WO2005020935A2

WO2005020935A2 - Method and composition of administering radioprotectants

Info

Publication number: WO2005020935A2
Application number: PCT/US2004/003514
Authority: WO
Inventors: Venkataraman Srinivasan; Thomas M. Seed; K. Sree Kumar
Original assignee: Henry M. Jackson Foundation For The Advancement Of Military Medicine, Inc.
Priority date: 2003-02-06
Filing date: 2004-02-06
Publication date: 2005-03-10
Also published as: WO2005020935A3

Abstract

The present invention relates to methods and compositions for the prevention and treatment of radiation-associated tissue damage. Specifically, the present invention relates to methods for simultaneously delivery of amifostine and Vitamine E at the target sites of 0 mammal to enhance the therapeutical effect and to 35duce the toxicity attributabe to amifostine. The present invention 0lso relates to @h03maceutical compositions for the prevention and treatment of 0 radiation-associated tissue damage. The present pharmaceutical compositions are particularly useful for the protection to against radiation-induced suppression of the hematopoietic system as well as to enhance bone marrow stem cells activity. The present invention further relates to 0 pharmaceutical kit for the prevention and treatment of 0 radiation-associated tissue damage.

Description

TITLE OF THE INVENTION

METHOD AND COMPOSITION OF ADMINISTERING RADIOPROTECTANTS

This invention was made with United States Government support. The

Government may have certain rights in the invention. This application claims priority from U.S. Provisional Application Serial No. 60/445,236 filed February 6, 2003. The entirety of that provisional application is incorporated herein by reference. Field of the Invention The present invention is directed to compositions and methods for the prevention and treatment of radiation-associated tissue injury. Specifically, the present invention relates to methods for effective delivery of radiation-protective phosphorothioate and Vitamin E into a mammal using a liposomal system. These methods are particularly useful in the enhancement of the protective response while reducing the toxicity attributable to radiation-protective phosphorothioate. BACKGROUND OF THE INVENTION Acute and protracted (low dose/low dose rate) ionization radiation may lead to hematopoietic and genomic alterations. It is generally accepted that DNA is the crucial target in the cytotoxic effects of ionizing radiation. There is considerable evidence to support the view that DNA double-stranded (ds) breaks are particularly important. The DNA damage results from both direct ionization in the DNA molecule (direct effect) and by indirect effects mediated by the radiolysis products of water. Carbon-centred radicals on the deoxyribose moiety of DNA are thought to be the precursors of strand breaks. Amifostine, (s-2-(3-aminopropyl-amino)ethylphosphorothioic acid) (WR- 2721), is a radioprotection agent that has been approved by the U.S. Food and Drug Administration for clinical use. However, efficacious doses of amifostine are associated with significant toxicity to the recipient [Landauer et al., Adv. Space Res., 12:273-283, (1992)]. Limited attempts have also been made to reduce toxicity by subcutaneous administration instead of intravenous in the clinic. Sodicoff et al and Lamperti et al have demonstrated limited use of a transdermal delivery system for amifostine [Sodicoff et al., Radiat. Res., 121:212-219, (1990);

Lamperti et al., Radiat. Res., 124:194-200, (1990)]. However, amifostine is not effective when given orally. Yet another approach of chemically modifying the drug has been attempted to improve availability and reduce toxicity [Bacolod et al., J of liquid Chromatography & related tech., 19:1277-1289, (1996)]. Vitamin E, a lipophilic compound, is a membrane antioxidant that reacts with peroxy, alkoxy, and other radicals [Machlin et al., FASEB J. 1 :441-445, (1987)]. A number of studies suggest that vitamin E enhances the growth inhibitory effect of various tumor treatment modalities such as radiation, chemotherapeutic agents, and hyperthermia [(Prasad et al., In: Vitamins, nutrition, and cancer, Prasad KN ed. Basal: Karger; 76-104(1984)]. For example, Vitamin E protects against adriamycin cardiotoxicity without compromising the effectiveness of the drug [Myers et al, Cancer Treat. Rep., 60:961-961, (1976)]. Selective protection of murine erythroid progenitor cells from drug induced toxicity [Gogu et al., Proc. Am. Assoc. Cancer Res. 31:404, (1990)] and lowering of the lethality of recombinant human tumor necrosis factor (TNF) have also been observed with vitamin E administration [Satomi et al., JBiol. Response Mod. 7:54-64, (1988)]. The radioprotective effect of vitamin E has been studied by Srinivasan et al. (Srinivasan et al., Int. J. Radio Oncology Biol. Phys., 23:841-845, 1992). It was found that a single injection of vitamin E before or after irradiation significantly increase the survival rate in mice. Moreover, the radioprotective effect of phosphorothioate is enhanced by vitamin E, suggesting that it is possible to use combinations of agents with different protective mechanisms of action at less toxic doses, or to reduce the toxicity of the major protective compound by adding another agent. In this study, however, the lipophilic vitamin E was injected subcutaneously (s.c.) and the hydrophilic phosphorothioate (WR-3689, a methyl analog of amifostine) was administered intraperitoneally (i.p.). SUMMARY OF THE INVENTION The present invention is directed to a drug delivery system for co- administration of a radioprotective phosphorothioate and vitamin E. The drug delivery system can be used for the prevention and treatment of radiation-related tissue injury. One aspect of the present invention relates to a method for simultaneous delivery of a radioprotective phosphorothioate and vitamin E to the target sites of a mammal. The method comprising the steps of preparing liposomes comprising a lipid, a radioprotective phosphorothioate and vitamin E; and administering the liposomes to a mammal. Another aspect of the invention relates to a pharmaceutical composition for preventing and treating radiation-associated tissue damage. The pharmaceutical composition comprises a radioprotective phosphorothioate, vitamin E, and a liposome comprising a hydrophilic core and a hydrophobic encapsulation layer. Yet another aspect of the invention relates to a pharmaceutical kit for preventing and treating radiation-associated tissue injure. The kit comprises dehydrated liposomes comprising a radioprotective phosphorothioate and vitamin E, and a rehydration solution for rehydrating the liposomes. BRIEF DESCRIPTION OF THE FIGURES Figure 1 illustrates a liposomal delivery system which can be used to deliver amifostine and vitamin E to a target site of a mammal through one delivery system. This liposomal structure contains of a hydrophilic core and a hydrophobic envelop. Figure 2 show the phosphorus estimation at Absorbance 820 nM used to quantitate phospholipids content of liposomal formulations. Figures 3 a and 3b illustrate a typical elution profile for amifostine and a typical assay profile under special assay conditions. Figure 3a shows elution profile for 200 pmole/20μl injection. In a high pressure liquid chromatography with an electrochemical detection system. Figure 3b shows assay profile, picomole level measurement under the special conditions: mobile phase consists of 100 mM monochloroacetic acid, 3.5% acetonitrile, 300 mM hexane suphonic acid, 0.5 mM cysteamine, pH 2.8, run with 30°C oven temperature, flow rate of 1 ml/min, electrochemical detectors maintained at 200mV potential. Figure 4 is a stability test of liposomes containing amifostine. Amifostine is encapsulated and incubated at 37°C under in vitro conditions. The retention of the drug in the liposome fraction is an indication of drug stability in the formulation. Figure 5 Comparison of elution profile for free Amifostine as compared to liposomally encapsulated Amifostine on Sephadex G25. Figure 6 is a general flowchart illustrating a method for evaluating the radioprotective efficacy of amifostine encapsulated in liposome in cell culture and under in vivo survival studies. Figure 7 illustrates sparing of phosphorothioate by vitamin E in mice (13 Gy) in which vitamin E was administered sc while phosphorothioate was administered i.p. at 1 hr and 30 min before radiation respectively. DETAILED DESCRIPTION OF THE INVENTION One aspect of the present invention relates to a method for an effective co- administration of radiation-protective phosphorothioate and vitamin E using liposomal systems. The co-administration of phosphorothioate and vitamin E provides effective protection for radiation-associated tissue damage while reducing phosphorothioate-related toxicity. A liposomal structure contains a hydrophilic core and a hydrophobic envelop as shown in Figure 1. The contrasting properties of the core and the envelope facilitate incorporation of both a water soluble radioprotector (e.g. phosphorothioate) and a lipophilic radioprotector (e.g. vitamin E). Therefore, the liposomal structure provides an ideal system for simultaneous delivery of radiation- protective phosphorothioate and vitamin E. Liposomes are formulated based on the requirement of the delivery of specific drugs. Drugs may be released on the first interaction with macrophages or be bound and tagged for a targeted release [Romero et al. Medicina, 61 :205-214, (2001)]. Controlled release by pegylation of lipids in liposomal preparations is yet another option [Reddy Ann Pharmacother 34:915-923, (2000)]. The characteristics of liposomes, such as size and composition, can be modified during the preparation of the liposomes (Avanti Polar Lipids, Technical notes). In the present invention, the liposomes are formulated to contain optimal levels of radiation-protective phosphorothioate in the aqueous central core and vitamin E in the outer envelop/sheath. In an embodiment, a lipid mixture of one or more lipids and vitamin E is dissolved in an organic solvent. In a preferred embodiment, the lipid mixture contains phospholipids, cholesterol, vitamin E, and phosphoethanolamine, and the organic solvent is chloroform. More preferred, the lipid mixture contains DPPC-dipalmitoyl-sn-glycero-3-phosphocholine, DMPG- Dimyristoyl-sn-glycero-3-[phosphor-rac-(l-glycerol)], cholesterol, alpha tocopherol and DPSE- 1 ,2-distearoyl-sn-glycero-3-phosphoethanolamine-N- [methoxy(polyethylene glycol)-2000]. Most preferred, the lipid mixture contains

