Antibody capable of binding specifically to ab-oligomer, and use thereof   

The present application is a continuation of U.S. application Ser. No. 12/533,348, filed Jul. 31, 2009, now pending. U.S. application Ser. No. 12/533,348, is a nonprovisional of provisional U.S. Application No. 61/085,545, filed Aug. 1, 2008, now abandoned, and a continuation-in-part of International Application No. PCT/JP2009/052039, filed Feb. 6, 2009, now pending. The present application is also a continuation-in-part of International Application No. PCT/JP2009/052039, filed Feb. 6, 2009, now pending. International Application No. PCT/JP2009/052039 claims priority to Japanese Patent Application No. 2008-028386, filed Feb. 8, 2008, now abandoned, and Japanese Patent Application No. 2008-201058, filed Aug. 4, 2008, now abandoned. The entire contents of these applications are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to antibodies that specifically bind to Aβ oligomers and uses thereof.

BACKGROUND OF THE INVENTION

Various evidence has shown that deterioration of memory arises from synaptic dysfunction triggered by soluble Aβ oligomers (see Klein W L, Trends Neurosci. 24: 219-224, 2001; and Selkoe D J, Science 298: 789-791, 2002). Excessive accumulation and deposition of Aβ oligomers may be the trigger for a series of pathological cascades that lead to Alzheimer\'s disease (AD). Therefore, therapeutic intervention targeting Aβ oligomers may be effective for blocking these cascades. However, findings on core molecules of this amyloid cascade hypothesis which are responsible for neurodegeneration, particularly on neurodegeneration mediated by Aβ oligomers, originate from in vitro experiments (see Hass C et al.: Nature Review 8: 101-12, 2007). This neurodegeneration has not been proven directly in vivo. The greatest defect of previously reported in vivo experiments is that they failed to demonstrate synaptic toxicity of endogenous Aβ oligomers due to the lack of conformation-specific molecular tools (see Lee E B, et al.: J. Biol. Chem. 281: 4292-4299, 2006). There has been known no technique capable of proving the toxicity within the human brain, an aspect which is difficult to demonstrate even in Alzheimer\'s disease mouse models. Thus, the in vivo neurotoxicity of endogenous Aβ has been often disregarded. It has been unknown why NFT formation and loss of nerve cells precede senile plaque formation in the human entorhinal cortex, and how Aβ

SUMMARY

The present invention was achieved in view of the above circumstances. An objective of the present invention is to provide antibodies that bind specifically to Aβ oligomers, and uses thereof. More specifically, the present invention provides antibodies that bind specifically to Aβ oligomers, methods for detecting Aβ oligomers using the antibodies, methods for diagnosing Alzheimer\'s disease using the antibodies, and pharmaceutical agents comprising the antibodies.

The present inventors produced monoclonal antibodies that are specific to only soluble amyloid β (Aβ) oligomers and do not recognize soluble Aβ monomers which are physiological molecules, and confirmed that the antibodies have the following:

(1) anti-neurotoxic activity; (2) activity to suppress Aβ amyloid fibril formation; (3) specificity to recognize only Aβ oligomers; (4) ability to capture Aβ oligomers in AD brain; and (5) ability to prevent the development of Alzheimer\'s disease-like phenotypes (memory impairment, brain Aβ accumulation) in APPswe transgenic mice (Tg2576).

Using an ultrafiltration/molecular sieve method, among the antibodies produced, monoclonal 1A9 and 2C3 were determined to specifically recognize oligomers of 30 kDa or more, mainly 100 kDa or more, but not monomers of approximately 4.5 kDa. The two antibodies were confirmed to have neurotoxicity-neutralizing activity by evaluating the neutralizing effect against Aβ 1-42-induced neurotoxicity in PC12 cells differentiated into nerve cells. Thioflavin T assay and electron microscopy showed that the antibodies have activity to suppress Aβ amyloid fibril formation. The ability of 1A9 and 2C3 to capture Aβ oligomers in AD brain was confirmed by immunoprecipitation using the antibodies in the presence of SDS-stable 4-, 5-, 8-, and 12-mers. Furthermore, to determine the in vivo neurotoxicity in the human brain, the amount of polymers recognized by the antibodies was evaluated in the human entorhinal cortex mostly at Braak NFT Stages I to III. By particularly focusing on the 12-mer, which has been reported to have neurotoxicity in animal studies, it was confirmed that the polymer accumulation precedes the occurrence of cognitive impairment, and is increased with the progression of Braak NFT stage. This result shows for the first time that the 12-mer, which is specifically recognized by the antibodies, is a conformational assembly that causes in vivo neurotoxicity in the human brain. The present inventors also discovered that the oligomeric conformational structure recognized by the antibodies is present in cerebrospinal fluid (CSF), and is increased in AD patients. The present inventors used 1 A9 or 2C3 in passive immunotherapy by intravenous injection as with other neurological disorders. It was confirmed that Tg2576 mice are protected from memory impairment, senile plaque formation, synaptic dysfunction, and Aβ accumulation by subchronic passive immunotherapy, without harmful side-effects. The results obtained by the present inventors demonstrated for the first time that monoclonal 1A9 and 2C3 are promising candidates for therapeutic antibodies for preventing Alzheimer\'s disease-like phenotypes in Tg2576 mice, which are expected to show their effect by conventional peripheral intravenous administration, and thus there is no need to consider brain transfer.

