AU6129080A - Method and system for the controlled release of biologically active substances to a body fluid - Google Patents

Description

Description

Method and System for the Controlled Release of Biologically Active

Substances to a Body Fluid

Technical Field The present invention relates to a chemical method for the con¬ trolled release and delivery of biologically active substances to body fluids.

Background Art

The use of systems for the slow delivery of medications is known in the art. These systems have been suggested for a wide range of diseases where accurate control of the concentration of released agent is not necessarily critical.

Most "controlled-release" systems known to the prior art how¬ ever (see e.g. Sears, USP 4,145,410, who shows drug release from cap- sules which are enzy atically labile) are incapable of releasing medication at intervals and concentrations which are in direct pro¬ portion to the amount of a metabolite present in the human body. The delivery or release of drug in these prior art systems is thus not literally "controlled", but is simply a slow release, independent of external or internal factors.

For example, although injectable insulin has been available for the treatment of diabetes mellitus for over fifty years, it is ap¬ parent that the simple replacement of the hormone is not sufficient to prevent the pathological sequelae associated with this disease. The development of these sequelae is believed to reflect an inabili¬ ty to provide exogenous insulin proportional to varying blood glu¬ cose concentrations experienced by the patient. To solve this pro¬ blem several biological and bioengineering approaches to develop a more physiological insulin delivery system have been suggested. Metas et al (Diabetes 25, 785 (1976)) describe the transplant¬ ation into a diabetic animal, of pancreatic tissue from a healthy an¬ imal. The transplanted tissue provides a ready source of insulin whose release is controlled primarily by the level of glucose in the blood. This approach has only succeeded with highly inbred strains of animals, however, since tissue rejection otherwise be- comes a limiting factor. Obtaining sufficient quantities of accept¬ ably pure islet tissue for future clinical applications also poses significant problems.

Chick (Science, 187, 847 (1975)) avoids the problem of tissue rejection by culturing pancreatic islets on the outside of semiper- eable tube-shaped membranes, bundles of which are enclosed by a cy¬ lindrical shell. Blood flows through the inner tubes when the sys¬ tem is interposed into the circulation of an animal providing nutri¬ ents to the cells. Glucose and insulin pass across the membrane, while larger immunologically active substances remain inside. The use of cultured tissue however implies that the system is only viable for short periods of time. Mechanical problems, such as clogging of the inner tubes by blood also prevent its extensive use.

Soeldner et al (NIH publication No. 76-854 (1976), pp. 267)de- scribe a glucose, sensitive electrode which utilizes immobilized glu¬ cose oxidase to produce electric current inversely proportional to the blood glucose level. Glucose oxidase is a very unstable enzyme in this system, and thus limits the use of such an electrode.

Colton et al (Transplantation and Clinical Immunology, X, 165- 173, Amsterdam, 1978) discuss a system which would eventually in¬ clude an electronic glucose sensor, an insulin reservoir and pump, and electronics con .ecting the two. If the sensor finds glucose levels rising, an appropriate amount of insulin would be pumped into the bloodstream - automatically. This system utilizes a platinum electrode catalyst for oxidizing glucose in the sensor. This results in less specific electrodes which show interference with other meta¬ bolites and so cannot be used with reliabil ty.

All of these prior art systems take into account the critical relationship between the blood glucose levels and insulin released, and thus attempt to provide the necessary feedback response which would allow the release of insulin to be controlled directly by the amount of blood sugar present at any particular time. However, the systems suffer from a general lack of reproducibility, long-term effectiveness and reliability. None of them have been put into ex- tensive use because of this. A reliable feedback system which does not depend on the use of electrodes or transplanted tissue has not

OMP yet been developed. The use of such a simple internally controlled system would greatly expand the use of control!ed-release medications. It would be particularly useful in the feedback controlled release of other hormones such as so atostatin, and of modified pharmacolog- ical compounds such as enzyme inhibitors and hypoglycemic agents.

Disclosure of Invention

It is therefore an object of the invention to provide a safe and reliable feedback-controlled release drug delivery system. Another object of the invention is to provide a drug release system which is internally controlled. Still another object of the invention is to provide a controlled drug release system for hormone deficiency diseases.

A further object of the invention is to provide a method for periodically and control1ably delivering drugs, especially hormones, to human biological fluids.

