Induced thermal resistance in the mouse ear

Liquid crystal elastomer based dynamic device for urethral support: Potential treatment for stress urinary incontinence

Stress urinary incontinence (SUI) is characterized by the involuntary loss of urine due to increased intra-abdominal pressure during coughing, sneezing, or exercising. SUI affects 20-40% of the female population and is exacerbated by aging. Severe SUI is commonly treated with surgical implantation of an autologous or a synthetic sling underneath the urethra for support. These slings, however, are static, and their tension cannot be non-invasively adjusted, if needed, after implantation. This study reports the fabrication of a novel device based on liquid crystal elastomers (LCEs) capable of changing shape in response to temperature increase induced by transcutaneous IR light. The shape change of the LCE-based device was characterized in a scar tissue phantom model. An in vitro urinary tract model was designed to study the efficacy of the LCE-based device to support continence and adjust sling tension with IR illumination. Finally, the device was acutely implanted and tested for induced tension changes in female multiparous New Zealand white rabbits. The LCE device achieved 5.6% ± 1.1% actuation when embedded in an agar gel with an elastic modulus of 100 kPa. The corresponding device temperature was 44.9 °C ± 0.4 °C, and the surrounding agar temperature stayed at 42.1 °C ± 0.4 °C. Leaking time in the in vitro urinary tract model significantly decreased (p < 0.0001) when an LCE-based cuff was sutured around the model urethra from 5.2min ± 1min to 2min ±0.5min when the cuff was illuminated with IR light. Normalized leak point force (LPF) increased significantly (p = 0.01) with the implantation of an LCE-CB cuff around the bladder neck of multiparous rabbits. It decreased significantly (p = 0.023) when the device was actuated via IR light illumination. These results demonstrate that LCE material could be used to fabricate a dynamic device for treating SUI in women.

Hyperthermia classic article commentary: 'Re-induction of hsp70 synthesis: an assay for thermotolerance' by Gloria C. Li and Johnson Y. Mak, International Journal of Hyperthermia 1989;5:389-403

Of the many heat shock proteins (HSPs), hsp70 appears to correlate best with heat resistance, either permanent or transient. We have investigated various approaches to quantify the concentration of hsp70, and examined the relationship between hsp70 and cells' thermal sensitivity during the development and decay of thermotolerance in model systems. Specifically, experiments were performed to determine the possibility of using the rate of synthesis of hsp70 after a second test heat shock to predict the kinetics of thermotolerance in tumor cells in vitro and in animal tumor models. We found that the cells' ability to re-initiate hsp70 synthesis in response to the test heat shock inversely correlated with retained thermotolerance. These data suggest the level of hsp70 in thermotolerant cells regulates the rate of synthesis of additional hsp70 in response to the subsequent heat challenge. Furthermore, the results showed that the rate of re-induction of hsp70 synthesis after a test heat shock can be used as a rapid measure of retained thermotolerance. This study suggests an approach for quantifying the level of retained thermotolerance during fractionated hyperthermia.

THERMAL DOSE REQUIREMENT FOR TISSUE EFFECT: EXPERIMENTAL AND CLINICAL FINDINGS

In this review we have summarized the basic principles that govern the relationships between thermal exposure (Temperature and time of exposure) and thermal damage, with an emphasis on normal tissue effects. We have also attempted to identify specific thermal dose information (for safety and injury) for a variety of tissues in a variety of species. We address the use, accuracy and difficulty of conversion of an individual time and temperature (thermal doses) to a standardized value (eg equivalent minutes at 43 degrees C) for comparison of thermal treatments. Although, the conversion algorithm appears to work well within a range of moderately elevated temperatures (2-15 deg C) above normal physiologic baseline (37-39 deg C) there is concern that conversion accuracy does not hold up for temperatures which are minimally or significantly above baseline. An extensive review of the literature suggests a comprehensive assessment of the "thermal does-to-tissue effect" has not previously been assembled for most individual tissues and never been viewed in a semi-comprehensive (tissues and species) manner. Finally, we have addressed the relationship of thermal does-to-effect vs. baseline temperature. This issues is important since much of the thermal dose-to-effect information has been accrued in animal models with baseline temperatures 1-2 deg higher than that of humans.

Ultraviolet B-induced apoptosis of keratinocytes in murine skin is reduced by mild local hyperthermia

Two components of sunlight, ultraviolet (UV) B (290-320 nm) and infrared (greater than 700 nm), each cause damage to the skin. However, we recently identified a protective response in which heat reduces UVB-induced killing of cultured keratinocytes. Here, this investigation is extended to the living epidermis. The effects of hyperthermic preconditioning upon UVB-induced apoptosis were studied morphologically with hematoxylin and eosin staining, and biochemically with TUNEL (terminal deoxynucleotide transferase nick-end labeling) to measure endonucleolytic cleavage of DNA in situ. Anesthetized SKH-1 hairless mice were exposed to UVB light (0 to 120 mJ/cm2), after which their skin was biopsied at 24 h and paraffin sections were stained with hematoxylin and eosin or with TUNEL. Apoptotic keratinocytes were found to increase after UVB in a dose-related manner. In contrast, if one flank of the mouse was pretreated at 40 degrees C for 1 h and both flanks subsequently were UVB-irradiated at 6 h, the resulting formation of apoptotic cells was reduced twofold or more in the heated flank. Protection appeared by 3 h, reached a maximum at 6 h, and disappeared by 12 h. In summary, heat induces a transient protective effect that reduces UVB-mediated death of keratinocytes in skin at physiologically attainable doses of heat and UVB.

