OUR APPROACH TOWARDS DEVELOPING A SPECIFIC TUMOR-TARGETED MRI CONTRAST AGENT FOR THE BRAIN

This review presents various aspects of the technological development, and their assessment in the design of a contrast agent for MRI, tailo red to visualise tumours in the brain. First, it was demonstrated that magnetite as a contrast agent exhibited a much stronger relaxivity th an gadolinium. The prepared magnetite particles bound to dextran, were also shown to be of appropriate size by electron microscopy. After th eir intravenous injection into rats with blood-brain barrier disruptio n, the lesion was strongly enhanced by T2-shortening. Furthermore, mon oclonal antibodies directed against small cell lung carcinoma, proved to be able to penetrate into tumours, which had been raised by implant ation of the small cell lung carcinoma cells into the brains of nude r ats. As to the essential step, it was demonstrated in vitro that magne tite particles coupled to monoclonal antibodies by the biotin-streptav idin binding, could be bound to the target cells of the antibody, chan ging the relaxation rates of the latter. Finally it could be shown in vitro that an alternative approach, using lymphocytes to be targeted t o tumour cells, also proved feasible, in that these lymphocytes could be labelled with magnetite that had been incorporated into liposomes. Further developments will be the in vivo assessment of the acquired pr ogress in experimental animals, before clinical application is warrant ed.