Etravirine (ETR) is a second-generation nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) active against common human immunodeficiency virus type 1 (HIV-1) drug-resistant strains. This study was designed to determine the extent to which each of the Y181C or G190A mutations in RT might confer resistance to ETR and other members of the NNRTI family of drugs. Recombinant HIV-1 RT enzymes containing either the Y181C or the G190A mutation, or both mutations in tandem, were purified. Both RNA- and DNA-dependent DNA polymerase assays were performed in order to determine the extent to which each of these mutations might confer resistance in cell-free biochemical assays against each of ETR, efavirenz, and nevirapine. Both the biochemical and the cell-based phenotypic assays confirmed the susceptibility of G190A-containing enzymes and viruses to ETR. The results of this study indicate that the G190A mutation is not associated with resistance to ETR.
Pediatric patients infected with human immunodeficiency virus (HIV) are now living longer, healthier lives due to the advent of combined antiretroviral (ARV) therapy, including regimens that often contain non-nucleoside reverse transcriptase inhibitors (NNRTIs). However, first-generation NNRTIs such as nevirapine (NVP) and efavirenz (EFV) have a low genetic barrier to resistance, and both drugs can become ineffective with a single viral point mutation. New agents with activity against resistant viral strains must be available to salvage children and adolescents with virologic failure after NNRTI use. One such drug, etravirine, an oral second-generation NNRTI approved for use in the US in heavily treatment-experienced HIV-1-infected adults in 2008, is accumulating data in this younger population. Etravirine became approved by the US Food and Drug Administration in early 2012 to be used in combination with other ARV medications in HIV-1-infected children aged 6 years to <18 years who are failing their regimens with HIV-1 strains resistant to NNRTIs and other ARVs. This approval was largely based on data from a prospective, open-label, phase II clinical trial in this age group prescribed etravirine at 5.2 mg/kg twice daily (up to the adult dose of 200 mg twice daily) in combination with an investigator-selected optimized background regimen. Currently available 48-week follow-up data show complete viral suppression (<50 copies/mL) in 56% of the patients, with relatively few serious adverse events attributed to the drug. Additional studies and case reports from the field suggest its utility in clinical practice. This review is designed to increase the background understanding of this drug in pediatric HIV providers, to lay out the current pediatric data to support its use, and to define its practical role in the treatment of HIV-infected children now and in the future.
salvage; resistance; children; adolescents; NNRTI; perinatal
Human immunodeficiency virus (HIV) type-1 non-nucleoside and nucleoside reverse transcriptase inhibitors (NNRTIs) are key drugs of highly active antiretroviral therapy (HAART) in the clinical management of acquired immune deficiency syndrome (AIDS)/HIV infection.
First-generation NNRTIs, nevirapine (NVP), delavirdine (DLV) and efavirenz (EFV) are drugs with a low genetic barrier and poor resistance profile, which has led to the development of new generations of NNRTIs. Second-generation NNRTIs, etravirine (ETR) and rilpivirine (RPV) have been approved by the Food and Drug Administration and European Union, and the next generation of drugs is currently being clinically developed. This review describes recent clinical data, pharmacokinetics, metabolism, pharmacodynamics, safety and tolerability of commercialized NNRTIs, including the effects of sex, race and age differences on pharmacokinetics and safety. Moreover, it summarizes the characteristics of next-generation NNRTIs: lersivirine, GSK 2248761, RDEA806, BILR 355 BS, calanolide A, MK-4965, MK-1439 and MK-6186.
This review presents a wide description of NNRTIs, providing useful information for researchers interested in this field, both in clinical use and in research.
human immunodeficiency virus; non-nucleoside reverse transcriptase inhibitors; nevirapine; delavirdine; efavirenz; etravirine; rilpivirine; next-generation non-nucleoside reverse transcriptase inhibitors
Etravirine is a novel nonnucleoside reverse transcriptase inhibitor (NNRTI) specifically designed to suppress the replication of viruses resistant to the three currently approved NNRTIs efavirenz, nevirapine, and delavirdine.
To assess the evidence for the place of etravirine in the treatment of HIV-1 infection.
In combination with a ritonavir-boosted protease inhibitor etravirine has demonstrated high antiviral activity against strains exhibiting up to three NNRTI resistance mutations. The drug appears to be well tolerated, with only nausea and rash occuring significantly more frequently with etravirine compared with placebo. Of note, neuropsychologic side effects that frequently limit the use of efavirenz were not reported more frequently with etravirine.
