Long-acting integrase inhibitor protects macaques from intrarectal simian/human immunodeficiency virus

HIV Pre-Exposure Prophylaxis

Pre-exposure prophylaxis (PrEP) of human immunodeficiency virus (HIV) represents the most significant breakthrough in the HIV prevention field over the past decade. PrEP is an effective strategy in preventing the transmission of HIV across all populations, providing high adherence. The current PrEP options include oral daily and on-demand tenofovir-based regimens, long-acting injections of cabotegravir, and a 1-month dapivirine vaginal ring. As a component of a multifaceted prevention approach, extensive deployment of PrEP holds the promise to significantly reduce the global HIV epidemic. Nonetheless, barriers still exist in terms of uptake, adherence, and persistence, while disparities in PrEP accessibility remain a concern.

Long-acting cabotegravir pharmacokinetics with and without oral lead-in for HIV PrEP

Long-acting cabotegravir is approved for pre-exposure prophylaxis and combination HIV treatment, both initiated with optional short-term oral lead-in (OLI). We evaluated the impact of OLI on long-acting cabotegravir pharmacokinetics. Cabotegravir plasma concentrations were compared between HIV-positive participants initiating injections with (n = 278) or without (n = 110) OLI in phase III treatment study FLAIR and in HIV-negative participants using OLI (n = 263) in pivotal pre-exposure prophylaxis studies HPTN 083 and HPTN 084. Cabotegravir pharmacokinetic profiles were simulated in three populations (assigned-male-at-birth, 50%-assigned-female-at-birth, and assigned-female-at-birth) under three scenarios: first injection given (A) 1 or (B) 3 days after final OLI dose (OLI-injection gap) or (C) without OLI. The PK objective was 80% of participants achieving 4× in vitro protein-adjusted 90% maximal inhibitory concentration (PA-IC90) and 50% achieving 8× PA-IC90. Observed trough concentrations (Cτ) were similar with and without OLI (P > 0.3). With a 3-day OLI-injection gap, simulated pre-injection Cτ remained above PK objective. Approximately 1-2 weeks after the first injection, simulated PK profiles became nearly identical among all scenarios. Without OLI, it was predicted that 80% of participants achieve 4× PA-IC90 in 1.2, 1.8, and 2.8 days after the first injection in each population, respectively, and 50% achieve 8× PA-IC90 in 1.4, 2.1, and 3.8 days, respectively. Observed long-acting cabotegravir exposure was similar with or without OLI, supporting optional OLI use. Cabotegravir exposure was predicted to remain above PK objective for OLI-injection gaps of ≤3 days and rapidly achieve PK objective after first injection without OLI. Findings are consistent between assigned-male-at-birth and assigned-female-at-birth populations.This study is registered with ClinicalTrials.gov as NCT02720094.

Multitasking Pharmacophores Support Cabotegravir-Based Long-Acting HIV Pre-Exposure Prophylaxis (PrEP)

Cabotegravir is an integrase strand transfer inhibitor (INSTI) for HIV treatment and prevention. Cabotegravir-based long-acting pre-exposure prophylaxis (PrEP) presents an emerging paradigm for infectious disease control. In this scheme, a combination of a high efficacy and low solubility of anti-infection drugs permits the establishment of a pharmaceutical firewall in HIV-vulnerable groups over a long period. Although the structure-activity-relationship (SAR) of cabotegravir as an INSTI is known, the structural determinants of its low solubility have not been identified. In this work, we have integrated multiple experimental and computational methods, namely X-ray diffraction, solid-state NMR (SSNMR) spectroscopy, solution NMR spectroscopy, automated fragmentation (AF)-QM/MM and density functional theory (DFT) calculations, to address this question. The molecular organization of cabotegravir in crystal lattice has been determined. The combination of very-fast magic-angle-sample-spinning (VF MAS) SSNMR and solution NMR, as supported by AF-QM/MM and DFT calculations, permits the identification of structural factors that contribute to the low aqueous solubility of cabotegravir. Our study reveals the multitasking nature of pharmacophores in cabotegravir, which controls the drug solubility and, meanwhile, the biological activity. By unraveling these function-defining molecular features, our work could inspire further development of long-acting HIV PrEP drugs.

HIV Pre-Exposure Prophylaxis: New and Upcoming Drugs to Address the HIV Epidemic

Human immunodeficiency virus (HIV) pre-exposure prophylaxis (PrEP) provides a critical intervention toward ending the HIV epidemic and protecting people with reasons to utilize PrEP. PrEP options continue to expand as new administration modalities offer the potential to tailor PrEP use for individual success. We have provided the evidence for new and emerging antiretroviral agents for PrEP (cabotegravir, lenacapavir, dapivirine, and broadly neutralizing antibodies), divided into pharmacology, animal model, and human data, accompanied by a summary and suggested place in therapy. Cabotegravir is a US Food and Drug Administration (FDA)-approved intramuscular injection given every 2 months with a strong body of evidence demonstrating efficacy for HIV PrEP, lenacapavir administered subcutaneously every 6 months is currently under investigation for HIV PrEP, dapivirine vaginal ring is an available PrEP option for women in certain areas of Africa, and broadly neutralizing monoclonal antibodies have been challenged in demonstrating efficacy in phase 1-2 study for HIV PrEP to date. Clinical literature for individual agents is discussed with data from major studies summarized in tables. This review provides a detailed overview of recently available and premier candidate PrEP drugs.

A novel formulation enabled transformation of 3-HIV drugs tenofovir-lamivudine-dolutegravir from short-acting to long-acting all-in-one injectable

OBJECTIVE

To develop an injectable dosage form of the daily oral HIV drugs, tenofovir (T), lamivudine (L), and dolutegravir (D), creating a single, complete, all-in-one TLD 3-drug-combination that demonstrates long-acting pharmacokinetics.

DESIGN

Using drug-combination-nanoparticle (DcNP) technology to stabilize multiple HIV drugs, the 3-HIV drugs TLD, with disparate physical-chemical properties, are stabilized and assembled with lipid-excipients to form TLD-in-DcNP . TLD-in-DcNP is verified to be stable and suitable for subcutaneous administration. To characterize the plasma time-courses and PBMC concentrations for all 3 drugs, single subcutaneous injections of TLD-in-DcNP were given to nonhuman primates (NHP, M. nemestrina ).

RESULTS

Following single-dose TLD-in-DcNP , all drugs exhibited long-acting profiles in NHP plasma with levels that persisted for 4 weeks above predicted viral-effective concentrations for TLD in combination. Times-to-peak were within 24 hr in all NHP for all drugs. Compared to a free-soluble TLD, TLD-in-DcNP provided exposure enhancement and extended duration 7.0-, 2.1-, and 20-fold as AUC boost and 10-, 8.3-, and 5.9-fold as half-life extension. Additionally, DcNP may provide more drug exposure in cells than plasma with PBMC-to-plasma drug ratios exceeding one, suggesting cell-targeted drug-combination delivery.

CONCLUSIONS

This study confirms that TLD with disparate properties can be made stable by DcNP to enable TLD concentrations of 4 weeks in NHP. Study results highlighted the potential of TLD-in-DcNP as a convenient all-in-one, complete HIV long-acting product for clinical development.

EFdA efficiently suppresses HIV replication in the male genital tract and prevents penile HIV acquisition

Sexually transmitted HIV infections in heterosexual men are acquired through the penis. Low adherence to condom usage and the fact that 40% of circumcised men are not protected indicate the need for additional prevention strategies. Here, we describe a new approach to evaluate the prevention of penile HIV transmission. We demonstrated that the entire male genital tract (MGT) of bone marrow/liver/thymus (BLT) humanized mice is repopulated with human T and myeloid cells. The majority of the human T cells in the MGT express CD4 and CCR5. Direct penile exposure to HIV leads to systemic infection including all tissues of the MGT. HIV replication throughout the MGT was reduced 100-1,000-fold by treatment with 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA), resulting in the restoration of CD4+ T cell levels. Importantly, systemic preexposure prophylaxis with EFdA effectively protects from penile HIV acquisition. IMPORTANCE Over 84.2 million people have been infected by the human immunodeficiency virus type 1 (HIV-1) during the past 40 years, most through sexual transmission. Men comprise approximately half of the HIV-infected population worldwide. Sexually transmitted HIV infections in exclusively heterosexual men are acquired through the penis. However, direct evaluation of HIV infection throughout the human male genital tract (MGT) is not possible. Here, we developed a new in vivo model that permits, for the first time, the detail analysis of HIV infection. Using BLT humanized mice, we showed that productive HIV infection occurs throughout the entire MGT and induces a dramatic reduction in human CD4 T cells compromising immune responses in this organ. Antiretroviral treatment with novel drug EFdA suppresses HIV replication in all tissues of the MGT, restores normal levels of CD4 T cells and is highly efficient at preventing penile transmission.

