The radiation response of KHT sarcomas following nicotinamide treatment and carbogen breathing

The Role of Imaging Biomarkers to Guide Pharmacological Interventions Targeting Tumor Hypoxia

Hypoxia is a common feature of solid tumors that contributes to angiogenesis, invasiveness, metastasis, altered metabolism and genomic instability. As hypoxia is a major actor in tumor progression and resistance to radiotherapy, chemotherapy and immunotherapy, multiple approaches have emerged to target tumor hypoxia. It includes among others pharmacological interventions designed to alleviate tumor hypoxia at the time of radiation therapy, prodrugs that are selectively activated in hypoxic cells or inhibitors of molecular targets involved in hypoxic cell survival (i.e., hypoxia inducible factors HIFs, PI3K/AKT/mTOR pathway, unfolded protein response). While numerous strategies were successful in pre-clinical models, their translation in the clinical practice has been disappointing so far. This therapeutic failure often results from the absence of appropriate stratification of patients that could benefit from targeted interventions. Companion diagnostics may help at different levels of the research and development, and in matching a patient to a specific intervention targeting hypoxia. In this review, we discuss the relative merits of the existing hypoxia biomarkers, their current status and the challenges for their future validation as companion diagnostics adapted to the nature of the intervention.

Imaging of Tumor Hypoxia for Radiotherapy: Current Status and Future Directions

Tumor regions that are transiently or chronically undersupplied with oxygen (hypoxia) and nutrients, and enriched with acidic waste products, are common due to an abnormal and inefficient tumor vasculature, and a deviant highly glycolytic energy metabolism. There is compelling evidence that tumor hypoxia is strongly linked to poor prognosis since oxygen-deprived cells are highly resistant to therapy including radio- and chemotherapy, and survival of such cells is a primary cause of disease relapse. Despite a general improvement in cancer survival rates, hypoxia remains a formidable challenge. Recent progress in radiation delivery systems with improved spatial accuracy that allows dose escalation to hypoxic tumors or even tumor subvolumes, and the development of hypoxia-selective drugs, including bioreductive prodrugs, holds great promise for overcoming this obstacle. However, apart from one notable exception, translation of promising preclinical therapies to the clinic have largely been disappointing. A major obstacle in clinical trials on hypoxia-targeting strategies has been the lack of reliable information on tumor hypoxia, which is crucial for patient stratification into groups of those that are likely to benefit from intervention and those who are not. Further, in many newer trials on hypoxia-selective drugs the choice of cancer disease and combination therapy has not always been ideal, especially not for clinical proof of principle trials. Clearly, there is a pending need for clinical applicable methodologies that may allow us to quantify, map and monitor hypoxia. Molecular imaging may provide the information required for narrowing the gap between potential and actual patient benefit of hypoxia-targeting strategies. The grand majority of preclinical and clinical work has focused on the usefulness of PET-based assessment of hypoxia-selective tracers. Since hypoxia PET has profound inherent weaknesses, the use of other methodologies, including more indirect methods that quantifies blood flow or oxygenation-dependent flux changes through ATP-generating pathways (eg, anaerobic glycolysis) is being extensively studied. In this review, we briefly discuss established and emerging hypoxia-targeting strategies, followed by a more thorough evaluation of strengths and weaknesses of clinical applicable imaging methodologies that may guide timely treatment intensification to overcome hypoxia-driven resistance. Historically, most evidence for the linkage between hypoxia and poor outcome is based on work in the field of radiotherapy. Therefore, main emphasis in this review is on targeting and imaging of hypoxia for improved radiotherapy.

Tumor oxygenation and cancer therapy-then and now

In 2012, cancer affected 14.1 million people worldwide and was responsible for 8.2 million deaths. The disease predominantly affects aged populations and is one of the leading causes of death in most western countries. In tumors, the aggressive growth of the neoplastic cell population and associated overexpression of pro-angiogenic factors lead to the development of disorganized blood vessel networks that are structurally and functionally different from normal vasculature. A disorganized labyrinth of vessels that are immature, tortuous and hyperpermeable typifies tumor vasculature. Functionally, the ability of the tumor vasculature to deliver nutrients and remove waste products is severely diminished. A critical consequence of the inadequate vascular networks in solid tumors is the development of regions of hypoxia [low oxygen tensions typically defined as oxygen tensions (pO₂ values) < 10 mm Hg]. Tumor cells existing in such hypoxic environments have long been known to be resistant to anticancer therapy, display an aggressive phenotype, and promote tumor progression and dissemination. This review discusses the physiological basis of hypoxia, methods of detection, and strategies to overcome the resulting therapy resistance.

The Clinical Application of Ozonetherapy

The reader may be eager to examine in which diseases ozonetherapy can be proficiently used and she/he will be amazed by the versatility of this complementary approach (Table 9 1). The fact that the medical applications are numerous exposes the ozonetherapist to medical derision because superficial observers or sarcastic sceptics consider ozonetherapy as the modern panacea. This seems so because ozone, like oxygen, is a molecule able to act simultaneously on several blood components with different functions but, as we shall discuss, ozonetherapy is not a panacea. The ozone messengers ROS and LOPs can act either locally or systemically in practically all cells of an organism. In contrast to the dogma that “ozone is always toxic”, three decades of clinical experience, although mostly acquired in private clinics in millions of patients, have shown that ozone can act as a disinfectant, an oxygen donor, an immunomodulator, a paradoxical inducer of antioxidant enzymes, a metabolic enhancer, an inducer of endothelial nitric oxide synthase and possibly an activator of stem cells with consequent neovascularization and tissue reconstruction.

