Enhancement of tumor radiosensitivity and reduced hypoxia-dependent binding of a 2-nitroimidazole with normobaric oxygen and carbogen: a therapeutic comparison with skin and kidneys

Transcutaneous application of CO2 enhances the antitumor effect of radiation therapy in human malignant fibrous histiocytoma

Sarcomas are relatively resistant because of hypoxia. We previously demonstrated that the transcutaneous CO(2) therapy reduced hypoxic conditions in human malignant fibrous histiocytoma (MFH). Therefore, we hypothesized that transcutaneous CO(2) therapy could enhance the antitumor effect of radiation therapy in human MFH. Our purpose was to evaluate the effects of transcutaneous CO(2) therapy on the antitumor efficacy of X-ray irradiation using MFH. First, in an in vitro study, we assessed apoptotic activity and reactive oxygen species (ROS) production using flow cytometric and immunoblot analysis at 24 h after X-ray irradiation under three different oxygen conditions (normoxic, reoxygenated and hypoxic). In addition, in the in vivo study, 24 male athymic BALB/c nude mice with MFH tumors that were inoculated in the dorsal subcutaneous area were randomized into four groups: control, CO(2), X-ray irradiation and combination (CO(2) and X-ray irradiation). Treatments were performed twice weekly for 2 weeks, four times in total. Tumor volume was calculated. All tumors were excised and apoptotic activity, ROS production, related proteins and HIF-1α expression were assessed using flow cytometric and immunoblot analysis. The in vitro study revealed that X-ray irradiation induced increased apoptosis and ROS production in MFH cells under normoxic and reoxygenated conditions relative to hypoxic conditions (P<0.01). In the in vivo study, tumor volume in the combination group was reduced to 28, 42 and 47% of that in the control, CO(2), and X-ray groups, respectively (P<0.05). Apoptotic activity and ROS production in the combination group were strongly increased with decreasing HIF-1α expression relative to the control, CO(2) and X-ray groups. The transcutaneous CO(2) system enhanced the antitumor action of X-ray irradiation and could be a novel therapeutic tool for overcoming radio-resistance in human malignancies.

Tumor reoxygenation following administration of Mitogen-Activated Protein Kinase inhibitors: a rationale for combination with radiation therapy

BACKGROUND AND PURPOSE

The relevance of Mitogen Activated Protein Kinase (MAPK) inhibitors as co-treatments for radiation therapy is investigated, with special focus on a potential link between the MAPK pathway and tumor hypoxia, which is a critical determinant for response to therapy.

MATERIALS AND METHODS

The effects of two MAPK inhibitors, Sorafenib and PD0325901, were monitored daily using in vivo EPR (Electron Paramagnetic Resonance) oximetry in FSaII and TLT tumor models in order to identify a window of reoxygenation, during which tumor blood flow, oxygen consumption and radiation sensitivity were assessed.

RESULTS

Reoxygenation was shown after two days of treatments with Sorafenib or PD0325901 in two tumor models, which was further successfully exploited with Sorafenib for improving the radiation response of FSaII tumors by a factor of 1.5. The increase in tumor oxygenation was shown to be the result of two major factors: (i) an increase in blood flow for Sorafenib, that might be linked to its anti-angiogenic effect (vascular normalization), and (ii) a decrease in oxygen consumption for Sorafenib and PD0325901, due to an alteration of the mitochondrial activity.

CONCLUSION

We evidenced tumor reoxygenation in vivo following MAPK inhibition and suggest a rationale for the combination of radiation therapy with Sorafenib.

