Phase 2 trial of a neurokinin-1 receptor antagonist for the treatment of chronic itch in patients with epidermolysis bullosa: A randomized clinical trial

Rapid elucidation of agonist-driven regulation of the neurokinin 1 receptor using a GPCR phosphorylation immunoassay

Agonist-induced phosphorylation is a crucial step in the activation/deactivation cycle of G protein-coupled receptors (GPCRs), but direct determination of individual phosphorylation events has remained a major challenge. We have recently developed a bead-based immunoassay for the quantitative assessment of agonist-induced GPCR phosphorylation that can be performed entirely in 96-well plates, thus eliminating the need for western blot analysis. In the present study, we adapted this assay to three novel phosphosite-specific antibodies directed against the neurokinin 1 (NK1) receptor, namely pS338/pT339-NK1, pT344/pS347-NK1, and pT356/pT357-NK1. We found that substance P (SP) stimulated concentration-dependent phosphorylation of all three sites, which could be completely blocked in the presence of the NK1 receptor antagonist aprepitant. The other two endogenous ligands of the tachykinin family, neurokinin A (NKA) and neurokinin B (NKB), were also able to induce NK1 receptor phosphorylation, but to a much lesser extent than substance P. Interestingly, substance P promoted phosphorylation of the two distal sites more efficiently than that of the proximal site. The proximal site was identified as a substrate for phosphorylation by protein kinase C. Analysis of GPCR kinase (GRK)-knockout cells revealed that phosphorylation was mediated by all four GRK isoforms to similar extents at the T344/S347 and the T356/T357 cluster. Knockout of all GRKs resulted in abolition of all phosphorylation signals highlighting the importance of these kinases in agonist-mediated receptor phosphorylation. Thus, the 7TM phosphorylation assay technology allows for rapid and detailed analyses of GPCR phosphorylation.

Mechanism underlying pruritus in recessive dystrophic epidermolysis bullosa: Role of interleukin-31 from mast cells and macrophages

BACKGROUND

Pruritus is a highly burdensome symptom in patients with epidermolysis bullosa, especially recessive dystrophic epidermolysis bullosa (RDEB); however, only a few studies have assessed the molecular pathogenesis of RDEB-associated pruritus. Interleukin (IL)-31 is a key cytokine implicated in pruritus associated with dermatologic diseases such as atopic dermatitis and prurigo nodularis.

OBJECTIVE

To investigate the role and cellular source of IL-31 in RDEB-associated pruritus.

METHODS

Serum and skin samples were obtained from 11 RDEB patients and 11 healthy controls. Pruritus visual analogue scale scores were determined. Serum levels of IL-31 and thymic stromal lymphopoietin (TSLP) were examined by enzyme-linked immunosorbent assay (ELISA). The expression of IL-31 and other pruritus mediators in the skin were examined through immunofluorescence staining, and their correlation with pruritus severity was analysed.

RESULTS

Serum IL-31 and TSLP were elevated in RDEB patients. IL-31 expression was increased in RDEB skin and positively correlated with pruritus severity. Most of the IL-31-expressing cells were mast cells, and some were CD206(+) M2-like macrophages. The number of substance P(+) cells was also increased in the patients' skin, and most of them were mast cells. The number of substance P(+) mast cells was correlated with the number of IL-31(+) dermal infiltrates. The number of IL-4Rα- and IL-13-expressing cells and expression of TSLP and periostin increased in RDEB skin, but without a correlation to pruritus score.

CONCLUSION

The increased production of skin IL-31 from mast cells and M2-like macrophages may be the mechanism underlying pruritus in RDEB.

Beyond the Surface: A Narrative Review Examining the Systemic Impacts of Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare genetic disease resulting from inadequate type VII collagen (C7). Although recurrent skin blisters and wounds are the most apparent disease features, the impact of C7 loss is not confined to the skin and mucous membranes. RDEB is a systemic disease marred by chronic inflammation, fibrotic changes, pain, itch, and anemia, significantly impacting QOL and survival. In this narrative review, we summarize these systemic features of RDEB and promising research avenues to address them.

