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Background: Dolutegravir (DTG) is an integrase strand-transfer inhibitor (INSTI) used for treatment of human immunodeficiency virus (HIV)-infected individuals. Owing to its high genetic barrier to resistance, DTG has been clinically investigated as maintenance monotherapy to maintain viral suppression and to reduce complication and healthcare costs. Our study aims to explain the underlying mechanism related to the emergence of a S230R substitution in patients who experienced virologic failure while using DTG monotherapy., Methods: We evaluated the effect of the S230R substitution in regard to integrase enzyme activity, viral infectivity, replicative capacity, and susceptibility to different INSTIs by biochemical and cell-based assays., Results: The S230R substitution conferred a 63% reduction in enzyme efficiency. S230R virus was 1.29-fold less infectious than wild-type virus but could replicate in PM1 cells without significant delay. Resistance levels against DTG, cabotegravir, raltegravir, and elvitegravir in tissue culture were 3.85-, 3.72-, 1.52-, and 1.21-fold, respectively, in virus with the S230R substitution., Conclusions: Our data indicate that the S230R substitution is comparable to the previously reported R263K substitution in some respects. Virologic failure during DTG monotherapy can occur through the development of the S230R or R263K mutation, without the need for high-level DTG resistance.

Introduction: To date, three HIV integrase strand transfer inhibitors (INSTIs), i.e. raltegravir, elvitegravir and dolutegravir, have been approved for clinical use. Recent research has focused on new integrase inhibitors including those targeting non-catalytic sites of HIV integrase. Areas covered: This paper reviews two investigational INSTIs in phase I and II clinical trials, bictegravir (BIC) and cabotegravir (CAB), as well as an investigational noncatalytic integrase inhibitor (NCINI) termed BI 224436. Expert opinion: Data from phase I and II clinical trials demonstrate that CAB has good efficacy and is well-tolerated. CAB is promising because it can be formulated both orally and as a long-acting (LA) injectable for treatment and prevention of HIV infection. Since LA-CAB formulation offers the possibility of favourable dosing, it may help individuals who struggle with adherence issues. BIC also represents a promising safe, effective and well-tolerated drug that can be administered as a single once-daily regimen in coformulation with emtricitabine and tenofovir alafenamide (FTC/TAF). Ongoing phase III trials should clarify optimal doses and reveal the potential clinical advantages of these new drugs and formulations over other current regimens. Exploration of novel HIV integrase inhibitors acting through mechanisms different from those of INSTIs is still needed.

Objectives: To compare the effectiveness of HIV integrase inhibitor monotherapy between raltegravir and dolutegravir as an approach to simplify therapy., Methods: We evaluated and compared the efficacy of 20 week monotherapy with dolutegravir or raltegravir in humanized mice (HSC-NSG) infected with HIVBaL. Plasma HIV RNA was measured by quantitative RT-PCR (limit of detection of 150 copies/45 μL of plasma) and drug levels by LC-MS/MS. Escape viruses were genotyped and analysed for replication capacity and drug susceptibility in tissue culture., Results: Drug-untreated control mice maintained constant viraemia throughout the study. Virus isolates from these mice were susceptible to both raltegravir (EC50 of <8 nM) and dolutegravir (EC50 of <1 nM). Mice treated with raltegravir or dolutegravir had plasma drug levels comparable to those in humans. Monotherapy with raltegravir initially suppressed HIV viraemia, but failed to maintain suppression in 4/4 mice. Viruses from raltegravir failing mice developed mutations G140G/S and Q148H/K, and were resistant to both raltegravir (EC50 values of >100 nM) and dolutegravir (EC50 values ranging from 8.8 to 13.3 nM). Monotherapy with dolutegravir suppressed viraemia in 5/5 of mice, but viraemia rebounded in one animal. The virus from this mouse had mutations E138K, G140S, Q148H, N155H and S230R, was highly resistant to both raltegravir (EC50 of >1000 nM) and dolutegravir (EC50 of 550 nM), and replicated to levels similar to those of control viruses in PBMCs., Conclusions: Monotherapy with either raltegravir or dolutegravir does not consistently maintain HIV suppression, suggesting that dual therapy may be required in simplification strategies., (© The Author 2017. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