Targeting tumor perfusion and oxygenation to improve the outcome of anticancer therapy

Radiotherapy and chemotherapy are widespread clinical modalities for cancer treatment. Among other biological influences, hypoxia is a main factor limiting the efficacy of radiotherapy, primarily because oxygen is involved in the stabilization of the DNA damage caused by ionizing radiations. Radiobiological hypoxia is found in regions of rodent and human tumors with a tissue oxygenation level below 10 mmHg at which tumor cells become increasingly resistant to radiation damage. Since hypoxic tumor cells remain clonogenic, their resistance to the treatment strongly influences the therapeutic outcome of radiotherapy. There is therefore an urgent need to identify adjuvant treatment modalities aimed to increase tumor pO(2) at the time of radiotherapy. Since tumor hypoxia fundamentally results from an imbalance between oxygen delivery by poorly efficient blood vessels and oxygen consumption by tumor cells with high metabolic activities, two promising approaches are those targeting vascular reactivity and tumor cell respiration. This review summarizes the current knowledge about the development and use of tumor-selective vasodilators, inhibitors of tumor cell respiration, and drugs and treatments combining both activities in the context of tumor sensitization to X-ray radiotherapy. Tumor-selective vasodilation may also be used to improve the delivery of circulating anticancer agents to tumors. Imaging tumor perfusion and oxygenation is of importance not only for the development and validation of such combination treatments, but also to determine which patients could benefit from the therapy. Numerous techniques have been developed in the preclinical setting. Hence, this review also briefly describes both magnetic resonance and non-magnetic resonance in vivo methods and compares them in terms of sensitivity, quantitative or semi-quantitative properties, temporal, and spatial resolutions, as well as translational aspects.

Rat epigastric flap survival and VEGF expression after local copper application

BACKGROUND

Copper has been used in wound healing since ancient times, and copper insufficiency seems to impair wound healing. Much less is known about the local effects of copper application on wound healing.

METHODS

The authors studied 30 male Sprague-Dawley rats weighing between 250 and 350 g for 5 days. Full-thickness random skin flaps, measuring 1.5 x 7.5 cm, were elevated on the epigastric region. The rats were randomized into two groups according to the local treatment that was used. In group 1 (20 animals), 1 ml of copper ointment was applied on the flap bed after flap suturing. In group 2 (10 animals), 1 ml of placebo ointment (petroleum jelly) was used. Intraperitoneal injection of 30 mg/kg body weight of Hypoxyprobe-1 was performed in each rat on the fourth postoperative day and all animals were killed 3 hours later. Histologic examination of the distal end of the flaps was used for detection of hypoxic tissue changes. Expression, density, and extent of vascular endothelial growth factor activity was detected with the aid of immunocytochemistry.

RESULTS

All rats survived throughout the study period. This experimental study showed that local application of copper at the random flap bed may promote wound-related angiogenesis by inducing vascular endothelial growth factor expression. The authors demonstrated statistically significant flap survival after local copper application at the flap bed.

CONCLUSION

The marked benefits of copper application in flap survival in this experimental model may guarantee its clinical application in flaps with questionable viability.

Oxygen levels in normal and previously irradiated human skin as assessed by EF5 binding

The oxygen status of skin is a controversial topic. Skin is radiosensitive, suggesting it is well-oxygenated. However, it can be further sensitized with nitroimidazole drugs, implying that it is partially hypoxic. Skin oxygen levels are difficult to measure with either electrodes or the hypoxia-monitoring agent (3)H-misonidazole. For the latter, binding has previously been reported to be high in murine skin, but this could be attributed to either non-oxygen-dependent variations in nitroreductase activity, drug metabolism, and/or actual oxygen gradients. We obtained tumor and skin from patients given EF5, a 2-nitroimidazole tissue hypoxia monitor. We performed immunohistochemical studies using highly specific monoclonal antibodies for the hypoxia-dependent production of EF5 tissue adducts. Some tissue sections were counterstained using either Ki67 for proliferation or CD31 for vessels. We found that the human dermis is well-oxygenated, the epidermis is modestly hypoxic and portions of some sebaceous glands and hair follicles are moderately to severely hypoxic. Normal and irradiated skin had similar oxygenation patterns. Control studies demonstrated that these observations are not due to tissue variations in nitroreductase activity. The importance of the highly heterogeneous distribution of oxygen in skin requires further study, but recent investigations suggest that skin hypoxia may have important clinical ramifications including mediating cellular transformation.

