Metformin inhibits melanoma cell metastasis by suppressing the miR-5100/SPINK5/STAT3 axis

Melanoma is the most lethal skin cancer characterized by its high metastatic potential. It is urgent to find novel therapy strategies to overcome this feature. Metformin has been confirmed to suppress invasion and migration of various types of cancer. However, additional mechanisms underlying the antimetastatic effect of metformin on melanoma require further investigation. Here, we performed microarray analysis and uncovered an altered mRNA and miRNA expression profile between melanoma and nevus. Luciferase reporter assay confirmed that miR-5100 targets SPINK5 to activate STAT3 phosphorylation. Migration and wound healing assays showed that the miR-5100/SPINK5/STAT3 axis promotes melanoma cell metastasis; the mechanism was proven by initiation of epithelial-mesenchymal transition. Co-immunoprecipitation (Co-IP) further confirmed an indirect interaction between SPINK5 and STAT3. Furthermore, metformin dramatically inhibited miR-5100/SPINK5/STAT3 pathway, and decreased B16-F10 cell metastasis to lung in C57 mouse module. Intriguingly, pretreatment of metformin before melanoma cell injection improved this effect further. These findings exposed the underlying mechanisms of action of metformin and update the use of this drug to prevent metastasis in melanoma.