title: Impact of drug transporters on cellular resistance towards saquinavir and darunavir.
abstract: OBJECTIVE
  Highly active antiretroviral therapy is complicated by drug-drug interactions and the development of viral resistance. Drug interactions involve transporters that may critically affect the pharmacokinetics of many antiretroviral drugs and contribute to the formation of functional sanctuary sites. We therefore investigated the effect of saquinavir and darunavir on drug transporter expression and functional consequences for cellular resistance towards these compounds.
  
  
  METHODS
  Induction of transporters was investigated in LS180 cells over a period of 4 weeks by means of RT-PCR, and for some transporters also at the protein and functional levels. Cellular resistance was measured by growth inhibition assays.
  
  
  RESULTS
  Incubation with 10 µM darunavir for 1 week significantly increased mRNA expression of P-glycoprotein (P-gp/MDR1/ABCB1) 3.8-fold and of organic anion-transporting polypeptide 2B1 (SLCO2B1) 1.9-fold. In contrast, 10 µM saquinavir significantly increased mRNA expression of P-gp 5.7-fold, multidrug resistance-associated protein 1 (MRP1/ABCC1) 2.3-fold, MRP2/ABCC2 4.5-fold, MRP3/ABCC3 2.0-fold, MRP4/ABCC4 1.8-fold, MRP5/ABCC5 3.8-fold, breast cancer resistance protein (BCRP/ABCG2) 4.1-fold, SLCO1B1 4.6-fold, SLCO2B1 1.8-fold and SLCO3A1 1.8-fold. P-gp induction was also confirmed at the protein and functional levels. Induction by darunavir caused an increase in cellular resistance towards this compound, as measured in growth inhibition assays; however, saquinavir treatment did not cause reduced sensitivity of cells, indicating unchanged intracellular concentration. Hence, induction by darunavir increased drug efflux and might therefore lead to a suboptimal intracellular concentration of darunavir.
  
  
  CONCLUSIONS
  The study revealed substantial induction of several drug transporters by saquinavir and darunavir, possibly leading to decreased efficacy of antiretrovirals and drugs used to treat co-morbidity.
authors.affiliation: Department of Clinical Pharmacology and Pharmacoepidemiology, University of Heidelberg, Im Neuenheimer Feld 410, D-69120 Heidelberg, Germany.
authors.forename: Sonja Katharina
authors.initials: SK
authors.lastname: König
authors.forename: Melanie
authors.initials: M
authors.lastname: Herzog
authors.forename: Dirk
authors.initials: D
authors.lastname: Theile
authors.forename: Nadine
authors.initials: N
authors.lastname: Zembruski
authors.forename: Walter Emil
authors.initials: WE
authors.lastname: Haefeli
authors.forename: Johanna
authors.initials: J
authors.lastname: Weiss
mesh_terms: D044966:Anti-Retroviral Agents / Q000378:metabolism* / Q000494:pharmacology*; D001692:Biological Transport; D002460:Cell Line; D000069454:Darunavir; D024882:Drug Resistance, Viral; D015870:Gene Expression / Q000187:drug effects; D020869:Gene Expression Profiling; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D000089762:Multidrug Resistance-Associated Protein 2; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019258:Saquinavir / Q000378:metabolism* / Q000494:pharmacology*; D013449:Sulfonamides / Q000378:metabolism* / Q000494:pharmacology*
chemical_list: C000715087:ABCC2 protein, human; D044966:Anti-Retroviral Agents; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D012333:RNA, Messenger; D013449:Sulfonamides; D019258:Saquinavir; D000069454:Darunavir