Protection Against Rectal Chimeric Simian/Human Immunodeficiency Virus Transmission in Macaques by Rectal-Specific Gel Formulations of Maraviroc and Tenofovir

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.

The ex vivo pharmacology of HIV-1 antiretrovirals differs between macaques and humans

Non-human primates (NHP) are widely used for the pre-clinical assessment of antiretrovirals (ARVs) for HIV treatment and prevention. However, the utility of these models is questionable given the differences in ARV pharmacology between humans and macaques. Here, we report a model based on ex vivo ARV exposure and the challenge of mucosal tissue explants to define pharmacological differences between NHPs and humans. For colorectal and cervicovaginal explants in both species, high concentrations of tenofovir (TFV) and maraviroc were predictive of anti-viral efficacy. However, their combinations resulted in increased inhibitory potency in NHP when compared to human explants. In NHPs, higher TFV concentrations were measured in colorectal versus cervicovaginal explants (p = 0.042). In humans, this relationship was inverted with lower levels in colorectal tissue (p = 0.027). TFV-resistance caused greater loss of viral fitness for HIV-1 than SIV. This, tissue explants provide an important bridge to refine and appropriately interpret NHP studies.

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Tenofovir-maraviroc combinations show greater potency in NHP than in human tissue

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Opposite drug distribution in mucosal tissues was observed between both species

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Greater loss of viral replication fitness with RT mutations for SIV than for HIV-1

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Ex vivo tissue models are a bridge between NHP studies and human clinical trials

A Randomized, Open-Label, Crossover Phase 1 Safety and Pharmacokinetic Study of Oral Maraviroc and Maraviroc 1% Gel (the CHARM-03 Study)

The Combination HIV Antiretroviral Rectal Microbicide-3 (CHARM-03) study was a randomized, open-label, crossover Phase 1 safety and pharmacokinetic (PK) study of oral maraviroc (MVC) and MVC 1% gel. At a single site, healthy HIV-uninfected men and women were enrolled and randomized to an open label crossover sequence of eight consecutive daily exposures to MVC 300 mg dosed orally, MCV 1% gel dosed rectally, and MVC 1% gel dosed vaginally. Male participants received oral and rectal dosing and female participants received oral, rectal, and vaginal dosing. Assessments were undertaken at baseline and following each 8-day period and included collection of plasma, rectal/cervical tissue (CT), and rectal/endocervical/vaginal fluids. Eleven men and nine women were enrolled. Two participants withdrew from the study before receiving study product. There were 25 adverse events, of which 24 were Grade 1 (G1) and one was G2 (unrelated). After eight doses, MVC was quantifiable in all samples following oral, rectal, or vaginal product administration. The highest drug concentrations in plasma, rectal tissue (RT), and CT were associated with oral, rectal, and vaginal drug delivery, respectively. There were significant reductions in tissue drug concentrations when rectal and cervical biopsies were incubated in media before tissue processing for PK (p < .0001). Only oral MVC was associated with limited protection in the rectal explant HIV challenge model (p < .05). There were no immunological changes in RT, and all products were acceptable to participants. In conclusion, all products were found to be safe and acceptable and did not induce local inflammation. The lack of ex vivo efficacy demonstrated in study samples may be due to rapid disassociation of MVC from the explant tissue. ClinicalTrials.gov Identifier: NCT02346084.

Pharmacokinetics of vaginally applied integrase inhibitors in macaques

OBJECTIVES

We conducted a detailed pharmacokinetic assessment in macaques treated with vaginal gels formulated with HIV integrase strand transfer inhibitors (INSTIs) to better understand drug distribution and identify INSTI concentrations associated with previously demonstrated in vivo protection against vaginal simian HIV challenge.

METHODS

Six macaques received vaginal gel containing 1% raltegravir (30 mg) once-weekly over 6 weeks. Following a washout period, five macaques received once-weekly gel containing 0.23% L-870,812 (7 mg). Drug concentrations were measured in plasma, mucosal fluids and vaginal tissues at baseline and 2, 5 and 24 h post-dosing.

