A cell-free enzymatic activity assay for the evaluation of HIV-1 drug resistance to protease inhibitors

Due to their high frequency of genomic mutations, human retroviruses often develop resistance to antiretroviral drugs. The emergence of drug-resistant human immunodeficiency virus type 1 (HIV-1) is a significant obstacle to the effective long-term treatment of HIV infection. The development of a rapid and versatile drug-susceptibility assay would enable acquisition of phenotypic information and facilitate determination of the appropriate choice of antiretroviral agents. In this study, we developed a novel in vitro method, termed the Cell-free drug susceptibility assay (CFDSA), for monitoring phenotypic information regarding the drug resistance of HIV-1 protease (PR). The CFDSA utilizes a wheat germ cell-free protein production system to synthesize enzymatically active HIV-1 PRs directly from PCR products amplified from HIV-1 molecular clones or clinical isolates in a rapid one-step procedure. Enzymatic activity of PRs can be readily measured by AlphaScreen (Amplified Luminescent Proximity Homogeneous Assay Screen) in the presence or absence of clinically used protease inhibitors (PIs). CFDSA measurement of drug resistance was based on the fold resistance to the half-maximal inhibitory concentration (IC50) of various PIs. The CFDSA could serve as a non-infectious, rapid, accessible, and reliable alternative to infectious cell-based phenotypic assays for evaluation of PI-resistant HIV-1.

A Longitudinal Analysis of Healthcare Costs after Treatment Optimization following Genotypic Antiretroviral Resistance Testing: Does Resistance Testing pay off?

Objective

To assess the impact of antiretroviral therapy optimized by genotypic antiretroviral resistance testing (GRT) on healthcare costs over a 2-year period in patients after antiretroviral treatment failure.

Study design

Non-randomized, prospective, tertiary care, clinic-based study.

Patients

One-hundred and forty-two HIV patients enrolled in the ‘ZIEL’ study and the Swiss HIV Cohort Study who experienced virological treatment failure.

Methods

For all patients GRT was used to optimize the antiretroviral treatment regimen. All healthcare costs during 2 years following GRT were assessed using micro-costing. Costs were separated into ART medication costs and healthcare costs other than ART medication (that is, non-ART medication costs, in-patient costs and ambulatory [out-patient] costs). These cost estimates were then split into four consecutive 6-month periods (period 1–4) and the accumulated cost for each period was calculated. Univariate and multivariate regression modelling techniques for repeated measurements were applied to assess the changes of healthcare costs over time and factors associated with healthcare costs following GRT.

Results

Overall healthcare costs after GRT decreased over time and were significantly higher in period 1 (32%; 95% confidence interval [CI]: 18–47) compared with period 4. ART medication costs significantly increased by 1,017 (95% CI: 22–2,014) Swiss francs (CHF) from period 1–4, whereas healthcare costs other than ART medication costs decreased substantially by a factor of 3.1 (95% CI: 2.6–3.7) from period 1 to period 4. Factors mostly influencing healthcare costs following GRT were AIDS status, costs being 15% (95% CI: 6–24) higher in patients with AIDS compared with patients without AIDS, and baseline viral load, costs being 12% (95% CI: 6–17) higher in patients with each log increase in plasma RNA.

Conclusions

Optimized antiretroviral treatment regimens following GRT lead to a reduction of healthcare costs in patients with treatment failure over 2 years. Patients in a worse health state (that is, a positive AIDS status and high baseline viral load) will experience higher overall costs.

Low Genetic Barrier to Large Increases in HIV-1 Cross-Resistance to Protease Inhibitors during Salvage Therapy

HIV-1 resistance to protease inhibitors (PIs) is characterized by extensive cross-resistance within this drug class. Some PIs, however, appear less affected by cross-resistance and are often prescribed in salvage therapy regimens for patients who have failed previous PI treatment. To examine the capacity of HIV-1 to adapt to these treatment changes, we have followed the evolution of HIV-1 protease genotypes and phenotypes in 21 protease-inhibitor-experienced patients in whom 26 weeks of an aggressive salvage regimen associating lopinavir, amprenavir and ritonavir failed to suppress viral replication. Baseline genotypes exhibited a median of seven resistance mutations in the protease. After 26 weeks of treatment, changes in protease genotypes were seen in 13/21 patients. The evolution of these protease genotypes was rapid, with more than one-third of the changes occurring during the first 6 weeks. Although the mean number of additional mutations was small (2.15 new mutations at week 26) these mutations were sufficient to promote remarkable changes in resistance phenotype. In several patients, some of the new mutations were found to exist before salvage treatment as part of minority quasi-species. Thus, in the face of the strong pharmacological pressure exerted by combinations of PIs to which it has never been exposed, and in spite of limited cross-resistance to these drugs before salvage therapy, HIV-1 can rapidly adapt its resistance genotype and phenotype at a minimal evolutionary cost.

Updated European Recommendations for the Clinical Use of HIV Drug Resistance Testing

In most European countries, HIV drug resistance testing has become a routine clinical tool. However, its practical implementation in a clinical context is demanding. The European HIV Drug Resistance Panel was established to make recommendations to clinicians and virologists on this topic and to propose quality control measures. The panel recommends resistance testing for the following indications: i) drug-naive patients with acute or recent infection; ii) therapy failure, including suboptimal treatment response, when treatment change is considered; iii) pregnant HIV-1-infected women and paediatric patients with detectable viral load when treatment initiation or change is considered; and iv) genotype source patient when post-exposure prophylaxis is considered. In addition, for drug-naive patients with chronic infection in whom treatment is to be started, the panel suggests that resistance testing should be strongly considered and recommends testing the earliest sample for drug resistance if suspicion of resistance is high or prevalence of resistance in this population exceeds 10%. The panel does not favour genotyping over phenotype, however it is anticipated that genotyping will be used more often because of its greater accessibility, lower cost and faster turnaround time. For the interpretation of resistance data, clinically validated systems should be used to the greatest extent possible. It is mandatory that laboratories performing HIV resistance tests take regular part in quality assurance programs. Similarly, it is necessary that HIV clinicians and virologists take part in continuous education and meet regularly to discuss problematic clinical cases. Indeed, resistance test results should be used in the context of all other clinically relevant information for predicting therapy response. The panel also encourages the timely collection of epidemiological information to estimate the impact of transmission of resistant HIV and the prevalence of HIV-1 non-B subtypes in the different European countries.