Treating cancer with heat: hyperthermia as promising strategy to enhance apoptosis

The fundamental idea and the effects of heat on cancer cells are well known. However, the results obtained in therapy by hyperthermia (HT) alone have been only partially satisfactory. Treatment at temperatures between 40 and 44°C is cytotoxic for cells in an environment with a low oxygen partial pressure and low pH, conditions that are found specifically within tumour tissue, due to insufficient blood perfusion. Under such conditions radiotherapy is less effective, and systemically applied cytotoxic agents will reach such areas in lower concentrations than in well-perfused areas. Therefore, clinically, it is preferred to use hyperthermia in combination with radiation therapy and chemotherapy. Hyperthermia can be applied by several methods: local hyperthermia by external or internal energy sources; regional hyperthermia by perfusion of organs or limbs, or by irrigation of body cavities; and whole-body hyperthermia. Number of studies have reported the combination of thermo-radiotherapy. Consequently, much attention has been focussed on identifying agents among the conventional chemotherapeutic substances that can sensitise tumour cells to hyperthermia-induced damage with minimal effects on normal cells. In this review, we overviewed important mechanisms of hyperthermia-induced apoptosis and the substances which can act as heat sensitisers in cancer therapy