Pretreatment and Acquired Drug Resistance in Children With Human Immunodeficiency Virus Type 1 in Jos, Nigeria

We determined pretreatment and acquired human immunodeficiency virus (HIV) drug resistance among children with HIV type 1 (HIV-1) in Jos, Nigeria. The majority (71%) of those who failed first-line antiretroviral therapy were on a nevirapine-containing regimen. The prevalence of pretreatment (48%) and acquired (76%) HIV drug resistance mutations was high in our study. Wider access to HIV drug resistance testing after treatment failure is necessary to optimize second-line treatment options among children with HIV in Nigeria.

Doravirine and Islatravir Have Complementary Resistance Profiles and Create a Combination with a High Barrier to Resistance

Doravirine (DOR), a non-nucleoside reverse transcriptase inhibitor (NNRTI), was approved for treatment of HIV-1 infection in 2018. In the pivotal phase 3 trials, DRIVE-FORWARD and DRIVE-AHEAD, 7 out of 747 (0.9%) treatment-naive participants treated with DOR plus two nucleos(t)ide reverse transcriptase inhibitors (NRTIs) met protocol-defined virologic failure criteria and showed phenotypic resistance to DOR at week 48. The most common DOR resistance-associated mutation (RAM) detected in 5 of the 7 resistant isolates was F227C. Six isolates bearing NRTI RAMs (M184V and/or K65R) were resistant to lamivudine (3TC) and emtricitabine (FTC) but not to other approved NRTIs. All DOR-resistant isolates were susceptible or hypersusceptible (fold change of <0.25) to islatravir (ISL), a nucleoside reverse transcriptase translocation inhibitor (NRTTI). Isolate hypersusceptibility to ISL required F227C, in contrast to zidovudine, an NRTI, which required M184V. Based on the frequent emergence of F227C, we hypothesized that DOR and ISL would create a combination (DOR/ISL) with a high barrier to resistance. In de novo resistance selection studies in MT4-GFP cells (MT4 cells engineered to express green fluorescent protein), DOR/ISL synergistically prevented viral breakthrough at a threshold of 2× the half-maximal inhibitory concentration (IC₅₀). DOR/ISL exhibited a higher barrier to resistance than DOR/3TC and dolutegravir (DTG)/3TC. Resistance analysis showed no emergence of substitutions at F227, an observation consistent with its ability to confer hypersusceptibility to ISL. Overall, the data demonstrate that DOR/ISL creates a 2-drug combination with a higher barrier to resistance, consistent with the reported clinical activity.

Structural Basis of 2-Phenylamino-4-phenoxyquinoline Derivatives as Potent HIV-1 Non-Nucleoside Reverse Transcriptase Inhibitors

New target molecules, namely, 2-phenylamino-4-phenoxyquinoline derivatives, were designed using a molecular hybridization approach, which was accomplished by fusing the pharmacophore structures of three currently available drugs: nevirapine, efavirenz, and rilpivirine. The discovery of disubstituted quinoline indicated that the pyridinylamino substituent at the 2-position of quinoline plays an important role in its inhibitory activity against HIV-1 RT. The highly potent HIV-1 RT inhibitors, namely, 4-(2′,6′-dimethyl-4′-formylphenoxy)-2-(5″-cyanopyridin-2″ylamino)quinoline (6b) and 4-(2′,6′-dimethyl-4′-cyanophenoxy)-2-(5″-cyanopyridin-2″ylamino)quinoline (6d) exhibited half-maximal inhibitory concentrations (IC50) of 1.93 and 1.22 µM, respectively, which are similar to that of nevirapine (IC50 = 1.05 µM). The molecular docking results for these two compounds showed that both compounds interacted with Lys101, His235, and Pro236 residues through hydrogen bonding and interacted with Tyr188, Trp229, and Tyr318 residues through π–π stacking in HIV-1 RT. Interestingly, 6b was highly cytotoxic against MOLT-3 (acute lymphoblastic leukemia), HeLA (cervical carcinoma), and HL-60 (promyeloblast) cells with IC50 values of 12.7 ± 1.1, 25.7 ± 0.8, and 20.5 ± 2.1 µM, respectively. However, 6b and 6d had very low and no cytotoxicity, respectively, to-ward normal embryonic lung (MRC-5) cells. Therefore, the synthesis and biological evaluation of 2-phenylamino-4-phenoxyquinoline derivatives can serve as an excellent basis for the development of highly effective anti-HIV-1 and anticancer agents in the near future.

Epistasis and entrenchment of drug resistance in HIV-1 subtype B

The development of drug resistance in HIV is the result of primary mutations whose effects on viral fitness depend on the entire genetic background, a phenomenon called 'epistasis'. Based on protein sequences derived from drug-experienced patients in the Stanford HIV database, we use a co-evolutionary (Potts) Hamiltonian model to provide direct confirmation of epistasis involving many simultaneous mutations. Building on earlier work, we show that primary mutations leading to drug resistance can become highly favored (or entrenched) by the complex mutation patterns arising in response to drug therapy despite being disfavored in the wild-type background, and provide the first confirmation of entrenchment for all three drug-target proteins: protease, reverse transcriptase, and integrase; a comparative analysis reveals that NNRTI-induced mutations behave differently from the others. We further show that the likelihood of resistance mutations can vary widely in patient populations, and from the population average compared to specific molecular clones.

New strategy for identifying potential natural HIV-1 non-nucleoside reverse transcriptase inhibitors against drug-resistance: an in silico study

Non-nucleosides reverse transcriptase inhibitors (NNRTIs), specifically targeting the HIV-1 reverse transcriptase (RT), play a unique role in anti-AIDS agents due to their high antiviral potency, structural diversity, and low toxicity in antiretroviral combination therapies used to treat HIV. However, due to the emergence of new drug-resistant strains, the development of novel NNRTIs with adequate potency, improved resistance profiles and less toxicity is highly required. In this work, a novel virtual screening strategy combined with structure-based drug design was proposed to discover the potential inhibitors against drug-resistant HIV strains. Seven structure-variant RTs, ranging from the wild type to a hypothetical multi-mutant were regarded as target proteins to perform structure-based virtual screening. Totally 23 small molecules with good binding affinity were identified from the Traditional Chinese Medicine database (TCM) as potential NNRTIs candidates. Among these hits, (+)-Hinokinin has confirmed anti-HIV activity, and some hits are structurally identical with anti-HIV compounds. Almost all these hits are consistent with external experimental results. Molecular simulations analysis revealed that top 2 hits (Pallidisetin A and Pallidisetin B) bind stably and in high affinity to HIV-RT, which are ready to be experimental confirmed. These results suggested that the strategy we proposed is feasible, trustworthy and effective. Our finding might be helpful in the identification of novel NNRTIs against drug-resistant, and also provide a new clue for the discovery of HIV drugs in natural products.Communicated by Ramaswamy H. Sarma.