Place in therapy:
Given its high activity against most NNRTI-resistant strains and its very good tolerability, etravirine is of high value for pretreated patients with NNRTI resistance and protease inhibitor exposure. Efforts should be made to demonstrate activity in switching strategies (due to toxicity) and earlier lines of failure or in the setting of primary NNRTI resistance in order to explore the potential of the drug beyond salvage therapy.
etravirine; HIV-1; evidence
Recently, mutations in the connection subdomain (CN) and RNase H domain of HIV-1 reverse transcriptase (RT) were observed to exhibit dual resistance to nucleoside and nonnucleoside reverse transcriptase inhibitors (NRTIs and NNRTIs). To elucidate the mechanism by which CN and RH mutations confer resistance to NNRTIs, we hypothesized that these mutations reduce RNase H cleavage and provide more time for the NNRTI to dissociate from the RT, resulting in the resumption of DNA synthesis and enhanced NNRTI resistance. We observed that the effect of the reduction in RNase H cleavage on NNRTI resistance is dependent upon the affinity of each NNRTI to the RT and further influenced by the presence of NNRTI-binding pocket (BP) mutants. D549N, Q475A, and Y501A mutants, which reduce RNase H cleavage, enhance resistance to nevirapine (NVP) and delavirdine (DLV), but not to efavirenz (EFV) and etravirine (ETR), consistent with their increase in affinity for RT. Combining the D549N mutant with NNRTI BP mutants further increases NNRTI resistance from 3- to 30-fold, supporting the role of NNRTI-RT affinity in our NNRTI resistance model. We also demonstrated that CNs from treatment-experienced patients, previously reported to enhance NRTI resistance, also reduce RNase H cleavage and enhance NNRTI resistance in the context of the patient RT pol domain or a wild-type pol domain. Together, these results confirm key predictions of our NNRTI resistance model and provide support for a unifying mechanism by which CN and RH mutations can exhibit dual NRTI and NNRTI resistance.
Etravirine (ETV) is a second-generation nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) introduced recently for salvage antiretroviral treatment after the emergence of NNRTI-resistant human immunodeficiency virus type 1 (HIV-1). Following its introduction, two naturally occurring mutations in HIV-1 RT, V106I and V179D, were listed as ETV resistance-associated mutations. However, the effect of these mutations on the development of NNRTI resistance has not been analyzed yet. To select highly NNRTI-resistant HIV-1 in vitro, monoclonal HIV-1 strains harboring V106I and V179D (HIV-1V106I and HIV-1V179D) were propagated in the presence of increasing concentrations of efavirenz (EFV). Interestingly, V179D emerged in one of three selection experiments from HIV-1V106I and V106I emerged in two of three experiments from HIV-1V179D. Analysis of recombinant HIV-1 clones showed that the combination of V106I and V179D conferred significant resistance to EFV and nevirapine (NVP) but not to ETV. Structural analysis indicated that ETV can overcome the repulsive interactions caused by the combination of V106I and V179D through fine-tuning of its binding module to RT facilitated by its plastic structure, whereas EFV and NVP cannot because of their rigid structures. Analysis of clinical isolates showed comparable drug susceptibilities, and the same combination of mutations was found in some database patients who experienced virologic NNRTI-based treatment failure. The combination of V106I and V179D is a newly identified NNRTI resistance pattern of mutations. The combination of polymorphic and minor resistance-associated mutations should be interpreted carefully.
We characterized pairwise and higher order patterns of non-nucleoside reverse transcriptase inhibitor (NNRTI)-selected mutations because multiple mutations are usually required for clinically significant resistance to second-generation NNRTIs.
Patients and methods
We analysed viruses from 13 039 individuals with sequences containing at least one of 52 published NNRTI-selected mutations, including 1133 viruses from individuals who received efavirenz but no other NNRTI and 1510 viruses from individuals who received nevirapine but no other NNRTI. Of the 17 reported etravirine resistance-associated mutations (RAMs), Y181C/I/V, L100I, K101P and M230L were considered major based on published in vitro susceptibility data.
Efavirenz preferentially selected for 16 mutations, including L100I (14% versus 0.1%, P < 0.001), K101P (3.3% versus 0.4%, P < 0.001) and M230L (2.8% versus 1.3%, P = 0.004), whereas nevirapine preferentially selected for 12 mutations, including Y181C/I/V (48% versus 6.9%, P < 0.001). Twenty-nine pairs of NNRTI-selected mutations covaried significantly, including Y181C with seven other mutations (A98G, K101E/H, V108I, G190A/S and H221Y), L100I with K103N, and K101P with K103S. Two pairs (Y181C + V179F and Y181C + G190S) were predicted to confer >10-fold decreased etravirine susceptibility. Seventeen percent of sequences had three or more NNRTI-selected mutations, mostly in clusters of covarying mutations. Many clusters had Y181C plus a non-major etravirine RAM; few had more than one major etravirine RAM.
