Circulating metabolites of the human immunodeficiency virus protease inhibitor nelfinavir in humans: Structural identification, levels in plasma, andantiviral activities

Nelfinavir mesylate (Viracept, formally AG1343) is a potent and orally bioa vailable human immunodeficiency virus (HIV) type I (HIV-I) protease inhibit or (K-i = 2 nM) and is being widely prescribed in combination with HIV reve rse transcriptase inhibitors fur the treatment of HIV infection. The curren t studies evaluated the presence of metabolites circulating in plasma follo wing the oral administration of nelfinavir to healthy volunteers and HIV-in fected patients, as well as the levels in plasma and antiviral activities o f these metabolites. The results showed that the parent drug was the major circulating chemical species, followed in decreasing abundance by its hydro xy-t-butylamide metabolite (M8) and 3'-methoxy-4'-hydroxynelfinavir (M1). A ntiviral assays with HIV-1 strain RF-infected CEM-SS cells showed that the 50% effective concentrations (EC,,) of nelfinavir, Ms, and M1 were 30, 34, and 151 nM, respectively, and that the corresponding EC,, against another H IV-1 strain, IIIB, in MT-2 cells were 60, 86, and 653 nM, Therefore, appare ntly similar in vitro antiviral activities were demonstrated for nelfinavir and Ms, whereas an approximately 5- to Ii-fold-lower level of antiviral ac tivity was observed for M1, The active metabolite, M8, showed a degree of b inding to human plasma proteins similar to that of nelfinavir (ca, 98%), Co ncentrations in plasma of nelfinavir and its metabolites in 10 HIV-positive patients receiving nelfinavir therapy (750 mg three times per day) were de termined by a liquid chromatography tandem mass spectrometry assay. At stea dy state (day 28), the mean plasma nelfinavir concentrations ranged from 1. 73 to 4.96 muM and the Mg concentrations ranged from 0.55 to 1.96 muM, wher eas the M1 concentrations were low and ranged from 0.09 to 0.19 muM In conc lusion, the findings from the current studies suggest that, in humans, nelf inavir forms an active metabolite circulating at appreciable Levels in plas ma. The active metabolite Ms may account for some of the antiviral activity associated with nelfinavir in the treatment of HN disease.