Structural and pharmacological evaluation of a novel non-nucleoside reverse transcriptase inhibitor as a promising long acting nanoformulation for treating HIV

Combination antiretroviral therapy (cART) has been proven effective in inhibiting human immunodeficiency virus type 1 (HIV-1) infection and has significantly improved the health outcomes in acquired immune deficiency syndrome (AIDS) patients. The therapeutic benefits of cART have been challenged because of the toxicity and emergence of drug-resistant HIV-1 strains along with lifelong patient compliance resulting in non-adherence. These issues also hinder the clinical benefits of non-nucleoside reverse transcriptase inhibitors (NNRTIs), which are one of the vital components of cART for the treatment of HIV-1 infection. In this study, using a computational and structural based drug design approach, we have discovered an effective HIV -1 NNRTI, compound I (Cmpd I) that is very potent in biochemical assays and which targets key residues in the allosteric binding pocket of wild-type (WT)-RT as revealed by structural studies. Furthermore, Cmpd I exhibited very potent antiviral activity in HIV-1 infected T cells, lacked cytotoxicity (therapeutic index >100,000), and no significant off-target effects were noted in pharmacological assays. To address the issue of non-adherence, we developed a long-acting nanoformulation of Cmpd I (Cmpd I-NP) using poly (lactide-coglycolide) (PLGA) particles. The pharmacokinetic studies of free and nanoformulated Cmpd I were carried out in BALB/c mice. Intraperitoneal administration of Cmpd I and Cmpd I-NP in BALB/c mice revealed prolonged serum residence time of 48 h and 30 days, respectively. The observed serum concentrations of Cmpd I in both cases were sufficient to provide >97% inhibition in HIV-1 infected T-cells. The significant antiviral activity along with favorable pharmacological and pharmacokinetic profile of Cmpd I, provide compelling and critical support for its further development as an anti-HIV therapeutic agent.

Prediction of the binding mode and resistance profile for a dual-target pyrrolyl diketo acid scaffold against HIV-1 integrase and reverse-transcriptase-associated ribonuclease H

The rapid emergence of drug-resistant variants is one of the most common causes of highly active antiretroviral therapeutic (HAART) failure in patients infected with HIV-1. Compared with the existing HAART, the recently developed pyrrolyl diketo acid scaffold targeting both HIV-1 integrase (IN) and reverse transcriptase-associated ribonuclease H (RNase H) is an efficient approach to counteract the failure of anti-HIV treatment due to drug resistance. However, the binding mode and potential resistance profile of these inhibitors with important mechanistic principles remain poorly understood. To address this issue, an integrated computational method was employed to investigate the binding mode of inhibitor JMC6F with HIV-1 IN and RNase H. By using per-residue binding free energy decomposition analysis, the following residues: Asp64, Thr66, Leu68, Asp116, Tyr143, Gln148 and Glu152 in IN, Asp443, Glu478, Trp536, Lys541 and Asp549 in RNase H were identified as key residues for JMC6F binding. And then computational alanine scanning was carried to further verify the key residues. Moreover, the resistance profile of the currently known major mutations in HIV-1 IN and 2 mutations in RNase H against JMC6F was predicted by in silico mutagenesis studies. The results demonstrated that only three mutations in HIV-1 IN (Y143C, Q148R and N155H) and two mutations in HIV-1 RNase H (Y501R and Y501W) resulted in a reduction of JMC6F potency, thus indicating their potential role in providing resistance to JMC6F. These data provided important insights into the binding mode and resistance profile of the inhibitors with a pyrrolyl diketo acid scaffold in HIV-1 IN and RNase H, which would be helpful for the development of more effective dual HIV-1 IN and RNase H inhibitors.

Diaryl ethers with carboxymethoxyphenacyl motif as potent HIV-1 reverse transcriptase inhibitors with improved solubility

In search of new non-nucleoside reverse transcriptase inhibitors (NNRTIs) with improved solubility, two series of novel diaryl ethers with phenacyl moiety were designed and evaluated for their HIV-1 reverse transcriptase inhibition potentials. All compounds exhibited good to excellent results with IC₅₀ at low micromolar to submicromolar concentrations. Two most active compounds (7e and 7 g) exhibit inhibitory potency comparable or even better than that of nevirapine and rilpivirine. Furthermore, SupT1 and CD4⁺ cell infectivity assays for the most promising (7e) have confirmed its strong antiviral potential while docking studies indicate a novel binding interactions responsible for high activity.

Potential of small-molecule fungal metabolites in antiviral chemotherapy

Various viral diseases, such as acquired immunodeficiency syndrome, influenza, and hepatitis, have emerged as leading causes of human death worldwide. Scientific endeavor since invention of DNA-dependent RNA polymerase of pox virus in 1967 resulted in better understanding of virus replication and development of various novel therapeutic strategies. Despite considerable advancement in every facet of drug discovery process, development of commercially viable, safe, and effective drugs for these viruses still remains a big challenge. Decades of intense research yielded a handful of natural and synthetic therapeutic options. But emergence of new viruses and drug-resistant viral strains had made new drug development process a never-ending battle. Small-molecule fungal metabolites due to their vast diversity, stereochemical complexity, and preapproved biocompatibility always remain an attractive source for new drug discovery. Though, exploration of therapeutic importance of fungal metabolites has started early with discovery of penicillin, recent prediction asserted that only a small percentage (5-10%) of fungal species have been identified and much less have been scientifically investigated. Therefore, exploration of new fungal metabolites, their bioassay, and subsequent mechanistic study bears huge importance in new drug discovery endeavors. Though no fungal metabolites so far approved for antiviral treatment, many of these exhibited high potential against various viral diseases. This review comprehensively discussed about antiviral activities of fungal metabolites of diverse origin against some important viral diseases. This also highlighted the mechanistic details of inhibition of viral replication along with structure-activity relationship of some common and important classes of fungal metabolites.

Preformulation and Vaginal Film Formulation Development of Microbicide Drug Candidate CSIC for HIV prevention

PURPOSE

5-chloro-3-[phenylsulfonyl] indole-2-carboxamide (CSIC) is a highly potent non-nucleoside reverse transcriptase inhibitor (NNRTI) of HIV-1 which has been shown to have a more desirable resistance profile than other NNRTIs in development as HIV prevention strategies. This work involves generation of preformulation data for CSIC and systematic development of a cosolvent system to effectively solubilize this hydrophobic drug candidate. This system was then applied to produce a polymeric thin film solid dosage form for vaginal administration of CSIC for use in prevention of sexual acquisition of HIV.

METHODS

Extensive preformulation, formulation development, and film characterization studies were conducted. An HPLC method was developed for CSIC quantification. Preformulation tests included solubility, crystal properties, stability, and drug-excipient compatibility. Cytotoxicity was evaluated using both human epithelial and mouse macrophage cell lines. Ternary phase diagram methodology was used to identify a cosolvent system for CSIC solubility enhancement. Following preformulation evaluation, a CSIC film formulation was developed and manufactured using solvent casting technique. The developed film product was assessed for physicochemical properties, anti-HIV bioactivity, and Lactobacillus biocompatibility during 12-month stability testing period.

RESULTS

Preformulation studies showed CSIC to be very stable. Due to its hydrophobicity, a cosolvent system consisting of polyethylene glycol 400, propylene glycol, and glycerin (5:2:1, w/w/w) was developed, which provided a uniform dispersion of CSIC in the film formulation. The final film product met target specifications established for vaginal microbicide application.

