Acute changes of systemic parameters in tumour-bearing rats, and of tumour glucose, lactate, and ATP levels upon local hyperthermia and/or hyperglycaemia

Targeting hypoxia in solid and haematological malignancies

Tumour hypoxia is a known and extensively researched phenomenon that occurs in both solid and haematological malignancies. As cancer cells proliferate, demand for oxygen can outstrip supply reducing tumour oxygenation. In solid tumours this is contributed to by disorganized blood vessel development. Tumour hypoxia is associated with resistance to treatment, more aggressive disease behaviour and an increased likelihood of metastatic progression. It can be measured using both invasive and non-invasive methods to varying degrees of accuracy. The presence of hypoxia stimulates a complex cellular network of downstream factors including Hypoxia Inducible Factor 1 (HIF1), C-X-C motif chemokine 4 (CXCR4) and Hypoxia‐inducible glycolytic enzyme hexokinase‐2 (HK2) amongst many others. They work by affecting different mechanisms including influencing angiogenesis, treatment resistance, immune surveillance and the ability to metastasize all of which contribute to a more aggressive disease pattern. Tumour hypoxia has been correlated with poorer outcomes and worse prognosis in patients. The correlation between hypoxic microenvironments and poor prognosis has led to an interest in trying to therapeutically target this phenomenon. Various methods have been used to target hypoxic microenvironments. Hypoxia-activated prodrugs (HAPs) are drugs that are only activated within hypoxic environments and these agents have been subject to investigation in several clinical trials. Drugs that target downstream factors of hypoxic environments including HIF inhibitors, mammalian target of rapamycin (mTOR) inhibitors and vascular endothelial growth factor (anti-VEGF) therapies are also in development and being used in combination in clinical trials. Despite promising pre-clinical data, clinical trials of hypoxia targeting strategies have proven challenging. Further understanding of the effect of hypoxia and related molecular mechanisms in human rather than animal models is required to guide novel therapeutic strategies and future trial design. This review will discuss the currently available methods of hypoxia targeting and assessments that may be considered in planning future clinical trials. It will also outline key trials to date in both the solid and haemato-oncology treatment spheres and discuss the limitations that may have impacted on clinical success to date.

Combined hyperthermia and chlorophyll-based photodynamic therapy: tumour growth and metabolic microenvironment

The effects of combined and simultaneously applied localised 43 degrees C hyperthermia (HT) and an antivascular bacteriochlorophyll-serine-based photodynamic therapy (Bchl-ser-PDT) on tumour growth and several microenvironmental parameters were examined. Rats bearing DS-sarcomas were allocated to treatment groups: (i) sham-treatment (control), (ii) Bchl-ser-PDT (20 mg kg(-1) i.v.), (iii) localised HT, (iv) Bchl-ser-PDT+HT. The light source used was an infrared-A irradiator, which, by use of appropriate filters, delivered the different ranges of wavelengths required. Following treatment, tumour volume was monitored. The greatest tumour growth inhibition was seen with Bchl-ser-PDT+HT, and subsequent experiments identified the pathophysiological basis for this effect. Red blood cell flux in tumour microvessels declined rapidly upon Bchl-ser-PDT+HT, reaching approximately 10% of initial values by the end of treatment. Similarly, tumour oxygenation worsened, reaching almost anoxic levels by the end of the treatment period. Assessment of metabolic parameters showed a pronounced increase in lactate levels and a decrease in ATP concentrations after combined treatment. The results presented suggest that vascular collapse and flow stasis resulting in a deterioration of tumour oxygenation and a switch from oxidative to glycolytic glucose turnover are key elements in the tumour eradication seen with this novel approach in which an antivascular PDT and HT are combined and simultaneously applied.