Efficacy of oral JAK1 or JAK1/2 inhibitor for treating refractory pruritus in dystrophic epidermolysis bullosa: A retrospective case series

Refractory pruritus is the most distressing, disease-related symptom in patients with dystrophic epidermolysis bullosa (DEB), inducing an itch-scratch-blister cycle. Chronic inflammation is a hallmark of DEB, thus upregulation of inflammatory cytokines and Janus kinase (JAK) signaling may play a role in DEB-related pruritus. We retrospectively reviewed the medical records of DEB patients with refractory pruritus who were treated with either baricitinib, a JAK1/2 inhibitor, or upadacitinib, a selective JAK1 inhibitor. Patients received baricitinib (4 mg) or upadacitinib (15 mg) once a day for 2-32 weeks. A total of 12 DEB patients (six recessive DEB and six dominant DEB) were included in this study. The mean±SD baseline pruritus visual analog scale (VAS) score was 7.5 ± 1.7. Upadacitinib or baricitinib treatment resulted in a rapid and sustained decrease in itch. Four out of 12 patients (33.3%) and seven out of 10 patients (70%) showed a decrease of at least 3 points in the pruritus VAS score from baseline at weeks 2 and 4, respectively. The mean percentage changes from baseline in pruritus VAS scores at weeks 2 and 4 were -42.9% and -52.7%, respectively. Subgroup analysis showed greater reductions in the pruritus VAS score in the baricitinib group (n = 5) compared to the upadacitinib group (n = 7), and in patients with epidermolysis bullosa pruriginosa (n = 3) compared to other subtypes of DEB (n = 9); however, these differences did not reach statistical significance. Three out of 10 (33.3%) patients showed at least a 2-point reduction in pain intensity from baseline at week 4. Eight out of 12 patients (66.7%) also showed a reduction in the number of new blisters, which correlated with a reduction in the pruritus score. No patient discontinued treatment because of serious adverse events. Our results suggest that JAK1 or JAK1/2 inhibitors could be a promising treatment option for DEB-related pruritus. Long-term safety should be assessed in future studies.

Measuring the impact of pruritus in patients with epidermolysis bullosa: evaluation with an itch-specific instrument

Pruritus is one of the most debilitating symptoms for patients with epidermolysis bullosa (EB). This study aimed to assess the burden of itch and to address its dimensions across patients with EB. Forty-six patients with EB were recruited from the Saudi EB registry to participate. All participants completed the Leuven Itch Scale. The sample included 5 patients with EB simplex (EBS), 3 with junctional EB (JEB), 34 with dystrophic EB (DEB), and 4 patients had unknown type. Overall, 97.8% patients reported itch. In patients with itch, 73.3% reported that it was often or always present, longer than 2h Itch episodes was reported by JEB (66.7%) and recessive DEB (3.2%). Itch, in all its dimensions, was worst in patients with JEB and DEB than EBS. Itch occurred mostly in a hot environment (80%), when sweating (71.1%), in healing wounds (40%), and during dressing change (35.6%) whereas cold environment resulted in itch in only (2.2%). The burden of pruritus increased with increasing age. This study highlights a challenging area in EB care with a need for specific treatments.

An update on mechanisms of pruritus and their potential treatment in primary cutaneous T-cell lymphoma

