Islatravir in combination with doravirine for treatment-naive adults with HIV-1 infection receiving initial treatment with islatravir, doravirine, and lamivudine: a phase 2b, randomised, double-blind, dose-ranging trial

The Current Pipeline of Antiretroviral Therapy: Expanding Options and Filling Gaps

Highly effective antiretroviral therapy (ART) has transformed human immunodeficiency virus (HIV) care in the past 3 decades. 30 years ago, how many would have imagined that a single-tablet daily ART regimen containing different drug classes could achieve sustained HIV-1 suppression and halt disease progression to acquired immunodeficiency syndrome (AIDS)? Despite this remarkable achievement, challenges in HIV care remain that require further innovation for ART. In this review, we focus on newly approved antiretroviral agents and those undergoing phase 2/3 clinical trials. These new antiretrovirals hold great promise to expand treatment options and fill gaps in HIV care.

Intracellular islatravir-triphosphate half-life supports extended dosing intervals

Antiretroviral therapy has substantially reduced morbidity, mortality, and disease transmission in people living with HIV. Islatravir is a nucleoside reverse transcriptase translocation inhibitor that inhibits HIV-1 replication by multiple mechanisms of action, and it is in development for the treatment of HIV-1 infection. In preclinical and clinical studies, islatravir had a long half-life (t½) of 3.0 and 8.7 days (72 and 209 hours, respectively); therefore, islatravir is being investigated as a long-acting oral antiretroviral agent. A study was conducted to definitively elucidate the terminal t½ of islatravir and its active form islatravir-triphosphate (islatravir-TP). A single-site, open-label, non-randomized, single-dose phase 1 study was performed to evaluate the pharmacokinetics and safety of islatravir in plasma and the pharmacokinetics of islatravir-TP in peripheral blood mononuclear cells after administration of a single oral dose of islatravir 30 mg. Eligible participants were healthy adult males without HIV infection between the ages of 18 and 65 years. Fourteen participants were enrolled. The median time to maximum plasma islatravir concentration was 1 hour. Plasma islatravir concentrations decreased in a biphasic manner, with a t½ of 73 hours. The t½ (percentage geometric coefficient of variation) of islatravir-TP in peripheral blood mononuclear cells through 6 weeks (~1008 hours) after dosing was 8.1 days or 195 hours (25.6%). Islatravir was generally well tolerated with no drug-related adverse events observed. Islatravir-TP has a long intracellular t½, supporting further clinical investigation of islatravir administered at an extended dosing interval.

Current status of the small molecule anti-HIV drugs in the pipeline or recently approved

Human Immunodeficiency Virus (HIV) is the causative agent of Acquired Immunodeficiency Syndrome (AIDS) with high morbidity and mortality rates. Treatment of AIDS/HIV is being complicated by increasing resistance to currently used antiretroviral (ARV) drugs, mainly in low- and middle-income countries (LMICs) due to drug misuse, poor drug supply and poor treatment monitoring. However, progress has been made in the development of new ARV drugs, targeting different HIV components (Fig. 1). This review aims at presenting and discussing the progress made towards the discovery of new ARVs that are at different stages of clinical trials as of July 2024. For each compound, the mechanism of action, target biomolecule, genes associated with resistance, efficacy and safety, class, and phase of clinical trial are discussed. These compounds include analogues of nucleoside reverse transcriptase inhibitors (NRTIs) - islatravir and censavudine; non-nucleoside reverse transcriptase inhibitors (NNRTIs) - Rilpivirine, elsulfavirine and doravirine; integrase inhibitors namely cabotegravir and dolutegravir and chemokine coreceptors 5 and 2 (CC5/CCR2) antagonists for example cenicriviroc. Also, fostemsavir is being developed as an attachment inhibitor while lenacapavir, VH4004280 and VH4011499 are capsid inhibitors. Others are maturation inhibitors such as GSK-254, GSK3532795, GSK3739937, GSK2838232, and other compounds labelled as miscellaneous (do not belong to the classical groups of anti-HIV drugs or to the newer classes) such as obefazimod and BIT225. There is a considerable progress in the development of new anti-HIV drugs and the effort will continue since HIV infections has no cure or vaccine till now. Efforts are needed to reduce the toxicity of available drugs or discover new drugs with new classes which can delay the development of resistance.

Switch to fixed-dose doravirine (100 mg) with islatravir (0·75 mg) once daily in virologically suppressed adults with HIV-1 on bictegravir, emtricitabine, and tenofovir alafenamide: 48-week results of a phase 3, randomised, controlled, double-blind, non-inferiority trial

BACKGROUND

Doravirine and islatravir is an investigational, once-daily regimen with high antiviral potency, favourable safety and tolerability, and a low propensity for resistance. We investigated a switch from bictegravir, emtricitabine, and tenofovir alafenamide to doravirine (100 mg) and islatravir (0·75 mg) in virologically suppressed adults with HIV-1.

