A Dextran Coated Silica Aerogel Used as a Drug Carrier System and a Dextran Coated Silica Aerogel Production Method

Abstract

The present invention relates to a dextran (D) coated silica aerogel used as a drug carrier system in colon cancer treatment and a dextran (D) coated silica aerogel production method in which silica aerogels were synthesized with the Sol-Gel method are modified with amine groups and are coated with dextran (D) or dextran aldehyde (DA) to obtain said dextran (D) coated silica aerogel (S).

Claims

1. A production method of a dextran (D) coated silica aerogel that is used as a drug carrier system, the method comprising the steps of: modifying surfaces of silica aerogels (S) which are synthesized by sol-gel method, and coating the modified silica aerogels (S) with dextran (D) or dextran aldehyde.

2. A dextran-coated silica aerogel production method according to claim 1, wherein a Schiff Base reaction is carried out between amine groups on the surface of the silica aerogels (S) modified with 3-(aminopropyl)triethoxysilane (A) by using glutaraldehyde (G) crosslinker for the dextran (D)-silica aerogel (S) conjugation, and aldehyde groups in the glutaraldehyde and dextran (D) is coated to silica surface by means of glutaraldehyde (G).

3. A dextran-coated silica aerogel production method according to claim 1, wherein stable imide bonds are created between the aldehyde groups of the dextran aldehyde (DA) structure and the amine groups of the APTES modified silica aerogel surface, for the dextran aldehyde (DA)-silica aerogel (S) conjugation.

4. A dextran (D) coated silica aerogel production method according to claim 1, wherein sodium silicate and water mixing preferably at a ratio of 1:10 at ambient temperature and creating sol to obtain sodium silicate sourced silica aerogels (S).

5. A dextran-coated silica aerogel production method according to claim 4, wherein gelation pH is adjusted by adding 1 M HCl so that pH value is 4 during the mixing procedure.

6. A dextran-coated silica aerogel production method according to claim 4, wherein the gel is aged in an air dryer at 50° C. preferably for 24 hours with the aim to strengthen the network structure of the gel obtained and washed with water in order to remove the salts within the gel structure after the aging step.

7. A dextran-coated silica aerogel production method according to claim 6, wherein a washing process is carried out with ethanol for preferably three times in order to remove the water in the pores after washing with water and gels which were put into ethanol, are kept in an air dryer at 50° C. for preferably 24 hours.

8. A dextran-coated silica aerogel production method according to claim 7, wherein a washing operation is performed with n-hexane three times in order to remove the ethanol in the pores of the gel and the gels are kept in an air dryer at 50° C. in n-hexane and repeating the washing with n-hexane for three times within 24 hours.

9. A dextran-coated silica aerogel production method according to claim 8, wherein the synthesized silica aerogels (S) are dried in an air spray dryer, the inlet temperature of which is adjusted to 190° C. and outlet temperature is adjusted to 80° C.

10. A dextran-coated silica aerogel, used as a drug carrier system in colon cancer treatment.

11. A dextran aldehyde coated silica aerogel, used as a drug carrier system in colon cancer treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0011] “A dextran (D) coated silica aerogel used as a drug carrier system and a dextran (D) coated silica aerogel production method” which is conducted to achieve the object of the present invention, are shown in the figures; wherein

[0012] FIG. 1 illustrates the appearance of the dextran (D) coated silica aerogel (a) and dextran aldehyde (DA) coated silica aerogel (b) of the inventive production method.

[0013] The production method of a dextran (D) coated silica aerogel used as a drug carrier system comprises the process steps of; [0014] Surface modification of silica aerogels synthesized by sol-gel method, [0015] The modified silica aerogels (S) being coated with dextran (D) or dextran aldehyde (DA).

[0016] In the inventive production method, for the dextran-silica conjugation using glutaraldehyde (G) crosslinker, a “Schiff Base” reaction is carried out between the amine groups on the surfaces of the APTES modified silica aerogels (S) and the aldehyde groups of glutaraldehyde, and dextran (D) is being coated on the silica surface by means of glutaraldehyde (G).

