Potent Heterocyclic Ligands for Human Complement C3a Receptor

Astrocyte-secreted C3 signaling impairs neuronal development and cognition in autoimmune diseases

Neuromyelitis optica (NMO) arises from primary astrocytopathy induced by autoantibodies targeting the astroglial protein aquaporin 4 (AQP4), leading to severe neurological sequelae such as vision loss, motor deficits, and cognitive decline. Mounting evidence has shown that dysregulated activation of complement components contributes to NMO pathogenesis. Complement C3 deficiency has been shown to protect against hippocampal neurodegeneration and cognitive decline in neurodegenerative disorders (e.g., Alzheimer's disease, AD) and autoimmune diseases (e.g., multiple sclerosis, MS). However, whether inhibiting the C3 signaling can ameliorate cognitive dysfunctions in NMO remains unclear. In this study, we found that the levels of C3a, a split product of C3, significantly correlate with cognitive impairment in our patient cohort. In response to the stimulation of AQP4 autoantibodies, astrocytes were activated to secrete complement C3, which inhibited the development of cultured neuronal dendritic arborization. NMO mouse models exhibited reduced adult hippocampal newborn neuronal dendritic and spine development, as well as impaired learning and memory functions, which could be rescued by decreasing C3 levels in astrocytes. Mechanistically, we found that C3a engaged with C3aR to impair neuronal development by dampening β-catenin signalling. Additionally, inhibition of the C3-C3aR-GSK3β/β-catenin cascade restored neuronal development and ameliorated cognitive impairments. Collectively, our results suggest a pivotal role of the activation of the C3-C3aR network in neuronal development and cognition through mediating astrocyte and adult-born neuron communication, which represents a potential therapeutic target for autoimmune-related cognitive impairment diseases.

Exploring naltrexamine derivatives featuring azaindole moiety via nitrogen-walk approach to investigate their in vitro pharmacological profiles at the mu opioid receptor

In the present work, we reported the application of a nitrogen-walk approach on developing a series of novel opioid ligands containing an azaindole moiety at the C6-position of the epoxymorphinan skeleton. In vitro study results showed that introducing a nitrogen atom around the indole moiety not only retained excellent binding affinity, but also led to significant functional switch at the mu opioid receptor (MOR). Further computational investigations provided corroborative evidence and plausible explanations of the results of the in vitro studies. Overall, our current work implemented a series of novel MOR ligands with high binding affinity and considerably low efficacy, which may shed light on rational design of low efficacy MOR ligands for opioid use disorder therapeutics.

Structural insights from an in silico molecular docking simulation of complement component 3a receptor 1 with an antagonist

Complement component 3a receptor 1 (C3aR) is an anaphylatoxin receptor that mediates inflammatory processes. Although considerable effort has gone into discovering the antagonists and agonists of C3aR, structural insights are required to search for effective ligands and to elucidate their binding modes and the mechanism of activation and inactivation. No experimental structural data of C3aR have yet been reported. We investigated the binding mode of an antagonist of C3aR using a combination of homology modeling, ligand docking, molecular dynamics simulations, and binding free energy calculations. We produced a plausible binding model consistent with the reported experimental data. We believe that this model is appropriate for the identification of new C3aR antagonists, as it can distinguish between antagonists and decoy compounds.

Exploiting the role of stereoelectronic effects to design the antagonists of the human complement C3a receptor

Stereoelectronic effects are crucial in governing the conformational behaviour of small molecules bearing heterocyclic rings adjacent to amides.

Potent Thiophene Antagonists of Human Complement C3a Receptor with Anti-Inflammatory Activity

Structure-activity relationships for a series of small-molecule thiophenes resulted in potent and selective antagonism of human Complement C3a receptor. The compounds are about 100-fold more potent than the most reported antagonist SB290157. A new compound JR14a was among the most potent of the new antagonists in vitro, assessed by (a) inhibition of intracellular calcium release (IC₅₀ 10 nM) induced in human monocyte-derived macrophages by 100 nM C3a, (b) inhibition of β-hexosaminidase secretion (IC₅₀ 8 nM) from human LAD2 mast cells degranulated by 100 nM C3a, and (c) selectivity for human C3aR over C5aR. JR14a was metabolically stable in rat plasma and in rat liver microsomes and efficacious in rats when given orally to suppress rat paw inflammation, macrophage and mast cell activation, and histopathology induced by intraplantar paw administration of a C3aR agonist. Potent C3aR antagonists are now available for interrogating C3a receptor activation and suppressing C3aR-mediated inflammation in mammalian physiology and disease.

