Microangiographic and histologic analysis of the effects of hyperthermia on murine tumor vasculature

External Basic Hyperthermia Devices for Preclinical Studies in Small Animals

Simple Summary

The application of mild hyperthermia can be beneficial for solid tumor treatment by induction of sublethal effects on a tissue- and cellular level. When designing a hyperthermia experiment, several factors should be taken into consideration. In this review, multiple elementary hyperthermia devices are described in detail to aid standardization of treatment design.

Abstract

Preclinical studies have shown that application of mild hyperthermia (40–43 °C) is a promising adjuvant to solid tumor treatment. To improve preclinical testing, enhance reproducibility, and allow comparison of the obtained results, it is crucial to have standardization of the available methods. Reproducibility of methods in and between research groups on the same techniques is crucial to have a better prediction of the clinical outcome and to improve new treatment strategies (for instance with heat-sensitive nanoparticles). Here we provide a preclinically oriented review on the use and applicability of basic hyperthermia systems available for solid tumor thermal treatment in small animals. The complexity of these techniques ranges from a simple, low-cost water bath approach, irradiation with light or lasers, to advanced ultrasound and capacitive heating devices.

Development and evaluation of an isolated limb infusion model for investigation of drug delivery kinetics to solid tumors by thermosensitive liposomes and hyperthermia

The combined administration of thermosensitive liposomes (TSLs) and hyperthermia (HT) has been increasingly shown to be a powerful tool for the treatment of solid tumors. At present, it is hypothesized that the circulation of TSLs through the vasculature of a heated tumor results in the rapid release of the entrapped drug, followed by its uptake and distribution within the tumor microenvironment. However, simple questions on the transport kinetics of TSLs through the heated tumor and how much drug is retained upon passage of TSLs through the tumor microcirculation have not been investigated in an experimental setting to-date. The present work describes a novel methodology for investigating these parameters by isolated limb infusion (ILI), developed in a rat model of sarcoma. This approach was used to assess the efficacy of Doxorubicin (Dox) delivery by TSL in a heated (42°C) tumor following a single passage of TSL through the tumor vasculature. Analysis of the effluent post-ILI, whole-tumor histological sections, and tissue homogenates revealed that upon a single passage, Dox delivery by TSL at 42°C did not exceed delivery under conventional (i.e. free Dox) or physiological (i.e. TSL at 37°C, or normothermia; NT) conditions. In fact, mathematical modeling demonstrated that at least thirteen passages are required to obtain the intratumoral Dox levels typically achieved using TSL (i.e. ~5%ID/g). Overall, this work investigates TSL-based determinants for achieving efficacious drug delivery using a model of ILI in tumor-bearing rats and the results bear important implications for TSL disposition in vivo.

Thermosensitive liposomal cisplatin in combination with local hyperthermia results in tumor growth delay and changes in tumor microenvironment in xenograft models of lung carcinoma

Treatment efficacy of a heat-activated thermosensitive liposome formulation of cisplatin (CDDP), known as HTLC, was determined in xenograft models of non-small-cell lung carcinoma. The short-term impact of local hyperthermia (HT) on tumor morphology, microvessel density and local inflammatory response was also evaluated. The HTLC formulation in combination with local HT resulted in a significant advantage in therapeutic effect in comparison with free drug and a non-thermosensitive liposome formulation of CDDP (i.e. Lipoplatin^TM) when administered at their maximum tolerated doses. Local HT-induced widespread cell necrosis and a significant reduction in microvessel density in the necrotic regions of tumors. CD11b-expressing innate leukocytes were demonstrated to infiltrate and reside preferentially at the necrotic rim of tumors, likely as a means to phagocytose-damaged tissue. Colocalization of CD11b with a marker of DNA damage (i.e. γH2AX) revealed a small portion of CD11b-expressing leukocytes that were possibly undergoing apoptosis as a result of HT-induced damage and/or the short lifespan of leukocytes. Overall, HT-induced tissue damage (i.e. at 24-h post-treatment) alone did not result in significant improvements in treatment effect, rather, the enhancement in tumor drug availability was correlated with improved therapeutic outcomes.

Lanthanum strontium manganese oxide (LSMO) nanoparticles: a versatile platform for anticancer therapy

Multiple uses of LSMO nanoparticles in anticancer therapy.

Enhanced tumour uptake of radiolabelled antibodies by hyperthermia. Part II: Application of the thermal equivalency equation

Clinical application of local hyperthermia as a means for modulating drug and macro-molecular tumour uptake have been slow to develop, due in part to the difficulty in designing and comparing heating protocols. The thermal isodose formula developed by Sapareto and Dewey is used in cytotoxicity and radiosensitization hyperthermia protocols to compare different time/temperature combinations; however, its relevance to other end-points has not been evaluated. The current study was undertaken to determine whether heating protocols of different time and temperature, but predicted to be thermally equivalent by this formula, had similar effects on the tumour and normal tissue distribution of radiolabelled tumour-specific (anti-tenascin 81C6) and non-specific (anti-dansyl TPS3.2) monoclonal antibodies (mAbs). Two thermally equivalent heating protocols, 4 h at 41.8 degrees C and 45 min at 43 degrees C, were compared in mice with subcutaneous D54 MG human glioma xenografts. A 4-fold increase in xenograft localization of 81C6 mAb was achieved relative to that in non-heated control groups with both heating protocols. Both hyperthermia protocols also resulted in improved tumour:normal tissue ratios. However, differences in absolute tumour and normal tissue uptake were seen, suggesting that the thermal isodose formula has limited usefulness in the design and comparison of hyperthermia protocols for enhancing the tumour uptake of radiolabelled mAbs.

