A Monoclonal Antibody Targeting ALK2 As a Potential Therapeutic Agent for Anemia of Inflammation

Background: Iron homeostasis is primarily regulated by hepcidin, a hormone predominantly expressed in the liver. Hepcidin activates the degradation of the transmembrane iron exporter ferroportin, thereby downregulating the release of iron from cells. Hepcidin expression is, at least partly, regulated in response to signaling of the type I TGF-β receptor ALK2, via SMAD2/3 phosphorylation. IL-6, which is commonly elevated in chronic kidney disease (CKD) and other inflammatory conditions, upregulates hepcidin expression and reduces serum iron bioavailability. As a result, chronic inflammatory conditions are often accompanied by secondary anemia of inflammation (AI).

We have previously demonstrated that ALK2 inhibition suppressed hepcidin expression in rodents, monkeys and healthy humans. We further described that administration of a selective small molecule ALK2 kinase inhibitor (KTI-2338) reversed changes in hepcidin and iron in a mouse model of CKD, supporting the potential benefit of ALK2 inhibition in AI. Another approach to targeting ALK2 signaling is use of a neutralizing antibody. KTI-018 is a neutralizing ALK2 antibody with high affinity and selectivity for ALK2. This biologic has been demonstrated to reduce serum hepcidin and increase serum iron in healthy non-human primates.

Aims: To further elucidate the specific contribution of ALK2 signaling as a driver in AI, and to determine the therapeutic potential of the antibody in this type of anemia, we assessed the effect of KTI-018 in the CKD mouse model.

Methods: The study was conducted with 6-week-old male C57Bl/6 mice. Mice in the CKD cohort (CKD) were treated with once daily oral administration of adenine, a compound that metabolizes to 2,8-dihydroxyadenine, forming crystals in the proximal tubular epithelia and causing inflammation and fibrosis in the kidneys. Mice in the control cohort (healthy) received once daily oral administration of vehicle.

Upon confirmation of disease, the CKD cohort was subdivided into two groups. The treatment group received twice weekly intraperitoneal treatment with KTI-018 (CKD-KTI-018), and the control group received tris-buffered saline (CKD-TBS). Healthy mice received TBS only. All mice were maintained on their assigned daily adenine or vehicle regimen. At day 53, the study was terminated and hematologic parameters, serum hepcidin, iron, and IL-6 levels were assessed.

Results: After 42 days of adenine or vehicle administration, serum hepcidin, serum iron, and hematologic parameters were assessed in representative cohorts of CKD-TBS and healthy mice. The CKD-TBS cohort experienced changes associated with anemia of inflammation as compared to the healthy mice, including increased hepcidin, decreased serum iron, and decreased hematologic parameters. The differences between the healthy and CKD-TBS groups were maintained through the duration of the study.

At study termination, CKD-TBS mice had increased serum IL-6 levels (218%), elevated serum hepcidin (149%), and reduced serum iron (-30%) as compared to the healthy mice. Laboratory findings characteristic of anemia were present in the CKD-TBS group, including decreased red blood cells (-6.1%), hemoglobin (-13.2%), and reticulocyte hemoglobin content (-9.3%) as compared to healthy mice.

In contrast, CKD-KTI-018 mice had decreased serum hepcidin (-25%) and increased serum iron (59%) as compared to CKD-TBS mice. This restoration of serum iron corresponded to improvements in red blood cells, hemoglobin, and reticulocyte hemoglobin content, which were increased by 7.6%, 9.6%, and 6.7%, respectively, in the CKD-KTI-018 mice as compared to the CKD-TBS mice. These results demonstrate that, by decreasing serum hepcidin, KTI-018 increased the bioavailability of iron, which led to the restoration of hematologic parameters and appeared to reverse AI in mice.

Discussion: In this study, a neutralizing ALK2 antibody decreased serum hepcidin, increased serum iron and consequently reversed AI in a mouse model of CKD. These results support the role of ALK2 signaling in AI and suggest that inhibition of ALK2 may be a potential treatment approach for anemia resulting from CKD and other chronic inflammatory diseases. Future studies will explore if ALK2 inhibition may prevent or treat progression of CKD itself, and the role that ALK2 inhibition may play in other chronic inflammatory conditions associated with elevated hepcidin.