Invention relates to antibodies with a specificity to an abnormally truncated form of tau protein which is conformationally different from normal tau and does not bind to normal tau protein, conformationally different tau proteins ("tauons") and diagnostic and therapeutical aspects in relation to Alzheimer's disease and related tauopathies.

Description of the Invention

The invention relates to Alzheimer's disease and to other tauopathies.

This application is a U.S. national phase application under 35 U.S.C .sctn. 371 of PCT Application No. PCT/EP02/00897 filed 29 Jan. 2002, which claims priority to Austrian Application No. A 175/2001 filed 2 Feb. 2001.

Alzheimer's disease (AD) is the most common chronic neurodegenerative disorder which is characterized clinically by a progressive and irreversible loss of cognitive and behavioral function. The disease can persevere for over 10 years, advancing from mild symptoms to extremely severe manifestations. AD afflicts approximately 10% of the population over the age of 65 and 20% of the population over the age of 80. As a result of growing of Western societies, the number of persons afflicted is rising: already there are five million sufferers in the USA alone and by the end of the year 2000, there will be roughly 18 million people with dementia in the world. Of these, it is thought, that about two third of cases, i.e. 12 million, will be Alzheimer's disease. It is the fourth largest killer in the Western world after the heart diseases, cancer and strokes. The number of people with dementia is rising quickly. By 2025, there will be twice the number of people with dementia in the developed world as there were in 1980. The cost to the society for looking after the sufferers is enormous. For example, the costs to the US society for diagnosing and managing AD, primarily for custodial care, is currently estimated at US $80 billion annually. Currently, neither presymptomatic diagnostic test nor cure for AD is available. The disease is therefore clinically diagnosed after appearance of symptoms primarily by exclusion of other forms of dementia. Accumulation of the classical hallmarks, senile (neuritic) plaques and neurofibrillary tangles (NFT) in the AD brains, observed 93 years ago by the Bavarian psychiatrist Alois Alzheimer in 1907, still remain the neuropathological characteristic of AD.

The common denominator of intracellular neurofibrillary structures (neurofibrillary tangles, dystrophic neurites, and neuropil threads) are paired helical filaments (PHFs). The major protein subunit of the PHFs is microtubule associated protein tau in abnormally hyperphosphorylated form (Grundke-Iqbal et al., 1986; Wischik et al., 1988 a,b). Neurons with neurofibrillary changes degenerate, and the degree of this degeneration directly correlates with the degree of dementia in the affected individuals (Blessed et al., 1968).

Normal tau is a microtubule associated protein that distributes mainly to axons. Tau protein is taking part in modulating the assembly, spatial organization and behavior of microtubules (MT) in neurons and probably glial cell bodies (Drewes et al., 1998; Drubin and Kirschner, 1986; Lo-Presti et al., 1995). Tau proteins are encoded by a single gene located on chromosome 17, but are detected as multiple isoforms in tissue extracts from adult brains (Goedert et al., 1989; Himmler A., 1989; Kosik et al., 1989). Heterogeneity of tau proteins is in part due to alternative splicing, giving rise to six isoforms in the adult human brain. These distinct isoforms differ by the presence or absence of 29- or 58-amino acid inserts in the amino-terminal region and by the addition or deletion of a tandem repeat (which can be repeated either 3 or 4 times) in a carboxy-terminal region of tau referred to as microtubule binding domain. This region is composed of imperfect repeats of 31 or 32 amino acid residues. In humans, the smallest tau isoform contains 352 amino acid residues with three tandem repeats in the MT-binding domain and no amino terminal inserts, whereas the largest isoform contains 441 residues with four repeats and both amino terminal inserts. For simplicity, all numbering in this patent application refers to the longest human tau protein isoform, htau40, containing all inserts (441 amino acid long) according to Goedert et al. (1989).

