Safety, tolerability, and systemic absorption of dapivirine vaginal microbicide gel in healthy, HIV-negative women

Development and verification of mechanistic vaginal absorption and metabolism model to predict systemic exposure after vaginal ring and gel application

AIMS

The current work describes the development of mechanistic vaginal absorption and metabolism model within Simcyp Simulator to predict systemic concentrations following vaginal application of ring and gel formulations.

METHODS

Vaginal and cervix physiology parameters were incorporated in the model development. The study highlights the model assumptions including simulation results comparing systemic concentrations of 5 different compounds, namely, dapivirine, tenofovir, lidocaine, ethinylestradiol and etonogestrel, administered as vaginal ring or gel. Due to lack of data, the vaginal absorption parameters were calculated based on assumptions or optimized. The model uses release rate/in vitro release profiles with formulation characteristics to predict drug mass transfer across vaginal tissue into the systemic circulation.

RESULTS

For lidocaine and tenofovir vaginal gel, the predicted to observed AUC0-t and Cmax ratios were well within 2-fold error limits. The average fold error (AFE) and absolute AFE indicating bias and precision of predictions range from 0.62 to 1.61. For dapivirine, the pharmacokinetic parameters are under and overpredicted in some studies due to lack of formulation composition details and relevance of release rate used in ring model. The predicted to observed AUC0-t and Cmax ratios were well within 2-fold error limits for etonogestrel and ethinylestradiol vaginal ring (AFEs and absolute AFEs from 0.84 to 1.83).

CONCLUSION

The current study provides first of its kind physiologically based pharmacokinetic framework integrating physiology, population and formulation data to carry out in silico mechanistic vaginal absorption studies, with the potential for virtual bioequivalence assessment in the future.

Transport and Permeation Properties of Dapivirine: Understanding Potential Drug-Drug Interactions

The dapivirine (DPV) vaginal ring was developed by the nonprofit International Partnership for Microbicides (IPM) for reducing the risk of HIV infection. A clinical study (IPM 028) showed that concomitant use of the DPV ring and miconazole (MIC) altered DPV pharmacokinetic profile. In this work, we investigated whether or not DPV transport and permeation contributed to the observed DPV-MIC interaction. Our study evaluated the interaction between DPV and several transporters that are highly expressed in the human female reproductive tract, including MRP1, MRP4, P-gp, BCRP, and ENT1, using vesicular and cellular systems. We also evaluated the impact of DPV/MIC on cellular tight junctions by monitoring transepithelial electrical resistance with the Ussing chamber. Lastly, we evaluated the effect of MIC on DPV permeability across human cervical tissue. Our findings showed that DPV was not a substrate of MRP1, MRP4, P-gp, BCRP, or ENT1 transporters. Additionally, DPV did not inhibit the activity of these transporters. DPV, MIC, and their combination also did not disrupt cellular tight junctions. MIC did not affect DPV tissue permeability but significantly reduced DPV tissue levels. Therefore, our results suggest that the DPV-MIC interaction is not due to these five transporters, altered tight junction integrity, or altered tissue permeability.

Recent Advances in the Excipients Used in Modified Release Vaginal Formulations

The formulation of an ideal vaginal drug delivery system (DDS), with the requisite properties, with respect to safety, efficacy, patient compliance, aesthetics, harmonization with the regulatory requirements, and cost, requires a meticulous selection of the active ingredients and the excipients used. Novel excipients defined by diversity and multifunctionality are used in order to ameliorate drug delivery attributes. Synthetic and natural polymers are broadly used in pharmaceutical vaginal formulations (solid, semi-solid dosage forms, implantable devices, and nanomedicines) with a promising perspective in improving stability and compatibility issues when administered topically or systemically. Moreover, the use of biopolymers is aiming towards formulating novel bioactive, biocompatible, and biodegradable DDSs with a controllable drug release rate. Overviewing vaginal microenvironment, which is described by variable and perplexed features, a perceptive choice of excipients is essential. This review summarizes the recent advances on the excipients used in modified vaginal drug delivery formulations, in an attempt to aid the formulation scientist in selecting the optimal excipients for the preparation of vaginal products.

Drug-releasing vaginal rings for HIV/STI and pregnancy prevention: A review of recent advances and clinical applications

INTRODUCTION

Adolescent girls and young women (AGYW), as well as pre- and post-menopausal women globally would benefit from expanded choice to address their sexual and reproductive health (SRH) needs related to Human Immunodeficiency Virus (HIV), sexually transmitted infections (STIs) and pregnancy prevention. Lack of adequate preventative vaccines for HIV/STIs reinforces public health prioritization for options women may use independently to mitigate risk for infectious disease and unplanned pregnancy. Drug releasing intravaginal rings (IVR) represent one such technology that has garnered attention based on the modality's success recently as a pre-exposure prophylaxis (PrEP) delivery option and its impact on reduction in HIV risk.

AREAS COVERED

: This article provides a synopsis of three IVR technologies in active clinical development for prevention of HIV, STI, and unintended pregnancy demonstrating advancements in terms of compatibility with a wide range of drug types with a focus on dapivirine-based silicone rings (International Partnership for Microbicides (IPM), tenofovir-based polyurethane rings (CONRAD), and pod-based rings (Oak Crest Institute of Science).

EXPERT OPINION

The goals of IVR research are to reduce burdens of HIV/STIs and unplanned pregnancies. Through the evolution of IVR technologies, the potential exists to trigger integration of healthcare services through formulation of products with multiple indications.

Validation and implementation of an ultrasensitive liquid chromatographic-tandem mass spectrometric (LC-MS/MS) assay for dapivirine quantitation in breast milk

BACKGROUND

The non-nucleoside reverse transcriptase inhibitor dapivirine has been evaluated as a topical microbicidal agent to prevent HIV-1 acquisition. Several clinical trials have evaluated the pharmacokinetics of dapivirine when administered as a 25-mg intravaginal ring. Recent studies have focused on the distribution of dapivirine into breast milk. Drug distribution during lactation and breastfeeding can have implications in terms of infant drug exposure. Thus, sensitive bioanalytical tools are required to characterize the pharmacokinetics of dapivirine in breast milk.

METHODS

Whole breast milk was spiked with dapivirine and internal standard. Lipid content was disrupted via pre-treatment with n-hexane, and supernatants were subjected to solid phase extraction. Extracted materials were subjected to liquid chromatographic-tandem mass spectrometric (LC-MS/MS) analysis. Separation occurred using a Waters BEH C8, 50 × 2.1 mm UPLC column with a 1.7 µm particle size and dapivirine was detected on an API 5000 mass analyzer. Methods were validated in accordance with FDA Bioanalytical Method Validation recommendations.

RESULTS

The analytical method was optimized for dapivirine extraction from breast milk. The analytical measuring range of the assay was 10-1000 pg/mL. Calibration curves were generated via weighted linear regression of standards. Intra- and inter-assay precision and accuracy studies demonstrated %CVs ≤ 14.6% and %DEVs ≤ ±12.7%. Stability and matrix effects studies were also conducted and deemed acceptable. The method was applied to a previously reported phase 1 clinical trial and demonstrated appropriate performance in the quantitation of dapivirine in breast milk samples from lactating women.

CONCLUSIONS

An ultrasensitive LC-MS/MS assay has been developed and validated for the quantitation of dapivirine in breast milk. The described method meets validation acceptance criteria and has been applied to a phase 1 clinical trial.

Clinical testing of antiretroviral drugs as future prevention against vaginal and rectal transmission of HIV infection - a review of currently available results

The original purpose of vaginally applied microbicides was to slow down the HIV epidemic among the population until an effective vaccination was developed. Nowadays, antiretrovirals applied in the form of gels or vaginal rings are considered most prominent in this field and are tested via vaginal or, rarely, rectal applications in numerous clinical studies (9 different antiretroviral drugs in 33 clinical studies, especially in Africa). Only tenofovir (1 % gel) and dapivirine (25 mg in vaginal ring) progressed into the phase III clinical testing. Their efficiency depended on the user´s strict adherence to the application regimen (for tenofovir 54 %, for dapivirine 61 % in participants over 25 years of age). Despite this, they are expected to be important and effective tools of preventive medicine in the near future. This review summarizes the results obtained during long-term clinical testing (2005-2018) of antiretroviral drugs against vaginal and rectal transmission of HIV infection.

