The nonnucleoside reverse transcriptase inhibitor MIV-150 in carrageenan gel prevents rectal transmission of simian/human immunodeficiency virus infection in macaques

Approved HIV reverse transcriptase inhibitors in the past decade

HIV reverse transcriptase (RT) inhibitors are the important components of highly active antiretroviral therapies (HAARTs) for anti-HIV treatment and pre-exposure prophylaxis in clinical practice. Many RT inhibitors and their combination regimens have been approved in the past ten years, but a review on their drug discovery, pharmacology, and clinical efficacy is lacking. Here, we provide a comprehensive review of RT inhibitors (tenofovir alafenamide, rilpivirine, doravirine, dapivirine, azvudine and elsulfavirine) approved in the past decade, regarding their drug discovery, pharmacology, and clinical efficacy in randomized controlled trials. Novel RT inhibitors such as islatravir, MK-8504, MK-8507, MK8583, IQP-0528, and MIV-150 will be also highlighted. Future development may focus on the new generation of novel antiretroviral inhibitors with higher bioavailability, longer elimination half-life, more favorable side-effect profiles, fewer drug-drug interactions, and higher activities against circulating drug-resistant strains.

Marine algal antagonists targeting 3CL protease and spike glycoprotein of SARS-CoV-2: a computational approach for anti-COVID-19 drug discovery

The COVID-19 pandemic has severely destructed human life worldwide, with no suitable treatment until now. SARS-CoV-2 virus is unprecedented, resistance against number of therapeutics and spreading rapidly with high mortality, which warrants the need to discover new effective drugs to combat this situation. This current study is undertaken to explore the antiviral potential of marine algal compounds to inhibit the viral entry and its multiplication using computational analysis. Among the proven drug discovery targets of SARS-CoV-2, spike glycoprotein and 3-chymotrypsin-like protease are responsible for the virus attachment and viral genome replication in the host cell. In this study, the above-mentioned drug targets were docked with marine algal compounds (sulfated polysaccharides, polysaccharide derivatives and polyphenols) using molecular docking tools (AutoDockTools). The obtained results indicate that κ-carrageenan, laminarin, eckol, trifucol and β-D-galactose are the top-ranking compounds showing better docking scores with SARS-CoV-2 targets, than the current experimental COVID-19 antiviral drugs like dexamethasone, remdesivir, favipiravir and MIV-150. Further, molecular dynamic simulation, ADMET and density functional theory calculations were evaluated to substantiate the findings. To the best of our knowledge, this is the first report on in silico analysis of aforesaid algal metabolites against SARS-CoV-2 targets. This study concludes that these metabolites can be curative for COVID-19 in the hour of need after further validations in in vitro and in vivo testings.Communicated by Ramaswamy H. Sarma.

Carrageenans as Broad-Spectrum Microbicides: Current Status and Challenges

Different kinds of red algae are enriched with chemically diverse carbohydrates. In particular, a group of sulfated polysaccharides, which were isolated from the cell walls of red algae, gained a large amount of attention due to their broad-spectrum antimicrobial activities. Within that group, carrageenans (CGs) were expected to be the first clinically applicable microbicides that could prevent various viral infections due to their superior antiviral potency and desirable safety profiles in subclinical studies. However, their anticipated beneficial effects could not be validated in human studies. To assess the value of a second attempt at pharmacologically developing CGs as a new class of preventive microbicides, all preclinical and clinical development processes of CG-based microbicides need to be thoroughly re-evaluated. In this review, the in vitro toxicities; in vivo safety profiles; and in vitro, ex vivo, and in vivo antiviral activities of CGs are summarized according to the study volume of their target viruses, which include human immunodeficiency virus, herpesviruses, respiratory viruses, human papillomavirus, dengue virus, and other viruses along with a description of their antiviral modes of action and development of antiviral resistance. This evaluation of the strengths and weaknesses of CGs will help provide future research directions that may lead to the successful development of CG-based antimicrobial prophylactics.

MIV-150 and zinc acetate combination provides potent and broad activity against HIV-1

We previously showed that the combination of the non-nucleoside reverse transcriptase inhibitor (NNRTI) MIV-150 with zinc acetate (ZA) formulated in a carrageenan (CG; MZC) gel provided macaques significant protection against vaginal simian-human immunodeficiency virus-RT (SHIV-RT) challenge, better than either MIV-150/CG or ZA/CG. The MZC gel was shown to be safe in a phase 1 clinical trial. Herein, we used in vitro approaches to study the antiviral properties of ZA and the MIV-150/ZA combination, compared to other NNRTIs. Like other NNRTIs, MIV-150 has EC₅₀ values in the subnanomolar to nanomolar range against wild type and NNRTI or RT-resistant HIVs. While less potent than NNRTIs, ZA was shown to be active in primary cells against laboratory-adapted and primary HIV-1 isolates and HIV-1 isolates/clones with NNRTI and RT resistance mutations, with EC₅₀ values between 20 and 110 μM. The MIV-150/ZA combination had a potent and broad antiviral activity in primary cells. In vitro resistance selection studies revealed that previously described NNRTI-resistant mutations were selected by MIV-150. ZA-resistant virus retained susceptibility to MIV-150 (and other RTIs) and MIV-150-selected virus remained sensitive to ZA. Notably, resistant virus was not selected when cultured in the presence of both ZA and MIV-150. This underscores the potency and breadth of the MIV-150/ZA combination, supporting preclinical macaque studies and the advancement of MZC microbicides into clinical testing.

