Investigation of the Impact of the H310A FcRn Region Mutation on 89 Zr-Immuno-PET Brain Imaging with a BBB-Shuttle Anti‑Amyloid Beta Antibody.

Purpose: In the emerging field of antibody treatments for neurodegenerative diseases, reliable tools are needed to evaluate new therapeutics, diagnose and select patients, monitor disease progression, and assess therapy response. Immuno-PET combines the high affinity and exceptional specificity of monoclonal antibodies with the non-invasive imaging technique positron emission tomography (PET). Its application in neurodegenerative disease brain imaging has been limited due to the marginal uptake across the blood-brain barrier (BBB). The emergence of BBB-shuttle antibodies with enhanced uptake across the BBB extended immuno-PET to brain imaging. We recently reported about specific brain uptake of a bispecific aducanumab mTfR antibody in APP/PS1 TG mice using ⁸⁹ Zr-immuno-PET. However, a sufficient target-to-background ratio was reached at a relatively late scanning time point of 7 days post-injection. To investigate if a better target-to-background ratio could be achieved earlier, an aducanumab BBB-shuttle with a mutated Fc region for reduced FcRn affinity was evaluated.
Procedures: Adu ^H310A -8D3 and Adu-8D3 were modified with DFO*-NCS and subsequently radiolabeled with ⁸⁹ Zr. The potential influence of the H310A mutation, modification with DFO*-NCS, and subsequent radiolabeling on the in vitro binding to amyloid-beta and mTfR1 was investigated via amyloid-beta peptide ELISA and FACS analysis using mTfR1 transfected CHO-S cells. Blood kinetics, brain uptake, in vivo PET imaging and target engagement of radiolabeled Adu ^H310A -8D3 were evaluated and compared to non-mutated Adu-8D3 in APP/PS1 TG mice and wild-type animals as controls.
Results: Radiolabeling was performed with sufficient radiochemical yields and radiochemical purity. In vitro binding to amyloid-beta and mTfR1 showed no impairment. [ ⁸⁹ Zr]Zr-Adu ^H310A -8D3 showed faster blood clearance and earlier differentiation of amyloid-beta-related brain uptake compared to [ ⁸⁹ Zr]Zr-Adu-8D3. However, only half of the brain uptake was observed for [ ⁸⁹ Zr]Zr-Adu ^H310A -8D3.
Conclusions: Although a faster blood clearance of Adu ^H310A -8D3 was observed, it was concluded that no beneficial effects for ⁸⁹ Zr-immuno-PET imaging of brain uptake were obtained.
(© 2024. The Author(s).)