Is sensitization with nicotinamide and carbogen dependent on nicotinamide concentration at the time of irradiation?

PURPOSE

To determine whether tumour radiosensitization and the therapeutic benefit of administering carbogen with nicotinamide depend upon irradiating at the time of peak drug concentration.

MATERIALS AND METHODS

Local tumour control of CaNT tumours in CBA mice and acute skin reactions in albino WHT mice were assessed after treatment with 10 X-ray fractions in air, carbogen alone or combined with 0.1, 0.2 or 0.5 mg g(-1) nicotinamide, injected 15, 30 or 60 min before irradiation. Plasma and tumour drug pharmacokinetics were performed.

RESULTS

Nicotinamide was rapidly taken up into tumours; a six- and threefold higher concentration was obtained with 0.5 mg g(-1) compared with 0.1 and 0.2 mg g(-1), respectively. Tumour, but not skin, radiosensitization increased as the dose of nicotinamide increased (p = 0.03), but at each dose level there was no significant difference in radiosensitivity when irradiations were done at or after the time of peak concentration. An almost eightfold increase in plasma levels increased tumour enhancement ratios from 1.74 to 1.92 (p < 0.0001). In tumours all schedules gave significant enhancement relative to carbogen alone (p < or = 0.04).

CONCLUSIONS

Tumour and skin radiosensitivity was independent of time of nicotinamide administration. Higher drug concentrations were not mirrored by proportionally higher enhancement ratios. Lower plasma levels than previously suggested significantly enhanced tumour radiosensitivity relative to carbogen alone. The clinical implications of these findings are discussed.

Dynamics of tumor oxygenation and red blood cell flux in response to inspiratory hyperoxia combined with different levels of inspiratory hypercapnia

BACKGROUND AND PURPOSE

Increasing arterial oxygen partial pressure (pO2) by breathing hyperoxic gases is an effective means of improving tumor oxygenation, although the efficacy of adding CO2 to the inspiratory gas has been discussed controversially. This study aimed at analyzing the impact of different inspiratory CO2 fractions on the time course of oxygenation and perfusion changes in experimental tumors during and after inspiratory hyperoxia.

MATERIAL AND METHODS

Perfusion and oxygenation of rat DS-sarcomas were studied during spontaneous breathing of pure oxygen or hyperoxic gas mixtures containing different CO2 fractions (1, 2.5 or 5%). Red blood cell (RBC) flux was assessed as a measure of tumor perfusion using the laser Doppler technique and temporal changes in mean tumor pO2 were measured polarographically.

RESULTS

Mean tumor pO2 increased 3.6-fold with pure oxygen, approx. 3.3-fold when 1 or 2.5% CO2 was added and 2.7-fold during carbogen breathing. RBC flux also increased by 25-30% with all gases. With pure oxygen and with 1% CO2 (+99% O2), perfusion changes paralleled those of the mean arterial blood pressure whereas with higher CO2 fractions, a decrease in resistance to flow was observed. The differences found with the various gas mixtures were more pronounced after the end of hyperoxia. With pure oxygen, perfusion immediately returned to pretreatment values whereas with higher CO2 fractions perfusion remained elevated for at least 30 min.

CONCLUSIONS

Higher inspiratory CO2 fractions (2.5 or 5%) lead to a prolonged improvement of tumor perfusion after the end of inspiratory hyperoxia when compared with pure oxygen breathing. Since no principal differences in oxygenation and perfusion were seen between the gases containing 2.5 and 5% CO2, the former may be preferable for inspiratory hyperoxia.

Early wound healing exhibits cytokine surge without evidence of hypoxia

OBJECTIVE

To ascertain the spatial and temporal relation of wound hypoxia to the cell types involved, expression of selected angiogenic cytokines, the proliferative status of cells in the wound site, and angiogenesis.

SUMMARY BACKGROUND DATA

Hypoxia is considered to drive the angiogenic response by upregulating angiogenic cytokines observed during wound healing. But this correlation has not been shown on a cell-to-cell basis in vivo because of limitations in measuring tissue PO2 at the cellular level.

