Perfluorochemicals and hyperbaric oxygen in radiation therapy

Hyperbaric oxygen and radiation therapy: a review

About 5% of cancer patients treated with radiotherapy will have severe late-onset toxicity. Hyperbaric oxygen therapy (HBOT) has been used as a treatment for radiation injuries for decades, with many publications presenting data from small series or individual cases. Moreover, we know that the hypoxic areas of tumours are more resistant to radiation. HBOT increases the oxygen tension in tissues and, theoretically, it should enhance the efficiency of radiotherapy. To better understand how HBOT works, we carried out this bibliographic review. We found Grade B and C evidence that at pressures exceeding 2 absolute atmospheres (ata), HBOT reduced late-onset radiation injuries to the head and neck, bone, prostate and bladder. It also appeared to prevent osteoradionecrosis after exodontia in irradiated areas. Finally, HBOT at 2 ata increased the effectiveness of radiation in head and neck tumours and achieved promising results in the local control of high-grade gliomas.

Hyperthermia can alter tumor physiology and improve chemo- and radio-therapy efficacy

Hyperthermia has demonstrated clinical success in improving the efficacy of both chemo- and radio-therapy in solid tumors. Pre-clinical and clinical research studies have demonstrated that targeted hyperthermia can increase tumor blood flow and increase the perfused fraction of the tumor in a temperature and time dependent manner. Changes in tumor blood circulation can produce significant physiological changes including enhanced vascular permeability, increased oxygenation, decreased interstitial fluid pressure, and reestablishment of normal physiological pH conditions. These alterations in tumor physiology can positively impact both small molecule and nanomedicine chemotherapy accumulation and distribution within the tumor, as well as the fraction of the tumor susceptible to radiation therapy. Hyperthermia can trigger drug release from thermosensitive formulations and further improve the accumulation, distribution, and efficacy of chemotherapy.

Detection of (19)F-labeled biopharmaceuticals in cell cultures with magnetic resonance

Magnetic resonance (MR) studies of the therapeutic efficacy of fluorinated drugs have recently become possible due to improvements in detection including the application of very strong magnetic fields up to 9.4Tesla (T). These advances allow tracking, identification, and quantification of (19)F-labeled biopharmaceuticals using (19)F MR imaging ((19)F MRI) and spectroscopy ((19)F MRS). Both techniques are noninvasive, are nondestructive, and enable serial measurements. They also allow for controlled and systematic studies of cellular metabolism in cancerous tissue in vivo (small animals and humans) and in vitro (body fluids, cells culture, tissue extracts and isolated tissues). Here we provide an overview of the (19)F MRI and (19)F MRS techniques used for tracking (19)F labeled anticancer chemotherapeutics and antibodies which allow quantification of drug uptake in cancer cells in vitro.

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.

Regional drug delivery with radiation for the treatment of Ewing's sarcoma. In vitro development of a taxol release system

Recently, several studies have suggested the radiosensitizing effect of taxol, a microtubular inhibitor. Our overall hypothesis is that a combination of radiation and taxol may demonstrate therapeutic efficacy over doses of either individually. Studies examining taxol use have mostly focused on systemic administration, which can lead to undesired effects. To circumvent these side effects, we propose a locally administered polymeric microsphere delivery system combined with radiation therapy for the treatment of Ewing's sarcoma. The present study focuses on the in vitro ability of taxol when present as a microencapsulated drug delivery system, and delivered locally at the site of the sarcoma/tumor, to block cells in the G2/M phase of the cell cycle and potentially enhance the radiation sensitivity of cells. Using the bioresorbable poly(anhydride-co-imide), poly[pyromellityl-imidoalanine-1,6-bis(carboxy-phenoxy)hexane] (PMA-CPH), and the radiosensitizing agent taxol, a microsphere based delivery system was fabricated. A solvent evaporation technique was used to encapsulate taxol at doses of 1%, 5%, and 10% in PMA-CPH microspheres. Release kinetics studies demonstrated that the total amount of taxol released and the release rate were directly dependent on loading percentage. Taxol's bioactivity and radiosensitizing ability were measured using flow cytometry. Co-culture of Ewing's sarcoma cells with and without taxol-loaded microspheres demonstrated that released taxol retained its bioactivity and effectively blocked cells in the radiosensitive G2/M phase of mitosis. The taxol-radiation delivery system studied achieved an 83% decrease in tumor cell count compared to control. Taxol effectively sensitized Ewing's sarcoma cells to radiation with radiosensitivity shown to be independent of radiation dose at levels of dosages studied. This work has demonstrated that taxol can be effectively released from a biodegradable PMA-CPH microsphere delivery system while maintaining potent combined cytotoxic and radiosensitizing abilities.