Microcirculatory function, tissue oxygenation, microregional redox status and ATP distribution in tumors upon localized infrared-A-hyperthermia at 42 degrees C

Since local hyperthermia (HT) affects microenvironmental parameters, the aim of the study was to analyze the impact of 42 degrees C-HT on microcirculatory function, tumor pO2, microregional redox status and ATP distribution in experimental rat tumors. Subcutaneously growing DS-sarcomas were treated with localized HT using infrared-A radiation resulting in a mean tumor temperature of 42 degrees C. The relative red blood cell (RBC) flux in the tumor was assessed using the laser Doppler technique and the mean tumor pO2 measured continuously using O2-sensitive catheter electrodes. In a second series of experiments, the microregional distribution of the mitochondrial redox status and ATP concentration was measured. Although the average RBC flux increased by 63%, tumor pO2 rose only by approx. 6%. No distinct changes were seen in the mitochondrial redox status. The microregional distribution of the redox status as well as of the ATP concentration showed considerable heterogeneity. In conclusion, although 42 degrees C-HT leads to a distinct improvement in tumor perfusion, there is practically no change in the oxygenation status. The latter finding can be explained by an equivalent increase in the oxygen consumption rate of the cells which increases by approx. 58% at 42 degrees C compared to normothermia.

Nifedipine improves blood flow and oxygen supply, but not steady-state oxygenation of tumours in perfusion pressure-controlled isolated limb perfusion

Isolated limb perfusion allows the direct application of therapeutic agents to a tumour-bearing extremity. The present study investigated whether the dihydropyridine-type Ca(2+)-channel blocker nifedipine could improve blood flow and oxygenation status of experimental tumours during isolated limb perfusion. Perfusion was performed by cannulation of the femoral artery and vein in rats bearing DS-sarcoma on the hind foot dorsum. Perfusion rate was adjusted to maintain a perfusion pressure of 100-140 mmHg throughout the experiment. Following equilibration, nifedipine was continuously infused for 30 min (8.3 microg min(-1) kg(-1) BW). During constant-pressure isolated limb perfusion, nifedipine can significantly increase perfusion rate (+100%) and RBC flux (+60%) through experimental leg tumours. "Steal phenomena" in favour of the surrounding normal tissue and oedema formation were not observed. Despite the increased oxygen availability (+63%) seen upon application of this calcium channel blocker, nifedipine does not result in a substantial reduction of tumour hypoxia, most probably due to an increase in O(2) uptake with rising O(2) supply to the tumour-bearing hind limb. Nifedipine application during isolated limb perfusion can enhance tumour microcirculation and may therefore promote the delivery (pharmacokinetics) of anti-cancer drugs to the tumour and by this improve the efficacy of pressure-controlled isolated limb perfusion.

Tumor hypoxia: definitions and current clinical, biologic, and molecular aspects

Tissue hypoxia results from an inadequate supply of oxygen (O(2)) that compromises biologic functions. Evidence from experimental and clinical studies increasingly points to a fundamental role for hypoxia in solid tumors. Hypoxia in tumors is primarily a pathophysiologic consequence of structurally and functionally disturbed microcirculation and the deterioration of diffusion conditions. Tumor hypoxia appears to be strongly associated with tumor propagation, malignant progression, and resistance to therapy, and it has thus become a central issue in tumor physiology and cancer treatment. Biochemists and clinicians (as well as physiologists) define hypoxia differently; biochemists define it as O(2)-limited electron transport, and physiologists and clinicians define it as a state of reduced O(2) availability or decreased O(2) partial pressure that restricts or even abolishes functions of organs, tissues, or cells. Because malignant tumors no longer execute functions necessary for homeostasis (such as the production of adequate amounts of adenosine triphosphate), the physiology-based definitions of the term "hypoxia" are not necessarily valid for malignant tumors. Instead, alternative definitions based on clinical, biologic, and molecular effects that are observed at O(2) partial pressures below a critical level have to be applied.