Vascular function and tissue injury in murine skin following hyperthermia and photodynamic therapy, alone and in combination

The murine tail has been used as a model for injury to skin when hyperthermia (HT) and photodynamic therapy (PDT) using haematoporphyrin derivative, are used in combination. Skin injury by either agent alone was quantitated by the probability of tail necrosis as a function of dose of agent. 'Tolerance' doses of each modality were given and changes in skin vascular function were measured by the rate of clearance of 133Xenon. This was promptly inhibited but restored to normal by 7 days. The absolute numbers of hypodermal vessels of different sizes were measured in tail cross-sections and capillary numbers were found to be greatly reduced between 1 and 7 days, and restored to normal by 21-28 days. When a tolerance dose of PDT was followed at 1, 7, 21 and 28 days by test doses of HT, or vice versa, marked enhancements in probability of necrosis were observed when the interval was 1 or 7 days (Enhancement ratio (ER)PDT-HT = 1.5 and ERHT-PDT = 1.8). Prolonging the interval between modalities to 21-28 days spared the tissue (ERHT-PDT/21 DAYS = 1.1; ERPDT-HT/28 DAYS = 1.0). Close temporal apposition of PDT and HT, such as has been advocated to improve tumour control, may also increase injury to normal tissue through vascular effects common to both.

Thermotolerance and the heat shock response in normal human keratinocytes in culture

Protective responses of normal human epidermal keratinocytes in culture, after exposure to elevated temperatures ("heat shock"), were examined. Cell viability, measured 24-48 h after a 20-min heat challenge at temperatures between 37 degrees C and 54 degrees C, declined sharply within a narrow 2 degrees-3 degrees C range. However, conditioning with a mild thermal pretreatment (40 degrees C or 42 degrees C for 1 h) protected the keratinocytes against a subsequent heat challenge. This induced thermotolerance was apparent when cells were challenged at 1, 3, and 6 h after the thermal pre-treatment, but disappeared by 24 h. Heating conditions that induce thermotolerance also stimulated the synthesis of heat-shock proteins (hsp) in these cells. Inductions of prominent 35S-methionine labeled bands at 70, 78, and 90 kDa were observed. However, the increases in synthesis of these heat-shock proteins did not correlate well with thermotolerance, because large increases were also observed at certain elevated temperatures that did not produce improved survival. Keratins observed in these cells (50 and 58 kDa classes) were not induced by heat shock. The development of thermotolerance, and the induction of hsp, were both completely blocked by 3'-deoxyadenosine (cordycepin), an inhibitor of newly synthesized messenger RNA, but not by adenosine, the normal analog. While heat-inducible mRNA apparently mediate some function important for the development of thermotolerance, the nature of that role remains speculative. Overall, our findings establish the existence of a functional thermal protective mechanism in human keratinocytes that appears to require the synthesis of new mRNA.

Histopathological changes in the skin and subcutaneous tissues of mouse legs after treatment with hyperthermia

The right hind legs of mice wee heated in a waterbath at 44 degrees C. The animals were killed at various time intervals after exposure. Tissue damage was studied histologically. After 15 min exposure light and reversible changes were seen including oedema and some neutrophilic inflammatory infiltration immediately after treatment. After 30 min exposure an extensive inflammatory infiltrate and strong oedema were seen during the first days after treatment. Adjacent to areas in the skin with strong oedema extensive muscular necrosis was observed. The muscular tissue regenerated almost completely in three weeks. After 60 min heating the histological picture was dominated by massive necrosis of muscle, subcutaneous fat tissue and skin during the first week after treatment followed by local ulceration. From about the 7th day after treatment regeneration of the epithelium started and granulation tissue could be observed in the margin of the ulceration. Healing of the skin was completed at about day 21 after treatment. Our results indicate that heat induced tissue damage in some tissues is due to a direct effect on the cells composing the tissue (e.g., fat cells in subcutaneous fat) but that, in most other tissues (e.g., muscle and skin) it is a consequence of damage to the vasculature.

The kinetics of vascular thermotolerance in SCK tumors of A/J mice

Development of thermotolerance has been observed in diverse biological systems. Despite the important role of blood circulation in heat-induced tissue damage, little is known about vascular thermotolerance. The kinetics of vascular thermotolerance in SCK tumors of A/J mice was investigated in this study. A single heating at 43.5 degrees C or 44.5 degrees C for 1 hr caused marked damage in tumor vasculature, as demonstrated by a marked decrease in Rb-86 uptake (% of injected dose/g of dried tissue). The tumor vasculature became resistant or tolerant to subsequent heatings at those temperatures when the tumors were preheated at 42.5 degrees C for 1 hr. Vascular thermotolerance became significant at 5 hr and reached its maximum at 18 hr after preheating at 42.5 degrees C. When the vascular thermotolerance was at its peak, heating at temperatures as high as 44.5 degrees C for 1 hr could not reduce the tumor blood flow. The vascular thermotolerance decayed considerably but not completely at 72 hr after the preheating. The vascular thermotolerance may exert a profound implication on the response of tissues, including tumors, to multiple heatings.

Thermotolerance in the mouse foot estimated at various levels of normal tissue damage

The effect of fractionated 43.7 degrees C water bath heating on the skin of CDF1 mice was investigated. The normal tissue damage was scored at five levels (from slight redness and oedema to loss of a toe or greater damage) according to an arbitrary score system. The heating time to induce a given level of damage in half of the treated animals (RD50) was used as an end point. The feet were exposed either to a single treatment at 43.7 degrees C for different time periods or to a priming treatment of 30 min. at 43.7 degrees C followed at different intervals by a second graded heat treatment at 43.7 degrees C. In all treatment schedules, the score level increased proportionally with heating time, and the score system offered a good description of the acute skin damage following hyperthermia. The priming heat treatment induced thermotolerance with a time course independent of the score level chosen to estimate the heat response. The thermotolerance developed rapidly, reached a maximum within a 24 hr. interval, and then decayed slowly. The degree of thermotolerance was calculated by means of two previously described formulas for the thermotolerance ratio (TTR). The kinetics of thermotolerance in the skin of mice was independent of the TTR formula, whereas the degree of thermotolerance depended on both the score level and the TTR formula used.

Re-induction of hsp70 synthesis: an assay for thermotolerance

Of the many heat shock proteins (HSPs), hsp70 appears to correlate best with heat resistance, either permanent or transient. We have investigated various approaches to quantify the concentration of hsp 70, and examined the relationship between hsp70 and cells' thermal sensitivity during the development and decay of thermotolerance in model systems. Here, experiments were performed to determine the possibility of using the rate of synthesis of hsp70 after a second test heat shock to predict the kinetics of thermotolerance. Specifically, we studied the relationship between the retained thermotolerance in a murine tumor cell line SQ-1 and a human tumor cell line, HCT-8, after fractionated heat doses and the cells' ability to re-initiate synthesis of hsp70 in response to an additional test heat dose in vitro. Monolayers of cells were exposed to a first heat treatment (e.g., 41 degrees C, 4 h) and then incubated at 37 degrees C for 0-72 h. At various times after the first heat treatment, cells were either challenged with a 45 degrees C, 45 min heat shock to assess the residual thermotolerance by colony formation, or labelled with [35S]methionine before or after an additional test heat dose (e.g. 43.5 degrees C, 15 min). We found that the cells' ability to re-initiate hsp70 synthesis in response to the test heat shock inversely correlated with retained thermotolerance. Our data suggest the level of hsp70 in thermotolerant cells regulates the rate of synthesis of additional hsp70 in response to the subsequent heat challenge. Furthermore, the results showed that the rate of re-induction of hsp70 synthesis after a test shock can be used as a rapid measure of retained thermotolerance. This study suggests an approach for quantifying the level of retained thermotolerance during a course of fractionated hyperthermia.

Thermotolerance induced by fractionated hyperthermia: dependence of the interval between fractions

The induction of thermotolerance by fractionated hyperthermia was investigated in the mouse ear. Ears were heated at 43.5 degrees C by immersion in water. One to ten treatments of 20 min were followed by test treatments. Thermotolerance was assessed as the increase in the duration of the test treatment required for a thermal response in 50 per cent of the ears (NT50). A single treatment induced thermotolerance which reached a maximum at 24 h when the NT50 was increased by a factor of 2.4. The same maximum was observed after each fractionated treatment used in the present study. The time course of development, however, depended on the interval between fractions. (1) When the interval was too short to allow development of thermotolerance after a single fraction (4 h), thermotolerance was not induced during fractionated treatment but it developed during the first 24 h after treatment. (2) When the interval between fractions allowed the maximal development of thermotolerance (24 h), this maximum was maintained during fractionated treatment and persisted for 24 h after treatment. (3) When the interval allowed some decay of thermotolerance (72 or 168 h) there was a further increase to maximal thermotolerance after each fraction. The decay of thermotolerance from the maximum did not depend on the interval between fractions. These results indicate that the degree of thermotolerance may fluctuate during fractionated hyperthermia.

Influence of prior heat treatment on the effects of heat alone or combined with X-rays on mouse stromal tissue

The tumour bed effect assay was used to study the sensitivity of mouse stromal tissue to heat applied alone or combined with irradiation. Prior heat treatment, 30 min at 43 degrees C, of the tumour bed led to thermotolerance. After priming, thermotolerance developed fully within 24 h and it had disappeared completely after about 10 days. The kinetics of development and decay of thermotolerance in this slowly dividing tissue is similar to that which we had observed previously in skin. When decay rates of several normal tissues with different proliferation characteristics are compared, it is obvious that there is not a clear relationship between proliferation rate of the presumed target cells in the tissue and thermotolerance decay rate.

Differential kinetics of thermal resistance (thermotolerance) between murine normal and tumor tissues

The kinetics of thermotolerance were studied in mouse normal and tumor tissues. Early generation isotransplants of a spontaneous fibrosarcoma, FSa-II, were used. Tumor cell suspension was transplanted into the C3Hf/Sed mouse foot. Hyperthermia was given by immersing animal feet into a water bath. The TG (tumor growth) time, the time required for half the treated tumors to reach 1000 mm3 from the first treatment day, was the end point. Foot reaction was studied as a normal tissue response. The RD50, the treatment time that induces a loss of one toe or greater reaction in half the treated animals, was analyzed. Thermotolerance developed rapidly and extensively in normal and tumor tissues. A significant difference was observed in the decay of thermotolerance between these tissues. The decay of thermal resistance was incomplete in the murine foot tissue, even at 14 days after the initial heat treatment. Although some experimental difficulties were involved in the tumor study, present results suggest a complete decay of thermotolerance in the FSa-II tumor in 8 days after a 7.5 min treatment of 45.5 degrees C. Thermal resistance again developed in both tissues following the second heat treatment, which was given 7 or 8 days after the first heat treatment. The development, maximum magnitude and decay of the second thermal resistance was comparable to those of the first thermal resistance in each tissue.

Modification of the thermal sensitivity of the murine foot and tumour by prior hypoxic treatment

The response of Furth's murine mastocytoma to heat and the effect of prior heating and hypoxic treatment by clamping on the thermal sensitivity of the murine foot and the tumour were investigated. Two different-sized tumours, with average diameters of 3-4 mm and 7-8 mm were used. The tumour response to heat was evaluated by tumour growth (TG) time. Thermotolerance developed in both the foot and tumour tissues by a prior heating for 5 or 10 min at 45 degrees C. Hypoxic treatment resulted in dual effects on tumours. A 10 or 20 min hypoxic pretreatment increased thermal sensitivity of the tumour, while more than a 30 min hypoxic pretreatment induced thermotolerance. In contrast, a 20 min hypoxic treatment induced thermotolerance in the normal tissues. These results indicate that an appropriate period of prior hypoxic treatment may lead to a differential response between normal and tumour tissues.

