The effect of mild hyperthermia on a cultured rat malignant fibrous histiocytoma (MFH) cell line, MFH-ZNR, was imestigated. MFH cells in log-phase (growing phase) were heated at 4I0-44"C for I hr. Hyperthermic treatment at 41°C did not substantially affect cell proliferadon and treatment at 44°C caused necrosis. After hyperthermic treatment at 42" or 43"C, proliferation of MFH cells was arrested and morphological changes characteristic of apoptosis, cell shrinkage accompanying apoptotic bodies and chromatin condensation, became apparent. Hyperthermia-induced apoptosis was further confirmed by terminal deoxynucleotidyl transferase staining and a ladder pattern on agarose gel electrophoresis. Flow qtometric analysis indicated that the population in the GI phase of the cell cycle significantly decreased with a concomitant increase in apoptotic cells, indicating that apoptosis might occur mainly in the GI phase population.Q 19% Wifey-Liss, Inc.Hyperthermia is generally recognized as an effective and attractive tool in anti-tumor therapy (Dewey et al., 1989). We frequently employ hyperthermia against several malignant bone and soft tissue tumors in combination with radiation and chemotherapy. During these treatments, we noticed that malignant fibrous histiocytoma (MFH), one of the most commonly occurring malignant tumors of soft tissues, was exceptionally sensitive and susceptible to hyperthermia. From an in vitro cell biological viewpoint, it is of interest to define the unique behavior of MFH cells among other bone or soft tissue malignant tumor cells derived from osteosarcoma, rhabdomyosarcoma and liposarcoma. To date, however, little has been reported in terms of experimental studies on hyperthermiainduced anti-tumor effects on malignant tumor cells in the orthopedic field, except for an in vivo experiment using mouse fibrosarcoma (Stewart and Denekamp, 1978). Therefore, we have started to investigate the specific effect of hyperthermia on MFH cell growth in vitro. During the initial course of in vitro experiments, we found that MFH cells underwent a critical temperature-dependent cell death, including an apoptosis-like appearance at 42"43"C and necrosis-like appearance at 2 44°C. These observations prompted us to study in detail the biological changes induced by hyperthermia in the MFH cell.In the current study, we characterize the morphological and biochemical alterations of MFH cells induced by hyperthermia resulting in apoptosis and discuss the clinical advantage of hyperthermia in MFH.
MATERIAL AND METHODS
Cell cultureThe rat malignant fibrous histiocytoma cell line MFH-2NR was kindly provided by the Department of Oncological Pathology of Nara Medical College. MFH-NR2 was induced from rat cells by 4-hydroxyaminoquinoline l-oxide (Konishi et al., 1982(Konishi et al., , 1984 Mii et af., 1982). Primary cultures of rat fibroblasts were prepared from adult rats, and 3rd generations were used for experiments. Both cells were cultured in DMEM supplemented with 10% (v/v) FBS, 2 X 104 U/1 penicillin G and 200 mg/l st...