Radiotherapy combined with simultaneous chemotherapy with mitomycin-C and 5-fluorouracil for inoperable head and neck cancer

The feasibility and effectiveness of a combined chemoradiotherapy treatment modality for locally advanced head and neck cancer was tested in a phase II trial. From March 1995 to June 1998, 35 patients with advanced squamous cell carcinoma of the head and neck were treated with a continuous intravenous infusion of 5-fluorouracil (600 mg m-2 24 h-1 for Days 1 to 5 (120 h)) and mitomycin-C (10 mg m-2 intravenously) on Day 5 during the first week of radiotherapy and on Day 36. 31 patients had stage IV disease; 4 patients had stage III; and 1 patient had stage II. Patient ages ranged from 42-69 years (median 56.7 years). The tumours involved were as follows: oral cavity (n = 11); oropharynx (n = 14); hypopharynx/larynx (n = 10). Radiotherapy was delivered to a total dose of 70 Gy with conventional fractionation (2 Gy per fraction, five times a week). Chemotherapy was well tolerated and all patients received the intended dose. Mild nausea occurred in five patients. After a mean follow-up of 21 months (range 10-44 months), 8 (23%) patients remain alive. A complete response was seen in 28 (80%) patients. When a recurrence appeared, it was within the first year after treatment. 1- and 2-year overall survival rates were 46% and 23%, respectively. Grade 3 mucositis occurred in 17% of patients. Grade 1-2 thrombopaenia occurred in 3 (9%) patients, grade > 2 leukopaenia in 4 (11%) patients, and grade > or = 2 anaemia in 3 (9%) patients. We observed a treatment interruption of maximum 1 week for six patients owing to mucositis. Febrile neutropaenia or aplasia were not observed. The concomitant use of 5-fluorouracil, mitomycin-C and radiotherapy in locally advanced head and neck carcinoma is well tolerated in this group of patients. This protocol showed good locoregional response with a very low toxicity profile.

RSR13, a synthetic allosteric modifier of hemoglobin, as an adjunct to radiotherapy: preliminary studies with EMT6 cells and tumors and normal tissues in mice

RSR13, 2[4-[[(3,5dimethylanilino)carbonyl]methyl]phenoxy]-2-methylpropion ic acid, a synthetic allosteric modifier of hemoglobin, reduces the affinity of hemoglobin for oxygen. The experiments reported here examined the effect of treatment with RSR13, combined with oxygen breathing, on the radiation response of EMT6 mammary tumors in BALB/c mice and of two normal tissues. RSR13 plus oxygen breathing increased the response of EMT6 tumors to irradiation. RSR13 had no discernible effects on tumors rendered maximally hypoxic by nitrogen asphyxiation, no discernible cytotoxic effects in EMT6 tumors, and no effect on the viability or radiation response of EMT6 cells in vitro under either aerobic or hypoxic conditions. The effects of RSR13 therefore reflect changes in tumor oxygenation, rather than a direct cytotoxic or radiosensitizing effect of the drug. RSR13 plus oxygen reduced the hypoxic fraction to 9% from the value of 24% found in both air-breathing and oxygen-breathing mice. Treatment with RSR13 plus oxygen did not alter the radiation response of the bone marrow progenitor cells (CFU-S) or acute radiation reactions in the skin. The improvement in tumor radiation response produced by treatment with RSR13 plus oxygen, combined with the absence of enhanced radiation reactions in the normal tissues, support further testing of RSR13 as an adjunct to radiotherapy.

Effects of a 100% perfluorooctylbromide emulsion on ischemia/reperfusion injury following cardioplegia

Protective effects of a perfluorooctylbromide emulsion on myocardial ischemia and reperfusion (MI/R) injury were evaluated in a modified Langendorff rat heart preparation. Isolated rat hearts were equilibrated in Krebs-Henseleit solution (KH) for 35 minutes and perfused with either cardioplegic solution (CPS) or a 100% perfluorooctylbromide (PFOB) emulsion in CPS for 3 minutes. Hearts were then bathed in the emulsion or CPS. Both groups were subjected to 30 minutes of ischemia. Following 30 minutes of ischemia and 30 minutes of reperfusion with KH solution, hearts subjected to the 100% PFOB emulsion showed improved recovery of left ventricular function. Tissue activities of the antioxidant enzymes glutathione peroxidase, superoxide dismutase, and catalase were not affected by the emulsion in this model. Activity of lactate dehydrogenase (LDH) in the bathing medium was elevated at the end of the experimental period in both control and PFOB-treated hearts. The PFOB emulsion reduced the decline in ATP and GSH levels produced by cardioplegia and subsequent reperfusion. No differences were noted in oxidized glutathione (GSSG) levels. These data suggest that the PFOB emulsion provides some protection for the myocardium against injury associated with cardioplegia.

