PERFLUOROBROMOALKYL ETHERS FOR USE AS X-RAY CONTRAST AGENTS

Abstract: The invention relates to the use of a perfluorobromoalkyl ether of the formula C m F 2m+1 OC n F 2n Br where m and n inde­ pendently are integers of from 2 to 6, as a contrast agent in a method of X-raying animals. The ether is used either neat or in an aqueous dispersion such as an emulsion.

Description: "Use of perfluorobromoalkyl ethers as X-ray contrast agents" This invention relates to the use of perfluorobromoalkyl ethers as X-ray radiopaque agents particularly in connection with radiation contrast imaging in animals, including humans. Radiopaque materials are useful, for example, in quantitating coronaryarteryocclusive disease, in stroke, and in other occlusive diseases. Use of brominated fluorocarbons, such as perfluorooctyl bromide, as radiopaque materials has been reported in the article by D.M. Long, et al entitled "Radiopaque Applications of Brominated Fluorocarbon Compounds in Experimental Animals and Human Subjects" appearing in Biochemistry Involving Carbon-Fluorine Bonds, edited by Robert Filler, ACS Symposium Series No. 28, 1976, pages 171-189. US-A 3,778,381 (Rosano et al) and US-A 3,453,333 (Litt et al) describe perfluorohaloalkyl ethers related to the ether compounds of this invention. In accordance with the present invention it has been found that perfluorobromoalkyl ethers, as represented by perfluoro-l-bromobutyl-isopropyl ether, are excellent radiopaque materials. They are used in a method of rendering an internal region of an animal opaque to X- rays, which comprises introducing the radiopaque agent into the region. The ethers are stable to light and heat and are X-ray opaque. The ethers can be used neat or in aqueous dispersions, are relatively nontoxic, and transpire from mice at a good rate. In general, perfluoro chemicals having an ether linkage tend to be retained for very long periods in the reticuloendothelial system ("RES11) of animals. The perfluorobromoalkyl ethers, however, have been found to transpire rapidly through the lungs, indicating that they are not retained in tissues as are other ethers. The perfluorobromoalkyl ethers may be represented by the formula (I): CmF2msl OCF Br (I) n n 2n where n and m independently are integers of 2 to 6, preferably 2 to 4. Thus, the ethers may contain from 4 to 12 carbon atoms as straight or branched-chain alkyl groups. Such ethers are RES-phobic, i.e., they will leave or will not be retained by the reticuloendothelial system of the body. Specific ethers within the scope of formula (I) include: F-l-bromoethylethyl ether F-l-bromoethylisopropyl ether F-l-bromopropylisopropyl ether F-l-bromobutyl isopropyl ether F-l-bromobutylethyl ether F-l-bromobutylpentyl ether F-l-bromohexylispropyl ether Generally, the ether can be prepared from an iodide precursor. For example, perfluoro-l-bromobutyl isopropyl ether is readily prepared from perfluoro-l-iodobutylisopropyl ether by a free radical halogen exchange with bromine in the presence of ultraviolet (actinic) light as follows: EMI2.1 The foregoing reaction gives an essentially quantitative conversion of the iodide compound to the desired bromide. Preparation of various iodide ether precursors and other methods of conversion to the bromides are disclosed, for example, in US-A 3,453,333, US-A 3,470,256 and US-A 3,547,861 and in "Formation of Fluorinated Ethers in a Modified Halohydrin Reaction", Journal of Organic Chemistry, Vol. 33, No. 5, May, 1968, pages 1839-1844. Use of (CF3)2 CFOC4F8I to prepare other ethers is disclosed in US-A 3,790,607, US-A 3,781,370 and US-A 3,637,868. The ethers will vary somewhat in their radiopacity; those ethers having higher bromine to carbon weight ratios will exhibit greater contrast. The higher bromine content ethers, having fewer carbon atoms, will be less expensive to synthesize. However, the lower carbon content ethers, such as perfluoro-l-bromoethylisopropyl ether, (CF3)2CFOC2F4Br, also have higher vapour pressures and therefore will transpire more rapidly from animals. Accordingly, the selection of an ether for use in a particular radiopaque application will depend upon