Hexa-histidine tag as a novel alternative for onestep direct labelling of a single-chain Fv antibody fragment with Tc-99m

From genetic material of hybridoma cells, we have generated a recombinant s ingle-chain antibody fragment (scFv antibody) specific to carcinoembryonic antigen (CEA), which can substitute an intact murine monoclonal immunoglobu lin G1 (IgG1) antibody, also developed by our group, and used in clinical p ractice for many years. In this paper, we examine a novel one-step method f or direct Tc-99m labelling of a recombinant anti-CEA scFv fragment through a C-terminal peptide tag containing a six-histidine sequence. This C-termin al peptide tag does not affect antigen binding, and was employed as a strat egy for the one-step method of direct 99'Tc labelling of a recombinant anti body fragment, based on the criteria of Zamora and Rhodes (Zamora PO, Rhode s BA. Imidazoles as well as thiolates in proteins bind technetium-99m. Bioc onj Chem 1992; 3: 493-498). This is a novel technique for the rapid labelli ng of molecules, suitable for in vivo trials. The method yields >95% labell ing efficiency without major effects on biological or in vitro stability. ( (C) 2001 Lippincott Williams & Wilkins).