RadioLabeling of the Mutant form of Anti-PlGF Nanobody by 99mTc-Tricarbonyl

Abstract

Background: Molecular imaging is a highly effective method for diagnosing cancer and evaluating treatment. A molecular tracer often consists of two segments: A targeting segment, which can be antibodies, antibody fragments, or VHH (nanobody), and a detection segment, such as radioisotopes. The small size of VHH allows for excellent tissue penetration and fast clearance, resulting in minimal nonspecific background, which makes them appealing for use as imaging agents. 99m-technetium (99mTc), one of the well-known radioisotopes, is particularly useful in routine clinical imaging. Objectives: This study aims to construct 99mTc-anti-placenta growth factor (PlGF) nanobody and assess its radiochemical purity (RCP). Methods: The mutant form of anti-PlGF nanobody was expressed in E. coli TG1 and purified using Ni-NTA column affinity chromatography. The purified nanobodies were confirmed by SDS-PAGE and western blotting. A 99mTc-tricarbonyl solution was added to phosphate-buffered saline (PBS) containing the mutant nanobody for labeling, and the mixture was purified using a PD-10 column. Results: The RCP of 99mTc-tricarbonyl is > 98%. After the addition of radioisotopes to the mixture of nanobodies, purity reached 70% in 2 hours and remained constant during incubation. After purifying the labeled nanobody, activity was measured, and the highest amount of labeled nanobodies was collected in the second part. The stability of the labeled nanobody in PBS and in competition with histidine for 4 hours was checked by thin-layer chromatography (TLC). Conclusions: The findings of this study reveal that the RCP of the labeled nanobody was above 95% after 4 hours, indicating the labeled antibody's stability. These results are promising and could be utilized in future in vitro and in vivo studies.