The future of HIV microbicides: challenges and opportunities

Microbicides for Topical HIV Immunoprophylaxis: Current Status and Future Prospects

Microbicides, which are classified as topical antiseptic agents, are a revolutionary advancement in HIV prevention aimed to prevent the entry of infectious agents into the human body, thus stopping the sexual transmission of HIV and other sexually transmitted diseases. Microbicides represent the promise of a new age in preventive measures against one of the world's most pressing health challenges. In addition to their direct antiviral effects during HIV transmission, microbicides also influence vaginal mucosal immunity. This article reviews microbicides by presenting different drug classifications and highlighting significant representatives from each group. It also explains their mechanisms of action and presents information about vaginal mucosal immune responses, emphasizing the critical role they play in responding to HIV during sexual transmission. The article discusses the following groups of microbicides: surfactants or membrane disruptors, vaginal milieu protectors, anionic polymers, dendrimers, carbohydrate-binding proteins, HIV replication inhibitors (reverse transcriptase inhibitors), and multi-purpose prevention technologies, which combine protection against HIV, other sexually transmitted diseases, and contraception. For each chemical compound, the article provides a brief overview of relevant preclinical and clinical research, emphasizing their potential as microbicides. The article offers insights into the multifaceted impact of microbicides, which signify a pivotal step forward in the pursuit of effective and accessible pre-exposure prophylaxis (PrEP).

Results of a phase 1, randomized, placebo-controlled first-in-human trial of griffithsin formulated in a carrageenan vaginal gel

HIV pre-exposure prophylaxis (PrEP) is dominated by clinical therapeutic antiretroviral (ARV) drugs. Griffithsin (GRFT) is a non-ARV lectin with potent anti-HIV activity. GRFT’s preclinical safety, lack of systemic absorption after vaginal administration in animal studies, and lack of cross-resistance with existing ARV drugs prompted its development for topical HIV PrEP. We investigated safety, pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity of PC-6500 (0.1% GRFT in a carrageenan (CG) gel) in healthy women after vaginal administration. This randomized, placebo-controlled, parallel group, double-blind first-in-human phase 1 study enrolled healthy, HIV-negative, non-pregnant women aged 24–45 years. In the open label period, all participants (n = 7) received single dose of PC-6500. In the randomized period, participants (n = 13) were instructed to self-administer 14 doses of PC-6500 or its matching CG placebo (PC-535) once daily for 14 days. The primary outcomes were safety and PK after single dose, and then after 14 days of dosing. Exploratory outcomes were GRFT concentrations in cervicovaginal fluids, PD, inflammatory mediators and gene expression in ectocervical biopsies. This trial is registered with ClinicalTrials.gov, number NCT02875119. No significant adverse events were recorded in clinical or laboratory results or histopathological evaluations in cervicovaginal mucosa, and no anti-drug (GRFT) antibodies were detected in serum. No cervicovaginal proinflammatory responses and no changes in the ectocervical transcriptome were evident. Decreased levels of proinflammatory chemokines (CXCL8, CCL5 and CCL20) were observed. GRFT was not detected in plasma. GRFT and GRFT/CG in cervicovaginal lavage samples inhibited HIV and HPV, respectively, in vitro in a dose-dependent fashion. These data suggest GRFT formulated in a CG gel is a safe and promising on-demand multipurpose prevention technology product that warrants further investigation.

Lipid Nanocarriers for Anti-HIV Therapeutics: A Focus on Physicochemical Properties and Biotechnological Advances

Since HIV was first identified, and in a relatively short period of time, AIDS has become one of the most devastating infectious diseases of the 21st century. Classical antiretroviral therapies were a major step forward in disease treatment options, significantly improving the survival rates of HIV-infected individuals. Even though these therapies have greatly improved HIV clinical outcomes, antiretrovirals (ARV) feature biopharmaceutic and pharmacokinetic problems such as poor aqueous solubility, short half-life, and poor penetration into HIV reservoir sites, which contribute to the suboptimal efficacy of these regimens. To overcome some of these issues, novel nanotechnology-based strategies for ARV delivery towards HIV viral reservoirs have been proposed. The current review is focused on the benefits of using lipid-based nanocarriers for tuning the physicochemical properties of ARV to overcome biological barriers upon administration. Furthermore, a correlation between these properties and the potential therapeutic outcomes has been established. Biotechnological advancements using lipid nanocarriers for RNA interference (RNAi) delivery for the treatment of HIV infections were also discussed.

Multipurpose Prevention Technologies: Oral, Parenteral, and Vaginal Dosage Forms for Prevention of HIV/STIs and Unplanned Pregnancy

There is a high global prevalence of HIV, sexually transmitted infections (STIs), and unplanned pregnancies. Current preventative daily oral dosing regimens can be ineffective due to low patient adherence. Sustained release delivery systems in conjunction with multipurpose prevention technologies (MPTs) can reduce high rates of HIV/STIs and unplanned pregnancies in an all-in-one efficacious, acceptable, and easily accessible technology to allow for prolonged release of antivirals and contraceptives. The concept and development of MPTs have greatly progressed over the past decade and demonstrate efficacious technologies that are user-accepted with potentially high adherence. This review gives a comprehensive overview of the latest oral, parenteral, and vaginally delivered MPTs in development as well as drug delivery formulations with the potential to advance as an MPT, and implementation studies regarding MPT user acceptability and adherence. Furthermore, there is a focus on MPT intravaginal rings emphasizing injection molding and hot-melt extrusion manufacturing limitations and emerging fabrication advancements. Lastly, formulation development considerations and limitations are discussed, such as nonhormonal contraceptive considerations, challenges with achieving a stable coformulation of multiple drugs, achieving sustained and controlled drug release, limiting drug-drug interactions, and advancing past preclinical development stages. Despite the challenges in the MPT landscape, these technologies demonstrate the potential to bridge gaps in preventative sexual and reproductive health care.

Topical microbicides for preventing sexually transmitted infections

BACKGROUND

This is a updated version of our Cochrane Review published in Issue 6, 2012. Sexually-transmitted infections (STIs) continue to rise worldwide, imposing an enormous morbidity and mortality burden. Effective prevention strategies, including microbicides, are needed to achieve the goals of the World Heath Organization (WHO) global strategy for the prevention and control of these infections.

OBJECTIVES

To determine the effectiveness and safety of topical microbicides for preventing acquisition of STIs, including HIV.

SEARCH METHODS

We undertook a comprehensive search of the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, LILACS, CLIB, Web of Science, ClinicalTrials.gov, WHO International Clinical Trials Registry Platform, and reference lists of relevant articles up to August 2020. In addition, we contacted relevant organisations and experts.

SELECTION CRITERIA

We included randomised controlled trials of vaginal microbicides compared to placebo (except for nonoxynol-9 because it is covered in related Cochrane Reviews). Eligible participants were sexually-active non-pregnant, WSM and MSM, who had no laboratory confirmed STIs.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened and selected studies, extracted data, and assessed risks of bias in duplicate, resolving differences by consensus. We conducted a fixed-effect meta-analysis, stratified by type of microbicide, and assessed the certainty of the evidence using the GRADE approach.

