Pozelimab, a Human Antibody Against Complement Factor C5, Demonstrates Robust Inhibition of Alternative Complement Activity Both in Normal Human Serum and in Phase I Normal Healthy Volunteers

Abstract

INTRODUCTION: Blockade of complement factor C5 has demonstrated benefit in paroxysmal nocturnal hemoglobinuria, atypical hemolytic uremic syndrome, generalized myasthenia gravis and neuromyelitis optica. We have completed a Phase I study of pozelimab, a fully human anti-C5 IgG4, in healthy volunteers. Pozelimab was well tolerated and resulted in dose-dependent inhibition of hemolytic activity through the classical complement pathway in normal healthy volunteers. Complete inhibition of hemolytic activity was maintained over a 4-week dosing period by a weekly subcutaneous (SC) regimen following an intravenous (IV) loading dose (ASH2018 abstract). OBJECTIVE: To further characterize the impact of pozelimab on the alternative complement pathway activity, we investigated the effect of pozelimab on alternative pathway-mediated hemolysis using an AH50 assay in the completed first-in-human (FIH) study. In addition, we compared the effect of pozelimab in both alternative and classical pathway hemolysis assays with those of in-house eculizumab and in-house ravulizumab in pooled normal human serum (NHS) samples, ex vivo. METHODS: In total, 56 subjects were randomized to 4 sequential ascending IV single dose cohorts plus 2 sequential ascending SC single dose cohorts followed by 1 multiple dose cohort (consisting of an IV loading dose and weekly SC doses). Each cohort consisted of 8 subjects randomized to receive pozelimab or placebo (6 active: 2 placebo). Serum collected at multiple time-points was utilized to assess the effect of pozelimab on alternative pathway activity. For ex vivo spike experiments, pooled NHS was used to compare the hemolytic function of pozelimab, in-house produced eculizumab and in-house produced ravulizumab. Comparator antibodies were synthesized from published sequence. The alternative pathway (AP) and classical pathway (CP) hemolysis assays were performed based on lysis of rabbit red blood cells (RBCs) and sensitized sheep RBCs, respectively. Both assays measure the amount of hemoglobin released from red blood cells at 412 nm. RESULTS: In the FIH study, baseline AH50 was comparable across treatment groups with a mean of 110 U/mL (standard deviation = 19, n = 56). Pozelimab exposure led to dose-dependent inhibition of AH50. In all 4 IV dosing cohorts, peak suppression of hemolysis was observed at end of infusion (EOI). Maximal suppression of hemolysis was approximately −85% change from baseline. This was achieved with the 30 mg/kg IV group and the repeat dose 15 mg/kg IV + 400 mg SC QW group. In the 2 SC cohorts, peak suppression of hemolysis was observed 3-7 days post dosing, which was consistent with observed peak concentrations of pozelimab in serum. In an ex vivo spike study, pozelimab, in-house eculizumab and in-house ravulizumab were spiked into 10, 25 or 48% pooled NHS for AP, and 5, 10 or 25% for CP. The results from AP hemolysis assays showed that, for a given concentration of spiked antibody, the maximal suppression of hemolysis for all the antibodies decreased with increased percentage of serum (Figure). The maximal suppression of hemolysis was consistently higher (32-169%) for pozelimab compared with in-house eculizumab, and lower for in-house ravulizumab compared with pozelimab and in-house eculizumab at all serum percentages tested. The results from CP hemolysis assays showed that, although the maximal suppression of hemolysis was similar for all antibodies tested, in-house ravulizumab was required to be at least a log higher in concentration to achieve a similar effect as the other two anti-C5 antibodies. CONCLUSIONS: Ex vivo studies with pooled NHS demonstrate that pozelimab robustly blocks both CP and AP hemolysis. In-house ravulizumab appeared to be less potent compared with in-house eculizumab in both CP and AP hemolysis assays. The Phase I healthy volunteer study of pozelimab demonstrated dose-dependent and significant inhibition of alternative pathway hemolysis, with the maximal suppression of hemolysis approximately −85% change from baseline. Figure Disclosures Devalaraja-Narashimha: Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Ni:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Huang:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Wang:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Chaudhari:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Prasad:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Harari:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Rankin:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Morton:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Weyne:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. OffLabel Disclosure: The drug is pozelimab and it is a fully human anti-C5 IgG4 being tested a Phase 1 study in healthy volunteers.

Treatment of Rare Inflammatory Kidney Diseases: Drugs Targeting the Terminal Complement Pathway

“…This fully humanized antibody against C5 has been shown to suppress C5 levels and hemolysis in human serum and mice models in a more potent manner compared to eculizumab and ravulizumab ( 154 , 155 ). In a Phase 1 study in healthy subjects, pozelimab also showed 70% bioavailability after subcutaneous administration, allowing for more versatile administration options, such as weekly subcutaneous 400 mg administrations after a 15 mg/kg intravenous loading dose ( 156 ).…”

A review of the treatment landscape in paroxysmal nocturnal haemoglobinuria: where are we now and where are we going?

“…Pozelimab, a fully human monoclonal immunoglobulin G4P (IgG4P) antibody directed against C5, has been trialled in healthy volunteers has demonstrated complement inhibition with a reduction in the complement function assay CH50 and a favourable safety profile. 35 Zilucopan, a daily SC injection showed promising results; however, the company have been taken over and looks to not be pursing PNH as a disease area of interest. 37 Similarly, nomacopan, a daily SC injection for PNH, presented at the 23rd European congress of haematology in 2018, showed a reduction in LDH and was well tolerated by eight patients, although it is no longer being developed by the company for PNH.…”

The importance of terminal complement inhibition in paroxysmal nocturnal hemoglobinuria

“… 77 Tesidolumab is a monoclonal antibody under development in a proof-of-concept phase 2 study in untreated patients with PNH; preliminary results are not yet available. 73 , 83 Pozelimab is a monoclonal antibody that demonstrated complement inhibition in healthy volunteers, 93 and an open-label, single-arm, phase 2 study is ongoing in patients with PNH who are either complement-inhibitor-naïve or have not recently received a complement inhibitor. 84 Zilucopan is a synthetic macrocyclic peptide inhibitor of complement C5.…”