Although major etravirine RAMs rarely occur in combination, 2 of 29 pairs of covarying mutations were associated with >10-fold decreased etravirine susceptibility. Viruses with three or more NNRTI-selected mutations often contained Y181C in combination with one or more minor etravirine RAMs; however, phenotypic and clinical correlates for most of these higher order combinations have not been published.
Multidrug resistance; etravirine; antiviral therapy
Potential topical retrovirucides or vaginal microbicides against human immunodeficiency virus type 1 (HIV-1) include nonnucleoside reverse transcriptase inhibitors (NNRTIs). To be successful, such agents have to be highly active against cell-free virions. In the present study, we developed a new real-time PCR-based assay to measure the natural endogenous reverse transcription (NERT) activity directly on intact HIV-1 particles in the presence of reverse transcriptase (RT) inhibitors. We further evaluated the permeability to nevirapine (NVP) and efavirenz (EFV) and their retention within nascent viral particles. We also demonstrated the NVP and EFV inhibitory effects on NERT activity and the impact of resistance mutations measured directly by this new strategy. Furthermore, the results showed a clear correlation between NERT activity and classical infectivity assays. The 50% inhibitory concentrations (IC50s) of NVP and EFV were demonstrated to be up to 100-fold higher for cell-free than for cell-associated virions, suggesting that cell-free virions are less permeable to these drugs. Our results suggest that NVP and EFV penetrate both the envelope and the capsid of HIV-1 particles and readily inactivate cell-free virions. However, the characteristics of these NNRTIs, such as lower permeability and lower retention during washing procedures, in cell-free virions reduce their efficacies as microbicides. Here, we demonstrate the usefulness of the NERT real-time PCR as an assay for screening novel antiretroviral compounds with unique mechanisms of action.
Suboptimal treatment of human immunodeficiency virus type 1 (HIV-1) infection with nonnucleoside reverse transcriptase inhibitors (NNRTI) often results in the rapid selection of drug-resistant virus. Several amino acid substitutions at position 190 of reverse transcriptase (RT) have been associated with reduced susceptibility to the NNRTI, especially nevirapine (NVP) and efavirenz (EFV). In the present study, the effects of various 190 substitutions observed in viruses obtained from NNRTI-experienced patients were characterized with patient-derived HIV isolates and confirmed with a panel of isogenic viruses. Compared to wild-type HIV, which has a glycine at position 190 (G190), viruses with 190 substitutions (A, C, Q, S, V, E, or T, collectively referred to as G190X substitutions) were markedly less susceptible to NVP and EFV. In contrast, delavirdine (DLV) susceptibility of these G190X viruses increased from 3 to 300-fold (hypersusceptible) or was only slightly decreased. The replication capacity of viruses with certain 190 substitutions (C, Q, V, T, and E) was severely impaired and was correlated with reduced virion-associated RT activity and incomplete protease (PR) processing of the viral p55gag polyprotein. These defects were the result of inadequate p160gagpol incorporation into virions. Compensatory mutations within RT and PR improved replication capacity, p55gag processing, and RT activity, presumably through increased incorporation of p160gagpol into virions. We observe an inverse relationship between the degree of NVP and EFV resistance and the impairment of viral replication in viruses with substitutions at 190 in RT. These observations may have important implications for the future design and development of antiretroviral drugs that restrict the outgrowth of resistant variants with high replication capacity.
Nonnucleoside reverse transcriptase inhibitors (NNRTIs) target HIV-1 reverse transcriptase (RT) by binding to a pocket in RT that is close to, but distinct, from the DNA polymerase active site and prevent the synthesis of viral cDNA. NNRTIs, in particular, those that are potent inhibitors of RT polymerase activity, can also act as chemical enhancers of the enzyme's inter-subunit interactions. However, the consequences of this chemical enhancement effect on HIV-1 replication are not understood. Here, we show that the potent NNRTIs efavirenz, TMC120, and TMC125, but not nevirapine or delavirdine, inhibit the late stages of HIV-1 replication. These potent NNRTIs enhanced the intracellular processing of Gag and Gag-Pol polyproteins, and this was associated with a decrease in viral particle production from HIV-1-transfected cells. The increased polyprotein processing is consistent with premature activation of the HIV-1 protease by NNRTI-enhanced Gag-Pol multimerization through the embedded RT sequence. These findings support the view that Gag-Pol multimerization is an important step in viral assembly and demonstrate that regulation of Gag-Pol/Gag-Pol interactions is a novel target for small molecule inhibitors of HIV-1 production. Furthermore, these drugs can serve as useful probes to further understand processes involved in HIV-1 particle assembly and maturation.
