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

Brief Report: Bictegravir/Emtricitabine/Tenofovir Alafenamide Efficacy in Participants With Preexisting Primary Integrase Inhibitor Resistance Through 48 Weeks of Phase 3 Clinical Trials

BACKGROUND

Preexisting drug resistance limits the utility of HIV antiretroviral therapy. Studies have demonstrated safety and efficacy of bictegravir/emtricitabine/tenofovir alafenamide (B/F/TAF), including in patients with M184V/I substitutions.

SETTING

We investigated virologic outcomes through 48 weeks of B/F/TAF treatment in individuals with preexisting primary integrase strand transfer inhibitor resistance (INSTI-R).

METHODS

Preexisting INSTI-R was retrospectively evaluated from 7 B/F/TAF studies. INSTI-R was assessed by historical genotypes and/or baseline RNA or DNA sequencing. Viral loads were measured at all visits.

RESULTS

Preexisting primary INSTI-R substitutions were detected in 20 of the 1907 participants (1.0%). The 20 participants were predominantly male (75%), were Black (65%), had HIV-1 subtype B (85%), and had baseline median CD4 counts of 594 cells/mm3 and median age of 52 years. Most of the participants (n = 19) were virologically suppressed at baseline and had one primary INSTI-R substitution, E92G, Y143C/H, S147G, Q148H/K/R, N155S, or R263K, +/-secondary substitutions. All suppressed participants maintained virologic suppression throughout 48 weeks without any viral blips. One treatment-naive participant had virus with Q148H+G140S that was fully sensitive to bictegravir but only partially to dolutegravir (phenotype <2.5-fold change and >4-fold change, respectively). With a baseline viral load of 30,000 copies/mL, this participant was virologically suppressed by week 4 and maintained <50 copies/mL through week 48.

CONCLUSIONS

This small cohort with primary INSTI-R achieved and/or maintained virologic suppression through 48 weeks of B/F/TAF treatment. Consistent with the potent in vitro activity of bictegravir against most INSTI-R patterns, B/F/TAF may be a potential treatment option for patients with select preexisting INSTI-R, if confirmed by further studies.

Virologic failure after 48 weeks of raltegravir-based regimen in low HIV-1 incidence setting

Background

With the advent of next generation integrase strand transfer inhibitors, the rates of virologic failure in treated subjects are expected to decrease. In this study, we analyzed the mutation patterns leading to virologic failure before and after starting integrase strand transfer inhibitor-based regimen as first-line or salvage therapy.

Methods

Between 2016 and 2019, blood samples were received from 258 patients with HIV-1 infection. Plasma HIV-1 RNA concentrations, and pol gene sequences were determined at baseline, and 16–48 weeks of treatment with integrase strand transfer inhibitor-based regimen. Only patients who did not achieve viral suppression at 48 weeks of integrase strand transfer inhibitor-based treatment were eligible for the current study.

Results

Virologic failure was observed in seven patients on raltegravir-based regimen. All patients with virologic failure but one were infected with CRF01_AE virus subtype. Raltegravir based-regimen was offered as first-line therapy for four patients, and as salvage therapy for three patients. M184V mutation associated with high level resistance to lamivudine and emtricitabine was detected in six out of seven patients. Primary mutations (Y143C, N155H, T66I, G118R, E138K) conferring high level resistance to raltegravir were detected in only three patients. Pre-existing polymorphic integrase mutation (T97A) was detected in two patients. Furthermore, two patients reported low adherence to treatment.

Conclusions

Emergence of primary mutations in the integrase gene can account for virologic failure in less than half of patients on raltegravir-based regimen. Low adherence to treatment, pre-existing accessory mutations, and resistance to reverse transcriptase inhibitors may have some role in virologic outcome.

Evaluation of virological response and resistance profile in HIV-1 infected patients starting a first-line integrase inhibitor-based regimen in clinical settings

BACKGROUND

Virological response and resistance profile were evaluated in drug-naïve patients starting their first-line integrase inhibitors (INIs)-based regimen in a clinical setting.

