Genetic correlates of in vivo viral resistance to indinavir, a human immunodeficiency virus type 1 protease inhibitor.

Indinavir (IDV) (also called CRIXIVAN, MK-639, or L-735,524) is a potent and selective inhibitor of the human immunodeficiency virus type 1 (HIV-1) protease. During early clinical trials, in which patients initiated therapy with suboptimal dosages of IDV, we monitored the emergence of viral resistance to the inhibitor by genotypic and phenotypic characterization of primary HIV-1 isolates. Development of resistance coincided with variable patterns of multiple substitutions among at least 11 protease amino acid residues. No single substitution was present in all resistant isolates, indicating that resistance evolves through multiple genetic pathways. Despite this complexity, all of 29 resistant isolates tested exhibited alteration of residues M-46 (to I or L) and/or V-82 (to A, F, or T), suggesting that screening of these residues may be useful in predicting the emergence of resistance. We also extended our previous finding that IDV-resistant viral variants exhibit various patterns of cross-resistance to a diverse panel of HIV-1 protease inhibitors. Finally, we noted an association between the number of protease amino acid substitutions and the observed level of IDV resistance. No single substitution or pair of substitutions tested gave rise to measurable viral resistance to IDV. The evolution of this resistance was found to be cumulative, indicating the need for ongoing viral replication in this process. These observations strongly suggest that therapy should be initiated with the most efficacious regimen available, both to suppress viral spread and to inhibit the replication that is required for the evolution of resistance.

In vivo emergence of HIV-1 variants resistant to multiple protease inhibitors.

Inhibitors of the human immunodeficiency virus type 1 (HIV-1) protease have entered clinical study as potential therapeutic agents for HIV-1 infection. The clinical efficacy of HIV-1 reverse transcriptase inhibitors has been limited by the emergence of resistant viral variants. Similarly, variants expressing resistance to protease inhibitors have been derived in cell culture. We now report the characterization of resistant variants isolated from patients undergoing therapy with the protease inhibitor MK-639 (formerly designated L-735,524). Five of these variants, isolated from four patients, exhibited cross-resistance to all members of a panel of six structurally diverse protease inhibitors. This suggests that combination therapy with multiple protease inhibitors may not prevent loss of antiviral activity resulting from resistance selection. In addition, previous therapy with one compound may abrogate the benefit of subsequent treatment with a second inhibitor.

L-735,524: an orally bioavailable human immunodeficiency virus type 1 protease inhibitor.

To date, numerous inhibitors of the human immunodeficiency virus type 1 protease have been reported, but few have been studied extensively in humans, primarily as a consequence of poor oral bioavailability in animal models. L-735,524 represents a class of human immunodeficiency virus type 1 protease inhibitors, termed hydroxyaminopentane amides, that incorporate a basic amine into the hydroxyethylene inhibitor backbone. L-735,524 is a potent inhibitor of virus replication in cell culture and inhibits the protease-mediated cleavage of the viral precursor polyproteins that results in the production of noninfectious progeny viral particles. The compound is effective against viruses resistant to reverse transcriptase inhibitors and is synergistically active when used in combination with reverse transcriptase inhibitors. Most importantly, L-735,524 exhibits good oral bioavailability and plasma pharmacokinetic profiles in two species of laboratory animals by using clinically acceptable formulations. Accordingly, the compound was selected for evaluation of safety and pharmacokinetic studies in humans.

Comparison of vancomycin and penicillin for viral isolation.

Penicillin was compared with vancomycin for use in diagnostic virology to inhibit bacterial contamination of clinical specimens. Vancomycin when combined with gentamicin and amphotericin B was found to be more effective in lowering the overall contamination rate than when penicillin was combined with these antibiotics (penicillin group, 14.9% versus vancomycin group, 6.2%; P less than 0.001). Of the contaminants grown in the presence of penicillin, 72% were gram-positive cocci, primarily coagulase-negative staphylococci. The number of gram-positive contaminants in the presence of vancomycin was reduced to zero. There was little difference in the rates of gram-negative rod or fungus contamination. The viral isolation rate in noncontaminated specimens was similar with either penicillin or vancomycin, but was reduced when specimens became contaminated. The time for virus detection and the morphology of cytopathology were similar in penicillin- and vancomycin-treated specimens. Vancomycin is an effective alternative to penicillin in reducing the growth of contaminants in viral isolation specimens.