LABELING OF MONOCLONAL-ANTIBODIES WITH RE-186 USING THE MAG3 CHELATE FOR RADIOIMMUNOTHERAPY OF CANCER - A TECHNICAL PROTOCOL

A detailed technical protocol is provided for reproducible and aseptic al production of stable Re-186-monoclonal antibody conjugates. Labeled Mab E48 IgG and its F(ab'), fragment which are promising candidates f or radioimmunotherapy of squamous cell carcinoma of the head and neck were used for evaluation. S-benzoylmercaptoacetyltriglycine (S-benzoyl -MAG3) was used as a precursor. Rhenium-186-MAG3 was prepared via a un ique solid-phase synthesis, after which known strategies for esterific ation and conjugation to Mab IgG/F(ab'), were applied. The biodistribu tion of Re-184-E48 F(ab'), in tumor-bearing nude mice was found to be comparable to that of analogously labeled Tc-99m-E48 F(ab'), or I-131- E48 F(ab')2, indicating that the intrinsic behavior of the antibody re mains preserved when using this labeling technique. Radiolytic decompo sition of Re-186-E48 IgG/F(ab')2 solutions of 10 mCi . ml-1 was effect ively reduced by the antioxidant ascorbic acid. Upon increase of the R e-MAG3 molar amount, a conjugation of seven to eight Re-MAG3 molecules per Mab molecule was generally the maximum ratio that could chemicall y be obtained. Such a ratio did not impair the immunoreactivity or alt er the in vivo biodistribution characteristics of the immunoconjugate, making this labeling procedure suitable for general clinical applicat ion.