Exploiting a novel conformational switch to control innate immunity mediated by complement protein C3a

Complement C3a is an important protein in innate and adaptive immunity, but its specific roles in vivo remain uncertain because C3a degrades rapidly to form the C3a-desArg protein, which does not bind to the C3a receptor and is indistinguishable from C3a using antibodies. Here we develop the most potent, stable and highly selective small molecule modulators of C3a receptor, using a heterocyclic hinge to switch between agonist and antagonist ligand conformations. This enables characterization of C3 areceptor-selective pro- vs. anti-inflammatory actions in human mast cells and macrophages, and in rats. A C3a receptor-selective agonist induces acute rat paw inflammation by first degranulating mast cells before activating macrophages and neutrophils. An orally administered C3a receptor-selective antagonist inhibits mast cell degranulation, thereby blocking recruitment and activation of macrophages and neutrophils, expression of inflammatory mediators and inflammation in a rat paw edema model. These novel tools reveal the mechanism of C3a-induced inflammation and provide new insights to complement-based medicines.

Complement C3a is an important protein in innate and adaptive immunity, but its roles in vivo are unclear. Here the authors develop novel chemical agonists and antagonists for the C3a receptor, and show that they modulate mast cell degranulation and inflammation in a rat paw edema model

New concepts on the therapeutic control of complement anaphylatoxin receptors

The complement system is a pivotal driver of innate immunity, coordinating the host response to protect against pathogens. At the heart of the complement response lie the active fragments, C3a and C5a, acting through their specific receptors, C3aR, C5aR1, and C5aR2, to direct the cellular response to inflammation. Their potent function however, places them at risk of damaging the host, with aberrant C3a and C5a signaling activity linked to a wide range of disorders of inflammatory, autoimmune, and neurodegenerative etiologies. As such, the therapeutic control of these receptors represents an attractive drug target, though, the realization of this clinical potential remains limited. With the success of eculizumab, and the progression of a number of novel C5a-C5aR1 targeted drugs to phase II and III clinical trials, there is great promise for complement therapeutics in future clinical practice. In contrast, the toolbox of drugs available to modulate C3aR and C5aR2 signaling remains limited, however, the emergence of new selective ligands and molecular tools, and an increased understanding of the function of these receptors in disease, has highlighted their unique potential for clinical applications. This review provides an update on the growing arsenal of drugs now available to target C5, and C5a and C3a receptor signaling, and discusses their utility in both clinical and pre-clinical development.

The Necessary Nitrogen Atom: A Versatile High-Impact Design Element for Multiparameter Optimization

There is a continued desire in biomedical research to reduce the number and duration of design cycles required to optimize lead compounds into high-quality chemical probes or safe and efficacious drug candidates. The insightful application of impactful molecular design elements is one approach toward achieving this goal. The replacement of a CH group with a N atom in aromatic and heteroaromatic ring systems can have many important effects on molecular and physicochemical properties and intra- and intermolecular interactions that can translate to improved pharmacological profiles. In this Perspective, the "necessary nitrogen atom" is shown to be a versatile high-impact design element for multiparameter optimization, wherein ≥10-, 100-, or 1000-fold improvement in a variety of key pharmacological parameters can be realized.

Proteinases, Their Extracellular Targets, and Inflammatory Signaling

Given that over 2% of the human genome codes for proteolytic enzymes and their inhibitors, it is not surprising that proteinases serve many physiologic-pathophysiological roles. In this context, we provide an overview of proteolytic mechanisms regulating inflammation, with a focus on cell signaling stimulated by the generation of inflammatory peptides; activation of the proteinase-activated receptor (PAR) family of G protein-coupled receptors (GPCR), with a mechanism in common with adhesion-triggered GPCRs (ADGRs); and by proteolytic ion channel regulation. These mechanisms are considered in the much wider context that proteolytic mechanisms serve, including the processing of growth factors and their receptors, the regulation of matrix-integrin signaling, and the generation and release of membrane-tethered receptor ligands. These signaling mechanisms are relevant for inflammatory, neurodegenerative, and cardiovascular diseases as well as for cancer. We propose that the inflammation-triggering proteinases and their proteolytically generated substrates represent attractive therapeutic targets and we discuss appropriate targeting strategies.

Tactical Approaches to Interconverting GPCR Agonists and Antagonists

There are many reported examples of small structural modifications to GPCR-targeted ligands leading to major changes in their functional activity, converting agonists into antagonists or vice versa. These shifts in functional activity are often accompanied by negligible changes in binding affinity. The current perspective focuses on outlining and analyzing various approaches that have been used to interconvert GPCR agonists, partial agonists, and antagonists in order to achieve the intended functional activity at a GPCR of therapeutic interest. An improved understanding of specific structural modifications that are likely to alter the functional activity of a GPCR ligand may be of use to researchers designing GPCR-targeted drugs and/or probe compounds, specifically in cases where a particular ligand exhibits good potency but not the preferred functional activity at the GPCR of choice.