Copper and Antibiotics: Discovery, Modes of Action, and Opportunities for Medicinal Applications

Copper is a ubiquitous element in the environment as well as living organisms, with its redox capabilities and complexation potential making it indispensable for many cellular functions. However, these same properties can be highly detrimental to prokaryotes and eukaryotes when not properly controlled, damaging many biomolecules including DNA, lipids, and proteins. To restrict free copper concentrations, all bacteria have developed mechanisms of resistance, sequestering and effluxing labile copper to minimize its deleterious effects. This weakness is actively exploited by phagocytes, which utilize a copper burst to destroy pathogens. Though administration of free copper is an unreasonable therapeutic antimicrobial itself, due to insufficient selectivity between host and pathogen, small-molecule ligands may provide an opportunity for therapeutic mimicry of the immune system. By modulating cellular entry, complex stability, resistance evasion, and target selectivity, ligand/metal coordination complexes can synergistically result in high levels of antibacterial activity. Several established therapeutic drugs, such as disulfiram and pyrithione, display remarkable copper-dependent inhibitory activity. These findings have led to development of new drug discovery techniques, using copper ions as the focal point. High-throughput screens for copper-dependent inhibitors against Mycobacterium tuberculosis and Staphylococcus aureus uncovered several new compounds, including a new class of inhibitors, the NNSNs. In this review, we highlight the microbial biology of copper, its antibacterial activities, and mechanisms to discover new inhibitors that synergize with copper.

Low Frequency of Drug-Resistant Variants Selected by Long-Acting Rilpivirine in Macaques Infected with Simian Immunodeficiency Virus Containing HIV-1 Reverse Transcriptase

Preexposure prophylaxis (PrEP) using antiretroviral drugs is effective in reducing the risk of human immunodeficiency virus type 1 (HIV-1) infection, but adherence to the PrEP regimen is needed. To improve adherence, a long-acting injectable formulation of the nonnucleoside reverse transcriptase (RT) inhibitor rilpivirine (RPV LA) has been developed. However, there are concerns that PrEP may select for drug-resistant mutations during preexisting or breakthrough infections, which could promote the spread of drug resistance and limit options for antiretroviral therapy. To address this concern, we administered RPV LA to macaques infected with simian immunodeficiency virus containing HIV-1 RT (RT-SHIV). Peak plasma RPV levels were equivalent to those reported in human trials and waned over time after dosing. RPV LA resulted in a 2-log decrease in plasma viremia, and the therapeutic effect was maintained for 15 weeks, until plasma drug concentrations dropped below 25 ng/ml. RT mutations E138G and E138Q were detected in single clones from plasma virus in separate animals only at one time point, and no resistance mutations were detected in viral RNA isolated from tissues. Wild-type and E138Q RT-SHIV displayed similar RPV susceptibilities in vitro, whereas E138G conferred 2-fold resistance to RPV. Overall, selection of RPV-resistant variants was rare in an RT-SHIV macaque model despite prolonged exposure to slowly decreasing RPV concentrations following injection of RPV LA.

Triple combination of carbosilane dendrimers, tenofovir and maraviroc as potential microbicide to prevent HIV-1 sexual transmission

AIM

To research the synergistic activity by triple combinations of carbosilane dendrimers with tenofovir and maraviroc as topical microbicide.

METHODS

Cytotoxicity, anti-HIV-1 activity, vaginal irritation and histological analysis of triple combinations were determined. Analysis of combined effects and the median effective concentration were performed using CalcuSyn software.

RESULTS

Combinations showed a greater broad-spectrum anti-HIV-1 activity than the single-drug, and preserved this activity in acid environment or seminal fluid. The strongest combinations were G2-STE16/G2-S24P/tenofovir, G2-STE16/G2-S16/maraviroc and G2-STE16/tenofovir/maraviroc at 2:2:1, 10:10:1 10:5:1 ratios, respectively. They demonstrated strong synergistic activity profile due to the weighted average combination indices varied between 0.06 and 0.38. No irritation was detected in female BALB/c mice.

CONCLUSION

The three-drug combination increases their antiviral potency and act synergistically as potential microbicide.