STUDY DESIGN

Virological success (VS) and virological rebound (VR) after therapy start were assessed by survival analyses. Drug-resistance was evaluated at baseline and at virological failure.

RESULTS

Among 798 patients analysed, 38.6 %, 27.1 % and 34.3 % received raltegravir, elvitegravir and dolutegravir, respectively. Baseline resistance to NRTIs, NNRTIs, PIs and INIs was: 3.9 %, 13.9 %, 1.6 % and 0.5 %, respectively. Overall, by 12 months of treatment, the probability of VS was 95 %, while the probability of VR by 36 months after VS was 13.1 %. No significant differences in the virological response were found according to the INI used. The higher pre-therapy viremia strata was (<100,000 vs. 100,000-500,000 vs. > 500,000 copies/mL), lower was the probability of VS (96.0 % vs. 95.2 % vs. 91.1 %, respectively, P < 0.001), and higher the probability of VR (10.2 % vs. 15.8 % vs. 16.6 %, respectively, P = 0.010). CD4 cell count <200 cell/mm³ was associated with the lowest probability of VS (91.5 %, P < 0.001) and the highest probability of VR (20.7 %, P = 0.008) compared to higher CD4 levels. Multivariable Cox-regression confirmed the negative role of high pre-therapy viremia and low CD4 cell count on VS, but not on VR. Forty-three (5.3 %) patients experienced VF (raltegravir: 30; elvitegravir: 9; dolutegravir: 4). Patients failing dolutegravir did not harbor any resistance mutation either in integrase or reverse transcriptase.

CONCLUSIONS

Our findings confirm that patients receiving an INI-based first-line regimen achieve and maintain very high rates of VS in clinical practice.

Antiviral activity of HIV-1 integrase strand-transfer inhibitors against mutants with integrase resistance-associated mutations and their frequency in treatment-naïve individuals

The development of resistance to human immunodeficiency virus 1 (HIV-1) integrase strand-transfer inhibitors (INSTI) has been documented; however, knowledge of the impact of pre-existing integrase (IN) mutations on INSTI resistance (INSTI-R) is still evolving. The frequency of HIV-1 IN mutations in 2177 treatment-naïve subjects was investigated, along with the INSTI susceptibility of site-directed mutant viruses containing major and minor INSTI-R mutations. Total 6 of 39 minor INSTI-R mutations (M50I, S119P/G/T/R, and E157Q) were found in >1% of IN-treatment-naïve subjects with no impact on INSTI susceptibility. When each combined with major INSTI-R mutation, M50I, S119P, and E157Q led to decreased susceptibility to elvitegravir but remained sensitive to dolutegravir and bictegravir.

Simultaneous Estimation and Validation of Tenofovir Disoproxil Fumarate, Emtricitabine and Efavirenz by RP-HPLC Method in Combined tablet Dosage Form

Introduction:

The purpose of this study is the development and validation of assay test for Tenofovir Disoproxil Fumarate (TDF), Emtricitabine (FTC) and Efavirenz (EFV) in combined tablet dosage form by Reverse Phase (RP) HPLC.

Materials and Methods:

The assay method by HPLC was found to be linear in the concentration range of 15-150 µg/mL, 10-100 µg/mL and 30-300 µg/mL for TDF, FTC, and EFV, respectively. Successful separation of combined drugs was achieved by isocratic elution on a Phenomenex® C8 column (250 mm × 4.6 mm, 5µm). The mobile phase was composed of buffer pH: 7.0 ± 0.05 potassium dihydrogen phosphate, acetonitrile and methanol (40:40:20 v/v) at the flow rate of 1 mL/min using UV detection at 262 nm, column oven temperature 25ºC, and injection volume 20 µL.

Results:

The analytical results were validated by recovery studies. All the parameters of validation were in the acceptance range. This developed method was successfully applied for simultaneous estimation the amount of TDF, FTC and EFV in the bulk and marketed dosage forms.