Assessment of changes in murine tumor oxygenation in response to nicotinamide using 19F NMR relaxometry of a perfluorocarbon emulsion

The oxygen dependencies of the 19F NMR spin-lattice relaxation rates (R1 = 1/T1) of a perfluorocarbon emulsion sequestered in a murine tumor model has been used to evaluate nicotinamide, a radiosensitizer believed to act through enhanced tissue oxygenation. Fluorine-19 NMR spectroscopic measurements from solid Radiation-Induced Fibrosarcoma (RIF-1) tumors in C3H mice showed a statistically significant improvement in tumor pO2 for a Nicotinamide-treated group, with a delta pO2 = 4.7 +/- 3 torr ( = mm Hg) (Mean +/- SEM) at t = 60 min (P < .01), and 4.5 +/- 3 at t = 70 min post intraperitoneal injection (P < 0.02) as compared with saline-treated Controls, while several other time points for which t > 30 min were significant at the P < 0.05 level. Both groups had n = 10, and the statistics were based on Student's one-tailed group t test. By comparison, in another study group where breathing gas was switched from air to 100% O2, a statistically insignificant increase of 2 torr was realized in tumor pO2 (n = 9). The maximal treatment effect occurs at a delay of 60 to 70 min, consistent with results obtained by other investigators using radiobiology techniques. Fluorine-19 spectroscopic relaxometry can measure therapeutically meaningful changes in in vivo tumor pO2 and represents an improvement in expenditures of time, animal resources, and statistical power over conventional radiobiological methods.

Influence of tumour physico-chemical conditions on interleukin-2-stimulated lymphocyte proliferation

The proliferative response of murine lymphocytes to interleukin-2 (IL-2) was examined under physico-chemical conditions present in solid tumours, namely low oxygen and glucose concentrations and acidic pH. Lymphocytes were cultured for four days in 30 U ml-1 IL-2 to simulate serum IL-2 concentrations attainable with high-dose systemic IL-2 therapy. Lymphocyte proliferation was significantly (P < 0.05) reduced by low oxygen concentrations (both anoxia [0% O2] and hypoxia [10%, low glucose (6 mg dl-1), or acidic pH (6.7 or 6.4). Moderate glucose concentration (32 mg dl-1), or neutral pH (7.0) did not impair proliferation. This study indicates that impairment of lymphocyte proliferation by tumour physico-chemical conditions may be a factor in the relatively poor success rate of IL-2/LAK cell immunotherapy.

Fluosol and hyperbaric oxygen as an adjunct to radiation therapy in the treatment of malignant gliomas: a pilot study

Several clinical trials have been reported using Fluosol and oxygen breathing as an adjunct to radiation. Theoretical considerations and animal experiments, however, indicate that a combination of perfluorochemicals and hyperbaric oxygen (HBO) increases tumor oxygenation and radiation response to a greater extent than is seen either with a perfluorochemical and normobaric oxygen or with HBO alone. This is the first report of a pilot study of the use of Fluosol and HBO with radiation in humans. Twenty patients with anaplastic astrocytoma or glioblastoma multiforme were treated in a phase I trial of radiation with Fluosol and HBO at three atmospheres. Total Fluosol dose was escalated from 42 ml/kg in six courses to 80 ml/kg in four courses. Patients were irradiated in an HBO chamber with 600 cGy weekly fractions following Fluosol administration. Sixteen patients completed treatment; no interruption was necessitated by treatment toxicity. The addition of Fluosol/HBO did not increase the incidence of HBO related toxicities. No significant chronic toxicities were seen. This pilot study demonstrates that Fluosol and HBO can safely be used as an adjunct to radiation in the treatment of human tumors.

Effects of hyperbaric oxygen and a perfluorooctylbromide emulsion on the radiation responses of tumors and normal tissues in rodents

Perfluorochemical emulsions are being examined in many laboratory and clinical studies as possible adjuncts to radiotherapy and chemotherapy. The studies reported here examine the clinical potential of hyperbaric oxygen (HBO) in combination with a highly concentrated perfluorochemical emulsion (Oxygent) containing 100% w/v perfluorooctylbromide (PFOB). HBO alone produced only a small improvement in the radiation response of BA1112 tumors in WAG/rij rats, while regimens combining HBO with Oxygent produced much greater radiation sensitization. A sham emulsion, formulated without the O2-carrying PFOB, did not alter the radiation response of the tumors in comparison with that seen with HBO alone. Neither HBO nor Oxygent plus HBO altered the radiosensitivity of bone marrow progenitor cells in BALB/c mice. HBO alone augmented skin reactions in BALB/c mice, but addition of Oxygent did not alter the skin reactions in comparison to those seen with HBO alone. Regimens combining Oxygent with HBO selectively increased the radiation sensitivity of tumors relative to normal tissues, thereby enhancing the therapeutic ratio. These results support the potential usefulness of perfluorochemical emulsions and HBO in clinical radiation therapy.

Preclinical evaluation of Oxygent as an adjunct to radiotherapy

These studies examine the potential value of a concentrated emulsion of perfluorooctylbromide (perflubron; Oxygent, Alliance Pharmaceutical Corp.) as an adjunct to radiotherapy. The effects of Oxygent on solid tumors were examined using EMT6 mammary tumors in BALB/c mice and BA1112 rhabdomyosarcomas in WAG/rij rats. Treatment with Oxygent plus O2, carbogen (95% O2/5% CO2), or hyperbaric oxygen (HBO) increased the effects of radiation on the tumors. Analyses of tumor cell survival curves and measurements of intratumor pO2 showed that this potentiation reflected an increase in the proportion of well-oxygenated tumor cells. Neither treatment of the animals with carbogen, O2, or HBO alone nor treatment of air-breathing rodents with Oxygent produced changes of similar magnitude. Treatment with a vehicle emulsion containing all the components of Oxygent except the perflubron did not alter tumor radiosensitivity, showing that tumor radiosensitization required the oxygen-transporting perfluorocarbon, and did not result from any biologic or physiologic effects of other components of the emulsion. These studies also examined the effects of Oxygent on the radiation responses of mouse skin and bone marrow. Oxygent selectively increased the radiation sensitivity of tumors relative to these normal tissues, thereby increasing the therapeutic ratio and producing therapeutic gain. Oxygent appears to warrant further testing as an adjunct to cancer therapy.

