Prevalence and incidence of resistance to zidovudine and other antiretroviral drugs

Long-Acting Rilpivirine (RPV) Preexposure Prophylaxis Does Not Inhibit Vaginal Transmission of RPV-Resistant HIV-1 or Select for High-Frequency Drug Resistance in Humanized Mice

The antiretroviral drug rilpivirine was developed into a long-acting formulation (RPV LA) to improve adherence for preexposure prophylaxis (PrEP) to prevent HIV-1 transmission. A concern is that RPV LA will not inhibit transmission of drug-resistant HIV-1 and may select for drug-resistant virus. In female humanized mice, we found that RPV LA inhibited vaginal transmission of WT or 3-fold RPV-resistant HIV-1 but not virus with 30-fold RPV resistance. In animals that became infected despite RPV LA PrEP, WT HIV-1 dissemination was delayed until genital and plasma RPV concentrations waned. RPV resistance was detected at similar low frequencies in untreated and PrEP-treated mice that became infected. These results indicate the importance of maintaining RPV at a sustained threshold after virus exposure to prevent dissemination of HIV-1 after vaginal infection and low-frequency resistance mutations conferred low-level resistance, suggesting that RPV resistance is difficult to develop after HIV-1 infection during RPV LA PrEP.

As a long-acting formulation of the nonnucleoside reverse transcriptase inhibitor rilpivirine (RPV LA) has been proposed for use as preexposure prophylaxis (PrEP) and the prevalence of transmitted RPV-resistant viruses can be relatively high, we evaluated the efficacy of RPV LA to inhibit vaginal transmission of RPV-resistant HIV-1 in humanized mice. Vaginal challenges of wild-type (WT), Y181C, and Y181V HIV-1 were performed in mice left untreated or after RPV PrEP. Plasma viremia was measured for 7 to 10 weeks, and single-genome sequencing was performed on plasma HIV-1 RNA in mice infected during PrEP. RPV LA significantly prevented vaginal transmission of WT HIV-1 and Y181C HIV-1, which is 3-fold resistant to RPV. However, it did not prevent transmission of Y181V HIV-1, which has 30-fold RPV resistance in the viruses used for this study. RPV LA did delay WT HIV-1 dissemination in infected animals until genital and plasma RPV concentrations waned. Animals that became infected despite RPV LA PrEP did not acquire new RPV-resistant mutations above frequencies in untreated mice or untreated people living with HIV-1, and the mutations detected conferred low-level resistance. These data suggest that high, sustained concentrations of RPV were required to inhibit vaginal transmission of HIV-1 with little or no resistance to RPV but could not inhibit virus with high resistance. HIV-1 did not develop high-level or high-frequency RPV resistance in the majority of mice infected after RPV LA treatment. However, the impact of low-frequency RPV resistance on virologic outcome during subsequent antiretroviral therapy still is unclear.

IMPORTANCE The antiretroviral drug rilpivirine was developed into a long-acting formulation (RPV LA) to improve adherence for preexposure prophylaxis (PrEP) to prevent HIV-1 transmission. A concern is that RPV LA will not inhibit transmission of drug-resistant HIV-1 and may select for drug-resistant virus. In female humanized mice, we found that RPV LA inhibited vaginal transmission of WT or 3-fold RPV-resistant HIV-1 but not virus with 30-fold RPV resistance. In animals that became infected despite RPV LA PrEP, WT HIV-1 dissemination was delayed until genital and plasma RPV concentrations waned. RPV resistance was detected at similar low frequencies in untreated and PrEP-treated mice that became infected. These results indicate the importance of maintaining RPV at a sustained threshold after virus exposure to prevent dissemination of HIV-1 after vaginal infection and low-frequency resistance mutations conferred low-level resistance, suggesting that RPV resistance is difficult to develop after HIV-1 infection during RPV LA PrEP.

Molecular diagnostics: parallels between infectious disease and emerging oncology testing

Evolving molecular techniques used in the clinical laboratory are becoming increasingly important across nearly all fields of medicine. An increased understanding of carcinogenesis and the use of targeted cancer therapies has resulted in a demand for new types of molecular oncology test to help in cancer diagnosis and as tools to predict response to targeted therapeutics for cancer patients. Understanding the need for and the function of these emerging molecular oncology tests by both clinicians and laboratorians is often problematic. Although many of these molecular testing techniques and strategies are relatively new to oncology, similar testing has been performed in the field of infectious diseases for many years and is now widely accepted and understood. Recognizing the parallels between the molecular testing that is now standard for infectious diseases and testing being introduced to aid in the care of cancer patients will accelerate the acceptance, implementation and correct utilization of molecular assays for oncology.

Bifunctional inhibition of HIV-1 reverse transcriptase: a first step in designing a bifunctional triphosphate

The onset of resistance to approved anti-AIDS drugs by HIV necessitates the search for novel inhibitors of HIV-1 reverse transcriptase (RT). Developing single molecular agents concurrently occupying the nucleoside and nonnucleoside binding sites in RT is an intriguing idea but the proof of concept has so far been elusive. As a first step, we describe molecular modeling to guide focused chemical syntheses of conjugates having nucleoside (d4T) and nonnucleoside (TIBO) moieties tethered by a flexible polyethylene glycol (PEG) linker. A triphosphate of d4T-6PEG-TIBO conjugate was successfully synthesized that is recognized as a substrate by HIV-1 RT and incorporated into a double-stranded DNA.

Addition of extended zidovudine to extended nevirapine prophylaxis reduces nevirapine resistance in infants who were HIV-infected in utero

BACKGROUND

In the Post-Exposure Prophylaxis of Infants (PEPI)-Malawi trial, most women received single-dose nevirapine (NVP) at delivery, and infants in the extended study arms received single-dose NVP along with 1 week of daily zidovudine (ZDV), followed by either extended daily NVP or extended daily NVP and ZDV up to 14 weeks of age. Although extended NVP prophylaxis reduces the risk of postnatal HIV transmission, it may increase the risk of NVP resistance among infants who are HIV-infected despite prophylaxis.