HIV can spread by both cell-free and cell-to-cell transmission. Here, we show that many of the amino acid changes in Env that are close to the CD4 binding pocket can affect HIV replication. We generated a number of mutant viruses that were unable to infect T cells as cell-free viruses but were nevertheless able to infect certain T cell lines as cell-associated viruses, which was followed by reversion to the wild type. However, the activation of JAK-STAT signaling pathways caused the inhibition of such cell-to-cell infection as well as the reversion of multiple HIV Env mutants that displayed differences in their abilities to bind to the CD4 receptor. Specifically, two T cell activators, interleukin-2 (IL-2) and phorbol 12-myristate 13-acetate (PMA), both capable of activation of JAK-STAT pathways, were able to inhibit cell-to-cell viral transmission. In contrast, but consistent with the above result, a number of JAK-STAT and mTOR inhibitors actually promoted HIV-1 transmission and reversion. Hence, JAK-STAT signaling pathways may differentially affect the replication of a variety of HIV Env mutants in ways that differ from the role that these pathways play in the replication of wild-type viruses. IMPORTANCE Specific alterations in HIV Env close to the CD4 binding site can differentially change the ability of HIV to mediate infection for cell-free and cell-associated viruses. However, such differences are dependent to some extent on the types of target cells used. JAK-STAT signaling pathways are able to play major roles in these processes. This work sheds new light on factors that can govern HIV infection of target cells., (Copyright © 2017 American Society for Microbiology.)

Background: Attempts to eradicate HIV from cellular reservoirs are vital but depend on a clear understanding of how viral variants are transmitted and survive in the different cell types that constitute such reservoirs. Mutations in the env gene of HIV may be able to exert a differential influence on viral transmission ability in regard to cell-free and cell-associated viral forms., Methods: The ability of HIV containing an env G367R mutation in cell-free and cell-associated viruses to cause infection and to revert to wild-type was measured using several T cell lines. To determine factors that might potentially influence the reversion of G367R, we studied each of entry inhibitors, inhibitors of cellular endocytosis, and modulators of cell growth and activation., Results: We demonstrate that an HIV-1 variant containing a G367R substitution within the CD4 binding site of gp120 was non-infectious as free virus in culture but was infectious when infected cells were co-cultured with certain T cell lines or when cells were transfected by a relevant proviral plasmid. Differences in viral infectivity by cell-associated G367R viruses were determined by the type of target cell employed, regardless which type of donor cell was used. Reversion was slowed or inhibited by entry inhibitors and by inhibitors of cellular endocytosis. Interleukin 2 was able to block G367R reversion in only one of the T cell lines studied but not in the other, while phorbol 12-myristate 13-acetate (PMA) inhibited G367R reversion in all the T cell lines., Conclusions: Env-defective HIV may have a different phenotype as cell-free versus cell-associated virus. The persistence of defective forms can potentially lead to the emergence of virulent forms. The heterogeneity of cell types that constitute the HIV reservoir can contribute to viral variability, even among similar types of cells. This is the first demonstration of a mutation in the HIV envelope, i.e. G367R, that can compromise infection by cell-free virus but less severely by cell-associated virus and that does so in a cell type-dependent manner.

Clinical resistance to rilpivirine (RPV), a novel nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI), is associated an E-to-K mutation at position 138 (E138K) in RT together with an M184I/V mutation that confers resistance against emtricitabine (FTC), a nucleoside RT inhibitor (NRTI) that is given together with RPV in therapy. These two mutations can compensate for each other in regard to fitness deficits conferred by each mutation alone, raising the question of why E138K did not arise spontaneously in the clinic following lamivudine (3TC) use, which also selects for the M184I/V mutations. In this context, we have investigated the role of a N348I connection domain mutation that is prevalent in treatment-experienced patients. N348I confers resistance to both the NRTI zidovudine (ZDV) and the NNRTI nevirapine (NVP) and was also found to be associated with M184V and to compensate for deficits associated with the latter mutation. Now, we show that both N348I alone and N348I/M184V can prevent or delay the emergence of E138K under pressure with RPV or a related NNRTI, termed etravirine (ETR). N348I also enhanced levels of resistance conferred by E138K against RPV and ETR by 2.2- and 2.3-fold, respectively. The presence of the N348I or M184V/N348I mutation decreased the replication capacity of E138K virus, and biochemical assays confirmed that N348I, in a background of E138K, impaired RT catalytic efficiency and RNase H activity. These findings help to explain the low viral replication capacity of viruses containing the E138K/N348I mutations and how N348I delayed or prevented the emergence of E138K in patients with M184V-containing viruses.