HIV-1 encodes reverse transcriptase (RT), an enzyme that is essential for virus replication. Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are allosteric inhibitors of the HIV-1 RT. In HIV-1-infected cells NNRTIs block the RT-catalyzed synthesis of a double-stranded DNA copy of the viral genomic RNA, which is an early step in the virus life cycle. Potent NNRTIs have the novel feature of promoting the interaction between the two RT subunits. However, the importance of this effect on the inhibition of HIV-1 replication has not been defined. In this study, the authors show that potent NNRTIs block an additional step in the virus life cycle. NNRTIs increase the intracellular processing of viral polyproteins called Gag and Gag-Pol that express the HIV-1 structural proteins and viral enzymes. Enhanced polyprotein processing is associated with a decrease in viral particles released from NNRTI-treated cells. NNRTI enhanced polyprotein processing is likely due to the drug binding to RT, expressed as part of the Gag-Pol polyprotein and promoting the interaction between separate Gag-Pol polyproteins. This leads to premature activation of the Gag-Pol embedded HIV-1 protease, resulting in a decrease in full-length viral polyproteins available for assembly and budding from the host cell membrane. This study provides proof-of-concept that small molecules can modulate the interactions between Gag-Pol polyproteins and suggests a new target for the development of HIV-1 antiviral drugs.
Nonnucleoside reverse transcriptase inhibitors (NNRTIs) have proven efficacy against human immunodeficiency virus type 1 (HIV-1). However, in the setting of incomplete viral suppression, efavirenz and nevirapine select for resistant viruses. The diarylpyrimidine etravirine has demonstrated durable efficacy for patients infected with NNRTI-resistant HIV-1. A screening strategy used to test NNRTI candidates from the same series as etravirine identified TMC278 (rilpivirine). TMC278 is an NNRTI showing subnanomolar 50% effective concentrations (EC50 values) against wild-type HIV-1 group M isolates (0.07 to 1.01 nM) and nanomolar EC50 values against group O isolates (2.88 to 8.45 nM). Sensitivity to TMC278 was not affected by the presence of most single NNRTI resistance-associated mutations (RAMs), including those at positions 100, 103, 106, 138, 179, 188, 190, 221, 230, and 236. The HIV-1 site-directed mutant with Y181C was sensitive to TMC278, whereas that with K101P or Y181I/V was resistant. In vitro, considerable cross-resistance between TMC278 and etravirine was observed. Sensitivity to TMC278 was observed for 62% of efavirenz- and/or nevirapine-resistant HIV-1 recombinant clinical isolates. TMC278 inhibited viral replication at concentrations at which first-generation NNRTIs could not suppress replication. The rates of selection of TMC278-resistant strains were comparable among HIV-1 group M subtypes. NNRTI RAMs emerging in HIV-1 under selective pressure from TMC278 included combinations of V90I, L100I, K101E, V106A/I, V108I, E138G/K/Q/R, V179F/I, Y181C/I, V189I, G190E, H221Y, F227C, and M230I/L. E138R was identified as a new NNRTI RAM. These in vitro analyses demonstrate that TMC278 is a potent next-generation NNRTI, with a high genetic barrier to resistance development.
We identified clinical isolates with phenotypic resistance to nevirapine (NVP) in the absence of known nonnucleoside reverse transcriptase inhibitor (NNRTI) mutations. This resistance is caused by N348I, a mutation at the connection subdomain of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). Virologic analysis showed that N348I conferred multiclass resistance to NNRTIs (NVP and delavirdine) and to nucleoside reverse transcriptase inhibitors (zidovudine [AZT] and didanosine [ddI]). N348I impaired HIV-1 replication in a cell-type-dependent manner. Acquisition of N348I was frequently observed in AZT- and/or ddI-containing therapy (12.5%; n = 48; P < 0.0001) and was accompanied with thymidine analogue-associated mutations, e.g., T215Y (n = 5/6) and the lamivudine resistance mutation M184V (n = 1/6) in a Japanese cohort. Molecular modeling analysis shows that residue 348 is proximal to the NNRTI-binding pocket and to a flexible hinge region at the base of the p66 thumb that may be affected by the N348I mutation. Our results further highlight the role of connection subdomain residues in drug resistance.
