Rigel's R289 Shows Promising RBC Transfusion Independence In Phase 1b Trial In Lower-Risk MDS

(RTTNews) - Rigel Pharmaceuticals, Inc. (RIGL), a commercial-stage biotechnology company focused on hematologic disorders and cancer, announced encouraging updated data from its ongoing Phase 1b study of drug candidate R289 in patients with relapsed or refractory (R/R) lower-risk myelodysplastic syndrome on Sunday.

Myelodysplastic syndrome (MDS) is a group of disorders caused by poorly formed or dysfunctional blood cells, leading to various health complications. Patients with myelodysplastic syndrome often experience anemia and thrombocytopenia, requiring extended periods of red blood cell or platelet transfusions to manage these symptoms.

The Phase 1b study of R289 includes two parts - dose escalation and dose expansion.

Enrollment in the dose escalation part of the study was completed this July.

According to the updated data from the study announced yesterday, R289 continues to be generally well tolerated and at doses of 500 mg or higher taken once daily (QD), preliminary efficacy was observed in elderly, heavily pre-treated lower-risk MDS patients.

Red blood cell transfusion independence (RBC-TI) was achieved by 33% (6/18) of evaluable transfusion-dependent patients receiving R289 at doses of 500 mg or more once daily (QD), including 40% (2 of 5) of those receiving the 500 mg twice-daily dose.

The data were presented in an oral session at the 67th American Society of Hematology (ASH) Annual Meeting and Exposition on December 7, 2025.

The first patient in the dose expansion part of the Phase 1b study of R289 was dosed this October. Up to 40 patients are expected to be randomized to either 500 mg once or twice daily to determine the recommended Phase 2 dose for future clinical trials.

Rigel looks forward to completing the dose-expansion phase of the study and anticipates selecting the recommended Phase 2 dose for future clinical studies in the second half of 2026.

On Friday, RIGL shares closed trading 3.25% higher at $48.92.