METHODS

Using punch biopsy wounds in rats as a wound healing model, the distributions of vascular endothelial growth factor, transforming growth factor-beta, tumor necrosis factor-alpha, and pimonidazole adducts (as a hypoxia marker) were followed immunohistochemically during the healing process.

RESULTS

Hypoxia was absent on day 1 after wounding, even though angiogenesis and maximal expression of cytokines were observed in the wounds. Hypoxia peaked in the granulation tissue stage at day 4 and correlated with increased cellularity and cellular proliferation. Hypoxia started to decrease after day 4 and was limited to the remnant blood vessels and epithelial layer in the scar tissue.

CONCLUSIONS

Induction of angiogenic cytokines early during wound healing may be due to triggering mechanisms other than hypoxia. Alternatively, the unique pattern of development and decline of cellular hypoxia as wound cellularity and proliferation regress suggest its involvement in initiating vascular regression during the later stages of healing.

Characterization and validation of noninvasive oxygen tension measurements in human glioma xenografts by 19F-MR relaxometry

PURPOSE

The aim of this study was to characterize and to validate noninvasive 19F-magnetic resonance relaxometry for the measurement of oxygen tensions in human glioma xenografts in nude mice. The following three questions were addressed: 1. When perfluorocarbon compounds (PFCs) are administrated intravenously, which tumor regions are assessed by 19F-MR relaxometry? 2. Are oxygen tension as detected by 19F-MR relaxometry (pO2/relaxo) comparable to Eppendorf O2-electrode measurements (pO2/electrode)? 3. Can 19F-MR relaxometry be used to detect oxygen tension changes in tumor tissue during carbogen breathing?

METHODS AND MATERIALS

Slice-selective 19F-MR relaxometry was carried out with perfluoro-15-crown-5-ether as oxygen sensor. The PFC was injected i.v. 3 days before the 19F-MR experiments. Two datasets were acquired before and two after the start of carbogen breathing. The distribution of PFCs and necrotic areas were analyzed in 19F-Spin Echo (SE) density MR images and T2-weighted 1H-SE MR images, respectively. One day after the MR investigations, oxygen tensions were measured by oxygen electrodes in the same slice along two perpendicular tracks. These measurements were followed by (immuno)histochemical analysis of the 2D distribution of perfused microvessels, hypoxic cells, necrotic areas, and macrophages.

RESULTS

The PFCs mainly became sequestered in perfused regions at the tumor periphery; thus, 19F-MR relaxometry probed mean oxygen tensions in these regions throughout the selected MR slice. In perfused regions of the tumor, mean PO2/relaxo values were comparable to mean PO2/electrode values, and varied from 0.03 to 9 mmHg. Median pO2/electrode values of both tracks were lower than mean pO2/relaxo values, because low pO2 electrode values that originate from hypoxic and necrotic areas were also included in calculations of median pO2/electrode values. After 8-min carbogen breathing, the average PO2/relaxo increase was 3.3 +/- 0.8 (SEM) mmHg and 2.1 +/- 0.6 (SEM) after 14 min breathing.

CONCLUSIONS

We have demonstrated that PFCs mainly became sequestered in perfused regions of the tumor. Here, mean PO2/relaxo values were comparable to mean PO2electrode values. In these areas, carbogen breathing was found to increase the PO2/relaxo values significantly.

The optimal combination of hyperthermia and carbogen breathing to increase tumor oxygenation and radiation response

PURPOSE

To determine the most effective combination of carbogen breathing with mild temperature hyperthermia (MTH) to increase the oxygenation and radiation response in murine tumors.

METHODS AND MATERIALS

MTH at 41.5 degrees C for 60 min was applied by immersion of the tumor in a precisely controlled water bath. The tumor pO2 was measured with a polarographic microelectrode. The radiation response of the tumor was determined using the in vivo/in vitro assay for surviving tumor cells.

