Affibody-Mediated Sequestration of Amyloid β Demonstrates Preventive Efficacy in a Transgenic Alzheimer’s Disease Mouse Model

Abstract

Different strategies for treatment and prevention of Alzheimer’s disease (AD) are currently under investigation, including passive immunization with anti-amyloid β (anti-Aβ) monoclonal antibodies (mAbs). Here, we investigate the therapeutic potential of a novel type of Aβ-targeting agent based on an affibody molecule with fundamentally different properties to mAbs. We generated a therapeutic candidate, denoted Z SYM73 -albumin-binding domain (ABD; 16.8 kDa), by genetic linkage of the dimeric Z SYM73 affibody for sequestering of monomeric Aβ-peptides and an ABD for extension of its in vivo half-life. Amyloid precursor protein (APP)/PS1 transgenic AD mice were administered with Z SYM73 -ABD, followed by behavioral examination and immunohistochemistry. Results demonstrated rescued cognitive functions and significantly lower amyloid burden in the treated animals compared to controls. No toxicological symptoms or immunology-related side-effects were observed. To our knowledge, this is the first reported in vivo investigation of a systemically delivered scaffold protein against monomeric Aβ, demonstrating a therapeutic potential for prevention of AD.

An Affibody Molecule Is Actively Transported into the Cerebrospinal Fluid via Binding to the Transferrin Receptor

“…The CSF bioavailability of the control protein Z SYM73 -ABD was 0.12%, 0.16%, and 0.29% at 3 h, 24 h, and 48 h, respectively ( Figure 4E). The CSF bioavailability of Z SYM73 -ABD is in accordance with a recent study carried out in rats [27] and reflects values reported for passive protein uptake into the CNS [43]. The fusion of scFv8D3 to Z SYM73 -ABD led to an 9-fold increase in CSF bioavailability after 24 h indicating an active transport mechanism into CSF.…”

“…In this study, we investigated CSF bioavailability of affibody fusion proteins after administrating a therapeutically relevant dose of 87.8 nmol/kg. These doses are comparable to doses administered in a preclinical study of Z SYM73 -ABD and significantly larger than doses used in previous studies exploiting TfR brain uptake using the 8D3 antibody [27,28,44].…”

“…It has recently been shown that Z SYM73 -ABD treatment leads to prevention of the amyloid burden build up in both cortex and hippocampus as well as prevention of cognitive function decline in APP/PS1 double transgenic mice. The brain bioavailability of Z SYM73 -ABD in mice is however unknown [27].…”

“…When bound, the aggregation-prone parts of Aß are buried in a tunnel-like cavity and the affibody efficiently inhibits the aggregation. In an APP/PS1 double transgenic mouse study, treatment with Z SYM73 led to prevention of the amyloid burden build up in both cortex and hippocampus as well as prevention of decline in cognitive function [27].…”

“…It has previously been demonstrated that the CNS uptake of rat 8D3 mAb against mouse TfR is substantially higher than for non-TfR binding antibodies [28][29][30]. We genetically fused Z SYM73 to a single-chain variable fragment (scFv) of the 8D3 mAb and an engineered albumin-binding domain (ABD) [31], which was included also in the preclinical study with Z SYM73 [27]. The engineered ABD and its binding to serum albumin has been shown in a number of both preclinical and clinical studies to prolong the circulatory half-life of fusion proteins by decreasing renal filtration and indirect recycling via the neonatal Fc receptor [32][33][34][35].…”