METHODS

We analyzed 88 infants in the PEPI-Malawi trial who were HIV-infected in utero and who received prophylaxis for a median of 6 weeks prior to HIV diagnosis. HIV genotyping was performed using the ViroSeq HIV Genotyping System.

RESULTS

At 14 weeks of age, the proportion of infants with NVP resistance was lower in the extended NVP and ZDV arm than in the extended NVP arm (28/45, 62.2% vs. 37/43, 86.0%; P = 0.015). None of the infants had ZDV resistance. Addition of extended ZDV to extended NVP was associated with reduced risk of NVP resistance at 14 weeks if prophylaxis was stopped by 6 weeks (54.5 vs. 85.7%, P = 0.007) but not if prophylaxis was continued beyond 6 weeks (83.3 vs. 87.5%, P = 1.00).

CONCLUSION

Addition of extended ZDV to extended NVP prophylaxis significantly reduced the risk of NVP resistance at 14 weeks in infants who were HIV-infected in utero, provided that HIV infection was diagnosed and the prophylaxis was stopped by 6 weeks of age.

Characterization of the interacting domain of the HIV-1 fusion peptide with the transmembrane domain of the T-cell receptor

HIV infection is initiated by the fusion of the viral membrane with the target T-cell membrane. The HIV envelope glycoprotein, gp41, contains a fusion peptide (FP) in the N terminus that functions together with other gp41 domains to fuse the virion with the host cell membrane. We recently reported that FP co-localizes with CD4 and T-cell receptor (TCR) molecules, co-precipitates with TCR, and inhibits antigen-specific T-cell proliferation and pro-inflammatory cytokine secretion. Molecular dynamic simulation implicated an interaction between an alpha-helical transmembrane domain (TM) of the TCRalpha chain (designated CP) and the beta-sheet 5-13 region of the 16 N-terminal amino acids of FP (FP(1-16)). To correlate between the theoretical prediction and experimental data, we synthesized a series of mutants derived from the interacting motif GALFLGFLG stretch (FP(5-13)) and investigated them structurally and functionally. The data reveal a direct correlation between the beta-sheet structure of FP(5-13) and its mutants and their ability to interact with CP and induce immunosuppressive activity; the phenylalanines play an important role. Furthermore, studies with fluorescently labeled peptides revealed that this interaction leads to penetration of the N terminus of FP and its active analogues into the hydrophobic core of the membrane. A detailed understanding of the molecular interactions mediating the immunosuppressive activity of the FP(5-13) motif should facilitate evaluating its contribution to HIV pathology and its exploitation as an immunotherapeutic tool.

Strategies for the optimal sequencing of antiretroviral drugs toward overcoming and preventing drug resistance

Drug regimens now offer more potent, less toxic and more durable choices in the treatment of HIV disease than ever before. This has led to a need to consider the convenient, sequential use of active antiretroviral combinations. Ritonavir-boosted protease inhibitors (PIs) can now be potentially sequenced in a manner that uses the least cross-resistance-prone PI at the start of therapy while leaving the most cross-resistance-prone drug for later, if the latter retains activity against commonly observed drug-resistant forms. Similarly, such new drugs as tenofovir, abacavir and emtricitabine, which make up current nucleoside backbone options, can be potentially sequenced, since each of them selects for an individual pattern of resistance mutations that are generally distinct from those selected by previously popular thymidine analogs such as zidovudine and stavudine.

A randomised trial comparing genotypic and virtual phenotypic interpretation of HIV drug resistance: the CREST study

Objectives:

The aim of this study was to compare the efficacy of different HIV drug resistance test reports (genotype and virtual phenotype) in patients who were changing their antiretroviral therapy (ART).

Design:

Randomised, open-label trial with 48-week followup.

Setting:

The study was conducted in a network of primary healthcare sites in Australia and New Zealand.

Participants:

Patients failing current ART with plasma HIV RNA > 2000 copies/mL who wished to change their current ART were eligible. Subjects were required to be > 18 years of age, previously treated with ART, have no intercurrent illnesses requiring active therapy, and to have provided written informed consent.

Interventions:

Eligible subjects were randomly assigned to receive a genotype (group A) or genotype plus virtual phenotype (group B) prior to selection of their new antiretroviral regimen.

Outcome Measures:

Patient groups were compared for patterns of ART selection and surrogate outcomes (plasma viral load and CD4 counts) on an intention-to-treat basis over a 48-week period.

Results:

Three hundred and twenty seven patients completing > one month of followup were included in these analyses. Resistance tests were the primary means by which ART regimens were selected (group A: 64%, group B: 62%; p = 0.32). At 48 weeks, there were no significant differences between the groups for mean change from baseline plasma HIV RNA (group A: 0.68 log copies/mL, group B: 0.58 log copies/mL; p = 0.23) and mean change from baseline CD4+ cell count (group A: 37 cells/mm³, group B: 50 cells/mm³; p = 0.28).

Conclusions:

In the absence of clear demonstrated benefits arising from the use of the virtual phenotype interpretation, this study suggests resistance testing using genotyping linked to a reliable interpretive algorithm is adequate for the management of HIV infection.

Background: Antiretroviral drugs are used to treat patients with HIV infection, with good evidence that they improve prognosis. However, mutations develop in the HIV genome that allow it to evade successful treatment—known as drug resistance—and such mutations are known against every class of antiretroviral drug. Resistance can cause treatment failure and limit the treatment options available. Different types of tests are often used to detect resistance and to work out whether patients should switch to a different drug regimen. Currently, the different types of tests include genotype testing (direct sequencing of genes from virus samples infecting a patient); phenotype testing (a test that assesses the sensitivity of a patient's HIV sample to different drugs), and virtual phenotype testing (a way of interpreting genotype data that estimates the likely viral response to different drugs). The researchers of this study did a trial to find out whether providing an additional virtual phenotype report would be beneficial to patients, as compared with a genotype report alone. The main outcome was HIV viral load after 12 months of treatment, but the researchers also looked at differences in drug regimens prescribed, number of treatment changes in the study, and changes in CD4+ (the type of white blood cell infected by HIV) counts.