MIV-150/zinc acetate gel inhibits cell-associated simian-human immunodeficiency virus reverse transcriptase infection in a macaque vaginal explant model

The transmission of both cell-free and cell-associated immunodeficiency viruses has been demonstrated directly in multiple animal species and possibly occurs in humans, as suggested by genotyping of the infecting human immunodeficiency virus (HIV) in acutely infected women and in semen from their partners. Therefore, a microbicide may need to block both mechanisms of HIV transmission to achieve maximum efficacy. To date, most of the preclinical evaluation of candidate microbicides has been performed using cell-free HIV. New models of mucosal transmission of cell-associated HIV are needed to evaluate candidate microbicide performance. The MIV-150/zinc acetate/carrageenan (MZC) gel protects Depo-Provera-treated macaques against cell-free simian-human immunodeficiency virus reverse transcriptase (SHIV-RT) infection when applied vaginally up to 8 h before challenge. We recently demonstrated the potent activity of MZC gel against cell-free SHIV-RT in macaque vaginal explants. In the current study, we established a cell-associated SHIV-RT infection model of macaque vaginal tissues and tested the activity of MZC gel in this model. MZC gel protected tissues against cell-associated SHIV-RT infection when present at the time of viral exposure or when applied up to 4 days prior to viral challenge. These data support clinical testing of the MZC gel. Overall, our ex vivo model of cell-associated SHIV-RT infection in macaque vaginal mucosa complements the cell-free infection models, providing tools for prioritization of products that block both modes of HIV transmission.

Barrier methods for human immunodeficiency virus prevention

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

Short communication: a repeated simian human immunodeficiency virus reverse transcriptase/herpes simplex virus type 2 cochallenge macaque model for the evaluation of microbicides

Epidemiological studies suggest that prevalent herpes simplex virus type 2 (HSV-2) infection increases the risk of HIV acquisition, underscoring the need to develop coinfection models to evaluate promising prevention strategies. We previously established a single high-dose vaginal coinfection model of simian human immunodeficiency virus (SHIV)/HSV-2 in Depo-Provera (DP)-treated macaques. However, this model does not appropriately mimic women's exposure. Repeated limiting dose SHIV challenge models are now used routinely to test prevention strategies, yet, at present, there are no reports of a repeated limiting dose cochallenge model in which to evaluate products targeting HIV and HSV-2. Herein, we show that 20 weekly cochallenges with 2-50 TCID50 simian human immunodeficiency virus reverse transcriptase (SHIV-RT) and 10(7) pfu HSV-2 results in infection with both viruses (4/6 SHIV-RT, 6/6 HSV-2). The frequency and level of vaginal HSV-2 shedding were significantly greater in the repeated exposure model compared to the single high-dose model (p<0.0001). We used this new model to test the Council's on-demand microbicide gel, MZC, which is active against SHIV-RT in DP-treated macaques and HSV-2 and human papillomavirus (HPV) in mice. While MZC reduced SHIV and HSV-2 infections in our repeated limiting dose model when cochallenging 8 h after each gel application, a barrier effect of carrageenan (CG) that was not seen in DP-treated animals precluded evaluation of the significance of the antiviral activity of MZC. Both MZC and CG significantly (p<0.0001) reduced the frequency and level of vaginal HSV-2 shedding compared to no gel treatment. This validates the use of this repeated limiting dose cochallenge model for testing products targeting HIV and HSV-2.

[Microbicides for preventing sexually transmitted infections: Current status and strategies for preclinical evaluation of new candidates]

Microbicides are a new tool, still under investigation, which could help prevent infection by the human immunodeficiency virus (HIV) and other sexually transmitted infections (STIs). Increasing evidence shows that the complexity of sexual transmission of viral pathogens requires the identification of compounds able to block the early events during the cycle of viral infection. In this manuscript we provide a comprehensive review of the different microbicide strategies that have been studied or are currently being considered for STI prevention, particularly emphasizing those having the potential to block HIV infection. The manuscript also reviews the complex process that is required to conduct future clinical studies in humans and concludes with a brief discussion of the strategies that could be part of the immediate future in microbicide research.

Formulation and delivery of anti-HIV rectal microbicides: advances and challenges

Men and women engaged in unprotected receptive anal intercourse (RAI) are at higher risk of acquiring HIV from infected partners. The implementation of preventive strategies is urgent and rectal microbicides may be a useful tool in reducing the sexual transmission of HIV. However, pre-clinical and first clinical trials have been able to identify limitations of candidate products, mostly related with safety issues, which can in turn enhance viral infection. Indeed, the development of suitable formulations for the rectal delivery of promising antiretroviral drugs is not an easy task, and has been mostly based on products specifically intended for vaginal delivery, but these have been shown to provide sub-optimal outcomes when administered rectally. Research and development in the rectal microbicide field are now charting their own path and important information is now available. In particular, specific formulation requirements of rectal microbicide products that need to be met have just recently been acknowledged despite additional work being still required. Desirable rectal microbicide product features regarding characteristics such as pH, osmolality, excipients, dosage forms, volume to be administered and the need for applicator use have been studied and defined in recent years, and specific guidance is now possible. This review provides a synopsis of the field of rectal microbicides, namely past and ongoing clinical studies, and details on formulation and drug delivery issues regarding the specific development of rectal microbicide products. Also, future work, as required for the advancement of the field, is discussed.