Background The results of several clinical trials suggest that the integrase inhibitor dolutegravir may be less prone than other drugs to the emergence of HIV drug resistance mutations in treatment-naive patients. We have shown that the R263K mutation commonly emerged during tissue culture selection studies with dolutegravir and conferred low levels of resistance to this drug while simultaneously diminishing both HIV replication capacity and integrase enzymatic activity. E138K has been identified as a secondary mutation for dolutegravir in selection studies and has also been observed as a secondary mutation in the clinic for the integrase inhibitors raltegravir and elvitegravir. Methods We used biochemical cell-free strand-transfer assays and tissue culture assays to characterize the effects of the E138K/R263K combination of mutations on resistance to dolutegravir, integrase enzyme activity and HIV-1 replication capacity. Results We show here that the addition of the E138K substitution to R263K increased the resistance of HIV-1 to dolutegravir but failed to restore viral replication capacity, integrase strand-transfer activity and integration within cellular DNA. We also show that the addition of E138K to R263K did not increase the resistance to raltegravir or elvitegravir. The addition of the E138K substitution to R263K was also less detrimental to integrase strand-transfer activity and integration than a different secondary mutation at position H51Y that had also been selected in culture. Conclusions The E138K substitution failed to restore the defect in viral replication capacity that is associated with R263K, confirming previous selection studies that failed to identify compensatory mutation(s) for the latter primary mutation. This study suggests that the R263K resistance pathway may represent an evolutionary dead end for HIV in treatment-naive individuals who are treated with dolutegravir and will need to be confirmed by the long-term use of dolutegravir in the clinic. [ABSTRACT FROM PUBLISHER]

Background First-generation integrase strand-transfer inhibitors (INSTIs), such as raltegravir (RAL) and elvitegravir (EVG), have been clinically proven to be effective antiretrovirals for the treatment of HIV-positive patients. However, their relatively low genetic barrier for resistance makes them susceptible to the emergence of drug resistance mutations. In contrast, dolutegravir (DTG) is a newer INSTI that appears to have a high genetic barrier to resistance in vivo. However, the emergence of the resistance mutation R263K followed by the polymorphic substitution M50I has been observed in cell culture. The M50I polymorphism is also observed in 10-25% of INSTI-naïve patients and has been reported in combination with R263K in a patient failing treatment with RAL. 2 Results Using biochemical cell-free strand-transfer assays and resistance assays in TZM-bl cells, we demonstrate that the M50I polymorphism in combination with R263K increases resistance to DTG in tissue culture and in biochemical assays but does not restore the viral fitness cost associated with the R263K mutation. Conclusions Since the combination of the R263K mutation and the M50I polymorphism results in a virus with decreased viral fitness and limited cross-resistance, the R263K resistance pathway may represent an evolutionary dead-end. Although this hypothesis has not yet been proven, it may be more advantageous to treat HIV-positive individuals with DTG in first-line than in second or third-line therapy. [ABSTRACT FROM AUTHOR]

Background: Clinical studies have shown that integrase strand transfer inhibitors can be used to treat HIV-1 infection. Although the first-generation integrase inhibitors are susceptible to the emergence of resistance mutations that impair their efficacy in therapy, such resistance has not been identified to date in drug-naïve patients who have been treated with the second-generation inhibitor dolutegravir. During previous in vitro selection study, we identified a R263K mutation as the most common substitution to arise in the presence of dolutegravir with H51Y arising as a secondary mutation. Additional experiments reported here provide a plausible explanation for the absence of reported dolutegravir resistance among integrase inhibitor-naïve patients to date Results: We now show that H51Y in combination with R263K increases resistance to dolutegravir but is accompanied by dramatic decreases in both enzymatic activity and viral replication. Conclusions: Since H51Y and R263K may define a unique resistance pathway to dolutegravir, our results are consistent with the absence of resistance mutations in antiretroviral drug-naive patients treated with this drug. [ABSTRACT FROM AUTHOR]

