Thermal enhancement of the radiosensitivity using cultured normal and neoplastic cells

Radiation and/or hyperthermia sensitivity of human melanoma cells after several days of incubation in media lacking serum or certain serum components

PURPOSE

Complete serum and single growth factors have been reported to protect cells against the effects of hyperthermia. The phenomenon is not very well understood, especially with regard to the relative importance of the various serum components. There is also a need to clarify the possible involvement of changes in proliferation. The influence of serum and growth factors on radiation sensitivity has not been studied in detail. The present communication is an attempt to at least partly fill these gaps. Cells were exposed to X-rays and/or heat after incubation in sufficiently supplemented medium and media lacking certain serum components. Differences in clonogenic survival were recorded and related to the proliferative status under the various conditions.

METHODS AND MATERIALS

Human melanoma cells (MeWo) were used throughout. Cells were incubated for 3 or 6 days (a) in Ham's F12 medium with 20% fetal calf serum; (b) in medium without serum, but supplemented with the following components: insulin, transferrin, Na-selenite, and a lipid-protein complex; (c) to (f) in media lacking one or the other of these components; (g) in unsupplemented medium. Colony formation ability served as a measure of cell survival after exposure to radiation (250 kV X-rays) and/or hyperthermia (heating at 43 degrees C). In parallel, cell proliferation was characterized by the bromodeoxyuridine (BrdU) labeling index and the Ki-67 growth fraction, both determined by two-parameter flow cytometry.

RESULTS AND CONCLUSIONS

Sensitivity was hardly influenced by 3 days of incubation in medium containing no supplement at all, whereas after 6 days under the same conditions survival curves both of irradiated and hyperthermia-treated cells had a strongly reduced shoulder or were considerably steeper. Experiments with media lacking only one or the other serum component, showed that deprivation of insulin, transferrin, and sodium selenite led to no more than a modest increase in cell killing, whereas the effects in medium lacking lipid-protein complex were about the same as in medium containing no supplement at all. Sensitivity changes did not seem to be due to the lack of serum or certain of its components per se, but were very well correlated with changes in proliferation as characterized by BrdU labeling index or the Ki-67 growth fraction.

Correlation between slowly repairable double-strand breaks and thermal radiosensitization in the human HeLa S3 cell line

The effect of heat on double-strand breaks (dsb) repair was compared with thermal radiosensitization using HeLa S3 cells. Cells were exposed to a combined treatment of X-irradiation followed by heat (44 degrees C, 0.5 h) separated by time intervals up to 8 h. DNA dsb were measured by PFGE and survival by the colony forming assay. In non-heated HeLa S3 cells repair of dsb was biphasic with the majority of breaks being repaired fast with a half-time of 14 min and only a minority were repaired slowly with a half-time of 130 min. Heat applied immediately after irradiation was found to cause an increase in both half-times but mainly to result in an increased fraction of slowly repairable dsb. The latter effect was shown to result from the formation of additional dsb. The number of additional dsb declined when irradiation and heat were separated by an interval at 37 degrees C with a half-time of 120 +/- 30 min. This half-time was similar to the half-time of 100 +/- 20 min found for the loss of thermal radiosensitization studied for the same protocol. Both processes were recently found also to correlate in CHO cells but occurred much faster in rodent cells than in the human HeLa S3 cells used in the current study. These results show that in human cells, unlike previously suggested on the basis of rodent cells, thermal radiosensitization is still a substantial contributor to the killing efficacy of a combined treatment even when irradiation and heat are separated by a time internal of 4 h.

Effect of the combination of hyperthermia and irradiation on human colon cancer cells

The combination of hyperthermia and radiation is considered to have a synergistic effect on mammalian cells, which depends on temperature and duration of time of the hyperthermia and on the sequence in which the modalities are given. The response of cultured colon cancer cells to hyperthermia and ionizing radiation was evaluated using the flow cytometry method by measuring DNA damage. The enhanced DNA damage after combined treatment with hyperthermia and irradiation was recognized after both sequences: heat followed by radiation as well as radiation followed by heat. The results demonstrated that the sequence of radiation plus heat produced more DNA damage on colon cancer cells than did the reverse order. The clinical application of these results is discussed.

Surface morphological study of Ehrlich ascites tumor cells exposed to microwave irradiation and heat

Microwave irradiation of EAT cells caused an increase in length and number of surface microvilli. The tumor cells tend to form large aggregates by means of extensive interdigitation of surface microvilli. On the other hand, heat hyperthermia caused a decrease of surface microvilli but an increase of surface blebs. Hence the surface morphology of EAT cells after in vitro exposure to microwave irradiation differs markedly from that after heat hyperthermia.

