Synthesis and Evaluation of a Zr-89-Labeled Monoclonal Antibody for Immuno-PET Imaging of Amyloid-β Deposition in the Brain.

PURPOSE: The aim of this study was to evaluate the in vitro and in vivo characteristics of [(89)Zr]JRF/AβN/25, a radiolabeled monoclonal antibody directed against amyloid-β (Aβ).

PROCEDURES: JRF/AβN/25 was labeled with (89)Zr following modification with desferal. The affinity of the tracer for Aβ1-40 was determined in a saturation binding assay. In vitro stability was evaluated, and in vivo plasma stability and biodistribution of [(89)Zr]Df-Bz-JRF/AβN/25 were determined in wild-type mice. To evaluate whether the antibody can cross the blood-brain barrier, brain uptake in wild-type mice was additionally assessed by ex vivo autoradiography.

RESULTS: [(89)Zr]Df-Bz-JRF/AβN/25 was obtained in an average radiochemical yield of 50 % and a radiochemical purity of >97 %. A saturation binding assay demonstrated specific binding of [(89)Zr]Df-Bz-JRF/AβN/25 to Aβ1-40 with nanomolar affinity. The tracer was stable in buffer and proved to be stable in vivo with >92 % intact monoclonal antibody (mAb) remaining in the plasma at 48 h post injection. A biodistribution study showed a slow blood clearance with no significant accumulation of activity in any of the organs. Furthermore, [(89)Zr]Df-Bz-JRF/AβN/25 demonstrated modest brain penetration, which slowly decreased in time. This cerebral uptake was confirmed by ex vivo autoradiography.

CONCLUSIONS: [(89)Zr]Df-Bz-JRF/AβN/25 binds with high affinity to Aβ1-40. The tracer displays an acceptable in vivo stability and is able to cross the blood-brain barrier. [(89)Zr]Df-Bz-JRF/AβN/25 might therefore be a potential candidate for in vivo imaging of Aβ deposition in the brain.