Anti-PCSK9 Antibody Pharmacokinetics and Low-Density Lipoprotein-Cholesterol Pharmacodynamics in Nonhuman Primates Are Antigen Affinity–Dependent and Exhibit Limited Sensitivity to Neonatal Fc Receptor–Binding Enhancement

Abstract

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged as an attractive therapeutic target for cardiovascular disease. Monoclonal antibodies (mAbs) that bind PCSK9 and prevent PCSK9:low-density lipoprotein receptor complex formation reduce serum low-density lipoprotein-cholesterol (LDL-C) in vivo. PCSK9-mediated lysosomal degradation of bound mAb, however, dramatically reduces mAb exposure and limits duration of effect. Administration of high-affinity mAb1:PCSK9 complex (1:2) to mice resulted in significantly lower mAb1 exposure compared with mAb1 dosed alone in normal mice or in PCSK9 knockout mice lacking antigen. To identify mAb-binding characteristics that minimize lysosomal disposition, the pharmacokinetic behavior of four mAbs representing a diverse range of PCSK9-binding affinities at neutral (serum) and acidic (endosomal) pH was evaluated in cynomolgus monkeys. Results revealed an inverse correlation between affinity and both mAb exposure and duration of LDL-C lowering. Highaffinity mAb1 exhibited the lowest exposure and shortest duration of action (6 days), whereas mAb2 displayed prolonged exposure and LDL-C reduction (51 days) as a consequence of lower affinity and pH-sensitive PCSK9 binding. mAbs with shorter endosomal PCSK9:mAb complex dissociation half-lives (,20 seconds) produced optimal exposure-response profiles. Interestingly, incorporation of previously reported Fc-region amino acid substitutions or novel loop-insertion peptides that enhance in vitro neonatal Fc receptor binding, led to only modest pharmacokinetic improvements for mAbs with pH-dependent PCSK9 binding, with only limited augmentation of pharmacodynamic activity relative to native mAbs. A pivotal role for PCSK9 in mAb clearance was demonstrated, more broadly suggesting that therapeutic mAb-binding characteristics require optimization based on target pharmacology.

The interplay of non-specific binding, target-mediated clearance and FcRn interactions on the pharmacokinetics of humanized antibodies

“…22,25 In the case of an anti-PCSK9 mAb series, an alternate pathway of clearance of mAb-target make engineered Fc-FcRn interactions less influential. 34 In this study, disengaging the formed complex was critical in allowing the mAb to be cleared through a predominantly FcRn mediated process, where Fc mutations demonstrated benefit. 34 This process is somewhat analogous to the charge surface interactions described here.…”

“…34 In this study, disengaging the formed complex was critical in allowing the mAb to be cleared through a predominantly FcRn mediated process, where Fc mutations demonstrated benefit. 34 This process is somewhat analogous to the charge surface interactions described here. The charge interaction is an alternate pathway or clearance mechanism that makes the mAb inaccessible to FcRn mediated disposition.…”

“…It is postulated that for antibodies directed to high turnover targets, the peripheral IgG clearance is driven through target binding. 24,27,34 The literature is generally consistent in describing the need to either saturate TMD or engineer a pH sensitivity into the receptor/target interaction to demonstrate the benefit of Fc mutations that enhance FcRn binding. 22,25 In the case of an anti-PCSK9 mAb series, an alternate pathway of clearance of mAb-target make engineered Fc-FcRn interactions less influential.…”

PCSK9 inhibition-mediated reduction in Lp(a) with evolocumab: an analysis of 10 clinical trials and the LDL receptor's role

“…Fully human anti-PCSK9 mAbs (mAb1, mAb2, mAb3, and mAb4) were all of the IgG2 subclass, and were generated as previously described (30,31). The IgG2 control mAb utilized for in vivo studies was a human anti-keyhole limpet hemocyanin antibody (Amgen Inc., Thousand Oaks, CA).…”

“…The IgG2 control mAb utilized for in vivo studies was a human anti-keyhole limpet hemocyanin antibody (Amgen Inc., Thousand Oaks, CA). The anti-PCSK9 mAbs differed in binding affinity at neutral and acidic pH, leading to differences in half-life and duration of LDL-C lowering (mAb1 < mAb3 < mAb4 < mAb2) (31). Fully human anti-LDLR antibodies were generated by immunizing XenoMouse with human LDLR extracellular domain and human EGFa:EGFb-Fc and selecting high-affinity antibodies binding at the EGFa:EGFb domain region (data not shown).…”