A number of neurological diseases are known to have filamentous cellular inclusions containing microtubule associated protein tau e.g. Alzheimer's disease (AD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), Pick's disease (PiD) and a group of related disorders collectively termed frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17), amyotropic lateral sclerosis (ALS), Creutzfeldt-Jakob disease (CJD), dementia pugilistica (DP), Gerstmann-Straussler-Scheinker disease (GSSD), Lewy body disease and Huntington disease (Dickinson et al., 1998; DiFiglia et al., 1997; Forno, 1986; Hirano and Zimmerman, 1962; Nishimura et al., 1995; Prusiner 1996; Reed et al., 1998; Roberts, 1998; Schmidt et al., 1996; Shankar et al., 1989; Spillantini et al., 1998). Although the etiology, clinical symptoms, pathologic findings and the biochemical composition of inclusions in these diseases are different, there is emerging evidence suggesting that the mechanisms involved in aggregation of normal cellular proteins to form various filamentous inclusions are comparable. It is believed, that an initial alteration in conformation of microtubule associated protein tau, that initiates generation of nuclei or seeds for filament assembly, is a key feature. This process can be influenced by the posttranslational modification of normal proteins, by mutation or deletion of certain genes and by factors that bind normal proteins and thus alter their conformation. The tau protein is very hydrophilic. It can be readily extracted from brain tissue or cultured cells. In comparison, filamentous tau extracted from Alzheimer's diseased brain tissues is relatively insoluble. Besides phosphorylation, insoluble and normal soluble tau differ in the extent of posttranslational modifications, which include glycosylation, glycation, ubiquitination and racemization (Kenessey et al., 1995; Ko et al., 1999; Mori et al., 1987; Wang et al., 1996; Yan et al., 1994).

The mechanism by which tau protein is modified to take part in filament formation in AD is unknown. Tau is one of the most soluble proteins known (Cleveland 1977 a,b; Lee et al. 1988) and therefore its aggregation in AD is particularly enigmatic. Phosphorylation of tau affects the potential of tau to form aggregates, producing either stimulatory or inhibitory effects, presumably depending on the site of phosphorylation (Crowther et al., 1994; Schneider et al., 1999). Many in vitro studies demostrate that in the presence of the reducing agent, dithiothreitol (DTT), unsaturated free fatty acids, RNA or glycosaminoglycans, normal tau can be transformed into filaments (Goedert et al., 1996; Kampers et al., 1996; Perez et al., 1996; Wilson and Binder, 1997). Furthermore, the process of filament formation can also be accelerated by the presence of cross-linked tau generated through oxidation at Cys322 (Schweers et al., 1995). The parameters that have been varied in different filament assembly studies have included tau protein concentration, pH, and ionic strength of the incubation is many fold higher than exists in the cytoplasm under physiological conditions. Examination of in vitro formed tau filaments by scanning transmission electron microscopy (STEM) showed that these filaments differ from native paired helical filaments (Ksiezak-Reding, 1998). In the absence of glycans or RNA, no PHF-like filaments are detectable in samples containing unphosphorylated or phosphorylated wild type tau; normal tau. Studies of chemically cross-linked, heparin treated tau indicate that heparin treatment induces conformational change in tau protein (Paudel and Li, 1999). Taken together the in vitro data suggest (a) that the microtubule binding domain is important for assembly of tau filaments; and (b) that formation of tau filaments requires conformational change(s) of tau. Simultaneously these studies show that none of tau modifications described, are alone capable to induce filamentous tau formations that correlate with clinical expression of Alzheimer's disease. Identification and description of factors important for the initiation of tau changes leading to filament formation in disease conditions would be important for the development of presymptomatic diagnostic markers and therapeutic agents to interfere the progression of tauopathies.

An object of the present invention is therefore to provide a reliable drug target for early therapeutic intervention in Alzheimer's disease and other tauopathies. Furthermore it is desired to provide a specific monoclonal antibody capable of specific detection and interaction with this drug target. This antibody should not only be suitable for presymtomatic detection of the molecule but for inhibition and elimination of this molecule as well, hence being suitable for presymtomatic diagnosis, treatment and prevention of Alzheimer's disease and other tauopathies.