MAIN RESULTS

We included eight trials from the earlier version of the review and four new trials, i.e. a total of 12 trials with 32,464 participants (all WSM). We did not find any eligible study that enrolled MSM or reported fungal STI as an outcome. We have no study awaiting assessment. All 12 trials were conducted in sub-Saharan Africa, with one having a study site in the USA, and another having a site in India. Vaginal microbicides tested were BufferGel and PRO 2000 (1 trial, 3101 women), Carraguard (1 trial, 6202 women), cellulose sulphate (2 trials, 3069 women), dapivirine (2 trials, 4588 women), PRO 2000 (1 trial, 9385 women), C31G (SAVVY) (2 trials, 4295 women), and tenofovir (3 trials, 4958 women). All microbicides were compared to placebo and all trials had low risk of bias. Dapivirine probably reduces the risk of acquiring HIV infection: risk ratio (RR) 0.71, (95% confidence interval (CI) 0.57 to 0.89, I² = 0%, 2 trials, 4588 women; moderate-certainty evidence). The other microbicides may result in little to no difference in the risk of acquiring HIV (low-certainty evidence); including tenofovir (RR 0.83, 95% CI 0.68 to 1.02, cellulose sulphate (RR 1.20, 95% CI 0.74 to 1.95, BufferGel (RR 1.05, 95% CI 0.73 to 1.52), Carraguard (RR 0.89, 95% CI 0.71 to 1.11), PRO 2000 (RR 0.93, 95% CI 0.77 to 1.14), and SAVVY (RR 1.38, 95% CI 0.79 to 2.41). Existing evidence suggests that cellulose sulphate (RR 0.99, 95% CI 0.37 to 2.62, 1 trial, 1425 women), and PRO 2000 (RR 0.95, 95% CI 0.73 to 1.23) may result in little to no difference in the risk of getting herpes simplex virus type 2 infection (low-certainty evidence). Two studies reported data on tenofovir's effect on this virus. One suggested that tenofovir may reduce the risk (RR 0.55, 95% CI 0.36 to 0.82; 224 participants) while the other did not find evidence of an effect (RR 0.94, 95% CI 0.85 to 1.03; 1003 participants). We have not reported the pooled result because of substantial heterogeneity of effect between the two studies (l² = 85%). The evidence also suggests that dapivirine (RR 1.70, 95% CI 0.63 to 4.59), tenofovir (RR 1.27, 95% CI 0.58 to 2.78), cellulose sulphate (RR 0.69, 95% CI 0.26 to 1.81), and (Carraguard (RR 1.07, 95% CI 0.75 to 1.52) may have little or no effect on the risk of acquiring syphilis (low-certainty evidence). In addition, dapivirine (RR 0.97, 95% CI 0.89 to 1.07), tenofovir (RR 0.90, 95% CI 0.71 to 1.13), cellulose sulphate (RR 0.70, 95% CI 0.49 to 0.99), BufferGel (RR 0.97, 95% CI 0.65 to 1.45), Carraguard (RR 0.96, 95% CI 0.83 to 1.12), and PRO 2000 (RR 1.01, 95% CI 0.84 to 1.22) may result in little to no difference in the risk of acquiring chlamydia infection (low-certainty evidence). The evidence also suggests that current topical microbicides may not have an effect on the risk of acquiring gonorrhoea, condyloma acuminatum, trichomoniasis, or human papillomavirus infection (low-certainty evidence). Microbicide use in the 12 trials, compared to placebo, did not lead to any difference in adverse event rates. No study reported on acceptability of the intervention.  AUTHORS' CONCLUSIONS: Current evidence shows that vaginal dapivirine microbicide probably reduces HIV acquisition in women who have sex with men. Other types of vaginal microbicides have not shown evidence of an effect on acquisition of STIs, including HIV. Further research should continue on the development and testing of new microbicides.

Effectiveness of vaginal microbicides in preventing HIV transmission

OBJECTIVE

To evaluate the evidence on the effectiveness of vaginal microbicides in preventing HIV transmission in women.

METHODS

Systematic review through a comprehensive search of relevant electronic databases for eligible randomised controlled trials (RCTs) published through June 2019. Two authors independently screened titles and abstracts according to eligibility criteria, then extracted data and assessed risk of bias of included studies. We conducted a random-effects meta-analysis of risk ratios (RR) of HIV infection and assessed heterogeneity using chi-squared and I² tests. Sources of heterogeneity were investigated through subgroup analysis, publication bias was assessed using funnel plots, and certainty of evidence was graded using GRADEPro software.

RESULTS

We included 18 RCTs which enrolled 40,048 sexually active, HIV-negative, non-pregnant women, aged 16 years and older, mainly from sub-Saharan Africa. The intravaginal ring containing dapivirine significantly reduced HIV risk by 29% (RR 0.71, 95% CI: 0.57-0.89; 2 RCTs, 4,564 women, moderate certainty of evidence). Estimates of effect of tenofovir 1% (RR 0.83, 95% CI: 0.65-1.06), nonoxynol-9 (RR 1.15, 95% CI: 0.93-1.42), cellulose sulphate (RR 1.16, 95% CI: 0.61-2.21), SAVVY (RR 1.34, 95% CI: 0.69-2.59), Carraguard (RR 0.89, 95% CI: 0.71-1.10), BufferGel (RR 1.02, 95% CI: 0.71-1.46), 0.5% PRO2000 (RR 0.88, 95% CI: 0.60-1.28) and 2% PRO2000 (RR 0.81, 95% CI: 0.58-1.12) failed to reach statistical significance; each had low certainty of evidence.

CONCLUSION

The long-acting intravaginal ring containing dapivirine significantly reduced risk of HIV transmission in women by 29%. The remaining microbicides had no evident effect.

Aerosol Delivery of Synthetic mRNA to Vaginal Mucosa Leads to Durable Expression of Broadly Neutralizing Antibodies against HIV

There is a clear need for low-cost, self-applied, long-lasting approaches to prevent human immunodeficiency virus (HIV) infection in both men and women, even with the advent of pre-exposure prophylaxis (PrEP). Broadly neutralizing antibodies represent an option to improve HIV prophylaxis, but intravenous delivery, cold-chain stability requirements, low cervicovaginal concentrations, and cost may preclude their use. Here, we present an approach to express the anti-GP120 broadly neutralizing antibody PGT121 in the primary site of inoculation, the female reproductive tract, using synthetic mRNA. Expression is achieved through aerosol delivery of unformulated mRNA in water. We demonstrated high levels of antibody expression for over 28 days with a single mRNA administration in the reproductive tract of sheep. In rhesus macaques, neutralizing antibody titers in secretions developed within 4 h and simian-HIV (SHIV) infection of ex vivo explants was prevented. Persistence of PGT121 in vaginal secretions and epithelium was achieved through the incorporation of a glycosylphosphatidylinositol (GPI) anchor into the heavy chain of the antibody. Overall, we present a new paradigm to deliver neutralizing antibodies to the female reproductive tract for the prevention of HIV infections.

Unexpected synergistic HIV neutralization by a triple microbicide produced in rice endosperm

Our paper provides an approach for the durable deployment of anti-HIV agents in the developing world. We developed a transgenic rice line expressing three microbicidal proteins (the HIV-neutralizing antibody 2G12 and the lectins griffithsin and cyanovirin-N). Simultaneous expression in the same plant allows the crude seed extract to be used directly as a topical microbicide cocktail, avoiding the costs of multiple downstream processes. This groundbreaking strategy is realistically the only way that microbicidal cocktails can be manufactured at a cost low enough for the developing world, where HIV prophylaxis is most in demand.

The transmission of HIV can be prevented by the application of neutralizing monoclonal antibodies and lectins. Traditional recombinant protein manufacturing platforms lack sufficient capacity and are too expensive for developing countries, which suffer the greatest disease burden. Plants offer an inexpensive and scalable alternative manufacturing platform that can produce multiple components in a single plant, which is important because multiple components are required to avoid the rapid emergence of HIV-1 strains resistant to single microbicides. Furthermore, crude extracts can be used directly for prophylaxis to avoid the massive costs of downstream processing and purification. We investigated whether rice could simultaneously produce three functional HIV-neutralizing proteins (the monoclonal antibody 2G12, and the lectins griffithsin and cyanovirin-N). Preliminary in vitro tests showed that the cocktail of three proteins bound to gp120 and achieved HIV-1 neutralization. Remarkably, when we mixed the components with crude extracts of wild-type rice endosperm, we observed enhanced binding to gp120 in vitro and synergistic neutralization when all three components were present. Extracts of transgenic plants expressing all three proteins also showed enhanced in vitro binding to gp120 and synergistic HIV-1 neutralization. Fractionation of the rice extracts suggested that the enhanced gp120 binding was dependent on rice proteins, primarily the globulin fraction. Therefore, the production of HIV-1 microbicides in rice may not only reduce costs compared to traditional platforms but may also provide functional benefits in terms of microbicidal potency.

