Preparation technology of camptothecin derivative-loaded targeted long-acting liposome

Abstract

The invention relates to a preparation technology of a camptothecin derivative targeted long-acting liposome. Firstly, a long-acting liposome with a targeting function is prepared, folic acid is modified on the surface of the liposome to realize an active targeting function, a metal copper ion and triethanolamine system is used for increasing the drug loading ratio of the liposome, and then the drug loading ratio and the photo-thermal performance of the camptothecin derivative are enhanced by utilizing the pi-pi conjugation effect of the camptothecin derivative and indocyanine green. The long-acting liposome prepared by the invention is uniform in particle size distribution and good in dispersity, can effectively protect a camptothecin lactone ring from being hydrolyzed and inactivated, prolongs the half-life period and stability of a medicine, and effectively solves the problems of poor water solubility, high toxicity, low bioavailability and the like of camptothecin. The prepared targeted long-acting liposome has a targeting property on folate receptor overexpressed tumor cells, further improves the anti-tumor effect of the drug, reduces the toxic and side effects on normal cells, can be applied to targeted therapy of the anti-tumor drug, and has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of anti-tumor drug delivery systems, and in particular relates to a method for preparing camptothecin derivative targeted long-acting liposomes. Background Art

[0002] Malignant tumors are one of the common diseases that seriously threaten human life and health in the world today. The main treatment methods currently include surgery, chemotherapy and radiotherapy, and chemotherapy is currently a common treatment method for tumors. Since most anti-tumor drugs lack the ability to specifically recognize tumor cells, chemotherapy kills normal cells while killing tumor cells, resulting in large toxic side effects. After chemotherapy drugs enter the systemic blood circulation through injection, they must undergo steps such as protein binding, metabolism, and excretion, and less drugs reach the tumor site. Therefore, to increase the concentration of chemotherapy drugs in the tumor area, it is necessary to increase the concentration of drugs that reach tumor cells. Tumor-targeted drug delivery systems can solve this problem. Using new formulation technologies, a new type of nano-drug delivery system for anti-tumor drugs is studied, which can improve the targeting of tumor cells, increase the drug concentration in the tumor area, and reduce the toxic side effects on normal cells.

[0003] Camptothecin and its derivatives are an important class of natural products. They exist in the roots, barks and fruits of the plant Camptotheca acuminata of the genus Ecliptae of the Davidiaceae family, and have certain therapeutic effects on lung cancer, gastric cancer, prostate cancer, breast cancer, etc. Although they have strong anti-tumor activity, they have problems such as poor solubility, unstable lactone ring structure and obvious side effects, which seriously limit their clinical application.

[0004] As a new drug carrier, liposomes have been widely studied in the process of tumor treatment. They are lipid bilayer closed vesicles composed of phospholipids and cholesterol, with good biocompatibility, biodegradability, low toxicity, low immunogenicity and other advantages. General camptothecin liposome preparations have serious shortcomings such as short half-life, poor stability, and high toxicity and side effects, which limit their clinical application. Long-acting liposomes can effectively prolong the drug action time, reduce the dosage, improve the efficacy and reduce the accumulation of drugs in the kidneys, thereby reducing the nephrotoxicity during treatment. The development of new long-acting liposomes of camptothecin and hydroxycamptothecin with targeting function can protect the camptothecin lactone ring, avoid hydrolysis and inactivation, increase the half-life, stability and targeting of the drug, and effectively solve the problems of poor water solubility, high toxicity and low bioavailability of camptothecin.

[0005] Folic acid (FA) is a water-soluble vitamin with a high affinity for folate receptors. Folate receptors are highly expressed on a variety of tumor cells, but lowly expressed on normal cells. Using folic acid molecules to recognize folate receptors can achieve targeted delivery of tumor drugs, reduce damage to normal cells, and improve therapeutic effects. Folic acid-modified liposomes can reduce the interaction with plasma proteins, opsonins, antibodies, and enzymes through surface modification, thereby increasing their stability in the blood and prolonging the circulation time of drugs in the body. Folic acid modification may help reduce the immunogenicity of liposomes and reduce clearance in the body, thereby improving the bioavailability of drugs. Folic acid-modified liposomes can achieve targeted release of drugs, increase the concentration of drugs at the tumor site, and thus enhance the anti-tumor effect.