Hyperthermic enhancement of tumor radiosensitization strategies

Local hyperthermia of living tissue can cause significant increases in blood flow and oxygenation depending on time-temperature history. Increases in perfusion of the abnormal and insufficient vasculature found in solid tumors may increase tumor oxygenation, thereby increasing the radiation sensitivity of the tumor. We hypothesized that local heating of tumor would increase the oxygenation of the tumor tissue and allow other oxygenating agents to further modify tumor oxygenation and radiation response. In the present study the effect of moderate temperature hyperthermia (MTH) at 41.5-42.5 degrees C for 30-60 min, 250 mg/kg nicotinamide, or carbogen breathing (95% O2/5% CO2) on the radiation sensitivity of FSaII murine fibrosarcomas or R3230 AC rat adenocarcinomas was studied. Individually, these treatments increased the tumor cell sensitivity to single dose 10-15 Gy X-irradiation by 1-5 fold on average, as measured by the in vivo/in vitro tumor excision assay. The combination of tumor MTH with nicotinamide or carbogen breathing increased the radiation sensitivity by 3-5 fold in FSaII tumors and 10-30 fold in R3230 tumors with varying levels of statistical significance. Finally, the triple combination of adjuvant MTH, nicotinamide and carbogen breathing increased the radiation-induced cell death in FSaII tumors to a similar extent as the dual combinations of MTH, nicotinamide or heat, carbogen breathing. However, in R3230 AC tumors the triple adjuvant combination significantly increased radiation-induced cell killing compared to all other dual adjuvant treatments (p < 0.04). To interrogate the mechanism by which heating alters tumor physiology, nitric oxide production in tumor and endothelial cells in culture and tumor tissue after heating was studied. Heating caused an increase in nitric oxide production over a 24 h period after treatment. Subsequently, inhibiting the enzymatic production of NO with L-NAME was found to increase heat-induced growth delay of FSaII tumors. The cause and effect of increased nitric oxide production and the response of the tumor vasculature to heat are discussed in the context of the tumor radiosensitization achieved by heating, carbogen breathing and nicotinamide.

Restoration of normoxia by ozone therapy may control neoplastic growth: a review and a working hypothesis

In contrast to normal tissues, tumors thrive in hypoxic environments. This appears to be because they can metastasize and secrete angiopoietins for enhancing neoangiogenesis and further tumor spread. Thus, during chronic ischemia, normal tissues tend to die, while neoplasms tend to grow. During the past two decades, it has been shown in arteriopathic patients that ozonated autohemotherapy is therapeutically useful because it increases oxygen delivery in hypoxic tissues, leading to normoxia. Although several oxygenation approaches have been tested, none is able to restore normoxia permanently in patients with cancer. We postulate that a prolonged cycle of ozonated autohemotherapy may correct tumor hypoxia, lead to less aggressive tumor behavior, and represent a valid adjuvant during or after chemo- or radiotherapy. Moreover, it may re-equilibrate the chronic oxidative stress and reduce fatigue.

Preclinical studies on how to deal with patient intolerance to nicotinamide and carbogen

BACKGROUND AND PURPOSE

Accelerated radiation carbogen nicotinamide (ARCON) therapy is generally well tolerated, but some patients experience intolerance to nicotinamide and carbogen (95% O(2)+5% CO(2)). This study investigated the effect of reducing both the nicotinamide dose and carbogen CO(2) content on radiation response.

MATERIALS AND METHODS

A C3H mouse mammary carcinoma grown in the right rear foot of female CDF1 was used and treated when at 200 mm(3). Nicotinamide was intraperitoneally injected 20 min prior to irradiation. Carbogen (CO(2) content of either 2 or 5%, balance O(2)) breathing was started 5 min before, and continued during, additional treatments. Radiation was given locally to tissues of restrained non-anaesthetised mice either as a single or fractionated (10 fractions in 12 days) schedule. The endpoints were local tumour control at 90 days, development of moist desquamation 11-23 days after treatment of normal foot skin, or tumour oxygenation measured with the Eppendorf electrode.

RESULTS

The TCD50 values in this tumour following single or fractionated radiation treatment were 52 and 71Gy, respectively. Carbogen (5% CO(2) content) breathing with every radiation treatment in the fractionated schedule significantly (Chi-squared test; P<0.05) enhanced radiation response (ER 1.25). Significant enhancements were also seen with nicotinamide given either as 10x120 mg/kg (ER 1.25), 6x120 mg/kg (ER 1.11) or 10x90 mg/kg (ER 1.18), although the 6x120 schedule was significantly less effective than 10x120. Combining nicotinamide with carbogen resulted in ERs of 1.39-1.44, and these were independent of the nicotinamide treatments. There was also no significant difference in the enhancement of tumour radiation response or improved tumour oxygenation status if the CO(2) content of the gas breathing was varied from 0% (i.e. 100% O(2)) to 2 or 5% (balance O(2)), although a CO(2) content of 2% did give a smaller enhancement of radiation-induced normal skin damage than 5%.

