title: Equilibrative-sensitive nucleoside transporter and its role in gemcitabine sensitivity.
abstract: Salvage of preformed nucleosides requires transport across the plasma membrane by sodium-dependent (concentrative) and sodium-independent (equilibrative) mechanisms. These transport systems are also the route of cellular uptake for nucleoside analogues, including gemcitabine (2',2'-difluorodeoxycytidine), a deoxycytidine analogue used in the treatment of pancreatic cancer. To determine whether gemcitabine cytotoxicity is influenced by the equilibrative-sensitive nucleoside transporter (es-NT), basal levels of the es-NT were quantified in three human pancreatic cancer cell lines (PANC-1, HS-766T, and PK-8) and one human bladder cancer cell line (MGH-U1) by flow cytometric analysis, and the results were compared with gemcitabine cytotoxicity assessed by clonogenic assay. To determine whether the salvage pathway of DNA synthesis can be up-regulated by inhibiting de novo DNA synthesis, combination experiments were carried out using the thymidylate synthase (TS) inhibitors 5-fluorouracil or raltitrexed with gemcitabine in a concurrent and sequential fashion. No relationship between basal es-NT and gemcitabine cytotoxicity was demonstrated. For two pancreatic cell lines, sequence-dependent effects of the combination of TS inhibitors and gemcitabine were seen with maximum effect when the TS inhibitors preceded gemcitabine. This was also associated with a significant increase in es-NT levels caused by the TS inhibitors. Thus, modulation of the es-NT by pretreatment with TS inhibitors may have the potential to improve the therapeutic benefit of gemcitabine.
authors.affiliation: Department of Pharmacology, University of Toronto, Ontario, Canada.
authors.forename: D R
authors.initials: DR
authors.lastname: Rauchwerger
authors.forename: P S
authors.initials: PS
authors.lastname: Firby
authors.forename: D W
authors.initials: DW
authors.lastname: Hedley
authors.forename: M J
authors.initials: MJ
authors.lastname: Moore
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000493:pharmacokinetics / Q000633:toxicity*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000633:toxicity; D002352:Carrier Proteins / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000633:toxicity*; D033705:Equilibrative Nucleoside Transport Proteins; D005434:Flow Cytometry; D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D005472:Fluorouracil / Q000008:administration & dosage / Q000633:toxicity; D006801:Humans; D020128:Inhibitory Concentration 50; D010190:Pancreatic Neoplasms / Q000188:drug therapy / Q000378:metabolism; D011684:Purine Nucleosides / Q000378:metabolism; D011799:Quinazolines / Q000008:administration & dosage / Q000633:toxicity; D013876:Thiophenes / Q000008:administration & dosage / Q000633:toxicity; D014407:Tumor Cells, Cultured; D001749:Urinary Bladder Neoplasms / Q000188:drug therapy / Q000378:metabolism; D000093542:Gemcitabine
chemical_list: D000964:Antimetabolites, Antineoplastic; D002352:Carrier Proteins; D033705:Equilibrative Nucleoside Transport Proteins; D005452:Fluoresceins; D005456:Fluorescent Dyes; D011684:Purine Nucleosides; D011799:Quinazolines; D013876:Thiophenes; D003841:Deoxycytidine; C079645:5-(SAENTA-x8)fluorescein; C068874:raltitrexed; D005472:Fluorouracil; D000093542:Gemcitabine