Radioimmunotherapy (RIT) delivers radionuclides to tumors through antibody-based targeting. However, radiolabeling with high-linear energy transfer (LET) isotopes like Lu-177 can induce aggregation, reducing antibody stability and bioactivity. In this study, we evaluated 177LuLu-DOTA-Trastuzumab, a HER2-targeting radioimmunoconjugate, to assess how conjugation chemistry, radiolabeling conditions, and purification methods affect aggregation and therapeutic performance. Dynamic light scattering (DLS) was used to monitor aggregation throughout formulation. Higher chelator-to-antibody ratios and increased radioactivity caused significant aggregation, which was not detected by conventional SEC-HPLC or radio-TLC quality control methods. Compared to the diagnostic isotope Cu-64, the therapeutic isotope Lu-177 exhibited markedly greater aggregation, reflecting the stronger radiolytic stress from high LET isotopes. Aggregation inversely correlated with HER2-specific uptake and tumor accumulation in vivo. Centrifugal membrane filtration removed aggregates more effectively than PD-10 columns. In HER2-positive mouse models, aggregate-free 177LuLu-DOTA-Trastuzumab achieved higher tumor accumulation and resulted in ∼65% tumor growth inhibition by day 21. These findings demonstrate that DLS is a sensitive and practical quality control tool. Given the greater aggregation risk in therapeutic radiolabeling, aggregate monitoring is especially critical for ensuring the safety, consistency, and effectiveness of radioimmunotherapy agents.
Nguyen et al. (Tue,) studied this question.