The effect of pH on cell lethality induced by hyperthermic treatment

Local Microwave Hyperthermia in Cancer Therapy. Preliminary Report

From February 1981 to September 1981, 16 patients (19 fields) with histologically proven malignancy (10 squamous carcinoma, 4 melanoma, 1 adenocarcinoma, 1 chordoma) were treated with hyperthermia combined with radiotherapy or chemotherapy (1 patient). There were 5 females and 11 males; average age was 65 years, range 45 to 94 years; 15 patients had a Karnofsky index greater than 50%. Hyperthermia (42.5 44.0 °C) was induced by 250 MHz to 1 GHz microwaves (BSD - 1000 Unit). Thermometry was performed by means of non-perturbing probes placed in intratumorally inserted catheters and by measurement of skin temperatures. After hyperthermia plus radiotherapy (18 fields), 9 patients showed 100% response, 5 a volume regression of more than 50%, 3 less than 50% and 1 no change. After chemotherapy plus hyperthermia, 1 patient showed no change. No significant side effects were observed (3 skin burns in 147 hyperthermia treatment sessions).

Self-harm to preferentially harm the pathogens within: non-specific stressors in innate immunity

Therapies with increasing specificity against pathogens follow the immune system's evolutionary course in maximizing host defence while minimizing self-harm. Nevertheless, even completely non-specific stressors, such as reactive molecular species, heat, nutrient and oxygen deprivation, and acidity can be used to preferentially harm pathogens. Strategic use of non-specific stressors requires exploiting differences in stress vulnerability between pathogens and hosts. Two basic vulnerabilities of pathogens are: (i) the inherent vulnerability to stress of growth and replication (more immediately crucial for pathogens than for host cells) and (ii) the degree of pathogen localization, permitting the host's use of locally and regionally intense stress. Each of the various types of non-specific stressors is present during severe infections at all levels of localization: (i) ultra-locally within phagolysosomes, (ii) locally at the infected site, (iii) regionally around the infected site and (iv) systemically as part of the acute-phase response. We propose that hosts strategically use a coordinated system of non-specific stressors at local, regional and systemic levels to preferentially harm the pathogens within. With the rising concern over emergence of resistance to specific therapies, we suggest more scrutiny of strategies using less specific therapies in pathogen control. Hosts' active use of multiple non-specific stressors is likely an evolutionarily basic defence whose retention underlies and supplements the well-recognized immune defences that directly target pathogens.

The heat shock response: Role in radiation biology and cancer therapy

Since prehistoric times, elevated temperatures have been used to treat cancer in a variety of forms. In modern times (the last 40 years) efforts have concentrated on combining heat with other anti-tumour modalities, principally ionizing radiation and some chemotherapeutic drugs. Despite the emphasis on combined therapy, rodent data relating to heat sensitivity and thermal tolerance development assumed principal importance. These considerations suggested treating at 43 degrees C as a target temperature and fractionation schemes emphasizing thermal tolerance avoidance. Concomitantly crucial data on heat-induced tumour reoxygenation and its temperature dependence were largely ignored. In reality these were unrealistic and undesirable goals. The preponderance of evidence now suggests that lower temperatures (40-42 degrees C) administered more frequently, optimally immediately before and during each administration of ionizing radiation, are likely to yield optimal results. Factoring in trimodality therapy and other combinations of chemotherapeutic drugs will require some modifications of such fractionation schemes.