Local Application of Hyperthermia in the Esophagus with a Heatable Malleable Thermoplastic Stent

OBJECTIVE

This study measures the effect of hyperthermia applied through a heatable stent in the esophagus in order to investigate whether this procedure offers a therapeutic option for tumor treatment.

MATERIAL AND METHODS

Thermoplastic malleable stents, with the capacity to be heated after implantation, were placed endoscopically in the middle third of the esophagi of 30 pigs. After placement the stents were heated in vivo for 60 min at temperatures ranging from 43 to 52 degrees C. Temperature was measured in the surrounding tissue at various distances from the stent, determining heat penetration. The esophagi were histologically examined after 7 days.

RESULTS

The maximal heating temperature tolerated in the esophagi without transmural necrosis was 46.5 degrees C, when applied twice for 60 min with a pause of 48 h. With this procedure a tumor damaging temperature of 42.5 degrees C was achieved at a maximum distance of 12 mm surrounding the stent.

CONCLUSION

Application of hyperthermia through a heatable stent in the esophagus is feasible. The maximal depth of therapeutic temperature achieved by this procedure (12 mm) is not sufficient to heal esophageal cancer, but may be of palliative value.

Histopathological observations of the antivascular effects of physiotherapy ultrasound on a murine neoplasm

This study evaluates the histopathological changes that follow insonation of a neoplasm with physiotherapy ultrasound. In 27 mice (C3HV/HeN strain), a subcutaneous melanoma (K1735(22)) was insonated with continuous physiotherapy ultrasound (1 MHz; spatial-average-temporal-average = 2.3 W cm(-2)). Analyses of contrast enhanced (0.1 mL Optison) power Doppler observations showed that insonation significantly (p < 0.05) increased the avascular area in the neoplasm. The predominant acute effect of insonating the neoplasm was an apparently irreparable dilation of the tumor capillaries with associated intercellular oedema; other immediate effects were haemorrage and increased intercellular fluid. Liquefactive necrosis of neoplastic cells was a delayed effect. There was a high correlation (R2 = 0.91) between the percent area affected on histologic examination and the percent increase in avascularity of the neoplasm in the Doppler study. In conclusion, physiotherapy ultrasound produced histologic changes in the tumor vasculature that were consistent with observations made by contrast enhanced power Doppler ultrasound.

The antivascular action of physiotherapy ultrasound on murine tumors

This study was aimed at determining if physiotherapy ultrasound (US) affected the fragile and leaky angiogenic blood vessels in a tumor. In 22 C3HV/HeN mice, a subcutaneous melanoma (K1735(22)) was insonated (1, 2 or 3 min) with continuous 1-MHz low-intensity (spatial-average temporal-average = 2.28 W cm(-2)), physiotherapy US. Contrast-enhanced (0.1 mL Optison) power Doppler US observations were made and histogram analyses of the images were performed. Before insonation, all but 7% of the tumor was perfused. The avascular area in tumors receiving 3-min treatment increased to 82% (p < 0.001). A linear regression analysis showed that each min of insonation led to a 25% reduction in tumor vascularity; the antivascular activity persisted for 24 h. Histology demonstrated disruption of vascular walls and tumor cell death in areas of vascular congestion and thrombosis. Physiotherapy US particularly targeted the vascular structures, and the effects on tumor cells appeared to be secondary to the resultant ischemia.

The impact of surgery and mild hyperthermia on tumor response and angioneogenesis of malignant melanoma in a rat perfusion model

Background

The aim of this experimental study was to determine the effect of mild hyperthermia on tumor response and angioneogenesis in an isolated limb perfusion model with a human melanoma xenograft.

Methods

A human melanoma xenograft was implanted into the hindlimbs of 30 athymic nude rats. The animals were randomized into five groups: group I: control, group II: sham group, group III: external hyperthermia with a tissue temperature of 41.5°C for 30 minutes without ILP, group IV: normothermic ILP (tissue temperature 37°C for 30 minutes, group V: hyperthermic ILP (tissue temperature 41.5°C for 30 minutes). Tumor response was evaluated by tumor size determination and immunohistochemical analysis 6 weeks postoperatively. Tissue sections were investigated for expression of CD34 and basic fibroblast growth factor (bFGF).

Results

Average tumor volumes of the controls (I) increased from 105 mm³ to 1388 mm³. In the sham operated group (II) tumor volumes were significantly larger than in group I. Tumor volumes in group IV were significantly smaller than in group I and lowest in group V. There were no significant differences in size between group I and group III after six weeks. In group III and IV each, 5 animals showed tumor progression and one had a partial tumor response. In group V only 2 animals showed tumor progression. Immunhistochemical analysis of the tissue sections demonstrated that angioneogenesis was more pronounced in group II than in group I and less pronounced in group IV and V compared with group I.