What this trial shows: The researchers found that the main endpoint of the trial (HIV viral load after 12 months) was no different in patients whose clinicians had received a virtual phenotype report as well as a genotype report, compared with those who had received a genotype report alone. In addition, the average number of drugs prescribed was no different between patients in the two different arms of the trial, and there was no difference in number of drug regimen changes, and no change in immune response (measured using CD4+ cell levels). However, more drugs predicted to be sensitive were prescribed by clinicians who got both a genotype and virtual phenotype report, as compared with clinicians who received only the genotype report.

Strengths and limitations: The size of the trial (338 patients recruited) was large enough to properly test the hypothesis that providing a virtual phenotype report as well as a genotype report would result in lower HIV viral loads. Randomization of patients to either intervention ensured that the comparison groups were well-balanced, and the researchers also tested whether selection bias had affected the results (i.e., testing for the possibility that clinicians could predict which intervention participants would receive, and change recruitment into the trial as a result). They found no evidence for selection bias occurring within the trial. However, interpreting the results is difficult because the trial did not directly compare the two different testing platforms, but rather looked at whether providing a virtual phenotype report as well as a genotype report was better than providing a genotype report alone. The investigators also acknowledge that since the trial was conducted, the cutoffs for interpreting genotype information as resistant have been lowered. The findings may therefore not translate precisely to the current situation.

Contribution to the evidence: Other cohort studies and clinical trials have shown that patients offered resistance testing respond better to antiretroviral therapy compared with those who were not, but the clinical effectiveness of different resistance testing methods is not known. This study provides additional data on the respective benefits of genotype testing versus genotype plus provision of virtual phenotype. Another trial comparing genotype versus virtual phenotype has also found that the different interpretation methods perform similarly.

Prevalence of transmitted HIV-1 drug resistance and the role of resistance algorithms: data from seroconverters in the CASCADE collaboration from 1987 to 2003

OBJECTIVES

To examine factors influencing the rate of transmitted drug resistance (TDR) among seroconverters, with particular emphasis on 3 widely used genotypic drug resistance algorithms.

METHODS

The study used data from CASCADE (Concerted Action on Seroconversion to AIDS and Death in Europe), a collaboration of seroconverter cohorts in Europe and Canada. Genotypic resistance data were derived within 18 months of the last seronegative test or date of laboratory evidence of acute infection and before the initiation of antiretroviral therapy. The Stanford algorithm was used to analyze each individual's nucleotide sequence. A multivariate logistic model was used to assess independent relationships between the presence of TDR and exposure category, sex, age at seroconversion, and year of seroconversion. The paper also describes 3 alternative definitions of resistance: the Stanford algorithm, the key resistance mutations defined by the International AIDS Society, and the Agence Nationale de Recherches sur le Sida (ANRS) algorithm.

RESULTS

Forty-five of 438 patients (10.3%) seroconverting between 1987 and 2003 were infected with a drug-resistant HIV-1 variant. Forty patients (9.1%) showed resistance mutations to only 1 class of antiretroviral drugs, 2 (0.5%) to 2 classes, and 3 (0.7%) to 3 classes of antiretroviral therapy. It was suggested that individuals seroconverting later in calendar time were more likely to have TDR (relative risk 3.89 and 95% CI: 0.84 to 18.02, and relative risk 4.69 and 95% CI: 1.03 to 21.31, for 1996-1999 and 2000-2003, respectively, compared with pre-1996; P trend = 0.08). This trend was apparent regardless of the definition of TDR used. The total estimated proportion of individuals with TDR varied between 10.3% and 15.5% according to which definition was used.

CONCLUSIONS

Evidence was found for the rise of TDR over time. A specific definition of what constitutes TDR rather than a simple list of mutations is needed.

The impact of the M184V substitution on drug resistance and viral fitness

Treatment of HIV/AIDS with antiretroviral therapy can result in HIV-1 drug resistance, limiting its use. Resistance mutations arise prior to therapy due to errors in HIV-1 replication, and are also spread by sexual and other modes of transmission. However, it is also generally believed that resistance is due to multiple drug mutations to any single or combination of antiretroviral agents selected during viral replication in the presence of incompletely suppressive drug regimens. In the case of protease inhibitors and most nucleoside analog reverse transcriptase inhibitors, drug resistance is due to the accumulation of mutations in the HIV-1 protease and reverse transcriptase genes respectively. However, in the case of non-nucleoside reverse transcriptase inhibitors, a single primary drug mutation is usually sufficient to abrogate antiviral activity. This is also true of certain specific mutations, such as M184V in the reverse transcriptase enzyme, resulting in resistance to the nucleoside analog, lamivudine (Epivir, GlaxoSmithKline). However, it is thought that lamivudine may still contribute to the effectiveness of antiretroviral therapy, even after the appearance of the M184V mutation. M184V may affect sensitivity to other drugs, such as zidovudine (Retrovir, GlaxoSmithKline), in HIV-1 variants that already contain resistance mutations to zidovudine, during concomitant treatment with lamivudine. M184V also has a positive effect on HIV-1 RT fidelity, reducing spontaneous HIV mutagenesis. Processivity of the reverse transcriptase enzyme may be affected by mutations such as M184V, and this may be a major determinant of viral replication fitness.

