Quantitative studies of microcirculatory function in malignant tissue: influence of temperature on microvascular hemodynamics during the early growth of the BA 1112 rat sarcoma

Procedures and applications of long-term intravital microscopy

Intravital microscopy (IVM) is increasingly used in biomedical research to study dynamic processes at cellular and subcellular resolution in their natural environment. Long-term IVM especially can be applied to visualize migration and proliferation over days to months within the same animal without recurrent surgeries. Skin can be repetitively imaged without surgery. To intermittently visualize cells in other organs, such as liver, mammary gland and brain, different imaging windows including the abdominal imaging window (AIW), dermal imaging window (DIW) and cranial imaging window (CIW) have been developed. In this review, we describe the procedure of window implantation and pros and cons of each technique as well as methods to retrace a position of interest over time. In addition, different fluorescent biosensors to facilitate the tracking of cells for different purposes, such as monitoring cell migration and proliferation, are discussed. Finally, we consider new techniques and possibilities of how long-term IVM can be even further improved in the future.

Video-rate resonant scanning multiphoton microscopy: An emerging technique for intravital imaging of the tumor microenvironment

The abnormal tumor microenvironment fuels tumor progression, metastasis, immune suppression, and treatment resistance. Over last several decades, developments in and applications of intravital microscopy have provided unprecedented insights into the dynamics of the tumor microenvironment. In particular, intravital multiphoton microscopy has revealed the abnormal structure and function of tumor-associated blood and lymphatic vessels, the role of aberrant tumor matrix in drug delivery, invasion and metastasis of tumor cells, the dynamics of immune cell trafficking to and within tumors, and gene expression in tumors. However, traditional multiphoton microscopy suffers from inherently slow imaging rates-only a few frames per second, thus unable to capture more rapid events such as blood flow, lymphatic flow, and cell movement within vessels. Here, we report the development and implementation of a video-rate multiphoton microscope (VR-MPLSM) based on resonant galvanometer mirror scanning that is capable of recording at 30 frames per second and acquiring intravital multispectral images. We show that the design of the system can be readily implemented and is adaptable to various experimental models. As examples, we demonstrate the utility of the system to directly measure flow within tumors, capture metastatic cancer cells moving within the brain vasculature and cells in lymphatic vessels, and image acute responses to changes in a vascular network. VR-MPLSM thus has the potential to further advance intravital imaging and provide new insight into the biology of the tumor microenvironment.

Wide-field functional imaging of blood flow and hemoglobin oxygen saturation in the rodent dorsal window chamber

The rodent dorsal window chamber is a widely used in vivo model of the microvasculature. The model consists of a 1cm region of exposed microvasculature in the rodent dorsal skin that is immobilized by surgically implanted titanium frames, allowing the skin microvasculature to be visualized. We describe a detailed protocol for surgical implantation of the dorsal window chamber which enables researchers to perform the window chamber implantation surgery. We further describe subsequent wide-field functional imaging of the chamber to obtain hemodynamic information in the form of blood oxygenation and blood flow on a cm size region of interest. Optical imaging techniques, such as intravital microscopy, have been applied extensively to the dorsal window chamber to study microvascular-related disease and conditions. Due to the limited field of view of intravital microscopy, detailed hemodynamic information typically is acquired from small regions of interest, typically on the order of hundreds of μm. The wide-field imaging techniques described herein complement intravital microscopy, allowing researchers to obtain hemodynamic information at both microscopic and macroscopic spatial scales. Compared with intravital microscopy, wide-field functional imaging requires simple instrumentation, is inexpensive, and can give detailed metabolic information over a wide field of view.

A local hyperthermia treatment which enhances antibody uptake in a glioma xenograft model does not affect tumour interstitial fluid pressure

Solid tumours have an elevated interstitial fluid pressure (IFP) due to the lack of normal lymphatics, increased permeability of tumour vasculature and an expanding cell population within a potentially limited space. This elevated IFP has been proposed to be an important barrier to the delivery of drugs and marcromolecules. We have demonstrated that local hyperthermia (4 h, 41.8 degrees C) is capable of significantly enhancing the uptake of radiolabelled monoclonal antibodies (mAbs) in D-54 MG glioma xenografts grown subcutaneously in athymic mice. To determine if this increased uptake was attributable to alterations in the tumour IFP, pressure measurements using the wick-in-needle technique were made in tumours after hyperthermia treatment. These pressure measurements were taken at various time points from 4 to 90 h following the initiation of the hyperthermia and compared with pressures taken concurrently in untreated tumours. In addition, pressures were measured following a 2 h, 41.8 degrees C hyperthermia treatment, a protocol which does not result in elevated uptake of radiolabeled mAbs. No significant differences were seen at any time point in IFP measured in the tumours receiving either hyperthermia treatment when compared with untreated tumours. Thus, we conclude that the mechanism by which this hyperthermia regimen enhances mAb uptake in this human glioma xenograft model is not due to alternations in tumour IFP.

Vascular thermal adaptation in tumors and normal tissue in rats

PURPOSE

The vascular thermal adaptation in the R3230 adenocarcinoma, skin and muscle in the legs of Fischer rats was studied.

METHODS AND MATERIALS

The legs of Fischer rats bearing the R3230 AC adenocarcinoma (subcutaneously) were heated once or twice with a water bath, and the blood flow in the tumor, skin and muscle of the legs was measured with the radioactive microsphere method.

