Thermal distributions in a water bath heated mouse tumor

Accurate Three-Dimensional Thermal Dosimetry and Assessment of Physiologic Response Are Essential for Optimizing Thermoradiotherapy

Simple Summary

Many clinical trials have shown benefit for adding hyperthermia (heat) treatment to radiotherapy. Despite overall success, some patients do not derive maximum benefit from this combination treatment. Tumor hypoxia (low oxygen concentration) is a major cause for radiotherapy treatment resistance. In this paper, we examine the question of whether hyperthermia reduces hypoxia and, if so, whether reduction in hypoxia is associated with treatment outcome. The review is focused mainly on several clinical trials conducted in humans and companion dogs with cancer treated with hyperthermia and radiotherapy. Detailed measurements of temperature, hypoxia and perfusion were made and compared with treatment outcome. These analyses show that reoxygenation after hyperthermia occurs in patients and is related to treatment outcome. Further, reoxygenation is most likely caused by variable intra-tumoral temperatures that improve perfusion and reduce oxygen consumption rate. Directions for future research on this important issue are indicated.

Abstract

Numerous randomized trials have revealed that hyperthermia (HT) + radiotherapy or chemotherapy improves local tumor control, progression free and overall survival vs. radiotherapy or chemotherapy alone. Despite these successes, however, some individuals fail combination therapy; not every patient will obtain maximal benefit from HT. There are many potential reasons for failure. In this paper, we focus on how HT influences tumor hypoxia, since hypoxia negatively influences radiotherapy and chemotherapy response as well as immune surveillance. Pre-clinically, it is well established that reoxygenation of tumors in response to HT is related to the time and temperature of exposure. In most pre-clinical studies, reoxygenation occurs only during or shortly after a HT treatment. If this were the case clinically, then it would be challenging to take advantage of HT induced reoxygenation. An important question, therefore, is whether HT induced reoxygenation occurs in the clinic that is of radiobiological significance. In this review, we will discuss the influence of thermal history on reoxygenation in both human and canine cancers treated with thermoradiotherapy. Results of several clinical series show that reoxygenation is observed and persists for 24–48 h after HT. Further, reoxygenation is associated with treatment outcome in thermoradiotherapy trials as assessed by: (1) a doubling of pathologic complete response (pCR) in human soft tissue sarcomas, (2) a 14 mmHg increase in pO2 of locally advanced breast cancers achieving a clinical response vs. a 9 mmHg decrease in pO2 of locally advanced breast cancers that did not respond and (3) a significant correlation between extent of reoxygenation (as assessed by pO2 probes and hypoxia marker drug immunohistochemistry) and duration of local tumor control in canine soft tissue sarcomas. The persistence of reoxygenation out to 24–48 h post HT is distinctly different from most reported rodent studies. In these clinical series, comparison of thermal data with physiologic response shows that within the same tumor, temperatures at the higher end of the temperature distribution likely kill cells, resulting in reduced oxygen consumption rate, while lower temperatures in the same tumor improve perfusion. However, reoxygenation does not occur in all subjects, leading to significant uncertainty about the thermal–physiologic relationship. This uncertainty stems from limited knowledge about the spatiotemporal characteristics of temperature and physiologic response. We conclude with recommendations for future research with emphasis on retrieving co-registered thermal and physiologic data before and after HT in order to begin to unravel complex thermophysiologic interactions that appear to occur with thermoradiotherapy.

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.

Localized versus regional hyperthermia: comparison of xenotransplants treated with a small animal ultrasound system and waterbath limb immersion