These objects are addressed with the present invention which relates in one aspect to an antibody with a specificity to abnormal forms of tau protein which are conformationally different from normal tau, said antibody being non-specific for a normal tau protein. Such abnormal forms of tau proteins represent a novel family of molecules, intra- and extra-neuronally located soluble and insoluble, preferably abnormally truncated, forms of tau proteins, which are conformationally different from normal tau (Novak et al., 1991, 1993). It could be shown with the present invention that these conformationally different forms of tau proteins--which are called "tauons" within the present specification--are seeds, nucleation centers in a self-propagating process of filamentous tau formations that is correlative to clinical expression of Alzheimer's disease thus tauons are important therapeutic targets for Alzheimer's disease. The tauons according to the present invention may be abnormally truncated tau proteins. Biological activity of tauons can be inhibited in vitro and inside of neurons by the antibodies according to the present invention. These antibodies have a capacity to stain presence of tauons in presymtomatic stages I, II and III of AD, which makes them suitable for presymtomatic diagnosis of this disease. It is critical for the antibodies according to the present invention that only the conformationally different form of tau protein (i.e. the "tauon") is recognized by this antibody whereas the normal tau protein does not bind to the antibodies according to the present invention.

Within the course of the present invention AD truncated forms of microtubule associated protein tau were purified to homogenity and shown to be a major part of filamentous tau isolations from Alzheimer's diseased neurons. The amino acid sequence data indicated that the backbone of tauons is indistinguishable from that of protein tau but tauons could be distinguished immunologically from normal human tau by the different conformation as revealed by the conformation specific monoclonal antibodies according to the present invention. Specific examples for such antibodies are the monoclonal antibody DC-11 which is produced by the hybridoma cell line which was deposited in the European Collection of Cell Cultures (ECACC) under deposit No. 00082216 and monoclonal antibody DC-11/I which is produced by the hybridoma cell line DC-11/I and was deposited in the ECACC under deposit No. 00082215. This family of monoclonal antibodies which is provided with the present invention is defined by recognition of tauon-specific conformation without recognizing normal human soluble tau. The different conformation compared to normal human tau, was attributed pathologically to abnormal truncation at the N-terminus or at the C-terminus or at both termini of tau molecule in the samples tested so far from Alzheimer's disease patients. Interestingly, the different conformation was regardless of tau isoform and level of phosphorylation. The indispensable pathological requirements for tauons to attain typical conformation is presence of prolin rich and microtubule binding domains and truncated flanking region(s). Furthermore tauons could be distinguished from normal human tau by their pathological activities, namely that tauons represent a seed, nucleation center, that initiates tau aggregation and tauons disassemble microtubules assembled from normal tau and tubulin. Tauons preincubated with antibodies according to the present invention, especially monoclonal antibodies of the DC-11 family, showed no diassemble capacity or assembled microtubules from normal tau and tubulin. Moreover, tauons cause upon microinjection to differentiated human neurons significant displacement of endogenous tau from microtubule bound tau fraction, retraction of neuronal processes and degeneration of the cells. If tauons are microinjected together with monoclonal antibodies according to the present invention, no neurodegenerative changes were observed in differentiated neurons. This shows that the antibodies according to the present invention, especially the DC-11 monoclonal antibodies, inhibit tauons activity intraneuronally and therefore could be used as intracellular drugs (for example as therapeutic intracellular antibodies, intrabodies). Immunohistologically, as seen with the antibodies according to the present invention, tauons occur already in presymptomatic stages I, II and III in pre-.alpha.-neurons, in both the transenthorinal and enthorinal region of AD, therefore, after proper coupling of tracers, antibodies according to the present invention could be used for intravital presymptomatic diagnosis for AD.

Preferably, the antibody according to the present invention exhibits a specificity of at least 50%, preferably at least 90% to the conformationally different form of tau ("tauon") compared to the antibody DC-11. Specificity may be tested by any standard test available for detecting antibody's specificity, e.g. ELISA tests, radioimmuno-assays, atomic force microscopy with cantilever-bound binding partners, etc.

Generally, all antibodies which are specifically reactive with the conformationally different tau protein, especially abnormally truncated forms thereof, but not with normal soluble tau are also included within the scope of the present invention.

Preferably, the antibody according to the present invention is said to be "specifically reactive" with a molecule if it is capable of binding with a molecule to thereby couple the molecule to the antibody. The term "epitope" is meant to refer to that portion of an antigen which can be recognized and bound by an antibody. An antigen may have one or more than one epitope. An "antigen" is capable of inducing an animal to produce antibody capable of binding to an epitope of that antigen. The specific reaction referred to above is meant to indicate that the antigen will immunoreact, in a highly selective manner, with its corresponding antibody and not with the multitude of other antibodies which may be evoked by other antigens.