Conclusions

Our results suggest that even a surgical manipulation such as a skin incision promotes tumor growth, probably by induction of growth factors like bFGF.

External hyperthermia of 41.5°C tissue temperature for 30 minutes only has no impact on tumor growth and angioneogenesis in vivo.

Induction of vascular endothelial growth factor (VEGF) by hyperthermia and/or an angiogenesis inhibitor

Intratumoral localization of vascular endothelial growth factor (VEGF) following administration of hyperthermia (HT) and/or anti-angiogenic drugs (TNP-470) was evaluated using SCC VII tumours in C3H/He mice. Hyperthermia at 44.0 degrees C for 30 min was given with a water bath on day 0. TNP-470 (100 mg/kg) was administered alone or after HT on day 0 and day 3. Histological changes on day 4 were evaluated by haematoxylin-eosin (HE) staining and immunohistochemical staining for VEGF. The percentage of the necrotic area relative to the entire tumour area (the % necrotic area) was measured on HE stains. The average % necrotic area of the untreated SCC VII tumours was 7%, while those of tumours treated with TNP-470 alone and HT alone were 27 or 65%, respectively. When HT and TNP-470 were combined, the % necrotic area was 82%, which was significantly higher than that caused by HT alone (p < 0.05). Immunohistochemical staining for VEGF in untreated SCC VII tumours was weak, although strong staining for VEGF was noted in untreated EMT-6 tumours of BALB/c mice, which have spontaneous central necrosis. After administration of HT and/or TNP-470, layer-shaped staining by VEGF was observed in the residual SCC VII tumour cells adjacent to the necrotic area. In conclusion, the expression of VEGF increased in response to administration of HT and/or TNP-470. Hypoxia caused by heat-induced vascular damage may be attributable to increased expression of VEGF in SCC VII tumours.

Vascular endothelial growth factor-induced tumor angiogenesis and tumorigenicity in relation to metastasis in a HT1080 human fibrosarcoma cell model

Although vascular endothelial growth factor (VEGF) is well known to be a potent mitogen for vascular endothelial cells, the role of VEGF in a developmental process of tumor angiogenesis and metastatic potential remains poorly understood. The present study was designed to investigate VEGF-induced vascular formation from a spatiotemporal viewpoint and to analyze VEGF-enhanced metastatic potential using stable clones of HT1080 human fibrosarcoma cells transfected with VEGF cDNA (S) or with vector alone (V). Microangiography revealed massive angiogenesis in the S cell-derived tumors and demonstrated that the angiogenesis occurred not in the tumor itself, but rather around the S cell tumor early after inoculation into the thigh muscles of mice. Thereafter, the angiogenesis extended in and around the tumor. The tumorigenicity of the S cells was higher than the V cells in the subcutaneous (s.c.) space, intraperitoneal space, liver and spleen. However, neither S cells nor V cells metastasized to the liver after an intrasplenic injection. Few apoptotic cells were detected in the S cell tumor, but many apoptotic cells were scattered in the V cell tumor. Our results indicate that VEGF facilitates tumorigenicity in various organs, possibly due to inducing angiogenesis in and around the tumor and preventing tumor cells from undergoing apoptosis, and suggest that VEGF may augment metastatic potential, by accelerating proliferative activity after reaching the target organ. Furthermore, VEGF-induced angiogenesis occurred preferentially around the tumor at an early period of tumor development, followed by neovascularization into the tumor.

Efficacy of CDDP and AGM-1470 chemotherapy against lung metastasis in rat osteosarcoma depends on the timing of combined administration

The efficacy of combination therapy with cis-diammine-dichloroplatinum (II) (CDDP) and o-(chloroacetyl-carbamoyl) fumagillol (AGM-1470) was evaluated experimentally using a transplantable rat osteosarcoma line, previously established in our laboratory, with a high potential for metastasis. Tumor-bearing male Fischer 344 rats were administered CDDP (2.5 mg/kg) together with, or after discontinuation of, AGM-1470 treatment (10 mg/kg/body weight/week). When CDDP was administered three days after discontinuation of AGM-1470 the most pronounced antimetastatic effects were observed, although the antitumor effect was approximately the same.

Alteration in the hypoxic fraction of quiescent cell populations by hyperthermia at mild temperatures

We investigated oxygenation of quiescent (Q) tumour cells in vivo by mild heat treatment. C3H/He mice bearing SCC VII tumours received BrdU continuously for 5 days via implanted mini-osmotic pumps, to label all proliferating (P) cells. The tumours were then irradiated after treatment, and were excised, minced and trypsinized. The tumour cell suspension thus obtained were incubated with cytochalasin-B (a cytokinesis blocker), and the micronucleus (MN) frequency in cells without BrdU labelling was determined using immunofluorescence staining for BrdU. This MN frequency was then used to calculate the surviving fraction of unlabelled cells from the regression line for the relationship between the MN frequency and the surviving fraction of total (P + Q) tumour cells. Thus, a cell survival curve could be determined for the cells not labelled with BrdU, which can be regarded as the Q cells in a tumour for all practical purposes. The MN frequency in total tumour cell population was determined from the irradiated tumours that were not pretreated with BrdU. Assays performed immediately after irradiation of both normally aerated and hypoxic tumours showed that Q cells contained higher hypoxic fractions than the total tumour cell population. Mild heat treatment (40.0 degrees C, 60 min) before irradiation decreased the hypoxic fraction, even when is was combined with nicotinamide administration. In contrast, mild heating did not decrease the hypoxic fraction when the mice were placed in a circulating carbogen (95% O2/5% CO2) chamber. Therefore, mild heat treatment was thought to preferentially oxygenate the chronically hypoxic fraction.