Activity, safety, and immunological effects of hydroxyurea added to didanosine in antiretroviral-naive and experienced HIV type 1-infected subjects: a randomized, placebo-controlled trial, ACTG 307

We performed a 24-week, placebo-controlled, comparative trial of hydroxyurea (HU) monotherapy, didanosine(ddI) monotherapy, and the combination of ddI plus HU administered as 1000 mg qd or 1500 mg qd in antiretroviral-naive and experienced subjects with CD4+ lymphocyte counts of 200-700 cells/mm3. Enrollment included 134 subjects. HU enhanced the antiviral activity of ddI by 1.0 log10 copies/ml after 8 weeks of therapy, with sustained responses over 24 weeks. HU alone over 4 weeks had no effect. Lamivudine resistance had little impact on antiretroviral activity when examined across treatment arms. Increases in absolute CD4+ T cell counts, but not CD4+ T cell percentages, were less in subjects who received HU compared to ddI monotherapy, and lymphoproliferative responses to antigenic and mitogenic stimuli were not altered. Subjects who received HU 1500 mg were more likely to experience dose-limiting hematological toxicities compared to those who received 1000 mg, without any additional antiviral benefit. HU may continue to have a role as a component of HIV therapy.

Reverse transcriptase-based DNA vaccines against drug-resistant HIV-1 tested in a mouse model

Drug resistance is becoming a problem in the treatment of the human immunodeficiency virus type one (HIV-1). To obtain therapeutic DNA vaccines that would target multiple drug-resistance (DR) mutations, we cloned genes for DR HIV-1 reverse transcriptase (RT) and codon-optimized synthetic genes encoding clusters of human CTL epitopes located at the sites of DR-mutations (RT minigenes) and antibody and CTL-epitope tags. Expression of RT genes/minigenes in eukaryotic cells was confirmed by Western blotting and immunofluoresence staining with RT- or tag-specific antibodies. Immunization of mice with DR-RT gene induced no RT-specific antibodies. Immunization of HLA-A(*)0201-transgenic mice with RT minigenes induced RT-specific cellular responses detected by interferon-gamma secretion. This documents first steps in creating therapeutic vaccine against drug-resistant HIV strains.

Update on didanosine

Didanosine (ddl) has been a cornerstone of HIV management since it was made available in October 1991. Didanosine was originally introduced as an alternative to zidovudine (ZDV) for patients who were intolerant of ZDV or experienced disease progression during ZDV monotherapy. Didanosine is now used extensively as an integral component of multidrug combination regimens in both adults and children with HIV infection, and is now available for once-daily administration in the United States, Canada, and Europe. The recently approved Videx EC is an enteric-coated didanosine capsule dosed as one capsule, once daily. This paper provides an update of recently published studies on the use of ddl in combination anti-HIV therapy. In particular, these studies examine the rationale for the use of ddl as first-line anti-HIV therapy, and describe newer findings concerning its long-term efficacy, side effects, compliance, resistance, and once-daily use. The increased survival of HIV-infected patients is largely attributed to the introduction of the triple combination drug therapy but is probably also due to the long-term clinical efficacy of ddl.

Frequency of mutations conferring resistance to nucleoside reverse transcriptase inhibitors in human immunodeficiency virus type 1-infected patients in Korea

A nested PCR and direct sequencing methods were used to define human immunodeficiency virus type 1(HIV-1) reverse transcriptase codons 41 to 219 in DNA from 127 peripheral blood mononuclear cell samples obtained from 35 patients treated with nucleoside reverse transcriptase inhibitors (NRTI). The follow-up period after the initiation of NRTI therapy was 61.8 +/- 31 months (mean and standard deviation). In addition to NRTI therapy, 32 of 35 patients were simultaneously treated with Korean red ginseng. The annual decrease in the CD4(+) T-cell count over 5 years was 13.2/microl. Twenty-eight (80%) of the 35 patients had mutations conferring resistance to NRTI. The frequencies of K70R, T215S/Y/F (i.e., mutation of T at codon 215 to S, Y, or F), D67N/E, K219Q, T69N/S/A, M41L, and L210W mutations conferring resistance to zidovudine were 57.6, 36.4, 36.4, 27.2, 24.2, 21.2, and 12.1%, respectively. Mutations conferring resistance to didanosine and lamivudine were detected in 2 (L74V and M184I; 14.2%) of 11 patients tested and in 4 (M184V; 57%) of 7 patients tested, respectively. In particular, the frequency of T69N/S/A increased sharply after more than 48 months of zidovudine monotherapy. However, Q151M was not detected. As the first report on the frequency of NRTI resistance mutations in Korea, our data suggest that genotypic antiretroviral drug testing should be considered for the design of better drug regimens to improve the management of HIV-1-infected patients.

Effect of target cell availability on HIV-1 production in vitro

OBJECTIVE

The recovery of CD4 target cells following antiretroviral therapy may facilitate virus production and escape from antiretroviral suppression. To address this hypothesis, we directly examined whether the CD4 target cell number increases viral production in the presence of suboptimal therapy.

DESIGN

The effect of the CD4 T cell number on HIV-1 replication with a suboptimal dose of zidovudine was studied in vitro.

METHODS

Varying numbers of CD4 T cells were infected with HIV-1 and treated with 1 nM zidovudine. Virus production was measured by p24 antigen capture enzyme-linked immunosorbent assay. Partial sequencing of HIV-1 pol was performed to assess zidovudine-resistant mutations.

RESULTS

Wild type virus production was found to increase eightfold in cultures with 100 x 10(4) cells compared with cultures with 10 x 10(4) cells. The IC90 of zidovudine was 4 logs higher in cultures with 16 x 10(4) cells compared with cultures with 1 x 10(4) cells. No zidovudine-resistant mutations were found.

CONCLUSION

Target cell availability may play a direct role in wild type HIV-1 resurgence following therapy.

Use of the sensitive/less-sensitive (detuned) EIA strategy for targeting genetic analysis of HIV-1 to recently infected blood donors

OBJECTIVE

To corroborate the validity of the recently developed sensitive/less sensitive (S/LS) dual enzyme immunoassay (EIA) strategy for the detection of recently infected individuals and to genetically analyze recently transmitted strains of HIV-1 in a US blood donor population.