Primary cutaneous T-cell lymphomas (CTCL), which include mycosis fungoides (MF) and Sézary syndrome (SS), are a group of lymphoproliferative disorders characterized by clonal accumulation of neoplastic T-lymphocytes in the skin. Severe pruritus, one of the most common and distressing symptoms in primary CTCL, can significantly impair emotional well-being, physical functioning, and interpersonal relationships, thus greatly reducing quality of life. Unfortunately, effectively managing pruritus remains challenging in CTCL patients as the underlying mechanisms are, as of yet, not fully understood. Previous studies investigating the mechanisms of itch in CTCL have identified several mediators and their corresponding antagonists used for treatment. However, a comprehensive overview of the mediators and receptors contributing to pruritus in primary CTCL is lacking in the current literature. Here, we summarize and review the mediators and receptors that may contribute to pruritus in primary CTCL to explore the mechanisms of CTCL pruritus and identify effective therapeutic targets using the PubMed and Web of Science databases. Studies were included if they described itch mediators and receptors in MF and SS. Overall, the available data suggest that proteases (mainly tryptase), and neuropeptides (particularly Substance P) may be of greatest interest. At the receptor level, cytokine receptors, MRGPRs, and TRP channels are most likely important. Future drug development efforts should concentrate on targeting these mediators and receptors for the treatment of CTCL pruritus.

Itch in recessive dystrophic epidermolysis bullosa: findings of PEBLES, a prospective register study

BACKGROUND

Itch is common and distressing in epidermolysis bullosa (EB) but has not previously been studied in depth in different recessive dystrophic EB (RDEB) subtypes.

OBJECTIVES

As part of a prospective register study of the natural history of RDEB we explored features of itch, medications used, and correlation with disease severity and quality of life.

METHODS

Fifty individuals with RDEB aged 8 years and above completed the Leuven Itch Scale (LIS) (total 243 reviews over a 7-year period). Data included itch frequency, severity, duration, distress, circumstances, consequences, itch surface area and medications for itch. The iscorEB disease severity score and the validated EB quality of life tool, QOLEB, were compared to LIS domains and analysed by RDEB subtype.

RESULTS

Itch was frequent, present in the preceding month in 93% of reviews. Itch severity and distress were significantly greater in severe (RDEB-S) and pruriginosa (RDEB-Pru) subtypes compared to intermediate RDEB (RDEB-I). Itch medications were reported in just over half of reviews including emollients, topical corticosteroids and antihistamines; the proportion of participants not using medication despite frequent pruritus suggests limited efficacy. In inversa RDEB (RDEB-Inv) and RDEB-I, LIS domains correlated with iscorEB and QOLEB. In contrast to previous studies, correlations were lacking in RDEB-S suggesting that global disease burden relatively reduces the contribution of itch.

CONCLUSIONS

This comprehensive study of RDEB-associated itch highlights differences between RDEB subtypes, suggests an unmet need for effective treatments and could serve as control data for future clinical trials incorporating itch as an endpoint.

The Role of Substance P Within Traumatic Brain Injury and Implications for Therapy

This review examines the role of the neuropeptide substance P within the neuroinflammation that follows traumatic brain injury. It examines it in reference to its preferential receptor, the neurokinin-1 receptor, and explores the evidence for antagonism of this receptor in traumatic brain injury with therapeutic intent. Expression of substance P increases following traumatic brain injury. Subsequent binding to the neurokinin-1 receptor results in neurogenic inflammation, a cause of deleterious secondary effects that include an increased intracranial pressure and poor clinical outcome. In several animal models of TBI, neurokinin-1 receptor antagonism has been shown to reduce brain edema and the resultant rise in intracranial pressure. A brief overview of the history of substance P is presented, alongside an exploration into the chemistry of the neuropeptide with a relevance to its functions within the central nervous system. This review summarizes the scientific and clinical rationale for substance P antagonism as a promising therapy for human TBI.

