iuropaisches Patentamt UUb iuropean Patent Office ij) Publication number: J 35/ \1 )ffice europeen des brevets 5) EUROPEAN PATENT APPLICATION £) Application number: 89115945.1 © Int. Cl.s: A61K 9/127 §) Date of filing: 29.08.89 §) Priority: 29.08.88 JP 214542/88 © Applicant: NIPPON FINE CHEMICAL CO., LTD. 4-9, Bingomachi 2-chome Chuo-ku S) Date of publication of application: Osaka-shi Osaka-fu(JP) 07.03.90 Bulletin 90/10 © Inventor: Nanba, Yukihiro S) Designated Contracting States: 10-21, Kasumigaoka 5-chome Tarumi-ku DE FR GB IT Kobe-shi Hyogo-ken(JP) Inventor: Ueno, Toshiya Takasago-ryo 203 2134-2, Ihozaki Iho-cho Takasago-shi Hyogo-ken(JP) Inventor: Sakakibara, Toshiyuki 2-9-30, Maikodai Tarumi-ku Kobe-shi Hyogo-ken(JP) © Representative: Barz, Peter, Dr. et al Patentanwalte Dipl.-lng. G. Dannenberg Dr. P. Weinhoid, Dr. D. Gudei Dipl.-lng. S. Schubert, Dr. P. Barz Siegfriedstrasse 8 D-8000 Munchen 40(DE) © Method for preparing lipid powder for use in preparing liposomes and method for preparing liposomes. © The present invention provides (1) a method for preparing lipid powder for use in the preparing liposome, which comprises supplying at a constant speed an organic solvent solution of lipids having liposome membrane forming ablility to a tubular heater heated externally, evaporating the organic solvent in the heater to prepare a mixture substantially of solids and organic solvent vapor and introducing this mixture at a high speed into a vacuum chamber of not more than 300 mm Hg, to volatilize the organic solvent instantaneously and dry the solids, and \ (2) a method for preapring liposomes comprising dispersing the lipid powder obtained by the above 1 method (1) into an aqueous solvent. If) o o r> CO CL LU Xerox Copy Centre EP 0 357 005 A1 METHOD FOR PREPARING LIPID POWDER FOR USE IN PREPARING LIPOSOMES AND METHOD FOR PREPARING LIPOSOMES The present invention relates to a method for preparing lipid powder for use in preparing liposomes and a method for preparing liposomes. Liposomes are closed vesicles composed of lipid bilayers and can carry various substances in the inside aqueous phase or between the lipid membranes. Therefore, investigations have been undertaken to 5 utilize as drug delivery systems liposomes with fat-soluble or amphipathic substances such as physiologi- cally active substances (drugs etc.) entrapped therein. For example, missile therapy has been developed wherein cancer cells are selectively attacked by an anticancer agent-containing liposomes combined with a cancer surface-specific antibody. Liposomes with a physiologically active substance entrapped therein are usually prepared by dissolving 70 lipids which have ability to form liposome membrane, for example phospholipids, cholesterols, acidic phospholipids, etc., in an organic solvent, distilling off the solvent to some extent from this lipid solution to obtain a lipid mixture, adding an aqueous solution of the physiologically active substance to the lipid mixture and stirring the mixture vigorously. The lipid mixture according to the above method is a dense solid and can not be fully hydrated when mixed with the aqueous solution of physiologically acitive 75 substance with stirring. The hydration becomes more difficult with increasing lipid concentration of the lipid mixture. Therefore, such a conventional method has various problems. More specifically, the spacing between the lipid membranes, which is very small, results in a reduced efficiency in encapsulating the physiologically active substances or reduces the encapsulating volume of the liposomes. The loss of lipids increases, i.e., the ratio of the lipids consumed for forming liposomes to the total amount of lipids used 20 reduces. Further, defects in the lipid membrane, which frequently occur, result in reduced stability and leakage of the physiologically acitive substance entrapped. In the specification, the encapsulating efficiency means the ratio of the amount of physiologically active substance entrapped to the total amount of physiologically acitive substance used (V7V). The encapsulating volume means the total volume of the inside aqueous phase of liposomes formed by one mole of lipids. 25 Furthermore, the above conventional method, when practiced industrially for mass production of liposomes aggravates the above problems, encounters difficulty in selecting the conditions for the distillation of solvent and requires a specific device for vigorous stirring to entail an increased cost. Therefore, the above conventional method has great difficulties in placing liposome compositions into practical use. In order to overcome the above problems, various methods have been proposed. 