Rare emergence of drug resistance in HIV-1 treatment-naïve patients after 48 weeks of treatment with elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide

Surveillance of HIV-1 transmitted integrase strand transfer inhibitor resistance in the UK

Background

HIV treatment guidelines have traditionally recommended that all HIV-positive individuals are tested for evidence of drug resistance prior to starting ART. Testing for resistance to reverse transcriptase inhibitors and PIs is well established in routine care. However, testing for integrase strand transfer inhibitor (InSTI) resistance is less consistent.

Objectives

To inform treatment guidelines by determining the prevalence of InSTI resistance in a national cohort of recently infected individuals.

Patients and methods

Recent (within 4 months) HIV-1 infections were identified using a Recent Infection Testing Algorithm of new HIV-1 diagnoses in the UK. Resistance-associated mutations (RAMs) in integrase, protease and reverse transcriptase were detected by ultradeep sequencing, which allows for the sensitive estimation of the frequency of each resistant variant in a sample.

Results

The analysis included 655 randomly selected individuals (median age = 33 years, 95% male, 83% MSM, 78% white) sampled in the period 2014 to 2016 and determined to have a recent infection. These comprised 320, 138 and 197 samples from 2014, 2015 and 2016, respectively. None of the samples had major InSTI RAMs occurring at high variant frequency (≥20%). A subset (25/640, 3.9%) had major InSTI RAMs occurring only as low-frequency variants (2%–20%). In contrast, 47/588 (8.0%) had major reverse transcriptase inhibitor and PI RAMs at high frequency.

Conclusions

Between 2014 and 2016, major InSTI RAMs were uncommon in adults with recent HIV-1 infection, only occurring as low-frequency variants of doubtful clinical significance. Continued surveillance of newly diagnosed patients for evidence of transmitted InSTI resistance is recommended to inform clinical practice.

HIV-1 Virologic Rebound Due to Coadministration of Divalent Cations and Bictegravir

A potential drug-drug interaction exists between divalent and trivalent cations (Ca2+, Fe3+, Mg2+, Al3+, Zn2+) and HIV-1 integrase strand transfer inhibitors (INSTIs). There are limited case reports describing the clinical significance of this potential interaction and none to our knowledge identifying zinc co-administration with INSTIs. In this report we present a patient taking bictegravir/emtricitabine/tenofovir alafenamide who became viremic after ingesting zinc and calcium supplements and later was able to obtain virologic re-suppression after discontinuing supplements. This case represents a potential significant drug interaction between a commonly prescribed antiretroviral drug class and readily available over-the-counter divalent cation products.

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.

An evaluation of elvitegravir plus cobicistat plus tenofovir alafenamide plus emtricitabine as a single-tablet regimen for the treatment of HIV in children and adolescents

INTRODUCTION

Approximately 2.1 million of the estimated 36 million infected with HIV are children or adolescents. International guidelines for HIV-1 Infection suggest starting antiretrovirals (ARV) at the moment of diagnosis. Many factors limit the optimization of antiretroviral therapy in children and adolescents: lack of pediatric formulations, poor adherence, metabolic and pharmacokinetic changes associated withnormal child development and puberty. Areas covered: Three integrase inhibitors are approved by the US Food and Drug Administration and by European Medical Agency for children and adolescents with HIV-1 infection. Raltegravir is approved for children aged 4 weeks to 18 years, while dolutegravir and elvitegravir co-formulated with cobicistat, emtricitabine, and tenofovir alafenamide (E/C/FTC/TAF) are approved for children from 6 years of age. This article evaluates E/C/FTC/TAF as a treatment option. Expert opinion: E/C/FTC/TAF was well tolerated, and the antiretroviral activity and tolerability data of this combination support the use in children and adolescents. However, the studies regarding E/C/FTC/TAF in children and adolescents are scant. Consequently, additional studies investigating its safety and efficacy in children are paramount.