RESULTS

In the FSaII fibrosarcoma the median pO2 increased from a control value of 6.5 +/- 0.5 mm Hg to 16.6 +/- 1.1 mm Hg immediately after MTH and was 10.9 +/- 1.3 mm Hg 24 h later. Carbogen breathing for 5 min increased the FSaII pO2 to 19.9 +/- 2.1 mm Hg. Carbogen breathing for 5 min beginning immediately after MTH increased the median pO2 more than 5 times to 35.4 +/- 3.8 mm Hg. This combined treatment also substantially increased the response of the tumors to a radiation exposure of 20 Gy. In another tumor model, the SCK mammary carcinoma, MTH treatment increased the median pO2 from the control level of 4.4 +/- 0.2 mm Hg to 12.6 +/- 1.2 mm Hg, and it returned to 4.3 +/- 0.3 mm Hg 24 h later. Carbogen breathing for 5 min increased the SCK tumor pO2 to 17.1 +/- 1.4 mm Hg. The median SCK pO2 was increased about 7 times to 31.2 +/- 4.2 mm Hg when MTH was followed immediately with carbogen breathing for 5 min. The radiation response was also markedly increased by this combination. When the animals breathed carbogen for 15 or 30 min, the pO2 and radiosensitivity in both tumor types either remained the same or was lower than that after 5 min of breathing. In addition, both FSaII and SCK tumors were radiosensitized 24 h after MTH treatment alone or with 5 min of carbogen breathing.

CONCLUSIONS

A shorter carbogen breathing time immediately after MTH causes the most tumor radiosensitization. The results of this study also demonstrate that MTH increases radiosensitivity with and without carbogen breathing up to 24 h after the mild hyperthermia treatment.

Spectroscopic imaging of the water resonance with short repetition time to study tumor response to hyperoxia

A variety of treatments that modulate tumor oxygen tension are used clinically to improve the outcome of radiotherapy. High resolution, noninvasive measurements of the effects of these treatments would greatly facilitate the development of improved therapies and could guide treatment of cancer patients. Previous work demonstrated that magnetic resonance (MR) gradient echo imaging of the water proton resonance detects changes in T2* and T1 in tumors during hyperoxia that may reflect increased tumor oxygenation. This report describes the use of high resolution MR spectroscopic imaging with short repetition time (TR = 0.2 s) to improve the accuracy with which changes in T2* and T1 are measured. Mammary adenocarcinomas grown in the hind limbs of rats were studied. Carbogen inhalation was used to induce hyperoxia. A single 2-mm slice through the center of tumors and underlying muscle was imaged at 4.7 Tesla with in-plane resolution of approximately 1.2 mm and frequency resolution of 5.8 Hz. The peak integral increased by an average of 6% in tumors during carbogen inhalation suggesting a decrease in T1 (n = 8, P < 0.001). Peak height increased by an average of 15% in tumors during carbogen inhalation (n = 8, P < 0.001). The large difference between increases in peak height and peak integral demonstrates that the width of the water resonance decreased. Assuming a Lorentzian lineshape, an average increase of 12% in T2* was observed in tumors. In muscle, peak integral and peak height increased slightly (about 1.2% and 3%, respectively; P < 0.02) during carbogen inhalation but no significant change in T2* was observed. Spectroscopic imaging detects changes in the water proton resonance in tumors during hyperoxia accurately and reproducibly with high signal-to-noise ratio and allows clear separation of T1 and T2* effects. Increases in T2* may be due to decreased deoxyhemoglobin in tumor blood vessels (i.e., the BOLD effect) and may provide a clinically useful index of increases in tumor oxygenation.

Administration of nicotinamide during a five- to seven-week course of radiotherapy: pharmacokinetics, tolerance, and compliance

BACKGROUND AND PURPOSE

Nicotinamide was administered daily as a liquid formulation to head and neck cancer patients receiving a 5- to 7-week course of radiotherapy. The pharmacokinetics, compliance, and tolerance of this drug formulation were studied.

