In vitro cell viability assay and calculation of combination indices.

5,000 to 10,000 cells/well were plated in triplicates in 96 well plates one day prior to addition of the inhibitors at the indicated final concentrations. After 5 or 7 days of culture, viability assay was measured using Resazurin colorimetric analysis as described (15). For drug interaction studies, cells were cultured in triplicates in the presence of six fixed-ratio concentrations for 72 hours followed by Alamar Blue viability assay. Combination indices were calculated using Compusyn software as described (16). All experiments were done at least three times in triplicates and one set of data most representative of the overall data was presented.