Effect of lactic acid in tumours on antitumour activity of hyperthermia

The change of lactic acid concentration in the tumour after intraperitoneal administration of 5 g/kg glucose, and the effect of the lactic acid concentration on antitumour activity of hyperthermia were studied in an experimental murine tumour. The lactic acid concentration in SCC VII tumours transplanted into the legs of C3H/HeJ male mice was measured by gas chromatography. Local hyperthermic treatment to the tumour was performed with a water bath at 43 degrees C for 40 min. Antitumour effects were evaluated by measuring tumour volume doubling time (DT) as an index. The mean concentration of lactic acid in the tumour was 10.4 mumol/g in the no-treatment group. The lactic acid concentration gradually increased after glucose administration, reaching a significantly high concentration of 20.0 mumol/g at 90 min later. The DTs in the no-treatment group and hyperthermia alone group were 2.4 and 3.7 days respectively. The DTs in the glucose administration groups shortly before, 30 and 60 min before the hyperthermia were 3.6, 3.6 and 5.6 days respectively. The DT in the 60 min group was significantly extended (p < 0.0001). Hyperthermia during the period of increased lactic acid concentration significantly prolonged the DT of the tumour. These results clearly showed that an increase of lactic acid concentration in the tumour improved the effect of local hyperthermia.

Therapeutic hyperthermia

Those diseases that medicines do not cure, are cured by the knife, and those diseases that the knife cannot cure are cured by fire. And those diseases that fire does not cure are to be reckoned wholly incurable.

Tumour-growth inhibition by induced hyperglycaemia/hyperlactacidaemia and localized hyperthermia

The present study was undertaken to exploit pathophysiological properties of solid tumours for a tumour-specific therapy. Experiments were carried out on DS-sarcomas implanted s.c. in the hind foot dorsum of Sprague Dawley rats. Treatment strategies included tumour acidification, lactate accumulation and disturbance of the microcirculation by induced systemic hyperglycaemia/hyperlact-acidaemia (15-25/10 mmol/L; for 60 min) as well as localized hyperthermia (water-bath; 43 degrees C, 30 min.). A special infusion solution was developed for the systemic treatment containing glucose, lactic acid and organic buffer without inorganic ions. Growth kinetics of tumour volume and animal survival were taken as endpoints in order to quantify therapeutic efficiency. After a single treatment with combined modalities, i.e., with hyperglycaemia/hyperlactacidaemia and hyperthermia, approximately 50% of the tumours showed complete remission in three independent series of experiments; around 40% of the animals survived more than two months. In the untreated control group, all animals died from the disease within 10-15 days after tumour implantation. The overall effect on tumour volume changes of the combined therapy was supra-additive compared to that of treatment with hyperthermia or hyperglycaemia/hyperlactacidaemia alone. However, treated animals either showed a dramatic response to the combination of treatments with complete tumour remission or hardly responded at all, justifying a subdivision into responders and non-responders. Pathophysiological mechanisms responsible for this behaviour have to be elucidated in future studies. Nevertheless, the present study represents an approach to an efficient tumour therapy with a potential application in clinical oncology in the not too distant future.

Accumulation of purine catabolites in solid tumors exposed to therapeutic hyperthermia

Intensified adenosine triphosphate (ATP) degradation following therapeutic hyperthermia is often observed in solid tumors. As a result, accumulation of purine catabolites can be expected together with formation of protons at several stages during degradation to the final product, uric acid. Proton formation in turn can contribute to the development of heat-induced acidosis. Furthermore, oxidation of hypoxanthine and xanthine may result in generation of reactive oxygen species, which may lead to DNA damage, lipid peroxidation and protein denaturation, thus also contributing to heat-induced cytotoxicity. In hyperthermia experiments a tumor-size-dependent, significant increase in the levels of the following catabolites has been demonstrated: [symbol: see text] [IMP + GMP] (sum of guanosine and inosine monophosphate levels), inosine, hypoxanthine, xanthine and uric acid, along with a drop in ATP and guanosine triphosphate (GTP) levels. These data suggest that formation of reactive oxygen species and protons during purine degradation may indeed play a significant role in the antitumor effect of hyperthermia.