Arrhenius relationships from the molecule and cell to the clinic

There are great differences in heat sensitivity between different cell types and tissues. However, for an isoeffect induced in a specific cell type or tissue by heating for different durations at different temperatures varying from 43-44 degrees C up to about 57 degrees C, the duration of heating must be increased by a factor of about 2 (R value) when the temperature is decreased by 1 degrees C. This same time-temperature relationship has been observed for heat inactivation of proteins, and changing only one amino acid out of 253 can shift the temperature for a given amount of protein denaturation from 46 degrees C to either 43 or 49 degrees C. For cytotoxic temperatures <43-44 degrees C, R for mammalian cells and tissues is about 4-6. Many factors change the absolute heat sensitivity of mammalian cells by about 1 degrees C, but these factors have little effect on Rs, although the transition in R at 43-44 degrees C may be eliminated or shifted by about 1 degrees C. R for heat radiosensitization are similar to those above for heat cytotoxicity, but Rs for heat chemosensitization are much smaller (usually about 1.1-1.2). In practically all of the clinical trials that have been conducted, heat and radiation have been separated by 30-60 min, for which the primary effect should be heat cytotoxicity and not heat radiosensitization. Data are presented showing the clinical application of the thermal isoeffect dose (TID) concept in which different heating protocols for different times at different temperatures are converted into equivalent minutes (equiv) min at 43 degrees C (EM(43)). For several heat treatments in the clinic, the TIDs for each treatment can be added to give a cumulative equiv min at 43 degrees C, namely, CEM(43). This TID concept was applied by Oleson et al. in a retrospective analysis of clinical data, with the intent of using this approach prospectively to guide future clinical studies. Considerations of laboratory data and the large variations in temperature distributions observed in human tumors indicate that thermal tolerance, which has been observed for mammalian cells for both heat killing and heat radiosensitization, probably is not very important in the clinic. However, if thermal tolerance did occur in the clinical trials in which fractionation schemes were varied, it probably would not have been detected because with only the two-three-fold change in treatment time that occurs when comparing one versus two fractions per week, or three versus six total fractions, little difference would be expected in the response of the tumors since both thermal doses were extremely low on the dose-response curve. Data are shown which indicate that in order to test for thermal tolerance in the clinic and to have a successful phase III trial, the thermal dose should be increased about five-fold compared with what has been achieved in previous clinical trials. This increase in thermal dose could be achieved by increasing the temperature about 1.5 degrees C (from 39.5 to 41.0 degrees C in 90% of the tumor) or by increasing the total treatment time about five-fold. The estimate is that 90% of the tumor should receive a cumulative thermal dose (CEM(43)) of at least 25; this is abbreviated as a CEM(43) T(90) of 25. This value of 25 compares with 5 observed by Oleson et al. in their soft tissue sarcoma study. Arguments also are presented that thermal doses much higher than the CEM(43) T(90) induce the hyperthermic damage that causes the tumors to respond, and that the minimum CEM(43) T(90) of 25 only predicts which tumors that receive a certain minimal thermal dose in <90% of the regions of the tumors will respond. For example, in addition to a minimal CEM(43) T(90) of 25 a minimum CEM(43) T(50) of about 400 also may be required for a response. Finally, continuous heating for approximately 2 days at about 41 degrees C during either interstitial low dose-rate irradiation or fractionated high dose-rate irradiation, which we estimate could give a CEM(43) of 75, should be considered in order to enhance heat radiosensitization of the tumor as well as heat cytotoxicity. In order to exploit the use of hyperthermia in the clinic, we need a better understanding of the biology and physiology of heat effects in tumors and various normal tissues. As an example of an approach for mechanistic studies, one specific study is described which demonstrates that damage to the centrosome of CHO cells heated during G(1) causes irregular divisions that result in multinucleated cells that do not continue dividing to form colonies. This may or may not be relevant for heat damage in vivo. However, since normal tissues vary in thermal sensitivity by a factor of 10, similar approaches are needed to describe the fundamental lethal events that occur in the cells comprising the different tissues.

Enhancement of thermoradiotherapy by glucose administration for superficial malignant tumours

The effect of hyperglycemia on the thermoradiotherapy of superficial malignant tumours was investigated. Glucose administration alone (500 ml of 10% glucose by intravenous drip infusion) reduced the tumour blood flow, when measured by laser Doppler flowmetry, to 66.1% of the baseline level at 30 minutes after the beginning of glucose infusion. Forty patients received glucose in tandem during the hyperthermia and radiotherapy (group A), and 38 patients received thermoradiotherapy alone (group B). The mean Tave (the average temperature of all intratumoural sensors) in group A was 43.4 +/- 1.1 degrees C while that in group B was 42.5 +/- 1.2 degrees C, i.e., glucose administrations significantly increased the tumour temperature (p < 0.01). In group A, complete tumour response (CR) was observed in 12 patients (30.0%), partial response (PR) in 25 patients (62.5%) and no response (NR) in three patients (7.5%). In group B, seven (18.4%), 20 (52.7%) and 11 (28.9%) patients showed CR, PR and NR, respectively. The tumour response rates were significantly different between two treatment groups (p < 0.05). The frequency of side effects of hyperthermia in groups A and B were 22.5 and 21.1%, respectively. This study suggests that hyperglycemia enhances the effectiveness of thermoradiotherapy.