Investigation of thermotolerance in mouse testis

The effect of a two-fraction heat treatment on mouse testis has been assessed by measuring testis weight loss at 1 week after treatment. The rate of repair of 'sublethal' heat damage following the first treatment was dependent on the severity of the treatment. Using a primary treatment of 41.5 degrees C for 30 min, the weight loss following a test treatment of 41.5 degrees C for 30 min returned to that of the test treatment alone within an interval of 16-24 h. Using a milder primary treatment of 40.0 degrees C for 30 min, repair of sublethal heat damage appeared to be complete by 1-2 h. When a single test treatment was used, there was no evidence of heat-induced thermal resistance (thermotolerance) following primary treatments of 40.0 or 41.5 degrees C for 30 min, for periods up to 24 h between treatments. A small degree of thermotolerance could, however, be demonstrated following the most severe primary treatment used if full dose: effect curves were obtained. Thermotolerance, manifest as a decrease in slope, was maximal at approximately 4 h after the primary treatment. The results are discussed with reference to other normal tissue data.

Experimental studies of thermotolerance in vivo. I. The baby rat tail model

A detailed study of the kinetics and magnitude of thermotolerance has been made using the endpoint of loss of vertebrae in the baby rat tail. A range of different priming treatments was used and for analysis each priming treatment (PT) was given in terms of the heat sensitivity of the tissue as defined by the single treatment (Ds) required for a given effect, i.e. fractional priming treatment PT/Ds. A considerable degree of thermotolerance could be induced so that at maximum the tissue sensitivity was reduced by a factor of more than four in heating time to produce a given effect, or by more than the equivalent of 2 degrees C. The main results of the study were: (a) that the time to reach maximum thermotolerance depends primarily on PT/Ds, independent of the particular conditions used in the priming treatment; (b) that the extent of the maximum also depends primarily on PT/Ds, but the precise form of the relationship depends on the method used to define thermotolerance; and (c) that the rate of decay of thermotolerance is independent of the priming treatment. The implications of these results for clinical hyperthermia are briefly discussed.

The significance of thermotolerance after 41 degrees C hyperthermia: in vivo and in vitro tumor and normal tissue investigations

We have investigated the development of thermotolerance in both tumors and normal tissues after 41 degrees C for durations as brief as 15 minutes. The murine RIF tumor, treated by both local radiofrequency and systemic methods, was assayed for thermotolerance by both tumor growth and cell survival analyses. The murine leg and ear, treated by conductive methods, were assayed using pre-defined tissue damage scoring systems. All of these treatments quickly induced substantial levels of thermotolerance. In the tumor studies using local heating, RIF mean diameter doubling time decreased from 17.8 days to a minimum of 13.0 days with a 9 hr interval between 41.0 degrees C for 15 minutes and 44.0 degrees C for 30 minutes (9 hr D1-D2); cell survival increased from 1.2 X 10(-2) to 3.4 X 10(-1) (same interval). Both assays showed some degree of tolerance present immediately after 41.0 degrees C for 15, 30 or 60 minutes (0 hr D1-D2). In the tumor studies using systemic heating, the kinetic pattern of the induced tolerance was similar to that observed after local heating. In the leg studies, 41.0 degrees for 30 minutes increased the time at 45 degrees C necessary to induce a specified level of tissue damage (mean score of 7) by a maximum of 1.8 times (24 hr D1-D2). The kinetic pattern was similar to that for the tumors. In the ear studies, 41.0 degrees C for 30 minutes increased the time at 45 degrees C necessary to induce ear necrosis in 50% of animals by a maximum of 3.5 times (48 hr D1-D2). The peak tolerance level occurred later for the ears, which have a lower normal temperature of 28-30 degrees C, than for the tumors or legs. These results indicate that: thermotolerance can begin to appear in tumors during treatment if hyperthermia sessions involve initial low thermal exposures (near 41 degrees C) for 15 minutes or longer; thermotolerance can develop in tumors after systemic heating and occurs with a kinetic pattern similar to that following local heating; and normal tissues also can develop high levels of thermotolerance after similar thermal exposures.

Thermal distributions in a water bath heated mouse tumor

In the past several years numerous investigators have employed various mouse tumor systems and a variety of heating methods to examine the effects of hyperthermia in vivo. These studies have led, in some cases, to different results in tumor response in what appear to be similar experiments. Our results indicate that these discrepancies may in part be attributable to variations in intratumor temperature and depend strongly upon the method and conditions of heating employed. In all cases, we have employed the C3H mammary carcinoma tumor system with the tumor implanted in the right hind limb of the mouse. All tumors were 7-9 mm in diameter at the time of the experiments. Water bath heating was employed with the animals under one of four possible conditions: the presence or absence of anesthesia, and the use or lack of core cooling. Thermometry was performed with an array of multiple microthermocouples, each less than 150 micron in diameter, implanted in the tumor in a grid-like pattern. Significant variations (1.0 degrees C for no anesthesia, p less than .01; 1.3 degrees C for Thorazine/Ketamine, p less than .001) in intratumor temperature were found across the tumor in the unperturbed state. These variations were essentially eliminated under all hyperthermic conditions. Control of core (rectal) temperature (with or without anesthesia) reduced the intratumor temperatures even though the water bath temperature was held constant resulting in variations between water bath and tumor temperatures of from 0.1-0.8 degrees C.

