| PATENT ASSIGNEE'S COUNTRY | USA |
| UPDATE | 12.99 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 07.12.99 |
| PATENT TITLE |
Method and compositions for solubilization and stabilization of polypeptides, especially proteins |
| PATENT ABSTRACT |
The invention provides a method for the solubilization and/or stabilization of polypeptides, especially proteins, using cyclodextrin selected from the group consisting of hydroxypropyl, hydroxyethyl, glucosyl, maltosyl and maltotriosyl derivatives of .beta.- and .gamma.-cyclodextrin. Solubilized and/or stabilized compositions comprising a polypeptide, especially a protein, and the selected cyclodextrin are also described. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 29.06.89 |
| PATENT REFERENCES CITED |
Grand and Hackh's Chemical Dictionary, Fifth Ed., p. 431 (1987). Brewster et al., Pharmaceutical Res., vol. 8, No. 6 pp. 792-795 (1991). Uekama, 1987, topics in Pharmaceutical Sciences 181-194. Okada et al., 1988, Chem. Pharm. Bull. 36:2176-2185. Koizumi et al., 1987, Chem. Pharm. Bull. 35:3413-3418. Yamamoto et al., 1989, Intl. Journal of Pharmaceutics 49:163-171. Wang et al., 1988, Parenteral Formulations of Proteins and Peptides: Stability and Stabilizers 42:2S-S26. Uekama, Mar., 1985, Pharmacy International pp. 61-65. Pitha, 1984, J. Inclusion Phenomena 2:477-485. Fenyvesi, 1984, Chem. Pharm. Bull. 32(2):665-669. Uekama et al., 1985, International Journal of Pharmaceutics 23:35-42. Pitha et al., 1985, J. Pharmaceutical Sciences 74(9):987-990. Pitha et al., 1986, International J. Pharmaceutics 29:73-82. Uekama et al., 1987, CRC Critical Reviews in Therapeutic Drug Carrier Systems 3(1):1-40. Okada et al., 1988, Chem. Pharm. Bull. 36(6):2176-2185. |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A method for formulating IL-2, said method comprising combining said IL-2 with an effective formulating amount of cyclodextrin selected from the group consisting of hydroxypropyl, hydroxyethyl, glucosyl, maltosyl and maltotrisosyl derivatives of .beta. and .gamma.-cyclodextrin. 2. A method according to claim 1, wherein said cyclodextrin is in an aqueous solution. 3. A method according to claim 2, wherein said aqueous solution comprises from 0.1% (w/v) to about 60% (w/v) of cyclodextrin. 4. A method according to claim 3, wherein said aqueous solution comprises from about 0.2% (w/v) to about 60% (w/v) of cyclodextrin. 5. A method according to claim 1, wherein said cyclodextrin is hydroxypropyl-.beta.-cyclodextrin. 6. A method according to claim 5, wherein said hydroxypropyl-.beta.-cyclodextrin is in an aqueous solution. 7. A method according to claim 6, wherein said aqueous solution comprises from 0.1% (w/v) to about 60% (w/v) of hydroxypropyl-.beta.-cyclodextrin. 8. A method according to claim 7, wherein said aqueous solution comprises from about 0.2% (w/v) to about 60% (w/v) of hydroxypropyl-.beta.-cyclodextrin. 9. A method according to claim 2, comprising lyophilizing the aqueous solution containing said IL-2 and said cyclodextrin. 10. A composition comprising IL-2 and an effective formulating amount of cyclodextrin selected from the group consisting of hydroxypropyl, hydroxyethyl, glucosyl, maltosyl and maltotriosyl derivatives of .beta.- and .gamma.-cyclodextrin. 11. An aqueous composition according to claim 10. 12. A composition according to claim 11, comprising from 0.1% (w/v) to about 60% (w/v) of cyclodextrin. 13. A composition according to claim 12, comprising from about 0.2% (w/v) to about 60% (w/v) of cyclodextrin. 14. A composition according to claim 11, wherein said cyclodextrin is hydroxypropyl-.beta.-cyclodextrin. 15. A composition according to claim 14, comprising from 0.1% (w/v) to about 60% (w/v) of hydroxypropyl-.beta.-cyclodextrin. 16. A composition according to claim 15, comprising from about 0.2% (w/v) to about 60% (w/v) of hydroxypropyl-.beta.-cyclodextrin. 17. A lyophilized composition comprising IL-2 and an effective stabilizing amount of cyclodextrin selected from the group consisting of hydroxypropyl, hydroxyethyl, glucosyl, maltosyl and maltotriosyl derivatives of .beta.- and .gamma.-cyclodextrin. 18. A composition according to claim 17, comprising a cyclodextrin to polypeptide weight ratio of from about 1:1 to about 200:1. 19. A composition according to claim 18, comprising a cyclodextrin to polypeptide weight ratio of from about 2:1 to about 50:1. 20. A composition according to claim 17, wherein said cyclodextrin is hydroxypropyl-.beta.-cyclodextrin. 21. A composition according to claim 20, comprising a cyclodextrin to polypeptide weight ratio of from about 1:1 to about 200:1. 22. A composition according to claim 21, comprising a cyclodextrin to polypeptide weight ratio of from about 2:1 to about 50:1. 23. A composition according to claim 17, suitable for human or veterinary administration. 24. A composition according to claim 17, suitable for in vitro use. |
| PATENT DESCRIPTION |
OF THE INVENTION The present invention relates to a method for the solubilization and/or stabilization of polypeptides, especially proteins, by means of selected cyclodextrin derivatives. Solubilized and/or stabilized compositions comprising a polypeptide, especially a protein, and selected cyclodextrin derivatives are also described. BACKGROUND OF THE INVENTION Cyclodextrins are cyclic oligosaccharides. The most common cyclodextrins are .alpha.-cyclodextrin, which is composed of a ring of six glucose residues; .beta.-cyclodextrin, which is composed of a ring of seven glucose residues; and .gamma.-cyclodextrin, which is composed of a ring of eight glucose units. The inside cavity of a cyclodextrin is lipophilic, while the outside of the cyclodextrin is hydrophilic; this combination of properties has led to widespread study of the natural cyclodextrins, particularly in connection with pharmaceuticals, and many inclusion complexes have been reported. .beta.-Cyclodextrin has been of special interest because of its cavity size, but its relatively low aqueous solubility (about 1.8% w/v at 25.degree. C.) and attendant nephrotoxicity have limited its use in the pharmaceutical field. Attempts to modify the properties of the natural cyclodextrins have resulted in the development of heptakis (2,6-di-O-methyl)-.beta.-cyclodextrin, heptakis (2,3,6-tri-O-methyl)-.beta.-cyclodextrin, hydroxypropyl-.beta.-cyclodextrin, .beta.-cyclodextrin-epichlorohydrin polymer and others. For a comprehensive review of cyclodextrins and their use in pharmaceutical research, see Pitha et al, in Controlled Drug Delivery, ed. S. D. Bruck, Vol. I, CRC Press, Boca Raton, Fla., pp. 125-148 (1983). For an even more recent overview, see Uekama et al, in CRC Critical Reviews in Therapeutic Drug Carrier Systems, Vol. 3 (1), 1-40 (1987); Uekama, in Topics in Pharmaceutical Sciences 1987, eds. D. D. Breimer and P. Speiser, Elsevier Science Publishers B. V. (Biomedical Division), 181-194 (1987); and Pagington, Chemistry in Britain, pp. 455-458 (May 1987). Inclusion complexes of .alpha.-, .beta.- or .gamma.