Modulation of tumor oxygenation and radiosensitivity by a perfluorooctylbromide emulsion

Perfluorocarbon nanodroplets can reoxygenate hypoxic tumors in vivo without carbogen breathing

Nanoscale perfluorocarbon (PFC) droplets have enormous potential as clinical theranostic agents. They are biocompatible and are currently used in vivo as contrast agents for a variety of medical imaging modalities, including ultrasound, computed tomography, photoacoustic and 19F-magnetic resonance imaging. PFC nanodroplets can also carry molecular and nanoparticulate drugs and be activated in situ by ultrasound or light for targeted therapy. Recently, there has been renewed interest in using PFC nanodroplets for hypoxic tumor reoxygenation towards radiosensitization based on the high oxygen solubility of PFCs. Previous studies showed that tumor oxygenation using PFC agents only occurs in combination with enhanced oxygen breathing. However, recent studies suggest that PFC agents that accumulate in solid tumors can contribute to radiosensitization, presumably due to tumor reoxygenation without enhanced oxygen breathing. In this study, we quantify the impact of oxygenation due to PFC nanodroplet accumulation in tumors alone in comparison with other reoxygenation methodologies, in particular, carbogen breathing. Methods: Lipid-stabilized, PFC (i.e., perfluorooctyl bromide, CF3(CF2)7Br, PFOB) nanoscale droplets were synthesized and evaluated in xenograft prostate (DU145) tumors in male mice. Biodistribution assessment of the nanodroplets was achieved using a fluorescent lipophilic indocarbocyanine dye label (i.e., DiI dye) on the lipid shell in combination with fluorescence imaging in mice (n≥3 per group). Hypoxia reduction in tumors was measured using PET imaging and a known hypoxia radiotracer, [18F]FAZA (n≥ 3 per group). Results: Lipid-stabilized nanoscale PFOB emulsions (mean diameter of ~250 nm), accumulated in the xenograft prostate tumors in mice 24 hours post-injection. In vivo PET imaging with [18F]FAZA showed that the accumulation of the PFOB nanodroplets in the tumor tissues alone significantly reduced tumor hypoxia, without enhanced oxygen (i.e., carbogen) breathing. This reoxygenation effect was found to be comparable with carbogen breathing alone. Conclusion: Accumulation of nanoscale PFOB agents in solid tumors alone successfully reoxygenated hypoxic tumors to levels comparable with carbogen breathing alone, an established tumor oxygenation method. This study confirms that PFC agents can be used to reoxygenate hypoxic tumors in addition to their current applications as multifunctional theranostic agents.

Radiosensitization of Hs-766T Pancreatic Tumor Xenografts in Mice Dosed with Dodecafluoropentane Nano-Emulsion-Preliminary Findings

Tumor hypoxia is an important mediator of radiation therapy resistance. We conducted a study to investigate whether an oxygen therapeutic based upon dodecafluoropentane (DDFP) nano-emulsion (NVX-108) could increase tumor PO2 in hypoxic tumors and improve radiation response. Pancreatic (Hs-766T) tumor xenografts were grown in the flanks of 29 SCID mice. Direct tumor PO2 measurements were performed in 9 mice treated with 0.3, 0.45 and 0.6 cc/kg NVX-108 (2% w/vol DDFP) in order to assess the dose dependent increase in tumor PO2. Twenty mice were randomized into 3 groups including control (no treatment), carbogen breathing treated with 12 Gy radiation, and carbogen breathing treated with 12 Gy radiation and NVX-108 (0.6 cc/kg NVX-108 administered as 30 minute IV infusion at time of radiation). Tumor volume was monitored to assess treatment efficacy. Results showed that tumor PO2 increased in NVX-108 treated mice up to 400% with the greatest effect seen at the highest dose of 0.6 cc/kg. Tumor growth was significantly reduced in both treatment groups relative to controls (p < 0.0001). The combination of carbogen, radiation, and NVX-108 demonstrated a 2-fold reduction in average tumor volume compared to carbogen plus radiation treatment (p = 0.01). Further study of NVX-108 as a radiation sensitizer is warranted.