The response of xenotransplants were compared with waterbath immersion vs focal ultrasound (US) hyperthermia using tumour growth delay, immunhistochemistry and histopathology assays. Waterbath hyperthermia was performed by limb immersion. Precautions were taken to minimize total body heating by surrounding the mouse with plastic insulators. Thermometry was performed with clinical-grade, 20-gauge needle thermocouples and monitored with a Labthermics unit. Significant differences in cytotoxicity between ultrasound and waterbath treatment of tumors at 43 degrees C were observed as determined by TUNNEL assay. Conversely, contralateral (non-treated) tumours in animals treated with similar temperature demonstrated no significant differences between modalities. Western blot analysis revealed increased hsp70 induction at 43 degrees C in waterbath vs focal ultrasound hyperthermia. Comparison of tumour growth delay between tumours heated with waterbath vs ultrasound at 43 degrees C but not at 41 degrees C revealed significant differences. This is the first study comparing localized vs regional hyperthermia using the small animal ultrasound system (SAHUS) delivery system. Consistent ultrasound hyperthermia can be achieved throughout a xenotransplant. At equivalent temperature of 43 degrees C for 60?min, waterbath hyperthermia demonstrated greater local response vs ultrasound hyperthermia.

Therapeutic outcome and side-effects after radiotherapy, chemotherapy and/or hyperthermia treatment of head and neck tumour xenografts

The aim of the study was to optimise the still unsatisfactory therapeutic results in head and neck cancer by studying the results and the side-effects of radiotherapy, chemotherapy and/or local hyperthermia treatment of human tumour xenografts. Mice carrying human-derived head and neck squamous cell carcinoma xenografts with a mean volume of 100 mm(3) received 5x2 Gy, cisplatin or ifosfamide and/or local hyperthermia at 41/41.8 degrees C. Haematocrit and tumour volumes were determined two or three times per week, respectively, until day 25 or day 60. At day 60, the highest number of complete remissions (CRs) (80%) was observed in the triple modality therapy group with radiation, local hyperthermia at 41.8 C and cisplatin at a dosage of 2 mg/kg body weight (b.w.). Therapeutic side-effects were moderate weight loss and a mild anaemia. Thus, with regard to the long-term tumour-free survival, the most effective treatment was the combination of radiotherapy, cisplatin and local hyperthermia at 41.8 C.

Evaluation of temperature increase with different amounts of magnetite in liver tissue samples

RATIONALE AND OBJECTIVES

The biologic effects of magnetically induced heating effects using iron oxide, magnetite, were examined in vitro in liver tissue samples as a first step toward potential applications in cancer therapy.

METHODS

For the determination of the temperature profile around an iron oxide sample, a cylinder containing 170 mg of magnetite was constructed and placed into pureed liver tissue from pig, together with thermocouples of copper and constantan wires positioned at defined distances from it. Temperature measurements were performed during the exposure to an alternating magnetic field (frequency: 400 kHz; amplitude: approximately 6.5 kA/m) generated by a circular coil (90 mm of diameter). Moreover, variable amounts of magnetite (dissolved in approximately 0.2 mL physiologic saline) were injected directly into carrageenan gels. During the exposure to a magnetic field for 4 minutes the temperature increase was determined in the area of iron oxide deposition using a thermocouple. Additionally, variable amounts of magnetite were injected directly into isolated liver tissue samples (diameter: 20 mm; height: 30 mm) and exposed to a magnetic field for 2 minutes. The extent of the induced macroscopically visible tissue alterations (light brown colorations caused by heating) was examined by means of volume estimations. The degrees of cellular necrosis were investigated by histopathologic studies.

RESULTS

The temperature profile around a magnetite cylinder revealed a significant decrease of temperature difference between the beginning and the end of heating, depending on increasing distance from the sample center. The extent of the temperature difference correlated with increasing heating time. No significant variations of temperature were observed at a distance of approximately 12 mm from the sample center. A good correlation (r = 0.98) between the injected amounts (31 to 200 mg) and the temperature increase since the start of heating (6.8-33.7 degrees C) in the area of iron oxide deposits was detected. The volume of damaged liver tissue was approximately seven times higher than the injected volume of iron oxide dispersion. Histologically different degrees of cellular necrosis were observed.

CONCLUSIONS

The parameters determined in this article show that iron oxides are able to induce considerable heating effects in the surroundings. After an adequate optimization of the technical procedure, it is conceivable that heating properties of magnetites can be used in future cancer treatments.

