In Vitro Effects and Biological Potential of Long Duration, Moderate Hyperthermia. In: Seegenschmiedt MH, Sauer R, editors. Interstitial and Intracavitary Thermoradiotherapy. Berlin: Springer Berlin Heidelberg; 1993. pp. 21-9. [DOI: 10.1007/978-3-642-84801-8_3]

Thermotolerance effects on thermoradiosensitization in human glioma cells

Human glioma cells were tested to evaluate thermotolerance (TT) development and its effect on radiosensitization. The data show that long duration mild hyperthermia (LDMH) at 40, 41 and 42 degrees C when given before acute irradiation resulted in increased radiosensitization with heating time. Furthermore, radiosensitization was not reduced by TT. When LDMH was given before 45 degrees C hyperthermia there was evidence of TT development which reduced radiosensitization compared to heating at 45 degrees C alone. For 40 and 41 degrees C heating the effect was maximum for the 8 h heating time while for 42 degrees C it was generally maximum for the 4 h heating time. At longer heating times of 24 to 48 h the effect of TT declined. Thus while LDMH itself does not display TT for radiosensitization it can in fact produce a TT effect on radiosensitization when used in a stepup-heating protocol with 45 degrees C.

Chronic thermotolerance with continued cell proliferation

The human colon adenocarcinoma cell line, NSY42129, is capable of proliferation at 41.1 degrees C. This ability appears to be due to a type of chronic thermotolerance, as opposed to selection or adaptation, that allows these cells to traverse S phase at elevated temperatures. Four other human cell lines were studied for their ability to proliferate at 41.1 degrees C. Of those only one, also a colon adenocarcinoma, showed the ability to sustain proliferation at 41.1 degrees C. While all the cell lines examined showed increased levels of the major heat shock proteins at 41.1 degrees C, the cellular amounts of these proteins did not correlate with their ability to proliferate at 41.1 degrees C. However, the ability of the cells to proliferate at 41.1 degrees C did correlate with their ability to sustain elevated rates of synthesis of hsp70 and hsp90. These results could have implications in the clinical application of hyperthermia, particularly the use of long duration moderate hyperthermia.

Cell killing, DNA polymerase inactivation and radiosensitization to low dose rate irradiation by mild hyperthermia in four human cell lines

Four human cell lines (one fibroblast, two melanoma and one glioma) were evaluated for their responses to hyperthermia and thermalradiosensitization. For mild hyperthermia (40-42 degrees C), there was little to no chronic thermotolerance development during protracted heating for up to 72 h. In addition, there was no significant thermotolerance for polymerase inactivation during mild hyperthermia. For high temperature hyperthermia, polymerase beta was more thermal sensitive than aphidicolin sensitive polymerase alpha + delta + epsilon, (termed polymerase alpha) but during mild hyperthermia ther relative sensitivities were reversed. Polymerase beta was resistant to mild hyperthermia and polymerase alpha was very sensitive. Within each cell line there was a correlation between polymerase alpha inactivation and the degree of radiosensitization (TER) and amongst the cell lines the most radiation resistant cell line had less polymerase alpha inactivation than the most sensitive cell line for similar values of TER's. These data indicate that, amongst the cell lines, radiosensitivity and polymerase alpha sensitivity may influence TER and that for a given cell line, or possibly tumour, polymerase alpha inactivation may have potential as an indicator to determine TER for mild hyperthermia treatments in radiosensitization to low dose rates.

Thermotolerance in human glioma cells

Human glioma cells held in plateau phase were tested for the development of chronic and acute thermotolerance. Long duration, mild hyperthermia at 39-42 degrees C for up to 48 h showed no development of chronic thermotolerance. Heating at 45 degrees C immediately after mild hyperthermia showed that acute thermotolerance did develop for 40-42 degrees C heating. This thermotolerance developed at about the same rate for the three inducing temperatures (40-42 degrees C) but the decay characteristics were temperature dependent. In fact, for 42 degrees C heating thermosensitization to subsequent 45 degrees C heating was achieved after 48 h of heating. These data show that chronic and acute thermotolerance may be different in human glioma cells.