Direct incorporation of lipophilic nanoparticles into monodisperse perfluorocarbon nanodroplets via solvent dissolution from microfluidic-generated precursor microdroplets

Multifunctional medical agents based on imaging or therapy nanoparticles (NPs) incorporated into perfluorocarbon (PFC) droplets are promising new agents for cancer detection and treatment. For the first time, monodisperse PFC nanodroplets labeled with NPs have been produced. Lipophilic, as-synthesized, hydrocarbon-stabilized NPs are directly miscibilized into lipophobic PFCs using a removable cosolvent, diethyl ether (DEE), which eliminates the need of the typical time-consuming and expertise-specific NP surface modification steps previously required for NP incorporation into PFCs. This NP-DEE/PFC solution is then used to synthesize monodisperse, micrometer-scale, DEE-infused NP-PFC precursor droplets in water using microfluidics. After precursor microdroplet generation, the DEE cosolvent is removed by dissolution and evaporation, resulting in dramatically smaller, monodisperse, NP-labeled nanodroplets, with final droplet sizes far smaller than the minimum droplet size limit of the microfluidic system, and easily controlled by the amount of DEE mixed in the PFC phase prior to precursor droplet synthesis. Using this technique, unmodified lipophilic quantum dot (QD) NPs were integrated into monodisperse and PFC nanodroplets 165 times smaller in volume than the precursor microdroplets, with dimensions down to 470 nm. The final droplet sizes scaled with the PFC concentrations in the precursor microdroplets, and the QDs remain localized within the droplets after DEE is removed from the system. This method is robust and versatile, and it comprises a platform technology for other unmodified lipophilic NPs and molecules to be incorporated into different types of PFC droplets for the production of new NP-PFC hybrid agents for medical imaging and therapy applications.

Preliminary studies with a new hypoxia-selective cytotoxin, KS119W, in vitro and in vivo

Agents with selective toxicity to hypoxic cells have shown promise as adjuncts to radiotherapy. Our previous studies showed that the bioreductive alkylating agent KS119 had an extremely large differential toxicity to severely hypoxic and aerobic cells in cell culture, and was effective in killing the hypoxic cells of EMT6 mouse mammary tumors in vivo. However, the limited solubility of that compound precluded its development as an anticancer drug. Here we report our initial studies with KS119W, a water-soluble analog of KS119. The cytotoxicity of KS119W to EMT6 cells in vitro was similar to that of KS119, with both agents producing only minimal cytotoxicity to aerobic cells even after intensive treatments, while producing pronounced cytotoxicity to oxygen-deficient cells. This resulted in large differentials in the toxicities to hypoxic and aerobic cells (>1,000-fold at 10 μM). Low pH had only minimal effects on the cytotoxicity of KS119W. Under hypoxic conditions, EMT6 cells transfected to express high levels of either human or mouse versions of the repair protein O(6)-alkylguanine-DNA alkyltransferase, which is also known as O(6)-methylguanine DNA-methyltransferase, were much more resistant to KS119W than parental EMT6 cells lacking O(6)-alkylguanine-DNA alkyltransferase, confirming the importance of DNA O-6-alkylation to the cytotoxicity of this agent. Studies with EMT6 tumors in BALB/c Rw mice using both tumor cell survival and tumor growth delay assays showed that KS119W was effective as an adjunct to irradiation for the treatment of solid tumors in vivo, producing additive or supra-additive effects in most combination regimens for which the interactions could be evaluated. Our findings encourage additional preclinical studies to examine further the antineoplastic effects of KS119W alone and in combination with radiation, and to examine the pharmacology and toxicology of this new bioreductive alkylating agent so that its potential for clinical use as an adjuvant to radiotherapy can be evaluated.

Effects of the Perfluorochemical Emulsion FMIQ on the Radiation Response of EMT6 Tumours

The effects of FMIQ, a perfluorochemical emulsion based on perfluoro-N-methyldecahydroisoquinoline, were examined using BALB/c mice and EMT6 mammary carcinomas. The radiobiological effects of FMIQ were similar to those found previously for Fluosol in the same tumour/host system. Although the perfluorochemical content (20% w/v) and oxygen-carrying capacity of FMIQ are similar to those of Fluosol, the formulation of FMIQ offers some advantages over that of Fluosol. For example, FMIQ has greater stability during storage. FMIQ also is formulated without pluronic F-68 and is based on a perfluorochemical (FMIQ) having a shorter tissue dwell time than the perfluorotripropylamine in Fluosol; it therefore may produce fewer side-effects than Fluosol. The lifetime of the circulating perfluorochemical droplets in BALB/c mice was longer than FMIQ than for Fluosol; this could offer an advantage in fractionated radiotherapy. These findings give reason to expect that FMIQ may prove to be a better emulsion than Fluosol for clinical use as an adjunct to cancer therapy.

