Celltiter 96 non radioactive assay

The CellTiter 96 Non-Radioactive Assay (Promega) was used according to manufacturer’s instructions. Briefly, cells were seeded in a 24 well plate and treated for 48 h with vehicle, gefitinib, lapatinib, trastuzumab, and (or) EHop-016 or MBQ-167 at the indicated concentrations. After incubation, the MTT (3-(4,5-dymethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide) reagent was added to the plate (40 μL/well). The plates were incubated for 4 h at 37 °C, followed by the addition of stop solution, and the plates were incubated to facilitate solubilization of formed formazan salts. The absorbance was measured at 570 nm using a microplate reader. Fold resistance for therapy resistant cell lines was quantified, as described in [44 (link)], by the ratio of the half maximal inhibitory concentration (IC₅₀) of the therapy resistant cell line by the IC₅₀ of the therapy sensitive cells.