A strategic action framework for multipurpose prevention technologies combining contraceptive hormones and antiretroviral drugs to prevent pregnancy and HIV

OBJECTIVE

Multipurpose prevention technologies (MPTs) are an innovative class of products that deliver varied combinations of human immunodeficiency virus (HIV) prevention, other sexually transmitted infection (STI) prevention, and contraception. Combining separate strategies for different indications into singular prevention products can reduce the stigma around HIV and STI prevention, improve acceptability of and adherence to more convenient products, and be more cost-effective by addressing overlapping risks.

METHODS

This article outlines a strategic action framework developed as an outcome of a series of expert meetings held between 2014 and 2016. The meetings focused on identifying opportunities and challenges for MPTs that combine hormonal contraception (HC) with antiretroviral drugs into single products. The framework aims to present an actionable strategy, by addressing key research gaps and outlining the key areas for progress, to guide current and future HC MPT development.

RESULTS

We identified eight primary action areas for the development of impactful HC MPTs, and includes aspects from epidemiology, pharmacology, clinical trial design, regulatory requirements, manufacturing and commercialisation, behavioural science, and investment needs for research and development.

CONCLUSION

Overall, the challenges involved with reconciling the critical social-behavioural context that will drive MPT product use and uptake with the complexities of research and development and regulatory approval are of paramount importance. To realise the potential of MPTs given their complexity and finite resources, researchers in the MPT field must be strategic about the way forward; increased support among policy-makers, advocates, funders and the pharmaceutical industry is critical.

A randomised trial of a contraceptive vaginal ring in women at risk of HIV infection in Rwanda: Safety of intermittent and continuous use

Background

Contraceptive vaginal rings could play a role in expanding the contraceptive method mix and in preparing communities for the introduction of HIV prevention and multipurpose rings.

Methods

We conducted an open label single-centre randomised clinical trial of intermittent versus continuous use of NuvaRing® in Kigali, Rwanda, in 2013–2014. We randomised 120 HIV-negative women 1:1 to intermittent use (three rings with a ring-free week in between rings) or continuous use (four rings without ring-free weeks). Women underwent an interview, counselling, and a speculum examination, and were tested for pregnancy, bacterial vaginosis (BV) by Nugent scoring, yeasts and trichomonads on wet mount, and sexually transmitted infections.

Findings

Only one woman withdrew early. Deliberate ring removals were rare, but spontaneous ring expulsions occurred during 14% of ring use periods. There were no incident pregnancies, serious adverse events, serious social harms, or early discontinuations for safety reasons. Systemic side effects were uncommon, and local side effects were not significantly differently distributed between groups except for lower abdominal pain (P = 0.013). The incidence of vaginal yeasts during ring use was high: 22% of intermittent users and 27% of continuous users had incident vaginal yeasts at one or multiple ring removal visits (P = 0.666), and symptomatic vaginal yeast cases were more common in the continuous than intermittent users (P = 0.031). In contrast, mean Nugent scores improved over time in both groups.

Conclusions

Intermittent and continuous NuvaRing® use were safe in Rwandan women and improved Nugent scores over time. However, attention should be paid to ring expulsions and to a potential increased risk of vaginal candidiasis.

Sustained release of the candidate antiretroviral peptides T-1249 and JNJ54310516-AFP from a rod insert vaginal ring

Administration of biomacromolecular drugs in effective quantities from conventional vaginal rings is hampered by poor drug permeability in the polymers from which rings are commonly constructed. Here, we report the formulation development and testing of rod insert rings for sustained release of the candidate antiretroviral peptides T-1249 and JNJ54310516-AFP (JNJ peptide), both of which have potential as HIV microbicides. Rod inserts were prepared comprising antiviral peptides T-1249 or JNJ peptide in combination with a hydrophilic excipient (sodium chloride, sodium glutamate, lactose or zinc acetate) dispersed at different loadings within a medical grade silicone elastomer. The inserts were tested for weight change and swelling when immersed in simulated vaginal fluid (SVF). Dye migration into the inserts was also assessed visually over 28 days. In vitro release of T-1249 and JNJ peptide from rings containing various insert types was tested. Weight change and degree of swelling of rods immersed in SVF was dependent on the type and concentration of excipient present. The rods displayed the following rank order in terms of weight change: sodium glutamate > zinc acetate ≈ sodium chloride > lactose. The weight change and degree of swelling of the inserts did not correlate with the level of dye uptake observed. In vitro release of T-1249 was improved through addition of lactose, sodium chloride and sodium glutamate, while release of JNJ peptide was improved through addition of sodium chloride or sodium glutamate. Sustained release of hydrophobic peptides can be achieved using a rod insert ring design formulated to include a hydrophilic excipient. Release rates were dependent upon the type of excipient used. The degree of release improvement with different inserts partially reflects their ability to imbibe surrounding fluid and swell in aqueous environments.

The Effect of Commonly Used Excipients on the Epithelial Integrity of Human Cervicovaginal Tissue

Pharmaceutical excipients are widely used in vaginal drug products. The epithelial integrity of the cervicovaginal tissue is important for HIV-1 prevention. However, the effects of excipients on cervicovaginal epithelium remain unknown. This study aims at assessing the effects of vaginal product excipients on the integrity of human cervicovaginal epithelium and on a lead HIV prevention antiretroviral drug, tenofovir (TFV). In the current study, nine excipients commonly used in vaginal formulations were incubated for 6 h with excised human ectocervical tissue. The effects of the excipients were examined by measuring the transepithelial electrical resistance (TEER), epithelial morphology, paracellular/transcellular permeability, and cell viability. The efficacy of TFV for preventing HIV-1 infection in the ex vivo cultured ectocervix was also tested. We found that disodium ethyl-enediaminetetraacetate (EDTA), sorbic acid, and benzoic acid had no effect on the tissue TEER. Butylated hydroxyanisole, glycerin, propylene glycol, methylparaben, and propylparaben slightly to moderately decreased tissue TEER, whereas citric acid significantly decreased the TEER in a time-dependent manner. Tissue morphology observed post-exposure strongly correlated with TEER data; however, a less strong correlation was observed between paracellular permeability and TEER data after exposure to different excipients. In addition, treatment with EDTA, methylparaben, and propylene glycol at tested levels had no effect on the efficacy of TFV in preventing tissue HIV-1 infection. In conclusion, the combined measurements of TEER, morphology, permeability, and viability using human cervicovaginal tissue represent a clinically relevant platform for safety evaluation of excipients and formulated products for HIV-1 prevention.

Historical development of vaginal microbicides to prevent sexual transmission of HIV in women: from past failures to future hopes

Infection with human immunodeficiency virus (HIV) remains a global public health concern and is particularly serious in low- and middle-income countries. Widespread sexual violence and poverty, among other factors, increase the risk of infection in women, while currently available prevention methods are outside the control of most. This has driven the study of vaginal microbicides to prevent sexual transmission of HIV from men to women in recent decades. The first microbicides evaluated were formulated as gels for daily use and contained different substances such as surfactants, acidifiers and monoclonal antibodies, which failed to demonstrate efficacy in clinical trials. A gel containing the reverse transcriptase inhibitor tenofovir showed protective efficacy in women. However, the lack of adherence by patients led to the search for dosage forms capable of releasing the active principle for longer periods, and hence to the emergence of the vaginal ring loaded with dapivirine, which requires a monthly application and is able to reduce the sexual transmission of HIV. The future of vaginal microbicides will feature the use of alternative dosage forms, nanosystems for drug release and probiotics, which have emerged as potential microbicides but are still in the early stages of development. Protecting women with vaginal microbicide formulations would, therefore, be a valuable tool for avoiding sexual transmission of HIV.