Especially preferred antibodies according to the invention are derived from deposited hybridoma cell lines DC-11 (ECACC deposit No. 00082216) and DC-11/I (ECACC deposit No. 00082215) exhibit high specificity and selectivity and will react with conformationally different form of tau ("tauon"), but not with normal soluble tau. Specificity may be tested by any standard test available for detecting antibody's specificity, e.g. ELISA tests, radioimmuno-assays, etc.

"Antibody" as used herein is meant to include intact molecules and fragments thereof as well as synthetic and biological derivatives thereof, such as for example Fab, F(ab').sub.2 an F.sub.V fragments-free or expressed e.g. on the surface of filamentous phage on pIII or pVIII or other surface proteins, or on the surface of bacteria, which are capable of binding an antigen. Fab, F(ab').sub.2 and F.sub.V fragments lack the F.sub.C fragments of intact antibody, clear more rapidly from the circulation and may have less non-specific tissue binding of antibody. Furthermore F.sub.V antibody (often called as minibody) can be easily engineered to carry on its C-terminus specific tracer and used for early intravital presymtomatic diagnosis of AD, since stage I, II and III of AD that is recognized by the antibodies according to the present invention is not associated with intellectual decline.

Within the present invention, monoclonal antibodies or monoclonal antibody fragments are preferred. Therefore, according to another aspect the present invention also relates to hybridoma cell lines producing a monoclonal antibody according to the present invention.

The term "tau" as used in the present application refers to the longest isoform of human microtubule associated protein tau containing all alternatively spliced inserts as described in M. Goedert et al., 1989.

According to another aspect of the present application the invention relates to an abnormally truncated form of tau protein which is a conformationally different form of tau protein, said conformationally different form of tau protein specifically recognizeable by an antibody according to the present invention.

Accordingly, the present invention is drawn to a novel family of molecules intra- and extraneuronally located soluble and insoluble abnormally truncated form of tau proteins which are conformationally different from normal tau and are called "tauons".

"Tauons" therefore are conformationally different forms of tau protein which are specifically recognized by the antibodies according to the present invention. Tauons useful in the present invention comprise the sequence according to SEQ ID No:1 and may be flanked by further amino acids (see SEQ ID NO:2 and SEQ ID NO:3). The tauons conveniently are in the range from about 100 to 400 amino acids and represent truncated forms of tau protein in this range. The tauons according to the present invention may be abnormally truncated at the N- or C-terminus or at both termini (see FIGS. 2-13, see Original Patent). The term "abnormally truncated" as used herein refers to tau peptides ("tauons") identified in diseased neurons in AD with tauon specific monoclonal antibodies provided with the present invention.

Abnormally truncated forms of human tau proteins--tauons--can be prepared by using any of numerous well known synthetic recombinant techniques. Briefly, most of the techniques which are used to transform cells, construct vectors, extract messenger RNA, prepare cDNA libraries, and the like are widely practiced in the art, and most practitioners are familiar with the standard resource materials which describe specific conditions and procedures. However, for convenience, the following paragraphs may serve as a guideline.

The most commonly used prokaryote system for the production of recombinant proteins remains E. coli, however, other microbial strains may also be used, such as Bacilli, for example Bacillus subtilis, various species of Pseudomonas, or other bacterial strains. In such prokaryotic systems, plasmid vectors which contain replication sites and control sequences derived from a species compatible with the host are used. Commonly used prokaryotic control sequences include promoters for transcription initiation, optionally with an operator, along with ribosome binding site sequences.

A wide variety of eukaryotic hosts are also now available for production of recombinant foreign proteins. As in bacteria, eukaryotic hosts may be transformed with expression systems which produce the desired protein directly, but more commonly, signal sequences are provided to effect the secretion of the protein. Eukaryotic systems have the additional advantage that they are able to process introns which may occur in the genomic sequences encoding proteins of higher organisms. Eucaryotic systems also provide a variety of processing mechanisms which result in, for example, glycosylation, oxidation or derivatization of certain amino acid residues, conformational control, and so forth.

