title: Characterization of the mechanism of zidovudine uptake by rat conditionally immortalized syncytiotrophoblast cell line TR-TBT.
abstract: OBJECTIVE
  To characterize the uptake mechanism of zidovudine (AZT), a nucleoside reverse transcriptase inhibitor, in syncytiotrophoblast cells using the TR-TBT 18d-1 cell line previously established by our group.
  
  
  METHODS
  The effects of several transporter inhibitors on the initial and steady-state apical uptake of AZT by TR-TBT 18d-1 were characterized, in order to identify the transporter(s) involved.
  
  
  RESULTS
  Initial uptake of AZT was sodium-independent and saturable; the K(m) value was about 16 microM. Nitrobenzylthioinosine (NBMPR), probenecid and cimetidine each had little effect on the saturable AZT uptake, indicating that well characterized transporters, such as organic anion transporters (OATs and OATPs), organic cation transporters (OCTs) and equilibrative nucleoside transporters (ENTs), are not involved. However, thymidine and 2'-deoxyuridine strongly inhibited AZT uptake. These results suggest that an unidentified nucleoside uptake transporter is responsible for the uptake of AZT. Cyclosporin A, Ko143 and probenecid had little effect on AZT accumulation by TR-TBT 18d-1 cells, suggesting that transporter-mediated efflux of AZT is not substantial.
  
  
  CONCLUSIONS
  Our results indicate that saturable AZT uptake into TR-TBT 18d-1 is mediated by a so-far-unidentified transporter.
authors.affiliation: Department of Pharmaceutics, Kyoritsu University of Pharmacy, 1-5-30 Shibakoen, Minato-ku, Tokyo 105-8512, Japan. sai-ys@kyoritsu-ph.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Sai
authors.forename: T
authors.initials: T
authors.lastname: Nishimura
authors.forename: S
authors.initials: S
authors.lastname: Shimpo
authors.forename: T
authors.initials: T
authors.lastname: Chishu
authors.forename: K
authors.initials: K
authors.lastname: Sato
authors.forename: N
authors.initials: N
authors.lastname: Kose
authors.forename: T
authors.initials: T
authors.lastname: Terasaki
authors.forename: C
authors.initials: C
authors.lastname: Mukai
authors.forename: S
authors.initials: S
authors.lastname: Kitagaki
authors.forename: N
authors.initials: N
authors.lastname: Miyakoshi
authors.forename: Y-S
authors.initials: YS
authors.lastname: Kang
authors.forename: E
authors.initials: E
authors.lastname: Nakashima
mesh_terms: D000465:Algorithms; D000818:Animals; D019380:Anti-HIV Agents / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003627:Data Interpretation, Statistical; D004347:Drug Interactions; D015726:Giant Cells / Q000166:cytology / Q000378:metabolism; D033703:Nucleoside Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D027361:Organic Anion Transporters / Q000037:antagonists & inhibitors / Q000378:metabolism; D027701:Organic Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D014327:Trophoblasts / Q000378:metabolism*; D015215:Zidovudine / Q000378:metabolism*
chemical_list: D019380:Anti-HIV Agents; D033703:Nucleoside Transport Proteins; D027361:Organic Anion Transporters; D027701:Organic Cation Transport Proteins; D015215:Zidovudine