Rigel Pharmaceuticals has enrolled the first participant in the dose expansion segment of its Phase Ib trial assessing R289 for relapsed or refractory (R/R) lower-risk myelodysplastic syndrome (MDS).
R289 is a selective and potent dual inhibitor of interleukin receptor-associated kinases 1 and 4 (IRAK1/4).
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Rigel chief medical officer Lisa Rojkjaer said: “Today marks an important step in the evaluation of R289 for the treatment of patients with transfusion dependent lower-risk MDS, a disease with a persistent unmet need despite the availability of approved agents.
“In the dose expansion phase of this study, patients with transfusion dependent R/R lower-risk MDS will be randomised to receive a 500mg R289 dose either once or twice daily.
“The outcome of this phase of the study will be the selection of the recommended Phase II dose of R289 for future clinical studies. We remain grateful to our investigators for their continued support of our programme.”
The open-label Phase Ib trial is designed to assess the pharmacokinetics, safety, tolerability and preliminary efficacy in participants with MDS.
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By GlobalDataOnce the dose has been determined, the company will assess an exploratory group of participants with lower-risk MDS, who are ineligible for erythropoiesis-stimulating agents, at the recommended Phase II dose.
Rigel completed subject enrolment for the dose escalation segment in July 2025 and expects to share updated data later this year.
R289, a prodrug of R835, previously received orphan drug designation to treat MDS, as well as fast-track designation for previously treated, transfusion-dependent lower-risk MDS, from the US Food and Drug Administration.
In January 2025, Rigel enrolled the first subject in a Phase I trial of its oral spleen tyrosine kinase inhibitor, fostamatinib, for sickle cell disease. The trial is designed to assess the tolerability and safety of the therapy’s escalating doses.