These and other objects of the invention have been attained by providing a process for feedback controlled delivery of a biological¬ ly active substance to an animal body fluid which comprises contact¬ ing said fluid with a reversible complex of a conjugate (1) and a binding macromolecule (2), wherein said conjugate (1) comprises a biologically active portion which is intended to be proportionately released into a body fluid stream in response to varying concentra¬ tion levels of a component of said body fluid stream, and a complex- ing substrate portion which conjugates with said biologically active portion and which is characterized by affinity to said binding macro¬ molecule (2) competitively or non-competitively with said variable component of said body fluid; thereby causing the component^"present in said body fluid to complex to said binding macromolecule and to release said conjugate (1) therefrom into said fluid. The objects of the invention have also been attained by provid¬ ing a process for the controlled delivery of a biologically active hypoglycemic substance to a glucose containing human body fluid which comprises contacting said fluid with a reversible complex of (1) a biologically active hypoglycemic substance which is a conjugate be- tween a carbohydrate and a hypoglycemic agent, and (2) a binding macromolecule having affinity for glucose and for the carbohydrate portion of said conjugate (1); thereby causing the glucose present in said fluid to complex to said binding macromolecule and to release said conjugate into said fluid. Other objects of the invention have also been attained by pro¬ viding: a controlled release medication system which comprises a re¬ versible complex of (1) a biologically active hypoglycemic substance which is a conjugate between a carbohydrate and a hypoglycemic agent and (2) a binding macromolecule having affinity for glucose and for the carbohydrate portion of said conjugate.

Brief Description of Drawings

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying draw¬ ings, wherein:

Figure 1 is the elution profile from a column of immobilized concanavalin A, of insulin (A) and maltose-insulin conjugate (B) in the presence of glucose as eluant (arrows). Figure 2 is the elution profile from a column of immobilized concanavalin A of a maltose-insulin in the presence of pulses of in¬ creasing glucose concentration.

Best Mode for Carrying Out the Invention

The drug delivery system of the present invention comprises a reversible non-covalent complex (B:A-C) between a binding macromole¬ cule (B) and a conjugate of a biologically active substance (A) with a complexing substance (C). The conjugate (A-C) contains a biologic¬ ally active portion (A) and a complexing portion (C). Equations (1) and (2) show a first embodiment for the operation of the system. This embodiment will be called directly competitive in analogy to the well-known kinetic system of competitive inhibition for enzymes. (Mahler and Cordes, Biological Chemistry, 2d Edition (1971) pp. 295- 297.)

OMPI

Complex B:A-C free B free conjugate

The complex B:A-C is initially in reversible chemical equilibrium with the separated components B and A-C (eq. 1). The binding site of B can only recognize molecules of shape C, either when these are free in solution or when they are coupled to another component such as in conjugate C-A. The degree of association of B with conjugate A-C is ideally very high, so that when no or little C is present in¬ dependently, the system lies mostly on the B:C-A side of the equili¬ brium (1), and there are very few free, unassociated B molecules present in solution (eq. 1). However, when the concentration levels of C increase in the system, the molecules of C start competing for the available binding sites on B and the equilibrium represented by equation (2) becomes more important. The few unassociated bind¬ ing molecules B (which are always present) enter into complexation with C and because of the law of mass action, this event causes other B:A-C complexes to become dissociated. In this fashion, the mole¬ cules of conjugate A-C are released into the medium when the concen¬ tration of free C increases in the medium. Through the intermediacy of binding molecule B, the free concentration of C regulates and controls the appearance of free conjugate A-C in the medium. It is unnecessary that free C and the complexing portion of conjugate A-C corresponding to C, be molecularly exactly identical. It is only necessary that both show complexing affinity for binding molecule B, that they be capable of forming reversible complexes therewith, and that they displace each other from B as a function of concentra¬ tion, according to the equilibria represented by equations (1) and (2). A system where free C and conjugated C are not identical can therefore also be used in the present invention and is represented by the following equations (3) and (4):

Conjugate A-C in equation (3) is recognized by B although complexing portion C is, in overall structure, different than C. The recogni¬ tion sites of both C and C molecules are, however, exactly alike. C and C bind at the same site and displace each other from the site. A second embodiment of the system which is useful in the present invention is one wherein the displacement of conjugate A-C (or A-C), or more precisely, the blocking of the available site on B for its complexation therewith occurs non-competitively. In this embodi¬ ment, B has two sites, one of which complexes which conjugate C-A or C-A, and the other one with free C. The binding sites are structurally different but they interact by ^"negative feedback. When C binds at its own site, this binding causes the second site, which is the site for C-A or C-A, to change structurally so that its affi¬ nity for the conjugate is decreased. Such an embodiment is represent- ed by equation (5):

