Chronic Intermittent Administration of HIF Prolyl Hydroxylase Inhibitor Significantly Induces Erythropoietin and Increases Total Hemoglobin in Normal Rhesus Macaques.

Introduction: Injectable recombinant erythropoietin (rHuEPO) is used in many clinical disorders of anemia. Prior attempts at EPO induction by gene transfer strategies were problematic rendering them less attractive. Hypoxia inducible factor (HIF) is important in mediating EPO expression and erythropoiesis. Under normoxic conditions, HIF-alpha protein is usually undetectable due to rapid inactivation by oxygen-dependent HIF prolyl hydroxylases (HIF-PH). In hypoxic conditions or with HIF-PH inhibitors, HIF-alpha protein levels are increased and maintained due to reduced activity of HIF-PH. Upon stabilization HIF-alpha is transported to the nucleus to increase the expression of EPO, aminolevulinic acid synthase (ALAS), iron-transport proteins, nitric oxide synthase, and others. FG-2216 is an orally active HIF-PH inhibitor that induces EPO expression and erythropoiesis in vitro and in vivo, and improves iron bioavaliability by increasing iron mobilization from intestinal and macrophage stores and by decreasing hepcidin expression. Here we report on the pharmacokinetics and pharmacodynamics of FG-2216 to induce EPO expression and erythropoiesis in non-human primates with chronic intermittent oral dosing.

Methods: FG-2216 was obtained from FibroGen, Inc. FG-2216 was given to rhesus macaques (4-7 yrs old) by oral gavage. Drug and EPO levels were measured at 0,2,4,8,10,24,48, and 72 hours following a single dose of 40 or 60mg/kg. 40 or 60mg/kg of drug was then given twice a week to 5 male animals for 3–6 months. After 6–8 weeks of twice weekly dosing at 60mg/kg, weekly 15–20% weight per volume phlebotomy was introduced for 6–8 weeks to simulate chronic anemia while drug dosing was continued. Weekly weights, complete blood counts, and metabolic profiles were obtained to assess efficacy and safety. Two male animals received vehicle control.

Results: FG-2216 is rapidly absorbed and has excellent oral bioavailability, with peak plasma drug concentration between 1–2 hours and a half-life of 7–8 hours. The pharmacokinetic curves were dose-proportional and predictable. After 6–8 weeks of 2 doses per week, all animals tolerated the drug without significant side effects, and animal weights were stable with no changes in serum electrolytes, hepatic, or renal parameters. Peak plasma EPO increased from a baseline of <20 to 132 and 1950 mIU/ml after 40 and 60 mg/kg doses, respectively. There were transient 2-3 fold increases in reticulocytes. All treated animals demonstrated an increase in total hemoglobin: 11.95 +/− 0.33 g/dL (baseline), 13.17 +/− 0.32 (40mg/kg), and 14.58 +/− 0.64 (60mg/kg). Absolute hemoglobin increases ranged from 0.66 to 1.8 (40mg/kg) and 0.97 to 4.04 (60mg/kg) g/dL. When phlebotomy was introduced with continued FG-2216 dosing, treated animals maintained their hemoglobin, 14.03 +/− 0.06 g/dL, while control animals had their hemoglobin reduced to 11.54 +/− 0.09g/dL.

Conclusion: FG-2216 is an orally bioavailable HIF-PH inhibitor that is well tolerated and a potent inducer of EPO, with greater than 50-fold increases in EPO above baseline with a 60mg/kg dose. When administered orally twice a week, FG-2216 significantly increases total hemoglobin in normal rhesus macaques. Under the stress of weekly phlebotomy, FG-2216 maintained the hemoglobin of treated animals in the normal range, averaging 2.5 g/dL higher than animals receiving placebo. These results have broad clinical implications.