Rigel Pharmaceuticals Reports Promising Phase 1b Results for R289 in Lower-Risk MDS Treatment

### Rigel Pharmaceuticals Advances in Treatment for Lower-Risk Myelodysplastic Syndromes

Rigel Pharmaceuticals, Inc., a biotechnology company specializing in hematologic disorders and cancer, reports encouraging preliminary findings from its ongoing Phase 1b study of R289, an oral prodrug of R835. The study focuses on patients with relapsed or refractory lower-risk myelodysplastic syndrome (MDS), a condition often characterized by ineffective blood cell production and requiring frequent transfusions. The results, shared by Dr. Guillermo Garcia-Manero at the 67th American Society of Hematology Annual Meeting, underline R289's potential to address a critical need for effective therapies in this challenging patient population.

In the study, R289 demonstrates a red blood cell transfusion independence (RBC-TI) rate of 33% among transfusion-dependent patients taking doses of 500 mg once daily or higher, with an even more promising 40% rate in those on a 500 mg twice-daily regimen. The trial enrolls 33 patients, primarily elderly individuals with a median age of 75, who have undergone an average of three prior treatment lines. This patient demographic poses significant challenges, as 76% have received prior therapy with luspatercept, and 61% exhibit a high transfusion burden. Such results suggest that R289 may provide a much-needed option for patients who have limited therapeutic alternatives.

The safety profile of R289 appears favorable, with the most frequently reported treatment-emergent adverse events being diarrhea (30%) and fatigue (27%). Rigel's Chief Medical Officer, Dr. Lisa Rojkjaer, highlights the urgent need for new treatments in this area and expresses optimism about R289's role in improving patient outcomes. The study's median treatment duration of 5.5 months indicates sustained engagement among the participants, reflecting the potential of R289 to offer long-term benefits in a population that has been extensively pre-treated. The trial is set to complete its dose expansion phase by the second half of 2026, with plans to randomize up to 40 patients to determine the recommended Phase 2 dose.

In addition to R289's promising results, Rigel Pharmaceuticals continues to focus on developing innovative therapies for hematologic conditions. The company’s commitment to addressing unmet medical needs in this space is evident as it advances its clinical programs. As the healthcare landscape evolves, Rigel's research endeavors position the company to potentially play a significant role in transforming treatment paradigms for lower-risk MDS patients.