_OMPI

In the absence of fluid component C, the affinity of B for conjugate A-C is high. The A-C conjugate is therefore co plexed with B. In the presence of C however, the affinity of B for A-C is much lower, and A-C is released into the medium. In this second embodiment, the concentration levels of free C directly control the release of conjugate A-C into the body fluid. This manner of operation of the system is called non-competitive in analogy to the type of enzyme inhibition called non-competitive inhibition (Mahler and Cordes, Bio¬ logical Chemistry, 2nd Edition, pp. 295-298 (1971)). Binding macromolecule B can by any of a number of well-known macromolecular entities which exhibit molecular recognition and re¬ versible binding of other micro- or macromolecules. B is preferably a natural binding protein, such as an antibody, an enzyme, a regula¬ tory protein, a drug receptor site or the like. It is also possible to use synthetically modified binding molecules, such as chemically modified proteins. Such modified proteins sometimes have increased or decreased affinities for their substrates when compared to their natural unmodified counterparts. By "macromoe cule" is also meant a conjugate of a smaller molecule which shows binding characteris- tics, with a larger polymeric molecule which, by itself does not. The polymeric molecule would therefore serve as support for the binding smaller molecule and the whole arrangement would therefore be a binding macromolecule. By choosing the appropriate binding macro¬ molecule it becomes possible to control the nature of the released therapeutic drug and its release concentrations. Among examples of binding proteins B, antibodies and lectins are the most preferred. Antibodies can be prepared and purified from animals in standard fashion (Eisen, H.N. "Immunology", Harper & Row, 1974). Antibodies have the advantage of being induceable in an animal by challenge with an appropriate anti genie agent. Since this agent can be chosen from any chemical family, e.g., amino acids, carbohydrates, their respect¬ ive polymeric derivatives, or the like, the resulting antibodies may have a wide range of binding specificity and affinity. Lectins are also particularly useful in this invention. Lectins are carbohy¬ drate-binding proteins of plants and animals with a wide variety of specificities for carbohydrates, (Lis et al, Ann. Review of Biochem¬ istry, 42, 541 (1973); I.J. Goldstein and C. E. Hayes, Adv. in Carbo¬ hydrate Chemistry and Biochemistry, Vol. 35, R.S. Tipson and D. Hor- ton, eds. (Academic Press, New York, 1978, pp. 128-341), herein in¬ corporated by reference). For example, concanavalin A, a Jack Bean lectin, has specificity for α-D annopyranose and α-D glucopyranose; soybean lectins are specific for α and β-D-N-acetylgalactosamine and -D-galactose units and wheat germ lectin is specific for β-D-N-ace- tyl glucosamine.

Preferably, a manno-oligosaccharide containing from 2 to 7 (1, 2) -D-mannopyranosyl residues is used as the carbohydrate.

The molecular complexation reaction, between binding macromole¬ cule B and molecule C, or the C or C portion of conjugate A-C, has to be reversible and non-covalent. This bonding between B and C (or B and A-C) is caused by non-covalent forces such as hydrophobic, ion- ic, hydrogen bonding forces and the like. These interactions have been well studied in the art and their effects on molecular affinity and recognition are described, for example in. Korol kovas et al , "Essentials of Medicinal Chemistry", pp. '44-81, Wiley, 1976, which is herein incorporated by reference. Such reversible interactions are exemplified by the interaction between an enzyme and its sub¬ strate or a competitive inhibitor thereof; and antibody with its an¬ tigen, or a drug receptor site and its drug.

The functional relation between component C present in the body fluid and the biologically active agent A is very important. The biologically active conjugate A-C (or A-C) is released in propor¬ tionate amounts to the levels of component C present in the body fluid. Agent A therefore can be a hormone-type substance which directly regulates the levels of C in the fluid, by for example, caus¬ ing a decrease of the levels of C. Agent A, however need not be directly functionally related to component C but only indirectly. In such case, increasing levels of C in the fluid would release con¬ jugate A-C (or A-C) which then, via its biologically active portion A, will act on a biological system unrelated or only indirectly re¬ lated to component C. The system will then release A-C into the fluid as a function of the concentration of any metabolite being "monitored". In a preferred embodiment, however, A is a hormone or hormone-like substance and C is a metabolite participating in a- feed¬ back regulatory loop with A.