-cyclodextrin or their mixtures with a variety of drugs have been described by numerous parties and various advantages have been attributed to the complexes. These descriptions include the following: Among the patents listed above, only Hirai et al U.S. Pat. No. 4,659,696 appears to relate to proteins or polypeptides. It would appear from the claims of the Hirai et al patent, however, that an inclusion complex is not formed and that what the invention provides is a pharmaceutical composition consisting essentially of a physical mixture of a hydrophilic, physiologically active polypeptide and cyclodextrin, said composition being a uniform mixture in dosage form. The cyclodextrin may be .alpha.-, .beta.- or .gamma.-cyclodextrin, or a cyclodextrin derivative, exemplified by tri-O-methylcyclodextrin and triaminocyclodextrin, .alpha.-cyclodextrin being particularly preferred. The physiologically active peptide may be thyrotropin releasing hormone, luteinizing hormone-releasing hormone, insulin, somatostatin, growth hormone, prolactin, adrenocorticotrophic hormone, melanocyte stimulating hormone, or many others. The composition is designed for nasal, vaginal or rectal preparation, i.e. a non-oral or non-injectable route of administration is used. Matsuyama et al, Drug Development and Industrial Pharmacy, 13(15), 2687-2691 (1987), have reported on the thermodynamics of binding aromatic amino acids to .alpha.-, .beta.- and .gamma.-cyclodextrin. Human serum albumin, which contains aromatic amino acids, was also tested as a protein model. The authors suggest that cyclodextrins may protect peptides from enzymatic hydrolysis. Also, according to Sekisui Chemical Co., Ltd.'s Japanese Kokai Tokkyo Koho JP 59/104556 (84/104556), published Jun. 16, 1984, cyclized oligosaccharides such as .beta.-cyclodextrin have been recently used in protein stabilizers which prevent denaturation of proteins and enzymes in blood. Human blood mixed with octylphenoxypoly(ethoxyethanol) and .beta.-cyclodextrin was maintained for 24 hours with little change. Inclusion complexes of 2,6-di-O-methyl-.beta.-cyclodextrin with dibenzo[bd]pyran derivatives and salts having analgesic, antiemetic and narcosis-potentiating activities have been described in Nogradi et al U.S. Pat. No. 4,599,327; increased water solubility and thus improved biological activity have been claimed for the complexes. A review of the pharmaceutical applications of such methylated cyclodextrins has been published by Uekama, Pharm. Int., March 1985, 61-65; see also Pitha, Journal of Inclusion Phenomena 2, 477-485 (1984). Cyclodextrin polymer has been reported by Fenyvesi et al, Chem. Pharm. Bull. 32 (2), 665-669 (1984) to improve the dissolution of furosemide. Improvements in the dissolution and absorption of phenytoin using a water-soluble .beta.-cyclodextrin epichlorohydrin polymer have been described by Uekama et al, International Journal of Pharmaceutics, 23, 35-42 (1985). Hydroxypropyl-.beta.-cyclodextrin (HPBCD or HPCD) and its preparation by propylene oxide addition to .beta.-cyclodextrin were described in Gramera et al U.S. Pat. No. 3,459,731 nearly 20 years ago. Gramera et al also described the analogous preparation of hydroxyethyl-.beta.-cyclodextrin by ethylene oxide reaction with .beta.-cyclodextrin. Much more recently, Pitha and co-workers have described the improved preparation of this cyclodextrin derivative and its effects on the dissolution of various drug molecules. Pitha U.S. Pat. No. 4,596,795, dated Jun. 24, 1986, describes inclusion complexes of sex hormones, particularly testosterone, progesterone, and estradiol, with specific cyclodextrins, preferably hydroxypropyl-.beta.-cyclodextrin and poly-.beta.-cyclodextrin. The complexes enable the sex hormones to be successfully delivered to the systemic circulation via the sublingual or buccal route; the effectiveness of this delivery is believed to be due to "the high dissolution power of hydrophilic derivatives of cyclodextrins, the non-aggregated structure of their complexes with steroids, and their low toxicity and irritancy of mouth tissue". Success with other cyclodextrins, including poly-.gamma.-cyclodextrin and hydroxypropyl-.gamma.-cyclodextrin, have also been noted in the Pitha patent. See also Pitha et al, J. Pharm. Sci., Vol. 74, No. 9, 987-990 (September 1985), concerning the same and related studies. Pitha et al also describe in the J. Pharm. Sci. article the storage stability of tablets containing a testosterone-hydroxypropyl-.beta.-cyclodextrin complex and the lack of toxicity of the cyclodextrin itself, as well as the importance of the amorphous nature of the cyclodextrin derivatives and their complexes with drugs in improving dissolution properties. The improved, optimized preparation and purification of hydroxypropyl-.beta.-cyclodextrin have been recently described by Pitha et al, International Journal of Pharmaceutics 29, 73-82 (1986). In the same publication, the authors have described increased water solubility for 32 drugs in concentrated (40 to 50%) aqueous solutions of hydroxypropyl-.beta.-cyclodextrin; improved solubilization of acetaminophen, apomorphine, butylated hydroxytoluene, chlorthalidone, cholecalciferol, dexamethasone, dicumarol, digoxin, diphenylhydantoin, estradiol, estriol, ethinylestradiol-3-methyl ether, ethisterone, furosemide, hydroflumethiazide, indomethacin, iproniazid phosphate, 17-methyltestosterone, nitroglycerin, norethindrone, ouabain, oxprenolol, progesterone, retinal, retinoic acid (all trans and salt forms), retinol, spironolactone, sulpiride, testosterone and theophylline was noted. The authors indicated this to be an extension of their earlier work with hydroxypropyl-.beta.-cyclodextrin, which was previously found effective for oral administration of the sex hormones to humans. Their later work reported in Pitha et al, International Journal of Pharmaceutics 29, 73-82 (1986), has also been very recently described in Pitha U.S. Pat. No. 4,727,064, dated Feb. 23, 1988. That patent claims a composition containing an amorphous complex of cyclodextrin and a drug, and a method of producing a stabilizing amorphous complex of a drug and a mixture of cyclodextrins comprising (1) dissolving an intrinsically amorphous mixture of cyclodextrin derivatives which are water soluble and capable of forming inclusion complexes with drugs in water; and (2) solubilizing lipophilic drugs into aqueous media to form a solution and form a solubilized drug/cyclodextrin complex. Work with numerous drugs has been reported in the patent, but none involves proteins or other peptides. The patent describes the preparation of various substituted amorphous cyclodextrins, including hydroxypropyl-.beta.-cyclodextrin and hydroxypropyl-.gamma.-cyclodextrin, the latter by analogous condensation of propylene oxide with .gamma.-cyclodextrin. Uekama et al, CRC Critical Reviews in Therapeutic Drug Carrier Systems, Vol. 3 (1), pp. 140 (1987), have described the characteristics of various cyclodextrins, including hydroxypropyl-.beta.-cyclodextrin. The authors have presented data showing improved solubilization in water in the presence of 15 mg/mL of HPBCD for the drugs carmofur, diazepam, digitoxin, digoxin, flurbiprofen, indomethacin, isosorbide dinitrate, phenytoin, prednisolone, progesterone and testosterone. In a discussion of the metabolism and toxicity of cyclodextrins, Uekama et al have indicated that cyclodextrins at low-moderate concentrations (usually 3-8% w/v and higher) cause hemolysis, and that the methylated cyclodextrins have higher hemolytic activity than the natural cyclodextrins. Hydroxypropyl-.beta.