A comparison of HER2/neu accumulations of Ga-67-labeled anti-HER2 antibody with chemically and site-specifically conjugated bifunctional chelators.

Monoclonal antibodies (mAb) developed to target specific cancers have achieved considerable success to date. To further enhance therapeutic efficacy, monoclonal antibodies may be conjugated with a cytotoxic drug or radioisotope. We present the development of a new method based on site-specific conjugation (SSC) for targeting HER2. The study design involves a comparison of the accumulation of Ga-67-labeled anti-HER2 antibodies with SSC (SSC-mAb) versus conventional chemical conjugation (Chem-mAb) in HER2-positive tumors. In vitro, the HER2-binding capacity of SSC-mAb and Chem-mAb was comparable. However, in vitro, the rate of tumor accumulation increased gradually with SSC-mAb not only in the tumors but also in the blood and other organs. The SSC may improve targeted antigen-specific cancer radioimmunotherapy and may, due to higher retention, reduce the amount of treatment required.