RESULTS

The blood flow in control R3230 AC tumors was 23.9 ml/100 g/min. The tumor blood flow increased about 1.5 times in 30 min and then markedly decreased upon heating at 44.5 degrees C for 90 min. In the tumors preheated 16 h earlier at 42.5 degrees C for 60 min, reheating at 44.5 degrees C increased the tumor blood flow by 2.5-fold in 30 min. Contrary to the decline in blood flow following an initial increase during the 44.5 degrees C heating without preheating, the tumor blood flow remained elevated throughout the 90 min reheating at 44.5 degrees C. These results indicated that thermal adaptation or thermotolerance developed in the tumor vasculatures after the preheating at 42.5 degrees C for 60 min. The magnitude of vascular thermal adaptation in the tumors 24 h and 48 h after the preheating, as judged from the changes in blood flow, were smaller than that 16 h after the preheating. Heating at 42.5 degrees C for 60 min induced vascular thermal adaptation also in the skin and muscle, which peaked in 48 h and 24 h, respectively, after the heating.

CONCLUSION

Heating at 42.5 degrees C for 1 h induced vascular thermal adaptation in the R3230 AC tumor, skin, and muscle of rats that peaked 16-48 h after the heating. When the tumor blood vessels were thermally adapted, the tumor blood flow increased upon heating at temperatures that would otherwise reduce the tumor blood flow. Such an increase in tumor blood flow may hinder raising the tumor temperature while it may increase tumor oxygenation.

Tumour vasculature--a potential therapeutic target

The tumour vasculature is vital for the establishment, growth and metastasis of solid tumours. Its physiological properties limit the effectiveness of conventional anti-cancer strategies. Therapeutic approaches directed at the tumour vasculature are reviewed, suggesting the potential of anti-angiogenesis and the targeting of vascular proliferation antigens as cancer treatments.

Enhancement of the effectiveness of methotrexate for the treatment of solid tumours by application of local hyperthermia

Investigations were performed to assess the influence of hyperthermia on the pharmacokinetics of a chemotherapeutic drug and on the effectiveness of combined treatments for induction of tumour cell death and growth delay of experimental tumours. Treatments consisted of methotrexate (MTX, 20 mg/kg ip), hyperthermia at 43 degrees C during 60 min (HT60) or 90 min (HT90) and combined chemo-hyperthermia using various time intervals up to 24 h. The results indicate that, for MTX + HT90, concentrations in excess of 0.02 mg/kg are maintained in tumour tissue during at least 22 days, whereas after the other single and combined treatments, the concentration decreased below this level within 5-8 days. The combinations of MTX + HT90 also were more effective with respect to tumour growth delay, 26-28 days, and frequency of partial remissions, 75-100%, as compared to the other treatments: 7-12 days and 0-28% respectively. These observations correlate well with cell survival data. It is concluded that hyperthermia can enhance the effectiveness of MTX and that variation of time-intervals between administration of MTX and hyperthermia as well as the duration of the hyperthermic treatment have a great influence on tumour responses. Unfortunately, also toxic effects were induced distantly from the site of local hyperthermic treatment by the combination of MTX + HT90 which was most effective with respect to tumour eradication.

Endothelial cells and hyperthermia

Most radiation oncologists are aware of the effects of clinical hyperthermia on neoplastic cells. Its effects on blood vessels, however, are not as well recognized. Yet, since the 1960s a number of investigators have described and categorized the effects of hyperthermia on microvessels (in vivo), and on cultured endothelial cells (EC) (in vitro). Both EC and microvessels can be lethally damaged by the hyperthermia doses used as antineoplastic therapy. In vitro data indicate that capillary EC are moderately sensitive to hyperthermia. Proliferating EC are more thermosensitive suggesting that microvessels of malignant neoplasms (which contain many proliferating EC) are more affected than microvessels of normal tissues. This differential sensitivity of microvessels has also been observed in blood flow studies. Furthermore, hyperthermia inhibits angiogenesis. Thus, some of the antineoplastic effects of heat are caused by ischaemia due to obstruction or destruction of the tumour vessels or to inability to form new vessels. Sublethal EC damage can also be demonstrated, resulting in decreased synthesis of most proteins including adhesion molecules (as well as increased expression of a few such as heat shock proteins) and producing reversible loss of cytoskeletal elements. The therapeutic advantage provided by the higher thermal sensitivity of neoplastic vessels should be exploited further, perhaps by developing strategies specifically aimed to the tumour microvasculature.

Review article: angiogenesis, neovascular proliferation and vascular pathophysiology as targets for cancer therapy

