A COMPOSITION PROVIDING IMPROVED CLEARANCE OF BIOACTIVE SUBSTANCES FROM THE BLOODSTREAM

Abstract: A pharmaceutical or diagnostic composition comprises, in separate containers, (a) a capturing agent capable of binding to a bioactive substance as well as to a ligand or ligand analogue which is able to bind to a cellular receptor; and (b) a ligand or ligand analogue capable of binding to a cellular receptor as well as to said capturing agent. The composition may be used for providing the rapid clearance of bioactive substances from the circulation.

Description: A COMPOSITION PROVIDING IMPROVED CLEARANCE OF BIOACTIVE SUBSTANCES FROM THE BLOODSTREAM FIELD OF INVENTION The present invention relates to a pharmaceutical or diagnostic composition which, when administered to a subject, is capable of providing an improved clearance of a bioactive substance from the bloodstream. The invention further relates to methods of providing such improved clearance for diagnostic or therapeutic purposes. BACKGROUND OF THE INVENTION It is known to use antibodies or conjugates of an antibody and a diagnostically or therapeutically active agent to neutralize a biologically active substance, such as a toxin (e.g. lipopolysaccharide; cf. , for instance, S.S. Martiny et al., Crit. Care Med. 16, 1988, pp. 629-635), or to diagnose a specific condition .in vivo (cf., for instance, J.F. Chatal, Monoclonal Antibodies in Im unoscintiαraphv. CRC Press, Florida, USA, 1990) , or to target a drug to cells expressing a specific antigen, e.g. tumour cells (cf. , for instance, US 4,357,273, EP 336 405 or EP 269 188). Such use of antibodies for diagnostic purposes suffers from the drawback that the rate of clearance or elimination of the antibody (conjugate) from the bloodstream is generally rather slow so that, for an appreciable period of time, the background activity from the circulating diagnostic agent will be too high to permit an accurate diagnosis of the condition in question. This, of course, is a particular disadvantage in case of an acute condition requiring immediate diagnosis and treatment. Similarly, when antibodies or antibody conjugates are administered for therapeutic purposes, e.g. to neutralize a toxin or a drug, it would be a considerable advantage to eliminate the active substance from the circulation fairly rapidly in cases where the neutralization of the activ substance is less than optimal (this has been described fo lipopolysaccharide, cf. L.S. Young et al.. Rev. Infect. Pis. 11. Suppl. 7, 1989, pp. S1564-S1571, or B.J. Appelmelk et al., Miccrob. Pathogen. 5, 1988, pp. 251-257). In EP 308 208, it is suggested to use a conjugate of a antibody which has been modified so that it is able to bind t a marker produced by a tumour or infectious lesion and glycoside residue capable of binding to the hepatocyt asialoglycoprotein receptor for the diagnosis or treatment o tumours and infectious lesions. The clearance of the conjugat from the circulation may be deferred by continuously infusin an inhibitor which, by binding to the same receptor, blocks binding of the conjugate. The method for providing enhanced clearance suggested in EP 308 208 suffers from the drawback that, even when infusion of the inhibitor has ceased, it takes some time before it no longer has any effect, i.e. before the hepatocyte receptor is no longer blocked. This makes the conjugate less favourable for use in emergency situations where rapid diagnosis and treatment is essential. Furthermore, it would not be convenient fo patients to whom the conjugate is administered to be subjected to continuous infusion of the inhibitor for a period of time of up to several days (this is particularly relevant in case of tumour diagnosis and/or treatment) . The object of the present invention is to provide an improved composition and method for providing a faster rate of clearance of biologically active substances from the circulation. SUMMARY OF THE INVENTION Accordingly, the present invention relates to a pharmaceutical or diagnostic composition comprising, in separate containers, (a) a capturing agent capable of binding to a bioactive substance as well as to a ligand or ligand analogue which is able to bind to a cellular receptor; and (b) a ligand or ligand analogue capable of binding to a cellular receptor as well as to said capturing agent. In the present context, the term "capturing agent" is used to indicate a substance which, by binding to the bioactive substance, makes it possible to locate, neutralize and/or remove the bioactive substance in question. The term "bioactive substance" is used to indicate any substance which has a biological function or exerts a biological effect in the human or animal body or is formed in the human or animal body in response to a biological process (which might, for instance, be a pathological process) or is released to the circulation in response to a biological process. The term "ligand" is intended to indicate a substance which, in nature, is capable of binding to a particular cellular receptor, while the term "ligand analogue" is used to indicate a substance which is similarly capable of binding to the same cellular receptor. The ligand analogue may be a derivative of the native ligand which has retained its ability to bind to the cellular receptor in question. The term "cellular receptor" is intended to indicate a receptor located on cell surfaces and comprising an extracellular domain with ligand-binding properties. Some receptors have a transmembrane domain which anchors the receptor in the cell membrane and a cytoplasmic domain which generates a cellular signal in response to ligand binding. Other receptors may be anchored to the cell membrane by a phospholipid chain or indirectly by non-covalent binding to transmembrane proteins. Still other receptors are glycolipids which are anchored in the cell membrane by their lipid chains. In the process of receptor-mediated endocytosis, ligand binding to receptors induces the collection of ligand-recept complexes in coated pits on the cell surface. The subsequently invaginate to form coated vesicles which fuse wi lysosomes followed by enzymatic transformation of the conten of the vesicles (cf. I.H. Pastan and M.C. Willingham, Ann. Re Phvsiol. 43. 1981, pp. 239-250) . Endocytotic vesicles may al form from uncoated regions on the plasma membrane (cf. Alberts et al.. The Molecular Biology of the Cell. Gerla Publ. Inc., New York & London, 1983),. Furthermore, phagocytosi may be induced by binding to specific receptors (cf. Albert et al, op. cit.) . Insoluble immunocomplexes may thus be take up by Kupffer cells via IgG-Fc receptors (cf. B. Smedsrød al., Biochem. J. 266, 1990, pp. 313-327; S.M. Van der Laan Klamer et al., Scand. J. Immunol. 23. 1986, pp. 441-447). The binding between the capturing agent and the ligand o ligand analogue may be effected either by providing th capturing agent with means to bind the ligand or by providin the ligand or ligand analogue with means to bind the capturin agent. Alternatively, the binding between the capturing agen and the ligand or ligand analogue may be effected by providin (complementary) binding means on both the capturing agent an the ligand or ligand analogue. In another aspect, the present invention relates to a metho of providing the rapid clearance of a bioactive substance fro the circulation, the method comprising administering, to subject in need hereof, (a) an effective amount of a capturing agent capable of bindin to a bioactive substance as well as to a ligand or ligan analogue which is able to bind to a cellular receptor, followed, after a suitable interval, by administration of (b) an effective amount of a ligand or ligand analogue capabl of binding to a cellular receptor as well as to said capturin agent . The present method has the advantage that the interval with which the capturing agent and subsequently the ligand or ligand analogue is administered may be varied at will according to the time it is estimated to take for the capturing agent to bind a sufficient amount of the bioactive substance. Likewise, the method is flexible with respect to the receptor cell through which the bioactive substance is eliminated, making it possible to avoid overloading a particular organ through which the bioactive substance would normally be excreted, e.g. the kidneys. Furthermore, patients receiving this treatment are not significantly inconvenienced by being subjected to the method. It should be noted that the bioactive substance need not-in each instance be eliminated from the body through receptor binding and cellular uptake. Rather, the cells may also act as a storage facility for the bioactive substance resulting in a protracted release of the bioactive substance to the bloodstream. In this way, the acute toxicity to the excreting organ (e.g. the kidneys) or normally metabolizing organ (e.g. the thyroid gland) may be significantly reduced. The