FDA and EMA Grant Orphan Drug Designations to GSK’s Momelotinib for Life-Threatening VEXAS Syndrome

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FDA and EMA Grant Orphan Drug Designations to GSK’s Momelotinib for Life-Threatening VEXAS Syndrome

(IN BRIEF) GSK has announced that momelotinib, a differentiated JAK inhibitor marketed as Ojjaara or Omjjara in approved indications, has received orphan drug designations from the US Food and Drug Administration and the European Medicines Agency for the treatment of VEXAS syndrome. VEXAS is a rare, progressive and life-threatening haemato-inflammatory condition with rheumatologic and haematologic features, no approved treatments and a reported five-year mortality rate of 30% to 40%. The designations were supported by retrospective evidence suggesting that JAK inhibitors may offer therapeutic benefit in VEXAS syndrome, as well as a case report indicating that momelotinib may improve symptoms, inflammation and haematological manifestations. GSK is advancing the planned phase II/III ATLAS trial to evaluate momelotinib’s efficacy and safety in VEXAS syndrome and support future global regulatory submissions. The trial is part of momelotinib’s broader development programme across haematological conditions, building on its existing approvals for myelofibrosis in the US, EU, UK and Japan.

(PRESS RELEASE) LONDON, 12-Jun-2026 — /EuropaWire/ — GSK has announced that momelotinib, a JAK inhibitor with a differentiated mechanism of action, has received orphan drug designations from both the US Food and Drug Administration and the European Medicines Agency for the treatment of VEXAS syndrome.

VEXAS, short for Vacuoles, E1 enzyme, X-linked, Autoinflammatory, Somatic syndrome, is a rare and life-threatening haemato-inflammatory condition. It is a clonal myeloid disorder with both rheumatologic and haematologic clinical features, and is associated with severe symptoms, disease progression and poor prognosis.

The condition has a reported five-year mortality rate of 30% to 40%, and there are currently no approved treatment options. Diagnosis is confirmed through genetic testing for mutations in the UBA1 gene. Because UBA1 is located on the X chromosome and the mutation is somatic, VEXAS syndrome predominantly affects men over the age of 50.

The orphan drug designations support development and regulatory evaluation for medicines that may treat or prevent rare disorders. GSK said the designations for momelotinib were supported by retrospective case studies suggesting that JAK inhibitors may provide a therapeutic option for VEXAS syndrome, as well as evidence from a case report indicating potential clinical benefit from momelotinib treatment.

That case report showed improvements in symptoms, VEXAS-related inflammation and haematological manifestations. GSK is now advancing clinical development through the planned phase II/III ATLAS trial, which will evaluate the efficacy and safety of momelotinib in patients with VEXAS syndrome and support planned global regulatory submissions.

The ATLAS study design is being presented at the 2026 European Hematology Association Congress, taking place from June 11 to 14. The trial forms part of GSK’s broader development programme for momelotinib across multiple haematological conditions.

Momelotinib, marketed as Ojjaara in the US and Omjjara in other markets, is already approved in the United States for adults with intermediate- or high-risk myelofibrosis and anaemia. It is also approved in the European Union and the United Kingdom for adults with myelofibrosis who have disease-related splenomegaly or symptoms and moderate to severe anaemia, and in Japan for the treatment of myelofibrosis.

Momelotinib acts through inhibition of three key signalling pathways: Janus kinase 1, Janus kinase 2 and activin A receptor type I. Inhibition of JAK1 and JAK2 may help improve constitutional symptoms and splenomegaly, while inhibition of ACVR1 can reduce circulating hepcidin levels, potentially contributing to anaemia-related benefit.

VEXAS syndrome is characterised by a broad range of inflammatory manifestations, including prolonged fever, weight loss, uveitis, relapsing chondritis, neutrophilic dermatosis, vasculitis and lung involvement. Patients may also develop haematologic complications such as macrocytic anaemia, thrombocytopenia and progressive bone marrow failure, which can evolve into haematologic malignancy.

The orphan drug designations in the US and EU mark an important step in GSK’s efforts to explore momelotinib’s potential in an area of high unmet medical need. With no approved therapies currently available for VEXAS syndrome, the ATLAS trial will be central to assessing whether momelotinib can provide a new treatment pathway for patients living with this rare and severe disorder.

