Hyperthermic treatment of canine tibia through RF inductive heating of an intramedullary nail: a new experimental approach to hyperthermia for metastatic bone tumours

Photothermal stress triggered by near infrared-irradiated carbon nanotubes promotes bone deposition in rat calvarial defects

The bone regenerative healing process is often prolonged, with a high risk of infection particularly in elderly and diseased patients. A reduction in healing process time usually requires mechanical stress devices, chemical cues, or laser/thermal therapies. Although these approaches have been used extensively for the reduction of bone healing time, the exact mechanisms involved in thermal stress-induced bone regeneration remain unclear. In this study, we investigated the effect of optimal hyperthermia on rat calvarial defects in vivo and on osteogenesis in vitro. Photothermal stress stimulation was carried out using a new photothermal device, composed of an alginate gel including in carbon nanotubes and their irradiator with near-infrared light. Photothermal stress (15 min at 42℃, every day), trigged by near-infrared-induced carbon nanotube, promoted bone deposition in critical-sized calvarial defects compared with nonthermal stress controls. We recently reported that our novel DNA/protamine complex scaffold induces bone regeneration in calvarial defects. In this study, photothermal stress upregulated bone deposition in DNA/protamine-engrafted calvarial defects. Furthermore, photothermal stress significantly induced expression of osteogenic related genes in a time-dependent manner, including alkaline phosphatase, osterix, and osteocalcin. This was observed in DNA/protamine cells, which were expanded from regenerated tissue engrafted into the DNA/protamine scaffold, as well as in human MG63 preosteoblasts. In summary, this novel carbon nanotube-based photothermal stress approach upregulated expression of osteogenic-related genes in preosteoblasts, resulting in promotion of mineral deposition for enhanced bone repair.

A novel hyperthermia treatment for bone metastases using magnetic materials

Patients with bone metastases in the extremities sometimes require surgical intervention to prevent deterioration of quality of life due to a pathological fracture. The use of localized radiotherapy combined with surgical reinforcement has been a gold standard for the treatment of bone metastases. However, radiotherapy sometimes induces soft tissue damage, including muscle induration and joint contracture. Moreover, cancer cells are not always radiosensitive. Hyperthermia has been studied since the 1940s using an experimental animal model to treat various types of advanced cancer, and studies have now reached the stage of clinical application, especially in conjunction with radiotherapy or chemotherapy. Nevertheless, bone metastases have several special properties which discourage oncologists from developing hyperthermic therapeutic strategies. First, the bone is located deep in the body, and has low thermal conductivity due to the thickness of cortical bone and the highly vascularized medulla. To address these issues, we developed new hyperthermic strategies which generate heat using magnetic materials under an alternating electromagnetic field, and started clinical application of this treatment modality. The purpose of this review is to summarize the latest studies on hyperthermic treatment in the field of musculoskeletal tumors, and to introduce the treatment strategy employing our novel hyperthermia approach.

Effects of hyperthermia on heat shock protein expression, alkaline phosphatase activity and proliferation in human osteosarcoma cells

Hyperthermia can be used as a possible adjuvant therapy in treatment of cancer patients. In this study, the direct effect of hyperthermia on osteosarcoma derived cell lines HOS85, MG-63 and SaOS-2 was investigated. Heat shock at 42 degrees C inhibited proliferation significantly in all three cell lines tested. Furthermore a sub-lethal heat shock (42 degrees C, 1 h) decreases alkaline phosphatase activity, the absolute marker for osteoblast-like cells, in all of the three cell lines. Hsp70 was expressed constitutively and was found to be upregulated in a time-dependent manner; by up to 150% in Western blot analysis. The results of this study indicate that heat shock has an inhibitory effect on human osteosarcoma cells. These data suggest that hyperthermia has an anti-tumour effect on cancers of the bone and might, therefore, become an adjuvant treatment option.

Novel hyperthermia for metastatic bone tumors with magnetic materials by generating an alternating electromagnetic field

