Rui-Qin Liu

Cloning and characterization of ADAMTS11, an aggrecanase from the ADAMTS family.

Aggrecan is responsible for the mechanical properties of cartilage. One of the earliest changes observed in arthritis is the depletion of cartilage aggrecan due to increased proteolytic cleavage within the interglobular domain. Two major sites of cleavage have been identified in this region at Asn341-Phe342 and Glu373-Ala374. While several matrix metalloproteinases have been shown to cleave at Asn341-Phe342, an as yet unidentified protein termed “aggrecanase” is responsible for cleavage at Glu373-Ala374 and is hypothesized to play a pivotal role in cartilage damage. We have identified and cloned a novel disintegrin metalloproteinase with thrombospondin motifs that possesses aggrecanase activity, ADAMTS11 (aggrecanase-2), which has extensive homology to ADAMTS4 (aggrecanase-1) and the inflammation-associated gene ADAMTS1. ADAMTS11 possesses a number of conserved domains that have been shown to play a role in integrin binding, cell-cell interactions, and extracellular matrix binding. We have expressed recombinant human ADAMTS11 in insect cells and shown that it cleaves aggrecan at the Glu373-Ala374 site, with the cleavage pattern and inhibitor profile being indistinguishable from that observed with native aggrecanase. A comparison of the structure and expression patterns of ADAMTS11, ADAMTS4, and ADAMTS1 is also described. Our findings will facilitate the study of the mechanisms of cartilage degradation and provide targets to search for effective inhibitors of cartilage depletion in arthritic disease.

The Thrombospondin Motif of Aggrecanase-1 (ADAMTS-4) Is Critical for Aggrecan Substrate Recognition and Cleavage

Aggrecanase-1 (ADAMTS-4) is a member of thea disintegrin andmetalloprotease withthrombospondin motifs (ADAMTS) protein family that was recently identified. Aggrecanase-1 is one of two ADAMTS cartilage-degrading enzymes purified from interleukin-1-stimulated bovine nasal cartilage (Tortorella, M. D., Burn, T. C., Pratta, M. A., Abbaszade, I., Hollis, J. M., Liu, R., Rosenfeld, S. A., Copeland, R. A., Decicco, C. P., Wynn, R., Rockwell, A., Yang, F., Duke, J. L., Solomon, K., George, H., Bruckner, R., Nagase, H., Itoh, Y., Ellis, D. M., Ross, H., Wiswall, B. H., Murphy, K., Hillman, M. C., Jr., Hollis, G. F., and Arner, E.C. (1999) Science 284, 1664–1666; 2 Abbaszade, I., Liu, R. Q., Yang, F., Rosenfeld, S. A., Ross, O. H., Link, J. R., Ellis, D. M., Tortorella, M. D., Pratta, M. A., Hollis, J. M., Wynn, R., Duke, J. L., George, H. J., Hillman, M. C., Jr., Murphy, K., Wiswall, B. H., Copeland, R. A., Decicco, C. P., Bruckner, R., Nagase, H., Itoh, Y., Newton, R. C., Magolda, R. L., Trzaskos, J. M., and Burn, T. C. (1999) J. Biol. Chem. 274, 23443–23450). The aggrecan products generated by this enzyme are found in cartilage cultures stimulated with cytokines and in synovial fluid from patients with arthritis, suggesting that aggrecanase-1 may be important in diseases involving cartilage destruction. Here we demonstrate that the thrombospondin type-1 (TSP-1) motif located within the C terminus of aggrecanase-1 binds to the glycosaminoglycans of aggrecan. Data from several studies indicate that this binding of aggrecanase-1 to aggrecan through the TSP-1 motif is necessary for enzymatic cleavage of aggrecan. 1) A truncated form of aggrecanase-1 lacking the TSP-1 motif was not effective in cleaving aggrecan. 2) Several peptides representing different regions of the TSP-1 motif effectively blocked aggrecanase-1 cleavage of aggrecan by preventing the enzyme from binding to the substrate. 3) Aggrecanase-1 was not effective in cleaving glycosaminoglycan-free aggrecan. Taken together, these data suggest that the TSP-1 motif of aggrecanase-1 is critical for substrate recognition and cleavage.

Characterization of human aggrecanase 2 (ADAM-TS5): substrate specificity studies and comparison with aggrecanase 1 (ADAM-TS4)

ADAM-TS5 (aggrecanase 2), one of two cartilage aggrecanases is a member of the ADAM protein family. Like ADAM-TS4 (aggrecanase 1) the enzyme cleaves cartilage aggrecan at the Glu(373)-Ala(374) bond, a marker of aggrecanase activity. In this study we have characterized the substrate specificity of ADAM-TS5 and compared it with that of ADAM-TS4. The recombinant human ADAM-TS5, like ADAM-TS4 cleaves aggrecan at Glu(1480)-Gly(1481), Glu(1667)-Gly(1668), Glu(1771)-Ala(1772) and Glu(1871)-Leu(1872) bonds more readily than at the Glu(373)-Ala(374) bond. In addition, ADAM-TS5 exhibited an additional site of cleavage in the region spanning residues Gly(1481) and Glu(1667), representing a unique cleavage of ADAM-TS5. ADAM-TS5 cleaved aggrecan approximately 2-fold slower than ADAM-TS4. Neither ADAM-TS5 nor ADAM-TS4 was able to cleave the extracellular matrix proteins fibronectin, thrombospondin, type I collagen, type II collagen, gelatin or general protein substrates such as casein and transferrin. Finally, the zymogen of stromelysin (MMP-3) was not activated by either ADAM-TS4 or ADAM-TS5.

Photochemically enhanced binding of small molecules to the tumor necrosis factor receptor-1 inhibits the binding of TNF-alpha.

The binding of tumor necrosis factor alpha (TNF-α) to the type-1 TNF receptor (TNFRc1) plays an important role in inflammation. Despite the clinical success of biologics (antibodies, soluble receptors) for treating TNF-based autoimmune conditions, no potent small molecule antagonists have been developed. Our screening of chemical libraries revealed that N-alkyl 5-arylidene-2-thioxo-1,3-thiazolidin-4-ones were antagonists of this protein–protein interaction. After chemical optimization, we discovered IW927, which potently disrupted the binding of TNF-α to TNFRc1 (IC50 = 50 nM) and also blocked TNF-stimulated phosphorylation of Iκ-B in Ramos cells (IC50 = 600 nM). This compound did not bind detectably to the related cytokine receptors TNFRc2 or CD40, and did not display any cytotoxicity at concentrations as high as 100 μM. Detailed evaluation of this and related molecules revealed that compounds in this class are “photochemically enhanced” inhibitors, in that they bind reversibly to the TNFRc1 with weak affinity (ca. 40–100 μM) and then covalently modify the receptor via a photochemical reaction. We obtained a crystal structure of IV703 (a close analog of IW927) bound to the TNFRc1. This structure clearly revealed that one of the aromatic rings of the inhibitor was covalently linked to the receptor through the main-chain nitrogen of Ala-62, a residue that has already been implicated in the binding of TNF-α to the TNFRc1. When combined with the fact that our inhibitors are reversible binders in light-excluded conditions, the results of the crystallography provide the basis for the rational design of nonphotoreactive inhibitors of the TNF-α–TNFRc1 interaction.

Both 5-arylidene-2-thioxodihydropyrimidine-4,6(1H,5H)-diones and 3-thioxo-2,3-dihydro-1H-imidazo[1,5-a]indol-1-ones are light-Dependent tumor necrosis factor-α antagonists

Based on the realization that N-alkyl 5-arylidene-2-thioxo-1,3-thiazolidin-4-ones are tumor necrosis factor-alpha antagonists, we discovered two additional classes of antagonists: 3-thioxo-2,3-dihydro-1H-imidazo[1,5-a]indol-1-ones (via rational design) and 5-arylidene-2-thioxodihydropyrimidine-4,6(1H,5H)-diones (via computer-guided screening). Chemical modification of the lead structures showed that the structure-activity relationship profiles for both of these series were dependent on the electronic properties of the molecules. Subsequent studies showed that they were light-dependent inhibitors.

Potent and selective aggrecanase inhibitors containing cyclic P1 substituents

Anti-succinate hydroxamates with cyclic P1 motifs were synthesized as aggrecanase inhibitors. The N-methanesulfonyl piperidine 23 and the N-trifluoroacetyl azetidine 26 were the most potent aggrecanase inhibitors both having an IC(50)=3nM while maintaining >100-fold selectivity over MMP-1, -2, and -9. The cyclic moieties were also capable of altering in vivo metabolism, hence delivering low clearance compounds in both rat and dog studies as shown for compound 14.

Discovery of N-Hydroxy-2-(2-oxo-3-pyrrolidinyl)acetamides as potent and selective inhibitors of tumor necrosis factor-α converting enzyme (TACE)

New inhibitors of tumor necrosis factor-alpha converting enzyme (TACE) were discovered using an N-hydroxy-2-(2-oxo-3-pyrrolidinyl)acetamide scaffold. The series was found to be potent in a porcine TACE (pTACE) assay with IC(50)s typically below 5 nM. For most compounds, selectivity for pTACE relative to MMP-1,-2, and -9 is at least 300-fold. Compound 2o was potent in inhibition of TNFalpha production in a human whole blood assay (WBA) with an IC(50) of 0.42 micro M.

Synthesis and structure-activity relationship of a novel, achiral series of TNF-α converting enzyme inhibitors

Replacement of the amide functionality in IM491 (N-hydroxy-(5S,6S)-1-methyl-6-[[4-(2-methyl-4-quinolinylmethoxy)anilinyl]carbonyl]5-piperidinecarboxamide) with a sulfonyl group led to a new series of alpha,beta-cyclic and beta,beta-cyclic gamma-sulfonyl hydroxamic acids, which were potent TNF-alpha converting enzyme (TACE) inhibitors. Among them, inhibitor 4b (N-hydroxy-(4S,5S)-1-methyl-5-[[4-(2-methyl-4-quinolinylmethoxy)phenyl]sulfonylmethyl]-4-pyrrolidinecarboxamide) exhibited IC50 values of < 1 nM and 180 nM in porcine TACE (pTACE) and cell assays, respectively, with excellent selectivity over MMP-1, -2, -9 and -13 and was orally bioavailable with an F value of 46% in mice.

A microplate assay specific for the enzyme aggrecanase.

We have identified a 41-residue peptide, bracketing the aggrecanase cleavage site of aggrecan, that serves as a specific substrate for this enzyme family. Biotinylation of the peptide allowed its immobilization onto streptavidin-coated plates. Aggrecanase-mediated hydrolysis resulted in an immobilized product that reveals an N-terminal neoepitope, recognized by the specific antibody BC-3. This assay is highly specific for aggrecanases; MMPs were inactive in this assay. Reduction of the peptide size below 30 amino acids resulted in a significant diminution of activity. Using the immobilized 41-residue peptide as a substrate, we have developed a 96-well microplate-based assay that can be conveniently used for high-throughput screening of samples for aggrecanase activity and for discovery of inhibitors of aggrecanase activity.

Discovery of a small molecule antagonist of the parathyroid hormone receptor by using an N-terminal parathyroid hormone peptide probe

Once-daily s.c. administration of either human parathyroid hormone (PTH)-(1–84) or recombinant human PTH-(1–34) provides for dramatic increases in bone mass in women with postmenopausal osteoporosis. We initiated a program to discover orally bioavailable small molecule equivalents of these peptides. A traditional high-throughput screening approach using cAMP activation of the PTH/PTH-related peptide receptor (PPR) as a readout failed to provide any lead compounds. Accordingly, we designed a new screen for this receptor that used a modified N-terminal fragment of PTH as a probe for small molecule binding to the transmembrane region of the PPR, driven by the assumption that the pharmacological properties (agonist/antagonist) of compounds that bound to this putative signaling domain of the PPR could be altered by chemical modification. We developed DPC-AJ1951, a 14 amino acid peptide that acts as a potent agonist of the PPR, and characterized its activity in ex vivo and in vivo assays of bone resorption. In addition, we studied its ability to initiate gene transcription by using microarray technology. Together, these experiments indicated that the highly modified 14 amino acid peptide induces qualitatively similar biological responses to those produced by PTH-(1–34), albeit with lower potency relative to the parent peptide. Encouraged by these data, we performed a screen of a small compound collection by using DPC-AJ1951 as the ligand. These studies led to the identification of the benzoxazepinone SW106, a previously unrecognized small molecule antagonist for the PPR. The binding of SW106 to the PPR was rationalized by using a homology receptor model.