Changes in microregional perfusion, oxygenation, ATP and lactate distribution in subcutaneous rat tumours upon water-filtered IR-A hyperthermia

The effect of hyperthermia on microcirculatory and metabolic parameters in s.c. DS-sarcomas of different sizes on the hind foot dorsum of SD-rats was investigated. Hyperthermia was carried out using a novel water-filtered, infrared-A radiation technique. Heating was performed at a rate of 0.5 degrees C/min until 44 degrees C was achieved in the tumour centre, which was maintained for 60 min. Using a multichannel laser Doppler flowmeter, red blood cell flux could be assessed continuously and at several sites within the tumour tissue simultaneously. Substantial inter-site variations in laser Doppler flux (LDF) were observed during hyperthermia which were independent of tumour size, site of measurement, and temperature at the site of measurement, indicating that single site measurements of tumour LDF are poor predictors of the mean response of a tumour to hyperthermia. When mean LDF was considered, decreases in red blood cell fluxes occurred that were more pronounced the greater the tumour volume. In no case was vascular stasis observed. Hyperthermia did not affect tumour oxygenation substantially. Microregional and global assessment of lactate and ATP concentrations demonstrated increased lactate and decreased ATP levels following hyperthermia. Tumour glucose levels were increased following hyperthermia, possibly due to an enlarged distribution space resulting from development of interstitial oedema. Changes in lactate and ATP levels and the lack of changes in tumour oxygenation suggest a modification of energy metabolism following hyperthermia in the form of increased ATP hydrolysis, intensified glycolysis and impaired oxidative phosphorylation.

Tumor oxygenation in anemic rats: effects of erythropoietin treatment versus red blood cell transfusion

Anemia was induced in rats by the development of a hemorrhagic ascites. These animals also bore solid tumors (DS-sarcomas) on the hind foot dorsum. The effects of two methods for anemia correction on oxygenation in the solid tumors were compared in this study. Anemia was corrected either chronically by erythropoietin administration (1000 IU/kg) over 14 days (EPO) or acutely by transfusion with red blood cells (TR). Non-anemic and untreated anemic animals served as controls. Tumor oxygenation was determined in anesthetized animals using polarographic needle electrodes and pO2 histography. The reduction in hematocrit and hemoglobin content found in anemic animals could successfully be corrected either by EPO or by TR. Anemia resulted in a worsening of tumor oxygenation which could partially be reversed by EPO or TR in small tumors (< 1.4 ml). In larger tumors (> or = 1.4 ml), neither method of anemia correction resulted in significant changes in tumor oxygenation.

Lactate release and uptake in hepatoma 7288CTC perfused in situ with L-[(U)-14C]lactate or D-[(U)-14C]glucose