MATERIALS AND METHODS

Blood samples were drawn and nicotinamide levels determined in 40 head and neck cancer patients. On the first treatment day serial samples were obtained followed by daily samples at the time of irradiation during the first and last full weeks of the treatment. Side-effects of nicotinamide were monitored.

RESULTS

In all patients peak concentrations greater than 700 nmol/ml could be obtained 0.25-3 h (mean 0.83 +/- 0.73 h) after drug intake. During the first week of treatment plasma levels at the time of irradiation were adequate in 82% of the samples. This decreased to 59% in the last week of treatment which can be partly attributed to reduced compliance. The most important side-effect of nicotinamide was nausea with or without vomiting occurring in 65% of the patients. Severe side-effects were associated with high plasma concentrations over subsequent days. Tolerance improved after a 25% reduction of dose in six of seven patients but plasma levels at the time of irradiation fell below 700 nmol/ml in four out of six of these patients.

CONCLUSIONS

Peak plasma concentrations above the 700 nmol/ml level were obtained in all patients but these concentrations could not be reproduced during the entire course of the treatment in a significant portion of the subjects. Side-effects of nicotinamide are associated with plasma concentrations and tolerance can be improved by a moderate reduction of dose.

Hyperfractionation: where do we stand?

Hyperfractionation is generally expected to allow an escalation of total dose, thereby increasing tumour control rate, without increasing the risk of late complications. The purpose of this review is to assess the empirical evidence for this therapeutic gain from hyperfractionated radiotherapy. Although extensive clinical data have been accumulated until now, especially on treatment of head and neck cancer, the line of evidence is not consistent. The present analysis indicates that the dose per fraction generally used in standard radiotherapy is already a good choice.

Comparison of two techniques for detecting tumour hypoxia: a fluorescent immunochemical method and an in vitro colony assay

The aim of this study was to compare the percentage of hypoxic cells obtained with two methods: an in vitro colony assay and a new method based on immunodetection of a marker for hypoxic cells (NITP) which could be used in patients. These studies have been carried out using one rodent tumour EMT6 (a mammary carcinoma) and one human tumour HRT18 (a rectal adenocarcinoma). The hypoxic cell fraction was assessed in control mice and in mice receiving two treatments: 250 mg/kg nicotinamide + carbogen, and 250 mg/kg nicotinamide + carbogen + 4 ml/kg perflubron emulsion. The two treatments increased the radiosensitivity of the two cell lines, nicotinamide plus carbogen plus perflubron emulsion having the greatest radiosensitising effect. For untreated and treated tumours, the percentage of hypoxic cells obtained with the in vitro colony assay were comparable to those obtained with immunodetection using NITP. Whatever the treatment, NITP detection was a convenient test to detect the hypoxic cell fraction in the two solid tumours we have studied.

Radiosensitisation in normal tissues with oxygen, carbogen or nicotinamide: therapeutic gain comparisons for fractionated x-ray schedules

METHODS

Radiosensitisation with oxygen, carbogen or nicotinamide alone and oxygen or carbogen combined with nicotinamide was compared in early and late responding normal tissues in rodents. X-ray treatments were delivered as single doses or fractionated schedules of 2 fractions in 1 day, 2, 12 and 36 fractions in an overall time of 12 days and 10 fractions in 5 or 12 days. Acute skin reactions, survival of intestinal crypts, breathing rate, reduction in the packed red-cell volume and clearance of 51Cr-EDTA were used as assays of epidermal, gut, lung and renal damage.

RESULTS

Relative to air-breathing mice, carbogen or oxygen produced a small, and not always significant, increase in sensitivity (enhancement ratios < or = 1.15) in gut, lung and kidneys; however, in skin a dose enhancement of 1.2-1.3 was observed. The effect of nicotinamide in air, carbogen or oxygen was studied only in lung and gut. The drug produced variable but generally significant increases in radiosensitisation ( < or = 1.26) in all three gases. Relative to treatments in air, enhancement ratios for nicotinamide alone were usually slightly higher than those observed when either carbogen or oxygen were administered without the drug. With all three modifiers (i.e. oxygen, carbogen, nicotinamide alone or for the drug-gas combinations) there was no significant change in the enhancement ratios observed as the number of radiation dose fractions was varied.