DESIGN

The S/LS EIA strategy was used to identify 33 recently infected subjects among 281 enrolled HIV-1 seropositive blood donors (from a total of 410 HIV-1 infected subjects identified from 5 230 463 blood donations screened by participating US blood centers in 1995-1996).

METHODS

We analysed three host response and viral characteristics were associated with recent HIV-1 infection: rapidly increasing EIA optical density (OD) values, genetically homogeneous env gene quasispecies, and putative non-syncytium inducing env V3 loop sequences. The drug resistance genotypes of the recently transmitted strains were determined by DNA sequencing.

RESULTS

Increasing EIA OD values, clonal HIV-1 quasispecies and V3 loop sequences with inferred NSI phenotypes were generally detected in LS EIA non-reactive samples. Thirty-two subtype B and one CRF02_AG recombinant HIV-1 were detected. Genetic evidence for drug resistance to zidovudine (K70R) and non-nucleoside analog reverse transcriptase inhibitors (V108I) was detected in one strain each, and three other strains showed the presence of accessory protease inhibitor resistance mutations.

CONCLUSIONS

Immunologic and virologic results further substantiate the validity of the S/LS EIA strategy for the detection of recent infections and illustrate its use for targeting molecular and epidemiological investigations to incident cases identified from large cross-sectional screening programs, rather than the more costly and logistically difficult longitudinal studies.

Long-term intake of Korean red ginseng in HIV-1-infected patients: development of resistance mutation to zidovudine is delayed

We have observed that CD4+ T cell counts in human immunodeficiency virus (HIV)-1-infected patients treated with only Korean red ginseng (KRG) are maintained or even increased for a prolonged period. In the present study, we investigated whether the development of resistance mutations in reverse transcriptase (RT) to zidovudine (ZDV) is delayed by combined therapy with KRG and ZDV. Nested polymerase chain reaction (PCR) and direct sequencing methods were used to define RT codons 41, 67, 70, 210, 215 and 219 of the HIV-1 pol gene in DNA from peripheral blood mononuclear cells (PBMC) samples from 18 patients. Nine of these eighteen patients were in the KRG group and had been treated with KRG for 60 +/- 15 months (range: 38-82) and ZDV, and nine were in the control group and had been treated with ZDV only. The patients in the KRG group had been treated with ZDV for 75 +/- 24 months, and CD4+ T cell counts were maintained from 239 +/- 85 to 234 +/- 187 microliters-1 (P > 0.05) during the study period, whereas the patients in the control group had been treated with ZDV for 51 +/- 31 months, and their CD4+ T cell counts decreased from 272 +/- 97 to 146 +/- 154 microliters-1 (P < 0.01). In samples within 24 months of ZDV therapy, the overall incidence of 6 resistance mutations to ZDV was 4.2% and 47% in the KRG and control group (P < 0.01), respectively. In samples after 24 months of therapy, the incidence was 21.7% and 56.3% in the KRG and control group (P < 0.01), respectively. These data suggest that the maintenance of CD4+ T cell counts by ZDV and KRG-intake for a prolonged period might be indirectly associated with delayed development of resistance to ZDV by KRG-intake.

Prevalence and predictive value of overweight in an urban HIV care clinic

OBJECTIVE

To determine the prevalence and predictive value of overweight in an urban HIV clinic.

METHODS

Medical records of all new adult, nonpregnant registrants in 1996 in an urban HIV clinic with at least one height and weight measurement were reviewed. Body mass index (BMI) at clinic enrollment was calculated, and prevalence of overweight was thus determined. The subsequent clinical course of the overweight group was compared with that of a randomly selected group of gender-stratified non-overweight patients.

RESULTS

At baseline, 12.6% of men and 32.5% of women were overweight. Female gender and lack of AIDS diagnosis were independently associated with overweight. More than one half of women and 19.6% of men were overweight at some point during the study. Providers were more likely to properly acknowledge underweight than overweight. Among patients without AIDS, there was a trend toward slower disease progression and lower viral load in overweight patients, despite similar baseline CD4+ lymphocyte counts and similar time to initiation of highly active antiretroviral therapy. In multivariate proportional hazards analyses, lower baseline BMI and falling BMI during follow-up were independently predictive of progression to AIDS.

CONCLUSIONS

Overweight was a common and underrecognized finding, particularly among women. Overweight patients may progress more slowly to AIDS than non-overweight patients.

Analysis of HIV-1 mutation patterns in patients failing antiretroviral therapy

The emergence of mutations encoding drug resistance is supposed to be a significant limitation to the clinical efficacy of inhibitor compounds directed against specific HIV-1 enzymatic targets. We have used a commercial test (Visible Genetics Inc., Paris, France) to study the prevalence of mutations occurred in HIV-1 protease and reverse transcriptase (RT) genes in 93 HIV-1 infected patients treated with at least one regimen containing a protease inhibitor (PI) and failing to the current therapeutic regimen. Protease mutations conferring resistance to at least one PI were detected in 46/93 (49.4%) of strains, 25 (26.8%) of which showed resistance to all PIs. Reverse transcriptase mutations conferring resistance to at least one RT inhibitor were detected in 57/93 (61.2%) of strains, 18 (19.3%) of which showed resistance to all RT inhibitors. The most frequent RT mutations were T215Y/F, M41L, and M184V (41.9, 40.8, and 40.8%, respectively), while L63P, L10R/V, and A71V/T (58, 41.9, and 34.4%, respectively) were the most represented protease substitutions. We have found no mutations encoding for multiple dideoxynucleoside resistance (Q151M or T69SS). Twelve of our patients (12.9%) had no mutation encoding drug resistance and were completely sensitive to all RT and protease inhibitors. Therefore, not all virological failures are caused by HIV-1 genomic resistance.

