Prevalence of the HIV-1 protease mutation I47A in clinical practice and association with lopinavir resistance

Viral proteases as therapeutic targets

Some medically important viruses-including retroviruses, flaviviruses, coronaviruses, and herpesviruses-code for a protease, which is indispensable for viral maturation and pathogenesis. Viral protease inhibitors have become an important class of antiviral drugs. Development of the first-in-class viral protease inhibitor saquinavir, which targets HIV protease, started a new era in the treatment of chronic viral diseases. Combining several drugs that target different steps of the viral life cycle enables use of lower doses of individual drugs (and thereby reduction of potential side effects, which frequently occur during long term therapy) and reduces drug-resistance development. Currently, several HIV and HCV protease inhibitors are routinely used in clinical practice. In addition, a drug including an inhibitor of SARS-CoV-2 main protease, nirmatrelvir (co-administered with a pharmacokinetic booster ritonavir as Paxlovid®), was recently authorized for emergency use. This review summarizes the basic features of the proteases of human immunodeficiency virus (HIV), hepatitis C virus (HCV), and SARS-CoV-2 and discusses the properties of their inhibitors in clinical use, as well as development of compounds in the pipeline.

Temporal Trends in HIV-1 Mutations Used for the Surveillance of Transmitted Drug Resistance

In 2009, a list of nonpolymorphic HIV-1 drug resistance mutations (DRMs), called surveillance DRMs (SDRMs), was created to monitor transmitted drug resistance (TDR). Since 2009, TDR increased and antiretroviral therapy (ART) practices changed. We examined the changing prevalence of SDRMs and identified candidate SDRMs defined as nonpolymorphic DRMs present on ≥ 1 expert DRM list and in ≥0.1% of ART-experienced persons. Candidate DRMs were further characterized according to their association with antiretrovirals and changing prevalence. Among NRTI-SDRMs, tenofovir-associated mutations increased in prevalence while thymidine analog mutations decreased in prevalence. Among candidate NRTI-SDRMs, there were six tenofovir-associated mutations including three which increased in prevalence (K65N, T69deletion, K70G/N/Q/T). Among candidate NNRTI-SDRMs, six that increased in prevalence were associated with rilpivirine (E138K/Q, V179L, H221Y) or doravirine (F227C/L) resistance. With the notable exceptions of I47A and I50L, most PI-SDRMs decreased in prevalence. Three candidate PI-SDRMs were accessory darunavir-resistance mutations (L10F, T74P, L89V). Adding the candidate SDRMs listed above was estimated to increase NRTI, NNRTI, and PI TDR prevalence by 0.1%, 0.3%, and 0.3%, respectively. We describe trends in the prevalence of nonpolymorphic HIV-1 DRMs in ART-experienced persons. These data should be considered in decisions regarding SDRM list updates and TDR monitoring.

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.

The Geogenomic Mutational Atlas of Pathogens (GoMAP) web system

We present a new approach for pathogen surveillance we call Geogenomics. Geogenomics examines the geographic distribution of the genomes of pathogens, with a particular emphasis on those mutations that give rise to drug resistance. We engineered a new web system called Geogenomic Mutational Atlas of Pathogens (GoMAP) that enables investigation of the global distribution of individual drug resistance mutations. As a test case we examined mutations associated with HIV resistance to FDA-approved antiretroviral drugs. GoMAP-HIV makes use of existing public drug resistance and HIV protein sequence data to examine the distribution of 872 drug resistance mutations in ∼ 502,000 sequences for many countries in the world. We also implemented a broadened classification scheme for HIV drug resistance mutations. Several patterns for geographic distributions of resistance mutations were identified by visual mining using this web tool. GoMAP-HIV is an open access web application available at http://www.bio-toolkit.com/GoMap/project/

Complex patterns of protease inhibitor resistance among antiretroviral treatment-experienced HIV-2 patients from Senegal: implications for second-line therapy