A potent combination microbicide that targets SHIV-RT, HSV-2 and HPV

Prevalent infection with human herpes simplex 2 (HSV-2) or human papillomavirus (HPV) is associated with increased human immunodeficiency virus (HIV) acquisition. Microbicides that target HIV as well as these sexually transmitted infections (STIs) may more effectively limit HIV incidence. Previously, we showed that a microbicide gel (MZC) containing MIV-150, zinc acetate (ZA) and carrageenan (CG) protected macaques against simian-human immunodeficiency virus (SHIV-RT) infection and that a ZC gel protected mice against HSV-2 infection. Here we evaluated a modified MZC gel (containing different buffers, co-solvents, and preservatives suitable for clinical testing) against both vaginal and rectal challenge of animals with SHIV-RT, HSV-2 or HPV. MZC was stable and safe in vitro (cell viability and monolayer integrity) and in vivo (histology). MZC protected macaques against vaginal (p<0.0001) SHIV-RT infection when applied up to 8 hours (h) prior to challenge. When used close to the time of challenge, MZC prevented rectal SHIV-RT infection of macaques similar to the CG control. MZC significantly reduced vaginal (p<0.0001) and anorectal (p = 0.0187) infection of mice when 10(6) pfu HSV-2 were applied immediately after vaginal challenge and also when 5×10(3) pfu were applied between 8 h before and 4 h after vaginal challenge (p<0.0248). Protection of mice against 8×10(6) HPV16 pseudovirus particles (HPV16 PsV) was significant for MZC applied up to 24 h before and 2 h after vaginal challenge (p<0.0001) and also if applied 2 h before or after anorectal challenge (p<0.0006). MZC provides a durable window of protection against vaginal infection with these three viruses and, against HSV-2 and HPV making it an excellent candidate microbicide for clinical use.

MIV-150-containing intravaginal rings protect macaque vaginal explants against SHIV-RT infection

Recent studies demonstrated that intravaginal rings (IVRs) containing 100 mg of the nonnucleoside reverse transcriptase inhibitor (NNRTI) MIV-150 significantly protect macaques against a chimeric simian-human immunodeficiency virus that expresses the HIV-1 HxB2 reverse transcriptase (SHIV-RT) when present before and after vaginal challenge. The objectives of this study were to (i) evaluate the pharmacodynamics (PD) of MIV-150 in vaginal fluids (VF) and in ectocervical and vaginal tissues following 100-mg MIV-150 IVR exposure and to (ii) gain more insight whether pharmacokinetics (PK) of MIV-150 can predict PD. MIV-150 in VF collected at 1 day and 14 days post-MIV-150 IVR insertion inhibited ex vivo SHIV-RT infection in vaginal biopsy specimens from untreated animals (not carrying IVRs) in a dose-dependent manner. Previous PK studies demonstrated a significant increase of ectocervical and vaginal tissue MIV-150 concentrations 14 days versus 1 day post-IVR insertion, with the highest increase in vaginal tissue. Therefore, we tested PD of MIV-150 in tissues 14 days post-MIV-150 IVR insertion. Ex vivo SHIV-RT infection of vaginal, but not ectocervical, tissues collected 14 days post-MIV-150 IVR insertion was significantly inhibited compared to infection at the baseline (prior to MIV-150 IVR exposure). No changes in vaginal and ectocervical tissue infection were observed after placebo IVR exposure. Overall, these data underscore the use of the ex vivo macaque explant challenge models to evaluate tissue and VF PK/PD of candidate microbicides before in vivo animal efficacy studies. The data support further development of MIV-150-containing IVRs.

Exposure to MIV-150 from a high-dose intravaginal ring results in limited emergence of drug resistance mutations in SHIV-RT infected rhesus macaques

When microbicides used for HIV prevention contain antiretroviral drugs, there is concern for the potential emergence of drug-resistant HIV following use in infected individuals who are either unaware of their HIV infection status or who are aware but still choose to use the microbicide. Resistant virus could ultimately impact their responsiveness to treatment and/or result in subsequent transmission of drug-resistant virus. We tested whether drug resistance mutations (DRMs) would emerge in macaques infected with simian immunodeficiency virus expressing HIV reverse transcriptase (SHIV-RT) after sustained exposure to the potent non-nucleoside reverse transcriptase inhibitor (NNRTI) MIV-150 delivered via an intravaginal ring (IVR). We first treated 4 SHIV-RT-infected animals with daily intramuscular injections of MIV-150 over two 21 day (d) intervals separated by a 7 d drug hiatus. In all 4 animals, NNRTI DRMs (single and combinations) were detected within 14 d and expanded in proportion and diversity with time. Knowing that we could detect in vivo emergence of NNRTI DRMs in response to MIV-150, we then tested whether a high-dose MIV-150 IVR (loaded with >10 times the amount being used in a combination microbicide IVR in development) would select for resistance in 6 infected animals, modeling use of this prevention method by an HIV-infected woman. We previously demonstrated that this MIV-150 IVR provides significant protection against vaginal SHIV-RT challenge. Wearing the MIV-150 IVR for 56 d led to only 2 single DRMs in 2 of 6 animals (430 RT sequences analyzed total, 0.46%) from plasma and lymph nodes despite MIV-150 persisting in the plasma, vaginal fluids, and genital tissues. Only wild type virus sequences were detected in the genital tissues. These findings indicate a low probability for the emergence of DRMs after topical MIV-150 exposure and support the advancement of MIV-150-containing microbicides.

