Correlation between human immunodeficiency virus genotypic resistance and virologic response in patients receiving nelfinavir monotherapy or nelfinavir with lamivudine and zidovudine

Protease Inhibitors for the Treatment of HIV/AIDS: Recent Advances and Future Challenges

Acquired Immunodeficiency Syndrome (AIDS) is a chronic disease characterized by multiple life-threatening illnesses caused by a retro-virus, Human Immunodeficiency Virus (HIV). HIV infection slowly destroys the immune system and increases the risk of various other infections and diseases. Although, there is no immediate cure for HIV infection/AIDS, several drugs targeting various cruxes of HIV infection are used to slow down the progress of the disease and to boost the immune system. One of the key therapeutic strategies is Highly Active Antiretroviral Therapy (HAART) or ' AIDS cocktail' in a general sense, which is a customized combination of anti-retroviral drugs designed to combat the HIV infection. Since HAART's inception in 1995, this treatment was found to be effective in improving the life expectancy of HIV patients over two decades. Among various classes of HAART treatment regimen, Protease Inhibitors (PIs) are known to be widely used as a major component and found to be effective in treating HIV infection/AIDS. For the past several years, a variety of protease inhibitors have been reported. This review outlines the drug design strategies of PIs, chemical and pharmacological characteristics of some mechanism-based inhibitors, summarizes the recent developments in small molecule based drug discovery with HIV protease as a drug target. Further discussed are the pharmacology, PI drug resistance on HIV PR, adverse effects of HIV PIs and challenges/impediments in the successful application of HIV PIs as an important class of drugs in HAART regimen for the effective treatment of AIDS.

Urbanization, trace metal pollution, and malaria prevalence in the house sparrow

Anthropogenic pollution poses a threat for the environment and wildlife. Trace metals (TMs) are known to have negative effects on haematological status, oxidative balance, and reproductive success in birds. These pollutants particularly increase in concentration in industrialized, urbanized and intensive agricultural areas. Pollutants can also interfere with the normal functioning of the immune system and, as such, alter the dynamics of host-parasite interactions. Nevertheless, the impact of pollution on infectious diseases has been largely neglected in natural populations of vertebrates. Here, we used a large spatial scale monitoring of 16 house sparrow (Passer domesticus) populations to identify environmental variables likely to explain variation in TMs (lead, cadmium, zinc) concentrations in the feathers. In five of these populations, we also studied the potential link between TMs, prevalence of infection with one species of avian malaria, Plasmodium relictum, and body condition. Our results show that lead concentration is associated with heavily urbanized habitats and that areas with large woodland coverage have higher cadmium and zinc feather concentrations. Our results suggest that lead concentration in the feathers positively correlates with P. relictum prevalence, and that a complex relationship links TM concentrations, infection status, and body condition. This is one of the first studies showing that environmental pollutants are associated with prevalence of an infectious disease in wildlife. The mechanisms underlying this effect are still unknown even though it is tempting to suggest that lead could interfere with the normal functioning of the immune system, as shown in other species. We suggest that more effort should be devoted to elucidate the link between pollution and the dynamics of infectious diseases.

HIV-1 protease mutations and protease inhibitor cross-resistance

The effects of many protease inhibitor (PI)-selected mutations on the susceptibility to individual PIs are unknown. We analyzed in vitro susceptibility test results on 2,725 HIV-1 protease isolates. More than 2,400 isolates had been tested for susceptibility to fosamprenavir, indinavir, nelfinavir, and saquinavir; 2,130 isolates had been tested for susceptibility to lopinavir; 1,644 isolates had been tested for susceptibility to atazanavir; 1,265 isolates had been tested for susceptibility to tipranavir; and 642 isolates had been tested for susceptibility to darunavir. We applied least-angle regression (LARS) to the 200 most common mutations in the data set and identified a set of 46 mutations associated with decreased PI susceptibility of which 40 were not polymorphic in the eight most common HIV-1 group M subtypes. We then used least-squares regression to ascertain the relative contribution of each of these 46 mutations. The median number of mutations associated with decreased susceptibility to each PI was 28 (range, 19 to 32), and the median number of mutations associated with increased susceptibility to each PI was 2.5 (range, 1 to 8). Of the mutations with the greatest effect on PI susceptibility, I84AV was associated with decreased susceptibility to eight PIs; V32I, G48V, I54ALMSTV, V82F, and L90M were associated with decreased susceptibility to six to seven PIs; I47A, G48M, I50V, L76V, V82ST, and N88S were associated with decreased susceptibility to four to five PIs; and D30N, I50L, and V82AL were associated with decreased susceptibility to fewer than four PIs. This study underscores the greater impact of nonpolymorphic mutations compared with polymorphic mutations on decreased PI susceptibility and provides a comprehensive quantitative assessment of the effects of individual mutations on susceptibility to the eight clinically available PIs.

HIV-1 Subtypes and Response to Combination Antiretroviral Therapy in Europe

Background

Combination antiretroviral therapy (cART) may vary in ability to suppress viral load and increase CD4+ T-cell count in people infected with different HIV-1 subtypes, possibly due to differences in resistance development. Antiretroviral drugs have predominantly been developed in Western Europe/North America on the basis of the most prevalent subtype, B. However, non-B subtypes are increasingly spreading worldwide.

Objective

To compare virological and immunological response to cART between patients infected with B and non-B subtypes across Europe.

Design

EuroSIDA prospective, observational cohort with 11,928 HIV-1-infected patients.

Methods

Response to cART was analysed in patients with subtypes determined pre-cART, via multivariable logistic regression on the first measurements 6–12 months after starting cART. A virological response was defined as a viral load <500 copies/ml and immunological response as a CD4+ T-cell count increase of ≥100 cells/mm3.

Results

Forty-five percent of patients were antiretroviral naive at initiation of cART. Virological suppression was achieved by 58% of 689 subtype-B-infected patients and 66% of 102 non-B-infected patients ( P=0.159). After adjustment for potential confounders, there was no significant difference in odds of achieving virological suppression (non-B compared with B; odds ratio [OR]: 1.05, 95% confidence interval [CI]: 0.58–1.93, P=0.866). An immunological response was achieved by 43% of 753 B-infected patients and 48% of 114 non-B-infected patients ( P=0.334). After adjustment, there was no significant difference in odds of an immunological response (OR: 1.17, 95% CI: 0.73–1.87, P=0.524).

Conclusions

There was no evidence of significant differences in virological or immunological response to cART between patients infected with HIV-1 B and non-B subtypes.

Simplifying the treatment of HIV infection with ritonavir-boosted protease inhibitors in antiretroviral-experienced patients

PURPOSE

The rationale, advantages, and disadvantages of attempting to enhance the efficacy of a primary protease inhibitor (PI) with ritonavir in the management of HIV infection, especially in patients who have previously undergone highly active antiretroviral therapy (HAART), are discussed.

SUMMARY

PIs are pivotal components of the HAART regimens used to fight HIV infection. Long-term viral suppression remains a major clinical challenge. Certain pharmacologic features of many PIs, such as their limited oral bioavailability, necessitate burdensome dosage schedules, creating a barrier to patient adherence. Compliance may be further compromised by adverse events. Any factors that undermine adherence may increase the risk that plasma drug concentrations will be suboptimal and that viral resistance and subsequent treatment failure will develop. The pharmacokinetic enhancement, or "boosting," of PI levels with low-dose ritonavir may increase PI potency and efficacy, as well as decrease the emergence of viral resistance, reduce the pill burden, and simplify administration. A number of clinical studies suggest that PI-boosted regimens are safe and effective in HIV-infected patients who have been previously treated with antiretroviral agents, but more research is needed.

CONCLUSION

PI boosting with ritonavir can improve PI pharmacokinetics so that potency and efficacy are increased and regimens are simplified, thereby potentially reducing antiretroviral resistance and promoting patient adherence.