[0006] Copper metal ions (Cu2 + ) can enhance the stability of liposome membrane by interacting with components such as phospholipids or cholesterol in liposome membrane, thereby reducing the rupture or fusion of liposomes in vivo and in vitro. Triethanolamine, as an organic small molecule, can enhance the drug loading capacity and release characteristics of liposomes by changing the fluidity of liposome membrane or forming hydrogen bonds with membrane components. The modification of copper ions can give liposomes specific biological functions, such as interacting with copper ion receptors on the surface of certain cells to improve the targeting of liposomes. Through the complexation of metal ions with drug molecules, the sustained release effect of drugs can be achieved and the circulation time of drugs in the body can be prolonged. By enhancing the stability and targeting of liposomes, the concentration of drugs in the lesion site is increased, thereby improving the efficacy. By controlling the release rate and targeting of drugs, the distribution of drugs to normal tissues is reduced and toxic side effects are reduced. Explore new modification methods and develop long-acting liposomes with better performance as drug carriers to meet clinical treatment needs.

[0007] Photothermal therapy (PTT) is a new anti-tumor strategy that can effectively thermally ablate tumor cells. However, PTT may induce heat resistance in tumor cells, affecting the killing effect. Therefore, combining PTT with chemotherapy can effectively make up for the shortcomings of various methods in tumor treatment. Among various photosensitizers, indocyanine green (ICG) has been approved by the US Food and Drug Administration (FDA) as a near-infrared dye for medical diagnosis because of its considerable photothermal conversion ability and low cytotoxicity. However, the application of free ICG is subject to many limitations in aqueous solution, including instability and self-aggregation in aqueous solution, which greatly affects the effect of tumor treatment. Indocyanine green and camptothecin can form a π-π conjugated structure, which greatly improves solubility and stability. Summary of the invention

[0008] The purpose of the present invention is to prepare a targeted long-acting liposome loaded with camptothecin derivatives, to develop a new camptothecin targeted drug delivery system in view of the problems of poor water solubility, high toxicity and low bioavailability of camptothecin, to provide camptothecin pharmaceutical intermediates and low-toxicity products, to achieve sustained and controlled release of camptothecin drugs, to improve its tumor targeting, thereby significantly improving its anti-cancer activity, to provide an alternative product to highly toxic camptothecin, and to further improve its market application value.

[0009] A method for preparing a camptothecin derivative-loaded targeted long-acting liposome comprises the following steps:

[0010] (1) Soy lecithin, cholesterol, and polyethylene glycol 2000 (PEG2k) are dissolved in chloroform according to a certain molar ratio and ultrasonically mixed. The organic solvent containing lipids is placed in a round-bottom flask, and the organic solvent is completely evaporated under reduced pressure using a rotary evaporator to leave a uniform lipid film. The formed lipid film is added to phosphate buffered saline (PBS), and the hydration temperature is controlled at 50°C-70°C and stirred for 2 hours. The formed liposome dispersion is ultrasonically treated in an ice-water bath, extruded using a 100 nm polycarbonate membrane to control the particle size, and the liposomes are eluted and purified by a Sephadex G-75 column to obtain long-acting liposomes.

[0011] (2) The activated folic acid was reacted with polyethylene glycol 2000 (PEG2k) at a molar ratio of 1:1 to obtain folic acid-PEG2k, which was then ultrasonically mixed with soybean lecithin and cholesterol in a certain proportion and placed in a round-bottom flask. The organic solvent was completely evaporated using a rotary evaporator. Phosphate buffer (PBS) was added to the formed lipid film, and the hydration temperature was controlled at 50℃-70℃ and stirred for 2h. The formed liposome dispersion was ultrasonically treated in an ice-water bath, extruded using a 100nm polycarbonate membrane, the particle size was controlled, and the liposomes were eluted and purified by Sephadex G-75 column to obtain folic acid-modified long-acting liposomes. (3) Soybean lecithin, cholesterol, and polyethylene glycol 2000 (PEG2k) were mixed in a certain proportion to obtain a lipid film obtained by ultrasonic rotary evaporation, and a mixed solution of copper sulfate and triethanolamine after adjusting the pH with hydrochloric acid was added to hydrate the lipid film. The lipid was suspended at 60℃-65℃ for 25-30min and allowed to stand for 7 seconds. The liposomes were extruded through a 100 nm polycarbonate membrane and eluted through a Sephadex G-75 column for purification. The elution process used phosphate buffered saline (PBS), and 0.3 mL fractions were collected to obtain long-acting liposomes modified with metal copper ions.

