Tenofovir diphosphate concentrations and prophylactic effect in a macaque model of rectal simian HIV transmission

Drug Metabolism and Transport Capacity of Endothelial Cells, Pericytes, and Astrocytes: Implications for CNS Drug Disposition

Therapeutically targeting the brain requires interactions with endothelial cells, pericytes, and astrocytes at the blood brain barrier (BBB). We evaluated regional and cell-type specific drug metabolism and transport mechanisms using rhesus macaques and in vitro treatment of primary human cells. Here, we report heterogenous distribution of representative drugs, tenofovir (TFV), emtricitabine (FTC), and their active metabolites, which cerebrospinal fluid measures could not reflect. We found that all BBB cell types possessed functional drug metabolizing enzymes and transporters that promoted TFV and FTC uptake and pharmacologic activation. Pericytes and astrocytes emerged as pharmacologically dynamic cells that rivaled hepatocytes and were uniquely susceptible to modulation by disease and treatment. Together, our findings demonstrate the importance of considering the BBB as a unique pharmacologic entity, rather than viewing it as an extension of the liver, as each cell type possesses distinct drug metabolism and transport capacities that contribute to differential brain drug disposition.

Ex-vivo rectal tissue infection with HIV-1 to assess time to protection following oral preexposure prophylaxis with tenofovir disoproxil/emtricitabine

OBJECTIVES

We wished to assess time to protection from HIV-1 infection following oral tenofovir disoproxil and emtricitabine (TDF/FTC) as preexposure prophylaxis (PrEP), using ex-vivo rectal tissue infections and drug concentration measures in blood and rectal tissue.

DESIGN/METHODS

Participants from the ANRS PREVENIR study (NCT03113123) were offered this sub-study after a 14-day wash-out. We used an ex-vivo model to evaluate rectal tissue HIV-1 susceptibility before and after PrEP, 2 h after two pills or 7 days of a daily pill of TDF/FTC. PrEP efficacy was expressed by the difference (after-before) of 14-day cumulative p24 antigen levels. TFV-DP and FTC-TP levels were measured in rectal tissue and PBMCs and correlated with HIV-1 infection.

RESULTS

Twelve and 11 men were analyzed in the 2 h-double dose and 7 days-single dose groups, respectively. Cumulative p24 differences after-before PrEP were -144 pg/ml/mg (IQR[-259;-108]) for the 2 h-double dose group ( P  = 0.0005) and -179 pg/ml/mg (IQR [-253;-86]) for the 7 days-single dose group ( P  = 0.001), with no differences between groups ( P  = 0.93). Rectal TFV-DP was below quantification after a double dose, but FTC-TP levels were similar to levels at 7 days. There was a significant correlation between rectal FTC-TP levels and p24 changes after a double dose ( R  = -0.84; P  = 0.0001).

CONCLUSION

Oral TDF/FTC provided similar protection against HIV-1 infection of rectal tissue 2 h after a double dose or 7 days of a daily dose. At 2 h, this protection seems driven by high FTC-TP concentrations in rectal tissue. This confirms the importance of combining TDF and FTC to achieve early protection.

Nucleoside Triphosphate Diphosphohydrolase 1 Exhibits Enzymatic Activity toward Tenofovir Diphosphate

