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Purpose: Several HSP-70 genes have been cloned and sequenced in human cells. Among these genes, the HSP-70A mRNA and protein levels correlate best with the development and decay of thermotolerance and intrinsic thermal sensitivity. Leukemic and nonleukemic human tumor cells express low levels of the normally heat inducible HSP-70A mRNA in control nonheated cells. Using a competitive quantitative polymerase chain reaction, we have measured the levels of mRNA for this gene and have correlated it with both transient and intrinsic thermal sensitivity of tumor cells. Such studies were also extended to tumor samples obtained from patients., Methods and Materials: In these studies, the plasmid phHSP-70 which contains the entire human HSP-70A gene was modified by the insertion of the T7 promoter at the 5'-end untranslated region as well as the insertion of a 23 bp synthetic linker at the BamH1 site in the promoter region of the HSP-70A gene. The PCR primers were located such that the amplified fragment contained the linker. Using the T7 polymerase, the HSP-70A mRNA was transcribed from this plasmid (phHSP-70L) in vitro. A known amount of HSP-70A mRNA was then added to the total RNA prepared from the cell samples or from the tumor tissues obtained from patients. Using the components of the PCR reaction plus known amounts of HSP-70A mRNA synthesized from phHSP-70L and unknown amounts of total cellular RNA, the samples were amplified and analysed on a denaturing acrylamide gel. The PCR products obtained from phHSP-70L were 23 bp larger than the PCR products obtained from the cell samples due to the addition of the synthetic linker to the HSP-70A gene in phHSP-70L and therefore, the two products could be easily distinguished from each other and quantitated. The alpha-32P-dCTP incorporated in each sample was quantitated by AMBIS Scanner. When the 32P-counts were equal in the known and the unknown samples, the amount of the HSP-70A mRNA was taken to be equal in the known and the unknown sample., Results: The results show that HSP-70A mRNA levels can be used to predict the survival levels during the development and decay of thermotolerance. In nonleukemic human tumor cell lines, there are as much as 40-50-fold induction of HSP-70A mRNA levels during the peak of thermotolerance. In leukemic cell lines, however, HSP-70A mRNA levels are induced only by three-fold during the same time period. These differences between the levels of HSP-70A mRNA positively correlate with the amount of tolerance development in leukemic and nonleukemic tumor cells. HSP-70A mRNA levels also vary in different tumor cells under nonheated conditions and there is a positive correlation between HSP-70A mRNA levels in nonleukemic human tumor cells and the level of their intrinsic thermal resistance., Conclusion: HSP-70A mRNA levels can be used to predict the intrinsic thermal sensitivity of nonleukemic human tumor cells.

Leukemic cells appear to develop less thermotolerance and then to lose their thermotolerance more rapidly than do other tumor cell lines. The reason for this phenomenon is not known. After heat shock (or other environmental stresses), mammalian cells preferentially synthesize a set of proteins known as heat shock proteins (HSPs). HSP-28 and the various isoforms of HSP-70 have been suggested as being responsible for the development of thermotolerance. In these studies, we have attempted to determine by their expression with HSPs positively correlate with the development and decay of thermotolerance and whether the expression of these genes could explain the differing thermotolerance response observed between leukemic and nonleukemic tumor cells. Polymerase chain reaction was used to detect the expression of HSP-28 and several HSP-70 genes. Our data indicate that the expression of all three heat-inducible HSP-70 genes, 70A (Hunt and Morimoto, Proc. Natl. Acad. Sci. USA, 82: 6455-6459, 1985), 70B (Voellmy et al., Proc. Natl. Acad. Sci. USA, 82: 4949-4953, 1985), and 70B' (Leung et al., Biochem J., 267: 125-132, 1990) correlate with the development and decay of thermotolerance in nonleukemic tumor cell lines after heat or arsenite treatment. HSP-28 (Hickey et al., Nucleic Acids Res., 4: 4127-4145, 1986) failed to correlate with thermotolerance development; it was not induced after 45 degrees C primary heat shock. In leukemic cells, however, none of the HSPs were induced for extended periods of time. The lack of coordinate expression of HSP genes in cells of myeloid origin may explain the poor induction and maintenance of thermotolerance that is observed in these cells.