RESULTS

The median maximum concentration (Cmax) for raltegravir and L-870,812 in plasma was below the limit of quantification and 41.1 ng/mL, respectively. The Cmax in vaginal fluids (1441 and 1250 μg/mL) and tissues (266.7 and 368.4 μg/g) was achieved 2-5 h after dosing, respectively. A similar half-life was observed for raltegravir and L-870,812 in vaginal fluids (8-10 h) and remained 3-4 orders of magnitude above the protein-adjusted IC95 (0.016 and 0.106 μg/mL, respectively) at 24 h. Drug concentrations in vaginal fluids correlated well with those in vaginal tissues (Pearson r ≥ 0.788). Both drugs were consistently detected in rectal fluids 2 h after vaginal dosing, albeit at much lower levels (31-92-fold) than those in vaginal fluids.

CONCLUSIONS

To the best of our knowledge, this study provides the first data on INSTI levels in vaginal tissues associated with in vivo protection and demonstrates rectal drug distribution of INSTIs after vaginal dosing. These findings may inform dose selection for topical products with INSTIs for HIV prevention.

Maraviroc Oral Disintegration Tablet: Analytical Design of Experiments (DoE) for Assessment and Comparison of In-Vitro Dissolution Profiles

Background:

The bioavailability of a drug in a solid oral dose depends on its release from the drug product and its balance in dissolution. Compared with a reference drug, the newly developed formulation needs to establish bioequivalence by comparing the dissolution profile.

Objective:

To compare dissolution profiles of a newly developed maraviroc oral disintegration tablet and the reference Axentri® tablet. The current research was designed to establish and validate an integral analytical consistency by Quality by Design (QbD) approach to quantify maraviroc from dissolution samples using the RP-HPLC method.

Methods:

Maraviroc was formulated into an orally disintegrating tablet using a direct compression technique at different concentrations of sodium starch glycolate as super disintegrants and talc and magnesium stearate as glidants. The dissolution test in 0.1N HCl was performed according to standard procedures to predict bioequivalence. The results of dissolution tests were analyzed using the QbD Box Behnken Design multivariate RP-HPLC method.

Results:

The optimized formulation (F2) was selected as it showed 90% drug release in 5 min and a disintegration time of 22 sec with dissolution profiles to the marketed reference to meet the FDA requirements of f2 similarity factor statistics. The integrated analytical QbD method was statistically analyzed by ANOVA, counter-plot, and 3D response surface plots, which demonstrated that the model is statistically significant. The developed method was validated as per ICH guidelines Q2 (R1).

Conclusion :

In conclusion, maraviroc oral disintegrating tablets have been well prepared, and superior statement consistency is established by the implementation of the QbD analytical method for orally disintegrating tablet excellence and adoption.

Development, Characterization and In Vivo Pharmacokinetic Assessment of Rectal Suppositories Containing Combination Antiretroviral Drugs for HIV Prevention

Receptive anal intercourse (RAI) contributes significantly to HIV acquisition underscoring the need to develop HIV prevention options for populations engaging in RAI practices. We explored the feasibility of formulating rectal suppositories with potent antiviral drugs for on-demand use. A fixed-dose combination of tenofovir (TFV) and elvitegravir (EVG) (40 mg each) was co-formulated in six different suppository bases (three fat- and three water-soluble). Fat-soluble witepsol H15 and water-soluble polyethylene glycol (PEG) based suppositories demonstrated favorable in vitro release and were advanced to assess in vivo pharmacokinetics following rectal administration in macaques. In vivo drug release profiles were similar for both suppository bases. Median concentrations of TFV and EVG detected in rectal fluids at 2 h were 1- and 2-logs higher than the in vitro IC50, respectively; TFV-diphosphate levels in rectal tissues met or exceeded those associated with high efficacy against rectal simian HIV (SHIV) exposure in macaques. Leveraging on these findings, a PEG-based suppository with a lower dose combination of tenofovir alafenamide (TAF) and EVG (8 mg each) was developed and found to achieve similar rectal drug exposures in macaques. This study establishes the utility of rectal suppositories as a promising on-demand strategy for HIV PrEP and supports their clinical development.

Mucoadhesive Microspheres of Maraviroc and Tenofovir Designed for Pre-Exposure Prophylaxis of HIV-1: An in vitro Assessment of the Effect on Vaginal Lactic Acid Bacteria Microflora

Purpose

To formulate and evaluate microspheres of the antiretroviral drugs maraviroc and tenofovir intended for a candidate vaginal microbicide and assess its effect on the vaginal lactic acid bacteria microflora.

