Self-regulating hyperthermia induced using thermosensitive ferromagnetic material

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Hyperthermia has been used for many years to treat variety of malignant tumors. The Curie temperature (Tc) is a transition point at which magnetic materials lose of its magnetic properties, which causes a cessation of current and thus heat production. The Tc enables automatic temperature control throughout a tumor as a result of the self-regulating nature of the thermosensitive material. We have developed a method of magnetically induced hyperthermia using thermosensitive ferromagnetic particles (FMPs) with low Tc (43℃) enough to mediate automatic temperature control.B16 melanoma cells were subcutaneously injected into the backs of C57BL/6 mice, after which tumors were allowed to grow to 5mm in diameter. FMPs were then injected into the tumors, and the mice were divided into three groups: group-I (no hyperthermia; control), group-II (one hyperthermia treatment) and group-III (hyperthermia twice a week for 4 weeks) . When exposed to a magnetic field, the FMPs showed a sharp rise in heat production, reaching the Tc in tissue within 7min, after which the tissue temperature stabilized at around the Tc. In groups-I and II, all mice died within 30 to 45days. In group-III, however, 6 of 10 mice remained alive 120days after beginning treatment.Our findings suggest that repeated treatment with magnetically induced self-regulating hyperthermia, mediated by FMPs with a low Tc, is an effective means of suppressing melanoma growth. A key advantage of this hyperthermia system is that it is minimally invasive, requiring only a single injection for repeated treatments with automatic temperature control.