CONCLUSIONS

The hydrophobic drug candidate CSIC was successfully formulated with high loading capacity in a vaginal film by means of a cosolvent system. The developed cosolvent strategy is applicable for incorporation of other hydrophobic drug candidates in the film platform.

Structural and Preclinical Studies of Computationally Designed Non-Nucleoside Reverse Transcriptase Inhibitors for Treating HIV infection

The clinical benefits of HIV-1 non-nucleoside reverse transcriptase (RT) inhibitors (NNRTIs) are hindered by their unsatisfactory pharmacokinetic (PK) properties along with the rapid development of drug-resistant variants. However, the clinical efficacy of these inhibitors can be improved by developing compounds with enhanced pharmacological profiles and heightened antiviral activity. We used computational and structure-guided design to develop two next-generation NNRTI drug candidates, compounds I and II, which are members of a class of catechol diethers. We evaluated the preclinical potential of these compounds in BALB/c mice because of their high solubility (510 µg/ml for compound I and 82.9 µg/ml for compound II), low cytotoxicity, and enhanced antiviral activity against wild-type (WT) HIV-1 RT and resistant variants. Additionally, crystal structures of compounds I and II with WT RT suggested an optimal binding to the NNRTI binding pocket favoring the high anti-viral potency. A single intraperitoneal dose of compounds I and II exhibited a prolonged serum residence time of 48 hours and concentration maximum (C_max) of 4000- to 15,000-fold higher than their therapeutic/effective concentrations. These C_max values were 4- to 15-fold lower than their cytotoxic concentrations observed in MT-2 cells. Compound II showed an enhanced area under the curve (0-last) and decreased plasma clearance over compound I and efavirenz, the standard of care NNRTI. Hence, the overall (PK) profile of compound II was excellent compared with that of compound I and efavirenz. Furthermore, both compounds were very well tolerated in BALB/c mice without any detectable acute toxicity. Taken together, these data suggest that compounds I and II possess improved anti-HIV-1 potency, remarkable in vivo safety, and prolonged in vivo circulation time, suggesting strong potential for further development as new NNRTIs for the potential treatment of HIV infection.

HIV-1 drug resistance and resistance testing

The global scale-up of antiretroviral (ARV) therapy (ART) has led to dramatic reductions in HIV-1 mortality and incidence. However, HIV drug resistance (HIVDR) poses a potential threat to the long-term success of ART and is emerging as a threat to the elimination of AIDS as a public health problem by 2030. In this review we describe the genetic mechanisms, epidemiology, and management of HIVDR at both individual and population levels across diverse economic and geographic settings. To describe the genetic mechanisms of HIVDR, we review the genetic barriers to resistance for the most commonly used ARVs and describe the extent of cross-resistance between them. To describe the epidemiology of HIVDR, we summarize the prevalence and patterns of transmitted drug resistance (TDR) and acquired drug resistance (ADR) in both high-income and low- and middle-income countries (LMICs). We also review to two categories of HIVDR with important public health relevance: (i) pre-treatment drug resistance (PDR), a World Health Organization-recommended HIVDR surveillance metric and (ii) and pre-exposure prophylaxis (PrEP)-related drug resistance, a type of ADR that can impact clinical outcomes if present at the time of treatment initiation. To summarize the implications of HIVDR for patient management, we review the role of genotypic resistance testing and treatment practices in both high-income and LMIC settings. In high-income countries where drug resistance testing is part of routine care, such an understanding can help clinicians prevent virological failure and accumulation of further HIVDR on an individual level by selecting the most efficacious regimens for their patients. Although there is reduced access to diagnostic testing and to many ARVs in LMIC, understanding the scientific basis and clinical implications of HIVDR is useful in all regions in order to shape appropriate surveillance, inform treatment algorithms, and manage difficult cases.

Adherence to Antiretroviral Therapy and Virologic Failure: A Meta-Analysis

The often cited need to achieve ≥95% (nearly perfect) adherence to antiretroviral therapy (ART) for successful virologic outcomes in HIV may present a barrier to initiation of therapy in the early stages of HIV. This meta-analysis synthesized 43 studies (27,905 participants) performed across >26 countries, to determine the relationship between cut-off point for optimal adherence to ART and virologic outcomes. Meta-analysis was performed using a random-effect model to calculate pooled odds ratios with corresponding 95% confidence intervals. The mean rate of patients reporting optimal adherence was 63.4%. Compared with suboptimal adherence, optimal adherence was associated with a lower risk of virologic failure (0.34; 95% CI: 0.26-0.44). There were no significant differences in the pooled odds ratios among different optimal adherence thresholds (≥98-100%, ≥95%, ≥80-90%). Study design (randomized controlled trial vs observational study) (regression coefficient 0.74, 95% CI: 0.04-1.43, P < 0.05) and study region (developing vs developed countries; regression coefficient 0.56, 95% CI: 0.01-1.12, P < 0.05) remained as independent predictors of between-study heterogeneity, with more patients with optimal adherence from developing countries or randomized controlled trials experiencing virologic failure. The threshold for optimal adherence to achieve better virologic outcomes appears to be wider than the commonly used cut-off point (≥95% adherence). The cut-off point for optimal adherence could be redefined to a slightly lower level to encourage the prescribing ART at an early stage of HIV infection.

Focus on Chirality of HIV-1 Non-Nucleoside Reverse Transcriptase Inhibitors

Chiral HIV-1 non-nucleoside reverse transcriptase inhibitors (NNRTIs) are of great interest since one enantiomer is often more potent than the corresponding counterpart against the HIV-1 wild type (WT) and the HIV-1 drug resistant mutant strains. This review exemplifies the various studies made to investigate the effect of chirality on the antiretroviral activity of top HIV-1 NNRTI compounds, such as nevirapine (NVP), efavirenz (EFV), alkynyl- and alkenylquinazolinone DuPont compounds (DPC), diarylpyrimidine (DAPY), dihydroalkyloxybenzyloxopyrimidine (DABO), phenethylthiazolylthiourea (PETT), indolylarylsulfone (IAS), arylphosphoindole (API) and trifluoromethylated indole (TFMI) The chiral separation, the enantiosynthesis, along with the biological properties of these HIV-1 NNRTIs, are discussed.

Assessment of etravirine resistance in HIV-1-infected paediatric patients using population and deep sequencing: final results of the PIANO study

BACKGROUND

We assessed etravirine resistance in treatment-experienced, HIV-1-infected children (n=41)/adolescents (n=60) who received twice-daily etravirine 5.2 mg/kg and a background regimen (boosted protease inhibitor plus nucleoside/nucleotide reverse transcriptase inhibitors, optional enfuvirtide/raltegravir) in a Phase II, open-label, multicentre trial (PIANO).

METHODS

In addition to phenotypes, viral genotypes were assessed by population and deep sequencing (PS and DS) in virological failures (VFs; baseline and end point) and responders (baseline). Minority resistance-associated mutations (RAMs) were defined as those with frequencies above 1% and not detected with PS.