Hormones are substances secreted by endocrine glands or in tis¬ sues and released into the bloodstream, ^"by which they are transported to other tissues where, by selectively binding to specific receptors, they exert their effects. Hormones possess a wide range of chemical structures: peptides, steroids, derivatives of amino acids and der¬ ivatives of fatty acids. Hormones are glandular or tissue-originat¬ ed. Among the common glandular hormones useful with the system of the present invention are the pituitary and hypothala ic polypeptide hormones such as oxytocin, arginine-vasopressin, lysin-vasopressin, adrenocorticotropin (ACTH), follicle-stimulating hormone (FSH); soma- totropin (GH), luteinizing hormone (LH), melanocyte-stimulating hor¬ mone (MSH), prolactin, thyroid-stimulating hormone (TSH); the para- thyroid hormone; calcitonin; the hormones of the pancreas such as insulin; glucagon and somatostatin, the adrenal cortical hormones such as mineralocorticoids as aldosterone and desoxycorticosterone, glucocorticoids as cortisone and hydrocortisone, sexual hormones as androgens, anabolic steroids, estrogens, progestagens. Among the common tissue hormones useful in the method of the present invention are, for example, hista ine, norepinephrine, serotonin_*, prostaglan- dins, prostacyclins, and thromboxanes. Any of these hormones or their biologically active analogues or derivatives can be used in the preparation of the A-C conjugate of the present invention. The coupling molecule C is the substance whose varying levels will proportionately release active conjugate A-C (or A-C). In a prefererd embodiment, C is a fluid component whose levels are reg- ualted by A-C. In such case, C has to be in functinal relation to

— 91z.lL to molecule A, since as explained above, its levels are regulated by A. Most preferably, C is chosen so that a feedback loop exists be¬ tween C and A; i.e., when the levels of C increase in the blood, the levels of A increase under normal circumstances, thus returning the level of C, and in turn A, to their equilibrium positions.

It is crucial that after the chemical coupling of C to A, the complexing portion of the conjugate A-C corresponding to C, preserve the affinity of the original C to the binding macromolecule B and that it be displaced therefrom by increasing concentrations of free C. Furthermore, it is useful to choose or chemically modify C in such manner that it will be easily chemically coupled to A, to yield conjugate A-C. Examples of coupling molecules C (given with their regulatory active substances) are: glucose (regulated by insulin and also by other hypoglycemic agents such as sulfonylureas and bi- guanides); calcium (regulated by calcitonin); cortisone(regulated by ACTH); progesterone (regulated by LH); testosterone (regulated by LH); thyroid hormones (regulated by TSH); prolactin (regulated by pro!actin-release inhibiting hormone); growth hormone (regulated by growth hormone releasing-inhibiting hormone); electrolytes (regulat- ed by mineralocorticoids).

The coupling between A and C can be carried out directly by us¬ ing appropriate functional groups on both molecules or by using a bridging or spacer group between them. Nucleophilic groups on one component, such as free -OH or -NH₂ or -SH can be reacted with elec- trophilic groups on the other component, such as esters, ketones, al¬ dehydes and the like, to give covalent adducts. The coupling be¬ tween a peptide containing free amino groups and a carbohydrate con¬ taining aldehyde groups can be carried out to yield an imine (^C=N) which, in the presence of a reducing agent such as NaBH^, KBH^, Na CNBH₃ will give primary or secondary amines. This type of reaction is well exemplified in the prior art, as demonstrated by Gray, G.R., Archives of Biochemistry and Biophysics, 163, 426 (1974) or by Wil¬ son, G., J. of Biol. Chemistry 253_, 2070 (1978), both of which are herein incorporated by reference. Another possible coupling react- ion is that between free amines on proteins and ester functions on proteins or carbohydrates, to give amides. In the latter case of course, the naturally occurring free carboxylic acids of the protein or carbohydrate have to be chemically esterified first, as by react¬ ion with a diazoalkane such as diazomethane.

The final bond between A and C has to be stable and irreversible and is, most preferably, covalent. The properties of the conjugate A-C or A-C are such that it should retain both the reversible affinity and binding characterist¬ ics of C and the biological activity of A. Its properties are there¬ fore a composite of those of both its constituents. The choice of appropriate coupling partners and coupling methods are critical. Chemical attachment of the type required by the present invention might lead to a great or even total loss of binding or of regulatory activity, or both. It is crucial that none of these activities be lost after coupling.