Chemical radiosensitizers in cancer therapy

The development of effective low-LET radiation therapy for cancer has been hindered by the lack of consistent differential responses to radiation between tumor and normal tissues. One major difference between many solid tumors and the surrounding normal stroma is the presence of hypoxic foci in solid tumors due to the inadequate supply of nutritional needs as a result of the breakdown of microvasculature. Consequently, failure of conventional radiotherapy and local recurrences are in part attributed to the radioresistant hypoxic cell populations, present in the tumor. Local cure/control rates of a tumor can be increased only by an effective increase in the radiation dose. At the same time, an increase in such a dose would damage the oxic normal stroma, more than the hypoxic tumor cells. Hence, specific modification of tumor radiosensitivity by the use of chemical radiosensitizers, in combination with conventional radiotherapy, is an attractive alternative. Many clinicians and radiotherapists are skeptical about the outcome of using radiosensitizers in patients. Nevertheless, a vast amount of information is currently available regarding the first- and second-generation radiosensitizers both in murine and in human tumors. As a result, it is hoped that eventually a radiosensitizing drug would be discovered/synthesized that will overcome the drawbacks so far encountered in their use in the clinic. In this article, the development of chemical radiosensitizers since the early sixties, the basis for their selection, their mechanism(s) of action, and the results obtained with the various groups of radiosensitizers are reviewed.

Enhancement of fractionated radiation therapy by an experimental concentrated perflubron emulsion (Oxygent) in the Lewis lung carcinoma

The concentrated Perflubron emulsion, Oxygent, in combination with breathing a 95% oxygen atmosphere, significantly enhanced the response of the murine Lewis lung carcinoma to fractionated radiation therapy. Administration of 4 to 12 g PFC/kg was most effective if administered prior to each x-ray fraction, however, alternated day and even once weekly administration of 8 or 12 PFC/kg and 95% oxygen breathing with each x-ray fraction resulted in significant improvements in tumor growth delay.

Modulation of tumor oxygenation and radiosensitivity by a perfluorooctylbromide emulsion

The effect of a concentrated perfluorooctylbromide emulsion (Oxygent) on the radiosensitivity and oxygenation of solid tumors was examined using EMT6 mammary tumors in BALB/c mice and BA1112 rhabdomyosarcomas in WAG/rij rats. Treatment with Oxygent plus carbogen or oxygen breathing increased the radiosensitivity of both tumors. Analysis of tumor cell survival data and polarographic measurements of intratumoral pO2 indicated that this potentiation reflected an increase in the proportion of well-oxygenated tumor cells. Treatments with carbogen breathing alone, with Oxygent plus air-breathing, or with a vehicle emulsion containing all the components except the perfluorocarbon did not produce comparable improvements in tumor radiosensitivity. Concentrated perfluorooctylbromide emulsions appear to warrant further development and preclinical testing as adjuncts to cancer therapy.

Improvement in RBC flux, acidosis and oxygenation in tumour microregions by Fluosol-DA 20%

Using laser Doppler flowmetry, we investigated the effects of Fluosol-DA 20% on RBC flux in FSaII tumours and on RBC flux in normal skin of C3H mice. The RBC flux in tumours was significantly increased; however, the RBC flux in normal skin fluctuated only slightly after the treatment with Fluosol-DA 20%. Since an increase in RBC flux by Fluosol-DA 20% may facilitate the removal of acidic metabolites from the tumours, the effects of Fluosol-DA 20% on intratumour pH was also measured. We also measured intratumour pO2 after various dosages of Fluosol-DA 20% with carbogen inhalation. We concluded that the administration of Fluosol-DA 20% selectively increased the RBC flux in tumours compared to that in normal skin. Moreover, carbogen inhalation combined with increasing dosages up to 36 ml/kg of Fluosol-DA 20% effectively enhanced tumour oxygenation in FSaII tumours.

Keynote address: the influence of microenvironmental factors on the activity of radiation and drugs

The inherent radio- and chemosensitivity of tumor cells clearly affects their response to treatment. Accumulating evidence, however, suggests that the biochemical and physiological status of the cell during treatment is at least as important. In this review, a critique of the current evidence for, and extent of, microenvironmental heterogeneity in tumors is presented, emphasizing human tumor cells in situ. The expected consequences of those changes on cellular response to radiation and chemotherapy is then briefly reviewed. Finally, the continuing interest in developing new therapeutic strategies for which the tumor microenvironment is an asset (as opposed to a liability) is discussed in the context of the dynamic nature of tumors, and the complexity of adequately analyzing combination treatments.