-cyclodextrin is said to cause hemolysis beginning at 4.5 mM. The authors have further indicated that parenteral administration of large doses of cyclodextrins should be avoided, but that ".gamma.-cyclodextrin and hydroxypropyl-.beta.-cyclodextrin seem to be useful in drug solubilization for injections and liquid preparations used for mucous membranes." Use with polypeptides such as proteins is not mentioned. JANSSEN PHARMACEUTICA N.V.'s International Patent Application No. PCT/EP84/00417, published under International Publication No. WO85/02767 on Jul. 4, 1985, has described pharmaceutical compositions comprising inclusion compounds of drugs, which are unstable or only sparingly soluble in water, with partially etherified .beta.-cyclodextrin derivatives having hydroxyalkyl and optionally additional alkyl groups. Among the cyclodextrin derivatives contemplated are hydroxypropyl-.beta.-cyclodextrin and hydroxyethyl-.beta.-cyclodextrin, while the drugs include non-steroidal anti-rheumatic agents, steroids, cardiac glycosides and derivatives of benzodiazepine, benzimidazole, piperidine, piperazine, imidazole and triazole. Preferred drugs include etomidate, ketoconazole, tubulazole, itraconazole, levocabastine and flunarizine. The pharmaceutical compositions of the invention include oral, parenteral and topical formulations, with 4 to 10% solutions of cyclodextrin derivatives being utilized to solubilize various drugs. Improved solubilities of indomethacin, digitoxin, progesterone, dexamethasone, hydrocortisone and diazepam using 10% HPBCD are shown, and an injectable formulation of diazepam in 7% HPBCD is specifically described. The relatively low cyclodextrin concentrations used reflect a desire to avoid or minimize the hemolytic effects observed at higher cyclodextrin concentrations. Carpenter et al, The Journal of Pediatrics, 111, 507-512 (October 1987) describe intravenous infusion of 2-hydroxypropyl-.beta.-cyclodextrin, prepared as a 5% solution in water, to treat severe hypervitaminosis A. It was found that, during infusion, circulating retinyl esters increased transiently, while total vitamin A excreted in the urine was enhanced after infusion. Thus, intravenous infusion of 5% HPBCD was found to decrease in vivo levels of the vitamin, presumably by complexing with the vitamin and removing some of the excess from the body. Formulation of a particular dihydropyridine pyridinium salt redox system for brain-specific delivery of estradiol "in a water-soluble .beta.-hydroxy-cyclodextrin" is reported by Bodor and co-workers in Estes et al, "Use of a Chemical Redox System for Brain Enhanced Delivery of Estradiol Decreases Prostate Weight," in Biological Approaches to the Controlled Delivery of Drugs., ed. R. L. Juliano, Annals of the New York Academy of Sciences, Volume 507, 1987, 334-336. JANSSEN PHARMACEUTICA N.V.'s European Patent Application No. 86200334.0, published under EPO Publication No. 0197571 on Oct. 15, 1986, describes .gamma.-cyclodextrin derivatives which are .gamma.-cyclodextrin substituted with C.sub.1 -C.sub.6 alkyl, hydroxy C.sub.1 -C.sub.6 alkyl, carboxy C.sub.1 -C.sub.6 alkyl or C.sub.1 -C.sub.6 alkyloxycarbonyl C.sub.1 -C.sub.6 alkyl or mixed ethers thereof. Among the specific derivatives named are hydroxypropyl-.gamma.-cyclodextrin and hydroxyethyl-.gamma.-cyclodextrin. Compositions comprising the cyclodextrin derivatives and a drug are also described. See also corresponding Muller U.S. Pat. No. 4,764,604, dated Aug. 16, 1988. The inclusion characteristics of yet other derivatized cyclodextrins have also been described in the literature. Studies of branched cyclodextrins which are glucosyl and maltosyl derivatives of .alpha.-, .beta.- and .gamma.-cyclodextrin and their inclusion complexes with drugs have recently been reported. Uekama, in Topics in Pharmaceutical Sciences 1987., eds. D. D. Breimer and P. Speiser, Elsevier Science Publishers B. V. (Biomedical Division), 181-194 (1987), has described the effects on bio-pharmaceutical properties of maltosyl and glucosyl cyclodextrin derivatives, including enhanced drug absorption. In that publication, Uekama again indicated that the natural cyclodextrins caused hemolysis in the order of .gamma.<.alpha.<.beta.. In the case of chemically modified cyclodextrins, the order changed to hydroxyethyl-.beta. Koizumi et al, Chem. Pharm. Bull. 35 (8), 3413-3418 (1987), have reported on inclusion complexes of poorly water-soluble drugs with glucosyl cyclodextrins, namely 6-O-.alpha.-D-glucosyl-.beta.-CD (G.sub.1 -.alpha.-CD), 6-O-.alpha.-D-glucosyl-.beta.-CD (G.sub.1 -.beta.-CD) and 6A, 6.sup.D -di-O-.alpha.-D-glucosyl-.beta.-CD (2G.sub.1 -.beta.-CD). Okada et al, Chem. Pharm. Bull. 36 (6), 2176-2185 (1988), have reported on the inclusion complexes of poorly water-soluble drugs with maltosyl cyclodextrins, namely 6-O-.alpha.-maltosyl-.alpha.-CD (G.sub.2 -.alpha.-CD), 6-O-.alpha.-maltosyl-.beta.-CD (G.sub.2 -.beta.-CD), 6-O-.alpha.-maltosyl-.gamma.-CD (G.sub.2 -.gamma.-CD), 6-O-.alpha.-maltotriosyl-.alpha.-CD (G.sub.3 -.alpha.-CD), 6-O-.alpha.-maltotriosyl-.beta.-CD (G.sub.3 -.beta.-CD) and 6-O-.alpha.-maltotriosyl-.gamma.-CD (G.sub.3 -.gamma.-CD). Yamamoto et al, in International Journal of Pharmaceutics 49, 163-171 (1989), have described physicochemical properties of branched .beta.-cyclodextrins such as glucosyl-.beta.-cyclodextrin, maltosyl-.beta.-cyclodextrin and di-maltosyl-.beta.-cyclodextrin, and their inclusion characteristics. Those authors report that the branched .beta.-cyclodextrins are better solubilizers for poorly water-soluble drugs and have less hemolytic activity than .beta.-cyclodextrin itself, and they suggest that glucosyl-.beta.-cyclodextrin and maltosyl-.beta.-cyclodextrin may be especially useful in parenteral preparations. The patent literature reflects much recent work on the branched cyclodextrins carried out by Japanese workers, as discussed below. Japanese Kokai 63-135402 (TOKUYAMA SODA KK), published Jun. 7, 1988, describes compositions consisting of maltosyl-.beta.-cyclodextrin and at least one of digitoxin, nifedipine, flulubiprophene, isosorbide nitrate, phenytoin, progesterone or testosterone. The compositions have improved water solubility and reduced erythrocyte destruction, are safe for humans and can be used as injections, eye drops, syrups, and for topical and mucous membrane application. Japanese Kokai 62-281855 (DAIKIN KOGYO KK), published Dec. 7, 1987, describes stable, water-soluble inclusion compounds of maltosyl-.beta.-cyclodextrin with a variety of vitamins and hormones, e.g. steroid hormones such as prednisolone, hydrocortisone and estriol. These lipophilic vitamins and hormones can thus be used as aqueous solutions. Japanese Kokai 63-036793 (NIKKEN CHEM KK), published Feb. 17, 1988, describes the preparation of dimaltosyl-.gamma.-cyclodextrin and its general use in medicines. Japanese Kokai 62-106901 (NIKKEN CHEM KK), published May 18, 1987, describes the preparation of diglucosyl-.beta.-cyclodextrin and its general use for pharmaceuticals. Japanese Kokai 61-236802 (NIKKEN CHEM KK), published Oct. 22, 1986, describes the preparation of maltosyl-.gamma.