Safety, Tolerability and Efficacy of Narsoplimab, a Novel MASP-2 Inhibitor for the Treatment of IgA Nephropathy

Introduction: Narsoplimab is a human monoclonal antibody against mannan-associated lectin-binding serine protease-2 (MASP-2). Now in a phase 3 study, narsoplimab was evaluated in a staged phase 2 study assessing safety and effectiveness in high-risk patients with IgA nephropathy (IgAN). Methods: Substudy 1 was a single-arm open-label study of 12 weekly infusions and tapered corticosteroids, with 6 weeks of follow-up. In substudy 2, patients were randomized 1:1 to receive a course of treatment consisting of once-weekly narsoplimab or vehicle infusions for 12 weeks. After 6 weeks of follow-up, both substudy 2 groups could continue in an open-label extension, receiving 1 or more narsoplimab courses at the investigator's discretion. Results: The most commonly reported adverse events (AEs) included headache, upper respiratory infection, and fatigue. Most AEs were mild or moderate and transient. No treatment-related serious AEs were reported. All 4 patients who were enrolled in substudy 1 had reductions in 24-hour urine protein excretion (UPE) at week 18, ranging from 54% to 95% compared with baseline. In substudy 2, the vehicle and narsoplimab groups had similar proteinuria reductions at week 18. Eight patients (3 vehicle, 5 narsoplimab) continued in the dosing extension; all received narsoplimab. Median reduction in 24-hour UPE in these 8 patients was 61.4% at 31 to 54 weeks postbaseline. Estimated glomerular filtration rates (eGFR) remained stable in both substudies. Conclusion: This interim analysis suggests that narsoplimab treatment is safe, is well tolerated, and may result in clinically meaningful reductions in proteinuria and stability of eGFR in high-risk patients with advanced IgAN.