Methods

Ionic gelation technique was used to formulate maraviroc and tenofovir microspheres with subsequent characterization. The effect of varying concentrations of the polymer, crosslinking agent and the curing time on the outcome variables viz: particle size, mucoadhesion and encapsulation efficiency were investigated. Lactic acid bacteria were isolated from the vagina of healthy women using standard microbiologic methods. The analysis of their 16S rRNA sequence data identified Lactobacillus fermentum and Enterococcus faecalis strains which were assigned GenBank accession numbers. The efficacy of the microspheres on HIV-1BaL strain was evaluated using TZM-bl indicator cells.

Results

The optimal maraviroc and tenofovir microspheres had particle sizes of (434.82 µm and 456.18 µm), mucoadhesion of (93.3% and 90%) and encapsulation efficiency (92.80% and 78.9%) respectively. Maraviroc release kinetics followed a zero-order model and tenofovir was released via Higuchi model. The assay of a 1 mg/mL suspension of the microspheres on the strains of Lactobacillus fermentum and Enterococcus faecalis showed a viability of 93.9% and 89.7%, respectively. There was a statistically significant difference between the mean absorbance readings of the test agent and that of the positive control (P = 0.001). The microspheres elicited a progressive decline in HIV infectivity until at a concentration of 1 μg/mL.

Conclusion

The antiretroviral drugs loaded in the microspheres, had good mucoadhesion which is a potential for prolonged residence time in the vagina. The antiretroviral drugs were adequately released from the microspheres and showed efficacy against the HIV-1 BaL virus strain. There was no significant disruption in the growth of the lactic acid bacteria which constitute valuable bacteria microflora of the vagina.

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In vitro inhibitory effect of maraviroc on the association of the simian immunodeficiency virus envelope glycoprotein with CCR5

Asian macaques infected with simian immunodeficiency viruses (SIVs) isolated from African non-human primates develop a disease similar to human AIDS. SIV enters its target cells by binding to CD4 and a coreceptor, typically CCR5. Maraviroc is an entry inhibitor of human immunodeficiency virus type 1 (HIV-1) that prevents the interaction between CCR5 and the surface subunit gp120 of the viral envelope glycoprotein (Env). Thus far, the activity of maraviroc on SIV entry has been poorly studied. Here, we determined in vitro pharmacological parameters of the effect of maraviroc on the SIV Env association with CCR5. Cell-to-cell fusion inhibition assays were used to compare the susceptibility to maraviroc of the SIVsmmPBj Env-CCR5 interaction with that of HIV-1BaL Env. Analysis of dose-response curves and determination of IC₅₀ values demonstrate that increasing concentrations of maraviroc inhibit the membrane fusion activity of SIVsmmPBj Env in a manner and to an extent similar to that of HIV-1BaL Env.

CCR5: Established paradigms and new frontiers for a 'celebrity' chemokine receptor

Because of the level of attention it received due to its role as the principal HIV coreceptor, CCR5 has been described as a 'celebrity' chemokine receptor. Here we describe the development of CCR5 inhibitory strategies that have been developed for HIV therapy and which are now additionally being considered for use in HIV prevention and cure. The wealth of CCR5-related tools that have been developed during the intensive investigation of CCR5 as an HIV drug target can now be turned towards the study of CCR5 as a model chemokine receptor. We also summarize what is currently known about the cell biology and pharmacology of CCR5, providing an update on new areas of investigation that have emerged in recent research. Finally, we discuss the potential of CCR5 as a drug target for diseases other than HIV, discussing the evidence linking CCR5 and its natural chemokine ligands with inflammatory diseases, particularly neuroinflammation, and certain cancers. These pathologies may provide new uses for the strategies for CCR5 blockade originally developed to combat HIV/AIDS.

Efficacy of Vaginally Administered Gel Containing Emtricitabine and Tenofovir Against Repeated Rectal Simian Human Immunodeficiency Virus Exposures in Macaques

Vaginal microbicides containing antiretrovirals (ARVs) have shown to prevent vaginally acquired human immunodeficiency virus (HIV), but these products may not protect women who engage in anal sex. Intravaginal dosing with ARVs has shown to result in drug exposures in rectal tissues, thus raising the possibility of dual compartment protection. To test this concept, we investigated whether intravaginal dosing with emtricitabine (FTC)/tenofovir (TFV) gel, which fully protected macaques against repeated vaginal exposures to simian human immunodeficiency virus (SHIV), protects against rectal SHIV exposures. Pharmacokinetic studies revealed rapid distribution of FTC and TFV to rectal tissues and luminal fluids, albeit at concentrations 1-2 log10 lower than those in the vaginal compartment. Efficacy measurements against repeated rectal SHIV challenges demonstrated a 4.5-fold reduction in risk of infection in macaques that received intravaginal FTC/TFV compared to placebo gel (P = .047; log-rank test). These data support the concept of dual compartment protection by vaginal dosing and warrants developing ARV-based vaginal products with improved bidirectional dosing.