Preclinical Considerations for Long-acting Delivery of Tenofovir Alafenamide from Subdermal Implants for HIV Pre-exposure Prophylaxis

PURPOSE

Long-acting formulations of the potent antiretroviral prodrug tenofovir alafenamide (TAF) hold potential as biomedical HIV prevention modalities. Here, we present a rigorous comparison of three animal models, C57BL/6 J mice, beagle dogs, and merino sheep for evaluating TAF implant pharmacokinetics (PKs).

METHODS

Implants delivering TAF over a wide range of controlled release rates were tested in vitro and in mice and dogs. Our existing PK model, supported by an intravenous (IV) dosing dog study, was adapted to analyze mechanistic aspects underlying implant TAF delivery.

RESULTS

TAF in vitro release in the 0.13 to 9.8 mg d-1 range with zero order kinetics were attained. Implants with equivalent fabrication parameters released TAF in mice and sheep at rates that were not statistically different, but were 3 times higher in dogs. When two implants were placed in the same subcutaneous pocket, a two-week creep to Cmax was observed in dogs for systemic drug and metabolite concentrations, but not in mice. Co-modeling IV and TAF implant PK data in dogs led to an apparent TAF bioavailability of 9.6 in the single implant groups (compared to the IV group), but only 1.5 when two implants were placed in the same subcutaneous pocket.

CONCLUSIONS

Based on the current results, we recommend using mice and sheep, with macaques as a complementary species, for preclinical TAF implant evaluation with the caveat that our observations may be specific to the implant technology used here. Our report provides fundamental, translatable insights into multispecies TAF delivery via long-acting implants.

Attenuated Mycobacterium tuberculosis vaccine protection in a low-dose murine challenge model

Bacillus Calmette-Guérin (BCG) remains the only approved tuberculosis (TB) vaccine despite limited efficacy. Preclinical studies of next-generation TB vaccines typically use a murine aerosol model with a supraphysiologic challenge dose. Here, we show that the protective efficacy of a live attenuated Mycobacterium tuberculosis (Mtb) vaccine ΔLprG markedly exceeds that of BCG in a low-dose murine aerosol challenge model. BCG reduced bacterial loads but did not prevent establishment or dissemination of infection in this model. In contrast, ΔLprG prevented detectable infection in 61% of mice and resulted in anatomic containment of 100% breakthrough infections to a single lung. Protection was partially abrogated in a repeated low-dose challenge model, which showed serum IL-17A, IL-6, CXCL2, CCL2, IFN-γ, and CXCL1 as correlates of protection. These data demonstrate that ΔLprG provides increased protection compared to BCG, including reduced detectable infection and anatomic containment, in a low-dose murine challenge model.

Updating the Adherence-Response for Oral Emtricitabine/Tenofovir Disoproxil Fumarate for Human Immunodeficiency Virus Pre-Exposure Prophylaxis Among Cisgender Women

Using intraerythrocytic tenofovir-diphosphate data from the emtricitabine/tenofovir disoproxil fumarate arms of HIV Prevention Trials Network (HPTN) 083 (men) and HPTN 084 (women), approximately 99% efficacy was achieved at a lower adherence threshold in HPTN 083 (≥2 doses/week) compared with HPTN 084 (daily), suggesting higher adherence is necessary for women vs men.

Extended Analysis of HIV Infection in Cisgender Men and Transgender Women Who Have Sex with Men Receiving Injectable Cabotegravir for HIV Prevention: HPTN 083

HPTN 083 demonstrated that injectable cabotegravir (CAB) was superior to oral tenofovir disoproxil fumarate-emtricitabine (TDF-FTC) for HIV prevention in cisgender men and transgender women who have sex with men. We previously analyzed 58 infections in the blinded phase of HPTN 083 (16 in the CAB arm and 42 in the TDF-FTC arm). This report describes 52 additional infections that occurred up to 1 year after study unblinding (18 in the CAB arm and 34 in the TDF-FTC arm). Retrospective testing included HIV testing, viral load testing, quantification of study drug concentrations, and drug resistance testing. The new CAB arm infections included 7 with CAB administration within 6 months of the first HIV-positive visit (2 with on-time injections, 3 with ≥1 delayed injection, and 2 who restarted CAB) and 11 with no recent CAB administration. Three cases had integrase strand transfer inhibitor (INSTI) resistance (2 with on-time injections and 1 who restarted CAB). Among 34 CAB infections analyzed to date, diagnosis delays and INSTI resistance were significantly more common in infections with CAB administration within 6 months of the first HIV-positive visit. This report further characterizes HIV infections in persons receiving CAB preexposure prophylaxis and helps define the impact of CAB on the detection of infection and the emergence of INSTI resistance.

Cabotegravir: The First Long-Acting Injectable for HIV Preexposure Prophylaxis

OBJECTIVE

Review the pharmacology, pharmacokinetics, efficacy, safety, and role of long-acting injectable cabotegravir (CAB-LA) in HIV preexposure prophylaxis (PrEP).

DATA SOURCES

A literature search was performed using PubMed and Google Scholar (2012 to April 2022) with the search terms cabotegravir, preexposure prophylaxis, and PrEP. Other resources included abstracts presented at recent conferences, the manufacturer's Web site, prescribing information, and review articles.

STUDY SELECTION AND DATA EXTRACTION

All English-language articles of studies assessing the efficacy and safety of CAB-LA for PrEP were included.

DATA SYNTHESIS

CAB-LA is the first long-acting injectable therapy approved for HIV-1 PrEP in both men and women. It is a suspension given intramuscularly every other month. CAB-LA has been shown to be more effective than daily oral tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) in preventing HIV-1 infection among high-risk individuals. Two phase 3 trials were stopped early on the basis of superior efficacy of CAB-LA. The most common adverse effects were injection site reactions (ISRs), although they tended to decrease over time, and few participants in clinical trials discontinued use due to ISRs.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

CAB-LA may be particularly useful for individuals with known adherence problems to oral therapy, those with renal impairment, and those with decreased bone mineral density. However, CAB-LA is more expensive than generic TDF/FTC and may be associated with weight gain.

CONCLUSIONS

CAB-LA is the first long-acting injectable agent for HIV PrEP. It is more effective than oral TDF/FTC, is well-tolerated aside from ISRs, and has few clinically significant drug-drug interactions.

Ultra-long-acting in-situ forming implants with cabotegravir protect female macaques against rectal SHIV infection

Ultra-long-acting delivery platforms for HIV pre-exposure prophylaxis (PrEP) may increase adherence and maximize public health benefit. We report on an injectable, biodegradable, and removable in-situ forming implant (ISFI) that is administered subcutaneously and can release the integrase inhibitor cabotegravir (CAB) above protective benchmarks for more than 6 months. CAB ISFIs are well-tolerated in female mice and female macaques showing no signs of toxicity or chronic inflammation. In macaques, median plasma CAB concentrations exceed established PrEP protection benchmarks within 3 weeks and confer complete protection against repeated rectal SHIV challenges. Implant removal via a small incision in 2 macaques at week 12 results in a 7- to 48-fold decrease in plasma CAB levels within 72 hours. Modeling to translate CAB ISFI dosing suggests that a 3 mL injection would exceed protective benchmarks in humans for over 5 months post administration. Our results support the clinical advancement of CAB ISFIs for ultra-long-acting PrEP in humans.

Human Immunodeficiency Virus Type 1 RNA Levels in Rectal and Seminal Compartments After Switching to Long-Acting Cabotegravir Plus Rilpivirine: A Longitudinal Study

Human immunodeficiency virus type 1 RNA levels were longitudinally evaluated in 211 rectal and 152 seminal samples from 12 virologically suppressed participants switching to monthly long-acting cabotegravir plus rilpivirine or continuing with daily dolutegravir-abacavir-lamivudine. Maintenance of viral suppression in rectal and seminal compartments was comparable, and blips occurred with similar frequency with both treatment regimens.

CLINICAL TRIALS REGISTRATION

NCT02938520.

The Long-Acting Cabotegravir Tail as an Implementation Challenge: Planning for Safe Discontinuation

The long-acting feature of cabotegravir, an integrase-inhibitor highly effective in preventing acquisition of HIV in adolescents and adults, is both its greatest strength and a challenge to its implementation. Cab-LA is administered at 8-week intervals (after an initial loading dose) but has a long, variable drug "tail" that may leave users vulnerable to future drug resistance if they contract HIV during this critical period. The potential for cab-LA to meaningfully contribute to ending the HIV Epidemic is hindered by, among other factors, limited resources to guide patients and providers on how to safely discontinue injections. We suggest three key strategies to overcome this specific challenge: (1) Comprehensive patient education and counseling about the drug tail; (2) Training and coaching PrEP care teams, including clinical and non-clinical staff, on communication around the tail; (3) Adherence support strategies, including monitoring of cabotegravir drug levels after discontinuation, for a personalized medicine approach to safe discontinuation.