Tenofovir (TFV; prescribed as TFV disoproxil fumarate and TFV alafenamide prodrugs) is currently used for HIV prevention and treatment. TFV must be phosphorylated twice into TFV-diphosphate (TFV-DP) to become pharmacologically active. Previously, we reported heterogeneity in TFV-DP distribution in colorectal tissue (a putative site of HIV infection) sections collected from research participants receiving a TFV-containing enema. This observed heterogeneity is likely multifactorial. Of note, TFV-DP is structurally similar to ATP. It is known that nucleotidases such as nucleoside triphosphate diphosphohydrolases (NTPDases) dephosphorylate ATP. Thus, it was hypothesized that NTPDase-mediated dephosphorylation plays a role in regulating TFV-DP levels in colorectal tissue. To test this hypothesis, recombinant NTPDase proteins (NTPDase 1, 3, 4, 5, 6, and 8) were incubated, individually, with TFV-DP to determine their abilities to dephosphorylate TFV-DP in vitro. Following incubations, TFV-DP dephosphorylation was determined using both malachite green phosphate assays and ultrahigh-performance liquid chromatography tandem mass spectrometry. From these, NTPDase 1 exhibited the highest activity toward TFV-DP. Further, enzyme kinetic analysis revealed Michaelis-Menten kinetics for NTPDase 1-mediated TFV-DP dephosphorylation. Next, immunoblot analyses were conducted to confirm the expression of NTPDase 1 protein in human colorectal tissue. Liquid chromatography coupled to mass spectrometry proteomics analysis was used to measure the relative abundance of NTPDases in human colorectal tissue among healthy adult individuals (n = 4). These analyses confirmed the high abundance of NTPDase 1 in human colorectal tissue. Taken together, results suggest that NTPDase 1 may contribute to the regulation of TFV-DP levels. The above data provide important insights into the dephosphorylation of TFV-DP. SIGNIFICANCE STATEMENT: Nucleoside triphosphate diphosphohydrolases (NTPDases) that are involved in enzymatic ATP dephosphorylation may contribute to tenofovir-diphosphate (TFV-DP) dephosphorylation, leading to its inactivation. In this study, the NTPDases responsible for TFV-DP dephosphorylation in vitro and their expression in human colorectal tissue were investigated. Through this work, it was demonstrated that NTPDase 1 has the highest activity toward TFV-DP dephosphorylation, and it was abundant in human colorectal tissue. Importantly, these studies will increase our understanding of TFV-DP disposition.

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.

Islatravir for the treatment and prevention of infection with the human immunodeficiency virus type 1

PURPOSE OF REVIEW

To discuss the potential role of islatravir (ISL), a novel reverse transcriptase translocation inhibitor, in the treatment and prevention of human immunodeficiency virus type 1 (HIV-1) infection.

RECENT FINDINGS

Islatravir (4'-ethynyl-2-fluoro-2'-deoxyadenosine, MK-8591) is a long-acting first-in-class nucleoside reverse transcriptase translocation inhibitor with the potential for versatile dosing routes and dosing intervals. It demonstrated robust antiviral activity when dosed once daily and once weekly in HIV-1-infected individuals and SIV-infected rhesus macaques. In clinical trials of ISL in combination with doravirine and lamivudine, daily oral administration resulted in high levels of virologic suppression in HIV-infected individuals. In preclinical studies, ISL dosed orally once-weekly as preexposure prophylaxis (PrEP), protected rhesus macaques against SHIV infection via the mucosal route in the low-dose rectal challenge model. Most recently, data in healthy HIV-1-uninfected individuals demonstrated the feasibility of formulating of ISL as an implant. In these studies, levels of intracellular ISL-triphosphate were consistent with the potential for a once-yearly implantable administration of ISL as PrEP.

SUMMARY

Islatravir is a promising new agent for both the treatment and prevention of HIV-1 infection.

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.

The Pre-clinical Toolbox of Pharmacokinetics and Pharmacodynamics: in vitro and ex vivo Models

Prevention strategies against sexual transmission of human immunodeficiency virus (HIV) are essential to curb the rate of new infections. In the absence of a correlate of protection against HIV infection, pre-clinical evaluation is fundamental to facilitate and accelerate prioritization of prevention candidates and their formulations in a rapidly evolving clinical landscape. Characterization of pharmacokinetic (PK) and pharmacodynamic (PD) properties for candidate inhibitors is the main objective of pre-clinical evaluation. in vitro and ex vivo systems for pharmacological assessment allow experimental flexibility and adaptability at a relatively low cost without raising as significant ethical concerns as in vivo models. Applications and limitations of pre-clinical PK/PD models and future alternatives are reviewed in the context of HIV prevention.

Nanoencapsulation introduces long-acting phenomenon to tenofovir alafenamide and emtricitabine drug combination: A comparative pre-exposure prophylaxis efficacy study against HIV-1 vaginal transmission

