Effect of hyperthermia on AKR lymphoma variants differing in degree of malignancy.

The effect of hyperthermic treatment on AKR lymphoma cells of varying malignancy was investigated. Tumor cells were pretreated at 37 or 43 degrees C and then injected to mice. The effect on the highly malignant variant, TAU-38, was compared to that on the low-malignancy variant, TAU-39, following both subcutaneous (s.c.) and intravenous (i.v.) inoculation. Hyperthermia showed no effect on the TAU-39 variant following s.c. inoculation on the primary tumors or mice survival, but the TAU-38 variant exhibited a significant delay of tumor appearance following treatment, namely, decreased tumor size and increased life span. Following i.v. inoculation, in both variants, hyperthermia caused a significant decrease in metastatic spread and an increased life span. We conclude that hyperthermia, in addition to exerting a greater effect on the high-malignancy variant, acts at the late phases of metastasis. Hyperthermia might therefore have a place in the management of cancer in its advanced disseminated phase.

Augmentative effects of intracellular chemotherapy penetration combined with hyperthermia in human ovarian cancer cells lines.

A significant proportion of ovarian cancer patients do not achieve a complete response to chemotherapy, due mainly to the evolution of clones resistant to cytotoxic drugs. Exploring possibilities to overcome this resistance constitutes a challenge in the study of ovarian cancer experimental therapy. In the present study, we tested the effect of hyperthermia (40 and 43 degrees C) in combination with adriamycin on three human epithelial ovarian cell lines: OC-109, OC-238, and OC-7-NU. The first was derived from the mucinous and the other two from serous cystadenocarcinomas, and all proved to be tumorigenic in nude mice. FACS analysis showed a pronounced increase in intracellular adriamycin accumulation in the presence of hyperthermia. A significant effect (P < 0.0005) observed at 40 degrees C was even more pronounced at 43 degrees C with the three cell lines. High percentages of cells (up to 70%) shifted into higher fluorescence intensities. The lines differed in their sensitivity to the hyperthermia-induced increase in adriamycin accumulation. Under mild conditions, the OC-109 line was more sensitive than the OC-238 and the OC-7-NU lines. Quantitative determination of intraneoplastic adriamycin by spectrofluorometry also showed a hyperthermia-related increase in intracellular adriamycin (P < 0.005). Our results may indicate that supranormal temperature might serve as an alternative chemosensitizer which lacks the deleterious side effects of other chemosensitizing options.

Differential sensitivity to hyperthermia of the F1 and F10 B16 melanoma variants.

The currently available antitumoral therapeutic modalities are most often inefficient against metastatic disease. The metastatic phenotype has been shown to be largely determined by cell membrane properties. The cell membrane could therefore be considered as a possible target for antimetastatic drugs. In the present study we examined the effect of hyperthermia (the antitumoral effect of which is based, at least partly, on an action on the cell membrane) on the F1 and F10 variants of B16 melanoma. Cells of the more malignant variant, F10, were found to be markedly more sensitive to hyperthermic treatment than those of the less malignant one, F1. One hour in-vitro treatment by supranormal temperatures (ranging from 40 to 46 degrees C) resulted in a differential effect with regard to both proliferating capacity of the cells in vitro and tumorigenic ability following inoculation to mice. Our present results in the B16 melanoma corroborate data obtained by us in another tumour system, the AKR lymphoma. Study of the effect of membrane-acting agents on tumour variants differing in degree of malignancy might result in the finding of antitumoral agents efficient against advanced cancer.

Effect of hyperthermia and thermochemotherapy on primary and metastatic tumour cells of AKR lymphoma.

The cure of metastatic disease constitutes a serious problem. Recent findings showed cell membrane differences between slightly and highly metastasizing tumour cells, suggesting that since this cell organelle determines the metastatic phenotype, it might serve as a target for future drugs programmed against advanced cancer. The cell membrane has also been shown to be involved in the evolution of drug resistance which often accompanies tumour progression. In the present study, the effect of hyperthermia--an antitumoral treatment modality partly exerting its effect on the cell membrane--on primary and metastatic AKR lymphoma cells was compared. The effect of hyperthermia in conjunction with adriamycin (ADR) on the two cell types was also tested. Hyperthermic treatment, alone and in combination with ADR, was more effective in reducing the tumorigenicity of cells derived from metastatic tumours than of the primary tumour cells. Fluorescent microscopy and cytofluorometry showed that the increased effect of ADR by hyperthermia was due to an increased drug uptake at the supranormal temperature.

Combined effect in vitro of chemotherapy with agents acting on the cell membrane of Lewis lung carcinoma.

The treatment of cancer is often impeded by the emergence of drug-resistant clones. Drug resistance is in many cases due to a decreased drug accumulation in the tumor cell. Membrane-acting agents, by increasing cell permeability, might counteract the loss of sensitivity to drugs. In the present study, the effect of two membrane-acting agents, hyperthermia and the calcium channel blocker verapamil, on the action of adriamycin (ADR) on Lewis lung carcinoma (3LL) was examined. Hyperthermia increased drastically the antitumoral effect of ADR. The effectiveness of the combined ADR-hyperthermia treatment was proportional to the ADR dose and to the degree of hyperthermia. Verapamil had a similar effect but at higher ADR doses. Treatment modalities designed for the circumvention of drug resistance could be one approach in the attempt to find a way to control cancer.