Commonly used eukaryotic systems include yeast, insect cells, mammalian cells, avian cells, and cells of higher plants. The list is not exhaustive. Suitable promoters are available which are compatible and operable for use in each of these host types as well as are termination sequences and enhancers, as e.g., the baculovirus polyhedron promoter. As above, promoters can be either constitutive or inducible. For example, in mammalian system, the MTII promoter can be induced by the addition of heavy metal ions.

The particulars for the construction of expression systems suitable for desired host are known to those in the art. For recombinant production of the protein, the DNA encoding it is suitable ligated into the expression system of choice, and the system is then transformed into the compatible host cell which is then cultured and maintained under conditions wherein expression of the foreign gene takes place. The tauons of this invention produced this way, are recovered from the culture, either by lysing the cells or from the culture medium as appropriate and known to those in the art.

Correct ligations for plasmid construction can be confirmed by the first transforming a suitable host with the ligation mixture. Successful transformants are selected by ampicillin, tetracycline or other antibiotic resistance or using other markers depending on the mode of plasmid construction, as is understood in the art.

The present invention therefore relates to a preparation of tauons, especially from human or recombinant resources, being essentially free of other proteins, especially from normal tau proteins. Such preparations may be provided by procedures involving an immunoaffinity step using the antibodies according to the present invention. Preferably, the preparation according to the present invention contains more than 80% tauons, especially more than 95% tauons, of total protein.

Further the present invention also relates to a kit for detecting tauons, abnormally truncated forms of tau protein, which are conformationally different from normal tau in a sample of Alzheimer's disease brain tissue or in a sample of a body fluid comprising an antibody according to the present invention and a suitable container for providing the sample. It is possible to provide the antibodies in a kit for detecting or isolating of tauons. With the help of antibodies according to the present invention tauon proteins may be detected and isolated from various sources including Alzheimer's diseased neurons of transenthorinal, enthorinal region and hippocampus. Tauons isolated in this way may be further used as immunogen for immunization e.g. of mice for construction of hybridomas producing specific monoclonal antibodies against tauons not recognizing normal full length tau. This method comprises identifying and releasing neurons from transenthorinal, enthorinal and hippocampal region of Alzheimer's diseased brain tissues into the solution preserving abnormal conformation of tauons.

After preparation and purification, tauons are used as immunogens and injected subcutaneously to mice in monthly intervals. Spleens from these animals are used for construction of hybridomas producing monoclonal antibodies against tauons. These can be produced using well-established hybridoma techniques first introduced by Kohler and Milstein (see M. Kohler and C. Milstein, "Continuous Cultures of Fused Cells Secreting Antibody of Pre-Defined Specificity", Nature, 256, pp. 495-497, 1975). After a sufficient long immunization, antibody-producing lymphocytes are obtained from the animal either from the spleen, lymph nodes or peripheral blood. Preferably, the lymphocytes are obtained from the spleen. The splenic lymphocytes are then fused with a myeloma cell line, usually in the presence of a fusing agent such as polyethylene glycol (PEG). Any of number of myeloma cell lines may be used as a fusion partner according to standard techniques; for example the P3-NS1/1-Ag4-1, P3-x63-Ag8.653 myeloma lines. The resulting cells, which include the desired hybridomas, are then grown in a selective medium, such as HAT medium, in which unfused parental myeloma or lymphocyte cell eventually die. Only the hybridoma cells survive and can be grown under limiting conditions to obtain isolated clones. The supernatants of the hybridomas are screened for the presence of antibody of that desired specificity, e.g. by immunoassay techniques using the antigen that had been used for immunization. Positive clones can then be subcloned under limiting dilution condition or on soft agar and the monoclonal antibody produced can be isolated. Hybridomas produced according to these methods can be propagated in vitro or in vivo (in ascites fluid) using techniques known in the art. Commonly used methods for purfying monoclonal antibodies include ammonium sulphated precipitation, ion exchange, chromatography, and affinity chromatography (see e.g., H. Zola et al., "Techniques for the Production and Characterization of Monoclonal Antibodies", in Monoclonal Hybridoma Antibodies: Techniques and Applications, J. G. R. Hurell (ed.), pp. 51-52 (CRC Press 1982)).