how much contrast is required, how quickly it is desired to have the ether leave the body and, of course, how toxic the ether is to the animal. With respect to toxicity, some toxicity may be tolerable by the animal; hence, while a totally non-toxic material is preferred, a lower level of toxicity may be acceptable depending on the species of animal, the state of health of the animal, and other considerations of a pharmacological nature. Since the perfluorobromoalkyl ethers are also good oxygen and carbon dioxide carriers, they can double as blood substitutes when suitably emulsified or dispersed in an aqueous medium or can be admixed with other perfluorocarbon blood substitutes, in the manner described in US-A 3,911,138 and US-A 4,105,798 and other blood substitute literature. Moreover, the ethers are highly miscible with or are good solvents for perfluorocarbon blood substitutes (such as those of the aforementioned patents) and therefore can be used as diluents for other perfluorocarbon blood substitutes or as solvents for perfluorocarbon blood substitutes which are normally solids. The ethers can be used neat or mixed with water to form aqueous dispersions such as emulsions. Water emulsions of the oil-in-water or water-in-oil-type may be used. The greater the amount of perfluorobromoalkyl ether, the greater the opacity. The emulsions can contain aboutl0% to about 90% by volume of water, preferably 50-90t by volume, and the perfluorobromoalkyl ether may comprise as high as about 95% by volume and as low as about¯58 by volume of the emulsion, preferably about 5-20% by volume. Mixtures of different ethers can be used. Normally, the emulsion will contain about 0.5-102 by weight, preferably 1-5% by weight, of an emulsifier based on the water content of the emulsion. The specific emulsifier employed is not critical, but it should itself be non-toxic Qr the toxicity should be tolerable, and it should form a relatively stable emulsion. Preferred emulsifiers are the non-ionic types, such as yolk phospholipid, a surfactant known to be harmless to humans. Also suitable are the polyoxyethylenes, polyoxypropylenes and copolymers thereof, available commercially under the "Pluronic" trademark, and the fluorinated surfactants described in US-A 3,828,085 and US-A 3,547,995. Nonionic fluorine containing surfactants are particularly preferred. The fluorinated alkyl esters are one class of these surfactants, and are commercially available from 3M Company under the designations FC-93, FC-95, FC-128, FC-143, FC-430 and FC-431. The more preferred nonionic, fluorine containing surfactants, from the standpoint of their exceptional ability to form dispersions which maintain a range of small particle size over substantial periods of time, of the order of 35 weeks to a year or more, even at room temperature, are the fluorinated amidoamine oxides described in US-A 3,828,085 (Price et al) and US-A 3,547,995 (Bartlett). These compounds may be generically described by the formula (1): EMI5.1 wherein Rf is a perfluoroalkyl radical of 1 to about 25 carbon atoms or a polyfluoroalkoxyalkyl radical wherein the alkoxy group may contain 3 to about 40 carbon atoms of which at least a major portion thereof are perfluorinated and the alkyl group may contain 2 to about 40 carbon atoms, fluorinated or unfluorinated; Y is a hydrogen or alkyl of 1 to 6 carbon atoms; R is an alkylene radical of the formula: -C H 2z - z wherein z is an integer of 1 to 6; and Q is an aliphatic amine oxide radical of the formula: EMI5.2 wherein R5 and R6 are each alkyl radicals of 1 to 6 carbon atoms or hydroxy terminated alkyl radicals of 2 to 6 carbon atoms. In all cases the alkoxy, alkyl and alkylene groups may be straight or branched chain. Thus, in one aspect the invention also provides an aqueous dispersion comprising a perfluorobromoalkyl ether as defined above and a fluorinated amidoamine oxide of the above formula (1). Preferred subclasses of the surfactants of the foregoing patents are those of the following formulae (2) and (3): EMI5.3 wherein n is at least 3 (preferably 3-10), x is at least 2 (preferably 2-6), y is at least 1 (preferably 2-6), and