Daily oral antiretroviral (ARV) drugs for pre-exposure prophylaxis (PrEP) has proven efficacy for diverse groups of high-risk individuals. However, daily dosing regimen has augmented non-adherence. These experiments comparatively investigated the long-acting (LA) PrEP potency of subcutaneous (SubQ) administrated tenofovir alafenamide (TAF) and emtricitabine (FTC) loaded nanoparticles (NPs) to solution in humanized (hu) mice. TAF + FTC NPs and TAF + FTC solution (each drug at 200 mg/kg) were administered to hu-CD34-NSG mice (n = 3/time point) for plasma and tissue pharmacokinetic parameter estimation using LC-MS/MS. NP enhanced tissue ARV assimilation compared to plasma. The same dose was administered for PrEP efficacy in HIV-1 challenged hu-BLT mice (n = 5/group). The hu-BLT mice were vaginally challenged with a transmission-founder (T/F) virus at 5 × 10⁵ TCID₅₀ inoculation, on day 4, 7 and 14 post-SubQ treatments (PT) and were compared to infected-untreated-control hu-BLT mice. By 21 days PT, 100% TAF + FTC solution-treated and control-untreated mice were infected. However, TAF + FTC NPs resulted in significant (p = .0002) protection from HIV-1 (day 4: 80%, day 7 and 14: 60%, respectively) compared to control mice. This proof-of-concept study demonstrated detectable TAF/FTC vaginal levels among TAF + FTC NP-treated hu-BLT mice correlating with prolonged PrEP efficacy, thus establishing long-acting TAF + FTC NPs as a potential PrEP modality.

Transcutaneously refillable nanofluidic implant achieves sustained level of tenofovir diphosphate for HIV pre-exposure prophylaxis

Pre-exposure prophylaxis (PrEP) with antiretroviral (ARV) drugs are effective at preventing human immunodeficiency virus (HIV) transmission. However, implementation of PrEP presents significant challenges due to poor user adherence, low accessibility to ARVs and multiple routes of HIV exposure. To address these challenges, we developed the nanochannel delivery implant (NDI), a subcutaneously implantable device for sustained and constant delivery of tenofovir alafenamide (TAF) and emtricitabine (FTC) for HIV PrEP. Unlike existing drug delivery platforms with finite depots, the NDI incorporates ports allowing for transcutaneous refilling upon drug exhaustion. NDI-mediated drug delivery in rhesus macaques resulted in sustained release of both TAF and FTC for 83 days, as indicated by concentrations of TAF, FTC and their respectively metabolites in plasma, PBMCs, rectal mononuclear cells and tissues associated with HIV transmission. Notably, clinically relevant preventative levels of tenofovir diphosphate were achieved as early as 3 days after NDI implantation. We also demonstrated the feasibility of transcutaneous drug refilling to extend the duration of PrEP drug delivery in NHPs. Overall, the NDI represents an innovative strategy for long-term HIV PrEP administration in both developed and developing countries.

The averted infections ratio: a novel measure of effectiveness of experimental HIV pre-exposure prophylaxis agents

Tenofovir disoproxil fumarate combined with emtricitabine is a highly effective oral pre-exposure prophylaxis (PrEP) agent for preventing the acquisition of HIV. This effectiveness has consequences for the design and analysis of trials assessing experimental PrEP regimens, which now generally include an active-control tenofovir disoproxil fumarate plus emtricitabine group, rather than a placebo group, as a comparator. Herein, we describe major problems in the interpretation of the primary measure of effectiveness proposed for these trials, namely the ratio of HIV incidence in the experimental agent group to that in the active-control group. We argue that valid interpretation requires an assumption about one of two parameters: either the incidence among trial participants had they not received PrEP or the effectiveness of tenofovir disoproxil fumarate plus emtricitabine within the trial. However, neither parameter is directly observed because of the absence of a no-treatment group, thus requiring the use of external evidence or subjective judgment. We propose an alternative measure of effectiveness based on the concept of averted infections, which incorporates one of these parameters. The measure is simple to interpret, has clinical and public health relevance, and is a natural preservation-of-effect criterion for assessing statistical non-inferiority. Its adoption could also allow the use of smaller sample sizes, currently a major barrier to the assessment of experimental PrEP regimens.

Comparison of tenofovir plasma and tissue exposure using a population pharmacokinetic model and bootstrap: a simulation study from observed data

