Rigel Pharmaceuticals' R289, a potent and selective dual inhibitor of IRAK1 and IRAK4, has received Fast Track designation from the U.S. Food and Drug Administration (FDA) for the treatment of patients with previously treated transfusion-dependent lower-risk myelodysplastic syndrome (MDS). This designation aims to expedite the development and review process for R289, which is currently being investigated in an ongoing Phase 1b clinical trial.
The Fast Track designation underscores the significant unmet need for effective therapies in this patient population, particularly the elderly who face progressive cytopenias, notably anemia, and have limited treatment options. According to Rigel, R289 targets inflammatory signaling, potentially improving the lives of those living with lower-risk MDS.
Clinical Trial Details
The ongoing Phase 1b trial (NCT05308264) is an open-label, single-arm, multicenter study. It includes a 3+3 dose escalation phase (up to 12 patients) and a dose expansion phase (up to 10 patients). The dose escalation phase will determine the maximum tolerated dose, starting with an initial oral dose of 250 mg R289 once daily, progressing to 500 mg once daily. Dose-limiting toxicities will be assessed at both doses for 28 days. Patients who do not experience dose-limiting toxicities will remain on their respective dose level as long as they demonstrate clinical benefit without toxicity.
In the dose expansion phase, additional patients will be enrolled to receive the maximum tolerated dose previously determined. The primary endpoint is safety and tolerability. Secondary endpoints include preliminary efficacy, pharmacokinetics of R289, and changes from baseline in plasma and bone marrow biomarkers.
Mechanism of Action
R289, a prodrug of R835, has demonstrated the ability to block inflammatory cytokine production in response to toll-like receptor (TLR) and interleukin-1 receptor (IL-1R) family signaling in preclinical studies. TLRs and IL-1Rs play a critical role in the innate immune response, and dysregulation of these pathways can lead to various inflammatory conditions. Chronic stimulation of both receptor systems is thought to cause the pro-inflammatory environment in the bone marrow responsible for persistent cytopenias in lower-risk MDS patients.
Implications for Patients
The Fast Track designation may allow for more frequent interactions with the FDA during drug development and eligibility for Accelerated Approval and Priority Review. Raul Rodriguez, president and CEO of Rigel Pharmaceuticals, stated that by targeting inflammatory signaling, R289 has the potential to meaningfully improve the lives of those living with this disease.