R1 and R2 R1 and R2 independently are alkyl radicals containing 1-6 carbon atoms; EMI6.1 wherein n is at least 1 (preferably 3-10), z is at R1 and R2 least 1 (preferably 2-6), and R1 and R2 independently are alkyl radicals containing 1 to 6 carbon atoms. Specific amidoamine oxides within the scope of the above formula are the products described in Examples 1-6 of US-A 3,828,085, namely: EMI6.2 The aqueous dispersions of the invention are prepared by any mixing technique which will provide a uniform blend of the ingredients, and preparation accordingly may be readily accomplished by the skilled formulator. When formulating the dispersions of the invention for systemic administration, it is important not only to add electrolytes and other materials to render the a dispersions physiologically acceptable (such as isotonic with mammalian cells), but also to adjust the pH, if necessary. Among the additives commonly used to render fluids physiologically acceptable are buffers such as sodium bicarbonate, and mixtures such as Ringer's Solution. Other materials conventionally employed in pharmaceutical preparations and known to the skilled formulator may also be added to the dispersions. These include viscosity modifiers, stabilizers (against degradation due to freezing or contamination, for example), anti-freeze agents, diluents, encoding agents, and the like. Among such additives may be mentioned glycerin, dimethylsulfoxide, ("DMSO), various gelatins both natural and synthetic, and polyols such as sorbitol. The perfluoro compound and surfactant components may be blended into water in any proportions which will provide uniform dispersions. Typical proportions are about 5 to 508 perfluoro compound based on the vo-lume of the total composition and about 0.5 to 10% of the surfactant based on the total weight of the composition. Preferred proportions are about 10-30% by volume of the perfluoro compound and about 2-5% by weight of the surfactant, but proportions in particular cases may be varied depending on dispersability of the PFC, particle size desired, and similar considerations. The aqueous dispersions more usually comprise emulsions, preferably of the oil-in-water type but also including water-in-oil emulsions. In some cases the emulsions have a very fine particle size and appear transparent or solution-like to the unaided eye. Ahe micro-emulsions which can be formulated with the dispersants of US-A 3,828,085 have.this characteristic and are preferred. Colloidal suspensions, while not excluded from use in this invention, are less preferred, particularly for systemic administration, because of their larger particle size range and less stability. The above-identified blood substitute and surfactant patents provide exeellent guidance to formulation of the dispersions, and attention is directed to the patents for such purpose. The perfluorobromoalkyl ether contrast agents of the invention can be used in a variety of radioimaging applications for medical and veterinary diagnostic purposes. Fields of radiographical use include, for example, gastroenterography, alveolography, bronchography, lymphography, ventriculomyelography, splenography, cholecystography, pancreatography, renal angiography and retrograde urography. With specific reference to renal angiography, the bromoethers of this invention, when employed for instance as emulsions, are unique in that they are not excreted in the urine. Moreover, all the arteries, arterioles, venules and veins of the kidney stand out very clearly. On the other hand, an X-ray made with a conventional iodinated, water-soluble contrast agent provides a solid black, kidney-shaped silhouette because the agent is excreted so rapidly. Inthe case of lymphangiography, the known water-soluble contrast agents are syrupy and therefore it is very difficult to use a tiny 30 gauge needle for their administration. The pertluorobromoalkyl ether contrast agents, however, go through such a needle very easily and, therefore, facilitate the diagnostic procedure. When the. ether, neat or as an aqueous dispersion, is used as a radiopaque agent, it can be introduced into the animal by various