The A62V and S68G mutations in HIV-1 reverse transcriptase partially restore the replication defect associated with the K65R mutation

Thymidine Analogue Mutations with M184V Significantly Decrease Phenotypic Susceptibility of HIV-1 Subtype C Reverse Transcriptase to Islatravir

Islatravir (ISL) is the first-in-class nucleoside reverse transcriptase translocation inhibitor (NRTtI) with novel modes of action. Data on ISL resistance are currently limited, particularly to HIV-1 non-B subtypes. This study aimed to assess prevalent nucleos(t)ide reverse transcriptase inhibitor (NRTI)-resistant mutations in HIV-1 subtype C for their phenotypic resistance to ISL. Prevalent single and combinations of NRTI-resistant mutations were selected from a routine HIV-1 genotypic drug resistance testing database and introduced into HIV-1 subtype C-like pseudoviruses, which were then tested for ISL susceptibility. Single NRTI-resistant mutations were susceptible or showed only a low level of resistance to ISL. This included thymidine analogue mutations (TAMs, i.e., M41L, D67N, K70R, T215FY, and K219EQ) and non-TAMs (i.e., A62V, K65R, K70ET, L74IV, A114S, Y115F, and M184V). Combinations of M184V with one or more additional NRTI-resistant mutations generally displayed reduced ISL susceptibilities. This was more prominent for combinations that included M184V+TAMs, and particularly M184V+TAM-2 mutations. Combinations that included M184V+K65R did not impact significantly on ISL susceptibility. Our study suggests that ISL would be effective in treating people living with HIV (PLWH) failing tenofovir disoproxil fumarate (TDF)/lamivudine (3TC) or TDF/emtricitabine (FTC)-containing regimens, but would be less effective in PLH failing zidovudine (AZT) with 3TC or FTC-containing regimens.

Distinct Clusters of HIV-1 CRF01_AE in Zhejiang, China: High-Risk Transmission Cluster 4 Requires Heightened Surveillance

Background

HIV-1 CRF01_AE is becoming the predominant HIV-1 subtype among patients in China. The distribution and characteristics of transmission clusters of HIV-1 CRF01_AE in Zhejiang, Eastern China remains unclear. This study analyzed the epidemiologic characteristics and transmission clusters of HIV-1 CRF01_AE in Zhejiang.

Methods

Plasma samples obtained from 152 patients of HIV-1 CRF01_AE not undergoing ART were used to amplify HIV-1 pol and env gene. CRF01_AE drug resistance mutations (DRM) prevalence was analysed using Stanford University's HIV Drug Resistance Database. A phylogenetic tree was constructed using FastTree (version 2.1.11) based on the GTR nucleotide substitution model and visualized using Figtree (version 1.4.4) and The Interactive Tree of Life; the Chinese HIV Gene Sequence Data Platform was used to construct genetic transmission networks.

Results

Majority samples could be grouped into CRF01_AE transmission Clusters 1 (11.2%), 4 (64.5%), and 5 (7.2%). The CD4+ T-cell counts in Cluster 1, 4a, 4b are lower than 5 were 15, 38, 30, and 248 cells/mm3, respectively (P < 0.05). The high X4 tropism rates were 13.2%, 11.8%, 20.0%, and 0.0% in Clusters 1, 4a, 4b, and 5, respectively. DRM rates in Clusters 4a and 4b were 17.6%, and 25.45% respectively (P < 0.05), whereas they were 17.6% and 18.2% in Clusters 1 and 5, respectively. In total, 24 transmission genetic networks, comprising 72 sequences and 61 links, were discovered; of them, 61.2%, 11.7%, and 18.2% were from Clusters 4, 1, and 5, respectively (P < 0.05).

Conclusion

In Zhejiang, different CRF01_AE clusters displayed unique clinic features. Cluster 4, particularly Cluster 4b, was considered a high-risk transmission cluster. The surveillance of epidemiology of HIV-1 should be enhanced to minimize its transmission.

Efficacy of first-line ART regimens based on tenofovir in HIV-infected patients with pre-existing A62V mutation in reverse transcriptase

INTRODUCTION

The amino acid substitution A62V in reverse transcriptase was identified as a mutation correlated with virologic failure in patients on first-line therapy including tenofovir (TDF) and tenofovir alafenamide (TAF). A62V is a typically polymorphic mutation in HIV-1 sub-subtype A6, which is the most widespread virus variant in Russia.

MATERIALS AND METHODS

The European EuResist (EIDB) database was queried to form two equivalent groups of patients: group 1 ‒ patients with A62V at baseline treated with TDF or TAF on the first-line therapy, group 2 ‒ patients without A62V at baseline treated with TDF or TAF on the first-line therapy. Each group included 23 patients.

RESULTS

There was no statistical difference between the two groups in virologic efficacy in 4, 12, and 24 weeks after the start of antiretroviral therapy (ART) and in the frequency of virologic failures.

CONCLUSION

This study has some limitations, and the exact role of A62V in the efficacy of the first-line ART based on tenofovir deserves further investigation.

HIV-1 Resistance to Islatravir/Tenofovir Combination Therapy in Wild-Type or NRTI-Resistant Strains of Diverse HIV-1 Subtypes

Tenofovir disoproxil fumarate (TDF) and islatravir (ISL, 4'-ethynyl-2-fluoro-2'-deoxyadensine, or MK-8591) are highly potent nucleoside reverse transcriptase inhibitors. Resistance to TDF and ISL is conferred by K65R and M184V, respectively. Furthermore, K65R and M184V increase sensitivity to ISL and TDF, respectively. Therefore, these two nucleoside analogs have opposing resistance profiles and could present a high genetic barrier to resistance. To explore resistance to TDF and ISL in combination, we performed passaging experiments with HIV-1 WT, K65R, or M184V in the presence of ISL and TDF. We identified K65R, M184V, and S68G/N mutations. The mutant most resistant to ISL was S68N/M184V, yet it remained susceptible to TDF. To further confirm our cellular findings, we implemented an endogenous reverse transcriptase assay to verify in vitro potency. To better understand the impact of these resistance mutations in the context of global infection, we determined potency of ISL and TDF against HIV subtypes A, B, C, D, and circulating recombinant forms (CRF) 01_AE and 02_AG with and without resistance mutations. In all isolates studied, we found K65R imparted hypersensitivity to ISL whereas M184V conferred resistance. We demonstrated that the S68G polymorphism can enhance fitness of drug-resistant mutants in some genetic backgrounds. Collectively, the data suggest that the opposing resistance profiles of ISL and TDF suggest that a combination of the two drugs could be a promising drug regimen for the treatment of patients infected with any HIV-1 subtype, including those who have failed 3TC/FTC-based therapies.

Antiviral activity of tenofovir alafenamide (TAF) against HIV-1 clinical isolates harboring K65R

Tenofovir alafenamide (TAF) is a prodrug of the nucleoside reverse transcriptase (RT) inhibitor tenofovir (TFV). Compared to the earlier TFV prodrug, TFV disoproxil fumarate (TDF), TAF achieves more than fourfold-higher intracellular levels of its active metabolite TFV diphosphate (TFV-DP) in clinical studies, while achieving a significant reduction of TFV systemic exposure. Resistance to TFV has been well established, with the K65R mutation in RT as the signature mutation. Here we evaluated the in vitro activity of TAF and TDF in patient-derived HIV-1 isolates harboring the K65R mutation. Clinical isolates containing K65R were cloned into the pXXLAI construct (n = 42). In vitro phenotypic susceptibility of the constructs to TAF and TDF was evaluated in an MT-2 cell HIV assay and in viral breakthrough assays modeling physiological concentrations of TAF and TDF. TAF and TDF susceptibility were highly correlated in K65R-containing mutants, ranging from 2.7- to 3.0-fold (K65R alone) and 1.2- to 27.6-fold (K65R+ other RT mutations) relative to wild-type. In viral breakthrough assays mimicking differences in physiological concentrations, TAF inhibited breakthrough of 40 of 42 clinical isolates, while the TDF equivalent only inhibited 32 of 42 isolates tested. TAF displayed a higher barrier to resistance than TDF in this panel of K65R-containing clinical isolates.

Prevalence of drug resistant HIV-1 forms in patients without any history of antiretroviral therapy in the Republic of Guinea

To study the structure of human immunodeficiency virus (HIV)-1 drug resistance (DR) in patients with newly diagnosed infection. Residents of the Republic of Guinea (N = 2168) were tested for HIV using enzyme-linked immunosorbent assay (ELISA). Individuals with a positive result were further examined for the presence of viral load in blood plasma. HIV was analyzed using Sanger sequencing. The obtained sequences were genotyped using REGA (version 3.0) and analyzed in MEGA 7. Analysis for the presence of DR mutations was performed using the Stanford University HIV DR Database. Serological markers of HIV were detected in 239 people, which represents 11.02% of the entire sample. HIV RNA was detected in 58 people. The following subtypes were seen: HIV CRF02_AG (41.9%); A1 (29.1%); A3 (12.9%); URF A1_G (12.9%); and G (3.2%). In 25% of patients, at least one significant mutation was encountered leading directly to HIV DR. The mutations encountered cause resistance to NRTI and NNRTI; one case of multiple resistance was identified. Major resistance to protease inhibitor was not seen. The detection of HIV-1 mutations associated with DR, in individuals who have never received antiretroviral therapy, is a cause for concern. It suggests that: new infections are occurring with strains that already have resistance; and the expansion of resistance is not always directly associated with selective drug pressure. Among the likely reasons for the high prevalence of primary HIV DR in the Republic of Guinea, drug availability is probably the key. The consequence of this is the lack of adherence of patients to treatment, the formation and transmission of resistant variants of the virus in the population. These findings suggest the need to test patients for resistant virus variants before initiating treatment.