The occurrence of thermotolerance in non-proliferating rat hepatocytes in primary culture

The occurrence of thermotolerance, induced by an initial heat treatment at 42 degrees C for 30 min, was studied in adult non-proliferating rat hepatocytes in primary culture. Heat treatment at 42 degrees C for 30 min did not affect cell morphology, cell attachment, Na+, K+ pump activity, K+ content and lactate dehydrogenase accumulation into the medium. In contrast, after exposure to 44 degrees C for 30 min a dramatic change in all these parameters was observed. However, of the cells, which remained attached to the substratum 24 h after treatment, Na+, K+ pump activity and K+ content appeared to be normal compared with untreated cells. Cells, pre-treated at 42 degrees C for 30 min, followed by incubation at 37 degrees C for 16 h, were found to be completely thermal resistant against heat treatment at 44 degrees C, as judged by cell morphology, detachment from the substratum, lactate dehydrogenase accumulation, Na+, K+ pump activity and K+ content. These results show that induction and development of thermotolerance can be studied in non-proliferating cells in primary culture.

Hyperthermia for cancer: a practical perspective

A causal relationship between hyperpyrexia and tumor regression was first suggested in 1866, when Busch reported the cure of a histologically diagnosed sarcoma in a middle-aged woman, following a bout of erysipelas. Over the years, interest in the effect of heat on cancer has remained alive, but this interest has increased dramatically in recent years. The literature on this subject is broadly reviewed and the clinical results discussed. It is apparent from clinical studies thus far that it is a relatively simple undertaking to treat superficial neoplasms with hyperthermia. However, the major challenges in clinical thermotherapy pertain to patients with deeply situated tumors. The lack of safe and reliable methods of monitoring temperature in deep tissues is a major impediment to a thorough understanding of thermal dosimetry in clinical hyperthermia, and routine thermal dosimetry in clinical hyperthermia will have to await the development of reliable noninvasive thermometry. As responses have been reported with modest levels of hyperthermia, the need for thermometry is somewhat lessened, given that invasive monitoring is imperfect and somewhat risky when used in deeply seated tumours. The eventual place of thermotherapy in the treatment of malignant tumours in man is as yet unclear and must be rigourously and thoroughly assessed in well-designed, prospective, randomized patient trials.

Clinical results of radiofrequency hyperthermia combined with radiation in the treatment of radioresistant cancers

Clinical results of radiothermotherapy applied to 40 radioresistant tumors in 36 patients were reported. Hyperthermia was administered locally using two radiofrequency (RF) capacitive heating equipment systems developed in our institution under the collaboration of Yamamoto Vinyter Co. Ltd. Hyperthermia was given twice weekly immediately after irradiation. Intratumor temperatures of 41 degrees C to 44 degrees C were maintained for 30 to 60 minutes. Radiation doses varied from 32 Gy to 60 Gy. Of the 40 tumors treated, 21 (53%) showed complete response, 16 (40%) partial response, and 3 (7%) no response when the tumor response was assessed by tumor size measurement. Of eight patients who had matched tumors treated with either radiation alone or radiation plus hyperthermia, six patients showed better response in tumors treated with radiothermotherapy than in tumors treated with radiation alone. Skin reactions following radiothermotherapy and radiation alone were comparable. The tumor response was greatly dependent on the tumor size. Greater response was observed in small tumors, although histologic examinations and long-term follow-up studies revealed an excellent effect of radiothermotherapy on the large tumors as well as on the small tumors. Tumor responses correlated with tumor center temperatures but not with histologic features. Our clinical results indicate that RF hyperthermia combined with radiation has a therapeutic benefit in the treatment of radioresistant cancers.

A study of the effects of prior heat treatment on the skin reaction of mouse feet after heat alone or combined with X-rays: influence of misonidazole

The skin of mouse feet was used to study the effects of hyperthermic treatment, either alone or combined with irradiation. The present experiments show that a priming heat treatment induces resistance both to a subsequent heat treatment and to a subsequent combined irradiation-heat treatment. The development of resistance to a combined irradiation-heat treatment after a priming heat treatment (30 min at 43 degrees C) was relatively slow (18-24 h) compared to development of resistance to a heat treatment without irradiation (6 h). Misonidazole, when administered prior to heat treatment only, did not influence the heat-induced skin reaction. However, when misonidazole was administered prior to combined irradiation-heat treatment, a slight but significant increase of the skin reaction was observed. Also, in combination with misonidazole resistance to combined treatment was observed by a priming heat treatment.

The induction of thermotolerance in the ear of the mouse by fractionated hyperthermia

The development of thermotolerance in ears of mice was investigated after fractionated hyperthermia. Ears were heated at 43.5 degrees C by immersion in a water bath and the response was measured in terms of the heating time required to cause thermal necrosis in 50% of the ears (NT50). Three types of treatment were given: (1) single treatments, for which the NT50 was 42 minutes; (2) priming treatments, which caused little visible effect but induced thermotolerance. These treatments were given as 1-10 daily fractions, the total heating time ranging from 20-630 minutes; (3) test treatments which were given at various times after priming and were varied to estimate the NT50. Thermotolerance was defined as an increase in the test NT50 for preheated ears relative to the single treatment NT50. It has been suggested that thermotolerance induced by a single priming treatment may be increased by giving additional heat treatments which would not be tolerated by normal cells. In the mouse ear, the maximum thermotolerance induced by a single priming treatment of 20 min at 43.5 degrees C was seen after 24 hr when the test NT50 was about 2.5 times the single NT50. The effect of giving up to nine additional daily treatments of 70 min, each of which would cause necrosis in ears that had not received prior hyperthermia, was measured. The maximum thermotolerance observed was equal to that after a single 20 minute priming treatment but thermotolerance decreased as the number of 70 min treatments was increased from four to nine. The effects of repeating a treatment (20 min or 5 min) which was tolerated by normal ears and induced maximal or less than maximal resistance were compared. The interval between each fraction (24 hr or 12 hr respectively) was equal to the time at which maximal thermotolerance was observed after one treatment. For each regimen, the degree of resistance seen after 2 to 10 exposures was similar to that after the appropriate single treatment. This resistance was maintained throughout the course of priming treatment and decayed after the last fraction. Thus for this regimen, thermotolerance depended on the duration of each treatment rather than on the number of treatments given.