RESULTS

By week 48, 41/101 (40.6%) patients experienced VF; 17/41 (41.5%) VFs and 22/54 (40.8%) responders had ≥1 baseline etravirine RAM by PS, mainly A98G, K101E, V106I and G190A. Baseline minority etravirine RAMs (n) were detected in 8/40 VFs (V90I [2], A98G [1], L100I [1], V106I [1], E138G [1] and Y181C [2]) and 5/38 responders (V90I [3], A98G [1], V106I [1] and E138G [1]). The most frequent emerging non-nucleoside reverse transcriptase inhibitor RAMs detected by PS (≥3 VFs; n) were the etravirine RAMs Y181C (8), V90I (3), L100I (3) and E138A (3). In 15 of 29 (51.7%) VFs with baseline DS/PS and end point PS data, ≥1 emerging etravirine RAM was detected by PS, which was not detected at baseline by DS in most cases (12/15 [80.0%]). In 10/26 (38.5%) VFs with baseline/end point DS data, ≥1 additional emerging minority etravirine RAM was detected.

CONCLUSIONS

Patterns of etravirine resistance in adults, adolescents and children experiencing VF are similar. The presence of minority etravirine RAMs at baseline was not consistently associated with treatment failure. ClinicalTrials.gov: NCT00665847.

Investigational reverse transcriptase inhibitors for the treatment of HIV

INTRODUCTION

While considerable advances have been made in the development of antiretroviral agents, there is still work to be done. Reverse transcriptase inhibitors are important drugs for the treatment of HIV, and considerable research is currently ongoing to develop new agents and to modify currently existing agents.

AREAS COVERED

Herein, the authors discuss both investigational nucleoside reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs), including agents that are in various stages of development. They also discuss novel formulations that are being investigated for currently available drugs, and discuss the advantages that these new formulations may provide.

EXPERT OPINION

New formulations and co-formulations of currently existing antiretrovirals will represent an important area of development, as a means to improve adherence for HIV-positive individuals. New formulations will continue to be developed, with a focus on allowing for less-frequent administration, as well increasing drug concentrations at local sites such as vaginal tissue, rectal tissue and sites in the immune system.

Baseline antiretroviral resistance mutations and treatment-emergent resistance in HIV-1 RNA-suppressed patients switching to EVG/COBI/FTC/TDF or continuing on their PI-, NNRTI-, or RAL-based regimen

BACKGROUND

Stably suppressed HIV-1-infected patients that switched to elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate (EVG/COBI/FTC/TDF) from regimens containing FTC/TDF plus a ritonavir-boosted protease inhibitor (PI + RTV), nonnucleoside reverse transcriptase inhibitor (NNRTI), or raltegravir in phase 3 studies STRATEGY-PI, STRATEGY-NNRTI, and GS-US-236-0123 maintained high rates of virologic suppression through 48 weeks. In this article, resistance analyses for these studies are described.

METHODS

HIV-1 historical genotypes obtained before therapy initiation were analyzed for preexisting/transmitted resistance (-R) in protease and reverse transcriptase (RT) and subtype. Patients with resistance to FTC/TDF were excluded. Viral isolates with HIV-1 RNA ≥400 copies per milliliter at confirmed virologic failure, discontinuation, or week 48 were analyzed for protease, RT, and integrase genotype and phenotype.

RESULTS

Historical genotypes from 626/628 subjects that switched to EVG/COBI/FTC/TDF indicated 25% had ≥1 primary resistance mutation in protease and/or RT. NNRTI-R was identified in 15%, NRTI-R in 8.3%, and PI-R in 3.7% of subjects. Week 48 virologic success rates (HIV-1 RNA <50 copies per milliliter) were 94% for all patients treated with EVG/COBI/FTC/TDF, 94% with preexisting resistance, 93% with subtype B, and 96% with non-B subtypes. Altogether, 2 subjects qualified for postbaseline resistance analyses. Neither had emergent resistance, and both resuppressed to HIV-1 RNA <50 copies per milliliter with no change in therapy.

CONCLUSIONS

Switching antiretroviral regimens to EVG/COBI/FTC/TDF in HIV-1 RNA-suppressed FTC/TDF-sensitive patients resulted in maintained virologic suppression through 48 weeks. Similar virologic success rates were achieved irrespective of the presence of preexisting resistance mutations or subtype. The lack of emergent resistance through 48 weeks supports utility of EVG/COBI/FTC/TDF for treatment-experienced patients seeking regimen modification or simplification.

Current perspectives on HIV-1 antiretroviral drug resistance

Current advancements in antiretroviral therapy (ART) have turned HIV-1 infection into a chronic and manageable disease. However, treatment is only effective until HIV-1 develops resistance against the administered drugs. The most recent antiretroviral drugs have become superior at delaying the evolution of acquired drug resistance. In this review, the viral fitness and its correlation to HIV-1 mutation rates and drug resistance are discussed while emphasizing the concept of lethal mutagenesis as an alternative therapy. The development of resistance to the different classes of approved drugs and the importance of monitoring antiretroviral drug resistance are also summarized briefly.

Development of a sensitive amplified luminescent proximity homogeneous assay to monitor the interactions between pTEFb and Tat

The viral transactivator protein (Tat) plays an essential role in the replication of human immunodeficiency type 1 virus (HIV-1) by recruiting the host positive transcription elongation factor (pTEFb) to the RNA polymerase II transcription machinery to enable an efficient HIV-1 RNA elongation process. Blockade of the interaction between Tat and pTEFb represents a novel strategy for developing a new class of antiviral agents. In this study, we developed a homogeneous assay in AlphaLISA (amplified luminescent proximity homogeneous assay) format using His-tagged pTEFb and biotinylated Tat to monitor the interaction between Tat and pTEFb. On optimizing the assay conditions, the signal-to-background ratio was found to be greater than 10-fold. The assay was validated with untagged Tat and peptides known to compete with Tat for pTEFb binding. The Z' of the assay is greater than 0.5, indicating that the assay is robust and can be easily adapted to a high-throughput screening format. Furthermore, the affinity between Tat and pTEFb was determined to be approximately 20 pM, and only 7% of purified Tat was found to be active in forming tertiary complex with pTEFb. Development of this assay should facilitate the discovery of a new class of antiviral agents providing HIV-1 patients with broader treatment choices.

In vitro characterization of MK-1439, a novel HIV-1 nonnucleoside reverse transcriptase inhibitor

Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are a mainstay of therapy for treating human immunodeficiency type 1 virus (HIV-1)-infected patients. MK-1439 is a novel NNRTI with a 50% inhibitory concentration (IC50) of 12, 9.7, and 9.7 nM against the wild type (WT) and K103N and Y181C reverse transcriptase (RT) mutants, respectively, in a biochemical assay. Selectivity and cytotoxicity studies confirmed that MK-1439 is a highly specific NNRTI with minimum off-target activities. In the presence of 50% normal human serum (NHS), MK-1439 showed excellent potency in suppressing the replication of WT virus, with a 95% effective concentration (EC95) of 20 nM, as well as K103N, Y181C, and K103N/Y181C mutant viruses with EC95 of 43, 27, and 55 nM, respectively. MK-1439 exhibited similar antiviral activities against 10 different HIV-1 subtype viruses (a total of 93 viruses). In addition, the susceptibility of a broader array of clinical NNRTI-associated mutant viruses (a total of 96 viruses) to MK-1439 and other benchmark NNRTIs was investigated. The results showed that the mutant profile of MK-1439 was superior overall to that of efavirenz (EFV) and comparable to that of etravirine (ETR) and rilpivirine (RPV). Furthermore, E138K, Y181C, and K101E mutant viruses that are associated with ETR and RPV were susceptible to MK-1439 with a fold change (FC) of <3. A two-drug in vitro combination study indicated that MK-1439 acts nonantagonistically in the antiviral activity with each of 18 FDA-licensed drugs for HIV infection. Taken together, these in vitro data suggest that MK-1439 possesses the desired properties for further development as a new antiviral agent.