Radiofrequency capacitive heaters: the effect of coupling medium resistivity on power absorption along a mouse leg

A capacitive radiofrequency source in conjunction with a temperature-controlled electromagnetic coupling medium has the potential of delivering uniform heating distributions in a mouse leg for experimental studies to investigate the use of hyperthermia as a treatment for cancer. The system has been adopted by a number of groups who have confirmed that uniform temperatures can be achieved in the presence of blood flow along a one-dimensional line which extends between the plates across the leg. In this paper, a simple mathematical model is presented and verified experimentally to demonstrate that parallel-plate capacitive radiofrequency heaters produce an inherent absorbed power distribution along the leg which is determined by the impedances across the loads. Hence, the thicker or thinner regions of the leg can be preferentially heated by using a coupling medium with lower or higher salinity, respectively. Uniform power absorption along the mouse leg required that the coupling medium had equivalent electrical properties to those of tissue.

Effects of glutathione or polyamine depletion on in vivo thermosensitization

Investigations with the melphalan-sensitive and -resistant human rhabdomyosarcoma xenografts TE-671 and TE-671 MR were performed to examine the effect of glutathione and polyamine modulation on thermosensitivity. Regimens of intraperitoneally injected and orally administered buthionine sulfoximine were utilized to achieve glutathione depletion to 8.7% and 13% of control levels in TE-671 and TE-671 MR, respectively. Animals treated with L-buthionine-S,R-sulfoximine and 42 degrees C or 43 degrees C hyperthermia for 70 min showed no detectable growth delays beyond those observed for hyperthermia alone. Hyperthermia at 42 degrees C of disaggregated TE-671 and TE-671 MR xenografts following growth in short-term culture was performed following preincubation with buthionine sulfoximine or 0.9% saline. Buthionine sulfoximine-mediated glutathione depletion produced a significant increase in hyperthermia-induced cytotoxicity only with TE-671 MR at 43 degrees C. Polyamine depletion was achieved with a 7-day orally administered course of MDL 72.175DA [(2R,5R)-6-heptyne,5-diamine dihydrochloride], an irreversible inhibitor of ornithine decarboxylase. Although this treatment caused significant depletion of intracellular putrescine and spermidine levels, spermine levels remained relatively unaffected. No significant growth delays were observed in either xenograft line for animals treated with MDL 72.175DA or MDL 72.175DA plus hyperthermia as compared with untreated controls. These results contrast with previous work performed in vitro showing synergism between glutathione or polyamine depletion and hyperthermia, and indicate that further studies are needed.

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.

Enhancement of melphalan-induced gastrointestinal toxicity in mice treated with regional hyperthermia and BSO-mediated glutathione depletion

Both hyperthermia and glutathione depletion have been shown to increase the antineoplastic activity of melphalan. Investigations were carried out to define the toxicity and activity of melphalan given in conjunction with local (right hind limb) hyperthermia and L-buthionine-SR-sulphoximine (BSO)-mediated glutathione depletion to athymic mice bearing the melphalan-resistant human rhabdomyosarcoma xenograft TE-671 MR. Administration of 0.5 of the 10% lethal dose of melphalan to mice treated with BSO and hyperthermia (42 degrees C for 70 min) resulted in a 53% mortality rate. The mortality rates for mice treated with melphalan alone (2.5%), hyperthermia alone (0%), melphalan plus BSO (13.5%), melphalan plus hyperthermia (12.0%) and BSO plus hyperthermia (0%) were substantially lower than triple therapy. Histological examination of kidney, liver, colon, and small intestine sections taken from non-tumour-bearing animals revealed a marked increase in damage to the small intestine (cryptal necrosis and epithelial denudement) in animals receiving triple therapy compared with animals receiving any other treatment combination. Gavage administration of sterile water (1 ml twice a day) completely prevented mortality in animals receiving triple therapy. Treatment of tumour-bearing animals with triple therapy plus gavage demonstrated a statistically significant increase in tumour growth delay compared with animals receiving any other treatment combination.