Effect of hyperthermia on hypoxic cell fraction in tumor

The effect of hyperthermia on the proportion of hypoxic cells in SCK mammary tumor of A/J mice was investigated. About 45% of clonogenic cells in the unheated control tumor were radiobiologically hypoxic. Upon heating with a 43.5 degree C water bath for 30 min, the proportion of hypoxic cells increased and then decreased: it was 95% at 5 hr and 60% at 12 and 24 hr after heating. Despite the increase in the proportion of hypoxic cells 5 hr after heating, the absolute number of hypoxic cells in the tumors at this time was significantly smaller than that in the unheated control tumors because of a decrease in the total number of surviving tumor cells. The initial increase in the proportion of hypoxic cells after heating may be attributed mainly to vascular occlusion. Proliferation of cells in the oxic area, and thus an increase in oxic cell number, appears to account for the decline in the proportion of hypoxic cells from 5 hr after heating.

The response of six mouse tumours to combined heat and X rays: implications for therapy

The response of six types of mouse tumour to single doses of X rays alone or to X rays in combination with moderate hyperthermia (42.5 degrees C/60 min) has been assessed using delay in tumour regrowth. Thermal sensitization was observed in five of the six tumours. The degree of sensitization varied with the size of the X-ray dose, being larger at higher doses. The degree of sensitization also depended on the sequence and separation of the heat and irradiation. The thermal sensitization has been measured in terms of the X-ray doses to produce the same level of tumour damage with or without heat, i.e. thermal enhancement ratios. These TER values, measured for X-ray doses in excess of 20 Gy, are not greater in any of the tumours than in a range of normal tissues, if the X rays and heat are given in close succession. Separation of the heat and X rays reduces the TER values slightly, but some effect is still apparent at 3--24 hours. In normal tissues the effect of heat is totally lost within four hours. Comparison of these tumour data with published normal tissue data indicates a therapeutic advantage if the heat and X rays are separated by more than one hour. This therapeutic gain is most reliably achieved and heat given after irradiation.

Combination hyperthermia and radiation therapy for cutaneous malignant melanoma

The clinical studies were carried out to evaluate whether radiation combined with hyperthermia would evoke better local tumor control than that achieved with radiation alone. Using an inductive method of radiofrequency heating at 27.12 MHz and radiation therapy, 37 lesions in 14 patients were treated with heat alone, radiation alone and heat in combination with radiation. In patients who completed the planned course of the combined therapy with an adequate follow-up period of more than six months, 16 out of 18 lesions (in 9 patients) had a complete response, whereas only 1 out of 8 lesions (in 5 patients) had a permanent regression after radiation alone. The amount of radiation dose necessary to achieve a satisfactory tumor control in combination with radiofrequency heating has been 3000 rad (300 rad X 10 in 4 weeks) to 3200 rad (400 rad X 8 in 4 weeks). Importance of the temperature measurements of both tumor and the adjacent normal tissue is discussed.

Combined treatment of a solid tumour by local hyperthermia and actionomycin D

(BALB/c X C57BL/6)F1 mice bearing an SV-40 fibrosarcoma in the limb were injected with 0.045, 0.09 and 0.18 microgram/g body wt actinomycin D into the tumour. Similar animals were also treated with local hyperthermia (39.7 degrees, 42.3 degrees and 43.6 degrees C intratumour temperature for 30 min). The marked increase in median survival time following the combination of drug and local hyperthermia indicates that the combined treatment has a synergistic effect in the control of solid tumours. The median survival time of animals receiving the two treatments in immediate succession was higher than in animals with 30 min between treatments. This has important implications for the therapy of human cancer.

Hyperthermia and host-cell reactivation of adenovirus 12

Exposure of cultured human fibroblasts to hyperthermia delayed the host-cell reactivation of UV-irradiated human adenovirus type 12 (AD12). The experimental design consisted of irradiating human AD12 with UV doses ranging from 180 to 1800 ergs/mm2, infecting human cell populations at 37 degrees C, exposing the infected cells for 7 h to 39.5 degrees C and 41.8 degrees C, returning them to 37 degrees C and estimating the frequency of cells with intranuclear viral inclusion bodies (IB) 41 and 89 h after hyperthermia treatment. Hyperthermia reduced the fractions of fibroblasts with viral IB in the 41 h samples. By 89 h the capacity to form IB in the treated cells was comparable to that in control cells. Hyperthermia of 39.5 and 41.8 degrees C for 7 h did not affect the replication of nonirradiated AD12. The pattern of host-cell reactivation of AD12 following hyperthermia was compared to that in DNA repair deficient xeroderma pigmentosum cell populations.

Hyperthermia and cancer

The effects of heat and its possible significance in cance therapy have been documented for more than a century. Hyperthermia has been widely investigated as an alternative or adjuvant to conventional therapies such as surgery, radiation, and chemotherapy. The clinical reports are interesting, notwithstanding some harmful side effects and other complications which, however, may be attributable to an advanced stage of the disease at the time of treatment. In view of the extreme difficulty in matching suitable controls for cancer patients undertaking such therapy, it is essential to extend knowledge of the effects of hyperthermia on normal and neoplastic tissue by experimental studies. Further, the different methods of utilizing heat therapy have need for substantial technological improvements. To stimulate interest in this area, we have gathered together in this review some of the more pertinent reports on the application of hyperthermia to neoplastic and normal tissues as observed clinically and in the laboratory.