METHODS

We conducted a phase 3, multicentre, randomised, active-controlled, double-blind, double-dummy, non-inferiority trial at 89 research, community, and hospital-based clinics in 11 countries. Adults aged 18 years or older with fewer than 50 HIV-1 RNA copies per mL for at least 3 months on bictegravir (50 mg), emtricitabine (200 mg), and tenofovir alafenamide (25 mg) and no history of previous virological failure on any past or current regimen were randomly assigned (1:1) by a computer-generated randomisation allocation schedule, with block randomisation based on a block size of four, to switch to doravirine (100 mg) and islatravir (0·75 mg) or continue bictegravir, emtricitabine, and tenofovir alafenamide orally once daily, with matching placebos taken by all participants. Participants, investigators, study staff, and sponsor personnel involved in study drug administration or clinical evaluation of participants were masked to treatment assignment until week 48. Participants were instructed at each visit to take one tablet from each of the two bottles received, one of study drug and one of placebo, once daily, and participants were assessed at baseline and weeks 4, 12, 24, 36, and 48. The primary endpoint was the proportion of participants with greater than or equal to 50 HIV-1 RNA copies per mL at week 48 in the full analysis set (ie, all participants who received at least one dose of study drug; US Food and Drug Administration snapshot; prespecified non-inferiority margin 4%). The study is ongoing, with all remaining participants in post-treatment follow-up, and is registered with ClinicalTrials.gov, NCT04223791.

FINDINGS

We screened 726 individuals for eligibility between Feb 18 and Sept 3, 2020, of whom 643 (88·6%) participants were randomly assigned to a treatment group (183 [28·5%] women and 460 [71·5%] men). 322 participants were switched to doravirine (100 mg) and islatravir (0·75 mg) and 321 continued bictegravir, emtricitabine, and tenofovir alafenamide (two participants [one with a protocol deviation and one who withdrew] assigned to bictegravir, emtricitabine, and tenofovir alafenamide did not receive treatment). The last follow-up visit for the week 48 analysis occurred on Aug 26, 2021. At week 48, two (0·6%) of 322 participants in the doravirine and islatravir group compared with one (0·3%) of 319 participants in the bictegravir, emtricitabine, and tenofovir alafenamide group had greater than or equal to 50 HIV-1 RNA copies per mL (difference 0·3%, 95% CI -1·2 to 2·0). The per-protocol analysis showed consistent results. 25 (7·8%) participants in the doravirine and islatravir group had headache compared with 23 [7·2%] participants in the bictegravir, emtricitabine, and tenofovir alafenamide group; 101 (31·4%) compared with 98 (30·7%) had infections; and eight (2·5%) participants in each group discontinued therapy due to adverse events. 32 (9·9%) participants had treatment-related adverse events in the islatravir and doravirine group comapred with 38 (11·9%) in the bictegravir, emtricitabine, and tenofovir alafenamide group. In the islatravir and doravirine group, CD4 cell counts (mean change -19·7 cells per μL) and total lymphocyte counts (mean change -0·20 × 109/L) were decreased at 48 weeks.

INTERPRETATION

Switching to daily doravirine (100 mg) and islatravir (0·75 mg) was non-inferior to bictegravir, emtricitabine, and tenofovir alafenamide at week 48. However, decreases in CD4 cell and total lymphocyte counts do not support the further development of once-daily doravirine (100 mg) and islatravir (0·75 mg).

FUNDING

Merck Sharp & Dohme, a subsidiary of Merck & Co.

Switch to fixed-dose doravirine (100 mg) with islatravir (0·75 mg) once daily in virologically suppressed adults with HIV-1 on antiretroviral therapy: 48-week results of a phase 3, randomised, open-label, non-inferiority trial

BACKGROUND

Doravirine and islatravir is an investigational, once-daily, single-tablet regimen with high antiviral potency, favourable safety and tolerability, and low propensity for resistance. We report week 48 results from a phase 3 trial evaluating switch from stable, oral antiretroviral therapy (ART) to the fixed combination of doravirine (100 mg) and islatravir (0·75 mg).

METHODS

This phase 3, multicentre, randomised, active-controlled, open-label, non-inferiority trial was conducted at 77 research, community, and hospital-based clinics in 15 countries. Adults aged 18 years or older with fewer than 50 HIV-1 RNA copies per mL on any oral, two-drug or three-drug ART regimen for at least 3 months, and no history of previous virological failure on any past or current regimen were randomly assigned (1:1) by a computer-generated randomisation schedule to switch to doravirine (100 mg) and islatravir (0·75 mg) or to continue their baseline ART regimen. Block randomisation was based on a block size of four, and randomisation was stratified by baseline regimen (ie, protease inhibitor, integrase inhibitor, or other). Participants in the doravirine and islatravir group were instructed to take one tablet at approximately the same time each day, and participants in the baseline ART group continued to take the medication according to the locally approved label. HIV-1 RNA and safety evaluations were done at baseline and weeks 4, 12, 24, 36, and 48. CD4 cell counts were measured at baseline, week 24, and week 48. The primary endpoint was proportion of participants with greater than or equal to 50 HIV-1 RNA copies per mL at week 48 in the full analysis set (ie, all participants who received at least one dose of study drug) using the US Food and Drug Administration snapshot approach and prespecified non-inferiority margin of 4%. This study is registered with ClinicalTrials.gov (NCT04223778) and is completed.

