o-Vanillin binds covalently to MAL/TIRAP Lys-210 but independently inhibits TLR2.

Toll-like receptor (TLR) innate immunity signalling protects against pathogens, but excessive or prolonged signalling contributes to a range of inflammatory conditions. Structural information on the TLR cytoplasmic TIR (Toll/interleukin-1 receptor) domains and the downstream adaptor proteins can help us develop inhibitors targeting this pathway. The small molecule o-vanillin has previously been reported as an inhibitor of TLR2 signalling. To study its mechanism of action, we tested its binding to the TIR domain of the TLR adaptor MAL/TIRAP (MALTIR). We show that o-vanillin binds to MALTIR and inhibits its higher-order assembly in vitro. Using NMR approaches, we show that o-vanillin forms a covalent bond with lysine 210 of MAL. We confirm in mouse and human cells that o-vanillin inhibits TLR2 but not TLR4 signalling, independently of MAL, suggesting it may covalently modify TLR2 signalling complexes directly. Reactive aldehyde-containing small molecules such as o-vanillin may target multiple proteins in the cell.

MCC950 reduces autophagy and improves cognitive function by inhibiting NLRP3-dependent neuroinflammation in a rat model of Alzheimer's disease.

Alzheimer's disease (AD) is the seventh most common cause of mortality and one of the major causes of disability and vulnerability in the elderly. AD is characterized by gradual cognitive deterioration, the buildup of misfolded amyloid beta (Aß) peptide, and the generation of neurofibrillary tangles. Despite enormous scientific progress, there is no effective cure for AD. Thus, exploring new treatment options to stop AD or at least slow down its progress is important. In this study, we investigated the potential therapeutic effects of MCC950 on NLRP3-mediated inflammasome-driven inflammation and autophagy in AD. Rats treated with streptozotocin (STZ) exhibited simultaneous activation of the NLRP3 inflammasome and autophagy, as confirmed by Western blot, immunofluorescence, and co-immunoprecipitation analyses. MCC950, a specific NLRP3 inhibitor, was intraperitoneally administered (50 mg/kg body weight) to rats with AD-like symptoms induced by intracerebroventricular STZ injections (3 mg/kg body weight). MCC950 effectively suppressed STZ-induced cognitive impairment and anxiety by inhibiting NLRP3-dependent neuroinflammation. Moreover, our findings indicate that MCC950 exerts neuroprotective effects by attenuating autophagy in neuronal cells. The inhibiting effects of MCC950 on inflammasome activation and autophagy were reproduced in vitro, provding further mechansistic insights into MCC950 therapeutic action. Our findings suggest that MCC950 impedes the progression of AD and may also improve cognitive function through the mitigation of autophagy and NLRP3 inflammasome inhibition.

Are Manufacturing Patents to Blame for Biosimilar Market Launch Delays?

OBJECTIVES: Biosimilar market launch delays are likely costing healthcare systems billions of dollars and preventing patients accessing affordable biologic therapies sooner. Many claim these delays are mostly caused by originator biologics' large patent portfolios asserted during litigation against biosimilar developers, particularly that the manufacturing patents filed after the originator is approved is an important driver of these delays. Our objective was to investigate the accuracy of these claims. METHODS: We reviewed US Court document submissions for litigation data, including the details of patents asserted against biosimilar owners, and collated biosimilar market launch dates from publicly available databases. RESULTS: We find that, although approximately half of all patents asserted in litigation were manufacturing patents, a greater proportion of composition, active pharmaceutical ingredient, and treatment patents are associated with longer market launch delays, whereas a greater proportion of manufacturing patents are associated with shorter market launch delays. CONCLUSIONS: Our results suggest that manufacturing patents were having less of an impact on market launch delays than other types of patents. Our findings have implications for both biosimilar and originator developers, as well as patent policy and its association with healthcare accessibility.

Characterization and inhibition of inflammasome responses in severe and non-severe asthma.

BACKGROUND: Increased airway NLRP3 inflammasome-mediated IL-1ß responses may underpin severe neutrophilic asthma. However, whether increased inflammasome activation is unique to severe asthma, is a common feature of immune cells in all inflammatory types of severe asthma, and whether inflammasome activation can be therapeutically targeted in patients, remains unknown. OBJECTIVE: To investigate the activation and inhibition of inflammasome-mediated IL-1ß responses in immune cells from patients with asthma. METHODS: Peripheral blood mononuclear cells (PBMCs) were isolated from patients with non-severe (n = 59) and severe (n = 36 stable, n = 17 exacerbating) asthma and healthy subjects (n = 39). PBMCs were stimulated with nigericin or lipopolysaccharide (LPS) alone, or in combination (LPS + nigericin), with or without the NLRP3 inhibitor MCC950, and the effects on IL-1ß release were assessed. RESULTS: PBMCs from patients with non-severe or severe asthma produced more IL-1ß in response to nigericin than those from healthy subjects. PBMCs from patients with severe asthma released more IL-1ß in response to LPS + nigericin than those from non-severe asthma. Inflammasome-induced IL-1ß release from PBMCs from patients with severe asthma was not increased during exacerbation compared to when stable. Inflammasome-induced IL-1ß release was not different between male and female, or obese and non-obese patients and correlated with eosinophil and neutrophil numbers in the airways. MCC950 effectively suppressed LPS-, nigericin-, and LPS + nigericin-induced IL-1ß release from PBMCs from all groups. CONCLUSION: An increased ability for inflammasome priming and/or activation is a common feature of systemic immune cells in both severe and non-severe asthma, highlighting inflammasome inhibition as a universal therapy for different subtypes of disease.

Response to Comment on "Inflammasome inhibition prevents α-synuclein pathology and dopaminergic neurodegeneration in mice".

We have replicated our original finding of elevated cleaved caspase-1 in mouse brains and neuroprotection by an NLRP3 inflammasome inhibitor in two mouse models of Parkinson's disease.

NLRP3 Inflammasome-Targeting Nanomicelles for Preventing Ischemia-Reperfusion-Induced Inflammatory Injury.

Ischemia-reperfusion (I/R) injury is a disease process that affects several vital organs. There is widespread agreement that the NLRP3 inflammasome pathway plays a crucial role in the development of I/R injury. We have developed transferrin-conjugated, pH-responsive nanomicelles for the entrapment of MCC950 drug. These nanomicelles specifically bind to the transferrin receptor 1 (TFR1) expressed on the cells of the blood-brain barrier (BBB) and thus help the cargo to cross the BBB. Furthermore, the therapeutic potential of nanomicelles was assessed using in vitro, in ovo, and in vivo models of I/R injury. Nanomicelles were injected into the common carotid artery (CCA) of a middle cerebral artery occlusion (MCAO) rat model to achieve maximum accretion of nanomicelles into the brain as blood flows toward the brain in the CCA. The current study reveals that the treatment with nanomicelles significantly alleviates the levels of NLRP3 inflammasome biomarkers which were found to be increased in oxygen-glucose deprivation (OGD)-treated SH-SY5Y cells, the I/R-damaged right vitelline artery (RVA) of chick embryos, and the MCAO rat model. The supplementation with nanomicelles significantly enhanced the overall survival of MCAO rats. Overall, nanomicelles exerted therapeutic effects against I/R injury, which might be due to the suppression of the activation of the NLRP3 inflammasome.

Clostridium perfringens virulence factors are nonredundant activators of the NLRP3 inflammasome.

Inflammasome signaling is a central pillar of innate immunity triggering inflammation and cell death in response to microbes and danger signals. Here, we show that two virulence factors from the human bacterial pathogen Clostridium perfringens are nonredundant activators of the NLRP3 inflammasome in mice and humans. C. perfringens lecithinase (also known as phospolipase C) and C. perfringens perfringolysin O induce distinct mechanisms of activation. Lecithinase enters LAMP1+ vesicular structures and induces lysosomal membrane destabilization. Furthermore, lecithinase induces the release of the inflammasome-dependent cytokines IL-1ß and IL-18, and the induction of cell death independently of the pore-forming proteins gasdermin D, MLKL and the cell death effector protein ninjurin-1 or NINJ1. We also show that lecithinase triggers inflammation via the NLRP3 inflammasome in vivo and that pharmacological blockade of NLRP3 using MCC950 partially prevents lecithinase-induced lethality. Together, these findings reveal that lecithinase activates an alternative pathway to induce inflammation during C. perfringens infection and that this mode of action can be similarly exploited for sensing by a single inflammasome.

MCC950 Regulates Stem Cells Destiny Through Modulating SIRT3-NLRP3 Inflammasome Dynamics During Oxygen Glucose Deprivation.

Ischemic stroke is the major cause of death and morbidity worldwide. Stem cell treatment is at the forefront of ischemic therapeutic interventions. However, the fate of these cells following transplantation is mostly unknown. The current study examines the influence of oxidative and inflammatory pathological events associated with experimental ischemic stroke (oxygen glucose deprivation (OGD)) on the stem cell population (human Dental Pulp Stem Cells, and human Mesenchymal Stem Cells) through the involvement of the NLRP3 inflammasome. We explored the destiny of the above-mentioned stem cells in the stressed micro (-environment) and the ability of MCC950 to reverse the magnitudes. An enhanced expression of NLRP3, ASC, cleaved caspase1, active IL-1ß and active IL-18 in OGD-treated DPSC and MSC was observed. The MCC950 significantly reduced NLRP3 inflammasome activation in the aforementioned cells. Further, in OGD groups, oxidative stress markers were shown to be alleviated in the stem cells under stress, which was effectively relieved by MCC950 supplementation. Interestingly, whereas OGD increased NLRP3 expression, it decreased SIRT3 levels, implying that these two processes are intertwined. In brief, we discovered that MCC950 inhibits NLRP3-mediated inflammation by inhibiting the NLRP3 inflammasome and increasing SIRT3. To conclude, according to our findings, inhibiting NLRP3 activation while enhancing SIRT3 levels with MCC950 reduces oxidative and inflammatory stress in stem cells under OGD-induced stress. These findings shed light on the causes of hDPSC and hMSC demise following transplantation and point to strategies to lessen therapeutic cell loss under ischemic-reperfusion stress.

Immunity against Moraxella catarrhalis requires guanylate-binding proteins and caspase-11-NLRP3 inflammasomes.

Moraxella catarrhalis is an important human respiratory pathogen and a major causative agent of otitis media and chronic obstructive pulmonary disease. Toll-like receptors contribute to, but cannot fully account for, the complexity of the immune response seen in M. catarrhalis infection. Using primary mouse bone marrow-derived macrophages to examine the host response to M. catarrhalis infection, our global transcriptomic and targeted cytokine analyses revealed activation of immune signalling pathways by both membrane-bound and cytosolic pattern-recognition receptors. We show that M. catarrhalis and its outer membrane vesicles or lipooligosaccharide (LOS) can activate the cytosolic innate immune sensor caspase-4/11, gasdermin-D-dependent pyroptosis, and the NLRP3 inflammasome in human and mouse macrophages. This pathway is initiated by type I interferon signalling and guanylate-binding proteins (GBPs). We also show that inflammasomes and GBPs, particularly GBP2, are required for the host defence against M. catarrhalis in mice. Overall, our results reveal an essential role for the interferon-inflammasome axis in cytosolic recognition and immunity against M. catarrhalis, providing new molecular targets that may be used to mitigate pathological inflammation triggered by this pathogen.

Increased core body temperature exacerbates defective protein prenylation in mouse models of mevalonate kinase deficiency.

