Cytotoxic Effects Of Hyperthermia Research Articles

Cordycepin enhances hyperthermia-induced apoptosis and cell cycle arrest by modulating the MAPK pathway in human lymphoma U937 cells.

Hyperthermia induces cancer cell death. However, the cytotoxic effect of hyperthermia is not sufficient. Cordycepin can also induce apoptosis in cancer cells and enhance the antitumoral activity of irradiation. To examine cordycepin-mediated enhancement of hyperthermia-induced apoptosis, this study investigated the combined effects and apoptotic mechanisms of hyperthermia and cordycepin on human leukemia U937 cells. Cell viability and apoptosis were measured using MTT assays, Hoechst 33342 staining and Annexin V/PI double staining. The distribution of the cell cycle and sub-G1 phase, reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) were examined by flow cytometry. The expression of related proteins was analyzed by western blotting. Combined treatment with hyperthermia and cordycepin markedly augmented apoptosis by upregulating Bax and suppressing Bcl-2, Bid and activated caspase 3 and 8 expression, and apoptosis was decreased by Z-VAD-fmk (a pan caspase inhibitor). We also found that the MMP was significantly decreased and excessive ROS generation occurred. The combination treatment also induced arrest in the G2/M phase by downregulating cyclin dependent kinase 1 (CDK1) and cyclin B1 protein expression. Furthermore, it was observed that mitogen-activated protein kinase (MAPK) pathway including ERK, JNK and p38 signals was involved in the induction of apoptosis. The phosphorylated p38 and JNK were increased and ERK phosphorylation was decreased by the combined treatment. In addition, N-acetyl-L-cysteine (NAC) significantly protected the cells by restoring ROS levels and the activity of caspase-3, inactivating the MAPK pathway. Cordycepin significantly enhanced hyperthermia-induced apoptosis and G2/M phase arrest in U937 cells. The combined treatment enhanced apoptosis through the MAPK pathway and mitochondrial dysfunction, and these effects could be rescued by NAC. We report for the first time that cordycepin can be used as a hyperthermia sensitizer to treat leukemia.

Cytotoxic effects of hyperthermia, chemotherapy (Navelbine) and radiation on glioma spheroids

Abstract Introduction Glioblastoma multiform (GBM) is the most common malignant primary brain tumor in humans. Current conventional treatment could not effectively increase the survival rate of patients who suffered from GBM. In clinical view, some experiments which can mimic in vivo conditions to evaluate anticancer agent effects on tumors are very useful. We can fairly reach to this goal using 3-dimentional spheroids rather than monolayer culture. The aim of this study was to determine the cytotoxicity caused by Navelbine, hyperthermia and radiation on glioma spheroids. Methods The spheroid cells were separately or simultaneously treated with the doses of 7.5 μg/ml Navelbine for 50.3 h, irradiated with 2 Gy and incubated at 43 °C for 1 h. Comet and colony formation assays were applied to assess the DNA damages and survival rate of the cells. Results In both comet and colony formation assays, cell damage in all treated groups was significantly higher in comparison with control group ( P 0.05). Moreover, the synergistic effect of combined groups such as: hyperthermia and radiotherapy, Navelbine and radiotherapy and combination of Navelbine-hyperthermia-radiotherapy was observed. Conclusions Combined agents with low concentration can cause a synergistic effect on treatment procedure and increased damages in multicellular spheroids.

Photothermal ablation of human lung cancer by low-power near-infrared laser and topical injection of indocyanine green.

