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

Liposome encapsulated perfluorohexane enhances radiotherapy in mice without additional oxygen supply

Background

To investigate the effect of perfluorochemical preparations in enhancing radiotherapy, perfluocarbon nanoparticles were by encapsulating perfluorohexane into liposome [lip(PFH)].

Methods

After intravenous injection, lip(PFH) could accumulate in the tumor site over time, with a prominent accumulation in tumor 24 h post injection. X-ray was delivered to the tumor site 24 h after the injection of lip(PFH) under room air. The experimental mice were randomized into four groups: control (saline), lip(PFH) (lip(PFH) only), X-ray (X-ray only), and lip(PFH) + X-ray (lip(PFH) with X-ray radiation). Tumor volume and histology were monitored to assess treatment efficacy.

Results

Tumor growth was significantly reduced in mice received lip(PFH) and X-ray compared with X-ray only. The histological data also revealed more destruction of tumor tissue in lip(PFH) + X-ray group compared with X-ray only. In addition, lip(PFH) did not show any significant tissue damage to major organs or induce significant liver/kidney dysfunction.

Conclusions

Lip(PFH) could accumulate in the tumor site and enhance radiotherapy without additional oxygen supply.

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.

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.

Oxygen carriers and cancer chemo- and radiotherapy sensitization: bench to bedside and back

After over a century of preclinical and clinical development, a number of artificial oxygen carriers based either on perfluorochemicals or hemoglobins are currently in advanced clinical trials for their ability to replace red blood cells and to ensure adequate tissue oxygenation in case of acute anemia or infarction. On the other hand, intravenous administration of perflourocarbone emulsions or hemoglobin solutions were effective in increasing the oxygenation throughout experimental tumors, and fueled by exciting new developments in the field, some products are experimentally and clinically investigated as cancer chemo- and radiosensitizing agents. This review is to provide a first overview of the current status of artificial oxygen carriers as a oxygen therapeutics in cancer chemo- and radiotherapy sensitization.

Accuracy of fluorocrit in determination of blood perflubron concentration

Previous studies examining the radiosensitizing effects of perfluorochemical emulsions have based dose recommendations on a measurement known as fluorocrit. The fluorocrit is the proportion of blood volume occupied by perfluorochemicals and is measured using standard hematocrit procedures. This measurement is inherently crude and subject to error and variability between different individuals measuring the same sample. Furthermore, the fluorocrit method has not been compared to other quantitative methods to determine its reliability. The purpose of this study was to compare fluorocrit measurements to those obtained by gas chromatographic analysis. A 90% w/v perflubron emulsion was administered to six normal dogs once weekly for four weeks and peripheral blood samples were obtained at specified time points for analysis. A total of 123 blood samples were analyzed by both methods. The relationship between blood fluorocrit and plasma perflubron concentration measured by gas chromatography was examined using regression models. Based on the modest predictive value (r2 = 0.3683) of the derived statistical model, we conclude that fluorocrit measurement is an inaccurate method of estimation of blood perflubron concentration. Caution must, therefore, be exercised when extrapolating data and dose recommendations from reports of studies using flurocrit as the only estimate of blood perflubron concentration.

Hypoxia and drug resistance

Biologically and therapeutically important hypoxia occurs in many solid tumor masses. Hypoxia can be a direct cause of therapeutic resistance because some drugs and radiation require oxygen to be maximally cytotoxic. Cellular metabolism is altered under hypoxic conditions. Hypoxia can result in drug resistance indirectly if under this condition cells more effectively detoxify the drug molecules. Finally, there is evidence that hypoxia can enhance genetic instability in tumor cells thus allowing more rapid development of drug resistance cells. The current review describes the effects of hypoxia on tumor response to a variety of anti-cancer agents and also describes progress toward therapeutically useful methods of delivering oxygen to tumors in an effort to overcome therapeutic resistance due to hypoxia. Finally, the use of hypoxic cell selective cytotoxic agents as a means of addressing hypoxic 'drug resistance' is discussed.