CONCLUSIONS

Both the nicotinamide dose, but not the frequency, and carbogen CO(2) content may be reduced in patients experience intolerance without any significant loss of sensitisation.

Radiotherapy and chemotherapy with or without carbogen and nicotinamide in inoperable biopsy-proven glioblastoma multiforme

BACKGROUND

Nicotinamide and carbogen have been shown to enhance the radiation effect in tumour models.

PURPOSE

Prospective evaluation of the toxicity and efficacy of carbogen and nicotinamide with external beam radiotherapy in the management of inoperable glioblastoma.

PATIENTS AND METHODS

From April 1995 to December 1997, 33 patients with inoperable biopsy-proven glioblastoma multiforme (GBM) were enrolled in a phase II trial, to undergo radiotherapy (59.4 Gy in 1.8 Gy/fraction), intra-arterial cerebral chemotherapy (ACNU 100 mg/m(2), three cycles), carbogen breathing (15 l/min), and nicotinamide (85 mg/kg). This experimental group was compared to a control group of 38 patients with inoperable GBM treated with radiotherapy and three cycles of nitrosourea-based chemotherapy from January 1990 to March 1995, in our institution.

RESULTS

In the experimental group, carbogen breathing was well tolerated, but only 51.5% of patients completed daily nicotinamide over the 6.5-week treatment period. Nausea and vomiting were the most frequent side effects of nicotinamide. No significant difference in overall survival was observed among the two treatment groups: median survival times were 36.7 and 35.3 weeks for patients treated with carbogen and nicotinamide, and for those treated in the control group, respectively.

CONCLUSION

The association of carbogen and nicotinamide with radiotherapy is feasible, but tolerable only in 51.5% of patients with GBM. Carbogen and nicotinamide did not appear to modify the evolution of glioblastoma.

Quantitative tissue perfusion measurements in head and neck carcinoma patients before and during radiation therapy with a non-invasive MR imaging spin-labeling technique

PURPOSE

Tumor blood flow, tumor tissue perfusion and oxygen supply have substantial influence on the responsiveness of tumors to radiotherapy. This study was aimed at implementing and evaluating a non-invasive functional magnetic resonance (MR) imaging spin-labeling technique at a main magnetic field strength of 2T for measuring tissue perfusion changes in head and neck carcinoma patients before and during radiotherapy.

METHODS

Tissue perfusion was determined quantitatively in ten patients with head and neck cancer. Five patients were investigated twice during radiation therapy. For perfusion measurements, a non-invasive MR spin-labeling technique was employed: The longitudinal relaxation time T(1) was measured with segmented Snapshot-FLASH imaging after either slice-selective or non-selective spin inversion. Perfusion values were calculated pixelwise employing a two-compartment tissue model. With this technique no contrast agents are required so that repetitive measurements are possible. Perfusion images with a slice thickness of 10mm and an in-plane resolution of 1.9x2.8mm(2) were acquired at a total scan time of 8:30min per scan.

RESULTS

With the non-invasive MR imaging technique it was possible to visualize tumor and normal tissue perfusion as well as perfusion changes in the course of radiotherapy with a spatial resolution of less than 3mm. Among the investigated subjects measured tumor perfusion and changes in perfusion were heterogenous. In 4/5 patients studied at the start and end of radiotherapy, perfusion decreased, while in one patient there was an increase.

CONCLUSIONS

A method is presented that allows non-invasive and repetitive characterization of tissue perfusion. This parameter may be used for treatment stratification, especially in treatments that use vasomodulation or anti-angiogenic agents.

In vivo measurement of regional oxygenation and imaging of redox status in RIF-1 murine tumor: effect of carbogen-breathing

The purpose of this study was to noninvasively monitor tumor oxygenation and redox status during hyperoxygenation treatment, such as carbogen-breathing, in a murine tumor model using in vivo electron paramagnetic resonance (EPR) spectroscopy and imaging techniques. The study was performed using implanted lithium phthalocyanine (LiPc) microcrystals as the oximetry probe and 3-carbamoylproxyl (3-CP) as the redox probe in RIF-1 tumors implanted in the upper hind leg of C3H mice. Repetitive measurements of pO(2) from the same tumors as a function of tumor growth (8-24 mm in size) showed that the tumors were hypoxic and that the tumor pO(2) values were decreasing with tumor growth. Carbogen-breathing mostly showed an increase in the tumor oxygenation, although there were considerable variations in the magnitude of change among the tumors. The pharmacokinetic studies with 3-CP showed a significant decrease in the overall tumor reduction status in the carbogen-breathing mice. Spatially resolved (imaging) pharmacokinetic data over the tumor volume were obtained to visualize the distribution of the redox status within the tumor. The redox images of the tumor in the air-breathing mice showed significant heterogeneity in the magnitude and spatial distribution of reducing equivalents. On carbogen-breathing the tissue reduction status decreased considerably, with a concomitant decrease in the heterogeneity of distribution of the redox status. The results suggest that 1) carbogen-breathing considerably enhances tissue oxygenation and significantly decreases the redox status in RIF-1 tumor, and 2) changes in the magnitude and distribution of the redox status within the tumor volume during carbogen-breathing are correlated with the increased tissue oxygenation.