The importance of thermotolerance for the clinical treatment with hyperthermia

Thermotolerance (i.e. a temporary heat resistance following a prior heat treatment) is a general phenomenon occurring in both normal tissues and tumours. Besides affecting a fractionated heat treatment, thermotolerance may also influence the effect of fractionated combined heat and radiation. The importance of thermotolerance for fractionated clinical hyperthermia is discussed on the basis of a series of in vitro experiments in L1A2 cells and in vivo studies of a C3H mouse mammary carcinoma. If maximal tumour interaction is wanted, thermotolerance should be avoided, but it would be preferable in normal tissues in order to reduce the amount of damage. Unfortunately, there is a considerable variation in the kinetics and magnitude of thermotolerance between different tissues, and it is currently not possible to predict how thermotolerance will develop in a given tumour or normal tissue. However, both the magnitude and the kinetics appear to depend on the heat damage induced by the priming heat treatment. Thus, in a given tissue, thermotolerance will develop later, but will reach a higher maximum by a larger priming heat treatment. It follows that if a homogeneous temperature cannot be applied to a given tissue, different parts will develop thermotolerance at different kinetic patterns. Therefore, at the time of subsequent heat treatment, the tissue may express different heat sensitivities in different areas. With the current knowledge, the best way to overcome the problems of thermotolerance when heat is given alone or sequentially with radiotherapy will be by application of a single or few, but large heat fractions given with an interval that allows thermotolerance to develop and decay before the next hyperthermic treatment is given. With a simultaneous heat and radiation treatment which optimally requires heating in association with all radiation fractions, the fractionation interval should also be long, which is complicated by the fact that such long fractionation intervals may not result in an optimal radiation treatment.

Thermal radiosensitization in Chinese hamster (V79) and mouse C3H 10T 1/2 cells. The thermotolerance effect

The sensitivity of V79 cells and normal or morphologically transformed C3H-10T 1/2 cells to X-rays, heat or heat plus X-rays was examined. The normal and transformed C3H-10T 1/2 cell lines were equally sensitive to heat at 42.0 degrees C and radiation. The V79 cells were more heat sensitive. Thermal radiosensitization occurred for all 3 cell lines for the combined heat and radiation treatments and was greatest for simultaneous treatment. Recovery occurred when the treatments were separated by an incubation interval at 37 degrees C. For the V79 cells, recovery was much greater for X-rays preceding heat compared to X-rays following heat. This difference was not as great in the C3H-10T 1/2 cell lines. The transformed C3H-10T 1/2 cells were more sensitive compared to the normal for the simultaneous treatment or for heating followed by irradiation. For prolonged heating at 42.0 degrees C, after which thermotolerance occurred in all 3 cell lines, the radiosensitivity still increased as a function of heating time even though no additional cell killing occurred from the heat treatment alone. For heating V79 cells at 41.0 degrees C no further increase in radiosensitivity occurred, as cells became thermotolerant during prolonged heating. Also for the development of thermotolerance during incubation at 37 degrees C between two heat treatments, thermal radiosensitization decreased demonstrating that thermotolerance can affect radiosensitization by hyperthermia.

Blood flow changes in transplanted mouse tumours and skin after mild hyperthermia

The influence of moderate hyperthermia on the vascular perfusion of four different tumour types and of normal mouse skin was investigated. The 86Rb extraction technique was used to measure changes in perfusion relative to total cardiac output, both during and after a one hour heat treatment at 42.5 degrees C. Perfusion of the SA FA tumour increased slightly during the first 30 minutes of heating but had returned to control values by the end of a 1 hour heating period. After heating, the relative perfusion of all four tumour types fell significantly below control values by 24 hours and remained low for 1-2 days (SA FA tumour) before returning to control values. Relative perfusion of normal skin was progressively increased during heating and remained elevated for 24 hours after the end of treatment before returning to control levels.

Studies on fractionated hyperthermia in experimental animals systems III. Uneven daily doses

The effect of daily hyperthermia on the murine normal and tumor tissues was investigated. Tumors were early generation isotransplants of a fibrosarcoma (FSa-II) and a mammary carcinoma (MCa) in C3Hf/Sed mice. Hyperthermia was given by immersing animal feet into a water bath at 45.5 degrees C. Tumor response was studied by TG time assay (determination of the time required for half of the treated animals' tumors to reach 1000 mm3 from the treatment day). Average peak foot reaction was also investigated to compare the therapeutic effectiveness of various fractionation regimens. In the first experiment the first dose (D1) of 10 min was followed by 10, 20, or 30 min daily doses. The treatment regimen "D1 of 10 min + daily 30 min" resulted in a significant therapeutic gain. The smaller doses were unable to overcome the repopulation of surviving tumor cells and the increasing magnitude of thermal resistance. To overcome tumor cell repopulation and thermal resistance, a regimen of increasing daily doses was attempted without success. These results indicated that doses following a D1 of 10 min must be as large as 30 min to obtain a therapeutic gain. Any fractionation regimens for MCa tumors, which developed the greatest thermal resistance among our animal tumors tested, failed to result in a therapeutic gain.