Protease inhibitor (PI)-based antiretroviral therapy (ART) can effectively suppress HIV-2 plasma load and increase CD4 counts; however, not all PIs are equally active against HIV-2, and few data exist to support second-line therapy decisions. To identify therapeutic options for HIV-2 patients failing ART, we evaluated the frequency of PI resistance-associated amino acid changes in HIV-2 sequences from a cohort of 43 Senegalese individuals receiving unboosted indinavir (n = 18 subjects)-, lopinavir/ritonavir (n = 4)-, or indinavir and then lopinavir/ritonavir (n = 21)-containing ART. Common protease substitutions included V10I, V47A, I54M, V71I, I82F, I84V, L90M, and L99F, and most patients harbored viruses containing multiple changes. Based on genotypic data, we constructed a panel of 15 site-directed mutants of HIV-2ROD9 containing single- or multiple-treatment-associated amino acid changes in the protease-encoding region of pol. We then quantified the susceptibilities of the mutants to the HIV-2 "active" PIs saquinavir, lopinavir, and darunavir using a single-cycle assay. Relative to wild-type HIV-2, the V47A mutant was resistant to lopinavir (6.3-fold increase in the mean 50% effective concentration [EC50]), the I54M variant was resistant to darunavir and lopinavir (6.2- and 2.7-fold increases, respectively), and the L90M mutant was resistant to saquinavir (3.6-fold increase). In addition, the triple mutant that included I54M plus I84V plus L90M was resistant to all three PIs (31-, 10-, and 3.8-fold increases in the mean EC50 for darunavir, saquinavir, and lopinavir, respectively). Taken together, our data demonstrate that PI-treated HIV-2 patients frequently harbor viruses that exhibit complex patterns of PI cross-resistance. These findings suggest that sequential PI-based regimens for HIV-2 treatment may be ineffective.

Lopinavir/ritonavir-based antiretroviral therapy in human immunodeficiency virus type 1-infected naive children: rare protease inhibitor resistance mutations but high lamivudine/emtricitabine resistance at the time of virologic failure

BACKGROUND

Lopinavir/ritonavir (LPV/r) is now the protease inhibitor regimen of choice in the first-line antiretroviral therapy for children <6 years of age.

METHODS

We included all the human immunodeficiency virus (HIV) type 1-infected highly active antiretroviral therapy (HAART)-naive children who started an LPV/r-based regimen between 2000 and 2009 at the Necker Hospital (Paris, France). Virologic failure (VF) was defined as an HIV-RNA ≥50 copies/mL. Resistance genotypic test was performed in case of VF.

RESULTS

A total of 43 children were included at a median age of 4.8 years (1.8-8.0). Median level of HIV RNA and percentage of CD4 cell count was 5.5 log₁₀ copies/mL (4.6-6) and 15% (8-27.5), respectively. HAART included LPV/r and 2 nucleoside reverse-transcriptase inhibitors, mainly lamivudine (3TC), zidovudine, and/or abacavir. The median follow-up period was 36 months (18-72). Less than 50 copies/mL of HIV RNA was observed in 46%, 67%, and 70% of the children at months 6, 9, and 12, respectively. In all, 20 children (46.5%) experienced a VF. The risk factors of primary VF were a young age and a low socioeconomic status. The genotypic resistance test, performed for 18 of 20 children with VF, revealed 1 LPV/r-resistant virus and protease inhibitor-related major mutations without LPV/r resistance in 2 other children. Of the 18 children with VF, 15 received a 3TC-based HAART: 12 of 15 (80%) harbored a 3TC-resistant virus. No virus resistant to zidovudine or abacavir was found.

CONCLUSION

In all, 70% of HAART-naive children had virologic success at month 12. The selection of LPV-resistant strains was a rare event. A high rate of selection of 3TC-mutations strengthens the recommendation to prefer a first-line 3TC-sparing regimen, particularly for children with risk factors of poor adherence.

The L76V mutation in HIV-1 protease is potentially associated with hypersusceptibility to protease inhibitors Atazanavir and Saquinavir: is there a clinical advantage?