Comparison of Dapivirine Vaginal Gel and Film Formulation Pharmacokinetics and Pharmacodynamics (FAME 02B)

While preexposure prophylaxis with oral tenofovir/emtricitabine reduces HIV acquisition rates, poor adherence to and acceptability of vaginal gels and the potential for evolving drug resistance have led to development of vaginal film formulations and other antiretroviral drugs, respectively, including the non-nucleoside reverse transcriptase inhibitor dapivirine. In this two-arm crossover study of a novel fast-dissolving dapivirine film and a previously studied semisolid dapivirine gel, 10 healthy women received a single 1.25 mg vaginal dose of each study product; one withdrew after the first dose. Clinical, pharmacokinetic, and antiviral pharmacodynamic assessments (ex vivo HIV-BaL challenge of tissue explants) were performed over 168 h postdose. Six of ten participants experienced mild to moderate adverse effects, similar between products, with no severe adverse events or adverse events attributed to study products. There were no statistically significant differences in plasma, cervicovaginal fluid (CVF), or cervical tissue dapivirine concentrations between the gel and film (all p > .05). CVF dapivirine concentrations were 1.5 and 6 log₁₀ greater than tissue and plasma concentrations, respectively (p < .001). Both film and gel demonstrated reduced cervical tissue infectivity after ex vivo HIV challenge 5 h postdose, compared to baseline and 72-h postdose biopsies (p < .05 for gel, p = .06 for film). There was no difference in ex vivo explant HIV challenge between gel and film. The dapivirine film and gel performed similarly in terms of tolerability, pharmacokinetics, and antiviral effect. Dapivirine film may provide an alternative to pharmacokinetically comparable dapivirine gel formulations. Effectiveness remains to be tested.

Safety and Efficacy of a Dapivirine Vaginal Ring for HIV Prevention in Women

BACKGROUND

The incidence of human immunodeficiency virus (HIV) infection remains high among women in sub-Saharan Africa. We evaluated the safety and efficacy of extended use of a vaginal ring containing dapivirine for the prevention of HIV infection in 1959 healthy, sexually active women, 18 to 45 years of age, from seven communities in South Africa and Uganda.

METHODS

In this randomized, double-blind, placebo-controlled, phase 3 trial, we randomly assigned participants in a 2:1 ratio to receive vaginal rings containing either 25 mg of dapivirine or placebo. Participants inserted the rings themselves every 4 weeks for up to 24 months. The primary efficacy end point was the rate of HIV type 1 (HIV-1) seroconversion.

RESULTS

A total of 77 participants in the dapivirine group underwent HIV-1 seroconversion during 1888 person-years of follow-up (4.1 seroconversions per 100 person-years), as compared with 56 in the placebo group who underwent HIV-1 seroconversion during 917 person-years of follow-up (6.1 seroconversions per 100 person-years). The incidence of HIV-1 infection was 31% lower in the dapivirine group than in the placebo group (hazard ratio, 0.69; 95% confidence interval [CI], 0.49 to 0.99; P=0.04). There was no significant difference in efficacy of the dapivirine ring among women older than 21 years of age (hazard ratio for infection, 0.63; 95% CI, 0.41 to 0.97) and those 21 years of age or younger (hazard ratio, 0.85; 95% CI, 0.45 to 1.60; P=0.43 for treatment-by-age interaction). Among participants with HIV-1 infection, nonnucleoside reverse-transcriptase inhibitor resistance mutations were detected in 14 of 77 participants in the dapivirine group (18.2%) and in 9 of 56 (16.1%) in the placebo group. Serious adverse events occurred more often in the dapivirine group (in 38 participants [2.9%]) than in the placebo group (in 6 [0.9%]). However, no clear pattern was identified.

CONCLUSIONS

Among women in sub-Saharan Africa, the dapivirine ring was not associated with any safety concerns and was associated with a rate of acquisition of HIV-1 infection that was lower than the rate with placebo. (Funded by the International Partnership for Microbicides; ClinicalTrials.gov number, NCT01539226 .).

A Phase 1 Trial to Assess the Safety, Acceptability, Pharmacokinetics, and Pharmacodynamics of a Novel Dapivirine Vaginal Film

BACKGROUND

Films may deliver antiretroviral drugs efficiently to mucosal tissues. In this first in-human trial of a vaginal film for delivering the nonnucleoside reverse transcriptase inhibitor dapivirine, safety, pharmacokinetics, and pharmacodynamics of film and gel formulations were compared with placebo.

METHODS

Sixty-one healthy HIV-negative women were randomized to daily dapivirine (0.05%) or placebo gel, or dapivirine (1.25 mg) or placebo film for seven days. The proportion of participants experiencing grade 2 and higher adverse events related to study product were compared. Plasma dapivirine concentrations were quantified. Paired cervical and vaginal tissue biopsies obtained ∼2 hours after the last dose were measured for tissue drug concentration and exposed to HIV in an ex vivo challenge assay.

RESULTS

Two grade 2 related adverse events occurred in the placebo film group. Women randomized to gel and film products had 4 log10 higher of dapivirine in cervical and vaginal tissues than plasma. Although gel and film users had comparable plasma dapivirine concentrations, tissue concentrations of dapivirine were 3-5 times higher in the gel users when compared with film users. HIV replication in the ex vivo challenge assay was significantly reduced in vaginal tissues from women randomized to dapivirine film or gel; furthermore, tissue drug concentrations were highly correlated with HIV protection. Women rated the film more comfortable with less leakage but found it more difficult to insert than gel.

DISCUSSION

Both film and gel delivered dapivirine at concentrations sufficient to block HIV ex vivo. This proof-of-concept study suggests film formulations for microbicides merit further investigation.

Safety, Acceptability and Adherence of Dapivirine Vaginal Ring in a Microbicide Clinical Trial Conducted in Multiple Countries in Sub-Saharan Africa

Background

This was the first microbicide trial conducted in Africa to evaluate an antiretroviral-containing vaginal ring as an HIV prevention technology for women.

Objectives

The trial assessed and compared the safety, acceptability and adherence to product use of a 4-weekly administered vaginal ring containing the antiretroviral microbicide, dapivirine, with a matching placebo ring among women from four countries in sub-Saharan Africa.

Methods

280 Healthy, sexually active, HIV-negative women, aged 18 to 40 years were enrolled with 140 women randomised to a dapivirine vaginal ring (25 mg) and 140 women to a matching placebo ring, inserted 4-weekly and used over a 12-week period. Safety was evaluated by pelvic examination, colposcopy, clinical laboratory assessments, and adverse events. Blood samples for determination of plasma concentrations of dapivirine were collected at Weeks 0, 4 and 12. Residual dapivirine levels in returned rings from dapivirine ring users were determined post-trial. Participant acceptability and adherence to ring use were assessed by self-reports.

Results

No safety concerns or clinically relevant differences were observed between the dapivirine and placebo ring groups. Plasma dapivirine concentrations immediately prior to ring removal were similar after removal of the first and third ring, suggesting consistent ring use over the 12-week period. No clear relationship was observed between the residual amount of dapivirine in used rings and corresponding plasma concentrations. Self-reported adherence to daily use of the vaginal rings over the 12-week trial period was very high. At the end of the trial, 96% of participants reported that the ring was usually comfortable to wear, and 97% reported that they would be willing to use it in the future if proven effective.

Conclusions

The dapivirine vaginal ring has a favourable safety and acceptability profile. If proven safe and effective in large-scale trials, it will be an important component of combination HIV prevention approaches for women.

Trial Registration

ClinicalTrials.gov NCT01071174

Phase 1 Safety, Pharmacokinetics, and Pharmacodynamics of Dapivirine and Maraviroc Vaginal Rings: A Double-Blind Randomized Trial

BACKGROUND

Variable adherence limits effectiveness of daily oral and intravaginal tenofovir-containing pre-exposure prophylaxis. Monthly vaginal antiretroviral rings are one approach to improve adherence and drug delivery.