Importance of preheating temperature and time for the induction of thermotolerance in a solid tumour in vivo

The importance of the priming heat treatment temperature and heating time for the degree and kinetics of thermotolerance was investigated in a C3H mammary carcinoma inoculated into the feet of CDF1 mice. A single heat treatment in the range 41.5-44.5 degrees C resulted in a linear relationship between heating time and tumour growth time (i.e. the time for tumours to reach a volume five times that of the first treatment day). An Arrhenius plot showed an inflection point at 42.5 degrees C with activation energies of 635 and 1508 kJ/mol, respectively, above and below 42.5 degrees C. The degree and kinetics of thermotolerance were independent of the preheating temperature, if the heating time was adjusted to give the same level of heat damage. A pretreatment at these temperatures with a tumour growth time of approximately 10 days, equivalent to 30 min at 43.5 degrees C, resulted in maximal thermotolerance at a 16-h interval with a thermotolerance ratio (TTRmax) of approximately 5.2. Preheating of the tumours at 43.5 degrees C for 3.5, 7.5, 15, 30, or 45 min, showed that if the preheating time was increased, both the TTRmax and the time interval necessary to develop TTRmax increased, both being linear functions of the duration of the preheating time. Maximal thermotolerance was obtained at intervals of 2, 4, 8, 16, and 28 h with TTRmax of 1.6, 2.2, 3.7, 5.2, and 7.7, respectively.

Influence of low pH on the development and decay of 42 degrees C thermotolerance in CHO cells

The development, magnitude and decay of thermotolerance in Chinese hamster ovary cells heated to 42 degrees C at pH 6.7 was examined. The cells were exposed to single or fractionated heat treatments with 0 to 168 hours elapsing between the treatments. Administration of a specified heat treatment in two fractions at low pH substantially reduced the lethal effect of heat. The rate of hyperthermic cell killing was reduced by a factor of approximately 2.5 in preheated cells compared to cells not receiving prior heat treatment. Tolerance to second heat treatments was apparent when 3 hours at 37 degrees C separated the treatments, and was near maximum when 6 hours separated the treatments. Beginning about 96 hours after the initial heat treatment, resistance to second heat treatments began to decline, and was not evident when 168 hours at 37 degrees C separated the treatments. In contrast to these results, a sparing effect as a result of dose fraction was not observed at pH 7.4. At pH 7.4, cells developed thermotolerance during the initial heat treatment and additional culturing at 37 degrees C was without additional effect. Nevertheless, the sensitivity of cells to hyperthermia was greater at pH 6.7 than at pH 7.4. This pH sensitizing effect was more pronounced in cells exposed to single heat treatments than in cells exposed to fractionated treatments at 42 degrees C.

Effect of prior hyperthermia on subsequent thermal enhancement of radiation damage in mouse intestine

Hyperthermia given in conjunction with X-rays results in a greater level of radiation injury than following X-rays alone, giving a thermal enhancement ratio (TER). The effect of prior hyperthermia ('priming') on TER was studied in the small intestine of mouse by giving 42 X 0 degrees C for 1 hour at various times before the combined heat and X-ray treatments. Radiation damage was assessed by measuring crypt survival 4 days after radiation. TER was reduced when 'priming' hyperthermia was given 24-48 hours before the combined treatments. The reduction in effectiveness of the second heat treatment corresponded to a reduction in hyperthermal temperature of approximately 0 X 5 degrees C, a value similar to that previously reported for induced resistance to heat given alone ('thermotolerance') (Hume and Marigold 1980). However, the time courses for development and decay of the TER response were much longer than those for 'thermotolerance', suggesting that different mechanisms are involved in thermal damage following heat alone and thermal enhancement of radiation damage.

Correlation between synthesis of heat shock proteins and development of thermotolerance in Chinese hamster fibroblasts

Synthesis of a family of proteins called "heat shock" proteins is induced or enhanced in cells in response to various environmental stresses, suggesting that these proteins may perform functions essential to cell survival. Because a brief, nonlethal heat treatment can dramatically induce a transient resistance to a subsequent lethal heat treatment (thermotolerance), we examined the effect of heat treatment (41-46 degrees C) on protein synthesis and cell survival in plateau-phase Chinese hamster fibroblast (HA-1) cells. After heat treatments that either drastically inhibited total protein synthesis (46 degrees C) or did not suppress it (41 degrees C), the synthesis of heat shock proteins was greatly enhanced over that in unheated cells, and cell survival was increased 10(2)- to 10(6)-fold when cells were challenged by a subsequent lethal heat treatment. The synthesis of heat shock proteins correlated well with the development of thermotolerance, and the stability of these proteins correlated well with the persistence of thermotolerance up to 36 hr. Sodium arsenite, hypoxia, and ethanol also induced both the synthesis of heat shock proteins and transient thermotolerance. A qualitative analysis of individual proteins suggests that the synthesis and persistence of polypeptides of Mr 70,000 or 87,000 most closely conformed to the kinetics of thermotolerance.

Studies on fractionated hyperthermia in experimental animal systems II. Response of murine tumors to two or more doses

The effect of multiple hyperthermia and the kinetics of thermal resistance were studied in experimental murine tumors. A spontaneous C3Hf mouse mammary carcinoma, MCa had a chemically-induced fibrosarcoma, FAa-1, were used. Assay methods included determination of the TCD50, i.e., the treatment time to yield a tumor control in half the treated animals and TG (tumor growth) time analysis, i.e., the time required for a tumor to reach a given size after first treatment. After equal dose fractions the TCD50 of MCa increased with increasing overall treatment time. This increase was most predominant when treatments were given with a time interval of one day. Isoeffect curves for the MCa were comparable to those for normal tissue damage (foot reaction), which was reported in the first part of this series of communications. The kinetics of thermal resistance in the MCa was compared with that in FSa-I since the fractionated hyperthermia for the FSa-I was reported to have resulted in an appreciable therapeutic gain. The magnitude of thermal resistance was far greater in the MCa than in the FSa-I, although the kinetics of thermal resistance was similar in both tumors; i.e., (a) the resistance reached a maximum in 24 hours after treatment and then decayed slowly, and (b) the development of thermal resistance increased with increasing initial dose. The thermal resistance in these tumors appeared to be greater than that in animal feet.