Background

Although being considered as a rarely observed HIV-1 protease mutation in clinical isolates, the L76V-prevalence increased 1998-2008 in some European countries most likely due to the approval of Lopinavir, Amprenavir and Darunavir which can select L76V. Beside an enhancement of resistance, L76V is also discussed to confer hypersusceptibility to the drugs Atazanavir and Saquinavir which might enable new treatment strategies by trying to take advantage of particular mutations.

Results

Based on a cohort of 47 L76V-positive patients, we examined if there might exist a clinical advantage for L76V-positive patients concerning long-term success of PI-containing regimens in patients with limited therapy options.

Genotypic- and phenotypic HIV-resistance tests from 47 mostly multi-resistant, L76V-positive patients throughout Germany were accomplished retrospectively 1999-2009. Five genotype-based drug-susceptibility predictions received from online interpretation-tools for Atazanavir, Saquinavir, Amprenavir and Lopinavir, were compared to phenotype-based predictions that were determined by using a recombinant virus assay along with a Virtual Phenotype™(Virco). The clinical outcome of the L76V-adapted follow-up therapy was determined by monitoring viral load for 96 weeks.

Conclusions

In this analysis, the mostly used interpretation systems overestimated the L76V-mutation concerning Atazanavir- and SQV resistance. In fact, a clear benefit in drug susceptibility for these drugs was observed in phenotype analysis after establishment of L76V. More importantly, long-term therapy success was significantly higher in patients receiving Atazanavir and/or Saquinavir plus one L76V-selecting drug compared to patients without L76V-selecting agents (p = 0.002).

In case of L76V-occurrence ATV and/or SQV may represent encouraging options for patients in deep salvage situations.

[AIDS Study Group/Spanish AIDS Plan consensus document on antiretroviral therapy in adults with human immunodeficiency virus infection (updated January 2010)]

OBJECTIVE

This consensus document is an update of antiretroviral therapy recommendations for adult patients with human immunodeficiency virus infection.

METHODS

To formulate these recommendations a panel made up of members of the Grupo de Estudio de Sida (Gesida, AIDS Study Group) and the Plan Nacional sobre el Sida (PNS, Spanish AIDS Plan) reviewed the advances in the current understanding of the pathophysiology of human immunodeficiency virus (HIV) infection, the efficacy and safety of clinical trials, and cohort and pharmacokinetic studies published in biomedical journals or presented at scientific meetings. Three levels of evidence were defined according to the data source: randomized studies (level A), cohort or case-control studies (level B), and expert opinion (level C). The decision to recommend, consider or not to recommend ART was established in each situation.

RESULTS

Currently, the treatment of choice for chronic HIV infection is the combination of three drugs of two different classes, including 2 nucleosides or nucleotide analogs (NRTI) plus 1 non-nucleoside (NNRTI) or 1 boosted protease inhibitor (PI/r), but other combinations are possible. Initiation of ART is recommended in patients with symptomatic HIV infection. In asymptomatic patients, initiation of ART is recommended on the basis of CD4 lymphocyte counts, plasma viral load and patient co-morbidities, as follows: 1) therapy should be started in patients with CD4 counts below 350 cells/microl; 2) When CD4 counts are between 350 and 500 cells/microl, therapy should be started in case of cirrhosis, chronic hepatitis C, high cardiovascular risk, HIV nephropathy, HIV viral load above 100,000 copies/ml, proportion of CD4 cells under 14%, and in people aged over 55; 3) Therapy should be deferred when CD4 are above 500 cells/microl, but could be considered if any of previous considerations concurs. Treatment should be initiated in case of hepatitis B requiring treatment and should be considered for reduce sexual transmission. The objective of ART is to achieve an undetectable viral load. Adherence to therapy plays an essential role in maintaining antiviral response. Therapeutic options are limited after ART failures but undetectable viral loads maybe possible with the new drugs even in highly drug experienced patients. Genotype studies are useful in these situations. Drug toxicity of ART therapy is losing importance as benefits exceed adverse effects. Criteria for antiretroviral treatment in acute infection, pregnancy and post-exposure prophylaxis are mentioned as well as the management of HIV co-infection with hepatitis B or C.