Measurement of intratumor pH by pH indicator used in 19F-magnetic resonance spectroscopy. Measurement of extracellular pH decrease caused by hyperthermia combined with hydralazine

RATIONALE AND OBJECTIVES

Without affect of metabolic changes, the authors measured intratumor pH by using 19F-magnetic resonance spectroscopy (MRS) with a fluorine compound (ZK-150471) on the basis of a calibration curve by pH electrode.

METHODS

Using the 4.7-tesla magnetic resonance apparatus, a fluorine compound that had acid-base equilibrial change and was impermeable within cell membranes was used. The fluorine compound was injected intravenously. The signal was obtained from mouse mammary cancer by creating an experimental tumor on the leg of mice. And the tumors, which were heated with and without hydralazine. The pH evaluated from chemical shift of the fluorine compound. The pH data was obtained from an electrode for reference.

RESULTS

The pH of nontreated tumors (n = 25) were 6.94 + 0.091. The pH decreased to 6.772 + 0.169 at 20 minutes even after 20 minutes of heating, and decreased to < 6.71 at 40 minutes after every heating time. The pH decreased to 6.456 at 20 minutes after 15 minutes of heating combined with hydralazine, and to 6.416 at 40 minutes after same treatment.

CONCLUSIONS

It is possible to measure the extracellular pH by 19F-MRS with the fluorine compound noninvasively in vivo, even after heating.

Temporary vascular occlusion and glucose: effects on tumour and normal tissue pH in animal experiments

The relationship between duration of a period of vascular occlusion and magnitude of pH decrease in tumour and normal tissue was investigated in rats. To acidify tissue pH further, moderate dose glucose (2.4-3.0 g.kg(-1).hr(-1)) was administered intravenously through a catheter positioned in a tail vein, immediately after the clamp was released. This sequence of pH modifying modalities was chosen since it is employed in clinical regional isolation perfusion for recurrence of malignant melanoma of the limbs. Tumour pH in rat rhabdomyosarcoma BA1112 decreased more than normal tissue pH under 10, 20, 30 or 60 min of temporary vascular occlusion. Administration of glucose following any period of clamping always decreased tumour pH further. The largest pH decrease (0.29 pH units) was obtained after 30 min of clamping followed by 60 min glucose and 60 min saline infusion. In the clinic the combination of a maximum of 30 min of clamping followed by moderate dose glucose infusion, which can decrease tumour pH effectively, can be easily achieved in the setting of regional isolation perfusion. It can be used for treatment modalities that are known to be enhanced at lowered tissue pH, such as hyperthermia and certain chemotherapeutic drugs. These results form the basis for studying the therapeutic gain which can be obtained with this model.

Arrhenius relationships from the molecule and cell to the clinic

There are great differences in heat sensitivity between different cell types and tissues. However, for an isoeffefct induced in a specific cell type or tissue by heating for different durations at different temperatures varying from 43-44 degrees C up to about 57 degrees C, the duration of heating must be increased by a factor of about 2 (R value) when the temperature is decreased by 1 degrees C. This same time-temperature relationship has been observed for heat inactivation of proteins, and changing only one amino acid out of 253 can shift the temperature for a given amount of protein denaturation from 46 degrees C to either 43 or 49 degrees C. For cytotoxic temperatures < 43-44 degrees C, R for mammalian cells and tissues is about 4-6. Many factors change the absolute heat sensitivity of mammalian cells by about 1 degrees C, but these factors have little effect on Rs, although the transition in R at 43-44 degrees C may be eliminated or shifted by about 1 degrees C. R for heat radiosensitization are similar to those above for heat cytotoxicity, but Rs for heat chemosensitization are much smaller (usually about 1.1-1.2). In practically all of the clinical trials that have been conducted, heat and radiation have been separated by 30-60 min, for which the primary effect should be heat cytotoxicity and not heat radiosensitization. Data are presented showing the clinical application of the thermal isoeffect dose (TID) concept in which different heating protocols for different times at different temperatures are converted into equiv min at 43 degrees C (EM43). For several heat treatments in the clinic, the TIDs for each treatment can be added to give a cumulative equiv min at 43 degrees C, viz., CEM43. This TID concept was applied by Oleson et al. in a retrospective analysis of clinical data, with the intent of using this approach prospectively to guide future clinical studies. Considerations of laboratory data and the large variations in temperature distributions observed in human tumours indicate that thermal tolerance, which has been observed for mammalian cells for both heat killing and heat radiosensitization, probably is not very important in the clinic.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of sensitivity to hyperthermia by lonidamine in human cancer cells

