A new link between apoptosis induced by the metformin derivative HL156A and autophagy in oral squamous cell carcinoma.

The metformin derivative HL156A exerts antitumoral effects in various cancers. Despite evidence in the literature, the underlying molecular mechanisms have not been clearly elucidated. Here, we examined the antiproliferative role and mechanism of HL156A in oral squamous cell carcinoma (OSCC). Using MTT and colony formation assays, we found that HL156A exerts an antiproliferative effect in oral cancer cells in a concentration-dependent manner. Flow cytometry was used to analyze the cell cycle distribution and apoptosis. Exposure to HL156A induced cell cycle arrest at the G2/M transition and increased apoptosis rates, associated with the increased caspase-3/PARP activity. On the other hand, HL156A induced autophagy, as demonstrated by autophagic vacuole staining and quantification of autolysosome-associated LC3BI/II proteins. Interestingly, inhibition of autophagy with chloroquine (CQ) increased the extent of apoptosis and promoted the antiproliferative effect of HL156A in OSCC cell lines, suggesting that autophagy mitigates HL156A-induced apoptosis. The relevance of these observations was confirmed in an in vivo system, as cotreatment with HL156A and CQ inhibited tumor growth in a xenograft mouse model of oral cancer. These results showed that HL156A has an antiproliferative effect associated with cell cycle arrest and apoptosis and induces autophagy to protect cells against apoptosis.