P. Vaupel

Enhanced radiosensitivity in experimental tumours following erythropoietin treatment of chemotherapy-induced anaemia.

The radiosensitivity of solid tumours in anaemic rats treated with recombinant human erythropoietin (rhEPO, epoetin beta) was studied. Anaemia was induced by a single dose of carboplatin (45 mg kg(-1) i.v.), resulting in a reduction in the haemoglobin concentration by 30%. In a second group, the development of anaemia was prevented by rhEPO (1000 IU kg(-1)) administered s.c. three times per week starting 6 days before the carboplatin application. Three days after carboplatin treatment, DS-sarcomas were implanted subcutaneously onto the hind foot dorsum. Neither carboplatin nor rhEPO treatment influenced tumour growth rate. Five days after implantation, tumours were irradiated with a single non-curative dose (10 Gy), resulting in a growth delay with a subsequent regrowth of the tumours. In the rhEPO-treated group, the growth delay lasted significantly longer (9.5 days vs. 4.5 days) and the regrowth was slower (6.0 days vs. 4.1 days) compared with the anaemic group. These data suggest that the correction of chemotherapy-induced anaemia by rhEPO (epoetin beta) treatment increases tumour radiosensitivity, presumably as a result of an improved oxygen supply to tumour tissue.

Heterogeneous Oxygenation of Rectal Carcinomas in Humans: A Critical Parameter for Preoperative Irradiation?

Tissue oxygenation was measured in 10 patients with differentiated adenocarcinoma in a very localized region in the middle part of the rectum (grade I - II, clinical stage II) by means of a cryophotometric micromethod. The results obtained clearly show that the oxygenation of differentiated rectal adenocarcinoma is distinctly lower than that of the normal rectal mucosa; tissue hypoxia or even anoxia are a common feature in those tumors; There exist considerable inter- individual differences among tumors of the same clinical staging and histological grading; substantial intra- individual heterogeneities in the oxygenation are evident within the same tumor and even within neighbouring microareas of the tissue. These findings imply that the commonly used classifications do not allow any conclusions concerning the oxygenation status, and probably the radiosensitivity of a tumor, respectively.

In vivo targets of recombinant human tumour necrosis factor-alpha: blood flow, oxygen consumption and growth of isotransplanted rat tumours.

The impact of recombinant human tumour necrosis factor-alpha (1 microgram kg-1 to 1 mg kg-1; 6.6 x 10(6) U mg protein-1) on blood flow, oxygen consumption and growth of a moderately TNF-sensitive rat tumour (DS-carcinosarcoma) was studied. Tumour growth was stimulated at low TNF doses (1 and 10 micrograms kg-1) and significantly retarded at higher TNF dose levels (0.1 and 1 mg kg-1). Growth changes were concomitant with variations in oxygen consumption, lactate release and acidification of the metabolic micromilieu. Both single and repeated application of low TNF doses (1-10 micrograms kg-1 i.v.) increased tumour perfusion whereas single administration of high TNF dose levels (0.1-1 mg kg-1 i.v.) reduced tumour blood flow. After repeated application of high TNF doses tumours shrank to such small sizes that perfusion measurements could not be performed within the observation period of two weeks. It is concluded that TNF effects on solid tumours are at least partially mediated by changes in tumour perfusion. Thus, an altered tumour sensitivity towards other treatment modalities, e.g. irradiation, chemotherapy or hyperthermia, can be expected after TNF therapy. A beneficial TNF effect would critically depend on the dose level employed and on the sequence and timing of various combination regimes.

Circulatory and metabolic responses of malignant tumors during localized hyperthermia.