Induction thermochemotherapy increases therapeutic gain factor for the fractionated radiotherapy given to a mouse fibrosarcoma

PURPOSE

It has been shown that thermochemotherapy (TC) given prior to radiation reduces the number of clonogens, with a resultant decrease in the tumor control radiation dose. The purpose of this article was to investigate using an animal tumor model how this clonogen reduction affects subsequent fractionated radiotherapy, including repopulation of surviving clonogens, and whether the induction TC can increase the therapeutic gain factor (TGF).

METHODS AND MATERIALS

The single-cell suspensions prepared from the fourth-generation isotransplants of a spontaneous fibrosarcoma, FSa-II, were transplanted into the C3Hf/Sed mouse foot. TC was given by heating tumors at 41.5 degrees C for 30 min immediately after an intraperitoneal injection of cyclophosphamide (200 mg/kg) when tumors reached an average diameter of 4 mm. Fractionated radiotherapy (R) with equally graded daily doses was initiated 24 h after TC either in air (A) or under hypoxic conditions (H). The 50% tumor control dose (TCD50) and the radiation dose to induce a score 2.0 reaction (complete epilation with fibrosis) in one-half of irradiated animals, RD50(2.0), were obtained, and the TGF was calculated. Our previous results on the fractionated radiotherapy using the same tumor system served as controls.

RESULTS

The TCD50(A, single dose) and TCD50(H, single dose) following TC+R were 52.2 and 57.3 Gy, respectively, which were 14.0 and 20.4 Gy lower than those following radiation alone. The TCD50(A, TC+R) increased only slightly when the number of fractions was increased from one to 10 doses, and all TCD50s were significantly lower than the TCD50(A, R alone). Both TCD50(H, TC+R) and TCD50(H, R alone) increased consistently from a single dose to 20 doses, but all TCD50(H, TC+R) were significantly lower than the TCD50(H, R alone). Regarding the normal tissue reaction, the RD50 values both following TC+R and R alone increased consistently from a single dose to 20 daily doses. However, the RD50(TC+R) and RD50(R alone) for each corresponding number of fractions was not significantly different, resulting in the TGFs significantly > 1.0 for combined TC+R treatments, with the exception of 20 daily doses given in air.

CONCLUSION

The induction TC decreased the TCD50 values substantially without altering the RD50 for a late reaction, resulting in an significant increase in the TGF. These results encourage the use of TC as an induction treatment prior to fractionated radiotherapy.

Reduction of hypoxic cells in solid tumours induced by mild hyperthermia: special reference to differences in changes in the hypoxic fraction between total and quiescent cell populations

C3H/He mice bearing SCC VII tumours received 5-bromo-2'-deoxyuridine (BrdU) continuously for 5 days via implanted mini-osmotic pumps in order to label all proliferating (P) cells. The tumours were then heated at 40 degrees C for 60 min. At various time points after heating, tumour-bearing mice were irradiated while alive or after being killed. Immediately after irradiation, the tumours were excised, minced and trypsinized. The tumour cell suspensions obtained were incubated with cytochalasin-B (a cytokinesis blocker), and the micronucleus (MN) frequency in cells without BrdU labelling, which could be regarded as quiescent (Q) cells, was determined using immunofluorescence staining for BrdU. The MN frequency in the total (P+Q) tumour cell population was determined from the irradiated tumours that were not pretreated with BrdU. The MN frequency of BrdU unlabelled cells was then used to calculate the surviving fraction of the unlabelled cells from the regression line for the relationship between the MN frequency and the surviving fraction of total (P+Q) tumour cells. In general, Q cells contained a greater hypoxic fraction (HF) than the total tumour cell population. Mild heating decreased the HF of Q cells more markedly than in the total cell population, and the minimum values of HFs of both total and Q cell populations were obtained 6 h after heating. Two days after heating, the HF of total tumour cells returned to almost that of unheated tumours. In contrast, the HF of Q cells did not return to the HF level of unheated tumours until 1 week after heating. It was thought that irradiation within 12 h after mild heating might be a potentially promising therapeutic modality for controlling radioresistant Q tumour cells.