Towards new functional nanostructures for medical imaging

Nanostructures represent a promising new type of contrast agent for clinical medical imaging modalities, including magnetic resonance imaging, x-ray computed tomography, ultrasound, and nuclear imaging. Currently, most nanostructures are simple, single-purpose imaging agents based on spherical constructs (e.g., liposomes, micelles, nanoemulsions, macromolecules, dendrimers, and solid nanoparticle structures). In the next decade, new clinical imaging nanostructures will be designed as multi-functional constructs, to both amplify imaging signals at disease sites and deliver localized therapy. Proposals for nanostructures to fulfill these new functions will be outlined. New functional nanostructures are expected to develop in five main directions: Modular nanostructures with additive functionality; cooperative nanostructures with synergistic functionality; nanostructures activated by their in vivo environment; nanostructures activated by sources outside the patient; and novel, nonspherical nanostructures and components. The development and clinical translation of next-generation nanostructures will be facilitated by a combination of improved clarity of the in vivo imaging and biological challenges and the requirements to successfully overcome them; development of standardized characterization and validation systems tailored for the preclinical assessment of nanostructure agents; and development of streamlined commercialization strategies and pipelines tailored for nanostructure-based agents for their efficient translation to the clinic.

Using High Spectral and Spatial Resolution Bold MRI to Choose the Optimal Oxygenating Treatment for Individual Cancer Patients

We evaluate whether high spectral and spatial resolution (HiSS) BOLD MRI can correctly rank the effects of three tumor-oxygenating treatments on radiosensitivity in BA1112 rhabdomyosarcomas (n = 5). Significant decreases in spectral linewidth predict that treatment with carbogen gas combined with a perfluorocarbon emulsion will increase radiosensitivity more than either treatment alone, which agrees with the known effects of these treatments on hypoxic fraction. High-resolution maps show that tumor response to each treatment is spatially heterogeneous, and that there is a paradoxical response to the treatments in 7-12% of tumor pixels. Because HiSS MRI emphasizes changes in necrotic and/or hemorrhagic regions, it is more sensitive to oxygenation changes compared to conventional MRI. These results demonstrate that HiSS MRI is a practical, noninvasive method that could be used to choose the treatment that maximizes the size and extent of increases in tumor oxygenation for individual patients.

MRI measurements correctly predict the relative effects of tumor oxygenating agents on hypoxic fraction in rodent BA1112 tumors

PURPOSE

We evaluate whether magnetic resonance imaging (MRI) with blood oxygenation level-dependent (BOLD) contrast correctly predicts the relative effects of tumor-oxygenating agents on hypoxic fraction in BA1112 rhabdomyosarcomas in WAG/Rij rats.

METHODS AND MATERIALS

The response of ten tumors to carbogen (95% O(2)/5% CO(2)), a perfluorocarbon emulsion (PFC), and the combination of PFC + carbogen was studied with high spectral and spatial resolution MR imaging of the water resonance at 4.7 Tesla. Decreases in MR signal linewidth indicate increases in tumor blood oxygen levels.

RESULTS

Average MR signal linewidth was decreased 2.0% by carbogen, 2.5% by PFC + air, and 4.9% by PFC + carbogen. PFC + carbogen caused a larger linewidth decrease than either treatment alone (p < 0.04 by ANOVA). Maps of pixels responding to treatment indicate that combining PFC with carbogen significantly enlarges the area of the tumor in which oxygen levels are increased (p < 0.01 by ANOVA).

CONCLUSION

MRI predicts that PFC + carbogen will increase radiosensitivity more than either treatment alone; this agrees with the known effects of these treatments on hypoxic fraction. Utilizing MRI to choose the treatment that maximizes the size and extent of increases in tumor oxygenation could reduce hypoxic fraction.

Efficacy of agents counteracting hypoxia in fractionated radiation regimes

BACKGROUND AND PURPOSE

Solid tumours contain hypoxic cells which are resistant to radiotherapy. This study compares the efficacy of several strategies to counteract diffusion-limited hypoxia, or intermittent hypoxia in a fractionated regimen of 1 to 6 x 2 Gy.