Rare emergence of drug resistance in HIV-1 treatment-naïve patients receiving elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide for 144 weeks

BACKGROUND

The single tablet regimen (STR) composed of elvitegravir (E), cobicistat (C), emtricitabine (F), and tenofovir alafenamide (TAF) (E/C/F/TAF) was compared to the STR composed of E, C, F, and tenofovir disoproxil fumarate (TDF) (E/C/F/TDF) in 2 phase 3 studies in 1733 HIV-1 infected treatment-naïve adults. Superior efficacy of E/C/F/TAF compared to E/C/F/TDF was demonstrated at Week 144 with 84% treatment success compared to 80%, respectively, along with significantly better outcomes of bone and renal safety.

OBJECTIVES

Analyze the emergence of HIV-1 resistance in treatment-naïve adults receiving E/C/F/TAF for 144 weeks.

STUDY DESIGN

We conducted an integrated resistance analysis of the 2 Phase 3 studies, comprising pretreatment HIV-1 sequencing for all participants (N = 1733) and post-baseline HIV-1 resistance analysis for participants with virologic failure (HIV-1 RNA ≥400 copies/mL).

RESULTS

Primary resistance-associated mutations (RAMs) were observed pre-treatment in 7.4% (NRTI-RAMs), 18.1% (NNRTI-RAMs), and 3.3% (PI-RAMs) of enrolled subjects. Baseline HIV-1 subtype or pre-existing RAMs did not affect E/C/F/TAF treatment response at week 144. Virologic failure resistance analyses were conducted for 28/866 (3.2%) and 30/867 (3.5%) patients in the E/C/F/TAF and E/C/F/TDF arms, respectively. Over the 3-year study, the rate of resistance emergence remained low at 1.4% in each group (12/866 in E/C/F/TAF; 12/867 in E/C/F/TDF). Resistant virus emerged in 24 patients who developed resistance to antiretrovirals in the regimens (E/C/F/TAF: M184V/I [1.3%], INSTI-RAMs [0.9%], K65R/N [0.2%]; E/C/F/TDF: M184V/I [1.0%], INSTI-RAMs [0.9%], K65R/N [0.5%]).

CONCLUSIONS

Resistance emergence was rare (1.4%) with similar patterns of emergent mutations in both groups. M184V/I was the most prevalent RAM (1.2% overall).

Role of tenofovir alafenamide (TAF) in the treatment and prophylaxis of HIV and HBV infections

Tenofovir (TFV) is the cornerstone of the treatment and prophylaxis of HIV infections. It has been routinely used in its prodrug form TDF (tenofovir disoproxil fumarate) combined with emtricitabine ((-)FTC) and other antiretroviral agents. TDF has now been replaced by TAF (tenofovir alafenamide) which allows better uptake by the lymphoid tissue. In combination with elvitegravir (E), cobicistat (C), emtricitabine (F), TAF can be advocated as an STR (single tablet regimen, Genvoya®) for the treatment of HIV infections. In this combination, E and C may in the future be replaced by bictegravir. The prophylaxis of HIV infection is momentarily based upon Truvada®, the combination of F with TDF, which in the future may also be replaced by TAF. TAF (Vemlidy®) has also replaced TDF (Viread®) for the treatment of hepatitis B virus (HBV) infections. Both TDF and TAF offer little or no risk for virus-drug resistance. As compared to TDF, TAF limits the risk for nephrotoxicity and loss of bone mineral density. What remains to be settled, however, before the universal use of TAF could be recommended, is its safety during pregnancy and its applicability in the treatment of tuberculosis, in combination with rifampicin.

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.