In vivo 31P NMR study of combined hyperthermia and photodynamic therapies of mammary carcinoma in the mouse

Although the sequence and time interval effects of combined photodynamic therapy (PDT) and hyperthermia tumor treatments have been studied using survival curves, tumor regrowth, and cloning assays, the metabolic response to combined treatment measured by nuclear magnetic resonance (NMR) spectroscopy has not yet been clarified. In this study, mammary carcinoma in the flank of C3H mice was subjected to PDT (12.5 mg/kg Photofrin II, 632 +/- 1 nm at 200 J/cm2) and water bath hyperthermia (43.5 degrees C, 30 min) with no delay or 4 h delay between treatments. In vivo 31P-NMR spectroscopy was employed to measure energy metabolism and pH of the tumors before and serially after treatment for up to 1 week. The data revealed significant differences in the time course of high energy phosphate levels between treatment combinations, which may reflect the biological effectiveness of the combined treatments. Our observations indicate that 31P-NMR spectroscopy can be used to evaluate the metabolic response of tumors to treatment with combined PDT and hyperthermia.

Development of lymph node and pulmonary metastases after local irradiation and hyperthermia of footpad melanomas

C57BL/6 mice with syngeneic B16-F10 melanomas were treated 7 days after tumor inoculation into the footpad with local hyperthermia (HT) of 43.5 degrees C for 90 min. A combination of local 30 Gy X-irradiation (XRT) given 2, 4 or 12 h after HT cured the primary tumor in 34/35 mice, with irreversible damage to normal foot tissues in most of the animals. When 7.5, 10 or 15 Gy XRT were delivered 4, 18 or 24 h after HT, there were only a small number of cures and also a much smaller incidence of irreversible normal tissue damage. HT alone resulted in a significant (P less than 0.001) increase in metastases to regional lymph nodes (RLN) and the lungs. The 'curative' doses of combined XRT and HT resulted in a significant (P less than 0.001) decrease in metastasis to RLN and to the lungs. Conversely, subcurative doses of combined therapy resulted in an increase in RLN and lung metastasis (P less than 0.001). Abdominal lymph node metastasis, not usually seen in control mice, is markedly increased after HT alone or in combination with subcurative XRT (P less than 0.001). The overall survival of mice treated with HT alone is decreased (P less than 0.0028). The survival of mice treated with HT followed 4, 18 or 24 h later with 10 Gy XRT is further decreased (P less than 0.0025). These data show that subcurative HT, or XRT plus HT, increases the incidence of spontaneous metastasis in this syngeneic mouse melanoma model. Curative doses prevent this effect on metastasis, but there is an unacceptable incidence of irreversible damage to the tumor-bearing foot. The cause(s) of this phenomenon are not known.

A comparison between the effect of step-down heating in a tumour and a normal tissue in vivo

A comparison between the effect of step-down heating (SDH) obtained in a C3H mammary carcinoma grown in the feet of CDF1 mice and the skin of normal CDF1 feet is presented. Water-bath heating was used, and SDH was obtained by giving a 44.7 degrees C/10 min treatment followed by heating at 42.2 degrees C for variable times. Single heating at 42.2 degrees C and step-up heating (SUH), i.e. 42.2 degrees C followed by 44.7 degrees C/10 min, were used as controls. The endpoint was the heating time at 42.2 degrees C to obtain either a definite tumour growth time (TGT50) or a specific skin score level (RD50) in 50% of the animals. The effect of SDH and SUH was quantified by the step-down ratio (SDR), calculated as the ratio of the heating times at 42.2 degrees C to obtain the specific endpoint. In both assays the effect of SDH was seen as a significant left shift of the SDH dose-response curve compared to the curve for single heating and SUH. For the comparison of the tumour and the normal tissue response, damage levels with comparable heating times for single heating were used. The therapeutic effect was then investigated by calculating the therapeutic gain factor (TGF), where TGF = SDR(tumour)/SDR(normal tissue). Neither SUH nor SDH gave a TGF significantly different from 1. The results suggest that SDH may be used clinically to shorten the heating time without decreasing the therapeutic effect.