Human glioma (87MG) and squamous cell carcinoma of the head and neck UMSCC-1 were shown to be sensitized to hyperthermia by Lonidamine treatment before and during hyperthermia. The degree of thermal sensitization increased with increasing heating times and temperatures. In addition, the thermal sensitization by Lonidamine as well as cellular thermal sensitivity were dependent on pH and increased with the more acidic pH. Even though plateau phase cells were more thermally resistant than exponentially growing cells, Lonidamine treatment caused thermal sensitization under both conditions. These data show that Lonidamine may hold potential to enhance the effectiveness of hyperthermia in cancer treatment and that especially in tumours with low pH an enhanced therapeutic gain may be achieved.

Histopathology of prostatic tissue after transurethral hyperthermia

Histopathological changes were studied in four patients who had moderate to severe urinary outflow obstruction due to benign prostatic hyperplasia (BPH) and were treated with transurethral microwave hyperthermia (TUMH). All these patients received TUMH with a helical antenna using a BSD 300 unit. The temperature was controlled on the urethral surface at 45 degrees C +/- 1 degree C. Each treatment session lasted 70 min at this temperature. Histological changes were periurethral, extending up to 6 mm radially and 4-5 cm longitudinally. They were symmetrical and most severe in the immediate periurethral zone. The severity and distribution of these histological changes correlated well with the thermal profile of the helical antenna. Acute changes, observed 24-48 h following administration of a single TUMH session, consisted of periurethral oedema, parenchymal haemorrhages and occasional, partial small-vessel thrombosis. Selective coagulation necrosis of the parenchymal smooth muscles with sparing of smooth muscle fibres in the vessel walls was noted. Histopathological changes found in patients 7 or 26 days following the administration of 10 TUMH treatments given twice-weekly for 5 weeks showed more severe and deeper lesions. They consisted of interstitial haemorrhages, complete obliteration of blood vessel lumina due to thrombosis and further evidence of coagulation and haemorrhagic necrosis. Evidence of a reparative process with ingrowth of granulation tissue in various stages of organization was clearly demonstrated. The effect of TUMH on BPH-obstructed urethra is probably expressed through selective shrinking and retraction of the periurethral prostatic parenchyma due to organizing localized tissue necrosis and cicatrization. Details of this complex process will be presented.

Heat-induced cytotoxicity in H2O2-resistant Chinese hamster fibroblasts

Hydrogen-peroxide-resistant Chinese hamster fibroblasts, derived from the HA-1 cell line, were isolated following continuous culturing in the presence of progressively increasing concentrations of hydrogen peroxide. The hydrogen-peroxide-resistant phenotype has been stable for over 360 days following removal from H2O2 stress. These H2O2-resistant cell lines demonstrate increased resistance to hyperthermic cell killing mediated by continuous heating at 43 degrees C but not 45 degrees C. The relationship between mammalian cellular adaptation to oxidative stress mediated by H2O2 and resistance to 43 degrees C hyperthermia is discussed.