FINDINGS

Between Feb 18 and Oct 2, 2020, 740 individuals were screened for eligibility, of whom 672 (90·8%) participants (249 [37·1%] women and 423 [62·9%] men; median CD4 count of 678 cells per μL [IQR 496-868]) were randomly assigned to doravirine (100 mg) and islatravir (0·75 mg; n=336) or to continue baseline ART (n=336). The last follow-up visit occurred on Sept 8, 2021. At week 48, zero of 336 participants in the doravirine and islatravir group versus five (1·5%) of 336 participants in the baseline ART group had greater than or equal to 50 HIV-1 RNA copies per mL (difference -1·5, 95% CI -3·4 to -0·3). The per-protocol analysis showed consistent results. Headache was the most common adverse event in both groups (35 [10·4%] of 336 participants in the doravirine and islatravir group, 16 [4·8%] of 336 in the baseline ART group), infection rates were similar (113 [33·6%] in both groups), and discontinuations due to adverse events were low (seven [2·1%] vs one [0·3%]). 66 (19·6%) of 336 participants had treatment-related adverse events in the doravirine and islatravir group compared with 30 (8·9%) of 336 in the baseline ART group. In the islatravir and doravirine group, CD4 cell counts (mean change -30·3 cells per μL) and total lymphocyte counts (mean change -0·26 × 109/L) were decreased at 48 weeks.

INTERPRETATION

Switching to single-tablet doravirine (100 mg) and islatravir (0·75 mg) maintained viral suppression up to week 48 and was non-inferior to antiretroviral combinations used in clinical practice for adults with HIV-1; however, decreases in CD4 cell and total lymphocyte counts do not support further development of once-daily doravirine (100 mg) and islatravir (0·75 mg).

FUNDING

Merck Sharp & Dohme, a subsidiary of Merck & Co.

Variable antiviral activity of islatravir against M184I/V mutant HIV-1 selected during antiretroviral therapy

BACKGROUND

Islatravir is a new antiretroviral drug that inhibits the reverse transcriptase (RT) of HIV-1 through multiple mechanisms. It is proposed to be used in combination with doravirine, a new NNRTI. M184V/I mutations have been shown to reduce the in vitro antiviral activity of islatravir, but their effect when pre-selected during ART has not been investigated.

METHODS

HIV-1 rt sequences were obtained from four individuals of the Garrahan HIV cohort prior to, or during virological failure to ART. HIV-1 infectious molecular clones were constructed on an NL4-3 backbone, and infectious viruses were produced by transfection of 293T cells. Fold-changes in IC50 were calculated for each mutant versus the NL4-3 WT. HIV-1 phenotypic drug resistance was tested in vitro against NRTIs and NNRTIs.

RESULTS

In all the cases, M184I/V, either alone or in the presence of other mutations, was associated with reduced susceptibility to islatravir, abacavir and lamivudine. Viruses carrying M184V/I showed variable levels of resistance to islatravir (4.8 to 33.8-fold). The greatest reduction in susceptibility was observed for viruses carrying the mutations M184V + V106I (33.8-fold resistance) or M184V + I142V (25.2-fold resistance). For NNRTIs, the presence of V106I alone did not affect susceptibility to doravirine or etravirine, but showed a modest reduction in susceptibility to efavirenz (6-fold). Susceptibility to doravirine was slightly reduced only for one of the mutants carrying V106I in combination with Y181C and M184V.

CONCLUSIONS

Mutations and polymorphisms selected in vivo together with M184V/I depend on the viral genetic context and on ART history, and could affect the efficacy of islatravir once available for use in the clinic.

Islatravir: evaluation of clinical development for HIV and HBV

INTRODUCTION

Islatravir (ISL) is a nucleoside reverse transcriptase translocation inhibitor (NRTTI) that inhibits HIV RT through multiple mechanisms. Contrary to all approved NtRTIs, islatravir retains a 3'OH group. In vitro and clinical data show that ISL is an ultrapotent investigational drug with high tolerability.

AREAS COVERED

The historical development of islatravir and its mechanisms of HIV and HBV inhibition and resistance are covered. Additionally, the outcomes of Phase I and Phase II clinical trials are discussed.

EXPERT OPINION

Current first-line antiretroviral therapy, preexposure, and postexposure prophylactic interventions are highly effective in maintaining low or undetectable viral load. Despite these measures, an unusually high rate of new infections every year warrants developing novel antivirals that can suppress drug-resistant HIV and improve compliance. ISL, an NRTTI once deemed a long-acting drug, was placed on a clinical hold. The outcome of ongoing clinical trials with a reduced ISL dose will decide its future clinical application. Additionally, MK-8527, which inhibits HIV via same mechanism as that of ISL may supersede ISL. Data on ISL inhibition of HBV are scarce, and preclinical data show dramatically lower ISL efficacy against HBV than currently preferred nucleos(t)ide drugs, indicating that ISL may not be a potent anti-HBV drug.

