| Salvage of preformed nucleosides requires transport across the plasma membrane by specific transport proteins and subsequent conversion to their ribo- and deoxyribonucleotide forms. In mammalian cells, plasma membrane transport occurs by sodium-dependent (concentrative) and sodium-independent (equilibrative) mechanisms. These transport systems are also the route of cellular uptake for many synthetic nucleoside analogue agents used in cancer treatment, including gemcitabine (a novel deoxycytidine analogue). This thesis examines the in vitro effects of gemcitabine on cytotoxicity and the modulation of these effects by the es-nucleoside transporter and two DNA synthesis inhibitors (5-fluorouracil and tomudex), with a specific focus on pancreatic cancer.; Cytotoxicity was assessed by clonogenic assay in one human bladder (MGH-U1) and three human pancreatic cancer cell lines (PANC-1, HS-766T, PK-8). Basal levels of es-NT were quantified in all four cell lines by flow cytometric analysis. Combination experiments were carried out to determine if upregulating the es-NT modulates increases in sensitivity to gemcitabine. In two pancreatic cell lines (PANC-1, HS-766T), treatment with 5-FU followed by gemcitabine yielded increased cytotoxicity. This effect was also seen in the HS-766T cell line when pre-treated with tomudex. For these concentrations of 5-FU and tomudex, es-NT content was found to be increased over basal levels. |