It was previously found that certain nonnucleoside reverse transcriptase inhibitors (NNRTI) possess virucidal activity against human immunodeficiency virus type 1 (HIV-1), and it was suggested that the tight-binding mode of inhibition of reverse transcriptase might be important for this virucidal activity (Borkow et al., J. Virol. 71:3023-3030, 1997). To test this, we compared six different NNRTI, including three tight-binding NNRTI, namely UC781, efavirenz (EFV) (Sustiva), and 5-chloro-3-phenylsulfonylindole-2-carboxamide (CSIC), and three rapid-equilibrium NNRTI, delavirdine (DLV) (Rescriptor), nevirapine (NVP) (Viramune), and UC84, in a variety of virucidal tests. Incubation of isolated HIV-1 virions with UC781, EFV, or CSIC rapidly inactivated the virus, whereas DLV, NVP, and UC84 were ineffective in this respect. Exposure of H9+ cells chronically infected by HIV-1 to the tight-binding NNRTI abolished the infectivity of nascent virus subsequently produced by these cells following removal of extracellular drug, thereby preventing cell-to-cell virus transmission in the absence of exogenous drug. In contrast, cell-to-cell transmission of HIV was blocked by DLV, NVP, and UC84 only when the drug remained in the extracellular medium. Pretreatment of uninfected lymphocytoid cells with UC781, EFV, or CSIC, but not DLV, NVP, or UC84, protected these cells from subsequent HIV-1 infection in the absence of extracellular drug. The protective effect was dependent on both the dose of NNRTI and the viral load. The overall virucidal efficacy of the tight-binding NNRTI tested was CSIC > UC781 ≃ EFV. We conclude that the tight-binding mode of inhibition is an essential characteristic for virucidal NNRTI and that antiviral potency is an insufficient predictor for virucidal utility of NNRTI.
To identify factors associated with virological response (VR) to an etravirine (ETR)-based regimen, 243 patients previously treated with nonnucleoside reverse transcriptase inhibitors (NNRTIs) were studied. The impact of baseline HIV-1 RNA, CD4 cell count, past NNRTIs used, 57 NNRTI resistance mutations, genotypic sensitivity score (GSS) for nucleoside reverse transcriptase inhibitors (NRTIs) and protease inhibitors (PIs), and the number of new drugs used with ETR for the first time on the VR to an ETR regimen were investigated. Among the 243 patients, the median baseline HIV-1 RNA level was 4.4 log10 copies/ml (interquartile range [IQR], 3.7 to 4.9) and the median CD4 count was 175 cells/mm3 (IQR, 69 to 312). Patients had been previously exposed to a median of 6 NRTIs, 1, NNRTI, and 5 PIs. Overall, 82% of patients achieved a VR at month 2, as defined by a decrease of at least 1.5 log10 copies/ml and/or HIV-1 RNA level of <50 copies/ml. No difference in VR was observed between patients receiving or not a boosted PI in combination with ETR. Factors independently associated with a better VR to ETR were the number of drugs (among enfuvirtide, darunavir, or raltegravir) used for the first time in combination with ETR and the presence of the K103N mutation at baseline. Mutations Y181V and E138A were independently associated with poor VR, whereas no effect of the Y181C on VR was observed. In conclusion, ETR was associated with high response rates in NNRTI-experienced patients in combination with other active drugs regardless of the therapeutic class used.
Etravirine is an oral diarylpyrimidine compound, a second-generation human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase inhibitor (NNRTI) with expanded antiviral activity against NNRTI-resistant HIV-1, to be used in combination therapy for treatment-experienced patients. Compared with first-generation NNRTIs, etravirine has a high genetic barrier to resistance, and is better tolerated without the neuropsychiatric and hepatic side effects of efavirenz and nevirapine, respectively. Its safety profile is comparable to placebo with the exception of rash, which has been mild and self-limited in the great majority of patients. In phase III clinical trials among treatment-experienced patients harboring NNRTI-resistant HIV-1, etravirine in combination with an optimized background regimen (OBR) that included ritonavir-boosted darunavir demonstrated superior antiviral activity than the control OBR. In addition, patients on the etravirine arm had fewer AIDS-defining conditions, hospitalizations, and lower mortality compared with the OBR control arm.
