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

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.

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.

HIV-Enhancing and HIV-Inhibiting Properties of Cationic Peptides and Proteins

Cationic antimicrobial peptides and proteins have historically been ascribed roles in innate immunity that infer killing of microbial and viral pathogens and protection of the host. In the context of sexually transmitted HIV-1, we take an unconventional approach that questions this paradigm. It is becoming increasingly apparent that many of the cationic polypeptides present in the human genital or anorectal mucosa, or human semen, are capable of enhancing HIV-1 infection, often in addition to other reported roles as viral inhibitors. We explore how the in vivo environment may select for or against the HIV-enhancing aspects of these cationic polypeptides by focusing on biological relevance. We stress that the distinction between enhancing and inhibiting HIV-1 infection is not mutually exclusive to specific classes of cationic polypeptides. Understanding how virally enhancing peptides and proteins act to promote sexual transmission of HIV-1 would be important for the design of topical microbicides, mucosal vaccines, and other preventative measures.

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

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

Reviewing HIV-Related Research in Emerging Economies: The Role of Government Reviewing Agencies

Little research has explored the possible effects of government institutions in emerging economies on ethical reviews of multinational research. We conducted semi-structured, in-depth telephone interviews with 15 researchers, Research Ethics Committees (RECs) personnel, and a government agency member involved in multinational HIV Prevention Trials Network (HPTN) research in emerging economies. Ministries of Health (MOH) or other government agencies often play pivotal roles as facilitators or barriers in the research ethics approval process. Government agency RECs reviewing protocols may face particular challenges, as they can lack resources, be poorly organized, have inconsistent review processes and limited expertise, and use differing definitions of national interests, including upholding national reputation and avoiding potential exploitation and stigma of the country's population. The MOH/governmental review body may be affected by power dynamics and politics in study reviews; may consider issues both related and unrelated to research ethics as understood elsewhere; and may prioritize particular diseases, treatments, or interventions over other topics/types of research. Poor communication and deeply-rooted tensions may exist between sponsor and host countries, impeding optimal interactions and reviews. Investigators must understand and plan for the potential effects of governmental agencies on multinational collaborative research, including preserving adequate time for agency review, and contacting these agencies beforehand to address issues that may arise. Better understanding of these issues can aid and advance appropriate global scientific collaboration.

Poly(ethylene glycol) (PEG)-lactic acid nanocarrier-based degradable hydrogels for restoring the vaginal microenvironment

Women with bacterial vaginosis (BV) display reduced vaginal acidity, which make them susceptible to associated infections such as HIV. In the current study, poly(ethylene glycol) (PEG) nanocarrier-based degradable hydrogels were developed for the controlled release of lactic acid in the vagina of BV-infected women. PEG-lactic acid (PEG-LA) nanocarriers were prepared by covalently attaching lactic acid to 8-arm PEG-SH via cleavable thioester bonds. PEG-LA nanocarriers with 4 copies of lactic acid per molecule provided controlled release of lactic acid with a maximum release of 23% and 47% bound lactic acid in phosphate buffered saline (PBS, pH7.4) and acetate buffer (AB, pH4.3), respectively. The PEG nanocarrier-based hydrogels were formed by cross-linking the PEG-LA nanocarriers with 4-arm PEG-NHS via degradable thioester bonds. The nanocarrier-based hydrogels formed within 20 min under ambient conditions and exhibited an elastic modulus that was 100-fold higher than the viscous modulus. The nanocarrier-based degradable hydrogels provided controlled release of lactic acid for several hours; however, a maximum release of only 10%-14% bound lactic acid was observed possibly due to steric hindrance of the polymer chains in the cross-linked hydrogel. In contrast, hydrogels with passively entrapped lactic acid showed burst release with complete release within 30 min. Lactic acid showed antimicrobial activity against the primary BV pathogen Gardnerella vaginalis with a minimum inhibitory concentration (MIC) of 3.6 mg/ml. In addition, the hydrogels with passively entrapped lactic acid showed retained antimicrobial activity with complete inhibition G. vaginalis growth within 48 h. The results of the current study collectively demonstrate the potential of PEG nanocarrier-based hydrogels for vaginal administration of lactic acid for preventing and treating BV.

