P1488: COMBINING ALK2 INHIBITION WITH A MODIFIED ACTIVIN RECEPTOR IIA LIGAND TRAP PROVIDED ADDITIVE BENEFITS IN RESOLVING ANEMIA IN A MOUSE MODEL OF ANEMIA OF INFLAMMATION (2023)

Topic: 29. Iron metabolism, deficiency and overload Background: Patients with chronic inflammation, such as chronic kidney disease (CKD), often develop anemia of inflammation (AI). Inflammatory cytokines induce hepcidin to reduce iron availability for erythropoiesis. Inflammation also directly impairs erythropoiesis by suppressing erythroid progenitor differentiation, potentially via increased TGF-b superfamily signaling. We previously showed that KTI-m216 (m216), an investigational ALK2 neutralizing antibody, lowered serum hepcidin to increase serum iron and improve hemoglobin (Hb) in CKD mice and that RKER-050, an investigational modified activin receptor IIA ligand trap, improved ineffective erythropoiesis in MDS mice. Here, we sought to evaluate the combined advantage of increasing iron availability and promoting erythropoiesis to treat AI. Aims: To evaluate the m216 pharmacokinetic and pharmacodynamic (PKPD) relationship, establish its mechanism of action in alleviating anemia in CKD mice, and explore the therapeutic potential of combining m216-mediated hepcidin suppression with increased erythropoiesis by RKER-050 in AI. Methods: PKPD was examined in C57BL/6 male mice receiving a single subcutaneous (SC) dose of 3mg/kg m216 or isotype control. To induce CKD, mice were fed a control or 0.2% adenine diet with 40ppm iron (Ade40) for 5 wk. CKD mice were SC dosed with 3mg/kg m216 or isotype biweekly for 4 wk while continuing the Ade40 diet or switching to a 0.2% adenine with 3ppm low iron diet (Ade3). We also evaluated CKD mice on Ade40 diet receiving biweekly 3mg/kg isotype or m216 in combination with weekly PBS or 7.5mg/kg RKER-050 intraperitoneally for 4 wk. Results: Serum m216 was detected as early as 3h (8.4 µg/mL), reached Cmax at 24-48h (~25 µg/mL) and was undetectable by 7d. Serum hepcidin was significantly decreased between 3h and 72h, returned to control level at 96h, and rebounded higher than controls at 7d, whereas serum iron was increased at 24h, sustained up to 96h, and returned to control level at 7d. CKD mice developed AI features, including increased serum interleukin-6 and serum hepcidin, tissue iron retention, hypoferremia, and anemia. Serum hepcidin and spleen iron were reduced by >95% and 68%, respectively, in m216-treated mice on both Ade diets compared to mice given isotype control, and transferrin saturation (TS) increased by 65% in m216-treated mice compared to isotype control on Ade40 diet, with a similar trend in mice on Ade3 diet. Compared to CKD control on the same diet, m216-treated mice had similar improvements in Hb (+2.2 g/dL), hematocrit (+5.4%), and red blood cells (RBC;+1.1 M/µl), suggesting that dietary iron contribution is negligible in supporting erythropoiesis in CKD mice. Mice receiving m216 alone (m216+PBS) or a combined m216 and RKER-050 (combo) had a similar reduction in serum hepcidin (>91%) and spleen iron (>65%) and a similar increase in TS (>1.7-fold) when compared to CKD mice receiving isotype and PBS. Hb (g/dL) increased from 8.0 in CKD controls to 11.4 in 216+PBS and further improved to 13.5 in mice given the combo. RBC (M/µl) was 6.4 in CKD controls, increased to 8.3 in m216+PBS and to 9.8 in mice treated with combo. Importantly, Hb and RBC levels in mice receiving combo were similar to levels in non-CKD controls. Summary/Conclusion: KTI-m216 at 3mg/kg reduced hepcidin for 72h, and liberated spleen iron from the recycling pathway to increase iron availability, resulting in improved iron-restricted erythropoiesis in CKD mice. Combining the iron mobilization properties of KTI-m216 with the stimulation of erythropoiesis from RKER-050 increased the potential to resolve anemia in this AI model. Keywords: Erythropoieisis, Anemia, Hepcidin, Iron metabolism