Developments for the minimally invasive treatment of tumours by targeted magnetic heating

Purpose. Among the different minimally invasive methods for the treatment of tumours under investigation, the accumulation of magnetic material at the target region and the exposure to an alternating magnetic field comprises a highly selective approach. In the present study, we assessed if magnetic heating of tumour cells in vitro is feasible after binding of high-affinity magnetic nanoparticles to the tumour specific protein Her-2/neu, which is known to be expressed in 30% of breast cancers. Material and methods. Antibodies against the Her-2/neu protein (high-affinity probe) or non-specific gamma immunoglobulins (non-affinity probe, control) were coupled to the dextran shell of magnetic nanoparticles (mean total particle diameter, 150 nm). After incubation of Her-2/neu overexpressing SK-BR-3 tumour cells with the high-affinity probe, non-affinity probe or buffer, cell labelling was verified by electron microscopy. The iron content in cells was determined by atomic absorption spectroscopy. Moreover, cells were exposed to an alternating magnetic field (amplitude, 11 kA m−1; frequency, 410 kHz) for 2.8 min. Temperatures were measured using thermocouples. Results. A distinct cell labelling was observed by electron microscopy after incubation of cells with the high-affinity probe as compared to controls. Magnetic nanoparticles were found to be localized at the cell surface as well as in granules inside the cytoplasm. The iron content of high-affinity labelled cells (e.g. 76 µg/5 × 107 cells) was distinctly higher than in control cells (e.g. up to 25 µg/5 × 107 cells). During magnetic heating, temperature increases of up to approximately 8 °C were observed in relation to high-affinity labelled cells as compared to 1–2 °C in controls. Conclusion. Our results show that targeted magnetic heating of tumour cells seems to be feasible. Further investigations should focus on the corresponding relationships in the in vivo situation.