Introduction Drug resistance against dolutegravir (DTG) or the nucleosides with which it has been co-administered has never been observed in patients receiving this drug in first-line therapy. In contrast, a R263K mutation that confers low-level resistance (3-4 fold) to DTG has been selected by DTG in culture. Our group has ascribed the absence of resistance to DTG to the high fitness cost exacted by the R263K mutation and an inability of HIV to generate compensatory mutations. Materials and Methods We generated recombinant integrase enzymes and viruses containing various combinations of mutations and studied these enzymatically and in culture. We also selected for resistance against raltegravir (RAL) using viruses containing the R263K mutation. Results The R263K mutation alone conferred an approximate 3-fold level of resistance to DTG and a 40% loss in viral replicative capacity and recombinant integrase activity. Secondary mutations selected at positions H51Y or E138K did not individually affect either enzyme activity or DTG resistance, but the combination of R263K together with H51Y or E138K increased DTG resistance to about 7-fold accompanied by a ≈75% loss in each of viral replication capacity, and both in vitro and in vivo integrase activity. Conversely, combinations of R263K together with multiple resistance mutations for RAL and/or EVG at positions 92,143, 148 and 155 resulted in even further diminished enzymatic activity that may be incompatible with viral survival. Modelling of the 3-dimensional structure of integrase suggests that R263K is located in a region that may not permit further mutagenesis if secondary mutations at H51Y or E138K are also present. Moreover, integrase that contains R263K together with substitutions at positions 92, 143, 148 and 155 may be enzymatically inactive. The use of the R263K-containing virus to select for resistance to RAL led to the appearance of RAL-containing mutations but the loss of R263K. Conclusions Secondary mutations to R263K following selection with DTG have all led to diminished viral and enzymatic fitness, helping to explain why resistance to DTG in previously drug-naïve subjects has never been observed. The use of DTG in first-line therapy may prevent the facile development of drug resistance and help to forestall ongoing HIV transmission. [ABSTRACT FROM AUTHOR]

The emergence of HIV-1 drug resistance remains a major obstacle in antiviral therapy. M184I/V and E138K are signature mutations of clinical relevance in HIV-1 reverse transcriptase (RT) for the nucleoside reverse transcriptase inhibitors (NRTIs) lamivudine (3TC) and emtricitabine (FTC) and the second-generation (new) nonnucleoside reverse transcriptase inhibitor (NNRTI) rilpivirine (RPV), respectively, and the E138K mutation has also been shown to be selected by etravirine in cell culture. The E138K mutation was recently shown to compensate for the low enzyme processivity and viral fitness associated with the M184I/V mutations through enhanced deoxynucleoside triphosphate (dNTP) usage, while the M184I/V mutations compensated for defects in polymerization rates associated with the E138K mutations under conditions of high dNTP concentrations. The M184I mutation was also shown to enhance resistance to RPV and ETR when present together with the E138K mutation. These mutual compensatory effects might also enhance transmission rates of viruses containing these two mutations. Therefore, we performed tissue culture studies to investigate the evolutionary dynamics of these viruses. Through experiments in which E138K-containing viruses were selected with 3TC-FTC and in which M184I/V viruses were selected with ETR, we demonstrated that ETR was able to select for the E138K mutation in viruses containing the M184I/V mutations and that the M184I/V mutations consistently emerged when E138K viruses were selected with 3TC-FTC. We also performed biochemical subunit-selective mutational analyses to investigate the impact of the E138K mutation on RT function and interactions with the M184I mutation. We now show that the E138K mutation decreased rates of polymerization, impaired RNase H activity, and conferred ETR resistance through the p51 subunit of RT, while an enhancement of dNTP usage as a result of the simultaneous presence of both mutations E138K and M184I occurred via both subunits. [ABSTRACT FROM AUTHOR]