Antiretroviral therapy resistance mutations among HIV infected people in Kazakhstan

In Kazakhstan, the number of people living with HIV (PLHIV) has increased steadily by 39% since 2010. Development of antiretroviral therapy (ART) resistance mutations (ARTRM) is a major hurdle in achieving effective treatment and prevention against HIV. Using HIV pol sequences from 602 PLHIV from Kazakhstan, we analyzed ARTRMs for their association with factors that may promote development of ARTRMs. 56% PLHIV were infected with HIV subtype A6 and 42% with CRF02_AG. The ARTRM Q174K was associated with increased viral load and decreased CD4+ cell count, while infection with CRF02_AG was associated with a lower likelihood of Q174K. Interestingly, CRF02_AG was positively associated with the ARTRM L10V that, in turn, was observed frequently with darunavir administration. Infection with CRF02_AG was positively associated with the ARTRM S162A that, in turn, was frequently observed with the administration of nevirapine, also associated with lower CD4 counts. Zidovudine or Nevirapine receipt was associated with the development of the ARTRM E138A, that, in turn, was associated with lower CD4 counts. Determination of a patient's HIV variant can help guide ART choice in Kazakhstan. For example, PLHIV infected with CRF02_AG will benefit less from darunavir and nevirapine, and emtricitabine should replace zidovudine.

Genetic Diversity and Low Therapeutic Impact of Variant-Specific Markers in HIV-1 Pol Proteins

The emergence and spread of new HIV-1 variants pose a challenge for the effectiveness of antiretrovirals (ARV) targeting Pol proteins. During viral evolution, non-synonymous mutations have fixed along the viral genome, leading to amino acid (aa) changes that can be variant-specific (V-markers). Those V-markers fixed in positions associated with drug resistance mutations (DRM), or R-markers, can impact drug susceptibility and resistance pathways. All available HIV-1 Pol sequences from ARV-naïve subjects were downloaded from the United States Los Alamos HIV Sequence Database, selecting 59,733 protease (PR), 6,437 retrotranscriptase (RT), and 6,059 integrase (IN) complete sequences ascribed to the four HIV-1 groups and group M subtypes and circulating recombinant forms (CRFs). Using a bioinformatics tool developed in our laboratory (EpiMolBio), we inferred the consensus sequences for each Pol protein and HIV-1 variant to analyze the aa conservation in Pol. We analyzed the Wu–Kabat protein variability coefficient (WK) in PR, RT, and IN group M to study the susceptibility of each site to evolutionary replacements. We identified as V-markers the variant-specific aa changes present in >75% of the sequences in variants with >5 available sequences, considering R-markers those V-markers that corresponded to DRM according to the IAS-USA2019 and Stanford-Database 9.0. The mean aa conservation of HIV-1 and group M consensus was 82.60%/93.11% in PR, 88.81%/94.07% in RT, and 90.98%/96.02% in IN. The median group M WK was 10 in PR, 4 in RT, and 5 in IN. The residues involved in binding or catalytic sites showed a variability <0.5%. We identified 106 V-markers: 31 in PR, 28 in RT, and 47 in IN, present in 11, 12, and 13 variants, respectively. Among them, eight (7.5%) were R-markers, present in five variants, being minor DRM with little potential effect on ARV susceptibility. We present a thorough analysis of Pol variability among all HIV-1 variants circulating to date. The relatively high aa conservation observed in Pol proteins across HIV-1 variants highlights their critical role in the viral cycle. However, further studies are needed to understand the V-markers’ impact on the Pol proteins structure, viral cycle, or treatment strategies, and periodic variability surveillance studies are also required to understand PR, RT, and IN evolution.

Evaluation of CCR5-Δ32 mutation and HIV-1 surveillance drug-resistance mutations in peripheral blood mononuclear cells of long-term non progressors of HIV-1-infected individuals

Aim: This study aimed to evaluate chemokine receptor 5 delta 32 (CCR5-Δ32) mutation and HIV-1 surveillance drug-resistance mutations (SDRMs) in peripheral blood mononuclear cells of long-term non progressors (LTNPs) of HIV-1-infected individuals. Materials and methods: This research was performed on 197 treatment-naive HIV-1-infected patients. After follow-up, it was determined that 15 (7.6%) of these people were LTNPs. The PCR assay was performed to identify the CCR5 genotype and HIV-1 SDRMs. Results: One (6.7%) of the LTNPs was heterozygous (wt/Δ32) for the CCR5 delta 32 (CCR5Δ32). However, none of the individuals was homozygous for this mutation (Δ32/Δ32). Moreover, none of the LTNPs showed HIV-1 SDRMs. The CRF35-AD subtype was the most dominant subtype, with a percentage of 93.3%. Conclusion: Iranian elite controllers are negative for CCR5-delta 32 homozygous genotype and drug resistance against antiretroviral drugs.

Human Immunodeficiency Virus-1 Subtype-C Genetically Diversify to Acquire Higher Replication Competence in Human Host with Comorbidities

Unusual disease progression is observed in the HIV-1 infected patients who are either coinfected with Mycobacterium tuberculosis (Mtb) or concomitantly on intravenous drug use (IDU). The mechanism involved in the breakdown of host immune defense and the synergistic effect in both the conditions are still not well understood. In this study, we aimed to highlight the emergence of genetically diversified variants of virus in these two cohorts among HIV-1 subtype-C infected population from a Northern state of India. A cross-sectional study was performed on treatment-naïve HIV-1 subtype-C infected individuals constituting three different cohorts of HIV-1 monoinfected, HIV-1-M. tuberculosis (HIV-TB) coinfected, and HIV-1 infected individuals on substance abuse (HIV-IDU) for acquisition of genetic alterations in terms of frequency of drug resistance (DR) mutations in reverse transcriptase gene. The data reveal a significantly higher viral load, higher death rate, and higher frequency of major DR mutations in the genome of viral isolates from HIV-TB and HIV-IDU cohorts as compared with HIV monoinfected. Majority of the mutations found in the HIV-TB coinfected and HIV-IDU cohorts conferred high level of resistance to the first-line treatment regimen (Lamivudine with Tenofovir or zidovudine or Abacavir and Nevirapine or Efavirenz). Our findings support the hypothesis that the HIV-1 evolve while replicating in the host with Mtb coinfection or substance abuse, with the emergence and accumulation of genetically diversified quasi-species. Further studies are warranted to understand the association of such genetic variations with increased replication competence and faster rate of disease progression in such individuals.

Short Communication: Acquisition of Additional Nuclear Factor Kappa B Binding Sites in Long Terminal Repeat of Genetically Evolving HIV-1 Subtype C Viral Species in Host with Comorbidities

HIV-1 causes millions of deaths around the world. Higher disease progression and mortality are seen in HIV positive individuals with comorbidities. Two of the most pertinent conditions are coinfection with Mycobacterium tuberculosis and Intravenous Drug abuse. The mechanisms involved, however, still remain unresolved. To elucidate the mechanisms involved, we evaluated the genetic alterations in terms of additional nuclear factor kappa B (NF-κB) sites in the long terminal repeat (LTR) of HIV-1 subtype-C isolates from infected human individuals from North India, supposedly acquired by the emerging viral quasi-species in the infected host in presence of these two comorbid conditions. Interestingly the results indicate higher number of NF-κB sites in the viral isolates from HIV-tuberculosis coinfected (n = 26, 16 isolates with 3 sites and 10 isolates with 2 sites) and intravenous drug users (n = 20, 13 isolates with 3 sites and 7 isolates with 2 sites) compared to the mono-infected hosts (n = 30, 10 isolates with 3 sites, 18 isolates with 2 sites, 2 isolates with 1 site). The biological relevance of these alterations in the NF-κB sites within the HIV-1 LTR with respect to viral replicative capacity and HIV disease progression needs to be studied further.

The crosstalk between antiretrovirals pharmacology and HIV drug resistance

INTRODUCTION

The clinical development of antiretroviral drugs has been followed by a rapid and concomitant development of HIV drug resistance. The development and spread of HIV drug resistance is due on the one hand to the within-host intrinsic HIV evolutionary rate and on the other to the wide use of low genetic barrier antiretrovirals.

