CA1222457A - Crystallised carbohydrate matrix for biologically active substances, a process of preparing said matrix, and the use thereof - Google Patents

Abstract

CANADIAN PATENT APPLICATION

OF

ULF SCHR?DER

FOR

A CRYSTALLISED CARBOHYDRATE MATRIX FOR BIOLOGICALLY
ACTIVE SUBSTANCES, A PROCESS OF PREPARING SAID
MATRIX, AND THE USE THEREOF
Abstract of the Disclosure:

The invention shows that it is possible to produce a depot matrix for biologically active substances, con-sisting of carbohydrate microspheres, such that the carbohydrate polymers included in the microsphere are stabilised to a microsphere by crystallisation, which implies using non-covalent bonds, the substance enclosed retaining its biological activity,

Description

A C~YSrrALLISED CARBOHYDRATE MATRIX FOR ~IOLOGICALLY

AYD ~ sr ~ L~

~ . Biologically active substances supplied to an organism are, in most cases, rapidly digested by the organism. In view hereof, the supply of substances must be repeated at regular intervals in order to estab-lish a therapeutically active concentration within theorganism. Such supply of biologically active substances to organisms is important int.al. in the fields of human and veterinary medicine, or in controlling di~ferent types of infestants (such as insects, fungi etc.) in agriculture and forestry.
In order to avoid the disadvantages of repeated administration, it is endeavoured to find matrices which, together with the substance, provide a depot effect, by which is meant that the substance in one way or another is adsorbed, coupled to or enclosed in a matrix from which it is then released, via different mechanisms, during a prolonged period of time. The great advantage of this type oE administration is that the substance is supplied to the organism at a uniform rate;
the peaks and valleys in concentration encountered with normal administration are avoided. By biologically ac-tive preparations are meant such preparations or suh-stances as are capable of affecting organisms. Examples of such preparations are therapeutically active prepa-rations, insecticides or herbicides, enzymes, antibo-dies, antigens, allergens, hormones, live or killed and whoLe or decomposed microorganisms or virus. As practical examples of the fields of use of the present invention, mention may be made of 0 1. Insulin: Patients suffering from diabetes must inject insulin at regular intervals or during meals in order to maintain the blood sugar content at an acceptable level, Great advantages would be obtain able if a depot preparation of insulin could be administered in a simple man-ner, implying that the injection frequen-cy could be reduced considerably;

2. Vaccination: For the vaccination of humans, adju~ants cannot be used. However, it has been shown in literature that the immunogenic response will be far better if th~ body is subjected to long-time exposure of the antigen. For vaccination purposes, it is important that the depot matrix is not itself immunogenic, and that it can be excreted from the body. For example, vaccination tests conducted on human beings against bee allergens have shown that tllese allergens, dissolv-ed in water and injected subcutaneously, are excreted within 4 hours.
The production of depot matrices for different types of preparations is well-documented in literature, and some preparations are also commercially available.
The invention described in the present application 2S uses polymers as depot matrix. Different types of poly-mers are described in literature. (Chem. Eng, Commun.
(1980) 6, 1-48 or Int. J. Pharm. (1980) 7~ 1-18). Among the desirable properties of such a polymer preparation are the following:
1. The polymer should in itself be chemically inert in biological systems.
2. The polymer should be biologically well-characterised.

3. The polymer should be non-toxic and non-immunogenic.

4. The pol~mer should be excretable from the body via normal routes~

5. The polymer preparation should be readily adminis-trable.

~ ,2, ;~ 2 ~

6. The polymer preparation should be capable of releas-ing a biologically active substance, and the release rate of the active substance should be readily con-trollable.

7. The polymer preparation should be able to enclose and release substances of different molecular weights Existing polymer systems described in the above~mentioned sumrnary reviews are all of the type covalently cross-lin~-ed polymers in which the covalent cross-linkage in some cases is unstable in biological systemsl and in which the biologically active substance is covalently bonded to the polymer. This instability causes degradation of the polymer preparation, whereby the preparations are released.
A different type of release is obtained if crystal-line substances (such as crystallised proteinsj are enclosed in the covalently cross-linked polymer prepa ration. ~y utilising a varying degree of porosity in the polymer preparation, varying release times are ob-tained.
In general it may be said that it is endeavoured, in developing polymer preparations for administration of biologically active substances, to use polymers which are as "pure" as possible. One such "pure" polymer class is represented by the carbohydrates. Presentday methods of preparing carbohydrate matrices comprise a covalent coupling of the polymer chains included (GB 924054) or heat treatment tSE 4024/69) in order to obtain stable matrices ~escri tion oE the invention P ._. _ The invention is based upon a novel technique for stabilising carbohydrate polymers according to the append-ed claims. This -technique involves ernulsifying a solu-tion of the polymer in a hydrophobic emulsifying medium, whereby spherical droplets of the soluhle carbohydrate polymer are obtained in ~the emulsifying medium. To stabi-lise the sphere, the said emulsion is then poured into ,6,~

