A. MTS assay of RCC cell lines treated with TRAIL at the indicated dose for 24 hours. B. MTS assay of RCC cell lines treated with recombinant TRAIL (250 ng/ml) for 24 hours, IFNα (1000 IU/ml) for 72 hours, or a combination of IFNα for 72 hours with TRAIL added for the last 24 hours. (* p=0.002, ** p<0.001 vs. control, p=0.01 vs. TRAIL alone, # p=0.009, ## p=0.06, $ p<0.001 vs. control or TRAIL alone, student t-test) C–F: A-498 (C, E) or ACHN (D, F) cells were exposed to varying doses of IFNα (250 IU/ml to 4,000 IU/ml) for 72 hours, TRAIL (62.5 ng/ml to 1000 ng/ml) for 24 hours, or the combination of the two agents. Cell viability was determined utilizing the MTS method as described above. Synergy was then determined using the CalcuSyn software as described in the methods and shown in tabular format (C&D) and graphically (E&F) at ED50 (red line) and ED75 (green line).