Biophysical Characterization of Antibody Biopolymer Conjugate (ABC) Platform for Improved Therapy of Retinal Vascular Diseases

Abstract

Purpose : Intravitreally-administered therapies for retinal vascular diseases impose a significant treatment burden due to injection frequency. To address this, we have developed an antibody biopolymer conjugate (ABC) platform, in which a high molecular weight (800 kDa), hydrophilic, zwitterionic, and branched phosphorylcholine based biopolymer is site-specifically conjugated to a full length, humanized, and highly potent anti-VEGF antibody. We investigated the biophysical properties of an ABC in advanced clinical trials, KSI-301, using a series of spectroscopic and biochemical characterization assays.

Methods : Intermolecular interactions of KSI-301 or its payload antibody alone were assessed by size exclusion chromatography, dynamic and static light scattering, and zeta potential, under a range of pH and ionic conditions. Protein secondary and tertiary structure and stability were evaluated by circular dichroism (CD). The relative structural orientations of the antibody and biopolymer portions of KSI-301 were visualized by electron microscopy (EM). KSI-301 and protein FcRn binding and recycling properties were characterized using bioluminescence and endothelial cell-based assays.

Results : Light scattering measurements indicated polymer modifies antibody colloidal properties by reducing nonspecific interactions between protein molecules. These data coupled with CD analysis supported high thermal and steric stabilization of the ABC with preserved antibody secondary and tertiary structure. The 1:1 antibody:biopolymer conjugation ratio was supported by SEC-MALS, SDS-PAGE and EM. FcRn assays indicated that biopolymer conjugation to the antibody prevents FcRn recycling, contributing toward fast plasma clearance of ABCs.

Conclusions : The ABC platform stabilizes antibody structure and imparts favorable clinical properties, such as low nonspecific interactions and reduced antibody recycling through FcRn. These underlying biophysical properties may also contribute to the observed enhanced tissue penetration and improved treatment durability seen for ABC-based therapeutics such as KSI-301. In addition to KSI-301, various ABC platform based biologic or biologic + small molecule therapeutics are in earlier stages of development. Altogether, our continuing studies support the potential of the ABC platform to meaningfully improve or enable the treatment of a myriad of retinal diseases.

This is a 2021 ARVO Annual Meeting abstract.