MATERIALS AND METHODS

Nicotinamide (250 mg/kg), perflubron emulsion (Oxygent) (4 ml/kg), tirapazamine (SR4233) (0.10 mmol/kg) and carbogen breathing, administered alone or in combination, were investigated on two tumour cell lines: EMT6 (a rodent mammary carcinoma) and HRT18 (a human rectal adenocarcinoma) using a clonogenic assay. The radiosensitizing effect of the agents was assessed after 1 and 6 x 2 Gy for drugs used alone, and 1, 2, 4, 6 x 2 Gy for drugs used in combination.

RESULTS

At the end of the fractionated radiation regimen, the combination of nicotinamide + carbogen induced the greatest radiosensitization for EMT6 tumours, while greatest radiosensitization of HRT18 was obtained with nicotinamide + carbogen + tirapazamine.

CONCLUSION

The efficacy of the strategies for overcoming hypoxia using a fractionated regimen depends on the tumour cell line. These differences could be linked to differences in the initial percentages of acute and chronic hypoxic cells, and to changes in the two types of hypoxia during treatment.

Perfluorocarbons: recent developments and implications for neurosurgery

Over the last 30 years, perfluorocarbons (PFCs) have been extensively investigated as oxygen carriers. Early studies indicated that these compounds could be used as blood substitutes or protective agents against ischemia. Adverse characteristics such as instability, short intravascular half-life, and uncertainties concerning possible toxicity precluded wide clinical application. However, advances in PFC technology have led to the development of improved second-generation oxygen carriers that incorporate well-tolerated emulsifiers (egg-yolk phospholipids). The authors review recent developments in this field and consider the potential role of PFCs in future neurosurgical practice. Diagnostic applications could include their use to assess cerebral blood flow, local oxygen tension, and brain metabolism or to achieve enhanced imaging and precise staging of inflammatory, neoplastic, or vascular disease processes by means of computerized tomography, ultrasonography, and magnetic resonance studies. Therapeutic applications could include cerebral protection, an adjunctive role in radiotherapy of malignant brain tumors, protection against air embolism, the preservation of organs for transplantation, and ventilatory support in head-injured patients with compromised lung function. In addition, PFCs have been used successfully as a tool in ophthalmic microsurgery and potentially they could fulfill a similar role in microneurosurgery.

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.

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.

Radiosensitization of mouse skin by oxygen and depletion of glutathione

PURPOSE

To determine the oxygen enhancement ratio (OER) and shape of the oxygen sensitization curve of mouse foot skin, the extent to which glutathione (GSH) depletion radiosensitized skin, and the dependence of such sensitization on the ambient oxygen tension.

METHODS AND MATERIALS

The feet of WHT mice were irradiated with single doses of 240 kVp x-rays while mice were exposed to carbogen or gases with oxygen/nitrogen mixtures containing 8-100% O2. The anoxic response was obtained by occluding the blood supply to the leg of anesthetized mice with a tourniquet, surrounding the foot with nitrogen, and allowing the mice to breathe 10% O2. Further experiments were performed to assess the efficacy of this method to obtain an anoxic response. Radiosensitivity of skin was assessed using the acute skin-reaction assay. Glutathione levels were modified using two schedules of DL-buthionine sulphoximine (BSO) and diethylmaleate (DEM), which were considered to produce extensive and intermediate levels of GSH depletion in the skin of the foot during irradiation.

RESULTS

Carbogen caused the greatest radiosensitization of skin, with a reproducible enhancement of 2.2 relative to the anoxic response. The OER of 2.2 is lower than other reports for mouse skin. This may indicate that the extremes of oxygenation were not produced, although there was no direct evidence for this. When skin radiosensitivity was plotted against the logarithm of the oxygen tension in the ambient gas, a sigmoid curve with a K value of 17-21% O2 in the ambient gas was obtained. Depletion of GSH caused minimal radiosensitization when skin was irradiated under anoxic or well-oxygenated conditions. Radiosensitization by GSH depletion was maximal at intermediate oxygen tensions of 10-21% O2 in the ambient gas. Increasing the extent of GSH depletion led to increasing radiosensitization, with sensitization enhancement ratios of 1.2 and 1.1, respectively, for extensive and intermediate levels of GSH depletion. In mice exposed to 100% O2, a significant component of skin radiosensitivity was due to diffusion of oxygen directly through the skin. Pentobarbitone anesthesia radiosensitized skin in mice exposed to 100% O2 by a factor of 1.2, but did not further sensitize skin in mice exposed to carbogen.

