Maraviroc and reverse transcriptase inhibitors combinations as potential preexposure prophylaxis candidates

Broad-spectrum antiviral strategy: Host-targeting antivirals against emerging and re-emerging viruses

Viral infections are amongst the most prevalent diseases that pose a significant threat to human health. Targeting viral proteins or host factors represents two primary strategies for the development of antiviral drugs. In contrast to virus-targeting antivirals (VTAs), host-targeting antivirals (HTAs) offer advantages in terms of overcoming drug resistance and effectively combating a wide range of viruses, including newly emerging ones. Therefore, targeting host factors emerges as an extremely promising strategy with the potential to address critical challenges faced by VTAs. In recent years, extensive research has been conducted on the discovery and development of HTAs, leading to the approval of maraviroc, a chemokine receptor type 5 (CCR5) antagonist used for the treatment of HIV-1 infected individuals, with several other potential treatments in various stages of development for different viral infections. This review systematically summarizes advancements made in medicinal chemistry regarding various host targets and classifies them into four distinct catagories based on their involvement in the viral life cycle: virus attachment and entry, biosynthesis, nuclear import and export, and viral release.

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

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

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

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Opposite drug distribution in mucosal tissues was observed between both species

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

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

Medicinal chemistry strategies toward host targeting antiviral agents

Direct‐acting antiviral agents (DAAs) represent a class of drugs targeting viral proteins and have been demonstrated to be very successful in combating viral infections in clinic. However, DAAs suffer from several inherent limitations, including narrow‐spectrum antiviral profiles and liability to drug resistance, and hence there are still unmet needs in the treatment of viral infections. In comparison, host targeting antivirals (HTAs) target host factors for antiviral treatment. Since host proteins are probably broadly required for various viral infections, HTAs are not only perceived, but also demonstrated to exhibit broad‐spectrum antiviral activities. In addition, host proteins are not under the genetic control of viral genome, and hence HTAs possess much higher genetic barrier to drug resistance as compared with DAAs. In recent years, much progress has been made to the development of HTAs with the approval of chemokine receptor type 5 antagonist maraviroc for human immunodeficiency virus treatment and more in the pipeline for other viral infections. In this review, we summarize various host proteins as antiviral targets from a medicinal chemistry prospective. Challenges and issues associated with HTAs are also discussed.

Translational Approach to Predicting the Efficacy of Maraviroc-Based Regimens as HIV Preexposure Prophylaxis

Maraviroc-based regimens have been explored as preexposure prophylaxis (PrEP) against human immunodeficiency virus (HIV). In this study, we utilized mucosal tissue drug exposure data, combined with target concentrations generated in vitro, in a pharmacokinetic-pharmacodynamic analysis to predict the effects of drug combinations and adherence on PrEP efficacy. Mucosal tissue concentrations of maraviroc were measured in 24 healthy women. The 90% effective concentrations (EC₉₀) of maraviroc (alone and combined with tenofovir and emtricitabine) for protection against HIV were identified in CD4⁺ T cells. Monte Carlo simulations were performed to identify dosing strategies to protect colorectal and female genital tract (FGT) tissues from HIV infection. Colorectal maraviroc concentrations were 350-fold higher than in the FGT. Under steady-state conditions, our model predicted that one 300-mg dose/week was sufficient to protect colorectal tissue from HIV in 99% of the population, while 300 mg daily would protect the FGT in only 63% of the population. FGT protection increased to >90% when maraviroc was used in combination with tenofovir (5 doses/week) or emtricitabine (3 doses/week). Poor adherence resulted in a drastic decrease in efficacy in the FGT but not colorectal tissue. However, greater forgiveness was seen when maraviroc was combined with tenofovir or emtricitabine, suggesting that maraviroc should not be used alone as PrEP.