AREAS COVERED

We searched PubMed and Embase on 31 January 2020, for studies reporting antiretroviral resistance and pharmacology. In this review, we assessed the molecular target and mechanism of drug resistance development of the different antiretroviral classes focusing on the currently approved antiretroviral drugs. Then, we assessed the main pharmacokinetic/pharmacodynamic of the antiretrovirals. Finally, we retraced the history of antiretroviral treatment and its interconnection with antiretroviral worldwide resistance development both in , and middle-income countries in the perspective of 90-90-90 World Health Organization target.

EXPERT OPINION

Drug resistance development is an invariably evolutionary driven phenomenon, which challenge the 90-90-90 target. In high-income countries, the antiretroviral drug resistance seems to be stable since the last decade. On the contrary, multi-intervention strategies comprehensive of broad availability of high genetic barrier regimens should be implemented in resource-limited setting to curb the rise of drug resistance.

The S68G polymorphism is a compensatory mutation associated with the drug resistance mutation K65R in CRF01_AE strains

BACKGROUND

The rate of S68G mutation in human immunodeficiency virus type 1 (HIV-1) reverse transcriptase has increased and is closely related to the K65R mutation among CRF01_AE-infected patients who failed treatment. We aimed to explore the temporal association of S68G and K65R mutations and disclose the role of the former on susceptibility to nucleotide/nucleoside reverse transcriptase inhibitor (NRTI) and viral replication with the K65R double mutations among CRF01_AE-infected patients who failed treatment.

METHODS

The occurrence of S68G and K65R mutations was evaluated among HIV-1 of various subtypes in the global HIV Drug Resistance Database. The temporal association of S68G and K65R mutations was analyzed through next-generation sequencing in four CRF01_AE-infected patients who failed treatment with tenofovir/lamivudine/efavirenz. The impact of the S68G mutation on susceptibility to NRTI and replication fitness was analyzed using pseudovirus phenotypic resistance assays and growth competition assays, respectively.

RESULTS

The frequency of the S68G mutation increased by 1.4-9.7% in almost all HIV subtypes and circulating recombinant forms in treatment-experienced patients, except subtype F. The S68G mutation often occurred in conjunction with the K65R mutation among RTI-treated patients, with frequencies ranging 21.1-61.7% in various subtypes. Next-generation sequencing revealed that the S68G mutation occurred following the K65R mutation in three of the four CRF01_AE-infected patients. In these three patients, there was no significant change detected in the half maximal inhibitory concentration for zidovudine, tenofovir, or lamivudine between the K65R and K65R/S68G mutations, as demonstrated by the phenotypic resistance assays. Virus stocks of the K65R and K65R/S68G mutations were mixed with 4:6, 1:1, and 9:1 and cultured for 13 days, the K65R/S68G mutants outgrew those of the K65R mutants irrespective of the input ratio.

CONCLUSIONS

S68G may be a natural polymorphism and compensatory mutation of K65R selected by NRTIs in the CRF01_AE strain of HIV-1. This mutation does not affect susceptibility to NRTI; however, it improves the replication fitness of K65R mutants. This study deciphers the role of the S68G mutation in the HIV reverse transcriptase of the CRF01_AE strain and provides new evidence for the interpretation of drug-resistant mutations in non-B subtypes of HIV-1.

Human Immunodeficiency Virus Type 1 Drug Resistance Mutations Update

As treatment options coalesce around a smaller number of antiretroviral drugs (ARVs), data are emerging on the drug resistance mutations (DRMs) selected by the most widely used ARVs and on the impact of these DRMs on ARV susceptibility and virological response to first- and later-line treatment regimens. Recent studies have described the DRMs that emerge in patients receiving tenofovir prodrugs, the nonnucleoside reverse transcriptase inhibitors efavirenz and rilpivirine, ritonavir-boosted lopinavir, and the integrase inhibitors raltegravir and elvitegravir. Several small studies have described DRMs that emerge in patients receiving dolutegravir.

Week 48 resistance analysis of Elvitegravir/Cobicistat/Emtricitabine/Tenofovir DF versus Atazanavir + Ritonavir + Emtricitabine/Tenofovir DF in HIV-1 infected women (WAVES study GS-US-236-0128)

Background Women and those with non-B subtype HIV-1 are typically underrepresented in clinical trials. WAVES (GS-US-236-0128) was a double-blind phase 3b study among treatment-naïve HIV-1-infected women that demonstrated that elvitegravir/cobicistat/emtricitabine/tenofovir DF (EVG/COBI/FTC/TDF; N = 289) was superior to atazanavir + ritonavir + FTC/TDF (ATV + RTV + FTC/TDF; N = 286) for HIV-1 RNA < 50 copies/mL by FDA snapshot analysis at week 48. Here, we describe resistance development through week 48 in women with virologic failure and determine the impact of pre-existing mutations and HIV-1 subtype on viral suppression. Methods Genotypic analyses (population and deep sequencing) and phenotypic analyses of HIV-1 protease, reverse transcriptase (RT), and integrase (IN) were performed. The resistance analysis population (participants with HIV-1 RNA ≥ 400 copies/mL at confirmed virologic failure, at discontinuation ≥ week 8, or at week 48) had genotypic and phenotypic analyses at failure and baseline. Results The proportion of women qualifying for resistance analyses was similar between treatment groups (6.2% EVG/COBI/FTC/TDF; 7.3% ATV + RTV + FTC/TDF). Emergent resistance was rare (0% EVG/COBI/FTC/TDF; 1% ATV + RTV + FTC/TDF - 3 with M184V/I in RT). Deep sequencing of HIV-1 did not detect additional resistance development. Pre-existing mutations did not lead to virologic failure; most with the polymorphic primary IN substitution T97A (92%), or with substitutions in RT (i.e. A62V, V90I, K103N, or E138A/G/K/Q; 68-82%) demonstrated virologic suppression at week 48, with no resistance development except for one patient with M184V and pre-existing K103N in the ATV + RTV + FTC/TDF group. Most participants (74%) had non-B HIV-1, and subtype did not affect outcome. Conclusions Emergent resistance to study drugs was rare in this study of women, with no resistance observed among EVG/COBI/FTC/TDF-treated participants, despite a high proportion of participants with natural or transmitted viral mutations and non-B HIV-1 subtypes.

Commonly Transmitted HIV-1 Drug Resistance Mutations in Reverse-Transcriptase and Protease in Antiretroviral Treatment-Naive Patients and Response to Regimens Containing Tenofovir Disoproxil Fumarate or Tenofovir Alafenamide

Background

The presence of transmitted drug resistance mutations (TDRMs) in antiretroviral treatment (ART)-naive patients can adversely affect the outcome of ART.

Methods

Resistance testing was conducted in 6704 ART-naive subjects predominantly from the United States and Europe in 9 clinical studies conducted by Gilead Sciences from 2000 to 2013.

Results

The presence of TDRMs increased during this period (from 5.2% to 11.4%), primarily driven by an increase in nonnucleoside reverse-transcriptase (RT) inhibitor (NNRTI) resistance mutations (from 0.3% to 7.1%), particularly K103N/S (increase from 0.3% to 5.3%). Nucleoside/nucleotide RT inhibitor mutations were found in 3.1% of patients. Only 1 patient had K65R (0.01%) and 7 had M184V/I (0.1%), despite high use of tenofovir disoproxil fumarate (TDF), emtricitabine, and lamivudine and potential transmission of resistance to these drugs. At least 1 thymidine-analogue mutations was present in 2.7% of patients with 0.07% harboring T215Y/F and 2.7% harboring T215 revertant mutations (T215rev). Patients with the combination of M41L + L210W + T215rev showed full human immunodeficiency virus RNA suppression while receiving a TDF- or tenofovir alafenamide-containing regimen.

Conclusions

There was an overall increase of TDRMs among patients enrolling in clinical trials from 2000 through 2013, driven primarily by an increase in NNRTI resistance. However, the presence of common TDRMs, including thymidine-analogue mutations/T215rev, showed no impact on response to TDF- or tenofovir alafenamide-containing regimens.

Mutational Correlates of Virological Failure in Individuals Receiving a WHO-Recommended Tenofovir-Containing First-Line Regimen: An International Collaboration

Tenofovir disoproxil fumarate (TDF) genotypic resistance defined by K65R/N and/or K70E/Q/G occurs in 20% to 60% of individuals with virological failure (VF) on a WHO-recommended TDF-containing first-line regimen. However, the full spectrum of reverse transcriptase (RT) mutations selected in individuals with VF on such a regimen is not known. To identify TDF regimen-associated mutations (TRAMs), we compared the proportion of each RT mutation in 2873 individuals with VF on a WHO-recommended first-line TDF-containing regimen to its proportion in a cohort of 50,803 antiretroviral-naïve individuals. To identify TRAMs specifically associated with TDF-selection pressure, we compared the proportion of each TRAM to its proportion in a cohort of 5805 individuals with VF on a first-line thymidine analog-containing regimen. We identified 83 TRAMs including 33 NRTI-associated, 40 NNRTI-associated, and 10 uncommon mutations of uncertain provenance. Of the 33 NRTI-associated TRAMs, 12 - A62V, K65R/N, S68G/N/D, K70E/Q/T, L74I, V75L, and Y115F - were more common among individuals receiving a first-line TDF-containing compared to a first-line thymidine analog-containing regimen. These 12 TDF-selected TRAMs will be important for monitoring TDF-associated transmitted drug-resistance and for determining the extent of reduced TDF susceptibility in individuals with VF on a TDF-containing regimen.