The heterogeneity of response to hyperthermia of cells taken from different regions of tumors was tested in a model tumor system (RIF-1) in the mouse and in specimens from spontaneous tumors taken from dogs and humans at the time of surgical resection. Cell survival was assayed by clonogenic survival in the murine tumor and by dansyl lysine staining in tumors from all three species. Using survival as an endpoint, it was found that the extent of heterogeneity depended on the temperature to which the tumor was heated and the duration of exposure. By increasing either of these factors, the coefficient of variation was increased. The large heterogeneity seen after in vivo heating could not be explained entirely by inhomogeneous heating within the tumor as evidenced by temperature mapping. It is concluded that other microenvironmental factors such as blood flow, pH, O2, and nutrient supply may cause variations in the heat response of the tumor cells in vivo. Little, if any, evidence of cellular heterogeneity was evident for all three species when comparisons were made between samples of 100-200 mg. The canine and human tumors were considerably more heat resistant when dansyl lysine was used as an endpoint. In the RIF-1 tumors, heterogeneity of heat response was greater after in vitro heating than after in vivo heating when small biopsy samples (10-20 mg) were taken, suggesting that some cellular heterogeneity was present.

From March 1984 to February 1988, 70 patients with 179 separate treatment fields containing superficially located (less than 3 cm from surface) recurrent or metastatic malignancies were stratified based on tumor size, histology, and prior radiation therapy and enrolled in prospective randomized trials comparing two versus six hyperthermia treatments as an adjunct to standardized courses of radiation therapy. A total of 165 fields completed the combined hyperthermia-radiation therapy protocols and were evaluable for response. No statistically significant differences were observed between the two treatment arms with respect to tumor location; histology; initial tumor volume; patient age and pretreatment performance status; extent of prior radiation therapy, chemotherapy, hormonal therapy, or immunotherapy; or concurrent radiation therapy. The means for all fields of the averaged minimum, maximum, and average measured intratumoral temperatures were 40.2 degrees C, 44.8 degrees C, 42.5 degrees C, respectively, and did not differ significantly between the fields randomized to two or six hyperthermia treatments. The treatment was well tolerated with an acceptable level of complications. At 3 weeks after completion of therapy, complete disappearance of all measurable tumor was noted in 52% of the fields, greater than or equal to 50% tumor reduction was noted in 7% of the fields, less than 50% tumor reduction was noted in 21% of the fields, and continuing regression (monotonic regression to less than 50% of initial volume) was noted in 20% of the fields. No significant differences were noted in tumor responses at 3 weeks for fields randomized to two versus six hyperthermia treatments (p = 0.89). Cox regression analyses were performed to identify pretreatment or treatment parameters that correlated with duration of local control. Tumor histology, concurrent radiation doses, and tumor volume all correlated with duration of local control. The mean of the minimum intratumoral temperatures (less than 41 degrees C vs. greater than or equal to 41 degrees C) was of borderline prognostic significance in the univariate analysis, and added to the power of the best three covariate model. Neither the actual number of hyperthermia treatments administered nor the hyperthermia protocol group (two versus six treatments) correlated with duration of local control. The development of thermotolerance is postulated to be, at least in part, responsible for limiting the effectiveness of multiple closely spaced hyperthermia treatments.

A comparison of heat responses of cells from human and rodent tumors indicates the following: (1) human cells appear to be appreciably more heat-resistant than are rodent cells in the range 41-45 degrees C; (2) while rodent cells show a marked increase in sensitivity as the temperature is increased from 42 and 43 degrees C, this change occurs at approximately 44 degrees C or higher for the human lines examined; (3) rodent cells are unable to acquire thermotolerance during exposure to 43 degrees C; the human cells do so readily; (4) decay of tolerance tends to be complete in 72 h in rodent cells; in human cells it may take twice that time. These results may have important implications for the clinical use of hyperthermia.

The interaction of hyperthermia (41--45 degrees C) and chemotherapeutic agents frequently results in increased cytotoxicity over that predicted for an additive effect, although to date only a very limited number of drugs have been examined for such a possible interaction. At 42 degrees C, the upper limit of temperature useful for whole-body hyperthermia, the most promising agents of those examined to date appear to be the nitrosoureas and cis-platinum. Insufficient data exist for cyclophosphamide, whose long plasma half-life makes it an attractive candidate. Localized heating seems optimum at higher temperatures (43--45 degrees C). At these temperatures, not only those drugs effective at 42 degrees C but particularly bleomycin and possibly amphotericin B become candidates. No data exist in the literature on possible "thermic sensitizers," i.e., drugs which are noncytotoxic at 37 degrees C but which become effective at elevated temperatures. Two special cases are Adriamycin and actinomycin D. These drugs may be contraindicated for clinical use, since not only synergism but also protection by hyperthermia have been demonstrated, depending upon the time-sequence relationships of the heat and drug treatments.

The effects of exposure to ionizing radiations and to various chemotherapeutic agents on the survival of mammalian cells are compared. The relative importance of the cells' sensitivity, age response, proliferative state, and degree of oxygenation and the contributions of kinetic and repair phenomena are examined. Cell killing by high-LET radiations is influenced least by cellular or kinetic factors; thus tumors should show a relatively homogeneous response to this modality, while time-dose relationships should be of least importance. The effectiveness of antimetabolite therapy depends critically on the choice of the correct agents and on tailoring drug administration to the kinetics of both normal and malignant tissue.