a liquid capable of crystallising the carbohydrate poly-mer to a complex relatively insoluble in water.
Crystallisation implies that the type of bonds holding the carbohydrate polymers together in a micro-sphere is chemically characterised as non-covalent of the type hydrogen bonds~ ion bonds or van der Waals forces, the majority consisting of hydrogen bonds~
The resulting polymer matrix has such characteris-tics that it can retain biologically active substances in the non-covalently cross-linked polymeric lattice, the biologically active substance being released con-currently with the slow redissolution of the crystallis-ed carbohydrate matrix.
The simplest way of incorporating the biologically active substance is to admix it to the dissolved carbo-hydrate polymer before this is mixed with the emulsify-ing medium.
The matrix material in the production of these spheres or particles consists of carbohydrate polymers.
The technique described in the present invention makes it possible to use the carbohyclrates dextran, pullullan, glucogen, starch, agarose, cellulose, alginate, chitosan or carrageenan, and different derivatives thereof.
In some cases, also the carbohydrate per se may ~5 be of interest as a biologically active substance. One example hereof is the carbohydrate heparin which is used therapeutically as an anticoagulant.
As regards the molecular weight of the carbohy-drates, the tec}lllique has been shown to function wi-thin a very large range. For instance, crystallised carbo}-y-drate spheres have been produced from glucose, sucrose and maltose. Dextrans and dextrins having an average molecular weight from about 800 up to several millions have also been shown to function. ~he upper limit of the molecular weight in the preparation of crystallised carbohydrate spheres according to the present inven-tion is limited only by the solubility of the respec-tive carbohydrates in their solventsO