Sparse tissue sampling with intensive plasma sampling creates a unique data analysis problem in determining drug exposure in clinically relevant tissues. Tissue exposure may govern drug efficacy, as many drugs exert their actions in tissues. We compared tissue area-under-the-curve (AUC) generated from bootstrapped noncompartmental analysis (NCA) methods and compartmental nonlinear mixed effect (NLME) modeling. A model of observed data after single-dose tenofovir disoproxil fumarate was used to simulate plasma and tissue concentrations for two destructive tissue sampling schemes. Two groups of 100 data sets with densely-sampled plasma and one tissue sample per individual were created. The bootstrapped NCA (SAS 9.3) used a trapezoidal method to calculate geometric mean tissue AUC per dataset. For NLME, individual post hoc estimates of tissue AUC were determined, and the geometric mean from each dataset calculated. Median normalized prediction error (NPE) and absolute normalized prediction error (ANPE) were calculated for each method from the true values of the modeled concentrations. Both methods produced similar tissue AUC estimates close to true values. Although the NLME-generated AUC estimates had larger NPEs, it had smaller ANPEs. Overall, NLME NPEs showed AUC under-prediction but improved precision and fewer outliers. The bootstrapped NCA method produced more accurate estimates but with some NPEs > 100%. In general, NLME is preferred, as it accommodates less intensive tissue sampling with reasonable results, and provides simulation capabilities for optimizing tissue distribution. However, if the main goal is an accurate AUC for the studied scenario, and relatively intense tissue sampling is feasible, the NCA bootstrap method is a reasonable, and potentially less time-intensive solution.

Antiretroviral Drug Activity in Macaques Infected during Pre-Exposure Prophylaxis Has a Transient Effect on Cell-Associated SHIV DNA Reservoirs

Background

Pre-exposure prophylaxis (PrEP) with emtricitabine and tenofovir disoproxil fumarate (FTC/TDF) is a novel HIV prevention strategy. Suboptimal PrEP adherence and HIV infection creates an opportunity for continued antiretroviral drug activity during undiagnosed infection. We previously showed that macaques infected with SHIV during PrEP with FTC/TDF display reduced acute plasma viremias and limited virus diversity. We investigated the effect of PrEP on acute SHIV DNA dynamics and on the size of the persistent virus reservoir in lymphoid tissues.

Design

Cell-associated SHIV DNA levels in PBMCs were measured in 8 macaques infected during PrEP with FTC/TDF or single-agent TAF and was compared to those seen in untreated infections (n = 10). PrEP breakthrough infections continued treatment with 1–2 weekly drug doses to model suboptimal drug exposure during undiagnosed HIV infection in humans. SHIV DNA was also measured in lymphoid tissues collected from FTC/TDF PrEP breakthroughs after 1 year of infection.

Results

Compared to untreated controls, PrEP infections had reduced plasma RNA viremias both at peak and throughout weeks 1–12 (p<0.005). SHIV DNA levels were also reduced at peak and during the first 12 weeks of infection (p<0.043) but not throughout weeks 12–20. At 1 year, SHIV DNA reservoirs in lymphoid tissues were similar in size among macaques that received PrEP or placebo.

Conclusions

Antiviral drug activity due to PrEP limits acute SHIV replication but has only a transient effect on cell-associated SHIV DNA levels. Our model suggests that suboptimal drug exposure in persons that are taking PrEP and become infected with HIV may not be sufficient to reduce the pool of HIV-infected cells, and that treatment intensification may be needed to sustain potential virological benefits from the PrEP regimen.

Pre-exposure prophylaxis: a useful tool to prevent human immunodeficiency virus infection?

The aim of preventive measures against human immunodeficiency virus (HIV) is to reduce the incidence of HIV infection in the general population and in high-risk groups, such as men having sex with men (MSM), and to reduce the risk that a given individual will contract or spread the virus. Male and female condoms, post-exposure prophylaxis and circumcision are preventive methods currently recognized or promoted worldwide. Although modest success has been reported in a phase-III vaccine trial, other methods are being evaluated, such as vaginal and rectal microbicides, and pre-exposure prophylaxis (PrEP). Herein, we discuss results from prevention trials, especially those focusing on PrEP and particularly on recent results from 'on-demand' PrEP regimens. The efficacy of PrEP (rates of 0%-86%) is strongly correlated with adherence and plasma concentrations of antiretrovirals. Adverse events are rare. Selection of emtricitabine-resistant strains is mainly reported in individuals with an undiagnosed HIV infection using PrEP. PrEP is now strongly recommended in WHO prevention programmes for individuals at substantial risk for HIV with a view to controlling this epidemic by 2030.