-cyclodextrin and its general use with drugs. Japanese Kokai 61-197602 (NIKKEN CHEM KK), published Sep. 1, 1986, describes the preparation of maltosyl-.beta.-cyclodextrin and its expected use in medicines. Japanese Kokai 61-070996 (NIKKEN CHEM KK), published Apr. 11, 1986, describes the preparation of maltosyl-.alpha.-cyclodextrin and its general use in pharmaceuticals. Japanese Kokai 63-027440 (SANRAKU OCEAN), published Feb. 5, 1988, describes compositions containing a water-insoluble or slightly soluble drug together with glucosylated branched cyclodextrin. Among the drugs mentioned are steroid hormones. Japanese Kokai 62-164701 (SHOKUHIN SANGYO BIO), published Jul. 21, 1987, describes the preparation of diglucosyl-.alpha.-cyclodextrin and its general use in medicine. Japanese Kokai 62-003795 (TOKUYAMA SODA KK), published Jan. 9, 1987, describes production of glucose and maltoligosaccharide (2-4 glucose units) derivatives of .alpha.-, .beta.- and .gamma.-cyclodextrin and their use as stabilizers for pharmaceuticals. In recent years, there has been a tremendous increase in the number of products and potential products containing polypeptides, especially proteins, intended for therapeutic or diagnostic or analytical use. Typically, the proteins or other peptides are formulated in aqueous solution for injection or for use in diagnostic or analytical applications. Unfortunately, proteins often suffer from solubility and/or stability problems. Some proteins, for example, are not water-soluble. Others are soluble in water but still suffer from stability problems caused by protein degradation/denaturation, dimerization and/or polymerization, and the like, any of which may lead to inactivation. This seriously limits shelf-life and often imposes low-temperature storage requirements and restrictions on mechanical movement. There are numerous causes of protein/peptide instability or degradation, including covalent bond reactions, such as hydrolysis, and the denaturation process. In the case of denaturation, the conformation or three-dimensional structure of the protein is disturbed and the protein unfolds from its usual globular structure. Rather than refolding to its natural conformation, hydrophobic interaction may cause clumping of molecules together, or aggregation, or it may cause refolding to an unnatural conformation. Either of these end results entails diminution or loss of biological activity. For a summary of the causes of protein instability, see Wang et al, Journal of Parenteral Science and Technology, Technical Report No. 10, "Parenteral Formulations of Proteins and Peptides: Stability and Stabilizers", Supplement Volume 42, Number 25, 1988, pp. S3-S26. The Wang et al publication referenced above also summarizes the art's use of various excipients to stabilize parenteral formulations of proteins and other peptides, including use of serum albumin, amino acids, fatty acids and phospholipids, surfactants, metals, polyols, reducing agents, metal chelating agents, polyvinylpyrrolidone, hydrolyzed gelatin and ammonium sulfate, including agents used as cryoprotectants, which prevent or lessen denaturation under freezing conditions or lyophilization, such as carbohydrates, alcohols, polyvinylpyrrolidone and glutamic acid. Examples of excipients proposed by the art for stabilizing specific proteins are described in Hayashi et al U.S. Pat. No. 4,457,916, issued Jul. 3, 1984, KYOWA HAKKO KOGYO CO, LTD.'s European Patent Publication No. 0123291 and E. I. DUPONT DE NEMOURS AND COMPANY'S European Patent Publication No. 0231132. The Hayashi et al patent describes a method for stabilizing Tumor Necrosis Factor (TNF) by adding a stabilizing agent selected from a nonionic surfactant, at least one substance selected from D-glucose, D-galactose, D-xylose, D-glucuronic acid, a salt of D-glucuronic acid, trehalose, a dextran and a hydroxyethyl starch and mixtures thereof. The resultant aqueous solution or powder containing TNF is said to be capable of prolonged storage without loss of activity and stable on freezing, thawing, lyophilization, heat-treatment or the like. European Patent Publication No. 0123291, published Oct. 31, 1984, describes a method for stabilizing interferon involving addition of an alkali metal salt or magnesium chloride to interferon, optionally including addition of serum albumin and freeze-drying to further enhance stability. The patent publication also describes a method for stabilizing interferon by contacting it with a saccharide selected from the group consisting of dextran, chondroitin sulfuric acid, starch, glycogen, insulin, dextrin and alginic acid salt. European Patent Publication No. 0231132, published Aug. 5, 1987, relates to a recombinant interleukin-2 (IL-2) composition and process for making it. In discussing the prior art, the European publication refers to earlier European Patent Publication No. 0133767 as disclosing that gamma-interferon, obtainable from human leukocytes, can be stabilized by addition of albumin and/or a sugar. The sugars can include monosaccharides, disaccharides, sugar alcohols and mixtures thereof, e.g. glucose, mannose, galactose, fructose, sucrose, maltose, lactose, mannitol and xylitol. Also, European Patent Publication No. 0231132 acknowledges that protein (chymotrypsinogen and ribonuclease) stabilization using glycerol is reported by Gekko et al, Biochemistry 20, 4677-4686 (1981). European No. 0231132 itself relates to recombinant human IL-2 compositions comprising water, recombinant interleukin-2 and preferably a polyol. Suitable polyols are said to be water-miscible or water-soluble, for example polyhydroxy alcohols, monosaccharides and disaccharides including mannitol, glycerol, ethylene glycol, propylene glycol, trimethyl glycol, glucose, fructose, arabinose, mannose, maltose and sucrose. The polyol is said to increase the activity of the IL-2. Despite the foregoing, there remains a clear and pressing need in this art for a more effective and generally applicable method and compositions for the solubilization and stabilization of polypeptides such as proteins. SUMMARY OF THE INVENTION The present invention provides a method and compositions for stabilizing and/or solubilizing polypeptides, especially proteins, by means of cyclodextrin selected from the group consisting of hydroxypropyl, hydroxyethyl, glucosyl, maltosyl and maltotriosyl derivatives of .beta.- and .gamma.-cyclodextrin. Thus, in one aspect, the invention provides a method for solubilizing and/or stabilizing a polypeptide, said method comprising combining said polypeptide with an effective solubilizing and/or stabilizing amount of cyclodextrin selected from the group consisting of hydroxypropyl, hydroxyethyl, glucosyl, maltosyl and maltotriosyl derivatives of .beta.- and .gamma.-cyclodextrin. Preferably, an aqueous solution comprising said cyclodextrin is employed. In another aspect, the present invention provides a composition, especially an aqueous composition, comprising a polypeptide and an effective solubilizing and/or stabilizing amount of cyclodextrin selected from the group consisting of hydroxypropyl, hydroxyethyl, glucosyl, maltosyl and maltotriosyl derivatives of .beta.