HIV; antiretroviral therapy; non-nucleoside reverse transcriptase inhibitor
Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are potent and commonly prescribed antiviral agents used in combination therapy (CART) of human immunodeficiency virus type 1 (HIV-1) infection. The development of drug resistance is a major limitation of CART. Reverse transcriptase (RT) genotypes with the NNRTI resistance mutations K101E+G190S are highly resistant to efavirenz (EFV) and can develop during failure of EFV-containing regimens in patients. We have previously shown that virus with K101E+G190S mutations can replicate more efficiently in the presence of EFV than in its absence. In this study, we evaluated the underlying mechanism for drug-dependent stimulation, using a single-cycle cell culture assay in which EFV was added either during the infection or the virus production step. We determined that EFV stimulates K101E+G190S virus during early infection and does not affect late steps of virus replication, such as increasing the amount of active RT incorporated into virions. Additionally, we showed that another NNRTI, nevirapine (NVP), stimulated K101E+G190S virus replication during the early steps of infection similar to EFV, but that the newest NNRTI, etravirine (ETR), did not. We also showed that EFV stimulates K101E+Y188L and K101E+V106I virus, but not K101E+L100I, K101E+K103N, K101E+Y181C, or K101E+G190A virus, suggesting that the stimulation is mutation specific. Real-time PCR of reverse transcription intermediates showed that although the drug did not stimulate minus-strand transfer, it did stimulate minus-strand strong-stop DNA synthesis. Our results indicate that stimulation most likely occurs through a mechanism whereby NNRTIs stimulate priming or elongation of the tRNA.
Etravirine (ETR) is an expanded-spectrum nonnucleoside reverse transcriptase inhibitor (NNRTI) approved for use as an antiretroviral agent in treatment-experienced patients. Y181C and E138K in HIV-1 RT are among 20 different drug resistance mutations associated with ETR. However, E138K can be consistently selected by ETR when wild-type viruses but not viruses containing Y181C are grown in tissue culture. This study was carried out to evaluate any possible mechanisms that might explain antagonism between the Y181C and E138K mutations. Accordingly, we performed tissue culture studies to investigate the evolutionary dynamics of E138K in both a wild-type (WT) and a Y181C background. We also generated recombinant enzymes containing Y181C and E138K alone or in combination in order to study enzyme processivity, rates of processive DNA synthesis, enzyme kinetics, and susceptibility to ETR. We now show that the presence of the Y181C mutation prevented the emergence of E138K in cell culture and that the simultaneous presence of E138K and Y181C impaired each of enzyme activity, processivity, rate of processive DNA synthesis, and deoxynucleoside triphosphate (dNTP) affinity. The addition of E138K to Y181C also decreased the level of resistance to ETR compared to that obtained with Y181C alone.
Susceptibility to etravirine (ETR), an expanded-spectrum nonnucleoside reverse transcriptase inhibitor (NNRTI), is dependent on the type and number of NNRTI resistance-associated mutations (RAMs). Studies have shown that some HIV-1 subtypes may have natural polymorphisms described as ETR RAMs. This study addresses the prevalence of ETR RAMs in treatment-naïve patients infected with HIV-1 non-B subtypes and its potential impact on ETR susceptibility. The prevalence of ETR RAMs in 726 antiretroviral-naïve patients infected with non-B HIV-1 subtypes was studied. ETR genotypic resistance was interpreted according to Agence Nationale de Recherches sur le SIDA and Stanford algorithms. NNRTI phenotypic susceptibilities of samples with at least one ETR RAM were measured. Overall, 75 (10.3%) of 726 sequences harbored at least one ETR RAM: sequences from 72 patients (10%) each had one ETR RAM, and sequences from 3 patients (0.4%) each had two ETR RAMs (V90I and Y181C in one case and V90I and A98G in two cases). None of the viruses had three or more ETR RAMs, and none were consequently classified as resistant to ETR. All sequences with two ETR RAMs belonged to subtype CRF02_AG. The presence of one ETR RAM was statistically more frequent in subtype CRF02_AG than in other non-B subtypes (P = 0.004). Three new mutation profiles (E138A and V179I, Y181C and H221Y, and V90I and Y181C) showing decreased ETR phenotypic susceptibility were identified. In conclusion, although the prevalence of ETR RAMs in treatment-naïve patients infected with non-B HIV-1 subtypes was 10%, in most cases this had no significant impact on ETR susceptibility. However, the transmission of drug-resistant viruses with Y181C in a non-B genetic background has a potential for impact on ETR susceptibility.