invention further relates to a method of rapid jLn vivo detection of a pathological condition, the method comprising administering (a) an effective amount of a capturing agent capable of binding to a bioactive substance characteristic of the pathological condition in question as well as to a ligand or ligand analogue which is able to bind to a cellular receptor, followed, after a suitable interval, by administration of (b) an effective amount of a ligand or ligand analogue capable of binding to a cellular receptor as well as to said capturing agent so as to provide a rapid clearance of the capturing agent from the circulation. After the capturing agent has been cleared from t bloodstream, the visualization of any capturing agent bindi to the bioactive substance may be carried out by any suitab means of conducting in vivo diagnosis. The advantage of t present method is that interference from background activi caused by circulating capturing agent may be substantiall eliminated within a short period of time, making the metho particularly useful for diagnosing conditions where rapi treatment is essential. US 4,624,846 discloses a method of localizing a tumour b injecting a radiolabelled antibody against a tumour marke followed by injection, after a suitable interval permittin uptake of the antibody by the tumour, of an antibody agains the radiolabelled antibody whereby the level of circulatin radiolabelled antibody decreases by 10-85% in 2-72 hours. Thi rate of clearance is rather slow compared to that obtainabl with the composition of the present invention, making th method of US 4,624,846 less suitable for rapid diagnosis. US 4,634,586 discloses a method of radioimaging leukocytes b injecting a conjugate of an antibody reactive with a leukocyt surface molecule and a radioisotope chelated with an EDTA o DTPA derivative followed by the injection of an antibod against the conjugate in order to clear the conjugate/antibod complex through the reticuloendothelial system. In a dog study a large amount of anti-conjugate antibody injected afte injection of the conjugate is reported to result in clearanc of 90% of the conjugate within 15 minutes. It should, however be noted that elimination from dog circulation is, at any rate faster than elimination from human circulation. Furthermore it should be emphasized that the antibody conjugated with th radioisotope must be foreign to the species into which it i injected as the subsequently injected anti-conjugate antibod would otherwise not react specifically with the conjugate. Thi is not the case with the present composition and method, making it possible to utilize human (or humanized) substances as the capturing agent and ligand, thereby significantly reducing the risk of adverse immune reactions. In a further aspect, the present invention relates to the use of a capturing agent capable of binding a bioactive substance as well as a ligand or ligand analogue which is able to bind to a cellular receptor for the manufacture, in combination with a ligand or ligand analogue capable of binding to a cellular receptor as well as to said capturing agent, of a pharmaceutical composition providing the rapid clearance of a bioactive substance from the circulation. In a still further aspect, the present invention relates to the use of a capturing agent capable of binding a bioactive substance characteristic of a pathological condition as well as a ligand or ligand analogue which is able to bind to a cellular receptor for the manufacture, in combination with a ligand or ligand analogue capable of binding to a cellular receptor as well as to said capturing agent, of a diagnostic composition providing the rapid clearance of the capturing agent from the circulation and hence a rapid detection of the pathological condition in question. DETAILED DISCLOSURE OF THE INVENTION In one embodiment of the present invention, it is desired to clear the capturing agent rapidly from the circulation. This is particularly the case when the present composition is used for diagnostic purposes wherein, once the capturing agent is bound to the bioactive substance, it is a considerable advantage to eliminate any capturing agent remaining in the bloodstream quickly in order to avoid excessive background interference. In this embodiment, the capturing agent may be monofunctional which is to say that it is able to bind to one substance only In order for the diagnostic method of the invention to b operable, the ligand or ligand analogue may have to be modifie so as to be able to bind to the capturing agent as well as t the receptor. Alternatively, the bioactive substance and th ligand may be substantially identical. In the latter case administration of the bioactive substance, which when i circulates will act as a ligand binding to a specific cellula receptor, subsequently to the administration of the capturin agent will result in the clearance of unbound capturing agen from the circulation. Apart from this, the capturing agent ma be bifunctional which is understood to mean that it is capabl of binding to two different substances (typically the bioactiv substance and the ligand or ligand analogue which will b different) . Also when the capturing agent is bifunctional, -th ligand may be modified so as to be able to bind to th capturing agent. In another embodiment of the present invention, it is desire to clear the bioactive substance rapidly from the circulation This is particularly the case when the present composition i used for therapeutic purposes where binding to the capturin agent does not neutralize all the biological activity of th bioactive substance or where the binding affinity of th capturing agent is not high enough to reduce the " fre concentration of the bioactive substance to any significan extent. In such a case clearance of the bound bioactiv substance from the bloodstream will be important. In this embodiment, the capturing agent may be monofunctiona (as defined above) , in which case the ligand or ligand analogu will have to be modified so that it is able to bind both th capturing agent and the specific cellular receptor. Th bioactive substance will be different from the ligand or ligan analogue. Alternatively, the capturing agent may b bifunctional (as defined above) , in which case the th bioactive substance and the ligand or ligand analogue will typically be different. Also when the capturing agent is bifunctional, the ligand may be modified so as to be able to bind to the capturing agent. In case the capturing agent is monofunctional, it may comprise an antibody which is reactive with the bioactive substance, or a cellular receptor (other than the specific ligand-binding receptor) or a fragment thereof including the binding site for the bioactive substance. The ligand or ligand analogue may then be modified so as to comprise an antibody (including an anti- idiotype antibody) , a cellular receptor (other than the specific ligand-binding receptor) or a fragment thereof including the binding site for the capturing agent, or wherein the ligand or ligand analogue is modified with a bioactive substance or a derivative or fragment thereof capable of binding the capturing agent. In the present context, the term "antibody" is used to indicate any substance formed in the human or animal body or by a human or animal cell as a response to exposure to an antigen. The antibody may be a polyclocal or monoclonal antibody or may be one prepared by recombinant DNA techniques. The term also includes antibody fragments, such as Fab', F(ab') 2 or Fv fragments as well as single-domain antibodies. Monoclonal antibodies may be obtained by well-established methods, e.g. as described in A. Johnstone and R. Thorpe, I munochemistry in Practice. 2nd. Ed., Blackwell Scientific Publications, 1987, pp. 35-43. When prepared by recombinant DNA techniques, the antibody may be produced by cloning a DNA sequence coding for the antibody or a fragment thereof into a suitable cell, e.g. a microbial, plant, animal or human cell, and culturing the cell under conditions conducive to the production of the antibody or fragment in question and recovering the antibody or fragment thereof from the culture. Possible strategies for the preparation of cloned antibodies are discussed in, for instance, L. Riechmann et al.. Nature 332. 24 March 1988, p. 323 ff. , describing the preparation o chi eric antibodies of rat variable regions and human constan regions; M. Better et al.. Science 240. 20 May 1988, p. 104 ff. , describing the preparation of chimeric mouse-human Fa fragments; A. Sharra and A. Plύckthun, Science 240. 20 Ma 1988, pp. 1038-1040, describing the cloning of a immunoglobulin Fv fragment containing antigen-binding variable domains; and E.S. Ward et al., Nature 341. 