HIV RNA Screening Reduces Integrase Strand Transfer Inhibitor Resistance Risk in Persons Receiving Long-Acting Cabotegravir for HIV Prevention

BACKGROUND

The HPTN 083 trial demonstrated that long-acting cabotegravir (CAB-LA) was superior to tenofovir-disoproxil fumarate/emtricitabine for human immunodeficiency virus (HIV) preexposure prophylaxis (PrEP). Integrase strand transfer inhibitor (INSTI) resistance-associated mutations (RAMs) were detected in some participants with HIV infection. We used a low viral load INSTI genotyping assay to evaluate the timing of emergence of INSTI RAMs and assessed whether HIV screening with a sensitive RNA assay would have detected HIV infection before INSTI resistance emerged.

METHODS

Single-genome sequencing to detect INSTI RAMs was performed for samples with viral loads <500 copies/mL from 5 participants with previously identified INSTI RAMs and 2 with no prior genotyping results.

RESULTS

Major INSTI RAMs were detected in all 7 cases. HIV RNA testing identified infection before major INSTI RAMs emerged in 4 cases and before additional major INSTI RAMs accumulated in 1 case. Most INSTI RAMs were detected early when the viral load was low and CAB concentration was high.

CONCLUSIONS

When using CAB-LA PrEP, earlier detection of HIV infection with a sensitive RNA assay may allow for earlier treatment initiation with the potential to reduce INSTI resistance risk. Further studies are needed to evaluate the value and feasibility of HIV RNA testing with CAB-LA PrEP.

Long-acting injectable cabotegravir for PrEP: A game-changer in HIV prevention?

BACKGROUND

Long-acting injectable cabotegravir (CAB-LA) represents a new additional option for HIV prevention in people at substantial risk of HIV infection that may fill the gaps in pre-exposure prophylaxis (PrEP) uptake, adherence, and retention in users having difficulty with oral PrEP. Data from clinical trials demonstrated that CAB-LA was safe, highly effective, and well-accepted for HIV prevention. However, the occurrence of breakthrough HIV infections despite timely injections, HIV seroconversion timing and patterns, risk of selection and dissemination of resistance-associated mutations to integrase inhibitors, complexity of follow-up, logistical considerations, and its cost effectiveness compared with oral PrEP constitute significant issues for the integration of CAB-LA into clinical routine.

FINDINGS

These concerns need to be addressed before moving forward with large-scale implementation programmes. Pilot and implementation projects are required in the following areas: HIV testing algorithms, patient education, clinic procedures, protocols for switching and discontinuation, efficacy and safety in populations not included in clinical trials, and demedicalization processes. The development of models to increase the uptake of, adherence to, and persistence with and after CAB-LA injections will also be of paramount importance for success. Lessons learned from these projects will increase experience, staff expertise, and organizational and training capacities to support the roll-out of this new agent as part of HIV prevention programmes.

CONCLUSION

CAB-LA has not yet achieved its full potential in HIV prevention, and strong commitment from all stakeholders is required to push CAB-LA as a game-changer in HIV response.

Safety and efficacy of a biodegradable implant releasing tenofovir alafenamide for vaginal protection in a macaque model

OBJECTIVES

To advance the initiative of ending the global epidemic, long-lasting HIV protection is needed through sustained release of antiretroviral drugs for months to years. We investigated in macaques the safety and efficacy of biodegradable polycaprolactone implants releasing tenofovir alafenamide for HIV pre-exposure prophylaxis (PrEP).

METHODS

Implants were administered subcutaneously in the arm using a contraceptive trocar. Efficacy against vaginal simian-HIV (SHIV) infection was investigated in six pigtailed macaques that received two tenofovir alafenamide implants (0.35 mg/day), one in each arm, for a total release rate of tenofovir alafenamide at 0.7 mg/day. Macaques were exposed to SHIV twice weekly for 6 weeks. Statistical analyses were used to compare outcome with eight untreated controls. Histological assessments were performed on skin biopsies collected near implantation sites.

RESULTS

Median (range) tenofovir diphosphate level in PBMCs was 1519 (1068-1898) fmol/106 cells. All macaques with tenofovir alafenamide implants were protected against vaginal SHIV infection. In contrast, 7/8 controls were infected after a median of 4 SHIV exposures (P = 0.0047). Histological assessment of tissues near tenofovir alafenamide implant sites showed inflammation and necrosis in 5/6 animals, which were not evident by visual inspection.

CONCLUSIONS

We demonstrated complete protection against vaginal SHIV infection with two implants releasing a total of 0.7 mg of tenofovir alafenamide per day. We also identified tenofovir diphosphate concentrations in PBMCs associated with complete vaginal protection. Consistent with previous findings, we observed adverse local toxicity and necrosis near the tenofovir alafenamide implant site. Improved tenofovir alafenamide implants that are safe and maintain high efficacy have the potential to provide long-lasting protection against vaginal HIV infection.

Long-Acting Injectable Cabotegravir for HIV Prevention: What Do We Know and Need to Know about the Risks and Consequences of Cabotegravir Resistance?

PURPOSE OF REVIEW

Cabotegravir is a potent integrase strand transfer inhibitor (INSTI) recently approved as a long-acting injectable formulation for HIV prevention (CAB-LA). We summarize what is known about cabotegravir pharmacokinetics, activity, and emergence of resistance from in vitro, macaque and clinical studies, and we evaluate the risk of resistance from CAB-LA with on-time injections and after CAB-LA discontinuation.

RECENT FINDINGS

The accumulation of multiple INSTI mutations is required for high-level cabotegravir resistance, and the same mutation combinations may cause cross-resistance to dolutegravir, which is widely used for first-line antiretroviral therapy in low- and middle-income countries. Though CAB-LA was highly effective in preventing HIV, breakthrough infections did occur in trials of CAB-LA despite on-time injections, resulting in selection of single and combinations of INSTI resistance mutations. As CAB-LA is scaled-up, prompt HIV diagnosis to prevent resistance, and resistance monitoring could help preserve the effectiveness of INSTIs for both HIV treatment and prevention.

A Pharmacokinetic Dose-Optimization Study of Cabotegravir and Bictegravir in a Mouse Pregnancy Model

Animal pregnancy models can be useful tools to study HIV antiretroviral safety and toxicity and to perform mechanistic studies that are not easily performed in humans. Utilization of clinically relevant dosing in these models improves the relevance of the findings. Cabotegravir and bictegravir are new integrase strand transfer inhibitors (INSTIs), recently approved for the treatment of people living with HIV. Studies of these drugs in pregnancy are very limited. The objective of this study was to perform a dose-optimization study of cabotegravir and bictegravir in a mouse pregnancy model with the goal of determining the dose that would yield plasma drug concentrations similar those observed in humans. Pregnant mice were administered increasing doses of cabotegravir or bictegravir in combination with emtricitabine and tenofovir by oral gavage from gestational day 11.5 to 15.5. Drug concentrations in the maternal plasma at 1 h and 24 h post drug administration and in the amniotic fluid at 1 h post drug administration were determined using high-performance liquid chromatography coupled with tandem mass spectrometry. A review of cabotegravir and bictegravir human pharmacokinetic studies are also reported. We hope these data will encourage studies of HIV antiretroviral safety/toxicity and mechanistic studies in animal pregnancy models.

The predictive value of macaque models of preexposure prophylaxis for HIV prevention

PURPOSE OF REVIEW

We review macaque models for preexposure prophylaxis (PrEP) for HIV prevention and highlight their role in advancing currently approved and novel PrEP agents.

RECENT FINDINGS

The development of the repeat low dose simian HIV (SHIV) challenge models represented a significant advancement in preclinical PrEP modeling that has allowed the investigation of PrEP under conditions that better mimic HIV exposures in humans. These models incorporate relevant drug pharmacology to inform drug correlates of PrEP protection. Models of rectal, vaginal, and penile infection are now available and have been found to predict clinical efficacy of all the currently approved PrEP strategies including daily oral PrEP with the combination of emtricitabine and tenofovir disoproxil fumarate or tenofovir alafenamide, and a long-acting formulation of the integrase inhibitor cabotegravir. These models are being used to test new PrEP modalities including the nucleoside reverse transcriptase-translocation inhibitor islatravir and long-acting capsid inhibitors. The SHIV models have also been supplemented by sexually transmitted infection co-infections with Chlamydia trachomatis, Treponema pallidum or Trichomonas vaginalis to assess the impact of inflammation on PrEP efficacy.

SUMMARY

Clinical efficacy validated current PrEP macaque models supporting their continued use to advance novel PrEP agents to improve global PrEP coverage.

Characterization of Human Immunodeficiency Virus (HIV) Infections in Women Who Received Injectable Cabotegravir or Tenofovir Disoproxil Fumarate/Emtricitabine for HIV Prevention: HPTN 084

BACKGROUND

HIV Prevention Trials Network 084 demonstrated that long-acting injectable cabotegravir (CAB) was superior to daily oral tenofovir (TFV) disoproxil fumarate (TDF)/emtricitabine (FTC) for preventing human immunodeficiency virus (HIV) infection in sub-Saharan African women. This report describes HIV infections that occurred in the trial before unblinding.