Pharmacokinetics and tolerance of weekly OXYGENT CA infusions in the dog

This study determined the OXYGENT CA (90% w/v perflubron emulsion, Alliance Pharmaceutical Corporation) dose necessary to achieve a 3-4% fluorocrit, and the tolerance of this dose administered once per week for four weeks to dogs. This study simulated OXYGENT CA use as a radiosensitizing agent. Six adult dogs were administered 6 ml/kg OXYGENT CA once per week for 4 weeks. Blood samples were collected following infusion, until fluorocrits were < or = 0.5%. One week after the fourth infusion, three dogs were necropsied. Liver biopsies were obtained from the remaining three dogs which were monitored 12 additional weeks. All dogs achieved fluorocrits > 3.0% (3.5-5.1%) with the 6 ml/kg dose. A 3 ml/kg dose did not provide a fluorocrit > 3.0%. Serum bilirubin concentrations were elevated at 24-hour sampling times and declined within 72 hours. Elevations in ALT, SAP, and bile acids were noted. Splenic and hepatic microvasculature fibrosis occurred in the long-term study dogs. Thrombocytopenia occurred in 5/6 dogs, necessitating exclusions of one dog from 2 infusions. However, 3/5 thrombocytopenic dogs had titers for Ehrlichia sp., which elicits thrombocytopenia. Therefore, we cannot conclude the effect of OXYGENT CA on platelets.

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.

Use of perfluorochemical emulsions in cancer therapy

Over the past 10 years, the use of perfluorochemical emulsions (PFCE) and carbogen or oxygen breathing has been explored as an adjuvant to radiation therapy and/or chemotherapy in the treatment of solid tumors. The rationale for the use of PFCE and oxygen breathing in this therapeutic setting is that solid tumor masses contain areas of hypoxia which are therapeutically resistant. Since x-rays and many chemotherapeutic agents require oxygen to be maximally cytotoxic and most normal tissues are well-oxygenated, the additional oxygen put in circulation by the PFCE should not increase the normal tissue toxicities produced by the various therapies. The largest body of preclinical work and all of the clinical studies in cancer conducted with PFCE, thus far, have been done with Fluosol-DA, 20%. Oxygen microelectrode studies have confirmed increased oxygenation in previously hypoxic tumor regions after the administration of Fluosol-DA and carbogen breathing. The preclinical studies have shown very positive effects with single dose and fractionated radiation in several rodent solid tumor models. Many widely used anticancer drugs including antitumor alkylating agents and adriamycin are enhanced by PFCE and carbogen breathing for longer time periods (6 h). More recently, several experimental concentrated PFCE preparations have become available and work with these is actively under way in several laboratories. Clinical studies with radiation and four or five chemotherapeutic drugs as single agents have indicated that Fluosol-DA followed by oxygen breathing can be administered safely in a variety of cancer therapeutic settings. Further clinical studies with Fluosol-DA are planned.

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.

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.

Influence of the 100% w/v perfluorooctyl bromide (PFOB) emulsion dose on tumour radiosensitivity

The radiosensitizing effect of a 100% w/v emulsion of a fluorocarbon, PFOB, which carries 4 times more oxygen than does Fluosol-DA 20% emulsion, was studied on two human tumour xenografts (HRT18 and HT29) and the murine tumour EMT6. This effect was compared with that obtained with carbogen alone. The fluorocrit (amount of fluorocarbon in the blood) and haematocrit remained unchanged from 7 to 65 min post-injection of the emulsion (8 ml/kg). Tumour-bearing mice were pretreated with 100% w/v PFOB emulsion doses ranging from 2 to 15 ml/kg in the presence of carbogen for 30 min prior to and during irradiation. The fluorocrit increased from 1.5% to 9.5% as the dose of 100% w/v PFOB emulsion increased from 2 to 15 ml/kg. The haematocrit remained the same for all the fluorocarbon emulsion doses used. Tumour radiosensitization varied with the fluorocarbon emulsion dose. Clinically relevant doses (2-4 ml/kg) of the 100% w/v PFOB emulsion plus carbogen produced significantly more radiosensitization than carbogen alone, with sensitizing enhancement ratios of 1.4 for EMT6 and 1.7 for HRT18. The radiosensitivity of HRT18 cells was thus very close to that obtained with normally oxygenated cells. For higher doses (8-15 ml/kg) the radiosensitizing effect of 100% w/v PFOB emulsion plus carbogen becomes comparable to that of carbogen alone. These experiments show that clinically useful doses of 100% w/v PFOB plus carbogen produced tumour radiosensitization only at relatively low fluorocrits. Thus the fluorocrit, and hence the fluorocarbon's oxygen-carrying capacity, is not the only factor involved in radiosensitizing tumour cells by oxygen-carrying fluorocarbon emulsions.

