title: Levels of human equilibrative nucleoside transporter-1 are higher in proliferating regions of A549 tumor cells grown as tumor xenografts in vivo.
abstract: 3'-Fluoro-3'-deoxythymidine (FLT) has been proposed for positron emission tomography (PET)-based identification of tumor chemosensitivity that is mediated by the human equilibrative nucleoside transporter-1 (ENT1). ENT1 facilitates transport of FLT into cells and elevated levels of FLT are associated with both larger FLT-PET signals and increased response to nucleoside-based chemotherapies. FLT-PET is also used as a measure of tumor proliferation. The present study examined the extent to which ENT1 levels vary in a proliferation-dependent manner in tumor cells in vivo.
  
  
  METHODS
  The human adenocarcinoma cell line A549 was used to establish tumor xenografts in nude mice. FLT uptake was measured in vivo using PET, and further examined ex vivo using autoradiography. FLT uptake patterns were compared to immunohistochemical (IHC) analysis of ENT1 and the proliferation markers Ki67 and BrdU.
  
  
  RESULTS
  Regional differences in FLT uptake matched differences in IHC proliferation markers. All cells stained for ENT1, but the staining intensity was twice as high for Ki67(+) cells than for Ki67(-) cells.
  
  
  CONCLUSIONS
  Under in vivo conditions, proliferating regions of tumors show increased FLT uptake and higher ENT1 levels than nonproliferating tumor regions.
authors.affiliation: Department of Radiation Oncology, Box 356069, University of Washington, Seattle, WA 98195 USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Plotnik
authors.forename: Camille
authors.initials: C
authors.lastname: Asher
authors.forename: Stephanie K
authors.initials: SK
authors.lastname: Chu
authors.forename: Robert S
authors.initials: RS
authors.lastname: Miyaoka
authors.forename: Gregory G
authors.initials: GG
authors.lastname: Garwin
authors.forename: Brian W
authors.initials: BW
authors.lastname: Johnson
authors.forename: Tiffany
authors.initials: T
authors.lastname: Li
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Krohn
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Schwartz
mesh_terms: D000230:Adenocarcinoma / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology*; D000077192:Adenocarcinoma of Lung; D000818:Animals; D001692:Biological Transport; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic; D015224:Dideoxynucleosides / Q000378:metabolism; D033721:Equilibrative Nucleoside Transporter 1 / Q000378:metabolism*; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology*; D008297:Male; D051379:Mice; D049268:Positron-Emission Tomography; D021381:Protein Transport
chemical_list: D015224:Dideoxynucleosides; D033721:Equilibrative Nucleoside Transporter 1; C438649:SLC29A1 protein, human; C002854:alovudine