Characterization of INCB00928, a Potent and Selective ALK2 Inhibitor for the Treatment of Anemia

A significant population of patients with myelofibrosis (MF) develop anemia and either require red blood cell (RBC) transfusions or have an inadequate response to the currently available therapies and become transfusion-dependent. In patients with MF, elevated levels of serum hepcidin, a key iron regulatory hormone, is associated with increased dependence on RBC transfusions and reduced overall survival. Elevated hepcidin expression has also been observed to cause severe functional iron deficiency anemia and is central to the pathophysiology of anemia of chronic disease. Thus, to ensure proper maintenance of iron homeostasis, hepcidin levels are tightly regulated. Specifically, the production of hepcidin is controlled by the bone morphogenetic protein (BMP) type I receptor ACVR1, a gene that encodes the serine/threonine kinase ALK2. In preclinical models, knockdown or complete loss of ALK2 decreases hepcidin production resulting in elevated serum iron levels. In this study, we report characterization of INCB00928, a novel small molecule inhibitor of ALK2 for the treatment of anemia. INCB00928 was observed to have subnanomolar activity against ALK2 and selectivity over ALK1 and ALK3 in biochemical enzyme assays. In cell-based profiling studies, INCB00928 inhibited ALK2 potently and selectively over ALK1 and ALK3 as determined by the inhibition of ligand-induced SMAD pathway signaling. Importantly, in both an immortalized human liver cell line as well as primary human hepatocytes, INCB00928 inhibited BMP-induced production of hepcidin with nanomolar activity. INCB00928 was also observed to have suitable absorption, distribution, metabolism, and excretion properties to be dosed in in vivo rodent studies. In tumor- and inflammation-induced mouse models of anemia, INCB00928 improved RBC count, hemoglobin, and hematocrit levels while decreasing hepcidin levels in a dose-dependent manner. Additionally, consistent with the improved symptoms of anemia, pSMAD1/5 inhibition was observed in a dose-dependent manner in liver tissues collected from INCB00928-treated mice. In summary, INCB00928 is a potent, selective, and orally available small molecule inhibitor of ALK2, which significantly reduces the production of hepcidin in human liver cells, primary hepatocytes, and in rodent models of anemia. For the majority of patients with MF, the management of anemia remains an unmet need. The preclinical findings from this study suggest ALK2 kinase inhibition with INCB00928 may be a promising novel treatment to reduce the production of hepcidin and improve MF-related anemia in humans, thus warranting further investigation.