Combined effects of an angiogenesis inhibitor (TNP-470) and hyperthermia

TNP-470, a synthetic analogue of fumagillin first isolated from Aspergillus fumigatus, is known to be a potent anti-angiogenic compound. The combined effects on tumour growth and tumour angiogenesis of TNP-470 and hyperthermia were investigated. The tumour used was SCCVII carcinoma of the C3H/He mouse. The tumour response was evaluated by the tumour growth (TG) time assay. The TG time is the time required for one-half of the treated tumours to reach three times the initial tumour volume. Significant delay of tumour growth was observed by TNP-470 alone (100 mg kg-1 x 2 or x 4), indicating that TNP-470 alone has antitumour effect in vivo. When TNP-470 (100 mg kg-1 x 2 or x 4) was administered after hyperthermia at 44 degrees C, the TG times of the combined treatment were significantly longer than those of heat alone (44 degrees C) or TNP-470 (100 mg kg-1 x 2 or x 4) alone. However, the TG time of combined treatment with TNP-470 and hyperthermia at 42 degrees C was quite similar to that of TNP-470 alone. This conflicting result on the combined effect of TNP-470 and hyperthermia may be related to the temperature-dependent vascular damage by hyperthermia. Dose-dependent inhibition of angiogenesis by TNP-470 was demonstrated in microangiograms obtained 4 days and 7 days after hyperthermia (44 degrees C for 30 min). It is, thus, suggested that the combined effect of TNP-470 and hyperthermia is attributable to the inhibition of angiogenesis by TNP-470 following heat-induced vascular damage.

A comparison of the physiological effects of RSU1069 and RB6145 in the SCCVII murine tumour

The physiological and therapeutic effects of the bioreductive agent RSU1069 (80 mg/kg i.p.) and its prodrug RB6145 (240 mg/kg i.p.) were investigated in the SCCVII tumour. Using laser Doppler flowmetry it was found that RSU1069 produced a significant 30% reduction in tumour blood flow 30 min after administration, while RB6145 had no effect. Tumour oxygenation, measured with an Eppendorf oxygen electrode, was unchanged by either agent except for a reduction in values less than 2.5 mmHg at 30 min after injection. Neither agent significantly altered tumour energy metabolism, assessed by 31P magnetic resonance spectroscopy. Both agents significantly increased tumour glucose content by a factor of 1.6-1.7 at 30 min after injection, but had no effect on glucose-6-phosphate or lactate levels. Tumour growth was significantly delayed by heating (42.5 degrees C, 60 min), and although neither RSU1069 nor RB6145 alone had any effect on tumour growth they produced a similar enhancement of the tumour response to heat. The therapeutic effects are consistent with the known conversion in vivo of one third of the pro-drug RB6145 to its active product RSU1069, however the physiological effects of the two agents in the SCCVII tumour are not identical.

Antitumour effect of irradiation followed by hyperglycemia and hyperthermia: the dependence on tumour size and blood flow

The interrelationship of three tumour parameters-volume, blood flow and growth delay-was evaluated after irradiation alone or combined with hyperglycemia (HG) and hyperthermia (HT). The experiments were performed on Ehrlich carcinoma tumours 5, 7 or 9 days after intramuscular implantation when they reached a mean volume of approximately 0.17, 0.46 or 0.90 cm3, respectively. Tumours were irradiated at a dose of 12.5 Gy. In groups of trimodality therapy, induction of HG (5i.p. injections of glucose during a 2-h period, total dose of glucose 10.4 g/kg) was started immediately after irradiation, and HT (water bath, 43 degrees C, 30 min) was given 3 h later. Regardless of the method of therapy, blood flow in the central part of each tumour was measured 4 and 7 h after irradiation by 133Xe clearance technique. It was shown that if tumours were treated by irradiation alone, both tumour blood flow and growth delay declined with increasing tumour volume. There was no correlation between individual values of tumour blood flow intensity and growth delay within each size group, and only all the data pooled together showed a significant direct relationship between these two parameters. In contrast, for radiotherapy with HG and HT, the antitumour effect increased with tumour volume. Blood flow was strongly inhibited by radio-modifiers; the larger tumours, the lower levels of perfusion were observed. There was a pronounced trend of increased tumour growth delay with decreased blood flow for tumours of the same volume, and these parameters were highly correlated if all individual data were analysed together regardless of tumour size. It was concluded that postirradiation blood flow inhibition plays a significant role in the tumouricidal effect of irradiation with HG and HT. The monitoring of tumour perfusion may be useful for the prediction of the effectiveness of such postirradiation modification, which is especially attractive in radiotherapy of large advanced tumours.

Discrepancies between measured changes of radiobiological hypoxic fraction and oxygen tension monitoring using two assay systems

PURPOSE

This study was conducted to assess the ability of computerized pO2 histography to measure changes in tumor oxygenation produced by low oxygen breathing.

METHODS AND MATERIALS

Female syngeneic C3H/Km mice bearing SCC VII/St carcinomas were used in these experiments. Changes in tumor oxygenation produced by the mice breathing 10% oxygen were assessed with computerized pO2 histography, 3H-misonidazole binding, and the paired survival curve assay of radiosensitivity.

RESULTS

The hypoxic cell fraction of the tumors in mice breathing 10% oxygen was 3.1 times higher than that of tumors in mice breathing normal air determined by an in vivo-in vitro clonogenic assay. Binding of radiolabeled misonidazole to the tumors in mice breathing 10% oxygen was also significantly higher than that to tumors in mice breathing normal air (p < 0.05). In addition, oxygen tension histograms for normal tissue showed a dramatic shift to a lower oxygen tension when the mice were breathing 10% oxygen. However, under identical conditions, there was only a minimal shift in the oxygen tension of tumor tissue. Although the number of oxygen tension readings in the relatively oxic class in tumor tissue was lower when the mice were breathing 10% oxygen than when breathing normal air, there was not a significant decrease in the median pO2 value for the tumor. The number of pO2 readings lower than 5 mmHg in the tumor was not affected by the 10% oxygen breathing.