Chronic pruritus: from pathophysiology to drug design

Pruritus, the most common symptom in dermatology, is an innate response capable of protecting skin against irritants. Nonetheless, when it lasts more than six weeks it is assumed to be a chronic pathology having a negative impact on people's lives. Chronic pruritus (CP) can occur in common and rare skin diseases, having a high prevalence in global population. The existing therapies are unable to counteract CP or are associated with adverse effects, so the development of effective treatments is a pressing issue. The pathophysiological mechanisms underlying CP are not yet completely dissected but, based on current knowledge, involve a wide range of receptors, namely neurokinin 1 receptor (NK1R), Janus kinase (JAK), and transient receptor potential (TRP) ion channels, especially transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential ankyrin 1 (TRPA1). This review will address the relevance of these molecular targets for the treatment of CP and molecules capable of modulating these receptors that have already been studied clinically or have the potential to possibly alleviate this pathology. According to scientific and clinical literature, there is an increase in the expression of these molecular targets in the lesioned skin of patients experiencing CP when compared with non-lesioned skin, highlighting their importance for the development of potential efficacious drugs through the design of antagonists/inhibitors.

How to get rid of itching

Itch is an unpleasant sensation arising from a variety of dermatologic, neuropathic, systemic, and psychogenic etiologies. Various itch pathways are implicated according to the underlying etiology. A variety of pruritogens, or itch mediators, as well as receptors have been identified and provide potential therapeutic targets. Recent research has primarily focused on targeting inflammatory cytokines and Janus kinase signaling, protease-activated receptors, substance P and neurokinin, transient receptor potential-vanilloid ion channels, Mas-related G-protein-coupled receptors (MRGPRX2 and MRGPRX4), the endogenous opioid and cannabinoid balance, and phosphodiesterase 4. Periostin, a newly identified pruritogen, should be further explored with clinical trials. Drugs targeting neural sensitization including the gabergic system and P2X3 are other potential drugs for chronic itch. There is a need for more targeted therapies to improve clinical outcomes and reduce side effects.

Integrated Management Strategies for Epidermolysis Bullosa: Current Insights

Epidermolysis bullosa (EB) is a group of rare genodermatoses that is characterized by skin fragility resulting from minor trauma. There are four major subtypes, namely, EB simplex, junctional EB, dystrophic EB and Kindler EB, depending upon the localization of defective protein and resulting plane of blister formation. The phenotype is heterogeneous in terms of severity and majority of them present at birth or neonatal period. Currently, the treatment is mainly supportive and requires multidisciplinary care. The complex molecular pathology creates difficulty in discovering a unified curative treatment approach. But with arduous efforts, significant progress has been made in the development of treatment strategies in the last decade. The management strategies range from targeting the underlying causative factor to symptom-relieving approaches, and include gene, mRNA, protein, cell and combination therapies. In this review, we enumerate the promising approaches that are currently under various stages of investigation to provide effective treatment for patients with EB.

Investigational Treatments for Epidermolysis Bullosa

Epidermolysis bullosa (EB) is a heterogeneous group of rare inherited blistering skin disorders characterized by skin fragility following minor trauma, usually present since birth. EB can be categorized into four classical subtypes, EB simplex, junctional EB, dystrophic EB and Kindler EB, distinguished on clinical features, plane of blister formation in the skin, and molecular pathology. Treatment for EB is mostly supportive, focusing on wound care and patient symptoms such as itch or pain. However, therapeutic advances have also been made in targeting the primary genetic abnormalities as well as the secondary inflammatory footprint of EB. Pre-clinical or clinical testing of gene therapies (gene replacement, gene editing, RNA-based therapy, natural gene therapy), cell-based therapies (fibroblasts, bone marrow transplantation, mesenchymal stromal cells, induced pluripotential stem cells), recombinant protein therapies, and small molecule and drug repurposing approaches, have generated new hope for better patient care. In this article, we review advances in translational research that are impacting on the quality of life for people living with different forms of EB and which offer hope for improved clinical management.

