Background & Objectives: The monoclonal antibody cetuximab binds to EGFR and thus provides an opportunity to create both imaging and therapeutic modalities that target this receptor. The potential of cetuximab as a radioimmunoconjugate was investigated and quality control tests (in vitro and in vivo) were performed as a first step in the production of a new radiopharmaceutical.
Methods : Cetuximab solution was dialyzed and concentrated using an Amicon Ultra-15 filter. Purified antibody was labeled with lutetium-177 using the acyclic bifunctional chelator, DOTA-NHS, and radioimmunoconjugates were purified by PD10 columns. Radiochemical purity and stability in buffer and human blood serum were determined using thin layer chromatography. Integrity of the radiolabeled complex was checked by SDS-PAGE. Preliminary biodistribution studies in normal mice model performed to determine radioimmunoconjugates distribution up to 72h.
Results: The radiochemical purity of the complex was 98±1%. The stabilities in phosphate buffer and in human blood serum at 96 hours post-preparation were 96±2 % and 78±4%, respectively. All of the samples, controls and radiolabeled antibodies, showed a similar pattern of migration in the gel electrophoresis. Biodistribution of Lu177-cetuximab was evaluated in normal mice and the highest ID/g% was observed in the blood (13.2±1.3% at 24 hours) and the liver (9.1±1.3% at 24 hours).
Conclusion: Our results show that DOTA-cituximab can be labeled with 177Lu. Lu177-cetuximab has sufficient stability and retains its integrity. The new complex could be considered for further evaluation in animals and possibly in humans as a new radiopharmaceutical for use in radioimmunotherapy of cancers.