DPPC, DMPG, cholesterol, vitamin E and DPSE at a mole ratio of 52.89:9.98:18.96:16.97:1.20. The solvent is evaporated under controlled conditions resulting in a uniform, thin lipid layer of lipid mix in the evaporating flask. A radiation-protective phosphorothioate dissolved in water is added to the flask containing lipid mix and mixed periodically to form liposomes. The free, unencapsulated phosphorothioate is separated from the liposomes by a process such as centrifugation and gel filtration. In another embodiment, lipid mix was prepared in the same way as indicated above. The residual solvent was removed by purging with a stream of argon. Phosphate buffered saline or water was added to the dried lipid mix layer in the evaporating flask and was sonicated briefly to form a liposome suspension. A radiation-protective phosphorothioate (e.g., WR-2721) was then added to the liposome suspension. The preparation was frozen and freeze-dried overnight. A small quantity of water was added to rehydrate the liposome and after mixing for 30 min additional water was added, The liposomal preparation was finally extruded through polycarbonate filters and liposomes stored at 4°C. The lipids may be natural, synthetic or semisynthetic (i.e., modified natural). Lipids useful in the invention include, and are not limited to, fatty acids, lysolipids, oils (including safflower, soybean and peanut oil), phosphatidylcholine with both saturated and unsaturated lipids including phosphatidylcholine; dioleoylphosphatidylcholine; dimyristoylphosphatidylcholine; dipentadecanoylphosphatidylcholine, dilauroylphosphatidylcholine, dipalmitoylphosphatidylcholine; distearoylphosphatidylcholine; phosphatidylethanolamines such as dioleoylphosphatidylethanolamine; phosphatidylserine; phosphatidylglycerol; phosphatidylmositol, sphingolipids such as sphingomyelin; glycolipids such as ganglioside GM1 and GM2; glucolipids; sulfatides; glycosphingolipids; phosphatidic acid; palmitic acid; stearic acid; arachidonic acid; oleic acid; lipids bearing polymers such as polyethyleneglycol, chitin, hyaluronic acid or polyvinylpyrrolidone; lipids bearing sulfonated mono-, di-, oligo- or polysaccharides; cholesterol, cholesterol sulfate and cholesterol hemisuccinate; tocopherol hemisuccinate, lipids with ether and ester-linked fatty acids, polymerized lipids (a wide variety of which are known in the art), diacetyl phosphate, stearylamine, cardiolipin, phospholipids with short chain fatty acids of about 6 to about 8 carbons in length, synthetic phospholipids with asymmetric acyl chains (e.g., with one acyl chain of about 6 carbons and another acyl chain of about 12 carbons), 6-(5-cholesten-3b-yloxy)-l-thio-β-D-galactopyranoside, digalactosyldiglyceride, 6-(5-cholesten-3β-yloxy)hexyl-6-amino-6-deoxy-l-thio-β- D-galacto pyranoside, 6-(5-cholesten-3β-yloxy)hexyl-6-amino-6-deoxyl-l-tl io-α- D-mann opyranoside, 12-(((7'-diethylamino-coumarin-3- yl)carbonyl)methylamino)-octadecanoic acid; N-[12-(((7'-diethylaminocoumarin-3- yl)carbonyl)methyl-amino) octadecanoyl]-2-aminopalmitic acid; (cholesteryl)4'- trimethyl-ammonio)butanoate; N-succinyldioleoylphosphatidylethanolamine; 1 ,2- dioleoyl-sn-glycerol; l,2-dipalmitoyl-sn-3-succinyl-glycerol; l,3-dipalmitoyl-2- succinylglycerol; l-hexadecyl-2-palmitoyl-glycerophosphoethanolamine and palmitoylhomocysteine, and/or combinations thereof. Vesicles or other structures may be formed of the lipids, either as monolayers, bilayers, or multilayers and may or may not have a further coating. The preferred lipid carrier may be in the form of a monolayer or bilayer, and the mono- or bilayer could be one or more layer of hydrophilic membrane around the central hydrophilic core. In the case of more than one mono- or bilayer, the mono- or bilayers may be concentric. The carrier may form a unilamellar liposome (comprised of one monolayer or bilayer), an oligolamellar liposome (comprised of about two or about three monolayers or bilayers) or a multilamellar liposome (comprised of more than about three monolayers or bilayers). The walls or membranes of a liposome may be substantially solid (uniform), or they may be porous or semi-porous. Lipids bearing hydrophilic polymers such as polyethyleneglycol (PEG), including and not limited to PEG 2000 MW and 5,000 MW are also useful for improving the stability and size distribution of organic halide-containing composition. The lipids also include cationic lipids and other derivatized lipids. Suitable cationic lipids include dimyristyl oxypropyl-3-dimethylhydroxy ethylammonium bromide (DMRIE), dilauryl oxypropyl-3-dimethylhydroxy ethylammonium bromide (DLRIE), -[l-(2,3-dioleoyloxyl)propal]-n,n,n-trimethylammonium sulfate