CONCLUSION

These findings indicate that increases in radiobiological hypoxic fraction produced by lower blood oxygen levels may not correlate well with the results of polarographic measurements of tumor pO2 levels.

The effect of hyperthermia on reoxygenation during the fractionated radiotherapy of two murine tumors, FSa-II and MCa

PURPOSE

To investigate the effect of hyperthermia on the tumor reoxygenation during fractionated irradiations. It has been shown that hyperthermia increases the size of hypoxic cell fraction in some murine tumors and reoxygenation is critical for successful radiotherapy.

METHODS AND MATERIALS

Tumors were early generation isotransplants of spontaneous murine fibrosarcoma (FSa-II) and mammary carcinoma (MCa) in C3Hf/Sed mice. Treatments were initiated when they reached an average diameter of 4 mm. A local heat treatment at 43.5 degrees C for 45 min was given in a constant temperature water bath 24 h before irradiation(s). This interval was selected to avoid heat-radiation interaction and to simply investigate the heat effect on the reoxygenation process. Tumors were irradiated under hypoxic conditions or in air and observed for recurrences for 120 days. The foot reaction of animals with controlled-tumors was scored on the last day of experiments. The TCD50 (50% tumor control dose) and RD50 (dose to induce partial foot atrophy in 50% of treated animals) were calculated.

RESULTS

The TCD50s following a various number of fractions were obtained for FSa-II and MCa with or without hyperthermia. The difference between the TCD50 (hypoxia) and TCD50 (in air) without hyperthermia increased with an increasing number of fractions, suggesting that significant reoxygenation occurred during the fractionated irradiation. The TCD50s (with heat, in air) were smaller than the TCD50s (radiation alone, in air) following fractionated irradiations, indicating that hyperthermia did not affect tumor reoxygenation. The difference between these TCD50 values was greater for heat-sensitive MCa than for heat-resistant FSa-II, suggesting that this difference was due to additive heat cytotoxicity. An unexpected observation was that heat significantly enhanced the foot reaction with no resultant therapeutic gain for both MCa and FSa-II tumors.

CONCLUSION

Hyperthermia given independently prior to fractionated irradiation did not affect tumor reoxygenation, nor was there a therapeutic gain for the two murine tumors. These results suggest that selective tumor heating is essential in clinical thermoradiotherapy.

The morphological effects of the anti-tumor agents flavone acetic acid and 5,6-dimethyl xanthenone acetic acid on the colon 38 mouse tumor

Flavone acetic acid and 5,6-dimethyl xanthenone acetic acid have a broad spectrum of anti-tumor activity in mice, and act by stimulating immune cells and inhibiting tumor blood flow, resulting in hemorrhagic necrosis within 24 hrs. To study the evolution of hemorrhagic necrosis, subcutaneous Colon 38 tumors were examined by light and electron microscopy from 30 min to 24 hrs after treatment with these agents, and measurements of tumor energy metabolites made. The results show that both agents cause apoptosis beginning at 30 min, and that by 4 hrs necrosis supervenes, accompanied by rupture of tumor blood vessels. The absence of early endothelial cell damage or thrombosis suggests that vessel rupture, and consequent loss of blood flow and energy metabolite depletion, is caused by loss of extravascular mechanical support by the tumor parenchyma.

Timing and sequence of hyperthermia in fractionated radiotherapy of a murine fibrosarcoma

PURPOSE

This study investigated the effect of timing and sequence of hyperthermia on fractionated radiotherapy, since it has been shown that the heat increases the size of hypoxic cell fraction which could affect the effect of subsequent radiation doses.

METHODS AND MATERIALS

Animal-tumors were early generation isotransplants of a spontaneous fibrosarcoma, FSa-II, in C3Hf/Sed mice. Tumor response was studied by tumor growth time and TCD50 (50% tumor control dose) assays. The tumor growth time is the time required for one-half of the treated tumors to reach 500 mm3 from the first treatment day. The TCD50 is a radiation dose to control one-half of the treated tumors for 120 days following treatments. One heat treatment at 43.5 degrees C for 45 min was given in a water bath in combination with fractionated doses independently (24 hr interval) or simultaneously (2 min interval). For the normal tissue study, the mouse foot was treated, and the acute foot reaction was scored daily and averaged. The late foot reaction was scored in animals used in the TCD50 assay that developed no recurrence for 120 days. The RD50(2.0) and RD50(5.0), or total radiation doses to induce an average score of 2.0 (complete epilation) and 5.0 (partial foot atrophy) in 50% of treated animals, were calculated.

RESULTS

Thermal radiosensitization was most prominent when heat was combined simultaneously with the first or last radiation dose in both the tumor growth time and TCD50 assays. However, the thermal enhancement was greatest when heat was given either with the first or last radiation dose in the TCD50 assay; whereas it was greatest when heat was administered with the last radiation dose in the tumor growth time assay. Both acute and late skin reactions were significantly potentiated by heat administered 24 hr before the first radiation dose.