Influence of limb restraint on the thermal response of bone marrow CFU-GM heated in situ

The method used to restrain anaesthetized (sodium pentobarbital) mice for in situ heating of tibial marrow affects the survival response of CFU-GM. Three methods of limb restraint, in addition to ischaemia induced by tourniquet, were examined for their relative effect on the thermal response of CFU-GM. The three methods of restraint were to secure only the toes with suture material to a submersion post in the water bath, to tape the foot, or to tape the leg. Temperatures in the lumen of the tibia were measured with a 100 micron (tip diameter) microthermocouple during representative experimental conditions. After heating in situ, bone marrow was extruded and CFU-GM cultured in standard soft agar conditions in lung-conditioned medium. The most restrictive restraining method, i.e. taping the leg, produced the greatest thermal response among the three restraining methods examined. The D0 (+/- 95% CI) of the 42 degrees C survival curve for CFU-GM was 22 +/- 4, 46 +/- 8, or 94 +/- 53 min for restraint of leg, foot, or toes, respectively. Survival reached a plateau by 100 min of heating indicative of the development of thermotolerance. The D0 of the 44 degrees C survival curve was 3 +/- 1, 6 +/- 2 and 16 +/- 6 min for restraint of leg, foot, or toes respectively. Ischaemia produced the most pronounced effect on the thermal response of tibial CFU-GM with D0 values of 2 +/- 1 or 3.6 +/- 1.5 min after exposure to 44 degrees C or 42 degrees C, respectively. The method of limb restraint affects the thermal sensitivity of CFU-GM most probably by blood flow obstruction and resultant pH decrease. Thus, precautions must be taken to ensure that limb restriction does not introduce artifacts in the hyperthermia response of normal tissues or tumours during heating in situ.

Hyperthermic "dose" dependent changes in intralesional pH

Following hyperthermia a dramatic drop in intra-lesional pH has occurred in a variety of experimental tumor systems. To date, no direct observations have been made that document the time course of such changes or the recovery from such changes over prolonged periods of time. These experiments were designed to measure intralesional pH as a function of time following "doses" of hyperthermia related to specific biological end points. All studies were conducted in the C3H-mammary carcinoma tumor model system. Intralesional temperature was continuously monitored throughout treatment and post treatment pH was measured with microelectrodes at several specific time points ranging from 4 hrs to 7 days. The pretreatment control value of mean pH was 6.73. At the TCD90 "dose" level the mean value of pH dropped to a level of 6.22 +/- .095 while following the TCD10 "dose" the value obtained was 6.55 +/- .148. Recovery of the pH to higher values followed similar time courses returning to maximum values approximately 3 days post treatment. The recovery, plateau levels of pH were however, separated by approximately .3 pH units with the higher "dose" curve always at lower values than that achieved following the lower "dose".

Radiation, hyperthermia, and their combination in treatment of chemically induced autochthonous tumors in mice

All autochthonous tumors induced chemically in the thighs of C3H/He mice showed recurrence after single X-irradiation with 20-60 Gy when they were 10 mm in diameter, although this treatment caused temporary, dose-dependent regression. Hyperthermia for 30 min at 43.0 degrees alone had little effect. However, in 2 of 16 mice, hyperthermia after irradiation at 60 Gy resulted in complete cure, i.e., survival of mice without recurrence for more than 120 days after treatment. These results indicate that the combined treatment of radiation and hyperthermia is necessary to obtain the cure of mouse autochthonous tumors.

Thermochemotherapy in vivo of a C3H mouse mammary carcinoma: single fraction heat and drug treatment