(DOTAP), dioleoylphosphatidylethanolamine (DOPE), dipalmitoylethylphosphatidylcholine (DPEPC), dioleoylphosphatidylcholine (DOPC), polylysine, lipopolylysine, didoceyl methylammonium bromide(DDAB), 2,3-dioleoyloxy-N-[2-(sperminecarboxamidoethyl]-N,N-di-methyl-l-propanamin ium trifluoroacetate (DOSPA), cetyltrimethylammonium bromide (CTAB), lysyl-

PE, 3, .beta.-[N,(N',N'-dimethylaminoethane)-carbamoyl]cholesterol (DC- Cholesterol, also known as DC-Choi), (-alanyl cholesterol, N-[l-(2,3- dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA), dipalmitoylphosphatidylethanolamine-5-carboxyspermylamide (DPPES), dicaproylphosphatidylethanolamine (DCPE), Dipalmitoylphosphatidylcholine (DPPC), dimyristoylphosphatidylglycerol (DMPG), distearoylphosphatidylethanolamine (DPSE), 4-dimethylaminopyridine (DMAP), dimyristoylphosphatidylethanolamine (DMPE), dioleoylethylphosphocholine (DOEPC), dioctadecylamidoglycyl spermidine (DOGS), N-[l-(2,3- dioleoyloxy)propyl]-N-[l-(2-hydroxyethyl)]-N,N-dimethylamtnonium iodide

(DOHME), Lipofectin (DOTMA+DOPE, Life Technologies, Inc., Gaithersburg, Md.), Lipofectamine (DOSPA+DOPE, Life Technologies, Inc., Gaithersburg, Md.), Transfectace (Life Technologies, Inc., Gaithersburg, Md.), Transfectam (Promega Ltd., Madison, Wis.), Cytofectin (Life Technologies Inc., Gaithersburg, Md.). Other representative cationic lipids include but are not limited to phosphatidylethanolamme, phospatidylcholine, glycero-3-ethylphosphatidylcholine and fatty acyl esters thereof, di- and trimethyl ammonium propane, di- and tri- ethylammonium propane and fatty acyl esters thereof. A derivative from this group is N-[l-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA). Additionally, a wide array of synthetic cationic lipids function as compounds useful in the invention. These include common natural lipids derivatized to contain one or more basic functional groups. Examples of lipids which may be so modified include but are not limited to dimethyldioctadecylammonium bromide, sphingolipids, sphingomyelin, lysolipids, glycolipids such as ganglioside GM1, sulfatides, glycosphingolipids, cholesterol and cholesterol esters and salts, N- succinyldioleoylphosphatidylethanolamine, 1 ,2,-dioleoyl-sn-glycerol, 1,3- dipalmitoyl-2-succinylglycerol, 1 ,2-dipahnitoyl-sn-3-succinylglycerol, 1 - hexadecyl-2-palmitoylglycerophosphatidylethanolamine and palmitoylhomocystiene. Other synthesized cationic lipids include, for example, N,N'-Bis

(dodecyaminocarbonylmethylene)-N,N'bis ((-N,N,N- trimethylammoniumethylaminocarbonylmethylene)ethylenediamine tetraiodide; N,N"-Bis (hexadecylaminocarbonylmethylene)-N,N',N"-tris ((-N,N,N- trimethylammoniumethylaminocarbonylmethylenedi-ethylenetriairiine hexaiodide; N,N'-Bis (dodecylaminocarbonylmethylene)-N,N"-bis((-N,N,N- trimethylammoniumethylami nocarbonylmethylene)cyclohexylene- 1 ,4-diamine tetraiodide; 1 , 1 ,7,7-tetra-((-N,N,N,N- tetramethylammoniumethylaminocarbonylmethylene)-3 -hexadecylaminocarbonyl- methylene-l,3,7-triaazaheptane heptaiodide; and N,N,N'N'-tetra((-N,N,N- trimethylammoniumethylaminocarbonyhrιethylene)-N^,-(l ,2-di oleoylglycero-3- phosphoethanolaminocarbonylmethylene) diethylenetriamine tetraiodide. Those of skill in the art will recognize that countless other natural and synthetic variants carrying positive charged moieties will also function in the invention. Additionally lipid moieties capable of polymerization are embraced in the invention as coatings for the liposomes. Examples of these include, but are not limited to, alkenyl and alkynyl moieties, such as oleyl and linoleyl groups, diacetylene, acryloyl and methacryloyli groups with or without polar groups to enhance water solubility, cyanoacrylate esters optionally carrying lipophilic esterifying groups or the compounds illustrated as A and B, below. A number of such compounds have been described, for example, in Klaveness et al., U.S. Pat.