Translation of biomedical prevention strategies for HIV: prospects and pitfalls

Early achievements in biomedical approaches for HIV prevention included physical barriers (condoms), clean injection equipment (both for medical use and for injection drug users), blood and blood product safety, and prevention of mother-to-child transmission. In recent years, antiretroviral drugs to reduce the risk of transmission (when the infected person takes the medicines; treatment as prevention) or reduce the risk of acquisition (when the seronegative person takes them; preexposure prophylaxis) have proven to be efficacious. Circumcision of men has also been a major tool relevant for higher prevalence regions such as sub-Saharan Africa. Well-established prevention strategies in the control of sexually transmitted diseases and tuberculosis are highly relevant for HIV (ie, screening, linkage to care, early treatment, and contact tracing). Unfortunately, only slow progress is being made in some available HIV-prevention strategies such as family planning for HIV-infected women who do not want more children and prevention of mother-to-child HIV transmission. Current studies seek to integrate strategies into approaches that combine biomedical, behavioral, and structural methods to achieve prevention synergies. This review identifies the major biomedical approaches demonstrated to be efficacious that are now available. We also highlight the need for behavioral risk reduction and adherence as essential components of any biomedical approach.

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.

Decreased cervical epithelial sensitivity to nonoxynol-9 (N-9) after four daily applications in a murine model of topical vaginal microbicide safety

BACKGROUND

The disappointing clinical failures of five topical vaginal microbicides have provided new insights into factors that impact microbicide safety and efficacy. Specifically, the greater risk for human immunodeficiency virus type 1 (HIV-1) acquisition associated with multiple uses of a nonoxynol-9 (N-9)-containing product has highlighted the importance of application frequency as a variable during pre-clinical microbicide development, particularly in animal model studies.

METHODS

To evaluate an association between application frequency and N-9 toxicity, experiments were performed using a mouse model of cervicovaginal microbicide safety. In this model system, changes in cervical and vaginal epithelial integrity, cytokine release, and immune cell infiltration were assessed after single and multiple exposures to N-9.

RESULTS

After the initial application of N-9 (aqueous, 1%), considerable damage to the cervical epithelium (but not the vaginal epithelium) was observed as early as 10 min post-exposure and up to 8 h post-exposure. Subsequent daily exposures (up to 4 days) were characterized by diminished cervical toxicity relative to single exposures of like duration. Levels of pro-inflammatory cytokines released into the cervicovaginal lumen and the degree of CD14-positive immune cell infiltration proximal to the cervical epithelium were also dependent on the number of N-9 exposures.

CONCLUSIONS

Rather than causing cumulative cervical epithelial damage, repeated applications of N-9 were characterized by decreased sensitivity to N-9-associated toxicity and lower levels of immune cell recruitment. These results provide new insights into the failure of N-9-based microbicides and illustrate the importance of considering multiple exposure protocols in pre-clinical microbicide development strategies.

Prevention interventions for human immunodeficiency virus in drug-using women with a history of partner violence

The intersecting epidemics of human immunodeficiency virus (HIV) and partner violence disproportionately affect women who use drugs. Despite accumulating evidence throughout the world linking these epidemics, HIV prevention efforts focused on these synergistic issues as well as underlying determinants that contribute to the HIV risk environment (eg, housing instability, incarceration, policing practices, survival sex) are lacking. This article highlights selected behavior change theories and biomedical approaches that have been used or could be applied in HIV prevention interventions for drug-using women with histories of partner violence and in existing HIV prevention interventions for drug-using women that have been gender-focused while integrating histories of partner violence and/or relationship power dynamics. To date, there is a paucity of HIV prevention interventions designed for drug-using women (both in and outside of drug treatment programs) with histories of partner violence. Of the few that exist, they have been theory-driven, culture-specific, and address certain aspects of gender-based inequalities (eg, gender-specific norms, relationship power and control, partner violence through assessment of personal risk and safety planning). However, no single intervention has addressed all of these issues. Moreover, HIV prevention interventions for drug-using women with histories of partner violence are not widespread and do not address multiple components of the risk environment. Efficacious interventions should target individuals, men, couples, and social networks. There is also a critical need for the development of culturally tailored combination HIV prevention interventions that not only incorporate evidence-based behavioral and biomedical approaches (eg, microbicides, pre-exposure prophylaxis, female-initiated barrier methods) but also take into account the risk environment at the physical, social, economic and political levels. Ultimately, this approach will have a significant impact on reducing HIV infections among drug-using women with histories of partner violence.

