Rigel Pharmaceuticals Inc. announced updated data from its ongoing Phase 1b clinical study evaluating R289, an oral prodrug of R835 and a dual IRAK1/4 inhibitor, in patients with relapsed or refractory lower-risk myelodysplastic syndrome (MDS). The results were presented at the 67th American Society of Hematology $(ASH)$ Annual Meeting and Exposition, held December 6-9, 2025. The study showed that R289 was generally well tolerated, and preliminary efficacy was observed at doses of 500 mg or higher. Of the evaluable transfusion-dependent patients receiving these doses, 33% (6 out of 18) achieved red blood cell transfusion independence, including 40% (2 out of 5) in the 500 mg twice daily group. Enrollment for the dose escalation phase was completed in July 2025, and the dose expansion phase is ongoing to determine the recommended Phase 2 dose. R289 has received Orphan Drug and Fast Track designations from the FDA for the treatment of lower-risk MDS.