Rigel Pharmaceuticals presented updated safety and efficacy data for its oral prodrug R289, a dual IRAK1/4 inhibitor, during an oral session at the 67th American Society of Hematology (ASH) Annual Meeting in Orlando. The presentation, led by Dr. Guillermo Garcia‑Manero, reported that the dose‑escalation phase of the Phase 1b study was completed in July 2025 and that the dose‑expansion phase began in October 2025 with up to 40 patients randomized to 500 mg once or twice daily.
The data, drawn from 33 patients enrolled as of October 28, 2025, show a 33 % red‑blood‑cell transfusion‑independence (RBC‑TI) rate in transfusion‑dependent patients receiving ≥500 mg once daily and a 40 % RBC‑TI rate in the 500 mg twice‑daily cohort. Common Grade 1/2 treatment‑emergent adverse events included diarrhea, constipation, and fatigue, confirming the favorable safety profile that has been maintained throughout the study.
R289’s performance is particularly noteworthy given the limited treatment options for relapsed or refractory lower‑risk myelodysplastic syndrome (LR‑MDS). The drug has received FDA Orphan Drug and Fast‑Track designations, underscoring the unmet medical need and the potential for accelerated development. Early efficacy signals in a heavily pre‑treated population suggest that R289 could become a first‑in‑class therapy for LR‑MDS patients who remain transfusion‑dependent.
Rigel’s strong Q3 2025 financial results—driven by robust sales of its commercial products TAVALISSE, GAVRETO, and REZLIDHIA—provide the financial foundation to support continued investment in R289. The company’s raised full‑year guidance reflects confidence in its commercial pipeline and the ability to fund future clinical milestones.
Chief Medical Officer Lisa Rojkjaer emphasized that the ongoing dose‑expansion data will inform the recommended Phase 2 dose, which is slated to begin in the second half of 2026. She noted that the preliminary efficacy and safety outcomes reinforce the company’s strategy of developing targeted small‑molecule inhibitors for hematologic disorders and position R289 as a key asset in Rigel’s pipeline.
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