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

Efaproxiral (RSR13) plus oxygen breathing increases the therapeutic ratio of carboplatin in EMT6 mouse mammary tumors

Carboplatin, a member of the platinum family of alkylating agents, is often used in combination with radiotherapy. Some studies, including a recent publication from our laboratory, have suggested that the cytotoxic effects of platinum compounds may be altered by changes in the post-treatment oxygenation. The study reported here assessed whether post-treatment changes in tumor oxygenation caused by oxygen breathing alone or in combination with efaproxiral (RSR13) altered the effects of carboplatin. Efaproxiral, which allosterically modifies hemoglobin-oxygen binding to increase tumor pO(2), has been shown to increase the effects of radiation in animal tumor models and is in a second, confirmatory phase III clinical trial as an adjuvant to radiotherapy. These studies with EMT6 tumors in BALB/c Rw mice used clonogenic assays to assess tumor cell survival and tumor growth studies to assess antineoplastic activity and treatment-related toxicity. Efaproxiral plus oxygen breathing for 5 hrs after carboplatin treatment significantly increased the antineoplastic effects of carboplatin. The increased antineoplastic effects of carboplatin produced by efaproxiral plus oxygen breathing occurred without a concomitant increase in host toxicity. These findings suggest that the increases in tumor oxygenation produced by Efaproxiral plus oxygen breathing increased the therapeutic ratio of carboplatin.

Chemical manipulations of tissue oxygenation for therapeutic benefit

Many new approaches are currently being explored to improve cancer treatment through hypoxic cell radiosensitization. Oxygen carriers, calcium antagonists, some drugs which shift the oxygen hemoglobin curve to the right improve the oxygen availability in the tumors. An alternative way to improve radiotherapy or chemotherapy is to increase tumor hypoxia either by shifting the hemoglobin oxygen dissociation curve to the left or by using vasodilators. This paper summarizes main results obtained in that field. The relevance of data obtained from animal experiments to clinical practice will be discussed.

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.

The influence of Fluosol-DA and carbogen breathing on the antitumor effects of cyclophosphamide in vivo

The effects of Fluosol-DA, an oxygen-carrying perfluorochemical emulsion, and carbogen breathing alone or in combination on the antitumor activity of cyclophosphamide (CTX) in vivo were investigated. The addition of 12 ml/kg Fluosol-DA immediately prior to CTX treatment exerted no effect on the antitumor effect of CTX on the RIF-1 tumor in C3H mice. On the other hand, carbogen breathing alone for 8 h significantly enhanced the antitumor effect of CTX, with a dose-modification factor of 1.29 +/- 0.07. The combination of Fluosol-DA and carbogen breathing further increased the effect of CTX, with a dose-modification factor of 1.63 +/- 0.05. There was no significant difference in animal lethality within the treatment groups. It was concluded that Fluosol-DA in combination with carbogen breathing may be useful for the enhancement of CTX chemotherapy of human neoplasms.

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.

Emulsified perfluorochemicals for oxygen-transport to tissues: effects on lymphoid system and immunological competence

Data from both in vivo and in vitro studies to assess lymphoid tissue and immune system responses to emulsified PFCs and their components have been discussed. It may be concluded that the extent to which PFC emulsions are retained in lymphoid tissues and their effects on the manifestation of humoral immune responses to immunological "challenges" is variable and depends upon: (1) Emulsion composition; (2) Dose administered; (3) Route of administration; (4) Tissue examined; (5) Timing of emulsion administration relative to immune challenge; and (6) Species studied. Such variability in the responses to emulsified PFCs has inevitably introduced difficulties in assessing their effects upon immunological competence. Further work is needed determine the extent to which lymphoid tissue functions may be altered by PFC emulsions and identify the active component(s) and mechanism(s) involved.

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.