Comparison of DMO and flow cytometric methods for measuring intracellular pH and the effect of hyperthermia on the transmembrane pH gradient

Intracellular pH (pHi) was measured in both unheated and heated cells by the distribution of the weak acid, 5,5-dimethyl-2,4-oxazolidinedione-2-14C (14C-DMO), and by the fluorescence intensity ratio (I530/I630) of the pH sensitive fluorescent dye, 2',7'-bis(carboxyethyl)-5,6-carboxy-fluorescein (BCECF), analyzed by flow cytometry (FCM). BCECF-loaded Chinese hamster ovary (CHO) cells were analyzed by FCM after they had incubated in fresh medium at 37 degrees C for 90 min, during which time a decrease in fluorescence ratio stabilized. After stabilization, the pHi determined for CHO cells by the FCM method at pHe values of 6.0-8.1 agreed-within 0.1 pH units with that determined by the 14C-DMO method. There is a pH gradient across the plasma membrane that is not affected by heat. In CHO cells, the gradient, determined by DMO and FCM, is less or greater than pHe by 0.30 and 0.15 pH units at pHe 7.4 and 6.3, respectively, and in NG108-15 cells, the gradient determined by DMO increases to 0.50 pH units at pHe 6.3. Both cells maintained their pH gradients for at least 4 h after heating, although 99.9% of the cells were reproductively dead (survival of 10(-3)) after heating at 45.5 degrees C either at the normal pHe of 7.4 or at a low pHe of 6.4-6.7.

Radiofrequency hyperthermia therapy of murine melanoma: a comparison of fractionated versus single-dose treatments

The effects of single and fractionated doses of radiofrequency hyperthermia were investigated in the treatment of cutaneous murine melanoma. S91 murine melanoma cells were implanted into preformed intradermal blister cavities on the backs of DBA/2J mice. Evaluation of treatment response was undertaken after single and fractionated doses of hyperthermia. A single 60-second treatment at 46 degrees C did not result in any complete regressions, while 3 weekly 46 degrees C treatments produced a 40% incidence of tumor regression. Higher temperature therapy was associated with improved cure rates. A single treatment for 60 seconds at 50 degrees C resulted in a 25% complete response rate while 3 weekly 50 degrees C treatments resulted in the eradication of 92% of the treated tumors. In those tumors that responded only partially to hyperthermia, fractionated low- (46 degrees C) and (50 degrees C) high-dose regimens resulted in significantly smaller melanomas than single-treatment schedules at the same temperatures. It is concluded that fractionated hyperthermia is an effective modality in the control of intracutaneous murine melanoma. If other cutaneous malignancies are also sensitive to heat, this may provide a useful nonsurgical means of treating skin cancer.

Effect of pH on development and decay of thermotolerance in CHO cells using fractionated heating at 43 degrees C

The development and decay of thermotolerance at pH 6.7, 7.1 and 7.7 was studied after fractionated hyperthermia at 43 degrees C using exponentially growing CHO cells. The maximum of thermotolerance and the time interval to reach this maximum were found to correlate with the survival decrement after the priming heat treatment. Both parameters were only affected by pH in so far as the pH altered survival after the priming treatment. Decay of thermotolerance was exponential. For a given priming heat treatment for the time t1, the half-time of decay, tau 1/2, increased linearly with increasing cell doubling time, tau d, measured for non-heated cells growing at different pH. On the other hand, for a given cell doubling time, tau d, the half-time, tau 1/2, increased exponentially with increasing duration of the priming heat treatment, t1. For all measured data the half-time of thermotolerance decay could be described by the equation tau 1/2 = alpha. tau d.exp(k.t1), with k = 2.2 +/- 0.2 h-1 and alpha = 0.094 +/- 0.009 for all pretreatments applied and all pH conditions tested. This relationship might indicate that the decay of thermotolerance is governed by a single mechanism.

Influence of hyperthermia, pH and culturing conditions on the electrical parameters of Chinese hamster V79 cells

Conductivity measurements in the frequency range 10 kHz-100 MHz have been performed on Chinese hamster fibroblasts V79 exposed to hyperthermia in different experimental conditions. The membrane electrical conductivity is decreased when cells are heated for 1 h at 44 degrees C or 3 h at 43 degrees C at pH 7.25. This effect has not been observed on cell samples following heating for 1 h at 43 degrees C at pH 7.25. However, if the pH of the culture medium is adjusted to 6.50 or 6.0 before hyperthermic exposure, a substantial decrease of membrane conductivity is observed. In cells maintained in partially spent medium before heating, a 3 h treatment at 43 degrees C at pH 7.25 does not produce any effect on membrane conductivity. The results of all these experiments seem to indicate that some alteration of the energy-driven mechanisms involved in active transport across the plasma membranes may be responsible for the observed effects.

