title: Atazanavir: effects on P-glycoprotein transport and CYP3A metabolism in vitro.
abstract: The effect of atazanavir on P-glycoprotein (P-gp) expression and activity, as well as its inhibitory potency against CYP3A activity, was evaluated in vitro. Induction of P-gp activity and expression was studied using LS180V cells. P-gp inhibition was studied using both LS180V cells and Caco-2 cells. P-gp activity was assessed by measuring P-gp-mediated rhodamine 123 (Rh123) transport, and P-gp expression was determined using SDS-polyacrylamide gel electrophoresis/Western blot analysis. CYP3A inhibition was tested using triazolam hydroxylation in human liver microsomes (HLM). Extended (3-day) exposure of LS180V cells to 30 microM atazanavir caused a 2.5-fold increase in immunoreactive P-gp expression as well as a concentration-dependent decrease of intracellular Rh123 to a mean 45% (S.D. 5.2%) of control. Acute exposure (2 h) of LS180V cells to atazanavir increased intracellular Rh123 concentrations up to 300% of control at 100 microM atazanavir. At 30 microM and above, acute atazanavir exposure reversed P-gp induction caused by 3-day pretreatment with 10 microM ritonavir. P-gp inhibition was also observed in Caco-2 cells, causing an effect comparable to that observed for the known P-gp inhibitor verapamil (50% of control). In HLM, atazanavir was an inhibitor of triazolam hydroxylation, with inhibitory potency greatly increased by preincubation. IC50 values with and without preincubation were 0.31 microM (S.D. 0.13) and 5.7 microM (S.D. 4.1), respectively. Thus, atazanavir is an inhibitor and inducer of P-gp as well as a potent inhibitor of CYP3A in vitro, suggesting a potential for atazanavir to cause drug-drug interactions in vivo.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA.
authors.forename: Elke S
authors.initials: ES
authors.lastname: Perloff
authors.forename: Su X
authors.initials: SX
authors.lastname: Duan
authors.forename: Paul R
authors.initials: PR
authors.lastname: Skolnik
authors.forename: David J
authors.initials: DJ
authors.lastname: Greenblatt
authors.forename: Lisa L
authors.initials: LL
authors.lastname: von Moltke
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000069446:Atazanavir Sulfate; D018938:Caco-2 Cells; D045744:Cell Line, Tumor; D051544:Cytochrome P-450 CYP3A; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007424:Intracellular Fluid / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology*; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D011725:Pyridines / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004791:Enzyme Inhibitors; D009842:Oligopeptides; D011725:Pyridines; D000069446:Atazanavir Sulfate; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating