Identification of small-molecule elastase inhibitors as antagonists of IL-36 cytokine activation

The role of interleukin-36 in health and disease states

The interleukin (IL)-1 superfamily upregulates immune responses and maintains homeostasis between the innate and adaptive immune systems. Within the IL-1 superfamily, IL-36 plays a pivotal role in both innate and adaptive immune responses. Of the four IL-36 isoforms, three have agonist activity (IL-36α, IL-36β, IL-36γ) and the fourth has antagonist activity (IL-36 receptor antagonist [IL-36Ra]). All IL-36 isoforms bind to the IL-36 receptor (IL-36R). Binding of IL-36α/β/γ to the IL-36R recruits the IL-1 receptor accessory protein (IL-1RAcP) and activates downstream signalling pathways mediated by nuclear transcription factor kappa B and mitogen-activated protein kinase signalling pathways. Antagonist binding of IL-36Ra to IL-36R inhibits recruitment of IL-1RAcP, blocking downstream signalling pathways. Changes in the balance within the IL-36 cytokine family can lead to uncontrolled inflammatory responses throughout the body. As such, IL-36 has been implicated in numerous inflammatory diseases, notably a type of pustular psoriasis called generalized pustular psoriasis (GPP), a chronic, rare, potentially life-threatening, multisystemic skin disease characterised by recurrent fever and extensive sterile pustules. In GPP, IL-36 is central to disease pathogenesis, and the prevention of IL-36-mediated signalling can improve clinical outcomes. In this review, we summarize the literature describing the biological functions of the IL-36 pathway. We also consider the evidence for uncontrolled activation of the IL-36 pathway in a wide range of skin (e.g., plaque psoriasis, pustular psoriasis, hidradenitis suppurativa, acne, Netherton syndrome, atopic dermatitis and pyoderma gangrenosum), lung (e.g., idiopathic pulmonary fibrosis), gut (e.g., intestinal fibrosis, inflammatory bowel disease and Hirschsprung's disease), kidney (e.g., renal tubulointerstitial lesions) and infectious diseases caused by a variety of pathogens (e.g., COVID-19; Mycobacterium tuberculosis, Pseudomonas aeruginosa, Streptococcus pneumoniae infections), as well as in cancer. We also consider how targeting the IL-36 signalling pathway could be used in treating inflammatory disease states.

IL-36 Cytokines: Their Roles in Asthma and Potential as a Therapeutic

Interleukin (IL)-36 cytokines are members of the IL-1 superfamily, which consists of three agonists (IL-36α, IL-36β and IL-36γ) and an IL-36 receptor antagonist (IL-36Ra). IL-36 cytokines are crucial for immune and inflammatory responses. Abnormal levels of IL-36 cytokine expression are involved in the pathogenesis of inflammation, autoimmunity, allergy and cancer. The present study provides a summary of recent reports on IL-36 cytokines that participate in the pathogenesis of inflammatory diseases, and the potential mechanisms underlying their roles in asthma. Abnormal levels of IL-36 cytokines are associated with the pathogenesis of different types of asthma through the regulation of the functions of different types of cells. Considering the important role of IL-36 cytokines in asthma, these may become a potential therapeutic target for asthma treatment. However, existing evidence is insufficient to fully elucidate the specific mechanism underlying the action of IL-36 cytokines during the pathological process of asthma. The possible mechanisms and functions of IL-36 cytokines in different types of asthma require further studies.

Small molecule approaches to treat autoimmune and inflammatory diseases (Part III): Targeting cytokines and cytokine receptor complexes

Chronic and dysregulated cytokine signaling plays an important role in the pathogenic development of many autoimmune and inflammatory diseases. Despite intrinsic challenges in the disruption of interactions between cytokines and cytokine receptors, many first-in-class small-molecule inhibitors have been discovered over the past few years. The third part of the digest series presents recent progress in identifying such inhibitors and highlights the application of novel research tools in the fields of structural biology, computational analysis, screening methods, biophysical/biochemical assays and medicinal chemistry strategy.

Augmentation therapy with alpha 1-antitrypsin: present and future of production, formulation, and delivery

Alpha 1-antitrypsin is one of the first protein therapeutics introduced on the market - more than 30 years ago - and, to date, it is indicated only for the treatment of the severe forms of a genetic condition known as alpha-1 antitrypsin deficiency. The only approved preparations are derived from plasma, posing potential problems associated with its limited supply and high processing costs. Moreover, augmentation therapy with alpha 1-antitrypsin is still limited to intravenous infusions, a cumbersome regimen for patients. Here, we review the recent literature on its possible future developments, focusing on i) the recombinant alternatives to the plasma-derived protein, ii) novel formulations, and iii) novel administration routes. Regulatory issues and the still unclear noncanonical functions of alpha 1-antitrypsin - possibly associated with the glycosylation pattern found only in the plasma-derived protein - have hindered the introduction of new products. However, potentially new therapeutic indications other than the treatment of alpha-1 antitrypsin deficiency might open the way to new sources and new formulations.

Review of nanotheranostics for molecular mechanisms underlying psychiatric disorders and commensurate nanotherapeutics for neuropsychiatry: The mind knockout

Bio-neuronal led psychiatric abnormalities transpired by the loss of neuronal structure and function (neurodegeneration), pro-inflammatory cytokines, microglial dysfunction, altered neurotransmission, toxicants, serotonin deficiency, kynurenine pathway, and excessively produced neurotoxic substances. These uncontrolled happenings in the etiology of psychiatric disorders initiate further changes in neurotransmitter metabolism, pathologic microglial, cell activation, and impaired neuroplasticity. Inflammatory cytokines, the outcome of dysfunctional mitochondria, dysregulation of the immune system, and under stress functions of the brain are leading biochemical factors for depression and anxiety. Nanoscale drug delivery platforms, inexpensive diagnostics using nanomaterials, nano-scale imaging technologies, and ligand-conjugated nanocrystals used for elucidating the molecular mechanisms and foremost cellular communications liable for such disorders are highly capable features to study for efficient diagnosis and therapy of the mental illness. These theranostic tools made up of multifunctional nanomaterials have the potential for effective and accurate diagnosis, imaging of psychiatric disorders, and are at the forefront of leading technologies in nanotheranostics openings field as they can collectively and efficiently target the stimulated territories of the cerebellum (cells and tissues) through molecular-scale interactions with higher bioavailability, and bio-accessibility. Specifically, the nanoplatforms based neurological changes are playing a significant role in the diagnosis of psychiatric disorders and portraying the routes of functional restoration of mental disorders by newer imaging tools at nano-level in all directions. Because of these nanotherapeutic platforms, the molecules of nanomedicine can penetrate the Blood-Brain Barrier with an increased half-life of drug molecules. The discoveries in nanotheranostics and nanotherapeutics inbuilt unique multi-functionalities are providing the best multiplicities of novel nanotherapeutic potentialities with no toxicity concerns at the level of nano range.

Interleukin-36 family dysregulation drives joint inflammation and therapy response in psoriatic arthritis

OBJECTIVES

IL-36 agonists are pro-inflammatory cytokines involved in the pathogenesis of psoriasis. However, their role in the pathogenesis of arthritis and treatment response to DMARDs in PsA remains uncertain. Therefore, we investigated the IL-36 axis in the synovium of early, treatment-naïve PsA, and for comparison RA patients, pre- and post-DMARDs therapy.

METHODS

Synovial tissues were collected by US-guided biopsy from patients with early, treatment-naïve PsA and RA at baseline and 6 months after DMARDs therapy. IL-36 family members were investigated in synovium by RNA sequencing and immunohistochemistry, and expression levels correlated with DMARDs treatment response ex vivo. Additionally, DMARDs effects on IL-36 were investigated in vitro in fibroblast-like synoviocytes.

RESULTS

PsA synovium displayed a reduced expression of IL-36 antagonists, while IL-36 agonists were comparable between PsA and RA. Additionally, neutrophil-related molecules, which drive a higher activation of the IL-36 pathway, were upregulated in PsA compared with RA. At baseline, the synovial expression of IL-36α was significantly higher in PsA non-responders to DMARDs treatment, with the differential expression being sustained at 6 months post-treatment. In vitro, primary PsA-derived fibroblasts were more responsive to IL-36 stimulation compared with RA and, importantly, DMARDs treatment increased IL-36 expression in PsA fibroblasts.

CONCLUSION

The impaired balance between IL-36 agonists-antagonists described herein for the first time in PsA synovium and the decreased sensitivity to DMARDs in vitro may explain the apparent lower efficacy of DMARDs in PsA compared with RA. Exogenous replacement of IL-36 antagonists may be a novel promising therapeutic target for PsA patients.

Interleukin-36: Structure, Signaling and Function

The IL-36 family belongs to a larger IL-1 superfamily and consists of three agonists (IL-36α/β/γ), one antagonist (IL-36Ra), one cognate receptor (IL-36R) and one accessory protein (IL-1RAcP). The receptor activation follows a two-step mechanism in that the agonist first binds to IL-36R and the resulting binary complex recruits IL-1RAcP. Assembled ternary complex brings together intracellular TIR domains of receptors which activate downstream NF-κB and MAPK signaling. Antagonist IL-36Ra inhibits the signaling by binding to IL-36R and preventing recruitment of IL-1RAcP. Members of IL-36 are normally expressed at low levels. Upon stimulation, they are inducted and act on a variety of cells including epithelial and immune cells. Protease mediated N-terminal processing is needed for cytokine activation. In the skin, the functional role of IL-36 is to contribute to host defense through inflammatory response. However, when dysregulated, IL-36 stimulates keratinocyte and immune cells to enhance the Th17/Th23 axis and induces psoriatic-like skin disorder. Genetic mutations of the antagonist IL-36Ra are associated with occurrence of generalized pustular psoriasis, a rare but life-threatening skin disease. Anti-IL-36 antibodies attenuate IMQ or IL-23 induced skin inflammation in mice, illustrating IL-36's involvement in mouse model of psoriasis. Other organs such as the lungs, the intestine, the joints and the brain also express IL-36 family members upon stimulation. The physiological and pathological roles of IL-36 are less well defined in these organs than in the skin. In this chapter, current progress on IL-36 protein and biology is reviewed with a discussion on investigative tools for this novel target.

Current perspectives on the interleukin-1 family as targets for inflammatory disease

Since the first description of interleukin-1 (IL-1) and the genesis of the field of cytokine biology, the understanding of how IL-1 and related cytokines play central orchestrating roles in the inflammatory response has been an area of intense investigation. As a consequence of these endeavours, specific strategies have been developed to target the function of the IL-1 family in human disease realizing significant impacts for patients. While the most significant advances to date have been associated with inhibition of the prototypical family members IL-1α/β, approaches to target more recently identified family members such as IL-18, IL-33 and the IL-36 subfamily are now beginning to come to fruition. This review summarizes current knowledge surrounding the roles of the IL-1 family in human disease and describes the rationale and strategies which have been developed to target these cytokines to inhibit the pathogenesis of a wide range of diseases in which inflammation plays a centrally important role.

Small Molecule IL-36γ Antagonist as a Novel Therapeutic Approach for Plaque Psoriasis

IL-36 cytokines are pro-inflammatory members of the IL-1 family that are upregulated in inflammatory disorders. Specifically, IL-36γ is highly expressed in active psoriatic lesions and can drive pro-inflammatory processes in 3D human skin equivalents supporting a role for this target in skin inflammation. Small molecule antagonists of interleukins have been historically challenging to generate. Nevertheless, we performed a small molecule high-throughput screen to identify IL-36 antagonists using a novel TR-FRET binding assay. Several compounds, including 2-oxypyrimidine containing structural analogs of the marketed endothelin receptor A antagonist Ambrisentan, were identified as hits from the screen. A-552 was identified as a the most potent antagonist of human IL-36γ, but not the closely related family member IL-36α, was capable of attenuating IL-36γ induced responses in mouse and human disease models. Additionally, x-ray crystallography studies identified key amino acid residues in the binding pocket present in human IL-36γ that are absent in human IL-36α. A-552 represents a first-in-class small molecule antagonist of IL-36 signaling that could be used as a chemical tool to further investigate the role of this pathway in inflammatory skin diseases such as psoriasis.

IL-36, IL-37, and IL-38 Cytokines in Skin and Joint Inflammation: A Comprehensive Review of Their Therapeutic Potential

The interleukin (IL)-1 family of cytokines is composed of 11 members, including the most recently discovered IL-36α, β, γ, IL-37, and IL-38. Similar to IL-1, IL-36 cytokines are initiators and amplifiers of inflammation, whereas both IL-37 and IL-38 display anti-inflammatory activities. A few studies have outlined the role played by these cytokines in several inflammatory diseases. For instance, IL-36 agonists seem to be relevant for the pathogenesis of skin psoriasis whereas, despite being expressed within the synovial tissue, their silencing or overexpression do not critically influence the course of arthritis in mice. In this review, we will focus on the state of the art of the molecular features and biological roles of IL-36, IL-37, and IL-38 in representative skin- and joint-related inflammatory diseases, namely psoriasis, rheumatoid arthritis, and psoriatic arthritis. We will then offer an overview of the therapeutic potential of targeting the IL-36 axis in these diseases, either by blocking the proinflammatory agonists or enhancing the physiologic inhibitory feedback on the inflammation mediated by the antagonists IL-37 and IL-38.

Cathepsin G cleaves and activates IL-36γ and promotes the inflammation of psoriasis

Background

IL-36γ is considered to be a valuable biomarker in psoriatic patients, which is expressed as an inactive precursor that needs to be proteolytically processed and activated, and neutrophil-derived proteases seemed to be potent activating enzymes of IL-36γ.

Objectives

This study aims to investigate the activation of IL-36γ by cathepsin G (CG) and neutrophil elastase (NE).

Materials and methods

We used inactive recombinant full-length (FL)-IL-36γ with different doses of NE or CG to stimulate HaCaT cells; neutrophil extracellular traps (NETs) were prepared to act on FL-IL-36γ and then stimulate HaCaT cells. Real-time quantitative PCR and ELISA were performed to detect CXCL-1 and CXCL-8 expression. We developed imiquimod-induced psoriasis-like mouse model to evaluate the effect of hypodermic injection of neutrophil-derived protease or its inhibitor. Histopathology and Western blotting were conducted for effect assessment.

Results

Purified CG cleaved and activated recombinant human FL-IL-36γ to promote CXCL-1 and CXCL-8 expression by human keratinocytes, and NETs activated FL-IL-36γ and the activation was inhibited by serpin A3. CG induced expression of a more truncated IL-36γ in psoriasiform lesion of mice and aggravated the psoriasis-like lesion induced by imiquimod, whereas recombinant serpin A3 alleviated the severity of the psoriasis-like mouse mode.

Conclusion

CG has the ability to cleave and activate IL-36γ and aggravate imiquimod-induced mouse psoriasiform lesion. Thus, CG-specific inhibitors might be promising therapeutic drugs for psoriasis.