The pharmacokinetics, pharmacodynamics, and mucosal responses to maraviroc-containing pre-exposure prophylaxis regimens in MSM

OBJECTIVE

HIV Prevention Trials Network 069/AIDS Clinical Trials Group A5305 was a study of 48-week oral pre-exposure prophylaxis (PrEP) regimens in MSM and transgender women. A rectal substudy was included to evaluate drug concentrations in rectal compartment vs. blood, gut-associated lymphoid tissue (GALT) responses to four antiretroviral PrEP regimens [maraviroc (MVC), MVC + emtricitabine (FTC), MVC + tenofovir (TFV) disoproxil fumarate, and TFV disoproxil fumarate + FTC], and to determine whether ARV exposure was associated with ex-vivo suppression of HIV infection in colorectal explants.

METHODS

C-C chemokine receptor type 5 (CCR5) genotype was characterized using PCR. At baseline and at Weeks 24, 48, and 49, GALT phenotype was characterized by flow cytometry, rectal biopsies were challenged with HIV-1BaL, and tissue and plasma pharmacokinetics were measured via mass spectrometry.

RESULTS

Exposure to MVC was not associated with increased expression of CD4+/CCR5+ HIV target T cells. Significant ex-vivo viral suppression compared with baseline was seen at Weeks 24 and 48, ranging from 1.4 to 1.8 log10 for all study regimens except the MVC-alone arm which did not show statistically significant viral suppression at Week 48. Tissue concentrations of TFV, TFV-diphosphate, and FTC were correlated with viral suppression.

CONCLUSION

MVC-containing HIV PrEP regimens did not increase GALT CD4+ T-cell activation or the CD4+/CCR5+ phenotype. No virologic suppression was seen with MVC-alone at Week 48 compared with combination regimens, suggesting MVC monotherapy might be less effective than combination antiretroviral PrEP regimens.

Pathogenic Viruses Commonly Present in the Oral Cavity and Relevant Antiviral Compounds Derived from Natural Products

Many viruses, such as human herpesviruses, may be present in the human oral cavity, but most are usually asymptomatic. However, if individuals become immunocompromised by age, illness, or as a side effect of therapy, these dormant viruses can be activated and produce a variety of pathological changes in the oral mucosa. Unfortunately, available treatments for viral infectious diseases are limited, because (1) there are diseases for which no treatment is available; (2) drug-resistant strains of virus may appear; (3) incomplete eradication of virus may lead to recurrence. Rational design strategies are widely used to optimize the potency and selectivity of drug candidates, but discovery of leads for new antiviral agents, especially leads with novel structures, still relies mostly on large-scale screening programs, and many hits are found among natural products, such as extracts of marine sponges, sea algae, plants, and arthropods. Here, we review representative viruses found in the human oral cavity and their effects, together with relevant antiviral compounds derived from natural products. We also highlight some recent emerging pharmaceutical technologies with potential to deliver antivirals more effectively for disease prevention and therapy.

Marginal Effects of Systemic CCR5 Blockade with Maraviroc on Oral Simian Immunodeficiency Virus Transmission to Infant Macaques