The present inventors also confirmed that passive immunotherapy using the 1A9 and 2C3 antibodies suppresses senile plaque amyloid formation and swollen dystrophic neurite formation. Furthermore, the present inventors discovered that a fraction of the 1A9 and 2C3 antibodies administered into the blood transfers into the brain.

As described above, the present inventors disclose herein that monoclonal 1A9 and 2C3, which are antibodies that specifically bind to Aβ oligomers, fulfill all of the diagnostic/therapeutic antibody criteria, and are promising candidates for therapeutic antibodies for diagnosing/preventing Alzheimer\'s disease.

Furthermore, as with the 1A9 and 2C3 antibodies, the present inventors successfully obtained the 5A5, 5A9, 4F7, 4H5, 6E4, and 61-14 antibodies which bind specifically to Aβ oligomers, but do not recognize Aβ monomers. The present inventors discovered that these six types of antibodies have activity to neutralize Aβ-induced neurotoxicity and to suppress Aβ amyloid fibril formation.

The present inventors disclose that the above-mentioned 5A5, 5A9, 4F7, 4H5, 6E4, and 6H4 antibodies are promising candidates for therapeutic antibodies for diagnosing/preventing Alzheimer\'s disease.

More specifically, the present invention provides the following:

[1] an antibody binding to an Aβ oligomer that binds to an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 1 and an L chain having the amino acid sequence of SEQ ID NO: 3; [2] an antibody binding to an Aβ oligomer that binds to an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 21 and an L chain having the amino acid sequence of SEQ ID NO: 23; [3] an antibody binding to an Aβ oligomer that binds to an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 41 and an L chain having the amino acid sequence of SEQ ID NO: 43; [4] an antibody binding to an Aβ oligomer that binds to an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 61 and an L chain having the amino acid sequence of SEQ ID NO: 63; [5] an antibody binding to an Aβ oligomer that binds to an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 81 and an L chain having the amino acid sequence of SEQ ID NO: 83; [6] an antibody binding to an Aβ oligomer that binds to an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 101 and an L chain having the amino acid sequence of SEQ ID NO: 103; [7] an antibody of any one of (1) to (38) below: (1) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 9 as CDR1, the amino acid sequence of SEQ ID NO: 11 as CDR2, and the amino acid sequence of SEQ ID NO: 13 as CDR3; (2) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 15 as CDR1, the amino acid sequence of SEQ ID NO: 17 as CDR2, and the amino acid sequence of SEQ ID NO: 19 as CDR3; (3) an antibody that comprises the H chain of (1) and the L chain of (2); (4) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 5 as VH; (5) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 7 as VL; (6) an antibody that comprises the H chain of (4) and the L chain of (5); (7) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 29 as CDR1, the amino acid sequence of SEQ ID NO: 31 as CDR2, and the amino acid sequence of SEQ ID NO: 33 as CDR3; (8) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 35 as CDR1, the amino acid sequence of SEQ ID NO: 37 as CDR2, and the amino acid sequence of SEQ ID NO: 39 as CDR3; (9) an antibody that comprises the H chain of (7) and the L chain of (8); (10) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 25 as VH; (11) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 27 as VL; (12) an antibody that comprises the H chain of (10) and the L chain of (11); (13) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 49 as CDR1, the amino acid sequence of SEQ ID NO: 51 as CDR2, and the amino acid sequence of SEQ ID NO: 53 as CDR3; (14) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 55 as CDR1, the amino acid sequence of SEQ ID NO: 57 as CDR2, and the amino acid sequence of SEQ ID NO: 59 as CDR3; (15) an antibody that comprises the H chain of (13) and the L chain of (14); (16) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 45 as VH; (17) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 47 as VL; (18) an antibody that comprises the H chain of (16) and the L chain of (17); (19) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 69 as CDR1, the amino acid sequence of SEQ ID NO: 71 as CDR2, and the amino acid sequence of SEQ ID NO: 73 as CDR3; (20) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 75 as CDR1, the amino acid sequence of SEQ ID NO: 77 as CDR2, and the amino acid sequence of SEQ ID NO: 79 as CDR3; (21) an antibody that comprises the H chain of (19) and the L chain of (20); (22) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 