Magnetite nanoparticles have been used in biological and medical applications, such as the separation of biological materials using magnetically labeled beads [1
], drug delivery and medicine [2
], or cell sorting, based on the fact that high magnetic flux density attracts magnetically labeled cells [3
]. We previously developed "magnetite cationic liposomes" (MCLs), which are cationic liposomes containing 10-nm magnetite nanoparticles, in order to improve the accumulation of magnetite nanoparticles in target cells using the electrostatic interaction between MCLs and the cell membrane [6
]. Currently, we have developed a tissue engineering technique using MCLs [7
]. Mesenchymal stem cells (MSCs), which can differentiate into multiple mesodermal tissues, can be isolated from bone marrow in a small number. Magnetically labeled MSCs were easily prepared, because our MCLs exhibited no toxicity against the MSCs in proliferation and differentiation, and then the MSCs were enriched into the localized area that the magnetic force can reach. Cell growth was promoted and a five-fold increase in cell number was obtained at 7 days after cell seeding [7
]. To establish 3D in vivo
-like tissues consisting of various types of cells, we applied MCLs to the co-culture system of rat hepatocytes and human aortic endothelial cells (HAECs). Magnetically labeled HAECs accumulated onto hepatocyte monolayers by magnetic force to form a heterotypic, layered construct with tight and close contact. Albumin secretion by hepatocytes was about three times higher than that of the control co-culture system without magnetic force [8
]. MCLs were also applied to construct multilayered keratinocyte sheets. On a 24-well ultra-low-attachment plate, a 5-layered keratinocyte sheet was first produced and a 10-layered epidermal sheet was formed in a high-calcium medium. The sheet formed ordinarily was detached from the bottom of the plate when the magnet was removed, and transplantation to the patient was easily performed [9
]. We have termed this culture methodology as "magnetic force-based tissue engineering (Mag-TE)". We have also used MCLs as a heating mediator for cancer hyperthermia, because magnetite nanoparticles generate heat under an alternating magnetic field (AMF) [10
Hyperthermia is one of the promising approaches in cancer therapy, and various methods have been employed in hyperthermia [14
]. The most commonly used heating method in clinical settings is capacitive heating using a radiofrequency (RF) electric field [16
]. However, heating tumors specifically 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 more desirable not only for superficially located tumors but also for deep-seated tumors. Some researchers have proposed inductive heating methods, using submicron magnetic particles, for hyperthermia [17
]. We have also developed MCLs for intracellular hyperthermia [6
], which showed a ten-fold higher affinity for the tumor cells than neutrally charged magnetoliposomes [10
]. Based on this feature, MCLs can be highly superior heating mediators. We previously demonstrated the efficacy of MCL-mediated hyperthermia in animals with several types of tumors, including B16 mouse melanoma [19
], T-9 rat glioma [11
], renal cell carcinoma [22
], and VX-7 squamous cell carcinoma in rabbit tongue [23
]. We also reported complete regression of mouse mammary carcinoma, larger than 15 mm in size, by frequent repeated hyperthermia [24
]. Although MCL-mediated hyperthermia was found to be very effective for inducing complete regression of tumors, no studies have investigated the biodistribution of MCLs after local injection.
Osteosarcoma is a primary malignant tumor of the bone that mostly occurs in growing children and young adults [25
]. Effective systemic adjuvant chemotherapy on the primary tumor and improvements in surgical resection techniques have improved the survival rate. However, these have not proved to be sufficiently effective, and a more effective protocol for the prevention and treatment of osteosarcoma is needed.
Therefore, in the present paper, our hyperthermia system was applied to hamster osteosarcoma and its hyperthermic effect was investigated.