[0012] (4) The folic acid-PEG2k obtained in (2) is ultrasonically mixed with soybean lecithin and cholesterol, and then rotary evaporated to obtain a lipid film, and then the mixed solution containing metal copper ions adjusted in (3) is added, extruded using a 100 nm polycarbonate membrane, and eluted and purified through a Sephadex G-75 column to obtain a long-acting liposome co-modified with folic acid and metal copper ions.

[0013] (5) Dissolve the camptothecin derivative and indocyanine green in methanol to a concentration of 10-300 μg / mL, and mix the two solutions evenly by ultrasonication at 25°C-35°C for 30 min.

[0014] (6) Adding the mixed solution of the camptothecin derivative and indocyanine green prepared in step (5) to the various long-acting liposomes prepared in steps (1) to (4), respectively, mixing by ultrasonication, and then stirring by magnetic stirring at 34° C. to 38° C. for 12 to 24 hours to obtain targeted long-acting liposomes loaded with camptothecin derivatives.

[0015] In the above technical solution, in step (1), the conditions for ultrasonic treatment of the mixed solution are: the ultrasonic power is 300W; and the treatment time is 10-20min.

[0016] In the above technical solution, in steps (1) to (4), the temperature of the rotary evaporator is controlled at 42°C-45°C.

[0017] In the above technical solution, in step (3), the adjusted pH value is 3.4-4.5.

[0018] In the above technical solution, in step (5), the camptothecin derivative is one of camptothecin, hydroxycamptothecin and irinotecan.

[0019] In the above technical solution, the diameter of the long-acting liposomes, the long-acting liposomes modified with folic acid, the long-acting liposomes modified with metal copper ions, and the long-acting liposomes modified with folic acid and metal copper ions is 90-180nm. A long-acting liposome loaded with camptothecin and its derivatives prepared by the above preparation method has a drug loading rate of 15%-29%.

[0020] The present invention provides a method for preparing a camptothecin derivative-loaded targeted long-acting liposome. Liposomes modified with polyethylene glycol 2000 (PEG2k) have higher stability in vitro and in vivo, which helps to protect the encapsulated drug from being released prematurely and ensure that the drug remains stable before reaching the target location. Liposomes modified with folic acid can specifically target tumor cells because many tumor cells overexpress folate receptors on their surfaces. This targeting can increase the concentration of the drug in tumor tissue while reducing damage to normal cells. Liposomes modified with polyethylene glycol 2000 (PEG2k) and folic acid can increase the accumulation of the drug in tumor tissue, thereby enhancing the efficacy of the drug. Through targeted delivery, the effect of the drug on normal tissues can be reduced, thereby reducing side effects. The addition of metal copper ions can achieve a sustained release effect of the drug and prolong the circulation time of the drug in the body. The prepared long-acting liposomes can effectively load camptothecin derivatives and indocyanine green, and the camptothecin derivatives and indocyanine green are combined in a π-π conjugated structure, which enhances the solubility and stability of the camptothecin derivatives.

[0021] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0022] The present invention co-modifies folic acid and metal copper ions on long-acting liposomes. The complex formed by copper ions and folic acid can exist stably under specific conditions, which helps to protect the liposomes from premature degradation during the in vivo circulation process, thereby prolonging the release time of the drug. The metal organic coordination polymer modified with folic acid can achieve high drug encapsulation rate and drug loading, and effectively improve the water solubility and drug utilization of the drug. Camptothecin derivatives and indocyanine green are combined with a π-π conjugated structure, which enhances the solubility and stability of camptothecin derivatives. The addition of indocyanine green increases the drug loading rate of long-acting liposomes for camptothecin derivatives. Indocyanine green can effectively convert near-infrared light into thermal energy, realize photothermal therapy, and further enhance the tumor treatment effect. The long-acting liposomes prepared by the present invention have simple process, good stability and biocompatibility, and can be applied to the targeted treatment of tumors. DETAILED DESCRIPTION