Delavirdine: a review of its use in HIV infection

Delavirdine, a bisheteroarylpiperazine derivative, is a non-nucleoside reverse transcriptase inhibitor (NNRTI) that allosterically binds to HIV-1 reverse transcriptase, inhibiting both the RNA- and DNA-directed DNA polymerase functions of the enzyme. Delavirdine in combination with nucleoside reverse transcriptase inhibitors (NRTIs) produced sustained reductions in plasma viral loads and improvements in immunological responses in large randomised, double-blind, placebo-controlled studies of 48 to 54 weeks' duration. In patients with advanced HIV infection, triple therapy with delavirdine, zidovudine and lamivudine, didanosine or zalcitabine for 1 year significantly prolonged the time to virological failure compared with dual therapy (delavirdine plus zidovudine or 2 NRTIs; p < 0.0001). After 50 weeks' treatment, plasma HIV RNA levels were below the limit of detection (LOD; <50 copies/ml) for 40% of patients receiving triple therapy but for only 6% of those receiving dual NRTI therapy. Preliminary results suggest that delavirdine also has beneficial effects on surrogate markers as a component of protease inhibitor-containing triple or quadruple regimens. At 16 to 48 weeks, the minimum mean reduction in plasma viral load from baseline was 2.5 log10 copies/ml and mean CD4+ counts increased by 100 to 313 cells/microl. The proportion of patients with plasma HIV RNAlevels below the LOD (usually 200 to 500 copies/ml) ranged from 48 to 100% after > or = 16 weeks. Delavirdine was also effective as a component of saquinavir soft gel capsule-containing salvage regimens. Since delavirdine shares a common metabolic pathway (cytochrome P450 3A pathway) with other NNRTIs, HIV protease inhibitors and several drugs used to treat opportunistic infections in patients infected with HIV, the drug is associated with a number of pharmacokinetic interactions. Some of these drug interactions are clinically significant, necessitating dosage adjustments or avoidance of co-administration. Delavirdine is not recommended for use with lovastatin, simvastatin, rifabutin, rifampicin, sildenafil, ergot derivatives, quinidine, midazolam, carbamazepine, phenobarbital or phenytoin. Importantly, the drug favourably increases the plasma concentration of several protease inhibitors. Delavirdine is generally well tolerated. Skin rash is the most frequently reported adverse effect, occurring in 18 to 50% of patients receiving delavirdine-containing combination therapy in clinical trials. Although a high proportion of patients developed a rash, it was typically mild to moderate in intensity, did not result in discontinuation or adjustment of treatment in most patients and resolved quickly. The occurrence of Stevens-Johnson syndrome was rare (1 case in 1,000 patients). A retrospective analysis of pooled clinical trial data indicated that there was no significant difference in the incidence of liver toxicity, liver failure or noninfectious hepatitis between delavirdine-containing and non-delavirdine-containing antiretroviral treatment groups. In addition, the incidence of lipodystrophy, metabolic lipid disorders, hyperglycaemia and hypertriglyceridaemia was not significantly different between these 2 treatment groups.

CONCLUSIONS

In combination with NRTIs. delavirdine produces sustained improvements in surrogate markers of HIV disease and prolongs the time to virological failure in adult patients with HIV infection. Preliminary data of delavirdine as a component of protease inhibitor-containing triple or quadruple highly active antiretroviral therapy regimens indicate that patients achieve marked improvements in virological and immunological markers. The drug is generally well tolerated, with a transient skin rash, typically of mild to moderate intensity, being the most common adverse effect. Delavirdine is an effective component of recommended antiretroviral treatment strategies for adult patients with HIV infection and, in combination with 2 NRTIs as a first-line therapy, the drug has the advantage of sparing protease inhibitors for subsequent use. Since delavirdine favourably increases plasma concentrations of several protease inhibitors, the drug may also be beneficial as a component of salvage therapy in combination with protease inhibitors.

Genotypic, phenotypic, and modeling studies of a deletion in the beta3-beta4 region of the human immunodeficiency virus type 1 reverse transcriptase gene that is associated with resistance to nucleoside reverse transcriptase inhibitors

Point mutations and inserts in the beta3-beta4 region of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) are associated with resistance to nucleoside analog inhibitors. This report describes HIV-1 strains from seven patients that were found to have a 3-bp deletion in the beta3-beta4 region of the RT gene. These patient strains also had a mean of 6.2 drug resistance-associated mutations in their RT genes (range, 3 to 10 mutations). The deletion was most frequently found in strains with the Q151M mutation. Nonnucleoside RT inhibitor mutations were found in six of seven strains. Culture-based drug sensitivity assays showed that deletion-containing isolates had reduced susceptibility to four to eight RT inhibitors. Site-directed mutagenesis experiments showed that the deletion alone conferred reduced susceptibility to nucleoside analogs. Changes in the three-dimensional models of the RT deletion mutants were consistently observed at the beta3-beta4 loop and at helices C and E in both the presence and the absence of dTTP. Loss of hydrogen bonds between the RT and dTTP were also observed in the RT deletion mutant. These results suggest that the deletion in the RT gene contributes to resistance to several nucleoside analogs through a complex interaction with other mutations in the RT gene.

Cost effectiveness of human immunodeficiency virus postexposure prophylaxis for healthcare workers

OBJECTIVE

The United States Public Health Service (USPHS) published recommendations for human immunodeficiency virus (HIV) postexposure prophylaxis (PEP) of healthcare workers in May 1998. The aim of this study was to analyse the cost effectiveness of the USPHS PEP guidelines.

DESIGN AND SETTING

This was a modelling study in the setting of the US healthcare system in 1989. The analysis was performed from the societal perspective; however, only HIV healthcare costs were considered and health-related losses of productivity were not included.

METHODS

A decision tree incorporating a Markov model was created for 4 PEP strategies: the current USPHS recommendations, triple drug therapy, zidovudine monotherapy or no prophylaxis. A probabilistic sensitivity analysis using a Monte Carlo simulation was performed. Confidence intervals (CIs) around cost-effectiveness estimates were estimated by a bootstrapping method.