CONCLUSIONS

Glutathione levels and the local oxygen tension at the time of irradiation were important determinants of mouse foot skin radiosensitivity. The extent to which GSH levels altered the radiosensitivity of skin was critically dependent on the local oxygen tension. These results have significant implications for potential clinical application of GSH depletion.

Tumour oxygenation, radiosensitivity, and necrosis before and/or after nicotinamide, carbogen and perflubron emulsion administration

Hypoxia is one of the factors involved in tumour resistance to radiotherapy. One way to improve tumour oxygenation is to use oxygen carriers such as perflubron emulsion plus carbogen or vasoactive drugs such as nicotinamide. The perflubron emulsion and carbogen act mainly on hypoxia caused by limited diffusion of oxygen; nicotinamide acts mainly on acute hypoxia. The aim was to correlate radiosensitivity and pO2 measurements (computerized pO2 histograph) after nicotinamide, perflubron emulsion and carbogen administration, and to determine the role of necrosis in this correlation. Two human tumour xenografts (HRT18, Na11 +) and one rodent tumour (EMT6) were used. Clonogenic assays and pO2 measurements were performed under similar conditions. The radiosensitization and oxygenation levels increased with all treatments. The maximal effects were found with the combination of nicotinamide (1 g/kg), perflubron emulsion and carbogen. A correlation between the radiosensitization and the pO2 measurements was found for the three cell lines with a cut-off point of 10 mmHg. The presence of necrosis could explain the low pO2 (< 2 mmHg) found even when complete radiosensitization was observed.

Assessment of micronucleus induction in SCCVII cells treated with bioreductive agents, WIN 59075 (SR 4233) and mitomycin C, under aerobic and hypoxic conditions

WIN 59075 (SR4233, tirapazamine) is a promising bioreductive antitumor agent preferentially more toxic to hypoxic cells and presently undergoing phase I clinical trials. In this investigation, we have examined the applicability of the cytokinesis-block micronucleus assay to assess the effects of bioreductive agents. SCCVII tumor cells were treated with WIN 59075 or mitomycin C at various concentrations under aerobic and hypoxic conditions. Significant induction of micronuclei in binucleate cells was demonstrated in a dose-dependent fashion and it appeared to be strongly correlated with the loss of clonogenicity in the colony assay. Both agents showed selectively higher toxicity to hypoxic cells than to aerobic cells and the ratios of the concentrations required to obtain the equivalent effects under aerobic and hypoxic conditions could be also estimated by this method as follows: the hypoxic toxicity ratios were 120-130 for WIN 59075 and 3.0-3.3 for mitomycin C. For several favorable characteristics, the cytokinesis-block micronucleus assay can provide an alternative, rapid, and reproducible means for evaluation of antitumor activities from chromosomal breakage caused by the bioreductive agents.

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.

The effect of the perflubron emulsion Oxygent on the calibration characteristics of polarographic oxygen electrodes

The perfluorocarbon emulsion Oxygent improves normal tissue oxygenation. A clinical trial is planned to evaluate this effect in tumors. Polarographic oxygen electrodes were calibrated in solutions of saline +/- perflubron to assess whether Oxygent influenced probe behavior. Calibrations were linear under both conditions. There were no major differences in estimated oxygen tensions.

Nicotinamide and carbogen: relationship between pO2 and radiosensitivity in three tumour lines

The effects of carbogen breathing, nicotinamide injection and their combination on tumour radiosensitivity were correlated with changes in tumour O2 tension to determine the relationship between radiosensitivity and measured pO2. The radiosensitivity (in vivo-in vitro colony assay) and O2 tension (computerized pO2 histograph KIMOC 6650) of two human xenografted tumours (HRT18 and Na11+) and one murine tumour (EMT6) were measured under similar experimental conditions. A single dose of radiation was delivered (8 Gy for HRT18 and Na11+, 12 Gy for EMT6). Carbogen breathing, nicotinamide injection, and their combination all significantly increased radiosensitivity in the three cell lines (p < 0.05); the most efficient treatment was carbogen plus nicotinamide. The radiosensitization was optimum for EMT6 and Na11+. Mean and median pO2 increased with all three treatments, except for carbogen breathing in EMT6. Carbogen breathing had little effect on the proportion of low pO2 values, but induced pO2 values > 30 mmHg in all three tumour lines. Nicotinamide decreased the proportion of low pO2 values. This effect is larger with the combination carbogen plus nicotinamide. Almost all pO2 values < 2.5 mmHg were eliminated for HRT18 and EMT6. The relationship between radiosensitization and pO2 was significant when pO2 was expressed as the percentage of values below 7, 8, 9 and 10 mmHg for the three lines.