means. Suitable methods include swallowing, injection, and catheterization. The amount used can vary substantially depending in part on the weight of the animal, and the particular region being X-rayed. The intensity (or amount) of the X-ray irradia tion can also influence the amount of ether used. The foregoing factors will routinely be taken into consideration by one skilled in the art to determine the effective amount for the condition being studied. The ether or ether dispersion should be rendered isotonic or otherwise physiologically acceptable to the blood prior to introduction into the bloodstream by the addition of salts (e.g. as Ringer solution), buffering agents (such as NaHCO3) or other additives commonly employed for such purpose. The following Example will further illustrate the invention without necessarily limiting the scope thereof, except as set forth in the appended claims. Example Perfluoro-l-bromobutylisopropyl ether, (CF3)CFO C4F8Br, is prepared in 85 yield by reacting bromine with (CF3)2CFOC4F8I in the presence of ultraviolet light. The product is purified using a Perkin Elmer Annular Still and preparative gas chromatography and is characterized by mass spectrometry and infrared spectroscopy. The ether has a boiling point of 113-1150C at 760 torr and a density of 1.861 g/cc at 240C. Molecular weight: 446 (calculated and found). The ether has an LD-50 of over 100 mls/kg as an emulsion containing 10% by volume of the ether and 90% by volume of 5% by weight Pluronic F68 surfactant in water, and therefore is relatively non-toxic. The Pluronic F68 surfactant is a polyoxyethylene-polyoxypropylene copolymer having a molecular weight of about 8200. The limits of the toxicity data are as follows: Table 1 Emulsion Number Alive at Time Shown Dose (ml/kg) 10 Min - I hour 7 days 100 3/4 3/4 3/4 75 4/4 - 4/4 4/4 50 4/4 4/4 4/4 To determine emulsion stability, the abovedescribed emulsion of theether, prepared by ultrasonication, is stored at 20C in a sealed Pyrex (trademark) tube in a refrigerator. Emulsion stability is determined by measurement of optical density initially and after several days storage of the samples using a Spectronic 20 apparatus and a suitable size cell. Comparison with emulsions in which perfluorodecalin or perfluorotributyl amine is substituted for the ether indicates that the ether emulsion is reasonably stable. Stability of other perfluorobrominated ether emulsions would be expected to vary. Transpiration is measured by injecting a mouse with the test emulsion described above and placing the mouse in an all-glass chamber through which oxygen flows at a rate of about 20 cc per minute. After 20 minutes, samples of the oxygen are removed using a microsyrinqe and analyzed by gas chromatography using an SE-30 column and an electron capture detector. By calibration of the detector with a standard prepared from the perfluorocompound of the emulsion, the rate at which the perfluoro compoutnd is transpired through the skin and lungs of the intact, awake mouse can. be calculated. Knowing the amount injected into the mouse and the rate at which is leaves over a period of time, the time at which all of the perfluoro compound would be gone can be calculated. The results of the foregoing procedure, as compared with essentially the same emulsions except for use of different pertluoro compounds (perfluoro decalin and perfluorooctylbromide), expressed in terms of the rates (rg/min.) at which the perfluoro compound leaves the mouse at lasped times of 5, 10, 20, 30 and 40 weeks, indicate that the perfluoro-l-bromobutylisopropyl ether leaves the body at a rate almost the same as perfluorodecalin (known to transpire quickly) and therefore has a desirable transpiration rate. Accumulation of the perfluoro-l-bromobutylisopropyl ether in the liver and spleen of mice infused with the above-described ether emulsion is determined by direct combustion of liver and spleen homogenates by sodium biphenyl followed by fluoride ion measurement with an electrode. The results are as follows where the infusion dose is 1008 cc/kg. Table 2 Wet Combustion Analysis of Liver and Spleen Days After Infusion