The Thomsen-Friedenreich disaccharide as antigen for in vivo tumor targeting with multivalent scFvs.

The Thomsen-Friedenreich disaccharide (TF(alpha)) is a promising antigen for tumor immunotargeting, since it is almost exclusively expressed on carcinoma tissues. So far, an obstacle preventing the exploitation of TF for immunotargeting has been the lack of suitable (non-IgM) antibodies with high affinity and specificity. Recently we reported on a novel strategy for generating antibodies toward small uncharged carbohydrates and the generation of recombinant antibodies toward TF. Among them, two multivalent scFv antibodies showed sub-micromolar functional affinities and appeared well suited for immunotargeting. In the present study, the trimeric scFv(1aa) and the tetrameric scFv(0aa) have been further developed for radioimmunotargeting. The scFvs were radiolabeled with (111)In using DTPA as chelator without losing binding activity or molecular stoichiometry. Binding affinities as high as 1 x 10(-7) M toward TF displayed on living cells were determined. Antibody biodistribution and tumor targeting efficacy were studied in TF-positive human breast cancer (ZR-75-1) bearing mice. TF was successfully targeted in vivo with tumor uptakes of approximately 11 and 8% ID/g after 24 h for the trimeric and tetrameric scFv, respectively. These results validate TF as a potent antigen for tumor targeting. The biodistribution of the scFvs was comparable to that reported for IgGs. In contrast to the IgGs, the serum clearance of the scFvs was very fast, which could be an advantage in a therapeutic setting. Furthermore, kidney uptake, which is often critical for small recombinant antibodies labeled with radio-metals, was low with the tetramer (11% ID/g). We conclude that the multimeric anti-TF scFvs are promising candidates to be further developed toward therapeutic application.