The present study was designed to evaluate the efficacy of photothermal ablation therapy for lung cancer by low-power near-infrared laser and topical injection of indocyanine green (ICG). In vitro study 1: an 808 nm laser with 250 mW was irradiated for 10 minutes using different dilutions of ICG and the temporal thermal effect was monitored. ICG (1 mL of 0.5 g/L) was heated to a temperature of >30°C from the base temperature by laser irradiation. In vitro study 2: the cytotoxic effect of hyperthermia on human lung cancer cells was examined in different temperature and time settings. Cell viability was quantified by both an MTS assay and reculturing. Fatal conditions evaluated by reculturing were as follows: thermal treatment at 55°C for 5 minutes, 53°C for 10 minutes, and 51°C for 15 minutes. The MTS assay study suggested that thermal treatment at 59°C for 5 minutes and 57°C for 20 minutes showed a severe cytotoxic effect. In vivo study: nude mouse subcutaneous NCI-H460 human lung cancer xenograft models were used for the study. Saline or 0.5 g/L of ICG was injected topically into the tumor (n=3/group). Tumors were irradiated with a laser at 500 mW for 10 minutes. Although the tumor diameter reached 1 cm within 24 days after treatment in all 3 mice using saline/laser, tumor sizes were gradually reduced in all 3 mice using the ICG/laser. In 2 of the 3 mice using ICG/laser, tumors had disappeared macroscopically. The efficacy of the photothermal ablation therapy by low-power near-infrared laser and a topical injection of ICG was clarified using a mouse subcutaneous a lung cancer xenograft model.

Antitumour Efficacy of Two Paclitaxel Formulations for Hyperthermic Intraperitoneal Chemotherapy (HIPEC) in an In Vivo Rat Model

To evaluate the tumour growth delay of a peritoneal carcinomatosis (PC) of colorectal origin after intraperitoneal chemotherapy with paclitaxel/randomly-methylated-β-cyclodextrin (Pac/RAME-β-CD) versus Taxol® at normo- and hyperthermic conditions in rats. Hyperthermic intraperitoneal chemotherapy (HIPEC) was performed 7 days post implantation of the tumour with both formulations at a Pac concentration of 0.24 mg/ml. Tumour evaluation was performed via positron emission tomography (PET) and magnetic resonance imaging (MRI) imaging, measuring tumour activity and tumour volume, respectively. Scans were taken at 2 and 7 days post treatment. PET and MRI data showed a significant reduction in tumour activity and tumour volume for rats treated with Pac/RAME-β-CD (at normo- and hyperthermic conditions), compared to the control group. Treatment with Taxol® did not result in a significant reduction of tumour activity and tumour volume. No significant differences between the normo- and hyperthermic conditions were observed for both formulations, indicating that hyperthermia and paclitaxel were not synergistic despite the direct cytotoxic effect of hyperthermia. Monitoring tumour growth via PET and MRI indicated that Pac/RAME-β-CD inclusion complexes had a significantly higher efficacy compared to Taxol® in a rat model for peritoneal carcinomatosis.

Cytotoxic Effect of Hyperthermia and Chemotherapy with Platinum Salt on Ovarian Cancer Cells: Results of an in vitro Study

Purpose: Hyperthermic intraperitoneal chemotherapy is continuously under evaluation in ovarian cancer. The purpose of the present study was to evaluate the effect of chemotherapy, drug concentration and temperature. Materials and Methods: A human ovarian carcinoma cell line was used. The effect of hyperthermia combined with chemotherapy was analyzed. Results: When hyperthermia was combined with chemotherapy, the 50% lethal dose (LD₅₀) decreased with the duration of exposure. The effect of temperature was similar between 39 and 43°C for a 30-min exposure. For a 60- to 90-min exposure, the LD₅₀ was equivalent between 38 and 43°C. Beyond 40°C, an increase in platinum salt concentration was necessary to obtain similar results according to the duration of exposure. Conclusions: The cytotoxic effect of the combination seemed to be potentiated and limited at 40°C.

Enhancement of cell killing by induction of apoptosis after treatment with mild hyperthermia at 42 degrees C and cisplatin.