A body of evidence that vascular-mediated damage occurs in murine tumours after many existing forms of anti-tumour therapy is rapidly accumulating (see Gray Conference Proceedings edited by Moore & West, 1991). Rapid conventional screens of cells in vitro or using leukaemias of lymphomas will not detect this mode of action and such screens will therefore miss effective agents. A change in the approach to experimental cancer therapy is needed to ensure that this important new avenue is fully investigated. Solid tumours will need to be studied and the importance of specific tumour cell biochemistry (e.g. on tissue factor procoagulant activity), of endothelial status and the immunocompetence of the host are all likely to be important. It is a subject of considerable debate at present whether transplanted subcutaneous mouse tumours are adequate models and whether they will reflect the response of spontaneous tumours, or even of transplants into other sites. Xenografts are not likely to be appropriate if the immuno-suppressed hosts lack the cells needed for the cytokine component of the pathway. The strategy of design and screening of new agents, for scheduling of existing agents and particularly the sequencing of adjunctive therapies are likely to be completely different for the "direct" tumor cell or "indirect" vascular-mediated approaches. It may eventually be appropriate to combine vascular manipulation with direct cytotoxicity aimed at malignant cells but the two mechanisms must be recognized as distinct entities and considered separately before attempting to coordinate them. It is important therefore to identify the "hallmarks" of vascular mediated injury and the means by which this can be distinguished from direct cell kill. These may be detectable in the tumour response but clues can also be gained from the side effects that are seen in normal tissues both with existing and with novel therapies (Figure 7). The appeal of vascular-mediated ischaemic therapy is that it is systemic and will have the potential of being effective on any tumour with a newly evoked vascular network, i.e. of about 1 mm in diameter, but it will be even more effective on large tumours than on small. Thus it should affect both large primary tumours and disseminated small metastases. The studies with many different anti-cancer agents have illustrated the potential complexity of responses that can appear to cause tumour cell death by collapse or occlusion of the blood supply. They have also focused attention on features of disparate agents, e.g. TNF, FAA, PDT, which may share similar pathways. No single feature of neovasculature can be highlighted as the sole route by which such antivascular therapy should be targeted. Rapid proliferation of the endothelial cells may prove to be a target, but it also influences differentiation characteristics, so that the immature cells will function abnormally. The permeability of these poorly formed vessels may lead to extravasation of proteins leading to increase interstitial pressures and by this means to an imbalance between intravascular and extravascular pressures and hence to collapse of the thin-walled vessels. Changes in systemic blood pressure, cardiac output, viscosity or coagulation and especially a redistribution of regional perfusion would all have differential effects in tumours and normal vessels. Clearly both vascular patho-physiology and the complexity of endothelial cell function and its imbalance in neovasculature will be important in understanding the mechanism of action of antivascular strategies. This very challenging boundary between oncology and a number of other medical and biological fields promises to lead to altered attitudes to existing therapies and the discovery of completely new classes of anti-cancer agents. The next decade should translate into clinical benefit for patients if the progress in this field continues to be as rapid as it has been in the late eighties. We must now determine what characteristics make one tumour more sensitive than another to agents such as heat, PDT, cytokines and FAA, and learn how to extrapolate from those rodent tumours to the human.

Vascular attack as a therapeutic strategy for cancer

The blood supply to all solid tumours consists of parasitized normal vessels and new vessels which have been induced to grow by the presence of the tumour. These vessels are inadequate in many respects, being tortuous, thin-walled, chaotically arranged, lacking innervation and with no predetermined direction of flow. The walls consist of a basement membrane lined with rapidly proliferating immature endothelial cells, and are more permeable than normal vessels. The spacing of the vessels and their average diameters are not optimal for nutrient provision. This paper focuses on the evidence that many existing therapies may already have, as part of their action, a vascular mediated process of killing tumour cells. This may result from local changes within individual vessels or from systemic alterations in blood pressure, viscosity, coagulability etc. The hallmarks of vascular injury are identified and the dangers of discarding useful anticancer agent by failing to understand their mechanism of action are highlighted.

The effects of fractionated hyperthermia on normal canine muscle blood flow

This study investigates the changes in normal canine muscle blood flow occurring during three fractions of 43 degrees C (60 min) hyperthermia. Blood flow was measured during heating at 1-, 3-, and 5-day intervals with a laser Doppler flowmeter. For 1-day intervals, blood flow oscillated during the first treatment reaching peak values of approximately 39 ml/min per 100 g of tissue after 8 min and 47 ml/min per 100 g of tissue after 40 min. Heatings at 1-day intervals showed both peaks in perfusion to persist during subsequent treatments with higher blood flows during later heatings. Results of the 3-day fractionated heating demonstrated lower blood flows during the second and third heatings than those at 1-day intervals. The third treatment of the 3-day fractionations showed a disappearance of the first peak and only a small increase in perfusion at the second peak (50 ml/min per 100 g of tissue). Perfusion studies at 5-day intervals demonstrated two peaks at approximately 15 and 40 min. Compared with the first treatment at 5-day intervals, the second and third treatments demonstrated decreased and increased peak perfusion values, respectively. This study suggests that the kinetics of blood flow changes during hyperthermia may be the result of several different mechanisms. There appear to be three different peaks which can be quantified during heating. These peaks may change during subsequent heating independently from one another. Further work must be performed to examine the physiological mechanisms responsible for each peak.

Heterogeneity in tumor microvascular response to radiation

Viable hypoxic cells have reduced radiosensitivity and could be a potential cause for treatment failure with radiotherapy. The process of reoxygenation, which may occur after radiation exposure, could increase the probability for control. However, incomplete or insufficient reoxygenation may still be a potential cause for local treatment failure. One mechanism that has been thought to be responsible for reoxygenation is an increase in vascular prominence after radiation. However, the effect is known to be heterogeneous. In this study, tumor microvascular hemodynamics and morphologies were studied using the R3230 Ac mammary adenocarcinoma transplanted in a dorsal flap window chamber of the Fischer-344 rat. Measurements were made before and after (at 24 and 72 hr) 5-Gy radiation exposure to assess microvascular changes and to explore possible explanations for the heterogeneity of the effect. There was considerable heterogeneity between tumors prior to radiation. Vascular densities ranged from 67 to 3000 vessels/mm3 and median vessel diameters from 22 to 85 microns. Pretreatment perfusion values varied by a factor of six. In irradiated tumors, conjoint increases in both vascular density and perfusion occurred in most tumors, although the degree of change was variable from one individual to the next. The degree of change in density was inversely related to median pretreatment diameter. Relative change in flow, as predicted by morphometric measurements, overestimated observed changes in flow measured hemodynamically. These results support that heterogeneity in tumor vascular effects from radiation are somewhat dependent on pretreatment morphology as well as relative change in morphology. Since changes in flow could not be completely explained by morphometric measurements, however, it is likely that radiation induced changes in pressure and/or viscosity contribute to the overall effect. Further work in this laboratory will investigate these hypotheses.

