title: Step-down heating in a C3H mammary carcinoma in vivo: effects of varying the time and temperature of the sensitizing treatment.
abstract: The effect of step-down heating (SDH), consisting of an initial sensitizing treatment (ST) performed at either 44.5 degrees C or 43.5 degrees C followed by a lower temperature test treatment (TT), was investigated in a C3H mammary carcinoma in vivo. A linear relationship between heating time and tumour growth delay was observed for all temperature combinations applied. At a given TT temperature, SDH increased the slope of the dose-response curve compared to the curve for tumours, single-heated without an initial ST. The slope of the SDH curves increased asymptotically towards a plateau value as the ST time at 44.5 degrees C was increased. The time-temperature relationship for single heating was described by a biphasic Arrhenius curve with activation energies of 1361 +/- 34 and 666 +/- 54 kJ/mol below and above an inflection point at 42.5 degrees C, respectively. For SDH, the Arrhenius curve gradually became straight with increasing ST time, and the activation energy saturated at a value of 425 +/- 25 kJ/mol. The reduction of the activation energy at an ST temperature of 43.5 degrees C was due rather to the extent of ST heat damage than to the ST time or temperature used. These results may be relevant for calculations of thermal doses, since even a short temperature peak (e.g. 44.5 degrees C/5 min) significantly changed the time-temperature relationship.
authors.affiliation: Danish Cancer Society, Department of Experimental Clinical Oncology, Aarhus, Denmark.
authors.forename: J C
authors.initials: JC
authors.lastname: Lindegaard
authors.forename: J
authors.initials: J
authors.lastname: Overgaard
mesh_terms: D000818:Animals; D005260:Female; D006358:Hot Temperature / Q000627:therapeutic use*; D008325:Mammary Neoplasms, Experimental / Q000628:therapy*; D051379:Mice; D008809:Mice, Inbred C3H; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors