Abstract:
Biomarkers for detecting aggrecanas-1 and/or aggrecanase-2 activity are disclosed. The biomarkers are specific peptide fragments of α2 macroglobulin.

Description:
[0001]     This application claims priority to U.S. Provisional application No. 60/490,564, filed Jul. 28, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The ADAMs (α disintegrin and metalloprotease) are a family of multidomain proteins with structural homology to snake venom metalloproteases. The archetypical ADAM protein has a prodomain, metalloprotease domain, disintegrin domain, and a cysteine-rich region. At least 18 of the ADAMs have now been identified and sequenced, and together with snake venom metalloproteases, make up the reprolysin family of zinc metalloproteases.  
         [0003]     Some members of the ADAM family contain thrombospondin motifs, and are referred to as ADAMTS (α disintegrin and metalloprotease with thrombospondin motifs). In particular, ADAMTS-4 and ADAMTS-5 have been shown to cleave aggrecan, and are thus believed to be responsible for the onset or progression or degenerative conditions characterized by degradation of aggrecan, especially aggrecan found in cartilage. ADAMTS-4 is also known as aggrecanase-1, and ADAMTS-5 is also called aggrecanase-2.  
         [0004]     Because ADAMTS-4 and ADAMTS-5 are implicated in aggrecan degradation, these proteinases are reasonable targets for therapeutic drugs to reduce or abolish the deleterious effects of these aggrecanases. In this regard, it would be useful to find biomarkers indicating aggrecanase activity. Since aggrecan is a substrate for ADAMTS-4 and ADAMTS-5, it would seem reasonable to use cleaved fragments of aggrecan as biomarkers. Unfortunately, aggrecan and its cleaved fragments are highly glycosylated, making it unsuitable for traditional detection methods such as enzyme linked immunosorbent assay (ELISA) without first removing the sugar residues. This subsequent deglycosylation step is both difficult and time consuming, limiting the value of using aggrecan fragments as biomarkers.  
         [0005]     Alpha-2-Macroglobulin (α2M) is a homotetramer of about 720 kDa, and is a general endoproteinase inhibitor circulating in blood at concentrations of 0.6-2 mg/ml, constituting about 2-4% of total plasma protein in humans. α2M is also present in synovial fluid. In its nascent form (SEQ ID NO. 1), α2M is about 1474 residues long. In the mature form (SEQ ID NO. 2) of α2M, the initial signal sequence of about 23 residues (SEQ ID NO. 3) is absent.  
         [0006]     α2M is able to inhibit all four classes of proteinases by a unique trapping mechanism. Each subunit of the α2M molecule contains a region referred to as the “bait region,” a short peptide stretch (about 39 amino acid residues in human α2M, SEQ ID NO. 4, from about residue 667 to about residue 706 of the mature protein) that is very susceptible to proteolytic cleavage by specific cleavage sites for different proteinases. When a proteinase cleaves the bait region, a conformational change is induced in α2M, which traps the proteinase. Following cleavage in the bait region a thiolester bond is hydrolyzed and mediates the covalent binding of α2M to the proteinase. The entrapped enzyme remains active against low molecular weight substrates, but activity against high molecular weight substrates is greatly reduced due to steric interference. Because the complex formation of proteinases with α2M is dependent on their proteolytic activities against the bait region, α2M is a useful tool for identifying unknown proteinases. (Nagase, H., Itoh, Y., and Binner, S. (1994)  Ann. N.Y. Acad. Sci.  732, 294-302). Indeed, some members of the ADAM and ADAMTS family of enzymes have been characterized by their inhibition by α2M.  
       SUMMARY OF THE INVENTION  
       [0007]     It has been found that α2M is an endogenous inhibitor of the cartilage aggrecanases, ADAMTS-4 and ADAMTS-5. Both ADAMTS-4 and ADAMTS-5 cleave α2M in the bait region between amino acids Met 690  and Gly 691 , generating the C-terminal neoepitope YESDVM 690  (Tyr-Glu-Ser-Asp-Val-Met 690 ) (SEQ ID NO. 6) and the N-terminal neoepitope  691 GRGHAR ( 691 Gly-Arg-Gly-His-Ala-Arg) (SEQ ID NO. 7). These cleavage sites in α2M are believed to be unique to aggrecanases. The present invention relates to these novel neoepitopes, and methods of detecting them. The present invention also provides for a method of determining the efficacy of aggrecanase inhibiting compounds, preferably aggrecanase inhibiting pharmaceutical compositions. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]     Antibodies were designed, using techniques well known in the art, to the new C-terminus SDVM 690  (SEQ ID NO. 8) and the N-terminus  691 GRGH (SEQ ID NO. 9) following specific cleavage of α2M at the Met 690 /Gly 691  bond by ADAMTS-4 and ADAMTS-5. Techniques to raise antibodies to neoepitopes formed by cleavage of collagen are described, for example, in U.S. Pat. No. 6,030,792, issued Feb. 29, 2000 to Otterness et al., the disclosure of which is incorporated herein by reference. The techniques of the present invention may be conducted in a similar fashion. In order to test the ability of these antibodies to detect ADAMTS-4 and ADAMTS-5 cleavage products, α2M (50 ng) was digested with 100 ng of ADAMTS-4 and ADAMTS-5 for varying periods of time (1 min, 2 min, 3 min, 5 min, 10 min, 15 min, and 30 min) at 37° C. Following the incubations the products were analyzed for anti-SDVM 690  and anti- 691 GRGH. Both neoepitopes were generated as early as after 2 minutes of incubation, and increased over time, up to after 30 minutes of incubation. Generation of the neoepitopes, as detected with these neoepitope antibodies, was inhibited in the presence of EDTA or in the presence of an aggrecanase-inhibitor:  
                         