Percent of Dose Remaining Liver Average Spleen 7 15.85 16.3 4.77 16.72 13 2.59 2.59 2.30 2.59 24 1.4 1.3 0.4 1.2 The data show that the ether went to the liver and spleen, and then left. In other experiments, tissue samples are taken from mice which are given intravenous doses of the abovedescribed emulsion containing the perfluoro-l-bromobutylisopropyl ether. The emulsion doses are 100, 75 and 50 cc/kg. The mice are sacrificed at 7, 13 and 24 days and samples of liver, spleen and kidney are removed, fixed and mounted for sectioning. Also, a sample of spleen is removed from a mouse at 330 days post-intusion. Some of these tissues are sectioned and examined. During the period when the ether is present in large amounts, microscopic examination reveals little or no mitosis of hepatocytes, but sone hypertrophy of nuclei is seen. Binucleated cells are observed and in one case as many as 538 are binucleated. Less than 12 of hepatocyte cytoplasm is occupied by the perfluorobromoalkyl ether. Some infiltration of mononuclear cells is observed and blast-like cells as well as fluorocarbon particles are found in the interstitium. The re-emulsification of the larger fluorocarbon particles into smaller particles, which normally precedes.the disappearance, is very near completion. By two weeks post-infusion, the liver is within normal limits with the exception of some phagocytes containing the perfluorobromo compound, and nuclei of hepatocytes are seen somewhat enlarged, but otherwise normal. A neat sample of the perfluoro-l-bromobutylisopropyl ether is injected into the trachea of an anesthetized rat through a plastic tube having a bevelled end. Serial X-rays are taken and show the ether to be a good contrast- agent. Similarly, the above-described emulsion containing the ether is intravenously injected into a mouse. X-rays (50 KVA applied) are taken two days later. The X-rays clearly show the liver and spleen, indicating±-hatthe ether is deposited in the reticuloendothelial system. The foregoing results thus demonstrate effective use of the ether as a radiopaque agent.

Claims: Claims 1. Use of a perfluorobromoalkyl ether of the formula: CmF2m+l0C F2nBr where m and n independently are integers of from 2 to 6, as a radiopaque agent. 2. Use according to Claim 1, wherein the ether is F-l bromobutylisopropyl -tether. 3. Use according to Claim 1 or 2, wherein the radiopaque agent comprises an aqueous dispersion of the ether. 4. Use according to Claim 3, wherein the aqueous dispersion contains 50-908 by volume of water, 0.5-10% by weight of a dispersant based on the water content, and 5-208 by volume of the ether. 5. Use according to any of Claims 1 to 4, in a method of radioimaging an internal region of an animal wherein a radiopaque agent is introduced into the region and the region is X-rayed while perfused with the radiopaque agent. 6. An aqueous dispersion comprising a perfluorobromoalkyl ether of the formula: CmF 2m+1OCnF 2nBr where m and n are independently integers of from 2 to 6, and a fluorinated amidoamine oxide of the formula (1): EMI14.1 wherein Rf is a perfluoroalkyl radical of 1 to 25 carbon atoms or a polyfluoroalkoxyalkyl radical wherein the alkoxy group contains 3 to 40 carbon atoms of which at least a major portion thereof are perfluorinated and the alkyl group contains 2 to 40 carbon atoms, fluorinated or unfluorinated; Y is a - hydrogen or alkyl of 1 to 6 carbon atoms; R is an alkylene radical of the formula: -C H wherein z is an integer of 1 to 6; and Q is an aliphatic amine oxide radical of the formula: EMI15.1 wherein R5 and R6 are each alkyl radicals of 1 to 6 carbon atoms or hydroxy terminated alkyl radicals of 2 to 6 carbon atoms. 7. A package comprising a perfluorobromoalkyl ether of the formula: CmF 2m+1OC F Br n 2n where m and n are independently integers of from 2 to 6, a container therefor, and instructions for application of the perfluorobromoalkyl ether as a radiopaque agent.

Inventors: CLARK, LELAND C., JR., TAMBORSKI, CHRIST
Applicants: ADAMANTECH, INC., CHILDREN'S HOSPITAL MEDICAL CENTER
Application year: 1984
Main classification: A61K49
IPC codes: C07C67, C07C41, C07C43, A61K49