Hypoxia as a target for combined modality treatments

There is overwhelming evidence that solid human tumours grow within a unique micro-environment. This environment is characterised by an abnormal vasculature, which leads to an insufficient supply of oxygen and nutrients to the tumour cells. These characteristics of the environment limit the effectiveness of both radiotherapy and chemotherapy. Measurement of the oxygenation status of human tumours has unequivocally demonstrated the importance of this parameter on patient prognosis. Tumour hypoxia has been shown to be an independent prognostic indicator of poor outcome in prostate, head and neck and cervical cancers. Recent laboratory and clinical data have shown that hypoxia is also associated with a more malignant phenotype, affecting genomic stability, apoptosis, angiogenesis and metastasis. Several years ago, scientists realised that the unique properties within the tumour micro-environment could provide the basis for tumour-specific therapies. Efforts that are underway to develop therapies that exploit the tumour micro-environment can be categorised into three groups. The first includes agents that exploit the environmental changes that occur within the micro-environment such as hypoxia and reduced pH. This includes bioreductive drugs that are specifically toxic to hypoxic cells, as well as hypoxia-specific gene delivery systems. The second category includes therapies designed to exploit the unique properties of the tumour vasculature and include both angiogenesis inhibitors and vascular targeting agents. The final category includes agents that exploit the molecular and cellular responses to hypoxia. For example, many genes are induced by hypoxia and promoter elements from these genes can be used for the selective expression of therapeutic proteins in hypoxic tumour cells. An overview of the various properties ascribed to tumour hypoxia and the current efforts underway to exploit hypoxia for improving cancer treatment will be discussed.

Improvement of tumor oxygenation by mild hyperthermia

There is now abundant evidence that oxygenation in rodent, canine and human tumors is improved during and for up to 1-2 days after heating at mild temperatures. An increase in tumor blood perfusion along with a decline in the oxygen consumption rate appears to account for the improvement of tumor oxygenation by mild hyperthermia. The magnitude of the increase in tumor pO(2), determined with oxygen-sensitive microelectrodes, caused by mild hyperthermia is less than that caused by carbogen breathing. However, mild hyperthermia is far more effective than carbogen breathing in increasing the radiation response of experimental tumors, probably because mild hyperthermia oxygenates both (diffusion-limited) chronically hypoxic and (perfusion-limited) acutely hypoxic cells, whereas carbogen breathing oxygenates only the chronically hypoxic cells. Mild hyperthermia is also more effective than nicotinamide, which is known to oxygenate acutely hypoxic cells, in enhancing the radiation response of experimental tumors. The combination of mild hyperthermia with carbogen or nicotinamide is highly effective in reducing the hypoxic cell fraction in tumors and increasing the radiation response of experimental tumors. A primary rationale for the use of hyperthermia in combination with radiotherapy has been that hyperthermia is equally cytotoxic toward fully oxygenated and hypoxic cells and that it directly sensitizes both fully oxygenated and hypoxic cells to radiation. Such cytotoxicity and such a radiosensitizing effect may be expected to be significant when the tumor temperature is elevated to at least 42-43 degrees C. Unfortunately, it is often impossible to uniformly raise the temperature of human tumors to this level using the hyperthermia devices currently available. However, it is relatively easy to raise the temperature of human tumors into the range of 39-42 degrees C, which is a temperature that can improve tumor oxygenation for up to 1-2 days. The potential usefulness of mild hyperthermia to enhance the response of human tumors to radiotherapy by improving tumor oxygenation merits continued investigation.

Fractionated irradiation combined with carbogen breathing and nicotinamide of two human glioblastomas grafted in nude mice

This study addressed the potential radiosensitizing effect of nicotinamide and/or carbogen on human glioblastoma xenografts in nude mice. U-87MG and LN-Z308 tumors were irradiated with either 20 fractions over 12 days or 5 fractions over 5 days in air-breathing mice, mice injected with nicotinamide, mice breathing carbogen, or mice receiving nicotinamide plus carbogen. The responses to treatment were assessed using local control and moist desquamation. In U-87MG tumors, the enhancement ratios (ERs) at the radiation dose required to produce local tumor control in 50% of the treated mice (TCD(50)) with nicotinamide and/or carbogen ranged from 1.13 to 1.24 for irradiation in 20 fractions over 12 days. In LN-Z308 tumors, the ERs at the TCD(50) with nicotinamide and/or carbogen ranged from 1.22 to 1.40 for irradiation in 5 fractions over 5 days and from 1.11 to 1.30 in 20 fractions over 12 days, respectively. Skin injury was slightly enhanced, with ERs ranged from 1.06 to 1.15 when radiation was combined with carbogen and/or nicotinamide. Thus carbogen and nicotinamide can slightly improve the radiation response of human glioblastoma xenografts.

