RADIOMETAL LABELING OF RECOMBINANT PROTEINS BY A GENETICALLY-ENGINEERED MINIMAL CHELATION SITE - TC-99M COORDINATION BY SINGLE-CHAIN FV ANTIBODY FUSION PROTEINS THROUGH A C-TERMINAL CYSTEINYL PEPTIDE

We describe a method to facilitate radioimaging with technetium-99m (Tc-99m) by genetic incorporation of a Tc-99m chelation site in recombinant single-chain Fv (sFv) antibody proteins, This method relies on fusion of the sFv C terminus with a Gly(4)Cys peptide that specifically coordinates Tc-99m, By using analogues of the 26-10 anti-digoxin sFv as our primary model, we find that addition of the chelate peptide, to form 26-10-1 sFv', does not alter the antigen-binding affinity of sFv, We have demonstrated nearly quantitative chelation of 0.5-50 mCi of Tc-99m per mg of 26-10-1 sFv' (1 Ci = 37 GBq), These Tc-99m-labeled sFv' complexes are highly stable to challenge with saline buffers, plasma, or diethylenetriaminepentaacetic acid. We find that the Tc-99m-labeled 741F8-1 sFv', specific for the c-erbB-2 tumor-associated antigen, is effective in imaging human ovarian carcinoma in a scid mouse tumor xenograft model. This fusion chelate methodology should be applicable to diagnostic imaging with (TC)-T-99m and radioimmunotherapy with Re-186 or Re-188, and its use could extend beyond the sFv' to other engineered antibodies, recombinant proteins, and synthetic peptides.