Tumor oxygenation after 1) carbogen and/or perflubron emulsion administration in tumor xenografts 2) carbogen administration in patients

This study examines the changes in tumor pO2 distribution assessed by polarography (KIMOC 6650, Eppendorf) in 1) two human tumor xenografts after carbogen inhalation with or without a perflubron (perfluorooctylbromide) emulsion (Oxygent, Alliance Pharmaceutical corp.) and in 2) human head and neck carcinomas after carbogen inhalation. Mice bearing HRT18 or NA11+ tumors were restrained and their body temperature was kept constant. Perflubron emulsion (4 ml/kg) was injected i.v. in the mice. In patients, oxygenation of the head and neck metastatic lymph nodes was assessed before and/or during carbogen exposure. The distribution of pO2 values shifted upwards during carbogen exposure in both animals and patients while the proportion of low pO2 values decreased. The maximal effect was obtained with patients after 1 to 6 minutes of carbogen exposure, but 4 patients still maintained very low pO2s. Carbogen plus 4 ml/kg perflubron emulsion was more efficient than carbogen alone for increasing hypoxic tumor pO2 in animals. If the animals data could be extrapolated to humans, then the effect of carbogen on tumor oxygenation should be increased by perflubron emulsion administration.

Radiosensitivity, blood perfusion and tumour oxygenation after perflubron emulsion injection

The effect of 90% and/or 100% w/v perflubron (perfluorooctyl bromide (PFOB); Alliance Pharmaceutical Corp.) emulsions on radiosensitivity, tumour relative perfusion and oxygenation was studied using EMT6 tumours in nude mice. Perflubron (2-15 ml/kg) emulsion was injected. The mice inhaled carbogen for 30 min and 60 min prior to irradiation. The radiosensitizing effect of the 90% w/v emulsion was maximal at 4 ml/kg. The tumour relative perfusion diminished after injection of both 100% and 90% w/v emulsions in carbogen-breathing mice at a dose of 15 ml/kg. This drop could explain the lack of efficiency of these treatments at this high concentration. Lastly, tumour oxygenation was increased after administration of perflubron emulsion plus carbogen.

Perfluorocarbon-based red blood cell substitutes

Since our review 5 years ago, a new generation of PFC emulsion has been developed and is undergoing extensive testing. This new generation is the result of the application of physicochemical principles, applied to both the choice of the PFC itself and the emulsifier, as well as advances in emulsion-producing technology. The efficacy of PFCs in general for oxygen transporting capability has been fully recognized, as exemplified by the limited license issued to Fluosol. The latter also represents the recognition of the relative absence of major toxicity of PFCs in general. The development of new products owes much to the lessons learned during the past 20 years and to advances made in the physical chemistry of PFCs. These advances now permit the rational selection or design of the most appropriate PFC and the design of emulsifiers best suited for the purpose. Perflubron represents a clear advance over the Fluosol-DA-type formulation. It is only one but the most advanced of the second-generation products. At least three other commercial entities (Hema-Gen/PFC, Green Cross, Adamantech) are also developing products based on the above principles. Five years ago we concluded that, in spite of the enormous complexity of PFC emulsions as large volume parenterals, they have shown remarkable biocompatibility. The advances in the past 5 years have confirmed this conclusion. The advances occurring during the past 5 years show that the application of the proper technology can lead to product improvement, and that PFC preparations with significant transfusional and nontransfusional potential are, in fact, feasible. It remains to be seen whether high PFC-content emulsion can be successfully deployed in initial, prehospital resuscitation situations. The high PFC content will reduce the absolute requirement for the maintenance of FIO2 > 0.8 in the case of Fluosol-DA for optimal efficacy. The second-generation products also seem to lend themselves to intraoperative use, because they can be removed from the blood postoperatively by plasmapheresislike methods. They are also suitable in combination with autologous blood donation/transfusion. All of these potential applications are in various stages of exploration and, if found to be efficacious, will likely conserve the supply of whole blood and blood components. The nontransfusional applications, particularly those in diagnostic imaging, seem to show substantial promise. Because they involve smaller doses than transfusional applications, they may enter clinical use earlier. The applications in radiation and chemotherapy of malignant diseases represent an intermediate position between the transfusional and nontransfusional uses.(ABSTRACT TRUNCATED AT 400 WORDS)