Current approaches do not eliminate all human immunodeficiency virus type 1 (HIV-1) maternal-to-infant transmissions (MTIT); new prevention paradigms might help avert new infections. We administered maraviroc (MVC) to rhesus macaques (RMs) to block CCR5-mediated entry, followed by repeated oral exposure of a CCR5-dependent clone of simian immunodeficiency virus (SIV) mac251 (SIVmac766). MVC significantly blocked the CCR5 coreceptor in peripheral blood mononuclear cells and tissue cells. All control animals and 60% of MVC-treated infant RMs became infected by the 6th challenge, with no significant difference between the number of exposures (P = 0.15). At the time of viral exposures, MVC plasma and tissue (including tonsil) concentrations were within the range seen in humans receiving MVC as a therapeutic. Both treated and control RMs were infected with only a single transmitted/founder variant, consistent with the dose of virus typical of HIV-1 infection. The uninfected RMs expressed the lowest levels of CCR5 on the CD4+ T cells. Ramp-up viremia was significantly delayed (P = 0.05) in the MVC-treated RMs, yet peak and postpeak viral loads were similar in treated and control RMs. In conclusion, in spite of apparent effective CCR5 blockade in infant RMs, MVC had a marginal impact on acquisition and only a minimal impact on the postinfection delay of viremia following oral SIV infection. Newly developed, more effective CCR5 blockers may have a more dramatic impact on oral SIV transmission than MVC.IMPORTANCE We have previously suggested that the very low levels of simian immunodeficiency virus (SIV) maternal-to-infant transmissions (MTIT) in African nonhuman primates that are natural hosts of SIVs are due to a low availability of target cells (CCR5+ CD4+ T cells) in the oral mucosa of the infants, rather than maternal and milk factors. To confirm this new MTIT paradigm, we performed a proof-of-concept study in which we therapeutically blocked CCR5 with maraviroc (MVC) and orally exposed MVC-treated and naive infant rhesus macaques to SIV. MVC had only a marginal effect on oral SIV transmission. However, the observation that the infant RMs that remained uninfected at the completion of the study, after 6 repeated viral challenges, had the lowest CCR5 expression on the CD4+ T cells prior to the MVC treatment appears to confirm our hypothesis, also suggesting that the partial effect of MVC is due to a limited efficacy of the drug. New, more effective CCR5 inhibitors may have a better effect in preventing SIV and HIV transmission.

Hypo-osmolar Formulation of Tenofovir (TFV) Enema Promotes Uptake and Metabolism of TFV in Tissues, Leading to Prevention of SHIV/SIV Infection

Oral preexposure prophylaxis (PrEP) has been approved for prophylaxis of HIV-1 transmission but is associated with high costs and issues of adherence. Protection from anal transmission of HIV using topical microbicides and methods congruent with sexual behavior offers the promise of improved adherence. We compared the pharmacokinetics (PK) and ex vivo efficacy of iso-osmolar (IOsm) and hypo-osmolar (HOsm) rectal enema formulations of tenofovir (TFV) in rhesus macaques. Single-dose PK of IOsm or HOsm high-dose (5.28 mg/ml) and low-dose (1.76 mg/ml) formulations of TFV enemas were evaluated for systemic uptake in blood, colorectal biopsy specimens, and rectal CD4⁺ T cells. Markedly higher TFV concentrations were observed in plasma and tissues after administration of the HOsm high-dose formulation than with all other formulations tested. TFV and TFV diphosphate (TFV-DP) concentrations in tissue correlated for the HOsm high-dose formulation, demonstrating rapid uptake and transformation of TFV to TFV-DP in tissues. TFV-DP amounts in tissues collected at 1 and 24 h were 7 times and 5 times higher, respectively (P < 0.01), than the ones collected in tissues with the IOsm formulation. The HOsm high-dose formulation prevented infection in ex vivo challenges of rectal tissues collected at 1, 24, and 72 h after the intrarectal dosing, whereas the same TFV dose formulated as an IOsm enema was less effective.

In situ depot formation of anti-HIV fusion-inhibitor peptide in recombinant protein polymer hydrogel

Most peptide drugs have short half-lives, necessitating frequent injections that may induce skin sensitivity reactions; therefore, versatile prolonged-release delivery platforms are urgently needed. Here, we focused on an oxidatively and thermally responsive recombinant elastin-like polypeptide with periodic cysteine residues (cELP), which can rapidly and reversibly form a disulfide cross-linked network in which peptide can be physically incorporated. As a model for proof of concept, we used enfuvirtide, an antiretroviral fusion-inhibitor peptide approved for treatment of human immunodeficiency virus (HIV) infection. cELP was mixed with enfuvirtide and a small amount of hydrogen peroxide (to promote cross-linking), and the soluble mixture was injected subcutaneously. The oxidative cross-linking generates a network structure, causing the mixture to form a hydrogel in situ that serves as an enfuvirtide depot. We fabricated a series of enfuvirtide-containing hydrogels and examined their stability, enfuvirtide-releasing profile and anti-HIV potency in vitro. Among them, hydrophobic cELP hydrogel provided effective concentrations of enfuvirtide in blood of rats for up to 8 h, and the initial concentration peak was suppressed compared with that after injection of enfuvirtide alone. cELP hydrogels should be readily adaptable as platforms to provide effective depot systems for delivery of other anti-HIV peptides besides enfuvirtide.