Topical Delivery of Tenofovir Disoproxil Fumarate and Emtricitabine from Pod-Intravaginal Rings Protects Macaques from Multiple SHIV Exposures

Topical preexposure prophylaxis (PrEP) against HIV has been marginally successful in recent clinical trials with low adherence rates being a primary factor for failure. Controlled, sustained release of antiretroviral (ARV) drugs may help overcome these low adherence rates if the product is protective for extended periods of time. The oral combination of tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) is currently the only FDA-approved ARV drug for HIV PrEP. A novel pod-intravaginal ring (IVR) delivering TDF and FTC at independently controlled rates was evaluated for efficacy at preventing SHIV162p3 infection in a rigorous, repeat low-dose vaginal exposure model using normally cycling female pigtailed macaques. Six macaques received pod-IVRs containing TDF (65 mg) and FTC (68 mg) every two weeks, and weekly vaginal exposures to 50 TCID₅₀ of SHIV162p3 began one week after the first pod-IVR insertion. All pod-IVR-treated macaques were fully protected throughout the study (P = 0.0002, Log-rank test), whereas all control animals became infected with a median of 4 exposures to infection. The topical, sustained release of TDF and FTC from the pod-IVR maintained protective drug levels in macaques over four months of virus exposures. This novel and versatile delivery system has the capacity to deliver and maintain protective levels of multiple drugs and the protection observed here warrants clinical evaluation of this pod-IVR design.

Resistance and cross-resistance profile of the diaryltriazine NNRTI and candidate microbicide UAMC01398

OBJECTIVES

The resistance development, cross-resistance to other NNRTIs and the impact of resistance on viral replicative fitness were studied for the new and potent NNRTI UAMC01398.

METHODS

Resistance was selected by dose escalation and by single high-dose selection against a comprehensive panel of NNRTIs used as therapeutics and NNRTIs under investigation for pre-exposure prophylaxis of sexual HIV transmission. A panel of 27 site-directed mutants with single mutations or combinations of mutations involved in reverse transcriptase (RT) inhibitor-mediated resistance was developed and used to confirm resistance to UAMC01398. Cross-resistance to other NNRTIs was assessed, as well as susceptibility of UAMC01398-resistant HIV to diarylpyrimidine-resistant viruses. Finally, the impact of UAMC01398 resistance on HIV replicative fitness was studied.

RESULTS

We showed that UAMC01398 has potent activity against dapivirine-resistant HIV, that at least four mutations in the RT are required in concert for resistance and that the resistance profile is similar to rilpivirine, both genotypically and phenotypically. Resistance development to UAMC01398 is associated with a severe fitness cost.

CONCLUSIONS

These data, together with the enhanced safety profile and good solubility in aqueous gels, make UAMC01398 an excellent candidate for HIV topical prevention.

Assessment of penile erection methods in rhesus macaques to model pharmacokinetics of antiretroviral drugs and penile infection with simian immunodeficiency virus

BACKGROUND

An established macaque model to assess HIV interventions against penile transmission is currently not available. Physiological changes during penile erections may affect susceptibility to infection and drug pharmacokinetics (PK). Here, we identify methods to establish erections in macaques to evaluate penile transmission, PK, and efficacy under physiologic conditions.

METHODS

Penile rigidity and length were evaluated in eight rhesus macaques following rectal electrostimulation (RES), vibratory stimulation (VS), or pharmacological treatment with Sildenafil Citrate (Viagra) or Alprostadil.

RESULTS

Rectal electrostimulation treatment increased penile rigidity (>82%) and length (2.5 ± 0.58 cm), albeit the response was transient. In contrast, VS alone or coupled with Viagra or Alprostadil failed to elicit an erection response.

CONCLUSION

Rectal electrostimulation treatment elicits transient but consistent penile erections in macaques. High rigidity following RES treatment demonstrates increased blood flow and may provide a functional model for penile PK evaluations and possibly simian immunodeficiency virus (SIV) transmission under erect conditions.

Nondaily preexposure prophylaxis for HIV prevention

PURPOSE OF REVIEW

To discuss nondaily preexposure prophylaxis (PrEP) modalities that may provide advantages compared with daily PrEP in cost and cumulative toxicity, but may have lower adherence forgiveness.

RECENT FINDINGS

Animal models have informed our understanding of early viral transmission events, which help guide event-driven PrEP dosing strategies. These models indicate early establishment of viral replication in rectal or cervicovaginal tissues, so event-driven PrEP should rapidly deliver high mucosal drug concentrations within hours of the potential exposure event. Macaque models have demonstrated the high biological efficacy for event-driven dosing of oral tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) against both vaginal and rectal virus transmission. In humans, the IPERGAY study demonstrated 86% efficacy for event-driven oral TDF/FTC dosing among men who have sex with men (MSM), while no similar efficacy data are available on women or heterosexual men. The HPTN 067 study showed that certain MSM populations adhere well to nondaily PrEP, whereas other populations of women adhere more poorly to nondaily versus daily regimens. Pharmacokinetic studies following oral TDF/FTC dosing in humans indicate that TFV-diphosphate (the active form of TFV) accumulates to higher concentrations in rectal versus cervicovaginal tissue, but nonadherence in trials complicates the interpretation of differential mucosal drug concentrations.