Arteriovenous differences (AVD) for glucose and lactic acid measured across tissue-isolated rat tumors in vivo have shown that individual tumors with similar rates of glucose consumption may either release or utilize lactic acid. The experiments described here investigated the relationships among arterial blood lactate concentrations and tumor lactate and glucose balances. AVDs for lactate, pyruvate, glucose, 14CO2, PO2, PCO2, pH, and lactate specific activities were measured across 17 tissue-isolated 7288CTC hepatomas perfused in situ with arterial blood containing 2.5 to 14.4 mmol/L lactate and either L-[(U)-14C]lactic acid or D-[(U)-14C]glucose. Measurements were made over a range of blood flow rates from 60% to 200% of the mean in vivo rate, 0.11 mL/min. Data collected during steady states were compared by regression analysis. Tumor lactate balance and the arterial blood lactate concentration were directly related (r = .895, n = 22, P < .01). Net negative and positive balances occurred below and above approximately 6.5 mmol/L arterial blood lactate, respectively. The mean intratumor lactate concentration for all tumors was 6.9 +/- 1.0 mmol/L (mean +/- SD, n = 13). Rates of 14C-lactate oxidation to 14CO2 (r = .716, n = 18, P < .01) and tumor venous/arterial blood 14C-lactate specific activity ratios (r = .845, n = 19, P < .01) were low during lactate release and were increased during lactate uptake. Total arterial blood lactate removal estimated from chemical and isotopic analyses was 23.1% +/- 11% and 43.0% +/- 16% (P < .05), respectively, for six lactate-utilizing tumors. Perfusions performed with 14C-glucose showed that approximately 50% of the glucose consumed during net negative lactate balance was released as 14C-lactate to the tumor venous blood, whereas only 5% was released as 14C-lactate during net positive lactate balance. The data support the following conclusions: Arterial blood lactate controls net lactate balance in solid tumors; high concentrations increase uptake. Lactate uptake inhibits lactate formation from glucose without changing the glucose balance. Lactate is release during net lactate uptake. Since lactate uptake may exceed glucose uptake, arterial blood lactate can be a substrate for tumor energy metabolism and growth.

Possible mechanisms involved in tumor radiosensitization following nicotinamide administration

Despite continued interest in the administration of nicotinamide (NA) as a tumor-specific radiosensitizer (an effect thought to be related to increases in tumor blood flow and oxygenation), little is known about the underlying mechanism(s) of this effect. The aim of this study was to investigate metabolic changes following NA application in both tumor and normal tissues. Increased concentrations of NAD+ were measured in DS-sarcomas, liver, and kidney tissue, with no changes in concentrations in resting skeletal muscle. Further investigations also examined the concentrations of glucose, lactate, ATP, ADP and AMP in tumor and resting skeletal muscle tissue following NA application. Here, the only change detected was an increase in lactate levels in tumor tissue. The changes in NAD+ concentrations described correlate well with reported changes in tissue blood flow measured following NA. On the basis of changes in tumor blood flow, oxygenation and metabolite concentrations found in this and other recent studies, possible mechanisms for tumor radiosensitization following nicotinamide administration are considered.

Intracellular acidosis in murine fibrosarcomas coincides with ATP depletion, hypoxia, and high levels of lactate and total Pi

Bioenergetic and metabolic status of murine FSaII tumours were evaluated using 31P MRS, acid extracts ('global' techniques) and quantitative bioluminescence ('microregional' assay). Data obtained from s.c. tumours of varying sizes (44-600 mm3) have been correlated with the oxygenation status evaluated using O2-sensitive needle electrodes. beta-NTP/Pi and phosphocreatine (PCr)/Pi ratios derived from 31P MRS were positively correlated to the median tissue pO2 values. pH declined during growth with intracellular acidosis being evident in tumours > 350 mm3. Whereas lactic acid formation greatly contributed to this decline in small- and medium-sized tumours, ATP hydrolysis and slowing down of the activities of pumps involved in pHi regulation seem to be major factors responsible for intracellular acidification in bulky tumours. PCr levels decreased at an early growth stage, whilst ATP concentrations dropped in bulky malignancies only, coinciding with a decrease in adenylate energy charge and a substantial rise in the levels of total Pi. MRS observable (mobile) Pi was consistently lower than [Pi] measured in acid extracts. On average, median pO2 values of ca 10 mmHg represent a critical threshold for energy metabolism. At higher median O2 tensions, levels of ATP, phosphomonoester and total Pi were relatively constant. This coincided with intracellular alkalosis or neutrality and stable adenylate ratios. On average, median pO2 values < 10 mmHg coincided with intracellular acidosis, ATP depletion, a drop in energy charge and rising Pi levels.