Fluosol: an oxygen-delivery fluid for use in percutaneous transluminal coronary angioplasty

Fluosol (20% intravascular perfluorochemical emulsion) is an oxygen-carrying emulsion used to deliver oxygen to ischemic myocardium during percutaneous transluminal coronary angioplasty (PTCA). Fluosol is composed of two perfluorochemicals, perfluorodecalin and perfluorotripropylamine. It has a high capacity for oxygen solubility, a low viscosity, and a small particle size. Following administration, the perfluorochemicals in fluosol are not metabolized. Rather, most are expired as gaseous particles through the lungs; the remainder are taken up by the organs of the reticuloendothelial system and later expired. When administered during balloon inflation in PTCA, fluosol preserves ventricular wall motion and global left ventricular ejection fraction. In addition, it minimizes ST segment changes and preserves cardiac output. Fluosol may be especially useful in patients who have poor contractile reserve, multivessel disease, or serious underlying illness. Other uses under investigation include limitation of myocardial infarct size and chemosensitization or radiosensitization of malignant tumors. Adverse effects secondary to the use of fluosol include ventricular arrhythmias, pruritus, bradycardia, chest pain, dyspnea, and increased respiratory rate. Fluosol must be thawed, admixed, warmed to body temperature, and oxygenated prior to intracoronary administration. The usual administration rate is 60 mL/min during each balloon inflation.

Effect of Fluosol-DA 20% and oxygen on response of C57BL/6 mice to whole-body irradiation

Normal tissue effects in mice due to combinations of a perfluorochemical emulsion, Fluosol-DA 20%, 100% oxygen, and whole-body irradiation were investigated. Eight-to-10-week-old C57BL/6 male mice were injected via the tail vein with 10 ml/kg of Fluosol-DA with and without subsequent exposure to oxygen for 60 minutes. Animals then received graded doses of whole-body radiation (4 MV photons) at a dose rate of 2.85 +/- .015 Gy/minute. Using linear regression analysis, the lethal doses of radiation to 50% and 10% of the animals within 30 days in the absence of Fluosol-DA and oxygen were 8.35 Gy (95% c.l.:7.77-8.93 Gy) and 6.73 Gy (95% cl.:6.21-7.25 Gy), respectively, and were unaffected by Fluosol-DA and/or oxygen pre-treatment. However, Fluosol-DA given alone or in combination with oxygen produced increased balding and decreased graying incidence in mice within 60 days, and resulted in depressed weight gain 15 to 60 days post-treatment. Normal tissue effects due to administration of Fluosol-DA and oxygen in combination with whole-body irradiation have been demonstrated but appear minimal compared to other anti-tumor modalities currently under investigation.

Radiation and chemotherapy sensitizers and protectors

Radiosensitizers and radioprotectors are part of the chemical modifier approach to cancer therapy whereby the state of the tumor cells and/or normal tissues are modified such that a therapeutic gain is achieved using conventional radiation or chemotherapy. Radiosensitization can be achieved by the use of oxygen-mimetic compounds, agents that alter DNA sensitivity to irradiation, maneuvers that alter DNA repair processes, and manipulation of tissue oxygenation. Standard chemotherapeutic agents such as cisplatin can be utilized in a manner that optimizes the radiosensitization properties. Protection and sensitization can occur by altering the thiol status of the cell. The chemical modifiers field is both developing novel approaches to cancer treatment and increasing the understanding of basic cancer biology.

New high O2 carrying perfluorochemical emulsions: toxicity, radiosensitivity of GM-CFC and development of metastases in mice

The effects of two new concentrated perfluorochemical emulsions based on F-66E and PFOB, which carry significantly more oxygen than Fluosol-DA 20%, were tested on normal tissues (toxicity and radiation response) and on the development of metastases from Lewis Lung Carcinoma (3LL) in female C57 BL/6 mice. Twenty one days after injection of F-66E or PFOB emulsions (15 ml/kg body weight), the spleen and liver weights were significantly increased but had returned to normal after 2-3 months. Splenomegaly already observed in 3LL bearing mice was significantly increased by F-66E emulsion injection. The radiosensitivity of GM-CFC was not altered when unanesthetized GM-CFC was not altered when unanesthetized mice were pretreated with F-66E emulsions and/or carbogen 1 hr prior to and during irradiation. The rate of tumor take and the period before detection of tumors were not modified when an emulsion of F-66E was injected simultaneously or 10 days after 3LL cells. Mean survival of mice, and the number of metastases on lung surfaces were similar in F-66E injected mice and control mice.

Radiation enhancement of lung nodule formation in mice is not potentiated by treatment with a perfluorochemical emulsion and carbogen

The ability of intravenously-injected mouse mammary tumor cells to form lung tumors is increased by irradiation of the thorax 24 h previously. We examined the effects of treatment with a perfluorochemical emulsion (Fluosol-DA, 20%) plus carbogen before and during irradiation on the radiation-induced enhancement of lung nodule formation. We found no evidence that treatment with Fluosol plus carbogen altered the development of tumor nodules in irradiated mouse lungs.

