The use of redox polymers in labelling procedures of proteins and peptides with 99mTc. I. Properties of redox polymers and technique of labelling.
BACKGROUND: Using a polymer-analogue reaction, redox polymers with a dextran matrix to anchor the end alpha(beta)-alanine-N,N'-diacetate group converted into the Sn(2+) cycle have been developed for the labelling of proteins, peptides, and labile compounds with (99m)Tc. The reaction kinetics and the labelling efficiency of (99m)Tc depend primarily on the degree of dextran matrix cross-linking and the qualitative nature of the redox polymer end groups. METHODS: Preparation for labelling takes place directly in basic protein and peptide solutions without adjusting pH or adding other adjuvants. Prior to the final modification into kit form, the redox polymers are removed by ultrafiltration. RESULTS: The results of labelling of model compounds (aspartic acid, cysteine) with (99m)Tc at various solution pH values clearly show that, at pH values over 6.0, it will be primarily the free end SH groups that will serve as binding sites for the proteins and peptides. To label proteins and peptides, we selected a redox polymer with G-25 cross-linking, which allows the achievement of a radiochemical purity over 95% and high stability of the labelled compounds. CONCLUSION: The method of radiolabelling compounds with (99m)Tc based on redox polymers was developed mainly to overcome the problems faced when using other conventional methods in the labelling of sensitive compounds.