Stable bioenergetic status despite substantial changes in blood flow and tissue oxygenation in a rat tumour

Experiments on s.c. rat tumours (DS sarcoma) were performed to determine whether chronic or acute changes in tumour perfusion necessarily lead to changes in tissue oxygenation and bioenergetic status since, as a rule, blood flow is thought to be the ultimate determinant of the tumour bioenergetic status. Based on this study, there is clear experimental evidence that growth-related or acute (following i.v. administration of tumour necrosis factor alpha) decreases in tumour blood flow are accompanied by parallel alterations in tissue oxygenation. In contrast, tumour energy status remains stable as long as flow values do not fall below 0.4-0.5 ml g-1 min-1, and provided that glucose as the main substrate can be recruited from the enlarged interstitial compartment. Perfusion rate seems to play a paramount role in determining energy status only in low-flow tumours or low-flow tissue areas.

Microregional distributions of glucose, lactate, ATP and tissue pH in experimental tumours upon local hyperthermia and/or hyperglycaemia

Microregional distributions of glucose, lactate and ATP concentrations as well as tissue pH values were determined in subcutaneous rat tumours during normothermia and normoglycaemia, and upon local hyperthermia (HT) and/or hyperglycaemia (HG). Experiments were performed in order to investigate whether, and to what extent, these adjuvant therapeutic measures applied alone or in combination can modify the bioenergetic and metabolic status, parameters that are known to markedly influence the therapeutic response of tumours to heat. Local HT was performed in a saline bath (44 degrees C/2 h) and HG was induced by i.v. infusion of glucose for 2.5 h (blood glucose levels during heating: 35-40 mM). Immediately after treatment, the microregional distributions of glucose, lactate and ATP concentrations were assessed using quantitative bioluminescence and single-photon counting. In corresponding histological sections the fraction of tumour tissue with changes indicating cellular damage was determined. For comparison, global levels of glucose, lactate, ATP, ADP and AMP were measured using enzymatic assays or HPLC. Tumour tissue pH values were recorded immediately after treatment with miniaturised needle glass pH electrodes. Upon HT alone, the microregional glucose distribution remained unchanged. Lactate concentrations significantly increased, resulting in a pH drop of about 0.20 pH units. Mean ATP concentrations decreased without an obvious change in the shape of the distribution curve. The fraction of tumour tissue showing cellular damage increased from 18% (in control tumours) to 27%. Upon HG alone, mean glucose and lactate levels in the tumours increased. Glucose, lactate and pH distributions became broader. Lactate accumulation results in a severe tumour acidosis (mean pH = 6.22). Mean ATP concentrations marginally decreased despite a higher glucose availability, probably because of poorer ATP yield resulting from changes in metabolic channelling (Crabtree effect). The fraction of tumour tissue exhibiting cellular damage was 23%. Following the combined treatment (HT/HG), glucose and lactate levels, and tissue pH were similar to those seen upon HG alone. However, ATP concentrations were lowest under this condition. The variation of tumour ATP concentrations is substantially reduced with only a few tumour areas remaining with ATP levels of at least 0.6 mumol/g. The ATP depletion upon HT/HG is accompanied by a drastic increase in the fraction of tissue areas exhibiting cellular damage to 61%. It may therefore be concluded that only the combined treatment can deplete ATP to such an extent that a pronounced cytotoxic effect is achieved.