Morphologic and hemodynamic comparison of tumor and healing normal tissue microvasculature

The purpose of this study was to compare microvascular morphometric and hemodynamic characteristics of a tumor and granulating normal tissue to develop quantitative data that could be used to predict microvascular characteristics which would be most likely associated with hypoxia. The dorsal flap window chamber of the Fisher 344 rat was used to visualize the microvasculature of 10 granulating and 12 tumor (R3230 AC adenocarcinoma) tissues at 2 weeks following surgical implantation of the chamber. Morphometric measurements were made from photomontages and video techniques were used to assess red cell velocities in individual vessels. The percent vascular volume of both tissues was close to 20%, but significant differences were noted in other morphometric and hemodynamic measurements. Individual vessel dimensions (length and diameter) in tumors averaged twice as large as those in granulating tissues. Furthermore, red cell velocities were twice as high in tumors as in granulating tissues. In addition to these large differences in average values, there was significant heterogeneity in tumor microvascular morphometry, indicating spatial nonuniformity compared with the granulating tissue. Approximations of vessel spacing, indicated an average of 257 and 118 microns in tumors and granulating tissues, respectively. Vessel densities were four times greater in granulating tissues than in tumor tissues. These results indicated that intervessel distances were more likely to result in hypoxia in tumors, especially considering the wide variability in that tissue. Analysis of flow branching patterns showed that vascular shunts occurred frequently in vessels ranging from 10 to 90 microns in diameter. The results of this study indicate, in this tumor model, that conditions such as low vascular density, vascular shunts, excessive vascular length and/or low red cell velocity exist to a greater extent than the granulating tissue control. These conditions are likely to be conductive to the development of hypoxia.

Low dose reirradiation in combination with hyperthermia: a palliative treatment for patients with breast cancer recurring in previously irradiated areas

Ninety-seven patients with breast cancer recurring in a previously irradiated area (mean dose 44 Gy) were reirradiated in combination with hyperthermia and had evaluable tumor responses. In the reirradiation series, radiotherapy was given twice weekly in most patients, with a fraction size varying from 200 to 400 cGy, the total dose varying from 8 to 32 Gy. Hyperthermia was given following the radiotherapy fractions. The combined treatment resulted in 35% complete and 55% partial responses. Duration of response was median 4 months for partial response and 26 months for complete response, respectively. The median survival time for all patients was 12 months. Acute skin reaction was mild, with more than moderate erythema in only 14/97 patients. Thermal burns occurred in 44/97 patients, generally at sites where pain sensation was decreased, and therefore they did not cause much inconvenience. In the 19 patients who survived more than 2 years, no late radiation damage was observed. When patients who received a "high dose" (greater than 29 Gy and hyperthermia) were compared with those who received a "low dose" (less than 29 Gy and hyperthermia), a higher complete response rate was observed in the high dose group (58% vs. 24%), whereas no difference in acute toxicity was found. We conclude that reirradiation with 8 x 4 Gy in combination with hyperthermia twice weekly is a safe, effective and well tolerated method for palliative treatment of patients with breast cancer recurring in previously irradiated areas.

Important prognostic factors influencing outcome of combined radiation and hyperthermia

Clinical experience with combined local-regional hyperthermia and radiation therapy has been rapidly accumulating over the past few decades. Its superior efficacy to the use of radiation alone has been demonstrated in several retrospective and prospective reports in the literature. It is evident now that there are several important factors that will influence the final outcome of the treated patients. The parameters that will be discussed in this paper include: I. Pretreatments factors: 1. tumor dimension 2. tumor histology 3. tumor site. II. Treatment factors: 1. radiation therapy dose 2. hyperthermia parameters: (a) thermal variables (b) number of heat treatments (c) sequence of hyperthermia and radiation treatments (d) hyperthermic device. Finally, evaluation of response and complications will also be discussed. The importance of abiding by an accepted reporting system will be emphasized, and clarification of times at which response assessments were made will also be discussed. With the availability of longer term follow-up, use of an actuarial method of reporting becomes more important. The future of hyperthermia and radiation remains very promising but a lot of questions still need to be answered by well-conducted and reported clinical trials.