SUMMARY

Event-driven dosing for TFV-based PrEP has promise for HIV prevention in MSM. Future research of event-driven PrEP in women and heterosexual men should be guided by a better understanding of the importance of mucosal drug concentrations for PrEP efficacy and its sensitivity to adherence.

Animal and human mucosal tissue models to study HIV biomedical interventions: can we predict success?

Introduction

Preclinical testing plays an integral role in the development of HIV prevention modalities. Several models are used including humanized mice, non-human primates and human mucosal tissue cultures.

Discussion

Pharmaceutical development traditionally uses preclinical models to evaluate product safety. The HIV prevention field has extended this paradigm to include models of efficacy, encompassing humanized mice, non-human primates (typically Asian macaques) and human mucosal tissue (such as cervical and colorectal). As our understanding of the biology of HIV transmission improves and includes the influence of human behaviour/biology and co-pathogens, these models have evolved as well to address more complex questions. These three models have demonstrated the effectiveness of systemic (oral) and topical use of antiretroviral drugs. Importantly, pharmacokinetic/pharmacodynamic relationships are being developed and linked to information gathered from human clinical trials. The models are incorporating co-pathogens (bacterial and viral) and the effects of coitus (mucosal fluids) on drug distribution and efficacy. Humanized mice are being tailored in their immune reconstitution to better represent humans. Importantly, human mucosal tissue cultures are now being used in early clinical trials to provide information on product efficacy to more accurately characterize efficacious products to advance to larger clinical trials. While all of these models have made advancements in product development, each has limitations and the data need to be interpreted by keeping these limitations in mind.

Conclusions

Development and refinement of each of these models has been an iterative process and linkages to data generated among each of them and from human clinical trials are needed to determine their reliability. Preclinical testing has evolved from simply identifying products that demonstrate efficacy prior to clinical trials to defining essential pharmacokinetic/pharmacodynamic relationships under a variety of conditions and has the potential to improve product selection prior to the initiation of large-scale human clinical trials. The goal is to provide researchers with ample information to make conversant decisions that guide optimized and efficient product development.

Pharmacokinetic profile of raltegravir, elvitegravir and dolutegravir in plasma and mucosal secretions in rhesus macaques

OBJECTIVES

Pharmacokinetic studies in animal models are important for assessing the prophylactic potential of antiretroviral drugs for HIV prevention. This study sought to identify clinically relevant doses of the marketed integrase inhibitors raltegravir, elvitegravir and dolutegravir in macaques and investigate drug penetration and antiviral activity in mucosal secretions.

METHODS

Macaques received one oral dose of raltegravir, elvitegravir or dolutegravir alone or in combination with emtricitabine and tenofovir disoproxil fumarate followed by drug level measurements in blood and rectal and vaginal secretions. Antiviral activity was investigated in TZM-bl cells exposed to SHIV162p3 in the presence of rectal secretions collected from treated animals.

RESULTS

Plasma drug concentrations with 50 mg/kg raltegravir or elvitegravir were within the range seen in humans receiving 400-800 mg of raltegravir or 800 mg of unboosted elvitegravir but lower than with 150 mg of elvitegravir boosted with cobicistat. AUC0-24 values for dolutegravir increased proportionally with the dose, with a calculated human-equivalent dose of 20 mg/kg. Elvitegravir showed the highest penetration in rectal and vaginal fluids despite the absence of pharmacological boosting, followed by raltegravir and dolutegravir. Rectal secretions collected at 24 h from treated macaques blocked infection of TZM-bl cells by 50% at dilutions of 1/1000 (raltegravir), 1/800 (dolutegravir) and >1/30 000 (elvitegravir).

CONCLUSIONS

We defined macaque doses of HIV integrase inhibitors that recapitulate human clinical doses, which will facilitate efficacy and dose escalation studies in macaques. High and sustained drug concentrations and activity in mucosal secretions suggest that integrase inhibitors are promising candidates for HIV prevention.