Orally Active Peptide Vector Allows Using Cannabis to Fight Pain While Avoiding Side Effects

RNA therapeutics in targeting G protein-coupled receptors: Recent advances and challenges

G protein-coupled receptors (GPCRs) are the major targets of existing drugs for a plethora of human diseases and dominate the pharmaceutical market. However, over 50% of the GPCRs remain undruggable. To pursue a breakthrough and overcome this situation, there is significant clinical research for developing RNA-based drugs specifically targeting GPCRs, but none has been approved so far. RNA therapeutics represent a unique and promising approach to selectively targeting previously undruggable targets, including undruggable GPCRs. However, the development of RNA therapeutics faces significant challenges in areas of RNA stability and efficient in vivo delivery. This review presents an overview of the advances in RNA therapeutics and the diverse types of nanoparticle RNA delivery systems. It also describes the potential applications of GPCR-targeted RNA drugs for various human diseases.

Allosteric Modulators of Serotonin Receptors: A Medicinal Chemistry Survey

Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter regulating numerous physiological functions, and its dysregulation is a crucial component of the pathological processes of schizophrenia, depression, migraines, and obesity. 5-HT interacts with 14 different receptors, of which 5-HT1A-1FRs, 5-HT2A-CRs, and 5-HT4-7Rs are G protein-coupled receptors (GPCRs), while 5-HT3R is a ligand-gated ion channel. Over the years, selective orthosteric ligands have been identified for almost all serotonin receptors, yielding several clinically relevant drugs. However, the high degree of homology between 5-HTRs and other GPCRs means that orthosteric ligands can have severe side effects. Thus, there has recently been increased interest in developing safer ligands of GPCRs, which bind to less conserved, more specific sites, distinct from that of the receptor's natural ligand. The present review describes the identification of allosteric ligands of serotonin receptors, which are largely natural compounds (oleamide, cannabidiol, THC, and aporphine alkaloids), complemented by synthetic modulators developed in large part for the 5-HT2C receptor. The latter are positive allosteric modulators sought after for their potential as drugs preferable over the orthosteric agonists as antiobesity agents for their potentially safer profile. When available, details on the interactions between the ligand and allosteric binding site will be provided. An outlook on future research in the field will also be provided.

Topoisomeric Membrane-Active Peptides: A Review of the Last Two Decades

In recent decades, bioactive peptides have been gaining recognition in various biomedical areas, such as intracellular drug delivery (cell-penetrating peptides, CPPs) or anti-infective action (antimicrobial peptides, AMPs), closely associated to their distinct mode of interaction with biological membranes. Exploiting the interaction of membrane-active peptides with diverse targets (healthy, tumoral, bacterial or parasitic cell membranes) is opening encouraging prospects for peptides in therapeutics. However, ordinary peptides formed by L-amino acids are easily decomposed by proteases in biological fluids. One way to sidestep this limitation is to use topoisomers, namely versions of the peptide made up of D-amino acids in either canonic (enantio) or inverted (retroenantio) sequence. Rearranging peptide sequences in this fashion provides a certain degree of native structure mimicry that, in appropriate contexts, may deliver desirable biological activity while avoiding protease degradation. In this review, we will focus on recent accounts of membrane-active topoisomeric peptides with therapeutic applications as CPP drug delivery vectors, or as antimicrobial and anticancer candidates. We will also discuss the most common modes of interaction of these peptides with their membrane targets.

Endocannabinoid System: Chemical Characteristics and Biological Activity

The endocannabinoid system (eCB) has been studied to identify the molecular structures present in Cannabis sativa. eCB consists of cannabinoid receptors, endogenous ligands, and the associated enzymatic apparatus responsible for maintaining energy homeostasis and cognitive processes. Several physiological effects of cannabinoids are exerted through interactions with various receptors, such as CB1 and CB2 receptors, vanilloid receptors, and the recently discovered G-protein-coupled receptors (GPR55, GPR3, GPR6, GPR12, and GPR19). Anandamide (AEA) and 2-arachidoylglycerol (2-AG), two small lipids derived from arachidonic acid, showed high-affinity binding to both CB1 and CB2 receptors. eCB plays a critical role in chronic pain and mood disorders and has been extensively studied because of its wide therapeutic potential and because it is a promising target for the development of new drugs. Phytocannabinoids and synthetic cannabinoids have shown varied affinities for eCB and are relevant to the treatment of several neurological diseases. This review provides a description of eCB components and discusses how phytocannabinoids and other exogenous compounds may regulate the eCB balance. Furthermore, we show the hypo- or hyperfunctionality of eCB in the body and how eCB is related to chronic pain and mood disorders, even with integrative and complementary health practices (ICHP) harmonizing the eCB.

The transmembrane domains of GPCR dimers as targets for drug development

G-protein-coupled receptors (GPCRs) can form homodimers or heterodimers that modulate specific signal transduction pathways to regulate a wide range of physiological and pathological functions. As such, GPCR dimers are novel drug targets for disorders including depression, hypertension, diabetes, and vascular dementia. The interaction between two receptors in a GPCR dimer involves a conformational change in the transmembrane domain (TMD). It has been demonstrated that the TMD has an important role in GPCR dimer formation and stability in vitro and in vivo. Moreover, increasing evidence shows that the TMD of GPCRs affects the function of dimers. Therefore, the TMD of GPCRs is an emerging target for the development of drugs to treat diseases that involve GPCR dimerization.