12 October 1989, pp. 544-546, describing the cloning of isolated antigen-binding variable domains ("single-domain antibodies") . The term "anti-idiotype antibody" refers to an antibody which is reactive with the epitope binding site of another antibody. The anti-idiotype antibody may be prepared by any one of the methods indicated above. In certain cases where the ligand or ligand analogue is modified with a bioactive substance, it may be necessary to modify the bioactive substance in order to reduce the risk of adverse effects arising from the administration of the modified ligand. Thus, if the bioactive substance is one which, in the unmodified state, would be toxic to the human or animal body, one may suitably employ a detoxified derivative thereof, e.g. a detoxified fragment thereof. It may, in any case, be preferred to use fragments of the bioactive substance as this will reduce the size of the modified ligand molecule. When the capturing agent in the composition of the invention is bifunctional, it may suitably comprise a bispecific antibody, i.e. an antibody which is reactive with two different antigens or epitopes. The bispecific antibody may, for instance, be synthesized chemically by cross-linking antibodies of different specificities or by combining one antibody fragment containing at least one epitope-binding site responsible for the reactivity of the antibody with the bioactive substance with another antibody fragment containing at least one epitope-binding site responsible for the reactivity of the antibody with the ligand or ligand analogue, to foxm a hybrid antibody (cf. , e.g., EP 179 872). Alternatively, bispecific antibodies may be formed by fusing two or more hybridomas, e.g. polydomas (cf. , for instance, NL 86-1542, EP 68 763 or EP 338 497), or by recombinant DNA techniques (e.g. as described by W.D. Huse et al.. Science 246, 1989, pp. 1275-1281 or E.S. Ward et al.. Nature 341. 1989, pp. 544-546) . The bifunctional capturing agent may also comprise a conjugate of an antibody and a cellular receptor (other than the specific ligand-binding receptor) or a fragment thereof comprising the binding site for the bioactive substance, a single-stranded oligonucleotide, an intercellular adhesion molecule, or a complexing agent (e.g. biotin, avidin, lectin or a drug) , or a conjugate of a cellular receptor (other than the specific ligand-binding receptor) or a fragment thereof comprising the binding site for the bioactive substance and a single-stranded oligonucleotide, an intercellular adhesion molecule, or a complexing agent (e.g. biotin, avidin, lectin or a drug) . In this case, too, the ligand or ligand analogue may be modified so as to comprise an antibody, a cellular receptor (other than the ligand-binding receptor) or a fragment thereof comprising a binding site for the capturing agent, a single- stranded oligonucleotide, an intercellular adhesion molecule or a complexing agent, each of which is capable of forming a conjugate with the part of the capturing agent which does not bind the bioactive substance. Thus, when the capturing agent comprises a single-stranded oligonucleotide, the ligand or ligand analogue will typically be modified with a complementary single-stranded oligonucleotide. Likewise, when the capturing agent comprises an intercellular adhesion molecule or a complexing agent, t ligand or ligand analogue will usually be modified with substance capable of binding the intercellular adhesi molecule and complexing agent (e.g. avidin or streptavidin the capturing agent is biotin, biotin if the capturing age is avidin, a carbohydrate if the capturing agent is a lecti etc.) , respectively. Suitable lectins may be derived from pla (cf. H. Lis and N. Sharon, Ann. Rev. Biochem. 42. 1973, pp 541-551) or mammalian sources (cf. B. Smedsrød et al., Bioche _____ 266. 1990, pp. 313-327, or Magnusson et al., Biochem. J 257. 1989, pp. 651-656). For diagnostic purposes, the capturing agent may suitably b provided with a label. The substance used to label th capturing agent may for instance be a radioactive isotope suc as In-Ill, Tc-99m, 1-131, 1-125 or 1-123 (cf. US 4,357,273, E 336 405 or EP EP 269 188) . Alternatively, the capturing agen may be labelled with a substance useful for magnetic resonanc imaging. Examples of such substances are magnetite particle which may be coated with the antibody and used for imagin substantially as described in S. Cerdan et al., Magneti Resonance in Medicine 12, 1989, pp. 151-163, or paramagneti atoms, e.g. C 13 or gadolinium (cf., for instance, J.C Saccavini et al.. Invest. Radiol.. Suppl. 1, 1989, pp. S292 S293, or P. Shrere and A. M. Aisen, Magnetic Resonance i Medicine 3. 1986, pp. 336-340). The cellular receptor to which the ligand or ligand analogu binds after binding to the capturing agent may be any recepto found in the body although it may advantageously be a recepto which is found in an organ through which waste products of th body are usually eliminated, e.g. the liver, the spleen, th bone marrow, the lungs, the kidneys, the skin or the placenta The liver has an important function as a scavenger in the bod (cf. B. Smedsrød et al., op. cit. ) . In the liver, th population of endothelial cells and Kupffer cells compose th hepatic reticuloendothelial system which is responsible for the uptake of various macromolecules, including nanoparticles and particulate matter, respectively (cf. E. Wisse et al. (Eds.), Cells of the Hepatic Sinusoid, Vol 2, The Kupffer cell Foundation, Rijswijk, The Netherlands, 1989) . Receptors responsible for the binding of such molecules include, i.a., the hyaluronan, collagen, PIIINP (N-terminal propeptide of collagen type III) , mannose/N-acetylglucosamine, complement, asialoglycoprotein and IgG Fc receptors (cf. B. Smedsrød et al., op. cit. ) . Binding of ligands to these receptors results in receptor-mediated endocytosis whereby vesicles containing the ligand-receptor complex are fused with lysosomes and subsequently degraded. Transcytosis to the parenchy al cells is another possibility (cf. B. Smedsrød et al., op. cit.) as is direct phagocytosis of the Kupffer cells which sequester particulate matter. A further suitable receptor is the hepatic receptor for tissue plasminogen activator. Identical or similar reticuloendothelial cells may also exist in other organs such as the spleen, the lungs, the bone marrow or the placenta. The cells in these organs may be equipped with special receptors characteristic of the organs. Other types of receptors include receptors for peptide or polypeptide hormones and growth factors shown in Table I below. Table I Receptors for growth factors epidermal growth factor, transforming growth factor, insulin-like growth factor, platelet- derived growth factor, i n t e r l e u k i n - l o: , i n t e r l e u k i n - 1 /? , interleukin-2 , colony stimulating factor, γ- interferon, nerve growth factors, tumour necrosis factor 14 Receptors for peptide hormones T3, T4, oxytαcin, histamine, vasopressin Receptors for polypeptide hormones growth hormone, insulin, glucagon, thyroid stimulating hormone, follicle-stimulatin hormone, luteinisin h o r o n e , adrenocorticotropi hormone, parathyroide hormone, prolactin, l i p o t r o p i n , cholecystokinin, calcitonin, secretin, atrialnatriuretic factor, endothelin, vasoactive intestinal p o l y p e p t i d e , trans f err in, tachykinin Intercellular adhesion factors intercellular adhesion molecule 1, endothelial leukocyte adhesion molecule 1, vascular cell adhesion molecule 1 When the corresponding ligands bind to these receptors, an intracellular signal is triggered in response. When such receptors are used for the elimination of the bioactive substance, care should be taken that the binding of the conjugate of the bioactive substance, capturing agent and ligand to the receptor should not trigger an intracellular signal to such a degree that it has any significant overall physiological impact. Another group of receptors are those located intracellularly which mainly bind hydrophobic ligands. Examples of such receptors are shown in Table II below Table II Receptors for vitamins Vitamin A, Vitamin D, retinoic acid Receptors for fatty acid derivatives prostaglandin Bl, D2, El, E2, F2, leukotriene, thromboxane B2 Receptors for steroid hormones t e s t o s t e r o n e , progesterone, cortisol, estradiol, aldosterone A third group of receptors are those which are located on cells of the nervous system, e.g. α-adrenergic, 3-adrenergic, epinephrine, adrenalin, dopamin, opiate (such as morphine, enkephaline, endorphin) angiotensin, adenosin, benzodiazepine, bradykinin, choline muscarinic, cholinergic nicotinic, GABA or serotonin receptors. These receptors may, in certain cases, be used for the elimination of the bioactive substance provided that they are sufficiently abundant and not protected by the blood-brain barrier. In this case, too, it is important that the physiological receptor response does not have any significant overall impact on the body. The spleen forms part of the reticuloendothelial clearance syrtem and as such includes similar cells as those described above for the liver sinusoids. However, the spleen may also contain specific receptors which are different from those of the liver. Apart from this general clearance function, the spleen sequestrates aged erythrocytes. The signal for the retention of erythrocytes in the spleen is not known (M.R. Clark, Phvsiol. Rev. 68. 