Therapeutic assessment of SEED: a new engineered antibody platform designed to generate mono- and bispecific antibodies

Abstract

The strand-exchange engineered domain (SEED) platform was designed to generate asymmetric and bispecific antibody-like molecules, a capability that expands therapeutic applications of natural antibodies. This new protein engineered platform is based on exchanging structurally related sequences of immunoglobulin within the conserved CH3 domains. Alternating sequences from human IgA and IgG in the SEED CH3 domains generate two asymmetric but complementary domains, designated AG and GA. The SEED design allows efficient generation of AG/GA heterodimers, while disfavoring homodimerization of AG and GA SEED CH3 domains. Using a clinically validated antibody (C225), we tested whether Fab derivatives constructed on the SEED platform retain desirable therapeutic antibody features such as in vitro and in vivo stability, favorable pharmacokinetics, ligand binding and effector functions including antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity. In addition, we tested SEED with combinations of binder domains (scFv, VHH, Fab). Mono- and bivalent Fab-SEED fusions retain full binding affinity, have excellent biochemical and biophysical stability, and retain desirable antibody-like characteristics conferred by Fc domains. Furthermore, SEED is compatible with different combinations of Fab, scFv and VHH domains. Our assessment shows that the new SEED platform expands therapeutic applications of natural antibodies by generating heterodimeric Fc-analog proteins.

Monovalent antibody design and mechanism of action of onartuzumab, a MET antagonist with anti-tumor activity as a therapeutic agent

“…3A). Although attempts at generating monovalent antibodies with slow clearance rates have been reported (46,47), most have a nonnative structure and increased risk of immunogenicity. The knob and hole mutations are buried in the C H 3-C H 3 interface and completely hidden from the surface (Fig.…”

A dual-targeting triplebody mediates preferential redirected lysis of antigen double-positive over single-positive leukemic cells

“…[19][20][21] DVD-Igs are tetravalent structures with two copies each of the two different binding sites, and they carry a homodimeric Fc-domain. Another new format is the Strand Exchange Engineered Domain (SEED) antibody 22,23 in which structurally-related subdomains…”

Progress in overcoming the chain association issue in bispecific heterodimeric IgG antibodies

“…The concept can be exploited for various IgG-like formats and was assessed in more detail for derivatives of C225, a chimeric anti-epidermal growth factor receptor antibody that was clinically developed as cetuximab (Erbitux ® ). 39 The aforementioned approaches of generating bispecific antibodies by introducing changes in the Fc interface region were also addressed by Zymeworks. The company developed a modeling platform called Azymetric TM to generate heterodimeric IgG1 antibodies, but details of this platform are not accessible yet.…”