Enhancement of tumor perfusion and oxygenation by carbogen and nicotinamide during single- and multifraction irradiation

Numerous experimental and clinical studies have been completed regarding the effects of carbogen and nicotinamide on tumor oxygenation and radiosensitivity. The current study incorporates three physiological measurement techniques to further define spatial variations in oxygen availability and development of hypoxia after single- and multifraction irradiation in KHT murine fibrosarcomas. Distances to anatomical and perfused blood vessels were measured using immunohistochemical and fluorescent staining, intravascular oxygen levels were determined cryospectrophotometrically, and tumor hypoxia was quantified using uptake of EF5, a marker of hypoxia. Carbogen, nicotinamide, and the combination of both all increased intravascular oxygen availability compared to controls. While nicotinamide had no effect on the number of perfused blood vessels in nonirradiated tumors, carbogen produced a substantial closing of vessels. After a single dose of 4 Gy, only the combination of nicotinamide and carbogen produced significant improvements in oxygen availability, while numbers of perfused vessels were significantly increased for nicotinamide, unchanged for the combination of nicotinamide and carbogen, and significantly decreased for carbogen. After 4 x 4-Gy fractions, oxygen availability was increased substantially with the combination of nicotinamide and carbogen, somewhat with carbogen, and not at all with nicotinamide. Tumor oxygenation changes were estimated by EF5/Cy3 intensity distributions, which demonstrated that manipulative agents could produce disparate effects on tumor hypoxia when combined with either single- or multifraction irradiation.

Nicotinamide as a radiosensitizer in tumours and normal tissues: the importance of drug dose and timing

BACKGROUND AND PURPOSE

Nicotinamide is a radiation sensitizer currently undergoing clinical testing. This was an experimental study to determine the importance of drug dose and time interval between drug administration and irradiation for radiosensitization.

MATERIALS AND METHODS

Nicotinamide (50-500 mg/kg) was injected intraperitoneally into CDFI or C3H mice and drug plasma pharmacokinetics were determined by HPLC. Radiosensitization was measured in tumours and normal tissues after local irradiation. The tumours were a C3H mammary carcinoma, the KHT sarcoma and the SCCVII carcinoma. Tumour response was assessed using either growth delay (C3H) or clonogenic survival (KHT/SCCVII). Normal tissue toxicities evaluated included early responding skin (development of moist desquamation of the foot) and late responding bladder (reservoir function estimated by cystometry) and lung (ventilation rate measured by plethysmography).

RESULTS

All nicotinamide peak plasma concentrations were seen within 30 min after injection. Irradiating tumours at peak times resulted in enhancement ratios (ERs) of 1.27 (C3H), 1.75 (KHT) and 1.45 (SCCVII) with high nicotinamide doses and 1.27 (C3H), 1.28 (KHT) and 1.36 (SCCVII) after giving clinically relevant doses (100-200 mg/kg). Lower ERs were observed when the time interval between drug injection and irradiation was increased beyond the peak time. Irradiating normal tissues at peak times after injecting 100-200 mg/kg nicotinamide gave ERs of 1.20 (skin), 0.90 (bladder) and 1.02 (lung).

CONCLUSIONS

Clinically achievable doses of nicotinamide will enhance tumour radiation damage while having minimal effects in normal tissues, but for the best tumour effect radiation should be given at the time of peak plasma drug concentrations.

Effects of carbogen plus fractionated irradiation on KHT tumor oxygenation

BACKGROUND AND PURPOSE

Numerous studies have demonstrated improvements in the oxygenation of tumor cells following both irradiation and carbogen breathing. The current studies were initiated to measure the combined effects of carbogen inhalation plus single and multi-dose irradiation on tumor oxygen availability, to better define the underlying physiological relationships.

MATERIALS AND METHODS

Using KHT murine sarcomas, radiation was delivered to the tumor-bearing legs of non-anesthetized mice. Tumors were quick-frozen prior to or following single or multifraction irradiation and carbogen breathing, and intravascular HbO2 saturation profiles were determined cryospectrophotometrically.

RESULTS

HbO2 levels for blood vessels located near the tumor surface initially decreased following 10 Gy irradiation, then increased and remained elevated. Interior HbO2 levels remained unchanged. Following 2.5 Gy, HbO2 changes were minimal. At 24 h following 10 Gy, HbO2 levels were significantly increased compared to non-irradiated controls, and carbogen breathing produced no additional benefit. At 24 h following five fractions of 2 Gy, HbO2 levels throughout the tumor volume were significantly higher in carbogen breathing animals than in air breathing controls.

CONCLUSIONS

Although peripheral blood vessels demonstrated substantial improvements in oxygenation following irradiation, oxygen availability nearer the tumor center remained at very low levels. The utility of carbogen in enhancing tumor oxygen availability was maintained following five clinically relevant fractions. At higher doses, radiation-induced enhancements in HbO2 levels overshadowed the carbogen effect. For either air or carbogen breathing, a decrease in the percentage of vessels with very low oxygen content did not appear to be a major factor in the reoxygenation of the KHT tumor.