Hyperthermia in cancer therapy

Tumor hyperthermia is a rediscovered technique of oncotherapy which has confirmed value in many studies on cell cultures, rodent and mammalian tumors as well as first investigations on patients with tumors. The biological basis for using heat in the treatment of cancer is well established. Various direct and indirect mechanisms are significant for the effect of hyperthermia on tumor tissue. Whereas there are already extensive studies on the direct effects of hyperthermia on DNA, RNA, and protein synthesis, energy metabolism, and the membrane properties of tumor cells, the indirect effects have only been investigated more closely in recent years. These are likewise important for the damage to the tumor tissue and are mediated above all via alterations in the microcirculation and the environment. The recently gained increasing significance of this new technique in combination with other treatment modalities is well documented. Technical problems of heat application must be overcome, especially in deeper tumors and problems of thermometry must be solved in order to be able to apply tumor hyperthermia not only to selected advanced or recurrent tumors, but in order to use it as the fourth pillar of tumor therapy besides surgery, radiotherapy and chemotherapy. This article considers the biological basis and important aspects of hyperthermia therapy in combination with radiotherapy and chemotherapy.

Laser Doppler flowmetry in subepidermal tumours and in normal skin of rats during localized ultrasound hyperthermia

Laser Doppler flowmetry has been applied to normal skin and to subepidermal tumours during localized ultrasound hyperthermia in the rat. In normal skin, 40 degrees C hyperthermia only induced a marginal increase in the red blood cell flux. Significant increases occurred after 20 min at 42 degrees C and after 4 min at 44 degrees C. During 44 degrees C hyperthermia maximum fluxes were reached after 24 min. Thereafter, the flow declined and finally approached preheating values. In contrast, in subepidermal tumours 40 degrees C hyperthermia on the average induced a slight decrease of the flux. During 42 degrees C hyperthermia a significant flow decrease was found after 40 min of heating. Following a transient increase in the laser Doppler flow during the heating-up period, 44 degrees C hyperthermia led to a significant impairment of the flux after 24 min. A total shutdown of RBC flux was observed in about 30 per cent of the tumours at 44 degrees C. Upon elevated tissue temperatures, pronounced inter-tumour variabilities in the time- and temperature-dependent changes of RBC flux were observed. Rhythmic oscillations of the RBC flux were found in some subepidermal tumours (0.40 +/- 0.05 cycles/min). Upon heating, these periodic flow variations slowed down significantly (0.20 +/- 0.04 cycles/min), whereas in normal skin the frequency of the flow fluctuations increased.

[Microvascular perfusion of malignant tumors--a therapeutic measure for enhancing the hyperthermia effect?]

Hypoxic regions of malignant tumors are poorly vascularized; they appear to be more susceptible to hyperthermia in vivo than tumor cells in vitro after an exposure to heat. In an attempt to explain this discrepancy, changes of microcirculatory flow in the tumor have been proposed as key mechanism for destroying adjacent tumor cells in particular. This study was conducted to define the impact of the microcirculation on tumor destruction after local hyperthermia. A transparent chamber was implanted in the dorsal skin fold and two permanent indwelling catheters placed in carotid artery and jugular vein of 45 Syrian golden hamsters. 48 h later, 4 X 10(4) cells of the amelanotic melanoma A-Mel-3 were implanted into the s.c. tissue covered by the chamber. 5 days later, at a tumor diameter of 3 mm, the microcirculation of this tumor was studied using intravital microscopy, a platinum multiwire electrode, television as well as micropuncture techniques for the determination of local PO2, microcirculatory blood flow and microvascular pressure. Measurements were taken at 30 degrees C and 15 min after reaching a tumor temperature of 35 degrees and 42.5 degrees C. When heating up the melanoma to 35 degrees C, an increase in capillary perfusion by 35% was noted. With an apparent maximum of capillary perfusion, there was no change in arteriolar pressure but a significant drop in venular pressure from 11.0 +/- 1.1 to 7.4 +/- 0.6 mmHg resulting in an increase of the arteriolo-venular pressure gradient while the systemic pressures were unchanged. At a tumor temperature of 42.5 degrees C, prestasis and stasis became apparent in capillaries and collecting venules. This was accompanied by a rise in capillary and venular pressure by 5 mmHg. At the same time, pronounced tissue hypoxia was present in the tumor with more than 50% of the values within the hypoxic range between 0 and 5 mmHg. Despite tissue hypoxia, the constriction of all tumor arterioles became evident 15-30 min after reaching a tumor temperature of 42.5 degrees C. The deterioration of tumor oxygenation was associated with damage of tumor cells such as swelling and destruction of mitochondria which was seen under the electron microscope. After 40 min at 42.5 degrees C, the attenuation of the endothelial lining around the entire vascular perimeter was seen in tumor capillaries.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of multiple heatings on the blood flow in RIF-1 tumours, skin and muscle of C3H mice

The effect of one to five multiple heatings on blood flow in the RIF-1 tumour, skin and muscle of C3H mice was studied. When heated for 1 h at 43.5 degrees C the tumour blood flow increased 1.8 times, and rapidly decreased after the heating to less than half the control value. The 2nd-5th heatings at 43.5 degrees C, applied at 1- or 3-day intervals, caused no further significant change in the tumour blood flow. In the skin and muscle the blood flow increased 5 times when heated for 1 h at 43.5 degrees C, and remained at 1.5-2.0 times of control for 1-3 days after the heating. The blood flow in the skin and muscle, particularly in the skin, was further increased by the 2nd-5th heatings applied at 3-day intervals, but not at 1-day intervals, albeit the additional increase was very small. Consequently, whereas the tumour blood flow was 5-6 times greater than that in the skin and muscle before heating, it was only about 1.5-2.0 times greater than that in the skin and muscle during the 1st heating. The tumour blood flow became more or less similar to the normal tissue blood flow during the 2nd-5th heatings given at 3-day intervals. The decline in the vascular response in normal and tumour tissues to the 2nd-5th heatings suggested development of vascular thermotolerance.