3-Hydroxyphthalic Anhydride- Modified Rabbit Anti-PAP IgG as a Potential Bifunctional HIV-1 Entry Inhibitor

Several studies have reported that amyloid fibrils in human semen formed from a naturally occurring peptide fragment of prostatic acidic phosphatase (PAP248-286), known as semen-derived enhancer of viral infection (SEVI), could dramatically enhance human immunodeficiency virus type 1 (HIV-1) infection. Accordingly, SEVI might serve as a novel target for new antiviral drugs or microbicide candidates for the prevention of sexually transmitted HIV. Theoretically, a special anti-PAP or anti-SEVI antibody could reduce the enhancement of viral infection by blocking the binding of HIV and SEVI fibrils. Here, 3-hydroxyphthalic anhydride modified anti-PAP248-286 antibody, named HP-API, exhibited broad-spectrum and highly effective anti-HIV-1 activities on different subtypes and tropism. By using time-of-addition, cell–cell fusion and a single-cycle HIV-1 infection assays, we demonstrated that HP-API is an HIV-1 entry/fusion inhibitor. Mechanism studies suggest that HP-API inhibited HIV-1 entry/fusion by targeting both HIV-1 gp120 envelop and CD4 receptor on the host cell specifically. It is noteworthy that HP-API abrogated the formation of SEVI fibrils and partially interfered with SEVI-mediated enhancement of HIV-1 infection. Based on these findings, HP-API could be considered a bifunctional HIV-1 entry/fusion inhibitor with high potential.

Semen-derived amyloidogenic peptides-Key players of HIV infection

Misfolding and amyloid aggregation of intrinsically disordered proteins (IDPs) are implicated in a variety of diseases. Studies have shown that membrane plays important roles on the formation of intermediate structures of IDPs that can initiate (and/or speed-up) amyloid aggregation to form fibers. The process of amyloid aggregation also disrupts membrane to cause cell death in amyloid diseases like Alzheimer's disease and type-2 diabetes. On the other hand, recent studies reported the membrane fusion properties of amyloid fibers. Remarkably, amyloid-fibril formation by short peptide fragments of highly abundant prostatic acidic-phosphatase (PAP) in human semen and are capable of boosting the rate of HIV infection up to 400,000-fold during sexual contact. Unlike the least toxic fully matured fibers of most amyloid proteins, the semen-derived enhancer of virus infection (SEVI) amyloid-fibrils of PAP peptide fragments are highly potent in rendering the maximum rate of HIV infection. This unusual property of amyloid fibers has witnessed increasing number of studies on the biophysical aspects of fiber formation and fiber-membrane interactions. NMR studies have reported a highly disordered partial helical structure in a membrane environment for the intrinsically disordered PAP peptide that promotes the fusion of the viral membrane with that of host cells. The purpose of this review article is to unify and integrate biophysical and immunological research reported in the previous studies on SEVI. Specifically, amyloid aggregation, dramatic HIV infection enhancing properties, membrane fusion properties, high resolution NMR structure, and approaches to eliminate the enhancement of HIV infection of SEVI peptides are discussed.

Application of nanotechnology for the development of microbicides

The vaginal route is increasingly being considered for both local and systemic delivery of drugs, especially those unsuitable for oral administration. One of the opportunities offered by this route but yet to be fully utilised is the administration of microbicides. Microbicides have an unprecedented potential for mitigating the global burden from HIV infection as heterosexual contact accounts for most of the new infections occurring in sub-Saharan Africa, the region with the highest prevalent rates. Decades of efforts and massive investment of resources into developing an ideal microbicide have resulted in disappointing outcomes, as attested by several clinical trials assessing the suitability of those formulated so far. The highly complex and multi-level biochemical interactions that must occur among the virus, host cells and the drug for transmission to be halted means that a less sophisticated approach to formulating a microbicide e.g. conventional gels, etc may have to give way for a different formulation approach. Nanotechnology has been identified to offer prospects for fabricating structures with high capability of disrupting HIV transmission. In this review, predominant challenges seen in microbicide development have been highlighted and possible ways of surmounting them suggested. Furthermore, formulations utilising some of these highly promising nanostructures such as liposomes, nanofibres and nanoparticles have been discussed. A perspective on how a tripartite collaboration among governments and their agencies, the pharmaceutical industry and academic scientists to facilitate the development of an ideal microbicide in a timely manner has also been briefly deliberated.

Microbicide vaginal rings: Technological challenges and clinical development

Vaginal rings (VRs) are flexible, torus-shaped, polymeric devices designed to sustain delivery of pharmaceutical drugs to the vagina for clinical benefit. Following first report in a 1970 patent application, several steroid-releasing VR products have since been marketed for use in hormone replacement therapy and contraception. Since 2002, there has been growing interest in the use of VR technology for delivery of drugs that can reduce the risk of sexual acquisition of human immunodeficiency virus type 1 (HIV-1), the causative agent of acquired immunodeficiency syndrome (AIDS). Although no vaginally-administered product has yet been approved for HIV reduction/prevention, extensive research efforts are continuing and a number of VR devices offering sustained release of so-called 'HIV microbicide' compounds are currently being evaluated in late-stage clinical studies. This review article provides an overview of the published scientific literature within this important field of research, focusing primarily on articles published within peer-reviewed journal publications. Many important aspects of microbicide-releasing VR technology are discussed, with a particular emphasis on the technological, manufacturing and clinical challenges that have emerged in recent years.

Colorectal delivery and retention of PEG-Amprenavir-Bac7 nanoconjugates--proof of concept for HIV mucosal pre-exposure prophylaxis

Local delivery of anti-HIV drugs to the colorectal mucosa, a major site of HIV replication, and their retention within mucosal tissue would allow for a reduction in dose administered, reduced dosing frequency and minimal systemic exposure. The current report describes a mucosal pre-exposure prophylaxis (mPrEP) strategy that utilizes nanocarrier conjugates (NC) consisting of poly(ethylene glycol) (PEG), amprenavir (APV), and a cell-penetrating peptide (CPP; namely Bac7, a fragment derived from bactenecin 7). APV-PEG NCs with linear PEGs (2, 5, 10, and 30 kDa) exhibited reduced (52-21%) anti-HIV-1 protease (PR) activity as compared to free APV in an enzyme-based FRET assay. In MT-2 T cells, APV-PEG3.4 kDa-FITC (APF) anti-HIV-1 activity was significantly reduced (160-fold, IC50 = 8064 nM) due to poor cell uptake, whereas it was restored (IC50 = 78.29 nM) and similar to APV (IC50 = 50.29 nM) with the addition of Bac7 to the NC (i.e., APV-PEG3.4 kDa-Bac7, APB). Flow cytometry and confocal microscopy demonstrated Bac7-PEG3.4 kDa-FITC (BPF) uptake was two- and fourfold higher than APF in MT-2 T cells and Caco-2 intestinal epithelial cells, respectively. There was no detectable punctate fluorescence in either cell line suggesting that BPF directly enters the cytosol thus avoiding endosomal entrapment. After colorectal administration in mice, BPF mucosal concentrations were 21-fold higher than APF concentrations. BPF concentrations also remained constant for the 5 days of the study suggesting that (1) the NC's structural characteristics (i.e., the size of the PEG carrier and the presence of a CPP) significantly influenced tissue persistence, and (2) the NCs were probably lodged in the lamina propria since the average rodent colon mucosal cell turnover time is 2-3 days. These encouraging results suggest that Bac7 functionalized NCs delivered locally to the colorectal mucosa may form drug delivery depots that are capable of sustaining colorectal drug concentrations. Although the exact mechanisms for tissue persistence are unclear and will require further study, these results provide proof-of-concept feasibility for mPrEP.

Cyanovirin-N produced in rice endosperm offers effective pre-exposure prophylaxis against HIV-1BaL infection in vitro

Cyanovirin-N produced in rice endosperm provides efficient pre-exposure prophylaxis against HIV-1 BaL infection in vitro. Cyanovirin-N (CV-N) is a lectin with potent antiviral activity that has been proposed as a component of microbicides for the prevention of infection with Human immunodeficiency virus (HIV). The production of protein-based microbicide components requires a platform that is sufficiently economical and scalable to meet the demands of the large at-risk population, particularly in resource poor developing countries. We, therefore, expressed CV-N in rice endosperm, because the dried seed is ideal for storage and transport and crude extracts could be prepared locally and used as a microbicide component without further purification. We found that crude extracts from rice seeds expressing up to 10 µg CV-N per gram dry seed weight showed dose-dependent gp120 binding activity, confirming that the protein was soluble, correctly folded and active. The recombinant lectin ((OS)CV-N) reduced the infectivity of HIV-1BaL (an R5 virus strain representing the majority of transmitted infections) by ~90 % but showed only weak neutralization activity against HIV-1RF (representative of X4 virus, rarely associated with transmission), suggesting it would be highly effective for pre-exposure prophylaxis against the vast majority of transmitted strains. Crude extracts expressing (OS)CV-N showed no toxicity towards human cells at working dilutions indicating that microbicide components produced in rice endosperm are safe for direct application as topical microbicides in humans.