Capacitive radiofrequency hyperthermia in the treatment of cutaneous murine melanoma

We have evaluated localized capacitive radiofrequency hyperthermia in the treatment of murine S91 melanoma. Two hundred and ten DBA/2J male mice were implanted with 1 X 10(6) S91 murine melanoma cells innoculated into a noninflammatory upper dermal suction blister cavity. Two tumors were implanted per animal, so that each animal served as its own control in evaluating the effects of temperature, treatment duration, and tumor size on tumor growth following radiofrequency hyperthermia treatment. The data supported the following conclusions: (1) capacitive radiofrequency hyperthermia is effective in the treatment of murine S91 melanoma; (2) duration of treatment between 10 and 60 seconds at 52 degrees C does not influence effectiveness; and (3) treatment temperatures greater than 49 degrees C are needed for maximal effectiveness in the treatment of these tumors. Based on these preliminary findings, high temperature, short duration capacitive radiofrequency hyperthermia may prove to be a useful modality in the treatment of certain cutaneous malignancies.

Clinically derived dose effect relationship for hyperthermia given in combination with low dose radiotherapy

A group of 36 patients, treated on 44 fields with fractionated treatments of local high-frequency induced hyperthermia and radiotherapy to the low total dose of 14-25 Gy, was retrospectively evaluated for differences between responders (i.e., complete and partial responders) and non-responders. A response rate of 86% was achieved, comprising 14% (6/44) complete and 73% (32/44) partial response. There was an indication that the probability of complete response is greater in smaller tumours. The tumour temperatures achieved were higher in the responders than in the non-responders. Logistic analysis was performed on the mean temperature achieved. This temperature parameter yielded a significant positive dose-effect relationship with regard to therapeutic effect, from which a 50% effective dose of 38.8 degrees C was calculated. The data indicate that to obtain the maximum therapeutic effect, i.e., greater than 95% response rate, tumour temperatures above 42.5 degrees C need to be achieved.

Integration of allogeneic lymphocyte immunotherapy with short-course chemotherapy and hypoenergic hyperthermia: a "triple-threat" treatment for disseminated cancer

A strategy for treatment of disseminated cancer is proposed which unites short-course chemotherapy, local hyperthermia, and allogeneic lymphocyte immunotherapy, designed and timed so as to optimize their synergistic interactions. Short-course chemotherapy potentiates allogeneic lymphocyte immunotherapy, and in turn is potentiated by subsequent courses of local hyperthermia. Response to hyperthermia can be enhanced by measures which selectively inhibit tumor blood flow, impair tumor energy metabolism, and produce tumor acidification; these include induction of prolonged hyperglycemia, and administration of selectively activated "hypoenergic" agents which inhibit or uncouple tumor respiration. It is anticipated that these methods will enable a significant advance in the control of metastasized solid tumors.