CONCLUSION

A significant observation in this study was that, in both the tumor growth time and TCD50 assays, heat given independently or simultaneously did not result in any therapeutic gain compared to the radiation alone treatment.

Prediction of treatment temperatures in clinical hyperthermia of locally advanced breast carcinoma: the use of contrast enhanced computed tomography

PURPOSE

Nineteen patients with locally advanced breast carcinoma were subjected to computed tomography examinations prior to thermoradiotherapy. Pre- and postcontrast computed tomography images were obtained, and tumor contrast enhancement was studied in relation to tissue perfusion, PERF, and steady state temperature, TS, in an attempt to develop an assay for prediction of treatment temperatures in clinical hyperthermia of breast carcinoma.

METHODS AND MATERIALS

PERF and TS were calculated from temperature data achieved during the first fraction of the heat treatment regimen. The computed tomography images were subjected to image analysis, and two parameters representing tumor contrast enhancement were calculated from the computed tomography numbers; the absolute increase in mean attenuation, delta N, and the fraction of the postcontrast attenuation values that was higher than the mean precontrast attenuation value, F+C.

RESULTS

delta N and F+C were clearly correlated to each other. The two parameters differed considerably among the patients, showing that the accumulation of contrast medium was higher in some tumors than in others. Tumor contrast enhancement increased with increasing PERF, suggesting that the accumulation of contrast medium in the tumors was determined mainly by the effective tissue perfusion. There was also a clear correlation between tumor contrast enhancement and TS. The tumors showing a high accumulation of contrast medium were more difficult to heat than those showing a low accumulation.

CONCLUSION

The results indicate that contrast enhanced computed tomography images may give information about the treatment temperatures that can be achieved in clinical hyperthermia of breast carcinoma. The computed tomography images may possibly be used to predict those tumors that can be heated to therapeutic temperatures.

Observations of thermal gradients in perfused tissues during water bath heating

Actual thermal gradients in perfused tissues are difficult to observe using thermocouples because of thermal conduction along the probes. We have used fine type-K (chromel-alumel) probes, which have a much lower thermal conductivity than equivalent-sized type-T (copper-constantan) thermocouples, to examine thermal gradients in two mouse tumour systems during water bath heating. The results indicate substantial heterogeneity in temperature distribution even in tumours transplanted in the foot and immersed to a depth of 2 cm in a 44 degrees C water bath for 20 min, i.e. thermal gradients greater than 1 degree C/mm were observed in KHT fibrosarcomas. The temperature heterogeneity for water bath heating is primarily a result of blood flow and appears to be tumour-specific. Temperature measurements using an excised perfused canine kidney demonstrate that increased perfusate volume flow increases the range of tissue temperatures. Consistent with theory, an artifactual improvement in temperature homogeneity resulted when temperature was measured using type-T thermocouples instead of type-K probes. These results emphasize the difficulties in obtaining accurate temperature measurements during experimental and clinical hyperthermia. Even extensive measurements of temperature in tissues may underestimate the true range of heterogeneity unless factors such as thermal smearing are controlled.

Temperature distribution in locally advanced breast carcinoma during hyperthermic treatment: relationship to perfusion, vascular density, and histology

Temperature distributions achieved during hyperthermic treatment of 16 patients with locally advanced breast cancer were analyzed in relation to tissue perfusion, vascular density, and histology of treated volume. Temperatures were measured using multi-sensor thermistor probes inserted in the center and periphery of the treatment volume. A steady state temperature, Ts, and a perfusion related parameter, PERF, were determined for each probe location. Vascular density and tissue composition were determined by histologic analysis of biopsies taken from the temperature probe locations before treatment. Both malignant and normal tissue were found in the biopsies, reflecting a diffusive tumor growth pattern. The malignant and normal tissue compartments were analyzed separately using stereologic techniques. Ts, PERF, vascular density, and tissue composition differed significantly between patients. There was a clear relationship between Ts and PERF, showing that the local tissue perfusion was decisive for the temperatures achieved. Ts and PERF showed a clear correlation with the normal tissue vascular density, but not with the malignant tissue vascular density; that is, the treatment temperatures achieved were mainly determined by the vascularization of the normal tissue compartment. Fraction of necrosis was the only tissue compartment parameter that showed a clear relationship to Ts and PERF. Ts increased and PERF decreased with increasing necrotic fraction.