Tumor radiation responses and tumor oxygenation in aging mice

EMT6 mouse mammary tumors transplanted into aging mice are less sensitive to radiation than are tumors growing in young adult animals. We hypothesized previously that this reflected a greater proportion of radiation resistant, hypoxic cells in the tumors of aging animals. The experiments reported here compare the radiation dose-response curves defining the survivals of tumor cells in aging mice and in young adult mice. Cell survival curves were assessed in normal air-breathing mice and in mice which had been asphyxiated with N2 to produce uniform hypoxia throughout the tumors. Analyses of these survival curves revealed that 41% of the viable malignant cells were severely hypoxic in tumors in aging mice, while only 19% of the tumor cells in young adult animals were radiobiologically hypoxic. This did not appear to reflect anemia in the old animals, as the hematocrits of young and aging tumor-bearing animals were similar. Treatment of aging animals with a perfluorochemical emulsion plus carbogen (95% O2/5% CO2) increased the radiation response of the tumors, apparently by improving tumor oxygenation and thereby decreasing the number of severely hypoxic, radiation resistant cells in the tumors.

Intermittent use of a perfluorochemical emulsion (Fluosol-DA 20%) and carbogen breathing with fractionated irradiation

Oxygen carrying perfluorochemical emulsions have been shown to enhance the response of animal tumors to large single doses of radiation. Clinically, however, perfluorochemical emulsions are being used with only some fractions in multiple fraction radiation courses. To test the efficacy of a perfluorochemical emulsion under conditions that are closer to those used in current clinical trials, BA1112 rat sarcomas were treated with three fractions per week of 6 Gy per fraction. Once a week, animals were infused i.v. with a perfluorochemical emulsion at 15 ml/kg, and allowed to breathe carbogen (95% O2:5% CO2) for 30 minutes prior to and during irradiation. The 50% tumor control dose was 93.1 (87.9-103.1) Gy in the control arm compared to 74.3 (64.9-83.9) Gy for the animals given the perfluorochemical infusion plus carbogen breathing. The dose modification factor for intermittent perfluorochemical infusion and carbogen breathing was 1.26 (1.15-1.40). In a similar fractionated schedule, the hypoxic cell radiosensitizer, misonidazole, given once per week at 600 mg/kg, gave a dose modification factor of 1.22 (1.14-1.32).

Preclinical studies of a perfluorochemical emulsion as an adjunct to radiotherapy

Tumor growth and tumor cell survival endpoints were used to examine the effects of a perfluorochemical emulsion, Fluosol-DA, 20%, and carbogen (95% O2/5% CO2) on EMT6 mouse mammary tumors in BALB/c mice. These studies defined the effects of the Fluosol dose on the hematocrit and fluorocrit of the mice and on the radiation response of the tumors. The effect of varying the duration of carbogen breathing before irradiation was examined; times of 5-60 min gave similar enhancements of tumor radiosensitivity. Potentiating effects were not observed when the tumors were irradiated 1-3 days after Fluosol injection, probably reflecting the observed clearance of the perfluorochemicals from the circulating blood. Fluosol injected 30 min-2 days before irradiation did not alter the radiation response of tumors in air-breathing or N2-asphyxiated mice. Together, these studies provided additional support for the hypothesis that the potentiation of tumor radiation response observed after treatment with Fluosol plus carbogen results from changes in O2 delivery to the hypoxic tumor cells by oxygenated perfluorochemical particles. This confirms the conclusion drawn on the basis of the observed changes in the tumor cell survival curve. Studies of tumor cell survival, tumor cell yield, tumor growth, and artificial lung metastasis formation revealed no effects of Fluosol treatment (without irradiation) on tumor progression or metastasis. Studies examining the effects of Fluosol plus carbogen on the growth of tumors irradiated with 5 Gy showed that the changes in tumor radiosensitivity observed using cell survival endpoints also occurred in tumors left in situ after irradiation with a radiation dose similar to those used in some clinical trials.

Mathematical modelling of oxygen supply and oxygenation in tumor tissues: prognostic, therapeutic, and experimental implications

Radiation response of some tumors is dependent on the oxygenation of the tumor tissue. To improve tissue oxygenation, attempts to increase a reduced hemoglobin concentration or to shift the dissociation curve of hemoglobin have been made. The aim of this paper is to estimate the influence of such measures on the volume of radiobiologically hypoxic tissue by means of a mathematical model. In addition, the influence of blood velocity and metabolic status of tumor tissues on tissue oxygenation is evaluated. The calculations show a strong influence on hypoxic tissue volume over a modest range of variation of physiological parameters, especially when interactions of several parameters may occur.