Practical management of epidermolysis bullosa: consensus clinical position statement from the European Reference Network for Rare Skin Diseases

Inherited epidermolysis bullosa (EB) comprises rare disorders that manifest with fragility and blistering of the skin and mucous membranes, with variable clinical severity. Management of EB is challenging due to disease rarity and complexity, the wide range of extracutaneous manifestations and a profound impact on daily life for the patient and family members. Although reference centres providing multidisciplinary care for EB exist in each European country, it is common for healthcare professionals that are not specialized in this rare disorder to treat EB patients. Here, experts of the European Reference Network for Rare and Undiagnosed Skin Diseases (ERN-Skin, https://ern-skin.eu) propose practical recommendations for the diagnosis and management of the commonest clinical issues, skin blisters and wounds, oral manifestations, pain and itch.

Chronic itch: emerging treatments following new research concepts

Until recently, itch pathophysiology was poorly understood and treatments were poorly effective in relieving itch. Current progress in our knowledge of the itch processing, the numerous mediators and receptors involved has led to a large variety of possible therapeutic pathways. Currently, inhibitors of IL-31, IL-4/13, NK₁ receptors, opioids and cannabinoids, JAK, PDE4 or TRP are the main compounds involved in clinical trials. However, many new targets, such as Mas-related GPCRs and unexpected new pathways need to be also explored.

Crosstalk Between Epithelial Cells, Neurons and Immune Mediators in HSV-1 Skin Infection

Herpes simplex virus type 1 (HSV-1) infection is highly prevalent in humans, with approximately two-thirds of the world population living with this virus. However, only a fraction of those carrying HSV-1, which elicits lifelong infections, are symptomatic. HSV-1 mainly causes lesions in the skin and mucosae but reaches the termini of sensory neurons innervating these tissues and travels in a retrograde manner to the neuron cell body where it establishes persistent infection and remains in a latent state until reactivated by different stimuli. When productive reactivations occur, the virus travels back along axons to the primary infection site, where new rounds of replication are initiated in the skin, in recurrent or secondary infections. During this process, new neuron infections occur. Noteworthy, the mechanisms underlying viral reactivations and the exit of latency are somewhat poorly understood and may be regulated by a crosstalk between the infected neurons and components of the immune system. Here, we review and discuss the immune responses that occur at the skin during primary and recurrent infections by HSV-1, as well as at the interphase of latently-infected neurons. Moreover, we discuss the implications of neuronal signals over the priming and migration of immune cells in the context of HSV-1 infection.

Neurokinin 1 Receptor Antagonists for Pruritus

Pruritus, commonly known as itch, is a very common symptom in numerous dermatological disorders and systemic diseases. It can manifest as acute, or when lasting longer than 6 weeks, it is considered chronic and can lead to significant distress and reduced quality-of-life of those suffering. Current therapeutics are limited and are lacking in efficacy, and the development of more effective treatments is needed. The neurokinin 1 receptor (NK1R) antagonists are a novel class of drugs that possess several properties such as antidepressant, anxiolytic and antiemetic activities. Recently, several studies have described the antipruritic activity of NK1R antagonists for treating chronic pruritus. In this review we outline the pathogenesis of chronic pruritus, the mechanism by which the neuropeptide substance P (SP) and its receptor NK1R may be targeted to inhibit pruritic activity, and the efficacy and tolerability of NK1R antagonists, which have been, or are currently being investigated for treating conditions where chronic pruritus is a major symptom. Increasing evidence from ongoing and completed studies demonstrates the importance of SP and NK1R signalling in mediating pruritic activity. Several NK1R antagonists have shown significant antipruritic activity and thus targeting the SP-NK1R pathway may provide a therapeutic option for treating chronic pruritus of certain origin/s in the foreseeable future.

Intravenous allogeneic umbilical cord blood-derived mesenchymal stem cell therapy in recessive dystrophic epidermolysis bullosa patients

BACKGROUND

Recessive dystrophic epidermolysis bullosa (RDEB) is an incurable disease that causes severe mucocutaneous fragility due to mutations in COL7A1 (encoding type VII collagen [C7]). In this phase I/IIa trial, we evaluated the safety and possible clinical efficacy of intravenous infusion of allogeneic human umbilical cord blood–derived mesenchymal stem cells (hUCB-MSCs) in patients with RDEB.

