ANTIBODY MAGNETITE NANOPARTICLES - IN-VITRO CHARACTERIZATION OF A POTENTIAL TUMOR-SPECIFIC CONTRAST AGENT FOR MAGNETIC-RESONANCE-IMAGING

Target-specific superparamagnetic contrast agents may allow the locali zation of specific tissues such as tumors by magnetic resonance imagin g (MRI). In this report the preparation and in vitro characterization of tumor-specific superparamagnetic particles (SMP) are described. Par ticles of uniform size (9.6 +/- 0.8 nm) were prepared from an alkaline solution of ferric and ferrous ions and isolated by differential cent rifugation. The resulting nanoparticle suspension is stabilized in buf fer using a polypeptide coat to which a monoclonal antibody, specific to carcinoembryonic antigen (CEA), was covalently attached at the hing e region. The resulting anti-CEA SMP have a hydrodynamic radius of les s than 50 nm, and specifically bind to CEA in vitro. The visualization of epitopes, present on a cell surface in very low density as expecte d for tumor antigens or receptors, may be achieved due to the high R2 relaxivity of 300 L mmol-1 s-1 of the contrast agent described here. F urthermore, the polypeptide coat chosen provides an ideal platform for the attachment of biological modifiers needed for the reduction of th e antigenicity and blood clearance rate of anti-CEA SMP.