Evolution of tenofovir-resistant HIV-1 isolates exposed to tenofovir alafenamide dose escalation

Resistance selection experiments using HIV-1 isolates harboring pre-existing tenofovir (TFV)-resistance (K65R, 3TAMs, and Q151M complex) were carried out with the novel tenofovir prodrug tenofovir alafenamide (TAF) as well as with tenofovir (TFV), to investigate the potential for additional resistance development in the presence of TAF or TFV. Extended resistance selection of these TFV resistance associated mutations (RAMs)-containing viruses with TAF or TFV did not lead to the accumulation of additional known RAMs, or significant additional phenotypic resistance, after 6 months in culture. Two new mutations were found during the selections (L429I, T69I) that were further characterized, and found to have very limited or no role in resistance to TAF or TFV. Notably, viral survival in the presence of drug increases could not be sustained and led to viral cure in cell culture, suggesting a lack of alternative resistance pathways for the mutant viruses.

Genome-Wide Association Study of HIV Whole Genome Sequences Validated using Drug Resistance

Background

Genome-wide association studies (GWAS) have considerably advanced our understanding of human traits and diseases. With the increasing availability of whole genome sequences (WGS) for pathogens, it is important to establish whether GWAS of viral genomes could reveal important biological insights. Here we perform the first proof of concept viral GWAS examining drug resistance (DR), a phenotype with well understood genetics.

Method

We performed a GWAS of DR in a sample of 343 HIV subtype C patients failing 1^st line antiretroviral treatment in rural KwaZulu-Natal, South Africa. The majority and minority variants within each sequence were called using PILON, and GWAS was performed within PLINK. HIV WGS from patients failing on different antiretroviral treatments were compared to sequences derived from individuals naïve to the respective treatment.

Results

GWAS methodology was validated by identifying five associations on a genetic level that led to amino acid changes known to cause DR. Further, we highlighted the ability of GWAS to identify epistatic effects, identifying two replicable variants within amino acid 68 of the reverse transcriptase protein previously described as potential fitness compensatory mutations. A possible additional DR variant within amino acid 91 of the matrix region of the Gag protein was associated with tenofovir failure, highlighting GWAS’s ability to identify variants outside classical candidate genes. Our results also suggest a polygenic component to DR.

Conclusions

These results validate the applicability of GWAS to HIV WGS data even in relative small samples, and emphasise how high throughput sequencing can provide novel and clinically relevant insights. Further they suggested that for viruses like HIV, population structure was only minor concern compared to that seen in bacteria or parasite GWAS. Given the small genome length and reduced burden for multiple testing, this makes HIV an ideal candidate for GWAS.

High fidelity simian immunodeficiency virus reverse transcriptase mutants have impaired replication in vitro and in vivo

The low fidelity of HIV replication facilitates immune and drug escape. Some reverse transcriptase (RT) inhibitor drug-resistance mutations increase RT fidelity in biochemical assays but their effect during viral replication is unclear. We investigated the effect of RT mutations K65R, Q151N and V148I on SIV replication and fidelity in vitro, along with SIV replication in pigtailed macaques. SIVmac239-K65R and SIVmac239-V148I viruses had reduced replication capacity compared to wild-type SIVmac239. Direct virus competition assays demonstrated a rank order of wild-type>K65R>V148I mutants in terms of viral fitness. In single round in vitro-replication assays, SIVmac239-K65R demonstrated significantly higher fidelity than wild-type, and rapidly reverted to wild-type following infection of macaques. In contrast, SIVmac239-Q151N was replication incompetent in vitro and in pigtailed macaques. Thus, we showed that RT mutants, and specifically the common K65R drug-resistance mutation, had impaired replication capacity and higher fidelity. These results have implications for the pathogenesis of drug-resistant HIV.

Biochemical characterization of a multi-drug resistant HIV-1 subtype AG reverse transcriptase: antagonism of AZT discrimination and excision pathways and sensitivity to RNase H inhibitors

We analyzed a multi-drug resistant (MR) HIV-1 reverse transcriptase (RT), subcloned from a patient-derived subtype CRF02_AG, harboring 45 amino acid exchanges, amongst them four thymidine analog mutations (TAMs) relevant for high-level AZT (azidothymidine) resistance by AZTMP excision (M41L, D67N, T215Y, K219E) as well as four substitutions of the AZTTP discrimination pathway (A62V, V75I, F116Y and Q151M). In addition, K65R, known to antagonize AZTMP excision in HIV-1 subtype B was present. Although MR-RT harbored the most significant amino acid exchanges T215Y and Q151M of each pathway, it exclusively used AZTTP discrimination, indicating that the two mechanisms are mutually exclusive and that the Q151M pathway is obviously preferred since it confers resistance to most nucleoside inhibitors. A derivative was created, additionally harboring the TAM K70R and the reversions M151Q as well as R65K since K65R antagonizes excision. MR-R65K-K70R-M151Q was competent of AZTMP excision, whereas other combinations thereof with only one or two exchanges still promoted discrimination. To tackle the multi-drug resistance problem, we tested if the MR-RTs could still be inhibited by RNase H inhibitors. All MR-RTs exhibited similar sensitivity toward RNase H inhibitors belonging to different inhibitor classes, indicating the importance of developing RNase H inhibitors further as anti-HIV drugs.

Drug Susceptibility and Viral Fitness of HIV-1 with Integrase Strand Transfer Inhibitor Resistance Substitution Q148R or N155H in Combination with Nucleoside/Nucleotide Reverse Transcriptase Inhibitor Resistance Substitutions

In clinical trials of coformulated elvitegravir (EVG), cobicistat (COBI), emtricitabine (FTC), and tenofovir disoproxil fumarate (TDF), emergent drug resistance predominantly involved the FTC resistance substitution M184V/I in reverse transcriptase (RT), with or without the tenofovir (TFV) resistance substitution K65R, accompanied by a primary EVG resistance substitution (E92Q, N155H, or Q148R) in integrase (IN). We previously reported that the RT-K65R, RT-M184V, and IN-E92Q substitutions lacked cross-class phenotypic resistance and replicative fitness compensation. As a follow-up, the in vitro characteristics of mutant HIV-1 containing RT-K65R and/or RT-M184V with IN-Q148R or IN-N155H were also evaluated, alone and in combination, for potential interactions. Single mutants displayed reduced susceptibility to their corresponding inhibitor classes, with no cross-class resistance. Viruses with IN-Q148R or IN-N155H exhibited reduced susceptibility to EVG (137- and 40-fold, respectively) that was not affected by the addition of RT-M184V or RT-K65R/M184V. All viruses containing RT-M184V were resistant to FTC (>1,000-fold). Mutants with RT-K65R had reduced susceptibility to TFV (3.3- to 3.6-fold). Without drugs present, the viral fitness of RT and/or IN mutants was diminished relative to that of the wild type in the following genotypic order: wild type > RT-M184V ≥ IN-N155H ≈ IN-Q148R ≥ RT-M184V + IN-N155H ≥ RT-M184V + IN-Q148R ≥ RT-K65R/M184V + IN-Q148R ≈ RT-K65R/M184V + IN-N155H. In the presence of drug concentrations approaching physiologic levels, drug resistance counteracted replication defects, allowing single mutants to outcompete the wild type with one drug present and double mutants to outcompete single mutants with two drugs present. These results suggest that during antiretroviral treatment with multiple drugs, the development of viruses with combinations of resistance substitutions may be favored despite diminished viral fitness.

Characterization of HIV-1 Resistance to Tenofovir Alafenamide In Vitro

Tenofovir alafenamide (TAF) is an investigational prodrug of the HIV-1 nucleotide reverse transcriptase (RT) inhibitor (NtRTI) tenofovir (TFV), with improved potency and drug delivery properties over the current prodrug, tenofovir disoproxil fumarate (TDF). TAF is currently in phase 3 clinical studies for the treatment of HIV-1 infection, in combination with other antiretroviral agents. Phase 1 and 2 studies have shown that TAF was associated with increased peripheral blood mononuclear cell (PBMC) drug loading and increased suppression of HIV-1 replication compared to treatment with TDF. In this study, selection of in vitro resistance to both TAF and the parent compound, TFV, led to the emergence of HIV-1 with the K65R amino acid substitution in RT with 6.5-fold-reduced susceptibility to TAF. Although TAF is more potent than TFV in vitro, the antiviral susceptibilities to TAF and TFV of a large panel of nucleoside/nucleotide RT inhibitor (NRTI)-resistant mutants were highly correlated (R(2) = 0.97), indicating that the two compounds have virtually the same resistance profile when assessed as fold change from the wild type. TAF showed full antiviral activity in PBMCs against primary HIV-1 isolates with protease inhibitor, nonnucleoside RT inhibitor (NNRTI), or integrase strand transfer inhibitor resistance but reduced activity against isolates with extensive NRTI resistance amino acid substitutions. However, the increased cell loading of TFV with TAF versus TDF observed in vivo suggests that TAF may retain activity against TDF-resistant mutant viruses.

