Inhibition of tumor growth in a xenograft model of glioblastoma treated with MSR-1 Magnetosomes and Alternating Magnetic Field

Magnetic Fluid Hyperthermia (MFH) involves the use of iron-based magnetic nanoparticles injected into the tumor mass (1, 2) to selectively heat malignant tissues. Magnetotactic bacteria, discovered in 1963, naturally produce iron nanoparticles named magnetosomes (MNs) that have been recently used in MFH of experimental tumors (3). We have extracted magnetosomes from a bacterial strain, Magnetospirillum griphiswaldense, and tested their usefulness in MFH applications. As observed by Transmission Electron Microscopy (TEM), MNs exhibit cuboctahedral structure, dimension of 42±9 nm and are organized in chains. In vivo studies were performed on subcutaneous tumors obtained by injecting human glioblastoma cells (U87 MG) in mice. Subjects treated with MNs were exposed three times in a week for 20 minutes to an alternating magnetic field (AMF) with strenght of 23 mT and frequency of 192 kHz.The efficacy of the treatment was assessed measuring tumor volumes in vivo by magnetic resonance imaging (MRI) and ex vivo by histology. MRI was able to map the injection site and distribution of MNs in the neoplastic mass. Alterations in signal intensity of tumor tissues were also visible and confirmed by histology. A sensible inhibition of the tumor growth was observed in animals exposed to AMF who received MNs, compared to controls. In a small number of animals an almost complete reduction of tumor mass was observed soon after MFH treatment. The results obtained show that hyperthermia protocols based on magnetic iron nanoparticles may serve as a potential method for the treatment of tumors although further investigations are necessary.