Bivalent Ligand Aiming Putative Mu Opioid Receptor and Chemokine Receptor CXCR4 Dimers in Opioid Enhanced HIV-1 Entry

Multitarget ligands that comprise opioid/nonopioid pharmacophores for pain management: Current state of the science

Chronic pain, which affects more than one-third of the world's population, represents one of the greatest medical challenges of the 21st century, yet its effective management remains sub-optimal. The 'gold standard' for the treatment of moderate to severe pain consists of opioid ligands, such as morphine and fentanyl, that target the µ-opioid receptor (MOP). Paradoxically, these opioids also cause serious side effects, including constipation, respiratory depression, tolerance, and addiction. In addition, the development of opioid-use disorders, such as opioid diversion, misuse, and abuse, has led to the current opioid crisis, with dramatic increases in addiction, overdoses, and ultimately deaths. As pain is a complex, multidimensional experience involving a variety of pathways and mediators, dual or multitarget ligands that can bind to more than one receptor and exert complementary analgesic effects, represent a promising avenue for pain relief. Indeed, unlike monomodal therapeutic approaches, the modulation of several endogenous nociceptive systems can often result in an additive or even synergistic effect, thereby improving the analgesic-to-side-effect ratio. Here, we provide a comprehensive overview of research efforts towards the development of dual- or multi-targeting opioid/nonopioid hybrid ligands for effective and safer pain management. We reflect on the underpinning discovery rationale by discussing the design, medicinal chemistry, and in vivo pharmacological effects of multitarget antinociceptive compounds.

Study of G protein-coupled receptors dimerization: From bivalent ligands to drug-like small molecules

In the past decades an increasing number of studies revealed that G protein-coupled receptors (GPCRs) are capable of forming dimers or even higher-ordered oligomers, which may modulate receptor function and act as potential drug targets. In this review, we briefly summarized the design strategy of bivalent GPCR ligands and mainly focused on how to use them to study and/or detect GPCP dimerization in vitro and in vivo. Bivalent ligands show specific properties relative to their corresponding monomeric ligands because they are able to bind to GPCR homodimers or heterodimers simultaneously. For example, bivalent ligands with optimal length of spacers often exhibited higher binding affinities for dimers compared to that of monomers. Furthermore, bivalent ligands displayed specific signal transduction compared to monovalent ligands. Finally, we give our perspective on targeting GPCR dimers from traditional bivalent ligands to more drug-like small molecules.

Beyond the Syndemic of Opioid Use Disorders and HIV: The Impact of Opioids on Viral Reservoirs

People with HIV are more likely to have opioid use disorder and to be prescribed opioids for chronic pain than the general population; however, the effects of opioids on the immune system and HIV persistence have not been fully elucidated. Opioids may affect HIV reservoirs during their establishment, maintenance, and reactivation by enhancing HIV infectivity and replication due to upregulation of co-receptors and impairment of innate antiviral responses. Opioids may also modulate immune cell functioning and microbial translocation and can reverse viral latency. In this review, we summarize the current findings for and against the modulating effects of opioids on HIV cellular and anatomical reservoirs, highlighting the current limitations that affect in vitro, ex vivo, and in vivo studies in the field. We propose further research targets and potential strategies to approach this topic.

The synthetic opioid fentanyl increases HIV replication and chemokine co-receptor expression in vitro

The US is experiencing a major public health crisis that is fueled by the illicit use of synthetic opioids including fentanyl. While several drugs of abuse can enhance viral replication and/or antagonize immune responses, the impact of specific synthetic opioids on HIV pathogenesis is poorly understood. Thus, we evaluated the effects of fentanyl on HIV replication in vitro. HIV-susceptible or HIV-expressing cell lines were incubated with fentanyl. HIV p24 synthesis and chemokine receptor levels were quantified by ELISA in culture supernatants and cell lysates, respectively. Addition of fentanyl resulted in a dose-dependent increase in HIV replication. Fentanyl enhanced expression of the HIV chemokine co-receptors CXCR4 and CCR5 and caused a dose-dependent decrease in cell viability. The opioid antagonist naltrexone blocked the effect of fentanyl on HIV replication and CCR5 receptor levels but not CXCR4 receptor levels. TLR9 expression was induced by HIV; however, fentanyl inhibited TLR9 expression in a dose-dependent manner. These data demonstrate that the synthetic opioid fentanyl can promote HIV replication in vitro. As increased HIV levels are associated with accelerated disease progression and higher likelihood of transmission, additional research is required to enhance the understanding of opioid-virus interactions and to develop new and/or optimized treatment strategies for persons with HIV and opioid use disorder.

