Analysis of HIV cross-resistance to protease inhibitors using a rapid single-cycle recombinant virus assay for patients failing on combination therapies

Abstract

To assess the patterns of HIV phenotypic cross-resistance to protease inhibitors (PI) in patients experiencing viral load rebound on combination therapy including a PI. Phenotypic analysis of sensitivity to indinavir, nelfinavir, saquinavir, ritonavir and amprenavir was carried out using a single-cycle recombinant virus assay. Viral protease was sequenced by automated dideoxynucleotide chain termination. Of the 108 patients studied, 68 had received indinavir, 50 ritonavir, 25 saquinavir and eight nelfinavir. The majority (71%) had received only one PI. The incidence of cross-resistance between indinavir, nelfinavir, ritonavir and saquinavir was high (60-90%). Cross-resistance to amprenavir was less frequent (37-40%). However there was some correlation between levels of sensitivity to amprenavir and indinavir (r2=0.34; P2 These results suggest that, although the total number of protease mutations correlates with the degree of cross-resistance, the specific mechanisms accounting for primary resistance and for cross-resistance may be different.