Mevalonate kinase deficiency (MKD) is characterized by recurrent fevers and flares of systemic inflammation, caused by biallelic loss-of-function mutations in MVK. The underlying disease mechanisms and triggers of inflammatory flares are poorly understood because of the lack of in vivo models. We describe genetically modified mice bearing the hypomorphic mutation p.Val377Ile (the commonest variant in patients with MKD) and amorphic, frameshift mutations in Mvk. Compound heterozygous mice recapitulated the characteristic biochemical phenotype of MKD, with increased plasma mevalonic acid and clear buildup of unprenylated GTPases in PBMCs, splenocytes, and bone marrow. The inflammatory response to LPS was enhanced in compound heterozygous mice and treatment with the NLRP3 inflammasome inhibitor MCC950 prevented the elevation of circulating IL-1ß, thus identifying a potential inflammasome target for future therapeutic approaches. Furthermore, lines of mice with a range of deficiencies in mevalonate kinase and abnormal prenylation mirrored the genotype-phenotype relationship in human MKD. Importantly, these mice allowed the determination of a threshold level of residual enzyme activity, below which protein prenylation is impaired. Elevated temperature dramatically but reversibly exacerbated the deficit in the mevalonate pathway and the defective prenylation in vitro and in vivo, highlighting increased body temperature as a likely trigger of inflammatory flares.

AICAR transformylase/IMP cyclohydrolase (ATIC) is essential for de novo purine biosynthesis and infection by Cryptococcus neoformans.

The fungal pathogen Cryptococcus neoformans is a leading cause of meningoencephalitis in the immunocompromised. As current antifungal treatments are toxic to the host, costly, limited in their efficacy, and associated with drug resistance, there is an urgent need to identify vulnerabilities in fungal physiology to accelerate antifungal discovery efforts. Rational drug design was pioneered in de novo purine biosynthesis as the end products of the pathway, ATP and GTP, are essential for replication, transcription, and energy metabolism, and the same rationale applies when considering the pathway as an antifungal target. Here, we describe the identification and characterization of C. neoformans 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) transformylase/5'-inosine monophosphate cyclohydrolase (ATIC), a bifunctional enzyme that catalyzes the final two enzymatic steps in the formation of the first purine base inosine monophosphate. We demonstrate that mutants lacking the ATIC-encoding ADE16 gene are adenine and histidine auxotrophs that are unable to establish an infection in a murine model of virulence. In addition, our assays employing recombinantly expressed and purified C. neoformans ATIC enzyme revealed Km values for its substrates AICAR and 5-formyl-AICAR are 8-fold and 20-fold higher, respectively, than in the human ortholog. Subsequently, we performed crystallographic studies that enabled the determination of the first fungal ATIC protein structure, revealing a key serine-to-tyrosine substitution in the active site, which has the potential to assist the design of fungus-specific inhibitors. Overall, our results validate ATIC as a promising antifungal drug target.

Clostridium septicum α-toxin activates the NLRP3 inflammasome by engaging GPI-anchored proteins.

Clostridium species are a group of Gram-positive bacteria that cause diseases in humans, such as food poisoning, botulism, and tetanus. Here, we analyzed 10 different Clostridium species and identified that Clostridium septicum, a pathogen that causes sepsis and gas gangrene, activates the mammalian cytosolic inflammasome complex in mice and humans. Mechanistically, we demonstrate that α-toxin secreted by C. septicum binds to glycosylphosphatidylinositol (GPI)-anchored proteins on the host plasma membrane, oligomerizing and forming a membrane pore that is permissive to efflux of magnesium and potassium ions. Efflux of these cytosolic ions triggers the activation of the innate immune sensor NLRP3, inducing activation of caspase-1 and gasdermin D, secretion of the proinflammatory cytokines interleukin-1ß and interleukin-18, pyroptosis, and plasma membrane rupture via ninjurin-1. Furthermore, α-toxin of C. septicum induces rapid inflammasome-mediated lethality in mice and pharmacological inhibition of the NLRP3 inflammasome using MCC950 prevents C. septicum-induced lethality. Overall, our results reveal that cytosolic innate sensing of α-toxin is central to the recognition of C. septicum infection and that therapeutic blockade of the inflammasome pathway may prevent sepsis and death caused by toxin-producing pathogens.