65 as VH; (23) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 67 as VL; (24) an antibody that comprises the H chain of (22) and the L chain of (23); (25) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 89 as CDR1, the amino acid sequence of SEQ ID NO: 91 as CDR2, and the amino acid sequence of SEQ ID NO: 93 as CDR3; (26) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 95 as CDR1, the amino acid sequence of SEQ ID NO: 97 as CDR2, and the amino acid sequence of SEQ ID NO: 99 as CDR3; (27) an antibody that comprises the H chain of (25) and the L chain of (26); (28) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 85 as VH; (29) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 87 as VL; (30) an antibody that comprises the H chain of (28) and the L chain of (29); (31) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 109 as CDR1, the amino acid sequence of SEQ ID NO: 111 as CDR2, and the amino acid sequence of SEQ ID NO: 113 as CDR3; (32) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 115 as CDR1, the amino acid sequence of SEQ ID NO: 117 as CDR2, and the amino acid sequence of SEQ ID NO: 119 as CDR3; (33) an antibody that comprises the H chain of (31) and the L chain of (32); (34) an antibody that comprises an H chain having the amino acid sequence of SEQ ID NO: 105 as VH; (35) an antibody that comprises an L chain having the amino acid sequence of SEQ ID NO: 107 as VL; (36) an antibody that comprises the H chain of (34) and the L chain of (35); (37) an antibody that comprises one or more amino acid substitutions, deletions, additions, and/or insertions in the antibody of any one of (1) to (36), which has equivalent activity to the antibody of any one of (1) to (36); and (38) an antibody that binds to the epitope bound by the antibody of any one of (1) to (36); [8] the antibody of [7], wherein the antibody is a chimeric antibody or a humanized antibody; [9] a composition comprising the antibody of any one of [1] to [8] and a pharmaceutically acceptable carrier; [10] an agent against cognitive impairment, which comprises the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [11] a therapeutic agent for Alzheimer\'s disease, which comprises the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [12] an agent for suppressing the progression of Alzheimer\'s disease, which comprises the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [13] an agent for suppressing senile plaque formation, which comprises the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [14] an agent for suppressing Aβ accumulation, which comprises the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [15] an anti-neurotoxic agent, which comprises the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [16] an agent for inhibiting Aβ amyloid fibril formation, which comprises the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [17] an agent against synaptic toxicity, which comprises the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [18] a method for detecting an Aβ oligomer, which comprises the step of detecting an Aβ oligomer contained in a sample collected from a subject using the antibody of any one of [1] to [8]; [19] a method of diagnosing whether or not a subject suffers from or is at a risk of developing Alzheimer\'s disease, which comprises using the antibody of any one of [1] to [8] to detect an Aβ oligomer in a sample collected from a subject; [20] a method of diagnosing whether or not a subject suffers from or is at a risk of developing Alzheimer\'s disease, which comprises the steps of: (a) contacting a sample collected from a subject with the antibody of any one of [1] to [8]; and (b) measuring the amount of Aβ oligomer in the sample, wherein the subject is determined to suffer from or be at a risk of developing Alzheimer\'s disease, when the amount measured in step (b) is higher than that of a healthy individual; [21] a method of diagnosing whether or not a subject suffers from or is at a risk of developing Alzheimer\'s disease, which comprises the steps of: (a) contacting a sample collected from a subject with the antibody of any one of [1] to [8] and an antibody that binds to an Aβ monomer; and (b) measuring the ratio of Aβ oligomer to Aβ monomer in the sample, wherein the subject is determined to suffer from or be at a risk of developing Alzheimer\'s disease, when the ratio measured in step (b) is higher than that of a healthy individual; [22] the method of any one of [18] to [21], wherein the sample is blood or cerebrospinal fluid; [23] a pharmaceutical agent for use in the method of any one of [18] to [21]; and [24] a kit for use in the method of any one of [18] to [21].

Furthermore, the present invention provides the following:

