ATAZANAVIR: EFFECTS ON P-GLYCOPROTEIN TRANSPORT AND CYP3A METABOLISM IN VITRO

• Published in: Drug metabolism and disposition Vol. 33; no. 6; pp. 764 - 770
• Main Authors: PERLOFF, Elke S, DUAN, Su X, SKOLNIK, Paul R, GREENBLATT, David J, VON MOLTKE, Lisa L
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Pharmacology and Experimental Therapeutics 01.06.2005
• Subjects: Antibiotics. Antiinfectious agents. Antiparasitic agents; Antiviral agents; Aryl Hydrocarbon Hydroxylases - antagonists & inhibitors; Aryl Hydrocarbon Hydroxylases - metabolism; Atazanavir Sulfate; ATP-Binding Cassette, Sub-Family B, Member 1 - metabolism; Biological and medical sciences; Caco-2 Cells; Cell Line, Tumor; Cytochrome P-450 CYP3A; Dose-Response Relationship, Drug; Enzyme Inhibitors - pharmacology; Humans; Intracellular Fluid - drug effects; Intracellular Fluid - enzymology; Intracellular Fluid - metabolism; Medical sciences; Oligopeptides - pharmacology; Oxidoreductases, N-Demethylating - antagonists & inhibitors; Oxidoreductases, N-Demethylating - metabolism; Pharmacology. Drug treatments; Protein Transport - drug effects; Protein Transport - physiology; Pyridines - pharmacology; Antiretroviral agent; Atazanavir; Enzyme; Isozyme; Cytochrome P450; Biological transport; P Glycoprotein; Enzyme inhibitor; Metabolism; In vitro; Antiviral; Pharmacokinetics; Protease inhibitor
• ISSN: 0090-9556; 1521-009X
• DOI: 10.1124/dmd.104.002931

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 μM 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 μM atazanavir. At 30 μM and above, acute atazanavir exposure reversed P-gp induction caused by 3-day pretreatment with 10 μM 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. IC 50 values with and without preincubation were 0.31 μM (S.D. 0.13) and 5.7 μM (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.