Novel bivalent ligands carrying potential antinociceptive effects by targeting putative mu opioid receptor and chemokine receptor CXCR4 heterodimers

The functional interactions between opioid and chemokine receptors have been implicated in the pathological process of chronic pain. Mounting studies have indicated the possibility that a MOR-CXCR4 heterodimer may be involved in nociception and related pharmacologic effects. Herein we have synthesized a series of bivalent ligands containing both MOR agonist and CXCR4 antagonist pharmacophores with an aim to investigate the functional interactions between these two receptors. In vitro studies demonstrated reasonable recognition of designed ligands at both respective receptors. Further antinociceptive testing in mice revealed compound 1a to be the most promising member of this series. Additional molecular modeling studies corroborated the findings observed. Taken together, we identified the first bivalent ligand 1a showing promising antinociceptive effect by targeting putative MOR-CXCR4 heterodimers, which may serve as a novel chemical probe to further develop more potent bivalent ligands with potential application in analgesic therapies for chronic pain management.

Toll-Like Receptor 4 in Pain: Bridging Molecules-to-Cells-to-Systems

Pain impacts the lives of billions of people around the world - both directly and indirectly. It is complex and transcends beyond an unpleasant sensory experience to encompass emotional experiences. To date, there are no successful treatments for sufferers of chronic pain. Although opioids do not provide any benefit to chronic pain sufferers, they are still prescribed, often resulting in more complications such as hyperalgesia and dependence. In order to develop effective and safe medications to manage, and perhaps even treat pain, it is important to evaluate novel contributors to pain pathologies. As such, in this chapter we review the role of Toll-like receptor 4, a receptor of the innate immune system, that continues to gain substantial attention in the field of pain research. Positioned in the nexus of the neuro and immune systems, TLR4 may provide one of the missing pieces in understanding the complexities of pain. Here we consider how TLR4 enables a mechanistical understanding of pain as a multidimensional biopsychosocial state from molecules to cells to systems and back again.

Drugs of Abuse and Their Impact on Viral Pathogenesis

Commonly misused substances such as alcohol, cocaine, heroin, methamphetamine, and opioids suppress immune responses and may impact viral pathogenesis. In recent years, illicit use of opioids has fueled outbreaks of several viral pathogens, including the human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV). This review focuses on the myriad of mechanisms by which drugs of abuse impact viral replication and disease progression. Virus–drug interactions can accelerate viral disease progression and lead to increased risk of virus transmission.

Structure-Based Design and Development of Chemical Probes Targeting Putative MOR-CCR5 Heterodimers to Inhibit Opioid Exacerbated HIV-1 Infectivity

Crystal structures of ligand-bound G-protein-coupled receptors provide tangible templates for rationally designing molecular probes. Herein, we report the structure-based design, chemical synthesis, and biological investigations of bivalent ligands targeting putative mu opioid receptor C-C motif chemokine ligand 5 (MOR-CCR5) heterodimers. The bivalent ligand VZMC013 possessed nanomolar level binding affinities for both the MOR and CCR5, inhibited CCL5-stimulated calcium mobilization, and remarkably improved anti-HIV-1BaL activity over previously reported bivalent ligands. VZMC013 inhibited viral infection in TZM-bl cells coexpressing CCR5 and MOR to a greater degree than cells expressing CCR5 alone. Furthermore, VZMC013 blocked human immunodeficiency virus (HIV)-1 entry in peripheral blood mononuclear cells (PBMC) cells in a concentration-dependent manner and inhibited opioid-accelerated HIV-1 entry more effectively in phytohemagglutinin-stimulated PBMC cells than in the absence of opioids. A three-dimensional molecular model of VZMC013 binding to the MOR-CCR5 heterodimer complex is constructed to elucidate its mechanism of action. VZMC013 is a potent chemical probe targeting MOR-CCR5 heterodimers and may serve as a pharmacological agent to inhibit opioid-exacerbated HIV-1 entry.