METHODS

Four adult and two pediatric patients with RDEB were treated with 3 intravenous injections of hUCB-MSCs (1 × 10⁶ to 3 × 10⁶ cells/kg) every 2 weeks and followed up for 8–24 months after treatment. The primary endpoint was safety. Secondary endpoints related to efficacy included clinical parameters, such as disease severity score, wound assessment, itch and pain score, and quality of life. C7 expression levels and inflammatory infiltrates in the skin, as well as serum levels of inflammatory markers and neuropeptides, were also assessed.

RESULTS

Intravenous hUCB-MSC infusions were well tolerated, without serious adverse events. Improvements in the Birmingham Epidermolysis Bullosa Severity Score, body surface area involvement, blister counts, pain, pruritus, and quality of life were observed with maximal effects at 56–112 days after treatment. hUCB-MSC administration induced M2 macrophage polarization and reduced mast cell infiltration in RDEB skin. Serum levels of substance P were decreased after therapy. Increased C7 expression was observed at the dermoepidermal junction in 1 of 6 patients at day 56.

CONCLUSION

To the best of our knowledge, this is the first clinical trial of systemic administration of allogeneic hUCB-MSCs in patients with RDEB, demonstrating safety and transient clinical benefits.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04520022.

FUNDING

This work was supported by Daewoong Pharmaceutical Co. Ltd. and Kangstem Biotech Co. Ltd.

Benefits and harms of NK1 R antagonists in pruritus: A systematic review and meta-analysis

Accumulating evidence has showed the possibility of using NK1R antagonists for the treatment of chronic pruritus. However, the benefit and risk profile of NK1R antagonists-serlopitant and aprepitant for the treatment of pruritus remains unclear. To assess the efficacy and safety of NK1R antagonists-serlopitant and aprepitant in patients with pruritus based on analysis of clinical trials. The current systematic review and meta-analysis was performed according to PRISMA guidelines. A total of 10 randomized clinical trials including 631 patients were enrolled. Four randomized controlled trials investigated the comparative treatment effect of serlopitant on pruritus. Our results showed that serlopitant had reasonable anti-pruritic effectiveness in patients, with mild toxicities. The overall proportion of 4-point improvement of NRS and VAS in serlopitant-treatment group were both significantly higher relative to placebo group (OR 2.345, 95%CI 1.557 to 3.531, P < .001; OR 3.308, 95% CI 1.949 to 5.616, P < .001). Serlopitant treatment was also found to be associated with a significant reduction in NRS score as compared with placebo (SMD -0.381, 95%CI -0.599 to -0.164, P = .001). Six clinical trials reported the treatment effect of aprepitant on pruritus. The meta-analysis result of fixed-effect model showed that there was no significant difference between aprepitant and controlled treatment in terms of improved pruritus VAS score (SMD -0.088, 95%CI -0.384 to 0.207, P = .558). There is promising high-quality evidence regarding the efficacy of serlopitant on pruritus. More large-sample randomized controlled trials with appropriate treatment regimen are urgently needed to further evaluate the effectiveness of aprepitant in pruritus.

A deep dive into UV-based phototherapy: Mechanisms of action and emerging molecular targets in inflammation and cancer