Local tumor hyperthermia in combination with radiation therapy. 1. Malignant cutaneous lesions

There is increasing evidence that the use of hyperthermia alone or in conjunction with other modalities may improve the therapeutic effectiveness of treatment of cancer. The present clinical studies were carried out to evaluate the response of normal and tumor tissues in patients with various cutaneous malignant lesions to repeated courses of hyperthermia alone or in conjunction with radiation therapy. Thirty-six patients with malignant cutaneous lesions (mycosis fungoides, Kaposi sarcoma, malignant melanoma, lymphoma cutis, and other metastatic skin lesions) have been studied. The heating methods used were: 1) temperature regulated water bath immersion; and 2) radiofrequency inductive heating. The normal tissue effects of the combined treatments of radiation and hyperthermia do not appear to be greater than those treated with radiation alone. The initial tumor regression rates were faster in patients treated with radiation plus hyperthermia than in radiation alone, particularly in patients with Kaposi sarcoma and lymphoma cutis. Among ten locally recurrent patients, seven showed significant prolonged benefits achieved by the combined treatments as compared with the radiation therapy alone. Fractionated hyperthermia alone caused significant tumor regression in four out of five patients. Possible mechanisms leading to the improved results from the combined treatments are discussed.

Local tumor hyperthermia in combination with radiation therapy. 1. Malignant cutaneous lesions

There is increasing evidence that the use of hyperthermia alone or in conjunction with other modalities may improve the therapeutic effectiveness of treatment of cancer. The present clinical studies were carried out to evaluate the response of normal and tumor tissues in patients with various cutaneous malignant lesions to repeated courses of hyperthermia alone or in conjunction with radiation therapy. Thirty-six patients with malignant cutaneous lesions (mycosis fungoides, Kaposi sarcoma, malignant melanoma, lymphoma cutis, and other metastatic skin lesions) have been studied. The heating methods used were: 1) temperature regulated water bath immersion; and 2) radiofrequency inductive heating. The normal tissue effects of the combined treatments of radiation and hyperthermia do not appear to be greater than those treated with radiation alone. The initial tumor regression rates were faster in patients treated with radiation plus hyperthermia than in radiation alone, particularly in patients with Kaposi sarcoma and lymphoma cutis. Among ten locally recurrent patients, seven showed significant prolonged benefits achieved by the combined treatments as compared with the radiation therapy alone. Fractionated hyperthermia alone caused significant tumor regression in four out of five patients. Possible mechanisms leading to the improved results from the combined treatments are discussed.

Effect of hyperthermia on malignant cells in vivo. A review and a hypothesis

The relevant literature is reviewed in an attempt to clarify the mechanism of heat-dependent tumor cell destruction in vivo. Malignant cells in vivo appear to be selectively destroyed by hyperthermia in the range of 41-43 degrees C. Heat evidently affects nuclear function, expressed by an inhibited RNA, DNA and protein synthesis and characteristic arrest or delay of cells in certain locations of the cell cycle. However, as these effects appear to be reversible and are observed in normal cells as well as malignant cells, they probably do not explain the hyperthermic induced selective in vivo destruction of malignant cells. Heat-induced cytoplasmic damage appears to be of more importance. Increased lysosomal activation is observed, and is further intensified by a relatively increased anaerobic glycolysis which develops selectively in tumor cells. A hypothesis is proposed and discussed which explains the marked and selective in vivo tumor cell destruction as a consequence of the enhancing effect on the cytoplasmic damage of certain environmental factors (e.g. increased acidity, hypoxia and insufficient nutrition.

Hyperthermic tumour-cell devitalization in vivo

A review of the morphologic, biochemical and clinical effects of hyperthermia on malignant cells indicates the presence of two principally different heat-induced alterations. (1) A 'destructive' lysosomal dependent cytoplasmic reaction dominates the tumour-cell devitalization in vivo, probably influenced by the characteristic tumour cell environment. (2) 'Repressive' nuclear abnormalities may be observed, but seem to be secondary in the in vivo reaction. However, under certain conditions (combined treatment modalities) this nuclear effect may be of importance.

The relationship between the time of fractionated and single doses of radiation and hyperthermia on the sensitization of an in vivo mouse tumor

The present study was undertaken to explore the relationship of the time interval between application of heat and irradiation on enhanced tumor cell sensitivity. Using the Ridgway osteogenic sarcoma grown in AKD2F1/J mice, local tumor hyperthermia (42.5 +/- .5 degrees C for 15 minutes) was applied at various time intervals before or after single or fractionated doses of x irradiation. Enhancement of tumor cell sensitivity by combined treatment with radiation and heat, as measured by delay in tumor growth, cure rates, and mean survival times was inversely proportional to the time interval between application of both modalities. The interactions associated with this increased sensitivity appear to be transitory, diminishing with time between treatments. Possible mechanisms of action for thermal sensitization may involve the reduction of oxygen dependence as well as a reduced recovery capacity of tumor cells.