No. 5,536,490. The disclosures of Klaveness et al., U.S. Pat. No. 5,536,490, are hereby incorporated herein by reference in their entirety. The vitamin E component in the liposome can be any member or a combination of members of the vitamin E family, which include alpha-, beta-, gamma-, and delta-tocopherol, as well as alpha-, beta-, gamma-, and delta- tocotrienol. Preferably, the vitamin E component is alpha-tocopherol. The organic solvent can be any organic solvent suitable for liposome formation. Examples include, but are not limited to, chloroform, methanol, ether, ethanol and acetone. Examples of radiation-protective phosphorothioate include, but are not limited to, amifostine (WR-2721), aminothiol (WR-1065), WR-638, WR-77913, WR-3689, WR-44923, WR-151327, and other effective chemical radioprotectors discovered in NCI sponsored radioprotector screening program (1980-1983) [see Brown et al., Parmac. Ther., 39:157-168, (1988)]; cysteamine, cysteamine derivatives such as disulfide cysteamine and N-glycylglycyl-S-acetyl cysteamine and other related radioprotectors such as AET (aminoethylisothiuroniixm bromide, HBr), MPG (mercaptopropynylglycine) and WR-2529, 3-[(2-mercaptoethyl)- amino]propionamide p-toluenesulfonate. The liposomes are then subject to a dehydration-rehydration process as suggested by Kirby and Gregoriadis [See Kirby et al., Biotechnology, 2:979-984,

(1984)]. For the dehydration of the liposomes, known methods such as lyophilization and spray drying may be applied. Preferably, lyophilization is applied. Saccharides such as sucrose or trehalose may be added as lyophilization aids. The saccharide may be added at least in the external liquid phase during the dehydration of liposomes. The concentration of the saccharide which can be added in the external liquid phase may generally be from 5 to 40%, preferably from 5 to 20%. As the rehydration solution, aqueous solutions containing salts such as physiological saline, neutral buffers such as phosphate buffers, saccharide solutions such as those containing glucose, or mixtures thereof may be used. The pH of the rehydration solution may preferably be in a neutral area such as in the range of from 6 to 8, more preferably from 6.5 to 7.5 pH adjusting buffers may be added in any manner so far as the aqueous solutions containing the closed vesicles have pHs in the neutral area during the rehydration process. For example, they may be added in the rehydration solutions, or alternatively, they may be added in liposomes at the time of lyophilization of the liposomes, or may be contained in both of the rehydration solution and lyophilized liposomes. The concentration of the pH adjusting buffer may generally be from 1 to 100 mM, preferably 5 to 50 mM. The rehydration can be carried out by dispersing the dehydrated liposomes in the rehydration solution under low temperature conditions. The low temperature condition herein used means a temperature below room temperature, usually a temperature of about 20°C or lower, i.e., a temperature ranging from about 20° C down to a temperature at which the rehydration solution does not freeze and can exist in the state of a solution. The temperature range between about 10° C to 0° C is preferred. The low temperature condition for the rehydration may be applied by any method so long as a temperature in the aforementioned range can be achieved. For example, either or both of the pharmaceutical container, e.g., a vial, containing the dehydrated closed vesicles, and the rehydration solution, may be cooled beforehand at a low temperature, or alternatively, the dehydrated closed vesicles may be dispersed in the rehydration solution while cooling under the low temperature condition using a suitable refrigerant during the rehydration process. Period of time for the rehydration is not particularly limited so long as it can achieve uniform dispersion of the closed vesicles in the rehydration solution. The period may vary depending on the size of a vessel, agitation rate and the like, and is generally about 1 minute or less. By maintaining the aforementioned low temperature condition during said period, a reduced leaking of the loaded substance is achievable and the dehydrated closed vesicles can be stably rehydrated. Another aspect of the invention relates to a pharmaceutical composition containing liposomes that encapsulate a radiation-protective phosphorothioate and vitamin E. The pharmaceutical composition is radioprotective under both acute and protracted radiation conditions. The present pharmaceutical composition not only provides protection against radiation-induced suppression of the hematopoietic system but also enhances bone marrow stem cell activity, and it provide a greater window of protection than radiation-protective phosphorothioate alone. The pharmaceutical composition can be used through intravascular, subcutaneous, intraperitoneal, or topical administration for radiation protection. Administration dose may appropriately be chosen depending on the source, dose rate and dose of radiation. In another embodiment, the pharmaceutical composition further contains a pharmaceutically acceptable carrier. As used herein the language "pharmaceutically acceptable carrier" is intended to include any and all solvents, solubilizers, fillers, stabilizers, binders, absorbents, bases, buffering agents, lubricants, controlled release vehicles, diluents, emulsifying agents, humectants, lubricants, dispersion media, coatings, antibacterial or antifungal agents, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration. The use of such media and agents for pharmaceutically active substances is well-known in the art. Except insofar as any conventional media or agent is incompatible with the active compound, use thereof in the compositions is contemplated. Supplementary agents can also be incorporated into the compositions. A pharmaceutical composition of the invention is formulated to be compatible with its intended route of administration. Examples of routes of administration include parenteral, e.g., intravenous, intradermal, subcutaneous, oral (e.g., inhalation), transdermal (topical), transmucosal, and rectal administration.

Solutions or suspensions used for parenteral, intradermal, or subcutaneous application can include the following components: a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine; propylene glycol or other synthetic solvents; antibacterial agents such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfate; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose pH can be adjusted with acids or bases, such as hydrochloric acid or sodium hydroxide. The parenteral preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic. Pharmaceutical compositions suitable for injectable use include sterile aqueous solutions (where water soluble) or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersion. For intravenous administration, suitable carriers include physiological saline, bacteriostatic water, or phosphate buffered saline (PBS). In all cases, the injectable composition should be sterile and should be fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), and suitable mixtures thereof. The proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the requited particle size in the case of dispersion and by the use of surfactants. Prevention of the action of microorganisms can be achieved by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, ascorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, such as sodium chloride, sugars, polyalcohols (e.g., manitol, sorbitol, etc.) in the composition. Prolonged absorption of the injectable compositions can be brought about by including in the composition an agent which delays absorption, for example, aluminum monostearate and gelatin. Sterile injectable solutions can be prepared by incorporating the active modulator (e.g., the liposomes containing amifostine and vitamine E) in the required amount in an appropriate solvent with one or a combination of ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the active compound into a sterile vehicle which contains a basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and freeze-drying which yields a powder of the active ingredient plus any additional desired ingredient from a previously sterile-filtered solution thereof. For administration by inhalation, the compounds are delivered in the form of an aerosol spray from a pressured container or dispenser which contains a suitable propellant, e.g., a gas such as carbon dioxide, or a nebulizer. Systemic administration can also be by transmucosal or transdermal means.