The effect of cancer treatment by ultrasound-induced hyperthermia in domestic pets was evaluated by computed tomography (CT) regarding changes in tumor volume and x-ray attenuation after intravenous contrast material. CT scanning is more accurate in measuring tumor volume than estimates after surface measurements. A decrease inn tumor volume and x-ray attenuation after contrast medium seems to be a valuable index of tumor response to hyperthermia.

Induction of hyperthermia by ultrasound is facilitated by the characteristics of sound absorption in tissue: at frequency of 500 kHz the penetration distance in muscle is about 12.5 cm. Energy deposition patterns can be shaped by focussing or by the use of multiple transducers. An initial clinical study has demonstrated the safety and efficacy of the heating technique. Temperatures of 43-45 degrees for 30-45 min were obtained in surface accessible tumors. 50 per cent of the treated tumors regressed either partially or totally. Normal tissue damage was minimal even in sites that had previously been heavily irradiated. A few patients given relatively small doses of X-irradiation in addition to the hyperthermia responded very well. Based upon these encouraging results, a new ultrasound system designed for heating of deep seated lesions has been built and tested.

At temperatures above 37 degrees C, the abilities of many, but not of all, anticancer drugs to kill cells increases substantially. The increased cytotoxic rate can vary smoothly with temperature (e.g., nitrosoureas or cis-platinum(II) diamminedichloride) or show a marked threshold near 43 degrees C (e.g., adriamycin or bleomycin). Clinically, the increased cell killing rate can be used in the combination of localized hyperthermia and systemic chemotherapy. Drugs can also be useful in the study of cell killing by heat. Aliphatic alcohols which mimic and interact with heat, tend to be localized in lipid-rich regions of the cell, i.e., membranes. Heat modifies the rate at which plant lectins agglutinate cells and also modifies capping rates; most likely, these changes reflected membrane alterations. Because other data strongly imply that proteins are involved in cell death, we think that the first step in hyperthermic killing of cells involves damage to specific membrane-associated proteins.

Results obtained in clinical studies in which ultrasound was used for hyperthermia induction are reviewed. High intensity ultrasound has certain advantages for the induction of local hyperthermia: Well-collimated beams can be produced, which makes good localization possible; ultrasound can be focused; and absorption in tissue is proportional to frequency, hence the depth of penetration can be controlled. Limitations include the fact that ultrasound is reflected from tissue-air interfaces and thus cannot be used to heat tumors in the lung. Local "hot spots" due to impedance mismatches that result in standing wave patterns may occur near bone. During clinical treatments, this latter problem is frequently associated with a patient's complaint of pain. The temperature generated depends both on ultrasound absorption coefficients, which vary among different tissues, and dissipation of heat, which varies due to local differences in blood flow rates. Thus inhomogeneities of heating in tissue may be observed despite uniform ultrasound fields. Clinical results with ultrasound-induced hyperthermia have been reported by groups at Stanford, M.D. Anderson Hospital, and Massachusetts Institute of Technology-Harvard. Approximately 40-50% of the superficial tumors showed an objective response to ultrasound hyperthermia in the range of 43 degrees -50 degrees C. Responses to heat alone were partial and transitory. Some radiation responses appeared to be improved by concomitant ultrasound hyperthermia.

The heat response of five human tumor biopsies has been examined using the fluorescent probe dansyl lysine and multiparameter flow cytometry. Dansyl lysine has previously been shown to possess specificity for heat killed mammalian cells. The human tumors tested included a cervical squamous cell carcinoma, malignant melanoma, colon adenocarcinoma, ovarian carcinoma, and a mesothelioma. The samples were excised, mechanically disrupted into single cell suspensions and heated in vitro for various lengths of time at 45 degrees C. The cells were returned to 37 degrees C incubation for 12 to 15 hours prior to staining with dansyl lysine. The fraction of cells staining dansyl lysine was quantitated by flow cytometry after gating on high forward angle light scatter and 90 degrees C light scatter. This gate excluded much of the normal cell contamination within the tumor sample. The data show that the heat response of human tumor biopsies varied significantly, with cervical carcinoma and malignant melanoma being the most resistant and the mesothelioma and ovarian carcinoma the most heat sensitive. Finally, evidence is presented for the expression of thermotolerance in ovarian carcinoma and mesothelioma biopsies pre-heated in vitro. Dansyl lysine appears to be useful in measuring the intrinsic cellular heat sensitivity of human tumors and in determining the kinetics of decay of thermotolerance following an initial heat exposure.