CONCLUSIONS

CD4 cells counts, viral load and patient co-morbidities are the most important reference factors to consider when initiating ART in asymptomatic patients. The large number of available drugs, the increased sensitivity of tests to monitor viral load, and the ability to determine viral resistance is leading to a more individualized therapy approach in order to achieve undetectable viral load under any circumstances.

Current and Novel Inhibitors of HIV Protease

The design, development and clinical success of HIV protease inhibitors represent one of the most remarkable achievements of molecular medicine. This review describes all nine currently available FDA-approved protease inhibitors, discusses their pharmacokinetic properties, off-target activities, side-effects, and resistance profiles. The compounds in the various stages of clinical development are also introduced, as well as alternative approaches, aiming at other functional domains of HIV PR. The potential of these novel compounds to open new way to the rational drug design of human viruses is critically assessed.

Impact of reduced dosing of lopinavir/ritonavir in virologically controlled HIV-infected patients: the Kaledose trial

BACKGROUND

It is debated whether a risk of protease inhibitor mutation selection in proviral DNA exists during intermittent HIV-1 viraemia thereby impacting long-term virological control.

METHODS

Virologically controlled patients treated with lopinavir/ritonavir were included in a 48 week pilot trial during which lopinavir/ritonavir dosage was reduced if lopinavir concentration was >5000 ng/mL at inclusion. Serum lipids were longitudinally assessed and proviral DNA was quantified and sequenced in patients experiencing transient viraemia.

RESULTS

Thirty-three virologically suppressed patients while on a lopinavir/ritonavir-containing regimen were included, of whom 28 [20 males, mean age 44.6 years (SD 10.9)] completed the 48 week follow-up as scheduled. A significant decrease in lopinavir level was noted [mean C(min), 7363 ng/mL (min, 5118; max, 12 415) at baseline versus 4319 ng/mL (min, 1427; max, 8683) at week 48, P < 0.03]. A significant decrease in triglycerides was also observed [1.73 mmol/L (SD 1.08) at baseline versus 1.34 mmol/L (SD 0.91) at week 48, P = 0.03], whereas no significant change occurred for total, high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol. In the 15 patients with transient viraemia, analysis of proviral DNA for antiretroviral resistance showed that mutations had occurred when compared with baseline genotypes in three patients: I47M (n = 2) and M46I (n = 1). Selection of these mutations was not associated with virological failure as all three patients had a sustained virological response without treatment modification after a 3 year follow-up.

CONCLUSIONS

This pilot study evaluating the biochemical and virological impact of a reduced dosing of lopinavir/ritonavir suggests that lower exposure to lopinavir/ritonavir could be associated with a significant decrease in triglycerides during treatment, without occurrence of resistance mutations that might impact the virological response to treatment.

Mutation T74S in HIV-1 subtype B and C proteases resensitizes them to ritonavir and indinavir and confers fitness advantage

OBJECTIVES

Several drug resistance and secondary mutations have been described in HIV-1 viruses from patients undergoing antiretroviral therapy. In this study, we assessed the impact of the protease substitution T74S on the phenotype and on the replicative fitness in HIV-1 subtypes B and C.

METHODS

HIV-1 molecular clones carrying subtype B or C proteases had these coding regions subjected to site-directed mutagenesis to include T74S alone or in combination with four known protease inhibitor (PI) primary drug resistance mutations. All clones were used in a phenotypic assay to evaluate their susceptibility to most commercially available PIs. The impact of T74S on virus fitness was also assessed for all viruses through head-to-head competitions and oligonucleotide ligation assays to measure the proportion of each virus in culture.

RESULTS

Viruses of both subtypes carrying T74S did not have their susceptibility altered to any tested PI. Viruses with the four resistance mutations showed strong resistance to most PIs with fold changes ranging from 5 to 300 times compared with their wild-type counterparts. Surprisingly, the addition of T74S to the multiresistant clones restored their susceptibilities to indinavir and ritonavir and partially to lopinavir, close to those of wild-type viruses. Most 74S-containing viruses were more fit than their 74T counterparts.