For transmucosal or transdermal administration, penetrants appropriate to the barrier to be permeated are used in the formulation. Such penetrants are generally known in the art, and include, for example, for transmucosal administration, detergents, bile salts, and fusidic acid derivatives. Transmucosal administration can be accomplished through the use of nasal sprays or suppositories. For transdermal administration, the bioactive compounds are formulated into ointments, salves, gels, or creams as generally known in the art. The compounds can also be prepared in the form of suppositories (e.g., with conventional suppository bases such as cocoa butter and other glycerides) or retention enemas for rectal delivery. It is especially advantageous to formulate compositions in dosage unit form for ease of administration and uniformity of dosage. Dosage unit form as used herein includes physically discrete units suited as unitary dosages for the subject to be treated; each unit contains a predetermined quantity of active compound calculated to produce the desired therapeutic effect in association with the required pharmaceutical carrier. The specification for the dosage unit forms of the invention are dictated by and directly dependent on the unique characteristics of the active compound and the particular therapeutic effect to be achieved, and the limitations inherent in the art of compounding such an active compound for the treatment of individuals. Toxicity and therapeutic efficacy of such compounds can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., for determining the LD50 (the dose lethal to 50% of the population) and the ED50 (the dose therapeutically effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the therapeutic index and it can be expressed as the ratio LD50/ED50. Compounds which exhibit large therapeutic indices are preferred. While compounds that exhibit toxic side effects may be used, care should be taken to design a delivery system that targets such compounds to the site of affected tissue in order to minimize potential damage to uninfected cells and, thereby, reduce side effects. The data obtained from the cell culture assays and animal studies can be used in formulating a range of dosage for use in humans. The dosage of such compounds lies preferably within a range of circulating concentrations that includes the ED50 with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration utilized. For any compound used in the method of the invention, the therapeutically effective dose can be estimated initially from cell culture assays. A dose may be formulated in animal models to achieve a circulating plasma concentration range that includes the IC50 (i.e., the concentration of the test compound which achieves a half-maximal inhibition of symptoms) as determined in cell culture. Such information can be used to more accurately determine useful doses in humans. Levels in plasma may be measured, for example, by high performance liquid chromatography. The pharmaceutical compositions can be included in a container, pack, or dispenser together with instructions for administration. The present invention also encompasses a pharmaceutical kit composed of two unit components, i.e., a dried preparation containing a dehydrated liposome (or liposomes) and a rehydration solution (or solutions) for rehydrating the liposome (or liposomes). In another embodiment, the liposomes are prepared in the absence of the radiation-protective phosphorothioate. The radiation-protective phosphorothioate is incorporated into the liposomes during the rehydration process. This embodiment also encompasses a pharmaceutical kit composed of three unit components, i.e a lyophilized preparation containing a radiation-protective phosphorothioate and a dried preparation containing the dehydrated liposomes prepared in the absence of the radiation-protective phosphorothioate, each of which is filled in a separate container, together with the rehydration solution. Where the three component kit is used, the dehydrated preparation containing the dehydrated liposomes is rehydrated under the low temperature condition in the manner described above, and then the radiation-protective phosphorothioate dissolved in a suitable solvent beforehand is added to the rehydrated closed vesicle solution. By these processes, the radiation- protective phosphorothioate can be taken into the liposomes by a potential energy generated between the inside and outside of the liposomes. Another aspect of the present invention provides for both prophylactic and therapeutic methods of treating a subject at risk for, susceptible to or diagnosed with radiation-associated tissue damage. In one embodiment, the invention provides a method for preventing in a subject radiation-associated tissue damage, by administering to the subject effective amount of a pharmaceutical composition containing radiation-protective phosphorothioate, preferably amifostine, and vitamin E in a liposome-based structure. In another embodiment, the invention provides a method for treating in a subject radiation-associated tissue damage, by administering to the subject effective amount of the pharmaceutical composition. The effective amount of radiation-protective phosphorothioate (such as amifostine) and vitamin E necessary to bring about prevention and /or therapeutic treatment of radiation-induced damage is not fixed per se. An effective amount is necessarily dependent upon the identity and form of phosphorothioate and vitamin E employed, the extent of the protection needed, or the severity of the radiation damage to be treated. Administration of the pharmaceutical composition can occur prior to the exposure to radiation, such that radiation-associated tissue damage is prevented or, alternatively, delayed in its progression. The appropriate dose and route of administration of the pharmaceutical composition can be determined based on the level of radiation exposure or potential risk of radiation. With regard to both prophylactic and therapeutic methods of treatment, such treatments may be specifically tailored or modified, based on knowledge obtained from the field of pharmacogenomics. "Pharmaco genomics," as used herein, includes the application of genomics technologies such as gene sequencing, statistical genetics, and gene expression analysis to drugs in clinical development and on the market. More specifically, the term refers the study of how a subject's genes determine his or her response to a drug (e.g., a subject's "drug response phenotype" or "drug response genotype"). Thus, another aspect of the invention provides methods for tailoring an individual's prophylactic or therapeutic treatment with the pharmaceutical composition according to that individual's drug response. Pharmacogenomics allows a clinician or physician to target prophylactic or therapeutic treatments to subjects who will most benefit from the treatment and to avoid treatment of subjects who will experience toxic drug-related side effects. Differences in metabolism of therapeutics can lead to severe toxicity or therapeutic failure by altering the relation between dose and blood concentration of the pharmacologically active drug. Thus, a physician or clinician may consider applying knowledge obtained in relevant pharmacogenomics studies in determining, for example, whether to administer amifostine and vitamine E as well as tailoring the dosage and/or therapeutic regimen of treatment with amifostine and vitamine E. Pharmacogenomics deals with clinically significant hereditary variations in the response to drugs due to altered drug disposition and abnormal action in affected persons. In general, two types of pharmacogenetic conditions can be differentiated. Genetic conditions transmitted as a single factor altering the way drugs act on the body (altered drug action) or genetic conditions transmitted as single factors altering the way the body acts on drugs (altered drug metabolism).