TMC125 is a potent new investigational nonnucleoside reverse transcriptase inhibitor (NNRTI) that is active against human immunodeficiency virus type 1 (HIV-1) with resistance to currently licensed NNRTIs. Sequential passage experiments with both wild-type virus and NNRTI-resistant virus were performed to identify mutations selected by TMC125 in vitro. In addition to “classic” selection experiments at a low multiplicity of infection (MOI) with increasing concentrations of inhibitors, experiments at a high MOI with fixed concentrations of inhibitors were performed to ensure a standardized comparison between TMC125 and current NNRTIs. Both low- and high-MOI experiments demonstrated that the development of resistance to TMC125 required multiple mutations which frequently conferred cross-resistance to efavirenz and nevirapine. In high-MOI experiments, 1 μM TMC125 completely inhibited the breakthrough of resistant virus from wild-type and NNRTI-resistant HIV-1, in contrast to efavirenz and nevirapine. Furthermore, breakthrough of virus from site-directed mutant (SDM) SDM-K103N/Y181C occurred at the same time or later with TMC125 as breakthrough from wild-type HIV-1 with efavirenz or nevirapine. The selection experiments identified mutations selected by TMC125 that included known NNRTI-associated mutations L100I, Y181C, G190E, M230L, and Y318F and the novel mutations V179I and V179F. Testing the antiviral activity of TMC125 against a panel of SDMs indicated that the impact of these individual mutations on resistance was highly dependent upon the presence and identity of coexisting mutations. These results demonstrate that TMC125 has a unique profile of activity against NNRTI-resistant virus and possesses a high genetic barrier to the development of resistance in vitro.
We previously identified a rare mutation in human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT), I132M, which confers high-level resistance to the nonnucleoside RT inhibitors (NNRTIs) nevirapine and delavirdine. In this study, we have further characterized the role of this mutation in viral replication capacity and in resistance to other RT inhibitors. Surprisingly, our data show that I132M confers marked hypersusceptibility to the nucleoside analogs lamivudine (3TC) and tenofovir at both the virus and enzyme levels. Subunit-selective mutagenesis studies revealed that the mutation in the p51 subunit of RT was responsible for the increased sensitivity to the drugs, and transient kinetic analyses showed that this hypersusceptibility was due to I132M decreasing the enzyme's affinity for the natural dCTP substrate but increasing its affinity for 3TC-triphosphate. Furthermore, the replication capacity of HIV-1 containing I132M is severely impaired. This decrease in viral replication capacity could be partially or completely compensated for by the A62V or L214I mutation, respectively. Taken together, these results help to explain the infrequent selection of I132M in patients for whom NNRTI regimens are failing and furthermore demonstrate that a single mutation outside of the polymerase active site and inside of the p51 subunit of RT can significantly influence nucleotide selectivity.
Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are the mainstays of therapy for the treatment of human immunodeficiency virus type 1 (HIV-1) infections. However, the effectiveness of NNRTIs can be hampered by the development of resistance mutations which confer cross-resistance to drugs in the same class. Extensive efforts have been made to identify new NNRTIs that can suppress the replication of the prevalent NNRTI-resistant viruses. MK-4965 is a novel NNRTI that possesses both diaryl ether and indazole moieties. The compound displays potency at subnanomolar concentrations against wild-type (WT), K103N, and Y181C reverse transcriptase (RT) in biochemical assays. MK-4965 is also highly potent against the WT virus and two most prevalent NNRTI-resistant viruses (viruses that harbor the K103N or the Y181C mutation), against which it had 95% effective concentrations (EC95s) of <30 nM in the presence of 10% fetal bovine serum. The antiviral EC95 of MK-4965 was reduced approximately four- to sixfold when it was tested in 50% human serum. Moreover, MK-4965 was evaluated with a panel of 15 viruses with NNRTI resistance-associated mutations and showed a superior mutant profile to that of efavirenz but not to that of etravirine. MK-4965 was similarly effective against various HIV-1 subtypes and viruses containing nucleoside reverse transcriptase inhibitor or protease inhibitor resistance-conferring mutations. A two-drug combination study showed that the antiviral activity of MK-4965 was nonantagonistic with each of the 18 FDA-licensed drugs tested vice versa in the present study. Taken together, these in vitro data show that MK-4965 possesses the desired properties for further development as a new NNRTI for the treatment of HIV-1 infection.