pH in human tumour xenografts: effect of intravenous administration of glucose

pH frequency distributions of tumours grown s.c. from 30 human tumour xenograft lines in rnu/rnu rats were analysed with the use of H+ ion-sensitive semi-microelectrodes prior to and following stimulation of tumour cell glycolysis by i.v. infusion of glucose. At normoglycemia, the average pH of the tumours investigated was 6.83 (range, 6.72-7.01; n = 268). Without exception, all xenografts responded to the temporary increase in plasma glucose concentration (PGC) from 6 +/- 1 to 30 +/- 3 mM by an accumulation of acidic metabolites, as indicated by a pH reduction to an average value of 6.43 (range, 6.12-6.78; n = 292). This pH value corresponds to a ten-fold increase in H+ ion activity in tumour tissue as compared to arterial blood. Tumour pH approached minimum values at 2-4 h after the onset of glucose administration and could be maintained at acidic levels for 24 h by controlled glucose infusion. Irrespective of pH variations between tumours grown from individual xenograft lines, there was no major difference in pH response to glucose between the four main histopathological tumour entities investigated, i.e. breast, lung and gastrointestinal carcinomas, and sarcomas. In tumours from several xenograft lines, an increase in blood glucose to only 2.5-times the normal value (14 mM) was sufficient to reduce the mean pH to 6.4. Glucose-induced acidosis was tumour-specific. The pH frequency distributions in liver, kidney and skeletal muscle of tumour-bearing rnu/rnu rats were only marginally sensitive to hyperglycemia (average pH, 6.97 vs normal value of 7.14). Tumour-selective activation of pH-sensitive anti-cancer agents, e.g. alkylating drugs, acid-labile prodrugs or pH-sensitive immunoconjugates may thus be feasible in a wide variety of human cancers.

Glucose effects in an ovarian cancer protocol of exceptional activity

A French multidrug protocol for stage III ovarian cancer has achieved 77% pathologic complete response, 100% total response, and 81% actuarial 4-year survival. Our analysis indicates that these rates exceed typical with very high statistical significance. Yet neither the drugs, the combined intravenous and intraperitoneal mode of delivery, nor potential bias in the predominantly suboptimal patient population appear to explain the protocol's exceptional results. Here we propose that the atypical administration of intraperitoneal glucose prior to drugs underlies the unusual activity of this protocol. We review studies demonstrating that high-dose glucose has pronounced effects on cancer cells, most notably, substantial potentiation of certain antineoplastic agents. We consider possible mechanisms of such glucose potentiation, including hypothesized osmotic effects that would be especially strong under intraperitoneal administration. We conclude that the French ovarian cancer protocol may represent a significant advance and that glucose potentiation may be more widely applicable as an adjunct to cancer chemotherapy.

Laser Doppler flux and tissue oxygenation of experimental tumours upon local hyperthermia and/or hyperglycaemia

Laser Doppler fluxmetry and oxygen partial pressure (pO2) histography have been applied to investigate the acute effects of hyperthermia (HT) and/or hyperglycaemia (HG) on microcirculatory function and tissue oxygenation of subcutaneous rat tumours growing on the dorsum of the hind foot. The experiments were performed to test whether, and to what extent, the two adjunct treatment modalities applied alone or in combination can modify these therapeutically relevant parameters. Local HT was performed in a saline bath (44 degrees C) for 2 h; HG was induced by i.v. infusion of 40% glucose solution for 2.5 h (blood glucose levels: 35-40 mM during heating). Laser Doppler flux (LDF) in superficial tumour tissue regions was recorded over the entire treatment period; tumour pO2 distribution was evaluated immediately after termination of the treatment. HG alone reduced the average LDF signal to 18% of the baseline reading before treatment, but did not influence the tumour oxygenation status and the proportion of pO2 readings occurring in the radiobiologically hypoxic class (pO2 = O-2.5 mm Hg). This phenomenon is most probably due to the occurrence of the Crabtree effect (reduction of the O2 consumption rate when excess glucose is available within a malignant tumour). Hyperthermia alone reduced LDF to approximately the same extent, and led to a rise in the number of pO2 readings in the hypoxic range with only minor changes in the average pO2. The combined treatment (HT/HG) neither increased the fraction of "hypoxic" pO2 readings nor intensified the flow drop already present at the end of the tumour heating. It is thus concluded that under hyperglycaemia the oxygenation status of normothermic and heated tumours is maintained. It may therefore be hypothesized that hyperthermia in conjunction with hyperglycaemia might be a better "radiosensitizer" than hyperthermia alone.