Measurement of end-capillary PO2 with positron emission tomography

The analysis of positron emission tomography measurements of oxygen metabolism has been extended to provide a quantitative estimate of end-capillary PO2. The principle of this extension rests on the idea that the oxygen extraction fraction can be used to calculate the end-capillary oxygen saturation of the blood. The relation between oxygen saturation and PO2 is obtained through the oxygen dissociation curve. Our studies show that in addition to the local oxygen extraction fraction, arterial PO2 and pH values are needed in the calculation, whereas fairly large variations in factors such as PCO2, hematocrit, hemoglobin, and plasma protein levels have little or no effect. Rough estimates of end-capillary PO2 can be made using standard O2 dissociation nomograms. Blood gas and acid-base properties of blood have been known for decades, making it possible to account accurately for individual differences that may be encountered when studying patients. Measurements in nine normal subjects yielded a mean end-capillary PO2 value of 31.2 mm Hg. The ability to make a quantitative visualization of altered patterns of end-capillary PO2 provides an additional dimension to the investigation of stroke disease and tumor metabolism.

The effect of fluosol-DA and oxygenation status on the activity of cyclophosphamide in vivo

The addition of Fluosol-DA followed by carbogen breathing increased the antitumor effect of cyclophosphamide as measured by both tumor growth delay and tumor cell survival assays. Under air breathing condition, cyclophosphamide (100 mg/kg) administered i.p. five times on alternate days produced a tumor growth delay in the FSaIIC fibrosarcoma of 8.0 +/- 0.8 days. Adding Fluosol-DA (0.3 ml) to treatment with cyclophosphamide followed by carbogen breathing increased tumor growth delay to 11.4 +/- 3.6 days, which was not statistically significantly different from that obtained with the drug plus carbogen breathing without Fluosol-DA. As the dose of Fluosol-DA was increased and administered with drug treatment followed by carbogen breathing for 6 h, increasing tumor growth delays of 15.0 +/- 1.5 days, 18.1 +/- 1.7 days and 29.4 +/- 2.2 days were observed with 0.1 ml, 0.2 ml and 0.3 ml Fluosol-DA, respectively. When 0.1 ml Fluosol-DA was administered in combination with cyclophosphamide and immediately followed by 1 h of hyperbaric oxygen (3 atm), a tumor growth delay of 13.7 +/- 1.2 days was observed. With 0.2 ml Fluosol-DA under these conditions, the tumor growth delay increased to 23.2 +/- 1.6 days, and with 0.3 ml Fluosol-DA the tumor growth delay was 35.6 +/- 3.2 days. Single doses of cyclophosphamide with and without Fluosol-DA (0.3 ml) and various conditions of oxygenation were used in an FSaIIC fibrosarcoma tumor cell survival assay. The addition of Fluosol-DA to this single-dose protocol produced a five- to tenfold increase in tumor cell kill compared to air-breathing drug-treated animals. There was no significant difference in the toxic effect of any of the treatment conditions on bone marrow.

Applicability of animal tumor data to cancer therapy in humans

The problem of applying experimental tumor studies to clinical cancer therapy is a complex one. The radiotherapy literature contains many examples of premature efforts to apply laboratory observations to the clinic, and many examples of failures to adequately consider animal tumor observations in the design of clinical studies. This review covers three areas: tumor hypoxia, where clinical trials based on animal tumor data have been conducted with radiosensitizers, hyperbaric oxygen, and systemic oxygen carriers; dose fractionation, where current trials of hyperfractionation are based in part on animal tumor studies; and chemo-radiotherapy, where clinical trials are only beginning to exploit concepts developed in animal tumor systems. The use of animal tumor systems extends past the screening of new agents. Animal tumor models can be used in biological, physiological, and pharmacological studies to elucidate the biological factors influencing the efficacy of therapeutic agents. Tumor studies can be combined with studies of normal tissues to predict the toxicities to be anticipated in clinical trials, and to assess the potential for therapeutic gain. Animal studies can also provide data which are useful in designing optimal clinical trials of new agents and maximizing the potential for successful clinical application of new approaches. In general, it is not possible to apply specific laboratory data directly to man. To translate, rather than transpose, information from the laboratory to the clinic, the model studies must be directed at evaluating principles, rather than merely quantifying results. Only through studies of mechanisms, by designing experiments to test or refute a hypothesis, will it be possible to apply model studies to man.

Enhancement of tumor radiation response by the combination of a perfluorochemical emulsion and hyperbaric oxygen

The presence of radioresistant hypoxic cells in tumors is believed to be one of the limiting factors in achieving local tumor control by radiotherapy. Treatment with hyperbaric oxygen during irradiation has been shown to improve the radiation response of many solid tumors in rodents and of some tumors in patients. Intravenous administration of perfluorochemical emulsions combined with oxygen breathing at atmospheric pressure has also been shown to improve the radiation response of several rodent tumors. Theoretical considerations suggest that the combination of a perfluorochemical emulsion and hyperbaric oxygen should be significantly more effective than either agent alone. This hypothesis was tested by examining the radiation response of BA1112 rhabdomyosarcomas growing in WAG/rij-Y rats. Treatment with a perfluorochemical emulsion, Fluosol-DA, plus hyperbaric oxygen (3 Atmospheres O2) significantly increased the radiation response of the malignant cells in these solid tumors. The observed changes in the tumor cell survival curve suggest that the combination of Fluosol-DA and HBO decreases the proportion of severely hypoxic cells in the tumor to less than 1.5% of the original value. The effect of the Fluosol-DA dose and the duration of pretreatment with HBO are described.