ZusammenfassungAn gewebsisolierten Tumoren der Ratte wurde mit Hilfe einer in situ-Perfusion der Einfluß einer lokalen Hyperthermie auf das Durchblutungsverhalten sowie die Sauerstoff- und Glucoseversorgung des Gewebes untersucht. Eine Erhöhung der Gewebetemperatur von 37 °C auf 39,5 °C führte hierbei zu einer signifikanten Zunahme der mittleren Tumordurchblutung. Ein weiterer Anstieg der mittleren Tumortemperatur auf 42 °C hatte eine Abnahme der Tumordurchblutung auf ein Niveau zur Folge, das etwas unter der Durchblutung bei 37 °C lag. Bei einigen Tumoren zeigten sich erhebliche Abweichungen von diesem mittleren Durchblutungsverhalten bei Hyperthermie. Die temperaturbedingten Durchblutungsänderungen gehen mit gleichsinnigen Veränderungen des Sauerstoffverbrauches und der Glucoseaufnahme des Tumorgewebes einher. Beide Verbrauchsgrößen sind demnach unter Hyperthermiebedingungen im wesentlichen eine Funktion der Durchblutung. Die Mikrozirkulation in den Tumoren scheint bei einer mäßigen Hyperthermie (39 °C–40 °C) verbessert zu sein; bei stärkerer Erwärmung des Gewebes wird sie eingeschränkt. Während vor allem eine Vasodilatation von Tumorgefäßen bei einer 39,5 °C-Hyperthermie für die Durchblutungssteigerung in Betracht zu ziehen ist, müssen als Ursachen für die Einschränkung der Tumordurchblutung bei 42 °C ein Verlust der Erythrocytenflexibilität (bei Vorliegen einer ausgeprägten Gewebsacidose) und das Auftreten multipler Mikrothromben mit konsekutiven Verschlüssen kleinster Tumorgefäße genannt werden.SummaryThe effect of localized hyperthermia on the circulatory responses and on the oxygen and glucose supply has been evaluated in tissue-isolated rat tumors utilizing an in situ perfusion system. On the average, localized hyperthermia caused a significant increase in total tumor blood flow after raising of the mean tumor temperature from 37 °C to 39.5 °C. At higher temperatures (42 °C) total tumor blood flow decreased to a level somewhat below the flow during normothermia. However, there were great interindividual differences in the response of blood flow to temperature. The changes in blood flow were paralleled by variations of the 02-consumption and of the glucose uptake of the tumor tissue. The alteration of the oxygen and glucose supply seem to be predominantly mediated through changes of tumor blood flow with temperature. Tumor microcirculation appears to be improved at moderate hyperthermic temperatures (39 °C–40 °C) and deteriorated at higher temperatures. Whereas a vasodilation of tumor vessels seems to be a paramount factor for flow improvements, a reduction of red blood cell flexibility due to severe tissue acidosis, multiple microthromboses as well as occlusions of microvessels should be taken into consideration as factors for flow impairments at higher tumor temperatures.

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.

L-glutamine: a major substrate for tumor cells in vivo?

SummaryFrom 65 human breast cancer xenografts investigated, a net glutamine uptake was found in 13 tumors (mean±SE: 15.7±4.5 nmol/g per min) whereas a net release (22.5±3.3 nmol/g per min) was observed in 40 tumors. In 12 tumors neither a significant net uptake nor a net release was obvious. There is experimental evidence that glutamine is taken up by cancer cells only at arterial concentrations>0.5 mM. Another parameter determining glutamine utilization by tumor cells may be the tissue oxygenation. In hypoxic or anoxic tumor areas, glutamine oxidation is unlikely since oxygen is required for the reoxidation of coenzymes which are reduced in the course of this metabolic pathway. The pronounced net release could be due to proteolysis within the tumors investigated. In ascitic fluid (DS-carcinosarcoma), glutamine accumulated during growth, implicating a reduction in the glutamine consumption rate, proposedly also due to a worsening of the oxygen supply to the suspended tumor cells. Thus, the generally held opinion that l-glutamine is a (if not the) major substrate for the energy metabolism of rapidly growing tumor cells should be reconsidered since evidence for this hypothesis has been derived mainly from in vitro system with abundant oxygen.