Drug delivery strategies and systems for HIV/AIDS pre-exposure prophylaxis and treatment

The year 2016 will mark an important milestone - the 35th anniversary of the first reported cases of HIV/AIDS. Antiretroviral Therapy (ART) including Highly Active Antiretroviral Therapy (HAART) drug regimens is widely considered to be one of the greatest achievements in therapeutic drug research having transformed HIV infection into a chronically managed disease. Unfortunately, the lack of widespread preventive measures and the inability to eradicate HIV from infected cells highlight the significant challenges remaining today. Moving forward there are at least three high priority goals for anti-HIV drug delivery (DD) research: (1) to prevent new HIV infections from occurring, (2) to facilitate a functional cure, i.e., when HIV is present but the body controls it without drugs and (3) to eradicate established infection. Pre-exposure Prophylaxis (PrEP) represents a significant step forward in preventing the establishment of chronic HIV infection. However, the ultimate success of PrEP will depend on achieving sustained antiretroviral (ARV) tissue concentrations and will require strict patient adherence to the regimen. While first generation long acting/extended release (LA/ER) DD Systems (DDS) currently in development show considerable promise, significant DD treatment and prevention challenges persist. First, there is a critical need to improve cell specificity through targeting in order to selectively achieve efficacious drug concentrations in HIV reservoir sites to control/eradicate HIV as well as mitigate systemic side effects. In addition, approaches for reducing cellular efflux and metabolism of ARV drugs to prolong effective concentrations in target cells need to be developed. Finally, given the current understanding of HIV pathogenesis, next generation anti-HIV DDS need to address selective DD to the gut mucosa and lymph nodes. The current review focuses on the DDS technologies, critical challenges, opportunities, strategies, and approaches by which novel delivery systems will help iterate towards prevention, functional cure and eventually the eradication of HIV infection.

Development of water-soluble polyanionic carbosilane dendrimers as novel and highly potent topical anti-HIV-2 microbicides

The development of topical microbicide formulations for vaginal delivery to prevent HIV-2 sexual transmission is urgently needed. Second- and third-generation polyanionic carbosilane dendrimers with a silicon atom core and 16 sulfonate (G2-S16), napthylsulfonate (G2-NS16) and sulphate (G3-Sh16) end-groups have shown potent and broad-spectrum anti-HIV-1 activity. However, their antiviral activity against HIV-2 and mode of action have not been probed. Cytotoxicity, anti-HIV-2, anti-sperm and antimicrobial activities of dendrimers were determined. Analysis of combined effects of triple combinations with tenofovir and raltegravir was performed by using CalcuSyn software. We also assessed the mode of antiviral action on the inhibition of HIV-2 infection through a panel of different in vitro antiviral assays: attachment, internalization in PBMCs, inactivation and cell-based fusion. Vaginal irritation and histological analysis in female BALB/c mice were evaluated. Our results suggest that G2-S16, G2-NS16 and G3-Sh16 exert anti-HIV-2 activity at an early stage of viral replication inactivating the virus, inhibiting cell-to-cell HIV-2 transmission, and blocking the binding of gp120 to CD4, and the HIV-2 entry. Triple combinations with tenofovir and raltegravir increased the anti-HIV-2 activity, consistent with synergistic interactions (CIwt: 0.33-0.66). No vaginal irritation was detected in BALB/c mice after two consecutive applications for 2 days with 3% G2-S16. Our results have clearly shown that G2-S16, G2-NS16 and G3-Sh16 have high potency against HIV-2 infection. The modes of action confirm their multifactorial and non-specific ability, suggesting that these dendrimers deserve further studies as potential candidate microbicides to prevent vaginal/rectal HIV-1/HIV-2 transmission in humans.

Nanoparticles as potential new generation broad spectrum antimicrobial agents

The rapid emergence of antimicrobial resistant strains to conventional antimicrobial agents has complicated and prolonged infection treatment and increased mortality risk globally. Furthermore, some of the conventional antimicrobial agents are unable to cross certain cell membranes thus, restricting treatment of intracellular pathogens. Therefore, the disease-causing-organisms tend to persist in these cells. However, the emergence of nanoparticle (NP) technology has come with the promising broad spectrum NP-antimicrobial agents due to their vast physiochemical and functionalization properties. In fact, NP-antimicrobial agents are able to unlock the restrictions experienced by conventional antimicrobial agents. This review discusses the status quo of NP-antimicrobial agents as potent broad spectrum antimicrobial agents, sterilization and wound healing agents, and sustained inhibitors of intracellular pathogens. Indeed, the perspective of developing potent NP-antimicrobial agents that carry multiple-functionality will revolutionize clinical medicine and play a significant role in alleviating disease burden.

Pyrazolo-Piperidines Exhibit Dual Inhibition of CCR5/CXCR4 HIV Entry and Reverse Transcriptase

We report novel anti-HIV-1 agents with combined dual host-pathogen pharmacology. Lead compound 3, composed of a pyrazole-piperidine core, exhibits three concurrent mechanisms of action: (1) non-nucleoside reverse transcriptase inhibition, (2) CCR5-mediated M-tropic viral entry inhibition, and (3) CXCR4-based T-tropic viral entry inhibition that maintains native chemokine ligand binding. This discovery identifies important tool compounds for studying viral infectivity and prototype agents that block HIV-1 entry through dual chemokine receptor ligation.

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.

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.

Novel intravaginal nanomedicine for the targeted delivery of saquinavir to CD4+ immune cells

The goal of this study was to develop and characterize an intravaginal nanomedicine for the active targeted delivery of saquinavir (SQV) to CD4(+) immune cells as a potential strategy to prevent or reduce HIV infection. The nanomedicine was formulated into a vaginal gel to provide ease in self-administration and to enhance retention within the vaginal tract. SQV-encapsulated nanoparticles (SQV-NPs) were prepared from poly(lactic-co-glycolic acid) (PLGA) and conjugated to antihuman anti-CD4 antibody. Antibody-conjugated SQV-NPs (Ab-SQV-NPs) had an encapsulation efficiency (EE%) of 74.4% + 3.7% and an antibody conjugation efficiency (ACE%) of 80.95% + 1.10%. Over 50% of total loaded SQV was released from NPs over 3 days. NPs were rapidly taken up by Sup-T1 cells, with more than a twofold increase in the intracellular levels of SQV when delivered by Ab-SQV-NPs in comparison to controls 1 hour post-treatment. No cytotoxicity was observed when vaginal epithelial cells were treated for 24 hours with drug-free Ab-NPs (1,000 μg/mL), 1% HEC placebo gel (200 mg/mL), or 1% HEC gel loaded with drug-free Ab-NPs (5 mg NPs/g gel, 200 mg/mL of gel mixture). Overall, we described an intravaginal nanomedicine that is nontoxic and can specifically deliver SQV into CD4(+) immune cells. This platform may demonstrate potential utility in its application as postexposure prophylaxis for the treatment or reduction of HIV infection, but further studies are required.

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.

Vaginal microbicides for reducing the risk of sexual acquisition of HIV infection in women: systematic review and meta-analysis

BACKGROUND

Each year more than two million people are newly infected with HIV worldwide, a majority of them through unprotected vaginal sex. More than half of new infections in adults occur in women. Male condoms and male circumcision reduce the risk of HIV acquisition; but the uptake of these methods is out of the control of women. We therefore aimed to determine the effectiveness of vaginal microbicides (a potential female-controlled method) for prevention of sexual acquisition of HIV in women.

METHODS

We conducted a comprehensive search of peer-reviewed and grey literature for publications of randomised controlled trials available by September 2012. We screened search outputs, selected studies, assessed risk of bias, and extracted data in duplicate; resolving differences by discussion and consensus.