Lack of impact of pre-existing T97A HIV-1 integrase mutation on integrase strand transfer inhibitor resistance and treatment outcome

T97A is an HIV-1 integrase polymorphism associated with integrase strand transfer inhibitor (INSTI) resistance. Using pooled data from 16 clinical studies, we investigated the prevalence of T97A (pre-existing and emergent) and its impact on INSTI susceptibility and treatment response in INSTI-naive patients who enrolled on elvitegravir (EVG)- or raltegravir (RAL)-based regimens. Prior to INSTI-based therapy, primary INSTI resistance-associated mutations (RAMs) were absent and T97A pre-existed infrequently (1.4%; 47 of 3367 integrase sequences); most often among non-B (5.3%) than B (0.9%) HIV-1 subtypes. During INSTI-based therapy, few patients experienced virologic failure with emergent INSTI RAMs (3%; 122 of 3881 patients), among whom T97A emerged infrequently in the presence (n = 6) or absence (n = 8) of primary INSTI RAMs. A comparison between pre-existing and emergent T97A patient populations (i.e., in the absence of primary INSTI RAMs) showed no significant differences in EVG or RAL susceptibility in vitro. Furthermore, among all T97A-containing viruses tested, only 38-44% exhibited reduced susceptibility to EVG and/or RAL (all of low magnitude; <11-fold), while all maintained susceptibility to dolutegravir. Of the patients with pre-existing T97A, 17 had available clinical follow-up: 16 achieved virologic suppression and 1 maintained T97A and INSTI sensitivity without further resistance development. Overall, T97A is an infrequent integrase polymorphism that is enriched among non-B HIV-1 subtypes and can confer low-level reduced susceptibility to EVG and/or RAL. However, detection of T97A does not affect response to INSTI-based therapy with EVG or RAL. These results suggest a very low risk of initiating INSTI-based therapy in patients with pre-existing T97A.

Antiviral Activity of Bictegravir (GS-9883), a Novel Potent HIV-1 Integrase Strand Transfer Inhibitor with an Improved Resistance Profile

Bictegravir (BIC; GS-9883), a novel, potent, once-daily, unboosted inhibitor of HIV-1 integrase (IN), specifically targets IN strand transfer activity (50% inhibitory concentration [IC₅₀] of 7.5 ± 0.3 nM) and HIV-1 integration in cells. BIC exhibits potent and selective in vitro antiretroviral activity in both T-cell lines and primary human T lymphocytes, with 50% effective concentrations ranging from 1.5 to 2.4 nM and selectivity indices up to 8,700 relative to cytotoxicity. BIC exhibits synergistic in vitro antiviral effects in pairwise combinations with tenofovir alafenamide, emtricitabine, or darunavir and maintains potent antiviral activity against HIV-1 variants resistant to other classes of antiretrovirals. BIC displayed an in vitro resistance profile that was markedly improved compared to the integrase strand transfer inhibitors (INSTIs) raltegravir (RAL) and elvitegravir (EVG), and comparable to that of dolutegravir (DTG), against nine INSTI-resistant site-directed HIV-1 mutants. BIC displayed statistically improved antiviral activity relative to EVG, RAL, and DTG against a panel of 47 patient-derived HIV-1 isolates with high-level INSTI resistance; 13 of 47 tested isolates exhibited >2-fold lower resistance to BIC than DTG. In dose-escalation experiments conducted in vitro, BIC and DTG exhibited higher barriers to resistance than EVG, selecting for HIV-1 variants with reduced phenotypic susceptibility at days 71, 87, and 20, respectively. A recombinant virus with the BIC-selected M50I/R263K dual mutations in IN exhibited only 2.8-fold reduced susceptibility to BIC compared to wild-type virus. All BIC-selected variants exhibited low to intermediate levels of cross-resistance to RAL, DTG, and EVG (<8-fold) but remained susceptible to other classes of antiretrovirals. A high barrier to in vitro resistance emergence for both BIC and DTG was also observed in viral breakthrough studies in the presence of constant clinically relevant drug concentrations. The overall virologic profile of BIC supports its ongoing clinical investigation in combination with other antiretroviral agents for both treatment-naive and -experienced HIV-infected patients.