[0023] In order to make the contents of the present invention easier to understand, the present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0024] Example 1 Preparation of a camptothecin derivative-loaded targeted long-acting liposome:

[0025] (1) Soybean lecithin, cholesterol, and polyethylene glycol 2000 (PEG2k) were dissolved in chloroform at a molar ratio of 0.59:0.36:0.05 and ultrasonically mixed. The organic solvent containing lipids was placed in a round-bottom flask, and the organic solvent was evaporated under reduced pressure using a rotary evaporator to leave a uniform lipid film. The formed lipid film was added to phosphate buffered saline (PBS), and the hydration temperature was controlled at 50°C-70°C and stirred for 2 hours. The formed liposome dispersion was ultrasonically treated in an ice-water bath, and then extruded using a 100 nm polycarbonate membrane to control the particle size. The liposomes were purified by elution through a Sephadex G-75 column to obtain long-acting liposomes.

[0026] (2) Dispersing 10 mg of camptothecin in 50 mL of methanol, dispersing 10 mg of indocyanine green in 50 mL of methanol, and mixing the two solutions evenly under ultrasonication at 25° C. for 30 min to obtain a mixed solution of camptothecin and indocyanine green;

[0027] (3) The obtained mixed solution of camptothecin and indocyanine green was added to the long-acting liposomes, the mass ratio of drug to long-acting liposomes was 1:1, the mixed solution was sonicated for 30 minutes, and then the solution was magnetically stirred for 24 hours. The mixture was centrifuged at 10000 rpm for 10 minutes, the supernatant was retained, and the precipitate after centrifugation was freeze-dried to obtain the camptothecin derivative-loaded targeted long-acting liposomes.

[0028] Example 2 Preparation of a long-acting liposome loaded with folic acid and carrying camptothecin derivatives:

[0029] (1) Activation of folic acid: 25 mg of folic acid was weighed and dissolved in anhydrous dimethyl sulfoxide (DMSO), and then appropriate amounts of N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) were added. The mixture was stirred magnetically at room temperature (25°C) in the dark to fully dissolve the folic acid, thereby obtaining a DMSO solution of folic acid activated ester, which was reddish brown in color.

[0030] (2) The activated folic acid was reacted with PEG2k in a molar ratio of 1:1 to obtain folic acid-PEG2k, which was then ultrasonically mixed with soybean lecithin and cholesterol in a certain proportion and placed in a round-bottom flask. The organic solvent was completely evaporated using a rotary evaporator. Phosphate buffered saline (PBS) was added to the formed lipid film, and the hydration temperature was controlled at 50°C-70°C and stirred for 2 hours. The formed liposome dispersion was ultrasonically treated in an ice-water bath, extruded using a 100 nm polycarbonate membrane to control the particle size, and the liposomes were purified by elution through a Sephadex G-75 column to obtain folic acid-modified long-acting liposomes.

[0031] (3) Disperse 10 mg of camptothecin in 50 mL of methanol, and disperse 10 mg of indocyanine green in 50 mL of methanol. Ultrasonicate at 25° C. for 30 min to mix the two solutions evenly to obtain a mixed solution of camptothecin and indocyanine green.

[0032] (4) The obtained mixed solution of camptothecin and indocyanine green was added to the folic acid-modified long-acting liposomes, the mass ratio of drug to long-acting liposomes was 1:1, the mixed solution was sonicated for 30 minutes, and then the solution was magnetically stirred for 24 hours. The mixture was centrifuged at 10000 rpm for 10 minutes, the supernatant was retained, and the precipitate after centrifugation was freeze-dried to obtain the camptothecin derivative-loaded targeted long-acting liposomes.

[0033] Example 3 Preparation of a long-acting liposome modified with metal copper ions loaded with camptothecin derivatives:

[0034] (1) Soybean lecithin, cholesterol, and polyethylene glycol 2000 (PEG2k) were mixed in a certain proportion to obtain a lipid film by ultrasonic rotary evaporation. The mixed solution after adjusting the pH with 2M hydrochloric acid was added to 0.3mL of an aqueous solution containing 100mM copper sulfate and 270mM triethanolamine to hydrate the lipid film. The lipid was suspended at 60℃-65℃ for 25-30min and allowed to stand for 7 seconds. The liposomes were extruded using a 100nm polycarbonate membrane and eluted and purified through a Sephadex G-75 column. The elution process used a PBS solution, and a 0.3mL fraction was collected to obtain a long-acting liposome modified with metal copper ions.