METHODS

Testing was performed using HIV diagnostic assays, viral load testing, a single-copy RNA assay, and HIV genotyping. Plasma CAB, plasma TFV, and intraerythrocytic TFV-diphosphate concentrations were determined by liquid chromatography-tandem mass spectrometry.

RESULTS

Forty HIV infections were identified (CAB arm, 1 baseline infection, 3 incident infections; TDF/FTC arm, 36 incident infections). The incident infections in the CAB arm included 2 with no recent drug exposure and no CAB injections and 1 with delayed injections; in 35 of 36 cases in the TDF/FTC arm, drug concentrations indicated low or no adherence. None of the cases had CAB resistance. Nine women in the TDF/FTC arm had nonnucleoside reverse-transcriptase inhibitor resistance; 1 had the nucleoside reverse-transcriptase inhibitor resistance mutation, M184V.

CONCLUSIONS

Almost all incident HIV infections occurred in the setting of unquantifiable or low drug concentrations. CAB resistance was not detected. Transmitted nonnucleoside reverse-transcriptase inhibitor resistance was common; 1 woman may have acquired nucleoside reverse-transcriptase inhibitor resistance from study drug exposure.

Safety, Tolerability, Pharmacokinetics, and Acceptability of Oral and Long-Acting Cabotegravir in HIV-Negative Chinese Men

Long-acting (LA) cabotegravir demonstrated superior efficacy versus daily oral standard-of-care for HIV-1 preexposure prophylaxis. This phase 1 study assessed safety, tolerability, pharmacokinetics, and acceptability of cabotegravir in 47 HIV-negative adult Chinese men at low risk of acquiring HIV-1. Participants received once-daily oral cabotegravir 30 mg for 4 weeks and, after a 1-week washout, five 600-mg (3-mL) intramuscular cabotegravir LA injections at weeks 5, 9, 17, 25, and 33. Pharmacokinetic plasma samples were intensively collected on day 27 (n = 17) and sparsely collected before each injection until 56 weeks after final injection (n = 47). Cabotegravir LA injections were acceptable and well tolerated. Common adverse events included injection site pain, injection site swelling, and upper respiratory tract infection. No drug-related serious adverse events or deaths occurred. Mean cabotegravir concentration remained above 1.33 μg/mL (8× in vitro protein-adjusted concentration for 90% of the maximum inhibition of viral growth [PA-IC₉₀]) before each injection and above 0.166 μg/mL (PA-IC₉₀) for >32 weeks after final injection. Trough concentrations remained above PA-IC₉₀ in nearly all participants and showed minimal accumulation. Noncompartmental pharmacokinetic analysis was performed. Geometric mean of terminal half-life was 1.89 and 47 days after oral and LA dosing, respectively. Cabotegravir concentrations were estimated to remain quantifiable for 48.7 weeks after final injection. Steady-state area under the concentration-time curve (AUC), peak concentration, trough concentration, terminal half-life, time to peak concentration, and apparent clearance after cabotegravir oral and LA dosing were similar to those estimated in non-Asian men in historical studies. These results support further clinical development of cabotegravir LA in China. (This study has been registered at ClinicalTrials.gov under registration no. NCT03422172.)

Sexually transmitted infections and depot medroxyprogesterone acetate do not impact protection from simian HIV acquisition by long-acting cabotegravir in macaques

OBJECTIVE

We had previously shown that long-acting cabotegravir (CAB-LA) injections fully protected macaques from vaginal simian HIV (SHIV) infection. Here, we reassessed CAB-LA efficacy in the presence of depot medroxyprogesterone acetate and multiple sexually transmitted infections (STIs) that are known to increase HIV susceptibility in women.

DESIGN

Two macaque models of increasing vaginal STI severity were used for efficacy assessment.

METHODS

The first study (n = 11) used a double STI model that had repeated exposures to two vaginal STI, Chlamydia trachomatis and Trichomonas vaginalis. Six animals were CAB-LA treated and five were controls. The second study (n = 9) included a triple STI model with repeated exposures to C. trachomatis, T. vaginalis and syphilis, and the contraceptive, depot medroxyprogesterone acetate (DMPA). Six animals were CAB-LA treated and three were controls. All animals received up to 14 vaginal SHIV challenges. A survival analysis was performed to compare the number of SHIV challenges to infection in the drug-treated group compared with untreated controls over time.

RESULTS

All six CAB-LA treated animals in both models, the double STI or the triple STI-DMPA model, remained protected after 14 SHIV vaginal challenges, while the untreated animals became SHIV-infected after a median of two challenges (log-rank P < 0.001) or one challenge (log-rank P = 0.002), respectively. Both models recapitulated human STI disease, with vaginal discharge, ulcers, and seroconversion.

CONCLUSION

In these high and sustained susceptibility models spanning more than 3 months, CAB-LA maintained complete efficacy, demonstrating robustness of the CAB-LA dose used in clinical trials, and suggesting its insensitivity to multiple STIs and DMPA.

A new paradigm for antiretroviral delivery: long-acting cabotegravir and rilpivirine for the treatment and prevention of HIV

PURPOSE OF REVIEW

Cabotegravir (CAB) and rilpivirine (RPV) is the first long-acting injectable antiretroviral therapy (ART) option approved for virologically suppressed adults with HIV-1. In addition, long-acting CAB is a promising agent for HIV preexposure prophylaxis (PrEP). This review focuses on phase 3 clinical trial results and implementation considerations for these long-acting ART and PrEP strategies.

RECENT FINDINGS

Long-acting CAB and RPV administered every 4 weeks demonstrated noninferiority to oral ART through week 96 in both the ATLAS and FLAIR studies, whereas ATLAS-2M found similar efficacy through 96 weeks when the long-acting injectable ART was administered every 8 weeks instead of every 4 weeks. For prevention, two phase 3 trials were stopped early due to fewer incident HIV infections in participants receiving long-acting CAB every 8 weeks compared with daily oral tenofovir disoproxil fumarate-emtricitabine for PrEP. The long-acting therapies were well tolerated across all clinical trials.

SUMMARY

Clinical trial results support the use of long-acting CAB for HIV PrEP and long-acting CAB and RPV as a switch strategy for adults with HIV-1 who are first virologically suppressed with oral ART. Implementation challenges persist, and data are urgently needed in populations who may benefit most from long-acting therapy, including adolescents, pregnant individuals, and those with barriers to medication adherence.

Long-acting capsid inhibitor protects macaques from repeat SHIV challenges

Because no currently available vaccine can prevent HIV infection, pre-exposure prophylaxis (PrEP) with antiretrovirals (ARVs) is an important tool for combating the HIV pandemic1,2. Long-acting ARVs promise to build on the success of current PrEP strategies, which must be taken daily, by reducing the frequency of administration3. GS-CA1 is a small-molecule HIV capsid inhibitor with picomolar antiviral potency against a broad array of HIV strains, including variants resistant to existing ARVs, and has shown long-acting therapeutic potential in a mouse model of HIV infection4. Here we show that a single subcutaneous administration of GS-CA1 provides long-term protection against repeated rectal simian-human immunodeficiency virus (SHIV) challenges in rhesus macaques. Whereas all control animals became infected after 15 weekly challenges, a single 300 mg kg-1 dose of GS-CA1 provided per-exposure infection risk reduction of 97% for 24 weeks. Pharmacokinetic analysis showed a correlation between GS-CA1 plasma concentration and protection from SHIV challenges. GS-CA1 levels greater than twice the rhesus plasma protein-adjusted 95% effective concentration conferred 100% protection in this model. These proof-of-concept data support the development of capsid inhibitors as a novel long-acting PrEP strategy in humans.

A new engineering process of biodegradable polymeric solid implants for ultra-long-acting drug delivery

We present a long-acting (LA) biodegradable polymeric solid implant (PSI) fabricated using a new process combining in-situ phase inversion and compression. This robust process allows fabrication of solid implants that can have different shapes and sizes, accommodate high drug payloads, and provide sustained drug release over several months. Herein the integrase inhibitor dolutegravir (DTG) was used to develop PSIs for HIV prevention. PSIs were fabricated using a three-step process by (a) phase inversion of DTG-loaded polymer solution to form an initial in-situ forming implant in an aqueous solution, (b) micronization of dried DTG-loaded solid implants, and (c) compression of the micronized DTG-loaded solid implants to form the PSI. High drug loading (up to 85 wt%) was achieved in the PSIs. DTG exhibited minimum burst release in the first 24 h (<6%) and sustained release kinetics over 6 months. The release kinetics of DTG can be fine-tuned by varying drug-loading concentration, the ratio of polymer (poly(lactic-co-glycolic acid), PLGA) to solvent (N-methyl-2-pyrrolidone, NMP) and polymer (PLGA) molecular weight in the precursor solution. The physical/chemical properties of DTG were retained post-storage under accelerated storage conditions (40 °C/75% relative humidity) for 6 months. The versatility of this technology makes it an attractive drug delivery platform for HIV prevention applications.