Sensitivity to thermochemotherapy of AKR lymphoma and B16 melanoma variants of malignancy.

Drug resistance, which so often accompanies tumor progression, has been shown to be related to changes in membrane properties which may result in decreased drug accumulation in the tumor cell. A correlation between sensitivity to thermochemotherapy and degree of malignancy was found in the AKR lymphoma system. Hyperthermia increased adriamycin (ADR) uptake and concomitantly its cytotoxicity to AKR lymphoma cells. Moreover, these effects were more pronounced on a variant of high malignancy (HM) than on a low malignancy (LM) one. Fluorescent microscopy, as well as cytofluorometry, indicated that lymphoma cells treated by ADR at 43 degrees C were more permeable to the cytotoxic agent than those exposed to the chemotherapeutic substance at 37 degrees C. Cytofluorometry indicated the presence of a minor cell subpopulation with low ADR uptake in the HM variant, not found in the LM one. Fluorocytometry also showed that the temperature-dependent increased ADR uptake was more marked in the HM than in the LM variant, explaining the differential effect of thermochemotherapy on the two lymphoma variants. However, correlation between degree of malignancy and sensitivity to thermochemotherapy is not a general feature. In contrast to the results obtained in the AKR lymphoma system, in the B16 melanoma the low malignancy variant, F1, was more markedly affected by the combined treatment than the F10 variant. The increased cytotoxic effect of ADR by supranormal temperatures in the F1 variant was shown to be due to an augmented drug uptake. The results suggest that drug resistance in late stages of tumor progression can be overcome by an agent acting on the cell membrane. However, the data also indicate the necessity of assaying cancer treatment modalities, including those designed to circumvent drug resistance, on various tumor system models.

A model for cancer treatment in advanced compared to early cancer.

Loss of sensitivity to drugs following tumor progression constitutes the main reason for failure of treatment in advanced cancer. In view of the dynamic nature of neoplasms, models of tumor progression should be used for the testing of drugs. In the present study, two variants of malignancy of AKR lymphoma were used as a model of tumor progression to test various treatment modalities. The two variants, TAU-39 (of low-malignancy) and TAU-38 (of high-malignancy) differed in the pattern of local tumor growth as well as in the rate of metastatic spread and mice killing capacity. The efficiency of chemotherapy, immunotherapy and hyperthermia on the two variants was compared. The low-malignancy tumor was more sensitive to adriamycin than the high-malignancy one. Administration of levan-activated macrophages at the tumor site inhibited the growth of TAU-39. However, growth of the high-malignancy variant was stimulated by macrophages. Hyperthermic treatment was, in contrast to the other treatments, more effective against the high - than against the low-malignancy tumor. Models of tumor progression used in tests for antitumoral drugs may help in the discovery of treatment modalities effective also for advanced stages of cancer.

Direct antitumor effect of the polysaccharide levan in mice: effects of drug concentration and time and temperature of incubation.

In vitro treatment of Lewis lung carcinoma cells with the polysaccharide levan was shown previously to reduce the oncogenicity of these cells by acting on the cell membrane. In the present study the direct effect of levan on the tumorigenicity of Lewis lung carcinoma in C57BL male mice was tested at different doses and intervals and temperatures of incubation. A dose-dependent decrease in tumorigenicity was observed: Doses of 0.5, 1, and 2 mg levan/2 X 10(5) cells/0.2 ml reduced tumor incidence by 30, 50, and 70%, respectively. Some degree of inhibition was observed even with a dose of 0.004 mg. The inhibitory effect was rapid; 5 minutes of incubation resulted in the same reduction in oncogenicity as 60 minutes. Inhibition at 0 degree C was as effective as inhibition at 37 degrees C. The lack of temperature effect indicates that enzymatic activity probably is not involved. The data presented here, together with previous data, suggest that levan induces a physical, rather than a chemical, change in the affected tumor cells. The polysaccharide appears to be loosely, noncovalently bound to the cell membrane.

Serial passage of tumors in mice in the study of tumor progression and testing of antineoplastic drugs.

AKR lymphoma cells derived from spontaneous tumors were serially transplanted at identical inocula. The degree of malignancy and sensitivity to the polysaccharide levan and methotrexate were tested at each transfer by assessing the lag of development of primary and distant tumors and survival of mice. A progressive increase in malignancy, accompanied by a loss of sensitivity to levan, were observed following serial passage of the lymphoma. Sensitivity to methotrexate was not affected. It is reasoned that, since serial passages permit a longer exposure of the tumor cells to selective forces of the internal milieu of the organism, better reflecting the situation in a long-life span animal, spontaneous and serial-passage tumors could serve as models for cancer therapy in humans.