In vitro evaluation of novel reverse transcriptase inhibitors TAF (tenofovir alafenamide) and OBP-601 (2,3-didehydro-3-deoxy-4-ethynylthymidine) against multi-drug resistant primary isolates of HIV-2

New antiretroviral drugs are needed to treat HIV-2 infected patients failing therapy. Herein, we evaluate the activity of novel reverse transcriptase inhibitors tenofovir alafenamide (TAF) and OBP-601(2,3-didehydro-3-deoxy-4-ethynylthymidine) against primary isolates from HIV-2 infected patients experiencing virologic failure. TAF and OBP-601 were tested against twelve primary isolates obtained from nine drug-experienced patients failing therapy and three drug naïve patients using a single-round infectivity assay in TZM-bl cells. The RT-coding region of pol was sequenced and the GRADE algorithm was used to identify resistance profiles and mutations. TAF and OBP-601 inhibited the replication of almost all isolates at a median EC₅₀ of 0.27 nM and 6.83 nM, respectively. Two isolates showed moderate-level resistance to OBP-601 or TAF and two other isolates showed high-level resistance to OBP-601 or to both drugs. With one exception, all resistant viruses had canonical nucleoside reverse transcriptase inhibitors (NRTIs)-associated resistance mutations (K65R, N69S, V111I, Y115F, Q151M and M184V). Our results show that TAF has potent activity against most multi-drug resistant HIV-2 isolates and should be considered for the treatment of HIV-2 infected patients failing therapy.

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.

Tenofovir alafenamide, emtricitabine, elvitegravir, and cobicistat combination therapy for the treatment of HIV

INTRODUCTION

Tenofovir alafenamide (TAF) is a novel prodrug of the nucleotide analogue reverse-transcriptase inhibitor, tenofovir. TAF has been co-formulated with emtricitabine (FTC), elvitegravir (EVG) and the EVG metabolic enhancer, cobicistat (COBI) as a single-tablet regimen being the first TAF-containing antiretroviral combination available. Areas covered: This article summarizes the available information on the pharmacology of the novel compound TAF and overviews TAF/FTC/EVG/COBI use for HIV-1 infected patients, with specific focus on clinical efficacy and safety data. Information sources include peer-reviewed scientific literature, conference proceedings and publically available regulatory reports. Compared to tenofovir disoproxil fumarate, TAF results in higher concentrations of the active metabolite tenofovir diphosphate within lymphoid cells, whereas plasma tenofovir exposure is about 90% lower. The efficacy and safety of TAF/FTC/EVG/COBI in treatment-naïve HIV-infected patients has been assessed in phase-III randomized trials, showing non-inferior virological suppression in comparison with TDF/FTC/EVG/COBI, and significantly lower renal and bone toxicity. In addition, TAF/FTC/EVG/COBI has demonstrated efficacy and safety as a switching strategy in suppressed HIV-1 infected individuals, including those with mild or moderate renal impairment. Expert commentary: Approval of the single-tablet TAF/FTC/EVG/COBI regimen is an important advance in HIV therapy, as it is associated with very high efficacy and a better kidney and bone safety profile compared to TDF-containing regimens due to the incorporation of TAF.

Infrequent development of drug resistance in HIV-1-infected treatment-naive subjects after 96 weeks of treatment with elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide or elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate

BACKGROUND

Tenofovir alafenamide (TAF) is a novel prodrug of the nucleotide reverse transcriptase inhibitor tenofovir (TFV) that loads lymphocytes with TFV-diphosphate more efficiently than tenofovir disoproxil fumarate (TDF). The single-tablet regimen (STR) comprising elvitegravir, cobicistat, emtricitabine and TAF (E/C/F/TAF) has demonstrated non-inferiority to the STR of E/C/F/TDF in clinical studies, with high proportions of subjects achieving HIV-1 RNA <50 copies/ml at week 48 that were maintained through week 96. A resistance analysis of the combined Phase III clinical studies through 96 weeks is described here.