Quantum Mechanical-Based Stability Evaluation of Crystal Structures for HIV-Targeted Drug Cabotegravir

The long-acting parenteral formulation of the HIV integrase inhibitor cabotegravir (GSK744) is currently being developed to prevent HIV infections, benefiting from infrequent dosing and high efficacy. The crystal structure can affect the bioavailability and efficacy of cabotegravir. However, the stability determination of crystal structures of GSK744 have remained a challenge. Here, we introduced an ab initio protocol to determine the stability of the crystal structures of pharmaceutical molecules, which were obtained from crystal structure prediction process starting from the molecular diagram. Using GSK744 as a case study, the ab initio predicted that Gibbs free energy provides reliable further refinement of the predicted crystal structures and presents its capability for becoming a crystal stability determination approach in the future. The proposed work can assist in the comprehensive screening of pharmaceutical design and can provide structural predictions and stability evaluation for pharmaceutical crystals.

Ethical issues in establishing the efficacy and safety of long-acting injectable pre-exposure prophylaxis for HIV prevention: the HPTN 083 trial

Two multinational clinical trials have shown safety and efficacy of long-acting injectable cabotegravir for HIV pre-exposure prophylaxis (PrEP). These results will alter the landscape of HIV prevention and related research. Nevertheless, designing and conducting this research involved several ethical issues. This Viewpoint describes how we managed ethical issues over the duration of one of these trials (HPTN 083). Specifically, we discuss the rationale for pursuing a long-acting injectable agent in the presence of effective oral PrEP, trial design choices, site selection and local standards of prevention, data monitoring and early stopping, effects of the COVID-19 pandemic, post-trial access, and assessment of long-term safety.

Cabotegravir for HIV Prevention in Cisgender Men and Transgender Women

BACKGROUND

Safe and effective long-acting injectable agents for preexposure prophylaxis (PrEP) for human immunodeficiency virus (HIV) infection are needed to increase the options for preventing HIV infection.

METHODS

We conducted a randomized, double-blind, double-dummy, noninferiority trial to compare long-acting injectable cabotegravir (CAB-LA, an integrase strand-transfer inhibitor [INSTI]) at a dose of 600 mg, given intramuscularly every 8 weeks, with daily oral tenofovir disoproxil fumarate-emtricitabine (TDF-FTC) for the prevention of HIV infection in at-risk cisgender men who have sex with men (MSM) and in at-risk transgender women who have sex with men. Participants were randomly assigned (1:1) to receive one of the two regimens and were followed for 153 weeks. HIV testing and safety evaluations were performed. The primary end point was incident HIV infection.

RESULTS

The intention-to-treat population included 4566 participants who underwent randomization; 570 (12.5%) identified as transgender women, and the median age was 26 years (interquartile range, 22 to 32). The trial was stopped early for efficacy on review of the results of the first preplanned interim end-point analysis. Among 1698 participants from the United States, 845 (49.8%) identified as Black. Incident HIV infection occurred in 52 participants: 13 in the cabotegravir group (incidence, 0.41 per 100 person-years) and 39 in the TDF-FTC group (incidence, 1.22 per 100 person-years) (hazard ratio, 0.34; 95% confidence interval, 0.18 to 0.62). The effect was consistent across prespecified subgroups. Injection-site reactions were reported in 81.4% of the participants in the cabotegravir group and in 31.3% of those in the TDF-FTC group. In the participants in whom HIV infection was diagnosed after exposure to CAB-LA, INSTI resistance and delays in the detection of HIV infection were noted. No safety concerns were identified.

CONCLUSIONS

CAB-LA was superior to daily oral TDF-FTC in preventing HIV infection among MSM and transgender women. Strategies are needed to prevent INSTI resistance in cases of CAB-LA PrEP failure. (Funded by the National Institute of Allergy and Infectious Diseases and others; HPTN 083 ClinicalTrials.gov number, NCT02720094.).

Multiparametric magnetic resonance imaging to characterize cabotegravir long-acting formulation depot kinetics in healthy adult volunteers

AIM

Cabotegravir long-acting (LA) intramuscular (IM) injection is being investigated for HIV preexposure prophylaxis due to its potent antiretroviral activity and infrequent dosing requirement. A subset of healthy adult volunteers participating in a Phase I study assessing cabotegravir tissue pharmacokinetics underwent serial magnetic resonance imaging (MRI) to assess drug depot localization and kinetics following a single cabotegravir LA IM targeted injection.

METHODS

Eight participants (four men, four women) were administered cabotegravir LA 600 mg under ultrasonographic-guided injection targeting the gluteal muscles. MRI was performed to determine injection-site location in gluteal muscle (IM), subcutaneous (SC) adipose tissue and combined IM/SC compartments, and to quantify drug depot characteristics, including volume and surface area, on Days 1 (≤2 hours postinjection), 3 and 8. Linear regression analysis examined correlations between MRI-derived parameters and plasma cabotegravir exposure metrics, including maximum observed concentration (C_max ) and partial area under the concentration-time curve (AUC) through Weeks 4 and 8.

RESULTS

Cabotegravir LA depot locations varied by participant and were identified in the IM compartment (n = 2), combined IM/SC compartments (n = 4), SC compartment (n = 1) and retroperitoneal cavity (n = 1). Although several MRI parameter and exposure metric correlations were determined, total depot surface area on Day 1 strongly correlated with plasma cabotegravir concentration at Days 3 and 8, C_max and partial AUC through Weeks 4 and 8.

CONCLUSION

MRI clearly delineated cabotegravir LA injection-site location and depot kinetics in healthy adults. Although injection-site variability was observed, drug depot surface area correlated with both plasma C_max and partial AUC independently of anatomical distribution.

Multicompartmental pharmacokinetic evaluation of long-acting cabotegravir in healthy adults for HIV preexposure prophylaxis

Aims

Cabotegravir is an integrase strand transfer inhibitor in clinical development as long‐acting (LA) injectable HIV preexposure prophylaxis.

Methods

This phase I study assessed pharmacokinetics of cabotegravir in plasma and anatomical sites associated with sexual HIV‐1 transmission after repeated oral and single intramuscular (IM) LA dosing in healthy adults. Following a 28‐day oral lead‐in period of cabotegravir 30 mg and a washout period of 14–42 days, participants were administered a single ultrasound‐guided gluteal IM cabotegravir LA 600‐mg injection. The study objective was to characterize cabotegravir concentrations in plasma, cervical, vaginal and rectal tissues, and cervicovaginal and rectal fluids and up to Week 12 after IM injection.

Results

Nineteen participants enrolled and 16 completed the study through Week 52. Cabotegravir was detected in plasma and all tissues and fluids. Median plasma cabotegravir concentrations exceeded the in vitro protein‐adjusted 90% maximal inhibitory concentration through Week 12. Median tissue‐ and fluid‐to‐plasma cabotegravir concentration ratios across all visits were 0.32 for rectal fluid and 0.08–0.16 for other tissues and fluids. Adjusted R² coefficients between cabotegravir concentrations in plasma and cervical, vaginal and rectal tissues were 0.78, 0.79 and 0.90, respectively. Injection‐site reactions were common (88% of participants) and were mostly grade 1 in intensity (82%). Two participants reported 11 non–drug‐related serious adverse events.

Conclusion

Concentrations of cabotegravir in tissues and fluids were proportional to plasma over time, with strong correlations between tissue and plasma concentrations. Cabotegravir LA tissue‐to‐plasma ratios may be important for understanding its use as preexposure prophylaxis.

Statistical approaches to accelerate the development of long-acting antiretrovirals for HIV pre-exposure prophylaxis

PURPOSE OF REVIEW

This review considers statistical issues in the design and analysis of the studies used to develop long-acting formulations of antiretrovirals for pre-exposure prophylaxis (PrEP).

RECENT FINDING

An abundant pipeline of products is maturing. Accelerating their evaluation as clinical products requires abandonment of noninferiority standards. Randomized trials should be based on the comparison of principled but innovative estimates of background HIV risk and enrich enrollment for those who do not desire current PrEP products. At every stage of testing, innovative analyses can be applied to help inform and accelerate later studies.

SUMMARY

The development of new long-acting PrEP regimens can be accelerated by innovations in design, ingenuity in synthesizing data sources, and application of causal inference methods.

Projected Impact of Concurrently Available Long-Acting Injectable and Daily-Oral Human Immunodeficiency Virus Preexposure Prophylaxis: A Mathematical Model

BACKGROUND

Long-acting injectable (LAI) human immunodeficiency virus (HIV) preexposure prophylaxis (PrEP) is reportedly efficacious, although full trial results have not been published. We used a dynamic network model of HIV transmission among men who have sex with men to assess the population impact of LAI-PrEP when available concurrently with daily-oral (DO) PrEP.

METHODS

The reference model represents the current HIV epidemiology and DO-PrEP coverage (15% among those with behavioral indications for PrEP) among men who have sex with men in the southeastern United States. Primary analyses investigated varied PrEP uptake and proportion selecting LAI-PrEP. Secondary analyses evaluated uncertainty in pharmacokinetic efficacy and LAI-PrEP persistence relative to DO-PrEP.

