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

Perfluorocarbons therapeutics in modern cancer nanotechnology for hypoxia-induced anti-tumor therapy

With an estimated failure rate of about 90%, immunotherapies that are intended for the treatment of solid tumors have caused an anomalous rise in the mortality rate over the past decades. It is apparent that resistance towards such therapies primarily occurs due to elevated levels of HIF-1 (Hypoxia-induced factor) in tumor cells, which are caused by disrupted microcirculation and diffusion mechanisms. With the advent of nanotechnology, several innovative advances were brought to the fore; and, one such promising direction is the use of perfluorocarbon nanoparticles in the management of solid tumors. Perfluorocarbon nanoparticles enhance the response of hypoxia-based agents (HBAs) within the tumor cells and have been found to augment the entry of HBAs into the tumor micro-environment. The heightened penetration of HBAs causes chronic hypoxia, thus aiding in the process of cell quiescence. In addition, this technology has also been applied in photodynamic therapy, where oxygen self-enriched photosensitizers loaded perfluorocarbon nanoparticles are employed. The resulting processes initiate a cascade, depleting tumour oxygen and turning it into a reactive oxygen species eventually to destroy the tumour cell. This review elaborates on the multiple applications of nanotechnology based perfluorocarbon formulations that are being currently employed in the treatment of tumour hypoxia.

In vivo clearance of 19F MRI imaging nanocarriers is strongly influenced by nanoparticle ultrastructure

Perfluorocarbons hold great promise both as imaging agents, particularly for ¹⁹F MRI, and in therapy, such as oxygen delivery. ¹⁹F MRI is unique in its ability to unambiguously track and quantify a tracer while maintaining anatomic context, and without the use of ionizing radiation. This is particularly well-suited for inflammation imaging and quantitative cell tracking. However, perfluorocarbons, which are best suited for imaging - like perfluoro-15-crown-5 ether (PFCE) - tend to have extremely long biological retention. Here, we showed that the use of a multi-core PLGA nanoparticle entrapping PFCE allows for a 15-fold reduction of half-life in vivo compared to what is reported in literature. This unexpected rapid decrease in ¹⁹F signal was observed in liver, spleen and within the infarcted region after myocardial infarction and was confirmed by whole body NMR spectroscopy. We demonstrate that the fast clearance is due to disassembly of the ~200 nm nanoparticle into ~30 nm domains that remain soluble and are cleared quickly. We show here that the nanoparticle ultrastructure has a direct impact on in vivo clearance of its cargo i.e. allowing fast release of PFCE, and therefore also bringing the possibility of multifunctional nanoparticle-based imaging to translational imaging, therapy and diagnostics.

Probing different perfluorocarbons for in vivo inflammation imaging by 19F MRI: image reconstruction, biological half-lives and sensitivity

Inflammatory processes can reliably be assessed by (19)F MRI using perfluorocarbons (PFCs), which is primarily based on the efficient uptake of emulsified PFCs by circulating cells of the monocyte-macrophage system and subsequent infiltration of the (19)F-labeled cells into affected tissue. An ideal candidate for the sensitive detection of fluorine-loaded cells is the biochemically inert perfluoro-15-crown-5 ether (PFCE), as it contains 20 magnetically equivalent (19)F atoms. However, the biological half-life of PFCE in the liver and spleen is extremely long, and so this substance is not suitable for future clinical applications. In the present study, we investigated alternative, nontoxic PFCs with predicted short biological half-lives and high fluorine content: perfluorooctyl bromide (PFOB), perfluorodecalin (PFD) and trans-bis-perfluorobutyl ethylene (F-44E). Despite the complex spectra of these compounds, we obtained artifact-free images using sine-squared acquisition-weighted three-dimensional chemical shift imaging and dedicated reconstruction accomplished with in-house-developed software. The signal-to-noise ratio of the images was maximized using a Nutall window with only moderate localization error. Using this approach, the retention times of the different PFCs in murine liver and spleen were determined at 9.4 T. The biological half-lives were estimated to be 9 days (PFD), 12 days (PFOB) and 28 days (F-44E), compared with more than 250 days for PFCE. In vivo sensitivity for inflammation imaging was assessed using an ear clip injury model. The alternative PFCs PFOB and F-44E provided 37% and 43%, respectively, of the PFCE intensities, whereas PFD did not show any signal in the ear model. Thus, for in vivo monitoring of inflammatory processes, PFOB emerges as the most promising candidate for possible future translation of (19)F MR inflammation imaging to human applications.