 
 2-dimethylamino-N-[1-(hydroxyamino)-carbonyl]-3,3-dimethyl-4-[(4-phenoxyphenyl)-sulphonyl]-butane. 
 
         [0010]     The neoepitope antibodies anti-SDVM 690  and anti- 691 GRGH were used to detect fragments of α2M in synovial fluids of patients with osteoarthritis. Preliminary experiments suggest the presence of the neoepitope SDVM 690  (SEQ ID NO. 8) in the synovial fluid of patients with osteoarthritis.  
         [0011]     These findings suggest that the neoepitopes SDVM 690  (SEQ ID NO. 8) and  691 GRGH (SEQ ID NO. 9), generated when α2M is cleaved by aggrecanases, are biomarkers for aggrecanase activity in arthritis or other conditions where pathological expression of aggrecanases are implicated. These neoepitopes are generated during the osteoarthritic process as illustrated by their detection in synovial fluid. Therefore, they are expected to be detectable in blood or urine as convenient markers of aggrecanase activity and of the ability of aggrecanase inhibitors to block this increased activity in disease. By detecting aggrecanase activity prior to gross manifestation of disease, such as overt tissue damage, it may be possible to arrest or slow the onset of aggrecanase mediated diseases at an early stage of such diseases.  
         [0012]     While the detection method employed in the foregoing examples was an ELISA assay, it will be appreciated that any appropriate assay could be employed for detection of the neoepitopes described. For example, mass spectroscopy could be used to detect the various neoepitopes.  
         [0013]     Other variations will occur to those skilled in the art in light of the foregoing disclosure. For example, the detection and monitoring of disease conditions other than osteoarthritis may find use in the methods of the present invention. Peptides that contain the sequences described may be prepared synthetically. Nucleotide sequences coding for the sequences described may be prepared for expression of such peptides. mRNA sequences may be prepared for detection of or translation of such peptides as well. All embodiments herein are merely exemplary, not limitative, and thus variations are within the intended scope of the appended claims.