RESULTS

Compared with the reference scenario, if 50% chose LAI-PrEP, 4.3% (95% simulation interval, -7.3% to 14.5%) of infections would be averted over 10 years. The impact of LAI-PrEP is slightly greater than that of the DO-PrEP-only regimen, based on assumptions of higher adherence and partial protection after discontinuation. If the total PrEP initiation rate doubled, 17.1% (95% simulation interval, 6.7%-26.4%) of infections would be averted. The highest population-level impact occurred when LAI-PrEP uptake and persistence improved.

CONCLUSIONS

If LAI-PrEP replaces DO-PrEP, its availability will modestly improve the population impact. LAI-PrEP will make a more substantial impact if its availability drives higher total PrEP coverage, or if persistence is greater for LAI-PrEP.

Lipophilic nanocrystal prodrug-release defines the extended pharmacokinetic profiles of a year-long cabotegravir

A once every eight-week cabotegravir (CAB) long-acting parenteral is more effective than daily oral emtricitabine and tenofovir disoproxil fumarate in preventing human immunodeficiency virus type one (HIV-1) transmission. Extending CAB dosing to a yearly injectable advances efforts for the elimination of viral transmission. Here we report rigor, reproducibility and mechanistic insights for a year-long CAB injectable. Pharmacokinetic (PK) profiles of this nanoformulated CAB prodrug (NM2CAB) are affirmed at three independent research laboratories. PK profiles in mice and rats show plasma CAB levels at or above the protein-adjusted 90% inhibitory concentration for a year after a single dose. Sustained native and prodrug concentrations are at the muscle injection site and in lymphoid tissues. The results parallel NM2CAB uptake and retention in human macrophages. NM2CAB nanocrystals are stable in blood and tissue homogenates. The long apparent drug half-life follows pH-dependent prodrug hydrolysis upon slow prodrug nanocrystal dissolution and absorption. In contrast, solubilized prodrug is hydrolyzed in hours in plasma and tissues from multiple mammalian species. No toxicities are observed in animals. These results affirm the pharmacological properties and extended apparent half-life for a nanoformulated CAB prodrug. The report serves to support the mechanistic design for drug formulation safety, rigor and reproducibility.

Long-Acting Cabotegravir for HIV/AIDS Prophylaxis

The retrovirus HIV-1 is the etiological agent of the decades-long AIDS pandemic. Although vaccination is the most common preexposure route to prevent acquisition of viral disease, scalable efficacious vaccination strategies have yet to be developed for HIV-1. By contrast, small molecule inhibitors of the HIV-1 enzymes reverse transcriptase, integrase, and protease have been developed that effectively block virus replication. Three different drug compounds are commonly prescribed for people living with HIV as once-daily oral tablets. Once-daily pills composed of two different reverse transcriptase inhibitors are moreover approved as preexposure prophylaxis (PrEP) treatment for virus naïve individuals who may partake in behaviors associated with increased risk of HIV-1 acquisition such as unprotected sex or injection drug use. Long-acting (LA) injectable HIV-1 enzyme inhibitors are at the same time being developed to sidestep adherence noncompliance issues that can arise from self-administered once-daily oral dosing regimens. Cabotegravir (CAB)-LA, which inhibits integrase strand transfer activity, has in recent clinical trials been shown to prevent HIV-1 acquisition more effectively than once-daily oral dosed reverse transcriptase inhibitors. In this Perspective, we examine bench to bedside aspects of CAB-LA treatment and development, starting from the biochemical basis of HIV-1 integration and pharmacological inhibition of integrase catalysis. We also review the results of recent clinical trials that evaluated CAB-LA, as well as the promises and challenges that surround its use for HIV/AIDS PrEP.

Antiretroviral drug exposure in urethral and glans surface sampling of the penis

BACKGROUND

HIV exposure to penile tissues provides a risk of acquisition among men, yet studies evaluating penile antiretroviral (ARV) drug distribution have been lacking. We measured ARVs on urethral and glans surface swabs collected following a dose of tenofovir alafenamide, emtricitabine, elvitegravir, darunavir and cobicistat.

METHODS

Thirty-five HIV-negative male participants provided urethral swabs, glans swabs, rectal swabs, blood and urine up to 96 h following a single dose of tenofovir alafenamide/emtricitabine/elvitegravir/cobicistat and darunavir. ARVs were measured by liquid chromatography-mass spectrometry with a lower limit of detection (LOD) of 1 ng/swab for swabs and 10 ng/mL for plasma and urine. Concentrations are reported as median and range.

RESULTS

Urethral swab emtricitabine and darunavir concentrations peaked at 4 h for emtricitabine (36 ng/swab; 3-307 ng/swab) and 8 h for darunavir (25 ng/swab; 2-52 ng/swab). Glans swab emtricitabine and darunavir concentrations peaked 24 h after dosing (emtricitabine 14 ng/swab, <LOD-328 ng/swab; darunavir 6 ng/swab, <LOD-149 ng/swab). Estimated peak urethral secretion emtricitabine and darunavir concentrations are between 10 and 20 μg/mL, similar to rectal secretions, 4-fold greater than in plasma, but 2-fold lower than in urine. Tenofovir and elvitegravir were detected on less than 20% of urethral or glans swabs collected within 24 h of dosing.

CONCLUSIONS

We document ARV dosing in the urethra and on the glans surface with high drug concentrations noted for emtricitabine and darunavir and lower tenofovir and elvitegravir concentrations. Data suggest a potential protective role of urethral emtricitabine or darunavir against penile HIV acquisition.

Characterization of HIV infection in cisgender men and transgender women who have sex with men receiving injectable cabotegravir for HIV prevention: HPTN 083

INTRODUCTION

The HIV Prevention Trials Network (HPTN) 083 trial demonstrated that long-acting cabotegravir (CAB-LA) was more effective than tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) for HIV prevention in cisgender men and transgender women who have sex with men. We characterized HIV infections that occurred in the blinded phase of HPTN 083.

METHODS

Retrospective testing included HIV testing, viral load testing, quantification of study drugs and HIV drug resistance testing.

RESULTS

Fifty-eight infections were evaluated, including 51 incident infections (12 CAB, 39 TDF/FTC). In many cases (5 CAB, 37 TDF/FTC), infection was associated with low or unquantifiable study drug concentrations. In four cases, infection occurred with on-time CAB-LA injections and expected plasma CAB concentrations. CAB exposure was associated with prolonged viral suppression and delayed antibody expression. In some cases, delayed HIV diagnosis resulted in CAB provision to participants with undetected infection, delayed antiretroviral treatment (ART), and emergence of drug resistance; most of these infections would have been detected earlier with viral load testing.

CONCLUSIONS

Early detection of HIV infection and prompt ART initiation could improve clinical outcomes in persons who become infected despite CAB-LA prophylaxis. Further studies are needed to elucidate the correlates of HIV protection in persons receiving CAB-LA.

Once-Weekly Oral Dosing of MK-8591 Protects Male Rhesus Macaques From Intrarectal Challenge With SHIV109CP3

BACKGROUND

MK-8591 (4'-ethynyl-2-fluoro-2'-deoxyadenosine [EFdA]) is a novel reverse transcriptase-translocation inhibitor.

METHODS

We assessed MK-8591 as preexposure prophylaxis in the rhesus macaque model of intrarectal challenge with simian/human immunodeficiency virus (SHIV). In study 1, 8 rhesus macaques received 3.9 mg/kg of MK-8591 orally on day 0 and once weekly for the next 14 weeks. Eight controls were treated with vehicle. All rhesus macaques were challenged with SHIV109CP3 on day 6 and weekly for up to 12 challenges or until infection was confirmed. The dose of MK-8591 was reduced to 1.3 and 0.43 mg/kg/week in study 2 and further to 0.1 and 0.025 mg/kg/week in study 3. In studies 2 and 3, each dose was given up to 6 times once weekly, and animals were challenged 4 times once weekly with SHIV109CP3.

RESULTS

Control macaques were infected after a median of 1 challenge (range, 1-4 challenges). All treated animals in studies 1 and 2 were protected, consistent with a 41.5-fold lower risk of infection (P < .0001, by the log-rank test). In study 3, at a 0.1-mg/kg dose, 2 rhesus macaques became infected, consistent with a 7.2-fold lower risk of infection (P = .0003, by the log-rank test). The 0.025-mg/kg dose offered no protection.

CONCLUSIONS

These data support MK-8591's potential as a preexposure prophylaxis agent.