1988, pp. 503-554), but the presence of a senescent antigen derived from the band 3 protein in combination with auto-antibodies against this antigen may be the signal that triggers the sequestration, e.g. via the Fc receptors (M.M.B. Kay, Proc. Natl. Acad. Sci. USA 81, 1984, pp. 5753-5757) . Apart from these receptors, other receptors are found in th spleen, such as corticotropin-releasing factor receptors, F receptors, atrial natriuretic peptide receptors, the interfero receptor, substance P receptors and tachykinin receptors. Receptors found in the kidneys include angiotensin vasopressin, neuropeptide Y, bradykinin, vasoactive intestina peptide, endothelin, prostaglandin E2, mineralocorticoid, α adrenergic, dopamine-1, serotonin, β-1 integrin or thiazid diuretic receptors. The mechanism for selective excretio includes binding of the conjugate of the bioactive substance capturing agent and ligand to a specific kidney receptor intracellular degradation or modification followed by releas to the tubular cells with subsequent secretion. The lungs have the largest blood flow of all organs and woul therefore be well suited for excretion of evaporatabl substances. Reticuloendothelial cells are also present in th lungs. Examples of lung receptors which may be suitable fo clearance of bioactive susbtances in this fashion ar histamine, endothelin, 0-adrenergic, interleukin-1, interferon γ, lung vasoactive intestinal peptide, muscarinic, adenosine substance P, benzodiazepine, atriopeptin III or leukotrien receptors. Examples of bone marrow receptors which might be useful for th present purpose are the Fc gamma RI, RII and RIII, interleuki 1 and 2, erythropoietin, transferrin, leukotriene benzodiazepine or so atostatin receptors. Due to the extremely large surface area of the skin, it may b a particularly appropriate target for depositing toxi components which cannot be excreted through any other orga without causing damage. Deposited toxic components may eithe be gradually re-routed to the bloodstream and excreted throug another organ (typically the liver) in doses which are smal enough not to cause any damage to that organ. The sweat gland may represent a direct route of excretion via appropriate receptors located in the glands (e.g. a vasoactive intestinal polypeptide-like receptor, cf. W. Kummer et al., Neurosci. Lett. 110, 1990, pp. 239-243). Examples of receptors on keratinocytes and skin fibroblasts which might be suitable for the present purpose are low-density lipoprotein, transferrin, interleukin-1 and -2, histamin HI and H2, glycocorticoid, vitamin D, retinoic acid or retinoic acid gamma receptors or integrin receptors for fibronectin, collagen or la inin. Intrauterine treatment of foetal disorders is believed to be feasible by the clearance method of the invention by utilizing one of the large number of receptors in the placenta. Examples of such receptors are Fc-γ, LDL, hemopexin, transferrin, α 2 - macroglobulin, ferritin, insulin, atrial natriuretic peptide, progesterone, estrogen, glucocorticoid, calcitonin, granulocyte colony stimulating factor 1, adenosine, /3-adrenergic, endothelin, interferon-γ, epidermal growth factor, insulin-like growth factor, opioid or thromboxane receptors. Receptors of the above categories may also be used to modify ligands or ligand analogues, or they may form part of the capturing agent, as indicated above. Consequently, suitable ligands or ligand analogues may be selected from the group consisting of a growth factor, a peptide or polypeptide hormone, a cytokine, a detoxified toxin, a vitamin, a steroid hormone, or a substance acting on the central nervous system, e.g. a substance capable of binding to any one of the receptors listed above. Other possible ligands may be hyaluronan (cf. B. Smedsrød et al., OP. cit. ) . chondroitin sulphate (cf. B. Smedsrød et al., op. cit. ) , N- terminal propeptide of collagen type III (cf. B. Smedsrød et al., op. cit. ) . mannose-terminated glycoconjugates (cf. B. Smedsrød et al., op. cit. , or B. Smedsrød et al., Thromb. Hae ostas. 59, 1988, pp. 480-484), a glycoside coupled to a bioactive substance capable of binding to the capturing agent 1 PCT/DK91/00215 18 (the glycoside binding to the asialoglycoprotein receptor o hepatocytes) or tissue plasminogen activator. In certai special cases, one might contemplate using as the ligand substance which does not bind to any specific receptor bu which is nevertheless bound to a specific organ (e.g. aprotini which is bound in the kidneys) . The bioactive substance which may be either detected o eliminated by the method of the invention may be a dru (including a narcotic drug) , e.g. an alkaloid such as digoxi or morphine, or an antidepressive (including tricycli antidepressives) , acetylsalicylic acid, paracetamol, antiepileptic, β-receptorblocker, neuroleptic, sympatomimetic, a toxin, e.g. an exotoxin or endotoxin (LPS) , snake venom, fungal poison (e.g. muscarine) , an inorganic poison such as heavy metal (e.g. lead, cadmium, mercury) , an organic poiso such as an alkaloid (e.g. nicotine, scopolamine, atropine) , tumour-associated antigen, optionally as present on neoplasti cells, a substance produced by a neoplastic cell, an activate leukocyte, an activated lymphocyte, a plasma cell, surface o circulating substances produced by cells, an antibody, i particular an autoantibody, a thrombus (or a component thereof) or a pathogen (e.g. virus, bacteria, fungi) or a componen thereof, such as a surface antigen. DESCRIPTION OF SPECIFIC EMBODIMENTS I. Detection of vascular thrombi Vascular thrombi may be rapidly detected by injecting a antibody which is specific for the seven first amino acids of the β-chain of human fibrin. These amino acids are not exposed on fibrinogen which implies that the antibody will react with fibrin, but not with fibrinogen (cf. K.Y. Huy et al., Science 212., 1983, pp. 1129-1132). More specifically, this fibrin-specific antibody is prepared by the method described in Huy et al., op. cit. , and labelled with 111 In essentially as described by Hnatowich, J. I mun. Meth. 65, 1983, pp. 147-157. By injecting this antibody, any fibrin present in the circulation (e.g. deep venous thrombi or lung emboli) will be labelled with the antibody. After about one hour, a 2-10-fold molar excess of tissue plasminogen activator (tPA) conjugated with the fibrin 3-chain heptapeptide mentioned above is then injected. This will result in rapid elimination of the background activity of the labelled antibody in the blood through the liver due to the binding of tPA to hepatic receptors, thereby improving the target-blood ratio of the labelled antibody to a significant degree. II. Diagnosis of vascular thrombi Vascular thrombi may also be detected by a method which is similar to the one described above, but in which a bispecific antibody reactive with the fibrin 3-chain heptapeptide as well with tPA is injected and in which background activity is cleared by means of unmodified tPA. More specifically, monoclonal antibodies reactive with the fibrin ,5-chain heptapeptide are prepared as described by Huy et al. , op. cit. Monoclonal antibodies reactive with human tPA are prepared as described in DK 4082/89. Immunoreactive bispecific antibodies are prepared from the two monoclonal antibodies by the method described in EP 179 872 and labelled with 111 In essentially as described by Hnatowich, J. Immun. Meth. 5, 1983, pp. 147-157. By injecting the bispecific antibody, any fibrin present in the circulation (e.g. deep venous thrombi or lung emboli) will be labelled with the antibody. After about one hour, a 2-10-fold molar excess of unmodified tPA (Actilyse ® , available from Boehringer Ingelheim) is then injected. This will result in rapid elimination of the background activity of the labelled antibody in the blood through the liver due to the binding of tPA to hepatic receptors, thereby improving the target-bloo ratio of the labelled antibody to a significant degree. III. Localization of tumours The localization of tumours by means of radiolabelle antibodies is an established technique (cf., for instance Chatal, Monoclonal Antibodies in Immunoscintigraphv, CRC Florida, 1989) . It is important to reduce the backgroun activity of the antibody (i.e. establish a high target-bloo ratio) in order to obtain a high sensitivity of the diagnosis Conventionally, this has been done by deferring tumou detection until the level of circulating labelled antibodie has diminished by natural elimination. The clearance o labelled antibodies may be accellerated by injecting bispecific