Reduced viral fitness and lack of cross-class resistance with integrase strand transfer inhibitor and nucleoside reverse transcriptase inhibitor resistance mutations

The most common pattern of emergent resistance in the phase III clinical trials of coformulated elvitegravir (EVG)-cobicistat (COBI)-emtricitabine (FTC)-tenofovir disoproxil fumarate (TDF) was the EVG resistance substitution E92Q in integrase (IN) with the FTC resistance substitution M184V in reverse transcriptase (RT), with or without the tenofovir (TFV) resistance substitution K65R. In this study, the effect of these IN and RT substitutions alone and in combination in the same genome on susceptibility to antiretroviral inhibitors and viral replication fitness was characterized. Single resistance substitutions (E92Q in IN [IN-E92Q], M184V in RT [RT-M184V], and K65R in RT [RT-K65R]) specifically affected susceptibility to the corresponding inhibitor classes, with no cross-class resistance observed. The IN-E92Q mutant displayed reduced susceptibility to EVG (50-fold), which was not impacted by the addition of RT-M184V or RT-K65R/M184V. Viruses containing RT-M184V had high-level resistance to FTC (>1,000-fold) that was not affected by the addition of IN-E92Q or RT-K65R. During pairwise growth competitions, each substitution contributed to decreased viral fitness, with the RT-K65R/M184V + IN-E92Q triple mutant being the least fit in the absence of drug. In the presence of drug concentrations approaching physiologic levels, however, drug resistance offset the replication defects, resulting in single mutants outcompeting the wild type with one drug present, and double and triple mutants outcompeting single mutants with two drugs present. Taken together, these results suggest that the reduced replication fitness and phenotypic resistance associated with RT and IN resistance substitutions are independent and additive. In the presence of multiple drugs, viral growth is favored for viruses with multiple substitutions, despite the presence of fitness defects.

A cell-based strategy to assess intrinsic inhibition efficiencies of HIV-1 reverse transcriptase inhibitors

During HIV-1 reverse transcription, there are increasing opportunities for nucleos(t)ide (NRTI) or nonnucleoside (NNRTI) reverse transcriptase (RT) inhibitors to stop elongation of the nascent viral DNA (vDNA). In addition, RT inhibitors appear to influence the kinetics of vDNA synthesis differently. While cell-free kinetic inhibition constants have provided detailed mechanistic insight, these assays are dependent on experimental conditions that may not mimic the cellular milieu. Here we describe a novel cell-based strategy to provide a measure of the intrinsic inhibition efficiencies of clinically relevant RT inhibitors on a per-stop-site basis. To better compare inhibition efficiencies among HIV-1 RT inhibitors that can stop reverse transcription at any number of different stop sites, their basic probability, p, of getting stopped at any potential stop site was determined. A relationship between qPCR-derived 50% effective inhibitory concentrations (EC50s) and this basic probability enabled determination of p by successive approximation. On a per-stop-site basis, tenofovir (TFV) exhibited 1.4-fold-greater inhibition efficiency than emtricitabine (FTC), and as a class, both NRTIs exhibited an 8- to 11-fold greater efficiency than efavirenz (EFV). However, as more potential stops sites were considered, the probability of reverse transcription failing to reach the end of the template approached equivalence between both classes of RT inhibitors. Overall, this novel strategy provides a quantitative measure of the intrinsic inhibition efficiencies of RT inhibitors in the natural cellular milieu and thus may further understanding of drug efficacy. This approach also has applicability for understanding the impact of viral polymerase-based inhibitors (alone or in combination) in other virus systems.

A uniquely prevalent nonnucleoside reverse transcriptase inhibitor resistance mutation in Russian subtype A HIV-1 viruses

BACKGROUND

The subtype A variant in the Former Soviet Union (A(FSU)) causes most of Russia's HIV-1 infections. However, the spectrum of drug-resistance mutations (DRMs) in antiretroviral experienced patients with this variant has not been studied.

METHODS

Between 2010 and 2013, genotypic resistance testing was performed on plasma samples from 366 antiretroviral-experienced patients in Siberia.

RESULTS

Three-hundred patients (82%) had subtype A(FSU) and 55 (15%) had CRF02_AG viruses. The pattern of DRMs was consistent with patient antiretroviral history with one exception. G190S was the most common nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance mutation, occurring in 55 (33%) subtype A(FSU) viruses from 167 NNRTI-experienced patients compared with none of 37 CRF02_AG viruses from NNRTI-experienced patients (P < 0.001). The next most common subtype A(FSU) NNRTI-resistance mutation, K103N, occurred in 25 (15%) viruses. Wild-type glycine (G) at position 190 is encoded by GGC in more than 99% of published A(FSU) strains. By contrast, G190 is encoded by GGA or GGG in 97% of other subtypes and in subtype A strains outside of the FSU. Therefore, G190S results from a single G→A transition: G (GGC) → S (AGC) almost exclusively in subtype A(FSU) viruses.

CONCLUSION

The predisposition of subtype A(FSU) to G190S is concerning because G→A is the most common HIV-1 mutation and because G190S causes higher levels of nevirapine and efavirenz resistance than K103N. This study exemplifies the need for characterizing the genetic mechanisms of resistance in diverse populations and warrants studies to verify that NRTI/NNRTI regimens are as efficacious in treating subtype A(FSU) as viruses belonging to other subtypes.

The lysine 65 residue in HIV-1 reverse transcriptase function and in nucleoside analog drug resistance

Mutations in HIV-1 reverse transcriptase (RT) that confer nucleoside analog RT inhibitor resistance have highlighted the functional importance of several active site residues (M184, Q151 and K65) in RT catalytic function. Of these, K65 residue is notable due to its pivotal position in the dNTP-binding pocket, its involvement in nucleoside analog resistance and polymerase fidelity. This review focuses on K65 residue and summarizes a substantial body of biochemical and structural studies of its role in RT function and the functional consequences of the K65R mutation.

Week 144 resistance analysis of elvitegravir/cobicistat/emtricitabine/tenofovir DF versus efavirenz/emtricitabine/tenofovir DF in antiretroviral-naive patients

BACKGROUND

Here, the baseline and emergent resistance to elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate (EVG/COBI/FTC/TDF) versus efavirenz (EFV)/FTC/TDF in HIV-1-infected antiretroviral-naive adults through 144 weeks from the randomized, ongoing, Phase III study GS-US-236-0102 is described.

METHODS

HIV-1 protease (PR) and reverse transcriptase (RT) were sequenced at screening; patients with HIV-1 resistant to EFV, FTC or TDF were excluded. Genotypic/phenotypic analyses were performed at virological failure confirmation and baseline for PR, RT and integrase (IN) for patients with virological failure and for patients with HIV-1 RNA≥400 copies/ml at weeks 48, 96, 144 or early study drug discontinuation. Retrospective, baseline, IN genotyping was conducted for EVG/COBI/FTC/TDF patients.

RESULTS

In the EVG/COBI/FTC/TDF group through week 144, HIV-1 from 10 patients (2.9%; 10/348 treated patients) developed primary IN strand transfer inhibitor (n=9) and/or nucleoside RT inhibitor resistance substitutions (n=10). The emergence of resistance decreased over time with 8, 2 and 0 patients developing HIV-1 resistance through week 48, post-week 48-96 and post-week 96-144, respectively. Emergent substitutions were E92Q (n=7), N155H (n=3), Q148R (n=1) and T66I (n=1) in IN, and M184V/I (n=10) and K65R (n=4) in RT. All 10 isolates had reduced susceptibility to EVG, FTC or TDF. Virus with EVG phenotypic resistance had cross-resistance to raltegravir. In the EFV/FTC/TDF group, virus from 14 patients (4.0%; 14/352 treated patients; 4 during weeks 96-144) developed a resistance substitution to EFV (n=14; K103N: n=13), FTC (M184V/I: n=4) or TDF (K65R: n=3).

CONCLUSIONS

Resistance development to EVG/COBI/FTC/TDF was infrequent through 144 weeks of therapy and decreased over time, consistent with durable efficacy.

Characterization of amino acids Arg, Ser and Thr at position 70 within HIV-1 reverse transcriptase

OBJECTIVES

The amino acid position 70 in HIV-1 reverse transcriptase (RT) plays an important role in nucleoside RT inhibitor (NRTI) resistance. K70R is part of the thymidine analog mutations, but also other amino acid changes have been associated with NRTI resistance, such as K70E and K70G. In this study, we investigated the in vivo selection of the HIV-1 RT mutations K70S and K70T and their in vitro effect on drug resistance and replication capacity.