Identification of Novel UGT1A1 Variants Including UGT1A1 454C>A through the Genotyping of Healthy Participants of the HPTN 077 Study

Cabotegravir (CAB) is an integrase strand-transfer inhibitor of HIV that has proven effective for HIV treatment and prevention in a long-acting injectable formulation, typically preceded by an oral formulation lead-in phase. Previous in vitro studies have demonstrated that CAB is primarily metabolized via glucuronidation by uridine diphosphate glucuronosyltransferase (UGT) 1A1 and 1A9. In this study, we performed next-generation sequencing of genomic DNA isolated from the HPTN 077 participants to explore the variants within UGT1A1 and UGT1A9. Additionally, to enable correlation of UGT1A1 and UGT1A9 genotypes with plasma CAB-glucuronide levels, we quantified glucuronidated CAB following both oral administration of CAB and intramuscular injection of long-acting CAB. From these studies, 48 previously unreported variants of UGT1A1 and UGT1A9 were detected. Notably, 5/68 individuals carried a UGT1A1 454C>A variant that resulted in amino acid substitution P152T, and the use of in silico tools predicted a deleterious effect of the P152T substitution. Thus, the impact of this mutant on a range of UGT1A1 substrates was tested using a COS-7 cell-based assay. The glucuronide conjugates of CAB, dolutegravir, and raltegravir, were not formed in the COS-7 cells expressing the UGT1A1 P152T mutant. Further, formation of glucuronides of raloxifene and 7-ethyl-10-hydroxycamptothecin were reduced in the cells expressing the UGT1A1 P152T mutant. Using the same approach, we tested the activities of two UGT1A9 mutants, UGT1A9 H217Y and UGT1A9 R464G, and found that these mutations were tolerated and decreased function, respectively. These data provide insight into previously unreported genetic variants of UGT1A1 and UGT1A9.

Design and Testing of a Cabotegravir Implant for HIV Prevention

Long-acting antiretroviral implants could help protect high-risk individuals from HIV infection. We describe the design and testing of a long-acting reservoir subcutaneous implant capable of releasing cabotegravir for several months. We compressed cabotegravir and excipients into cylindrical pellets and heat-sealed them in tubing composed of hydrophilic poly(ether-urethane) -. The implants have a 47 mm lumen length, 3.6 mm outer diameter, and 200 μm wall thickness. Four cabotegravir pellets were sealed in the membrane, with a total drug loading of 274 ± 3 mg. In vivo, the implants released 348 ± 107 μg/day (median value per implant, N = 41) of cabotegravir in rhesus macaques. Five implants generated an average cabotegravir plasma concentration of 373 ng/ml in rhesus macaques. The non-human primates tolerated the implant without gross pathology or microscopic signs of histopathology compared to placebo implants. Cabotegravir plasma levels in macaques dropped below detectable levels within two weeks after the removal of the implants.

Single-tablet regimen of emtricitabine/tenofovir disoproxil fumarate plus cobicistat-boosted elvitegravir increase adherence for HIV postexposure prophylaxis in sexual assault victims

BACKGROUND

Postexposure prophylaxis (PEP) is a recommended public health intervention after a sexual assault to prevent HIV infection.

METHODS

We conducted a retrospective case-control study on how use of a single-tablet regimen (STR) of elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate (Stribild) affected adherence to PEP and attendance of a follow-up visit to the STI clinic compared with those who received a multitablet regimen (MTR). Data from sexual assault victims consulting for PEP were prospectively recorded between January 2011 and December 2017. Data were systematically collected on patient demographics, time of medical contact, source risk factors, type of exposure, attendance to follow-up visit, reported completion of PEP and adherence based on pharmacy records.

RESULTS

A total of 422 patients received PEP following a sexual assault, of whom 52% had documented completion of a 28-day PEP regimen and 71% attended a follow-up clinic visit. Patients who received an elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate (EVG/COBI/FTC/TDF)-based STR had a similar likelihood of attending their first follow-up visit (OR: 0.97; 95% CI: 0.64 to 1.48, p=0.90) but were more likely to complete the PEP regimen (OR: 1.70; 95% CI: 1.16 to 2.50, p=0.007). After adjusting for confounders, those who were prescribed an STR regimen were more likely to complete the PEP regimen (OR: 1.66, 95% CI: 1.09 to 2.53, p=0.019) than those who were prescribed an MTR such as stavudine/lamivudine/lopinavir/ritonavir or zidovudine/lamivudine/indinavir/ritonavir.

CONCLUSIONS

Sexual assault victims who were prescribed an STR based on EVG/COBI/FTC/TDF were more likely to complete PEP than those who were prescribed an MTR.

Quantifying the contribution of Fc-mediated effector functions to the antiviral activity of anti-HIV-1 IgG1 antibodies in vivo

Virus-neutralizing monoclonal antibodies have been tested for the treatment or prevention of HIV-1 infection. Such an antibody can block virus infectivity and mediate killing of virus-infected cells by Fc-mediated effector functions. The relative contributions of these two antibody activities in vivo have not been quantified previously. By quantitatively analyzing results from experiments conducted in HIV-1–infected humanized mice and SHIV-infected rhesus macaques, we have determined that Fc-mediated effector functions contribute about 25–45% to the total antiviral activity of the anti–HIV-1 monoclonal antibodies tested.

In combating viral infections, the Fab portion of an antibody could mediate virus neutralization, whereas Fc engagement of Fc-γ receptors (FcγRs) could mediate an array of effector functions. Evidence abounds that effector functions are important in controlling infections by influenza, Ebola, or HIV-1 in animal models. However, the relative contribution of virus neutralization versus effector functions to the overall antiviral activity of an antibody remains unknown. To address this fundamental question in immunology, we utilized our knowledge of HIV-1 dynamics to compare the kinetics of the viral load decline (ΔVL) in infected animals given a wild-type (WT) anti–HIV-1 immunoglobulin G1 (IgG1) versus those given a Fc-Null variant of the same antibody. In three independent experiments in HIV-1–infected humanized mice and one pivotal experiment in simian–human immunodeficiency virus (SHIV)-infected rhesus macaques, an earlier and sharper decline in viral load was consistently detected for the WT antibody. Quantifications of the observed differences indicate that Fc-mediated effector functions accounted for 25–45% of the total antiviral activity in these separate experiments. In this study, Fc-mediated effector functions have been quantified in vivo relative to the contribution of virus neutralization mediated by the Fab.

Tail-phase safety, tolerability, and pharmacokinetics of long-acting injectable cabotegravir in HIV-uninfected adults: a secondary analysis of the HPTN 077 trial

BACKGROUND

Long-acting injectable cabotegravir is a novel integrase inhibitor currently in advanced clinical development for HIV prevention and treatment. We aimed to assess the terminal phase pharmacokinetics and safety of long-acting injectable cabotegravir in participants included in the HPTN 077 trial.

METHODS

HPTN 077 was a multicentre, double-blind, randomised, placebo-controlled phase 2a trial done at eight sites in Brazil, Malawi, South Africa, and the USA. Participants (aged 18-65 years), who were HIV-uninfected and at low-risk for HIV, were randomly assigned (3:1) to long-acting injectable cabotegravir (800 mg given three times at 12 week intervals or 600 mg given five times, administered at one 4 week interval, and every 8 weeks thereafter) or placebo. Participants were followed up to 76 weeks after final injection. In a prespecified analysis of secondary and exploratory outcomes, we assessed the safety, measured by the proportion of participants with grade 2 or worse adverse events, and pharmacokinetics, measured by apparent terminal phase half-life (t_1/2app) and estimated time to lower limit of quantification (LLOQ) of long-acting injectable cabotegravir during the injection phase (defined as the time between first injection and 12 weeks or 8 weeks after the last injection in cohort 1 or cohort 2 respectively) and tail phase (defined as the time between final injection and 52-76 weeks post-final injection). Safety was analysed in all participants who received at least one injection. Pharmacokinetic analyses included all participants who had received at least one injection and had at least three cabotegravir measurements higher than the LLOQ after the final injection. Pharmacokinetic outcomes were estimated using non-compartmental methods. The trial is completed, and was registered with ClinicalTrials.gov, NCT02178800.

FINDINGS

Between Feb 9, 2015, and May 27, 2016, 177 participants (134 participants in the cabotegravir group [74 participants in cohort 1; 60 participants in cohort 2] and 43 participants in the placebo group [25 participants in cohort 1; 18 participants in cohort 2) were enrolled and received at least one injection and thus were included in the safety analysis. The incidence of grade 2 or worse adverse events was significantly lower during the tail phase than the injection phase (p<0·0001). At 52-60 weeks after final injection, nine (23%) of 40 male participants had detectable cabotegravir concentrations and at week 76, four (13%) of 30 male participants had detectable cabotegravir concentrations compared with 52 (63%) of 82 female participants and 27 (42%) of 64 female participants at the same timepoints. The median time from the last injection to the time when cabotegravir concentration decreased below the LLOQ was 43·7 weeks (IQR 31·1-66·6; range 20·4-152·5) for male participants and 67·3 weeks (29·1-89·6; 17·7-225·5) for female participants (p=0·0003). t_1/2app was longer for female participants than male participants (geometric mean fold-change 1·33, 95% CI 1·06-1·68; p=0·014), and longer for participants with a high body-mass index (BMI) than those with a low BMI (1·31, 1·06-1·63; p=0·015).