Phenylspirodrimanes with anti-HIV activity from the sponge-derived fungus Stachybotrys chartarum MXH-X73

Seven new phenylspirodrimanes, named stachybotrins D-F (1, 3, 4), stachybocins E and F (5, 6), and stachybosides A and B (7, 8), and four known compounds (2, 9-11), were isolated from the sponge-derived fungus Stachybotrys chartarum MXH-X73. Their structures were determined by detailed analysis of spectroscopic data. The absolute configurations of 1-8 were determined by chemical hydrolysis and modified Mosher's and Marfey's methods. All compounds were tested in an anti-HIV activity assay, and compound 1 showed an inhibitory effect on HIV-1 replication by targeting reverse transcriptase. Further study exhibited that 1 could block NNRTIs-resistant strains (HIV-1RT-K103N, HIV-1RT-L100I,K103N, HIV-1RT-K103N,V108I, HIV-1RT-K103N,G190A, and HIV-1RT-K103N,P225H) as well as wild-type HIV-1 (HIV-1wt) with EC50 values of 7.0, 23.8, 13.3, 14.2, 6.2, and 8.4 μM, respectively.

Lersivirine - a new drug for HIV infection therapy

INTRODUCTION

Lersivirine (UK-453,061) is a novel second-generation non-nucleoside reverse transcriptase inhibitor (NNRTI). It binds reverse transcriptase in a distinct way leading to a unique resistance profile. The development of lersivirine was recently stopped in Phase IIb clinical development.

AREAS COVERED

This article describes the background of lersivirine, its pharmacodynamic and pharmacokinetic profile and its clinical efficacy in HIV-infected patients. Moreover, the authors review its resistance profile in addition to its possible interactions with coadministered drugs and safety and tolerability. The authors' evaluation is based on the articles retrieved from a Medline in addition to abstracts from major HIV conferences and workshops addressing lersivirine.

EXPERT OPINION

The authors believe that lersivirine has therapeutic potential for HIV-infected individuals with viral strains resistant against first-line NNRTIs. However, no large, well-powered studies have been conducted so far, which assess noninferiority against established antiretroviral agents. In February 2013, the developing company behind lersivirine halted further development as it was decided that it would not provide an improvement over existing therapies; perhaps this is an opportunity missed.

Role of the K101E substitution in HIV-1 reverse transcriptase in resistance to rilpivirine and other nonnucleoside reverse transcriptase inhibitors

Resistance to the recently approved nonnucleoside reverse transcriptase inhibitor (NNRTI) rilpivirine (RPV) commonly involves substitutions at positions E138K and K101E in HIV-1 reverse transcriptase (RT), together with an M184I substitution that is associated with resistance to coutilized emtricitabine (FTC). Previous biochemical and virological studies have shown that compensatory interactions between substitutions E138K and M184I can restore enzyme processivity and the viral replication capacity. Structural modeling studies have also shown that disruption of the salt bridge between K101 and E138 can affect RPV binding. The current study was designed to investigate the impact of K101E, alone or in combination with E138K and/or M184I, on drug susceptibility, viral replication capacity, and enzyme function. We show here that K101E can be selected in cell culture by the NNRTIs etravirine (ETR), efavirenz (EFV), and dapivirine (DPV) as well as by RPV. Recombinant RT enzymes and viruses containing K101E, but not E138K, were highly resistant to nevirapine (NVP) and delavirdine (DLV) as well as ETR and RPV, but not EFV. The addition of K101E to E138K slightly enhanced ETR and RPV resistance compared to that obtained with E138K alone but restored susceptibility to NVP and DLV. The K101E substitution can compensate for deficits in viral replication capacity and enzyme processivity associated with M184I, while M184I can compensate for the diminished efficiency of DNA polymerization associated with K101E. The coexistence of K101E and E138K does not impair either viral replication or enzyme fitness. We conclude that K101E can play a significant role in resistance to RPV.

Effect of mutations at position E138 in HIV-1 reverse transcriptase and their interactions with the M184I mutation on defining patterns of resistance to nonnucleoside reverse transcriptase inhibitors rilpivirine and etravirine

Impacts of mutations at position E138 (A/G/K/Q/R/V) alone or in combination with M184I in HIV-1 reverse transcriptase (RT) were investigated. We also determined why E138K is the most prevalent nonnucleoside reverse transcriptase inhibitor mutation in patients failing rilpivirine (RPV) therapy. Recombinant RT enzymes and viruses containing each of the above-mentioned mutations were generated, and drug susceptibility was assayed. Each of the E138A/G/K/Q/R mutations, alone or in combination with M184I, resulted in decreased susceptibility to RPV and etravirine (ETR). The maximum decrease in susceptibility to RPV was observed for E138/R/Q/G by both recombinant RT assay and cell-based assays. E138Q/R-containing enzymes and viruses also showed the most marked decrease in susceptibility to ETR by both assays. The addition of M184I to the E138 mutations did not significantly change the levels of diminution in drug susceptibility. These findings indicate that E138R caused the highest level of loss of susceptibility to both RPV and ETR, and, accordingly, E138R should be recognized as an ETR resistance-associated mutation. The E138K/Q/R mutations can compensate for M184I in regard to both enzymatic fitness and viral replication capacity. The favored emergence of E138K over other mutations at position E138, together with M184I, is not due to an advantage in either the level of drug resistance or viral replication capacity but may reflect the fact that E138R and E138Q require two distinct mutations to occur, one of which is a disfavorable G-to-C mutation, whereas E138K requires only a single favorable G-to-A hypermutation. Of course, other factors may also affect the concept of barrier to resistance.

Molecular mechanism of antagonism between the Y181C and E138K mutations in HIV-1 reverse transcriptase

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.