Ohtsubo, T., Igawa, H., Saito, T., Matsumoto, H., Park, H. J., Song, C. W., Kano, E. and Saito, H. Enhancement of Cell Killing by Induction of Apoptosis after Treatment with Mild Hyperthermia at 42 degrees C and Cisplatin. Radiat. Res. 156, 103-109 (2001). We examined the interactive effects of cisplatin (1.0 microg/ml) combined with hyperthermia on cell killing and on the induction of apoptosis in IMC-3 human maxillary carcinoma cells. The cytotoxic effects of hyperthermia on IMC-3 cells at 44 degrees C were greater than at 42 degrees C, as has been reported for many other cells. The induction of apoptosis, DNA fragmentation and poly(ADP-ribose) polymerase cleavage were greater after hyperthermia at 44 degrees C for 30 min compared with treatment at 42 degrees C for 105 min, even though both of these heat doses were isoeffective in reducing cell survival to 50%. Treatment with cisplatin at 37 degrees C for up to 120 min did not result in cytotoxicity or the induction of apoptosis. The enhancement ratio for treatment with cisplatin at 42 degrees C was greater than that at 44 degrees C. More apoptosis was induced after the treatment with cisplatin at 42 degrees C compared to treatment with cisplatin at 44 degrees C. Taking these findings together, the combination of cisplatin and hyperthermia at 42 degrees C appeared to be more effective than cisplatin with hyperthermia at 44 degrees C for the induction of apoptosis in IMC-3 cells.

Expression of inducible Hsp70 enhances the proliferation of MCF-7 breast cancer cells and protects against the cytotoxic effects of hyperthermia

Heat shock proteins (Hsps) are ubiquitous proteins that are induced following exposure to sublethal heat shock, are highly conserved during evolution, and protect cells from damage through their function as molecular chaperones. Some cancers demonstrate elevated levels of Hsp70, and their expression has been associated with cell proliferation, disease prognosis, and resistance to chemotherapy. In this study, we developed a tetracycline-regulated gene expression system to determine the specific effects of inducible Hsp70 on cell growth and protection against hyperthermia in MCF-7 breast cancer cells. MCF-7 cells expressing high levels of Hsp70 demonstrated a significantly faster doubling time (39 hours) compared with nonoverexpressing control cells (54 hours). The effect of elevated Hsp70 on cell proliferation was characterized further by 5-bromo-2'deoxyuridine labeling, which demonstrated a higher number of second and third division metaphases in cells at 42 and 69 hours, respectively. Estimates based on cell cycle analysis and mean doubling time indicated that Hsp70 may be exerting its growth-stimulating effect on MCF-7 cells primarily by shortening of the G0/G1 and S phases of the cell cycle. In addition to the effects on cell growth, we found that elevated levels of Hsp70 were sufficient to confer a significant level of protection against heat in MCF-7 cells. The results of this study support existing evidence linking Hsp70 expression with cell growth and cytoprotection in human cancer cells.

Intravenous infusion of glucose and the vasodilator sodium nitroprusside in combination with local hyperthermia: Effects on tumour pH and tumour response in the BT4An rat tumour model

The influence of sodium nitroprusside (SNP) induced hypotension on the extracellular tumour pH during local hyperthermia (HT), and on the cytotoxic effect of HT, was studied in the BT4 An tumour transplanted to the hind limb of BD IX rats. Experiments with intravenous infusion of glucose before the HT/SNP combination were also performed. Local waterbath HT was given at 44d`C. Sodium nitroprusside was administered as a continuous i.v. infusion to lower the mean arterial blood pressure to 60 mm Hg. Glucose was given as an i.v. infusion at a dosage of 4.8g/kg body weight in 60 min before HT. Extracellular tumour pH was measured by a needle type glass electrode. The tumour pH fell from 7.19 to 6.81, on average, after 60 min HT. Sodium nitroprusside induced hypotension during HT did not increase the pH fall after 1 h HT, but the pH 60 min after discontinuation of HT was lower in this group than in the HT alone group. Pre-treatment with glucose before HT gave similar results as the HT/SNP combination. When glucose was given before HT/SNP a highly relevant decline in tumour pH during HT from 7.22 to 5.95 was observed. In a separate tumour response experiment adding SNP to HT was found to prolong the tumour growth time. Pre-treatment with glucose before the HT/SNP combination prolonged the tumour growth time slightly. The applicability of this treatment protocol in the clinical treatment of patients is discussed.