METHODS

Recombinant viruses with RT mutations were generated to measure the in vitro drug susceptibility and replication capacity. Bayesian network analysis and three-dimensional modeling were performed to understand the selection and impact of the RT70 mutations.

RESULTS

K70S and K70T were found at a low frequency in RTI-experienced HIV-1 patients (0.10% and 0·20%). Baeyesian network learning identified no direct association with the in vivo exposure to any specific RTI. However, direct associations of K70S with mutations within the Q151M-complex and of K70T with K65R were observed. In vitro phenotypic testing revealed only minor effects of K70R/S/T as single mutations, associated with Q151M and within the context of the Q151M-complex.

DISCUSSION

These results suggest that the selection of K70S/T and their phenotypic impact are influenced by the presence of other mutations in RT. However, the low impact on in vitro phenotype here observed, alongside with the low in vivo prevalence, the exclusive direct association with known major RTI mutations and the unknown correlation with in vivo response, do not yet necessitate the inclusion of K70S/T in drug resistance interpretation systems.

The high cost of fidelity

The notoriously low fidelity of HIV-1 replication is largely responsible for the virus's rapid mutation rate, facilitating escape from immune or drug control. The error-prone activity of the viral reverse transcriptase (RT) is predicted to be the most influential mechanism for generating mutations. The low fidelity of RT has been successfully exploited by nucleoside and nucleotide analogue reverse transcriptase inhibitors (NRTIs) that halt viral replication upon incorporation. Consequently, drug-resistant strains have arisen in which the viral RT has an increased fidelity of replication, thus reducing analogue incorporation. Higher fidelity, however, impacts on viral fitness. The appearance of compensatory mutations in combination with higher fidelity NRTI resistance mutations and the subsequent reversion of NRTI-resistant mutations upon cessation of antiretroviral treatment lend support to the notion that higher fidelity exacts a fitness cost. Potential mechanisms for reduced viral fitness are a smaller pool of mutant strains available to respond to immune or drug pressure, slower rates of replication, and a limitation to the dNTP tropism of the virus. Unraveling the relationship between replication fidelity and fitness should lead to a greater understanding of the evolution and control of HIV.

Impact of primary elvitegravir resistance-associated mutations in HIV-1 integrase on drug susceptibility and viral replication fitness

Elvitegravir (EVG) is an effective HIV-1 integrase (IN) strand transfer inhibitor (INSTI) in advanced clinical development. Primary INSTI resistance-associated mutations (RAMs) at six IN positions have been identified in HIV-1-infected patients failing EVG-containing regimens in clinical studies: T66I/A/K, E92Q/G, T97A, S147G, Q148R/H/K, and N155H. In this study, the effect of these primary IN mutations, alone and in combination, on susceptibility to the INSTIs EVG, raltegravir (RAL), and dolutegravir (DTG); IN enzyme activities; and viral replication fitness was characterized. Recombinant viruses containing the six most common mutations exhibited a range of reduced EVG susceptibility: 92-fold for Q148R, 30-fold for N155H, 26-fold for E92Q, 10-fold for T66I, 4-fold for S147G, and 2-fold for T97A. Less commonly observed primary IN mutations also showed a range of reduced EVG susceptibilities: 40- to 94-fold for T66K and Q148K and 5- to 10-fold for T66A, E92G, and Q148H. Some primary IN mutations exhibited broad cross-resistance between EVG and RAL (T66K, E92Q, Q148R/H/K, and N155H), while others retained susceptibility to RAL (T66I/A, E92G, T97A, and S147G). Dual combinations of primary IN mutations further reduced INSTI susceptibility, replication capacity, and viral fitness relative to either mutation alone. Susceptibility to DTG was retained by single primary IN mutations but reduced by dual mutation combinations with Q148R. Primary EVG RAMs also diminished IN enzymatic activities, concordant with their structural proximity to the active site. Greater reductions in viral fitness of dual mutation combinations may explain why some primary INSTI RAMs do not readily coexist on the same HIV-1 genome but rather establish independent pathways of resistance to EVG.

Molecular basis of human immunodeficiency virus type 1 drug resistance: overview and recent developments

The introduction of potent combination therapies in the mid-90s had a tremendous effect on AIDS mortality. However, drug resistance has been a major factor contributing to antiretroviral therapy failure. Currently, there are 26 drugs approved for treating human immunodeficiency virus (HIV) infections, although some of them are no longer prescribed. Most of the available antiretroviral drugs target HIV genome replication (i.e. reverse transcriptase inhibitors) and viral maturation (i.e. viral protease inhibitors). Other drugs in clinical use include a viral coreceptor antagonist (maraviroc), a fusion inhibitor (enfuvirtide) and two viral integrase inhibitors (raltegravir and elvitegravir). Elvitegravir and the nonnucleoside reverse transcriptase inhibitor rilpivirine have been the most recent additions to the antiretroviral drug armamentarium. An overview of the molecular mechanisms involved in antiretroviral drug resistance and the role of drug resistance-associated mutations was previously presented (Menéndez-Arias, L., 2010. Molecular basis of human immunodeficiency virus drug resistance: an update. Antiviral Res. 85, 210-231). This article provides now an updated review that covers currently approved drugs, new experimental agents (e.g. neutralizing antibodies) and selected drugs in preclinical or early clinical development (e.g. experimental integrase inhibitors). Special attention is dedicated to recent research on resistance to reverse transcriptase and integrase inhibitors. In addition, recently discovered interactions between HIV and host proteins and novel strategies to block HIV assembly or viral entry emerge as promising alternatives for the development of effective antiretroviral treatments.

Evolution of drug-resistant viral populations during interruption of antiretroviral therapy

Analysis of a large number of HIV-1 genomes at multiple time points after antiretroviral treatment (ART) interruption allows determination of the evolution of drug-resistant viruses and viral fitness in vivo in the absence of drug selection pressure. Using a parallel allele-specific sequencing (PASS) assay, potential primary drug-resistant mutations in five individual patients were studied by analyzing over 18,000 viral genomes. A three-phase evolution of drug-resistant viruses was observed after termination of ART. In the first phase, viruses carrying various combinations of multiple-drug-resistant (MDR) mutations predominated with each mutation persisting in relatively stable proportions while the overall number of resistant viruses gradually increased. In the second phase, viruses with linked MDR mutations rapidly became undetectable and single-drug-resistant (SDR) viruses emerged as minority populations while wild-type viruses quickly predominated. In the third phase, low-frequency SDR viruses remained detectable as long as 59 weeks after treatment interruption. Mathematical modeling showed that the loss in relative fitness increased with the number of mutations in each viral genome and that viruses with MDR mutations had lower fitness than viruses with SDR mutations. No single viral genome had seven or more drug resistance mutations, suggesting that such severely mutated viruses were too unfit to be detected or that the resistance gain offered by the seventh mutation did not outweigh its contribution to the overall fitness loss of the virus. These data provide a more comprehensive understanding of evolution and fitness of drug-resistant viruses in vivo and may lead to improved treatment strategies for ART-experienced patients.

Selection and characterization of HIV-1 with a novel S68 deletion in reverse transcriptase

Resistance to human immunodeficiency virus type 1 (HIV-1) represents a significant problem in the design of novel therapeutics and the management of treatment regimens in infected persons. Resistance profiles can be elucidated by defining modifications to the viral genome conferred upon exposure to novel nucleoside reverse transcriptase (RT) inhibitors (NRTI). In vitro testing of HIV-1LAI-infected primary human lymphocytes treated with β-D-2',3'-dideoxy-2',3'-didehydro-5-fluorocytidine (DFC; Dexelvucitabine; Reverset) produced a novel deletion of AGT at codon 68 (S68Δ) alone and in combination with K65R that differentially affects drug response. Dual-approach clone techniques utilizing TOPO cloning and pyrosequencing confirmed the novel S68Δ in the HIV-1 genome. The S68Δ HIV-1 RT was phenotyped against various antiviral agents in a heteropolymeric DNA polymerase assay and in human lymphocytes. Drug susceptibility results indicate that the S68Δ displayed a 10- to 30-fold increase in resistance to DFC, lamivudine, emtricitabine, tenofovir, abacavir, and amdoxovir and modest resistance to stavudine, β-d-2',3'-oxa-5-fluorocytidine, or 9-(β-D-1,3-dioxolan-4-yl)guanine and remained susceptible to 3'-azido-3'-deoxythymidine, 2',3'-dideoxyinosine (ddI), 1-(β-D-dioxolane)thymine (DOT) and lopinavir. Modeling revealed a central role for S68 in affecting conformation of the β3-β4 finger region and provides a rational for the selective resistance. These data indicate that the novel S68Δ is a previously unrecognized deletion that may represent an important factor in NRTI multidrug resistance treatment strategies.

