David Dickens1, Andrew Owen, Ana Alfirevic, Munir Pirmohamed. 1. Department of Molecular and Clinical Pharmacology, The Wolfson Centre for Personalised Medicine, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
Abstract
BACKGROUND: P-glycoprotein (P-gp) is a multidrug efflux transporter that has a defined role in the absorption and disposition of drugs. Many studies have investigated the potential influence of ABCB1 polymorphisms on the disposition of its substrates. However, there remains significant controversy regarding the role of these polymorphisms. Our aim was to generate a P-gp expression system for single nucleotide polymorphisms (SNPs) and the reference sequence to assess the functional significance of these variants on transport. MATERIALS AND METHODS: P-gp reference, a P-gp ATPase deficient mutant (G534D) and a triple SNP variant of P-gp (1236C>T, 2677G>T, and 3435C>T) were expressed in Xenopus laevis oocytes and used to assess the influence of these SNPs on transport of digoxin and imatinib. The inhibition of P-gp-mediated transport in Caco-2 cells and oocytes was also assessed. RESULTS: No effect of the triple SNP variant of P-gp on molecular transport of digoxin or imatinib was observed. The rank order of inhibition of P-gp in Caco-2 cells and ABCB1-injected oocytes was tariquidar>elacridar>PSC-833>laniquidar>cyclosporine>verapamil>dipyridamole. CONCLUSION: These data suggest there is no functional consequence of these SNPs for molecular transport of model substrates or inhibition by model inhibitors for P-gp. Transporter-injected oocytes may be a useful tool for probing the mechanism for unexplained drug-drug interactions or to characterize therapeutic transport inhibitors.
BACKGROUND: P-glycoprotein (P-gp) is a multidrug efflux transporter that has a defined role in the absorption and disposition of drugs. Many studies have investigated the potential influence of ABCB1 polymorphisms on the disposition of its substrates. However, there remains significant controversy regarding the role of these polymorphisms. Our aim was to generate a P-gp expression system for single nucleotide polymorphisms (SNPs) and the reference sequence to assess the functional significance of these variants on transport. MATERIALS AND METHODS: P-gp reference, a P-gp ATPase deficient mutant (G534D) and a triple SNP variant of P-gp (1236C>T, 2677G>T, and 3435C>T) were expressed in Xenopus laevis oocytes and used to assess the influence of these SNPs on transport of digoxin and imatinib. The inhibition of P-gp-mediated transport in Caco-2 cells and oocytes was also assessed. RESULTS: No effect of the triple SNP variant of P-gp on molecular transport of digoxin or imatinib was observed. The rank order of inhibition of P-gp in Caco-2 cells and ABCB1-injected oocytes was tariquidar>elacridar>PSC-833>laniquidar>cyclosporine>verapamil>dipyridamole. CONCLUSION: These data suggest there is no functional consequence of these SNPs for molecular transport of model substrates or inhibition by model inhibitors for P-gp. Transporter-injected oocytes may be a useful tool for probing the mechanism for unexplained drug-drug interactions or to characterize therapeutic transport inhibitors.