CONCLUSIONS

Comparisons with fractionated X-ray studies done previously in rodent tumours indicate that a therapeutic benefit, relative to lung, gut and renal damage, would be observed with oxygen or carbogen alone but not with nicotinamide alone. The greatest gain would be achieved with the combination of carbogen and nicotinamide, with which a benefit was observed even relative to epidermal damage. These results indicate that some decrease in normal tissue tolerance could be observed when using these modifiers in clinical radiotherapy and, although small, the appropriate dose reductions should be considered; caution should be exercised especially when carbogen and nicotinamide are used in conjunction with the more radical accelerated schedules.

Evidence that hypoxia markers detect oxygen gradients in liver: pimonidazole and retrograde perfusion of rat liver

Nitroimidazole markers of tumour hypoxia bind to normoxic liver and the question has been raised whether this is due to low oxygen concentration or microregional activity of specialised nitroreductases. To answer this question, the binding patterns of the 2-nitroimidazole, pimonidazole, were compared following perfusion of surgically isolated rat livers in anterograde and retrograde directions. Perfusion at low flow rates in anterograde or retrograde directions can be used intentionally to alter oxygen gradients without altering enzyme distributions. Perfusion by means of the portal vein (anterograde direction) produced pimonidazole binding in the pericentral region of liver similar to that observed for pimonidazole binding in vivo. A complete reversal of this binding pattern occurred when the isolated liver was perfused by way of the central vein (retrograde direction). In this case, pimonidazole binding occurred in the periportal region. The extent and intensity of binding in the periportal region during perfusion in the retrograde direction was similar to that in the pericentral region during perfusion in the anterograde direction. It is concluded that low oxygen concentration rather than the non-homogeneous distribution of nitroreductase activity is the primary determinant of 2-nitroimidazole binding in liver.

Perfusion changes in the RIF-1 tumour and normal tissues after carbogen and nicotinamide, individually and combined

The strategy of combining carbogen breathing and nicotinamide to overcome chronic and acute hypoxia respectively is being evaluated clinically. The effects of both agents individually and in combination on relative perfusion of 400-700 mm3 RIF-1 tumours and normal tissues were measured by 86Rb extraction. Carbogen breathing alone for 6 min increased relative tumour perfusion by 50-70% compared with control at flow rates of 50 to 200 ml min-1, but the effect was lost at 300 ml min-1. All flow rates also produced similar increases in relative perfusion of lung, of between 36% and 58%, and smaller increases in skin, of between 20% and 34%. The minimum breathing time at 150 ml min-1 to produce a significant increase in relative tumour perfusion was 4.5 min, and the effect was maintained up to 9 min. Nicotinamide alone at 1000 mg kg-1 60 min before assay did not alter relative tumour perfusion. Comparing the combination of nicotinamide with 6 min carbogen breathing at 150 ml min-1 with carbogen breathing alone showed no difference in relative tumour perfusion; increases were of 36% and 42% respectively. Nicotinamide-induced alterations in microcirculation associated with reduction of acute hypoxia have therefore not been detected by 86Rb extraction. The perfusion-enhancing effect of carbogen in this tumour is probably an important component of its radiosensitising ability, in addition to its known ability to increase the oxygen-carrying capacity of the blood, and should be taken into consideration in clinical studies.