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

Background

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

Results

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

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

Conclusions

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

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

Tenofovir (TDF)-selected or abacavir (ABC)-selected low-frequency HIV type 1 subpopulations during failure with persistent viremia as detected by ultradeep pyrosequencing

Detection of drug resistance is critical for determining antiretroviral treatment options. Ultradeep pyrosequencing (UDPS; 454 Life Sciences) is capable of detecting virus variant subpopulations with much greater sensitivity than population sequencing, which typically has a detection limit around 20%. UDPS of the HIV-1 reverse transcriptase (RT) (amino acids 56-120) was performed to detect the key mutations K65R and L74V associated with tenofovir and abacavir use. Plasma specimens from subjects with persistent rebound viremia following suppression on tenofovir (n = 8) or abacavir (n = 9)-based therapy were studied. Samples from a subject treated with zidovudine/lamivudine/efavirenz with a similar loss of virologic response served as a control. HIV-1 plasma RNA was ≥3.68 log(10) copies/ml at all time points sequenced. The median number of UDPS sequences analyzed/time point was 33,246. Among the eight tenofovir-treated subjects, three showed high-frequency (>20%) RT K65R at the time of failure, whereas one showed low-frequency (<20%) L74V; no low-frequency K65R was detected in these subjects. Among the nine abacavir-treated subjects, three showed low-frequency K65R; no L74V was detected in these patients. No K65R or L74V was detected in the samples from the control subject. At failure, other RT mutations were detected, including low-frequency NNRTI-resistant species detected at ≥1 time point in nine subjects; the key NNRTI mutation K103N, however, was always observed at >20% frequency. Although UDPS is useful in the detection of low-frequency subpopulations with transmitted resistance in antiviral-naive patients, it may have less utility in treatment-experienced patients with persistent viremia on therapy.

A Leu to Ile but not Leu to Val change at HIV-1 reverse transcriptase codon 74 in the background of K65R mutation leads to an increased processivity of K65R+L74I enzyme and a replication competent virus

Background

The major hurdle in the treatment of Human Immunodeficiency virus type 1 (HIV-1) includes the development of drug resistance-associated mutations in the target regions of the virus. Since reverse transcriptase (RT) is essential for HIV-1 replication, several nucleoside analogues have been developed to target RT of the virus. Clinical studies have shown that mutations at RT codon 65 and 74 which are located in β3-β4 linkage group of finger sub-domain of RT are selected during treatment with several RT inhibitors, including didanosine, deoxycytidine, abacavir and tenofovir. Interestingly, the co-selection of K65R and L74V is rare in clinical settings. We have previously shown that K65R and L74V are incompatible and a R→K reversion occurs at codon 65 during replication of the virus. Analysis of the HIV resistance database has revealed that similar to K65R+L74V, the double mutant K65R+L74I is also rare. We sought to compare the impact of L→V versus L→I change at codon 74 in the background of K65R mutation, on the replication of doubly mutant viruses.

Methods

Proviral clones containing K65R, L74V, L74I, K65R+L74V and K65R+L74I RT mutations were created in pNL4-3 backbone and viruses were produced in 293T cells. Replication efficiencies of all the viruses were compared in peripheral blood mononuclear (PBM) cells in the absence of selection pressure. Replication capacity (RC) of mutant viruses in relation to wild type was calculated on the basis of antigen p24 production and RT activity, and paired analysis by student t-test was performed among RCs of doubly mutant viruses. Reversion at RT codons 65 and 74 was monitored during replication in PBM cells. In vitro processivity of mutant RTs was measured to analyze the impact of amino acid changes at RT codon 74.

Results

Replication kinetics plot showed that all of the mutant viruses were attenuated as compared to wild type (WT) virus. Although attenuated in comparison to WT virus and single point mutants K65R, L74V and L74I; the double mutant K65R+L74I replicated efficiently in comparison to K65R+L74V mutant. The increased replication capacity of K65R+L74I viruses in comparison to K65R+L74V viruses was significant at multiplicity of infection 0.01 (p = 0.0004). Direct sequencing and sequencing after population cloning showed a more pronounced reversion at codon 65 in viruses containing K65R+L74V mutations in comparison to viruses with K65R+L74I mutations. In vitro processivity assays showed increased processivity of RT containing K65R+L74I in comparison to K65R+L74V RT.

Conclusions

The improved replication kinetics of K65R+L74I virus in comparison to K65R+L74V viruses was due to an increase in the processivity of RT containing K65R+L74I mutations. These observations support the rationale behind structural functional analysis to understand the interactions among unique RT mutations that may emerge during the treatment with specific drug regimens.

Highly sensitive and quantitative detection of the H274Y oseltamivir resistance mutation in seasonal A/H1N1 influenza virus

A C-to-T transition mutation in the neuraminidase gene from seasonal A/H1N1 causes a His-to-Tyr mutation at amino acid position 275 (H274Y, universal N2 numbering), conferring resistance against oseltamivir (Tamiflu). This mutation was first detected in clinical samples in Europe during the 2007-2008 influenza season. Viruses with this mutation reached a prevalence of ∼11% by the end of the season in North American isolates tested by the CDC. We developed a highly sensitive and specific quantitative real-time reverse transcriptase PCR assay to detect the H274Y mutation. This assay utilizes a 5'-methyl-isocytosine (isoC) residue and fluorescent reporters on genotype-specific primers. During PCR, a quencher coupled to isoguanine (isoG) is site-specifically incorporated complementary to the isoC/dye, resulting in loss of fluorescence. Optimization of primers and assay conditions produced a limit of detection of 100 gene copies per reaction for both wild-type and H274Y genotypes. In samples with mixed populations, it can reliably detect as little as a 1% wild-type or 0.1% H274Y component. This high sensitivity makes the assay usable on samples with viral loads too low for dideoxy or pyrosequencing analysis. Additionally, the assay distinguishes seasonal A/H1N1 from A/H3N2, influenza B, or 2009 pandemic A/H1N1, making it useful for influenza virus subtyping as well as for drug resistance detection. We probed seasonal A/H1N1 samples from the 2005-2006, 2006-2007, and 2007-2008 influenza seasons. Data from the new assay closely matched available drug resistance genotype data previously determined by dideoxy sequencing. The H274Y mutation was only found in samples from the 2007-2008 season.

The Role of Nucleotide Excision by Reverse Transcriptase in HIV Drug Resistance

Nucleoside reverse transcriptase (RT) inhibitors of HIV block viral replication through the ability of HIV RT to incorporate chain-terminating nucleotide analogs during viral DNA synthesis. Once incorporated, the chain-terminating residue must be removed before DNA synthesis can continue. Removal can be accomplished by the excision activity of HIV RT, which catalyzes the transfer of the 3'-terminal residue on the blocked DNA chain to an acceptor substrate, probably ATP in most infected cells. Mutations of RT that enhance excision activity are the most common cause of resistance to 3'-azido-3'-deoxythymidine (AZT) and exhibit low-level cross-resistance to most other nucleoside RT inhibitors. The resistance to AZT is suppressed by a number of additional mutations in RT, most of which were identified because they conferred resistance to other RT inhibitors. Here we review current understanding of the biochemical mechanisms responsible for increased or decreased excision activity due to these mutations.

The K65R mutation in HIV-1 reverse transcriptase: genetic barriers, resistance profile and clinical implications

Resistance to antiviral therapy is the limiting factor in the successful management of HIV. In general, the K65R mutation is rarely selected (1.7-4%) with tenofovir disoproxil fumarate (TDF), abacavir (ABC), didanosine (ddI), and stavudine (d4T), as compared with the high incidence (>40%) of thymidine analog mutations associated with zidovudine and d4T. The high barrier to the development of K65R may reflect a combination of factors, including the high potency of K65R-selecting drugs, including recommended TDF/emtricitabine and ABC/lamivudine (ABC/3TC) combinations; the partial (low-intermediate level) profile of cross-resistance conferred by K65R to TDF, ABC and 3TC; the favorable viral fitness constraint imposed by K65R and the 3TC/emtricitabine-associated M184V mutations; the bidirectional antagonism between the K65R and thymidine analog mutation pathways; and unique RNA structural considerations in the region surrounding codon 65. Nevertheless, surprisingly high levels of treatment failures and K65R resistance may be associated with triple nucleoside analog regimens. The use of TDF + ABC, TDF + ddI and ABC + d4T in combination with 3TC or emtricitabine should be avoided. This selection of K65R may be reduced by the inclusion of zidovudine in two-four nucleoside reverse-transcriptase regimens. Clinical studies have demonstrated an increased frequency of K65R in association with suboptimal d4T and ddI regimens, as well as nevirapine and its resistance mutations Y181C and G190A. The potential for the development of the K65R mutation in subtype C is particularly problematic wherein a signature KKK nucleotide motif, at codons 64, 65 and 66 in reverse transcriptase, appear to lead to template pausing, facilitating the selection of K65R. Optimizing regimens may attenuate the emergence of K65R, leading to better long-term treatment management in different geographic settings. TDF-based regimens are the leading candidates for first- and second-line therapy, microbicides and chemoprophylaxis strategies.

