Metformin, a drug used to treat diabetes, alters the microRNA system and downregulates the expression of a cancer gene, reports a study published in Nature Communications this week. These findings provide an explanation for how metformin treatment may reduce cancer incidence in diabetes patients.

Metformin reduces insulin resistance and lowers blood glucose levels and multiple studies have shown that its use reduces the incidence of cancer. The way in which it succeeds is doing so, however, has remained unknown. Giovanni Blandino and colleagues showed that treatment of mice with metformin reduced tumour formation and can also reduce the size of pre-formed tumours. They found that in cells in culture metformin altered the pattern of expression of microRNAs, which modulate the expression genes. When they further analysed the genes that were altered in expression in cultured cells they found that the oncogene c-Myc was reduced in expression. These finding suggest that the anti-cancer effect of metformin in cells in culture results from the alteration of the production of microRNAs, which in turn modifies the expression of genes, including oncogenes.