Cell viability assay

The fraction of viable cells was determined on cells in culture using a luminescence based assay (CellTiter-Glo, Promega, Madison, WI, USA). Ren-01 and Ren-02 human RCC cells were plated in 96-well plates (10 000 cells/0.2 ml DMEM medium), allowed to adhere, and compounds (both from Pfizer, New York, NY, USA) were added. After 48 h, viability was determined using a multi-label counter (Victor² 1420 Wallac, Perkin-Elmer, Waltham, MA, USA). Chou-Talalay analysis was used to determine whether combination drug effects were antagonistic, additive or synergistic (Chou and Talalay, 1984).