Cell cycle progression during chronic hyperthermia in S phase CHO cells

Effects of the thermal environment on articular chondrocyte metabolism: a fundamental study to facilitate establishment of an effective thermotherapy for osteoarthritis

AIM

To facilitate establishment of an effective thermotherapy for osteoarthritis (OA), we investigated the effects of the thermal environment on articular chondrocyte metabolism in vitro.

METHODS

Chondrocytes were isolated from porcine knee joints, and cultured at 32°C, 37°C and 41°C. Cell proliferation and viability were assessed at Days 2, 4 and 8. In addition, TdT-mediated dUTP nick end labeling (TUNEL) assay was performed at Day 3 to determine the proportion of apoptotic chondrocytes. Analysis of genes specific for factors related to the cartilage extracellular matrix (ECM), cartilage destruction, and cartilage protection was performed at Day 2. Furthermore, evaluation of heat stress tolerance, and heat shock protein 70 (HSP70) mRNA expression and protein synthesis was performed at Day 2 and 3, respectively.

RESULTS

Cell proliferation was more at 37°C than at 32°C and 41°C. Cell viability and the number of TUNEL-positive cells were not affected until Day 8 and 3, respectively. The expression of the ECM-related genes was up-regulated at higher temperature. The expression of MMP13, a type II collagen destructive enzyme, and that of TIMP1 and TIMP2, which are MMP inhibitors, were up-regulated at higher temperatures. Finally, the chondrocytes cultured at 41°C may acquire heat stress tolerance, in part, due to the up-regulation of HSP70, and may inhibit apoptosis induced by various stresses, which is observed in OA.

CONCLUSIONS

The thermal environment affects articular chondrocyte metabolism, and a heat stimulus of approximately 41°C could enhance chondrocyte anabolism and induce heat stress tolerance.

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.

Sequence of treatment is important in the modification of camptothecin induced cell killing by hyperthermia

We investigated the modification of camptothecin (CPT)-induced cell killing by hyperthermia in a radioresistant human melanoma (Sk-Mel-3) and a human normal (AG1522) cell line. CPT, a topoisomerase (topo) I inhibitor, was given as a 1 h exposure at variable doses up to 34 microM; hyperthermia was given either before or following CPT treatment. Hyperthermia was given either as a treatment of 41 degrees C for 8 h (termed lower temperature hyperthermia, LTH) or 45 degrees C for 15 min (termed higher temperature hyperthermia, HTH). LTH preceding CPT treatment had no effect on Sk-Mel-3 but potentiated killing of AG1522 cells. HTH preceding CPT treatment, however, almost completely abrogated the toxicity of CPT to both Sk-Mel-3 and AG1522 cells. These results therefore provided evidence for a lack of enhancement of CPT toxicity towards Sk-Mel-3 cells when hyperthermia preceded treatment with CPT. There was also no potentiation of killing of both cell lines when LTH followed treatment with CPT. In contrast, the killing of Sk-Mel-3 cells was slightly potentiated, whereas that of AG1522 cells was reduced, when HTH followed CPT. These results therefore suggested a potential for enhancement of killing of Sk-Mel-3 relative to AG1522 cells when HTH, but not LTH, followed CPT treatment. In addition, we found that a preceding exposure ot HTH did not affect either accumulation or efflux of[3H]CPT in both cell lines. Thus the significantly reduced cytotoxicity observed under those conditions was not related simply to a modification of accumulation or efflux of CPT. We found no significant differences in the atalytic activities of topo I extracted from the nuclei of Sk-Mel-3 and AG1522 cells that were either heated under HTH conditions or that were no subjected to such treatment. These results therefore suggested that the substantial reduction of cytotoxicity seen when HTH preceded CPT treatment was also not due to an effect on topo I catalytic activity. Our results therefore demonstrate that the sequence of application of hyperthermia and CPT is very important in determining the amount and, possibly, selective potentiation of tumour relative to normal cell cytotoxicity.

