Biotinylated polyacrylamide-based metal-chelating polymers and their influence on antigen recognition following conjugation to a trastuzumab Fab fragment.

We report the synthesis and characterization of metal-chelating polymers (MCPs) with a terminal biotin and a polyacrylamide backbone harboring multiple diethylenetriaminepentaacetic acid (DTPA) chelating sites. These polymers are conjugated to a streptavidin (SAv)-modified Fab fragment of trastuzumab (tmFab) and subsequently complexed with (111)In through DTPA. Trastuzumab has specific targeting ability toward human epidermal growth factor receptor-2 (HER2), which is overexpressed on some types of breast cancer cells and ovarian cancer cells. (111)In can generate Auger electrons which cause lethal DNA double strand breaks. The radioimmunoconjugates (RICs) were designed to target HER2 overexpressing cancer cells and carry multiple copies of (111)In to these cells. The mole maximum specific activities of these polymers were investigated by loading the polymers with (111)In at an increasing (111)In to polymer ratio. The polymers show 55-fold to 138-fold higher maximum specific activity than DTPA modified tmFab-SAv. Moreover, the HER2 immunoreactivities of these RICs were evaluated by measuring their specific binding ability toward HER2 overexpressing SKOV-3 ovarian cancer cells. The results demonstrate that although in the presence of polymer there is increased nonspecific binding, HER2 targeting ability was retained, ensuring the radionuclide delivery ability of these RICs.