Thermotolerance kinetics and growth rate changes in the R1H tumour heated at 43 degrees C

Effect of Withaferin A on the development and decay of thermotolerance in B16F1 melanoma: a preliminary study

Protein synthesis inhibitors can suppress the development of thermotolerance in tumor tissues during [corrected] repeated heating. Withaferin A (WA), isolated from Withania somnifera has cytotoxic and inhibitory action on protein synthesis. In the present investigation, effect of WA on development and decay of thermotolerance in B16F1 melanoma was studied in C57BL mice. Tumors of 100 +/- 10 [corrected] mm(3) size were subjected to repeated hyperthermia (HT) at 43 degrees C for 30 minutes. WA was injected after first hyperthermia treatment. The tumor response was assessed by calculating the tumor growth delay (GD). The GD increased with increase in time gap between two hyperthermia treatments and was significantly higher (p < 0.05 to p < 0.001) in WA treated groups at all the respective time gaps (except at 0h and 120h) compared to hyperthermia alone group. WA increases the tumor response during repeated hyperthermia by reducing the magnitude of thermotolerance developed and by decreasing the recovery time from thermotolerance.

Changes in tumor oxygenation during a combined treatment with fractionated irradiation and hyperthermia: an experimental study

PURPOSE

To determine the influence of adjuvant hyperthermia on the oxygenation status of fractionated irradiated tumors.

METHODS AND MATERIALS

Oxygen partial pressure (pO2) in rat rhabdomyosarcomas (R1H) was measured sequentially at weekly intervals during a fractionated irradiation with 60Co-gamma-rays (60 Gy/20f/4 weeks) in combination with local hyperthermia (8 f(HT) at 43 degrees C, 1 h/4 weeks). Tumors were heated twice weekly with a 2450 MHz microwave device at 43 degrees C, 1 h starting 10 min after irradiation. The pO2 measurements (pO2-histograph, Eppendorf, Germany) were performed in anesthetized animals during mechanical ventilation and in hemodynamic steady state. All tumor pO2 measurements were correlated to measurements of the arterial oxygen partial pressure (paO2) determined by a blood gas analyzer.

RESULTS

The oxygenation status of R1H tumors decreased continuously from the start of the combined treatment, with increasing radiation dose and number of heat fractions. In untreated controls a median tumor pO2 of 23 +/- 2 mmHg (mean +/- SEM) was measured. Tumor pO2 decreased to 11 +/- 2 mmHg after 30 Gy + 4 HT (2 weeks), and to 6 +/- 2 mmHg after 60 Gy + 8HT (4 weeks). The increase in the frequency of pO2-values below 5 mmHg and the decrease in the range of the pO2 histograms [delta p(10/90)] further indicated that tumor hypoxia increased relatively rapidly from the start of combined treatment. After 60 Gy + 8HT 48 +/- 5% (mean +/- SEM) of the pO2-values recorded were below 5 mmHg.

CONCLUSIONS

These findings suggest that adjuvant hyperthermia to radiotherapy induces greater changes in tumor oxygenation than radiation alone [cf. (39)]. This might be of importance for the temporary application of hyperthermia in the course of a conventional radiation treatment.

Interstitial radiation and hyperthermia in the Dunning R3327 prostate tumour model: therapeutic efficacy depends on radiation dose-rate, sequence and frequency of heating

To determine the most effective means by which to apply the combined treatments of local tumour hyperthermia (LTH) with interstitial low dose-rate irradiation (IRT) we examined the significance of such factors as dose-rate of radiation, and the sequence and frequency of hyperthermia applications in the anaplastic Dunning prostate tumour subline R3327-AT1. IRT was carried out by the insertion of a single Ir-192 seed into the center of the tumour. For LTH treatments, the tumour-bearing leg was positioned in a circulating constant temperature water bath (43.5 +/- 0.1 degrees C) for 35 min. Neither LTH treatment alone nor the insertion of a dummy seed produced any change in tumour growth compared with sham-treated controls. With regard to the sequence of heating and IRT our results showed that during a 72-h treatment time (30 Gy, 40 cGy/h) a single heat treatment given just before the start of IRT was more efficient (TER = 1.47) in terms of growth delay than LTH given in the middle or the end of radiation treatment (TER approximately 1.0). The growth delay for both the 20 and 40 cGy/h groups appear to be linear with increasing dose for the IRT as well as the IRT + LTH groups. The higher dose-rate was more effective especially with respect to long-term delay in tumour growth in some of the animals. As TER at 40 cGy/h decreased subsequently with increasing treatment time from 1.47 to 1.25 at 60 Gy, we conclude that for treatment times > 72 h, one LTH just before IRT might not be sufficient. If multiple heat treatments are applied during a comparable time course, two LTH treatments one just before the start, the other at the end yielded the greatest local tumour control. In contrast, three LTH given daily were not more effective than the one LTH given just before the start of IRT. These data indicate a clear thermal enhancement of low dose-rate irradiation, with maximal sensitization when hyperthermia was given just before IRT. For multiple heatings a better understanding of the underlying mechanisms of sequencing and timing hopefully provides guidelines how to apply optimally both modalities in the treatment of cancer.