Preferably, the kit according to the present invention further contains means for detecting the binding event of said antibody binding to said conformationally different tau protein. Preferably secondary antibodies especially secondary antibodies which are specifically labeled. Also the magnetic beads technology may be used within the scope of the present invention as well as other protein identifying methods using antibodies. The method comprises identifying in a test sample from the person, tauon, which is abnormally truncated tau protein. "Test sample" as used herein refers to biological sample from the person that is suspected of containing tauons. Test sample can comprise brain tissue having abnormally truncated tau proteins, such as hippocampal tissue or frontal cortex tissue or, the test sample can comprise cerebrospinal fluid (CSF). In a preferred embodiment, the test sample comprises CSF and the protein identified is CSF-tauon. Identification of abnormally truncated tau proteins--tauons--conveniently comprises indentifying in the test sample antigens capable of binding with antibodies specifically reactive with abnormally truncated tau proteins--tauons--comprising the sequence (SEQ ID NO:1) and flanked by amino acids such that said tauons are in range from about 100 to 400 amino acids in length and characterized by tauon specific conformation different from normal soluble protein tau, or antibodies specifically reactive with abnormally truncated tau proteins--tauons--comprising the sequence (SEQ ID NO:1) and flanked by amino acids such that said tauons are in range from about 100 to 400 amino acids in length and characterized by tauon specific conformation different from normal soluble protein tau. The presence of a tauon indicates a disease associated with the accumulation of the tauons in AD patients and other sufferers with tauopathies.

A further aspect of the present invention relates to a method for detecting an abnormally truncated form of tau protein which is conformationally different from normal tau in a body fluid of a patient comprising mixing said body fluid with an antibody according to the present invention, detecting the presence of a binding event between the antibody and the conformationally different tau protein (tauon) and optionally measuring the amount of conformationally different tau protein being bound to said antibody. The presence of a tauon indicates a disease associated with the accumulation of the tauons in a person including AD and other tauopathies. The body fluid of a patient may be any biological test sample from a person that is suspected of containing tauons. This body fluid can comprise brain tissue such as hippocampal tissue or frontal or a cortex tissue or cerebrospinal fluid (CSF). In a preferred embodiment the body fluid comprises CSF and the protein identified is CSF-tauons.

This identification of tauons can conveniently be acomplished by biochemical or cytochemical means or by enzyme immunoassays such as decribed in many manuals of immunoassay producers as it is understood in the art. When biochemical means are used preferably 0.01 to 10 g, especially 0.5 to 1 g, of tissue containing diseased tau protein is used, run on a gel and identified by Western blot. Such a technique is believed do be adequate in the absence of age matched controls which have been shown to be non-reactive with the antibodies according to the present invention. Cytochemical means, staining, has shown no reactivity with normal tissue.

CSF from patients with AD and patients with non-AD neurological diseases as well as normal subjects were surveyed by ELISA to quantitate level of tauons. The CSF tauon level was significantly increased in AD patients as compared with that with patients with non AD neurological diseases and controls. In AD, the significant increase was found irrespective of age of onset, apolipoprotein E genotype and clinical stage. Western blots of AD CSF proteins reveal several immunoreactive bands with apparent molecular weight between 50 and 15 kD consistent with abnormally truncated tau proteins. These results indicate that CSF-tauons reflect that progressive accumulation of diseased tau caused by progression of AD.

According to a further aspect the antibodies according to the present invention may be used for the preparation of drug for the treatment of Alzheimer's disease patients. The antibodies may be biotechnologically modified into single chain molecules equipped with targeting sequence able to deliver them into the neuroblastoma cells expressing tauons. Inside of the present AD cellular model, antibodies bind tauons and interfere with their pathological effects (sequestration of normal tau) and increase the degradation of abnormally truncated forms of tau protein. In vitro assays (sequestration of tau protein, filament assembly, microtubule disassembly) with abnormally truncated tau proteins and their correlation with severity of Alzheimer's disease show that they are important drug targets.
 

Claim 1 of 14 Claims

1. An isolated DC-11 or DC-11/I antibody as produced by hybridoma cell line DC-11 (ECACC Deposit No: 00082215) or DC-11/I (ECACC Deposit No: 00082216).

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