- and .gamma.-cyclodextrin. In still another aspect, the invention provides a lyophilized composition comprising a polypeptide and an effective stabilizing amount of cyclodextrin selected from the group consisting of hydroxypropyl, hydroxyethyl, glucosyl, maltosyl and maltotriosyl derivatives of .beta.- and .gamma.-cyclodextrin. Preferably, the foregoing methods and compositions are directed toward improvements in biologically useful protein formulations. BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of the present invention will be apparent from the following detailed description and accompanying drawings, in which: FIG. 1 is a plot of fluorimeter units as an indication of initial light scattering for samples of interleukin-2 (IL-2) in increasing concentrations (percent w/v) of hydroxypropyl-.beta.-cyclodextrin (HPBCD); FIG. 2 is a plot of fluorimeter units as an indication of initial light scattering for samples of HPBCD formulations of IL-2 (1 mg/mL) with sucrose bulking; FIG. 3 is a bar graph depicting the results of an ultracentrifugation assay of samples of IL-2 formulated with HPBCD as compared to unformulated IL-2; and FIG. 4 is a semi-logarithmic plot depicting the biological activity of samples of IL-2 containing increasing concentrations of HPBCD. DETAILED DESCRIPTION OF THE INVENTION The polypeptides intended for use according to the present invention are any polypeptides which are biologically or industrially useful. A biologically useful polypeptide in accord with this invention is any polypeptide which can be employed in the diagnosis, cure, mitigation, treatment or prevention of disease or in the enhancement of desirable physical or mental development and conditions in man or animals. Polypeptides, especially proteins, for use in human and/or veterinary medicine or in diagnosis (in vivo or in vitro) are of particular interest. Industrially useful polypeptides are those employed analytically, in production or which are otherwise useful in chemical industry. Amino acids are organic compounds that have at least one amino (--NH.sub.2) group and at least one carboxyl (--COOH) group. Oligopeptides are amino acid oligomers which are formed by reacting amino and carboxyl groups from different amino acids to release a water molecule and form a peptide linkage. Polypeptides are amino acid polymers which are formed in the same way. Generally, oligopeptides have between 2 and 20 peptide linkages whereas polypeptides have more. Proteins are very large polypeptides. The amino acids which make up the polypeptides of the present invention may be natural or synthetic, may have the amino group attached to any noncarbonyl carbon atom (e.g., to the .alpha., .beta., .gamma., .delta. or .epsilon. carbon as measured from the .alpha.-COOH group of the amino acid), may exist as enantiomers (e.g. D- or L-) or diasteriomers, may have blocked carboxyl or amino groups and may have side chains which are hydrophobic, hydrophilic, acidic, basic or neutral. The synthetic polypeptides may contain reversed peptide linkages, in which case they must contain at least one diamine and one dicarboxylic acid monomer. The polypeptides intended for use in the methods and compositions of this invention include molecules to which nonpeptide prosthetic groups, such as carbohydrates, hemes and fatty acids, have been attached. The polypeptides include molecules made by living organisms or cells, molecules made by synthetic organic chemistry and molecules which are synthetically modified biological products. They may have an amino acid sequence identical to that of a natural substance or one altered by techniques such as site-directed mutagenesis. In addition to the covalent (primary) structure, the polypeptides may possess unique conformations (combinations of secondary, tertiary and quaternary structure) which affect their biological function, aqueous solubility and ability to interact with the cyclodextrins. The polypeptides may have many biological functions. They may act as enzymes; enzyme inhibitors; antibodies; antigens; transporters of electrons, oxygen, metal ions, or small organic molecules; ionophores; antibiotics; mitogens; hormones; growth regulators; neurotransmitters; cell surface recognition proteins; cell chemotactic factors; and cytotoxins. They may also be receptors, agonists, antagonists of the following: ionophores, antibiotics, mitogens, hormones, neurotransmitters, growth regulators, cell surface recognition proteins, cell chemotactic factors and cytotoxins. Uses for some of the preferred polypeptides of the invention include: immunization (as vaccine adjuvants), in vitro diagnostics (to increase the solubility/stability or lower the nonspecific binding of antigens or antibodies) and in vivo diagnostics and therapeutics (to increase the solubility/stability of therapeutic and diagnostic polypeptides). Preferred therapeutic targets of these polypeptides are cancers, such as melanoma, renal cell carcinoma, myeloma, leukemia, breast cancer, colorectal cancer, lymphoma, neuroblastoma, astrocytoma and glioma; auto-immune diseases, such as diabetes mellitus, rheumatoid arthritis and multiple sclerosis; immunodeficiency diseases; and infectious diseases. Among the polypeptides contemplated by the present invention are therapeutically useful polypeptides such as anti-sera, anti-toxins and antigens. Anti-sera may include, for example, antirabies, antivenin (black widow spider venom), hepatitis B immune globulin, tetanus immune globulin, intravenous immune globulin, pertussis immune globulin and rabies immune globulin. Anti-toxins may include, for example, those for diphtheria and tetanus; Rho(D) immune globulin; serum components, such as 5% normal human serum albumin, 5% plasma protein fraction, 20% normal human serum albumin, 25% normal human serum albumin, factor II, factor VII, factor VIII, factor IX, factor X and Xa, antithrombin III, transferrin, haptoglobin, fibro-nectin, gamma globulins, protein C, protein S and thrombin; toxoids, such as diphtheria and tetanus; vaccines, including attenuated vaccines (such as those for cholera, influenza, meningitis, Yersinia pestis or plague, pneumonia, poliomyelitis, rabies, typhoid and staphyloccocus) and live vaccines (such as those for poliomyelitis, measles, rubella and mumps); growth factors, hormones and like bioactive peptides, as illustrated by .alpha.-1-antitrypsin, atrial natriuretic factor (diuretic), calcitonin, calmodulin, choriogonadotropin (.alpha. and .beta.), colony stimulating factor, corticotropin releasing factor, .beta.