According to the process of the present invention the B:A-C (or B:A-C) complex is brought into intimate contact with the physio¬ logical human fluid to be treated. The controlled release of active conjugate A-C (or A-C) begins when the amount of free C in the fluid contacting the complexes reach a given critical high level. Virtu¬ ally no active conjugate is released when the levels of free C fall below the critical level. It is also possible to simultaneously con¬ tact the body fluid with complexes between B and active conjugates A-C, A-C" and A-C" wherein these conjugates have different affinity towards B. In this way, increasing levels of C in the fluid would release a steadily increasing amount of active conjugate. Still another possibility is to contact the body fluid with complexes be¬ tween B and A-C, A'-C and A"-C, where A, A' and A" represent biolo¬ gically active portions of the conjugate exhibiting different biolo¬ gical activities. In this mode, increasing levels of fluid compon¬ ent C will release two or more different substances which exhibit different biological effects.

By appropriate choice of B, A and C and of active analogues thereof, the possibility exists of treating a wide variety of dis¬ eases with individualized drug-delivery profiles.

The system of the present invention is ideally suited for use in externally or internally implanted devices, such as insulin pumps or the like. The complex B:A-C may be present in a serniperme- able or porous tube or fiber, which is brought into contact with hu¬ man fluid such as plasma. The pores of the tube or device are chos¬ en so that the complex and the binding molecule B cannot pass there¬ through and are "trapped" inside. The pores however are permeable to conjugate A-C and free component C. When the concentration of component C in the plasma reaches critical levels, conjugate A-C (or A-C) is released into the plasma. It passes freely through the pores of the tube or fibers and is assimilated into the body, while the B:C complex remains trapped behind. Exchanging the solution within the tubes periodically by fresh solution of B:A-C complex, simply replenishes the supply of drug. Another embodiment of the in¬ vention is to fix the binding macromolecule B covalently either di¬ rectly, or via a- spacer or bridging group, to the tube itself. The techniques of solid-state immobilization of enzymes and other pro- teins on resins, films, test tubes, glass beads and the like are well known (see e.g., Zaborsky, C. "Immobilized Enzymes" CRC Press, Cleve¬ land, 1973; Axen et al USP 3,645,852; Kraemer et al , USP 4,039,413). In this fashion, "cartridges" of a semiporous, semipermeable film such as cellulose can be prepared which contain covalently bound B in the form of its reversible complex B:A-C. Upon contact with body fluid and subsequent exchange of A-C by C, the cartridge becomes "spent" and can be readily replaced by a fresh one. The spent car¬ tridges can then be recycled by extensive dialysis against solution containing conjugate A-C. In a particularly preferred embodiment, this invention relates to a system for the delivery of active hypoglycemic agents, prefer¬ ably insulin, to the bloodstream of patients with diabetes mellitus. Diabetes mellitus is a hereditary disease characterized by the rela¬ tive or absolute deficiency of insulin. Insulin is a polypeptide hormone made of 2 chains of amino acids, molecular weight 6000. It is synthesized, stored and released from the pancreas primarily in response to blood glucose levels. Insulin carries out a variety of physiological functions such as for example, activation of transport systems for glucose and of certain enzymes involved- in increased glu- cose utilization, glycolysis, glycogenesis and lipogenesis. Absence of insulin thus causes an increase in the blood levels of glucose (hyperglyce ia) . ^•u ^-ⁱ-A

