Aggregation Issues in Radioactive Copper-Labeled Antibodies

Radioimmunoconjugates, formed by attaching radionuclides to monoclonal antibodies (mAbs) either directly or through bifunctional chelators, have advanced precision oncology by enabling targeted molecular imaging and therapy. Copper radioisotopes have gained increasing attention due to their diverse decay properties and potential for both diagnostic and therapeutic applications. Among these, Cu-64 is an attractive radionuclide for immuno-positron emission tomography (immunoPET) and theranostic applications owing to its favorable production route. It is particularly suitable for labeling mAb and antibody-derived fragments for immunoPET imaging. However, radiolabeling antibodies presents unique challenges in product quality control (QC), with aggregation being a critical yet under-addressed parameter. This review introduces the importance of Cu-radioisotopes and discusses purification strategies of immunoconjugates for clinically acceptable products. The focus then shifts to aggregation: its physicochemical drivers, reported cases in the literature, and its impact on pharmacokinetics and immunogenicity. We evaluate aggregation detection methods, highlighting dynamic light scattering (DLS) as a sensitive, orthogonal QC tool complementing conventional size-exclusion high-performance liquid chromatography. The effectiveness of DLS is demonstrated by recent data showing its superior sensitivity in identifying hidden aggregates that inversely correlate with tumor uptake. Finally, we present approaches to minimize aggregation and discuss the importance of regulatory concern of aggregate limits.