RESULTS

We identified 13 eligible trials that compared vaginal microbicides to placebo. These studies enrolled 35,905 sexually active HIV-negative women between 1996 and 2011; in Benin, Cameroon, Cote d'Ivoire, Ghana, Kenya, Malawi, Nigeria, South Africa, Tanzania, Uganda, Zambia, Zimbabwe, India, Thailand, and the United States of America. A small trial of 889 women found that tenofovir (a nucleotide reverse transcriptase inhibitor) significantly reduces the risk of HIV acquisition (risk ratio [RR] 0.63, 95% confidence intervals [CI] 0.43 to 0.93). Effectiveness data are not yet available from follow-up tenofovir trials being conducted in South Africa, Uganda, and Zimbabwe (1 trial) and multiple sites in South Africa (1 trial). We found no evidence of a significant effect for nonoxynol-9 (5 trials), cellulose sulphate (2 trials), SAVVY (2 trials), Carraguard (1 trial), PRO 2000 (2 trials), and BufferGel (1 trial) microbicides. The pooled RR for the effect of current experimental vaginal microbicides on HIV acquisition in women was 0.97, 95%CI 0.87 to 1.08. Although study results were homogeneous across the different drug classes (heterogeneity P = 0.17, I2 = 27%), the overall intervention effect was not statistically significant. Nonoxynol-9 significantly increased the risk of having adverse genital lesions but no other microbicide led to significant increases in adverse events.

CONCLUSIONS

There is not enough evidence at present to recommend vaginal microbicides for HIV prevention. Further high-quality research is needed to confirm the beneficial effects of tenofovir as well as continue the development and testing of new microbicides.

Plant made anti-HIV microbicides--a field of opportunity

HIV remains a significant global burden and without an effective vaccine, it is crucial to develop microbicides to halt the initial transmission of the virus. Several microbicides have been researched with various levels of success. Amongst these, the broadly neutralising antibodies and peptide lectins are promising in that they can immediately act on the virus and have proven efficacious in in vitro and in vivo protection studies. For the purpose of development and access by the relevant population groups, it is crucial that these microbicides be produced at low cost. For the promising protein and peptide candidate molecules, it appears that current production systems are overburdened and expensive to establish and maintain. With recent developments in vector systems for protein expression coupled with downstream protein purification technologies, plants are rapidly gaining credibility as alternative production systems. Here we evaluate the advances made in host and vector system development for plant expression as well as the progress made in expressing HIV neutralising antibodies and peptide lectins using plant-based platforms.

Hyperimmune bovine colostrum as a low-cost, large-scale source of antibodies with broad neutralizing activity for HIV-1 envelope with potential use in microbicides

Bovine colostrum (first milk) contains very high concentrations of IgG, and on average 1 kg (500 g/liter) of IgG can be harvested from each immunized cow immediately after calving. We used a modified vaccination strategy together with established production systems from the dairy food industry for the large-scale manufacture of broadly neutralizing HIV-1 IgG. This approach provides a low-cost mucosal HIV preventive agent potentially suitable for a topical microbicide. Four cows were vaccinated pre- and/or postconception with recombinant HIV-1 gp140 envelope (Env) oligomers of clade B or A, B, and C. Colostrum and purified colostrum IgG were assessed for cross-clade binding and neutralization against a panel of 27 Env-pseudotyped reporter viruses. Vaccination elicited high anti-gp140 IgG titers in serum and colostrum with reciprocal endpoint titers of up to 1 × 10(5). While nonimmune colostrum showed some intrinsic neutralizing activity, colostrum from 2 cows receiving a longer-duration vaccination regimen demonstrated broad HIV-1-neutralizing activity. Colostrum-purified polyclonal IgG retained gp140 reactivity and neutralization activity and blocked the binding of the b12 monoclonal antibody to gp140, showing specificity for the CD4 binding site. Colostrum-derived anti-HIV antibodies offer a cost-effective option for preparing the substantial quantities of broadly neutralizing antibodies that would be needed in a low-cost topical combination HIV-1 microbicide.

Virological and molecular characterization of a simian human immunodeficiency virus (SHIV) encoding the envelope and reverse transcriptase genes from HIV-1

Simian-human immunodeficiency virus encoding both reverse transcriptase (RT) and envelope genes of HIV-1 (RT Env SHIV) is important for evaluating biomedical prevention modalities for HIV/AIDS. We describe virological characterization of a clade B RT Env SHIV following infection of macaques via multiple routes. In vivo passage of the RT Env SHIV through Indian rhesus macaque enhanced infectivity. Expanded virus had minimal envelope heterogeneity and was inhibited by NNRTIs and CCR5 antagonists. Infection of macaques with RT Env SHIV via mucosal or intravenous routes resulted in stable infection accompanied by peak plasma viremia of approximately 5×10(6) copies/ml that was controlled beyond set point. Molecular homogeneity of the virus was maintained following in vivo passage. Inhibition of RT Env SHIV by RT and entry inhibitors and ease of in vivo transmission make it a useful model for testing the efficacy of combinations of entry and RT inhibitors in nonhuman primates.

Topical microbicides for prevention of sexually transmitted infections

BACKGROUND

Two decades of research on topical microbicides for prevention of sexually transmitted infections (STIs) have had limited success. However, new microbicide randomised controlled trial (RCT) data have recently been published; but these have not yet been the subject of a systematic review.

OBJECTIVES

To determine the effects of topical microbicides for prevention of the acquisition of STIs, including human immunodeficiency virus (HIV) infection, by women from men and by men who have sex with men (MSM).

SEARCH METHODS

In July 2011 we searched the Cochrane Central Register of Controlled Trials (CENTRAL), PubMed, EMBASE, Web of Science, NLM Gateway, CLIB, AIDS Education Global Information System, ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform; handsearched reference lists of relevant articles and contacted relevant organisations and experts.

SELECTION CRITERIA

RCTs of topical microbicides (except Nonoxynol-9) in sexually active, HIV-negative women or MSM. We excluded Nonoxynol-9 because previous systematic reviews showed that it does not have a significant effect on HIV or STIs.

DATA COLLECTION AND ANALYSIS

We assessed study eligibility, extracted data and assessed risk of bias in duplicate; resolving differences by discussion and consensus. We then conducted fixed-effect meta-analysis, stratified by type of microbicide.

MAIN RESULTS

We found that by the end of 2011, nine microbicide RCTs had either been conducted to term (one BufferGel and 0.5% PRO 2000, one Carraguard and one tenofovir trial) or stopped early due to safety concerns (two cellulose sulphate trials) or insufficient rate of HIV infection and low likelihood of showing a protective effect (one 2% PRO 2000, one tenofovir and two SAVVY trials). The nine RCTs enrolled 31,941 sexually active women between 2004 and 2011; in Benin, Ghana, Malawi, Nigeria, South Africa, Tanzania, Uganda, Zambia, Zimbabwe, India, and the US. A small proof-of-concept RCT found that tenofovir (a nucleotide reverse transcriptase inhibitor) reduced the risk of HIV acquisition (one trial, 889 women; risk ratio (RR) 0.63; 95% CI 0.43 to 0.93). Effectiveness data are not yet available from the second tenofovir RCT that enrolled 5000 women and was stopped early due to low likelihood of showing a protective effect. We found no evidence of an effect on HIV acquisition for cellulose sulphate (2 trials, n = 3069; RR 1.20; 95% CI 0.74 to 1.95), SAVVY (two trials, n = 4295; RR 1.38; 95% CI 0.79 to 2.41), Carraguard (one trial, n = 6202; RR 0.89; 95% CI 0.71 to 1.11), PRO 2000 (two trials, n = 12,486; RR 0.93, 95% CI 0.77 to 1.14) and BufferGel (one trial, n = 1546; RR 1.05; 95% CI 0.73 to 1.52). Tenofovir reduced the incidence of herpes simplex virus type 2 (HSV-2) infection (one trial, 426 women; RR 0.55; 95% CI 0.37 to 0.83) and cellulose sulphate reduced the risk of chlamydia infection (two trials, n = 3069; RR 0.70, 95% CI 0.49 to 0.99). However, there was no evidence of an effect of any microbicide on the acquisition of gonorrhoea, syphilis, condyloma acuminatum, trichomoniasis, or human papillomavirus (HPV) infection. A substudy of the Carraguard trial found the prevalence of high-risk HPV infection (HR-HPV) to be 23.5% in women on Carraguard and 23.0% on placebo (n = 1718; RR 1.02; 95% CI 0.86 to 1.21). After controlling for HR-HPV risk factors, the authors found that compliant Carraguard users were 0.62 (95% CI 0.41 to 0.94) times as likely to be HR-HPV positive as compliant placebo users. Overall, there was no significant difference in the incidence of adverse events between microbicide and placebo groups.