C...PI The system of the present invention wherein A is an active hypo¬ glycemic agent, C is glucose or an actively binding analogue thereof with complexing characteristics similar to those of glucose, and B is a carbohydrate-binding molecule, is readily applicable to the treat- ent of hyperglycemia. In particular, when the conjugate A-C is pre¬ pared from insulin and oligosaccharides such as maltose, and maltose- triose, the resulting conjugate retains hormonal activity. Any of the oligosaccharides described in Lis et al , Ann. Rev. of Biochemis¬ try, 42, 541 (1973), can be used. Furthermore, the oligosaccharide- insulin conjugate binds to a lectin such as concanavalin A and can be displaced therefrom by solutions with increasing glucose content. Various hypoglycemic agent-conjugates, complementary to the major combining sites of the lectins, can be synthesized and the products are stable. Since lectin binding affinity for various saccharides varies more than ten-fold, a mixture of different high- and low-af¬ finity semisynthetic conjugates can be combined to produce clinically desirable elution profiles. A number of active insulin derivatives have been prepared (Ellis, M.S. et al, Diabetologia T : 340, 1975; Tompkins, C.V. and Sonksen, P.H., Clin. Sci . and Mol . Med. 50_: 31, 1976; Darby, S.C. et al , Diabetologia 1_5_: 403, 1978). These deriva¬ tives and/or analogues can of course be used in the process of the present invention. It is also possible to synthesize other glycosy- lated hypoglycemic agents such glycosylated sulfonylureas and biguan- ides ( orolkovas et al , Essentials of Medicinal Chemistry, p. 605 (Wiley, 1976)). Glucose-activated release of these agents is then carried out according to the same system. Another application, is the preparation of glycosylated derivatives of somatostatin. This would provide glucose-controlled inhibition of the excessive gluca- gon secretion which is thought to exacerbate diabetic hyperglycemia. Yet another application of the system, in a mode where agent A is not a hormone involved in the regulation of component C, is for example the release of enzymatic inhibitors in diabetes mellitus. Studies in animals (Winegrad, A.I, et al , In Proceedings of the VII Congress of the International Diabetes Federation, ed.. W.J. Malaisse and J. Pirart, pp. 387-395, Excerpta Medica, Amsterdam), suggest that excessive conversion of glucose to sorbitol by the enzyme aldose reductase may be of etiologic significance in the pathogenesis of several diabetic complications. A variety of inhibitors for aldose reductasehave been prepared (Gabbay, L.H., Adv. Metab. Disorders Suppl. 2. New York, Academic Press, 1973, pp. 417-424; Dvornik, D. et al_: Science j_82_: 1146, 1973; Varma, S.D. et al , Science 188: 1215, 1975; M.J. Peterson et al , Metabolism 28: 456, 1979; Kinoshita, J.H. et al Metabolism 28: 462, 1979, all of which are herein incorporated by reference) with the purpose of decreasing the levels of activity of the enzyme. Any of these inhibitors could be conjugated to a car¬ bohydrate and used in the system of the present invention. When the levels of glucose increase in the blood, inhibitor-conjugates will be released, decreasing the possibility of damage due to sorbitol .

The synthesis of glomerular basement membrane (GBM) has also been reported to increase with increased levels of blood glucose (Spiro, R.G. and Spiro, M.J. Diabetes 20_: 641, 1971; Brownlee M. and Spiro, R.G. Diabetes 28_: 121, 1979). Excessive accumulation of this material is also a cause of damage in diabetes. Conjugating a carbo¬ hydrate to an inhibitor of an enzyme involved in the synthesis of GBM (Maragoudakis, M. et al , J. Phar . Exp. Ther. 204: 377, 1978, herein incorporated by reference) will then yield a substance capable of use in the process and system of the present invention.

Still another application of the present inveniton is in the * simultaneous release of a combination of hypoglycemic agents. Alburn et al (USP 3,912,807) have shown that the combination of somatostatin and insulin is very effective in the treatment of diabetes mellitus. Dietze et al (USP 4,150,121) have demonstrated that kinin-insulin combinations are useful in diabetes, and Laborit (USP 4,035,486) has shown that guanosine increases glucose utilization in diabetic ani¬ mals treated with insulin or acetylcholine. The system of the pre- sent invention can thus be simply adapted to the glucose-dependent release of drug combinations. For example, it is possible to contact the body fluid with two complexes: a first one comprising a lectin and a conjugate of carbohydrate and insulin, and a second one comprising a lectin and a conjugate of carbohydrate and guanosine. In this fashion raising glucose levels will release both guanosine and insu¬ lin into the body fluid.

C.. Having now generally described this invention, a further under¬ standing can be obtained by reference to a specific example which is provided herein for purposes of illustration only and is not intended to be limiting unless otherwise specified. I. Preparation of a Maltose-Insulin Conjugate

Maltose was incubated with porcine insulin (Lilly) at a Molar ratio of 650:1 for 5 days at 37°C in O.IM_^ sodium phosphate buffer pH 8.0. The incubation was carried out in the presence and absence of 0.251M sodium cyanoborohydride. Unreacted maltose was removed by gel filtration on Bio-gel P-G and the conjugated insulin was separated by affinity chroma tography on a Concanavalin A Sepharose 4B column. An¬ alysis of the product for carbohydrate (phenol sulfuric acid method, Dubois, M. et al, Analyt. Chem., 28, 350 (1956)) and for protein (Lowry, O.H. et al , J. Biol. Chem, 193, 265 (1951)) showed that af- ter a 5 day incubation, the derivative contained 1.76 moles of coval¬ ently bound carbohydrate per mole of insulin monomer. Since substi¬ tution of all three primary amino groups has been reported to result in the loss of hormone activity (Ellis, M.J. et al , Diabetologia, _15_, 403 (1978)), a 5 day incubation time was chosen to maximize yield while minimizing loss of biological activity.