Activities of atazanavir (BMS-232632) against a large panel of human immunodeficiency virus type 1 clinical isolates resistant to one or more approved protease inhibitors

To evaluate the cross-resistance profile of the human immunodeficiency virus type 1 protease inhibitor (PI) atazanavir (BMS-232632), a panel of 551 clinical isolates exhibiting a wide array of PI resistance profiles and a variety of genotypic patterns were assayed for susceptibility to atazanavir and six other PIs: amprenavir, indinavir, lopinavir, nelfinavir, ritonavir, and saquinavir. In general, reductions in atazanavir susceptibility in vitro required several amino acid changes and were relatively modest in degree, and susceptibility was retained among isolates resistant to one or two of the currently approved PIs. There was a clear trend toward loss of susceptibility to atazanavir, as isolates exhibited increasing levels of cross-resistance to multiple PIs. Atazanavir appeared to have a distinct resistance profile relative to each of the other six PIs tested based on susceptibility comparisons against this panel of resistant isolates. Analysis of the genotypic profiles of 943 PI-susceptible and -resistant clinical isolates identified a strong correlation between the presence of amino acid changes at specific residues (10I/V/F, 20R/M/I, 24I, 33I/F/V, 36I/L/V, 46I/L, 48V, 54V/L, 63P, 71V/T/I, 73C/S/T/A, 82A/F/S/T, 84V, and 90M) and decreased susceptibility to atazanavir. While no single substitution or combination of substitutions was predictive of atazanavir resistance (change, >3.0-fold), the presence of at least five of these substitutions correlated strongly with loss of atazanavir susceptibility. Mutations associated with reduced susceptibility to each of the other six PIs were also determined.

Prevalence and virologic consequences of HIV-1 genotype mutations detected in a cohort of 161 Italian patients receiving a nelfinavir-based highly active antiretroviral therapy

A cross-sectional study was carried out in our tertiary care hospital between January 1998 and December 2001. All 161 consecutive patients naive to nelfinavir and who had received a nelfinavir-based highly active antiretroviral therapy (HAART) of at least 24-week duration were extrapolated from the 802 adult HIV-infected subjects treated with antiretroviral therapy. All cases of virologic failure were considered and viral genotyped. Virologic failure occurred in 80 out of 161 nelfinavir-treated patients, all belonging to the experienced group. On the whole, only 11 patients (7%) developed the D30N substitution, whose 6 was in association with the N88D mutation. Among the 80 failed patients, the M184V mutation was detected in 52 (65%), while only 7 patients showed simultaneously the M184V, T215Y and K103N substitutions. In our HIV-infected population receiving a nelfinavir-based HAART, the D30N mutation has shown a low absolute frequency, while the detection of M184V substitution and the simultaneous occurrence of M184V, T215Y and K103N mutations were related to a more favorable virological response.

Selection of high-level resistance to human immunodeficiency virus type 1 protease inhibitors

Protease inhibitors represent some of the most potent agents available for therapeutic strategies designed to inhibit human immunodeficiency virus type 1 (HIV-1) replication. Under certain circumstances the virus develops resistance to the inhibitor, thereby negating the benefits of this therapy. We have carried out selections for high-level resistance to each of three protease inhibitors (indinavir, ritonavir, and saquinavir) in cell culture. Mutations accumulated over most of the course of the increasing selective pressure. There was significant overlap in the identity of the mutations selected with the different inhibitors, and this gave rise to high levels of cross-resistance. Virus particles from the resistant variants all showed defects in processing at the NC/p1 protease cleavage site in Gag. Selections with pairs of inhibitors yielded similar patterns of resistance mutations. A virus that could replicate at near-toxic levels of the three protease inhibitors combined was selected. The pro sequence of this virus was similar to that of the viruses that had been selected for high-level resistance to each of the drugs singly. Finally, a molecular clone carrying the eight most common resistance mutations seen in these selections was characterized. The sequence of this virus was relatively stable during selection for revertants in spite of displaying poor processing at the NC/p1 site and having significantly reduced fitness. These results reveal patterns of drug resistance that extend to near the limits of attainable selective pressure with these inhibitors and confirm the patterns of cross-resistance for these three inhibitors and the attenuation of virion protein processing and fitness that accompanies high-level resistance.

