analyzed by CCK8 assay and flow cytometry. Melanoma xenograft model was then established by subcutaneously injection with B16-F10 cells. Tumor growth was measured by immunohistochemistry. To further investigate the relative mechanism, the autophagy and PI3K/Akt/mTOR pathway were examined by immunofluorescence and Western blot. Results: Our results revealed that SIN dose dependently inhibited the proliferation of B16-F10 cells in vitro and attenuated melanoma growth in vivo. In addition, SIN treatment promoted the apoptosis of B16-F10 cells in a dose-dependent manner, as demonstrated by the increase in apoptotic cells, Bax/Bcl-2 ratio, and caspase-3 activity. Moreover, preconditioning with SIN dramatically enhanced autophagy activity by increasing Beclin-1 and LC3II/LC3I expression, in addition to decreasing p62 expression and augmenting the number of LC3 puncta, in B16-F10 cells. More importantly, autophagy inhibitor chloroquine partly abolished SIN’s effects on cell growth and apoptosis. Furthermore, our results showed that SIN-triggered activation of autophagy was mediated by PI3K/Akt/mTOR signaling pathway. Conclusion: Our study has identified a novel function of SIN and provided a molecular basis for potential applications of SIN in the treatment of melanoma and other cancers.