In vitro assessment of the potential cytotoxic effect of metformin on colorectal cancer cells

Metformin (Met), a biguanide molecule, is successfully used in the treatment of type 2 diabetes as the first line of therapy for many years now. Beside its antidiabetic effect exerted through the inhibition of gluconeogenesis in liver and increase of glucose uptake in peripheral tissues, it seems to possess an anticancer potential, demonstrated in breast, lung, hepatic and colorectal cancers. Colorectal cancer is responsible for 950 000 deaths just in 2020 and is considered to be one of the most prevalent types of cancer. The aim of the current study was to evaluate through a series of in vitro tests the cytotoxicity of Met in HT-29 and HCT- 116, two colorectal cancer cell lines and in a healthy colon cell line, CCD- 841 CoN. All three lines were stimulated with five concentrations of Met (5, 10, 25, 50, 75 mM) for 72 hours. Cellular viability was determined, followed by microscopical morphology analysis and immunofluorescence staining. Met has shown no cytotoxic effect towards CCD 841 CoN cells, whereas in both cancer cell lines showed a concentration-dependent decrease of viability. The morphology of the cancer cells was also changed directly proportional with the concentrations used, rounded, floating cells and decrease in confluency being observed. Moreover, Dapi staining was performed in order to spot changes at a nuclear level. After fixation and permeabilization of the cells, Dapi was added and nuclei shrinkage, intense fluorescence, condensation and fragmentation were seen. Therefore, Met exerts a selective cytotoxic effect in colon cancer cells through inducing apoptotic-like alterations.