Influence of scheduling, dose, and volume of administration of a perfluorochemical emulsion on tumor response to radiation therapy

Studies were carried out with a new, concentrated perfluorochemical emulsion (PFCE) of the perfluorochemical F44E (48% V/V). When given at 4, 1.6, or 1 g/kg in undiluted injection volumes iv 1 hr prior to a range of single doses of radiation with inspired carbogen dose modifying factors (DMF's) based on tumor growth delay (TGD) in the Lewis lung tumor of 2.5, 1.7, and 1.5, respectively, were produced. When the PFC dose was administered in a volume of 0.2 ml, the dose modifying factors produced by 4 g/kg (0.1 ml undiluted) did not change significantly (2.6), but the dose modifying factors produced by 1.6 g/kg (0.04 ml undiluted) and by 1.0 g/kg (0.025 ml undiluted) increased significantly to 2.0 and 1.8 (p less than 0.05), respectively. Using the tumor excision assay at 24 hr post treatment in the FSaIIC fibrosarcoma, administration of 6, 4, or 2 g/kg in 0.2 ml injections plus carbogen breathing 1 hr prior to and during treatment resulted in dose modifying factors of 1.5, 1.6, and 1.3, respectively. In a fractionated radiation protocol in the Lewis lung tumor using four daily fractions, a dose of 4 g/kg of PFC on days 1 and 3 proved superior to a dose of 2 g/kg daily (dose modifying factors 2.4 vs. 1.9, p less than 0.05). When a fractionated radiation regimen of 3 Gy daily X 5 and carbogen was used, PFC doses of 0.5, 1, 2, and 4 g/kg administered undiluted produced increasing tumor growth delays with increasing dose of PFCE and increasing frequency of administration. In addition, dilutions to 0.2 ml proved significantly more effective. In a 2-week fractionated radiation protocol using 2, 3, or 4 Gy daily X 5 weekly, PFCE given in 0.2 ml volume plus carbogen breathing daily at 4, 1.6, or 1 g/kg produced dose modifying factors of 2.0, 1.9, and 1.6, respectively. Finally, when used in a day 1, 3, and 5 radiation regimen for 3 weeks at 2, 3, or 4 Gy/fraction, 4 g/kg of PFCE given in a volume of 0.2 ml plus carbogen breathing produced a superior dose modifying factor (1.6) as compared with 1.6 or 1.0 g/kg (dose modifying factors 1.4 and 1.3, respectively). These results indicate that PFCE plus carbogen breathing effectively enhances the antitumor effects of both single dose and fractionated radiation.(ABSTRACT TRUNCATED AT 400 WORDS)

Tumor and normal tissue tolerance for fractionated low-dose-rate radiotherapy

Radiobiological evidence suggests that an improved therapeutic ratio might be achieved through the use of smaller than conventional dose fractions. The ultimate in small dose fractions for external beam radiotherapy would be fractionated low-dose-rate (LDR) irradiation, and clinical trials of fractionated external beam LDR therapy are already in progress. Using the BA1112 rat sarcoma, we have determined the 50% tumor control dose for LDR and for conventional-dose-rate (CDR) fractionated radiotherapy. These tumor control doses were compared to normal tissue tolerance doses for hemi-body irradiation in similar CDR and LDR schedules. Animals were treated 3 times per week without anesthesia using 10-19 fractions. LDR radiotherapy was done with 60Co at dose rates of 0.028-0.033 Gy/min; CDR radiotherapy was done with 250 kVp X rays at dose rates of 0.54-2.1 Gy/min. The tumor control dose modification factor (DMF) for LDR compared to CDR irradiation was 1.3 (1.0-1.5). For LDR and CDR hemi-body irradiation, the dose modification factor for 7 day lethality (gastrointestinal damage) was 1.7 (1.5-1.9), for 100 day morbidity was 1.8 (1.6-2.2), and for radiation nephritis at 90 days was 1.9 (1.7-2.3). The therapeutic gain factor for fractionated low-dose-rate irradiation compared to conventional-dose-rate fractionated radiotherapy was therefore 1.8/1.3 = 1.4 (1.2-1.8). The study shows that there is an experimental as well as a theoretical basis for anticipating a therapeutic benefit from the use of external beam fractionated LDR radiotherapy, and implies that the recognized therapeutic efficacy of brachytherapy is not due solely to the high localized dose.

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.

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.