The interaction between water bath hyperthermia (43.5 degrees C) and six cancer chemotherapeutic agents in vivo was studied in a transplantable C3H mouse mammary carcinoma grown s.c. in the feet of C3D2F1/Bom mice. Due to differences in tumour regrowth rate between treatment groups, both tumour growth time (TGT) and specific growth delay (SGD) were used as effect parameters. The largest tumour response was observed when the drug was given 15 min prior to heat--this timing was used for dose-effect experiments. Enhancement ratios were the ratios of slopes of dose-effect curves subjected to linear regression analysis. The drug enhancement ratio (DER) was not significantly larger than 1.0 for LD 1% of adriamycin, 5-fluorouracil, methotrexate and vincristine. For cyclophosphamide (CTX) and mitomycin C (MMC) both DER and TER (thermal enhancement ratio) were significantly larger than 1.0. The TGT ratios (SGD ratios in parentheses) were: DER (LD 1%): CTX 1.4 +/- 0.1 (2.1 +/- 0.1), MMC 1.3 +/- 0.1 (1.4 +/- 0.1); TER (43.5 degrees C 30 min): CTX 1.6 +/- 0.1 (2.7 +/- 0.2), MMC 2.8 +/- 0.5 (3.3 +/- 0.7). The data support the choice of CTX and MMC in preference to the other drugs investigated for clinical thermochemotherapy studies.

Increased antineoplastic activity of combined hyperthermic and bleomycin treatments in an adenocarcinoma after glutathione depletion in vivo

We have earlier shown that glutathione depletion, achieved by BSO administration, only marginally increases the antineoplastic activity of hyperthermic or bleomycin treatments in C3H mammary adenocarcinoma, grown subcutaneously in the hind paw of CBA mice. In this study we evaluated the role of glutathione depletion on the antineoplastic activity of combined hyperthermic and bleomycin treatments on the same tumour model system. The activity was recorded by determination of tumour volumes 12 days after treatment and by tumour regression frequencies. When hyperthermic and bleomycin treatments were combined, their respective effects on the 12-day volume values were additive, irrespective of treatment sequence and presence of BSO. However, BSO increased significantly the tumour regression frequencies accomplished by combined hyperthermic and bleomycin treatments, particularly of hyperthermic treatments given together with or 24 h after bleomycin. It is not possible to conclude, at present, whether this effect is caused by low glutathione levels.

Heat-stimulated nitroreductive bioactivation of the 2-nitroimidazole benznidazole in vitro

Hyperthermia enhances nitroimidazole cytotoxicity, possibly through increased nitroreductive bioactivation. Using C3H/He mouse liver microsomes and KHT tumour homogenates, we have investigated the effects of temperature (33-44 degrees) on the anaerobic nitroreduction of benznidazole (BENZO) to its amine metabolite in vitro. Microsomal nitroreductase activity was unaltered after 2 hr anaerobic incubation at 37 and 41 degrees. However at 44 degrees and 47 degrees, inactivation occurred with half-lives of 68 and 17 min respectively. At 33 degrees microsomal reduction rates were 45% lower than at 37 degrees. Reduction rates were increased by 22% at 41 compared to 37 degrees, and by 0-54% depending on substrate concentration at 44 degrees. Microsomal amine formation followed Michaelis-Menten kinetics up to 41 degrees. The 4 degrees rise from 33 to 37 degrees increased the apparent Vmax by 45% (from 0.54 to 0.98 nmol min-1 mg-1 protein) with a further increase of 32% occurring at 41 degrees. Apparent Km values were unaltered. Deviation from Michaelis-Menten kinetics was seen for amine formation at 44 degrees. The kinetics of parent drug disappearance exhibited deviation from the Michaelis-Menten relationship at all temperatures studied. KHT tumour BENZO amine formation rates were also markedly increased at elevated temperatures, e.g. by 26% at 37 degrees compared to 33 degrees and by a further 35% from 42.5 to 57.4 pmol min-1 mg-1 protein over the range 37-41 degrees. In contrast to the microsomal results, tumour reduction rates were enhanced by an average of 54% (range, 26-79%) at 44 degrees compared to 37 degrees at low as well as high substrate concentrations. These results support the hypothesis that hyperthermia-enhanced nitroimidazole cytotoxicity may be a result of increased nitroreductive bioactivation.