UV-based phototherapy (including psoralen plus UVA (PUVA), UVB and UVA1) has a long, successful history in the management of numerous cutaneous disorders. Photoresponsive diseases are etiologically diverse, but most involve disturbances in local (and occasionally systemic) inflammatory cells and/or abnormalities in keratinocytes that trigger inflammation. UV-based phototherapy works by regulating the inflammatory component and inducing apoptosis of pathogenic cells. This results in a fascinating and complex network of simultaneous events-immediate transcriptional changes in keratinocytes, immune cells, and pigment cells; the emergence of apoptotic bodies; and the trafficking of antigen-presenting cells in skin-that quickly transform the microenvironment of UV-exposed skin. Molecular elements in this system of UV recognition and response include chromophores, metabolic byproducts, innate immune receptors, neurotransmitters and mediators such as chemokines and cytokines, antimicrobial peptides, and platelet activating factor (PAF) and PAF-like molecules that simultaneously shape the immunomodulatory effects of UV and their interplay with the microbiota of the skin and beyond. Phototherapy's key effects-proapoptotic, immunomodulatory, antipruritic, antifibrotic, propigmentary, and pro-prebiotic-promote clinical improvement in various skin diseases such as psoriasis, atopic dermatitis (AD), graft-versus-host disease (GvHD), vitiligo, scleroderma, and cutaneous T-cell lymphoma (CTCL) as well as prevention of polymorphic light eruption (PLE). As understanding of phototherapy improves, new therapies (UV- and non-UV-based) are being developed that will modify regulatory T-cells (Treg), interact with (resident) memory T-cells and /or utilize agonists and antagonists as well as antibodies targeting soluble molecules such as cytokines and chemokines, transcription factors, and a variety of membrane-associated receptors.

Prevalence, pathophysiology and management of itch in epidermolysis bullosa

Epidermolysis bullosa (EB) is a highly diverse group of inherited skin disorders, resulting from mutations in genes encoding proteins of the dermoepidermal junction. Itch (pruritus) is one of the most common symptoms across all EB subtypes. It occurs in blistered or wounded sites, or manifests as a generalized phenomenon, thereby affecting both intact skin and healing wounds. The mechanism of pruritus in EB is unclear. It is likely that skin inflammation secondary to barrier disruption, wound healing cascades and dysregulated activation of epidermal sensory nerve endings are all involved in its pathophysiology on the molecular and cellular level. Understanding these mechanisms in depth is crucial in developing optimized treatments for people with EB and improving quality of life. This review summarizes current evidence on the prevalence, mechanisms and management of itch in EB.

Small molecule drug development for rare genodermatoses - evaluation of the current status in epidermolysis bullosa

Background

Hereditary epidermolysis bullosa (EB) comprises a heterogeneous group of rare genodermatoses, which are caused by mutations in genes involved in the maintenance of the structural and functional integrity of dermo-epidermal adhesion in various stratified epithelia. In severe variants, generalized skin disease, extracutaneous manifestations and multi-organ involvement cause considerable morbidity and mortality. Causal and early treatment by re-expression of a respective mutated gene is the major long-term goal in therapy development. However, characterization and targeted modulation of pathogenic molecular cascades in EB also holds great promise as a symptom-relieving approach to ameliorate phenotype, complications and quality of life. Small molecules are chemical structures of less than 900 Da that can diffuse across cell membranes and interfere with target biomolecules, thus influencing their function at different levels. They constitute the vast majority of active components of all approved drugs.

Methods

We performed PubMed and Google Scholar search for publications and screened FDA- and EMA-hosted clinical trial registries to identify studies using small molecule-based drugs for epidermolysis bullosa. Upon detailed analysis this resulted in the identification of a total of 84 studies.

Results

We identified 52 publications and 32 registered trials that investigate small molecules for their safety and efficacy as treatment for different aspects of epidermolysis bullosa. Further, a total of 38 different small molecules clinically used in EB were found. Most frequent outcome measures concerned wound healing, reduction in blister numbers, as well as reduction of itch and pain, predominantly for EBS and RDEB.

Conclusion

We provide a comprehensive summary of the current status of clinical small molecule development for EB and discuss prospects and limitations in orphan drug development for rare conditions like EB.

