Increased Fetal Hemoglobin (HbF) levels reduce the symptoms of SCD and increase the lifespan of patients. Because the curative strategies of bone marrow transplantation and gene therapy technologies remain unavailable to large numbers of patients, the development of a safe and effective pharmacological therapy that increases HbF offers the greatest potential for disease intervention. Although hydroxyurea increases HbF, a substantial proportion of patients fail to demonstrate an adequate

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... . Pharmacological inhibitors of DNA methyltransferase (DNMT1) and LSD1, two epigenome-modifying enzymes associated with the multi-protein co-repressor complex recruited to the repressed γ-globin gene, are powerful in vivo inducers of HbF. Hematological side-effects of these inhibitors limit feasible clinical exposures. We evaluated if administering these drugs in combination could reduce the dose and/or time of exposure to any single agent to minimize adverse effects while achieving additive or synergistic increases in HbF. The DNMT1 inhibitor decitabine (0.5mg/kg/d) and the LSD1 inhibitor RN-1 (0.25mg/kg/d) administered in combination 2 days per week produced synergistic increases in F cells, F retics, and γ-globin mRNA in normal baboons. Large increases in HbF and F cells were observed in both normal, non-anemic and anemic (phlebotomized) baboons. Combinatorial therapy targeting epigenome-modifying enzymes could thus be a useful strategy for producing larger increases in HbF to modify SCD clinical course.