Clinical significance of chemokine receptor antagonists

Introduction: Chemokine receptors are important therapeutic targets for the treatment of many human diseases. This study will provide an overview of approved chemokine receptor antagonists and promising candidates in advanced clinical trials.Areas covered: We will describe clinical aspects of chemokine receptor antagonists regarding their clinical efficacy, mechanisms of action, and re-purposed applications.Expert opinion: Three chemokine antagonists have been approved: (i) plerixafor is a small-molecule CXCR4 antagonist that mobilizes hematopoietic stem cells; (ii) maraviroc is a small-molecule CCR5 antagonist for anti-HIV treatment; and (iii) mogamulizumab is a monoclonal-antibody CCR4 antagonist for the treatment of mycosis fungoides or Sézary syndrome. Moreover, phase 3 trials are ongoing to evaluate many potent candidates, including CCR5 antagonists (e.g. leronlimab), dual CCR2/CCR5 antagonists (e.g. cenicriviroc), and CXCR4 antagonists (e.g. balixafortide, mavorixafor, motixafortide). The success of chemokine receptor antagonists depends on the selective blockage of disease-relevant chemokine receptors which are indispensable for disease progression. Although clinical translation has been slow, antagonists targeting chemokine receptors with multifaced functions offer the potential to treat a broad spectrum of human diseases.

Antiretroviral agents in pre-exposure prophylaxis: emerging and advanced trends in HIV prevention

OBJECTIVES

Antiretroviral agents (ARVs) have been the most promising line of therapy in the management of human immunodeficiency virus (HIV) infections. Some of these ARVs are used in the pre-exposure prophylaxis (PrEP) to suppress the transmission of HIV. Prophylaxis is primarily used in uninfected people, before exposure, to effectively prevent HIV infection. Several studies have shown that ART PrEP prevents HIV acquisition from sexual, blood and mother-to-child transmissions. However, there are also several challenges and limitations to PrEP. This review focuses on the current antiretroviral therapies used in PrEP.

KEY FINDINGS

Among ARVs, the most common drugs employed from the class of entry inhibitors are maraviroc (MVC), which is a CCR5 receptor antagonist. Other entry inhibitors like emtricitabine (FTC) and tenofovir (TFV) are also used. Rilpivirine (RPV) and dapivirine (DPV) are the most common drugs employed from the Non-nucleoside reverse transcriptase inhibitor (NNRTIs) class, whereas, tenofovir disoproxil fumarate (TDF) is primarily used in the Nucleoside Reverse Transcriptase Inhibitor (NRTIs) class. Cabotegravir (CAB) is an analog of dolutegravir, and it is an integrase inhibitor. Some of these drugs are also used in combination with other drugs from the same class.

SUMMARY

Some of the most common pre-exposure prophylactic strategies employed currently are the use of inhibitors, namely entry inhibitors, non-nucleoside reverse transcriptase inhibitors, nucleoside reverse transcriptase inhibitors, integrase and protease inhibitors. In addition, we have also discussed on the adverse effects caused by ART in PrEP, pharmacoeconomics factors and the use of antiretroviral prophylaxis in serodiscordant couples.

The Pre-clinical Toolbox of Pharmacokinetics and Pharmacodynamics: in vitro and ex vivo Models

Prevention strategies against sexual transmission of human immunodeficiency virus (HIV) are essential to curb the rate of new infections. In the absence of a correlate of protection against HIV infection, pre-clinical evaluation is fundamental to facilitate and accelerate prioritization of prevention candidates and their formulations in a rapidly evolving clinical landscape. Characterization of pharmacokinetic (PK) and pharmacodynamic (PD) properties for candidate inhibitors is the main objective of pre-clinical evaluation. in vitro and ex vivo systems for pharmacological assessment allow experimental flexibility and adaptability at a relatively low cost without raising as significant ethical concerns as in vivo models. Applications and limitations of pre-clinical PK/PD models and future alternatives are reviewed in the context of HIV prevention.