antibody reactive with a tumour-specific antigen a well as with tPA, followed by injection of tPA after th antibody has been bound to the tumour. More specifically, monoclonal antibodies reactive with huma carcinoembryonic antigen (CEA) is prepared according t standard procedures (cf. J.P. Mach et al., Immunology Today 2., 1981, pp. 239-242) . Monoclonal antibodies reactive with huma tPA are prepared as described in DK 4082/89. Immunoreactiv bispecific antibodies are prepared from the two monoclona antibodies by the method described in EP 179 872. Th bispecific antibodies are labelled with 111 In essentially a described by Hnatowich, J. Immun. Meth. 65, 1983, pp. 147-157. The labelled bispecific antibodies are then injected into patients with colorectal cancer and allowed to circulate for about 30 minutes followed by injection of a 2-10-fold molar excess of human tPA (Actilyse ® , available from Boehringer Ingelheim). This will result in rapid elimination of the labelled antibody from the circulation to a level at which the tumours are visualized clearly on the scintigrams (a level below about 10-25% of the original level, as determined by experiments with radiolabelled anti-CEA antibodies) . IV. Treatment of digoxin poisoning Overdosing of digoxin leading to intoxication represents a serious clinical problem because no efficacious antidote to the drug exists at present. Parenteral administration of antibodies specific for digoxin has previously been suggested in order to reduce the free concentration of the drug (cf. , for instance, D.H. Smith and V.P. Butler, J. Clin. Invest. .50, 1971, pp. 1738-1744; W. Clarke and E.A. Ra oska, Am. J. Emerg. Med. 6 (5) . 1988, pp. 465-470). The clinical efficacy of such treatment varies (S.S. Martiny et al., Crit. Care Med. 11(6), 1988, pp. 629-635) . A major drawback of this treatment is that potentially vital digoxin treatment cannot be initiated for quite some time after injection of the antibody. It may be assumed that more efficient elimination of the circulating antibody-digoxin complex would more rapidly reduce the free concentration of digoxin in the bloodstream. Such elimination may be effected by initially injecting a bispecific antibody reactive with digoxin as well as tPA in the bloodstream of an intoxicated patient. After about 10-30 minutes, tPA is injected in a 2-10-fold molar excess of the antibody. The complexes of digoxin, antibody and tPA (as well as antibody and tPA not bound to digoxin) are then bound to the tPA receptor in the liver (cf. D.C. Rijken et al. , Thro b. Res. 57, Suppl. 10, 1990, pp. 63-71) and excreted therefrom. More specifically, murine monoclonal antibodies reactive with human tPA are produced by the method described in DK 4082/89. Polyclonal antibodies against digoxin are prepared as described by D.H. Smith and V.P. Butler, op. cit. Immunoreactive bispecific antibodies are prepared from the two antibodies by the method described in EP 179 872. To test the theraputic efficacy of the method of the present 22 invention, four rabbits are treated with theraputic doses o digoxin (NEN, DuPont) for 5 days after which they ar intoxicated by administrating an overdose of 3 H-labelle digoxin (NEN, DuPont) . 6 hours later two of the rabbits ar treated with anti-digoxin antibody alone, while the other tw rabbits receive an equivalent dose of the bispecific antibod followed by a 2-10-fold molar excess of tPA (e.g. Actilyse ® available from Boehringer Ingelheim) about 30 minutes later. Comparison of the radioactive counts of plasma samples take from each group of rabbits in the course of the treatment i expected to show a significant decrease of the plasma conten of digoxin in the rabbits treated with the bispecific antibod and subsequently injected with tPA. V. Elimination of LPS from the circulation Endotoxin (LPS) plays a significant part in the pathogenesi of gram-negative septice ia (cf. T.B. Casale et al., J. Allerg Clin. Immunol. 85. 1990, pp. 45-51) . It has previously bee attempted, with varying degrees of success, to neutralize LPS by administering polyclonal or monoclonal anti-LPS antibodies (cf. L.S. Young et al.. Rev. Infect. Pis. 11, Suppl. 7, 1989, pp. S1564-S1571; B.J. Appelmelk et al., Microb. Pathogen 5., 1988, pp. 251-257) . A major obstacle to this approach is tha most anti-LPS antibodies do not protect against LPS toxicity. It is contemplated that elimination of LSP by the liver may be increased by administering a bispecific antibody which is reactive with LPS as well as with tPA, followed by injection of a suitable amount of tPA. More specifically, monoclonal antibodies reactive with LPS are prepared according to standard procedures (cf. M.N. Nys et al. , J. Infect. Pis. 162, 1990, pp. 1089-1095) . Monoclonal antibodies reactive with human tPA are prepared as described in PK 4082/89. Immunoreactive bispecific antibodies are prepared from the two monoclonal antibodies by the method described in EP 179 872. The bispecific antibodies are then injected into septicemic patients and allowed to circulate for about 30 to 60 minutes to bind a significant proportion of the endotoxin present, followed by injection of a 2-10-fold molar excess of human tPA (Actilyse ® , available from Boehringer Ingelheim) . This will result in a more rapid elimination of the LPS/antibody/tPA complex from the circulation. BRIEF PESCRIPTION OF THE PRAWINGS Fig. l is a graph showing the total radioactivity in plasma of In-Ill labelled anti-t-PA monoclonal antibody (MoAb) with and without subsequent injection of t-PA. Fig. 2 is a graph showing the immunoreactive part of In-1-11 labelled anti-t-PA MoAb with and without subsequent injection of t-PA. Fig. 3 is a scintigram showing the organ distribution in rabbits of In-Ill labelled anti-t-PA MoAb alone and complexed with t-PA. Fig. 4 is a graph showing the total radioactivity in human plasma of In-Ill labelled anti-t-PA MoAb before and after injection of t-PA. Fig. 5 is a graph showing the change in human organ di¬ stribution of In-Ill labelled anti-t-PA MoAb following in¬ jection of t-Pa. Fig. 6 shows two scintigrams of the crural region initially showing increased accumulation of In-Ill labelled anti-t-PA MoAb in the vascular bed of the right leg (A) , and after t-PA injection revealing the focal thrombus area (top of the right leg) (B) . Fig. 7 is a graph showing gelfiltration of a bispecific anti-t- 15 24 PA/anti-rabbit antibody. All fractions were tested for OP 280 an reactivity in a t-PA enzyme immunoassay (EIA) . All fraction were diluted 1:25000 before testing in the EIA system. Fig. 8 is a graph showing the concentration, determined by EIA of a bispecific anti-t-PA/anti-rabbit antibody in rabbit plasm with (indicated by squares) and without (indicated b triangles) injection of t-PA. Fig. 9 is a graph showing the total amount, determined by EIA of biotinylated bispecific anti-t-PA/anti-rabbit antibody i rabbit plasma with (indicated by squares) and withou (indicated by triangles) injection of t-PA. The present invention is illustrated in further detail in th following examples which are not in any way intended to limi the scope of the invention as claimed. Example 1 Monofunctional capturing agent (a) Production of a monoclonal antibody against t-PA Purification of t-PA antigen The t-PA used for the immunization of mice was purified a disclosed in Rijken, P.C. and Collen, P., J. Biol. Chem. 256, 1981, pp. 7035-41. The purified material contained >95% pur t-PA as determined by silver-stained SPS-polyacrylamide ge electrophoresis. Immunization of AKR mice with t-PA Purified t-PA obtained as described above was dialysed agains 0.15 M NaCl containing 0.01% (v/v) Tween 80, and th concentration was adjusted to 10 μg/ml. AKR mice were immunized 3 times at bi-weekly intervals. For the first two immunizations, each mouse was injected subcutaneously with 50 μl t-PA emulsified with 50 μl of Freunds's incomplete adjuvant (corresponding to 5 μg of t-PA/mouse) . The last immunization was identical to the first two, but was given intraperitoneally rather than subcutaneously. Two months later a mouse received an intravenous booster injection of 90 μl t-PA without any Freund's adjuvant. Cell fusion and culture of cells Three days after the intravenous t-PA booster, the spleen was removed, and a spleen cell suspension was prepared by carefully dissecting and disrupting the spleen. The resulting spleen cells were used for cell fusions as described in Petersen, L.C. et al., Thrombosis and Hae ostasis 57 (2), 1987, pp. 205-211. In brief, spleen cells were fused with X63-Ag8-6.5.3 myeloma cells in the presence of a polyethylene glycol solution. After fusion the cells were seeded in 10 96-well microtiter cell plates. Hybridoma supernatants were screened after two weeks growth by enzyme-linked immunosorbent assay using t-PA as the antigen. A positive clone was recloned several times by the technique of limiting dilution to ensure monoclonality. The cell line was then grown on a large scale in "cell factories" from NUNC in a medium consisting of RPMI 1640 (Gibco, UK) with 2% BMS (Gibco, UK) . Purification of the monoclonal antibody The hybridoma supernatants were concentrated. pH was adjusted to 8.3, after which the monoclonal antibody was purified at 4°C by adsorption to on a Protein A gel. Elution was performed with a citrate buffer pH 4.5. Production of F(ab) 2 fragments The purified monoclonal antibody (subclass IgG^ was digested with pepsin at a enzyme/substrate ratio of 1:100 at pH 4.30 for 16 h at 37°C. The reaction was stopped by adjusting the pH of the reaction mixture to pH 8.5 with solid Tris. The F(ab) 2 was separated from undigested IgG and low molecular weight products on a Ultrogel AcA 44 column. Purification of the antibody, pepsin digestion and purification of F(ab) 2 was monitored on silver-stained SPS-gels. Labelling of FfabK with indium The purified F(ab) 2 was labelled with indium essentially according to the method of Hnatowich (J.Immun.Methods. 