Prevention of the foreign body response to implantable medical devices by inflammasome inhibition.

SignificanceImplantable electronic medical devices (IEMDs) are used for some clinical applications, representing an exciting prospect for the transformative treatment of intractable conditions such Parkinson's disease, deafness, and paralysis. The use of IEMDs is limited at the moment because, over time, a foreign body reaction (FBR) develops at the device-neural interface such that ultimately the IEMD fails and needs to be removed. Here, we show that macrophage nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome activity drives the FBR in a nerve injury model yet integration of an NLRP3 inhibitor into the device prevents FBR while allowing full healing of damaged neural tissue to occur.

Aim2 suppresses cigarette smoke-induced neutrophil recruitment, neutrophil caspase-1 activation and anti-Ly6G-mediated neutrophil depletion.

Increased inflammasome responses are strongly implicated in inflammatory diseases; however, their specific roles are incompletely understood. Therefore, we sought to examine the roles of nucleotide-binding oligomerization domain-like receptor (NLR) family, pyrin domain-containing 3 (NLRP3) and absent in melanoma-2 (AIM2) inflammasomes in cigarette smoke-induced inflammation in a model of experimental chronic obstructive pulmonary disease (COPD). We targeted NLRP3 with the inhibitor MCC950 given prophylactically or therapeutically and examined Aim2-/- mice in cigarette smoke-induced experimental COPD. MCC950 treatment had minimal effects on disease development and/or progression. Aim2-/- mice had increased airway neutrophils with decreased caspase-1 levels, independent of changes in lung neutrophil chemokines. Suppressing neutrophils with anti-Ly6G in experimental COPD in wild-type mice reduced neutrophils in bone marrow, blood and lung. By contrast, anti-Ly6G treatment in Aim2-/- mice with experimental COPD had no effect on neutrophils in bone marrow, partially reduced neutrophils in the blood and had no effect on neutrophils or neutrophil caspase-1 levels in the lungs. These findings identify that following cigarette smoke exposure, Aim2 is important for anti-Ly6G-mediated depletion of neutrophils, suppression of neutrophil recruitment and mediates activation of caspase-1 in neutrophils.

Relationship between type 2 cytokine and inflammasome responses in obesity-associated asthma.

BACKGROUND: Obesity is a risk factor for asthma, and obese asthmatic individuals are more likely to have severe, steroid-insensitive disease. How obesity affects the pathogenesis and severity of asthma is poorly understood. Roles for increased inflammasome-mediated neutrophilic responses, type 2 immunity, and eosinophilic inflammation have been described. OBJECTIVE: We investigated how obesity affects the pathogenesis and severity of asthma and identified effective therapies for obesity-associated disease. METHODS: We assessed associations between body mass index and inflammasome responses with type 2 (T2) immune responses in the sputum of 25 subjects with asthma. Functional roles for NLR family, pyrin domain-containing (NLRP) 3 inflammasome and T2 cytokine responses in driving key features of disease were examined in experimental high-fat diet-induced obesity and asthma. RESULTS: Body mass index and inflammasome responses positively correlated with increased IL-5 and IL-13 expression as well as C-C chemokine receptor type 3 expression in the sputum of subjects with asthma. High-fat diet-induced obesity resulted in steroid-insensitive airway hyperresponsiveness in both the presence and absence of experimental asthma. High-fat diet-induced obesity was also associated with increased NLRP3 inflammasome responses and eosinophilic inflammation in airway tissue, but not lumen, in experimental asthma. Inhibition of NLRP3 inflammasome responses reduced steroid-insensitive airway hyperresponsiveness but had no effect on IL-5 or IL-13 responses in experimental asthma. Depletion of IL-5 and IL-13 reduced obesity-induced NLRP3 inflammasome responses and steroid-insensitive airway hyperresponsiveness in experimental asthma. CONCLUSION: We found a relationship between T2 cytokine and NLRP3 inflammasome responses in obesity-associated asthma, highlighting the potential utility of T2 cytokine-targeted biologics and inflammasome inhibitors.