[25] a method for preventing and/or treating cognitive impairment, which comprises the step of administering the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [26] a method for preventing and/or treating Alzheimer\'s disease, which comprises the step of administering the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [27] a method for suppressing the progression of Alzheimer\'s disease, which comprises the step of administering the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [28] a method for suppressing senile plaque formation, which comprises the step of administering the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [29] a method for suppressing Aβ accumulation, which comprises the step of administering the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [30] a method for neutralizing neurotoxicity, which comprises the step of administering the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [31] a method for inhibiting Aβ amyloid fibril formation, which comprises the step of administering the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [32] a method for neutralizing synaptic toxicity, which comprises the step of administering the antibody of any one of [1] to [8] or the composition of [9] as an active ingredient; [33] use of the antibody of any one of [1] to [8] or the composition of [9] in the production of an agent against cognitive impairment; [34] use of the antibody of any one of [1] to [8] or the composition of [9] in the production of a therapeutic agent for Alzheimer\'s disease; [35] use of the antibody of any one of [1] to [8] or the composition of [9] in the production of an agent for suppressing the progression of Alzheimer\'s disease; [36] use of the antibody of any one of [1] to [8] or the composition of [9] in the production of an agent for suppressing senile plaque formation; [37] use of the antibody of any one of [1] to [8] or the composition of [9] in the production of an agent for suppressing Aβ accumulation; [38] use of the antibody of any one of [1] to [8] or the composition of [9] in the production of an agent for neutralizing (suppressing) neurotoxicity; [39] use of the antibody of any one of [1] to [8] or the composition of [9] in the production of an agent for inhibiting Aβ amyloid fibril formation; [40] use of the antibody of any one of [1] to [8] or the composition of [9] in the production of an agent for neutralizing (suppressing) synaptic toxicity; [41] the antibody of any one of [1] to [8] or the composition of [9] for use in preventing and/or treating cognitive impairment; [42] the antibody of any one of [1] to [8] or the composition of [9] for use in preventing and/or treating Alzheimer\'s disease; [43] the antibody of any one of [1] to [8] or the composition of [9] for use in suppressing the progression of Alzheimer\'s disease; [44] the antibody of any one of [1] to [8] or the composition of [9] for use in suppressing senile plaque formation; [45] the antibody of any one of [1] to [8] or the composition of [9] for use in suppressing Aβ accumulation; [46] the antibody of any one of [1] to [8] or the composition of [9] for use in neutralizing (suppressing) neurotoxicity; [47] the antibody of any one of [1] to [8] or the composition of [9] for use in inhibiting Aβ amyloid fibril formation; and [48] the antibody of any one of [1] to [8] or the composition of [9] for use in neutralizing (suppressing) synaptic toxicity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents photographs and a graph showing the results of production and characteristic determination of oligomer-specific antibodies. A: Electrophoresis of immunogens. The Aβ 1-42 tetramer (black arrowhead) which is free of contamination of the Aβ 1-42 monomer (outlined arrowhead) was isolated using SDS-PAGE. Lane 1: Aβ 1-42 dissolved in 10 mM phosphate buffer; and Lane 2: Aβ 1-42 dissolved in distilled deionized water. B: Aβ amyloid, which is insoluble in a buffer but can be extracted using formic acid from the brain of Alzheimer\'s disease patients, was immunoprecipitated using the supernatant of a positive hybridoma cell culture, and the immune complex was selectively separated using protein-G agarose (Amersham). Nine clones were tested; lane 2 (asterisk) is 1A9 and lane 6 (double asterisk) is 2C3. C: Elution profile of SEC of a conditioned medium. Among the 24 SEC-collected fractions, fractions 8, 13, and 16 were subjected to 1A9 immunoprecipitation. Aβ immunoreactivity was detected using 4G8. The black arrowhead indicates the trimer and the outlined arrowhead indicates the dimer. Asterisk (*) indicates the anti-mouse IgG light chain.

FIG. 2 presents photographs and a graph showing the antitoxic activity of 1A9 and 2C3. A to F: Representative images of NGF-treated PC12 (PC12N) cells, which were exposed to seed-free Aβ 1-42 at 37° C. for 48 hours in the presence or absence of the antibodies (left half of each panel). Representative calcein AM/PI staining where live cells were stained green and dead cells were stained red (right half of each panel). G: The viability of cells exposed to seed-free Aβ 1-42 (25 μM) with the following antibodies: non-specific IgG2b (filled square); 4G8 (open triangle); 1A9 (open square); and 2C3 (filled circle).

FIG. 3 presents photographs and a graph showing the size and morphological characteristics of the toxic Aβ assemblies targeted by 1A9 and 2C3. A: The 540,000×g supernatant of Aβ 1-42 (25 μM) was subjected to a continuous molecular sieving process using ultrafiltration membranes having a molecular weight cutoff value of 3, 10, 30, and 100 kDa (Microcon). The four types of filtrates thus fractioned were named as follows: fraction 1 (<3 kDa), fraction 2 (3 to 10 kDa), fraction 3 (10 to 30 kDa), fraction 4 (30 to 100 kDa); and fraction 5 (>100 kDa) which was finally retained. The presence of Aβ 1-42 in each of the above-mentioned fractions was detected by 4G8 immunoblotting. B: Representative images of NGF-treated PC12 (PC12N) cells treated with the five fractions at 37° C. for 48 hours. The toxicity of each fraction was evaluated as described above for FIG. 2. C: The viability of cells treated with the 540,000×g supernatant of Aβ 1-42 and the five fractions (fractions 1 to 5). Similar results were obtained from two independent experiments. The values are presented in percentage (mean±SD) with respect to the control. D: Dot blot analysis of the five fractions (fractions 1 to 5). The blots were reacted with A11, 1A9, 2C3, and 4G8. E: AFM images of the five fractions. In fraction 5 (Fr. 5) that had the strongest toxicity, ring-shaped and bead-shaped structures were observed in addition to granular molecules.

