Pharmacodynamic characterization of gemcitabine cytotoxicity in an in vitro cell culture bioreactor system
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Gemcitabine, a pyrimidine nucleoside, is approved for the treatment of non-small cell lung cancer, pancreatic carcinoma, and breast cancer. Chemotherapy regimens are determined experimentally with static tissue culture systems, animal models, and in Phase I clinical trials. The aim of this study was to assess for gemcitabine-induced cell death following infusion of drug under clinically-relevant conditions of infusion rate and drug exposure in an in vitro bioreactor system.
To estimate an appropriate harvest time for cells from the bioreactor after drug treatment, we estimated the temporal relationship between gemcitabine treatment for 1 h and cell death at a later time point with monolayer growth assays (i.e., static culture). Afterward, 5.3 mg gemcitabine was infused over 0.5 h in the bioreactor, followed by mono-exponential decay, simulating patient concentration–time profiles (n = 4). Controls were run with drug-free media (n = 4). Cells were harvested from the bioreactor at a later time point and assessed for cell death by flow cytometry.
According to monolayer growth assay results, cytotoxicity became more apparent with increasing time. The EMax for cells 48 h after treatment was 50% and after 144 h, 93% (P = 0.022; t test), while flow cytometry showed complete DNA degradation by 120 h. Gemcitabine was infused in the bioreactor. The gemcitabine area under the concentration–time curve (AUC) was 56.4 μM h and the maximum concentration was 87.5 ± 2.65 μM. Flow cytometry results were as follows: the G1 fraction decreased from 65.1 ± 4.91 to 28.6 ± 12% (P = 0.005) and subG1 increased from 14.1 ± 5.28 to 42.6 ± 9.78% (P = 0.004) relative to control. An increase in apoptotic cells was observed by TUNEL assay.
The in vitro bioreactor system will be expanded to test additional cell lines, and will serve as a useful model system for assessing the role of drug pharmacokinetics in delivery of optimized anticancer treatment.