In order to understand the behavior of individual cells, single cell analyses have attracted attention since most cell-based assays provide data with values averaged across a large number of cells. Techniques for the manipulation and analysis of single cells are crucial for understanding the behavior of individual cells. In the present study, we have developed single cell culture arrays using magnetic force and a pin holder, which enables the allocation of the magnetically labeled cells on arrays, and have analyzed their dynamics. The pin holder was made from magnetic soft iron and contained more than 6000 pillars on its surface. The pin holder was placed on a magnet to concentrate the magnetic flux density above the pillars. NIH/3T3 fibroblasts that were labeled with magnetite cationic liposomes (MCLs) were seeded into a culture dish, and the dish was placed over the pin holder with the magnet. The magnetically labeled cells were guided on the surface where the pillars were positioned and allocated on the arrays with a high resolution. Single-cell patterning was achieved by adjusting the number of cells seeded, and the target cell was collected by a micromanipulator after removing the pin holder with the magnet. Furthermore, change in the morphology of magnetically patterned cells was analyzed by microscopic observation, and cell spreading on the array was observed with time duration. Magnetic force-based cell patterning on cell culture arrays would be a suitable technique for the analysis of cell behavior in studies of cell–cell variation and cell–cell interactions.

We have developed magnetite cationic liposomes (MCLs) and applied them to local hyperthermia as a mediator. MCLs have a positive charge and generate heat under an alternating magnetic field (AMF) by hysteresis loss. In this study, the effect of hyperthermia using MCLs was examined in an in vivo study of hamster osteosarcoma. MCLs were injected into the osteosarcoma and then subjected to an AMF. The tumor was heated at over 42°C, but other normal tissues were not heated as much. Complete regression was observed in 100% of the treated group hamsters, whereas no regression was observed in the control group hamsters. At day 12, the average tumor volume of the treated hamsters was about 1/1000 of that of the control hamsters. In the treated hamsters, no regrowth of osteosarcomas was observed over a period of 3 months after the complete regression. These results suggest that this treatment is effective for osteosarcoma.

Tyrosine analogs are good candidates for developing melanoma chemotherapies because melanogenesis is inherently toxic and expressed uniquely in melanocytic cells. The sulfur homolog of tyrosine, 4‐S‐cysteaminylphenol (4‐S‐CAP), was shown to be a substrate of melanoma tyrosinase and can cause selective cytotoxicity of melanocytes and melanoma cells. Previously, in order to improve the adsorption of magnetite nanoparticles to target cell surfaces, and generate heat in an alternating magnetic field (AMF) for cancer hyperthermia, we produced hyperthermia using magnetite cationic liposomes (MCL) that have a positive charge at the liposomal surface. In the present study, we constructed 4‐S‐CAP‐loaded MCL (4‐S‐CAP/MCL), which act as a novel modality, combining melanoma‐specific chemotherapy by 4‐S‐CAP with intracellular hyperthermia mediated by MCL. The 4‐S‐CAP/MCL exerted 4‐S‐CAP‐mediated anticancer effects on B16 melanoma cells in vitro and in vivo. Moreover, after intratumoral injection of 4‐S‐CAP/MCL in vivo, the melanoma nodules were heated to 45°C under an AMF. Significantly higher therapeutic effects were observed in mice treated with the combination therapy mediated by 4‐S‐CAP/MCL plus AMF irradiation compared with mice treated with 4‐S‐CAP/MCL alone (without AMF) or mice treated with hyperthermia alone (MCL + AMF irradiation). These results suggest that this novel therapeutic tool is applicable to the treatment of malignant melanoma. (Cancer Sci 2007; 98: 424–430)