Reduction of etoposide induced cell killing by hyperthermia can occur without changes in etoposide transport or DNA topoisomerase II activity

We investigated the modification of etoposide (i.e. VP-16)-induced cell killing by hyperthermia in a radioresistant human melanoma (Sk-Mel-3) and a human normal (AG1522) cell line. VP-16, a DNA topo II poison, was given as a 1 h exposure at variable doses up to 35 microM; hyperthermia was given either before or following VP-16 treatment. Hyperthermic treatment comprised one of the following: 41 degrees C for 8 h, 42 degrees C for 2 h or 45 degrees C for 15 min. Hyperthermia preceding VP-16 treatment reduced the cytotoxicity of the latter; the reduction of VP-16 cytotoxicity was directly proportional to the severity of the hyperthermic treatment. For a particular combination of hyperthermic dose and VP-16 concentration, generally similar responses were seen in both cell lines. There were no effects on VP-16 cytotoxicity when both Sk-Mel-3 and AG1522 cells were heated at 41 degrees C for 8 h following treatment with VP-16. However, heating both cell lines at 45 degrees C for 15 min following VP-16 treatment again reduced the amount of cytotoxicity associated with VP-16. In addition, we found that a preceding exposure to 45 degrees C, 15 min heating did not affect either cellular accumulation or efflux of [3H]VP-16 in both cell lines. This suggested that the reduction in VP-16 cytotoxicity observed under those conditions was not due to a modification of VP-16 transport. We found no differences between the catalytic activities of topo II extracted from nuclei of Sk-Mel-3 and AG1522 cells that were either heated at 45 degrees C for 15 min or that were not subjected to such treatment. These results therefore suggested that the substantial reduction of cytotoxicity seen when 45 degrees C, 15 min heating preceded VP-16 treatment was also not due to an effect on topo II catalytic activity. Our results therefore demonstrate that hyperthermia, given either before or after VP-16, can actually reduce the amount of VP-16 cytotoxicity and that this can occur without any overt changes in VP-16 accumulation and efflux or in topo II catalytic activity.

Thermotolerance in human glioma cells

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

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)

Changes in heat and radiation sensitivity during long duration, moderate hyperthermia in HeLa S3 cells

Step-up heating and thermal radiosensitization were studied at 41.5 degrees C in HeLa S3 cells under conditions where chronic thermotolerance was not expressed. In spite of this lack of thermotolerance expression, it was possible that thermotolerance to higher temperature treatment had developed. Accordingly, cells were incubated for various times at 41.5 degrees C, then immediately shifted up to 45 degrees C, whereupon heating continued for up to 75 min. Thermotolerance to 45 degrees C heating was observed after 8 hr incubation at 41.5 degrees C and decayed by 32 hr of continuous incubation at 41.5 degrees C. When the time of 45 degrees C treatment was extended to 150 min, the biphasic survival response indicated that chronic thermotolerance was expressed at 45 degrees C, even though it was not expressed during the 41.5 degrees C treatment. Thus, chronic thermotolerance can develop under conditions (e.g., at 41.5 degrees C) where it is not expressed, yet be expressed under other conditions (e.g., during 45 degrees C exposure). When cultures were x-irradiated after various periods of 41.5 degrees C treatment, maximum thermal radiosensitization was observed after 4 hr of incubation at 41.5 degrees C, for which no cell killing was observed due to heat alone. The radiosensitization observed decreased the Do and Dq values from about 1.3 Gy to 0.7 Gy and from about 2.0 Gy to 1.0 Gy, respectively. As the duration of the 41.5 degrees C pre-treatment was extended up to 32 hr, no additional thermal-radiosensitization was observed; all killing due to the heat exposure at 41.5 degrees C was additive to the radiation killing after the initial induction of thermal radiosensitization. These results demonstrate differences in the thermal and radiation responses of HeLa cells when compared to earlier studies using CHO cells and may be more relevant to the clinical setting.