We have developed a novel hyperthermic treatment modality using magnetic materials for metastatic bone tumors. The purpose of this study is to show the results of novel hyperthermia for metastatic bone tumors. This novel hyperthermic treatment modality was used for 15 patients with 16 metastatic bone lesions. In seven lesions, after curettage of the metastatic lesion followed by reinforcement with a metal intramedullary nail or plate, calcium phosphate cement (CPC) containing powdery Fe3O4 was implanted into the cavity. In one lesion, prosthetic reconstruction was then performed after an intralesional tumor excision. For the remaining eight lesions, metal intramedullary nails were inserted into the affected bone. Hyperthermic therapy was started at 1 week postoperatively. To comparatively evaluate the radiographic results of patients who underwent hyperthermia (HT group), we also assessed eight patients who received a palliative operation without either radiotherapy or hyperthermia (Op group), and 22 patients who received operation in combination with postoperative radiotherapy (Op + RT group). In HT group, all patients had an acceptable limb function with pain relief without any complications. On radiographs, 87, 38, and 91% were, respectively, considered to demonstrate an effective treatment outcome in HT group, Op group, and Op + RT group. The patients in HT group showed a statistically better radiographic outcome than the patients in Op group (P = 0.0042). But when compared between HT group and Op + RT group, there were no significant difference (P = 0.412). This first series of clinical hyperthermia using magnetic materials achieved good local control of metastatic bone lesion.

Mild heat shock induces proliferation, alkaline phosphatase activity, and mineralization in human bone marrow stromal cells and Mg-63 cells in vitro

Bone formation has been shown to be stimulated by local diathermy in vivo; however, the mechanisms involved in this heat-induced osteogenesis are unclear. In this study, we investigated the direct effect of temperature on human bone marrow-derived stromal cells (BMSCs) and the human osteoblast-like, osteosarcoma-derived MG-63 cells in culture conditions. Both cell types were shown to tolerate the transient exposure to mild heat shock conditions (1 h at 39-41 degrees C), and long-term (96 h) exposure at 39 degrees C stimulated DNA synthesis in BMSC but caused growth arrest in MG-63 cells. Furthermore, 1-h exposure to higher temperatures (42.5-45 degrees C) or continuous 96-h exposure to 40 degrees C or 41 degrees C inhibited the proliferation of both BMSCs and MG63 cells. The level of alkaline phosphatase (ALP) in these cells linearly correlated with the increase in temperature, and the ALP expression, either at the basal level or in response to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], was enhanced after a single 1-h exposure to 42.5 degrees C. In addition, continuous incubation at 39 degrees C or repeated transient exposure to 39/41 degrees C greatly enhanced the ability of BMSCs to form mineralizing nodules. The heat shock protein HSP70, which was expressed constitutively by BMSCs, was found to be up-regulated by hyperthermia (39 degrees C) and down-regulated at 33 degrees C. The expression of HSP70 could be induced in MG-63 cells by both low- and high-temperature conditions. These data suggest that treatment with a mild heat shock induces the proliferation and differentiation of osteoprogenitor cells, and the direct effects of temperature on bone-forming cells might be one of the mechanisms involved in heat-induced bone formation in vivo.

New ferromagnetic bone cement for local hyperthermia

We have developed a ferromagnetic bone cement as a thermoseed to generate heat by hysteresis loss under an alternate magnetic field. This material resembles bioactive bone cement in composition, with a portion of the bioactive glass ceramic component replaced by magnetite (Fe3O4) powder. The temperature of this thermoseed rises in proportion to the weight ratio of magnetite powder, the volume of the thermoseed, and the intensity of the magnetic field. The heat-generating ability of this thermoseed implanted into rabbit and human cadaver tibiae was investigated by applying a magnetic field with a maximum of 300 Oe and 100 kHz. In this system, it is very easy to increase the temperature of the thermoseed in bone beyond 50 degrees C by adjusting the above-mentioned control factors. When the temperature of the thermoseed in rabbit tibiae was maintained at 50 to 60 degrees C, the temperature at the interface between the bone and muscle (cortical surface) surrounding the material rose to 43 to 45 degrees C; but at a 10-mm distance from the thermoseed in the medullary canal, the temperature did not exceed 40 degrees C. These results demonstrate that ferromagnetic bone cement may be applicable for the hyperthermic treatment of bone tumors.

Anti-tumour effects of localized hyperthermia on an experimental bone tumour using an intramedullary nail

A new localized hyperthermia system for an experimental bone tumour in the rabbit tibia was developed. This system was composed of an induction coil, generator and a Kirschner wire, which was inserted into the medullary canal of the tibia as a heat-generating ferromagnetic implant. The metastatic bone tumour model was created by implantation of VX2 carcinoma in the medullary canal of the tibia diaphysis. The days after VX2 implantation, hyperthermia was induced for 50 min. Three weeks after the treatment, rabbits were sacrificed for histological and radiological evaluation. According to the semi-quantitative scoring system, anti-tumour effects of the single dose of hyperthermia was noted radiologically (p < 0.01) and histologically (p < 0.05) where the temperature was at a sufficient level to cause hyperthermia (> 42.5 degrees C). This new heating method, which is relatively simple and clinically applicable, appears to be promising for the treatment of metastatic tumours of the long bone.