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.

Protection against experimental small intestinal ischaemia-reperfusion injury with oxygenated perfluorochemical

BACKGROUND

Intestinal ischaemia-reperfusion (IR) injury frequently occurs in abdominal surgery. Perfluorochemical (PFC) can be used to oxygenate intestinal organs directly and allows adenosine 5'-triphosphate (ATP) production within the submerged organs during ischaemia. This study was designed to evaluate the protective effect of PFC in IR injury, focusing on cytokine production in rat small intestine.

METHODS

The superior mesenteric artery was occluded in rats for 60 min and the small bowel placed in an intestinal bag containing either normal saline (group 1), oxygenated saline (group 2) or oxygenated PFC (group 3). The arterial clip was subsequently removed, allowing reperfusion. The number of rats that survived for 7 days, tissue ATP levels, biochemical variables, tissue lipid peroxidation (LPO), bacterial cultures and histological changes were examined after reperfusion.

RESULTS

The use of oxygenated PFC in group 3 improved survival compared with the other groups. Serum creatine phosphokinase and lactate dehydrogenase levels in groups 1 and 2 reflected small intestinal damage, and plasma levels of tumour necrosis factor alpha and interleukin 6 were raised. In contrast, oxygenated PFC decreased these levels, and reduced LPO, bacterial translocation and augmented apoptosis of the small intestine after reperfusion.

CONCLUSION

An intestinal bag containing oxygenated PFC showed protective effects during bowel ischaemia.

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.

Overview of progress in the fluorocarbon approach to in vivo oxygen delivery

The development of fluorocarbon-based oxygen carriers has experienced rapid progress over the past few years. Fluosol has been approved for use during percutaneous transluminal coronary angioplasty (PTCA) for high-risk patients. Its clinical evaluation is being pursued as an adjunct to cancer therapy and for treatment of myocardial infarction in conjunction with thrombolytic therapy. O2-delivery efficacy has been achieved with the development of the new highly concentrated (4 to 5 times more concentrated than Fluosol), fluid, emulsions of perfluorooctyl bromide (perflubron), trade-named Oxygen. The stability of fluorocarbon emulsions has also improved considerably and the new emulsions can be stored unfrozen and are ready for use. The side-effect profile of these emulsions has been characterized as being the normal response of the body's phagocytes to the injection of particles, a response that is considered physiological rather than pathological in nature; it involves some products of arachidonic acid metabolism and can be controlled pharmacologically. Means of further stabilizing fluorocarbon emulsions, involving molecular-diffusion-controlling additives or fluorinated surfactants, including mixed fluorocarbon-hydrocarbon compounds, have been devised. Increased control over in vivo particle recognition, intravascular persistence and side effects, and at adapting emulsion characteristics to specific applications, is being investigated. The range of therapeutic applications is expanding. The concentrated emulsions will be able to serve as a temporary red blood cell substitute in many situations. Acute normovolemic hemodilution with fluorocarbon emulsions, used in conjunction with homologous predonation and other blood-sparing techniques, should afford greater flexibility, increase the margin of safety, and reduce or alleviate the need for autologous blood transfusion during surgical procedures. Fluorocarbon applications in the cardiovascular field include use during PTCA, for cardioplegia and reperfusion, and the treatment of myocardial infarction. Significant tumor growth delay has been achieved when concentrated emulsions are used in conjunction with cancer radio- or chemotherapy. Liquid ventilation has potential as a unique treatment for the adult and infant respiratory distress syndromes and for drug delivery. The radiopaque and versatile perflubron can also be used in contrast agents for diagnosis with computed X-ray tomography, magnetic resonance imaging and ultrasound, allowing the early detection and staging of cancer. Other potential applications investigated include the treatment of cerebral ischemia, organ and limb preservation, use as a tamponade during retinal repair, etc.

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.

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.

The use of fluorocarbon emulsions in cancer radiotherapy

The chemical and physical properties of perfluorochemical emulsions which highlight their advantages and disadvantages for use in cancer radiotherapy are summarized. The radiobiological properties of two emulsions are reviewed: we have chosen the Fluosol-DA 20% and the PFOB emulsion 100 v/w% which is one of the most promising second generation fluorocarbon emulsions. The radiosensitization obtained in a human tumor xenograft with PFOB emulsion is compared to that obtained with other modalities used to overcome the radioresistance of tumour cells linked to hypoxia.