A combination microbicide gel protects macaques against vaginal simian human immunodeficiency virus-reverse transcriptase infection, but only partially reduces herpes simplex virus-2 infection after a single high-dose cochallenge

Herpes simplex virus-2 (HSV-2) infection increases HIV susceptibility. We previously established a rhesus macaque model of vaginal HSV-2 preexposure followed by cochallenge with HSV-2 and simian/human immunodeficiency virus-reverse transcriptase (SHIV-RT). Using this model, we showed that a gel containing the nonnucleoside reverse transcriptase inhibitor (NNRTI) MIV-150 in carrageenan (CG) reduced SHIV-RT infection. To evaluate the efficacy of new generation microbicides against both viruses, we first established dual infection after single vaginal cochallenge with SHIV-RT and HSV-2 in HSV-2-naive macaques. All animals (6/6) became HSV-2 infected, with 4/6 coinfected with SHIV-RT. In a control group cochallenged with SHIV-RT and UV-inactivated HSV-2, 2/4 became SHIV-RT infected, and none had detectable HSV-2. Low-level HSV-2-specific antibody and T cell responses were detected in some HSV-2-infected animals. To test a CG gel containing MIV-150 and zinc acetate (MZC), which provided naive animals full protection from SHIV-RT for at least 8 h, MZC (vs. CG) was applied daily for 14 days followed by cochallenge 8 h later. MZC prevented SHIV-RT infection (0/9 infected, p=0.04 vs. 3/6 in CG controls), but only reduced HSV-2 infection by 20% (6/9 infected vs. 5/6 in CG, p=0.6). In HSV-2-infected animals, none of the gel-treated animals seroconverted, and only the CG controls had measurable HSV-2-specific T cell responses. This study shows the promise of MZC to prevent immunodeficiency virus infection (even in the presence of HSV-2) and reduce HSV-2 infection after exposure to a high-dose inoculum. Additionally, it demonstrates the potential of a macaque coinfection model to evaluate broad-spectrum microbicides.

Rectal microbicide development

The last few years have seen important progress in demonstrating the efficacy of oral pre-exposure prophylaxis, vaginal microbicides, and treatment as prevention as effective strategies for reducing the risk of acquiring or transmitting HIV infection. There has also been significant progress in the development of rectal microbicides. Preclinical non-human primate studies have demonstrated that antiretroviral microbicides can provide significant protection from rectal challenge with SIV or SHIV. Recent Phase 1 rectal microbicide studies have characterized the safety, acceptability, compartmental pharmacokinetics (PK), and pharmacodynamics (PD) of both UC781 and tenofovir gels. The tenofovir gel formulation used in vaginal studies was not well tolerated in the rectum and newer rectal-specific formulations have been developed and evaluated in Phase 1 studies. The PK/PD data generated in these Phase 1 studies may reduce the risk of advancing ineffective candidate rectal microbicides into late stage development. Tenofovir gel is currently poised to move into Phase 2 evaluation and it is possible that a Phase 2B/3 effectiveness study with this product could be initiated in the next 2-3 years.

The frequency of α₄β₇(high) memory CD4⁺ T cells correlates with susceptibility to rectal simian immunodeficiency virus infection

BACKGROUND

Integrin α₄β₇(high) (α₄β₇(high)) mediates the homing of CD4⁺ T cells to gut-associated lymphoid tissues, which constitute a highly favorable environment for HIV expansion and dissemination. HIV and simian immunodeficiency virus (SIV) envelope proteins bind to and signal through α₄β₇(high) and during acute infection SIV preferentially infects α₄β₇(high) CD4⁺ T cells. We postulated that the availability of these cells at the time of challenge could influence mucosal SIV transmission and acute viral load (VL).

METHODS

We challenged 17 rhesus macaques with 3000 TCID50 of SIVmac239 rectally and followed the subsets of α₄β₇(high) T cells and dendritic cells (DCs) by flow cytometry in blood and tissues, before and after challenge.

RESULTS

We found that the frequency of memory CD4⁺ T cells that expressed high levels of α₄β₇(high) (α₄β₇(high) memory CD4⁺ T cells) in blood before challenge correlated strongly with susceptibility to infection and acute VL. Notably, not only at the time of challenge but also their frequency 3 weeks before challenge correlated with infection. This association extended to the rectal tissue as we observed a strong direct correlation between the frequency of α₄β₇(high) memory CD4⁺ T cells in blood and rectum before and after challenge. The frequency of α4β7 myeloid DCs and α₄β₇(high) CD80⁺ DCs also correlated with infection and acute VL, whereas blood CCR5⁺ and CD69⁺ CD4⁺ T cells could not be associated with infection.

CONCLUSIONS

Our results suggest that animals with higher frequency of α₄β₇(high) CD4⁺ T cells in circulation and in rectal tissue could be more susceptible to SIV rectal transmission.

