Oral Administration of Low-Dose Decitabine and Tetrahydrouridine In Combination Increases Fetal Hemoglobin to Therapeutic Levels In the Absence of Cytotoxicity and Reduces Inter-Individual Drug Bioavailability In Baboons

Abstract 2147

Increased fetal hemoglobin (HbF) levels alleviate the symptoms and improve survival of patients with sickle cell disease and β-thalassemia. Because therapeutic options remain limited for a large group of patients refractory to hydroxyurea (HU) therapy, alternative therapeutic agents to increase HbF are urgently needed. Decitabine (DAC) increases HbF to therapeutic levels in sickle cell disease patients refractory to HU. Oral administration of DAC would ease administration, increase compliance, and lower costs. Previous studies showed that oral administration of high doses of DAC increased HbF levels in baboons (Lavelle et al Am J Hematol 82:981, 2007). The oral bioavailability of DAC is limited by the degradative action of cytidine deaminase (CDA), and patients with CDA polymorphisms associated with reduced CDA activity may exhibit increased risk of cytotocity. We hypothesized that oral administration of low-dose DAC in combination with the CDA inhibitor THU would improve the DAC concentration-time profile while avoiding high peak drug levels likely to cause DNA damage and cytotoxicity and reduce risks of cytotoxicity in patients with CDA polymorphisms. Pharmacokinetics (PK) analysis in six baboons following oral administration of high-dose DAC alone showed that a dose (10mg/kg) previously shown sufficient to induce maximal (62.3–72%) HbF levels in 3 of 5 baboons when administered daily for ten days was associated with a mean AUC value of 355min*ng/ml. PK analysis following administration of varying doses of DAC in combination with THU showed that this AUC of 355min*ng/ml was attained with a 0.5 mg/kg DAC dose administered orally in combination with THU. The effect of oral low-dose DAC in combination with THU on HbF was then evaluated in four baboons. Initially, a single baboon (7482) was treated at 0.5mg/kg/d 3X/week for 3 weeks followed by 2X/week for an additional 5 weeks. Three additional baboons (7484, 7472, and 7470) were treated with either 0.25 or 0.5mg/kg/d 2X/week for eight weeks. Results (Table 1) showed significant increases in HbF associated with modest decreases in ANC and increases in platelets in all animals.

Decreased DNA methylation in the 5' γ-globin gene region was observed in post-treatment BM samples by quantitative MassARRAY DNA methylation analysis. PK analysis showed that DAC bioavailability following oral administration of high-dose DAC alone differed 33 fold between 7470 and 7484 but only 1.3 fold following oral administration of low-dose DAC in combination with THU. Thus co-administration of low-dose DAC with THU reduced inter-individual variability of drug bioavailability and this was consistent with the similar HbF responses observed in these animals. Importantly, the ability of oral low dose DAC-THU to increase HbF to similar levels in the absence of cytotoxicity in two baboons differing in DAC bioavailability following oral administration of high-dose DAC alone predicts that oral low-dose DAC-THU in combination will reduce risks of cytotoxicity in patients with differences in DAC bioavailability due to CDA polymorphisms. These experiments have determined a dose and schedule of oral low-dose DAC in combination with THU that effectively increases HbF to therapeutic levels in the absence of cytotoxic effects in baboons and thus provide critical information important for the design of a future clinical trial of this drug combination in patients with sickle cell disease refractory to hydroxyurea therapy.