RESULTS

The costs (in 1997 US dollars) per quality-adjusted life-year (QALY) save by each strategy were as follows: monotherapy $US688 (95% CI: $US624 to $US750); USPHS recommendations $US5211 (95% CI: $US5126 to $US5293); and triple drug therapy $US8827 (95% CI: $US8715 to $US8940). The marginal cost per year of life saved was: USPHS recommendations $US81 987 (95% CI: $US80 437 to $US83 689); triple drug therapy $US970 451 (95% CI: $US924 786 to $US 1 014 429). Sensitivity testing showed that estimates of the probability of seroconversion for each category of exposure were most influential, but did not change the order of strategies in the baseline analysis. With the prolonged HIV stage durations and increased costs associated with recent innovations in HIV therapy, the marginal cost effectiveness of the USPHS PEP strategy was decreased to $US62 497/QALY saved. All 3 intervention strategies were cost effective compared with no postexposure prophylaxis.

CONCLUSIONS

Current USPHS PEP recommendations are marginally cost effective compared with monotherapy, but the additional efficacy of triple drug therapy for all risk categories is rewarded by only a small reduction in HIV infections at great expense. For the foreseeable future, assuming innovations in therapy that employ expensive drug combinations earlier in the HIV disease course to extend life expectancy and the increasing prevalence of HIV drug resistance, our model supports the use of the USPHS PEP guidelines.

Trends in Prevention of Mother-to-Child Transmission of HIV-1

Mother-to-child transmission (MTCT) of HIV is the predominant mode of HIV transmission in children worldwide. It is estimated that around 1.3 million children are living with HIV and that approximately 1,600 children are infected with HIV each day. Numerous clinical trials using antiretroviral drugs to reduce MTCT of HIV-1 have shown that perinatal transmission can be reduced effectively. Based on the PACTG 076 study administering a long antenatal zidovudine regimen, a signific ant reduction in vertical HIV-1 transmission has been achieved in the developed world. Trials conducted in developing countries have shown that perinatal transmission can be reduced effectively even using shorter and less costly antiretroviral regimens. Prevention of MTCT interventions have been implemented on a large scale in a number of developing countries.

Rapid Detection of Point Mutations by Fluorescence Resonance Energy Transfer and Probe Melting Curves in Candida Species

Background: The LightCyclerTM combines rapid amplification of nucleic acids in glass capillaries with melting curve analysis based on fluorescence resonance energy transfer for the sensitive detection of point mutations in various settings, such as drug resistance and hereditary diseases. Point mutations leading to an altered structure of lanosteroldemethylase, the target enzyme of the fungistatic azoles, are an important mechanism of acquired resistance in Candida albicans.

Methods: We screened 13 fluconazole-resistant C. albicans and 21 fluconazole-resistant C. tropicalis strains (minimum inhibitory concentration &gt;128 mg/L), isolated from patients with AIDS, for the presence of defined point mutations by comparing conventional cycle sequencing with a newly designed LightCycler-based assay.

Results: In C. tropicalis, 5 of 21 isolates showed the wild-type sequence, and 8 of 21 showed the homozygous nucleotide exchange thymine to cytosine at position 1554 (T1554C). A heterozygous genotype was detected in 8 of 21 isolates by the LightCycler, but in only 3 of 21 isolates by conventional cycle sequencing. In 2 of 13 C. albicans isolates, a homozygous point mutation leading to an amino acid exchange at position 464 (glycine to serine) was detected in both assays.

Conclusion: The LightCycler technique offers standardized, fast, sensitive, and reproducible detection of point mutations in different Candida spp.

Specific recognition of lamivudine-resistant HIV-1 by cytotoxic T lymphocytes

OBJECTIVE

The reverse transcriptase (RT) M184V mutation within the HLA-A2-restricted HIV-1 cytotoxic T lymphocyte (CTL) epitope VL9 (VIYQYMDDL; RT 179-187) not only induces drug escape against lamivudine but also abolished recognition by a CTL clone derived from a long-term non-progressor. To test whether the variant VL9 epitope containing the M184V mutation represents a new CTL epitope, we studied recognition of this epitope in a cohort of HLA-A2-positive HIV-1-infected patients.

METHODS

Peripheral blood mononuclear cells isolated from 28 HIV-1-infected patients were stimulated with the peptide VIYQYVDDL, containing the M1 84V mutation. Outgrowing cell lines were tested for specific recognition in a standard chromium-release assay.

RESULTS

In one subject, a CTL line could be isolated recognizing the peptide VIYQYVDDL in conjunction with HLA-A2. The CTL clone also recognized the M1841 mutation, but it failed to recognize the wild-type epitope VIYQYMDDL.

CONCLUSION

CTL can specifically recognize lamivudine-resistant HIV-1 variants. Therefore, the cellular immune response could have an important influence on the control of drug-resistant virus. Furthermore, this demonstrates that the immune system can generate new CTL specificities even in patients with advanced disease, as the M184V HIV variants emerges only after drug treatment. Specific immunotherapy against this epitope might be helpful in delaying or preventing lamivudine resistance.

Human immunodeficiency virus drug resistance testing: state of the art in genotypic and phenotypic testing of antiretrovirals

Antiretroviral drugs have significantly reduced death rates from the acquired immunodeficiency syndrome in the United States. They are highly effective in reducing viral replication, but their utility is threatened by rapid development of drug resistance. Although antiretroviral drug resistance testing is available by either genotyping or phenotyping, no consensus guidelines have been published regarding the appropriate use or interpretation of these new tests. Even though their role in clinical practice is not defined, it is important for clinicians to become familiar with relative advantages and disadvantages of genotypic and phenotypic testing and various mechanisms of antiretroviral resistance.

