Magnetic mesoporous silica spheres for hyperthermia therapy

Magnetic nanoparticles coated with materials having unique properties, such as ordered pore structures and large surface areas, hold great potential for multimodal therapies. This study reports on the biocompatibility of composites of maghemite nanoparticles embedded in an ordered mesoporous silica-matrix to form magnetic microspheres (MMS), and on their ability to conduct magnetic hyperthermia upon exposure to a low-frequency alternating magnetic field (AMF). MMS particles were efficiently internalized by human A549, Saos-2 and HepG2 cells, and were excluded from the nuclear compartment. MMS treatment did not interfere with morphological features or metabolic activities of the cells, indicating good biocompatibility of the material. MMS did not affect the endogenous heat-shock response of a HeLa-derived cell line that precisely reports the intensity of thermal stresses through changes in the activities of a stably integrated hsp70B promoter and a constitutive viral promoter. Maximum temperature in MMS suspensions increased to a range above 42 °C as a function of the amounts of particles exposed to AMF. Cell culture experiments showed that, by adjusting the amount of MMS and the time of exposure to AMF, heat treatments of mild to very high intensities could be achieved. Cell viability dropped as a function of the intensity of the heat treatment achieved by MMS and AMF exposures. The possibility of fine-tuning the heating power output, together with efficient uptake by tumor cells in vitro, makes MMS a promising agent by which to provide hyperthermia treatments aimed toward remission of solid tumors.