Hyperthermia in the multimodal therapy of advanced rectal carcinomas

The synergistic effects of hyperthermia (raising temperatures to 40 degrees C and above) when combined with radiotherapy and cytotoxic drugs and a modulation of immunological phenomena have been demonstrated in the laboratory. Pre-clinical data relating to hyperthermia are summed up, along with their implications for clinical application. Controlled studies of local and regional hyperthermia have been performed during recent years, and these show us that the adjunction of hyperthermia provides at least an improvement of local control compared with radiotherapy alone. Current clinical results are summarized. Therapy systems based on radiowave irradiation have been commercially available for regional hyperthermia of the pelvis since the mid 1980s. This technology allows us to perform sufficiently tolerable and effective regional hyperthermia on rectal carcinomas. Used as part of curative preoperative and postoperative multimodal therapeutic strategies, hyperthermia can lead to improvement in local control (resectability, down-staging, progression-free time, recurrence rate), at least for certain risk groups. The preoperative radio-chemo-thermotherapy of advanced primary and recurring rectal carcinoma, uT3/4, was tested in a phase-I/II study of 20 patients. Therapy procedure, acute toxicity, thermal parameters, and response are described and discussed for this patient group. The regimen proved to be sufficiently tolerable, and complications did not occur. Tumor resection was performed on 14 of the 20 patients; 13 of the procedures were R0-resections and one was an R2 resection. In 64% of the resected rectal carcinomas, histopathological down-staging of the pretherapeutic endosonographical stadium was achieved; in three of the patients, despite continued non-resectability, local control has now been maintained for more than 12 months. In two patients with nonresectable rectal carcinomas, local progress was seen during the neoadjuvant combination therapy.

Enhancement of the effectiveness of methotrexate for the treatment of solid tumours by application of local hyperthermia

Investigations were performed to assess the influence of hyperthermia on the pharmacokinetics of a chemotherapeutic drug and on the effectiveness of combined treatments for induction of tumour cell death and growth delay of experimental tumours. Treatments consisted of methotrexate (MTX, 20 mg/kg ip), hyperthermia at 43 degrees C during 60 min (HT60) or 90 min (HT90) and combined chemo-hyperthermia using various time intervals up to 24 h. The results indicate that, for MTX + HT90, concentrations in excess of 0.02 mg/kg are maintained in tumour tissue during at least 22 days, whereas after the other single and combined treatments, the concentration decreased below this level within 5-8 days. The combinations of MTX + HT90 also were more effective with respect to tumour growth delay, 26-28 days, and frequency of partial remissions, 75-100%, as compared to the other treatments: 7-12 days and 0-28% respectively. These observations correlate well with cell survival data. It is concluded that hyperthermia can enhance the effectiveness of MTX and that variation of time-intervals between administration of MTX and hyperthermia as well as the duration of the hyperthermic treatment have a great influence on tumour responses. Unfortunately, also toxic effects were induced distantly from the site of local hyperthermic treatment by the combination of MTX + HT90 which was most effective with respect to tumour eradication.

Heat shock proteins, thermotolerance, and their relevance to clinical hyperthermia

Mammalian cells, when exposed to a non-lethal heat shock, have the ability to acquire a transient resistance to subsequent exposures at elevated temperatures, a phenomenon termed thermotolerance. The mechanism(s) for the development of thermotolerance is not well understood, but earlier experimental evidence suggests that protein synthesis may play a role in its manifestation. On the molecular level, heat shock activates a specific set of genes, so-called heat shock genes, and results in the preferential synthesis of heat shock proteins. The heat shock response, specifically the regulation, expression and functions of heat shock proteins, has been extensively studied in the past decades and has attracted the attention of a wide spectrum of investigators ranging from molecular and cell biologists to radiation and hyperthermia oncologists. There is much data supporting the hypothesis that heat shock proteins play important roles in modulating cellular responses to heat shock, and are involved in the development of thermotolerance. This review summarizes some current knowledge on thermotolerance and the functions of heat shock proteins, especially hsp70. The relationship between thermotolerance development and hsp70 synthesis in tumours and in normal tissues is examined. The possibility of using hsp70 as an indicator for thermotolerance is discussed.

Arsenite induced sensitization and self-tolerance of Reuber H35 hepatoma cells

Our data show that a short incubation with arsenite (30-300 microM) induces a biphasic change in cellular sensitivity towards a second exposure to arsenite. A transient sensitization was followed by the development of self-tolerance. Sensitization was measured using the step-down protocol; i.e., application of a high dose of arsenite pretreatment (100 or 300 microM) followed immediately by incubation in a low dose of arsenite (1-30 microM), with extensive rinsing in between. Whereas no effect of 1 and 3 microM on cellular survival is observed without pretreatment, a large decrease in cell survival can be established when these low doses of arsenite are applied immediately after a 1 hr pretreatment with 100 or 300 microM arsenite. According to the step-down protocol, a high dose of toxic compounds is applied and is followed by prolonged incubation in a lower concentration of the initial toxic compound. This might be a more accurate model for studying the effects of toxic insults on cells and organisms in the manner in which they occur in their natural environment. The level of tolerance was determined by a 1 hr test treatment with 300 microM arsenite applied at different times after pretreatment. Using this fractionated treatment protocol, it was established that tolerance increases with the increasing time intervals between the sodium arsenite treatments, during the 6 hr studied. These observations suggest that sensitization gradually decreases, whereas tolerance develops. Furthermore, our data indicate that the condition of pretreatment determines the extent to which the early sensitivity increases, as well as the development of tolerance later on. A relatively high arsenite concentration leads to more sensitized cells, which are transformed into more tolerant cells in comparison with the effect of a lower arsenite concentration.

Winner of the Lund Science Award 1992. Thermosensitization induced by step-down heating. A review on heat-induced sensitization to hyperthermia alone or hyperthermia combined with radiation

A few minute's exposure to a high temperature (sensitizing treatment, ST) may substantially increase the cytotoxic and the radiosensitizing effect of a subsequent heating at a lower temperature (test treatment, TT). This phenomenon, which is known as step-down heating (SDH) or thermosensitization, has been observed both in cultured cells in vitro and in tumours and normal tissues in vivo. The effect of SDH increases with a lowering of TT temperature, but it is rapidly lost at temperatures very close to 37 degrees C. SDH-induced thermosensitization decays within a few hours, when an interval is inserted between ST and TT. In vitro results suggest an exponential decay of the SDH effect with half times ranging from 1.5- to 3.1 h. The effect of SDH increases with increasing ST time or temperature. For single heating, the Arrhenius plot is biphasic with activation energies of 500-800 and 1200-1700 kJ/mol above and below a break point temperature in the region 42.5-43.0 degrees C, respectively. For SDH, the Arrhenius plot gradually becomes monophasic with increasing severity of ST and it approaches asymptotically to an activation energy of about 400 kJ/mol. The reduction of the activation energy depends on cell survival after the priming ST and not on the specific ST heating time or temperature. SDH strongly enhances hyperthermic radiosensitization with a 5-6-fold reduction of the radiation dose required to achieve tumour control. The thermosensitizing and the radiosensitizing effects of SDH have several features in common. Both effects become more prominent when the TT temperature is decreased and when the ST heating time or temperature increases. In addition, the decay kinetics for both effects are comparable. For heat alone, the effect of SDH in tumour and normal tissue seems to be quantitatively similar. However, the therapeutic ratio may be increased by combining SDH with radiation. Biologically, the critical subcellular targets involved in the SDH effect have not been revealed. However, the ability of SDH to inhibit the clearance of heat-induced aggregation of proteins in the nucleus is interesting. Blockage of the nuclear function by proteins is a central theory in the present molecular biological models for both cell kill by heat and heat radiosensitization. Clinically, SDH may be an advantage since even a short exposure to high temperature increases the effect of an otherwise inadequate heat treatment. The disadvantages are that SDH complicates thermal dose calculations, and may cause unacceptable damage to normal tissue.

Responsiveness of the increase in C-fos mRNA levels depends on the inducer and the cell's past

In this paper we show that in C3H10T1/2 mouse fibroblasts, the inducibility of c-fos mRNA by heat shock or serum addition is strongly dependent on the cell's past. Four hours after a heat shock, a time point where the induced c-fos mRNA has disappeared, c-fos mRNA could not be induced again by a second heat shock. Four hours after serum addition, by which c-fos was induced, a second serum addition also failed to induce c-fos mRNA again. When, however, serum was added 4 hours after heat shock or heat shock was given 4 hours after serum addition, levels of c-fos mRNA could be enhanced again. The induction by serum of c-fos mRNA levels in thermotolerant cells might be related to their increased stimulation of DNA synthesis as compared to control cells.

A comparison between the effect of step-down heating in a tumour and a normal tissue in vivo

A comparison between the effect of step-down heating (SDH) obtained in a C3H mammary carcinoma grown in the feet of CDF1 mice and the skin of normal CDF1 feet is presented. Water-bath heating was used, and SDH was obtained by giving a 44.7 degrees C/10 min treatment followed by heating at 42.2 degrees C for variable times. Single heating at 42.2 degrees C and step-up heating (SUH), i.e. 42.2 degrees C followed by 44.7 degrees C/10 min, were used as controls. The endpoint was the heating time at 42.2 degrees C to obtain either a definite tumour growth time (TGT50) or a specific skin score level (RD50) in 50% of the animals. The effect of SDH and SUH was quantified by the step-down ratio (SDR), calculated as the ratio of the heating times at 42.2 degrees C to obtain the specific endpoint. In both assays the effect of SDH was seen as a significant left shift of the SDH dose-response curve compared to the curve for single heating and SUH. For the comparison of the tumour and the normal tissue response, damage levels with comparable heating times for single heating were used. The therapeutic effect was then investigated by calculating the therapeutic gain factor (TGF), where TGF = SDR(tumour)/SDR(normal tissue). Neither SUH nor SDH gave a TGF significantly different from 1. The results suggest that SDH may be used clinically to shorten the heating time without decreasing the therapeutic effect.