Rapid tissue oxygen tension mapping using 19F inversion-recovery echo-planar imaging of perfluoro-15-crown-5-ether

Fluorine-19 inversion-recovery, echo-planar imaging (IR-EPI) was used in conjunction with a new PFC emulsion, perfluoro-15-crown-5-ether, to map the spatial distribution of oxygen tension in murine liver, spleen and radiation induced fibrosarcoma (RIF-1) tumors. Intravenously administered PFC emulsions were allowed to sequester in the liver, spleen, and tumor 3 to 7 days prior to imaging experiments. Seven, 64 x 64 IR-EPIs were acquired with successively increasing inversion times (TI). A nonlinear least-squares regression algorithm was used to fit the seven two-dimensional matrices, on a pixel-by-pixel basis, to solve for the relaxation rate, R1, of the sequestered PFC. From in vitro calibration curves, the oxygen tension (pO2) was calculated from the measured R1. Oxygen tension maps were then murine liver and spleen were produced (in 2.5 min) to demonstrate the technique and changes in tissue oxygenation as a function of breathing gas (air and carbogen (95% O2-5% CO2)) are presented. Tissue pO2 maps from RIF-1 tumors (n = 5) were obtained in less than 10 min and changes in tumor pO2 were studied when the breathing gas was switched from air to carbogen. The results from tumor pO2 maps were compared with 19F MR spectroscopy measurements to check for consistency. Histogram analysis yielded an average liver and spleen pO2 of 43 torr and 26 torr for RIF-1 tumors when the animals were breathing air. Statistically significant changes in tumor oxygenation as a function of breathing gas were obtained from both pO2 maps (6 +/- 2 torr, P < 0.05) and 19F MR spectroscopy (13 +/- 3 torr, P < 0.01) as evaluated using the Student's paired t test.

Pharmacokinetics and tolerance of nicotinamide combined with radiation therapy in patients with glioblastoma multiforme

The pharmacokinetic properties of nicotinamide and its tolerance were studied in seven patients affected by glioblastoma multiforme and treated with two fractions per day of radiation therapy. Nicotinamide was given orally at two daily doses of 4 g and then 2 g separated by a 6-h-interval. The treatment was well tolerated in almost all patients and had no effect on blood pressure, cardiac rhythm or body temperature. Pharmacokinetic analysis showed peak plasma levels (Cmax) above 100 mg/l 45 minutes after the administration of both doses. This was followed by a biexponential decay of plasma concentrations with a thermal half life of 9.4h. Tumours were irradiated 1 hour after each drug dose to match with drug Cmax in plasma, and although it is too early to evaluate the tumour response, the drug levels achieved should be sufficient to improve radiation therapy.

Changes in the oxygenation of head and neck tumors during carbogen breathing

The oxygenation of head and neck tumors and changes during carbogen breathing were assessed in 20 patients. The median oxygen tension (pO2) for each patient was lower in tumors before breathing carbogen than in normal tissues. The median pooled pO2 of all the tumors was 20 mmHg; for normal tissue it was 60 mmHg. Low values (below 10 mmHg) were found in 4 patients for the normal tissue and in 18 patients for tumors. During carbogen breathing, the median (61 mmHg) pO2 readings for all tumors was higher than that recorded before carbogen breathing. The frequency of low (< 10 mmHg) pO2 values decreased with carbogen breathing in 11 patients; only 4 patients still exhibited very low values (< 2 mmHg). Maximal effect was obtained within 1-6 min of gas exposure. The pO2 stayed high under carbogen breathing in 15 out of 16 patients. Return to pre-carbogen levels of oxygenation occurred in 1 min after the end of gas exposure. These data suggest that carbogen breathing increases tumor oxygenation as assessed by polarography. The breathing time appears to be important for therapeutical use and should to be taken into consideration.

Pharmacokinetics of nicotinamide and its effect on blood pressure, pulse and body temperature in normal human volunteers

The pharmacokinetics of nicotinamide were studied in four human volunteers after oral doses of 1-6 g. Plasma concentrations and clearance rates of the vitamin were found to be dose-dependent, with a half-life of approximately 7-9 h for the two highest doses administered (4 and 6 g), approximately 4 h with 2 g and approximately 1.5 h with a 1-g dose. Peak concentrations ranged from 0.7 to 1.1 mumol.ml-1 after a 6-g dose. The time to reach peak plasma concentration was dose independent with a broad range from 0.73 to 3 h. In this study, nicotinamide had no detectable effect on blood pressure, pulse or body temperature.