FIG. 4 presents photographs and graphs showing the activity of 1A9 and 2C3 to suppress Aβ amyloid fibril formation. A: Amyloid fibril formation of Aβ 1-42 at various concentrations (10 μM (open square), 25 μM (filled diamond), and 50 μM (open circle)) was monitored by ThT assay at 37° C. for up to 72 hours. B: Coexisting antibody dose-dependent inhibition of amyloid fibril formation of Aβ 1-42 was observed for 2C3 (open circle). In contrast, the 1A9 (open square), 4G8 (filled triangle), and non-specific IgG (filled square) antibodies did not inhibit fibril-forming assembly of seed-free Aβ 1-42 (ThT-negative 540,000×g supernatant). C: Coexisting antibody dose-dependent inhibition of fibril-forming assembly of Aβ 1-42 was observed for 2C3 (open circle), and nearly complete inhibition was observed also for 1A9 (open square) at 3 μM. D: None of the test antibodies added after a 24-hour pre-incubation for Aβ 1-42 amyloid fibril formation could dissolve nor disassemble the Aβ 1-42 amyloid fibrils. E to G: EM images of Aβ 1-42 in the absence (Panel E) and presence of 2C3 (Panel F) and 1A9 (Panel G).

FIG. 5 presents photographs and graphs on toxicity-related Aβ 1-42 oligomers. A: Dot blot assay (upper half of Panel A): Aβ 1-42 monomers (25 μM) were incubated for a specified time (0 to 72 hours) at 37° C., and immobilized onto a nitrocellulose membrane, and subjected to dot blot assay that uses A11, 1A9, 2C3, or 4G8. The emergence of immunoreactivity-positive structures for each antibody was tested. Immunoreactivity intensity analysis (lower half of Panel A): The results of dot blot assay were analyzed semiquantitatively using the Multi Gauge v 3.0 software (Fuji Film, Tokyo). To correlate the oligomer formation and amyloid fibril formation, the ThT fluorescence value (the right Y axis) was overlaid on the same time axis. B: The Aβ 1-42 assembly after 0-, 2-, 4-, and 24-hour incubation at 37° C., and the change in Aβ 1-42 assembly after further 48-hour incubation. The Aβ 1-42 assembly was detected by 4G8 immunoblotting. C: The toxic activity of the above-mentioned various Aβ 1-42 assemblies. The viability of nerve cells was determined by the LIVE/DEAD assay as described for FIG. 2. D: The anti-neurotoxic activity of 1A9 and 2C3 was evaluated using various Aβ assemblies (the Aβ 1-42 assemblies formed at 37° C. for 0 and 2 hours (“0h” and “2h”); and the ThT-positive supernatant collected after ultracentrifugation at 540,000×g for two hours (“2h sup”)). Representative images of PC12N cells exposed to various Aβ 1-42 assemblies in the absence or presence of the antibodies are shown in the left half of Panel D (a: “0h”; b: “2h”; c: “2h sup”; d: “2h sup”+IgG2b; e: “2h sup”+1A9; f: “2h sup”+2C3). The viability of cells exposed to various Aβ 1-42 assemblies in the absence or presence of the antibodies is presented in percentage (mean±SD) with respect to the control, and this is shown in the right half of Panel D. Compared to the “0h” Aβ 1-42 assembly, the “2h” Aβ 1-42 assembly lowered the neurotoxicity. “2h sup” recovered the neurotoxicity to a degree similar to that of the “0h” Aβ 1-42 assembly. Non-specific IgG2b could not block the neurotoxicity induction of the “2h sup” Aβ 1-42 assembly. Monoclonal 1A9 completely inhibited the “2h sup”-induced neurotoxicity, while the ability of 2C3 to inhibit the toxicity was slightly inferior. In the experiments using the two monoclonal antibodies (mAbs), the antitoxic activity of the mAbs was observed at a mAb:Aβ mole ratio of 1:<25 to 50. This suggests that structurally different 1A9- and 2C3-recognized oligomeric assemblies exist at a relatively low concentration.

FIG. 6 presents photographs and graphs showing that soluble 1A9- and 2C3-recognized oligomers exist in the human brain. Antibodies against Aβ oligomers can detect senile plaques and vascular amyloids in AD brain only after pretreatment with Protease K. A: 1A9 staining; B: 2C3 staining; and C: A11 staining. D: 4G8 immunoblotting of 1A9- or 2C3-immunoprecipitated Aβ in buffer-soluble AD brain (lanes 1, 2, 4, and 5) and healthy control brain (lanes 3 and 6). Representative results for 1A9 and 2C3 are shown in the left and right half of the panel, respectively. E and F: Semiquantitative analysis (with actin control) of soluble 1A9-immunoreactive 12-mer (Panel E) and soluble 2C3-immunoreactive 12-mer (Panel F) in the human entorhinal cortex obtained from 50 autopsy cases of a healthy elderly population (Braak NFT Stage I or II: n=35; Braak NFT Stage III or IV: n=13; and Braak NFT Stage >IV, AD cases: n=2).

