Tetravalent Bispecific Tandem Antibodies Improve Brain Exposure and Efficacy in an Amyloid Transgenic Mouse Model

Abstract

Most antibodies display very low brain exposure due to the blood-brain barrier (BBB) preventing their entry into brain parenchyma. Transferrin receptor (TfR) has been used previously to ferry antibodies to the brain by using different formats of bispecific constructs. Tetravalent bispecific tandem immunoglobulin Gs (IgGs) (TBTIs) containing two paratopes for both TfR and protofibrillar forms of amyloid-beta (Aβ) peptide were constructed and shown to display higher brain penetration than the parent anti-Aβ antibody. Additional structure-based mutations on the TfR paratopes further increased brain exposure, with maximal enhancement up to 13-fold in wild-type mice and an additional 4–5-fold in transgenic (Tg) mice harboring amyloid plaques, the main target of our amyloid antibody. Parenchymal target engagement of extracellular amyloid plaques was demonstrated using in vivo and ex vivo fluorescence imaging as well as histological methods. The best candidates were selected for a chronic study in an amyloid precursor protein (APP) Tg mouse model showing efficacy at reducing brain amyloid load at a lower dose than the corresponding monospecific antibody. TBTIs represent a promising format for enhancing IgG brain penetration using a symmetrical construct and keeping bivalency of the payload antibody.

A Historical Review of Brain Drug Delivery

“…Owing to steric hindrance by the outer domain antibody, the affinity of the inner domain antibody was reduced [798]. A similar tetravalent tandem BSA was engineered with a TfRMAb and an AAA that targeted the protofibrillar form of the Abeta peptide [740]. In another monovalent TfRMAb format, a BSA was engineered that targeted the TfR as a monovalent antibody and BACE1 as a bivalent antibody using knob-in-hole technology [743].…”

“…In summary, since the initial report of the engineering of a tetravalent BSA that targets either the insulin receptor [696] or transferrin receptor [794], at least eight different formats have been used for engineering a BBB-penetrating BSA [695,697,[740][741][742][743][744]796,798]. The antibodies range from monovalent for both arms of the BSA, to bivalent for both arms of the BSA, and to monovalent for one arm and bivalent for the other arm.…”

Grabody B, an IGF1 receptor-based shuttle, mediates efficient delivery of biologics across the blood-brain barrier

“…Significant effort has been invested in developing strategies to overcome the limited delivery of biotherapeutics to the central nervous system (CNS) ( Do et al., 2020 ; Pardridge, 2020 ; Yu et al., 2014 ). One promising approach is to take advantage of receptor-mediated transcytosis (RMT), particularly the unidirectional transcytosis pathway by which macromolecules are internalized and transported from the apical to the basolateral plasma membranes in brain endothelial cells (BECs) ( Pardridge, 2020 ; Sehlin et al., 2020 ; Webster et al., 2016 ).…”

Kinetics of Blood–Brain Barrier Transport of Monoclonal Antibodies Targeting the Insulin Receptor and the Transferrin Receptor

“…The affinity of the BBB Trojan horses targeting the TfR range over several log orders of magnitude. High affinity TfRMAbs have a dissociation constant (K D ) of binding to the TfR ranging from 0.1 to 3 nM [21][22][23][24][25][26][27][28]. Moderate-affinity TfRMAbs have a KD of binding to the TfR ranging from 14 to 76 nM [26,27,[29][30][31][32].…”

“…High affinity TfRMAbs have a dissociation constant (K D ) of binding to the TfR ranging from 0.1 to 3 nM [21][22][23][24][25][26][27][28]. Moderate-affinity TfRMAbs have a KD of binding to the TfR ranging from 14 to 76 nM [26,27,[29][30][31][32]. Low-affinity TfRMAbs have a KD of binding to the TfR ranging from 111 to 300 nM [6,20,33,34].…”