Antiretroviral Treatment of HIV-2 Infection: Available Drugs, Resistance Pathways, and Promising New Compounds

Currently, it is estimated that 1-2 million people worldwide are infected with HIV-2, accounting for 3-5% of the global burden of HIV. The course of HIV-2 infection is longer compared to HIV-1 infection, but without effective antiretroviral therapy (ART), a substantial proportion of infected patients will progress to AIDS and die. Antiretroviral drugs in clinical use were designed for HIV-1 and, unfortunately, some do not work as well, or do not work at all, for HIV-2. This is the case for non-nucleoside reverse transcriptase inhibitors (NNRTIs), the fusion inhibitor enfuvirtide (T-20), most protease inhibitors (PIs), the attachment inhibitor fostemsavir and most broadly neutralizing antibodies. Integrase inhibitors work well against HIV-2 and are included in first-line therapeutic regimens for HIV-2-infected patients. However, rapid emergence of drug resistance and cross-resistance within each drug class dramatically reduces second-line treatment options. New drugs are needed to treat infection with drug-resistant isolates. Here, we review the therapeutic armamentarium available to treat HIV-2-infected patients, as well as promising drugs in development. We also review HIV-2 drug resistance mutations and resistance pathways that develop in HIV-2-infected patients under treatment.

Long-term follow-up of HIV-1 multi-drug-resistant treatment-experienced participants treated with etravirine, raltegravir and boosted darunavir: towards drug-reduced regimen? ANRS CO3 Aquitaine Cohort 2007-2018

OBJECTIVE

To assess the efficacy of raltegravir, etravirine and darunavir/ritonavir (TRIO regimen) in treatment-experienced patients with human immunodeficiency virus-1 (HIV-1) infection by describing the proportion of patients who experienced virological failure (VF) at Week 24. The secondary objectives were to assess the HIV-1 plasma viral load (pVL) after Week 24, the proportion of patients who were receiving dual therapy or monotherapy at the last visit, and the number of deaths.

METHODS

Patients from the ANRS CO3 Aquitaine Cohort who were prescribed the TRIO regimen between February 2007 and September 2018 were classified into two groups based on their pVL at study inclusion: the virological failure group (VFG; pVL >50 copies/mL) and the virologically suppressed group (VSG; pVL <50 copies/mL). The impact of baseline pVL and genotypic susceptibility score (GSS) on VF was analysed.

RESULTS

In total, 184 patients were enrolled in this study, with 123 (66.8%) in the VFG and 61 (33.2%) in the VSG. The median length of follow-up was 7.5 (interquartile range 4.1-9.6) years, and 29 (15.8%) patients died. Thirty-seven (25.5%) patients experienced VF at Week 24, including 32/145 (32.7%) in the VFG and 5/47 (10.6%) in the VSG (P<0.01). Resistance-associated mutations were detected in integrase, reverse transcriptase and protease for 7/37 (18.9%), 3/37 (8.1%) and 1/37 (2.7%) patients, respectively. High pVL and GSS at baseline were independently associated with VF. At the last visit, 76/184 (41.3%) patients were still receiving the TRIO regimen, while 55/184 (29.9%) were receiving dual therapy and 1/184 (0.5%) was receiving protease inhibitor monotherapy. Among the 56 patients receiving dual therapy or monotherapy, 51 (96.2%) had pVL <50 copies/mL.

CONCLUSION

Despite a high level of mutation resistance at baseline, long-term virological follow-up was favourable and one-third of patients were eligible for drug-reducing strategies.

Lenacapavir administered every 26 weeks or daily in combination with oral daily antiretroviral therapy for initial treatment of HIV: a randomised, open-label, active-controlled, phase 2 trial

BACKGROUND

Antiretroviral agents with novel mechanisms and dosing intervals could expand treatment options for people with HIV. Lenacapavir, an inhibitor of capsid protein that makes use of a unique mechanism, can be administered orally or subcutaneously. We sought to explore the efficacy of lenacapavir in various combination regimens as initial and maintenance therapy for HIV.

METHODS

In a phase 2, randomised, open-label, ongoing study at 41 investigational sites in the USA and Dominican Republic, we randomly assigned adults with HIV who had not previously received antiretrovirals to four groups (2:2:2:1). Randomisation was stratified by plasma HIV-1 RNA load (≤100 000 or >100 000 copies per mL) at screening. Groups 1 and 2 both received lenacapavir (927 mg) subcutaneously every 26 weeks (after 2 weeks of oral loading [600 mg on days 1 and 2, followed by 300 mg on day 8]) with oral daily emtricitabine (200 mg) and tenofovir alafenamide (25 mg) for 28 weeks followed by subcutaneous lenacapavir (927 mg) plus oral daily tenofovir alafenamide (25 mg, group 1) or bictegravir (75 mg, group 2). Group 3 received oral daily lenacapavir (600 mg on days 1 and 2, followed by 50 mg daily) with emtricitabine (200 mg) and tenofovir alafenamide (25 mg). Group 4 received oral daily bictegravir (50 mg), emtricitabine (200 mg), and tenofovir alafenamide (25 mg). Participants and investigators were not masked to group assignment. The primary endpoint was the percentage of participants with virological suppression (HIV-1 RNA <50 copies per mL) at week 54, analysed in the full analysis set (all randomly assigned participants who received at least one dose of study drug) using only on-treatment data. The safety outcome measures were incidences of treatment-emergent adverse events and graded laboratory abnormalities, analysed in the full analysis set. This study is registered at ClinicalTrials.gov, NCT04143594.