FIG. 7-1 present graphs showing that soluble 1A9- and 2C3-recognized oligomers exist in human CSF. Pooled whole cerebrospinal fluid (CSF) (AD=10 and NC=10) (Panels A and B) and pooled lipoprotein-depleted CSF (AD=10, and NC=10) (Panels C and D) were subjected to size exclusion chromatography (SEC). In Panels A and B, the collected fractions were analyzed for the distribution of Aβ 40 and Aβ 42 monomers by BNT77-BA27 and BNT77-BC05 ELISAs. Panels C and D show the presence of Aβ 40 and Aβ 42 oligomers captured by 1A9/2C3 mixed antibodies.

FIG. 7-2 is the continuation of FIG. 7-1. The amount of 1A9-recognized oligomeric assembly (1A9-BC05 and 1A9-BA27 ELISAs) and the amount of 2C3-recognized assembly (2C3-BC05 and 2C3-BA27 ELISAs) were measured for 12 AD cases (open circle) and 13 NC cases (filled circle) (Panels E and G). The oligomer/monomer ratio is shown in Panels F (1A9) and H (2C3).

FIG. 8 presents graphs showing that the onset of memory impairment in Tg2576 mice can be prevented by passive immunization treatment. 13-month-old Tg2576 mice were divided into the following three groups to perform learning/behavior tests: PBS-administered group: n=10; 1A9-administered group: n=13; and 2C3-administered group: n=11. All of the measured values were indicated as mean±SE. (A) Y-maze test. Spontaneous alteration behavior was monitored in each group during an eight-minute session of the Y-maze task. The results of one-way ANOVA were as follows: F(1, 52)=3.09, p<0.05; * p<0.05 in the comparison with PBS-administered Tg2576 mice. (B) Novel object recognition test. The retention session was performed 24 hours after training. The exploratory preference in a ten-minute session in the novel object recognition test was determined in each group. The results of two-way ANOVA were as follows: training/retention, F(1, 64)=31.53, p<0.01; animal group, F(2, 64) ˜7.49, p<0.01; repeated training/retention by the animal group, F(2, 64)=10.12, p<0.01; ** p<0.01 in the comparison with the corresponding untrained mice, ## p<0.01 in the comparison with PBS-administered Tg2576 mice. (C) The swimming path length during a 60-second session of water maze test was measured for each group. The results of two-way ANOVA were as follows: trial, F(9, 320)=20.46, p<0.01; animal group, F(2, 320)=12.59, p<0.01; repeated trial by the animal group, F(18, 320)=1.78, p<0.05; p<0.05, ** p<0.01 in the comparison with PBS-administered Tg2576 mice. Fear-conditioned learning test: Context-dependent (D) and clue-dependent freezing times (E) were determined. The results of two-way ANOVA were as follows: context-dependent test, F(2, 32)=5.94, p<0.01; clue-dependent test, F(2, 32)=7.33, p<0.01; * p<0.05 and ** p<0.01 in the comparison with PBS-administered Tg2576 mice.

FIG. 9 presents graphs and a photograph showing that the brain Aβ accumulation in Tg2576 can be prevented by passive immunotherapy. The hippocampus and cerebral cortex of three groups of 13-month-old Tg2576 mice (PBS-administered group, n=10; 1A9-administered group, n=13; and 2C3-administered group, n=11) were extracted in three continuous steps to prepare the buffer-soluble, SDS-soluble, and formic acid (FA)-extractable fractions. Each of the fractions was subjected to Aβ-specific ELISAs (WAKO kit: BNT77-BA27 for Aβ x-40; BNT77-BC05 for Aβ x-42). The accumulation of Aβ 40 (SDS and FA) and Aβ 42 (SDS) was found to be significantly suppressed only in the 1A9-treated group. The accumulation-suppressing effect for the A11-positive oligomer (4-mer) was confirmed in the SDS-soluble cerebral cortex fractions from the two antibody-treated groups.

FIG. 10 presents photographs and graphs on Aβ oligomers in the plasma and brain of Tg2576. A and B: As a result of ELISA analysis, no significant difference in the amount of Aβ x-40 and Aβ x-42 in the plasma was observed between the PBS-administered group and the immunotherapy group. C: Similarly, no difference in the Aβ 40/Aβ 42 ratio was observed among the three groups tested. D: As a result of dot blot analysis using pooled brain homogenates, no difference in the amount of physiological saline-soluble A11-positive oligomer was observed among the three groups tested. Hippocampus (left panel) and cerebral cortex (right panel). PBS-administered group, n=10; 1A9-administered group, n=13; and 2C3-administered group, n=11. E: According to immunoblot analysis using the anti-oligomer A11 antibody, the immunoreactivity of the Aβ tetramer in the SDS-extracted cerebral cortex fraction (right panel) was decreased in the 1A9- and 2C3-administered groups compared to the PBS-administered group. On the other hand, this was not observed in the hippocampus (left panel). F: Blood (albumin-depleted plasma, upper part of Panel F;

albumin/lipoprotein-depleted plasma, lower part of Panel F) was pooled from each of the groups, and subjected to A11 dot blot analysis. As a result, the A11 immunoreactivity was found to be increased in the 1A9- and 2C3-administered groups compared to the PBS-administered group (Panel F). The proportion of the lipoprotein-bound form of 2C3-recognized oligomers was higher than that of 1A9-recognized oligomers (lower part of Panel F). Furthermore, the A11 immunoblotting also showed positive signals at approximately 200 kDa, and the immunoreactivity was clearly increased in the 1A9- and 2C3-administered groups compared to the PBS-administered group (Panel G). From these results, it is conceivable that the therapeutic effect selective only to target Aβ oligomer molecules was obtained in the antibody-administered groups without affecting physiological molecules.

