Development of KER-012, a modified ActRIIB ligand trap, for the treatment of pulmonary arterial hypertension

Abstract Background Pulmonary Arterial Hypertension (PAH) is a debilitating disorder characterized by elevated pulmonary vascular resistance (PVR) due to severe constriction obliteration of pulmonary vessels (Tielemans 2019). The pathology of PAH is driven by endothelial dysfunction and vascular remodeling that leads to increased wall thickening and resistance to blood flow. Dysregulated TGF-β, specifically SMAD signaling, is a key molecular defect in proliferative thickening of pulmonary arterioles in PAH leading to increased arterial pressure and compensatory right ventricular hypertrophy, ultimately resulting in decompensated right heart failure. Increased levels of activin A, a TGF-β superfamily ligand, have been found in PAH patients, and in the lungs of hypoxia-induced pulmonary hypertensive mice (Yndestad 2009). KER-012 is an investigational modified ActRIIB ligand trap designed to bind and inhibit activin A, activin B, GDF8 and GDF11 to maximally inhibit SMAD2/3 (pro proliferative), while permitting SMAD1/5/9 (anti-proliferative) signaling. This profile is expected to rebalance defective SMAD signaling in PAH and potentially delay or reverse disease progression. Aim To evaluate safety and tolerability of KER-012 in healthy post-menopausal women (PMW) and present the planned design of a Phase 2 trial in participants with PAH. Methods A two-part Phase 1 study has been conducted with KER-012 in healthy PMW. Participants received either placebo or a single dose of KER-012 ranging between 0.75 and 5.0 mg/kg in Part 1 or multiple doses between 0.75 and 4.5 mg/kg in Part 2 subcutaneously once every 4 weeks over a 12-week period. Safety, PK and biomarkers of activin target engagement were assessed. Results KER-012 was generally well tolerated at dose levels up to 5 mg/kg as a single dose and at dose levels up to 4.5 mg/kg administered Q4W for a total of 3 doses (Table 1). Maximal target engagement of KER-012, as demonstrated by changes in biomarkers of activin inhibition, namely follicle stimulating hormone (FSH) and bone specific alkaline phosphatase (BSAP), was observed in this study. As previous studies with activin receptor type II ligand traps have shown a potentially dose-limiting increase in erythropoiesis, changes in red blood cells (RBC) were closely monitored in this study. KER-012 did not elicit any changes in hemoglobin or RBC count in the Phase 1 study (Figure 1). Summary KER-012 was generally well tolerated in healthy participants. The observ