Lamivudine can exert a modest antiviral effect against human immunodeficiency virus type 1 containing the M184V mutation

The M184V mutation in human immunodeficiency virus (HIV) reverse transcriptase is associated with high-level resistance to both (-)2',3'-dideoxy-3'-thiacytidine (3TC) and (-)2',3'-dideoxy-5-fluoro-3'-thiacytidine as well as low-level resistance to 2',3'-dideoxyinosine, 2',3'-dideoxycytidine, and abacavir. This mutation is also associated with diminished HIV replicative fitness as well as several functional changes in enzyme activity, including diminutions in polymerase processivity, pyrophosphorylysis, and nucleotide primer unblocking. Despite the fact that M184V encodes up to 1,000-fold resistance to 3TC, we asked whether this drug might still display some antiviral effect in regard to viruses containing this mutation. Cell-free assays revealed that high concentrations of 3TC triphosphate (i.e., >100 micro M) could affect chain termination and/or inhibit purified reverse transcriptase containing the M184V substitution. This effect became more pronounced with elongation of reverse transcriptase products. In newly infected cells (i.e., peripheral blood mononuclear cells), we found that the amount of full-length reverse transcriptase product was diminished in the presence of 2 to 10 micro M 3TC, although no decrease in the first product of the reverse transcriptase reaction, i.e., minus strong-stop DNA, was observed. In the presence of two other HIV inhibitors, e.g., nevirapine and indinavir, 3TC exerted additive effects in tissue culture at concentrations only marginally higher than the 50% inhibitory concentration (IC(50)). Reverse transcriptases cloned from clinical isolates harboring M184V in the context of multidrug resistance had similar IC(50) values for 3TC triphosphate compared to reverse transcriptase containing only the M184V mutation. These results suggest that viruses containing M184V can retain a higher degree of sensitivity to 3TC than previously assumed.

Drug resistance mutations and outcome of second-line treatment in patients with first-line protease inhibitor failure on nelfinavir-containing HAART

OBJECTIVES

To determine resistance mutations emerging in HIV-1-infected patients experiencing their first protease inhibitor (PI)-failure on nelfinavir-containing highly active antiretroviral therapy (HAART), and to assess virological response to rescue regimens.

METHODS

Plasma HIV-1 RNA from 24 patients failing nelfinavir-containing HAART was sequenced. Failure was defined as two consecutive measurements of viral load > 400 HIV-1 RNA copies/mL. Patients with previous failure on other PIs were excluded. Data on response to second-line treatment was extracted from patient files.

RESULTS

At failure primary protease mutations were found in 14 patients (58%). Ten patients had D30N (38%), five patients had L90M (19%), two patients had V82A/F (8%) and two patients had M46I/L (8%). Two patients had both D30N and L90M. Pronounced increases of secondary protease mutations were seen at codon 88 (Delta: 33%), codon 36 (Delta: 30%) and codon 71 (Delta: 17%). Of eight patients with N88D, seven also harboured D30N (P < 0.01). Polymorphisms at codon 63 were detected at baseline in all patients who developed primary resistance mutations at failure (P < 0.01). On rescue regimens, 78% achieved viral loads below limit of detection (BLD). The presence of primary protease mutations was not associated with a higher risk of failure on second-line treatment.

CONCLUSION

In patients failing nelfinavir-containing HAART, D30N was detected frequently and L90M occasionally. A pronounced accumulation of the secondary protease mutations N88D, M36I, and A71V/T was found, and D30N was strongly associated with N88D. A high proportion of patients became undetectable on second-line treatment and the presence of primary resistance mutations did not negatively affect the outcome of rescue regimens.

Managing failure to antiretroviral drugs in HIV-1-infected patients

Managing failure to antiretroviral therapies implies the addressing of several issues: the clinical stage, the virological and the immunological response to the failing regimen, together with drug history, resistance and exposure. Each of these issues will be discussed with the aim of providing useful data to design an optimal rescue antiretroviral therapy.