AUTHORS' CONCLUSIONS

Limited evidence suggests that vaginal tenofovir microbicides may reduce the risk of acquisition of HIV and HSV-2 infections in women; but other types of topical microbicides have not shown evidence of an effect on HIV or STI acquisition. Therefore, there is not enough evidence to recommend topical microbicides for HIV or STI prevention at present. Further studies are needed to confirm the beneficial effects of tenofovir microbicide gel in vaginal sex. In addition, further research should continue on the development and testing of new microbicides. If the effectiveness of the tenofovir and/or other microbicides is confirmed in further studies, there will need to be a clear pathway to rapid regulatory approval. Successful launch of the effective gel would depend on having in place appropriate mechanisms for distribution to the women who need it, along with a strategy for ensuring that they use it correctly.

The Surprising Role of Amyloid Fibrils in HIV Infection

Despite its discovery over 30 years ago, human immunodeficiency virus (HIV) continues to threaten public health worldwide. Semen is the principal vehicle for the transmission of this retrovirus and several endogenous peptides in semen, including fragments of prostatic acid phosphatase (PAP248-286 and PAP85-120) and semenogelins (SEM1 and SEM2), assemble into amyloid fibrils that promote HIV infection. For example, PAP248-286 fibrils, termed SEVI (Semen derived Enhancer of Viral Infection), potentiate HIV infection by up to 105-fold. Fibrils enhance infectivity by facilitating virion attachment and fusion to target cells, whereas soluble peptides have no effect. Importantly, the stimulatory effect is greatest at low viral titers, which mimics mucosal transmission of HIV, where relatively few virions traverse the mucosal barrier. Devising a method to rapidly reverse fibril formation (rather than simply inhibit it) would provide an innovative and urgently needed preventative strategy for reducing HIV infection via the sexual route. Targeting a host-encoded protein conformer represents a departure from traditional microbicidal approaches that target the viral machinery, and could synergize with direct antiviral approaches. Here, we review the identification of these amyloidogenic peptides, their mechanism of action, and various strategies for inhibiting their HIV-enhancing effects.

Characterization of UC781-tenofovir combination gel products for HIV-1 infection prevention in an ex vivo ectocervical model

HIV continues to be a problem worldwide. Topical vaginal microbicides represent one option being evaluated to stop the spread of HIV. With drug candidates that have a specific action against HIV now being studied, it is important that, when appropriate and based on the mechanism of action, the drug permeates the tissue so that it can be delivered to specific targets which reside there. Novel formulations of the nucleotide reverse transcriptase inhibitor tenofovir (TFV) and the nonnucleoside reverse transcriptase inhibitor UC781 have been developed and evaluated here. Gels with three distinct rheological properties were prepared. The three gels released both UC781 and TFV under in vitro conditions at concentrations equal to or above the reported 50% effective concentrations (EC(50)s). The drug concentrations in ectocervical tissues were well in excess of the reported EC(50)s. The gels maintain ectocervical viability and prevent infection of ectocervical explants after a HIV-1 challenge. This study successfully demonstrates the feasibility of using this novel combination of antiretroviral agents in an aqueous gel as an HIV infection preventative.

Future strategies in microbicide development

The reduction in human immunodeficiency virus (HIV) infection in women demonstrated by pericoital use of tenofovir gel has encouraged the continued development of microbicides. Novel approaches include new ways to deliver tenofovir, as well as products that contain different antiretroviral drugs, either as single agents or as combinations of antiretroviral drugs. Indeed, emphasis has renewed on the development of multipurpose prevention technologies, products designed to address multiple sexually transmitted infections. Dual-purpose contraceptive antiretroviral products are also being designed to prevent HIV and pregnancy. Since consistent and correct use of these products will be critical to their effectiveness, the active pharmaceutical ingredients must be delivered in acceptable vaginal dosage forms, such as gels, films and sustained-release vaginal rings. The development of different dosage forms will help ensure that women can find a method to protect themselves from HIV, pregnancy, and potentially other sexually transmitted infections.

Topical nonnucleoside reverse transcriptase inhibitor MC 1220 partially prevents vaginal RT-SHIV infection of macaques

The availability of an effective vaginal microbicide would be a major step toward containment of HIV transmission as well as allowing women self-protection against HIV infection. Here we evaluated the efficacy of vaginal application of the potent nonnucleoside reverse transcriptase inhibitor (NNRTI) MC 1220 against vaginal challenge of macaques with RT-SHIV, a chimeric simian immunodeficiency virus (SIV) containing the reverse transcriptase (RT) gene of HIV-1. Challenge infection of monkeys with RT-SHIV currently represents the only nonhuman primate model available to test the anti-HIV-1 effects of NNRTIs. Two different gel formulations containing different MC 1220 concentrations were evaluated for efficacy in female rhesus macaques exposed to RT-SHIV. Five groups of five animals each were treated with two different gel compositions containing no drug, 0.1% or 0.5% MC 1220, followed by vaginal RT-SHIV challenge 30 min later. One animal in each group treated with the low concentration of MC 1220 as well as one control animal remained uninfected after vaginal challenge. By contrast, three of the animals receiving 0.5% MC 1220 remained uninfected, suggesting a threshold of the drug. Despite being negative for plasma viral RNA and absence of seroconversion, almost all uninfected animals exhibited SIV-specific T cells, either in the periphery or in lymph nodes draining the portal of virus entry. Our results make MC 1220 a promising compound for further development as a topical microbicide and warrant additional testing with improved formulation, long-lasting vaginal delivery systems, or even combinations with other inhibitors.

Synergy against drug-resistant HIV-1 with the microbicide antiretrovirals, dapivirine and tenofovir, in combination

OBJECTIVE

To evaluate the candidate antiretroviral microbicide compounds, dapivirine (DAP) and tenofovir (TFV), alone and in combination against the transmission of wild-type and nonnucleoside reverse transcriptase inhibitor (NNRTI)-resistant HIV-1 from different subtypes.

DESIGN AND METHODS

We determined single-drug efficacy of the RTIs, DAP and TFV, against subtype B and non-B wild-type and NNRTI-resistant HIV-1 in vitro. To assess breadth of activity, compounds were tested alone and in combination against wild-type and NNRTI-resistant subtype C primary HIV-1 isolates and complimentary clonal HIV-1 from subtypes B, C and CRF02_AG to control for viral variation. Early infection was quantified by counting light units emitted from TZM-bl cells less than 48-h postinfection. Combination ratios were based on drug inhibitory concentrations (IC(50)s) and combined effects were determined by calculating combination indices.

RESULTS

Both candidate microbicide antiretrovirals demonstrated potent anti-NNRTI-resistant HIV-1 activity in vitro, albeit the combination protected better than the single-drug treatments. Of particular interest, the DAP with TFV combination exhibited synergy (50% combination index, CI(50) = 0.567) against subtype C NNRTI-resistant HIV-1, whereas additivity (CI(50) = 0.987) was observed against the wild-type counterpart from the same patient. The effect was not compounded by the presence of subdominant viral fractions, as experiments using complimentary clonal subtype C wild-type (CI(50) = 0.968) and NNRTI-resistant (CI(50) = 0.672) HIV-1, in lieu of the patient quasispecies, gave similar results.

CONCLUSION

This study supports the notion that antiretroviral drug combinations may retain antiviral activity against some drug-resistant HIV-1 despite subtype classification and quasispecies diversity.

The future of microbicides

There is an urgent need to develop vaginal microbicides to empower women to better control their own sexual life and to protect themselves against HIV and other sexually transmitted infections (STIs). Prevention of STIs with its 330 million cases a year would have a great global health impact. Because of their anatomy, women are up to 8 times more susceptible than men to STIs including HIV. Women who can't negotiate condom use with their male partners have no means of protecting themselves from these infections. In the last few years, especially after the recent failures of several microbicides in Phase III trials, there was increasing pressure from those favoring the use of a more targeted approach to introduce marketed antiretroviral drugs (ARVs) into microbicides. This Pre-Exposure Prophylaxis (PrEP) concept which targets only HIV using specific ARVs contrasts with the primary approach of broad spectrum microbicides which aimed at offering universal protection against several sexually transmitted pathogens. However, before using ARVs as PrEP for HIV prevention, there are still many important issues to consider. In this article, we compare both strategies, while reviewing the last 15 years of microbicide research and its future.