[0017] Also, for the dextran aldehyde-silica aerogel conjugation, glutaraldehyde (G) crosslinker is not needed and stable imide links are formed between the aldehyde groups of the dextran aldehyde (DA) structure and amine groups of the APTES modified silica aerogel surfaces. With the inventive production method, by means of the dextran (D) and dextran aldehyde (DA) coated on the surface of aerogels; the drug molecules loaded on the aerogels, while not being released during passage through the gastrointestinal system, are only released following the degradation of dextran (D) at the colon area where dextranase enzymes breaking down dextran (D) are found.

[0018] In the inventive production method, silica aerogels (S) are synthesized with a sodium silicate solution. In the drying step, an air spray dryer is used, thus, the collapse of the pores in the texture of the hydrophilic silica aerogels is prevented.

[0019] In the inventive production method, to obtain silica aerogels originating from sodium silicate, preferably 1:10 proportioned sodium silicate:water is mixed at room temperature and sol is composed. During the mixing procedure, the gelation pH is adjusted by adding 1 M HCl so that the pH value is 4. With the aim to strengthen the network structure, the gel is aged in the air dryer at 50° C. preferably for 24 hours, and after the aging step in order to remove the salts in the gel structure, washing with water is implemented. Preferably the washing process should be repeated 3 times. After washing with water in order to remove the water in the pores, preferably three times washing with ethanol is implemented and gels which are put into ethanol after washing are kept in the air dryer at 50° C. for 24 hours. For 24 hours, the washing process with ethanol is repeated 3 times. At the end of 24 hours, in order to remove the ethanol from the pores of the gel washing process with n-hexane is implemented 3 times and gels are kept in n-hexane in the air dryer at 50° C. for 24 hours and during the 24 hour period, the washing with n-hexane is repeated 3 times. The synthesized silica aerogels are dried in an air spray dryer set to 190° C. inlet temperature and 80° C. outlet temperature.

[0020] In the inventive production method, the surface of the synthesized silica aerogels (S) is modified by using APTES. In the invention, for the optimization of the silanization reaction of the silica surface with the APTES, the optimum APTES concentration information is reached by working at different APTES concentrations. For this, 500 mg silica aerogel (S) powder is ultrasonically dispersed in 250 ml toluene and the mixture obtained by adding APTES at different proportions (0.5%, 1%, 2%, 5%, 10%) into the solution, is mixed with a magnetic stirrer preferably 24 hours at 75° C. temperature. At the end of the mixing process which lasts 24 hours, with the mixture reaching room temperature, the unbonded silane agents are removed from the mixture. For this, the mixture is subjected to washing with toluene and preferably centrifuged at 4800 rpm' for 10 minutes and the washing process is repeated preferably three times.

[0021] The amine-modified silica aerogels obtained after washing, are dried at 80° C. in an air-drying oven.

[0022] Syntheses Stages, (a) Synthesis of silica aerogels, (b) The modification of the surface of the silica aerogel with APTES and Its loading with the drug 5-FU, (c) The coating of silica aerogel surface with dextran (D) and dextran aldehyde (DA).

[0023] In order to compare the drug adsorption capacities of the silica aerogels (S) obtained by the production method of the present invention, in the experimental study, drug loading is carried out into the pure silica aerogel (SiO.sub.2) and amine-modified (SiO.sub.2—NH.sub.2) silica aerogels (S), separately. In the experimental study, 5-Fluorouracil (5-FU), which is used in colon cancer treatment, is used as a model drug. Besides this, in order to observe effects of the change of the electrostatic interaction between the amine groups and 5-FU adherent to the pH, to the loading capacity, the loading solution in which the silica aerogels modified with amine groups (S) were, is sonicated for five minutes in the ultrasonic bath with the pH being adjusted to pH 5 and pH 8 and it is enabled that aerogels are dispersed homogeneously within the solution. In the experimental study, the loading process is carried out with magnetic stirrer being 24 hours at room temperature. At the end of 24 hours, the drug-loaded silica aerogels (S) are centrifuged and are left to dry on an air-drying oven at 50° C. for 24 hours.