Effect of temperature on blood flow and hypoxic fraction in a murine fibrosarcoma

The effect of hypo to hyperthermic temperatures on tumor blood flow and hypoxic cell fractions was studied in a murine fibrosarcoma transplanted in the hind leg of anesthetized mice. The blood flow to the tumor was assessed by the determination of the uptake of Thallium-201; the hypoxic cell fraction was estimated from cell survival curves derived from data based on lung colony assay. Over a temperature range of 18 degrees to 46 degrees C, the maximal blood flow occurred at 35 degrees C which was approximately two times greater than that at room temperature (24 degrees C) or at 39 degrees C. The hypoxic cell fraction at 35 degrees C was 11%, and was significantly less than that at 24 degrees C or at 39 degrees C. The hypoxic cell fractions at 24 degrees C and at 39 degrees C were 45% and 32%, respectively. These results suggest that the optimal radiation sensitivity of peripherally located tumors can be obtained by warming the tumors to temperatures where maximal blood flow and minimal hypoxic cell fraction occur.

Retrospective analysis of the response of tumours in patients treated with a combination of radiotherapy and hyperthermia

One hundred and twelve patients with various carcinomas were treated on 112 fields with radiotherapy and hyperthermia, using non-invasive techniques. Radiotherapy dose ranged from 13-70 Gy (except for one patient receiving hyperthermia alone) with a mean of 28.6 Gy. The combined treatment was primarily aimed at giving palliation; 79 per cent of the patients had received previous irradiation on the same area. Hyperthermia was given twice weekly following radiotherapy. From the temperature data collected, 12 different parameters expressing the hyperthermia 'dose' were derived. The various parameters for both treatment modalities, i.e. radiotherapy and hyperthermia, and some of the tumour parameters were statistically evaluated with respect to their influence on tumour response. The overall response rate was 87 per cent including 33 per cent complete response. The complete response rate increased with increasing radiotherapy total dose, i.e. from 23 per cent (14-25 Gy) and 38 per cent (28-36 Gy) to 60 per cent (greater than 38 Gy). A positive correlation between the tumour temperature parameter representative of the coldest spot in the tumour, and the level of response was found. Achievement of complete response appeared also to be determined to a considerable extent by radiotherapy total dose as well as tumour volume. The correlation between response level and the minimum hyperthermia dose parameters persisted, however, after correction for the influence of tumour volume and radiotherapy total dose. These results support the opinion that higher tumour response rates can be achieved by increasing the hyperthermia treatment level at the coldest spot in the tumour.

Tumour microcirculation as a target for hyperthermia

A great number of investigators have, independently, shown that tumour blood flow is affected by a hyperthermic treatment to a larger extent than normal tissue blood flow. While the majority of the studies on experimental tumours show a decrease and even a lapse in blood flow within the microcirculation during or after hyperthermia, the data on human tumours are less conclusive. Some of the investigators do not find a decrease in circulation, while others do. Obviously, this is an important field of investigation in the clinical application of hyperthermia because a shut down of the circulation would not only facilitate tumour heating (by reducing venous outflow, this reducing the 'heat clearance' from the tumour), but would also facilitate tumour cell destruction. The same holds for alterations that occur subsequently to the circulatory changes, like a heat-induced decrease of tissue pO2 and pH. If the frequently reported circulatory collapse of the tumour circulation could selectively be stimulated by, e.g. acidification or by vasoactive agents, hyperthermic treatment of patients would possibly be greatly facilitated and intensified. In hyperthermic tumour therapy a number of complex processes and interactions takes place, especially when the treatment is performed in combination with radiation therapy. One of them represents the group of processes related to the random probability of cell sterilization of individual tumour cells resulting in exponential survival curves which are typically evaluated with e.g. cell survival assays. This aspect has not been the issue of this paper. The other group of processes deals with the heat-induced changes in the micro-physiology of tumours and normal tissues which, as discussed before, may not only enhance the exponential cell kill, but which may also culminate in vascular collapse with the ensuing necrosis of the tumour tissue in the areas affected. If this takes place, a process of bulk killing of tumour cells results, rather than the random type of cell sterilization. At present it is not clear to what extent the various separate mechanisms contribute to the total effect of tumour control. With all these considerations in mind, one should be aware of the fact that effects, secondary to heat-induced vascular stasis alone will never be efficient enough to eliminate all tumour cells, even though a heat reservoir is created. This is so because some malignant cells will inevitably have already infiltrated normal, surrounding structures and will therefore not be affected by changes in the tumour vascular bed.(ABSTRACT TRUNCATED AT 400 WORDS)

Tumour growth delay, cell inactivation and vascular damage following hyperthermic treatment of a human melanoma xenograft

The effect of hyperthermia at 42.5 degrees C on a human melanoma xenograft in athymic mice was studied. The tumours were heated in vivo in a water-bath. Tumour growth delay and single-cell survival in vitro were used as endpoints. Qualitative information regarding heat-induced vascular damage was obtained from microangiographic analysis. Tumour growth delay after a given treatment was considerably longer than that expected from the cell survival measured in vitro immediately after treatment. Experiments in which removal of the tumours was delayed revealed that tumour cells were continuously dying for at least 24 hr after heat treatment. The volume of the tumour vasculature was considerably reduced after treatment, suggesting that the delayed cell death was attributed to vascular occlusion which resulted in an insufficient supply of oxygen and nutrients and an increased tumour acidity. The present work indicates that at least two mechanisms may be involved in heat-induced cell inactivation in our xenograft: firstly, direct cytotoxic effect of heat; secondly, indirect effect following heat-induced vascular damage.

