The optimum concentration of 3-MA to inhibit autophagy in part depends upon culture conditions of cells. Therefore, if 10 mM concentration was "toxic" I would use increasing concentrations (0, 2, 4, 6, 8, or 10 mM). This may provide a desirable concentration of 3-MA.
Hi Saeb, it depends on the cell type and the basal autophagy status. If autophagy is an important survival mechanism in your cells, totally blocking autophagy will for sure kill the cells. If I were you, I'll try different dosages of 3-MA in cells and choose one that efficiently inhibit autophagy but not kill the cells.