Development and Characterization of a Vaginal Film Containing Dapivirine, a Non- nucleoside Reverse Transcriptase Inhibitor (NNRTI), for prevention of HIV-1 sexual transmission

Dapivirine, a non-nucleoside reverse transcriptase inhibitor, is a potent and promising anti-HIV molecule. It is currently being investigated for use as a vaginal microbicide in two dosage forms, a semi-solid gel and a silicone elastomer ring. Quick-dissolving films are promising and attractive dosage forms that may provide an alternative platform for the vaginal delivery of microbicide drug candidates. Vaginal films may provide advantages such as discreet use, no product leakage during use, lack of requirement for an applicator for insertion, rapid drug release and minimal packaging and reduced wastage. Within this study the in vitro bioactivity of dapivirine as compared to the NNRTI UC781 was further established and a quick dissolve film was developed for vaginal application of dapivirine for prevention of HIV infection. The developed film was characterized with respect to its physical and chemical attributes including water content, mechanical strength, drug release profile, permeability, compatibility with lactobacilli and bioactivity. The anti-HIV activity of the formulated dapivirine film was confirmed in in vitro and ex vivo models. Importantly the physical and chemical properties of the film as well as its bioactivity were maintained for a period of 18 months. In conclusion, a vaginal film containing dapivirine was developed and characterized. The film was shown to prevent HIV-1 infection in vitro and ex vivo and have acceptable characteristics which make this film a promising candidate for testing as vaginal microbicide.

Formulation of tenofovir-loaded functionalized solid lipid nanoparticles intended for HIV prevention

The objective of this study is to engineer polylysine-heparin functionalized solid lipid nanoparticles (fSLNs) for the use of a vaginal microbicide delivery template for HIV prevention. The fSLNs are prepared using a modified phase-inversion technique followed by a layer-by-layer deposition method. The Box-Behnken experimental design is used to analyze the influence of three factors (X(1) = bovine serum albumin concentration, X(2) = pH of the aqueous phase, and X(3) = lipid amount) on the particle mean diameter (PMD) measured by dynamic light scattering (DLS). Tenofovir is used as a model anti-HIV microbicide. The SLNs are also characterized for morphology, zeta potential (ζ ), percent drug encapsulation efficiency (EE%), and cytotoxicity on a human vaginal epithelial cell line by electron microscopy, DLS, ultraviolet, and fluorescence spectroscopy, respectively. The statistical model predicts particle size (Y) with 90% confidence and the Y values are significantly affected by X(1) and X(2) . The produced fSLNs appear noncytotoxic and exhibit a platelet-like shape with respective PMD, EE%, and ζ value of 153 nm, 8.3%, and - 51 mV. These fSLNs intended to be administered topically have the potential to enhance cellular uptake of hydrophobic microbicides and outdistance the virus during the HIV/AIDS infection process, possibly leading to more effective prevention of the disease transmission.

Update on microbicide research and development - seeking new HIV prevention tools for women

Women and girls are especially vulnerable to HIV infection in sub-Saharan Africa, and in some of those countries, prevalence among young women can be up to 3 times higher than among men of the same age. Effective HIV prevention options for women are clearly needed in this setting. Several ARV-based vaginal microbicides are currently in development for prevention of HIV transmission to women and are discussed here. The concept of pre-exposure prophylaxis for the prevention of HIV transmission to women is introduced.

Vaginal microbicide gel for delivery of IQP-0528, a pyrimidinedione analog with a dual mechanism of action against HIV-1

Pyrimidinediones, a novel class of compounds, have previously been shown to possess antiviral activity at nanomolar concentrations. One member of this class of compounds, IQP-0528, was selected as the lead molecule for formulation development owing to its stability at physiologically relevant conditions, wide therapeutic window, and antiviral activity in the nanomolar range. Here, we report the development of two vaginal gels--3.0% hydroxyethyl cellulose (HEC) formulation and a 0.65% Carbopol formulation--for the sustained delivery of IQP-0528. Stability studies under accelerated conditions confirmed the chemical stability of IQP-0528 and mechanical stability of the gel formulation for 3 months. In vitro release studies revealed that diffusion-controlled release of IQP-0528 occurred over 6 h, with an initial lag time of approximately 1 h. Based on the drug release profile, the 3.0% HEC gel was selected as the lead formulation for safety and activity evaluations. The in vitro and ex vivo safety evaluations showed no significant loss in cell viability or significant inflammatory response after treatment with a 3.0% HEC gel containing 0.25% IQP-0528. In an in vitro HIV-1 entry inhibition assay, the lead formulation showed an 50% effective concentration of 0.14 μg/ml for gel in culture media, which corresponds to ∼0.001 μM IQP-0528. The antiviral activity was further confirmed by using polarized cervical explants, in which the formulation showed complete protection against HIV infection. In summary, these results are encouraging and warrant further evaluation of IQP-0528 gel formulations in in vivo models, as well as the development of alternative formulations for the delivery of IQP-0528 as a microbicide.

Structure-activity relationships of polybiguanides with activity against human immunodeficiency virus type 1

Previous investigations showing that polydisperse biguanide (PDBG) molecules have activity against human immunodeficiency virus type 1 (HIV-1) also suggested a relationship between PDBG biologic activity and the lengths of hydrocarbon linkers surrounding the positively charged biguanide unit. To better define structure-activity relationships, PDBG molecules with select linker lengths were evaluated for cytotoxicity, anti-HIV-1 activity, and in vivo toxicity. Results of the in vitro experiments demonstrated that increases in linker length (and, therefore, increases in compound lipophilicity) were generally associated with increases in cytotoxicity and antiviral activity against HIV-1. However, a relationship between linker length asymmetry and in vitro therapeutic index (TI) suggested structural specificity in the mechanism of action against HIV-1. Polyethylene hexamethylene biguanide (PEHMB; biguanide units spaced between alternating ethylene and hexamethylene linkers) was found to have the highest in vitro TI (CC₅₀/IC₅₀) among the compounds examined. Recent improvements in PEHMB synthesis and purification have yielded preparations of PEHMB with in vitro TI values of 266 and 7000 against HIV-1 strains BaL and IIIB, respectively. The minimal toxicity of PEHMB relative to polyhexamethylene biguanide (PHMB; biguanide units alternating with hexamethylene linkers) in a murine model of cervicovaginal microbicide toxicity was consistent with considerable differences in cytotoxicity between PEHMB and PHMB observed during in vitro experiments. These structure-activity investigations increase our understanding of PDBG molecules as agents with activity against HIV-1 and provide the foundation for further preclinical studies of PEHMB and other biguanide-based compounds as antiviral and microbicidal agents.

Increasing the effectiveness of vaginal microbicides: a biophysical framework to rethink behavioral acceptability

BACKGROUND

Microbicide candidates delivered via gel vehicles are intended to coat the vaginal epithelium after application. The coating process depends on intrinsic biophysical properties of the gel texture, which restricts the potential choices for an effective product: the gel first must be physically synthesizable, then acceptable to the user, and finally applied in a manner promoting timely adequate coating, so that the user adherence is optimized. We present a conceptual framework anchoring microbicide behavioral acceptability within the fulfillment of the product biophysical requirements.

METHODS

We conducted a semi-qualitative/quantitative study targeting women aged 18-55 in Northern California to assess user preferences for microbicide gel attributes. Attributes included: (i) the wait time between application and intercourse, (ii) the gel texture and (iii) the trade-off between wait time and gel texture. Wait times were assessed using a mathematical model determining coating rates depending upon the gel's physical attributes.

RESULTS

71 women participated. Results suggest that women would independently prefer a gel spreading rapidly, in 2 to 15 minutes (P<0.0001), as well as one that is thick or slippery (P<0.02). Clearly, thick gels do not spread rapidly; hence the motivation to study the trade-off. When asked the same question 'constrained' by the biophysical reality, women indicated no significant preference for a particular gel thickness (and therefore waiting time) (P>0.10) for use with a steady partner, a preference for a watery gel spreading rapidly rather than one having intermediate properties for use with a casual partner (P = 0.024).