METHODS

MTN-013/IPM 026, a multisite, double-blind, randomized, placebo-controlled trial in 48 HIV-negative US women, evaluated vaginal rings containing dapivirine (DPV) (25 mg) and maraviroc (MVC) (100 mg), DPV only, MVC only, and placebo used continuously for 28 days. Safety was assessed by adverse events. Drug concentrations were quantified in plasma, cervicovaginal fluid (CVF), and cervical tissue. Cervical biopsy explants were challenged with HIV ex vivo to evaluate pharmacodynamics.

RESULTS

There was no difference in related genitourinary adverse events between treatment arms compared with placebo. DPV and MVC concentrations rose higher initially before falling more rapidly with the combination ring compared with relatively stable concentrations with the single-drug rings. DPV concentrations in CVF were 1 and 5 log10 greater than cervical tissue and plasma for both rings. MVC was consistently detected only in CVF. DPV and MVC CVF and DPV tissue concentrations dropped rapidly after ring removal. Cervical tissue showed a significant inverse linear relationship between HIV replication and DPV levels.

CONCLUSIONS

In this first study of a combination microbicide vaginal ring, all 4 rings were safe and well tolerated. Tissue DPV concentrations were 1000 times greater than plasma concentrations and single drug rings had more stable pharmacokinetics. DPV, but not MVC, demonstrated concentration-dependent inhibition of HIV-1 infection in cervical tissue. Because MVC concentrations were consistently detectable only in CVF and not in plasma, improved drug release of MVC rings is needed.

Preclinical assessments of vaginal microbicide candidate safety and efficacy

Sexually transmitted infections like HIV, HPV, and HSV-2, as well as unplanned pregnancy, take a huge toll on women worldwide. Woman-initiated multipurpose prevention technologies that contain antiviral/antibacterial drugs (microbicides) and a contraceptive to simultaneously target sexually transmitted infections and unplanned pregnancy are being developed to reduce these burdens. This review will consider products that are applied topically to the vagina. Rectally administered topical microbicides in development for receptive anal intercourse are outside the scope of this review. Microbicide and microbicide/contraceptive candidates must be rigorously evaluated in preclinical models of safety and efficacy to ensure that only candidates with favorable risk benefit ratios are advanced into human clinical trials. This review describes the comprehensive set of in vitro, ex vivo, and in vivo models used to evaluate the preclinical safety and antiviral efficacy of microbicide and microbicide/contraceptive candidates.

The sheep as a model of preclinical safety and pharmacokinetic evaluations of candidate microbicides

When developing novel microbicide products for the prevention of HIV infection, the preclinical safety program must evaluate not only the active pharmaceutical ingredient but also the product itself. To that end, we applied several relatively standard toxicology study methodologies to female sheep, incorporating an assessment of the pharmacokinetics, safety, tolerability, and local toxicity of a dapivirine-containing human vaginal ring formulation (Dapivirine Vaginal Ring-004). We performed a 3-month general toxicology study, a preliminary pharmacokinetic study using drug-loaded vaginal gel, and a detailed assessment of the kinetics of dapivirine delivery to plasma, vaginal, and rectal fluid and rectal, vaginal, and cervical tissue over 28 days of exposure and 3 and 7 days after removal of the ring. The findings of the general toxicology study supported the existing data from both preclinical and clinical studies in that there were no signs of toxicity related to dapivirine. In addition, the presence of the physical dapivirine ring did not alter local or systemic toxicity or the pharmacokinetics of dapivirine. Pharmacokinetic studies indicated that the dapivirine ring produced significant vaginal tissue levels of dapivirine. However, no dapivirine was detected in cervical tissue samples using the methods described here. Plasma and vaginal fluid levels were lower than those in previous clinical studies, while there were detectable dapivirine levels in the rectal tissue and fluid. All tissue and fluid levels tailed off rapidly to undetectable levels following removal of the ring. The sheep represents a very useful model for the assessment of the safety and pharmacokinetics of microbicide drug delivery devices, such as the vaginal ring.

Characteristics of Women Enrolled into a Randomized Clinical Trial of Dapivirine Vaginal Ring for HIV-1 Prevention

Introduction

Women in sub-Saharan Africa are a priority population for evaluation of new biomedical HIV-1 prevention strategies. Antiretroviral pre-exposure prophylaxis is a promising prevention approach; however, clinical trials among young women using daily or coitally-dependent products have found low adherence. Antiretroviral-containing vaginal microbicide rings, which release medication over a month or longer, may reduce these adherence challenges.

Methods

ASPIRE (A Study to Prevent Infection with a Ring for Extended Use) is a phase III, randomized, double-blind, placebo-controlled trial testing the safety and effectiveness of a vaginal ring containing the non-nucleoside reverse transcriptase inhibitor dapivirine for prevention of HIV-1 infection. We describe the baseline characteristics of African women enrolled in the ASPIRE trial.

Results

Between August 2012 and June 2014, 5516 women were screened and 2629 HIV-1 seronegative women between 18–45 years of age were enrolled from 15 research sites in Malawi, South Africa, Uganda, and Zimbabwe. The median age was 26 years (IQR 22–31) and the majority (59%) were unmarried. Nearly 100% of participants reported having a primary sex partner in the prior three months but 43% did not know the HIV-1 status of their primary partner; 17% reported additional concurrent partners. Nearly two-thirds (64%) reported having disclosed to primary partners about planned vaginal ring use in the trial. Sexually transmitted infections were prevalent: 12% had Chlamydia trachomatis, 7% Trichomonas vaginalis, 4% Neisseria gonorrhoeae, and 1% syphilis.

Conclusions

African HIV-1 seronegative women at risk of HIV -1 infection were successfully enrolled into a phase III trial of dapivirine vaginal ring for HIV-1 prevention.

Precise engineering of dapivirine-loaded nanoparticles for the development of anti-HIV vaginal microbicides

Polymeric nanoparticles (NPs) have the potential to provide effective and safe delivery of antiretroviral drugs in the context of prophylactic anti-HIV vaginal microbicides. Dapivirine-loaded poly(d,l-lactic-co-glycolic acid) (PLGA) NPs were produced by an emulsion-solvent evaporation method, optimized for colloidal properties using a 3-factor, 3-level Box-Behnken experimental design, and characterized for drug loading, production yield, morphology, thermal behavior, drug release, in vitro cellular uptake, cytotoxicity and pro-inflammatory potential. Also, drug permeability/membrane retention in well-established HEC-1-A and CaSki cell monolayer models as mediated by NPs was assessed in the absence or presence of mucin. Box-Behnken design allowed optimizing monodisperse 170nm drug-loaded NPs. Drug release experiments showed an initial burst effect up to 4h, followed by sustained 24h release at pH 4.2 and 7.4. NPs were readily taken up by different genital and macrophage cell lines as assessed by fluorescence microscopy. Drug-loaded NPs presented lower or at least similar cytotoxicity as compared to the free drug, with up to around one-log increase in half-maximal cytotoxic concentration values. In all cases, no relevant changes in cell pro-inflammatory cytokine/chemokine production were observed. Dapivirine transport across cell monolayers was significantly decreased when mucin was present at the donor side with either NPs or the free drug, thus evidencing the influence of this natural glycoprotein in membrane permeability. Moreover, drug retention in cell monolayers was significantly higher for NPs in comparison with the free drug. Overall, obtained dapivirine-loaded PLGA NPs possess interesting technological and biological features that may contribute to their use as novel safe and effective vaginal microbicides.

Barrier methods for human immunodeficiency virus prevention

Condoms remain the most effective barrier against the sexual transmission of the human immunodeficiency virus (HIV). Male condoms have proven to be 80% to 90% effective, and female condoms have similar results. Poor adherence and improper use limit their effectiveness. In addition to condoms, microbicides are a promising barrier against HIV transmission. More than 50 candidate topical microbicide compounds have undergone preclinical or clinical testing in the last 10 years, but there are currently no US Food and Drug Administration (FDA)-approved compounds. Rectal microbicides are also being developed, as anal receptive sex is an effective mode of HIV transmission.