-endorphin, endothelial cell growth supplement, epidermal growth factor, erythropoietin, fibroblast growth factor, fibronectin, follicle stimulating hormone, granulocyte colony stimulating factor, growth hormone (somatotropin), growth hormone releasing factor (somatoliberin), insulin, insulin-like growth factor (somatomedin), an interferon (typically .alpha., .beta., .gamma.), an interleukin (typically 1, 2, 3, 4), lutropin, lymphotoxin, macrophage derived growth factor, macrophage inhibiting factor, macrophage stimulating factor, megakaryocyte stimulating factor, nerve growth factor, pancreatic endorphin, parathyroid hormone, platelet derived growth factor, relaxin, secretin, skeletal growth factor, superoxide dismutase, thymic hormone factor, thymic factor, thymopoeitin, thyrotropin, tissue plasminogen activator, transforming growth factor (.alpha. and .beta.), tumor necrosis factor, tumor angiogenisis factor, vasoactive intestinal polypeptide and wound angiogenesis factor; immunosuppressives, such as RhO (D) ISG and IVGG's; thrombolytics such as urokinase, streptokinase and tissue plasminogen activator; and antigens such as Rhus all (poison ivy), Rhus tox poison ivy-polyvalent and staphage lysate (staphyloccocus lysate). Other polypeptides contemplated by this invention are polypeptides specifically intended for veterinary use, including vaccines, animal growth factors and bovine interferons and interleukin-2. Illustrative vaccines include: bovine vaccines, for example those for anthrax, clostridium (multiple species), pasteurella, leptospira pomona, bovine diarrhea, brucillosis, parainfluenza, 3-respiratory syncytial virus, tetanus, vesicular stomatitis and staphylococcus; canine vaccines, for example those for bordetella, coronavirus, distemper, parvovirus, parainfluenza and rabies; equine vaccines, for example those for anthrax, encephalomyelitis, influenza, tetanus, rabies and streptococcus-strangles; feline vaccines, such as those for leukemia, pneumonitis-chlamydia and rabies; ovine vaccines, for example those for anthrax, blackleg, bluetongue, enterotoxemia, tetanus and vibriosis; and porcine vaccines, for example those for anthrax, enterotoxemia, dysentery, erysipelas, leptospirosis, parvovirus, pseudorabies, tetanus and rotavirus. Yet other polypeptides contemplated by this invention have use in immunology. These include monoclonal antibodies, polyclonal antibodies (unconjugated), second antibodies (alkaline phosphatase conjugated), immunoglobulin screening and isotyping kits, protein A products and immunoassay reagents. Among the monoclonal antibodies are those approved for use in diagnostic kits, for example IgE, peroxidase-anti-peroxidase conjugated, human chorionic gonadotropin, T cell, ferritin conjugated, carcinogenic embryonic antigen (CEA), OKT-II, anti-rabies, human growth hormone, Total T4, prolactin, 125I-IgE, UCG, thyroid stimulating hormone, chlamydia, gentamicin and rubella. Other useful monoclonal antibodies include monoclonal antibodies for human cell surface antigens, monoclonal antibodies for murine cell surface antigens, monoclonal antibodies to complement and blood proteins, monoclonal antibodies to immunoglobulins (human), monoclonal antibodies to neurological antigens, monoclonal antibodies to tumor markers, monoclonal antibodies to cell components, Epstein Barr virus antigens, human lymphocyte antigen (HIA) typing, hematology antibodies, leucocyte antibodies, bacterial antigens, parasitic antigens, T-cell lymphotropic virus (HIV-III) and cyloskeletal antibodies. Useful polyclonal antibodies (unconjugated) include affinity purified antibodies to immunoglobulins, antibodies to plant viruses, antisera to human isoenzymes and chromatographically purified antibodies. Useful alkaline phosphatase conjugated second antibodies include affinity purified antibodies to immunoglobulins, antibodies to plant viruses, biotin-conjugated antibodies, fluorescein-isothiocyanate-conjugated antibodies (FITC), gold-conjugated antibodies, peroxidase-conjugated antibodies, rhodamine conjugated antibodies and iodine-conjugated antibodies. Polypeptide immunoassay reagents include EIA grade enzymes, enzyme-antibody complexes, reagents for immunology, enzyme linked immunosorbent assays (ELISA) for use as standards or controls, immunoelectrophoresis (IEP) assays, radioimmunoassays (RIA) for use as standards or controls, nephelometry for use as standards or controls, nuclear antigens and coatings for kit tubes and plate wells. Other polypeptides contemplated by the present invention include polypeptides useful in cell biology/biochemistry, for example in serum-free cultures (as supplements and reagents for cell culture), in glycoprotein and carbohydrate research (endoglycosidoses, exoglycosidoses, enzymes for carbohydrate research, enzymes for analysis of glycoprotein oligosaccharides), as molecular weight markers (calibration proteins, e.g. for gel permeation chromatography, subunit proteins), proteases (for use in blood research, protein sequencing, tissue digestion and cell harvest, total digestion of proteins and immobilized proteases), cell surface recognition proteins (adenosine and analogs, cyclic nucleotides, phosphoinositides), phospholipases and bioluminescence assay reagents. Yet other polypeptides contemplated for use herein are polypeptides of particular interest in the field of molecular biology, including various enzymes and reagents. The enzymes can include labelling enzymes, modifying enzymes, nucleases, polymerases, sequencing enzymes and restriction enzymes. The reagents can include inhibitors, antibiotics and miscellaneous other reagents. Preferred polypeptides for use in accord with the instant invention include growth regulators. Among the preferred growth regulators are hematopoietic factors, which affect the maturation and proliferation of blood cells in lymphoid tissue and bone marrow; cytokines, which generally influence eukaryotic cell growth; and lymphokines, which affect lymphocyte growth. Specific polypeptides which are growth regulators or lymphokines are: interleukin 1, 2, 3 and 4; .alpha., .beta., and .gamma. interferons; granulocyte colony stimulating factor (G-CSF); granulocyte-macrophage CSF(GM-CSF); macrophage CSF(m-CSF); megakaryocyte CSF; multi CSF or IL-3 (also known as BPA, HCGF, MCGF and PSF); erythropoietin; lymphotoxin; tumor necrosis factor (TNF, also known as cachectin); .alpha. and .beta. transforming growth factor (TGF); platelet derived growth factor (PDGF); epidermal growth factor (EGF); nerve growth factor (NGF); insulin-like growth factor I and II (IGF I is also called somatomedin C); growth hormone (GF, also called somatotropin); and growth hormone releasing factor (GHRF, also called somatoliberin). See Clark et al, "The Human Hematopoietic Colony Stimulating Factors," Science, 1229-1237 (Jun. 5, 1987); Taniguchi, "Regulation of Cytokine Expression," Ann. Rev. Imm., 6, 439-464 (1988); and Watson et al, Molecular Biology of the Gene, Vol. II, 4th Ed., Benjamin/Cummings Publishing (1987). Other preferred polypeptides for use in accordance with this invention are fusion proteins. Fusion proteins are covalently linked proteins or portions of proteins. Thus, proteins or active fragments thereof having different purposes can be linked to provide a fused molecule having characteristics of both. Generally speaking, one of the proteins/protein fragments is a "seeker" and the other an "actor" or "destroyer". Illustrative such fusion proteins are pseudomonas exotoxin linked to IL-2, diphtheria toxin linked to IL-2 or either toxin linked to other proteins, or linkages between other proteins such as those preferred proteins described in the preceding paragraph, or portions thereog See U.S. Pat. Nos. 4,545,985; 4,468,382; and 4,675,382; all of which are incorporated by reference herein in their entireties and relied upon. Fusion proteins of IL-2 linked with toxin as described above are designed to kill cells with IL-2 receptors, thus find use in preventing graft-versus-host rejection. Other fusion proteins have varying utilities, depending on the proteins or portions thereof which are combined. Thus, for example, Substance P and a toxin form a fusion protein which can be used to relieve chronic pain, while .alpha.