The development of rectal microbicides for HIV prevention

INTRODUCTION

Individuals practicing unprotected receptive anal intercourse are at particularly high risk of HIV infection. Men who have sex with men in the developed and developing world continue to have disproportionate and increasing levels of HIV infection. The last few years have seen important progress in demonstrating the efficacy of oral antiretroviral pre-exposure prophylaxis, vaginal microbicides, and treatment as prevention, but there has also been significant progress in the development of rectal microbicides for HIV prevention.

AREAS COVERED

The purpose of this review is to summarize the status of rectal microbicide research and to identify opportunities, challenges, and future directions in this important field of HIV prevention research. The design of completed and ongoing Phase I rectal microbicide studies that include the generation of comprehensive pharmacokinetic/pharmacodynamic data may allow for more rational decisions about which rectal microbicides should be advanced to later stage development.

EXPERT OPINION

There is a strong rationale for the development of rectal microbicides for HIV prevention. Preclinical data provide supportive evidence for the feasibility of this approach, and there is significant interest in rectal microbicide development from communities at risk of HIV acquisition through unprotected receptive anal intercourse in both the developed and developing world. Demonstration of sustained safety, acceptability, and product adherence in the MTN-017 Phase II study of tenofovir 1% gel will be an important step in rectal microbicide development and will hopefully lead to Phase III effectiveness testing of this novel HIV prevention strategy.

Rectal pre-exposure prophylaxis (PrEP)

Rectal pre-exposure prophylaxis (PrEP) will be a critical component of HIV prevention products due to the prevalence of unprotected receptive anal intercourse among men who have sex with men and heterosexual couples. Given the biological considerations of this compartment and the complexity of HIV infection, design of a successful rectal microbicide product faces a number of challenges. Important information is being compiled to begin to address deficits in knowledge toward design of rectal PrEP products for men and women. Aspects of formulation development and preclinical and clinical evaluation of rectal products studied to date are summarized in this review. This article is based on a presentation at the "Product Development Workshop 2013: HIV and Multipurpose Prevention Technologies," held in Arlington, Virginia on February 21-22, 2013. It forms part of a special supplement to Antiviral Research.

Clinical use of vaginal or rectally applied microbicides in patients suffering from HIV/AIDS

Microbicides, primarily used as topical pre-exposure prophylaxis, have been proposed to prevent sexual transmission of HIV. This review covers the trends and challenges in the development of safe and effective microbicides to prevent sexual transmission of HIV Initial phases of microbicide development used such surfactants as nonoxynol-9 (N-9), C13G, and sodium lauryl sulfate, aiming to inactivate the virus. Clinical trials of microbicides based on N-9 and C31G failed to inhibit sexual transmission of HIV. On the contrary, N-9 enhanced susceptibility to sexual transmission of HIV-1. Subsequently, microbicides based on polyanions and a variety of other compounds that inhibit the binding, fusion, or entry of virus to the host cells were evaluated for their efficacy in different clinical setups. Most of these trials failed to show either safety or efficacy for prevention of HIV transmission. The next phase of microbicide development involved antiretroviral drugs. Microbicide in the form of 1% tenofovir vaginal gel when tested in a Phase IIb trial (CAPRISA 004) in a coitally dependent manner revealed that tenofovir gel users were 39% less likely to become HIV-infected compared to placebo control. However, in another trial (VOICE MTN 003), tenofovir gel used once daily in a coitally independent mode failed to show any efficacy to prevent HIV infection. Tenofovir gel is currently in a Phase III safety and efficacy trial in South Africa (FACTS 001) employing a coitally dependent dosing regimen. Further, long-acting microbicide-delivery systems (vaginal ring) for slow release of such antiretroviral drugs as dapivirine are also undergoing clinical trials. Discovering new markers as correlates of protective efficacy, novel long-acting delivery systems with improved adherence in the use of microbicides, discovering new compounds effective against a broad spectrum of HIV strains, developing multipurpose technologies incorporating additional features of efficacy against other sexually transmitted infections, and contraception will help in moving the field of microbicide development forward.

SIV infection of rhesus macaques of Chinese origin: a suitable model for HIV infection in humans

Simian immunodeficiency virus (SIV) infection of Indian-origin rhesus macaques (RM) has been widely used as a well-established nonhuman primate (NHP) model for HIV/AIDS research. However, there have been a growing number of studies using Chinese RM to evaluate immunopathogenesis of SIV infection. In this paper, we have for the first time reviewed and discussed the major publications related to SIV or SHIV infection of Chinese RM in the past decades. We have compared the differences in the pathogenesis of SIV infection between Chinese RM and Indian RM with regard to viral infection, immunological response, and host genetic background. Given AIDS is a disease that affects humans of diverse origins, it is of importance to study animals with different geographical background. Therefore, to examine and compare results obtained from RM models of Indian and Chinese origins should lead to further validation and improvement of these animal models for HIV/AIDS research.