The modlfication of these carbohydrate polymers to different types of derivatives can be carried out in such a manner that the ability of the carbohydrates to adsorb for example hydrophobic or charged substances, is changed. Examples of well-documented hydrophobic substituents are cholesterol, DEAE, or Ciba chrome blue which all can be covalently coupled in simple manner to the carbohydrate polymer. Correspondingly, charged groups of the type -SO4 or -NH2 can be covalently coupl-lQ ed to the carbohydrate matrix for adsorption of chargedsubstances. The above mentioned substituents are com-mercially available, coupled to the carbohydrate polymer dextran, from Pharmacia AB at Uppsala, Of the above-mentioned carbohydrate polymers, the polymers dextran, starch, glucogen, or pullullan are preferred on grounds previously described (see points 1-7, on ppO 2-3). The main reason is that these polymers are extremely well characterised in biological systems.
Of the above-mentioned polymers, however, dextran must be put in the first place as an example of a non enzy-matically (in tissue) degradable matrix for biologically active substances, Where starch, glucogen or pullullan is concerned, the alpha-amylase concentration determines the time of degradation and thus also the release time of the biologically active substances. In the case of dextran, it is only the physical parameters, such as the pH or ionic strength, which redissolve the crystal-lised matrix and thus control the release, The disadvantage of an enzymatically controlled release is that, in the case of for example alpha-amylase, the concentration thereof may vary within large ranges in body fluids for different diseases. In other cases, the enzyme concentrations may vary between patients or in the same patient at different times of the day and thus affect the release time of the biologically active substance.
The present invention describes how one prepares ~'~t~ 7 crystallised carbohydrate spheres with enclosed biolo-gically active substances. The method is characterised in that the carbohydrate polymer is dissolved in a sol-vent having a high dielectricity constant to a concen-tration lying within the range 0.1-200% (weight/volume).
By high dielectricity content is here meant a solvent or combinations of solvents having a dielectricity con-stant of more than about 35 r Useful such solvents are, inter alia, dimethyl formamide, ethylene glycol, dimethyl sulphoxide, water and formamide, or mixtu,es thereo.
The biologically active substance is added to this so-lution. The resulting mixture of dissolved carbohydrate polymer and biologically active substance is then emul-sified in an emulsion system comprising the said solu-tion and an emulsion medium consisting of a liquid whichis immiscible with said solution and which has the further characteristic of contributing to the formation of drop-lets of the carbohydrate solution in the emulsion medium.
As examples of useful emulsion media mention may be made of vegetable oils, preferably rapeseed or maize oil. Other useful hydrophobic emulsion media include paraffin oils or silicone oils. ~nother type of emulsion medium includes organic solvents in which one or more emulsifiers have been dissolved. Useful such organic solvents include, inter alia, xylene, toluene, ethyl benzene, diethyl benzene, propyl benzene~ ethylene chlo-ride and other similar solvents, as well as mixtures thereof.
The technique of using emulsion media in combina-tion with different emulsifiers in order to obtain va-rying diameters in the preparation of microspheres is well documented in literature and will not be described in detail in the present context.
To emulsify the emulsion, use is made of a soni-cator or high-pressure homogeniser. The resulting emul sion in which the carbohydrate solution is emulsified 2~ 7 in the form of droplets, is stabilised by transferring it to a liquid capable of crystalllsing the carbohydrate polymer, whereby the biologically active substance is enclosed. Useful such liquids are ethanol, methanol or acetone, although the latter is preferred. After crystallisation, the resulting matrix is further washed with acetone, whereupon drying is effected simplest by rotational evaporation or in a warming cupboard.
It is important that the enclosed subs-tances re-tain their biological activity also after release fromthe matrix.
In this respect, the present invention shows that hormonal proteins of the type insulin and interferon, en~ymes such as plasmin and beta-galactosidase as well as monoclonal antibodies retain their biological acti-vity after enclosure and subsequent release from the matrix.
In some cases, it is not possible to enclose sub-stances within the matrix. One then has the possibility of covalently coupling the substance to the matrix, in which case it is important that the technique of covalent coupling does not imply any appreciable de~
gree of cross-linking of the matrix because such cross-linking would completely annihilate the release mecha-nisms upon dissolution of the carbohydrate matrix, ashas previously been discussed.
Such a type of covalent coupling is obtained if use is made of tresyl chloride as the activatin~ sub-stance because this coupling technique does not result in cross-linking of the carbohydrate matrix (Biochem.
Biophys. Res. Comm. (1981) 102, 449-457).
The following Examples are not to be regarded as restrictive, but rather as illustrative of the main features of this invention.
EXA
1 gram of a 50% (weight/volume) aqueous solution of dextran, having a molecular weight of ~0,000, was 2 ~ 7 mixed with lO0 ul of an ovalbumin solution containing lOQ mg of ovalbumin/ml of water S ~1 of 125-I-labeled ovalbumin had previously been added to the latter solu-tion.
The dextran-ovalbumin solution was suspended in 25 ml of vegetable oil in a 100 ml ~eaker and cooled to ~4C The mixture was emulsified by ultrasonics for 1 minute~ whereupon the emulsion was poured into 200 ml of acetone in which the emulsifier Tween 80 had been dissolved to a concentration of 0.1~ ~weight~volume)~
While the emulsion was being carefully poured into the acetone solution~ 1t was stirred at about 1,000 rpm.
The resulting dextran spheres which had been stabilised by crystallisation and contained ovalbumin enclosed therein were washed 4 times more with the said acetone solution, whereupon they were air dried.
Normally, such a test gives a recovery of about 250 mg of spheres in which 60-70% of ovalbumin added have been enclosed in the carbohydrate matrix. The size of the spheres prepared by this technique lies between 0.01 and 10 um. By varying the composition of the emul-sion medium~ spheres having a diameter of up to 1 mm are readlly produced.
EXA~I
The same as in Example 1, but with the difference that the dextran was crystallised in methanol or etha-nol, instead of acetone~
EX~
The same as in Example 1, but with the difference that 0.2 g of starch was dissolved in water, and that the starch solution was emulsified in toluene contain-ing the emulsifier Gafac PE-S10 (5% weight/volume), instead o~ dextran and oil.

The same as in Example 1, but with the difference that 1 g of 0.2% agarose or carageenan at a tempera-ture of +~0C was used instead of dextran~
* a trademark ~ ~,fi ~t ~ 7 EXAMPLE S
The same as in Example l, but with the difference that l g alyinate was used instead of dextran and emul-sified by means of a 0,1~ admixture of the emulsifier Gafac RM-41Q into the oil instead of pure oil, .____ The same as in Exampie l, but with the difference that l g of l~ chitosan dissolved at pH 5 was used in-stead of dextran.