-melanocyte-stimulating hormone (MSH) and diphtheria toxin form a fusion protein designed to kill melanoma cells. Yet other preferred polypeptides for use herein are muteins, which are mutationally altered proteins. Preferred muteins are muteins of the preferred growth regulators and fusion proteins identified in the preceding paragraphs, and typically have the same purpose as the corresponding unaltered proteins. Especially preferred muteins include IL-2 muteins, described for example in U.S. Pat. Nos. 4,752,585 and 4,518,584, incorporated by reference herein in their entireties and relied upon; and muteins of .beta.-interferon, described for example in U.S. Pat. Nos. 4,737,462 and 4,588,585, incorporated by reference herein in their entireties and relied upon. The cyclodextrins contemplated for use herein are hydroxypropyl, hydroxyethyl, glucosyl, maltosyl and maltotriosyl derivatives of .beta.-cyclodextrin and the corresponding derivatives of .gamma.-cyclodextrin. The hydroxyalkyl groupings may contain one or more hydroxyl groups, e.g. hydroxypropyl (2-hydroxypropyl, 3-hydroxypropyl), dihydroxypropyl and the like. The glucosyl, maltosyl and maltotriosyl derivatives may contain one or more sugar residues, e.g. glucosyl or diglucosyl, maltosyl or dimaltosyl. Various mixtures of the cyclodextrin derivatives may be used as well, e.g. a mixture of maltosyl and dimaltosyl derivatives. Specific cyclodextrin derivatives for use herein include hydroxypropyl-.beta.-cyclodextrin (HPCD or HPBCD), hydroxyethyl-.beta.-cyclodextrin (HEBCD), hydroxypropyl-.gamma.-cyclodextrin (HPGCD), hydroxyethvl-.gamma.-cyclodextrin (HEGCD), dihydroxypropyl-.beta.-cyclodextrin (2HPBCD), glucosyl-.beta.-cyclodextrin (G.sub.1 -.beta.-CD or G.sub.1 BCD), diglucosyl-.beta.-cyclodextrin (2G.sub.1 -.beta.-D or 2G.sub.1 BCD), maltosyl-.beta.-cyclodextrin (G.sub.2 -.beta.-CD or G.sub.2 BCD), maltosyl-.gamma.-cyclodextrin (G.sub.2 -.gamma.-CD or G.sub.2 GCD), maltotriosyl-.beta.-cyclodextrin (G.sub.3 -.beta.-CD or G.sub.3 BCD), maltotriosyl-.gamma.-cyclodextrin (G.sub.3 -.gamma.-CD or G.sub.3 GCD) and dimaltosyl-.beta.-cyclodextrin (2G.sub.2 -.beta.-CD or 2G.sub.2 BCD), and mixtures thereof such as maltosyl-.beta.-cyclodextrin/dimaltosyl-.beta.-cyclodextrin. Hydroxypropyl-.beta.-cyclodextrin for use in the methods of the present invention is commercially available. Alternatively, it may be prepared by known methods, especially by use of the optimized procedure of Pitha et al, International Journal of Pharmaceutics, 29, 73-82 (1986). The following is a typical procedure using the Pitha et al method: 31 g of sodium hydroxide were dissolved in 250 mL of water. Then, 100 g of .beta.-cyclodextrin were added and the solvent was warmed to effect solution. The flask was cooled and 50 mL of propylene oxide were added. The flask was fitted with a dry ice/acetone condenser during the addition. The solution was allowed to come to room temperature and was stirred for 72 hours. The solution was then neutralized with concentrated hydrochloric acid and diluted with water. The solvent was removed in vacuo leaving a syrup which was taken up in ethanol. After stirring for 30 minutes at room temperature, the sodium chloride produced was removed by filtration. The filter cake was washed with ethanol and the combined ethanol layers were reduced in vacuo. The residue was dissolved in water and dialyzed in cellulose acetate (#7, 38 mm, 4.6 mL/cm, molecular weight cut off=1000, Fisher Scientific). After 5 hours at 0.degree. C., the solution was removed from the dialysis tubing and freeze-dried. The resulting solid was suspended in acetone and stirred overnight. The filtered solid was resuspended in acetone and stirred for 24 hours. The solid was collected by filtration and dissolved in 200 mL of water and then lyophilized. 75 grams of purified hydroxypropyl-.beta.-cyclodextrin were obtained. The degree of substitution was calculated by NMR and by comparison with an authentic sample. The Pitha et al method for preparation of HPBCD by condensation of propylene oxide with .beta.-cyclodexttin in alkaline aqueous solution unfortunately suffers from disadvantages, particularly in purification of the product. After completion of the condensation, the reaction mixture is neutralized with hydrochloric acid, water is evaporated under vacuum and the syrupy residue is dissolved in ethanol to precipitate sodium chloride, the main by-product of the reaction. After filtration, ethanol is evaporated under vacuum and the residue is dissolved in water and dialyzed to remove the remaining sodium chloride and polymerization products of propylene oxide. During dialysis, part of the hydroxypropyl-.beta.-cyclodextrin goes through the membrane and is lost. The dialysate is then freeze-dried, twice stirred in acetone and washed to remove the remaining polymerization products. Finally, hydroxypropyl-.beta.-cyclodextrin is freeze-dried again. The second freeze-drying is necessary because the product after washing with acetone is not homogeneous. To overcome these difficulties with the Pitha et al process, a new method has been developed by Maciej Smulkowski of the University of Florida, Gainesville, Fla. for the synthesis of HPBCD. This new method involves removal of sodium hydroxide from the reaction mixture by an ion exchange resin (H.sup.+); as a result, several time-consuming steps of Pitha et al's purification can be avoided. Moreover, the amount of sodium hydroxide used by Pitha et al (7 equivalents for one of .beta.-cyclodextrin) can be decreased to 2 equivalents of sodium hydroxide per cyclodextrin molecule, and still produce a product with the appropriate NMR and optical rotation. According to the new method, .beta.-cyclodextrin is first condensed with propylene oxide in alkaline solution. sodium hydroxide is removed on an ion exchange column (Dowex 50W-X8, H.sup.+ form), the eluate is evaporated under vacuum to one-half of the original volume, the remaining solution is freeze-dried, the resulting white solid is washed with acetone and freeze-dried again, then subjected to grinding and sieving. Possible modifications of this method include: (1) use of the ionic exchange resin for neutralization in the reaction flask, with filtration of the resin and washing on the filter funnel; (2) use of calcium, magnesium, lithium or potassim hydroxide to dissolve the cyclodextrin; (3) removal of hydroxides after the reaction by saturating the reaction mixture with carbon dioxide or neutralization with sulfuric acid in place of the ion exchange resin; (4) use of even less sodium hydroxide (between 1 and 2 equivalents); and (5) elimination of the second freeze-drying. The following is a typical procedure using the new, improved method: 50 g of .beta.