STATEMENT OF SIGNIFICANCE

In this paper, we present an anti-HIV peptide delivery system using oxidatively and thermally responsive polypeptides that contain multiple periodic cysteine residues as an injectable biomaterial capable of in situ self-gelation, and we demonstrate its utility as an injectable depot capable of sustained release of anti-HIV peptides. The novelty of this work stems from the platform employed to provide the depot encapsulating the peptide drugs (without chemical conjugation), which consists of rationally designed, genetically engineered polypeptides that enable the release rate of the peptide drugs to be precisely controlled.

A novel preventive strategy against HIV-1 infection: combinatorial use of inhibitors targeting the nucleocapsid and fusion proteins

The strategy of simultaneously attacking multiple targets is worthy of exploration in the field of microbicide development to combat HIV-1 sequence diversity and minimize the transmission of resistant variants. A combination of S-acyl-2-mercaptobenzamide thioester-10 (SAMT10), an inhibitor of the HIV-1 nucleocapsid protein (NCp7), and the fusion inhibitor sifuvirtide (SFT) may exert synergistic effects, since SFT can block viral fusion at an early stage of the viral cycle and SAMT10 can disrupt viral particles at a later stage. In this study, we investigated the effect of the combination of SAMT10 and SFT on HIV-1 infection using in vitro cell culture and ex vivo mucosal explant models. A range of doses for each compound was tested at 10-fold serial dilutions based on their 50% effective concentrations (EC₅₀). We observed a synergistic effect of SAMT10 and SFT in vitro against both the laboratory-adapted HIV-1 strain HIV-1_IIIB (subtype B, X4) and three pseudotyped viruses prevalent in Chinese sexually transmitted populations (SVPB16 (subtype B, R5), SVPC12 (subtype C, R5) and SH1.81 (CRF01_AE, R5)). In the ex vivo study, the EC₅₀ values of the inhibitor combinations were reduced 1.5- to 2-fold in colorectal mucosal explants compared to treatment with SAMT10 or SFT alone by using with HIV-1_IIIB. These results may provide a novel strategy for microbicide development against HIV-1 sexual transmission.

Nanoemulgel using a bicephalous heterolipid as a novel approach to enhance transdermal permeation of tenofovir

Improvements in permeation enhancement strategies, such as nanoemulsions (NEs) and nanoemulgels (NEGs), have led to a renewed interest in transdermal drug delivery (TDD). This study aimed to investigate the potential of LLA1E, a novel dendritic permeation enhancer, as an oily phase in the development of a NEG for the TDD of tenofovir (TNF). TNF loaded NEs (TNEs) were prepared and analysed for mean globule diameter (MGD), polydispersity index (PDI), zeta potential (ZP) and morphology. NEGs of the TNEs (TNEGs) were prepared and evaluated for ex vivo transdermal permeation efficacy. The skin integrity before and after the experiments was assessed using histology and transepithelial electrical resistance (TEER). TNEs had a MGD of 129.06±3.35nm, a PDI of 0.192±0.038 and a ZP of 20.9±2.02mV, with an incorporation efficiency of 91.94±0.84%. There was no significant change is these properties after incorporating the TNEs into the hydrogel, as MGD, PDI and ZP of TNEGs were found to be 136.13±5.21nm, 0.182±0.020 and -20.9±2.08mV respectively. Ex vivo permeation studies showed that the TNEG significantly enhanced the TNF permeation by 39.65-fold, with a cumulative amount of 1866.54±108.62μgcm^-2. Histological and TEER assessments showed no permanent effects on the skin by TNEG, indicating that this novel TNEG nanosystem has the potential to translate into clinical trials as treatment alternatives for HIV/AIDs patients.