[0024] In order to observe the effect of differently concentrated solutions to the loading behavior, the 5-FU/water solutions are prepared preferably 3 mg/ml and 6 mg/ml, and the effect of the drug concentration on the loading behavior is observed. It is enabled that the moisture on the surface of the silica aerogels is removed by having kept the silica aerogels (S) at 105° C. for 1 hour before drug loading. The loading process is carried out by adding 0.1 gram silica aerogel (S) into 50 ml of drug solutions with different drug concentrations and mixed for 24 hours at room temperature by a magnetic stirrer. At the end of hours, the drug-loaded silica aerogel (S) mixture is centrifuged for 10 minutes and it is enabled that the supernatant keeping the drug molecules which have not been loaded to the silica aerogels are separated. The absorbance of the supernatant is measured with the “Liquid Chromatography-Mass Spectrometer” device and the loaded drug concentration into silica aerogels (S) is calculated. The drug-loaded aerogels which were separated from the supernatant are dried in an air-drying oven at 50° C. for 24 hours.

[0025] In the inventive production method, in order to coat the surfaces of silica aerogels (S) with dextran (D), cross-linking with dextran (D)-glutaraldehyde (G) and linking with dextran aldehyde (DA) was used. For the coating procedure, the silica aerogels (S) which are functionalized with amine groups and loaded with the model drug first, are coated with dextran (D) (Mw: 75000) using glutaraldehyde (G) crosslinker. The optimization of the concentration of the glutaraldehyde in which silica aerogels are coated the best is made by preparing glutaraldehyde (G) solutions at different concentrations. A Sodium bicarbonate solution (NaHCO.sub.3) at pH 8.5, which is the appropriate pH for the Schiff Base reaction to occur between the amine groups bonded to silica aerogels (S) and the aldehyde groups in glutaraldehyde (G), is prepared (50 ml) and aerogel particles (0.1 g) are dispersed homogenously within the solution.

[0026] Glutaraldehyde (G) at different proportions (5% and 10% w/w GA/solution) is added and the mixture is mixed for 3 hours at room temperature and at the end of the mixing process, it is enabled that the reaction is stopped and stable secondary links are formed by adding cyanoborohydride (NaBH.sub.3CN)to the mixture. The particles obtained at the end of the reaction are dialyzed against distilled water overnight using the dialysis membrane and the silica aerogels (S) the surfaces of which were linked with glutaraldehyde (G) are dried on the air drying-oven at 50° C. Dextran (D) is dissolved in potassium chloride (KCl) solution (50 ml) with a 2 pH. Glutaraldehyde (G) linked silica aerogels (S) (0.1 g) are added into the dextran (D) solution and mixed for 24 hours at room temperature and the dextran (D) coated silica aerogels obtained at the end of the reaction are washed with water in order to remove the non-linked molecules and are subjected to the drying process on an air drying-oven at 50° C.

[0027] And in the procedure of linking with dextran aldehyde (DA), for the dextran aldehyde (DA) synthesis, 3.3 gram dextran (D) (Mw: 75000) is dissolved in 30 ml distilled water. 8 grams of sodium (meta) periodate (NaIO.sub.4) is dissolved in 70 ml distilled water. The NaIO.sub.4 solution has slowly been added to the dextran (D) solution and is mixed with a magnetic stirrer for 24 hours in the dark at room temperature. At the end of 24 hours, in order to remove the excess NaIO.sub.4, washing against distilled water overnight using the dialysis membrane in the dark at room temperature is applied. The solution obtained after the washing is dried by freezing with a freeze dryer. The dextran aldehyde (DA) synthesized in the former step so that the silica aerogels (S) are coated, is dissolved in distilled water (50 ml). The drug-loaded silica aerogels (0.1 g) are put into the dextran aldehyde (DA) solution, the pH of the solution is adjusted to 8.5 and it is mixed for 24 hours at room temperature with a magnetic stirrer. At the end of 24 hours, cyanoborohydride (NaBH.sub.4) (1 mg/ml) is added into the mixture and is mixed for 15 minutes. At the end of 15 minutes again NaBH.sub.4 (1 mg/ml) is added and it is enabled that the mixture is mixed for 30 more minutes. In order to remove substances that did not go into reaction, washing with distilled water using a dialysis membrane is carried out overnight. The dextran aldehyde (DA) coated silica aerogels (S) obtained after washing, are dried on an air drying-oven at 50° C.

