title: Differences in the expression of endogenous efflux transporters in MDR1-transfected versus wildtype cell lines affect P-glycoprotein mediated drug transport.
abstract: OBJECTIVE
  P-glycoprotein (Pgp) efflux assays are widely used to identify Pgp substrates. The kidney cell lines Madin-Darby canine kidney (MDCK)-II and LLC-PK1, transfected with human MDR1 (ABCB1) are used to provide recombinant models of drug transport. Endogenous transporters in these cells may contribute to the activities of recombinant transporters, so that drug transport in MDR1-transfected cells is often corrected for the transport obtained in parental (wildtype) cells. However, expression of endogenous transporters may vary between transfected and wildtype cells, so that this correction may cause erroneous data. Here, we have measured the expression of endogenous efflux transporters in transfected and wildtype MDCK-II or LLC cells and the consequences for Pgp-mediated drug transport.
  
  
  METHODS
  Using quantitative real-time RT-PCR, we determined the expression of endogenous Mdr1 mRNA and other efflux transporters in wildtype and MDR1-transfected MDCK-II and LLC cells. Transcellular transport was measured with the test substrate vinblastine.
  
  
  RESULTS
  In MDR1-transfected MDCK cells, expression of endogenous (canine) Mdr1 and Mrp2 (Abcc2) mRNA was markedly lower than in wildtype cells, whereas MDR1-transfected LLC cells exhibited comparable Mdr1 but strikingly higher Mrp2 mRNA levels than wildtype cells. As a consequence, transport of vinblastine by human Pgp in efflux experiments was markedly underestimated when transport in MDR1-transfected MDCK cells was corrected for transport obtained in wildtype cells. This problem did not occur in LLC cells.
  
  
  CONCLUSIONS
  Differences in the expression of endogenous efflux transporters between transfected and wildtype MDCK cells provide a potential bias for in vitro studies on Pgp-mediated drug transport.
authors.affiliation: Department of Pharmacology, University of Veterinary Medicine, Hannover, Germany.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Kuteykin-Teplyakov
authors.forename: Carlos
authors.initials: C
authors.lastname: Luna-Tortós
authors.forename: Kamila
authors.initials: K
authors.lastname: Ambroziak
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Löscher
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D004285:Dogs; D005786:Gene Expression Regulation; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D018374:LLC-PK1 Cells; D008954:Models, Biological; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013552:Swine; D014162:Transfection; D014747:Vinblastine / Q000493:pharmacokinetics*
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012333:RNA, Messenger; D014747:Vinblastine; C513055:ABCB1 protein, human; C000715087:ABCC2 protein, human