Prevalence of etravirine resistance associated mutations in HIV-1 strains isolated from infected individuals failing efavirenz: comparison between subtype B and non-B genetic variants

Etravirine (ETR) is a non-nucleoside analogue reverse transcriptase inhibitor (NNRTI) with a high genetic barrier to the development of resistance and with potential activity against Human immunodeficiency virus type 1 (HIV-1) strains resistant to first-generation NNRTIs. The objective of this study was to investigate the prevalence of ETR resistance associated mutations (RAMs) in HIV-1 strains isolated from infected individuals failing efavirenz (EFV), as well as to evaluate possible differences in the distribution of ETR RAMs between subtype B and non-B genetic variants. Nucleotide sequences of the protease and partial reverse transcriptase (RT) coding regions of the pol gene of 55 HIV-1 strains isolated from infected individuals failing EFV on regular follow-up at a reference center in Portugal, were retrospectively analyzed. The most prevalent ETR RAMs observed were L100I, V90I, and K101E, with a prevalence of 16.4% (n = 9), 9.1% (n = 5), and 5.5% (n = 3), respectively. Overall, 47.3% (n = 26) of the nucleotide sequences had at least one ETR RAM: 38.2% (n = 21) had one ETR RAM, 7.3% (n = 4) had two ETR RAMs and 1.8% (n = 1) had three ETR RAMs. No statistically significant differences were found in the distribution of ETR RAMs between subtype B and non-B genetic variants. The results demonstrate that ETR rescue therapy is a viable option in treatment-experienced individuals failing EFV and suggests that ETR may be equally useful in HIV-1 infections caused by different genetic variants.

Anti-human immunodeficiency virus type 1 activity of novel 6-substituted 1-benzyl-3-(3,5-dimethylbenzyl)uracil derivatives

Nonnucleoside reverse transcriptase (RT) inhibitors (NNRTIs) are important components of current combination therapies for human immunodeficiency virus type 1 (HIV-1) infection. In screening of chemical libraries, we found 6-azido-1-benzyl-3-(3,5-dimethylbenzyl)uracil (AzBBU) and 6-amino-1-benzyl-3-(3,5-dimethylbenzyl)uracil (AmBBU) to be highly active and selective inhibitors of HIV-1 replication in vitro. To determine the resistance profiles of these compounds, we conducted a long-term culture of HIV-1-infected MT-4 cells with escalating concentrations of each compound. After serial passages of the infected cells, escape viruses were obtained, and they were more than 500-fold resistant to the uracil derivatives compared to the wild type. Sequence analysis was conducted for RT of the escape viruses at passages 12 and 24. The amino acid mutation Y181C in the polymerase domain of RT was detected for all escape viruses. Docking studies using the crystal structure of RT showed that AmBBU requires the amino acid residues Leu100, Val106, Tyr181, and Trp229 for exerting its inhibitory effect on HIV-1. Four additional amino acid changes (K451R, R461K, T468P, and D471N) were identified in the RNase H domain of RT; however, their precise role in the acquisition of resistance is still unclear. In conclusion, the initial mutation Y181C seems sufficient for the acquisition of resistance to the uracil derivatives AzBBU and AmBBU. Further studies are required to determine the precise role of each mutation in the acquisition of HIV-1 resistance.

Antiretroviral therapy in treatment-naïve patients with HIV infection

PURPOSE OF REVIEW

This review discusses the current status of antiretroviral therapy (ART) in treatment-naïve patients. ART initiation in such patients needs to be carefully planned, as the aim of therapy has shifted from prolonging life to ensuring maintained adherence to ART and optimization of quality of life. There is a plethora of first-line antiretroviral agents available, and physicians must consider several patient-related and therapy-related factors before selecting the most appropriate initial ART.

RECENT FINDINGS

Current treatment guidelines recommend the use of nonnucleoside reverse transcriptase inhibitor (NNRTI), ritonavir-boosted protease inhibitor (PI), or integrase strand transfer inhibitor (INSTI)-based regimens in treatment-naïve patients. Treatment selection and modification to achieve optimal response is based primarily on regular assessment of viral load (and resistance testing if necessary) and CD4 cell count. The use of genotypic resistance testing, on initiation of therapy and on treatment failure, is becoming more widespread. In selected patients, due to increasing transmitted drug resistance (TDR), a PI-based regimen may be a better option. Classic ART combinations are being challenged by new combinations, although there is currently insufficient evidence to recommend use of the newer over classic combinations. Co-formulations of drugs and single-tablet regimens are fast becoming available and their convenience may increase patient treatment adherence.

SUMMARY

All drug classes currently available for first-line ART are efficacious and have good tolerability; however, differences between individual drugs must be carefully considered when deciding a first-line regimen. Each first-line regimen must be tailored to the individual patient to attain optimal efficacy, acceptable long-term tolerability, and good adherence to ART.

Antiviral activity and in vitro mutation development pathways of MK-6186, a novel nonnucleoside reverse transcriptase inhibitor

MK-6186 is a novel nonnucleoside reverse transcriptase inhibitor (NNRTI) which displays subnanomolar potency against wild-type (WT) virus and the two most prevalent NNRTI-resistant RT mutants (K103N and Y181C) in biochemical assays. In addition, it showed excellent antiviral potency against K103N and Y181C mutant viruses, with fold changes (FCs) of less than 2 and 5, respectively. When a panel of 12 common NNRTI-associated mutant viruses was tested with MK-6186, only 2 relatively rare mutants (Y188L and V106I/Y188L) were highly resistant, with FCs of >100, and the remaining viruses showed FCs of <10. Furthermore, a panel of 96 clinical virus isolates with NNRTI resistance mutations was evaluated for susceptibility to NNRTIs. The majority (70%) of viruses tested displayed resistance to efavirenz (EFV), with FCs of >10, whereas only 29% of the mutant viruses displayed greater than 10-fold resistance to MK-6186. To determine whether MK-6186 selects for novel resistance mutations, in vitro resistance selections were conducted with one isolate each from subtypes A, B, and C under low-multiplicity-of-infection (MOI) conditions. The results showed a unique mutation development pattern in which L234I was the first mutation to emerge in the majority of the experiments. In resistance selection under high-MOI conditions with subtype B virus, V106A was the dominant mutation detected in the breakthrough viruses. More importantly, mutant viruses selected by MK-6186 showed FCs of <10 against EFV or etravirine (ETR), and the mutant viruses containing mutations selected by EFV or ETR were sensitive to MK-6186 (FCs of <10).

Role of non-nucleoside reverse transcriptase inhibitors in treating HIV-infected children

The first-generation non-nucleoside reverse transcriptase inhibitors (NNRTIs), efavirenz and nevirapine, fulfil key roles in antiretroviral therapy for HIV-infected paediatric patients, from lowering the incidence of mother-to-child transmission during pregnancy and birth to treatment throughout childhood and adolescence. Both agents have established efficacy, safety and tolerability profiles, and also offer advantages over other classes of therapy in terms of regimen simplicity and availability across different treatment settings. Although the role of NNRTIs in paediatric treatment strategies is largely determined by experience in adult patients, results of the recent phase II/III PENPACT-1 trial in infants and children aged between 30 days and 18 years have shown that there are no significant differences in 4-year virological, immunological or clinical outcomes between NNRTIs and protease inhibitors as first- and second-line agents. However, results from the IMPAACT P1060 study (cohort 2), conducted in resource-limited settings, showed that infants under 36 months unexposed to NNRTIs were significantly more likely to fail treatment when started on a nevirapine-based regimen than those on a lopinavir/ritonavir-based regimen. Unfortunately, the use of efavirenz and nevirapine in children can be limited by rapid development of high-level resistance to one or both agents, which may reduce the availability of viable treatment options, particularly in resource-limited settings. Several therapeutic strategies addressing this issue are currently under investigation, but a significant need for new NNRTI-based treatment options remains. The more recently approved NNRTI, etravirine, has demonstrated efficacy and safety benefits in HIV-1-infected, NNRTI-resistant adult patients, with a higher genetic barrier to the development of resistance relative to the first-generation NNRTIs. Another NNRTI, rilpivirine (TMC278), is approved for use in HIV-1-infected, treatment-naïve adult patients and has demonstrated an improved tolerability profile compared with efavirenz. Although available data on etravirine in children are currently limited, ongoing trials will provide important information on the potential for their use in novel paediatric treatment strategies. This review examines the role of efavirenz and nevirapine in paediatric antiretroviral therapy in children within different treatment settings. In addition, this review also outlines available clinical data on etravirine and rilpivirine in the context of how these antiretrovirals may address some of the limitations of efavirenz and nevirapine in paediatric patients.