[0035] (2) Disperse 10 mg of camptothecin in 50 mL of methanol, and disperse 10 mg of indocyanine green in 50 mL of methanol. Ultrasonicate at 25° C. for 30 min to mix the two solutions evenly to obtain a mixed solution of camptothecin and indocyanine green.

[0036] (3) The obtained mixed solution of camptothecin and indocyanine green was added to the long-acting liposome modified with metal copper ions, the mass ratio of drug to long-acting liposome was 1:1, the mixed solution was sonicated for 30 minutes, and then the solution was magnetically stirred for 24 hours. The mixture was centrifuged at 10000 rpm for 10 minutes, the supernatant was retained, and the precipitate after centrifugation was freeze-dried to obtain the camptothecin derivative-loaded targeted long-acting liposome.

[0037] Example 4 Preparation of a long-acting liposome modified with folic acid and copper ions loaded with camptothecin derivatives:

[0038] (1) Weigh 25 mg of folic acid and dissolve it in anhydrous dimethyl sulfoxide (DMSO), then add appropriate amounts of N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), and stir magnetically at room temperature (25°C) in the dark to fully dissolve the folic acid, thereby obtaining a DMSO solution of folic acid activated ester, which is reddish brown. The activated folic acid is reacted with PEG2k at a molar ratio of 1:1 to obtain folic acid-PEG2k;

[0039] (2) Prepare 100 mM copper sulfate and 270 mM triethanolamine respectively, take appropriate amount of each solution to obtain a mixed solution, and adjust the pH of the mixed solution to 3.4-4.5 with 2 M hydrochloric acid;

[0040] (3) The obtained folic acid-PEG2k, soybean lecithin and cholesterol are dissolved in chloroform in a certain proportion, ultrasonically mixed and placed in a round-bottom flask, and the organic solvent chloroform is evaporated using a rotary evaporator. The mixed solution adjusted in (2) is added to the formed lipid film, and the hydration temperature is controlled to 50°C-70°C and stirred for 2 hours. The formed liposome dispersion is ultrasonically treated in an ice-water bath, extruded using a 100 nm polycarbonate membrane to control the particle size, and the liposomes are eluted and purified through a Sephadex G-75 column to obtain long-acting liposomes modified with folic acid and metal copper ions.

[0041] (4) Dispersing 10 mg of camptothecin in 50 mL of methanol, dispersing 10 mg of indocyanine green in 50 mL of methanol, and mixing the two solutions evenly under ultrasonication at 25° C. for 30 min to obtain a mixed solution of camptothecin and indocyanine green;

[0042] (5) The obtained mixed solution of camptothecin and indocyanine green was added to the long-acting liposomes modified with folic acid and metal copper ions, the mass ratio of drug to long-acting liposomes was 1:1, the mixed solution was sonicated for 30 minutes, and then the solution was magnetically stirred for 24 hours. The mixture was centrifuged at 10000 rpm for 10 minutes, the supernatant was retained, and the precipitate after centrifugation was freeze-dried to obtain the camptothecin derivative-loaded targeted long-acting liposomes.