Dual quantification of dapivirine and maraviroc in cervicovaginal secretions from ophthalmic tear strips and polyester-based swabs via liquid chromatographic-tandem mass spectrometric (LC-MS/MS) analysis

BACKGROUND

Topical microbicidal agents are being actively pursued as a modality to prevent HIV viral transmission during sexual intercourse. Quantification of antiretroviral agents in specimen sources where antiviral activity is elicited is critical, and drug measurements in cervicovaginal fluid can provide key information on local drug concentrations. Two antiretroviral drugs, dapivirine and maraviroc, have gained interest as vaginal microbicidal agents, and rugged methods are required for their quantification in cervicovaginal secretions.

METHODS

Cervicovaginal fluid spiked with dapivirine and maraviroc were applied to ophthalmic tear strips or polyester-based swabs to mimic collection procedures used in clinical studies. Following sample extraction and the addition of isotopically labeled internal standards, samples were subjected to liquid chromatographic-tandem mass spectrometric (LC-MS/MS) analysis using a Waters BEH C8, 50mm×2.1mm, 1.7μm particle size column, on an API 4000 mass analyzer operated in selective reaction monitoring mode. The method was validated according to FDA Bioanalytical Method Validation guidelines.

RESULTS

Due to the disparate saturation capacity of the tested collection devices, the analytical measuring ranges for dapivirine and maravirocin cervicovaginal fluid on the ophthalmic tear strip were 0.05-25ng/tear strip, and 0.025-25ng/tear strip, respectively. As for the polyester-based swab, the analytical measuring ranges were 0.25-125ng/swab for dapivirine and 0.125-125ng/swab for maraviroc. Dilutional studies were performed for both analytes to extended ranges of 25,000ng/tear strip and 11,250ng/swab. Standard curves were generated via weighted (1/x(2)) linear or quadratic regression of calibrators. Precision, accuracy, stability and matrix effects studies were all performed and deemed acceptable according to the recommendations of the FDA Bioanalytical Method Validation guidelines.

CONCLUSIONS

A rugged LC-MS/MS method for the dual quantification of dapivirine and maraviroc in cervicovaginal fluid using two unique collection devices has been developed and validated. The described method meets the criteria to support large research trials.

A safety and pharmacokinetic trial assessing delivery of dapivirine from a vaginal ring in healthy women

OBJECTIVES

Women-initiated HIV-prevention products are urgently needed. To address this need, a trial was conducted to assess the safety and pharmacokinetics of a silicone elastomer matrix vaginal ring containing 25 mg of the antiretroviral drug dapivirine when used continuously for 28 consecutive days.

METHODS

A double-blind, randomized, placebo-controlled trial was conducted in 16 healthy, HIV-negative women, 18-40 years of age, who were randomized 1:1 to use either the active or matching placebo ring for 28 days. Participants were followed during and for 28 days after ring use for safety and pharmacokinetic evaluations.

RESULTS

The dapivirine vaginal ring was safe and well tolerated with no differences in safety endpoints between the active and placebo ring. The concentration-time plots of dapivirine in vaginal fluid were indicative of a sustained release of dapivirine over the 28 days of use. Dapivirine vaginal fluid concentrations were highest near the ring, followed by the cervix and introïtus (mean Cmax of 80, 67 and 31 μg/g, respectively). Vaginal fluid concentrations of dapivirine on the day of ring removal (day 28) at all three collection sites exceeded by more than 3900-fold the IC99 for dapivirine in a tissue explant infection model. Plasma dapivirine concentrations were low (< 1 ng/ml) and remained well below those observed at the maximum tolerated dose for oral treatment (mean Cmax of 2286  ng/ml).

CONCLUSION

The dapivirine vaginal ring has a safety and pharmacokinetic profile that supports its use as a sustained-release topical microbicide for HIV-1 prevention in women.

The development and validation of an UHPLC-MS/MS method for the rapid quantification of the antiretroviral agent dapivirine in human plasma

BACKGROUND

Dapivirine is a non-nucleoside reverse transcriptase inhibitor designed to prevent HIV-1 viral replication and subsequent propagation. A sensitive method is required to quantify plasma concentrations to assess drug efficacy.

RESULTS

Dapivirine-spiked plasma was combined with acetonitrile containing deuterated IS and was processed for analysis. The method has an analytical measuring range from 20 to 10,000 pg/ml. For the LLOQ, low, mid and high QCs, intra- and inter-assay precision (%CV) ranged from 5.58 to 13.89% and 5.23 to 13.36%, respectively, and intra- and inter-day accuracy (% deviation) ranged from -5.61 to 0.75% and -4.30 to 6.24%, respectively.

CONCLUSION

A robust and sensitive LC-MS/MS assay for the high-throughput quantification of the antiretroviral drug dapivirine in human plasma was developed and validated following bioanalytical validation guidelines. The assay meets criteria for the analysis of samples from large research trials.

Increased Dapivirine tissue accumulation through vaginal film codelivery of dapivirine and Tenofovir

The HIV-1 replication inhibitor dapivirine (DPV) is one of the most promising drug candidates being used in topical microbicide products for prevention of HIV-1 sexual transmission. To be able to block HIV-1 replication, DPV must have access to the viral reverse transcriptase enzyme. The window for DPV to access the enzyme happens during the HIV-1 cellular infection cycle. Thus, in order for DPV to exert its anti-HIV activity, it must be present in the mucosal tissue or cells where HIV-1 infection occurs. A dosage form containing DPV must be able to deliver the drug to the tissue site of action. Polymeric films are solid dosage forms that dissolve and release their payload upon contact with fluids. Films have been used as vaginal delivery systems of topical microbicide drug candidates including DPV. For use in topical microbicide products containing DPV, polymeric films must prove their ability to deliver DPV to the target tissue site of action. Ex vivo exposure studies of human ectocervical tissue to DPV film revealed that DPV was released from the film and did diffuse into the tissue in a concentration dependent manner indicating a process of passive diffusion. Analysis of drug distribution in the tissue revealed that DPV accumulated mostly at the basal layer of the epithelium infiltrating the upper part of the stroma. Furthermore, as a combination microbicide product, codelivery of DPV and TFV from a polymeric film resulted in a significant increase in DPV tissue concentration [14.21 (single entity film) and 31.03 μg/g (combination film)], whereas no impact on TFV tissue concentration was found. In vitro release experiments showed that this observation was due to a more rapid DPV release from the combination film as compared to the single entity film. In conclusion, the findings of this study confirm the ability of polymeric films to deliver DPV and TFV to human ectocervical tissue and show that codelivery of the two agents has a significant impact on DPV tissue accumulation. These findings support the use of polymeric films for topical microbicide products containing DPV and/or TFV.

Modified silicone elastomer vaginal gels for sustained release of antiretroviral HIV microbicides

We previously reported nonaqueous silicone elastomer gels (SEGs) for sustained vaginal administration of the CCR5-targeted entry inhibitor maraviroc (MVC). Here, we describe chemically modified SEGs (h-SEGs) in which the hydrophobic cyclomethicone component was partially replaced with relatively hydrophilic silanol-terminated polydimethylsiloxanes (st-PDMS). MVC and emtricitabine (a nucleoside reverse transcriptase inhibitor), both currently under evaluation as topical microbicides to counter sexual transmission of human immunodeficiency virus type 1 (HIV-1), were used as model antiretroviral (ARV) drugs. Gel viscosity and in vitro ARV release were significantly influenced by st-PDMS molecular weight and concentration in the h-SEGs. Unexpectedly, gels prepared with lower molecular weight grades of st-PDMS showed higher viscosities. h-SEGs provided enhanced release over 24 h compared with aqueous hydroxyethylcellulose (HEC) gels, did not modify the pH of simulated vaginal fluid (SVF), and were shown to less cytotoxic than standard HEC vaginal gel. ARV solubility increased as st-PDMS molecular weight decreased (i.e., as percentage hydroxyl content increased), helping to explain the in vitro release trends. Dye ingression and SVF dilution studies confirmed the increased hydrophilicity of the h-SEGs. h-SEGs have potential for use in vaginal drug delivery, particularly for ARV-based HIV-1 microbicides.