30 For example, Unexamined Japanese Patent Publication No. 7932/1985 discloses a method for preparing liposomes at a higher temperature than in conventional method. By this method, however, thermolable drugs can not be entrapped in liposomes. Unexamined Japanese Patent Publication No. 7933/1985 discloses a method for preparing liposomes using lipids having liposome membrane forming ability in combination with polyols. However, the use of 35 polyols leads to difficulty in homogeneously dispersing cholesterols, which are important components of the lipid membrane of liposomes, therefore gives unstable liposome membranes and permits leakage of physiologically active substances entrapped. Unexamined Japanese Patent Publication No. 152531/1987 discloses a method for preparing liposomes comprising spray-drying into a powder a solution of lipids having liposome membrane forming ability with a 40 spray drier and mixing the powder with an aqueous solution of physiologically active substances. However, since this powder is likely to agglutinate, it has the drawback of being difficult to hydrate. Therefore, the liposomes prepared by dissolving this powder in water is low in ability to encapsulate physiologically active substances. This method further permits an increased loss of lipids. Furthermore, Examined Japanese Patent Publication No. 52724/1987 discloses a method for preparing 45 liposomes carrying a pysioligacally active substance, which comprises freeze-drying a solution of liposomes having liposome membrane forming ability and physioligically active substance into a powder and dissolv- ing the powder in water. However, this method requires expensive equipment for freeze-drying, and is time- consuming to distil the solvent off, hence a greatly increased production cost. Besides the above methods, a reverse-phase evaporation method is known, which comprises adding an so aqueous solution of physiologically active substance to a solution of lipids having liposome membrane forming ability, preparing liposomes by ultrasonic emulsification and distilling the solvent. However, this method has the probelm that it is difficult to distill the solvent off thoroughly and that the remaining solvent tends to give toxicity to a pharmaceutical preparation of liposomes or to inhibit the formation of liposome membrane. 2 !P 0 357 005 Al An object of the present invention is to provide a method tor preparing npia powaer useaii Tor me preparation of liposomes which powder is excellent in hydration ability and can be easily hydrated on an industrially in large amounts within a short period of time. Another object of the present invention is to provide a method for preparing lipid powder useful for the 5 preparation of liposomes which are excellent in fat-soluble or amphipathic substance encapsulating efficiency and encapsulating volume and moreover substantially free from leakage of the fat-soluble or amphipathic substance entrapped. A further object of the present invention is to provide a method for preparing liposomes of high quality in large quantities on an industrial scale, substantially without wasting the lipid starting material. o These objects and features of the present invention will be clarified by the following description. The present invention provides (1) a method for preparing lipid powder for use in the preparing liposome, which comprises supplying at a constant speed an organic solvent solution of lipids having liposome membrane forming ability to a tubular heater heated externally, evaporating the organic solvent in the heater to prepare a mixture 5 substantially of solids and organic solvent vapor and introducing this mixture at a high speed into a vacuum chamber of not more than 300 mm Hg, to volatilize the organic solvent instantaneously and dry the solids, and (2) a method for preapring liposomes comprising dispersing the lipid powder obtained by the above method (1 ) into an aqueous solvent. >o The inventors found that lipid powder is excellent in hydration ability and can be easily hydrated within a short period of time even on an industrial scale, when the powder is obtained by supplying at a constant speed an organic solvent solution of lipids having liposome membrane forming ability to a tubular heater heated externally, evaporating the organic solvent in the heater to prepare a mixture substantially of solids and organic solvent vapor and introducing this mixture at a high speed into a vacuum chamber of not more ;s than 300 mm Hg to volatilize the organic solvent instantaneously and dry the solids. The inventors further found that the liposomes prepared by hydration of said powder have high fat-soluble or amphipathic substances-encapsulating efficiency and large encapsulating volume and are substantially free from leakage of the active substances, and that the use of said powder makes it possible to