Metformin inhibits proliferation of PCT cells in vitro. (A) Top panel displays the dose-dependent decrease in the number of viable cells of the PC tumor line, XRPC24, after treatment with metformin. Cells were grown in vitro in presence of 3 different concentrations of metformin (1mM, 5mM, and 10mM) for 1, 2, or 3 days; then the number of cells was determined using the Cell Titer Blue assay. Statistical comparison of biologic replicates (n = 6) using a 2-tailed t test demonstrated the growth-inhibiting effect of metformin at all concentrations and time points compared with cells grown in absence of metformin (*P < .05). Metformin did not inhibit BM stroma cells, S-10 (bottom). (B) Inhibition of proliferation of PCT by metformin was confirmed in 3 additional lines of PCTs (ABPC20, AH2D11, TEPC2077) after 2 days in cell culture. Same conditions were used in all experiments.