A randomized male tolerance study of dapivirine gel following multiple topical penile exposures (MTN 012/IPM 010)

Dapivirine (DPV) is a nonnucleoside reverse transcriptase inhibitor with a favorable safety profile following vaginal application. A penile tolerance study was conducted prior to further development of DPV as a candidate vaginal microbicide. Twenty-four circumcised and 24 uncircumcised (N=48) healthy HIV-negative male participants aged 18 years or older were randomized 2:1:1 to apply DPV 0.05% gel, matched placebo gel, or universal placebo gel, respectively, to their penis once daily for 7 sequential days. The safety, acceptability, and pharmacokinetic profile of DPV 0.05% gel were assessed by the presence of Grade 2 or higher genitourinary adverse events (AEs) and systemic AEs, a behavioral questionnaire, and pharmacokinetic plasma blood draw, respectively, at the final clinic visit (FCV). There were no Grade 2 genitourinary AEs in 47 participants completing the FCV. One participant in the DPV arm failed to attend the FCV. There were 13 AEs reported; all were Grade 1 except one Grade 2 corneal laceration unrelated to study product. Participants liked the gel to a moderate extent, yet 72% reported they would be "very likely" to use a gel like the one they used in the study every time they have intercourse. DPV was detectable in plasma in all 23 DPV arm study participants at the FCV. On average, the circumcised participants' DPV concentrations were 54% of those in uncircumcised participants (p=0.07). Topical seven-day penile application of DPV 0.05% gel was locally and systemically safe, was acceptable to male participants, and resulted in systemic exposure to the drug.

Development of dapivirine vaginal ring for HIV prevention

In the continuing effort to develop effective HIV prevention methods for women, a vaginal ring containing the non-nucleoside reverse transcriptase inhibitor dapivirine is currently being tested in two safety and efficacy trials. This paper reviews dapivirine ring's pipeline development process, including efforts to determine safe and effective dosing levels as well as identify delivery platforms with the greatest likelihood of success for correct and consistent use. Dapivirine gel and other formulations were developed and tested in preclinical and clinical studies. Multiple vaginal ring prototypes were also tested, resulting in the current ring design as well as additional designs under consideration for future testing. Efficacy results from clinical trials are expected in 2015. Through ongoing consultations with national regulatory authorities, licensure requirements for dapivirine vaginal ring approval have been defined. This article is based on a presentation at the "Product Development Workshop 2013: HIV and Multipurpose Prevention Technologies," held in Arlington, Virginia on February 21-22, 2013. It forms part of a special supplement to Antiviral Research.

Novel preclinical models of topical PrEP pharmacodynamics provide rationale for combination of drugs with complementary properties

Background

The limited success of recent HIV topical pre-exposure prophylaxis clinical trials highlights the need for more predictive models of drug efficacy that better simulate what may happen during sexual exposure. To address this gap, we developed complementary in vitro models to evaluate the ability of drugs to retain anti-HIV activity if cells were washed with seminal plasma (simulating what may happen following exposure to ejaculate), and to protect drug-naive T cells (representing newly recruited immune cells) co-cultured with explants that had been pretreated with drug. We focused on tenofovir disoproxil fumarate (TDF), the non-nucleoside reverse transcriptase inhibitors dapivirine (DPV) and IQP-0528, and the entry inhibitors maraviroc (MVC) and the D-peptide chol-PIE-12 trimer (PIE12). Studies were extended to macaques and the ability of cervical biopsies obtained from animals treated with an intravaginal ring formulation of IQP-0528 to protect ex vivo co-cultured T cells was determined. The antiviral activity of cervicovaginal lavage samples against a primary Clade C isolate was also measured and correlated with drug levels.

Results

Cells exposed to TDF were equally protected from HIV whether or not the drug-treated cells were washed with medium or seminal plasma prior to challenge. In contrast, several-fold higher concentrations of NNRTIs and entry inhibitors were needed to attain similar levels of HIV inhibition following a wash with seminal plasma. Conversely, the NNRTIs and PIE12, but not TDF or MVC, were effectively transferred from ex vivo treated explants and protected co-cultured T cells. Biopsies obtained from IQP-0528 ring-treated macaques also protected co-cultured T cells with viral inhibition ranging from 42-72%. Antiviral activity correlated with the concentration of drug recovered. Combinations of TDF with IQP-0528 protected in both in vitro models.

Conclusions

Together, these models suggest that intracellularly retained drugs such as TDF may protect resident immune cells following coitus but sustained delivery may be required to protect immune cells subsequently recruited into the genital tract. Sustained delivery may also be critical for NNRTIs, which are rapidly transported out of cells and could be lost following sexual intercourse. An ideal approach may be a combination of drugs with complementary bioavailability profiles formulated for sustained delivery.

Using glycosaminoglycan/chemokine interactions for the long-term delivery of 5P12-RANTES in HIV prevention

5P12-RANTES is a recently developed chemokine analogue that has shown high level protection from SHIV infection in macaques. However, the feasibility of using 5P12-RANTES as a long-term HIV prevention agent has not been explored partially due to the lack of available delivery devices that can easily be modified for long-term release profiles. Glycosaminoglycans (GAGs) have been known for their affinity for various cytokines and chemokines, including native RANTES, or CCL5. In this work, we investigated used of GAGs in generating a chemokine drug delivery device. Initial studies used surface plasmon resonance analysis to characterize and compare the affinities of different GAGs to 5P12-RANTES. These different GAGs were then incorporated into drug delivery polymeric hydrogels to engineer sustained release of the chemokines. In vitro release studies of 5P12-RANTES from the resulting polymers were performed, and we found that 5P12-RANTES release from these polymers can be controlled by the amount and type of GAG incorporated. Polymer disks containing GAGs with stronger affinity to 5P12-RANTES resulted in more sustained and longer term release than did polymer disks containing GAGs with weaker 5P12-RANTES affinity. Similar trends were observed by varying the amount of GAGs incorporated into the delivery system. 5P12-RANTES released from these polymers demonstrated good levels of CCR5 blocking, retaining activity even after 30 days of incubation.

HIV PrEP Trials: The Road to Success

The global HIV epidemic cannot be controlled by current treatment or prevention strategies. Pre-exposure prophylaxis (PrEP) using antiretrovirals is a promising approach to curbing the spread of HIV transmission. Recently, four clinical trials demonstrated favorable results when antiretroviral PrEP was administered topically or orally. However, two additional trials were unable to demonstrate a benefit, indicating that further study is required to define the populations and conditions under which PrEP will be effective. Adherence is highly correlated with protection, yet the exact level of adherence required is unknown. Future studies may require increased drug exposure testing and more objective methods to monitor adherence in real-time. Although the development of drug resistance in the PrEP trials has been low, it remains a concern, as therapeutic options could be compromised for those who seroconvert while on PrEP.

Microbicide dosage forms

Microbicides are topically applied, user controlled dosage forms that are being developed to prevent the transmission of HIV during coitus. Early candidates focused on coitally dependent dosage forms such as gels and creams. More recent development has focused on broadening the coitally dependent options through the introduction of films and fast dissolving tablets. Additionally, it has become important to have longer acting products to minimize the burden of user compliance and thus vaginal rings have been developed providing sustained delivery of antiretroviral drugs. This chapter discusses the history of microbicides along with a detailed description of coitally dependent products, gels, films, tablets diaphragms, as well as coitally independent dosage forms such as vaginal rings and the introduction of a new technology, electrospun fibers.