These pharmacogenetic conditions can occur either as rare genetic defects or as naturally-occurring polymorphisms. For example, glucose-6-phosphate dehydrogenase deficiency (G6PD) is a common inherited enzymopathy in which the main clinical complication is hemolysis after ingestion of oxidant drugs (anti- malarials, sulfonamides, analgesics, nitrofurans) and consumption of fava beans. One pharmacogenomics approach to identifying genes that predict drug response, known as "a genome-wide association," relies primarily on a high- resolution map of the human genome consisting of already known gene-related sites (e.g., a "bi-allelic" gene marker map which consists of 60,000-100,000 polymorphic or variable sites on the human genome, each of which has two variants). Such a high-resolution genetic map can be compared to a map of the genome of each of a statistically substantial number of subjects taking part in a Phase II/III drug trial to identify genes associated with a particular observed drug response or side effect. Alternatively, such a high resolution map can be generated from a combination of some ten-million known single nucleotide polymorphisms (SNPs) in the human genome. As used herein, a "SNP" is a common alteration that occurs in a single nucleotide base in a stretch of DNA. For example, a SNP may occur once per every 1000 bases of DNA. A SNP may be involved in a disease process. However, the vast majority of SNPs may not be disease associated. Given a genetic map based on the occurrence of such SNPs, individuals can be grouped into genetic categories depending on a particular pattern of SNPs in their individual genome. In such a manner, treatment regimens can be tailored to groups of genetically similar individuals, taking into account traits that may be common among such genetically similar individuals. Alternatively, a method termed the "candidate gene approach," can be utilized to identify genes that predict drug response. According to this method, if a gene that encodes a drug target is known, all common variants of that gene can be fairly easily identified in the population and it can be determined if having one version of the gene versus another is associated with a particular drug response. As an illustrative embodiment, the activity of drug metabolizing enzymes is a major determinant of both the intensity and duration of drug action. The discovery of genetic polymorphisms of drug metabolizing enzymes (e.g., N-acetyltransferase 2 (NAT 2) and cytochrome P450 enzymes CYP2D6 and CYPZC19) has provided an explanation as to why some subjects do not obtain the expected drug effects or show exaggerated drug response and serious toxicity after taking the standard and safe dose of a drug. These polymorphisms are expressed in two phenotypes in the population, the extensive metabolizer and poor metabolizer. The prevalence of poor metabolizer phenotypes is different among different populations. For example, the gene coding for CYP2D6 is highly polymorphic and several mutations have been identified in poor metabolizers, which all lead to the absence of functional CYP2D6. Poor metabolizers of CYP2D6 and CYP2C19 quite frequently experience exaggerated drug response and side effects when they receive standard doses. If a metabolite is the active therapeutic moiety, poor metabolizers show no therapeutic response, as demonstrated for the analgesic effect of codeine mediated by its CYP2D6-formed metabolite morphine. The other extreme are the so called ultra-rapid metabolizers who do not respond to standard doses. Recently, the molecular basis of ultra-rapid metabolism has been identified to be due to CYP2D6 gene amplification. Alternatively, a method termed the "gene expression profiling" can be utilized to identify genes that predict drug response. For example, the gene expression of an animal dosed with a drug (e.g., gene expression in response to amifostine) can give an indication whether gene pathways related to toxicity have been turned on. Information generated from more than one of the above pharmacogenomics approaches can be used to determine appropriate dosage and treatment regimens for prophylactic or therapeutic treatment an individual. This knowledge, when applied to dosing or drug selection, can avoid adverse reactions or therapeutic failure and thus enhance therapeutic or prophylactic efficiency when treating a subject with radiation-protective phosphorothioate and vitamin E. Modifications to the above-described compositions and methods of the invention, according to standard techniques, will be readily apparent to one skilled in the art and are meant to be encompassed by the invention. The present invention is further illustrated by the following examples which should not be construed as limiting. The contents of all references, patents and published patent applications cited throughout this application, as well as the

Figures and Tables are incorporated herein by reference. EXAMPLE 1: General Methods 1. Liposomal preparation Dehydration-rehydration vesicle (DRV) approach [Kirby et al., Biotechnology 2:979-984 (1984)] is used to prepare liposomes with modifications.

Briefly, a lipid mixture containing phospholipid, cholesterol, vitamin E and phosphoethanolamine were incubated with amifostine at 37°C for 2 hours; intermittent mixing at 15 minutes interval during the entire 2 hours incubation. The liposomal preparation at this stage was diluted with 10 volumes of L-buffer (8.48g NaCl and 2.6 g HEPES in IL water at pH 7.4) and centrifuged at 10,000 m for 10 minutes at 4°C. The supernatant was carefully removed and the pellet was resuspended in L-buffer. The modified procedure resulted in 20-30% drug incoφoration in liposomes. 2. Particle size measurement Liposomal samples are diluted with "Isotone" solution and particle size measurements are carried out using Coulter particle size instrument. Standard beads of 1-10 micron size are used to quantitate the particle size of liposomes. 3. Amifostine analysis HPLC-electrochemical detector method has been standardized for analysis of amifostine in liposomal preparations as well as in biological samples. The methodology is very sensitive and can measure picomole quantities of amifostine in samples. Figures 3 a and 3b show typical chromatogram and a typical standard curve (response over a wide range of drug concentrations) for amifostine. 4. Phospholipid assay Samples of liposomes are extracted with chlorofoπn:methanol. The samples are hydro lyzed in the presence of sulfuric acid at 200 °C to yield inorganic phosphorous which is analyzed spectrophotometrically (Avanti Polar Lipids, Technical notes). Figure 2 shows the phosphorous estimation at A₈₂₀. 5. Vitamin E assay Liposome samples will be treated with 0.1 % BHT and with 100% ethanol to totally disperse liposomes for vitamin E assay. The ethanol extracts will be saved at -20°C until further analysis. HPLC based assay employing UV detection will be used to quantitate vitamin E content of liposomes. 6. Particle size reduction The liposomes which were described in "Liposomal preparation" having an average particle size of 2-3 micron and representing multilamellar vesicles (MLV). A microfluidizer equipment is used reducing particle size of liposomes in order for carrying out in vivo studies. Extrusion through polycarbonate filters using an extruder, such as Liposofast extruder (Avestin, Ottowa, Canada) will also be used to reduce particle sizes so that liposomes can be sterilized and used for in vivo studies. Results revealed that the presence of sulphydryl compounds (Amifostine) inhibited particle reduction significantly. Additional approaches to particle size reduction will be undertaken. 7. Determination of Storage conditions for liposomes Liposomes are reasonably stable at 4°C. It has been observed that the liposomes containing amifostine are stable up to 48 hours at 4°C. There are many methods available for storage of liposomes including freeze drying, freezing and incoφoration of liposomes in synthetic polymeric microspheres. Some of these will be tested and an optimal storage approach will be determined. EXAMPLE 2: Stability test of liposomes containing amifostine Preliminary studies were carried out on encapsulation of amifostine in a liposomal formulation containing phospholipid, cholesterol, vitamin E and polyethylene glycol containing phosphoethanoiamine (DPSE-Diphosphotidyl polyethylene glucol-2000, ethanoiamine). Data revealed that amifostine is encapsulated under the experimental conditions and that the drug remains encapsulated for 48 firs at 4°C (not shown) and up to 8 hrs at 37 °C (Figure 4). EXAMPLE 3: Development of HPLC/EC assay for amifostine The methodology was modified based on the assay disclosed in Pendergrass et al, J AO AC International, 85(2):551-554, (2002) for WR-1065, the thiol form of amifostine found in tissues. Figures 3a and 3b show a typical elution profile for amifostine and a typical assay profile (picomole level measurements) under the assay conditions (mobile phase consists of 100 mM monochloroacetic acid, 3.5% acetonitrile, 300 mM hexane sulphonic acid, 0.5 mM cysteamine, pH 2.8, run with 30 °C oven temperature, flow rate of 1 ml/min, electrochemical detector maintained at 200mV potential).