The effect of chronic and acute heat conditioning on the development of thermal tolerance

Survival studies with Chinese hamster ovary cells showed that thermal tolerance, which developed during chronic heating (treatment times greater than or equal to 1 hr) or after acute heating (treatment times less than 1 hr) involves similar mechanisms. For example, cells that expressed thermal tolerance during a 6-14 hr chronic heat treatment at 41.5 degrees C or 42 degrees C also expressed thermal tolerance to a subsequent acute treatment at 45.5 degrees C. Also, cells heated acutely for 10 min at 45.5 degrees C and incubated at 37 degrees C for 12 hr showed tolerance to both 45.5 degrees C acute and 42 degrees C chronic hyperthermia. Finally, thermal tolerance developed between fractionated acute heat treatment at 45.5 degrees C and fractionated chronic heat treatments at 42.5 degrees C. These data indicate that when cells are tolerant to chronic hyperthermia they are also tolerant to acute hyperthermia and that the reverse is also true.

Thermal resistance in a spontaneous murine tumour

Resistance to subsequent hyperthermia as a result of prior heating was investigated using a spontaneous murine tumour implanted into the feet of C3H/Sed mice. Tumours were treated by immersing the tumour-bearing foot into a constant-temperature hot water bath set at 45.5 degrees C and were given single and split doses of heat. Response was assessed using a tumour-growth time assay. Three aspects of thermally-induced resistance were particularly considered: the time course of development and decay; the importance of the magnitude of the priming dose and the influence of the size of the tumour at the time of treatment. Substantial resistance was induced in this tumour by short priming doses at 45.5 degrees C, rising rapidly 1-2 days after the first treatment and then starting to decay. There was no significant difference in the kinetics of thermal resistance induced in tumours treated at 4mm and those treated at 8 mm in size, although the large tumours were more sensitive to single doses of heat. Increasing the magnitude of the priming dose of heat resulted in an increase in the magnitude of resistance to the second dose. The results of this study are compared with results of similar studies in this and other laboratories using murine normal tissues and cells in culture. Possible clinical implications are considered.

Local hyperthermia and irradiation in cancer therapy

The preliminary experience at the Mallinckrodt Institute of Radiology with hyperthermia and irradiation is reported and current issues in clinical application of heat are reviewed. Twenty-nine lesions were treated with 400 rad fractions given every 72 hr (twice weekly) for a total dose of 2400 to 4000 rad followed by hyperthermia (1450-MHz or 915-MHz microwaves, 42.0 degrees -43 degrees, 90 min, every 72 h). Eight of 12 recurrent epidermoid carcinomas of the head and neck showed complete regression (67%) and one more than 50% response. Of 5 metastatic melanoma nodules treated with irradiation an hyperthermia, 4 (80%) showed complete regression of the tumors an 1 almost complete response. Of 9 recurrent adenocarcinoma of breast nodules in the chest wall treated with 3200 to 4000 rad 5 lesions exhibited complete regression and 2 others about 80%. Of 6 lesions treated with 1500 rad and hyperthermia (RTOG protocol), 2 metastatic melanomas showed complete regression (CR) and 3 tumors exhibited partial regression. Of the 35 sites treated, 4 (11%) developed blisters, 7 (20%) erythema only, 3 (8%) moist desquamation and 27 (77%) dry desquamation. Additional clinical trials are in progress to assess the potential value of hyperthermia alone or combined with irradiation in the treatment of selected cancer patients.

Effect of fractionated hyperthermia on hypoxic cells in vitro

The lethal response of asynchronous exponentially growing mouse lung (L1A2) cells heated to 42 degrees C under hypoxic conditions was demonstrated in vitro. Acutely hypoxic cells (i.e. heated immediately after 30 min of N2 plus CO2 gassing) and aerobic cells treated under the same extracellular pH were equally sensitive to a single hyperthermic treatment, and incubation under hypoxia for up to 24 hours prior to treatment did not influence cell survival. Similarly, under controlled pH conditions (pH within 7.0 to 7.4) recovery from hyperthermic damage demonstrated by two-dose hyperthermic fractionation (each of 1.5 hours at 42 degrees C) was identical in hypoxic and aerobic cells, and the highest recovery was found at a 10-hour interval. Preheating for 1.5 hours at 42 degrees C induced thermal resistance to a second treatment at 42 degrees C (thermotolerance). At the 10-hour interval the degree of thermotolerance was not influenced by incubation under hypoxic conditions (thermotolerance ratio, TTR equals 4.7 in both aerobic and hypoxic cells). The data indicate that hypoxic conditions do not influence the heat response in L1A2 cells to either a single or a two-dose fractionated hyperthermic treatment in which hypoxia or aerobic conditions were maintained in the interval between the heat treatment.

Fractionation studies with combined X rays and hyperthermia in vivo

The combined effects of single and fractionated doses of X rays and local heat were investigated using an experimental fibrosarcoma and normal mouse skin. Thermal enhancement ratios were measured from pairs of dose-response curves for both tumour and skin, and the therapeutic advantage of each treatment was then assessed by comparing the enhancement for tumour and skin. For single doses there was a therapeutic advantage when heat was applied three hours after X rays but not with heat applied immediately after irradiation. For two and five daily fractions with heat immediately after irradiation there was significantly less thermal sensitization in tumour than in skin; hence there was a therapeutic loss. When heat was applied at three hours after each fraction there was no thermal sensitization in either skin or tumour; the therapeutic ratio was therefore 1.0. The repair capacity of skin after fractionated X rays alone, or in combination with heat, was also investigated. Heat immediately after X rays caused a small decrease in the repair capacity between two fractions but no decreased repair capacity was observed with five fractions.