Use of the vasodilator sodium nitroprusside during local hyperthermia: Effects on tumor temperature and tumor response in a rat tumor model

The effect of a decrease in the mean arterial blood pressure (MAP) induced by sodium nitroprusside (SNP) on the tumor temperature during hyperthermia (HT), and on the cytotoxic effect of HT, was studied in the BT4An tumor transplanted to the hind limb of BD IX rats. Experiments with two different anesthetics, pentobarbital and the midazolam/fentanyl/fluanisone combination (MFF), were performed to secure reliable conclusions. In the tumor response experiments local waterbath HT at 44.0 degrees C was given for 60 min. Sodium nitroprusside was administered as a continuous intravenous infusion to lower the MAP to 60 or 80 mmHg during HT. In two other experiments the temperature at the base of the tumor during HT was measured before and during SNP infusion. In animals without tumor the temperature was measured subcutaneously on the foot during HT with or without SNP-induced hypotension. When SNP was given to lower the MAP to 60 mmHg during HT in MFF anesthetized animals, the median tumor growth time (TGT) was 70 days, compared to 14.5 days in the HT alone group. The corresponding figures were 127 and 12.1 days with pentobarbital anesthesia. In the HT + SNP group, more than 40% cure was observed in both experiments. No cures were seen in any of the other groups. Hyperthermia alone prolonged the TGT slightly, whereas SNP given alone had no effect, compared to controls. When the MAP was lowered to 80 mmHg by SNP infusion during HT (MFF anesthesia), the median TGT was 19.9 days, which was significantly longer than that in the HT alone group (10.9 days). In the MAP range from 60 to 120 mmHg, a nearly linear relationship between the MAP and the tumor temperature was found during HT in MFF anesthetized animals. With both anesthetics, the median temperature at the base of the tumor was about 0.8 degrees C higher during HT when the MAP was lowered to 60 mmHg by SNP. In animals without tumors, the temperature subcutaneously on the foot was 0.3 and 0.4 degrees C higher during SNP infusion in the MFF and pentobarbital group, respectively. We have developed a small animal model in inbred rats feasible for exploring the influence of a stable blood pressure reduction induced by SNP, on the effect of HT given alone or in combination with other treatment modalities to a transplantable tumor. The greatly increased cytotoxic effect of local waterbath HT in the present tumor response experiments is probably a consequence of increased tumor temperature during SNP infusion.

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Because the cytotoxic effect of hyperthermia in the 42-43°C range has been demonstrated, a transition temperature of the conventional liposomes have so far been 42°C to enhance the synergistic effect of hyperthermia and antitumor drugs. When considered this drug delivery system as clinical use, an important problem about this treatment is that the glioma cells invade wide portions of the brain and present technology has not yet been able to achieve the heating of the wide areas invaded by glioma cells. On the other hand, it has been remarked that the blood brain barrier(BBB) limits the ability of many antitumor drugs to penetrate the central nervous system. Despite of their greater cytotoxic effects on glioma cells in vitro, many drugs, such as adriamycin (ADM), have not so far been used mainly because they are regarded as being blocked by the BBB. In order overcome these roblems we prepared liposomes which brought a sharp release rate of ADM above 40°C. This liposome showed a significantly great antitumor effect against rat malignant gliomas which were transplanted into their legs at the temperature of 40°C. These results suggests that this procedure (1) contributes to the synergistic effect of hyperthermia and antitumor drugs in the regions heated above 42°C, (2) helps to deliver the antitumor drugs more widely with the temperature of 40°C, (3) gives a good chance to many antitumor drugs which have so far not been used from the problem of the BBB. We suggest that this advantage of our plan could outweigh the disadvantages of the conventional thermo-chemotherapy.