Emerging Therapeutic Options for Chronic Pruritus

Chronic pruritus, defined as an unpleasant sensation resulting in a need to scratch that lasts more than 6 weeks, is a prevalent and bothersome symptom associated with both cutaneous and systemic conditions. Due to complex pathogenesis and profuse contributing factors, chronic pruritus therapy remains challenging. Regardless of the well-established antipruritic properties of classic pharmacotherapy (topical therapy, phototherapy and systemic therapy), these methods often provide insufficient relief for affected individuals. Owing to the growing interest in the field of pruritic research, further experimental and clinical data have emerged, continuously supporting the possibility of instigating novel therapeutic measures. This review covers the most relevant current modalities remaining under investigation that possess promising perspectives of approval in the near future, especially opioidergic drugs (mu-opioid antagonists and kappa-opioid agonists), neurokinin-1 receptor antagonists, biologic drugs, Janus kinase inhibitors, ileal bile acid transporter inhibitors, aryl hydrocarbon receptor agonists and histamine H₄ receptor antagonists.

Genodermatoses with itch as a prominent feature

A number of inherited conditions cause chronic itch as a part of the recognized phenotype. Advances in the understanding of the genetic factors that cause these diseases elucidate the molecular underpinning of itch as a symptom. Our knowledge of the causes of chronic itch has also advanced, providing an opportunity to integrate the genetic pathophysiology with the molecular landscape of chronic itch mediators. This article reviews select genodermatoses that have itch as a predominant feature with a focus on the pathophysiology of the disease, how it may lead to itch and potential therapeutic targets.

Small molecule drugs for the treatment of pruritus in patients with atopic dermatitis

Chronic pruritus is a cardinal symptom of the inflammatory skin disease atopic dermatitis (AD). Pathogenic mechanisms in the periphery, spinal cord and the brain have been implicated in AD-related pruritus. Therefore, both systemic and topical administration of drugs could potentially provide relief. Despite efforts to elucidate the mechanisms behind AD-related pruritus and the relative contribution of peripheral nervous system and central nervous system (CNS), specific and successful treatment options have not yet been developed. Several small molecule drugs are currently being investigated to treat AD and AD-related pruritus. These small molecule drugs can be applied systemically but also topically, as they are able to penetrate into the skin due to their small size. Small molecule drugs specifically targeting peripheral itch transmission, e.g. peripherally selective κ-opioid receptors agonists and neurokinin 1 receptors antagonists, have so far been unable to improve AD-related pruritus when applied systemically, possibly because of the lack of CNS activity. Current evidence from clinical and preclinical trials with centrally acting or peripherally selective oral κ-opioid receptors agonists implies that CNS activity is required for an antipruritic effect. CNS activity is, however, directly associated with CNS-mediated side-effects. On the other hand, topical application of small molecules with anti-inflammatory activity such as Janus kinase inhibitors and phosphodiesterase 4 inhibitors, and also of κ-opioid receptor agonists, has shown promising results regarding their ability to reduce AD-related pruritus. In conclusion, topical application of anti-inflammatory compounds appears to be a highly promising strategy for the treatment of AD-related pruritus.

Antipruritic Effects of Kappa Opioid Receptor Agonists: Evidence from Rodents to Humans

Centrally administered bombesin induces scratching and grooming in rats. These behaviors were blocked by early benzomorphan kappa opioid receptor (KOR) agonists as reported by Gmerek and Cowan in 1984. This was the first evidence that KORs may be involved in the sensation of itch-like behaviors. Subsequent development of additional animal models for acute and chronic itch has led to important discoveries since then. For example, it was found that (a) gastrin-releasing peptide (GRP), natriuretic polypeptide b and their cognate receptors are keys for the transmission of itch sensation at the spinal cord level, (b) dynorphins (Dyns), the endogenous KOR agonists, work as inhibitory neuromodulators of itch at the spinal cord level, (c) in a mouse model for acute itch, certain KOR antagonists elicit scratching, (d) in mouse models of acute or chronic itch, KOR agonists (e.g., U50,488, nalfurafine, CR 845, nalbuphine) suppress scratching induced by different pruritogens, and (e) nalfurafine, CR 845, and nalbuphine are in the clinic or in clinical trials for pruritus associated with chronic kidney disease and chronic liver disease, as well as pruritus in chronic skin diseases.