On December 10, 2025, Rigel Pharmaceuticals Inc (RIGL) disclosed clinical and regulatory updates for its investigational drug R289. The 8-K filing disclosed that 33 percent (6 out of 18) of evaluable transfusion-dependent patients with relapsed or refractory lower-risk myelodysplastic syndrome (MDS) achieved red blood cell transfusion independence (RBC-TI) at doses of 500 mg or higher once daily.

The data comes from the Phase 1b study of R289, a potential treatment for myelodysplastic syndromes. According to the filing, the U.S. Food and Drug Administration (FDA) granted both Orphan Drug designation and Fast Track designation for R289 in previously-treated transfusion-dependent lower-risk MDS. The company completed the dose escalation phase in July 2025 and began the dose expansion phase in October 2025.

Rigel Pharmaceuticals announced plans to conclude the dose expansion phase and select the recommended Phase 2 dose by the second half of 2026. Chief Medical Officer Lisa Rojkjaer commented on the potential of R289, stating that new therapies are needed for patients with transfusion dependent lower-risk MDS.

"New therapies are needed for patients with transfusion dependent lower-risk MDS. We're pleased to share these updated study results, which underscore the potential of R289 to become a treatment option for these patients." — Lisa Rojkjaer, Chief Medical Officer, Rigel Pharmaceuticals Inc

Guillermo Garcia-Manero, M.D., presented updated data from the Phase 1b study at the American Society of Hematology (ASH) Annual Meeting on October 28, 2025. The filing notes that the company faces risks and uncertainties associated with clinical trials, drug development, and potential adverse decisions by regulatory authorities regarding R289.

"We look forward to concluding the dose expansion phase of the study and anticipate selection of the recommended Phase 2 dose for future clinical studies in the second half of 2026." — Lisa Rojkjaer, Chief Medical Officer, Rigel Pharmaceuticals Inc