Heat shock stimulates the release of arachidonic acid and the synthesis of prostaglandins and leukotriene B4 in mammalian cells

Heat shock has a profound influence on the metabolism and behavior of eukaryotic cells. We have examined the effects of heat shock on the release from cells of arachidonic acid and its bioactive eicosanoid metabolites, the prostaglandins and leukotrienes. Heat shock (42-45 degrees) increased the rate of arachidonic acid release from human, rat, murine, and hamster cells. Arachidonate accumulation appeared to be due, at least partially, to stimulation of a phospholipase A2 activity by heat shock and was accompanied by the accumulation of lysophosphatidyl-inositol and lysophosphatidylcholine in membranes. Induction of arachidonate release by heat did not appear to be mediated by an increase in cell Ca++. Stimulation of arachidonate release by heat shock in hamster fibroblasts was quantitatively similar to the receptor-mediated effects of alpha thrombin and bradykinin. The effects of heat shock and alpha thrombin on arachidonate release were inhibited by glucocorticoids. Increased arachidonate release in heat-shocked cells was accompanied by the accelerated accumulation of cyclooxygenase products prostaglandin E2 and prostaglandin F2 alpha and by 5-lipoxygenase metabolite leukotriene B4. Elevated concentrations of arachidonic acid and metabolites may be involved in the cytotoxic effects of hyperthermia, in homeostatic responses to heat shock, and in vascular and inflammatory reactions to stress.

Azo-dye-induced primary hepatoma and a gradual increase in thermosensitivity.

To determine whether or not the cytotoxic effects of hyperthermia are directed primarily to malignant cells, we examined changes in thermosensitivity during hepatocarcinogenesis in rats, as induced by 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB). The findings were compared with those in livers of rats fed a commercial diet. The cell viability was determined using the succinate dehydrogenase inhibition (SDI) test. The succinate dehydrogenase (SD) activity of liver cells, when exposed to heat (43 degrees C) for 2, 5, or 10 hr, decreased in a time-dependent manner, in each tissue. The decrease in SD activity was evident in 3'-Me-DAB liver for 5 hr of heat treatment on day 57, compared with findings in the normal liver. Significant differences were present for 2, 5, and 10 hr on days 93 and 136. Thus a chemically induced hepatoma is more sensitive to heat than are the normal cells. As this thermosensitivity gradually increased during the hepatocarcinogenesis, the malignant cells are particularly vulnerable to hyperthermia.

Biologic Rationale for Hyperthermia

This article discusses the basic biologic data relative to the use of hyperthermia as an adjuvant to ionizing radiation in the treatment of solid tumors. The cytotoxic effects of hyperthermia are presented, as are parameters that modify cellular sensitivity. In vivo physiologic changes associated with hyperthermia are also considered. Finally, the in vitro and in vivo interactions between hyperthermia and radiation are discussed, particularly as they relate to improved tumor response.

Growth Factors and Hyperthermia: II. Viability of Chinese Hamster Ovary HA-1 Cells during Serum Starvation and Hyperthermia

We tested the possibility that hyperthermia kills HA-1 cells in a manner analogous to growth factor deprivation. HA-1 cells were inactivated by serum starvation when incubated in Eagle's MEM at a density of 40 cells/cm2 or less. Cells became resistant to the absence of serum when the cell density was greater than 400 cells/cm2 or when lethally irradiated HA-1 feeder cells were present. The feeder cells exerted their effect through a diffusible factor. In addition, a 1:1 mixture of Eagle's MEM and Ham's F-12 enabled HA-1 cells to remain viable without serum. Ten days growth in Eagle's MEM + Ham's F-12 without serum resulted in the formation of microcolonies of cells. This indicated that growth factor deprivation was not lethal to HA-1 cells, and it suggested that they may have been partially transformed. The presence of the growth factors insulin, transferrin, and fibroblast growth factor (FGF) reduced cell killing by a small amount during conditions of serum starvation. After hyperthermia, the presence of growth factors again diminished cell killing by a modest amount (approximately twofold). Feeder cells also improved cell survival after hyperthermia. The effect of feeder cells was greatest when cells were trypsinized immediately after hyperthermia. When cells were not trypsinized after heating, feeder cells increased survival less than twofold. In summary, the absence of growth factors was not lethal to HA-1 cells, and therefore the cytotoxic effects of hyperthermia could not be explained fully by the failure to bind growth factors. HA-1 feeder cells secreted undefined, growth-promoting substances, but feeder cells exerted only a small positive effect on cell survival after hyperthermia when cells were not trypsinized after heating.