The insulin conjugate was stored at 4°C and was stable for at least seven weeks regardless of whether or not reducing agent had been added. II. Bioactivtty of Maltose-Insulin Conjugate The conjugate prepared in I was tested using the blood-glucose depression assay modified from the U.S. Pharmoacopeia (Vol. XVIII, 883-884 (1967)). Preparations varied from 78 to 95% of unmodified insulin bioactivity. The results are given in Table 1.

Table 1 BIOACTIVITY OF MALTOSE-INSULIN DERIVATIVE

ANIMAL BLOOD GLUCOSE DEPRESSION*

Maltose-insulin derivative Control insulin p

A 61 mg% . 75 mg%

B 64 mg% 70 mg%

C 66 mg 79 mg%

D 63 mg% 79 mg%

E 69 mg% 64 mg% Table 1 (continued) BIOACTIVITY OF MALTOSE-INSULIN DERIVATIVE

ANIMAL BLOOD-GLUCOSE DEPRESSION*

Maltose-insulin derivative Control insulin P

F 74 mg% 73 mq%

Mean + S.E.M. 66.17 + 1.92 73.33 + 2.35 <0.1

*After an overnight fast, each animal received 0.1 mg protein/100 gm body weight by subcutaneous injection. Each of the animals served as its own control, receiving the maltose-insulin derivative on day 1, and control insulin on day 2. Blood glucose depression was determin¬ ed 60 minutes after injection using a Beckman Glucose Analyzer 2. III. Binding of Maltose Insulin to Concanavalin A

Figure 1 shows the elution profile obtained from 20 mg of un¬ modified insulin (A) and maltose-insulin (B) applied to columns (24.0 X 1.5 cm I.D.) of immobilized Concanavalin A. Initial buffer was 1 mM MgCl₂, 1 mM CaCl₂, 50 mM NaCl , 25 mM sodium phosphate, pH 7.4. At the point indicated by the arrow, 0.2 M glucose in the col¬ umn buffer was begun. Fractions (2.0 ml) were collected at a flow rate of 10-15 ml/h. Unmodified insulin did not bind to Concanavalin A. When this material was applied to the lectin, all of the protein was recovered in the buffer wash, and none was eluted by the addition of glucose. In contrast, all of the maltose-insulin derivative was bound to Concanavalin A. None was eluted by the buffer wash, and all of the maltose-insulin derivative could be displaced from Con¬ canavalin A binding sites by a 1,000:1 molar excess of glucose. Figure 2 shows the elution profile obtained from 20 mg maltose- insulin derivative applied to a column (12.0 X 1.5 cm I.D.) of immo¬ bilized Concanavalin A. Initial buffer was 1 mM MgCl₂, 1 mM CaCl₂, 50 mM NaCl, 25 mM sodium phosphate, pH 7.4. Displacement of hormone was accomplished using 1.0 ml pulses of column buffer containing Varying amounts of glucose. Glucose content is indicated over the appropriate arrows. Fractions (1.7 ml) were collected at a flow rate of 10-15 ml/h. Glucose-pulse experiments with the lectin- bound maltose-insulin derivative demonstrate that hormone release is a function of the quantity of glucose present.

OHPI IPO Having now fully described this invention, it will be apparent to one of ordinary skill in the art that many changes and modifica¬ tions can be made thereto without departing from the spirit or scope of the invention set forth herein.

Claims (36)

Claims

1. A process for controlled delivery of a biologically active substance to an animal body fluid which comprises contacting said fluid with a reversible complex of a conjugate (1) and a binding macromolecule (2), wherein said conjugate (1) com¬ prises a biologically active portion which is intended to be propor¬ tionately released into a body fluid stream in response to varying amounts of a component of said body fluid stream, and a complexing substrate portion which conjugates with said biologically active por¬ tion and which is characterized by affinity to said binding macro¬ molecule (2), competitively or non-competitively with said variable component of said body fluid; thereby causing the component present in said body fluid to complex to said binding macromolecule and thus releasing said conjugate (1) therefrom into said fluid.