The induction of thermotolerance in the ear of the mouse by fractionated hyperthermia

The development of thermotolerance in ears of mice was investigated after fractionated hyperthermia. Ears were heated at 43.5 degrees C by immersion in a water bath and the response was measured in terms of the heating time required to cause thermal necrosis in 50% of the ears (NT50). Three types of treatment were given: (1) single treatments, for which the NT50 was 42 minutes; (2) priming treatments, which caused little visible effect but induced thermotolerance. These treatments were given as 1-10 daily fractions, the total heating time ranging from 20-630 minutes; (3) test treatments which were given at various times after priming and were varied to estimate the NT50. Thermotolerance was defined as an increase in the test NT50 for preheated ears relative to the single treatment NT50. It has been suggested that thermotolerance induced by a single priming treatment may be increased by giving additional heat treatments which would not be tolerated by normal cells. In the mouse ear, the maximum thermotolerance induced by a single priming treatment of 20 min at 43.5 degrees C was seen after 24 hr when the test NT50 was about 2.5 times the single NT50. The effect of giving up to nine additional daily treatments of 70 min, each of which would cause necrosis in ears that had not received prior hyperthermia, was measured. The maximum thermotolerance observed was equal to that after a single 20 minute priming treatment but thermotolerance decreased as the number of 70 min treatments was increased from four to nine. The effects of repeating a treatment (20 min or 5 min) which was tolerated by normal ears and induced maximal or less than maximal resistance were compared. The interval between each fraction (24 hr or 12 hr respectively) was equal to the time at which maximal thermotolerance was observed after one treatment. For each regimen, the degree of resistance seen after 2 to 10 exposures was similar to that after the appropriate single treatment. This resistance was maintained throughout the course of priming treatment and decayed after the last fraction. Thus for this regimen, thermotolerance depended on the duration of each treatment rather than on the number of treatments given.

Time-temperature relationship for hyperthermia induced stoppage of the microcirculation in tumors

The time-temperature dependence for microcirculation stoppage was investigated for the Rhabdomyosarcoma BA1112 growing in observation chambers ("sandwich chambers"). The tumor microcirculation could be observed continuously during the treatment, and the condition of the microcirculation was recorded every 15 minutes as "flowing" or "stoppage". By using large numbers of tumors, the 50% stoppage time (ST50) could be derived for the four temperatures investigated: 42 degrees, 42.5 degrees, 43 degrees and 43.5 degrees C. The respective ST50 values were 226, 152, 101 and 70 minutes. The results can be expressed as a log-linear relationship with a slope value of 0.4551 +/- 0.03 (SD) per degree centigrade. This value probably does not differ significantly from the "t 1/2 for every degree C" rule that has been found for the thermal response of many biological systems.

Physiological mechanisms in hyperthermia: a review

In experimental animal systems, hyperthermia at therapeutic temperature (43-45 degrees C) causes a profound increase in blood flow in normal tissues while it induces only meager and temporal increases in blood flow in tumors. A severe vascular occlusion and hemorrhage usually follows the increase in blood flow in the tumors at the above temperatures. Another pronounced physiological change in tumors by heat is a prompt decrease in intratumor pH. The decrease in intratumor pH would accentuate the thermokilling of tumor cells and also possibly inhibit repair of thermodamage and development of thermotolerance in tumors. The temperature in tumors may rise higher than that in normal tissues during heating because of inefficient heat dissipation from the tumor as a result of decrease blood flow or vascular occlusion. Thus, the differential effects of heat on vascular function and pH in tumors and normal tissues may result in a greater damage in tumors than in surrounding normal tissues. Further investigation is urgently needed to find out whether similar physiological changes occur in human tumors and normal tissues by hyperthermia.

Blood flow changes in transplanted mouse tumours and skin after mild hyperthermia

The influence of moderate hyperthermia on the vascular perfusion of four different tumour types and of normal mouse skin was investigated. The 86Rb extraction technique was used to measure changes in perfusion relative to total cardiac output, both during and after a one hour heat treatment at 42.5 degrees C. Perfusion of the SA FA tumour increased slightly during the first 30 minutes of heating but had returned to control values by the end of a 1 hour heating period. After heating, the relative perfusion of all four tumour types fell significantly below control values by 24 hours and remained low for 1-2 days (SA FA tumour) before returning to control values. Relative perfusion of normal skin was progressively increased during heating and remained elevated for 24 hours after the end of treatment before returning to control levels.