The same as in Example l, but with the difference that 3 g of ceLlulose wer~ di.ssolved in 150 g of N~-ethyl pyridine chloride and 75 g of dimethyl formamide, l g of this solution being used instead of dextran, ~XAMPLE 8 The same as in Example l, but wi-th the difference that a ~00~ (weight/volume) aqueous solution of sucrose was used instead of dextran, The same as in Example l, but with thc difference that a 30% (weight/volume) aqueous solution of glycogen was used instead of dextran, EX~MPLE 10 The same as in Example l, but with the difference that ovalbumin was not used, and that the per se bio~
logically active carbohydrate polymer heparin was dis-solved to a concentration of 50~ (weight/volume) in water and used instead of dextran for the production of crystallised spheres, EXAMPLE ll 100 mg of dried spheres accordi.ng to Example l were slurried in lO ml of PBS at p~l 7,2. At different times it was investigated how much of the enclosed oval~
bumin had been released from the spheres by filtrating the mixture through a filter having a molecular "cut-off" of 100,000.
With the above-mentioned spheres, a half-life of released ovalbumin of about 12 days is obtained, ~2'~

By varying the concentration or the mvlecular weight of the dextran polymer/ the half-lives can be varied in simple manner~ By increasing the concentration or using a higher molecular weight of the polymer, a lon~er half-life is obtained.

As in Example 1, it is possible to use substituted dextrans in the production of the spheres. To investigate the documented adjuvant effect of DEAE and SO4-subs-tituted dextrans, these were mixed with unsubstituted dextran at the ratios 0%, 33%, 66% and 100%. Such spheres with enclosed ovalbumin were then injected subcutaneously in mice, whereupon IgG and IgM antibodies a~ainst oval-bumin were determined by means of a so-called micro-titer-ELISA-method.
It proved that the immunological response was di-rectly correlated to the amount of adjuvant, and that the antibody titer of the mice that were given ovalbumin in unsubstituted dextran spheres was slgnificantly higher as compared with the mice injected with the ovalbumin merely dissolved in water.

To investigate whether a biologically active pro-tein retains its activity, insulin was enclosed in dextran spheres made from a 20~ (weight/volume) dextran solution.
The biological activity was then evaluated in that the insulin released from the spheres was shown to retain its capacity for in vitro stimulation of fat cells to produce fatty acids. At a release test conducted on enclosed insulin, tested in the same manner as in Example 2, but with 125-I insulin, there was obtained from spheres prepared from a 35% solution o~ dextran having a molecular weight of 500,000, a half-life of about 6 days.
EXAMPLE 1~
As in Example 10, interferon was enclosed in dextran spheres, whereupon the antiviral efect of the interferon was determined in a so-called plaque-assay.

~ ~ 2 ~ t 7 About 35~ of the antiviral effect of the interferon supplied could be detected.
EXAMPLE 1~
_._ As in Example 10, the enzyme plasmin was enclosed in dextran spheres~ whereupon its enzymatic activlty was determined by means of the substrate ~-D-Val-~eu-Lys-pNA after release from the spheres. The dried spheres contained about 1% of plasm.in with a recovery of the biological activity of about 75%, _.
As in Example 10, the enzyme beta-galactosidase was enclosed in dextran spheres, whereupon the enzyma-tic activity was determined after release from the ma-trix by means of the substrate ONPG.
The dried spheres contained about 5% of the enzyme with a recovery of biological activity of 70~O

As in Example 10, a monoclonal anti~ody directed against the protein PHA was enclosed in the spheres, whereupon its binding activity was determined in a so-called sandwich~ELISA after release from the matrix.
Recovery of the biological activity was 65%.
EXA*IPLE 18 _ As in Example 10, 125-I labeled biosynthetic growth 2S hormone was enclosed~ although in this instance an 80%
solution of a dextrin (Awedex W90, Stadex AB, Malmo) was employed.
Recovery of radioactivity was 100%.

A 200% (weight/volume) solution of maltose was prepared~ whereupon the pharmaceuticals metotrexate and vincristine (3H-labeled), respectively, were en-closed in spheres by the same technique as in Example 1.
Recovery of metotrexate was 82% and for vincristine 22%.

* a t.rademark ~l 2~ 7 EXl~MPLE 20 As in Example 19, metotrexate and vincristine were enclosed in the carbohydrates dextran Tl and glucose.
Recovery for metotrexate was for both carbohydrates 65%, an~ for vincristine a rec,overy of 40~ was obtained.

As in Example 1, spheres were produced, but with the difference that 1 g of 30% (weight/volume) dextran T500 was used as carbohydrate, and that 250 ul of al-bumin ~100 mg/ml) were added for enclosure, In this manner, 65% of added protein were enclosed,which corresponds to 40% of the dry weight of the spheres.

