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Heating properties of magnetite cationic liposomes (MCL) were investigated in ex vivo experiments using implanted cell pellets. The cell pellets, which consisted of rat glioma T9 cells into which MCL had been incorporated in a petri dish, were implanted subcntaneously in the left femoral region of female F344 rats. The rats were placed in a magnetic field generating coil and irradiated with an alternating magnetic field (384 Oe, 118 kHz) for 60 min. The cell pellets were heated to over 43°C by MCL in the magnetic field, hut other body parts of the rats were not heated. After 3 cycles of magnetic heating, all glioma cells were killed and no tumor take was observed.

Immunotherapy (IT) has become an accepted therapeutic modality. We previously reported that intracellular hyperthermia (IH) using magnetic nanoparticles induces antitumor immunity. We undertook these studies in order to study the combined effects of IT and IH on melanoma. Magnetite cationic liposomes (MCLs) have a positive surface charge and generate heat in an alternating magnetic field (AMF) due to hysteresis loss. MCLs were injected into a B16 melanoma nodule in C57BL/6 mice, which were subjected to AMF for 30 min. The temperature at the tumor reached 43°C and was maintained by controlling the magnetic field intensity. At 24 h after IH, interleukin-2 (IL-2) or granulocyte macrophage-colony stimulating factor (GM-CSF) was injected directly into the melanoma. Mice were divided into six groups: group I (control), group II (IH), group III (IL-2), group IV (GM-CSF), group V (IH + + + +IL-2), and group VI (IH + + + +GM-CSF). yperthermia has been used for many years to treat a wide variety of tumors both in experimental animals and patients.1) The most commonly used heating method in clinical settings is capacitive heating using a radiofrequency (RF) electric field.2) However, specifically heating tumors by capacitive heating using an RF electric field is difficult, because the heating characteristics are influenced by various factors, such as tumor size, position of electrodes, and adhesion of electrodes at uneven sites. From a clinical point of view, a simple heat mediator is preferable for superficially seated tumors such as cutaneous melanoma. Magnetic nanoparticles have been applied to generate hyperthermia in an attempt to overcome these disadvantages.3, 4) These magnetic nanoparticles generate heat in an alternating magnetic field (AMF) due to hysteresis loss. 5)We have developed "magnetite cationic liposomes" (MCLs) for intracellular hyperthermia (IH).6, 7) MCLs were developed to show improved adsorption and accumulation in tumor cells and have a ten-fold higher affinity for tumor cells than for neutrally charged magnetoliposomes due to electrostatic interaction with the negatively charged cell membrane.6) In our in vitro experiments, 55% of MCLs were incorporated into cells and the intracellular magnetic nanoparticles could generate heat under AMF.6) We have also demonstrated the efficacy of IH using MCLs against T-9 rat glioma in an in vivo study. 8)We previously reported that our IH system induced antitumor immunity. 9) Hyperthermia is known to induce heat shock proteins (HSPs).10) Because expression of HSP70 protects cells from heat-induced apoptosis, 11) HSP70 expression has been considered to be a complicating factor in hyperthermia. On the other hand, recent reports have shown the importance of HSPs, such as HSP70, HSP90 and glucose-regulated protein 96, in immune reactions.12, 13) HSP-mediated antitumor immunity was reported to cause a vaccine effect due to HSP-peptide complexes purified from human melanoma cells.14) With regard to the mechanism of antitumor immunity induced by IH, we demonstrated th...

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Magnetic particles for medical applications have been developed by many researchers. Since magnetic particles have unique magnetic features not present in other materials, they can be applied to special medical techniques. Separation, immunoassay, magnetic resonance imaging (MRI), drug delivery, and hyperthermia are enhanced by the use of magnetic particles. Magnetite cationic liposomes (MCLs), one of the group of cationic magnetic particles, can be used as carriers to introduce DNA into cells since their positively charged surface associates with the negatively charged DNA. They can also be used as heat mediators for cancer therapy. Magnetic particles conjugated with tumor-specific antibodies have enabled tumor-specific contrast enhancement in MRI. In addition, antibody-conjugated magnetic particles were shown to target renal cell carcinoma cells, and are applicable to the hyperthermic treatment of carcinomas. The use of magnetic particles with their unique features will further improve medical techniques.

Induction of antitumor immunity to T-9 rat glioma by intracellular hyperthermia using functional magnetic particles was investigated. Magnetite cationic liposomes (MCLs), which have a positive surface charge, were used as heating mediators for intracellular hyperthermia. Solid T-9 glioma tissues were formed subcutaneously on both femurs of female F344 rats, and MCLs were injected via a needle only into the left solid tumors (treatment side). The rats were then divided into two groups, which received no irradiation, or irradiation for 30 min given three times at 24-h intervals with an alternating magnetic field (118 kHz, 384 Oe). On the treatment side, the tumor tissue disappeared completely in many rats exposed to the magnetic field. The tumor tissue on the opposite side also disappeared completely, even though MCLs were not injected into the right solid tumors. To examine whether a long-lasting and tumor-specific immunity could be generated, the rats that had been cured by the hyperthermia treatment were rechallenged with T-9 cells 3 months later. After a period of transient growth, all tumors disappeared. Furthermore, immunocytochemical assay revealed that the immune response induced by the hyperthermia treatment was mediated by both CD8 Various methods have been employed, such as whole body hyperthermia, 2) radiofrequency hyperthermia, 3) and inductive hyperthermia using microwave antenna 4) or implantable needles. 5) However, it is always difficult to achieve uniform heating of the tumor region to the desired temperature without damaging normal tissue. Therefore, some researchers have proposed intracellular hyperthermia and developed submicron magnetic particles for this purpose.6-8) These magnetic particles are easily incorporated into cells and generate heat under an alternating magnetic field through hysteresis loss. 9) We have also developed 'magnetite cationic liposomes' (MCLs) for intracellular hyperthermia.10, 11) MCLs were developed to improve adsorption and accumulation into the tumor cells and show ten-fold higher affinity for tumor cells than neutrally charged magnetoliposomes, 10) owing to electrostatic interaction with the negatively charged cell membrane. 12,13) The hyperthermic effect of the MCLs was examined in vivo.14) MCLs were injected into solid tumors formed subcutaneously in F344 rats and the rats were irradiated three times for 30 min with an alternating magnetic field. Histological observations were carried out just after the irradiation and showed that some tumor cells survived, especially in the peripheral area. However, complete tumor regression was observed one month after the irradiation. We were interested in the possibility that antitumor immunity had been induced by the hyperthermic treatment using MCLs.In the present paper, it is demonstrated that our hyperthermia system can induce an antitumor immune response and the acquired immunity is long-lasting. MATERIALS AND METHODS MaterialsDilauroylphosphatidylcholine and dioleoylphosphatidylethanolamine were purchased from Sigma Ch...

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