Predictive Power of the Tumor Oxygenation Status

We have previously demonstrated with a prospective study in primary cancer of the uterine cervix (clinical size > 2 cm) that tumor hypoxia not only indicates decreased radiocurability but is generally associated with malignant progression of the disease. This finding also holds true for other tumor entities (soft tissue sarcomas, squamous cell carcinomas of the head and neck region), for lymph node metastases of head and neck lesions, and for locoregional recurrences of cervical cancers. All data available so far support our thesis that in cervical cancers (and in other solid tumors as well), tumor hypoxia and clinical aggressiveness in terms of resistance to therapy and tumor dissemination, are interrelated.

Blood Flow and Tissue Oxygenation of Human Tumors: An Update

It is generally accepted that tumor microcirculation, blood flow, oxygen and nutrient supply, tissue pH distribution, and the bioenergetic status (factors which are usually closely linked and which define the so-called cellular microenvironment) can markedly influence the therapeutic response of malignant tumors. Tumor blood flow is the major determinant for intra-tumor pharmacokinetics and (through modulation of the cellular microenvironment) of pharmacody-namics. The oxygen supply greatly determines the radiosensitivity of the tumors to be treated. The oxygen enhancement ratio, i.e., the ratio of doses with and without oxygen to produce the same biological effect is 2.7 to 3.0. O2 partial pressures (O2 tensions) of 3 to 4 mmHg (i.e., 0.5 to 0.6% O2) result in a sensitivity halfway between radiobiological hypoxia and full oxygenation (Vaupel, 1992).

Direct Measurement of Reoxygenation in Malignant Mammary Tumors after a Single Large Dose of Irradiation

Measurements of the tissue O2 partial pressure distribution in C3H mouse mammary adenocarcinomas were performed just before and 72 - 74 hrs. after X- irradiation using O2 microelectrodes of the gold in glass type. The results obtained before irradiation were similar to those usually obtained previously in fast growing murine tumors during advanced growth stages. After exposure to a single dose of 60 Gy, the distribution curve significantly changed. This change was particularly evident in the very low pO2 range which is of crucial importance for the efficacy of radiotherapy. Due to this improvement of the tumor tissue oxygenation the number of radioresistant cells can be drastically reduced in the post- irradiation period at the time of maximum reoxygenation. Judiciously chosen fractionated treatment regimens, thus, should maintain tumor cells in optimum radiosensitivity states.

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

SummaryArterial blood pressure and relevant parameters of the arterial blood (O2 and CO2 tensions, pH, haematocrit, serum electrolytes and osmolality) were determined in tumour-bearing rats upon local hyperthermia (HT) and/or hyperglycaemia (HG). Tumour heating was performed in a saline bath (44‡ C) for 120 min; hyperglycaemia was induced by i.v. infusion of 40% glucose solution for 150 min [blood glucose levels: 35–40 mM during heating; total amount of glucose: 1.19 g/100 g body wt.; infusion rates: 0.31 ml (100 g body wt.)−1 min−1 for 2 min, 0.02 ml (100 g body wt.)−1 min−1 for 88 min, and 0.01 ml (100 g body wt.)−1 min−1 for 60 min]. Immediately after treatment, glucose, lactate and ATP levels were determined in tumour and muscle specimens and compared to these values under normothermic (NT) and/ or normoglycaemic (NG) conditions. In all groups (NT/ NG, NT/HG, HT/NG, HT/HG) there were only minor but characteristic changes in blood parameters, which were mainly due to the volume and type of the infused fluids (glucose solution, saline). During hyperglycaemia, tumour glucose levels rose 13-to 17-fold, whereas muscle glucose concentrations exhibited only a 3-to 5-fold increase; lactate levels were 1.9–2.5 times higher in tumours than in muscle, indicating an increase in the metabolic differences between normal and malignant tissues. Despite an increased glucose availability, tumours did not show an improved energy status and, thus, would not be expected to develop a decrease in thermal sensitivity or stimulation in growth rate. The good systemic tolerability of the combined treatment (HT/HG) and the differential changes in malignant and normal tissue occurring under these conditions, support further attempts to manipulate tumour metabolic environment by glucose in order to achieve better therapeutic results.