The Need for Development of New HIV-1 Reverse Transcriptase and Integrase Inhibitors in the Aftermath of Antiviral Drug Resistance

The use of highly active antiretroviral therapy (HAART) involves combinations of drugs to achieve maximal virological response and reduce the potential for the emergence of antiviral resistance. There are two broad classes of reverse transcriptase inhibitors, the nucleoside reverse transcriptase inhibitors (NRTIs) and nonnucleoside reverse transcriptase inhibitors (NNRTIs). Since the first classes of such compounds were developed, viral resistance against them has necessitated the continuous development of novel compounds within each class. This paper considers the NRTIs and NNRTIs currently in both preclinical and clinical development or approved for second line therapy and describes the patterns of resistance associated with their use, as well as the underlying mechanisms that have been described. Due to reasons of both affordability and availability, some reverse transcriptase inhibitors with low genetic barrier are more commonly used in resource-limited settings. Their use results to the emergence of specific patterns of antiviral resistance and so may require specific actions to preserve therapeutic options for patients in such settings. More recently, the advent of integrase strand transfer inhibitors represents another major step forward toward control of HIV infection, but these compounds are also susceptible to problems of HIV drug resistance.

A silicone elastomer vaginal ring for HIV prevention containing two microbicides with different mechanisms of action

Vaginal rings are currently being developed for the long-term (at least 30 days) continuous delivery of microbicides against human immunodeficiency virus (HIV). Research to date has mostly focused on devices containing a single antiretroviral compound, exemplified by the 25mg dapivirine ring currently being evaluated in a Phase III clinical study. However, there is a strong clinical rationale for combining antiretrovirals with different mechanisms of action in a bid to increase breadth of protection and limit the emergence of resistant strains. Here we report the development of a combination antiretroviral silicone elastomer matrix-type vaginal ring for simultaneous controlled release of dapivirine, a non-nucleoside reverse transcriptase inhibitor, and maraviroc, a CCR5-targeted HIV-1 entry inhibitor. Vaginal rings loaded with 25mg dapivirine and various quantities of maraviroc (50-400mg) were manufactured and in vitro release assessed. The 25mg dapivirine and 100mg maraviroc formulation was selected for further study. A 24-month pharmaceutical stability evaluation was conducted, indicating good product stability in terms of in vitro release, content assay, mechanical properties and related substances. This combination ring product has now progressed to Phase I clinical testing.

A modified SILCS contraceptive diaphragm for long-term controlled release of the HIV microbicide dapivirine

BACKGROUND

There is considerable interest in developing new multipurpose prevention technologies to address women's reproductive health needs. This study describes an innovative barrier contraceptive device--based on the SILCS diaphragm--that also provides long-term controlled release of the lead candidate anti-HIV microbicide dapivirine.

STUDY DESIGN

Diaphragm devices comprising various dapivirine-loaded polymer spring cores overmolded with a nonmedicated silicone elastomer sheath were fabricated by injection molding processes. In vitro release testing, thermal analysis and mechanical characterization were performed on the devices.

RESULTS

A diaphragm device containing a polyoxymethylene spring core loaded with 10% w/w dapivirine provided continuous and controlled release of dapivirine over a 6-month period, with a mean in vitro daily release rate of 174 mcg/day. The mechanical properties of the new diaphragm were closely matched to the SILCS diaphragm.

CONCLUSIONS

The study demonstrates proof of concept for a dapivirine-releasing diaphragm with daily release quantities potentially capable of preventing HIV transmission. In discontinuous clinical use, release of dapivirine may be readily extended over 1 or more years.

Development and validation of a HPLC method for the assay of dapivirine in cell-based and tissue permeability experiments

Dapivirine, a non-nucleoside reverse transcriptase inhibitor, is being currently used for the development of potential anti-HIV microbicide formulations and delivery systems. A new high-performance liquid chromatography (HPLC) method with UV detection was developed for the assay of this drug in different biological matrices, namely cell lysates, receptor media from permeability experiments and homogenates of mucosal tissues. The method used a reversed-phase C18 column with a mobile phase composed of trifluoroacetic acid solution (0.1%, v/v) and acetonitrile in a gradient mode. Injection volume was 50μL and the flow rate 1mL/min. The total run time was 12min and UV detection was performed at 290nm for dapivirine and the internal standard (IS) diphenylamine. A Box-Behnken experimental design was used to study different experimental variables of the method, namely the ratio of the mobile phase components and the gradient time, and their influence in responses such as the retention factor, tailing factor, and theoretical plates for dapivirine and the IS, as well as the peak resolution between both compounds. The optimized method was further validated and its usefulness assessed for in vitro and ex vivo experiments using dapivirine or dapivirine-loaded nanoparticles. The method showed to be selective, linear, accurate and precise in the range of 0.02-1.5μg/mL. Other chromatographic parameters, namely carry-over, lower limit of quantification (0.02μg/mL), limit of detection (0.006μg/mL), recovery (equal or higher than 90.7%), and sample stability at different storage conditions, were also determined and found adequate for the intended purposes. The method was successfully used for cell uptake assays and permeability studies across cell monolayers and pig genital mucosal tissues. Overall, the proposed method provides a simple, versatile and reliable way for studying the behavior of dapivirine in different biological matrices and assessing its potential as an anti-HIV microbicide drug.

Combinations of griffithsin with other carbohydrate-binding agents demonstrate superior activity against HIV Type 1, HIV Type 2, and selected carbohydrate-binding agent-resistant HIV Type 1 strains

Carbohydrate-binding agents (CBAs) are potential HIV microbicidal agents with a high genetic barrier to resistance. We wanted to evaluate whether two mannose-specific CBAs, recognizing multiple and often distinct glycan structures on the HIV envelope gp120, can interact synergistically against HIV-1, HIV-2, and HIV-1 strains that were selected for resistance against particular CBAs [i.e., 2G12 mAb and microvirin (MVN)]. Paired CBA/CBA combinations mainly showed synergistic activity against both wild-type HIV-1 and HIV-2 but also 2G12 mAb- and MVN-resistant HIV-1 strains as based on the median effect principle with combination indices (CIs) ranging between 0.29 and 0.97. Upon combination, an increase in antiviral potency of griffithsin (GRFT) up to ∼12-fold (against HIV-1), ∼8-fold (against HIV-2), and ∼6-fold (against CBA-resistant HIV-1) was observed. In contrast, HHA/GNA combinations showed additive activity against wild-type HIV-1 and HIV-2 strains, but remarkable synergy with HHA and GNA was observed against 2G12 mAb- and MVN-resistant HIV-1 strains (CI, 0.64 and 0.49, respectively). Overall, combinations of GRFT and other CBAs showed synergistic activity against HIV-1, HIV-2, and even against certain CBA-resistant HIV-1 strains. The CBAs tested appear to have distinct binding patterns on the gp120 envelope and therefore do not necessarily compete with each other's glycan binding sites on gp120. As a result, there might be no steric hindrance between two different CBAs in their competition for glycan binding (except for the HHA/GNA combination). These data are encouraging for the use of paired CBA combinations in topical microbicide applications (e.g., creams, gels, or intravaginal rings) to prevent HIV transmission.

The nonnucleoside reverse transcription inhibitor MIV-160 delivered from an intravaginal ring, but not from a carrageenan gel, protects against simian/human immunodeficiency virus-RT Infection

We previously showed that a carrageenan (CG) gel containing 50 μM MIV-150 (MIV-150/CG) reduced vaginal simian/human immunodeficiency virus (SHIV)-RT infection of macaques (56%, p>0.05) when administered daily for 2 weeks with the last dose given 8 h before challenge. Additionally, when 100 mg of MIV-150 was loaded into an intravaginal ring (IVR) inserted 24 h before challenge and removed 2 weeks after challenge, >80% protection was observed (p<0.03). MIV-160 is a related NNRTI with a similar IC(50), greater aqueous solubility, and a shorter synthesis. To objectively compare MIV-160 with MIV-150, herein we evaluated the antiviral effects of unformulated MIV-160 in vitro as well as the in vivo protection afforded by MIV-160 delivered in CG (MIV-160/CG gel) and in an IVR under regimens used with MIV-150 in earlier studies. Like MIV-150, MIV-160 exhibited potent antiviral activity against SHIV-RT in macaque vaginal explants. However, formulated MIV-160 exhibited divergent effects in vivo. The MIV-160/CG gel offered no protection compared to CG alone, whereas the MIV-160 IVRs protected significantly. Importantly, the results of in vitro release studies of the MIV-160/CG gel and the MIV-160 IVR suggested that in vivo efficacy paralleled the amount of MIV-160 released in vitro. Hundreds of micrograms of MIV-160 were released daily from IVRs while undetectable amounts of MIV-160 were released from the CG gel. Our findings highlight the importance of testing different modalities of microbicide delivery to identify the optimal formulation for efficacy in vivo.

