title: Erlotinib, gefitinib, and vandetanib inhibit human nucleoside transporters and protect cancer cells from gemcitabine cytotoxicity.
abstract: OBJECTIVE
  Combinations of tyrosine kinase inhibitors (TKI) with gemcitabine have been attempted with little added benefit to patients. We hypothesized that TKIs designed to bind to ATP-binding pockets of growth factor receptors also bind to transporter proteins that recognize nucleosides.
  
  
  METHODS
  TKI inhibition of uridine transport was studied with recombinant human (h) equilibrative (E) and concentrative (C) nucleoside transporters (hENT, hCNT) produced individually in yeast. TKIs effects on uridine transport, gemcitabine accumulation, regulation of hENT1 activity, and cell viability in the presence or absence of gemcitabine were evaluated in human pancreatic and lung cancer cell lines.
  
  
  RESULTS
  Erlotinib, gefitinib and vandetanib inhibited [(3)H]uridine transport in yeast and [(3)H]uridine and [(3)H]gemcitabine uptake in the four cell lines. Treatment of cell lines with erlotinib, gefitinib, or vandetanib for 24 hours reduced hENT1 activity which was reversed by subsequent incubation in drug-free media for 24 hours. Greater cytotoxicity was observed when gemcitabine was administered before erlotinib, gefitinib, or vandetanib than when administered together and synergy, evaluated using the CalcuSyn Software, was observed in three cell lines resulting in combination indices under 0.6 at 50% reduction of cell growth.
  
  
  CONCLUSIONS
  Vandetanib inhibited hENT1, hENT2, hCNT1, hCNT2, and hCNT3, whereas erlotinib inhibited hENT1 and hCNT3 and gefitinib inhibited hENT1 and hCNT1. The potential for reduced accumulation of nucleoside chemotherapy drugs in tumor tissues due to inhibition of hENTs and/or hCNTs by TKIs indicates that pharmacokinetic properties of these agents must be considered when scheduling TKIs and nucleoside chemotherapy in combination.
authors.affiliation: Authors' Affiliations: Department of Oncology, University of Alberta; Department of Medical Oncology, Cross Cancer Institute, Edmonton, Alberta, Canada; and Department of Oncology, University of Oxford, Oxford, United Kingdom.
authors.forename: Vijaya L
authors.initials: VL
authors.lastname: Damaraju
authors.forename: Tara
authors.initials: T
authors.lastname: Scriver
authors.forename: Delores
authors.initials: D
authors.lastname: Mowles
authors.forename: Michelle
authors.initials: M
authors.lastname: Kuzma
authors.forename: Anderson J
authors.initials: AJ
authors.lastname: Ryan
authors.forename: Carol E
authors.initials: CE
authors.lastname: Cass
authors.forename: Michael B
authors.initials: MB
authors.lastname: Sawyer
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000378:metabolism / Q000494:pharmacology*; D001692:Biological Transport; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D000069347:Erlotinib Hydrochloride; D000077156:Gefitinib; D006801:Humans; D020128:Inhibitory Concentration 50; D033703:Nucleoside Transport Proteins / Q000037:antagonists & inhibitors*; D010880:Piperidines / Q000494:pharmacology*; D011799:Quinazolines / Q000494:pharmacology*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000378:metabolism; D014529:Uridine / Q000378:metabolism; D000093542:Gemcitabine
chemical_list: D000964:Antimetabolites, Antineoplastic; D033703:Nucleoside Transport Proteins; D010880:Piperidines; D011799:Quinazolines; D003841:Deoxycytidine; D000069347:Erlotinib Hydrochloride; D000077156:Gefitinib; D014529:Uridine; C452423:vandetanib; D000093542:Gemcitabine