Regional lymph node and pulmonary metastases after local hyperthermia of melanomas in C57BL/6 mice

The effects of local tumor hyperthermia on regional lymph node metastases are inconclusive. We studied the effects of hyperthermia on the incidence of popliteal, femoral, and abdominal lymph node metastases in C57BL/6 mice with primary B16 melanomas (F10 variant) growing subcutaneously in the left foot. Tumors were heated to 42.3, 43.5, and 44.2 degrees C for 90 minutes either 7 days after inoculation of 5 X 10(4) viable cells (microscopic tumor = mic) or when the tumors were approximately 3 mm in diameter (macroscopic tumor = mac). Femoral lymph node metastases occurred in 0/21 control animals and in 8/22 (36%), 11/19 (58%), and 11/17 (65%) animals whose primary tumors were heated to 42.3, 43.5, and 44.2 degrees C, respectively. For all three treatments, the increase in metastases as compared to controls was statistically significant (p less than 0.004, Fisher's exact test). The incidence of abdominal lymph node metastasis was slightly higher in the treated groups than controls. Twenty of 21 (95%) control mice developed popliteal lymph node metastases and hyperthermia-induced increases could not be demonstrated. Fifteen of 21 control mice killed 3 weeks after amputation of tumor-containing leg had pulmonary metastases with an average of 6 +/- 4 (standard deviation) lesions per affected mouse. Pulmonary metastases occurred in 22/22 (100%), 17/19 (89%), and 13/17 (76%) of mice whose tumors were heated to 42.3, 43.5, and 44.2 degrees C, respectively. The numbers of metastases for affected mice were significantly increased compared to controls for tumors heated to 43.5 and 44.2 degrees C (28 +/- 43, 43 +/- 52, 119 +/- 121, p greater than 0.02, p less than 0.006, p less than 0.002, for two sample T-test). While 0/8 mic tumors were cured 5/9 mac tumors heated to 44.2 degrees C disappeared (p less than 0.03, Fisher's exact test) and there was a growth delay in the remaining mice. Mic tumors, heated to 43.5 degrees C, had an accelerated onset of growth while mac tumors heated to this temperature had a slight growth delay. Growth of both mic and mac primary tumors heated to 42.3 degrees C was similar to controls. These results show that therapeutic and subtherapeutic local hyperthermia increases metastases to regional lymph nodes and to lungs even when primary tumor growth rate is partially or totally controlled.

Phototherapy of bladder cancer: dose/effect relationships

Hematoporphyrin derivative photodynamic therapy has very important clinical applicability in the diagnosis and treatment of transitional cell carcinoma of the bladder, but many aspects of the photodynamic process are yet to be elucidated. This paper investigates the role of dihematoporphyrin ether (DHE) concentration, the duration of light exposure, and the initial size of the tumors in the treatment of a transplantable murine transitional cell tumor system. The best results were noted in tumors less than six mm. in diameter when treated with 15 mg./kg. DHE and exposed to 100 to 180 minutes of visible light. Animals with small initial tumor size combined with higher DHE concentration and longer light exposure time were most likely to show tumor response.

Relationship between cellular glutathione and hyperthermic toxicity in mammary carcinoma in mice

This investigation evaluates in an in vivo system the possible correlation between the intracellular content of GSH and cysteine and thermal sensitivity and thermotolerance. The studies were performed on C3H mammary carcinomas, located on the hind paw of CBA mice. Intracellular thiols were measured by the HPLC technique and the degree of thermotolerance induction was determined from tumour growth rate studies. It was found that the intracellular GSH levels did not change significantly during thermotolerance induction, and that subtoxic hyperthermia induced a pronounced transient decrease in GSH down to 30 per cent of the control level. When the intracellular GSH level was decreased to the same extent, by pretreatment with D,L-buthionine-S-R-sulphoximine (BSO), thermotolerance was still inducible. Thus, the induction of heat-induced thermal resistance did not seem to be dependent on the intracellular GSH level. When hyperthermia and BSO were combined, the GSH levels were further reduced. Treatment with BSO slightly increased the toxicity of both thermotolerance-inducing and subtoxic hyperthermia. The cysteine concentrations increased several fold after BSO and heat treatments and contributed, under these conditions, to more than 25 per cent of the intracellular free reduced thiols. In general, there was no direct correlation between GSH and cysteine levels. It is concluded that thermotolerance induction does not depend on or cause changes in intracellular GSH levels and that subtoxic heat treatments induce a pronounced transient decrease in GSH concentration.