FINDINGS

Between Nov 22, 2019, and Aug 27, 2020, 249 people with HIV were screened, 183 participants were randomly assigned and 182 received a dose of antiretroviral drugs (52 in group 1, 53 in group 2, 52 in group 3, and 25 in group 4). 22 participants did not complete the full study course (five in group 1, 12 in group 2, four in group 3, and one in group 4). At week 54, virological suppression was 90% (47 of 52 patients) for group 1 (difference vs group 4: -2·6%, 95% CI -18·4 to 13·2), 85% (45 of 53) for group 2 (-7·1%, -23·4 to 9·3), 85% (44 of 52) for group 3 (-7·2%, -23·5 to 9·1), and 92% (23 of 25) for group 4. The most frequent non-injection-site adverse events with lenacapavir (subcutaneous or oral) were headache (13%, 21 of 157) and nausea (13%, 21 of 157). The most common lenacapavir-related injection-site reactions were erythema (27%, 28 of 105), swelling (23%, 24 of 105), and pain (19%, 20 of 105), which were generally mild or moderate. No serious adverse event related to study treatment occurred. Three participants discontinued subcutaneous lenacapavir because of grade 1 injection-site reactions (two for induration and one for erythema or swelling).

INTERPRETATION

Lenacapavir warrants further investigation as a potential antiretroviral used orally and as injection in combination with other antiretroviral drugs.

FUNDING

Gilead Sciences.

Safety and Pharmacokinetics of Islatravir in Individuals with Severe Renal Insufficiency

Islatravir (MK-8591) is a high-potency reverse transcriptase translocation inhibitor in development for the treatment of HIV-1 infection. Data from preclinical and clinical studies suggest that ~30% to 60% of islatravir is excreted renally and that islatravir is not a substrate of renal transporters. To assess the impact of renal impairment on the pharmacokinetics of islatravir, an open-label phase 1 trial was conducted with individuals with severe renal insufficiency (RI). A single dose of islatravir 60 mg was administered orally to individuals with severe RI (estimated glomerular filtration rate [eGFR] <30 mL/min/1.73 m²) and to healthy individuals without renal impairment (matched control group; eGFR ≥90 mL/min/1.73 m²). Safety and tolerability were assessed, and blood samples were collected to measure the pharmacokinetics of islatravir and its major metabolite 4'-ethynyl-2-fluoro-2'deoxyinosine (M4) in plasma, as well as active islatravir-triphosphate (TP) in peripheral blood mononuclear cells (PBMCs). Plasma islatravir and M4 area under the concentration-time curve from zero to infinity (AUC_0-∞) were ~2-fold and ~5-fold higher, respectively, in participants with severe RI relative to controls, whereas islatravir-TP AUC_0-∞ was ~1.5-fold higher in the RI group than in the control group. The half-lives of islatravir in plasma and islatravir-TP in PBMCs were longer in participants with severe RI than in controls. These findings are consistent with renal excretion playing a major role in islatravir elimination. A single oral dose of islatravir 60 mg was generally well tolerated. These data provide guidance regarding administration of islatravir in individuals with impaired renal function. (This study has been registered at ClinicalTrials.gov under registration no. NCT04303156.).

HIV nucleoside reverse transcriptase inhibitors

More than 40 years into the pandemic, HIV remains a global burden and as of now, there is no cure in sight. Fortunately, highly active antiretroviral therapy (HAART) has been developed to manage and suppress HIV infection. Combinations of two to three drugs targeting key viral proteins, including compounds inhibiting HIV reverse transcriptase (RT), have become the cornerstone of HIV treatment. This review discusses nucleoside reverse transcriptase inhibitors (NRTIs), including chain terminators, delayed chain terminators, nucleoside reverse transcriptase translocation inhibitors (NRTTIs), and nucleotide competing RT inhibitors (NcRTIs); focusing on their history, mechanism of action, resistance, and current clinical application, including long-acting regimens.

Brief Report: Efficacy and Safety of Oral Islatravir Once Daily in Combination With Doravirine Through 96 Weeks for Treatment-Naive Adults With HIV-1 Infection Receiving Initial Treatment With Islatravir, Doravirine, and Lamivudine

BACKGROUND

Islatravir (MK-8591) is a nucleoside reverse transcriptase translocation inhibitor in development for treatment and prevention of HIV-1. We present efficacy and safety data for islatravir and doravirine (DOR) through 96 weeks of the phase 2b trial (NCT03272347).

METHODS

In this randomized, double-blind, dose-ranging trial, participants initially received islatravir (0.25, 0.75, or 2.25 mg) with doravirine (100 mg) and lamivudine (3TC, 300 mg) or a fixed-dose combination of doravirine, 3TC, and tenofovir disoproxil fumarate (DOR/3TC/TDF) daily. Beginning at week 24, participants receiving islatravir stopped 3TC if HIV-1 RNA from the prior visit was <50 copies per milliliter and continued taking the assigned islatravir dose (still blinded) with doravirine. All islatravir groups transitioned to open-label use of 0.75 mg between weeks 60 and 84. Efficacy end points at week 96 included the proportion of participants maintaining HIV-1 RNA of <50 copies per milliliter (FDA Snapshot). Safety was assessed by adverse event (AE) reporting.