Cervicovaginal safety of the formulated, biguanide-based human immunodeficiency virus type 1 (HIV-1) inhibitor NB325 in a murine model

Vaginal microbicides that reduce or eliminate the risk of HIV-1 sexual transmission must do so safely without adversely affecting the integrity of the cervicovaginal epithelium. The present studies were performed to assess the safety of the biguanide-based antiviral compound NB325 in a formulation suitable for topical application. Experiments were performed using a mouse model of cervicovaginal microbicide application, which was previously shown to be predictive of topical agent toxicity revealed in microbicide clinical trials. Mice were exposed vaginally to unformulated NB325 or NB325 formulated in the hydroxyethyl cellulose “universal placebo.” Following exposures to formulated 1% NB325 for 10 min to 24 h, the vaginal and cervical epithelia were generally intact, although some areas of minimal vaginal epithelial damage were noted. Although formulated NB325 appeared generally safe for application in these studies, the low but observable level of toxicity suggests the need for improvements in the compound and/or formulation.

Decoding the membrane activity of the cyclotide kalata B1: the importance of phosphatidylethanolamine phospholipids and lipid organization on hemolytic and anti-HIV activities

Cyclotides, a large family of cyclic peptides from plants, have a broad range of biological activities, including insecticidal, cytotoxic, and anti-HIV activities. In all of these activities, cell membranes seem likely to be the primary target for cyclotides. However, the mechanistic role of lipid membranes in the activity of cyclotides remains unclear. To determine the role of lipid organization in the activity of the prototypic cyclotide, kalata B1 (kB1), and synthetic analogs, their bioactivities and affinities for model membranes were evaluated. We found that the bioactivity of kB1 is dependent on the lipid composition of target cell membranes. In particular, the activity of kB1 requires specific interactions with phospholipids containing phosphatidylethanolamine (PE) headgroups but is further modulated by nonspecific peptide-lipid hydrophobic interactions, which are favored in raft-like membranes. Negatively charged phospholipids do not favor high kB1 affinity. This lipid selectivity explains trends in antimicrobial and hemolytic activities of kB1; it does not target bacterial cell walls, which are negatively charged and lacking PE-phospholipids but can insert in the membranes of red blood cells, which have a low PE content and raft domains in their outer layer. We further show that the anti-HIV activity of kB1 is the result of its ability to target and disrupt the membranes of HIV particles, which are raft-like membranes very rich in PE-phospholipids.

In vitro surfactant structure-toxicity relationships: implications for surfactant use in sexually transmitted infection prophylaxis and contraception

BACKGROUND

The need for woman-controlled, cheap, safe, effective, easy-to-use and easy-to-store topical applications for prophylaxis against sexually transmitted infections (STIs) makes surfactant-containing formulations an interesting option that requires a more fundamental knowledge concerning surfactant toxicology and structure-activity relationships.

METHODOLOGY/PRINCIPAL FINDINGS

We report in vitro effects of surfactant concentration, exposure time and structure on the viability of mammalian cell types typically encountered in the vagina, namely, fully polarized and confluent epithelial cells, confluent but non-polarized epithelial-like cells, dendritic cells, and human sperm. Representatives of the different families of commercially available surfactants--nonionic (Triton X-100 and monolaurin), zwitterionic (DDPS), anionic (SDS), and cationic (C(n)TAB (n = 10 to 16), C(12)PB, and C(12)BZK)--were examined. Triton X-100, monolaurin, DDPS and SDS were toxic to all cell types at concentrations around their critical micelle concentration (CMC) suggesting a non-selective mode of action involving cell membrane destabilization and/or destruction. All cationic surfactants were toxic at concentrations far below their CMC and showed significant differences in their toxicity toward polarized as compared with non-polarized cells. Their toxicity was also dependent on the chemical nature of the polar head group. Our results suggest an intracellular locus of action for cationic surfactants and show that their structure-activity relationships could be profitably exploited for STI prophylaxis in vaginal gel formulations. The therapeutic indices comparing polarized epithelial cell toxicity to sperm toxicity for all surfactants examined, except C(12)PB and C(12)BZK, does not justify their use as contraceptive agents. C(12)PB and C(12)BZK are shown to have a narrow therapeutic index recommending caution in their use in contraceptive formulations.

CONCLUSIONS/SIGNIFICANCE

Our results contribute to understanding the mechanisms involved in surfactant toxicity, have a predictive value with regard to their safety, and may be used to design more effective and less harmful surfactants for use in topical applications for STI prophylaxis.

HIV envelope: challenges and opportunities for development of entry inhibitors

The HIV envelope proteins glycoprotein 120 (gp120) and glycoprotein 41 (gp41) play crucial roles in HIV entry, therefore they are of extreme interest in the development of novel therapeutics. Studies using diverse methods, including structural biology and mutagenesis, have resulted in a detailed model for envelope-mediated entry, which consists of multiple conformations, each a potential target for therapeutic intervention. In this review, the challenges, strategies and progress to date for developing novel entry inhibitors directed at disrupting HIV gp120 and gp41 function are discussed.

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.