Pharmacokinetics and efficacy of a vaginally administered maraviroc gel in rhesus macaques

OBJECTIVES

To investigate the pharmacokinetics (PK) of maraviroc, a CCR5-targeted HIV-1 entry inhibitor, in rhesus macaques following vaginal administration of various maraviroc-loaded aqueous hydroxyethylcellulose (HEC) gels, and to correlate the PK data with efficacy in a single high-dose vaginal SHIV-162P3 challenge model.

METHODS

Maraviroc concentrations in vaginal fluid (Weck-Cel(®) sponge), vaginal tissue (punch biopsy) and plasma were assessed over 72 h following single-dose vaginal application of various maraviroc-loaded HEC gels. The range of maraviroc gel concentrations was sufficiently broad (0.003%-3.3% w/w) that test gels included both fully solubilized and predominantly dispersed formulations. The efficacy of the HEC gels against a single high-dose vaginal SHIV-162P3 challenge was also measured, and correlated with the PK concentrations.

RESULTS

Maraviroc concentrations in vaginal fluid (range 10(4)-10(7) ng/mL), vaginal tissue (100-1200 ng/g) and plasma (<10(2) ng/mL) were highly dependent on maraviroc gel loading, irrespective of the form of the maraviroc component within the gel (solubilized versus dispersed). Fluid and plasma concentrations were generally highest 0.5 or 2 h after gel application, before declining steadily through to 72 h. Maraviroc concentrations in the various biological compartments correlated strongly with the extent of protection against vaginal SHIV-162P3 challenge. Complete protection was achieved with a 3.3% w/w maraviroc gel.

CONCLUSIONS

A high degree of correlation between PK and efficacy was observed. Based on the data obtained with the 3.3% w/w maraviroc gel, maintenance of vaginal fluid and tissue levels in the order of 10(7) ng/mL and 10(3) ng/g, respectively, are required for complete protection with this compound.

Antiviral drug resistance and the need for development of new HIV-1 reverse transcriptase inhibitors

Highly active antiretroviral therapy (HAART) consists of a combination of drugs to achieve maximal virological response and reduce the potential for the emergence of antiviral resistance. Despite being the first antivirals described to be effective against HIV, reverse transcriptase inhibitors remain the cornerstone of HAART. There are two broad classes of reverse transcriptase inhibitor, the nucleoside reverse transcriptase inhibitors (NRTIs) and nonnucleoside reverse transcriptase inhibitors (NNRTIs). Since the first such compounds were developed, viral resistance to them has inevitably been described; this necessitates the continuous development of novel compounds within each class. In this review, we consider the NRTIs and NNRTIs currently in both preclinical and clinical development or approved for second-line therapy and describe the patterns of resistance associated with their use as well as the underlying mechanisms that have been described. Due to reasons of both affordability and availability, some reverse transcriptase inhibitors with a low genetic barrier are more commonly used in resource-limited settings. Their use results in the emergence of specific patterns of antiviral resistance and so may require specific actions to preserve therapeutic options for patients in such settings.

In vitro profiling of the vaginal permeation potential of anti-HIV microbicides and the influence of formulation excipients

In the search for an effective anti-HIV microbicidal gel, limited drug penetration into the vaginal submucosa is a possible reason for failed protection against HIV transmission. To address this issue in early development, we here describe a simple in vitro strategy to predict the tissue permeation potential of vaginally applied drugs, based on solubility, permeability and flux assessment. We demonstrated this approach for four model microbicides (tenofovir, darunavir, saquinavir mesylate and dapivirine) and additionally examined the influence of formulation excipients on the permeation potential. When formulated in an aqueous-based HEC gel, high flux values across an HEC-1A cell layer were reached by tenofovir, as a result of its high aqueous solubility. In contrast, saquinavir and dapivirine fluxes remained low due to poor permeability and solubility, respectively. These low fluxes suggest limited in vivo tissue penetration, possibly leading to lack of efficacy. Dapivirine fluxes, however, could be enhanced up to 30-fold, by including formulation excipients such as polyethylene glycol 1000 (20%) or cyclodextrins (5%) in the HEC gels. Alternative formulations, i.e. emulsions or silicone elastomer gels, were less effective in flux enhancement compared to cyclodextrin-HEC gels. In conclusion, implementing the proposed solubility and permeability profiling in early microbicide development may contribute to the successful selection of promising microbicide candidates and appropriate formulations.

Controlled-release vaginal ring drug-delivery systems: a key strategy for the development of effective HIV microbicides

BACKGROUND

Over half of all HIV-infected adults are women and heterosexual intercourse is a significant mode of viral transmission. This review examines the potential for using polymeric vaginal ring systems to provide controlled delivery of HIV microbicides in order to prevent heterosexual transmission of the virus.

DISCUSSION

Continuous delivery of microbicides has the potential to be more effective than one-off dosing. Thus, controlled-release vaginal delivery devices are now a key area of HIV prevention research. Initial clinical trials on vaginal rings loaded with dapivirine (a candidate microbicide) have indicated that these products are safe and well tolerated by women. These devices are female-initiated, robust and capable of long-term delivery of the active agent.

CONCLUSIONS

Vaginal rings may offer an effective system for the controlled delivery of microbicides to prevent heterosexual transmission of HIV. Candidate vaginal ring microbicide products are now in clinical trials.

The importance of the vaginal delivery route for antiretrovirals in HIV prevention

The HIV/AIDS pandemic continues to be a global health priority, with high rates of new HIV-I infections persisting in young women. One HIV prevention strategy is topical pre-exposure prophylactics or microbicides, which are applied vaginally or rectally to protect the user from HIV and possibly other sexually transmitted infections. Vaginal microbicide delivery will be the focus of this review. Multiple nonspecific and specific antiretroviral microbicide products have been clinically evaluated, and many are in preclinical development, The events of HIV mucosal transmission and dynamics of the cervicovaginal environment should be considered for successful vaginal microbicide delivery. Beyond conventional vaginal formulations, intravaginal rings, tablets and films are employed as platforms in the hope to increase the likelihood of microbicide use. Furthermore, combining multiple antiretrovirals within a given formulation, combining a microbicide product with a vaginal device and integrating novel drug-delivery strategies within a microbicide product are approaches to successful vaginal-microbicide delivery.

An intravaginal ring for the simultaneous delivery of multiple drugs

Intravaginal delivery of microbicide combinations is a promising approach for the prevention of sexually transmitted infections, but requires a method of providing simultaneous, independent release of multiple agents into the vaginal compartment. A novel intravaginal ring (IVR) platform has been developed for simultaneous delivery of the reverse-transcriptase inhibitor tenofovir (TFV) and the guanosine analogue antiviral acyclovir (ACV) with independent control of release rate for each drug. The IVR is based on a pod design, with up to 10 individual polymer-coated drug cores embedded in the ring releasing through preformed delivery channels. The release rate from each pod is controlled independently of the others by the drug properties, polymer coating, and size and number of delivery channels. Pseudo-zero-order in vitro release of TFV (144 ± 10 µg day) and ACV (120 ± 19 µg day⁻¹) from an IVR containing both drugs was sustained for 28 days. The mechanical properties of the pod IVR were evaluated and compared with the commercially available Estring® (Pfizer, NY, NY). The pod-IVR design enables the vaginal delivery of multiple microbicides with differing physicochemical properties, and is an attractive approach for the sustained intravaginal delivery of relatively hydrophilic drugs that are difficult to deliver using conventional matrix IVR technology.