Cytotoxic effects of hyperthermia, 5-fluorouracil and their combination on a human leukemia T-Lymphoblast cell line, CCRF-CEM

The cytotoxic effects of 5-fluorouracil (FUra), hyperthermia, and the combination of these treatments were examined in a human T-lymphoblast cell line, CCRF-CEM. Simultaneous exposure of exponentially growing CCRF-CEM cells to hyperthermia (39 and 42°C) and FUra (10, 50, and 100 μ M) for 1 or 2 hr resulted in subadditive or additive cell kill. When CCRF-CEM cells were exposed to these agents in sequence (hyperthermia → FUra and FUra → hyperthermia) for 1 and 2 hr duration additive cell kill was also observed. Enhanced cytotoxic effects were observed when a longer exposure (4 and 8 hr) to FUra (100 μ M) followed heat (42° C for 1 and 2 hr). Heat exposure (42° C, 1 and 2 hr) induced a rapid decrease in the synthesis of DNA of CCRF-CEM cells, followed by a rebound increase at 12 hr and a new decrease at 24 hr. Flow cytometry demonstrated an accumulation of cells in the S phase at 12 hr after heat exposure, followed by a marked increase of the G + M population (maximum at 24 hr). The exposure time, and the sequence of administration of hyperthermia and FUra were critical determinants of cytotoxicity in this in vitro system and might constitute important variables of treatment when these two agents are used clinically.

Comparative Study of the Effects of Hyperthermia and BCNU on BCNU-Sensitive and BCNU-Resistant 9L Rat Brain Tumor Cells

1,3-Bis(2-chloroethyl)-1-nitrosourea (BCNU)-sensitive and BCNU-resistant 9L rat brain tumor cells were treated with BCNU at graded temperatures between 37 and 44 degrees C. The cytotoxic effects of hyperthermia alone on both cell lines were the same. Treating both cell lines with BCNU at temperatures above 37 degrees C caused a progressive increase in cell kill. All survival curves for drug-sensitive cells had shoulders followed by a region of exponential cell kill; dose enhancement ratios calculated at the 10% survival level ranged from 1.7 to 3.0. Survival curves for drug-resistant cells were exponential without a shoulder; dose enhancement ratios ranged from 3.3 to 8.4. For each cell line, a similar amount of the increased cell kill could be explained on the basis of the increases concentration of reactive species produced by hydrolysis of BCNU at elevated temperatures. The amount of cell kill that cannot be explained on this basis, however, suggests that factors other than an increase in the concentration of reactive species at higher temperatures are involved in the enhanced cell killing. Possible mechanisms include a heat-induced change in the structure of DNA chromatin and the effect of isocyanate deactivation of repair enzymes, both of which could lead to an increase in the number of crosslinks formed and therefore to an increase in cytotoxicity.

Portal vein perfusion of the isolated rat liver: some markers of hyperthermic liver damage.