RESULTS

One hundred twenty-one treatment-naive participants received the study drugs and were included in the analyses. Through week 96, HIV-1 RNA<50 copies per milliliter was maintained in 86.2% (25/29), 90.0% (27/30), and 67.7% (21/31) of participants in the 0.25-, 0.75-, and 2.25-mg islatravir groups, respectively, 81.1% (73/90) of the combined islatravir group, and 80.6% (25/31) of the DOR/3TC/TDF group. One participant in the 2.25-mg islatravir group had Protocol-Defined Virologic Failure after week 48. Drug-related AE rates were higher for DOR/3TC/TDF participants (22.6%) compared with islatravir (combined 7.8%). Two participants (2.2%) receiving islatravir with doravirine and one (3.2%) receiving DOR/3TC/TDF discontinued because of an AE.

CONCLUSIONS

Treatment regimens containing islatravir and doravirine maintained viral suppression through week 96 and were well tolerated regardless of dose.

How could HIV-1 drug resistance impact preexposure prophylaxis for HIV prevention?

PURPOSE OF REVIEW

To review current laboratory and clinical data on the frequency and relative risk of drug resistance and range of mutations selected from approved and investigational antiretroviral agents used for preexposure prophylaxis (PrEP) of HIV-1 infection, including tenofovir disproxil fumarate (TDF)-based oral PrEP, dapivirine ring, injectable cabotegravir (CAB), islatravir, lenacapavir and broadly neutralizing antibodies (bNAbs).

RECENT FINDINGS

The greatest risk of HIV-1 resistance from PrEP with oral TDF/emtricitabine (FTC) or injectable CAB is from starting or continuing PrEP after undiagnosed acute HIV infection. By contrast, the dapivirine intravaginal ring does not appear to select nonnucleoside reverse transcriptase inhibitor resistance in clinical trial settings. Investigational inhibitors including islatravir, lenacapavir, and bNAbs are promising for use as PrEP due to their potential for sustained delivery and low risk of cross-resistance to currently used antiretrovirals, but surveillance for emergence of resistance mutations in more HIV-1 gene regions (gag, env) will be important as the same drugs are being developed for HIV therapy.

SUMMARY

PrEP is highly effective in preventing HIV infection. Although HIV drug resistance from PrEP use could impact future options in individuals who seroconvert on PrEP, the current risk is low and continued monitoring for the emergence of resistance and cross-resistance during product development, clinical studies, and product roll-out is advised to preserve antiretroviral efficacy for both treatment and prevention.

Role of islatravir in HIV treatment and prevention: an update

PURPOSE OF REVIEW

To summarize recent updates on the potential role of islatravir for HIV treatment and prevention.

RECENT FINDINGS

Islatravir is an investigational antiretroviral agent with unique pharmacologic properties that facilitate flexible dosing regimens. Islatravir has demonstrated potent antiviral activity and a high barrier to resistance when combined with doravirine and lamivudine. A simplified two-drug HIV treatment regimen of islatravir combined with doravirine has also demonstrated comparable efficacy to standard of care three-drug regimens. The long half-life and high potency of islatravir's active metabolite may support its use as a long-acting option for HIV preexposure prophylaxis (PrEP). A once monthly oral dose of islatravir maintains effective concentrations of its active metabolite over the entire dosing interval. Furthermore, an investigational implantable formulation has been projected to provide efficacious concentrations for at least a year and exhibits comparable distribution into vaginal and rectal tissues making it a promising PrEP option for male and female individuals. Islatravir has minimal risks of drug interactions as it is not a substrate, inducer, or inhibitor of major drug metabolizers and transporters. Finally, clinical trials demonstrate islatravir's favorable safety profile revealing only mild and transient adverse events.

SUMMARY

Leveraging the unique pharmacological properties of islatravir offers opportunities for simplified HIV treatment regimens and long-acting PrEP making it a valuable addition to the antiretroviral arsenal.

Islatravir Has a High Barrier to Resistance and Exhibits a Differentiated Resistance Profile from Approved Nucleoside Reverse Transcriptase Inhibitors (NRTIs)

Islatravir (ISL) is a nucleoside reverse transcriptase translocation inhibitor (NRTTI) that inhibits human immunodeficiency virus (HIV) reverse transcription by blocking reverse transcriptase (RT) translocation on the primer:template. ISL is being developed for the treatment of HIV-1 infection. To expand our knowledge of viral variants that may confer reduced susceptibility to ISL, resistance selection studies were conducted with wild-type (WT) subtype A, B, and C viruses. RT mutations encoding M184I and M184V were the most frequently observed changes. Selection studies were also initiated with virus containing a single known resistance-associated mutation in RT (K65R, L74I, V90I, M184I, or M184V), and no additional mutations were observed. Antiviral activity assays were performed on variants that emerged in selection studies to determine their impact. M184I and M184V were the only single-codon substitutions that reduced susceptibility >2-fold compared to WT. A114S was an emergent substitution that when combined with other substitutions further reduced susceptibility >2-fold. Viruses containing A114S in combination with M184V did not replicate in primary blood mononuclear cells (PBMCs), consistent with the rare occurrence of the combination in clinical samples. While A114S conferred reduced susceptibility to ISL, it increased susceptibility to approved nucleoside reverse transcriptase inhibitors (NRTIs). This differential impact of A114S on ISL, an NRTTI, compared to NRTIs likely results from the different mechanisms of action. Altogether, the results demonstrate that ISL has a high barrier to resistance and a differentiated mechanism compared to approved NRTIs.