Catalytic efficiency and phenotype of HIV-1 proteases encoding single critical resistance substitutions

We have shown that a bacteriophage lambda genetic screen system may be useful in predicting the activity and phenotype of HIV-1 protease in the course of viral infection and antiretroviral therapy. This simple and rapid genetic screening system has been used here to characterize HIV-1 proteases encoding single primary resistance substitutions. Except for proteases with amino acid changes at positions 46 and 84, proteases containing single-resistance substitutions displayed a lower catalytic efficiency than the WT enzyme. Single mutants could be identified by their efficiency, demonstrating that modest differences in protease activity can be monitored with this simple assay. Overall, drug susceptibility could be reduced by introduction of single mutations. However, high-level protease inhibitor (PI) resistance was only achieved by multiple mutated proteases. The small but reproducible increase in resistance displayed by single mutants also demonstrated the ability of this genetic screen system for detecting minor reductions in drug susceptibility. These results show that the bacteriophage lambda genetic screen system used here is a useful tool in the analysis of specific contribution of mutations in the HIV protease-coding region or in specific cleavage sites that affect the process of PI resistance.

Virologic response to nelfinavir-based regimens: pharmacokinetics and drug resistance mutations (VIRAPHAR study)

OBJECTIVE

To assess the impact of HIV-1 protease and reverse transcriptase (RT) mutations, and pharmacokinetic parameters on virological responses to nelfinavir (NFV)-containing highly active antiretroviral therapy.

DESIGN

Naive or antiretroviral-experienced HIV-1-infected subjects were included in a non-randomized, observational cohort study and received two nucleoside RT inhibitors + NFV (750 mg three times per day or 1250 mg twice per day). Virologic success was defined as a virus load < 50 copies/ml for > 6 months.

METHODS

RT and protease genes were sequenced at baseline and at the time of virological failure. Plasma NFV trough concentration (Cmin), maximum concentration (Cmax), and AUC0-tau at steady-state were subjected to population pharmacokinetic analysis.

RESULTS

Patients (n = 154) enrolled between November 1998 and February 2000 started a twice per day (n = 84) or three times per day (n = 70) NFV-based regimen as first- (n = 48) or second-line therapy when protease inhibitor-naive (n = 64) or -experienced (n = 42). Median follow-up duration was 16 months. Virologic failure occurred in 88 patients. No significant differences were observed between twice per day and three times per day regimens. According to multivariate analysis, NFV Cmin and Cmax, CD4 cell count, number of baseline RT + protease gene mutations, D67N, M184V, T215F/Y in RT, and M36I in protease, were independent factors that were significantly predictive of failure. At failure, L10I, D30N, M36I, V77I, N88S/D or L90M protease mutations had emerged since baseline. Pharmacokinetic parameters were similar in patients with or without emergence of these neo-mutations. The more discriminating NFV Cmin efficacy-threshold was estimated to be 1 mg/l.

CONCLUSIONS

Our data confirm the association among individual pharmacokinetic parameters, genotype pattern and virological response to NFV-containing regimens.

Lopinavir-ritonavir versus nelfinavir for the initial treatment of HIV infection

BACKGROUND

Lopinavir is a newly developed inhibitor of human immunodeficiency virus (HIV) protease that, when formulated with ritonavir, yields mean trough plasma lopinavir concentrations that are at least 75 times as high as that needed to inhibit replication of wild-type HIV by 50 percent.

METHODS

We conducted a double-blind trial in which 653 HIV-infected adults who had not received antiretroviral therapy for more than 14 days were randomly assigned to receive either lopinavir-ritonavir (400 mg of lopinavir plus 100 mg of ritonavir twice daily) with nelfinavir placebo or nelfinavir (750 mg three times daily) with lopinavir-ritonavir placebo. All patients also received open-label stavudine and lamivudine. The primary efficacy end points were the presence of fewer than 400 HIV RNA copies per milliliter of plasma at week 24 and the time to the loss of virologic response through week 48.

