Study of R289 in Participants With Lower-risk Myelodysplastic Syndromes (LR MDS)

Inclusion Criteria:

Participant must be ≥ 18 years of age at the time of signing the informed consent.
Must have definitive diagnosis of MDS with very low, low, or intermediate-1 risk (International Prognostic Scoring System (IPSS)-R ≤ 3.5) and ≤5% bone marrow myeloblasts.
Must be relapsed, refractory/resistant, intolerant, or have inadequate response to therapies with known clinical benefits for MDS, such as TPOs, EPOs, luspatercept, and HMAs(i.e., azacytidine or decitabine). Participants with del (5q) must have failed prior lenalidomide therapy.

Must be blood transfusion dependent and meet at least one of the disease-related criteria for RBC transfusion, or platelet count within 8 weeks prior to initial administration of study treatment:

Symptomatic anemia untransfused with hemoglobin < 9.0 g/dL within 8 weeks of registration or red blood cell (RBC) transfusion dependent defined as receiving ≥ 2 units of packed red blood cells (PRBCs) within 8 weeks in the preceding 16 weeks for a hemoglobin <9.0 g/dL.
Clinically relevant thrombocytopenia (platelet counts of <100 × 109/L in at least 2 blood counts prior to study treatment and transfusion dependence).

All participants must have documented marrow iron stores. If marrow iron stain is not available, the transferrin saturation must be >20% or a serum ferritin > 100ng/100mL

Must have Eastern Cooperative Oncology Group (ECOG) performance status 0 to 2 at screening.

Must have adequate organ function, defined as:

Hepatic function:

aspartate amino transferase (AST) or alanine aminotransferase (ALT) ≤ 1.5 × upper limit of normal (ULN)
total bilirubin ≤ 1.5 × ULN
Renal function defined as creatinine clearance > 60 mL/min (using Cockcroft-Gault), or blood creatine < 1.5 mg/dL

Exclusion Criteria:

Prior treatment for MDS (i.e., TPOs, EPOs, luspatercept, HMAs) concluded < 4 weeks prior to study treatment
Clinically significant anemia resulting from iron, B12 or folate deficiencies, autoimmune or hereditary hemolysis, or GI bleeding.
MDS secondary to treatment with radiotherapy, chemotherapy, and/or immunotherapy for malignant or autoimmune diseases.
Diagnosis of chronic myelomonocytic leukemia.
History of uncontrolled seizures.
Uncontrolled bacterial or viral infection (i.e., documented HIV, hepatitis B or hepatitis C).

History of an active malignancy within the past 2 years prior to study entry, with the exception of:

Adequately treated in situ carcinoma of the cervix uteri
Adequately treated basal cell carcinoma or localized squamous cell carcinoma of the skin, or
Any other malignancy with a life expectancy of more than 2 years
History of or active, clinically significant, cardiovascular, respiratory, GI, renal, hepatic, neurological, psychiatric, musculoskeletal, genitourinary, dermatological, or other disorder that, in the Investigator's opinion, could affect the conduct of the study or the absorption, metabolism or excretion of the study treatment.
Prior history of bone marrow transplantation.
Marked baseline prolongation of QT/QTc interval (e.g., repeated demonstration of a QTc interval > 480 milliseconds [msec]) (Common Terminology Criteria for Adverse Events [CTCAE] Grade 1) using Fridericia's QT correction formula.
History of additional risk factors for TdP (e.g., symptomatic heart failure with left ventricular ejection fraction [LVEF] <40%, hypokalemia, family history of Long QT Syndrome).
Receiving any other concurrent chemotherapy, radiotherapy, or immunotherapy (within 2 weeks of initiating study treatment), or the toxicity of the relevant prior treatment has not been resolved yet.
Use of concomitant medications that prolong the QT/QTc interval during study treatment
Use of concomitant medications that are strong CYP3A or CYP2B6 inhibitors or inducers during study treatment