Carbogen and nicotinamide in the treatment of bladder cancer with radical radiotherapy

Carbogen and nicotinamide have been evaluated in a phase II study as hypoxia-modifying agents during radical radiotherapy for bladder cancer using a standard daily 20-fraction schedule. Three groups of patients have received (a) nicotinamide alone, given orally in a dose of 80 mg kg(-1) daily with 52.5 Gy in 20 fractions over 4 weeks, (b) carbogen alone, with 50 Gy in 20 fractions over 4 weeks, and (c) carbogen and nicotinamide, with 50-52.5 Gy in 20 fractions over 4 weeks. Ten patients were treated in each group. All patients completed carbogen and radiotherapy as prescribed, but only 45% completed daily nicotinamide over the 4-week treatment period. The end points of this study were acute bowel and bladder morbidity and local control at cystoscopy 6 months after treatment. An expected level of acute bowel and bladder morbidity was seen that reverted to normal in most patients by 12 weeks with no difference between the three treatment groups. Complete response rates at 6 months were seven out of ten (100%) in the nicotinamide alone group, nine out of ten (90%) in the carbogen alone group and seven out of ten (70%) in the carbogen and nicotinamide group. It is concluded that carbogen and nicotinamide may improve the results of daily fractionated radiotherapy in bladder cancer and that further evaluation is required.

Effect of carbogen breathing on tumour microregional blood flow in humans

BACKGROUND AND PURPOSE

Carbogen is currently being re-evaluated as a radiosensitiser. It acts primarily by increasing tissue pO2, although there is evidence to suggest that enhanced tumour blood flow may also be a component of its action.

MATERIALS AND METHODS

Ten tumours in eight patients with advanced malignant disease were studied. Up to six microprobes, each with an estimated sampling volume of 10(-2) mm3, were inserted into the tumours. Ten min of baseline readings were taken prior to a 10 min carbogen (95% O2/5% CO2) breathing period, measurements were continued for a further 10 min.

RESULTS

The results show that in 34 microregions analysed no overall change in tumour perfusion was seen with carbogen breathing. Individual tumour analysis demonstrated variation in response between patients to carbogen-after 6 min of carbogen four tumours showed an increase in blood flow by more than 10% of the pre-breathing value, two a decrease and four no change. The magnitude of change was small, with only two tumours fluctuating by more than 25%.

CONCLUSIONS

These findings confirm the presence of transient fluctuations in microregional blood flow in human tumours but suggest that the radiosensitising action of carbogen lies primarily in its effect on increasing the oxygen capacity of blood. This supports the addition of agents such as nicotinamide with carbogen in order to overcome both diffusion and perfusion limited hypoxia.

Enhancement of radiation effect by Ginkgo biloba extract in C3H mouse fibrosarcoma

BACKGROUND AND PURPOSE

Ginkgo biloba leaf extract (GBE) is known to increase peripheral blood circulation. The hypothesis that GBE may be able to enhance radiosensitivity of tumor by improving tumor blood flow and thus decreasing hypoxic fraction was tested.

MATERIALS AND METHODS

Fibrosarcoma (FSaII) growing in C3H mouse leg muscle was used as a tumor model. GBE was given i.p. 1 h before irradiation with or without priming dose given 1 day earlier. Effect on tumor and normal tissue radiation reaction was investigated.

RESULTS

Tumor growth delay by radiation was more elongated after two doses (1-day interval) of GBE than after a single dose. Radiation dose for 3-day tumor growth delay was decreased from 12.45 (10.97-13.93) Gy to 6.06 (3.89-8.22) Gy by two doses of GBE [enhancement ratio = 2.06 (1.32-2.79)]. Hypoxic cell fraction was 10.6% (6.3-18.2%) for control, 7.2% (3.8-14.0%) after a single dose (P = 0.18) and 2.7% (1.5-5.0%) after two doses (P < 0.001). Radiation effect on normal tissue, estimated by acute skin reaction and jejunal crypt assay, was not affected by GBE.

CONCLUSION

Ginkgo biloba extract enhances radiation effect on tumor without increasing acute normal tissue radiation damage in this model system probably by increasing tumor blood flow and further investigation for this possible radiosensitizer is needed.

Direct relationship between radiobiological hypoxia in tumors and monoclonal antibody detection of EF5 cellular adducts