FIG. 11 presents photographs and graphs showing that senile plaque amyloid formation (A: Aβ-specific antibody staining; and B: thioflavin-S-positive analysis) and swollen dystrophic neurite formation (C: synaptophysin-positive analysis) were suppressed in the Tg2576 mouse brain by passive immunization treatment.

FIG. 12 presents photographs showing the suppression of synaptic degeneration by passive immunization treatment with 1A9 and 2C3. Immunostaining of synaptophysin (left panels) and drebrin (right panels) in presynaptic and postsynaptic dot-like peripheral cells. Top: PBS administration; middle: 1A9 administration; and bottom: 2C3 administration.

FIG. 13 presents photographs showing the brain transfer of the antibodies by passive immunization treatment. The distribution of administered antibodies in the Tg2576 mouse brain is shown. Staining with anti-Aβ antibodies (left panels) and IgG (center panels). 1A9 administration (A), 2C3 administration (B), and PBS administration (C).

FIG. 14 presents photographs showing, by dot blot analysis, that the monoclonal antibodies 5A5, 5A9, 4F7, 4H5, 6E4, and 6H4 are specific to Aβ oligomers (3 to 96 hours), but do not recognize Aβ monomers (0 hour).

FIG. 15 presents graphs showing the Aβ oligomer-selective binding ability of the six types of antibodies (4F7, 4H5, 5A5, 5A9, 6E4, and 6H4). The vertical axis indicates the absorbance at a wavelength of 450 nm, and the horizontal axis indicates the concentration of Aβ oligomer or Aβ monomer used as an inhibitor. In each graph, the dashed line indicates the antibody-binding activity when the Aβ oligomer was used as the inhibitor, and the solid line indicates the antibody-binding activity when the Aβ monomer was used as the inhibitor.

FIG. 16 presents graphs showing the neutralizing activity of the six types of antibodies (4F7, 4H5, 5A5, 5A9, 6E4, and 6H4) against Aβ-induced neurotoxicity. The horizontal axis indicates the amount of antibody added, and the vertical axis shows the cytotoxicity relative to that under the antibody-free condition as the standard (see the equation in the figure). Control IgG (3F1), which is an antibody that does not bind to Aβ 42, was used for comparison.

FIG. 17 presents graphs showing the suppressing activity of the six types of antibodies (4F7, 4H5, 5A5, 5A9, 6E4, and 6H4) against Aβ amyloid fibril formation. The antibodies were added at three different concentrations to a Aβ 1-42 solution (12.5 μM). After incubation at 37° C. for 24 hours, the level of Aβ amyloid fibril formation was measured by the ThT fluorescence intensity method. The horizontal axis indicates the amount of antibody added, and the vertical axis shows the level of amyloid fibril formation by the antibody addition that is relative to the level of amyloid fibril formation without antibody addition as the standard.

DETAILED DESCRIPTION

The present invention will be described more specifically below.

As described above, the present inventors succeeded in obtaining antibodies that bind specifically to Aβ oligomers but not to Aβ monomers. That is, the present invention provides antibodies that bind to Aβ oligomers but not to Aβ monomers. The antibodies are preferably isolated or purified.

The terms “isolated” and “purified” used for substances (antibodies and such) of the present invention indicate that the substances do not substantially include at least one other substance that may be contained in the natural source. Therefore, “isolated antibodies” and “purified antibodies” refer to antibodies that do not substantially include cell materials such as hydrocarbons, lipids, or other contaminant proteins from the cell or tissue source from which the antibodies (proteins) are derived. When the antibodies are chemically synthesized, the terms refer to antibodies that do not substantially include chemical precursor substances or other chemical substances. In a preferred embodiment, the antibodies of the present invention are isolated or purified.

“Antibodies” refers to glycoproteins that have the same structural characteristics. Antibodies show binding specificity towards specific antigens. Herein, “antigens” refers to proteins that have the ability to bind to the corresponding antibodies, and induce antigen-antibody reactions in vivo.