The relevance of tumour pH to the treatment of malignant disease

The wide range of tumour pH values that have been determined in human tumours is shown in Fig. 4. It can be seen that tumour pH values may be very low, or may fall in the same range as the values found in normal tissues. This means that pH-mediated modification of therapeutic effectiveness will be patient specific, rather than a general phenomenon. That the pH of the cellular environment might influence the effectiveness of various therapeutic agents is not a new idea. The data published in this field to date concerning such effects have been discussed extensively and are summarized in Table IV. Here we can see that low pH leads to decreased cell survival following treatment with hyperthermia, radiotherapy combined with hyperthermia, radiosensitizers and various chemotherapeutic agents. Conversely, low pH affords some protection against radiation and some drugs. Most of these data were, of necessity, derived from in vitro studies. In vivo studies are in most cases not feasible due to the difficulty of isolating the effect of one selected factor. Low tumour pH is, in vivo, generally assumed to be closely interlinked with tissue hypoxia and low blood-flow levels, each of which may individually influence the experimental outcome. Moreover, most of the aforementioned in vitro studies were conducted under well-oxygenated conditions. As previously mentioned, euoxic cells can, under certain conditions, maintain a pH gradient over the cell membrane. This collapses with the onset of hypoxia, leading to intracellular acidification. Low oxygen levels have been shown to be characteristic of many tumours. Within these limitations it is thus evident that tumour pH values could have far-reaching consequences for therapy. If the in vitro findings should prove to be relevant to the clinical situation various applications are possible. Pre-selection of patients less likely to respond to certain (toxic) chemotherapeutic agents, or conversely selection of agents that are more likely to be effective in the pH range of the tumour to be treated are two examples. Alternatively, the exploitation of low tumour pH values is a possibility. Agents that form or release toxic derivatives in areas of low pH, e.g., pH-sensitive liposomes, will work selectively in such areas. Tumour selective therapy may also be possible in patients with higher tumour pH values if the tumour pH can be lowered. This has been achieved experimentally by the administration of hyperthermia at temperatures above 42 degrees C, or by the administration of glucose.(ABSTRACT TRUNCATED AT 400 WORDS)

Thermal dose determination in cancer therapy

With the rapid development of clinical hyperthermia for the treatment of cancer either alone or in conjunction with other modalities, a means of measuring a thermal dose in terms which are clinically relevant to the biological effect is needed. A comparison of published data empirically suggests a basic relationship that may be used to calculate a "thermal dose." From a knowledge of the temperature during treatment as a function of time combined with a mathematical description of the time-temperature relationship, an estimate of the actual treatment calculated as an exposure time at some reference temperature can be determined. This could be of great benefit in providing a real-time accumulated dose during actual patient treatment. For the purpose of this study, a reference temperature of 43 degrees C has been arbitrarily chosen to convert all thermal exposures to "equivalent-minutes" at this temperature. This dose calculation can be compared to an integrated calculation of the "degree-minutes" to determine its prognostic ability. The time-temperature relationship upon which this equivalent dose calculation is based does not predict, nor does it require, that different tissues have the same sensitivity to heat. A computer program written in FORTRAN is included for performing calculations of both equivalent-minutes (t43) and degree-minutes (tdm43). Means are provided to alter the reference temperature, the Arrhenius "break" temperature and the time-temperature relationship both above and below the "break" temperature. In addition, the effect of factors such as step-down heating, thermotolerance, and physiological conditions on thermal dose calculations are discussed. The equations and methods described in this report are not intended to represent the only approach for thermal dose estimation; instead, they are intended to provide a simple but effective means for such calculations for clinical use and to stimulate efforts to evaluate data in terms of therapeutically useful thermal units.

Time-temperature relationship for hyperthermia induced stoppage of the microcirculation in tumors

The time-temperature dependence for microcirculation stoppage was investigated for the Rhabdomyosarcoma BA1112 growing in observation chambers ("sandwich chambers"). The tumor microcirculation could be observed continuously during the treatment, and the condition of the microcirculation was recorded every 15 minutes as "flowing" or "stoppage". By using large numbers of tumors, the 50% stoppage time (ST50) could be derived for the four temperatures investigated: 42 degrees, 42.5 degrees, 43 degrees and 43.5 degrees C. The respective ST50 values were 226, 152, 101 and 70 minutes. The results can be expressed as a log-linear relationship with a slope value of 0.4551 +/- 0.03 (SD) per degree centigrade. This value probably does not differ significantly from the "t 1/2 for every degree C" rule that has been found for the thermal response of many biological systems.

Changes in acidity of mouse tumor by hyperthermia

The intratissue pH of SCK tumor and leg muscle of unanesthetized mice were determined before, during and after hyperthermia with the use of bulb type pH microelectrodes having pH-sensitive hemisphere 20-40 micron in outer radius. Intratumor pH was heterogeneous throughout tumor (range, 6.60-7.38; average, 6.96), and was more acidic than the intramuscle pH of mouse leg (average, 7.46). Hyperthermia at 43.5 degrees C for 30 min induced a further increase in acidity (decrease in pH of about 0.2 units) in tumor but not in muscle. The heat-induced acidity in tumor lasted for 12 hr following hyperthermia and then recovered to almost control pH value 24 hr after heating. The cause of the increase in acidity in the heated tumors is not clear, but it appears to result from an increase in the contents of acidic metabolites and a sluggish drainage of them due to induced vascular damage. The increased acidity in the heated tumors may inhibit the repair of thermal damage and sensitizes the tumor cells to subsequent heating.