Relationships between thermal dose and heat-induced tissue and vascular damage after thermoradiotherapy of locally advanced breast carcinoma

Twenty-four patients with locally advanced breast carcinoma were given thermoradiotherapy, and heat-induced damage to tissue and vasculature was studied in relation to thermal dose. Thermometry was performed using six to eight multi-point thermistor probes. Heat-induced damage was quantified by histopathological analysis of biopsies taken from the temperature probe locations shortly after treatment. Both tumour and normal tissue were found in the biopsies. Fraction of tissue and fraction of vessels with heat-induced damage were determined for the malignant and the normal tissue compartment separately, using stereological techniques. Clear relationships were found between these parameters and the largest thermal dose achieved in one heat fraction. The data were subjected to logit analysis, and the thermal doses (eqv. min at 43 degrees C) that caused massive necrosis in 50% of the tissue were calculated to be 116 +/- 31 for the malignant tissue compartment and 205 +/- 49 for the normal tissue compartment. Similarly, the thermal doses that caused damage to 50% of the vessels were found to be 63 +/- 34 and 144 +/- 46 for the malignant and the normal tissue compartment, respectively. Thus, the tumour tissue was more sensitive to heat than was the surrounding normal tissue, irrespective of whether necrosis or vessel damage was considered. This was probably a consequence of physiological and vascular differences between the two tissue compartments. Evidence for primary and secondary cell death was found both in the malignant and the normal tissue, although primary cell death probably was of minor importance in the normal tissue. The data indicate that selective heat-inactivation of tumour tissue is possible by external microwave hyperthermia of locally advanced breast carcinoma.

The radioresponsiveness of normal and tumour microvasculature

Mouse tails bearing DMH-II tumours were irradiated to a total of 80 Gy in 8 Gy fractions, twice a day for 5 consecutive days. The normal tail vasculature was minimally affected for up to 60 days post-irradiation. In contrast tumour capillaries which showed minor changes on day 6 post-irradiation were severely affected by day 14. DMH-II proved to be a radioresistant tumour. The radiation dose used in this experiment was the maximum total dose which could be tolerated by the mouse tail. The tumour began to regenerate at approximately 40 days post-irradiation. Tumour infiltrating into the surrounding normal tissue was observed by 60 days following irradiation. As the tumour regenerated, there was no accompanying regeneration of tumour capillaries. This study suggests that: a) tumour capillaries were more acutely radioresponsive than the normal microvasculature in the murine tail, and b) regenerating tumour did not elicit a neovascular response from the irradiated tumour bed.

Heat sensitivity and thermotolerance in vitro of human breast carcinoma, malignant melanoma and squamous cell carcinoma of the head and neck

Heat sensitivity and the development of thermotolerance of cells isolated directly from surgical specimens of human breast carcinoma, malignant melanoma and squamous cell carcinoma of the head and neck were studied in vitro using the Courtenay soft agar colony assay. The plating efficiency of some of the tumours was sufficiently high (0.3-20.4%) for survival curves covering up to two to three decades to be established. Experiments repeated with cells stored in liquid nitrogen showed that the survival assay gave highly reproducible results. Heat sensitivity of thermotolerant cells was studied by giving cells a conditioning heat treatment of 43.5 degrees C for 60 min and, after incubation at 37 degrees C for 24 h, second graded heat treatments at 43.5 degrees C. Significant differences in heat sensitivity and development of thermotolerance between the three tumour types were not found. However, the heat sensitivity, whether the cells were thermotolerant or not, differed considerably among individual tumours of each histological category. Do at 43.5 degrees C was found to be in the ranges of 23-59 min (breast carcinoma), 20-63 min (malignant melanoma) and 20-57 min (squamous cell carcinoma) for single-heated cells and 105-476 min (breast carcinoma). 102-455 min (malignant melanoma) and 87-400 min (squamous cell carcinoma) for thermotolerant cells. The heat sensitivity of cells made thermotolerant showed no significant correlation to the surviving fraction after the conditioning heat treatment. The study indicated that histological category is a poor parameter for assessment of clinical heat responsiveness of tumours. Breast carcinoma, malignant melanoma and squamous cell carcinoma are probably, from a thermobiological point of view, equally good candidates for clinical trial aimed at studying the potential usefulness of hyperthermia as an adjunct to radiation therapy and/or chemotherapy. The large differences in heat sensitivity and development of thermotolerance observed among individual tumours, irrespective of histological origin, suggested that an in vitro predictive assay for heat responsiveness would be very useful for stratification purposes in such clinical trials.

Radiofrequency (RF) capacitive hyperthermia combined with radiotherapy in the treatment of abdominal and pelvic deep-seated tumors

Thermal parameters and tumor response were determined in 33 abdominal and pelvic deep-seated tumors which were treated with hyperthermia in combination with radiation therapy. Hyperthermia was applied regionally for a total of 3-14 sessions (mean; 6.4 sessions), using an 8 MHz radiofrequency (RF) capacitive heating device. An average tumor temperature (Tav) of more than 42 degrees C was achieved in 17 (52%) tumors, and intratumor temperatures above 42 degrees C could be maintained for more than 20 min (effective heat session) in 103 (52%) of the 198 heat sessions. Of the 33 tumors, 4 tumors exhibited complete regression (CR), 7 PRa (80-99% regression), 7 PRb (50-79% regression) and 15 NR (less than 50% regression). Tumor response (CR + PRa) was apparently dependent on the thermal parameters. Tumors with Tav of more than 42 degrees C or those receiving more than three effective heat sessions showed a significantly higher response rate than those heated less effectively. This trend was also noted in minimum tumor temperature. As to radiation dose, most of the responders received a total of 60-70 Gy irradiation. The two characteristic features in tumor response in effectively heated tumors, were slow tumor regression and appearance of an intratumor low density area on post-treatment computed tomography.