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

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

Implementation of long-acting antiretroviral therapy in low-income and middle-income countries

PURPOSE OF REVIEW

With oral antiretroviral therapy, HIV has become a manageable chronic illness. However, UNAIDS targets for virologic suppression have not yet been attained in many low-income and middle-income countries (LMICs). Long-acting drug formulations hold promise to improve treatment outcomes. In this rapidly evolving area of research, we aim to review recent literature on the treatment of HIV with long-acting agents and identify implementation considerations for LMICs.

RECENT FINDINGS

Randomized controlled trials have shown that monthly long-acting injectable cabotegravir (CAB) and rilpivirine (RPV) is noninferior to oral ART, and 2-monthly CAB/RPV is noninferior to monthly injections. However, few people from LMICs were included. A modelling study predicts that in sub-Saharan Africa, injectable CAB/RPV is best targeted to those with poor adherence (HIV viral load >1000 copies/ml) in whom cost-effectiveness is greatest and risk of contributing to further resistance is no greater than continuation of oral ART. Other promising agents, such as lenacapavir are under investigation and may prove particularly useful in heavily treatment-experienced adults.

SUMMARY

Long-acting regimens are a promising advance in HIV treatment. By extending the dosing interval, increasing convenience and being discreet these regimens may reduce HIV treatment challenges. However, there are multiple implementation considerations in LMICs including the need for exclusion of hepatitis B, cold chain, oral bridging in case of missed dosing and switching during tuberculosis therapy. Efficacy and safety data are also awaited for settings without routine access to baseline resistance testing or regular viral load monitoring and for special populations, such as pregnancy, children and the elderly.

Approved HIV reverse transcriptase inhibitors in the past decade

HIV reverse transcriptase (RT) inhibitors are the important components of highly active antiretroviral therapies (HAARTs) for anti-HIV treatment and pre-exposure prophylaxis in clinical practice. Many RT inhibitors and their combination regimens have been approved in the past ten years, but a review on their drug discovery, pharmacology, and clinical efficacy is lacking. Here, we provide a comprehensive review of RT inhibitors (tenofovir alafenamide, rilpivirine, doravirine, dapivirine, azvudine and elsulfavirine) approved in the past decade, regarding their drug discovery, pharmacology, and clinical efficacy in randomized controlled trials. Novel RT inhibitors such as islatravir, MK-8504, MK-8507, MK8583, IQP-0528, and MIV-150 will be also highlighted. Future development may focus on the new generation of novel antiretroviral inhibitors with higher bioavailability, longer elimination half-life, more favorable side-effect profiles, fewer drug-drug interactions, and higher activities against circulating drug-resistant strains.

Two-Drug Regimens for HIV-Current Evidence, Research Gaps and Future Challenges

During the last 30 years, antiretroviral treatment (ART) for human immunodeficiency virus (HIV) infection has been continuously evolving. Since 1996, three-drug regimens (3DR) have been standard-of-care for HIV treatment and are based on a protease inhibitor (PI) or a non-nucleoside reverse transcriptase inhibitor (NNRTI) plus two nucleoside reverse transcriptase inhibitors (NRTIs). The effectiveness of first-generation 3DRs allowed a dramatic increase in the life expectancy of HIV-infected patients, although it was associated with several side effects and ART-related toxicities. The development of novel two-drug regimens (2DRs) started in the mid-2000s in order to minimize side effects, reduce drug-drug interactions and improve treatment compliance. Several clinical trials compared 2DRs and 3DRs in treatment-naïve and treatment-experienced patients and showed the non-inferiority of 2DRs in terms of efficacy, which led to 2DRs being used as first-line treatment in several clinical scenarios, according to HIV clinical guidelines. In this review, we summarize the current evidence, research gaps and future prospects of 2DRs.

Evaluating Islatravir Administered Via Microneedle Array Patch for Long-Acting HIV Pre-exposure Prophylaxis Using Physiologically Based Pharmacokinetic Modelling

BACKGROUND AND OBJECTIVES

Technologies for long-acting administration of antiretrovirals (ARVs) for the prevention and treatment of HIV are at the forefront of research initiatives aiming to tackle issues surrounding drug adherence with the current standard of once-daily oral administration. Islatravir (ISL) is an emerging ARV that shows promising characteristics for long-acting prevention and treatment both orally as well as through alternative routes of administration. Microneedle array patches (MAPs) are a pain-free and discreet transdermal delivery technology that offer extended-release administration of nanoparticulate drugs. This study aimed to utilise physiologically based pharmacokinetic (PBPK) modelling to predict the pharmacokinetics resulting from ISL administered via MAP and to identify key MAP characteristics required to sustain effective concentrations over extended dosing intervals.