-cyclodextrin were dissolved in a solution of 3.53 g of sodium hydroxide in 75 mL of water and treated with 29 mL of propylene oxide at 0.degree. C. The reaction mixture was maintained for 5 hours at that temperature, then was kept at room temperature for 42 hours. At the end of that time, the reaction mixture was passed through the Dowex 50W-X8 column (H.sup.+ form), the column was washed with water and the eluate was evaporated under vacuum to a volume of 100 mL, then freeze-dried. The resulting white solid was washed with acetone to give 51 g of HPCD, with the same degree of substitution (4.7) and NMR as the HPCD prepared by the Pitha et al method. Residue on ignition was 0.0%. Optical rotation also was identical to that of the Pitha et al product. Condensation of 25 g of .beta.-cyclodextrin using 7.71 g of sodium hydroxide gave similar results. A further improvement in the new, improved HPBCD synthesis utilizes activated carbon for purification of the solution prior to the last freeze-drying. Thus, when the aqueous solution from the Dowex 50 ionic exchange column was treated with activated carbon, most of the polymerization products were removed without loss of HPBCD, and the filtrate after only one washing with ethyl acetate was ready for final freeze-drying. In this way, only one freeze-drying was required. Crystallization of the final product instead of freeze-drying is also possible, at least on a small scale. The product from the modified new process (using activated carbon) appears to be superior to that of the original new process and the Pitha et al process. First, the product is snow white and produces a colorless aqueous solution, whereas solutions of the earlier products were yellow. Secondly, the product is not oily, which may be due to removal of more highly substituted, less soluble, oily cyclodextrins. HPBCD can be prepared in varying degrees of substitution, such as 5 or 7. Typically, the foregoing procedure is used to produce HPBCD (ASDS 7). The mass spectra for the isomeric mixture of HPBCD centers around 7 degrees of substitution. This spectra is obtained by "softly" ionizing the sample using fast atom bombardment. The generated spectra is similar to those previously reported (obtained by Californium-252 plasma desorption) in both the symmetry of the isomeric distribution and the numerical spread of the isomers formed. Hydroxyethyl-.beta.-cyclodextrin (HEBCD) can be prepared analogously to HPBCD, utilizing the improved procedure detailed above but substituting an equivalent quantity of ethylene oxide for the propylene oxide there employed. The synthesis of 2-hydroxypropyl-.gamma.-cyclodextrin (HPGCD) similarly uses the same basic procedure as for HPBCD, substituting-.gamma.-cyclodextrin for the .beta.-cyclodextrin starting material. However, because .gamma.-cyclodextrin contains eight glucose residues compared to seven for .beta.-cyclodextrin, the amount of propylene oxide used can be reduced in order to lower the degree of substitution. Use of 0.75 mole of propylene oxide per 0.077 mole of .gamma.-cyclodextrin (.about.20% excess considering 8 OH groups) affords HPGCD with a degree of substitution of 8, while use of 0.56 mole of propylene oxide (.about.10% less than equivalent) gives a degree of substitution of about 7. Hydroxyethyl-.gamma.-cyclodextrin (HEGCD) can be prepared similarly to HPGCD as described in the preceding paragraph, simply using an equivalent quantity of ethylene oxide in place of the propylene oxide. Thus, the hydroxyalkyl cyclodextrins intended for use herein can be prepared by procedures described by Pitha et al or variations thereof. Obtained by these procedures, the cyclodextrins are intrinsically amorphous mixtures. The importance of the amorphous nature of the cyclodextrins is described by Pitha et al, J. Pharm. Sci., Vol. 74, No. 9, 987-990 (September 1985) and in Pitha U.S. Pat. No. 4,727,064. The advantages of the amorphous nature of these materials are more pronounced at higher concentrations of cyclodextrin. For use with polypeptides, it is highly desirable to use cyclodextrin which is relatively free of impurities, i.e. oxidizing agents, peroxides, propylene oxide or other chemicals used to prepare the cyclodextrins, because oxidation can render the polypeptide less effective. Preferably, the impurity level will be below 100 .mu.M peroxide or its equivalent. The other cyclodextrins intended for use in the present invention, i.e. the glucosyl, maltosyl and maltotriosyl derivatives of .beta.- and .gamma.-cyclodextrin, are branched cyclodextrins which are highly soluble in water as compared to the parent cyclodextrins. These branched cyclodextrins can be produced by microbiological processes from the parent cyclodextrins. Glucosyl-.beta.-cyclodextrins can be obtained from the mother liquor of a large-scale .beta.-cyclodextrin synthesis with Bacillus ohbensis cyclomaltodextrin glucanotransferase; see Koizumi et al, Chem. Pharm. Bull., 35 (8), 3413-3418 (1987) and reference cited therein. Maltosyl and maltotriosyl .beta.- and .gamma.-cyclodextrins can be prepared from the parent cyclodextrin and maltose or mallotriose through the reverse action of Pseudomonas isoamylase or Klebsiella aerogenes pullulanase, while glucosyl-.gamma.-cyclodextrin can be prepared by enzymatic hydrolysis of maltosyl-.gamma.-cyclodextrin; see Okada et al, Chem. Pharm. Bull., 36 (6), 2176-2185 (1988) and references cited therein. The preparation of maltosyl-.beta.-cyclodextrin by reacting maltose with .beta.-cyclodextrin in the presence of pullulanase is also described in Japanese Kokai 61-287902, published Dec. 18, 1986, and Japanese Kokai 61-197602, published Sep. 1, 1986. A mixture of maltosyl-.beta.-cyclodextrin and various dimaltosyl-.beta.-cyclodextrins may be conveniently employed. See also Kainuma et al U.S. Pat. No. 4,668,626, issued May 26, 1987. Polypeptides such as proteins present unique solubility and stability problems as compared to other drug molecules. These are a reflection of the unique structure of the polypeptides. Proteins, for example, are very large molecules of high molecular weight having numerous hydrophobic and hydrophilic regions within a single molecule. Moreover, the three-dimensional structure or conformation of proteins is critical to their activity and can be easily affected detrimentally by the protein's environment, an unfavorable environment leading to aggregation. Thus, the solubilization and stabilization of these complex molecules is difficult to accomplish and the ability of an untried agent to achieve solubilization/stabilization, and to do so without appreciable loss of activity, cannot be readily predicted. However, the present inventors have determined that a selected group of cyclodextrins, i.e. the hydroxypropyl, hydroxyethyl, glucosyl, maltosyl and maltotriosyl derivatives of .beta.- and .gamma.-cyclodextrin (the hydroxypropyl and hydroxyethyl derivatives being preferably prepared in amorphous form as described hereinabove) are well-suited for use in solubilizing/stabilizing the polypeptides defined hereinabove, especially the proteins. The following examples illustrate the solubilization/stabilization results which can be achieved in accord with the present invention. These examples are not intended to limit the invention in any manner whatsoever. |
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