Drug sensitivity was analyzed using a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt/phenazine methosulfate (MTS/PMS) microtiter plate assay (CellTiter 96 Cell Proliferation Assay, Promega, Madison, WI). HEK-pcDNA3, HEK-MRP7-C17 and HEK293-MRP7-C18 were seeded in triplicate at 3000 cells per well in 96-well plates in DMEM containing 10% fetal bovine serum. Parental vector-transduced MEF3.8 cells (TKO-pBabe) and MRP7-transduced MEF3.8 cells (TKO-MRP7-7-21) were seeded at 1500 cells per well in 10% DMEM. All other cell lines were seeded at 3000 cells per well in 10% DMEM. The following day, drugs were added at various concentrations to the growth medium. Cellular proliferation assays were performed after 72 h of incubation in the presence of drug. Vincristine, vinblastine, paclitaxel, daunorubicin, cisplatin, 5-fluoro-2′-deoxyuridine, 5-fluoro-5′-deoxyuridine, 5-azacytidine, 5-fluorouracil, 6-thioguanine, 2′-chloro-2′ deoxythymidine, 2′,3′-dideoxycytidine, cytabarine, 6-mercaptopurine and buthionine sulfoximine were purchased from Sigma Chemical Company (St. Louis, MO). SN-38 was generously provided by Pharmacia Corporation (Kalamazoo, MI). Etoposide (Bristol Meyers Squibb, Princeton, NJ.), gemcitabine (Eli Lilly) and docetaxel (Aventis Pharmaceuticals, Bridgewater, NJ.) were obtained from the pharmacy of the Fox Chase Cancer Center. MAC231, MST997 and HTI286 were kindly provided by Wyeth Research. Epothilone B, epothilone A and phomopsin A were obtained from Calbiochem (La Jolla, CA.). PMEA (9-(-phosphonylmethoxynyl)adenine) was kindly provided by Gilead (Forest City, CA).