Claims

1. A method for preparing a camptothecin derivative-loaded targeted long-acting liposome, the preparation method comprising the following steps: (1) Soy lecithin, cholesterol, and polyethylene glycol 2000 (PEG2k) are dissolved in chloroform according to a certain molar ratio and ultrasonically mixed. The organic solvent containing lipids is placed in a round-bottom flask, and the organic solvent is completely evaporated under reduced pressure using a rotary evaporator to leave a uniform lipid film. The formed lipid film is added to phosphate buffered saline (PBS), and the hydration temperature is controlled at 50°C to 70°C and stirred for 2 hours. The formed liposome dispersion is ultrasonically treated in an ice-water bath, extruded using a 100 nm polycarbonate membrane to control the particle size, and the liposomes are eluted and purified by a Sephadex G-75 column to obtain long-acting liposomes. (2) The activated folic acid was reacted with polyethylene glycol 2000 (PEG2k) at a molar ratio of 1:1 to obtain folic acid-PEG2k, which was then ultrasonically mixed with soybean lecithin and cholesterol in a certain proportion and placed in a round-bottom flask. The organic solvent was completely evaporated using a rotary evaporator, and phosphate buffered saline (PBS) was added to the formed lipid film. The hydration temperature was controlled at 50°C to 70°C and stirred for 2 h. The formed liposome dispersion was ultrasonically treated in an ice-water bath, extruded using a 100 nm polycarbonate membrane to control the particle size, and the liposomes were purified by elution through a Sephadex G-75 column to obtain folic acid-modified long-acting liposomes. (3) Soybean lecithin, cholesterol, and polyethylene glycol 2000 (PEG2k) were mixed in a certain proportion to obtain a lipid film by ultrasonic rotary evaporation, and a mixed solution of copper sulfate and triethanolamine after adjusting the pH with hydrochloric acid was added to hydrate the lipid film. The lipid was suspended at 60°C to 65°C for 25-30 minutes and allowed to stand for 7 seconds. The liposomes were extruded using a 100nm polycarbonate membrane and eluted and purified through a Sephadex G-75 column. The elution process used a phosphate buffer solution (PBS), and a 0.3mL fraction was collected to obtain a long-acting liposome modified with metal copper ions. (4) After ultrasonically dispersing the folic acid-PEG2k obtained in (2) with soybean lecithin and cholesterol, rotary evaporation is performed to obtain a lipid film, and then the mixed solution containing metal copper ions mentioned in (3) is added, extruded using a 100 nm polycarbonate membrane, and purified by elution through a Sephadex G-75 column to obtain a liposome that is co-modified with folic acid and metal copper ions. (5) A camptothecin derivative (including camptothecin, 10-hydroxycamptothecin and irinotecan) having a concentration of 100-500 μg / mL methanol solution and a 10N300 μg / mL indocyanine green methanol solution were mixed, and the mixture was thoroughly mixed by ultrasonication at 25° C. to 35° C. for 30 min. (6) The mixed solution of the camptothecin derivative and indocyanine green prepared in step (5) is added to the various long-acting liposomes prepared in steps (1) to (4), respectively, and after ultrasonic mixing, the mixture is magnetically stirred at 34° C. to 38° C. for 12 h to 24 h to obtain targeted long-acting liposomes loaded with camptothecin derivatives.

2. The method for preparing a targeted long-acting liposome loaded with camptothecin derivatives according to claim 1, characterized in that: The molar ratio of the raw materials in step (1) is soybean lecithin: cholesterol: polyethylene glycol 2000 (PEG2k) = 0.59: 0.36: 0.

05.

3. The method for preparing a targeted long-acting liposome loaded with camptothecin derivatives according to claim 1, characterized in that: In step (1), the temperature of the rotary evaporator is controlled at 42°C-45°C.

4. The method for preparing a targeted long-acting liposome loaded with camptothecin derivatives according to claim 1, characterized in that: In step (3), the concentration of the copper sulfate solution is 80mM-120mM, and the concentration of triethanolamine is 200mM-300mM.

5. The method for preparing a targeted long-acting liposome loaded with camptothecin derivatives according to claim 1, characterized in that: The pH value after adjustment in step (3) is 3.4-4.

5.

6. The method for preparing a targeted long-acting liposome loaded with camptothecin derivatives according to claim 1, characterized in that: In step (5), the camptothecin derivative is one of camptothecin, hydroxycamptothecin and irinotecan; and in the camptothecin derivative drug solution, the solvent is methanol.

7. The camptothecin derivative-loaded targeted long-acting liposome prepared by any one of the preparation methods according to claims 1-6, characterized in that The prepared long-acting liposomes, the long-acting liposomes modified with folic acid, the long-acting liposomes modified with metal copper ions, and the long-acting liposomes modified with folic acid and metal copper ions have a diameter of 90-180nm.

8. The camptothecin derivative-loaded targeted long-acting liposome prepared by any one of the preparation methods according to claims 1-6, characterized in that The drug loading rate is 15%-29%.