RESULTS

At week 48, greater proportions of patients treated with lopinavir-ritonavir than of patients treated with nelfinavir had fewer than 400 copies of HIV RNA per milliliter (75 percent vs. 63 percent, P<0.001) and fewer than 50 copies per milliliter (67 percent vs. 52 percent, P<0.001). The time to the loss of virologic response was greater in the lopinavir-ritonavir group than in the nelfinavir group (hazard ratio, 2.0; 95 percent confidence interval, 1.5 to 2.7; P<0.001). The estimated proportion of patients with a persistent virologic response through week 48 was 84 percent for patients receiving lopinavir-ritonavir and 66 percent for those receiving nelfinavir. Both regimens were well tolerated, with the rate of discontinuation related to the study drugs at 3.4 percent among patients receiving lopinavir-ritonavir and 3.7 percent among patients receiving nelfinavir. Among patients with more than 400 copies of HIV RNA per milliliter at some point from week 24 through week 48, resistance mutations in HIV protease were demonstrated in viral isolates from 25 of 76 nelfinavir-treated patients (33 percent) and none of 37 patients treated with lopinavir-ritonavir (P<0.001).

CONCLUSIONS

For the initial treatment of HIV-infected adults, a combination regimen that includes lopinavir-ritonavir is well tolerated and has antiviral activity superior to that of a nelfinavir-containing regimen.

Antiretroviral prophylaxis of perinatal HIV-1 transmission and the potential impact of antiretroviral resistance

Since 1994, trials of zidovudine, zidovudine and lamivudine, and nevirapine have demonstrated that these antiretroviral drugs can substantially reduce the risk of perinatal HIV-1 transmission. With reductions in drug price, identification of simple, effective antiretroviral regimens to prevent perinatal HIV-1 transmission, and an increasing international commitment to support health care infrastructure, antiretrovirals for both perinatal HIV-1 prevention and HIV-1 treatment will likely become more widely available to HIV-1-infected persons in resource-limited countries. In the United States, widespread antiretroviral usage has been associated with increased antiretroviral drug resistance. This raises concern that drug resistance may reduce the effectiveness of perinatal antiretroviral prophylaxis as well as therapeutic intervention strategies. The purpose of this article is to review what is known about resistance and risk of perinatal HIV transmission, assess the interaction between antiretroviral resistance and the prevention of perinatal HIV-1 transmission, and discuss implications for current global prevention and treatment strategies.

Evolution of Antiretroviral Phenotypic and Genotypic Drug Resistance in Antiretroviral-Naive HIV-1-Infected Children Treated with Abacavir/Lamivudine, Zidovudine/Lamivudine or Abacavir/Zidovudine, with or without Nelfinavir (The Penta 5 Trial)

Purpose and methods

To describe the evolution of resistance to zidovudine (ZDV), lamivudine (3TC), abacavir (ABC) and nelfinavir (NFV), 113 previously untreated children in the PENTA 5 trial had resistance assayed at baseline, rebound and/or 24, 48, 72 weeks (VIRCO: phenotyping and genotyping with ‘Virtual Phenotype’ interpretation).

Results

At baseline, few reverse transcriptase mutations and no primary protease inhibitor mutations were observed. Time to detectable HIV-1 RNA with reduced phenotypic susceptibility to any drug was shortest in the ZDV+3TC arm (overall logrank P=0.02). Through a median follow-up of 55 weeks, at their last assessment 11 (28%), 16 (40%) and 13 (32%) children with detectable HIV-1 RNA and a resistance test available had mutations conferring resistance to none, one, or two or more trial drugs, respectively, according to the virtual phenotype. Reduced phenotypic susceptibility to ABC only occurred in the 3TC+ABC arm and required K65R and/or L74V in addition to M184V. NFV-resistant virus was selected slowly through D30N or L90M pathways, and selection of ZDV-resistant virus was rare.

Conclusions

Selection of 3TC-resistant virus was most frequent, followed by NFV and/or ABC; selection of ZDV-resistant virus was rare. Importantly, although in vitro, ABC selects for M184V as the first mutation, ABC did not select for M184V when combined with ZDV without 3TC. The most sustained HIV-1 RNA response was in the 3TC+ABC arm, but mutations conferring reduced susceptibility to 3TC and/or ABC evolved more frequently if virological failure occurred with 3TC+ABC than with ZDV+ABC.