METHODS

Genotypic and phenotypic susceptibility to antiretrovirals (ARVs) was evaluated for subjects with HIV-1 RNA ≥400 copies/ml at time of virological failure (VF) or early discontinuation.

RESULTS

Through week 96, VF resistance analyses were conducted for 24 subjects in each arm (2.8%, 24/866 and 2.8%, 24/867; for E/C/F/TAF and E/C/F/TDF arms, respectively). Primary resistance development to ARVs of the regimen occurred in 10 of 24 subjects in the E/C/F/TAF arm, and 8 of 24 subjects in the E/C/F/TDF arm (E/C/F/TAF: M184V/I, n=9; integrase strand-transfer inhibitor resistance-associated mutations [INSTI-RAMs], n=8; K65R/N, n=2; E/C/F/TDF: M184V/I, n=6; INSTI-RAMs, n=5; K65R/N, n=3). The emergent resistance mutations were similar between the treatment arms.

CONCLUSIONS

E/C/F/TAF achieved a high level of virological suppression in HIV-1 treatment-naive subjects through 96 weeks of treatment, with infrequent resistance development and comparable genotypic changes across both the E/C/F/TAF and E/C/F/TDF treatment groups.

High resistance barrier to tenofovir alafenamide is driven by higher loading of tenofovir diphosphate into target cells compared to tenofovir disoproxil fumarate

Tenofovir alafenamide (TAF) is a new oral prodrug of tenofovir (TFV) recently approved for the treatment of HIV-1 as part of the single-tablet regimen containing elvitegravir, cobicistat, emtricitabine, and TAF. Clinical dosing with TAF vs. tenofovir disoproxil fumarate (TDF) has shown improved bone and kidney safety, and has been associated with an increased concentration of the anti-HIV active moiety tenofovir diphosphate (TFV-DP) in the PBMCs of treated patients and a reduction of TFV systemic exposure. We have studied the potential benefit of this increased concentration of TFV-DP observed clinically in an in vitro model system. Using a newly developed virus breakthrough assay with TAF exposure set at physiological concentrations, we show that HIV-1 clinical isolates harboring TFV resistance mutations such as K65R, 3 or 4 thymidine-analog mutations (TAMs), Q151M/K65R, or T69 insertion complex could be inhibited by TAF, but not by TFV when used at clinically relevant concentrations for TDF. These data suggest that the inhibitory quotient (IQ) of TAF is projected to be higher than the IQ of TDF, and that TAF has the potential to inhibit viruses containing TDF resistance in the clinic.

Tenofovir alafenamide (TAF) as the successor of tenofovir disoproxil fumarate (TDF)

Tenofovir alafenamide (TAF) can be considered a new prodrug of tenofovir (TFV), as successor of tenofovir disoproxil fumarate (TDF). It is in vivo as potent against human immunodeficiency virus (HIV) at a 30-fold lower dose (10mg) than TDF (300mg). TAF has been approved in November 2015 (in the US and EU), as a single-tablet regimen (STR) containing 150mg elvitegravir (E), 150mg cobicistat (C), 200mg emtricitabine [(-)FTC] (F) and 10mg TAF, marketed as Genvoya®, on 01 March 2016 in the US as an STR containing 25mg rilpivirine (R), 200mg F and 25mg TAF, marketed as Odefsey®, and on 4 April 2016 in the US, as an STR containing 200mg F and 25mg TAF, marketed as Descovy®, for the treatment of HIV infections. STR combinations containing TAF and emtricitabine could be paired with a range of third agents, for example, darunavir and cobicistat. TAF has a much lower risk of kidney toxicity or bone density changes than TDF, and also offers long-term potential in the pre-exposure prophylaxis (PrEP) of HIV infections. TAF is specifically accumulated in lymphatic tissue, and in the liver, and hence also holds great potential for the treatment of hepatitis B virus (HBV) infections. Akin to TDF, TAF is converted intracellularly to TFV. Its active diphosphate metabolite (TFVpp) is targeted at the RNA-dependent DNA polymerase (reverse transcriptase) of either HIV or HBV.