Aβ proteins, which are the major constituents of amyloids, are peptides consisting of 40 to 42 amino acids, and are known to be produced from precursor proteins called amyloid precursor proteins (APPs) by the action of proteases. Besides amyloid fibrils collected in ultracentrifuged sediment fractions, the amyloid molecules produced from APPs include oligomeric non-fibrous assemblies in addition to soluble monomers. “Aβ oligomers” of the present invention refer to non-fibrous assemblies. The “Aβ oligomers” of the present invention include, for example, Aβ 40 (Aβ 1-40) oligomers and Aβ42 (Aβ 1-42) oligomers. For example, “Aβ42 oligomers” of the present invention are molecules showing a molecular weight of 45 to 160 kDa in SDS-PAGE, and 22.5 to 1,035 kDa in Blue Native PAGE. Using molecular sieves, the molecules are collected mainly in the >100 kDa retention solution. When observed under an atomic force microscope, the molecules show mixed morphologies of granular, bead-shaped, and ring-shaped molecules having a height of 1.5 to 3.1 nm. By the gel filtration method, the molecules can be eluted in the void volume fraction 8 with a molecular weight of 680 kDa or more, and in fraction 15 with a molecular weight of 17 to 44 kDa.

There is no limitation on the origin and form of the antibodies used in the present invention as long as they bind to Aβ oligomers but not to Aβ monomers.

“Antibodies” of the present invention include both monoclonal and polyclonal antibodies. The antibodies of the present invention also include any type of antibodies such as non-human animal antibodies, humanized antibodies, chimeric antibodies, human antibodies, the later-described minibodies, amino acid sequence-modified antibodies, modified antibodies conjugated to other molecules (for example, polymers such as polyethylene glycol), and sugar chain-modified antibodies.

Herein, the term “monoclonal antibodies” refers to antibodies that are obtained from a substantially homogeneous population of antibodies. That is, the individual antibodies constituting the population are identical with the exception of possible natural mutants that may be present in a trace amount. Monoclonal antibodies are highly specific and recognize a single antigenic site. Each of the monoclonal antibodies recognizes a single determinant of the antigen, in contrast to conventional (polyclonal) antibody preparations that typically contain different antibodies against different antigenic determinants (epitopes).

In addition to the above-mentioned specificity, monoclonal antibodies have the advantage that they can be synthesized from a hybridoma culture that is not contaminated with other immunoglobulins. Therefore, “monoclonal” indicates the characteristics of antibodies that can be obtained from a substantially homogeneous antibody population. This term does not indicate the requirement for any specific method for antibody production.

Basically, monoclonal antibodies can be produced by using known techniques. For example, they may be produced by the hybridoma method first described by Kohler and Milstein (Nature 256: 495-7, 1975), or by the recombinant DNA method (Cabilly et al., Proc. Natl. Acad. Sci. USA 81:3273-7, 1984), but the methods are not limited thereto. For example, when using the hybridoma method, an Aβ oligomer (for example, the Aβ tetramer described in the Examples) is used as a sensitizing antigen, and immunization is carried out according to a conventional immunization method. The obtained immune cells are fused with known parent cells by a conventional cell fusion method, and monoclonal antibody-producing cells can be screened and isolated using a conventional screening method.

The monoclonal antibodies of the present invention can be produced as follows. Synthetic Aβ 1-42 (Peptide Institute, Inc., Osaka) is dissolved in distilled deionized water or a 10 mM phosphate buffer solution, and this is incubated at 37° C. for 18 hours. Then, the peptides are separated by 4-12% SDS-PAGE, and visualized by CBB staining, and the portion of the Aβ 1-42 tetramer alone which is not contaminated with the Aβ 1-42 monomer is cut out and used as an antigen. On the other hand, a preparation containing a large amount of the Aβ 1-40 oligomer is prepared by mixing (i) a modified Aβ 1-40 prepared by chemically linking 6-carboxytetramethylrhodamine (6-TAMRA) (SIGMA) to the N terminus of a synthetic Aβ 1-40 peptide using a conventional method with (ii) synthetic Aβ 1-40 (Peptide Institute, Inc., Osaka) at a ratio of 5:100, 10:100, 20:100, 30:100, 40:100, 50:100, 60:100, 70:100, or 80:100, preferably 90:100, or more preferably 100:100, and carrying out polymerization reaction for three hours, preferably six hours, or more preferably 20 hours. Next, Balb-c mice are immunized with 2.5 μg of either the Aβ 1-42 tetramer or Aβ 1-40 oligomer emulsified using complete Freund\'s adjuvant by injecting the antigen into their foot pad. Subsequently, booster immunizations are carried out six times. Hybridomas are produced from the inguinal lymph node by fusion with Sp2/O—Ag14 cells using Polyethylene Glycol 1500.

The animals immunized with sensitizing antigens are not particularly limited, but are preferably selected considering the compatibility with parent cells used for cell fusion. Generally, rodents, lagomorphs, or primates are used. Rodents include, for example, mice, rats, and hamsters. Lagomorphs include, for example, rabbits. Primates include, for example, Catarrhini (old-world) monkeys such as Macaca fascicularis, Macaca mulatta, hamadryas, and chimpanzees.

Animals are immunized with sensitizing antigens according to known methods. For example, as a standard method, immunization is performed by intraperitoneal or subcutaneous injection of a sensitizing antigen into mammals.