INTERPRETATION

The clinical significance of the long pharmacokinetic tail of cabotegravir observed in female participants compared with male participants, and those with higher BMI compared with a lower BMI, need to be addressed in future trials.

FUNDING

National Institute of Allergy and Infectious Diseases.

Long-Acting Cabotegravir Protects Macaques Against Repeated Penile Simian-Human Immunodeficiency Virus Exposures

We used a novel penile simian-human immunodeficiency virus (SHIV) transmission model to investigate whether long-acting cabotegravir (CAB LA) prevents penile SHIV acquisition in macaques. Twenty-two macaques were exposed to SHIV via the foreskin and urethra once weekly for 12 weeks. Of these, 6 received human-equivalent doses of CAB LA, 6 received oral emtricitabine/tenofovir disoproxil fumarate, and 10 were untreated. The efficacy of CAB LA was high (94.4%; 95% confidence interval, 58.2%–99.3%) and similar to that seen with oral emtricitabine/tenofovir disoproxil fumarate (94.0%; 55.1%–99.2%). The high efficacy of CAB LA in the penile transmission model supports extending the clinical advancement of CAB LA preexposure prophylaxis to heterosexual men.

Long-acting injectable cabotegravir for the prevention of HIV infection

PURPOSE OF REVIEW

This review highlights the development of long-acting injectable cabotegravir (CAB LA) for HIV preexposure prophylaxis (PrEP), with a focus on phase 2 studies and later development.

RECENT FINDINGS

Early studies of CAB LA for HIV prevention offered promising pharmacokinetic data and paved the way for phase 2 studies, which have now been completed. On the basis of phase 2 data, dosing of CAB LA at 8-week intervals consistently delivers target trough concentrations in both men and women. Recent studies have shown no required dose adjustments for hepatic or renal disease and minimal drug--drug interactions. Additionally, injectable PrEP is desired by potential PrEP candidates. Still, gaps in knowledge remain with respect to implementation and delivery, the clinical significance of the pharmacologic tail, and dosing in key populations. Phase 3 trials are underway that are anticipated to inform some of these questions and provide efficacy and safety data to support regulatory submissions for CAB LA as a potential PrEP agent.

SUMMARY

Recent studies have defined an appropriate CAB LA dosing interval and offered insight into its safety profile. Phase 3 studies will provide much-anticipated efficacy data. If efficacious, CAB LA may provide a desirable PrEP option for those who face challenges to daily pill adherence. A more complete understanding of how to best integrate LA PrEP into service delivery models will be critical for success.

Epidemiological impact and cost-effectiveness of providing long-acting pre-exposure prophylaxis to injectable contraceptive users for HIV prevention in South Africa: a modelling study

INTRODUCTION

Although pre-exposure prophylaxis (PrEP.) is an efficacious HIV prevention strategy, its preventive benefit has not been shown among young women in sub-Saharan Africa, likely due to non-adherence. Adherence may be improved with the use of injectable long-acting PrEP methods currently being developed. We hypothesize that providing long-acting PrEP to women using injectable contraceptives, the most frequently used contraceptive method in South Africa, could improve adherence to PrEP, result in a reduction of new HIV infections, and be a relatively easy-to-reach target population. In this modelling study, we assessed the epidemiological impact and cost-effectiveness of providing long-acting PrEP to injectable contraceptive users in Limpopo, South Africa.

METHODS

We developed a deterministic mathematical model calibrated to the HIV epidemic in Limpopo. Long-acting PrEP was provided to 50% of HIV negative injectable contraceptive users in 2018 and scaled-up over two years. We estimated the number of HIV infections that could be averted by 2030 and the drug price of long-acting PrEP for which this intervention would be cost-effective over a time horizon of 40 years, from a healthcare payer perspective. In the base-case scenario we assumed long-acting PrEP is 75% effective in preventing HIV infections and 85% of infected individuals are on antiretroviral drug therapy (ART) by 2030. In sensitivity analyses we adjusted PrEP effectiveness and ART coverage. Costs between $519 and $1119 per disability-adjusted life-year (DALY) averted were considered potentially cost-effective, and <$519 as cost-effective.

RESULTS

Without long-acting injectable PrEP, 224,000 (interquartile range 176,000 to 271,000) new infections will occur by 2030; use of long-acting injectable PrEP could prevent 21,000 (17,000 to 26,000) or 9.8% (8.9% to 10.6%) new HIV infections by 2030 (including 6000 (4000 to 7000) in men). Long-acting PrEP would prevent 34,000 (29,000 to 39,000) or 12,000 (8000 to 15,000) at 75% and 95% ART coverage by 2030 respectively. To be considered potentially cost-effective the annual long-acting PrEP drug price should be <$16, and/or ART coverage remains at <85% in 2030.

CONCLUSIONS

Providing long-acting PrEP to injectable contraceptive users in Limpopo is only potentially cost-effective when long-acting PrEP drug prices are low. If low prices are not feasible, providing long-acting PrEP only to women at high risk of HIV infection will become important.

Pharmacokinetics and Pharmacodynamics of Cabotegravir, a Long-Acting HIV Integrase Strand Transfer Inhibitor

Available antiretroviral drugs have demonstrated effectiveness in both pre-exposure prophylaxis and treatment of HIV infection. However, some concerns still persist regarding these therapies, mainly related to patient adherence, drug toxicity and dosing convenience. Cabotegravir is a potent integrase strand transfer inhibitor with a chemical structure similar to dolutegravir that is under clinical evaluation both as oral and long-acting injectable (LAI) formulations for both the prevention or treatment of HIV infection. Indeed, preclinical and clinical studies have consistently shown that LAI cabotegravir is readily absorbed following intramuscular and subcutaneous administration, with an elimination half-life of approximately 40 days, permitting infrequent dosing, possibly once every 1 or 2 months (eventually combined with rilpivirine). Here, we reviewed the existing literature on the preclinical and clinical pharmacokinetics and pharmacodynamics of LAI cabotegravir, with emphasis on the actual pharmacokinetic challenges of this novel formulation, as well as its potential to act as a victim or perpetrator of drug-drug interactions.

Multifaceted HIV integrase functionalities and therapeutic strategies for their inhibition

Antiretroviral inhibitors that are used to manage HIV infection/AIDS predominantly target three enzymes required for virus replication: reverse transcriptase, protease, and integrase. Although integrase inhibitors were the last among this group to be approved for treating people living with HIV, they have since risen to the forefront of treatment options. Integrase strand transfer inhibitors (INSTIs) are now recommended components of frontline and drug-switch antiretroviral therapy formulations. Integrase catalyzes two successive magnesium-dependent polynucleotidyl transferase reactions, 3' processing and strand transfer, and INSTIs tightly bind the divalent metal ions and viral DNA end after 3' processing, displacing from the integrase active site the DNA 3'-hydroxyl group that is required for strand transfer activity. Although second-generation INSTIs present higher barriers to the development of viral drug resistance than first-generation compounds, the mechanisms underlying these superior barrier profiles are incompletely understood. A separate class of HIV-1 integrase inhibitors, the allosteric integrase inhibitors (ALLINIs), engage integrase distal from the enzyme active site, namely at the binding site for the cellular cofactor lens epithelium-derived growth factor (LEDGF)/p75 that helps to guide integration into host genes. ALLINIs inhibit HIV-1 replication by inducing integrase hypermultimerization, which precludes integrase binding to genomic RNA and perturbs the morphogenesis of new viral particles. Although not yet approved for human use, ALLINIs provide important probes that can be used to investigate the link between HIV-1 integrase and viral particle morphogenesis. Herein, I review the mechanisms of retroviral integration as well as the promises and challenges of using integrase inhibitors for HIV/AIDS management.

Synthesis of a long acting nanoformulated emtricitabine ProTide

While antiretroviral therapy (ART) has revolutionized treatment and prevention of human immunodeficiency virus type one (HIV-1) infection, regimen adherence, viral mutations, drug toxicities and access stigma and fatigue are treatment limitations. These have led to new opportunities for the development of long acting (LA) ART including implantable devices and chemical drug modifications. Herein, medicinal and formulation chemistry were used to develop LA prodrug nanoformulations of emtricitabine (FTC). A potent lipophilic FTC phosphoramidate prodrug (M2FTC) was synthesized then encapsulated into a poloxamer surfactant (NM2FTC). These modifications extended the biology, apparent drug half-life and antiretroviral activities of the formulations. NM2FTC demonstrated a >30-fold increase in macrophage and CD4+ T cell drug uptake with efficient conversion to triphosphates (FTC-TP). Intracellular FTC-TP protected macrophages against an HIV-1 challenge for 30 days. A single intramuscular injection of NM2FTC, at 45 mg/kg native drug equivalents, into Sprague Dawley rats resulted in sustained prodrug levels in blood, liver, spleen and lymph nodes and FTC-TP in lymph node and spleen cells at one month. In contrast, native FTC-TPs was present for one day. These results are an advance in the transformation of FTC into a LA agent.