Trastuzumab Conjugated Superparamagnetic Iron Oxide Nanoparticles Labeled with (225)Ac as a Perspective Tool for Combined α-Radioimmunotherapy and Magnetic Hyperthermia of HER2-Positive Breast Cancer

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 (225)Ac, 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 (131)I-labeled trastuzumab for quantification of the bound biomolecule. The obtained results show that one (225)Ac@Fe(3)O(4)-CEPA-trastuzumab bioconjugate contains an average of 8–11 molecules of trastuzumab. The labeled nanoparticles almost quantitatively retain (225)Ac (>98%) in phosphate-buffered saline (PBS) and physiological salt, and more than 90% of (221)Fr and (213)Bi over 10 days. In human serum after 10 days, the fraction of (225)Ac released from (225)Ac@Fe(3)O(4) was still less than 2%, but the retention of (221)Fr and (213)Bi decreased to 70%. The synthesized (225)Ac@Fe(3)O(4)-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 (225)Ac@Fe(3)O(4)-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.