CONCLUSIONS

Our results suggest that T74S is not a major drug resistance mutation, but it resensitizes multiresistant viruses to certain PIs. T74S is a bona fide accessory mutation, restoring fitness of multidrug-resistant viruses in both subtypes B and C. T74S should be further studied in clinical settings and considered in drug resistance interpretation algorithms.

Pattern and impact of emerging resistance mutations in treatment experienced patients failing darunavir-containing regimen

BACKGROUND

Ritonavir-boosted darunavir (DRV/r) has proven potent efficacy when used in heavily pretreated patients, harboring protease inhibitor-associated resistance mutations. Limited data are available on resistance pattern emerging in patients failing DRV/r and on subsequent remaining protease inhibitor options.

METHODS

Analysis of baseline and failure resistance genotypes were performed in patients experiencing virologic failure (>200 copies/ml) after at least 3 months on a DRV/r (600/100 mg twice daily)-containing regimen.

RESULTS

Twenty-five highly protease inhibitor-experienced patients were included. Baseline median human immunodeficiency virus type 1 RNA was 5 log10 copies/ml and number of total-protease inhibitor, major-protease inhibitor and DRV-associated-resistance mutations was 13, 4 and 3, respectively. Median viral replication duration on DRV/r selective pressure was 34 weeks. Emergence of DRV-associated-resistance mutations was observed in 72% (18/25) of patients, at codons L89I/M/V (32%), V32I (28%), V11I (20%), I47V/A (20%), I54L/M (20%), L33F/I (16%) and I50V (16%). A high risk of DRV resistance was observed in patients with 2 and 3 baseline DRV-associated-resistance mutations and in patients with more than 24 weeks of ongoing viral replication. According to 2007 ANRS algorithm, isolates classified as susceptible to ritonavir-boosted tipranavir decreased from baseline to failure from 76 to 60% and susceptible to DRV/r from 32 to 12%.

CONCLUSION

Emerging mutations observed after DRV/r failure were those already described to impact the DRV efficacy. Our study provided recommendations to firstly, reconsider lowering the cutoff number of DRV mutations to two; secondly, avoid keeping patients on a DRV-failing regimen for more than 24 weeks and thirdly, to examine the efficacy of using tipranavir after DRV failure.

Enzymatic and structural analysis of the I47A mutation contributing to the reduced susceptibility to HIV protease inhibitor lopinavir

Lopinavir (LPV) is a second-generation HIV protease inhibitor (PI) designed to overcome resistance development in patients undergoing long-term antiviral therapy. The mutation of isoleucine at position 47 of the HIV protease (PR) to alanine is associated with a high level of resistance to LPV. In this study, we show that recombinant PR containing a single I47A substitution has the inhibition constant (K(i) ) value for lopinavir by two orders of magnitude higher than for the wild-type PR. The addition of the I47A substitution to the background of a multiply mutated PR species from an AIDS patient showed a three-order-of-magnitude increase in K(i) in vitro relative to the patient PR without the I47A mutation. The crystal structure of I47A PR in complex with LPV showed the loss of van der Waals interactions in the S2/S2' subsites. This is caused by the loss of three side-chain methyl groups due to the I47A substitution and by structural changes in the A47 main chain that lead to structural changes in the flap antiparallel beta-strand. Furthermore, we analyzed possible interaction of the I47A mutation with secondary mutations V32I and I54V. We show that both mutations in combination with I47A synergistically increase the relative resistance to LPV in vitro. The crystal structure of the I47A/I54V PR double mutant in complex with LPV shows that the I54V mutation leads to a compaction of the flap, and molecular modeling suggests that the introduction of the I54V mutation indirectly affects the strain of the bound inhibitor in the PR binding cleft.

Prevalence and impact of HIV-1 protease mutation L76V on lopinavir resistance

Besides I47A, mutation L76V at the HIV protease gene has recently been proposed to cause lopinavir resistance. This change was present in 37 (2.7%) out of 1376 patients failing protease inhibitor containing regimens. Although 26 (70%) were on lopinavir, most had previously failed other protease inhibitors and carried multiple protease inhibitor resistance mutations. Therefore, L76V does not appear to be a primary lopinavir resistance change when the drug is used in combination therapy.