L-DOPA Receptor GPR143 Functionally Couples with Adrenergic α1B Receptor at the Second Transmembrane Interface

Adrenergic receptors (ADRs) are widely distributed in the peripheral and central nervous systems. We previously reported that L-3,4-dihydroxyphenylalanine (L-DOPA), the precursor of dopamine, sensitizes adrenergic α1 receptor (ADRA1) through a G protein-coupled receptor GPR143. Chimeric analysis, in which the transmembrane (TM) domains of GPR143 were replaced with those of GPR37, revealed that the second TM region was essential for the potentiation of phenylephrine-induced extracellular signal-regulated kinase (ERK) phosphorylation by GPR143. In HEK293T cells expressing ADRA1B, phenylephrine-induced ERK phosphorylation was augmented by the co-expression of GPR143, compared to the mock vector. Immunoprecipitation analysis revealed that a synthetic transactivator of the transcription peptide fused with TM2 of GPR143 (TAT-TM2) disrupts the interaction between GPR143 and ADRA1B. This TAT-TM2 peptide suppressed the augmentation of phenylephrine-induced ERK phosphorylation by GPR143 in HEK293T cells co-expressing ADRA1B and GPR143. These results indicate that the interaction between GPR143 and ADRA1B is required for the potentiation of ADRA1B-mediated signaling by GPR143. The TM2 region of GPR143 is a crucial dimeric interface for the functional coupling between ADRA1B and GPR143.

Examining Topoisomers of a Snake-Venom-Derived Peptide for Improved Antimicrobial and Antitumoral Properties

Ctn[15-34], the C-terminal section of crotalicidin (Ctn), a cathelicidin from a South American pit viper, is an antimicrobial and antitumoral peptide with remarkably longer stability in human serum than the parent Ctn. In this work, a set of topoisomers of both Ctn and Ctn[15-34], including the retro, enantio, and retroenantio versions, were synthesized and tested to investigate the structural requirements for activity. All topoisomers were as active as the cognate sequences against Gram-negative bacteria and tumor cells while slightly more toxic towards normal cells. More importantly, the enhanced serum stability of the D-amino-acid-containing versions suggests that such topoisomers must be preferentially considered as future antimicrobial and anticancer peptide leads.

Targeting Zika Virus with New Brain- and Placenta-Crossing Peptide–Porphyrin Conjugates

Viral disease outbreaks affect hundreds of millions of people worldwide and remain a serious threat to global health. The current SARS-CoV-2 pandemic and other recent geographically- confined viral outbreaks (severe acute respiratory syndrome (SARS), Ebola, dengue, zika and ever-recurring seasonal influenza), also with devastating tolls at sanitary and socio-economic levels, are sobering reminders in this respect. Among the respective pathogenic agents, Zika virus (ZIKV), transmitted by Aedes mosquito vectors and causing the eponymous fever, is particularly insidious in that infection during pregnancy results in complications such as foetal loss, preterm birth or irreversible brain abnormalities, including microcephaly. So far, there is no effective remedy for ZIKV infection, mainly due to the limited ability of antiviral drugs to cross blood–placental and/or blood–brain barriers (BPB and BBB, respectively). Despite its restricted permeability, the BBB is penetrable by a variety of molecules, mainly peptide-based, and named BBB peptide shuttles (BBBpS), able to ferry various payloads (e.g., drugs, antibodies, etc.) into the brain. Recently, we have described peptide–porphyrin conjugates (PPCs) as successful BBBpS-associated drug leads for HIV, an enveloped virus in which group ZIKV also belongs. Herein, we report on several brain-directed, low-toxicity PPCs capable of targeting ZIKV. One of the conjugates, PP-P1, crossing both BPB and BBB, has shown to be effective against ZIKV (IC₅₀ 1.08 µM) and has high serum stability (t_1/2 ca. 22 h) without altering cell viability at all tested concentrations. Peptide–porphyrin conjugation stands out as a promising strategy to fill the ZIKV treatment gap.

Disrupting GPCR Complexes with Smart Drug-like Peptides

G protein-coupled receptors (GPCRs) are a superfamily of proteins classically described as monomeric transmembrane (TM) receptors. However, increasing evidence indicates that many GPCRs form higher-order assemblies made up of monomers pertaining to identical (homo) or to various (hetero) receptors. The formation and structure of these oligomers, their physiological role and possible therapeutic applications raise a variety of issues that are currently being actively explored. In this context, synthetic peptides derived from TM domains stand out as powerful tools that can be predictably targeted to disrupt GPCR oligomers, especially at the interface level, eventually impairing their action. However, despite such potential, TM-derived, GPCR-disrupting peptides often suffer from inadequate pharmacokinetic properties, such as low bioavailability, a short half-life or rapid clearance, which put into question their therapeutic relevance and promise. In this review, we provide a comprehensive overview of GPCR complexes, with an emphasis on current studies using GPCR-disrupting peptides mimicking TM domains involved in multimerization, and we also highlight recent strategies used to achieve drug-like versions of such TM peptide candidates for therapeutic application.