A modified zinc acetate gel, a potential nonantiretroviral microbicide, is safe and effective against simian-human immunodeficiency virus and herpes simplex virus 2 infection in vivo

We previously showed that a prototype gel comprising zinc acetate (ZA) in carrageenan (CG) protected mice against vaginal and rectal herpes simplex virus 2 (HSV-2) challenge as well as macaques against vaginal simian-human immunodeficiency virus reverse transcriptase (SHIV-RT) challenge. In this work, we modified buffers and cosolvents to obtain a stable, nearly iso-osmolal formulation and evaluated its safety and efficacy against SHIV-RT and HSV-2. In vitro toxicity to lactobacilli and Candida albicans was determined. Macaques were given daily doses of ZA and CG (ZA/CG) or CG alone vaginally for 14 days and challenged with SHIV-RT 24 h later. Mice were challenged vaginally or rectally with HSV-2 immediately after a single gel treatment to measure efficacy or vaginally 12 h after daily gel treatment for 7 days to evaluate the gel's impact on susceptibility to HSV-2 infection. The modified ZA/CG neither affected the viability of lactobacilli or C. albicans nor enhanced vaginal HSV-2 infection after daily ZA/CG treatment. Vaginal SHIV-RT infection of macaques was reduced by 66% (P = 0.006) when macaques were challenged 24 h after the last dose of gel. We observed 60% to 80% uninfected mice after vaginal (P < 0.0001) and rectal (P = 0.008) high-dose HSV-2 challenge. The modified ZA/CG gel is safe and effective in animal models and represents a potential candidate to limit the transmission of HIV and HSV-2.

Rectal transmission of transmitted/founder HIV-1 is efficiently prevented by topical 1% tenofovir in BLT humanized mice

Rectal microbicides are being developed to prevent new HIV infections in both men and women. We focused our in vivo preclinical efficacy study on rectally-applied tenofovir. BLT humanized mice (n = 43) were rectally inoculated with either the primary isolate HIV-1JRCSF or the MSM-derived transmitted/founder (T/F) virus HIV-1THRO within 30 minutes following treatment with topical 1% tenofovir or vehicle. Under our experimental conditions, in the absence of drug treatment we observed 50% and 60% rectal transmission by HIV-1JRCSF and HIV-1THRO, respectively. Topical tenofovir reduced rectal transmission to 8% (1/12; log rank p = 0.03) for HIV-1JRCSF and 0% (0/6; log rank p = 0.02) for HIV-1THRO. This is the first demonstration that any human T/F HIV-1 rectally infects humanized mice and that transmission of the T/F virus can be efficiently blocked by rectally applied 1% tenofovir. These results obtained in BLT mice, along with recent ex vivo, Phase 1 trial and non-human primate reports, provide a critically important step forward in the development of tenofovir-based rectal microbicides.

Drug-eluting fibers for HIV-1 inhibition and contraception

Multipurpose prevention technologies (MPTs) that simultaneously prevent sexually transmitted infections (STIs) and unintended pregnancy are a global health priority. Combining chemical and physical barriers offers the greatest potential to design effective MPTs, but integrating both functional modalities into a single device has been challenging. Here we show that drug-eluting fiber meshes designed for topical drug delivery can function as a combination chemical and physical barrier MPT. Using FDA-approved polymers, we fabricated nanofiber meshes with tunable fiber size and controlled degradation kinetics that facilitate simultaneous release of multiple agents against HIV-1, HSV-2, and sperm. We observed that drug-loaded meshes inhibited HIV-1 infection in vitro and physically obstructed sperm penetration. Furthermore, we report on a previously unknown activity of glycerol monolaurate (GML) to potently inhibit sperm motility and viability. The application of drug-eluting nanofibers for HIV-1 prevention and sperm inhibition may serve as an innovative platform technology for drug delivery to the lower female reproductive tract.

A perspective on progress and gaps in HIV prevention science

In the past few years, the transdisciplinary field of HIV prevention has reached several milestones. Topically applied tenofovir gel provided significant protection from sexual transmission of HIV in a large-scale clinical trial and oral Truvada (emtricitabine/tenofovir disoproxil fumarate) was recently approved for preexposure prophylaxis (PrEP) following two successful clinical trials in men and women. These achievements are tempered by the disappointing results of other clinical trials, which highlight the complexities of prevention research. In this perspective, we discuss scientific and developmental gaps for topical chemoprophylaxis of the sexual transmission of HIV, which depends on the complex interactions between the pharmacokinetics and pharmacodynamics of drugs, formulation and delivery systems, anatomic site of transmission, and host mucosal immune defenses. Despite the considerable time and resources devoted to unraveling the initial steps in sexual transmission of HIV, current knowledge is based on animal models and human explanted tissue, which may not fully recapitulate what happens clinically. Understanding these events, including the role that sex hormones, semen, and mucosal secretions play in transmission, and the interplay between innate immunity, the mucosal environment, and drug efficacy is paramount. This drives some of the most pressing questions in the field.

