It has been proven and confirmed in numerous repeated tests, that the use of a combination of several therapeutic methods gives much better treatment results than in the case of separate
therapies. Particularly promising is the combination of ionizing radiation and magnetic
hyperthermia in one drug. To achieve this objective, magnetite nanoparticles have been modified in their core with α emitter 225Ac, in an amount affecting only slightly their magnetic properties. By 3-phosphonopropionic
acid (CEPA) linker nanoparticles were conjugated covalently with
trastuzumab (Herceptin®), a
monoclonal antibody that recognizes ovarian and
breast cancer cells overexpressing the HER2 receptors. The synthesized bioconjugates were characterized by transmission electron microscopy (TEM), Dynamic Light Scattering (DLS) measurement, thermogravimetric analysis (TGA) and application of 131I-labeled
trastuzumab for quantification of the bound biomolecule. The obtained results show that one 225Ac@Fe3O4-CEPA-
trastuzumab bioconjugate contains an average of 8-11 molecules of
trastuzumab. The labeled nanoparticles almost quantitatively retain 225Ac (>98%) in
phosphate-buffered saline (PBS) and physiological
salt, and more than 90% of 221Fr and 213Bi over 10 days. In human serum after 10 days, the fraction of 225Ac released from 225Ac@Fe3O4 was still less than 2%, but the retention of 221Fr and 213Bi decreased to 70%. The synthesized 225Ac@Fe3O4-CEPA-
trastuzumab bioconjugates have shown a high cytotoxic effect toward SKOV-3
ovarian cancer cells expressing HER2 receptor in-vitro. The in-vivo studies indicate that this bioconjugate exhibits properties suitable for the treatment of
cancer cells by intratumoral or post-resection injection. The
intravenous injection of the 225Ac@Fe3O4-CEPA-
trastuzumab radiobioconjugate is excluded due to its high accumulation in the liver, lungs and spleen. Additionally, the high value of a specific absorption rate (SAR) allows its use in a new very perspective combination of α
radionuclide therapy with magnetic
hyperthermia.