The cytotoxic effects of hyperthermia on tumours are readily measured. Parameters of injury to normal tissues are needed to evaluate therapeutic potential. Fifty-five isolated rat livers were perfused in vitro for 180 min in order to determine parameters of hyperthermic injury. During this period they were heated for 1 h at temperatures ranging from 37 degrees to 45 degrees and then assessed for evidence of hyperthermic injury. The most critical indicator of hyperthermic injury was sustained depression of bile production. Bile secretion decreased by 80% after heating at temperatures above 42 degrees. Aspartate amino transferase (AST) release increased significantly at temperatures of 42 degrees and above. Potassium and variable amounts of glucose were released into the medium during heating, reflecting temporary changes in metabolism at high temperatures.

Differential Cytotoxic Effects of Hyperthermia below and above 43°C Alone or Combined with X Irradiation

DIKOMEY, E. Differential Cytotoxic Effects of Hyperthermia below and above 430C Alone or Combined with X Irradiation. Radiat. Res. 88, 489-501 (1981). The effect of hyperthermia alone or combined with X irradiation on the proliferative capacity of CHO cells was studied for temperatures between 41 and 460C. For heat treatments in the range 41-430C or 43-460C, the Arrhenius plot yielded an inactivation energy of 417 ? 28 and 167 ? 16 kcal/mole, respectively. Hyperthermia at 42 and 450C, which by itself killed 10% of the cells, was combined with single X-ray doses ranging up to 7 Gy or with fractionated irradiation with two doses of 3 Gy. A mathematical description was developed to determine the effect of hyperthermia on repair of sublethal damage. At 370C sublethal damage was repaired with a half-time of 43.3 min. At 420C, hyperthermia accelerated the fixation of damage and enhanced repair of remaining sublethal damage, reducing the half-time to 19.3 min. In contrast, hyperthermia at 450C did not affect fixation of damage but depressed the rate of repair of sublethal damage, thus increasing the half-time to 83 min.

Effect of hyperthermia on differential cytotoxicity of a hypoxic cell radiosensitizer, Ro-07-0582, on mammalian cells in vitro.

There is now evidence that several classes of nitro compounds which have been used as radiosensitizers also function as cytotoxic agents specific for hypoxic cells. The 2-nitroimidazole, Ro-07-0582, (1-(2-nitroimidazol-1-yl)-3-methoxy-2-propanol) is a compound of this type, and its effectiveness as a cytotoxic agent is dependent on drug concentration, contact time and temperature. In vitro, Ro-07-0582 in air at 37 degrees C does not cause loss of cell viability at concentrations up to 2 mM, even when in contact for several days. In contrast, hypoxic cells do not tolerate much lower concentrations of drugs, even if the contact time is only a few hours. When the temperature is raised above 37 degrees C, there is a pronounced increase in the slope of the survival curves; for example, at 41 degrees C (for 1 mM Ro-07-0582, (200 microng/ml), the slope changes by a factor of 2-0 relative to that for 37 degrees C. For cells in air at 41 degrees C, as at 37 degrees C, there is no toxic effect at the concentration of drug tested. In the absence of drug, there is no cytotoxic effect of hyperthermia alone under these conditions. These results are discussed in terms of Arrhenius parameters.

Cytotoxic effects of hyperthermia and adriamycin on Chinese hamster cells.

Chinese hamster cells, exposed to simultaneous hyperthermia (43 degrees C) and adriamycin (ADM), were intially sensitized to the cytotoxic activity of ADM. If the duration of the combined treatment exceeded about 30 minutes, however, the cells became refractory to additional killing by ADM. If heat was applied before ADM exposure, the cells also could be rendered insensitive; this state persisted so that 24 hours after a 50-minute exposure to 43 degrees C, the cells still showed considerable resistance to ADM. The most reasonable explanation for the findings was that cell membrane permeability to ADM was initially increased by hyperthermia, but prolonged (greater than 30 min) heat exposure reversed this situation and inhibited additional ADM from penetrating to sensitive sites. However, the data yield no hints as to the precise mechanisms involved nor are they sufficiently precise to exclude other explanations. The results do point to precautions that must be observed if the combination of ADM and hyperthermia is to be used clinically.