Fig. 5. Cytotoxicity of ERK inhibitors in tumor cells. VX-11e and BVD-523 were tested for cytotoxic activity against A549 (NSCLC), DM122 (melanoma), and H82 (SCLC) cells. Cells were incubated with compounds at varying concentrations for 4 days followed by measurement of cell proliferation using established metabolic assays (WST-1). Dose–response curves were generated to evaluate cellular potency (EC₅₀ values) of compounds. (A) The EC₅₀ values for BVD-523 in cell lines were calculated as follows: A549, EC₅₀ = 400 nM (95% CI of 200–750 nM); DM122, EC₅₀ = 480 nM (95% CI of 270–870 nM). (B) The EC₅₀ values for VX-11e in cell lines were calculated as follows: A549, EC₅₀ = 770 nM (95% CI of 420–1400 nM); DM122, EC₅₀ = 370 nM (95% CI of 250–540 nM). (C) H82 cells were tested with the same inhibitor concentrations used in (A) and (B). VX-11e and BVD-523 were less cytotoxic in H82 cells, and substantial blockade of cell proliferation was only observed at 10 μM concentrations. Staurosporine (Stauro; pan-kinase inhibitor) was included as a positive control for our cytotoxicity experiments.