Etravirine, a second-generation non-nucleoside reverse transcriptase inhibitor (NNRTI), was approved in the USA in January, 2008, with approval in Europe expected later this year. It is dosed at 200 mg (two 100 mg tablets) twice daily foll owing a meal. It is approved for treatment of HIV-1 infection in adults failing a stable antiretroviral regimen with resistance to other NNRTIs and other antiretroviral agents. Etravirine is active against HIV with single mutations in the reverse transcriptase (e.g., K103N) that confer class resistance to first-generation NNRTIs. Clinical efficacy in Phase III trials has been demonstrated for up to 48 weeks of follow-up. In these Phase III trials, rash was the only adverse event that was significantly more prevalent with etravirine than with placebo. Etravirine has a tolerability and safety profile comparable to placebo with the exception of rash. Rash was generally grade 1 or 2, was not associated with prior NNRTI-related rash, was more common in women than in men, appeared a median of 12 days after treatment initiation and resolved spontaneously with continued therapy. Etravirine is the first agent in the NNRTI class that can be used for HIV-1 virus with resistance to other NNRTIs owing to a higher genetic barrier to resistance.
etravirine; HIV; Intelence™; non-nucleoside reverse transcriptase inhibitor; TMC125
The (alkylamino)piperidine bis(heteroaryl)piperizines (AAP-BHAPs) are a new class of human immunodeficiency virus type 1 (HIV-1)-specific inhibitors which were identified by targeted screening of recombinant reverse transcriptase (RT) enzymes carrying key nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance-conferring mutations and NNRTI-resistant variants of HIV-1. Phenotypic profiling of the two most potent AAP-BHAPs, U-95133 and U-104489, against in vitro-selected drug-resistant HIV-1 variants carrying the NNRTI resistance-conferring mutation (Tyr->Cys) at position 181 of the HIV-1 RT revealed submicromolar 90% inhibitory concentration estimates for these compounds. Moreover, U-104489 demonstrated potent activity against BHA-P-resistant HIV-1MF harboring the Pro-236->Leu RT substitution and significantly suppressed the replication of clinical isolates of HIV-1 resistant to both delavirdine (BHAP U-90152T) and zidovudine. Biochemical and phenotypic characterization of AAP-BHAPresistant HIV-1IIIB variants revealed that high-level resistance to the AAP-BHAPs was mediated by a Gly-190->Glu substitution in RT, which had a deleterious effect on the integrity and enzymatic activity of virion-associated RT heterodimers, as well as the replication capacity of these resistant viruses.
We investigated whether reverse transcriptase (RT) inhibitors (RTI) can be combined to inhibit human immunodeficiency virus type 1 (HIV-1) infection of colorectal tissue ex vivo as part of a strategy to develop an effective rectal microbicide. The nucleotide RTI (NRTI) PMPA (tenofovir) and two nonnucleoside RTI (NNRTI), UC-781 and TMC120 (dapivirine), were evaluated. Each compound inhibited the replication of the HIV isolates tested in TZM-bl cells, peripheral blood mononuclear cells, and colorectal explants. Dual combinations of the three compounds, either NRTI-NNRTI or NNRTI-NNRTI combinations, were more active than any of the individual compounds in both cellular and tissue models. Combinations were key to inhibiting infection by NRTI- and NNRTI-resistant isolates in all models tested. Moreover, we found that the replication capacities of HIV-1 isolates in colorectal explants were affected by single point mutations in RT that confer resistance to RTI. These data demonstrate that colorectal explants can be used to screen compounds for potential efficacy as part of a combination microbicide and to determine the mucosal fitness of RTI-resistant isolates. These findings may have important implications for the rational design of effective rectal microbicides.
We studied the evolution of nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance mutations among 29 human immunodeficiency virus type 1 (HIV-1)-infected patients who experienced virologic failure when receiving an NNRTI-containing regimen (nevirapine, delavirdine, or efavirenz) and subsequently switched to antiretroviral therapy without NNRTIs. Genotypic resistance was determined from plasma samples collected at the time of NNRTI withdrawal (baseline) and during follow-up. At baseline, 83% of patients had more than two thymidine analog resistance mutations (TAMs), and all had NNRTI resistance mutations. Mutations at codons 103, 181, and 190 were found in 62, 62, and 34% of the patients, respectively. Follow-up samples were available after a median time of 6 months in all patients and at 12 months in 22 patients. The mean number of resistance mutations to NNRTIs was significantly lower at months 6 (1.34 ± 1.04) and 12 (1.18 ± 1.05) than at month 0 (2.03 ± 1.02) (P < 0.009). The percentages of patients with at least one NNRTI resistance mutation were 100, 76, and 73% at baseline, month 6, and month 12, respectively (P < 0.0044). Overall, 70% of the patients had a mutation at codon 103 or 181 at month 12. The mean number of TAMs did not vary significantly during follow-up. Our data show that, in the context of maintained antiretroviral therapy, NNRTI resistance mutations persist in two-thirds of the patients in spite of NNRTI withdrawal. These results argue for the low impact of NNRTI resistance mutations on viral fitness and suggest that resistance mutations to different classes of drugs are associated on the same genome, at least in some of the resistant strains.