Resistance to HIV Protease Inhibitors:  A Comparison of Enzyme Inhibition and Antiviral Potency

• Published in: Biochemistry (Easton) Vol. 37; no. 24; pp. 8735 - 8742
• Main Authors: Klabe, Ronald M., Bacheler, Lee T., Ala, Paul J., Erickson-Viitanen, Susan, Meek, James L.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 16.06.1998
• Subjects: AIDS/HIV; Drug Resistance, Microbial; HIV Protease - genetics; HIV Protease - metabolism; HIV Protease Inhibitors - chemistry; HIV Protease Inhibitors - pharmacology; HIV-1 - physiology; Humans; Mutation; Structure-Activity Relationship; Virus Replication - drug effects
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi972555l

Resistance of HIV-1 to protease inhibitors has been associated with changes at residues Val82 and Ile84 of HIV-1 protease (HIV PR). Using both an enzyme assay with a peptide substrate and a cell-based infectivity assay, we examined the correlation between the inhibition constants for enzyme activity (K i values) and viral replication (IC90 values) for 5 active site mutants and 19 protease inhibitors. Four of the five mutations studied (V82F, V82A, I84V, and V82F/I84V) had been identified as conferring resistance during in vitro selection using a protease inhibitor. The mutant protease genes were expressed in Escherichia coli for preparation of enzyme, and inserted into the HXB2 strain of HIV for test of antiviral activity. The inhibitors included saquinavir, indinavir, nelfinavir, 141W94, ritonavir (all in clinical use), and 14 cyclic ureas with a constant core structure and varying P2, P2‘ and P3, P3‘ groups. The single mutations V82F and I84V caused changes with various inhibitors ranging from 0.3- to 86-fold in K i and from 0.1- to 11-fold in IC90. Much larger changes compared to wild type were observed for the double mutation V82F/I84V both for K i (10−2000-fold) and for IC90 (0.7−377-fold). However, there were low correlations (r 2 = 0.017−0.53) between the mutant/wild-type ratio of K i values (enzyme resistance) and the mutant/wild-type ratio of viral IC90 values (antiviral resistance) for each of the HIV proteases and the viruses containing the identical enzyme. Assessing enzyme resistance by “vitality values”, which adjust the K i values with the catalytic efficiencies (k cat/K m), caused no significant improvement in the correlation with antiviral resistance. Therefore, our data suggest that measurements of enzyme inhibition with mutant proteases may be poorly predictive of the antiviral effect in resistant viruses even when mutations are restricted to the protease gene.