Prnewswire·2025-12-07 14:30Core Insights - Rigel Pharmaceuticals announced updated data from its ongoing Phase 1b study of R289, an oral prodrug of R835, targeting relapsed or refractory lower-risk myelodysplastic syndrome (MDS) [1][2] - The study results were presented at the 67th American Society of Hematology Annual Meeting, highlighting the potential of R289 as a treatment option for patients with transfusion-dependent lower-risk MDS [1][2] Study Overview - The Phase 1b study is evaluating the safety, tolerability, pharmacokinetics, and preliminary efficacy of R289 in patients with relapsed or refractory lower-risk MDS [2] - Enrollment in the dose escalation phase was completed in July 2025, with the dose expansion phase starting in October 2025, involving up to 40 patients [2] Key Data Highlights - As of October 28, 2025, 33 patients were enrolled, with a median age of 75 and a median of 3 prior therapies [4] - R289 was generally well tolerated, with 33% of evaluable transfusion-dependent patients achieving durable red blood cell transfusion independence (RBC-TI) [3][4] - The most common treatment-emergent adverse events included diarrhea (30%), constipation (27%), and fatigue (27%) [4] Efficacy Results - Among evaluable transfusion-dependent patients, 6 out of 18 (33%) achieved RBC-TI lasting more than 8 weeks, with a median time to onset of 1.9 months [4] - Peak hemoglobin increases ranged from 2.9 to 6.1 g/dL compared to baseline in patients achieving RBC-TI [4] Regulatory Designations - R289 has received Orphan Drug designation and Fast Track designation from the FDA for the treatment of previously-treated transfusion-dependent lower-risk MDS [5]