GSK plc (LON:GSK) has announced that momelotinib has received Orphan Drug Designation from the US Food and Drug Administration and the European Medicines Agency for the treatment of VEXAS syndrome.
GSK said VEXAS, which stands for Vacuoles, E1 enzyme, X-linked, Autoinflammatory, Somatic syndrome, is a clonal myeloid disorder with rheumatologic and haematologic features. The company said it is a highly symptomatic progressive condition with a poor prognosis and a five-year mortality rate of 30% to 40%, with no approved treatment options currently available.
The designations were supported by retrospective case studies suggesting JAK inhibitors may be an effective treatment option for VEXAS syndrome, together with a case report indicating potential clinical benefit from momelotinib, including improvements in symptoms and VEXAS-related inflammation and haematological manifestations.
GSK said the planned phase II/III ATLAS trial will evaluate momelotinib’s efficacy and safety in VEXAS syndrome and will support planned global regulatory submissions. The study design is due to be presented at the 2026 European Haematology Association Congress, taking place from 11 to 14 June.
Momelotinib, marketed as Ojjaara and Omjjara, is already approved in the US for intermediate- or high-risk myelofibrosis in adults with anaemia. It is also approved in the EU and UK for myelofibrosis with disease-related splenomegaly or symptoms in adults with moderate to severe anaemia, and in Japan for myelofibrosis.
The company said momelotinib has a differentiated mechanism of action, inhibiting JAK1, JAK2 and ACVR1. Inhibition of JAK1 and JAK2 may improve constitutional symptoms and splenomegaly, while ACVR1 inhibition reduces circulating hepcidin levels and may help anaemia.