F18, a novel small-molecule nonnucleoside reverse transcriptase inhibitor, inhibits HIV-1 replication using distinct binding motifs as demonstrated by resistance selection and docking analysis

Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are one of the key components of antiretroviral therapy drug regimen against human immunodeficiency virus type 1 (HIV-1) replication. We previously described a newly synthesized small molecule, 10-chloromethyl-11-demethyl-12-oxo-calanolide A (F18), a (+)-calanolide A analog, as a novel anti-HIV-1 NNRTI (H. Xue et al., J. Med. Chem. 53:1397-1401, 2010). Here, we further investigated its antiviral range, drug resistance profile, and underlying mechanism of action. F18 consistently displayed potent activity against primary HIV-1 isolates, including various subtypes of group M, circulating recombinant form (CRF) 01_AE, and laboratory-adapted drug-resistant viruses. Moreover, F18 displayed distinct profiles against 17 NNRTI-resistant pseudoviruses, with an excellent potency especially against one of the most prevalent strains with the Y181C mutation (50% effective concentration, 1.0 nM), which was in stark contrast to the extensively used NNRTIs nevirapine and efavirenz. Moreover, we induced F18-resistant viruses by in vitro serial passages and found that the mutation L100I appeared to be the dominant contributor to F18 resistance, further suggesting a binding motif different from that of nevirapine and efavirenz. F18 was nonantagonistic when used in combination with other antiretrovirals against both wild-type and drug-resistant viruses in infected peripheral blood mononuclear cells. Interestingly, F18 displayed a highly synergistic antiviral effect with nevirapine against nevirapine-resistant virus (Y181C). Furthermore, in silico docking analysis suggested that F18 may bind to the HIV-1 reverse transcriptase differently from other NNRTIs. This study presents F18 as a new potential drug for clinical use and also presents a new mechanism-based design for future NNRTI.

Measuring enzymatic HIV-1 susceptibility to two reverse transcriptase inhibitors as a rapid and simple approach to HIV-1 drug-resistance testing

Simple and cost-effective approaches for HIV drug-resistance testing are highly desirable for managing increasingly expanding HIV-1 infected populations who initiate antiretroviral therapy (ART), particularly in resource-limited settings. Non-nucleoside reverse trancriptase inhibitor (NNRTI)-based regimens with an NRTI backbone containing lamivudine (3TC) or emtricitabine (FTC) are preferred first ART regimens. Failure with these drug combinations typically involves the selection of NNRTI- and/or 3TC/FTC- resistant viruses. Therefore, the availability of simple assays to measure both types of drug resistance is critical. We have developed a high throughput screening test for assessing enzymatic resistance of the HIV-1 RT in plasma to 3TC/FTC and NNRTIs. The test uses the sensitive “Amp-RT” assay with a newly-developed real-time PCR format to screen biochemically for drug resistance in single reactions containing either 3TC-triphosphate (3TC-TP) or nevirapine (NVP). Assay cut-offs were defined based on testing a large panel of subtype B and non-subtype B clinical samples with known genotypic profiles. Enzymatic 3TC resistance correlated well with the presence of M184I/V, and reduced NVP susceptibility was strongly associated with the presence of K103N, Y181C/I, Y188L, and G190A/Q. The sensitivity and specificity for detecting resistance were 97.0% and 96.0% in samples with M184V, and 97.4% and 96.2% for samples with NNRTI mutations, respectively. We further demonstrate the utility of an HIV capture method in plasma by using magnetic beads coated with CD44 antibody that eliminates the need for ultracentifugation. Thus our results support the use of this simple approach for distinguishing WT from NNRTI- or 3TC/FTC-resistant viruses in clinical samples. This enzymatic testing is subtype-independent and can assist in the clinical management of diverse populations particularly in resource-limited settings.

Low lopinavir plasma or hair concentrations explain second-line protease inhibitor failures in a resource-limited setting

BACKGROUND

In resource-limited settings, many patients, with no prior protease inhibitor (PI) treatment on a second-line, high genetic barrier, ritonavir-boosted PI-containing regimen have virologic failure.

METHODS

We conducted a cross-sectional survey to investigate the aetiology of virologic failure in 2 public health antiretroviral clinics in South Africa documenting the prevalence of virologic failure (HIV RNA load >500 copies/mL) and genotypic antiretroviral resistance; and lopinavir hair and plasma concentrations in a nested case-control study.

RESULTS

Ninety-three patients treated with a second-line regimen including lopinavir boosted with ritonavir were included, of whom 50 (25 cases, with virologic failure and 25 controls) were included in a nested case control study. Of 93 patients, 37 (40%) had virological failure, only 2 of them had had major PI mutations. The negative predictive values: probability of failure with lopinavir plasma concentration >1 µg/mL or hair concentrations >3.63 ng/mg for virologic failure were 86% and 89%, and positive predictive values of low concentrations 73% and 79%, respectively, whereas all virologic failures with HIV RNA loads above 1000 copies per milliliter, of patients without PI resistance, could be explained by either having a low lopinavir concentration in plasma or hair.

CONCLUSIONS

Most patients who fail a lopinavir/ritonavir regimen, in our setting, have poor lopinavir exposure. A threshold plasma lopinavir concentration (indicating recent lopinavir/ritonavir use) and/or hair concentration (indicating longer term lopinavir exposure) are valuable in determining the aetiology of virologic failure and identifying patients in need of adherence counselling or resistance testing.

Nevirapine once daily: pharmacology, metabolic profile and efficacy data of the new extended-release formulation

INTRODUCTION

Nevirapine (NVP), a non-nucleoside reverse transcriptase inhibitor, has been an important component of HIV infection treatment for many years. Currently, twice-a-day dosing is required for the successful application of NVP immediate release (IR), but there is potential for a more convenient once-a-day antiretroviral combination.

AREAS COVERED

The purpose of this article is to review the recent data on once-daily NVP extended release (XR) looking at all the important pharmacologic, pharmacokinetic and clinical data on NVP IR/XR through a systematic MEDLINE database search as well as a review of abstracts presented at international HIV meetings on NVP XR studies up to December 2010. The article provides the reader with an overview of all the pharmacodynamic and pharmacokinetic aspects of NVP IR/XR, as well as its preclinical and clinical efficacy and its safety.