Interleukin-1ß suppression dampens inflammatory leucocyte production and uptake in atherosclerosis.

AIMS: Targeting vascular inflammation represents a novel therapeutic approach to reduce complications of atherosclerosis. Neutralizing the pro-inflammatory cytokine interleukin-1ß (IL-1ß) using canakinumab, a monoclonal antibody, reduces the incidence of cardiovascular events in patients after myocardial infarction (MI). The biological basis for these beneficial effects remains incompletely understood. We sought to explore the mechanisms of IL-1ß-targeted therapies. METHODS AND RESULTS: In mice with early atherosclerosis (ApoE-/- mice on a high-cholesterol diet for 6 weeks), we found that 3 weeks of NACHT, LRR, and PYD domains-containing protein 3 (NLRP3)-inflammasome inhibition or anti-IL-1ß treatment (using either MCC950, an NLRP3-inflammasome inhibitor which blocks production and release of active IL-1ß, or a murine analogue of canakinumab) dampened accumulation of leucocytes in atherosclerotic aortas, which consequently resulted in slower progression of atherosclerosis. Causally, we found that endothelial cells from atherosclerotic aortas lowered expression of leucocyte chemoattractants and adhesion molecules upon NLRP3-inflammasome inhibition, indicating that NLRP3-inflammasome- and IL-1ß-targeted therapies reduced blood leucocyte recruitment to atherosclerotic aortas. In accord, adoptive transfer experiments revealed that anti-IL-1ß treatment mitigated blood myeloid cell uptake to atherosclerotic aortas. We further report that anti-IL-1ß treatment and NLRP3-inflammasome inhibition reduced inflammatory leucocyte supply by decreasing proliferation of bone marrow haematopoietic stem and progenitor cells, demonstrating that suppression of IL-1ß and the NLRP3-inflammasome lowered production of disease-propagating leucocytes. Using bone marrow reconstitution experiments, we observed that haematopoietic cell-specific NLRP3-inflammasome activity contributed to both enhanced recruitment and increased supply of blood inflammatory leucocytes. Further experiments that queried whether anti-IL-1ß treatment reduced vascular inflammation also in post-MI accelerated atherosclerosis documented the operation of convergent mechanisms (reduced supply and uptake of inflammatory leucocytes). In line with our pre-clinical findings, post-MI patients on canakinumab treatment showed reduced blood monocyte numbers. CONCLUSIONS: Our murine and human data reveal that anti-IL-1ß treatment and NLRP3-inflammasome inhibition dampened vascular inflammation and progression of atherosclerosis through reduced blood inflammatory leucocyte (i) supply and (ii) uptake into atherosclerotic aortas providing additional mechanistic insights into links between haematopoiesis and atherogenesis, and into the beneficial effects of NLRP3-inflammasome- and IL-1ß-targeted therapies.

NLRP3 inflammasome inhibition with MCC950 improves insulin sensitivity and inflammation in a mouse model of frontotemporal dementia.

