Maurer, Marcus

Introduction Indolent systemic mastocytosis (ISM) is a rare clonal mast cell disease driven by the KIT D816V mutation in nearly all patients. Patients with ISM can present with debilitating acute and chronic cutaneous, gastrointestinal, neurocognitive, and systemic symptoms caused by the release of inflammatory mediators from abnormal mast cells. In some patients, symptoms are not adequately controlled with best supportive care (BSC) medications. Elenestinib (BLU-263) is a novel, investigational, oral, next-generation tyrosine kinase inhibitor that potently and selectively inhibits KIT D816V with limited central nervous system penetration and pharmacokinetics (PK) that support once daily dosing. HARBOR (NCT04910685) is a randomized, double-blind, placebo-controlled, phase 2/3 study assessing efficacy and safety of elenestinib in patients with ISM. Methods Eligible adult patients with ISM, confirmed following central review of bone marrow (BM) pathology, clinical, and laboratory findings per World Health Organization criteria and a moderate-to-severe symptom score based on minimum mean total symptom score (TSS) of the ISM-Symptom Assessment Form (ISM-SAF©2018), were stratified by baseline serum tryptase (<20 ng/mL vs ≥20 ng/mL) and randomly assigned 3:1 to elenestinib 25 mg, 50 mg, or 100 mg once daily + BSC (“elenestinib”) or placebo + BSC (“placebo”). The primary objective of Part 1 was to determine the recommended dose based on safety, PK, and pharmacodynamics. Secondary endpoints included changes in biomarkers of disease burden (serum tryptase, KIT D816V variant allele fraction [VAF], and BM mast cells) and ISM-SAF TSS. Three additional open-label PK groups enrolled patients at 50 mg, 75 mg, and 100 mg to further characterize PK and safety. Results As of data cutoff on July 3, 2023, a total of 122 patients with ISM have received their assigned treatment in Part 1 of the study; 39 were blinded and randomized to elenestinib or placebo, and 83 were treated with open-label elenestinib in the PK groups (21 patients at 50 mg, 34 patients at 75 mg, and 28 patients at 100 mg). Baseline demographics were similar to those reported for the general ISM population. After 12 weeks of therapy, symptom improvement was observed for all dose cohorts, and symptom reduction by TSS was greater for patients on elenestinib versus placebo in the blinded portion of Part 1. Patients receiving elenestinib at 25 mg, 50 mg, and 100 mg doses showed reduction (mean percent) from baseline for tryptase (-15.4%, -50.9%, and -68.4% vs 3.3%, respectively) and KIT D816VVAF (-37.5%, -70.3%, and -77.0% vs -2.5%, respectively) as compared to placebo. Similar reductions in TSS and disease-related biomarkers were observed in the open-label PK cohorts. After a median treatment duration of 35.3 weeks, elenestinib was well-tolerated at all dose levels. There were no treatment-related serious adverse events and no treatment-related adverse events that led to drug discontinuation. Conclusion Elenestinib at all tested doses demonstrated beneficial effects on disease-related symptoms and biomarkers of mast cell burden in this large and maturing cohort of patients with ISM with a moderate-to-severe symptom burden. Elenestinib was well tolerated across all dose levels with a promising early benefit-risk profile in ISM. These preliminary findings will inform dosing for the planned Part 2 of HARBOR, which will examine elenestinib versus placebo in a randomized, blinded, placebo-controlled setting.

Summary Background The mechanisms for producing weals in chronic spontaneous (idiopathic) urticaria (CSU) are incompletely understood. Leucocyte infiltration with vascular leakage and expression of the potent vasoactive agents' calcitonin gene‐related peptide ( CGRP ) and vascular endothelial growth factor ( VEGF ) are features of late‐phase allergic skin reactions, previously proposed as a model of CSU . Objective To measure CGRP and VEGF expression in lesional and non‐lesional skin from CSU patients and to compare results with a control group. Methods Eight paired biopsies (one from 4–8 h spontaneous weals and one from uninvolved skin) were taken from eight patients with CSU and nine control subjects and studied by immunohistochemistry and confocal microscopy. Results Lesional skin in CSU contained significantly more CGRP + and VEGF + cells than non‐lesional skin. No significant differences were observed in CGRP and VEGF expression between non‐lesional skin and controls. In lesional skin, VEGF and CGRP co‐localised to UEA‐1+ blood vessels. CGRP was also expressed by neutrophils and eosinophils and to a lesser extent by CD90 + fibroblasts, mast cells, CD 3 + and CD 68 + cells. CGRP and VEGF expression was not related to the duration of disease. Conclusion and Clinical Relevance Increased expression of CGRP and VEGF in lesional, but not uninvolved, skin indicates that these potent vasoactive agents may play a role in wealing and tissue oedema in CSU so representing novel targets in therapy.

AbstractMastocytosis is an emerging differential diagnosis in patients with more or less specific mediator‐related symptoms. In some of these patients, typical skin lesions are found and the diagnosis of mastocytosis can be established. In other cases, however, skin lesions are absent, which represents a diagnostic challenge. In the light of this unmet need, we developed a diagnostic algorithm for patients with suspected mastocytosis. In adult patients with typical lesions of mastocytosis in the skin, a bone marrow (BM) biopsy should be considered, regardless of the basal serum tryptase concentration. In adults without skin lesions who suffer from mediator‐related or other typical symptoms, the basal tryptase level is an important parameter. In those with a slightly increased tryptase level, additional investigations, including a sensitive KIT mutation analysis of blood leucocytes or measurement of urinary histamine metabolites, may be helpful. In adult patients in whom (i) KIT D816V is detected and/or (ii) the basal serum tryptase level is clearly increased (>25–30 ng/ml) and/or (iii) other clinical or laboratory features suggest the presence of ‘occult’ mastocytosis or another haematologic neoplasm, a BM investigation is recommended. In the absence of KIT D816V and other signs or symptoms of mastocytosis or another haematopoietic disease, no BM investigation is required, but the clinical course and tryptase levels are monitored in the follow‐up. In paediatric patients, a BM investigation is usually not required, even if the tryptase level is increased. Although validation is required, it can be expected that the algorithm proposed herein will facilitate the management of patients with suspected mastocytosis and help avoid unnecessary referrals and investigations.

AbstractSchnitzler's syndrome is characterized by recurrent urticarial rash and monoclonal gammopathy, associated with clinical and biological signs of inflammation and a long‐term risk of AA amyloidosis and overt lymphoproliferation. An extensive literature review was performed, and the following questions were addressed during an expert meeting: In whom should Schnitzler's syndrome be suspected? How should the diagnosis of Schnitzler's syndrome be established? How should a patient with Schnitzler's syndrome be treated? How should a patient with Schnitzler's syndrome be followed up?. A diagnosis of Schnitzler's syndrome is considered definite in any patient with two obligate criteria: a recurrent urticarial rash and a monoclonal IgM gammopathy, and two of the following minor criteria: recurrent fever, objective signs of abnormal bone remodeling, elevated CRP level or leukocytosis, and a neutrophilic infiltrate on skin biopsy. It is considered probable, if only 1 minor criterion is present. In patients with monoclonal IgG gammopathies, diagnosis is definite if three minor criteria are present and possible if two are present. First‐line treatment in patients with significant alteration of quality of life or persistent elevation of markers of inflammation should be anakinra. Follow‐up should include clinical evaluation, CBC and CRP every 3 months and MGUS as usually recommended.