While the potential importance of hypoxia in limiting the sensitivity of tumor cells to ionizing radiation has long been appreciated, methods for accurately quantifying the number of radiation-resistant hypoxic cells within tumors have been lacking. We have used the pentafluorinated derivative [2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acet amide] of etanidazole (EF5), which binds selectively to hypoxic cells. The adducts formed between EF5 and cellular proteins in the hypoxic cells were detected using the specific monoclonal antibody (MAb), ELK3-51 conjugated to the flurochrome Cy3, and the number of hypoxic cells was quantified by flow cytometry. To verify the validity of this technique for the detection of hypoxic cells, mice bearing KHT sarcomas were treated with various agents to alter tumor oxygenation and hence vary the fraction of radiobiologically hypoxic tumor cells. The percentage of EF5 binding cells was then compared directly with the clonogenic survival of the tumor cells following radiation treatment under the various pretreatment conditions. The results showed that allowing the mice to breathe carbogen (5% CO2/95% O2) prior to irradiation reduced clonogenic cell survival approx. 6-fold and led to an absence of cells binding high levels of EF5. In contrast, pretreating the tumor-bearing animals with either hydralazine, which decreased tumor blood flow, or phenylhydrazine hydrochloride, which made the mice anemic, increased tumor cell survival following irradiation 2- to 4-fold, indicative of an increase in the fraction of hypoxic tumor cells. EF5 measurements made under identical conditions illustrated a shift in the cells in the tumor to high EF5 binding. Our results demonstrate that flow cytometric measurement by fluorescent MAb binding to EF5 adducts may relate directly to radiobiological hypoxia in KHT tumors measured by conventional methods.

Transient perfusion and radiosensitizing effect after nicotinamide, carbogen, and perflubron emulsion administration

In order to improve the effect of radiation on tumour response, nicotinamide, perflubron emulsion and carbogen were administered which act on both diffusion limited hypoxia and intermittent perfusion limited hypoxia. These treatments were used in different combinations. The maximal radiosensitizing effect was found with the combination of the three treatments. The aim of this study was to use a double staining method (Hoechst 33342 and DiOC7(3) to evaluate the influence of nicotinamide, perflubron emulsion and carbogen on transient perfusion in three tumour cell lines transplanted onto nude mice: one rodent (EMT6), two human (HRT18, a rectal adenocarcinoma; and Na11+, a melanoma). For untreated groups, the percentage of closed and mismatched vessels depended on the tumour cell line. Carbogen alone or carbogen plus perflubron emulsion decreased the number of mismatched and closed vessels only for the two human cell lines. Nicotinamide was effective in decreasing the percentage of mismatched and closed vessels only for the melanoma cell line. The combination of nicotinamide, carbogen and perflubron emulsion was the most effective at decreasing both percentage of mismatched and closed vessels in all three tumours studies. This combination was also the most effective at enhancing the radiation response in all three tumours.

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.

The mechanisms by which hyperbaric oxygen and carbogen improve tumour oxygenation

Hyperbaric oxygen (HBO) has been proposed to reduce tumour hypoxia by increasing the amount of dissolved oxygen in the plasma. That this actually occurs has not been verified experimentally. This study was performed to explore changes in tumour oxygenation induced by treatment with normobaric and hyperbaric oxygen and carbogen. R3230Ac mammary adenocarcinomas were implanted into Fisher 344 rats. Arterial blood gases, blood pressure and heart rate were monitored. Tumour oxygenation was measured polarographically in five sets of animals. They received either normobaric 100% oxygen, hyperbaric (3 atmospheres; atm) 100% oxygen, normobaric carbogen or hyperbaric (3 atm) carbogen (HBC) +/- bretylium. HBO reduced the mean level of low pO2 values (< 5 mmHg) from 0.49 to 0.07 (P = 0.0003) and increased the average median pO2 from 8 mmHg to 55 mmHg (P = 0.001). HBC reduced the level of low pO2 values from 0.82 to 0.51 (P = 0.002) an increased median pO2 from 2 mmHg to 6 mmHg (P = 0.05). Normobaric oxygen and carbogen did not change tumour oxygenation significantly. Sympathetic blockade with bretylium before HBC exposure improved oxygenation significantly more than HBC alone (low pO2 0.55-0.17, median pO2 4-17 mmHg). HBO and hyperbaric carbogen improved tumour oxygenation in this model, while normobaric oxygen or carbogen had no effect. Sympathetic-mediated vasoconstriction during hyperbaric carbogen caused it to be less effective than HBO. This mechanism also appeared to operate during normobaric carbogen breathing.

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.

The effects of carbogen and nicotinamide on intravascular oxyhaemoglobin saturations in SCCVII and KHT murine tumours

Considerable effort has been focused on devising methods for manipulating tumour oxygenation and thereby improving tumour radiosensitivity. The combination of nicotinamide and carbogen has been proposed to oxygenate both chronically and acutely hypoxic cells in tumours. However, results have varied markedly with both tumour model and measurement technique. The current objectives were (1) to determine whether changes in radiosensitivity following oxygen manipulation correlated with changes in tumour oxygenation and (2) to assess whether oxygenation was preferentially improved in specific tumour micro-regions. Using two murine tumour lines, the SCCVII carcinoma and the KHT sarcoma, tumour intravascular HbO2 saturations were measured cryospectrophotometrically following nicotinamide, carbogen or the combination. Generally, nicotinamide had minor effects on oxygenation, arguing against a substantial effect on acute hypoxia, while carbogen and the combination produced marked and equivalent improvements in oxygen availability. These results demonstrate that changes in tumour radiosensitivity may not agree with corresponding changes in oxygenation, even within a given tumour model, and that the efficacy of a given manipulative agent may vary substantially with tumour line. One possible explanation for these findings is that different subpopulations of clonogenic vs non-clonogenic cells may be oxygenated by alternative treatments.