About momelotinib

Momelotinib has a differentiated mechanism of action, with inhibitory ability along three key signalling pathways: Janus kinase (JAK) 1, JAK2, and activin A receptor, type I (ACVR1).4,5,6,7 Inhibition of JAK1 and JAK2 may improve constitutional symptoms and splenomegaly.4,5,7 Additionally, inhibition of ACVR1 leads to a decrease in circulating hepcidin levels, potentially contributing to anaemia-related benefit.4,5,6,7

The EU product information is available at: OMJJARA-EPAR-PRODUCT-INFORMATION_EN.PDF

The US product information is available at: OJJAARA-PI-PIL.PDF

About VEXAS syndrome

VEXAS syndrome is a recently classified clonal myeloid disorder with rheumatologic and haematologic clinical features. It is a highly symptomatic, severe, progressive condition with a poor prognosis and a 5-year mortality rate of 30-40%.1 The syndrome is characterised by a broad spectrum of inflammatory manifestations such as prolonged fever, weight loss, uveitis, relapsing chondritis, neutrophilic dermatosis, vasculitis and lung involvement.8,9,10,11,12,13 Additionally, patients often present with haematologic complications, including macrocytic anaemia, thrombocytopenia and progressive bone marrow failure, which can evolve to haematologic malignancy.8 Diagnosis is confirmed by genetic testing for the UBA1 gene mutation.14 As UBA1 is located on chromosome X and the mutation is somatic, VEXAS syndrome predominantly affects men aged over 50 years. There are currently no approved treatments for VEXAS syndrome.14

About GSK

GSK is a global biopharma company with a purpose to unite science, technology, and talent to get ahead of disease together. Find out more at www.gsk.com.

Cautionary statement regarding forward-looking statements

GSK cautions investors that any forward-looking statements or projections made by GSK, including those made in this announcement, are subject to risks and uncertainties that may cause actual results to differ materially from those projected. Such factors include, but are not limited to, those described in the “Risk Factors” section in GSK’s Annual Report on Form 20-F for 2025, and GSK’s Q1 Results for 2026.

References

  1. Kötter I, Krusche, M. VEXAS syndrome: an adult-onset autoinflammatory disorder with underlying somatic mutation. Current Opinion in Rheumatology 2025;37(1):21-31.
  2. Kiem D, Leisch M, Toth I, et al. Momelotinib is effective in treatment for VEXAS syndrome: Two cases within the AGMT Austrian myeloid registry. Eur J Haematol. 2025;0:1-4.
  3. ClinicalTrials.gov. National Library of Medicine (US). Identifier NCT07569081, A Study Evaluating the Efficacy and Safety of Momelotinib in Participants With Vacuoles, E1-enzyme, X-linked, Autoinflammatory, Somatic (VEXAS) Syndrome (ATLAS). Available at: https://clinicaltrials.gov/study/NCT07569081.
  4. Chifotides, HT, Bose, P, Verstovsek, S. Momelotinib: an emerging treatment for myelofibrosis patients with anemia. J Hematol Oncol. 2022;15(7):1-18.
  5. Verstovsek S, et al. MOMENTUM: momelotinib vs danazol in patients with myelofibrosis previously treated with JAKi who are symptomatic and anemic. Future Oncol. 2021;17(12):1449-1458.
  6. Asshoff M, et al. Momelotinib inhibits ACVR1/ALK2, decreases hepcidin production, and ameliorates anemia of chronic disease in rodents. Blood. 2017;129(13):1823-1830.
  7. Oh S, et al. ACVR1/JAK1/JAK2 inhibitor momelotinib reverses transfusion dependency and suppresses hepcidin in myelofibrosis phase 2 trial. Blood Adv. 2020;4(18):4282-4291.
  8. Barba T, Jamilloux Y, Durel CA, et al. VEXAS syndrome in a woman. Rheumatology (Oxford) 2021;60:e402-3.
  9. Ferrada MA, Sikora KA, Luo Y, et al. Somatic mutations in UBA1 define a distinct subset of relapsing polychondritis patients with VEXAS. Arthritis Rheumatol. 2021;73:1886-9.
  10. Georgin-Lavialle S, Terrier B, Guedon AF, et al. Further characterization of clinical and laboratory features in VEXAS syndrome: large-scale analysis of a multicentre case series of 116 French patients. Br J Dermatol. 2022;186:564-74
  11. Borie R, Debray MP, Guedon AF, et al. Pleuropulmonary Manifestations of Vacuoles, E1 Enzyme, X-Linked, Autoinflammatory, Somatic (VEXAS) Syndrome. Chest 2023;163:575-85.
  12. Sakuma M, Blombery P, Meggendorfer M, et al. Novel causative variants of VEXAS in UBA1 detected through whole genome transcriptome sequencing in a large cohort of hematological malignancies. Leukemia. 2023:1-12.
  13. Grayson PC, Patel BA, Young NS. VEXAS syndrome. Blood. 2021;137(26):3591-4.
  14. Mekinian AM, Georgin‐Lavaille S, Ferrada MA, et al. American College of Rheumatology Guidance Statement for Diagnosis and Management of VEXAS Developed by the International VEXAS Working Group Expert Panel. Arthritis Rheumatol. 2025 Aug 11. doi: 10.1002/art.43287.

Media Contact:

Email: corporate.media@gsk.com
Phone: +44 (0)20 8047 5502

SOURCE: GlaxoSmithKline plc

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