[0028] In the experimental study, the dialysis membrane method is used for the study of the in vitro release of the 5-Fluorouracil drug from the silica aerogels (S). First, for the studies of release in the enzyme-free environment, silica aerogels (S), which are dextran-coated and not coated, are put in simulated gastric fluid, the release behavior in gastric pH (1.2) and the effect of dextran (D) coating on the release are analyzed. At the end of two hours, the aerogels were put in simulated intestinal fluid, the pH of which was 6.8, and were held there for 15-18 hours and the release behaviors of the drug-loaded silica aerogels (S) against the changes of pH in the gastrointestinal system were compared.

[0029] Secondly, for the studies of release in an environment with an enzyme, in order to study the release of dextran (D) coated silica aerogels (S) depending on the presence of the enzyme, the release profile of silica aerogels (S) in a release environment containing dextranase (acetate buffer, pH 5.5) is studied. In order to define the concentration of 5-FU released from the silica aerogels (S) cumulative release values were calculated by time-dependent measurements taken with a “Liquid Chromatography-Mass Spectrometer” device.

[0030] As a result of experimental studies, silica aerogels (S) having a high surface area (520.53 m.sup.2/g) and pore diameters (5.73 nm) have been synthesized and it is observed that its surface being modified with amine has increased the drug loading and dextran (D) coating efficiency. It is seen that high drug loading efficiency occurred at pH 8 and when APTES (A) at the proportion 10% was used (611.96 mg/g drug/silica aerogel). The model drug 5-FU release behaviors of silica aerogels (S) coated in two different ways with dextran-glutaraldehyde and dextran aldehyde (DA), in the stomach (pH=1.2), intestines (pH=6.8) and colon tumor (pH=5.5) environments are studied separately. As a result, pure silica aerogels (S), which were not coated with dextran (D), have released 85-86% of the 5-FU drug at stomach-intestine and colon pHs within 24 hours. The release of the drug 5-FU from silica aerogels (S) after being coated with dextran (D) and dextran aldehyde (DA) in the stomach and intestine fluids within 24 hours has occurred at the values 1.68% and 3.49% respectively while occurring at enzyme-free colon pH 4.21% and 0.97% respectively.

[0031] The effect of the presence of enzyme to the release is studied by adding 2 U/ml dextranase enzyme in the acetate buffer which provided colon pH. 24 hours after the enzyme is added the release of drug 5-FU from dextran (D) and dextran aldehyde coated silica aerogels has shown an increase being 24.02% and 13.42% respectively. The coating of silica aerogels (S) with dextran (D) which is a natural polymer and dextran aldehyde (DA) which is a dextran derivative enables the 5-FU drug to reach the colon area without being affected by the pH changes and losing its effect and a controlled release with the effect of enzyme.

[0032] The silica aerogels (S) (SiO.sub.2) used in the inventive production method, are used as ideal drug carrier systems due to their high surface area and large pore volumes and their biocompatible structures having high porosity and their high adsorption capacity.

[0033] Due to the surfaces of silica aerogels (S) (SiO.sub.2) being able to be modified easily, by coating their surfaces with dextran (D) a controlled and colon targeted, potential drug carrier system is obtained.

[0034] Dextran (D), which is a biodegradable and biocompatible natural polymer is a polysaccharide. It is being preferred because of its features such as its wide molecular weight distribution, not being toxic, and being able to be eliminated from the body easily.

[0035] In the inventive production method, the surface of the silica aerogels (S) is modified with preferably 3-(aminopropyltriethoxysilane) (APTES) (A) (SiO.sub.2—NH.sub.2). Amine groups give the Schiff Base reaction with the aldehyde groups of glutaraldehyde, which is used as a crosslinker for dextran (D) coating (Silica Aerogel (S) @3-Aminopropyltriethoxysilane (APTES) (A)-SiO.sub.2—NH.sub.2). For the dextran (D) coating of the surface of silica aerogel (S), glutaraldehyde (G) crosslinker is used and the capacity of glutaraldehyde (G) bonding to the surface affects the dextran (D) coating efficiency directly. The coating of the surfaces of silica aerogels (S) with dextran (D) occurs between the aldehyde groups of the glutaraldehyde (G) bonded to the surface and hydroxyl groups of dextran (D) at acidic conditions. (Silica Aerogel (S) @ APTES (A) @ Glutaraldehyde (G)-(SiO.sub.2—NH.sub.2-GA))