Conventional radiotherapy combined with carbogen breathing and nicotinamide for malignant gliomas

High grade malignant gliomas are among the most radioresistant human tumors and total doses up to 80 Gy are inadequate to achieve long-term local control in most of the patients. Hypoxia has been demonstrated in primary brain tumors and may be one of the reasons for their radioresistance. In experimental models carbogen breathing and nicotinamide have been shown to act against hypoxia by different mechanisms and both modalities were tested in 16 patients with supratentorial malignant gliomas in combination with a conventional radiotherapy scheme (50 Gy in 25 daily fractions). The present study was performed to determine the feasibility and toxicity of conventional radiotherapy combined with carbogen breathing and nicotinamide. The unexpectedly high incidence of acute liver toxicity, the possible increase of subacute and late CNS toxicity, and the absence of a higher effectivity led us to reconsider this new treatment modality for patients with malignant gliomas.

Nicotinamide and other benzamide analogs as agents for overcoming hypoxic cell radiation resistance in tumours. A review

Oxygen deficient hypoxic cells, which are resistant to sparsely ionising radiation, have now been identified in most animal and some human solid tumours and will influence the response of those tumours to radiation treatment. This hypoxia can be either chronic, arising from an oxygen diffusion limitation, or acute, resulting from transient stoppages in microregional blood flow. Although clinical attempts to overcome hypoxia have met with some success, the results have been far from satisfactory, and efforts are still being made to find better methods. Extensive experimental studies, especially in the last decade, have shown that nicotinamide and structurally related analogs can effectively sensitise murine tumours to both single and fractionated radiation treatments and that they do so in preference to the effects seen in mouse normal tissues. The earliest studies suggested that this enhancement of radiation damage was the result of an inhibition of the repair mechanisms, as was well documented in vitro. However, recent studies in mouse tumours have shown that the primary mode of action actually involves a reduction in tumour hypoxia. More specifically, these drugs prevent transient cessations in blood flow, thus inhibiting the development of acute hypoxia. This novel discovery led to the suggestion that the potential role of these agents as radiosensitizers would be when combined with treatments that overcame chronic hypoxia. The first attempt to demonstrate this combined nicotinamide with hyperthermia and found that the enhancement of radiation damage by both agents together was greater than that seen with each agent alone. Similar results were later seen for nicotinamide combined with a perfluorochemical emulsion, carbogen breathing, and pentoxifylline, and in all these studies the effects in tumours were always greater than those seen in appropriate normal tissues. Of all the analogs, it is nicotinamide itself which has been the most extensively studied as a radiosensitizer in vivo and the one that shows the greatest effect in animal tumours. It is also an agent that has been well established clinically for the treatment of a variety of disorders, with daily doses of up to 6 g being considered reasonably safe and associated with a low incidence of side effects. This human dose is equivalent to 100-200 mg/kg in mice and such doses will maximally sensitize murine tumours to radiation. These findings have now resulted in phase I/II clinical trials of nicotinamide, in combination with carbogen breathing, as a potential radiosensitizing treatment.

Are direct measures of tumor oxygenation reflective of changes in tumor radiosensitivity following oxygen manipulation?

The present study investigates the correlation between tumor oxygen availability and radiosensitivity following oxygen manipulation. Previous work has shown that tumors may contain both diffusion- and perfusion-limited hypoxic cells. Recently, the combination of nicotinamide (NIC) administration plus carbogen breathing has been proposed as a means of targeting both hypoxic cell subpopulations. Intravascular HbO2 saturations were measured for KHT murine sarcomas following either NIC, carbogen breathing, or the combination, and compared with determinations of tumor cell survival under matched conditions. The percentage of vessels > or = 25% HbO2 increased significantly for both the carbogen and NIC-carbogen combination, while remaining unchanged from controls following NIC. These findings contrast with the survival data, where all treatments showed identical cell survival. A possible explanation is that different proportions of clonogenic versus nonclonogenic cells may be oxygenated by the alternative treatments. Thus direct determinations of alterations in tumor oxygenation may not reflect corresponding changes in radiosensitivity.

Reducing acute and chronic hypoxia in tumours by combining nicotinamide with carbogen breathing

The ability of nicotinamide and carbogen breathing to improve the radiation response of a C3H mammary carcinoma by reducing both acute and chronic hypoxia was investigated. Using a tumour growth delay assay the response of 200 mm3 foot tumours to local irradiation was found to be increased by either injecting nicotinamide (100-1,000 mg/kg) 20 min prior to irradiation, or by allowing mice to breathe carbogen for 10 min before and during the radiation treatment. The greatest radiosensitization occurred when nicotinamide and carbogen were combined. With a histological fluorescent staining technique nicotinamide was shown to prevent transient stoppages in microregional blood flow, and also appeared to improve tumour oxygenation as measured with an Eppendorf oxygen electrode, both effects being consistent with its ability to decrease perfusion limited acute hypoxia. Carbogen had no effect on vessel closure, but it significantly improved tumour oxygenation, which was indicative of it reducing diffusion limited chronic hypoxia.