Genotypic testing for human immunodeficiency virus type 1 drug resistance

There are 16 approved human immunodeficiency virus type 1 (HIV-1) drugs belonging to three mechanistic classes: protease inhibitors, nucleoside and nucleotide reverse transcriptase (RT) inhibitors, and nonnucleoside RT inhibitors. HIV-1 resistance to these drugs is caused by mutations in the protease and RT enzymes, the molecular targets of these drugs. Drug resistance mutations arise most often in treated individuals, resulting from selective drug pressure in the presence of incompletely suppressed virus replication. HIV-1 isolates with drug resistance mutations, however, may also be transmitted to newly infected individuals. Three expert panels have recommended that HIV-1 protease and RT susceptibility testing should be used to help select HIV drug therapy. Although genotypic testing is more complex than typical antimicrobial susceptibility tests, there is a rich literature supporting the prognostic value of HIV-1 protease and RT mutations. This review describes the genetic mechanisms of HIV-1 drug resistance and summarizes published data linking individual RT and protease mutations to in vitro and in vivo resistance to the currently available HIV drugs.

Salvage antiretroviral therapy in HIV infection

Highly-active antiretroviral (ARV) therapy (HAART) has lead to a sharp decline in AIDS-related morbidity and mortality. Treatment failure is a common, significant problem and as many as 50% of patients have detectable plasma HIV RNA despite being on combination ARV therapy. Clinicians must be knowledgeable about the reasons for treatment failure and the best options available for management. Treatment failure can occur because of non-compliance, drug discontinuation, lack of drug potency, inadequate drug plasma concentration and drug resistance. Strategies used when selecting salvage therapy include the use of resistance testing to choose a regimen, the exploitation of pharmacokinetic interactions by boosting protease inhibitor (PI) trough levels and counselling the patient on compliance. When selecting the agents to use in salvage therapy, the new regimen should ideally include as many new agents to which no or minimal resistance is anticipated and at least one new class of drugs if possible. Data on salvage therapy mostly comes from anecdotal reports and retrospective cohort studies. With a paucity of clinical trial data, clinicians are often forced to prescribe unproven regimens based on what is anticipated about cross-resistance and drug interactions. It is important that new agents and new targets continue to be developed as an increasing number of patients in practice have exhausted all treatment options.

Mutations in HIV-1 Reverse Transcriptase during Therapy with Abacavir, Lamivudine and Zidovudine in HIV-1-Infected Adults with No Prior Antiretroviral Therapy

Objective

To evaluate HIV-1 reverse transcriptase (RT) drug resistance in patients receiving abacavir, lamivudine and zidovudine therapy.

Methods

In a randomized, double-blind study, 173 anti-retroviral treatment-naive HIV-1-infected adults received abacavir/lamivudine/zidovudine or lamivudine/zidovudine for up to 48 weeks. After week 16, patients could switch to open-label abacavir/lamivudine/zidovudine, and those with plasma HIV-1 RNA (vRNA) >400 copies/ml could add other antiretrovirals. From weeks 16 to 48, samples with vRNA >400 copies/ml were collected for genotyping and phenotyping.

Results

At baseline, 90% of isolates were wild-type (WT). At week 16, vRNA was >400 copies/ml in seven of 72 (10%) patients receiving abacavir/lamivudine/zidovudine and in 41 of 66 (62%) receiving lamivudine/ zidovudine. At week 16, the genotypes in isolates from the abacavir/lamivudine/zidovudine group were M184V alone ( n=3 cases), WT ( n=3) and M184V plus thymidine analogue mutations (TAMs) ( n=1). The genotypes in isolates from the lamivudine/zidovudine group were M184V alone ( n=37), WT ( n=1) and M184V plus TAMs ( n=3). In the four cases where M184V plus TAMs were detected some mutations were present at baseline. Despite detectable M184V in 74% of patients on lamivudine/zidovudine, addition of abacavir with or without another antiretroviral therapy resulted in a reduction in vRNA, with 42 of 65 (65%) patients having week 48 vRNA <400 copies/ml (intent-to-treat with missing=failure). At week 48, the most common genotype was M184V alone in the abacavir/ lamivudine/zidovudine group (median vRNA 1–2 log10 below baseline), and M184V with or without TAMs in patients originally assigned to lamivudine/zidovudine. At week 48, phenotypic results were obtained for 11 isolates for patients from both arms, and all had reduced susceptibility to lamivudine but all remained sensitive to stavudine, all protease inhibitors and all non-nucleoside reverse transcriptase inhibitors. Three, three and two isolates had reduced susceptibility to abacavir, didanosine and zidovudine, respectively.

