Preparation and characteristics of magnetite-labelled antibody with the use of poly(ethylene glycol) derivatives.

With a view to the application of magnetic particles in cancer thermotherapy (hyperthermia), methods of preparing a bio-applicable magnetite with targeting activity towards cancer cells were investigated, and the properties of the material examined. Poly(ethylene glycol) (PEG)-magnetite 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 immobilization 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 method (109 mg of protein/g of PEG-magnetite) was also sufficiently high. The product, termed magnetite-labelled antibody, was of sub-micrometre 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/cm3 of cells. The PEG-magnetite generates heat at an evolution rate of 31.5 W/g, and the amount adsorbed to 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 magnetic field [at an intensity of 572 Oe (approx. 45.5 kA/m) and a frequency of 240 kHz]. This magnetite-labelled antibody is expected to be applicable clinically as a therapeutic agent for the induction of hyperthermia.