Small animal PET imaging of TAG-72 expressing tumor using 68Ga-NOTA-3E8 Fab radioimmunoconjugate

The tumor-associated glycoprotein TAG-72 is express ed in the majority of human adenocarcinomas but is rarely expressed in most normal tissues, which makes it a potential target for the diagnosis and therapy of a variety of human cancer. 3E8 is anti-TAG-72 humanized antibody. Antibody fragments have some advantages such as improved pharmacokinetics and reduced immunogenicity compared to whole IgG. 68Ga is a short-lived positron emitter (t1/268 min; β+, 88%) that is produced, independent from a cyclotron, by a 68Ge/68Ga generator. The parent nuclide 68Ge has a long half-life (270.8 day), allowing its use as a generator for more than 1 year. A 68Ga is labeled with antibodies through bifunctional chelators, which allows possible kit formulation and which wide availability of the nuclear imaging agents. In this study, Fab fragment of anti-TAG-72 humanized Ab (3E8) was conjugated with 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4, 7-triacetic acid (p-SCN-Bn-NOTA) and radiolabeled with 68Ga and acquire small animal PET image