Prediction of the binding mode and resistance profile for a dual-target pyrrolyl diketo acid scaffold against HIV-1 integrase and reverse-transcriptase-associated ribonuclease H

The rapid emergence of drug-resistant variants is one of the most common causes of highly active antiretroviral therapeutic (HAART) failure in patients infected with HIV-1. Compared with the existing HAART, the recently developed pyrrolyl diketo acid scaffold targeting both HIV-1 integrase (IN) and reverse transcriptase-associated ribonuclease H (RNase H) is an efficient approach to counteract the failure of anti-HIV treatment due to drug resistance. However, the binding mode and potential resistance profile of these inhibitors with important mechanistic principles remain poorly understood. To address this issue, an integrated computational method was employed to investigate the binding mode of inhibitor JMC6F with HIV-1 IN and RNase H. By using per-residue binding free energy decomposition analysis, the following residues: Asp64, Thr66, Leu68, Asp116, Tyr143, Gln148 and Glu152 in IN, Asp443, Glu478, Trp536, Lys541 and Asp549 in RNase H were identified as key residues for JMC6F binding. And then computational alanine scanning was carried to further verify the key residues. Moreover, the resistance profile of the currently known major mutations in HIV-1 IN and 2 mutations in RNase H against JMC6F was predicted by in silico mutagenesis studies. The results demonstrated that only three mutations in HIV-1 IN (Y143C, Q148R and N155H) and two mutations in HIV-1 RNase H (Y501R and Y501W) resulted in a reduction of JMC6F potency, thus indicating their potential role in providing resistance to JMC6F. These data provided important insights into the binding mode and resistance profile of the inhibitors with a pyrrolyl diketo acid scaffold in HIV-1 IN and RNase H, which would be helpful for the development of more effective dual HIV-1 IN and RNase H inhibitors.

Activity and structural analysis of GRL-117C: a novel small molecule CCR5 inhibitor active against R5-tropic HIV-1s

CCR5 is a member of the G-protein coupled receptor family that serves as an essential co-receptor for cellular entry of R5-tropic HIV-1, and is a validated target for therapeutics against HIV-1 infections. In the present study, we designed and synthesized a series of novel small CCR5 inhibitors and evaluated their antiviral activity. GRL-117C inhibited the replication of wild-type R5-HIV-1 with a sub-nanomolar IC₅₀ value. These derivatives retained activity against vicriviroc-resistant HIV-1s, but did not show activity against maraviroc (MVC)-resistant HIV-1. Structural modeling indicated that the binding of compounds to CCR5 occurs in the hydrophobic cavity of CCR5 under the second extracellular loop, and amino acids critical for their binding were almost similar with those of MVC, which explains viral cross-resistance with MVC. On the other hand, one derivative, GRL-10018C, less potent against HIV-1, but more potent in inhibiting CC-chemokine binding, occupied the upper region of the binding cavity with its bis-THF moiety, presumably causing greater steric hindrance with CC-chemokines. Recent studies have shown additional unique features of certain CCR5 inhibitors such as immunomodulating properties and HIV-1 latency reversal properties, and thus, continuous efforts in developing new CCR5 inhibitors with unique binding profiles is necessary.

Pharmaceutical Approaches to HIV Treatment and Prevention

Human immunodeficiency virus (HIV) infection continues to pose a major infectious disease threat worldwide. It is characterized by the depletion of CD4+ T cells, persistent immune activation, and increased susceptibility to secondary infections. Advances in the development of antiretroviral drugs and combination antiretroviral therapy have resulted in a remarkable reduction in HIV-associated morbidity and mortality. Antiretroviral therapy (ART) leads to effective suppression of HIV replication with partial recovery of host immune system and has successfully transformed HIV infection from a fatal disease to a chronic condition. Additionally, antiretroviral drugs have shown promise for prevention in HIV pre-exposure prophylaxis and treatment as prevention. However, ART is unable to cure HIV. Other limitations include drug-drug interactions, drug resistance, cytotoxic side effects, cost, and adherence. Alternative treatment options are being investigated to overcome these challenges including discovery of new molecules with increased anti-viral activity and development of easily administrable drug formulations. In light of the difficulties associated with current HIV treatment measures, and in the continuing absence of a cure, the prevention of new infections has also arisen as a prominent goal among efforts to curtail the worldwide HIV pandemic. In this review, the authors summarize currently available anti-HIV drugs and their combinations for treatment, new molecules under clinical development and prevention methods, and discuss drug delivery formats as well as associated challenges and alternative approaches for the future.