Mechanism of inhibition of the human immunodeficiency virus type 1 reverse transcriptase by d4TTP: an equivalent incorporation efficiency relative to the natural substrate dTTP

Among the clinically used nucleoside analogue inhibitors that target human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT), there is little detailed mechanistic information on the interactions of 2',3'-didehydro-2', 3'-dideoxythymidine-5'-triphosphate (d4TTP) with the enzyme. primer-template complex and how these interactions compare with those of the natural substrate, dTTP. Using a pre-steady-state kinetic analysis, we found that d4TTP was incorporated by HIV-1 RT just as efficiently as dTTP during both DNA- and RNA-dependent DNA synthesis. To our knowledge, these results represent the first observation of a 3'-modified nucleoside triphosphate analogue that has an incorporation efficiency comparable to that observed for the natural substrate during DNA synthesis by HIV-1 RT. This information provides a mechanistic basis for understanding the inhibition of HIV-1 RT by d4TTP as well as insight into the clinically observed lack of d4T resistance mutations in HIV-1 RT isolated from AIDS patients.

Didanosine: an updated review of its use in HIV infection

Didanosine, like zidovudine, stavudine and lamivudine, is a nucleoside analogue reverse transcriptase inhibitor (NRTI). In the target cell for HIV, didanosine is converted to its active moiety, dideoxyadenosine-5'-triphosphate (ddATP), which inhibits HIV reverse transcriptase and terminates viral DNA growth. It is now well established that didanosine therapy produces beneficial effects on virological and immunological markers of HIV disease and improves clinical outcome in adults or children with HIV infection. In numerous clinical trials, pronounced and sustained decreases in plasma HIV RNA levels and increases in CD4+ cell counts occurred in previously untreated or antiretroviral therapy-experienced patients treated with didanosine in combination with at least 1 other antiretroviral drug; zidovudine, stavudine, lamivudine, nevirapine, nelfinavir and hydroxyurea (hydroxycarbamide) are among the drugs that have been given in combination with didanosine. Of note, HIV RNA levels decreased to below the limits of detection in some patients receiving triple or dual therapy with didanosine-containing regimens. In double-blind, placebo-controlled trials, triple therapy with didanosine, zidovudine and nevirapine was significantly more effective than dual therapy with various combinations of these agents in improving surrogate disease markers in treatment-naive patients and in delaying disease progression or death in treatment-experienced patients with advanced disease. Improvements in virological and immunological markers were greater with didanosine-containing triple regimens than with dual therapy or monotherapy in comparative trials. Triple therapy with didanosine, stavudine and indinavir showed efficacy similar to that of various other triple therapy regimens in nonblind comparative trials. Comparator regimens included combinations of stavudine, lamivudine plus indinavir, zidovudine, lamivudine plus indinavir and didanosine, stavudine and nevirapine. Combination therapy with didanosine plus hydroxyurea as dual therapy or with a third agent produced marked and sustained decreases in HIV RNA levels in the plasma and in lymph nodes. Combination therapy with didanosine and zidovudine delays disease progression and prolongs survival in patients with intermediate or advanced HIV infection. In large, randomised, double-blind, clinical trials, dual therapy with didanosine plus zidovudine was significantly more effective than zidovudine monotherapy in preventing disease progression and prolonging survival in previously untreated or antiretroviral therapy-experienced patients with intermediate or advanced HIV infection. Pancreatitis and peripheral neuropathy are serious adverse effects of didanosine. These effects are dose-related and usually reversible after discontinuation of treatment. Nausea, vomiting, diarrhoea and/or abdominal pain have been reported in patients receiving treatment with the drug.

CONCLUSIONS

Didanosine is an effective and generally well tolerated drug in previously untreated and antiretroviral therapy-experienced patients with HIV infection. Given once or twice daily, it has an important role as a component of triple combination regimens for the treatment of patients with symptomatic or asymptomatic HIV infection.

Efficacy of antiretroviral agents against murine replication-competent retrovirus infection in human cells

Retroviral vectors for gene therapy are designed to minimize the occurrence of replication-competent retrovirus (RCR); nonetheless, it is possible that a vector-derived RCR could establish an infection in a patient. Since the efficacy of antiretroviral agents can be impacted by interactions between virus, host cell, and drug, five commonly used antiretroviral drugs were evaluated for their abilities to inhibit the replication of a murine leukemia virus (MLV)-derived RCR in human cells. The results obtained indicate that the combination of nucleoside analogs zidovudine and dideoxyinosine with the protease inhibitor indinavir effectively inhibits MLV-derived RCR replication in three human cell lines. In addition, MLV-derived RCR was found to be inherently resistant to the nucleoside analogs lamivudine and stavudine, suggesting that mutations conferring resistance to nucleoside analogs in human immunodeficiency virus type 1 have the same effect even in an alternative viral backbone.

New aza-dipeptide analogues as potent and orally absorbed HIV-1 protease inhibitors: candidates for clinical development

On the basis of previously described X-ray studies of an enzyme/aza-dipeptide complex,8 aza-dipeptide analogues carrying N-(bis-aryl-methyl) substituents on the (hydroxethyl)hydrazine moiety have been designed and synthesized as HIV-1 protease inhibitors. By using either equally (12) or orthogonally (13) protected dipeptide isosteres, symmetrically and asymmetrically acylated aza-dipeptides can be synthesized. This approach led to the discovery of very potent inhibitors with antiviral activities (ED50) in the subnanomolar range. Acylation of the (hydroxethyl)hydrazine dipeptide isostere with the L-tert-leucine derivative 29 increased the oral bioavailability significantly when compared to the corresponding L-valine or L-isoleucine derivatives. The bis(L-tert-leucine) derivatives CGP 75355, CGP 73547, CGP 75136, and CGP 75176 combine excellent antiviral activity with high blood concentration after oral administration. Furthermore, they show no cross-resistance with saquinavir-resistant strains and maintain activity against indinavir-resistant ones. Consequently they qualify for further profiling as potential clinical candidates.