EXPERT OPINION

NVP XR is as effective as NVP IR among HIV-infected patients with a similar safety profile. NVP XR requires careful monitoring during initiation, but its favorable lipid profile may be of clinical benefit in reducing the risk for coronary artery disease in HIV-infected patients who are receiving long-term antiretroviral therapy. Further research is needed to predict short-term toxicity.

Prevention of vertical transmission of HIV-1 in resource-limited settings

One of the most exciting areas of HIV research is that of prevention of vertical transmission from mother to child, since it accounts for 90% of childhood HIV infections, and therefore prevention in this context has an enormous potential impact on the spread of HIV among children. Focused research has yielded highly successful strategies for reducing infant infection rates, particularly in the developed world, and much work is underway to implement appropriate strategies in resource-limited settings, although this is not without challenges. Although transmission rates in some settings have been reduced to approximately 1%, scale-up and widespread implementation and application of strategic interventions for prevention of mother-to-child transmission of HIV during pregnancy, delivery and breastfeeding are needed in the developing world.

Characterization of genotypic and phenotypic changes in HIV-1-infected patients with virologic failure on an etravirine-containing regimen in the DUET-1 and DUET-2 clinical studies

The randomized, placebo-controlled Phase III DUET studies enrolled treatment-experienced, HIV-1-infected patients. We examined the genotypic and phenotypic changes at endpoint relative to baseline, including the emergence of individual reverse transcriptase (RT) mutations, in patients who received the non-nucleoside reverse transcriptase inhibitor (NNRTI) etravirine and experienced virologic failure by rebound by the time of the Week 96 analysis. Patients received etravirine 200 mg twice-daily in combination with a background regimen containing darunavir/ritonavir, investigator-selected nucleoside reverse transcriptase inhibitors, and optional enfuvirtide. Virologic failure by rebound occurred in 93 (15.5%) etravirine-treated patients (compared with 170 [28.1%] placebo-treated patients). Patients experiencing virologic failure had more baseline antiretroviral resistance and lower activity of the background regimen relative to those not experiencing failure. Emergence of NNRTI resistance-associated mutations was observed in 55 of 93 patients. The most frequently emerging RT mutations were V179F, V179I, and Y181C, with positions K101 and E138 also showing frequent changes. Mutations usually emerged in a background of multiple other NNRTI mutations and were, in most cases, associated with a decrease in phenotypic sensitivity to etravirine at endpoint. Further analysis is needed to clarify the role of mutations at position 138 as determinants of etravirine resistance.

Pharmacoeconomics of etravirine

HIV infection, particularly multidrug-resistant HIV, continues to be a major societal and economic challenge worldwide. Etravirine, a new (US FDA approved in 2008) non-nucleoside reverse transcriptase inhibitor, has been shown to be very effective in treating patients who have failed prior antiretroviral therapy. Clinical studies demonstrated that etravirine in combination with other antiretrovirals achieved superior levels of undetectable plasma HIV RNA and CD4 cell count increases that led to reductions in risk of death and development of AIDS-defining illnesses when compared with placebo. Etravirine was also shown to be generally well tolerated, with favorable CNS and psychiatric tolerability profiles. In addition, etravirine in combination with other antiretrovirals has been shown to improve quality of life and quality-adjusted life expectancy. Economic evaluations showed that the addition of etravirine to a regimen was associated with lower costs per person with an undetectable viral load and lower hospital-related costs compared with placebo.

Looking for an active conformation of the future HIV type-1 non-nucleoside reverse transcriptase inhibitors

HIV type-1 (HIV-1) non-nucleoside reverse transcriptase inhibitors (NNRTIs) are key drugs of highly active antiretroviral therapy (HAART) in the clinical management of AIDS/HIV infection. NNRTI-based HAART regimes effectively suppress viral reproduction, are not cytotoxic and show favourable pharmacokinetic properties. First-generation NNRTIs suffer the rapid selection of viral variants, hampering the binding of inhibitors into the reverse transcriptase (RT) non-nucleoside binding site (NNBS). Efforts to improve these first inhibitors led to the discovery of second-generation NNRTIs that proved to be effective against the drug-resistant mutant HIV-1 strains. The success of such agents launched a new season of NNRTI design and synthesis. This paper reviews the characteristics of second-generation NNRTIs, including etravirine, rilpivirine, RDEA-806, UK-453061, BIRL 355 BS, IDX 899, MK-4965 and HBY 097. In particular, the binding modes of these inhibitors into the NNBS of the HIV-1 RT and the most clinically relevant mutant RTs are analysed and discussed.

Recent advances in antiretroviral drugs

IMPORTANCE OF THE FIELD

Acquired immunodeficiency syndrome (AIDS) is one of the leading causes of death worldwide. Although the combination therapies of highly active antiretroviral therapy (HAART) have significantly contributed to virological suppression, improved immune function and quality of life, issues such as tolerability, drug-drug interactions and cross-resistance amongst members of a particular drug class still pose a significant barrier to long-term successful treatment. There is a constant need for newer anti HIV drugs with increased potency and improved pharmacokinetic properties either in the existing classes or drugs from new classes that target several new steps in HIV replication cycle.

AREAS COVERED IN THIS REVIEW

The authors have discussed newer antiretroviral drugs belonging to second-generation nucleoside analog reverse transcriptase inhibitors (amdoxovir, elvucitabine, apricitabine, racivir), non-nucleoside analog reverse transcriptase inhibitors (etravirine, rilpivirine), protease inhibitors (darunavir, tipranavir) as well as emerging new classes, i.e., fusion inhibitors (enfuvirtide, sifuvirtide), CCR5 inhibitors (maraviroc, vicriviroc, PRO 140, PRO 542), CD4-receptor inhibitors (ibalizumab), integrase inhibitors (raltegravir, elvitegravir, GSK-1349572), maturation inhibitors (bevirimat), cobicistat (pharmacoenhancer), lens epithelium-derived growth factor inhibitors and capsid assembly inhibitors.

WHAT THE READER WILL GAIN

The reader will gain an understanding of the mechanism of action, mechanism of resistance, stages of development and important clinical trials related to the newer antiretroviral drugs and future potential of these drugs.

TAKE HOME MESSAGE

The initial clinical trial data of these newer drugs are very encouraging for the long-term successful control of HIV in both treatment-naïve and treatment-experienced patients.

A review of the safety and tolerability profile of the next-generation NNRTI etravirine

The next-generation nonnucleoside reverse transcriptase inhibitor (NNRTI) etravirine (TMC125) has demonstrated durable virologic efficacy in clinical trials involving >1000 treatment-experienced, NNRTI-resistant, HIV-1-infected patients. In this clinical safety review, we show etravirine to be well tolerated with a proven safety record. The nature and magnitude of adverse events observed during treatment suggest that etravirine may offer improved tolerability over existing antiretrovirals, including NNRTIs. Notably, adverse events reported with etravirine treatment are generally mild to moderate in severity. Rash has been shown to occur with a higher incidence in etravirine-treated patients versus placebo, but cases are generally mild to moderate, occur within the first few weeks, and resolve with continued use. In addition, the rate of adverse event-related discontinuations is low with etravirine. In summary, the safety and tolerability profile of etravirine, combined with its virologic efficacy, suggest that the drug may be a valuable option for treatment-experienced patients with HIV-1 infection.