Biochemical aspects of heat sensitivity of tumour cells

Evidence for separate modes of action in thermal radiosensitization and direct thermal cell death

It is not known whether heat potentiation of radiation damage and direct heat death are mediated by the same or by different heat lesions within the cell. In this study, three types of experiments were performed on BP-8 murine sarcoma cells to provide evidence against a common mode of action: (1)Evaluation of the kinetics of cell death from heat, radiation, and combined heat-radiation treatments: direct heat death is rapid and essentially complete within 24-48 hours after heat exposure, whereas radiation death develops only after a delay period of several days. Radiosensitization by heat affects only the delayed component of cell death, that is, the radiation component of death. (2)Thermal radiosensitization and direct heat death as a function of heating time: thermal radiosensitization requires only short exposures to heat; prolonged heating does not further enhance this effect. In contrast, direct heat death increases with increasing duration of heat exposure. (3)Independent modification of radiosensitization and thermal death: addition of 5% glycerol to the incubation medium protects cells against direct heat death, but not against thermal radiosensitization. In combination, these findings suggest that heat potentiation of radiation lethality and direct heat death are two distinct phenomena mediated by different cellular mechanisms.

The effect of total body microwave hyperthermia and hepatic artery ligation on liver tumors--an experimental study in rats

The effect of general microwave hyperthermia and hepatic artery ligation (HAL) was tested on Wistar rats with a transplanted N-methyl-N-nitrosoguanidine-induced adenocarcinoma in the liver. Total body hyperthermia (41.5 degrees C for 1 hour, three times during 24 hours) was given on the same day as HAL, and 1, 2, and 3 days after. HAL induced a slower tumor growth than untreated controls. No additive effect was registered when total body microwave hyperthermia was added to HAL. When hyperthermia was added 2 days after HAL, there was a transient decrease in tumor volume as in the HAL series. Total body microwave hyperthermia added 3 days after HAL induced a faster tumor growth than after HAL alone. When hyperthermia was added the same day and 1 day after HAL, there was a 50% mortality.

Nonspecific stabilization of stress-susceptible proteins by stress-resistant proteins: a model for the biological role of heat shock proteins

It is demonstrated experimentally that addition of proteins that are themselves resistant to denaturation by heat or ethanol can nonspecifically stabilize other proteins that are ordinarily highly susceptible to inactivation. It is proposed that the diffusion-limited rate with which unfolded protein molecules encounter each other and become irreversibly crosslinked is reduced in the presence of substantial concentrations of an unreactive globular protein. We suggest that one of the functions of heat shock proteins, which are synthesized in large amounts after exposure of cells to increased temperature and other forms of stress, may be to stabilize other proteins kinetically in a similarly nonspecific fashion.

Massive heat-shock polypeptide synthesis in late chicken embryos: convenient system for study of protein synthesis in highly differentiated organisms

In cultured eucaryotic cells, heat treatments specifically induced the rapid synthesis of the so-called heat-shock polypeptides. To ascertain the physiological importance of this phenomenon for highly differentiated organisms, we attempted to determine whether the heat-shock response occurs in a living endothermic organism at extreme temperatures, and if so, whether the response is organ specific. We developed a procedure to label proteins efficiently in 5- to 18-day-old chicken embryos. Heat-shock polypeptides of identical sizes of 85,000, 70,000, and 25,000 daltons were synthesized predominantly in chicken embryo fibroblasts and in many different organs of 18-day-old embryos at 42.5 to 44 degrees C.

Massive heat-shock polypeptide synthesis in late chicken embryos: convenient system for study of protein synthesis in highly differentiated organisms

In cultured eucaryotic cells, heat treatments specifically induced the rapid synthesis of the so-called heat-shock polypeptides. To ascertain the physiological importance of this phenomenon for highly differentiated organisms, we attempted to determine whether the heat-shock response occurs in a living endothermic organism at extreme temperatures, and if so, whether the response is organ specific. We developed a procedure to label proteins efficiently in 5- to 18-day-old chicken embryos. Heat-shock polypeptides of identical sizes of 85,000, 70,000, and 25,000 daltons were synthesized predominantly in chicken embryo fibroblasts and in many different organs of 18-day-old embryos at 42.5 to 44 degrees C.

Iron and neoplasia

Normal and neoplastic cells (like nonpathogenic and pathogenic microorganisms) apparently have similar needs and tolerances for iron, but neoplastic cells (like pathogenic microorganisms) may exhibit altered mechanisms of iron acquisition that permit continued growth in host iron-restricted tissues. Excess iron tends to interfere with host defense against malignant cells (as well as against microbial invaders); severe iron deficiency may likewise be detrimental. Elevated temperature is more toxic towards neoplastic than to normal host cells; it is not yet known whether the site of action of heat might be associated with iron acquisition (as has been demonstrated for gram negative bacteria). Persons or animals with iron overload tend to be at greater risk than normal hosts in the development of neoplasms.Construction of animal models of iron overload, although difficult, is strongly indicated at this time. Based on such models, decisions then can be made about the extent to which (a) nutritional immunity against neoplastic cells is practiced by vertebrate hosts and (b) clinical procedures could be employed to strengthen such immunity as an adjunct to radiotherapy, chemotherapy, and surgery.