EXAMPLE 4: Temperature effect on amifostine liposomes (% drug loading^) The formation of liposome depends on various experimental conditions and depends on the physical characteristics of phospholipids such as gel phase transition temperature (Avanti Polar Lipid Ltd, technical notes). Several studies were carried out to optimize the formulation of liposomes. Studies revealed that amifostine incoφoration in the liposomes is temperature dependant. A protocol (dehydration-rehydration vesicles) which has been shown in literature to provide high yield of drug entrapment - 50% of water-soluble drugs- (Kirby et al., Supra, 1984) was found to provide only 2-3% amifostine incoφoration. The procedure involves heating at 65 °C for 30 minutes to bring about phase transition of liposomes and also involves sonication to bring about homogeneity of liposomal particles. The temperature was found to be critical in the stability of amifostine. Amifostine was significantly labile at 65 °C with 80%) loss occurring with 15 minutes at 65° C in a dose dependent fashion. EXAMPLE 5: Removal of unencapsulated-free drug by centrifugation The liposomal preparation includes a step where in the lipid mix (all the lipid components-phospholipid etc) is blended with excess of the drug. Kirby and Gregoriadis (Kirby et al., Supra, 1984) recommend removal of un-encapsulated free drug from liposomal preparation by washing the liposomal preparation with high molar buffer. It was found that in addition to the removal of the free amifostine, the centrifugation step in itself results in 30-40% loss of the phospholipid. Similar losses have been reported by others in literature [Reddy Ann Pharmacother, 34:915-923, (2000)]. However, the simplicity of the separation of free and encapsulated by simple centrifugation has been found to be advantageous in general. Recovery experiments indicated that the centrifugation loss superimposes on already low yield of the drug in the liposome. EXAMPLE 6: Sephadex G-25, gel filtration to separate free and-encapsulated drug Liposomes containing encapsulated drug were separated from the unencapsulated drug by the use of gel filtration. Liposomes come out in the void volume (as measured by blue dextran elution-data not shown) and represent first peak in Figure 5. Amifostine, on the other hand, is retained longer and comes out in later fractions and is represented as second peak in Figure 5. EXAMPLE 7: Cell culture Liposomes containing amifostine will be incubated at 37 °C for 1 hour with suspended cells (CHO-K1 from ATCC). These cells will be irradiated at various radiation doses and plated for colony forming/proliferative capacity. Additional studies at longer incubation periods either with adhering cell population or free suspended cell population with liposomes containing amifostine will also be undertaken. EXAMPLE 8: Optimization of the formulation of liposomes The puφose of this experiment is to establish standard preparation conditions for liposomes containing amifostine and vitamin E. Briefly the lipid mix contains DPPC (52.89 mole %), Cholesterol (18.96 mole %), vitamin E (16.97 mole %), DMPG (9.98 mole %) and phosphoethanolamine (DPSE) (1.2 mole %) will be dissolved in chloroform. The solvent will be evaporated under controlled conditions resulting in a uniform, thin lipid layer in the evaporating flask. Amifostine dissolved in water will be added to the flask containing lipid mix and mixed periodically over 1 hour. The free, unencapsulated amifostine will be separated by various approaches including centrifugation and Sephadex G25 gel filtration. The liposomal preparation will be assayed for phospholipid, particle size, amifostine and vitamin E concentrations. Stability tests under in vitro conditions will be undertaken after optimizing the composition of the lipid mix, and the preparation conditions to remove unencapsulated drug. EXAMPLE 9: Radiation and drug dose response studies

Experiment A: Effect of different doses of radiation on cell survival after irradiation The puφose of this experiment is to evaluate the radioprotective efficacy of amifostine encapsulated in liposome in cell culture. Aminothiol (WR-1065), the active drug form of amifostine, has been shown to be radioprotective under cell culture conditions. The prodrug, amifostine has not been shown to be effective when incubated with cell culture prior to irradiation. In the present experiment amifostine has been incoφorated in liposome to obtain sustained release under in vivo conditions. The cell culture model will be used to evaluate whether encapsulated amifostine will be transferred across the membrane and whether it has radioprotective characteristics. Based on the preliminary studies with encapsulated amifostine, attempts to encapsulate aminothiol (WR-1065) may also be developed for cell culture studies. Non-confluent CHO-K1 cells will be grown Vitacell F-12 medium (ATCC). Harvested cells will be incubated at 37 °C in the presence of various agents (see Figure 6) for 1 hour. Irradiation will be performed in the presence of the agents at 4°C. After irradiation excess agents will be washed and cells plated for survival study. Experiment B: Effect of various doses of amifostine encapsulated in liposomal preparation on cell survival after irradiation The protocol described in Experiment A will be used with various doses of amifostine in liposomal preparation varying from 0.5 mM to 4 mM (level used in the first experiment based on literature data). EXAMPLE 10: Radioprotective effect of amifostine and vitamin E Male CD2F1 mice were obtained from National Cancer Institute, Frederick,

