Effects of Ker-050 on Iron Metabolism: Exploratory Analyses from an Ongoing Phase 2 Study in Patients with Myelodysplastic Syndromes

Background: Iron overload (IO) is an important clinical consequence of transfusion-dependent myelodysplastic syndromes (MDS). For patients with high transfusion burden (HTB), limited treatment options are available to effectively treat anemia and reduce transfusion dependence. Transfusion dependence is an independent predictor of poor prognosis in MDS. It is associated with IO and elevated ferritin, a marker of intracellular iron storage that also predicts poor prognosis in MDS. When adjusting for transfusion burden, each 500 µg/L increase in ferritin above 1000 µg/L is associated with a 30% greater risk of death (Malcovati et al. 2006). IO also disrupts osteoprogenitors and erythroid precursors within the osteohematopoietic niche, leading to abnormal bone turnover and ineffective erythropoiesis (Bulycheva 2015). While iron chelators have shown some efficacy in managing IO, they introduce toxicities and have little effect on transfusion burden. Unmet need remains for treatments that effectively address anemia, IO, and reduce transfusion dependence in patients with MDS, especially those with HTB.

KER-050 is designed to alter signaling of TGF-β superfamily ligands, restoring balance to the osteohematopoietic niche, and promoting differentiation of erythroid and megakaryocytic precursors. It is a modified activin receptor type IIA ligand trap that inhibits TGF-β superfamily ligands, including activins A and B and growth and differentiation factors (GDFs) 8 and 11. To date, clinical data indicate that KER-050 induces sustained increases in reticulocytes and hemoglobin. Preliminary findings also show potential for KER-050 to induce erythroid response and reduce transfusion burden in patients with MDS, including those with HTB (Tan et al., 2022). KER-050 may also impact iron metabolism and this presentation explores the effects of KER-050 on indices of IO.

Methods: This Phase 2 study is evaluating KER-050 in participants with very low- to intermediate-risk MDS. Data presented are from Part 1 Dose Escalation which included 16 weeks of KER-050 treatment across 5 cohorts (0.75 to 5 mg/kg). Iron chelator therapy was permitted at the discretion of the investigator provided patients had been on a stable dose for 8 weeks prior to C1D1. Markers of IO and hematopoiesis were assessed as exploratory endpoints over the 16-week treatment period. Analyses presented evaluate the effect of KER-050 on these markers. Baseline markers of bone turnover were also assessed.

Results: A total of 31 patients were enrolled in Part 1 Dose Escalation; 26 were transfusion dependent, 18 with HTB (≥ 4 RBC units in 8 weeks prior to day 1). Seven HTB patients (38.9%) received iron chelator therapy. Baseline differences were noted in measures of iron status, erythropoiesis and bone turnover for non-transfused (NT), low transfusion burden (LTB), and HTB patients (Table 1). HTB patients had the highest baseline serum iron and ferritin levels. Preliminary findings indicate that KER-050 treatment was associated with decreases in serum ferritin for patients both with and without iron chelator therapy. Patients achieving transfusion independence (TI) experienced a 39.5% reduction (mean change: -619.4 ng/ml, range: -2118.4 to +243 ng/mL) in serum ferritin at Week 12 that was generally sustained at Week 16 and 20 (Figure 1). Similarly, over the same time period, serum iron and transferrin saturation (TSAT) decreased by 4.03 µmol/L (8.38%) and 5.3%, respectively, in patients achieving TI. Soluble transferrin receptor (sTfR) increased by 32.2% and remained elevated at subsequent visits.

Summary: Preliminary data from the 16-week Dose Escalation in this ongoing phase 2 study reveal differences in baseline iron biomarkers indicative of increasing iron overload with increasing transfusion burden. While nearly half of HTB patients received iron chelator therapy, this group had markedly elevated ferritin compared to NT and LTB patients at baseline. KER-050 treatment was associated with reductions in serum ferritin, irrespective of the use of iron chelation. Patients achieving TI experienced decreases in ferritin, iron and TSAT concurrent with increases in sTfR that were generally maintained through follow-up. The data suggest that, in addition to improving hematopoiesis and transfusion burden in MDS patients, KER-050 may reduce iron overload, a serious clinical complication impacting the survival of these patients.

Chee:Otsuka: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Ross:BMS: Honoraria; Celgene: Research Funding; Keros: Consultancy; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees. Wight:Janssen: Honoraria, Other: Travel Reimbursement; AbbVie: Honoraria, Other: Travel Reimbursement. Ross:Kadmon: Ended employment in the past 24 months; Keros Therapeutics: Current Employment. Feng:Keros Therapeutics: Current Employment; Biogen: Current equity holder in publicly-traded company, Ended employment in the past 24 months. Jiang:Keros Therapeutics: Current Employment; Repare Therapeutics: Ended employment in the past 24 months; Alkermes, Inc.: Current equity holder in publicly-traded company, Ended employment in the past 24 months. Natarajan:Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Graham:Keros Therapeutics: Current Employment; Alkermes, Inc.: Current equity holder in publicly-traded company, Ended employment in the past 24 months. Rovaldi:Keros Therapeutics: Current Employment. Cooper:Anokion Therapeutics: Current equity holder in private company, Ended employment in the past 24 months; Kadmon Corporation: Ended employment in the past 24 months; Keros Therapeutics: Current Employment. Salstrom:Homology Medicines, Inc.: Current equity holder in publicly-traded company, Ended employment in the past 24 months; Keros Therapeutics: Current Employment.