Modulation of gemcitabine accumulation by DNA-damaging agents: mechanisms and specificity in an in vitro model

Self-potentiation of the intracellular accumulation of gemcitabine accumulation occurs with repeated administration. Understanding the mechanism of this phenomena and its occurrence with other drugs is important for rational dosing of gemcitabine and design of gemcitabine combinations. The HCT116 cell line was used as a model of the in vivo findings to examine the effect of repeated gemcitabine exposure. HPLC analysis revealed a 10-fold increase in gemcitabine-triphosphate accumulation upon repeated gemcitabine exposure. The induction of accumulation was not associated with any changes in the dCK mRNA level. Comparable increases in gemcitabine-triphosphate were seen when the cells were pre-incubated with cytarabine and cisplatin. A lesser increase and no increase in GEM-TP were seen with oxaliplatin and 5'-azacytidine, respectively. In this model, induction of gemcitabine accumulation is likely to be mediated by post translational modification of dCK. The reduced effect of oxaliplatin compared to cisplatin is worthy of further study.