MD. CD2F1 mice were divided into various experimental groups with average body weight being in the range of 25-28 g/animal. Vitamin E was dispersed in a special emulsifier mix and diluted with sterile phosphate buffered saline. Vitamin E preparation was injected in experimental animals s.c. 1 hour prior to irradiation. WR-3689, methyl analog of amifostine was dissolved in phosphate buffered saline, sterilized by passing the solution through 0.22 u filter and injected i.p. 30 min before irradiation. Animals were placed in plexiglass containers and subjected to ionizing radiation using Cobalt60 gamma radiation. Animals were returned to their respective cages after exposure to ionizing radiation and monitored for survival for 30 days postirradiation. Appropriate vehicle controls were also included in the study. A group of animals received lower amount of WR-3689 and same amount of vitamin E as vitamin E alone group. Data are presented in figure 7. EXAMPLE 11: In vivo Evaluation of the efficacy of liposomal preparation of amifostine and vitamin E The puφose of this experiment is to evaluate radioprotective efficacy of liposomes containing amifostine in mice exposed to 3 Gy ionizing radiation at low dose rate (0.006 Gy/min). The endpoints will include measurement of hematological and cytogenetic and genomic parameters. This experiment will be done in two parts. In the first part, early arising changes in hematopoietic and cytogenetic endpoints (micronuclei) will be evaluated. In the second part, the observations on hematopoietic function (using above-mentioned parameters) and cytogenetic changes will be continued on a long term basis in order to document the nature and sequence of these changes that might reflect evolving hematopoietic disease (e.g.: leukemia). These studies will be carried out in C3H/HeN male mice. Table 1. Short Term Hematopoietic Study in C₃H HeN Male Mice

EXAMPLE 12: Determination of the effect of liposome encapsulated amifostine on the expression of onco genes Gene array is a powerful tool for screening large number of genes simultaneously, when target genes are unknown. Current proposal targets specific genes that are likely to be affected by radiation. These genes are known to be associated with radiation-induced carcinogenesis. Therefore, a more convenient RPA (Ribonuclease Protection Assay) will be used. Moreover, compare to gene array, RPA not only is more convenient, but also is less expensive and less time consuming. RPA is a highly sensitive and specific method for the detection and quantitation of mRNA species. RPA kit will be used from Pharmingen for evaluating the influence on oncogenes. The oncogenes that will be studied are c- jun, c-fos, and c-myc. The above description is for the puφose of teaching the person of ordinary skill in the art how to practice the present invention, and it is not intended to detail all those obvious modifications and variations of it which will become apparent to the skilled worker upon reading the description. It is intended, however, that all such obvious modifications and variations be included within the scope of the present invention, which is defined by the following claims. The claims are intended to cover the claimed components and steps in any sequence which is effective to meet the objectives there intended, unless the context specifically indicates the contrary.

Claims

We claim: 1. A method for the prevention and treatment of radiation-associated tissue damage to a mammal, said method comprising administering a liposome comprising therapeutically effective amounts of a radioprotective phosphorothioate and vitamin E to said mammal, wherein said radioprotective phosphorothioate and said vitamin E are simultaneously delivered to a target site of said mammal.

2. The method of Claim 1, wherein said radioprotective phosphorothioate is amifostine.

3. The method of Claim 1, wherein said liposome comprises a hydrophilic core and a hydrophobic encapsulation layer, and wherein said radioprotective phosphorothioate is within said hydrophilic core and said vitamin E is integrated into said hydrophobic encapsulation layer.

4. The method of Claim 1, wherein said liposome comprises phospholipids, cholesterol and phosphoethanolamine.

5. The method of Claim 4, wherein said phospholipids are DPPC and

DMPG.

6. The method of Claim 1, wherein said liposome comprises DPPC, Cholesterol, DMPG and DPSE.

7. The method of Claim 1, wherein said vitamine E is alpha tocopherol.

8. The method of Claim 6, wherein said liposome comprises DPPC,

Cholesterol, vitamin E, DMPG and DPSE at a mole ratio of 52.89:18.96:16.97:9.98:1.2.

9. The method of Claim 1, wherein said liposome is administered subcutaneously.

10. The method of Claim 1, wherein said liposome is administered intraperitoneally.

11. The method of Claim 1, wherein said liposome is administered intravascularly.

12. A pharmaceutical composition for the prevention and treatment of radiation-associated tissue damage to a mammal, said pharmaceutical composition comprising: a radioprotective phosphorothioate; vitamin E; and a liposome comprising a hydrophilic core and a hydrophobic encapsulation layer.

13. The pharmaceutical composition of Claim 12, further comprising a pharmaceutically acceptable carrier.

14. The pharmaceutical composition of Claim 12, wherein said liposome further comprises phospholipids, cholesterol and phosphoethanolamine 15. The pharmaceutical composition of Claim 14, wherein said phospholipids are DPPC and DMPG. 16. The pharmaceutical composition of Claim 12, wherein said liposome comprises DPPC, Cholesterol, DMPG and DPSE. 17. The pharmaceutical composition Claim 12, wherein said vitamine E is alpha tocopherol. 18. The pharmaceutical composition Claim 16, wherein said liposome comprises DPPC, Cholesterol, vitamin E, DMPG and DPSE at a mole ratio of 52.89:18.96:16.97:9.98:1.2. 19. The pharmaceutical composition of Claim 12, wherein said radioprotective phosphorothioate is amifostine. 20. The pharmaceutical composition of Claim 12, wherein said radioprotective phosphorothioate is incoφorated into said hydrophilic core of said liposome and said vitamin E is incoφorated into said hydrophobic encapsulation layer. 21. A pharmaceutical kit for the prevention and treatment of radiation- associated tissue damage to a mammal, said pharmaceutical kit comprising: a dehydrated liposome comprising a radioprotective phosphorothioate and vitamin E; a rehydration solution for rehydratmg said liposome. 22. The pharmaceutical kit of Claim 21, wherein said radioprotective phosphorothioate is amifostine. 23. A pharmaceutical kit for the prevention and treatment of radiation- associated tissue damage to a mammal, said pharmaceutical kit comprising a lyophilized preparation containing a radiation-protective phosphorothioate; a solvent for the radiation-protective phosphorothioate; a dehydrated liposome comprising vitamin E; and a rehydration solution for rehydrating said liposome, wherein said liposome comprises both said radiation-protective phosphorothioate and said vitamin E, and said liposome is prepared by rehydrating said dehydrated liposome with said rehydration solution, dissolving said radiation- protective phosphorothioate in said solvent, and mixing said rehydrated liposomes with said dissolved radiation-protective phosphorothioate. 24. The pharmaceutical kit of Claim 23, wherein said radioprotective phosphorothioate is amifostine.