Increase in tumor pO2 by perfluorochemicals and carbogen

The effects of perfluorochemicals (Fluosol-DA) in combination with carbogen (95% O2 and 5% CO2) breathing on the tumor pO2 was investigated. The pO2 in RIF-1 tumors grown in the leg of C3H mice was determined by polarographic method using oxygen microelectrodes with diameters of 50-60 micron. The average and median pO2 in the control RIF-1 tumors was about 13 mm Hg and 6 mm Hg, respectively. Carbogen breathing alone could cause a significant increase in pO2 in some tumors and Fluosol-DA injection (i.v.) alone caused a slight change in tumor pO2. When the animals were treated with both Fluosol-DA injection and carbogen breathing, the pO2 markedly increased in most of the tumors resulting in an average and median tumor pO2 of 80 mm Hg and 60 mm Hg, respectively. Such an increase in tumor pO2 may account for the previous observations by us and others that the response of experimental tumors to radiation could be markedly increased by treating the tumor-bearing animals with carbogen and Fluosol-DA.

The adaptive response of mouse tumours to anaemia and retransfusion

We have developed exchange transfusion methods to alter the hematocrit of tumour-bearing mice. The effects of anaemia and its correction by blood transfusion on the radiosensitivity of two mouse tumours (SCCVII/St and RIF-1) were studied using excision, in vivo/in vitro assay. An acute reduction in haematocrit caused a high degree of radioresistance equivalent to an increase in the hypoxic fractions by factors of 10 (SCCVII/St) and 30 (RIF-1). As the duration of the anaemia was prolonged, radioresistance was lost until within about 6 h normal radiosensitivity was observed even though the anaemia persisted. The restoration of the normal haematocrit by red blood cell transfusion after 24 h of anaemia caused increased radiosensitivity equivalent to a reduction in the hypoxic fraction by factors of 5 (SCCVII/St) and 10 (RIF-1), but again the effect was transient and normal radiosensitivity was re-established within 24-48 h of retransfusion. Measurements of 14C misonidazole (MISO) binding to RIF-1 tumours after these procedures indicated changes in the number of hypoxic cells which were qualitatively almost identical to those using the cell survival endpoint, leading us to believe that changes in oxygenation were responsible for the altered radiosensitivity. We feel that transfusion procedures could be used to advantage in the radiotherapy of some cancers.

Reactions of tumors and normal tissues in mice to irradiation in the presence and absence of a perfluorochemical emulsion

The effect of pre-treatment with the perfluorochemical emulsion, Fluosol-DA, on the radiation response of normal tissues and EMT6 mammary tumors in BALB/c mice was examined. Pre-treating tumor-bearing mice with .015 ml/g of Fluosol and 30 min of carbogen (95% O2/5% CO2) increased the number of tumor cells killed by irradiation with doses of 2.5-20 Gy; the change in the radiation dose-response curve was consistent with a reduction in the hypoxic fraction. Fluosol did not alter the response of tumors in air-breathing or N2-asphyxiated mice and carbogen alone did not alter the radiation response of this tumor significantly. Carbogen treatments 5-60 min in duration produced similar enhancements of tumor radiosensitivity in Fluosol-treated animals. Pre-treatment with Fluosol plus carbogen also increased the number of tumor cells killed by a fractionated regimen of four 2.5 Gy fractions given over 2 days. Pre-treatment with Fluosol-DA plus carbogen, therefore, increased the antineoplastic effects of radiotherapy in both single-dose and multi-fraction radiation regimens. In contrast, Fluosol did not increase the effect of radiation on the partially committed (CFU-GM) or pluripotent (CFU-S) stem cells of the bone marrow or on the CFU-GM of the spleen. The radiation response of the skin was only slightly enhanced by pre-treatment with Fluosol plus carbogen. These data show that treatment of mice with perfluorochemical emulsions plus carbogen can produce therapeutic gain by improving the radiation response of solid tumors, without producing an equivalent increase in the radiation response of potentially dose-limiting normal tissues. These findings encourage further evaluations of these agents as adjuncts to clinical radiotherapy.

Effect of a perfluorochemical emulsion on the development of artificial lung metastases in mice

Intravenous infusions of perfluorochemical emulsions, combined with administration of inspired oxygen or carbogen have been found to improve tumor oxygenation and increase the response of solid tumors in animals to radiotherapy. Fluosol-DA 20 per cent, the only perfluorochemical emulsion currently approved for testing in humans in the United States, has recently entered clinical trials as an adjunct to radiotherapy in the treatment of head and neck carcinoma. The studies reported here were undertaken as part of our laboratory evaluation of the safety and clinical potential of this oxygen-transport fluid as an adjunct to cancer therapy; they asked whether single or multiple treatments with Fluosol and an oxygen-enriched atmosphere produced immunologic perturbations, pulmonary damage, or other effects which altered the development of artificial lung metastases in experimental animals. Neither single nor multiple treatments with clinically relevant regimens of Fluosol and carbogen (95 per cent O2/5 per cent CO2) had any effect on the development of lung nodules from intravenously injected EMT6 tumor cells.