2. The process of Claim 1, wherein the biologically active por¬ tion of said conjugate (1) is selected from the group consisting of substances which physiologically regulate the concentration levels of said component in said body fluid.

3. The process of Claim 2, wherein the biologically active por¬ tion of said conjugate (1) is a hormone.

4. The process of Claim 1, wherein the complexing substrate portion of said conjugate (1) contains an analogue of said body fluid component wherein said analogue has affinity to said binding macro¬ molecule.

5. The process of Claim 1, wherein the biologically active por¬ tion and the complexing portion of said conjugate (1) are covalently bonded to each other.

6. The process of Claim 1, wherein said binding macromolecule (2) is a protein.

O PI

7. The process of Claim 1, wherein said binding macromolecule is a conjugate of a smaller molecule and a polymeric carrier.

8. The process of Claim 1, wherein the biologically active por¬ tion of said conjugate (1) is an enzyme inhibitor.

9. The process of Claim 1, wherein said complex comprises two or more conjugates (1) of varying affinity towards said binding macro¬ molecule (2).

10. The process of Claim 1, wherein said body fluid is blood.

11. The process of Claim 1, wherein said body fluid is contact- ed with said complex in a dialysis tube containing said complex.

12. The process of Claim 11, wherein said binding macromolecule (2) is immobilized in said dialysis tube.

13. The process of any of Claims 11 or 12, wherein said dialy¬ sis tube is present in a device implanted externally or internally to the human body.

14. A process for the controlled delivery of a biologically ac¬ tive hypoglycemic agent to a glucose containing human body fluid which comprises contacting said fluid with a reversible complex of (1) a biologically active hypoglycemic compound and (2) a binding macromolecule having affinity for glucose and for the carbohydrate portion of said conjugate (1); thereby causing the glucose present in said fluid to complex to said binding macromolecule and to release said conjugate into said fluid.

15. The process of Claim 14, wherein said binding macromolecule is a protein.

16. The process of Claim 15, wherein said protein is a lectin.

17. The process of Claim 16, wherein said lectin is Concanavalin

A.

18. The process of Claim 14, wherein said carbohydrate is mal¬ tose.

19. The process of Claim 14, wherein said hypoglycemic agent is insulin.

20. The process of Claim 14, wherein said reversible complex comprises at least two conjugates of different affinity towards bind¬ ing macromolecule (2).

21. The process of Claim 14, wherein said reversible complex ^* comprises at least two conjugates with different biologically active portions.

22. The process of Claim 21, wherein said two different biologi¬ cally active portions are guanosine and insulin.

23. The process of Claim 14, wherein said carbohydrate is a an- nooligosaccharide containing from 2 to 7 { 1 ~~?2) α-D-mannopyranosyl residues.

24. The process of Claim 14, wherein said hypoglycemic agent is a hypoglycemically active sulfonylurea.

25. A controlled release medication system which comprises a reversible complex of (1) a biologically active hypoglycemic substance which is a conjugate between a carbohydrate and a hypogly¬ cemic compound and (2) a binding macromolecule having affinity for glucose and for the carbohydrate portion of said conjugate.

26. The medication system of Claim 25, wherein said binding macromolecule is a protein.

27. The medication system of Claim 26, wherein said binding protein is a lectin.

O:ΛH

28. The medication system of Claim 27, wherein said lectin is Concanavalin A.

29. The medication system of Claim 25, wherein said carbohy¬ drate is maltose.

30. The system of Claim 25, wherein said hypoglycemic agent is insulin.

31. The medication system of Claim 25, wherein said complex is present in a dialysis tube.

32. The medication system of Claim 31, wherein said complex is immobilized in said tube.

33. The medication system of any of Claims 31 or 32, wherein said dialysis tube is present in a device implanted externally or in¬ ternally in the human body.

34. The medication system of Claim 25, wherein said reversible complex comprises at least two conjugates (1) having different affin¬ ity towards said binding macromolecule.

35. The medication system of Claim 25, wherein said reversible complex comprises at least two conjugates with different biological¬ ly active portions.

36. The medication system of Claim 35, wherein said carbohy¬ drate is a manno-oligosaccharide containing from 2 to 7 (l—?-2) -D- annopyranosyl residues.

cv.n V/IPO