PREPARATION AND CHARACTERISTICS OF MAGNETITE-LABELED ANTIBODY WITH THE USE OF POLY(ETHYLENE GLYCOL) DERIVATIVES

With a view to the application of magnetic particles in cancer thermot herapy (hyperthermia), methods of preparing a bio-applicable magnetite with targeting activity towards cancer cells were investigated, and t he properties of the material examined. Poly(ethylene glycol) (PEG)-ma gnetite consisting of magnetite (Fe3O4) and PEG with terminal carboxy or amino groups was prepared. Monoclonal antibody was then immobilized covalently on to the PEG-magnetite. Among three different immobilizat ion methods employed, the highest immobilization density of 492 mg of protein/g of PEG-magnetite was achieved by using water-soluble carbodi -imide. However, with respect to residual antibody activity, only the method in which IgG sugar chains were oxidized to give aldehyde groups for coupling to N-terminal PEG-magnetite was satisfactory, with about 60% of the activity surviving. The immobilization density by this met hod (109 mg of protein/g of PEG-magnetite) was also sufficiently high. The product, termed magnetite-labelled antibody, was of sub-micrometr e size and showed easy magnetophoresis. It was further elucidated that cancer-specific magnetite-labelled antibody bound to cancer cells at an amount of 50 mg of magnetite/cm(3) of cells. The PEG-magnetite gene rates heat at an evolution rate of 31.5 W/g, and the amount adsorbed t o the cells was calculated to be high enough to heat a tumour 1 cm in diameter to more than 42 degrees C in 30 s under an alternating magnet ic field [at an intensity of 572 Oe (approx. 45.5 kA/m) and a frequenc y of 240 kHz]. This magnetite-labelled antibody is expected to be appl icable clinically as a therapeutic agent for the induction of hyperthe rmia.