Predictive Factors for Response to a Boosted Dual HIV-Protease Inhibitor Therapy with Saquinavir and Lopinavir in Extensively Pre-Treated Patients

Objective

To evaluate predictive factors for therapy outcome of a boosted double-protease inhibitor (PI) regimen in 58 extensively pre-treated patients with HIV.

Methods

Patients received lopinavir/ritonavir 400/100 mg and saquinavir 1,000 mg twice daily without reverse transcriptase inhibitors (RTI). The primary outcome parameter was HIV RNA <400 copies/ml at week 48, secondary parameters were HIV-1 RNA and CD4+ T-cell count changes from baseline to week 48. Pharmacokinetics, genotypic resistance and clinical and individual parameters were correlated with the clinical outcome in regression analyses. Covariates for the analyses were minimum plasma concentration (Cmin), maximum plasma concentration, area under the concentration versus time curve, half-life and clearance of lopinavir and saquinavir, the genotypic inhibitory quotients (GIQ) of archived (GIQarch) and baseline PI resistance mutations, previously taken antiretrovirals, archived and baseline viral resistance mutations, baseline HIV-1 RNA and CD4+ T-cell count.

Results

The analyses detected correlations between the primary outcome parameter and several factors: baseline CD4+ T-cell count ( P=0.001); absence of mutations at V82T/A/F/I/S plus I54M/V/L ( P=0.002) or K20M/R ( P=0.010); and lopinavir CminGIQarch ( P=0.046). This regression model had a predictability of 97.0% for response to therapy. Covariates for the decrease of HIV-1 RNA from baseline to week 48 were baseline HIV-1 RNA ( P<0.001), lopinavir CminGIQarch ( P=0.013), presence/absence of mutations at V82T/A/F/I/S or I84A/V plus L10I/R/V/F, I54M/V/L or L63P ( P=0.018), and previously taken antiretrovirals ( P=0.034).

Conclusions

Baseline HIV-1 RNA <5.0 log10 and CD4+ T-cell count >200 cells/μl, lopinavir CminGIQarch >2,000 ng/ml and the absence of viral resistance mutations at V82T/A/F/I/S and I54M/V/L are highly predictive for therapeutic success of a regimen of saquinavir/lopinavir/ ritonavir without RTI in a heterogenic cohort of patients with an extensive pre-treatment history and highly variable pharmacokinetics.

Mutational patterns and correlated amino acid substitutions in the HIV-1 protease after virological failure to nelfinavir- and lopinavir/ritonavir-based treatments

Human immunodeficiency virus type 1 (HIV-1) antiviral drug resistance is a major consequence of therapy failure and compromises future therapeutic options. Nelfinavir and lopinavir/ritonavir-based therapies have been widely used in the treatment of HIV-infected patients, in combination with reverse transcriptase inhibitors. The aim of this observational study was the identification and characterization of mutations or combinations of mutations associated with resistance to nelfinavir and lopinavir/ritonavir in treated patients. Nucleotide sequences of 1,515 subtype B HIV-1 isolates from 1,313 persons with different treatment histories (including naïve and treated patients) were collected in 31 Spanish hospitals over the years 2002-2005. Chi-square contingency tests were performed to detect mutations associated with failure to protease inhibitor-based therapies, and correlated mutations were identified using statistical methods. Virological failure to nelfinavir was associated with two different mutational pathways. D30N and N88D appeared mostly in patients without previous exposure to protease inhibitors, while K20T was identified as a secondary resistance mutation in those patients. On the other hand, L90M together with L10I, I54V, A71V, G73S, and V82A were selected in protease inhibitor-experienced patients. A series of correlated mutations including L10I, M46I, I54V, A71V, G73S, and L90M appeared as a common cluster of amino acid substitutions, associated with failure to lopinavir/ritonavir-based treatments. Despite the relatively high genetic barrier of some protease inhibitors, a relatively small cluster of mutations, previously selected under drug pressure, can seriously compromise the efficiency of nelfinavir- and lopinavir/ritonavir-based therapies.

