In the present study, we further investigated this combination and the effects of paclitaxel on the mRNA levels, protein expression and specific activity of dCK and CDA based on our observations that paclitaxel reduces the systemic clearance in humans and the accumulation of the

metabolites in the laboratory. For this purpose, we treated three separate immortalized human NSCLC cell lines obtained from patients diagnosed with advanced disease that represent the more common histological subtypes. Methods Chemicals Gemcitabine (Gemzar®; 2′,2′-difluoro- 2′-deoxycytidine; dFdC) was a generous gift from Eli Lilly and Company (Indianapolis, IN) and dissolved in sterile distilled water. Paclitaxel Selleckchem IACS-010759 was purchased

from Sigma-Aldrich Company (St. Louis, MO) and dissolved in 0.1% acetic acid in methanol. Radiolabeled chlorodeoxyadenosine (8-3H-CdA, 7.8 Ci/mmol) was purchased from Moravek (Brea, CA). All other chemicals were of analytical grade. Cell culture The NSC large cell lung carcinoma H520 cell line (mutant-p53) was provided by Dr. William T. Beck (University of Illinois, Chicago, Illinois, USA). The NSC H460 squamous carcinoma cell line (wild-type p53) and H838 adenocarcinoma cell line (wild-type MK 8931 manufacturer p53) were obtained from the American Type Culture Collection (Manassas, Virginia, USA). The cells were grown in monolayers and maintained in exponential growth in RPMI-1640 medium containing 2 mM L-glutamine supplemented with 10% fetal bovine serum (FBS) and 1% penicillin (10,000 U penicllin per ml)-streptomycin (10 mg of streptomycin

per ml) at 37°C at 5% CO2. The medium was further supplemented with insulin (Gibco Life Technologies, Grand Island, New York, USA) for H520 cells. Growth inhibition assay Growth inhibition was determined using a dye exclusion assay with trypan blue staining followed by a cell count using a hemocytometer [18]. Briefly, ~3.5 × 105 cells were seeded in duplicate in 6-well flat Paclitaxel concentration bottom plates. After 24 hours, the cells were treated with vehicle-control, gemcitabine (ranged from 1 to 15,000 nM) or paclitaxel (ranged from 1 to 3,000 nM) for 24 hours. The fraction of affected cells and unaffected cells for the individual drugs was calculated compared to cells exposed to vehicle-control. The IC50 values were determined using linear regression analysis with the aide of CalcuSyn software (v. 2, Biosoft, Cambridge, UK). A multiple drug effect analysis was completed to predict the likely drug-drug interaction based on the principles of Chou and Talalay [19]. The combination index (CI) for each fraction affected was simulated and for the final evaluation, the averaged CI at 0.50, 0.75, 0.90 and 0.95 fraction affected was determined [20]. Briefly, ~1 × 106 cells were seeded in duplicate in 60 mm dishes.