Blood flow and intravascular volume of mammary adenocarcinoma 13726A and normal tissues of rat during and following hyperthermia

The effects of hyperthermia on blood flow and intravascular volume were studied in mammary adenocarcinoma 13762A growing subcutaneously in the leg of Fischer F344 rats. The blood flow was determined using microspheres labelled with 125I, and the blood volume was determined using red blood cells labelled with 51Cr. At the end of heating with water bath at 43.5 degrees C for 1 hour, there was a marked elevation of 51Cr in tumor. The 125I content in tumor also was mildly elevated. Histologically there was a greater number of patent blood vessels per unit area, and they were dilated and hyperemic. In addition, widespread and diffuse hemorrhage could be seen. It appeared, therefore, that the increased 51Cr and 125I label in the tumors immediately after heating was, at least in part, a result of leakage of the labels to extravascular space in addition to possible vasodilation and increased blood flow. At 1 and 5 hours after heating, tumor blood flow was considerably reduced, and at 16 hours both tumor blood flow and blood volume were considerably reduced. Histological examination demonstrated that the tumor blood vessels remained dilated and hyperemic after heating. The effect of heat on blood flow and blood volume in the skin and muscle adjacent to the tumors was also investigated. Blood flow and blood volume in the surrounding normal tissues were significantly elevated at the end of heating. Blood flow was relatively unchanged at 1, 5, and 16 hours after heating, but blood volume was reduced to about one half. These findings indicate that hyperthermia may induce greater damage to vasculature of tumors than normal tissues, and that vascular damage in tumors may take some time to express itself following moderate hyperthermia.

The influence of a heat pulse on the thermally induced damage to tumour microcirculation

The effect of an initial short period of higher-temperature heat application on the stoppage of the microcirculation in the experimental rhabdomyosarcoma BA1112 in 'sandwich' chambers was investigated. The treatment consisted of an initial heat pulse of 45 degrees C for 10 min which was followed by a continuous exposure at 42.5 degrees C for 3 hr. Using the 't1/2 per degrees C' rule, the time equivalent of the heat pulse was 94 min. Taking this contribution into account, the derived 50% stoppage time of 151 min is essentially the same as the 152 min observed for 42.5 degrees C only treatments. The data therefore indicate that the effect of a heat pulse in the treatment can be accounted for by the customary correction procedure of one time exposure doubling per degrees C. However, it appeared that the microcirculation in the surrounding tumour bed was impaired more than was expected by this treatment.

The effect of elevated temperature on the vasculature of mouse jejunum

The effect of elevated temperature on mouse jejunal vasculature was investigated. Both local and lower-body heating were employed, using a hot water bath; heating time was kept constant at 1 hour, bath temperatures ranging from 40.0 degrees C to 43.0 degrees C. Animals were sacrificed after heating, the erythrocytes were stained with benzidine and H2O2 and the blood vessels revealed by mounting in a clearing resin. The earliest damage seen was the disappearance of capillaries, followed by loss of progressively larger vessels. Loss is interpreted as destruction, not merely as interruption of blood flow. A gradient of sensitivity occurs from the inner layer of the jejunum to the outer, the threshold heating temperature required to produce vascular damage being lowest at the inside. Neither temperature gradient, nor early release of gastric juice from the stomach, appears responsible for this differential response. The mean length of intact venous tree was employed as a parameter for assessing the damage.

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.

Oxygenation of malignant tumors after localized microwave hyperthermia

The oxyhemoglobin saturation (HbO2) of single red blood cells within tumor microvessels (diameter: 3-12 micrometers) of DS-Carcinosarcoma was studied using a cryophotometric micromethod. In untreated control tumors (mean tissue temperature approx. 35 degrees C) the measured values scattered over the whole saturation range from zero to 100 sat. %, the mean being 51 sat. %. Upon heating at 40 degrees C for 30 min, the oxygenation of the tumor tissue significantly improved as compared with control conditions. After 40 degrees C-hyperthermia a mean oxyhemoglobin saturation of 66 sat. % was obtained. In contradistinction to this, after 43 degrees C-hyperthermia the tumor oxygenation was significantly lower and reached a mean HbO2 saturation value of 47 sat. %. A further temperature rise to 45 degrees C caused the oxygenation to drop drastically (mean oxyhemoglobin saturation value: 24 sat. %). This is due to a severe restriction of nutritive blood flow. The changes in tumor oxygenation after hyperthermia seem to be predominantly mediated through changes in tumor blood flow, including tumor microcirculation, which showed a similar temperature dependence. Metabolic effects probably play a minor role in the oxyhemoglobin saturation distribution within tumor microvessels.

Local hyperthermia and irradiation in cancer therapy

The preliminary experience at the Mallinckrodt Institute of Radiology with hyperthermia and irradiation is reported and current issues in clinical application of heat are reviewed. Twenty-nine lesions were treated with 400 rad fractions given every 72 hr (twice weekly) for a total dose of 2400 to 4000 rad followed by hyperthermia (1450-MHz or 915-MHz microwaves, 42.0 degrees -43 degrees, 90 min, every 72 h). Eight of 12 recurrent epidermoid carcinomas of the head and neck showed complete regression (67%) and one more than 50% response. Of 5 metastatic melanoma nodules treated with irradiation an hyperthermia, 4 (80%) showed complete regression of the tumors an 1 almost complete response. Of 9 recurrent adenocarcinoma of breast nodules in the chest wall treated with 3200 to 4000 rad 5 lesions exhibited complete regression and 2 others about 80%. Of 6 lesions treated with 1500 rad and hyperthermia (RTOG protocol), 2 metastatic melanomas showed complete regression (CR) and 3 tumors exhibited partial regression. Of the 35 sites treated, 4 (11%) developed blisters, 7 (20%) erythema only, 3 (8%) moist desquamation and 27 (77%) dry desquamation. Additional clinical trials are in progress to assess the potential value of hyperthermia alone or combined with irradiation in the treatment of selected cancer patients.