[0036] With the inventive production method, due to the surfaces of the silica aerogels (S) being coated with dextran (D), the release of the drug-loaded to the aerogels in the stomach and intestine fluids is prevented and colon targeted release is made. Thus, the dextran (D) coated onto the surface of the silica aerogels (S) being decomposed by only the dextranase enzymes present in the colon, the targeted release of the drug is enabled. (Silica Aerogel (S) @ APTES (A) @ Glutaraldehyde (G) @ Dextran (D)-(SiO.sub.2—NH.sub.2-Dex))

[0037] In the inventive production method, the surfaces of silica aerogels (S) are also coated with dextran aldehyde (DA) without using glutaraldehyde (G) crosslinker. Dextran aldehyde (DA) links to the amine groups on the surface of silica aerogel, with the aldehyde groups it has, with a Schiff Base reaction and enables the silica aerogel (S) carrying the drug to the colon effectively. (Silica Aerogel (S) @ APTES (A) @ Glutaraldehyde (G) @ Dextran Aldehyde (DA)-(SiO.sub.2—NH.sub.2-Dex-CHO))

[0038] With the inventive production method, dextran (D) coated silica aerogel (S) used in colon cancer treatment is obtained. Dextran (D) coated silica aerogel (S) is being used as a drug system for colon cancer treatment. In the production of dextran (D) coated silica aerogel (S), silica aerogels with high adsorbing capacity are used in order to be used in drug carrier system and silica aerogels are synthesized with sodium silicate which is biocompatible and economical, using the sol-gel method instead of organic structured, costly, toxic and expensive silica sources such as Tetraethylorthosilicate (TEOS), Tetramethylorthosilicate (TMOS) which are used during the synthesizing of many carrier systems and in the synthesizing of silica nanoparticles.

[0039] By this means, opposite to many studies present in the previous technique, drug loading at rather high amounts is implemented.

[0040] Although colon targeted carrier systems with dextran hydrogels, drugs conjugated with dextrans (D), polysaccharide-based carriers like pectin and chitosan, silica and similar nanoparticles and drug conjugates are present in the literature, a production method where silica aerogels are used with the aim of carrying to the colon and silica aerogels (S) are conjugated with dextran (D) is not present in the previous technique. With the inventive production method dextran (D)-silica aerogel (S) and dextran aldehyde (DA)-silica aerogel (S) organic-inorganic hybrid systems, which are new and effective, are obtained.

[0041] In the inventive production method, the process of coating dextran (D) and dextran aldehyde (DA), which is a derivative of dextran (D) onto silica aerogels (S), eliminates the necessity of using high-cost material as it takes place in the previous technique. Although the usage of molecules such as antibody, growth factor in the targeting of the chemotherapy drugs is present in the literature, the process of coating silica aerogels (S) with dextran (D) and dextran aldehyde (DA), a derivative of dextran (D), which are not affected by the acid environment and is inhibited by dextranase enzymes indigenous to the colon, reduces the cost and it is ensured that the drug is stably targeted to the colon.

[0042] The dextran (D) coated silica aerogel (S) obtained with the inventive production method and used as a drug carrier system can be taken orally, contrarily to the chemotherapy drugs which are applied via injection, used today, thus it is prevented that the drugs are removed from the body in a short time. This way, it is ensured that they reach the tumor area in the colon, and with the reduction of side effects based on chemotherapy drugs, healthy cells are not damaged and a more effective treatment application at one time is enabled. By means of the dextran (D) coated aerogels obtained with the inventive production method, a prolonged drug release is practiced, and the release rate can be controlled by adjusting the thickness of the layer of dextran (D) coated onto the surface.

[0043] It is possible to develop various versions of the dextran (D) coated silica aerogel to be used as a drug carrier system and a dextran (D) coated silica aerogel production method (1) which are the subjects of the invention, however, the invention cannot be limited by the examples explained herein and is as defined in the claims.