Structural basis for the role of the K65R mutation in HIV-1 reverse transcriptase polymerization, excision antagonism, and tenofovir resistance

K65R is a primary reverse transcriptase (RT) mutation selected in human immunodeficiency virus type 1-infected patients taking antiretroviral regimens containing tenofovir disoproxil fumarate or other nucleoside analog RT drugs. We determined the crystal structures of K65R mutant RT cross-linked to double-stranded DNA and in complexes with tenofovir diphosphate (TFV-DP) or dATP. The crystals permit substitution of TFV-DP with dATP at the dNTP-binding site. The guanidinium planes of the arginines K65R and Arg⁷² were stacked to form a molecular platform that restricts the conformational adaptability of both of the residues, which explains the negative effects of the K65R mutation on nucleotide incorporation and on excision. Furthermore, the guanidinium planes of K65R and Arg⁷² were stacked in two different rotameric conformations in TFV-DP- and dATP-bound structures that may help explain how K65R RT discriminates the drug from substrates. These K65R-mediated effects on RT structure and function help us to visualize the complex interaction with other key nucleotide RT drug resistance mutations, such as M184V, L74V, and thymidine analog resistance mutations.

Comparative analysis of in vitro processivity of HIV-1 reverse transcriptases containing mutations 65R, 74V, 184V and 65R+74V

While HIV-1 reverse transcriptase (RT) mutations of M to V at position 184 are commonly observed in the clinic, the double mutation of 65R+74V is rarely seen. It has been demonstrated that rapid R-->K reversion occurs at RT codon 65 during replication of HIV-1 in human peripheral blood mononuclear cells containing 65R+74V mutations and that processivity of the RT is reduced relative to wild type. However, clinical studies show that M184V can be detected after several months of therapy interruption, suggesting more effective processivity. Herein, the in vitro RT processivity of genetically engineered M184V and double mutant 65R+74V was compared. Virion-associated RTs of WT pNL4-3, K65R, L74V, M184V and 65R+74V were used to perform RT processivity assays in the presence of trap, poly(rC)-oligo(dG). Both RTs with 184V and 65R+74V mutations exhibited similar processivity when compared with each other and a significantly decreased processivity as compared to WT RT. Both mutant RTs synthesized shorter cDNA molecules (37-42 nt) relative to WT RT, which made longer (65-70 nt) cDNA molecules. Since these surprising biochemical results cannot explain the clinical phenotype, a hypothesis is presented to explain the discrepancy and suggest new approaches for future testing.

Genotypic analysis of the protease and reverse transcriptase of non-B HIV type 1 clinical isolates from naïve and treated subjects

One hundred and ninety-two pol sequences of drug-naïve and drug-experienced subjects infected with non-B HIV-1 subtypes were analyzed to identify treatment-related amino acid changes which might be relevant for drug-resistance and possibly not included in the accepted mutation list for the B subtype. The correspondence analysis identified non-B-specific and subtype-specific polymorphisms which should not be mistaken for mutations. Multiple chi(2) were performed to detect the differences between naïve vs treated subjects and between different subtypes. To verify the contribution of each single mutation to the resistance levels as predicted by the Virtual Phenotype-LM, simple univariate linear regression was used with fold resistance as a dependent variable and individual mutations as predictors. Commonly accepted protease (PR) and reverse transcriptase (RT) positions along with mutants at RT positions 118 and 90 were significantly associated with treatment. Two unusual PR (K14R and I66F) and five RT positions (E28K, S68G, H221Y, L228R/H and P294A) were also associated with treatment (p<0.01). Only minimal variations were observed with respect to commonly accepted amino acid changes. All amino acid changes correlated with treatment influenced the resistance levels to each single drug. Our findings demonstrate that there are no substantial differences regarding known resistance-associated mutations and the newly emergent substitutions between non-B and B subtype strains.

The human immunodeficiency virus type 1 nonnucleoside reverse transcriptase inhibitor resistance mutation I132M confers hypersensitivity to nucleoside analogs

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.

Apricitabine does not select additional drug resistance mutations in tissue culture in human immunodeficiency virus type 1 variants containing K65R, M184V, or M184V plus thymidine analogue mutations

Human immunodeficiency virus type 1 containing the reverse transcriptase mutation M184V or K65R or mutations M41L, M184V, and T215Y did not accumulate additional resistance mutations in the reverse transcriptase when increasing amounts of apricitabine drug pressure were applied. The original mutations were maintained by the presence of apricitabine but were lost when cultured without drug pressure.

HIV-1 reverse transcriptase inhibitor resistance mutations and fitness: a view from the clinic and ex vivo

Genetic diversity plays a key role in human immunodeficiency virus (HIV) adaptation, providing a mechanism to escape host immune responses and develop resistance to antiretroviral drugs. This process is driven by the high-mutation rate during DNA synthesis by reverse transcriptase (RT), by the large viral populations, by rapid viral turnover, and by the high-recombination rate. Drugs targeting HIV RT are included in all regimens of highly active antiretroviral therapy (HAART), which helps to reduce the morbidity and mortality of HIV-infected patients. However, the emergence of resistant viruses is a significant obstacle to effective long-term management of HIV infection and AIDS. The increasing complexity of antiretroviral regimens has favored selection of HIV variants harboring multiple drug resistance mutations. Evolution of drug resistance is characterized by severe fitness losses when the drug is not present, which can be partially overcome by compensatory mutations or other adaptive changes that restore replication capacity. Here, we review the impact of mutations conferring resistance to nucleoside and nonnucleoside RT inhibitors on in vitro and in vivo fitness, their involvement in pathogenesis, persistence upon withdrawal of treatment, and transmission. We describe the techniques used to estimate viral fitness, the molecular mechanisms that help to improve the viral fitness of drug-resistant variants, and the clinical implications of viral fitness data, by exploring the potential relationship between plasma viral load, drug resistance, and disease progression.

Prevalence, Genotypic Associations and Phenotypic Characterization of K65R, L74V and other HIV-1 RT Resistance Mutations in a Commercial Database

Background

Nucleoside reverse transcriptase inhibitor (NRTI)-associated mutations (NAMs) can affect response to treatment with NRTIs and might also result in HIV-1 with reduced replication capacity.

Methods

A large commercial HIV-1 database ( n=60,487) was analysed for the prevalence of NAMs, antiviral drug susceptibilities and viral replication capacity.

Results

Thymidine analogue mutations (TAMs) and M184V were the most commonly observed NAMs (>25%). L74V/I was detected in 11% of isolates. K65R was detected in 3.3% of isolates and its frequency remained stable from 2003 to 2006, similar to trends observed for other NAMs. TAMs were rarely observed in combination with K65R, but frequently associated with L74V/I. HIV-1 with K65R or L74V/I alone were fully susceptible to zidovudine and stavudine. K65R was associated with reduced susceptibility to tenofovir, didanosine, abacavir and lamivudine; L74V/I was associated with reduced susceptibility to abacavir and didanosine. The addition of M184V to either K65R or L74V/I improved susceptibility to tenofovir, zidovudine and stavudine, but reduced susceptibility to abacavir, didanosine and lamivudine. Other NAMs commonly associated with K65R were A62V, S68G and Y115F; their NRTI susceptibilities were similar to those of viruses containing K65R alone. The replication capacity for HIV-1 with M184V/I or K65R was significantly reduced compared with wild-type (median 68% and 72%, respectively; P<0.0001), whereas replication capacity for HIV-1 with L74V or TAMs was not significantly reduced (88% and 97%, respectively).

Conclusions

These results demonstrate a relative stability in the prevalence of HIV-1 clinical isolates with NAMs from 2003 to 2006. Differences between the genotypic patterns, phenotype and replication capacity associated with common NAMs are described.

Clinical significance of human immunodeficiency virus type 1 replication fitness

The relative fitness of a variant, according to population genetics theory, is that variant's relative contribution to successive generations. Most drug-resistant human immunodeficiency virus type 1 (HIV-1) variants have reduced replication fitness, but at least some of these deficits can be compensated for by the accumulation of second-site mutations. HIV-1 replication fitness also appears to influence the likelihood of a drug-resistant mutant emerging during treatment failure and is postulated to influence clinical outcomes. A variety of assays are available to measure HIV-1 replication fitness in cell culture; however, there is no agreement regarding which assays best correlate with clinical outcomes. A major limitation is that there is no high-throughput assay that incorporates an internal reference strain as a control and utilizes intact virus isolates. Some retrospective studies have demonstrated statistically significant correlations between HIV-1 replication fitness and clinical outcomes in some patient populations. However, different studies disagree as to which clinical outcomes are most closely associated with fitness. This may be in part due to assay design, sample size limitations, and differences in patient populations. In addition, the strength of the correlations between fitness and clinical outcomes is modest, suggesting that, at present, it would be difficult to utilize these assays for clinical management.