Whole-body hyperthermia in cancer therapy: a report of a phase I-II study

Twenty-seven patients were treated with whole-body hyperthermia alone or in combination with either chemotherapy or radiotherapy. Whole-body hyperthermia was performed in the Pomp-Siemens cabin with hot air and a warm water mattress, the patient being covered with plastic film to avoid cooling by perspiration. The heat treatment lasted for 2 hr at 41.8-42.0 degrees C. Toxicity, such as liver damage and respiratory problems, was considerable. There were two fatalities. Hyperthermia gave an improved therapeutic effect in 6 of the patients. Considerable pain relief was observed in 8 of 10 patients. Whole-body hyperthermia at 42 degrees C can be effective but the potential toxicity limits its use to those patients with severe complaints for whom no other palliative treatment is available.

The influence of a heat pulse on the thermally induced damage to tumour microcirculation

The effect of an initial short period of higher-temperature heat application on the stoppage of the microcirculation in the experimental rhabdomyosarcoma BA1112 in 'sandwich' chambers was investigated. The treatment consisted of an initial heat pulse of 45 degrees C for 10 min which was followed by a continuous exposure at 42.5 degrees C for 3 hr. Using the 't1/2 per degrees C' rule, the time equivalent of the heat pulse was 94 min. Taking this contribution into account, the derived 50% stoppage time of 151 min is essentially the same as the 152 min observed for 42.5 degrees C only treatments. The data therefore indicate that the effect of a heat pulse in the treatment can be accounted for by the customary correction procedure of one time exposure doubling per degrees C. However, it appeared that the microcirculation in the surrounding tumour bed was impaired more than was expected by this treatment.

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.

Sensitization of clonogenic malignant cells to hyperthermia by glucose-mediated, tumor-selective pH reduction

The fraction of clonogenic cells (as assayed by colony formation in semisolid agar medium) in neurogenic TV1A tumor transplants carried subcutaneously by hyperglycemic BDIX rats (serum glucose concentration 50 mmoles/1; average intratumoral pH 6.1) was reduced by a factor of approximately 2.5 X 10(3) after in vivo exposure to 42.2 degrees C for 1 h. The corresponding reduction factor for TV1A tumors in normoglycemic rats was about 20 (serum glucose concentration 6 mmoles/1; average intratumoral pH 6.9). Hyperglycemia without hyperthermic treatment reduced clonogenicity by a factor of about 18 ("glucose-mediated suicide").

Tumour pH in human mammary carcinoma

Human tumour pH was investigated using the new Philips C902S tissue pH electrode. In 22 mammary carcinomas a pH of 7.29 +/- 0.050 (S.E.M.) was observed, whereas in the human subcutis this value was 7.63 +/- 0.034. Tumour pH in some experimental rat tumours was slightly lower than in humans, 7.15 +/- 0.029 in rhabdomyosarcoma BA1112 and 7.07 +/- 0.024 in a small group of other miscellaneous rat tumours. Rat skeletal muscle was found to have a pH of 7.59 +/- 0.070. It is concluded that a small but highly significant (P less than 0.0001) pH difference exists between human mammary carcinoma and human subcutis. This difference is smaller than expected on the basis of animal studies.

Protection of heat induced cytoxicity by glycerol

Glycerol, at concentrations of 2-10% is a potent hyperthermic (43 degrees - 45 degrees C)protector of cultured Chinese hamster cells, V79. Furthermore, the sensitization effect of low pH on heat death is also drastically reduced by the addition of glycerol into the culture medium. Together with the known cellular effects of heat and the role of glycerol in various cellular structures and functions, the data suggest that microtubules and membranes may be involved in the expression of heat-induced cell death.