Nonhuman Primate Models for Studies of AIDS Virus Persistence During Suppressive Combination Antiretroviral Therapy

Nonhuman primate (NHP) models of AIDS represent a potentially powerful component of the effort to understand in vivo sources of AIDS virus that persist in the setting of suppressive combination antiretroviral therapy (cART) and to develop and evaluate novel strategies for more definitive treatment of HIV infection (i.e., viral eradication "cure", or sustained off-cART remission). Multiple different NHP models are available, each characterized by a particular NHP species, infecting virus, and cART regimen, and each with a distinct capacity to recapitulate different aspects of HIV infection. Given these different biological characteristics, and their associated strengths and limitations, different models may be preferred to address different questions pertaining to virus persistence and cure research, or to evaluate different candidate intervention approaches. Recent developments in improved cART regimens for use in NHPs, new viruses, a wider array of sensitive virologic assay approaches, and a better understanding of pathogenesis should allow even greater contributions from NHP models to this important area of HIV research in the future.

Short Communication: Limited Anti-HIV-1 Activity of Maraviroc in Mucosal Tissues

The potential of maraviroc (MVC), a small-molecule CCR5 antagonist, as a candidate to prevent HIV-1 sexual transmission by oral or topical dosing has not yet been completely established. Using relevant cellular and mucosal tissue explant models, we show partial antiviral activity of MVC when tested in multiple preclinical dosing strategies.

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.

Drug transporter gene expression in human colorectal tissue and cell lines: modulation with antiretrovirals for microbicide optimization

OBJECTIVES

The objectives of this study were to comprehensively assess mRNA expression of 84 drug transporters in human colorectal biopsies and six representative cell lines, and to investigate the alteration of drug transporter gene expression after exposure to three candidate microbicidal antiretroviral (ARV) drugs (tenofovir, darunavir and dapivirine) in the colorectal epithelium. The outcome of the objectives informs development of optimal ARV-based microbicidal formulations for prevention of HIV-1 infection.

METHODS

Drug transporter mRNA expression was quantified from colorectal biopsies and cell lines by quantitative real-time PCR. Relative mRNA expression was quantified in Caco-2 cells and colorectal explants after induction with ARVs. Data were analysed using Pearson's product moment correlation (r), hierarchical clustering and principal component analysis (PCA).

RESULTS

Expression of 58 of the 84 transporters was documented in colorectal biopsies, with genes for CNT2, P-glycoprotein (P-gp) and MRP3 showing the highest expression. No difference was noted between individual subjects when analysed by age, gender or anatomical site (rectum or recto-sigmoid) (r = 0.95-0.99). High expression of P-gp and CNT2 proteins was confirmed by immunohistochemical staining. Similarity between colorectal tissue and cell-line drug transporter gene expression was variable (r = 0.64-0.84). PCA showed distinct clustering of human colorectal biopsy samples, with the Caco-2 cells defined as the best surrogate system. Induction of Caco-2 cell lines with ARV drugs suggests that darunavir-based microbicides incorporating tenofovir may result in drug-drug interactions likely to affect distribution of individual drugs to sub-epithelial target cells.

CONCLUSIONS

These findings will help optimize complex formulations of rectal microbicides to realize their full potential as an effective approach for pre-exposure prophylaxis against HIV-1 infection.

Maraviroc: a review of its use in HIV infection and beyond

The human immunodeficiency virus-1 (HIV-1) enters target cells by binding its envelope glycoprotein gp120 to the CD4 receptor and/or coreceptors such as C-C chemokine receptor type 5 (CCR5; R5) and C-X-C chemokine receptor type 4 (CXCR4; X4), and R5-tropic viruses predominate during the early stages of infection. CCR5 antagonists bind to CCR5 to prevent viral entry. Maraviroc (MVC) is the only CCR5 antagonist currently approved by the United States Food and Drug Administration, the European Commission, Health Canada, and several other countries for the treatment of patients infected with R5-tropic HIV-1. MVC has been shown to be effective at inhibiting HIV-1 entry into cells and is well tolerated. With expanding MVC use by HIV-1-infected humans, different clinical outcomes post-approval have been observed with MVC monotherapy or combination therapy with other antiretroviral drugs, with MVC use in humans infected with dual-R5- and X4-tropic HIV-1, infected with different HIV-1 genotype or infected with HIV-2. This review discuss the role of CCR5 in HIV-1 infection, the development of the CCR5 antagonist MVC, its pharmacokinetics, pharmacodynamics, drug–drug interactions, and the implications of these interactions on treatment outcomes, including viral mutations and drug resistance, and the mechanisms associated with the development of resistance to MVC. This review also discusses available studies investigating the use of MVC in the treatment of other diseases such as cancer, graft-versus-host disease, and inflammatory diseases.