65, 147- 157 (1983) .Immunoreactivity of conjugates was confirmed by ELISA and with immunosorbent technique using t-PA as antigen. The immunochemical purity of the labelled antibody was determined as the percentage of antibody radioactivity capable of binding to a t-PA coupled Sepharose (Pharmacia AB, Sweden) column. The immunochemical purity of the conjugate was less than the radiochemical purity since some of the labelled antibody was immunological by non-reactive. The immunochemical purity of the antibody was 93%. (b) Biological background subtraction - animal study t-PA The t-PA used in the experiments was Actilyse obtained from Boehringer Ingelheim. Experimental design Two rabbits were injected intravenously with the antibody in dose/kg and specific radioactivity comparable to the human studies mentioned in Example 2. Rabbit 1 received antibody at t = 0 minutes. No t-PA was subsequently administered. Rabbit 2 received antibody at t = 0 minutes. At t = 120 minutes rabbit 2 received an intravenous injection of t-PA administered over a period of 1 minute. The injected amount of t-PA was in 3 x molar concentration of the administered antibody. Plasma activity Blood samples were taken at t = 0, 10, 20, 40, 60 min and 2, 4, 6, 12, and 24 hours after the antibody injection. In rabbit 2 additional samples were taken 5, 10, 20, 40, and 60 min after the injection of t-PA. For each sample, whole plasma activity was counted, and by regression analysis (Freelance Plus ver 3.01) these data were adjusted to an exponential curve and the overall biological half-life was calculated. All curves presented were corrected for physical decay. The results are shown in Fig. 1. T^ of the antibody was 10.3 h. When t-PA was added at t = 2 hours a dramatic decrease in plasma activity was observed. Within 10 min a 92% reduction was observed. The biological half-life of the radiolabelled immunoreactive antibody in plasma was determined as the half-life of t-PA binding activity. The results are shown in Fig. 2. Within 10 minutes after the injection of t-PA at t = 2 hours more than 99% of the immunoreactive antibody activity was eliminated from the plasma. The half-life of this elimination is 1 minute. A slight increase in activity - up to 1.6% - is seen in the hours after the initial elimination. This is undoubtedly caused by redistribution of the extravascular antibody pool. 28 Whole body activity After 24 hours the rabbits were sacrificed. Whole bod scintigrams of the rabbits were obtained. The results are show in Fig. 3. Antibody not complexed with t-PA was mainly locate in the kidneys, whereas antibody complexed with t-PA was almos exclusively found in the liver. It appears from these experiments that t-PA/anti-t-PA MoA complexes have a substantially shorter half-life in th organism than anti-t-PA alone. Furthermore, the experiment show that is is possible to exploit the rapid t-PA/anti-t-P MoAb clearance in vivo. The results of the study suggest tha the hepatic t-PA receptor is responsible for this increase i antibody clearance. The decline in total radioactivity is an essential paramete for imaging, in that the total plasma activity will decide th target/blood ratio. The reduction in t-PA binding radioactivit is a measure for the in vivo efficiency of the recepto elimination pathway. The decrease in total radioactivity wil be less than the reduction in t-PA binding radioactivity unles the conjugate is 100% immunochemically active. Example 2 Biological background substraction - human study A 77 year-old woman was admitted to hospital because o pronounced oedema of the right leg. An acute contras phlebography exposed signs of a thrombosis in one of th lateral crural veins of the right leg. Scintigraphy was performed using a radiolabelled monoclonal antibody prepare as described in example 1. The radiochemical purity was only 67%. One hour after injection of the radiolabelled antibody 5 mg of t-PA (Actilyse Boehringer Ingelheim) was injected. Plasma activity Blood samples were taken at regular intervals after the t-PA injection. For each sample, whole plasma radioactivity was counted in a well gamma-counter and plotted against time (Fig. 4) . Exponential regression analysis was performed on Freelance Plus ver 3.01). T<s of the initial phase was 4.8 h. After t-PA injection a substantial decrease in plasma activity was observed. Within 17 min a 50% reduction was observed. Scintigraphv Biodistribution: During t-PA injection a dynamic acquisition of the liver and heart region was performed on the gamma-camera with 60 frames lasting 15 sec each. Activity of the blood (heart region) and the liver were calculated and plotted against time. The shift in distribution from circulating blood activity to bound liver activity following injection is clearly demonstrated on Fig. 5. Thrombus detection: Initially, signs of stasis in the lower leg were revealed. However, the precise location of the thrombus could not be detected. After the t-PA injection, the activity in the dilated vascular bed diminished, and the thrombus area was detected (Fig. 6) . The biological background subtraction appears to improve the imaging technique, making it possible to detect thrombosis within a few hours. Example 3 Bifunctional capturing agent (a) Production of a monoclonal antibody against t-PA Purification of t-PA antigen The t-PA used for the immunization of mice was purified as disclosed in Rijken, D.C. and Collen, D. , J. Biol. Chem. 256, 1981. pp. 7035-41. The purified material contained >95% pure t-PA as determined by silver-stained SDS-polyacrylamide gel electrophoresis. Immunization of RBF/Dn mice with t-PA Purified t-PA obtained as described above was dialysed against 0.15 M NaCl containing 0.01% (v/v) Tween 80, and the concentra¬ tion was adjusted to 10 μg/ml. Origin of parent myeloma cell line: The myeloma cells used for production of the monoclonal anti¬ body 3 Fl were the FOX-NY myeloma line deficient in the selec¬ table enzyme marker locus adenosine phosphoribosyl transferase (ARPT " ) and hypoxanthine phosphoribosyl transferase (HRPT " ) . This myeloma cell line is "non-producing" cell line, ie. it does not secrete or synthesize any i munglobulin chains. Origin of animal strain RBF/Dn-strain mice (obtained from the Jackson Laboratory, Bar Harbor, Maine, USA) containing the RB (8.12)5Bnr Robertsonian translocation chromosome were used for production of monoclonal antibodies. Immunization and fusion RBF/Dn-strain mice were immunized three times at bi-weekly intervals with purified human t-PA. Antigen was emulsified 1:1 in Freund's incomplete adjuvant prior to immunization of the mice. Each mouse received 10 μg antigen with each immunization in a total volumen of 200 μl. One month after the last immuni- zation a mouse was boosted intravenously with 10 μg human t-PA. After another three days the mouse was sacrificed and the spleen removed for fusion with myeloma cells. Spleen cells from one mouse (10.2 x 10 7 cells) were fused with 2.5 x 10 7 cells of the FOX-NY cell line. The fused cells were seeded on BALB/strain mouse macrophage feeder cells in a total of 1096-well microtiter plates in a medium consisting of RPMI- 1640 with 15 % v/v fetal calf serum (Gibco of Flow) supple¬ mented with adenine (7.5 x 10 "5 M) , hypoxanthine (8 x 10 "4 M, aminopterin (8 x 10 "7 M) and thymidine (1.6 x 10 "5 M) (AHAT). Consequently, the exposure of cell fusion mixture to a medium requiring ARPT activity (ARPT* selection) eliminates both unfused ARPT " myelomas and ARPT " hybridomas. This results in increased stability of immunoglobulin producing hybridomas (R.T.Taggart and I.M.Samloff: Science 219 (1983) pp. 1228 - 1230) . Hybridoma supernatants were screened after two weeks' growth by enzyme linked immunosorbent assay using t-PA as the antigen. A positive clone was recloned several times by the technique of limiting dilution to ensure