Preclinical evaluation of gemcitabine/paclitaxel-interactions in human bladder cancer lines

Gemcitabine and paclitaxel are currently co-administered in clinical studies for bladder cancer as this drug combination may offer better tumor responses. However, the drugs may antagonize the cytotoxic capacity of each other due to cell cycle perturbations. In this study, we evaluated different application schedules to determine the efficacy of the combination and its potential interactions.

Bladder cancer cell lines were exposed to either gemcitabine or paclitaxel, in concentrations ranging from 1-1000 nM. The inhibition concentrations (IC) 20, 50 and 70 were assessed by MTT assay after 24, 48 and 72 hours. Then, the cytotoxic activity and apoptosis induction abilities of the combined agents using the IC20 concentration were analyzed by MTT and Annexin-V/PI staining, respectively. The effects on the cell cycle were assessed by flow cytometry of bromodeoxyuridine (BrdU) and propidium iodide (PI).

Gemcitabine and paclitaxel dose-dependently inhibited cell proliferation. Simultaneous application of gemcitabine/paclitaxel yielded superior cytotoxicity rates after 48 and 72 hours. Sequential treatment of cells showed similar results when gemcitabine was given 24 hours before paclitaxel. However, when paclitaxel was given before gemcitabine, the cell kill was less. Gemcitabine as well as paclitaxel have potent apoptosis inducing abilities. Cell cycle evaluation demonstrated a shift towards the S-phase after gemcitabine and a progressive G2/M block after paclitaxel treatment.

The combination of gemcitabine and paclitaxel in vitro yields superior cytotoxic efficacy, if given simultaneously or with gemcitabine first. While in vitro cell models may not necessarily predict clinical outcome, they do provide a basis for rational scheduling of drugs in clinical trials.