In present day treatment of bee allergies on human beings, successively higher doses of an aqueous solution of the allergen are injected.
To test whether the immunological response is changed if a depot preparation of bee allergens is used, bee allergen was enclosed in dextran spheres according to Example 1 and injected subcutaneously in mice,whereupon the immunological response with respect to IgG was deter-mincd at different times. For comparison, bee allergen and pure water and bee allergen suspended in Freund's complete adjuvant were injected. The antibody content in the group that had been c3iven bee allergen dissolved in water, showed a slight rise after 1 week and then receded to undetectable contents. On comparing the depot preparation to Freund's adjuvant, it was found that the antibody content rose more quickly when the bee allergens were enclosed in the depot matrix. After 10 weeks, the IgG contents in serum were still rising for both groups, which shows that the depot prepara-tion is highly efficient when it is clesired to obtain high contents of antibodies.

1 gram of aqueous solution of dextran having a molecular weight of 10,000 was mixed with 50 ~1 of the >L~ ~"

low~molecular pharmaceutical metotrexate. The total amount added was 5 mg which, besides, was 3-H-labeled.
The mixture was processed according to Example 1 and the result was that 92% of metrotrexate added were en-S closed in the dried spheres.

_._ To investigate the release from a matrix degradable by enzymes, the following test was carried out.
100 mg of spheres produced from starch dissolved in formamide accordiny to Example 1, were activate~
with tresyl chloride, whereupon 125-I myoglobin was coupled to the spheres. After careful washing to re-move adsorbed myoglobin, alpha-amylase was added in a concentration that was 100 times higher than in normal human serum. Within two hours, about 25~ of coupled myoglobin had been released from the matrix. By further increasing the amount of alpha amylase 10 times during the next 24 hours, a total release of about 45~ of coupl-ed myoglobin was obtained. During the last 24 hours, the alpha amylase concentration in the test was about20,000 times higher than in normal human serum~

Claims (13)

The embodiments of the invention in which an inclusive right or privilege is claimed are defined as follows:

1. A composition useful for the prolonged release of a biologically-active substance comprising a sphere or particle including a non-covalently cross-linked crystalline polymeric carbohydrate matrix, said matrix incorporating 0.001-50% by weight of an absorbed or covalently bonded biologically-active substance.

2. The composition of claim 1 wherein said sphere or particle has an average diameter within the range of 0.01-1,000 um.

3. The composition of claim 1 wherein said sphere or particle has an average diameter within the range of 0.01-1.0 um.

4. The composition of claim 1 wherein said carbohydrate is selected from the group consisting of dextran, starch and the derivatives thereof.

5. The composition of claim 1 wherein the carbohydrate is selected from the group consisting of alginate, chitosan, agarose, carrageenan, cellulose, glycogen, pullullan and the derivatives thereof.

6. The composition of claim 1 wherein said biologically-active substance is an antigen.

7. The composition of claim 1 wherein the biologically-active substance is insulin.

8. The composition of claim 1 wherein the biologically-active substance is an allergen.

9. The composition of claim 1 wherein the biologically-active substance is a growth hormone.

10. A process for producing a composition useful for the prolonged release of a biologically-active substance, comprising:
(a) forming a solution of a polymeric carbohydrate and a biologically-active substance in one or more hydrophillic solvents;

(b) emulsifying the mixture of the carbohydrate and the biologically-active substance in a liquid hydrophobic medium to form spherical droplets; and (c) introducing the emulsion into a crystallizing medium to form spheres having a non-covalently cross-linked crystalline polymeric carbohydrate matrix, said matrix incorporating 0.001-50% by weight of the biologically-active substance.

11. The process of claim 10 wherein the emulsification is conducted at 4-40°C so that the activity of the biologically-active substance is preserved.

12. The process of claim 10 wherein the droplets are crystallized by introducing them into a crystallizing medium comprising acetone, ethanol or methanol.

13. The composition useful for the prolonged release of a biologically-active substance comprising a sphere or particle including a non-covalently cross-linked crystalline polymeric carbohydrate matrix, said matrix incorporating 0.001-50% by weight of an absorbed or covalently bonded biologically-active substance, said composition being formed by a process comprising the steps of:
(a) forming a solution of a polymeric carbohydrate and a biologically-active substance in one or more hydrophillic solvents;
(b) emulsifying the mixture of the carbohydrate and the biologically-active substance in a liquid hydrophobic medium to form spherical droplets: and (c) introducing the emulsion into a crystallizing medium to form spheres having a non-covalently cross-linked crystalline polymeric carbohydrate matrix, said matrix incorporating 0.001-50% by weight of the biologically-active substance.