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

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

A single dose of a MIV-150/Zinc acetate gel provides 24 h of protection against vaginal simian human immunodeficiency virus reverse transcriptase infection, with more limited protection rectally 8-24 h after gel use

Previously we showed that repeated vaginal application of a MIV-150/zinc acetate carrageenan (MIV-150/ZA/CG) gel and a zinc acetate carrageenan (ZA/CG) gel significantly protected macaques from vaginal simian human immunodeficiency virus reverse transcriptase (SHIV-RT) infection. Gels were applied either daily for 2 weeks or every other day for 4 weeks, and the animals were challenged 4-24 h later. Herein, we examined the effects of a single vaginal dose administered either before or after virus challenge. Encouraged by the vaginal protection seen with MIV-150/ZA/CG, we also tested it rectally. Vaginal applications of MIV-150/ZA/CG, ZA/CG, and CG gel were performed once 8-24 h before, 1 h after, or 24 h before and 1 h after vaginal challenge. Rectal applications of MIV-150/ZA/CG and CG gel were performed once 8 or 24 h before rectal challenge. While vaginal pre-challenge and pre/post-challenge application of MIV-150/ZA/CG gel offered significant protection (88%, p<0.002), post-challenge application alone did not significantly protect. ZA/CG gel reduced infection prechallenge, but not significantly, and the effect was completely lost post-challenge. Rectal application of MIV-150/ZA/CG gel afforded limited protection against rectal challenge when applied 8-24 h before challenge. Thus, MIV-150/ZA/CG gel is a highly effective vaginal microbicide that demonstrates 24 h of protection from vaginal infection and may demonstrate efficacy against rectal infection when given close to the time of HIV exposure.

Rectal microbicide development

PURPOSE OF REVIEW

Individuals practicing unprotected receptive anal intercourse are at particularly high risk of HIV infection. Men who have sex with men (MSM) in the developed and developing world continue to have disproportionate and increasing levels of HIV infection. The past few years have seen important progress in demonstrating the efficacy of oral pre-exposure prophylaxis (PrEP), vaginal microbicides, and treatment as prevention, but there has also been significant progress in the development of rectal microbicides. The purpose of this review is to summarize the status of rectal microbicide research and to identify opportunities, challenges, and future directions in this important field of HIV prevention.

RECENT FINDINGS

Recent phase 1 rectal microbicide studies have characterized the safety, acceptability, compartmental pharmacokinetics, and pharmacodynamics of both UC781 and tenofovir gels. The tenofovir gel formulation used in vaginal studies was not well tolerated in the rectum and newer rectal-specific formulations have been developed and evaluated in phase 1 studies.

SUMMARY

Complex phase 1 studies have provided important data on candidate rectal microbicides. Tenofovir gel is poised to move into phase 2 evaluation and it is possible that a phase 2B/3 effectiveness study could be initiated in the next 2-3 years.

The Promise of Antiretrovirals for HIV Prevention

With an estimated 2.6 million new HIV infections diagnosed annually, the world needs new prevention strategies to partner with condom use, harm reduction approaches for injection drug users, and male circumcision. Antiretrovirals can reduce the risk of mother-to-child HIV transmission and limit HIV acquisition after occupational exposure. Macaque models and clinical trials demonstrate efficacy of oral or topical antiretrovirals used prior to HIV exposure to prevent HIV transmission, ie pre-exposure prophylaxis (PrEP). Early initiation of effective HIV treatment in serodiscordant couples results in a 96% decrease in HIV transmission. HIV testing to determine serostatus and identify undiagnosed persons is foundational to these approaches. The relative efficacy of different approaches, adherence, cost and long-term safety will affect uptake and impact of these strategies. Ongoing research will help characterize the role for oral and topical formulations and help quantify potential benefits in sub-populations at risk for HIV acquisition.

An intravaginal ring that releases the NNRTI MIV-150 reduces SHIV transmission in macaques

Microbicides may prevent HIV and sexually transmitted infections (STIs) in women; however, determining the optimal means of delivery of active pharmaceutical ingredients remains a major challenge. We previously demonstrated that a vaginal gel containing the non-nucleoside reverse transcriptase inhibitor MIV-150 partially protected macaques from SHIV-RT (simian/HIV reverse transcriptase) infection, and the addition of zinc acetate rendered the gel significantly protective. We test the activity of MIV-150 without the addition of zinc acetate when delivered from either ethylene vinyl acetate (EVA) or silicone intravaginal rings (IVRs). MIV-150 was successfully delivered, because it was detected in vaginal fluids and tissues by radioimmunoassay in pharmacokinetic studies. Moreover, EVA IVRs significantly protected macaques from SHIV-RT infection. Our results demonstrate that MIV-150-containing IVRs have the potential to prevent HIV infection and highlight the possible use of IVRs for delivering drugs that block HIV and other STIs.

Mucosal transmission of human immunodeficiency virus

Since the beginning of the AIDS pandemic, and following the discovery of the human immunodeficiency virus (HIV) as the etiological agent of the disease, it was clear that the virus gains access to the human host predominantly through the mucosal tissue after sexual exposure. As a consequence, the female genital tract (vaginal and cervical), as well as the rectal, penile, and oral mucosae have been extensively studied over the last thirty years towards a better understanding of--and to develop strategies to prevent--sexual HIV transmission. This review seeks to describe the biology of the events leading to HIV infection through the human mucosa and introduce some of the approaches attempted to prevent the sexual transmission of HIV.