Elvitegravir for the treatment of HIV

INTRODUCTION

Current antiretrovirals (ARVs) have demonstrated the ability to prolong the life of an HIV infected individual via suppression of the virus and subsequent restoration of immune function. Despite significant advancement, there remains an opportunity for improvement. One ARV that attempts to fill global HIV therapeutic needs by balancing convenience, safety, and efficacy is elvitegravir (EVG). Areas covered: Using MEDLINE/PubMed, a literature search was conducted for published articles on the safety and efficacy of EVG in the treatment of HIV infection. Expert opinion: EVG offers clinicians a convenient choice for HIV-positive patients that is safe and effective for both treatment-naïve and experienced patients, as well as an option for regimen simplification in virologically suppressed patients. EVG is conveniently co-formulated in fixed dose combination tablets to be taken once daily with food. EVG does not require dose adjustment for patients with severe renal impairment or mild to moderate liver disease. Importantly, EVG requires co-administration with a pharmacokinetic enhancer (i.e., ritonavir or cobicistat) in order to achieve therapeutic levels and facilitate once daily dosing. As a consequence, clinicians must carefully review concomitant medications and navigate potential drug-drug interactions mediated through potent inhibition of cytochrome P450 3A enzymes by ritonavir and cobicistat.

HIV-1 drug resistance and resistance testing

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

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.

Virological failure in two patients with HIV-1 RNA viral loads >1,000,000 copies/ml initiated on elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate

Very high baseline HIV-1 RNA viral loads require potent and robust antiretroviral regimens to achieve virological suppression. The coformulated single tablet regimen of elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate (EVG/COBI/FTC/TDF) is recommended by the US Department of Health and Human Services for the treatment of HIV-1 in treatment-naive adults and adolescents regardless of baseline CD4(+) T-cell count and viral load. We report two cases of HIV-infected, treatment-naive patients, with baseline HIV-1 RNA viral loads >1,000,000 copies/ml who were initiated on the single tablet regimen EVG/COBI/FTC/TDF, but failed to attain viral load suppression and developed resistance to the components of EVG/COBI/FTC/TDF.

Dolutegravir - a review of the pharmacology, efficacy, and safety in the treatment of HIV

Dolutegravir is the newest integrase strand transfer inhibitor to be approved for the treatment of human immunodeficiency virus (HIV) infection. Dolutegravir is equivalent or superior to existing treatment regimens in both treatment-naïve and treatment-experienced patients including those with previous raltegravir or elvitegravir failure. The consistent efficacy coupled with excellent tolerability and infrequent drug–drug interactions makes the co-formulation of dolutegravir with two nucleotide reverse-transcriptase inhibitors an attractive treatment option. This review summarizes the pharmacokinetics, adverse event profile, and efficacy of dolutegravir in the treatment of HIV.

Analysis of early resistance development at the first failure timepoint in elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate-treated patients

OBJECTIVES

The patterns of emergent HIV-1 drug resistance in patients failing a single-tablet regimen consisting of elvitegravir, boosted by cobicistat, plus emtricitabine and tenofovir disoproxil fumarate (EVG/COBI/FTC/TDF) include mutations in HIV-1 reverse transcriptase (RT) and integrase (IN). The order of development of mutations at early virological failure has not been described. The aim of this study was to determine the first resistance mutations to emerge during virological failure on EVG/COBI/FTC/TDF.

PATIENTS AND METHODS

Population sequencing was conducted at the first virological failure timepoint with HIV-1 RNA ≥400 copies/mL for each of the 18 patients with emergent resistance in the EVG/COBI/FTC/TDF arms of two randomized, double-blind, Phase 3 studies of EVG/COBI/FTC/TDF through Week 144.

RESULTS

At first failure compared with confirmed virological failure, 4 of the 18 patients had no detectable resistance mutation in their virus and only 51% of the RT and IN mutations were detected overall. M184V/I in RT was the first mutation to appear in many cases (n = 6) and was then followed by additional mutations in RT and IN. No case with development of resistance to the IN strand-transfer inhibitor prior to the development of M184V/I was detected.

CONCLUSIONS

The analysis of first failure found fewer patients with emergent resistance and fewer resistance mutations than the standard analysis at the later confirmation of virological failure. The early detection of resistance may preserve later treatment options.

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.