monoclonality. The cell line was then grown on a large scale in "cell factories" from NUNC in a medium consisting of RPMI 1640 (Gibco, UK) with 2% BMS (Gibco, UK) . Purification of the monoclonal antibody The hybridoma supernatants were concentrated. The pH was ad- justed to 8.3, after which the monoclonal antibody was purified at 4"C by adsorption to on a Protein A gel. Elution was performed with a citrate buffer pH 4.5. Production of Ffab fragments The purified monoclonal antibody (subclass IgG,) was digeste with pepsin at a enzyme/substrate ratio of 1:100 at a pH o 4.10 for 16 h at 37°C. The reaction was stopped by adjustin the pH of the reaction mixture to pH 8.5 with solid Tris. Th F(ab) 2 was separated from undigested IgG on a Protein A colum and further purification was performed on a Ultrogel AcA 4 column. Purification of the antibody, pepsin digestion an purification of F(ab) 2 was monitored on Coomassie-stained SDS gels. Purification of rabbit immunoglobulin Rabbit serum was adjusted to a pH of 7.5, after which th rabbit immunoglobulin was purified at 4°C by adsorption to o a Protein A gel. Elution was performed with a citrate buffe pH 3.5. Production af rabbit Ffab fragments The purified rabbit immunoglobulin was digested with pepsin a a enzyme/substrate ratio of 1:100 at pH 4.50 for 16 h at 37°C The reaction was stopped by adjusting the pH of the reactio mixture to pH 8.5 with solid Tris. The F(ab) 2 was separate from undigested IgG on a Protein A column and furthe purification was performed on a Ultrogel AcA 44 column. Purification of the antibody, pepsin digestion and purificatio of F(ab) 2 was monitored on Coomassie-stained SDS-gels. Biotinylation of rabbit immunoglobulin The purified rabbit F(ab) 2 was biotinylated with Biotinyl-e aminocaproic acid N-hydroxysuccinamidester (biotin-x-NHS) (Calbiochem 203188) . Immediately prior to use, biotin-x-NHS i dissolved in DMSO. The biotinylation was performed in a PB buffer pH 7.2 at 20°C with a molar ratio of biotin-x-NHS/F(ab) of 100. The biotinylation process was stopped after 2 hours by addition of 10 % v/v of i idazol buffer, 0.5 M pH 7.3. Preparation of a bifunctional FfabK Preparation of the bifunctional antibody was performed essentially according to Glennie, M.J. et al. J.Immunol, vol 139, page 2367-2375 1987. Reduction of biotinylated rabbit F(ab 1 ml purified biotinylated rabbitF(ab) 2 at a concentration of 10 mg/ml was reduced with 10 mM DTE flushed with nitrogen and stored for 60 minutes at 20°C followed by 30 minutes at 4°C. Separation af Fab from DTE was performed on a 1.5x15 cm Sephadex G-25 column equilibrated with 50 mM acetate buffer ph 5.3 with 2 mM EDTA. The eluted Fab was pooled and stored on ice before use. Reduction and maleimide coupling of murine Ffab 1 ml purified monoclonal anti t-PA F(ab) 2 at a concentration of 10 mg/ml was reduced with 10 mM DTE, flushed with nitrogen and stored for 60 minutes at 20°C followed by 30 minutes at 4°C. Separation af Fab from DTE was performed on a 1.5x15 cm Sephadex G-25 column equilibrated with 50 mM acetate buffer pH 5.3 containing 2 mM EDTA. The eluted Fab was pooled. To 3.2 ml Fab at a concentration of 1.55 mg/ml was added 1.6 ml 12 mM mM o-phenylene dimaleimide (o-PDM, SIGMA) dissolved in chilled dimethylformamide. After 30 minutes the maleidated Fab mal was separated from the other solutes in the reaction mixture by passage through a 2.5x 15 cm Sephadex G-25 column equilibrated with 50 mM sodium acetate pH 5.3 containing 2 mM EDTA. Coupling of murine Fab rnol with biotinylated rabbit Fab , ml Fab mal at a concentration of 0.41 mg/ml (82 nmol) was mixed with 3.3 ml biotinylated rabbit Fab at a concentration of 1.62 mg/ml (107 nmol) . The reaction mixture was concentrated to 2 mg/ml by ultrafiltration under nitrogen using a Amicon YM- 10 membrane in a chilled Amicon chamber (Amicon Ltd) . Gelfiltration of bispecific antibody The reaction mixture was gelfiltrated an a 1.5x100 cm Ultrogel AcA44 column equilibrated with 0.2 M phosphate buffer pH 6.0 containing 5 mM EDTA. The flow rate was 8 ml/h and the fractions were of 1 ml. EIA test of gelfiltrated bispecific antibody All fractions were assayed by EIA. 96-well plates were coated with human t-PA at a concentration of 1 μg/ml for 16 hours at room temperature. After blocking the plates, all fractions were assayed in this EIA. Fractions were tested in dilutions of 1:500 and 1:25000 in a PBS buffer containing 0.02% Tween 20 supplemented with 1 % BSA. Plates were washed after incubation for 1 hour. The plates were then incubated with streptavidin- peroxidase (Kirkegard and Perry Laboratories, Inc) in a dilution of 1:20000 in a PBS buffer supplemented with 0.5 M NaCl. After a final washing, the wells were incubated with 100 μl substrate buffer (citrate perborate buffer, pH 5.5, containing ortho-phenylenediamine, 0.8 mg/ml) for 5 minutes, after which the reaction was stopped by addition of 100 μl 2 M sulfuric acid to each well. Plates were read at 492 nm. Results are shown in Fig. 7. In this figure, absorbance in the EIA of all fractions diluted 1/x is depicted. Fractions containing bispecific antibodies as estimated by the EIA were pooled. The volume was 6 ml and the antibody concentration (determined as A 280 ) was 198 μg/ml. This pool af bispecific antibody was used for elimination experiments. (b) Biological background subtraction t-PA The t-PA used in the experiments was Actilyse obtained from Boehringer Ingelheim. Experimental design Four rabbits were injected intravenously with the bispecific antibody in a dose of 50 μg/rabbit. Rabbit 1 and 2 received antibody at t = 0 minutes. No t-PA was subsequently administered. Rabbit 3 and 4 received antibody at t = 0 minutes. At t = 60 minutes rabbit 3 and 4 received an in¬ travenous injection of t-PA administered over a period of 1 minute. The injected amount of t-PA was in 12 x molar concentration of the administered antibody. Plasma activity Blood samples were taken at t = 0, 10, 20, 40, 60 min and 2, 4, 6 after the antibody injection. In rabbit 3 and 4 additional samples were taken 5, 10, 20, 40, and 60 min after the injection of t-PA. The concentration of bispecific antibody was determined in the above mentioned EIA using a calibration curve (200 ng/ml to 0.78 ng/ml) of bispecific antibody in rabbit plasma. All samples were tested undiluted and diluted 1:10 in normal rabbit plasma. The results are shown in Fig. 8 in which each curve represents the mean value of two rabbit plasma samples. The half-life of the bispecific antibody in the control rabbits that did not receive any t-PA was approximately 4.5 hours. When t-PA was added at t = 1 hours a dramatic decrease in the serum concentration of the bispecific antibody was observed. Withi 10 min substantially all of the bispecific antibody had bee cleared from the bloodstream as evaluated by the EIA results. The results were verified in an EIA which measured the total amount of biotinylated antibody using a microtiter plate i which the wells were coated with streptavidin. The concentration of bispecific antibody in rabbit plasma was determined in this EIA using a calibration curve (200 ng/ml to 0.78 ng/ml) of bispecific antibody in rabbit plasma. The response of this calibration curve was unaffected by the addition of high concentrations of t-PA. Samples were incubated undiluted and diluted 1:10 in normal rabbit plasma. CAlibrators and samples were incubated for 1 hour. The plates were then incubated with streptavidin-peroxidase (Kirkegard and Perry Laboratories, Inc) in a dilution of 1:20000 in a PBS buffer supplemented with 0.5 M NaCl. After a final washing, the wells were incubated with 100 μl substrate buffer (citrate perborate buffer pH 5.5 supplemented with ortho-phenylenediamine 0.8 mg/ml) for 5 minutes, after which the reaction was stopped by addition of 100 μl 2 M sulfuric acid to each well. Plates were read at 492 nm. The results of are shown in Fig. 9 in which each curve represents the mean value of two rabbit plasma samples. All antibody concentrations are given as percentages, antibody concentrations measured after 10 minutes being set at 100%. The half-life of the bispecific antibody in control rabbits that dis not receive any t-PA was approximately 4 hours. Within 10 minutes after the administration of t-PA, a decrease in the concentration of biotinylated bispecific antibody of approximately 80% was observed. The results of this experiment show that the elimination of bispecific antibody as shown in Fig. 9 is not simply caused by a reaction between the bispecific antibody and t-PA making the compleks unable to bind to the solid phase t-PA in the EIA plate . It appears from these experiments that t-PA/anti-t-PA bi¬ specific antibodies have a substantially shorter half-life in the organism than bispecific antibodies alone. Furthermore, the experiments show that is is possible to exploit the rapid t- PA/anti-t-PA MoAb clearance in vivo.

