title: Weak binding of VX-478 to human plasma proteins and implications for anti-human immunodeficiency virus therapy.
abstract: VX-478 is a potent inhibitor of human immunodeficiency virus type 1 (HIV-1) protease (Ki, 0.6 nM) and of HIV-1 replication in antiviral assays (IC90, 80 nM). The fractional binding of VX-478 to human plasma and to purified plasma proteins was determined by equilibrium dialysis and difference UV spectrophotometry. Binding to alpha 1-acid glycoprotein (89% at 2 microM total drug concentration, Kd of 4 microM) accounts for its fractional binding in plasma (93%). Stopped-flow spectrophotometry methods showed that binding is a reversible two-step process. The measured dissociation rate constant approaches 100 s-1. The antiviral effect of VX-478 was determined in the presence of 45% human plasma, in which the IC90 increased by 1.5-fold compared with control experiments in the presence of 15% fetal bovine serum. The effects of protein binding on the antiviral activity of VX-478 are minor, as expected for a weak drug-protein interaction.
authors.affiliation: Vertex Pharmaceuticals Inc., Cambridge, MA 02139, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Livington
authors.forename: S
authors.initials: S
authors.lastname: Pazhanisamy
authors.forename: D J
authors.initials: DJ
authors.lastname: Porter
authors.forename: J A
authors.initials: JA
authors.lastname: Partaledis
authors.forename: R D
authors.initials: RD
authors.lastname: Tung
authors.forename: G R
authors.initials: GR
authors.lastname: Painter
mesh_terms: D000163:Acquired Immunodeficiency Syndrome / Q000188:drug therapy*; D000818:Animals; D000998:Antiviral Agents / Q000097:blood*; D001769:Blood; D001798:Blood Proteins / Q000378:metabolism*; D002219:Carbamates; D002417:Cattle; D005333:Fetus; D005663:Furans; D017320:HIV Protease Inhibitors / Q000097:blood*; D006801:Humans; D007700:Kinetics; D015394:Molecular Structure; D009961:Orosomucoid / Q000378:metabolism*; D011485:Protein Binding; D013056:Spectrophotometry, Ultraviolet; D013449:Sulfonamides / Q000097:blood*
chemical_list: D000998:Antiviral Agents; D001798:Blood Proteins; D002219:Carbamates; D005663:Furans; D017320:HIV Protease Inhibitors; D009961:Orosomucoid; D013449:Sulfonamides; C095108:amprenavir