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

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

The future of pre-exposure prophylaxis (PrEP) for human immunodeficiency virus (HIV) infection

INTRODUCTION

People at high risk for HIV acquisition should be offered pre-exposure prophylaxis (PrEP). Tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC) is currently the only medication recommended for pre-exposure prophylaxis (PrEP) by the Centers for Disease Control and Prevention (CDC) in people at high risk for HIV acquisition. This article will review medications currently under investigation and the future landscape of PrEP therapy. Areas covered: This article will review clinical trials that have investigated nontraditional regimens of TDF/FTC, antiretroviral agents from different drug classes such as integrase strand transfer inhibitors (INSTI), nucleoside reverse transcriptase inhibitors (NRTI), and non-nucleoside reverse transcriptase inhibitors (NNRTI) as potential PrEP therapies. Expert commentary: Currently, there are several investigational drugs in the pipeline for PrEP against HIV infection. Increased utilization of PrEP therapy depends on provider identification of people at high risk for HIV transmission. Advances in PrEP development will expand options and access for people and reduce the risk of HIV acquisition.

Progress and Perspectives on HIV-1 microbicide development

The majority of HIV-1 infections occur via sexual intercourse. Women are the most affected by the epidemic, particularly in developing countries, due to their socio-economic dependence on men and the fact that they are often victims of gender based sexual violence. Despite significant efforts that resulted in the reduction of infection rates in some countries, there is still need for effective prevention methods against the virus. One of these methods for preventing sexual transmission in women is the use of microbicides. In this review we provide a summary of the progress made toward the discovery of affordable and effective HIV-1 microbicides and suggest future directions. We show that there is a wide range of compounds that have been proposed as potential microbicides. Although most of them have so far failed to show protection in humans, there are many promising ones currently in pre-clinical studies and in clinical trials.

Human Immunodeficiency Virus Immune Cell Receptors, Coreceptors, and Cofactors: Implications for Prevention and Treatment

In the last three decades, extensive research on human immunodeficiency virus (HIV) has highlighted its capability to exploit a variety of strategies to enter and infect immune cells. Although CD4(+) T cells are well known as the major HIV target, with infection occurring through the canonical combination of the cluster of differentiation 4 (CD4) receptor and either the C-C chemokine receptor type 5 (CCR5) or C-X-C chemokine receptor type 4 (CXCR4) coreceptors, HIV has also been found to enter other important immune cell types such as macrophages, dendritic cells, Langerhans cells, B cells, and granulocytes. Interestingly, the expression of distinct cellular cofactors partially regulates the rate in which HIV infects each distinct cell type. Furthermore, HIV can benefit from the acquisition of new proteins incorporated into its envelope during budding events. While several publications have investigated details of how HIV manipulates particular cell types or subtypes, an up-to-date comprehensive review on HIV tropism for different immune cells is lacking. Therefore, this review is meant to focus on the different receptors, coreceptors, and cofactors that HIV exploits to enter particular immune cells. Additionally, prophylactic approaches that have targeted particular molecules associated with HIV entry and infection of different immune cells will be discussed. Unveiling the underlying cellular receptors and cofactors that lead to HIV preference for specific immune cell populations is crucial in identifying novel preventative/therapeutic targets for comprehensive strategies to eliminate viral infection.