Claims: 38 CLAIMS 1. A pharmaceutical or diagnostic composition comprising, in separate containers, (a) a capturing agent capable of binding to a bioactive substance as well as to a ligand or ligand analogue which is able to bind to a cellular receptor; and (b) a ligand or ligand analogue capable of binding to a cellular receptor as well as to said capturing agent. 2. A composition according to claim 1, wherein the capturing agent is an agent to be cleared rapidly from the circulation. 3. A composition according to claim 2, wherein the capturing agent is monofunctional, and wherein the ligand or ligand analogue is modified so as to be able to bind to the capturing agent. 4. A composition according to claim 2, wherein the capturing agent is monofunctional, and wherein the bioactive substance and the ligand are substantially identical. 5. A composition according to claim 1, wherein the bioactive substance is a substance to be cleared rapidly from the circulation. 6. A composition according to claim 5, wherein the capturing agent is monofunctional, and wherein the bioactive substance is different from the ligand or ligand analogue which is modified so as to be able to bind to the capturing agent. 7. A composition according to claim 5, wherein the capturing agent is bifunctional, and wherein the bioactive substance is different from the ligand or ligand analogue. 8. A composition according to claim 7, wherein the ligand or ligand analogue is modified so as to be able to bind to the capturing agent. 9. A composition according to claim 2 or 4, wherein the capturing agent is monofunctional and comprises an antibody or a cellular receptor (other than the specific ligand-binding receptor) or a fragment thereof including the binding site for the bioactive substance. 10. A composition according to claim 3 or 6, wherein the capturing agent is monofunctional, and wherein the ligand or ligand analogue is modified so as to comprise an antibody (including an anti-idiotype antibody) , a cellular receptor (other than the specific ligand-binding receptor) or a fragment thereof including the binding site for the capturing agent, or wherein the ligand or ligand analogue is modified with a bioactive substance or a derivative or fragment thereof capable of binding the capturing agent. 11. A composition according to claim 7, wherein the capturing agent is bifunctional and comprises (a) a bispecific antibody, (b) a conjugate of an antibody and a cellular receptor (other than the specific ligand-binding receptor) or a fragment thereof comprising the binding site for the bioactive substance, a single-stranded oligonucleotide, an intercellular adhesion molecule, or a complexing agent (e.g. biotin, avidin, lectin or a drug) , or (c) a conjugate of a cellular receptor (other than the specific ligand-binding receptor) or a fragment thereof comprising the binding site for the bioactive substance and a single-stranded oligonucleotide, an intercellular adhesion molecule, or a complexing agent (e.g. biotin, avidin, lectin or a drug) . 12. A composition according to claim 11, wherein the ligand o ligand analogue is modified so as to comprise an antibody, cellular receptor (other than the ligand-binding receptor) o a fragment thereof comprising a binding site for the capturin agent, a single-stranded oligonucleotide, an intercellula adhesion molecule or a complexing agent, each of which i capable of forming a conjugate with the part of the capturin agent which does not bind the bioactive substance. 13. A composition according to any of claims 1-12, wherein th agent is provided with a label. 14. A composition according to claim 13, wherein the label is selected from the group consisting of radioactive isotopes, magnetite particles, and paramagnetic atoms. 15. A composition according to any of claims 1-14, wherein the cellular receptor is a liver, spleen, bone marrow, lung, kidney, skin or placental receptor. 16. A composition according to any of claims 1-15, wherein the bioactive substance is a drug (including a narcotic drug) , e.g. an alkaloid such as digoxin or morphine, or an antidepressive (including tricyclic antidepressives) , acetylsalicylic acid, paracetamol, antiepileptic, ^-receptor blocker, neuroleptic, sympatomimetic, a toxin, e.g. an exotoxin or endotoxin (LPS) , snake venom, fungal poison (e.g. muscarine) , an inorganic poison such as a heavy metal (e.g. lead, cadmium, mercury) , an organic poison such as an alkaloid (e.g. nicotine, scopolamine, atropine) , a tumour-associated antigen, optionally as present on neoplastic cells, a substance produced by a neoplastic cell, an activated leukocyte, an activated lymphocyte, a plasma cell, surface or circulating substances produced by cells, an antibody, in particular an autoantibody, a thrombus (or a component thereof) or a pathogen (e.g. virus, bacteria, fungi) or a component thereof, such as a surface antigen. 17. A composition according to any of claims 1-16, wherein the ligand or ligand analogue is a growth factor, a peptide or polypeptide hormone, a cytokine, a detoxified toxin, a vitamin, a steroid hormone, a substance acting on the central nervous system, hyaluronan, , chondroitin, sulfate, N-terminal peptide of collagen type III, mannose-terminated glycoconjugates, a glycoside (coupled to a bioactive substance) or tissue plasminogen activator. 18. A method of providing the rapid clearance of a bioactive substance from the circulation, the method comprising administering, to a subject in need hereof, (a) an effective amount of a capturing agent capable of binding a bioactive substance as well as a ligand or ligand analogue which is able to bind to a cellular receptor, followed, after a suitable interval, by administration of (b) an effective amount of a ligand or ligand analogue capable of binding to a cellular receptor as well as to said capturing agent. 19. A method of rapid jln vivo detection of a pathological condition, the method comprising administering (a) an effective amount of a capturing agent capable of binding a bioactive substance characteristic of the pathological condition in question as well as a ligand or ligand analogue which is able to bind to a cellular receptor, followed, after a suitable interval, by administration of (b) an effective amount of a ligand or ligand analogue capable of binding to a cellular receptor as well as to said capturing agent so as to provide a rapid clearance of the capturing agent from the circulation. 42 20. Use of a capturing agent capable of binding a bioactiv substance as well as a ligand or ligand analogue which is abl to bind to a cellular receptor for the manufacture, i combination with a ligand or ligand analogue capable of bindin to a cellular receptor as well as to said capturing agent, o a pharmaceutical composition providing the rapid clearance o a bioactive substance from the circulation. 21. Use of a capturing agent capable of binding a bioactiv substance characteristic of a pathological condition as wel as a ligand or ligand analogue which is able to bind to cellular receptor for the manufacture, in combination with ligand or ligand analogue capable of binding to a cellula receptor as well as to said capturing agent, of a diagnostic composition providing the rapid clearance of the capturing agent from the circulation and hence a rapid detection of the pathological condition in question.

Inventors: SELMER JOHAN, SELMER, JOHAN
Applicants: NOVONORDISK AS, NOVO NORDISK A/S
Application year: 1991
Main classification: A61K49
IPC codes: A61K38, A61K39, A61K45, A61K47, A61K49, A61P3, C07K16, C07K19, G01N33