The NOD-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome has been implicated as a crucial component in both neurodegeneration and diabetes. However, the role of metabolic signalling pathways and the NLRP3 inflammasome in frontotemporal dementia remain largely elusive. We therefore investigated the effects of an NLRP3 inhibitor (MCC950) in a murine tau knock-in (PLB2TAU) model vs. wild-type (PLBWT) control mice. In male PLB2TAU mice (4 months at start of study), MCC950 treatment (20 mg/kg, for 12 weeks) improved insulin sensitivity and reduced circulating plasma insulin levels. Further molecular analysis suggested normalisation in insulin signalling pathways in both liver and muscle tissue. Treatment also resulted in improvements in inflammation and ER stress signalling, both peripherally and centrally, alongside a partial normalisation of phospho-tau levels. Overall, we provide evidence that MCC950 improved metabolic, inflammatory and frontotemporal dementia (FTD) relevant phenotypes in multiple tissues. NLRP3 inhibition may therefore offer a therapeutic approach to ameliorate FTD pathology.

Metabolic competition between host and pathogen dictates inflammasome responses to fungal infection.

The NLRP3 inflammasome has emerged as a central immune regulator that senses virulence factors expressed by microbial pathogens for triggering inflammation. Inflammation can be harmful and therefore this response must be tightly controlled. The mechanisms by which immune cells, such as macrophages, discriminate benign from pathogenic microbes to control the NLRP3 inflammasome remain poorly defined. Here we used live cell imaging coupled with a compendium of diverse clinical isolates to define how macrophages respond and activate NLRP3 when faced with the human yeast commensal and pathogen Candida albicans. We show that metabolic competition by C. albicans, rather than virulence traits such as hyphal formation, activates NLRP3 in macrophages. Inflammasome activation is triggered by glucose starvation in macrophages, which occurs when fungal load increases sufficiently to outcompete macrophages for glucose. Consistently, reducing Candida's ability to compete for glucose and increasing glucose availability for macrophages tames inflammatory responses. We define the mechanistic requirements for glucose starvation-dependent inflammasome activation by Candida and show that it leads to inflammatory cytokine production, but it does not trigger pyroptotic macrophage death. Pyroptosis occurs only with some Candida isolates and only under specific experimental conditions, whereas inflammasome activation by glucose starvation is broadly relevant. In conclusion, macrophages use their metabolic status, specifically glucose metabolism, to sense fungal metabolic activity and activate NLRP3 when microbial load increases. Therefore, a major consequence of Candida-induced glucose starvation in macrophages is activation of inflammatory responses, with implications for understanding how metabolism modulates inflammation in fungal infections.

Pharmacological characterisation of small molecule C5aR1 inhibitors in human cells reveals biased activities for signalling and function.

The complement fragment C5a is a core effector of complement activation. C5a, acting through its major receptor C5aR1, exerts powerful pro-inflammatory and immunomodulatory functions. Dysregulation of the C5a-C5aR1 axis has been implicated in numerous immune disorders, and the therapeutic inhibition of this axis is therefore imperative for the treatment of these diseases. A myriad of small-molecule C5aR1 inhibitors have been developed and independently characterised over the past two decades, however the pharmacological properties of these compounds has been difficult to directly compare due to the wide discrepancies in the model, read-out, ligand dose and instrumentation implemented across individual studies. Here, we performed a systematic characterisation of the most commonly reported and clinically advanced small-molecule C5aR1 inhibitors (peptidic: PMX53, PMX205 and JPE1375; non-peptide: W545011, NDT9513727, DF2593A and CCX168). Through signalling assays measuring C5aR1-mediated cAMP and ERK1/2 signalling, and ß-arrestin 2 recruitment, this study highlighted the signalling-pathway dependence of the rank order of potencies of the C5aR1 inhibitors. Functional experiments performed in primary human macrophages demonstrated the high insurmountable antagonistic potencies for the peptidic inhibitors as compared to the non-peptide compounds. Finally, wash-out studies provided novel insights into the duration of inhibition of the C5aR1 inhibitors, and confirmed the long-lasting antagonistic properties of PMX53 and CCX168. Overall, this study revealed the potent and prolonged antagonistic activities of selected peptidic C5aR1 inhibitors and the unique pharmacological profile of CCX168, which thus represent ideal candidates to fulfil diverse C5aR1 research and clinical therapeutic needs.