Conclusions

Abacavir retained efficacy against isolates with the M184V genotype alone. TAMs did not develop during 48 weeks of abacavir/lamivudine/zidovudine therapy and were uncommon when abacavir was added after 16 weeks of lamivudine/zidovudine therapy. Limited mutations upon rebound on this triple nucleoside combination allows for several subsequent treatment options.

Emergence of drug resistance mutations in a group of HIV-infected children taking nelfinavir-containing regimens

HIV-1-infected children are often treated with therapy regimens including protease inhibitors (PIs). We monitored the virologic response in a small group of pediatric patients undergoing therapy with regimens including the PI nelfinavir and determined whether new drug resistance mutations were present immediately after virologic failure. Seventeen reverse transcriptase inhibitor (RTI)-experienced children starting nelfinavir-containing therapy regimens were studied. After virologic failure, HIV-1 protease (PR) and RT sequences were examined for drug resistance mutations. Viral load levels decreased to <400 HIV RNA copies/ml in six patients and remained at <400 HIV RNA copies/ml in four patients. Three patients did not respond virologically; all three had mutations specific for one or more of their regimen drugs either before or soon after nelfinavir initiation. The virologic response was transient in eight patients whose viral loads did not decrease to <400 HIV RNA copies/ml. Genotypic data from seven of the eight patients revealed mutations specific for one or more of their regimen drugs after virologic rebound. PI resistance mutations occurred in eight patients: D30N in six, and L90M in three. In three patients, the only new mutation after failure was the RT mutation M184V. Despite virologic failure, sustained increases in CD4+ lymphocyte counts were noted in eight patients. We conclude that in this small group of pediatric patients, virologic failure occurred in all patients whose viral loads did not become undetectable after the switch to a nelfinavir-containing regimen. After failure, new drug resistance mutations were found in either PR or RT. Studies of larger cohorts are warranted to determine whether HIV-1 genotypic data can help in the formulation of effective salvage therapies in children.

Comparative CD4 T-cell responses of reverse transcriptase inhibitor therapy with or without nelfinavir matched for viral exposure

BACKGROUND

Therapy of HIV infection with protease inhibitors (PIs) may be associated with improvements in CD4 T-cell number via a mechanism that is independent of effects on plasma viral load (VL).

PURPOSE

To compare CD4 responses of patients who receive reverse transcriptase inhibitor (RTI) therapies with or without a PI, matched for viral exposure.

METHODS

Patient data were analyzed from two prospective randomized trials of antiviral therapy with or without nelfinavir. Total viral exposure over 24 weeks was estimated by viral area under the curve (AUC), which reflects baseline viral load, slope of virologic decay, viral nadir, and duration of suppression. Patients were stratified into quartiles on the basis of viral AUC, and CD4 T-cell responses were evaluated between PI-containing and RTI-only treatment groups within each quartile.

RESULTS

In both trials, patients receiving nelfinavir had greater CD4 T-cell increases than patients receiving RTI alone. Analysis of variance modeling revealed increased CD4 T-cell responses in PI-treated groups at all time points after the second week. These differences were significant (p <.05) at weeks 12, 24, 28, 32, 36, 40, and 48 in one study, and weeks 1, 2, 4, 6, 8, 12, 16, 20, 24, 28, 32, 36, and 44 in the other. Within quartiles matched for viral AUC, absolute CD4 T-cell change from baseline was greater in the PI-treated patients at 84% (101/120) of time points analyzed.

CONCLUSION

Nelfinavir-containing therapy is associated with enhanced increases in CD4 T-cell number compared to RTI therapy alone with equivalent antiviral effect. These data suggest that PIs influence CD4 T-cell number through a nonvirologic effect.