Method development for 14C-labeling of IgG antibodies in preparation for clinical trials

Carbon-14 (14C) labeling is a standard technology for tracing molecules and providing their pharmacokinetic profiles. However, its primary focus has been on small molecules, with limited application to biomacromolecules. Particularly in the development of new biological entities (NBE), the utilization of microdosing with a 14C-labeled biomacromolecule proves beneficial in the early stages of drug development, contributing to significant time and cost savings. This study investigates the 14C-labeling of antibody and explores the stability of 14C-labeled antibody under various storage conditions. In this study, the utilization of 14C-formaldehyde for labeling target antibodies at various molar ratios revealed a direct correlation between labeling efficiency and the quantity of 14C-formaldehyde applied: 1.5 mol/mol for 14C-labeled antibody with the use of 10 equivalents of 14C-formaldehyde, 3.8 mol/mol for 14C-labeled antibody with the use of 10 equivalents of 14C-formaldehyde, and 10.5 mol/mol for 14C-labeled antibody with the use of 60 equivalents of 14C-formaldehyde. All the reaction conditions exhibited no antibody degradation, as evidenced by the absence of a significant change in HPLC purity compared to the unlabeled antibody. Stability tests revealed that all groups maintained their purities over a 4-week period at both − 75 ± 10 °C and 5 ± 3 °C. Given safety concerns related to internal radiation exposure in potential human subjects during microdosing, this study established optimal conditions for employing 14C-labeled antibodies. Therefore, it is optimized that 10 equivalents of 14C-formaldehyde can be used for 14C-antibody labeling through reductive amination, storing the antibodies at 5 ± 3 °C, and assigning a storage period of 4 weeks. The findings from this study offer valuable insights into the effective application of 14C-labeling in microdosing studies, especially for larger molecules such as antibodies.