CONCLUSIONS

Biophysical constraints alter women's preferences regarding acceptable microbicide attributes. Product developers should offer a range of formulations in order to address all preferences. We designed a conceptual framework to rethink behavioral acceptability in terms of biophysical requirements that can help improve adherence in microbicide use ultimately enhancing microbicide effectiveness.

Microbicides in the prevention of HIV infection: current status and future directions

More than 28 years since the first cases of HIV/AIDS, there is still no cure or vaccine. The worst affected region is sub-Saharan Africa and, increasingly, it is young women who are bearing the brunt of the epidemic. Consequently, there is an urgent need for HIV prevention options for women in developing countries. Microbicides are topical products that can be used vaginally by women to impede sexual transmission of HIV and thus represent one of the most promising prevention strategies. Efficacy trials with early nonspecific microbicide gels have so far been unsuccessful, but the field has now switched its focus to products containing highly potent and highly specific antiretroviral drugs that are easier to use, and can be formulated in a variety of dosage forms to suit individual and regional preferences. However, these products have their own challenges, with a greater likelihood of absorption, and the potential for systemic toxicities or the development of resistance in infected individuals who are unaware of their HIV status. The conduct of clinical trials is complex for all microbicides, with limited availability of trial sites, difficulties in dose selection and safety monitoring, and a lack of a truly objective measure of adherence. Once a microbicide has been shown to be safe and effective, there will need to be a clear pathway to regulatory approval, and the successful launch of a product will depend on having in place appropriate methods for distribution to the women who need it, along with a strategy for ensuring that they use it correctly. This will require substantial effort in terms of education and community engagement, and these activities need to be initiated well in advance of microbicide rollout.

Microbicide research: current and future directions

PURPOSE OF REVIEW

Microbicide research has been in the forefront of scientific literature in recent months. Results of large-scale clinical trials have been announced with resultant investigations into the factors that may have contributed to the disappointing outcomes of the most promising candidates. This review takes into consideration clinical, basic scientific and behavioural research published on microbicides in the past 12-18 months.

RECENT FINDINGS

Two trials testing PRO 2000, a sulphated polymer, suggested that it has no effect on HIV. Basic science research revealed several facts such as the loss of antiviral activity of microbicides in the presence of seminal plasma. Methodological models suggested that dilution factors might impact on measures of efficacy. Advancement into safety testing of highly specific antiretroviral products such as tenofovir and UC781 for both rectal and vaginal use shows promise. Development of drug delivery systems such as intravaginal rings may alleviate some of the adherence challenges faced when using coitally dependant products.

SUMMARY

In the recent past, microbicide research has had disappointing outcomes. However, it has also provided a better understanding of factors that may reduce effectiveness of promising products, enabling the field to be better equipped to select and test new products.

Safety and anti-HIV assessments of natural vaginal cleansing products in an established topical microbicides in vitro testing algorithm

Background

At present, there is no effective vaccine or other approved product for the prevention of sexually transmitted human immunodeficiency virus type 1 (HIV-1) infection. It has been reported that women in resource-poor communities use vaginally applied citrus juices as topical microbicides. These easily accessible food products have historically been applied to prevent pregnancy and sexually transmitted diseases. The aim of this study was to evaluate the efficacy and cytotoxicity of these substances using an established topical microbicide testing algorithm. Freshly squeezed lemon and lime juice and household vinegar were tested in their original state or in pH neutralized form for efficacy and cytotoxicity in the CCR5-tropic cell-free entry and cell-associated transmission assays, CXCR4-tropic entry and fusion assays, and in a human PBMC-based anti-HIV-1 assay. These products were also tested for their effect on viability of cervico-vaginal cell lines, human cervical explant tissues, and beneficial Lactobacillus species.

Results

Natural lime and lemon juice and household vinegar demonstrated anti-HIV-1 activity and cytotoxicity in transformed cell lines. Neutralization of the products reduced both anti-HIV-1 activity and cytotoxicity, resulting in a low therapeutic window for both acidic and neutralized formulations. For the natural juices and vinegar, the IC₅₀ was ≤ 3.5 (0.8-3.5)% and the TC₅₀ ≤ 6.3 (1.0-6.3)%. All three liquid products inhibited viability of beneficial Lactobacillus species associated with vaginal health. Comparison of three different toxicity endpoints in the cervical HeLa cell line revealed that all three products affected membrane integrity, cytosolic enzyme release, and dehydrogenase enzyme activity in living cells. The juices and vinegar also exerted strong cytotoxicity in cervico-vaginal cell lines, mainly due to their acidic pH. In human cervical explant tissues, treatment with 5% lemon or lime juice or 6% vinegar induced toxicity similar to application of 100 μg/ml nonoxynol-9, and exposure to 10% lime juice caused tissue damage comparable to treatment with 5% Triton-X-100.

Conclusions

Lemon and lime juice and household vinegar do not fulfill the safety criteria mandated for a topical microbicide. As a result of their unphysiological formulation for the vaginal tract, they exhibit cytotoxicity to human cell lines, human vaginal tissues, and beneficial vaginal Lactobacillus species.

HIV-1 neutralization profile and plant-based recombinant expression of actinohivin, an Env glycan-specific lectin devoid of T-cell mitogenic activity

The development of a topical microbicide blocking the sexual transmission of HIV-1 is urgently needed to control the global HIV/AIDS pandemic. The actinomycete-derived lectin actinohivin (AH) is highly specific to a cluster of high-mannose-type glycans uniquely found on the viral envelope (Env). Here, we evaluated AH's candidacy toward a microbicide in terms of in vitro anti-HIV-1 activity, potential side effects, and recombinant producibility. Two validated assay systems based on human peripheral blood mononuclear cell (hPBMC) infection with primary isolates and TZM-bl cell infection with Env-pseudotyped viruses were employed to characterize AH's anti-HIV-1 activity. In hPMBCs, AH exhibited nanomolar neutralizing activity against primary viruses with diverse cellular tropisms, but did not cause mitogenicity or cytotoxicity that are often associated with other anti-HIV lectins. In the TZM-bl-based assay, AH showed broad anti-HIV-1 activity against clinically-relevant, mucosally transmitting strains of clades B and C. By contrast, clade A viruses showed strong resistance to AH. Correlation analysis suggested that HIV-1's AH susceptibility is significantly linked to the N-glycans at the Env C2 and V4 regions. For recombinant (r)AH expression, we evaluated a tobacco mosaic virus-based system in Nicotiana benthamiana plants as a means to facilitate molecular engineering and cost-effective mass production. Biochemical analysis and an Env-mediated syncytium formation assay demonstrated high-level expression of functional rAH within six days. Taken together, our study revealed AH's cross-clade anti-HIV-1 activity, apparent lack of side effects common to lectins, and robust producibility using plant biotechnology. These findings justify further efforts to develop rAH toward a candidate HIV-1 microbicide.

Microbicides and HIV prevention: lessons from the past, looking to the future

PURPOSE OF REVIEW

This review provides an update on developments in HIV microbicide research in the light of recent phase 3 efficacy studies and discusses how lessons learnt from early generation microbicide candidates can assist the development of future agents.

RECENT FINDINGS

Results of an interim analysis of a phase 3 trial suggested that cellulose sulfate increased the risk of HIV acquisition compared with placebo. Carraguard, SAVVY and Buffergel also failed to show any HIV protection in human efficacy trials. Recent research has focused on elucidating the reasons behind these failures as well as improving the assessment of safety and efficacy for the next generation of microbicide candidates. PRO 2000 0.5% gel is the only HIV microbicide candidate for which there are preliminary data suggesting efficacy in women. Antiretroviral agents and entry inhibitors may provide the key in the future to developing an effective HIV microbicide both for vaginal and rectal use.

SUMMARY

Development of a protective 'barrier' which can be controlled by the receptive partner independent of time of coitus remains a key goal in HIV prevention. A gel or ring-delivered combination of active anti-HIV agents may prove more efficacious than a single agent alone. Challenges in evaluating and manufacturing new candidates must be overcome before a well tolerated, effective, acceptable and affordable microbicide can be produced.