In vitro selection and characterization of human immunodeficiency virus type 2 with decreased susceptibility to lopinavir

Lopinavir (LPV)-ritonavir has demonstrated durable antiviral activity in human immunodeficiency virus type 1 (HIV-1)-infected antiretroviral-naïve and protease inhibitor (PI)-experienced patients. However, information on LPV activity against HIV-2 and the patterns of mutations in HIV-2 in response to selection by LPV is limited. The activity of LPV against three strains of HIV-2 was assessed and compared to activity against a reference HIV-1 strain. LPV demonstrated activity similar to that observed against HIV-1 in two HIV-2 strains (HIV-2(MS) and HIV-2(CBL-23)) tested. On the other hand, approximately 10-fold-reduced susceptibility was observed with the third HIV-2 strain, HIV-2(CDC310319). Passage of HIV-2(MS) with increasing concentrations of LPV selected mutations V47A and D17N in the HIV-2 protease gene. The introduction of both 17N and 47A either individually or together into HIV-2(ROD) molecular infectious clones showed that the single V47A substitution in HIV-2 resulted in a substantial reduction in susceptibility to LPV. In contrast, this mutant retained wild-type susceptibility to other PIs and appeared to be hypersusceptible to atazanavir and saquinavir.

HIV-infected patients receiving lopinavir/ritonavir-based antiretroviral therapy achieve high rates of virologic suppression despite adherence rates less than 95%

BACKGROUND

The observation that extremely high levels of medication adherence are required to achieve complete virologic suppression is based largely on studies of treatment-experienced patients receiving HIV protease inhibitor (PI)-based therapy without ritonavir boosting. This study aims to define the level of adherence needed to achieve virologic suppression in patients receiving boosted PI-based highly active antiretroviral therapy (HAART) with lopinavir/ritonavir.

METHODS

HIV-infected adults receiving a regimen containing lopinavir/ritonavir were recruited into a prospective, observational study of the relation between adherence to lopinavir/ritonavir and virologic outcomes. Adherence was measured using the Medication Event Monitoring System (MEMS; Aardex, Union City, CA). HIV-1 viral load (VL) was measured at week 24.

RESULTS

The final study population contained 64 subjects. Eighty percent had AIDS, 97% received lopinavir/ritonavir before enrollment, and most had more than 7 years of HAART experience. Mean adherence overall was 73%. Eighty percent and 59% achieved a VL <400 copies/mL and a VL <75 copies/mL, respectively. Mean adherence was 75% in those achieving a VL <75 copies/mL. High rates of virologic suppression were observed in all adherence quartiles, including the lowest quartile (range of adherence: 23.5%-53.3%).

CONCLUSIONS

Moderate levels of adherence can lead to virologic suppression in most patients taking lopinavir/ritonavir-based HAART.

Tipranavir: a new protease inhibitor for the treatment of antiretroviral-experienced HIV-infected patients

Tipranavir (TPV) is a novel non-peptidic protease inhibitor (PI). It binds strongly and selectively to the HIV-1 protease, is orally administered twice daily, boosted with low doses of ritonavir, and shows a favourable resistance profile. In the two registrational trials, named RESIST 1 and 2, TPV/ritonavir 500/200 mg b.i.d., along with an optimised antiretroviral backbone, provided better virologic responses than controls receiving standard of care ritonavir-boosted PI-based regimens. A total of 21 mutations at 16 protease codons have been shown to impact on TPV susceptibility and response rates. The TPV mutation score includes L10V, I13V, K20M/R/V, L33F, E35G, M36I, K43T, M46L, I47V, I54A/M/V, Q58E, H69K, T74P, V82L/T, N83D and I84V. Viruses containing eight or more of these mutations are generally resistant to the drug. TPV use is associated with an excess of grade 3/4 liver enzyme elevations compared with other ritonavir-boosted PIs, and the potential for drug-drug interactions is relevant and must be considered when prescribing TPV.