METHODS

A PBPK model describing the conversion of ISL to ISL-triphosphate (ISL-TP) and its whole-body disposition was developed and verified against observed clinical data for orally administered ISL in healthy adults. An intradermal PBPK model was integrated with the ISL PBPK model to predict the dose and nanoparticle release rate required for MAP administration strategies capable of achieving a minimum ISL-TP target concentration of 0.05 pmol/10⁶ PBMCs over extended dosing intervals. MAP design was limited to a maximum therapeutic area of 20 cm² with a dose loading of 4.09 mg/cm² and a minimum duration of 3 months. Due to the lack of available clinical data, a range of nanoparticle release rates and MAP bioavailability scenarios were simulated to provide an overview of potential clinical outcomes.

RESULTS

The ISL PBPK model was successfully verified, with predicted vs observed ratios falling within 0.5-2-fold. ISL MAP doses ranging from 15 to 80 mg were predicted to sustain ISL-TP concentrations above the minimum target concentration at 3, 6 and 12 months after administration. Nanoparticle release rate and MAP bioavailability were found to have a major impact on whether dosing strategies achieved the criteria. Minimum doses of 15 mg and 60 mg with a nanoparticle release rate of 0.0005 h^-1 and bioavailability ranging from 25 to 100% were predicted to achieve effective ISL-TP concentrations up to 3 and 6 months, respectively. Doses of 15 mg and 30 mg with a nanoparticle release rate of 0.0005 h^-1 were also able to attain the target concentration up to 6 months after MAP administration, albeit with a minimum bioavailability of 75% and 50%, respectively. Furthermore, when simulating a bioavailability of 100%, an 80 mg ISL MAP was predicted to sustain ISL-TP concentrations above the minimum target concentration up to 12 months after administration.

CONCLUSIONS

The ISL PBPK model successfully predicted ISL and ISL-TP pharmacokinetics across a range of orally administered regimens. The integrated intradermal PBPK model outlined optimal MAP dose and nanoparticle release rates for effective ISL-TP concentrations up to 12 months, providing justification for further investigation of ISL as a candidate for MAP administration.

Long-Acting Injectable Antiretroviral Agents for HIV Treatment and Prevention

Current oral antiretroviral agents provide highly effective treatment for patients infected with human immunodeficiency virus (HIV), and can be used as pre-exposure prophylaxis (PrEP) to prevent new HIV infections. Several single-tablet regimens with excellent antiviral efficacy have dramatically improved the quality of life of patients who can adhere to daily oral therapy. However, there is increasing demand on long-acting injectable antiretroviral agents for patients who cannot take oral agents or feel fatigue related to daily pill burden. Monthly long-acting (LA) cabotegravir (CAB) combined with rilpivirine (RPV) has recently been listed as optimizing agent for maintenance of HIV suppression in treatment-experienced patients whose viral load is undetectable for 3 to 6 months. Novel agents with different mechanism of action and long half-life extending dosing interval are being tested in phase 2 and 3 clinical trials. This review summarizes the data of efficacies and safety profiles of LA CAB with RPV regimen, and also new long-acting injectable antiretroviral agents in pipeline.

Update and latest advances in antiretroviral therapy

Since the first cases of AIDS appeared in 1981, human immunodeficiency virus type 1 (HIV-1) infection has reached pandemic proportions. Forty years later, research has led to the approval of more than 30 antiretroviral drugs, while combination therapies have turned HIV-1 infection into a chronic, but manageable disease. Still, drug toxicity and acquired and transmitted drug resistance remain as major threats to therapy success. In this review, we provide an overview on currently available anti-HIV drugs and the latest developments in antiretroviral therapy, focused on new antiretroviral agents acting on known and unexploited antiviral targets, prevention therapies aimed to improve available drug combinations, and research on new long-acting therapies, particularly those involving novel drug candidates such as lenacapavir or islatravir.

Long-acting antiretrovirals: a new era for the management and prevention of HIV infection

The long-acting antiretroviral cabotegravir and rilpivirine combination has just received FDA, EMA and Health Canada approval. This novel drug delivery approach is about to revolutionize the therapy of people living with HIV, decreasing the 365 daily pill burden to only six intramuscular injections per year. In addition, islatravir, a first-in-class nucleoside reverse transcriptase translocation inhibitor, is intended to be formulated as an implant with a dosing interval of 1 year or more. At present, long-acting antiretroviral therapies (LA-ARTs) are given at fixed standard doses, irrespectively of the patient's weight and BMI, and without consideration for host genetic and non-genetic factors likely influencing their systemic disposition. Despite a few remaining challenges related to administration (e.g. pain, dedicated medical procedure), the development and implementation of LA-ARTs can overcome long-term adherence issues by improving patients' privacy and reducing social stigma associated with the daily oral intake of anti-HIV treatments. Yet, the current 'one-size-fits-all' approach does not account for the recognized significant inter-individual variability in LA-ART pharmacokinetics. Therapeutic drug monitoring (TDM), an important tool for precision medicine, may provide physicians with valuable information on actual drug exposure in patients, contributing to improve their management in real life. The present review aims to update the current state of knowledge on these novel promising LA-ARTs and discusses their implications, particularly from a clinical pharmacokinetics perspective, for the future management and prevention of HIV infection, issues of ongoing importance in the absence of curative treatment or an effective vaccine.