A non-infectious cell-based phenotypic assay for the assessment of HIV-1 susceptibility to protease inhibitors

OBJECTIVES

HIV-1 genotyping is widely accepted as a diagnostic tool to optimize therapy changes in patients whose antiretroviral regimen is failing. Phenotyping can substantially complement the information obtained from genotyping, especially in the presence of complex mutational patterns. However, drug susceptibility tests are laborious and require biosafety facilities. We describe the molecular mechanism of a non-infectious HIV-1 protease phenotypic assay in eukaryotic cells and validate its applicability as a tool for monitoring drug resistance.

METHODS

A cloning vector containing the fusion protein green fluorescent protein-HIV-1 protease (GFP-PR) was modified to facilitate the insertion of HIV-1 protease from infected subjects. Real-time quantitative PCR and western blot analysis were used to establish the molecular mechanism of the new phenotypic assay. The method was validated by analysing HIV-1 protease from 46 clinical isolates. Statistical comparisons were made between values obtained using our assay and those reported from alternative standardized phenotypic assays.

RESULTS

The capacity of HIV-1 protease to cleave cellular translation factors, such as the eukaryotic translation initiation factor 4 (eIF4GI) and the poly(A)-binding protein (PABP), led to cyclical accumulation of GFP that varied with the dose of protease inhibitors. Validation and comparison revealed a significant correlation with the Virco TYPE HIV-1 test (P < 0.0001, Spearman's ρ = 0.60), the Antivirogram test (P = 0.0001, Spearman's ρ = 0.60) and the Stanford HIVdb (P < 0.0001, Spearman's ρ = 0.69).

CONCLUSIONS

This cell-based non-infectious phenotypic method with a well-understood molecular mechanism was highly reliable and comparable to other widely used assays. The method can be used for both phenotyping of HIV-1 viral isolates resistant to protease inhibitors and screening of new protease inhibitors.

Transient treatment exclusively containing nucleoside analogue reverse transcriptase inhibitors in highly antiretroviral-experienced patients preserves viral benefit when a fully active therapy was initiated

BACKGROUND

We determined whether coformulated zidovudine/lamivudine/abacavir plus tenofovir could maintain immune status in comparison with a genotype-guided salvage regimen in highly pretreated patients.

METHOD

This was a randomized pilot control-arm study. The primary endpoint was the proportion of patients who maintained their CD4+ T-cell count at Week 48.

RESULTS

Thirteen patients were randomized to the study arm and 10 to the control arm. At 48 weeks, 8 (64%) patients in the study arm and 10 (100%) in the control arm maintained their immune status (p = .09). No new AIDS-defining events occurred. Three patients (27%) in the study arm and 5 (50%) in the control arm achieved an undetectable viral load (p = .39). When a fully suppressive regimen was initiated, 69% of patients in the study arm (9 patients) and 60% (6 patients) in the control arm reached <50 copies at 96 weeks (p = .98).

CONCLUSION

Although no statistically significant differences in immunological course were observed between the arms, the control group achieved better results after 48 weeks. This transient therapy could be reserved for specific patients in whom the risk of incomplete adherence or toxicity compromises efficacy while they are awaiting a fully active drug, without jeopardizing viral efficacy when a fully suppressive regimen is initiated.