Imidazo[5,1-f][1,2,4]triazin-2-amines as novel inhibitors of polo-like kinase 1.

The synthesis and biological activities of imidazo[5,1-f][1,2,4]triazin-2-amines (imidazotriazines) as novel polo-like kinase 1 inhibitors are reported.

Development and characterization of a highly specific and sensitive sandwich ELISA for detection of aggrecanase-generated aggrecan fragments.

OBJECTIVE: To develop an enzyme linked immunosorbent assay (ELISA) to quantify the levels of specific aggrecan fragments generated by aggrecanase-mediated cleavage at the 373Glu-374 Ala bond within the aggrecan interglobular domain. METHODS: The ELISA employs a commercially available monoclonal antibody to capture aggrecan fragments containing keratan sulfate (KS). Aggrecan fragments generated by cleavage at the Glu-Ala bond were then detected using a monoclonal neoepitope antibody (mAb OA-1) that specifically recognizes the N-terminal sequence 'ARGSVIL'. RESULTS: The mAb OA-1 antibody was highly specific for the immunizing neoepitope peptide since neither peptides spanning the cleavage site nor mutated peptides were detected. Aggrecan fragments generated by ADAMTS-4 digested human aggrecan monomers and from IL-1-stimulated human cartilage explants were quantified by the ELISA, and we observed increased sensitivity of the ELISA compared to mAb OA-1 Western analysis. We also observed that the basal, as well as IL-1-stimulated production of ARGS aggrecan fragments from human articular cartilage explants was blocked by a selective aggrecanase inhibitor, consistent with generation of the ARGS neoepitope in human articular cartilage being mediated by aggrecanase. Using purified human aggrecan digested by ADAMTS-4 as standard to quantify ARGS aggrecan fragments in human synovial fluids, we determined that the calculated amount of ARGSVIL-aggrecan fragments by ELISA measurement is in agreement with the published levels of these fragments, supporting its potential utility as a biomarker assay for osteoarthritis. CONCLUSION: We have developed an assay that detects and quantifies specific aggrecan fragments generated by aggrecanase-mediated cleavage. Because aggrecanase mediates degradation of human articular aggrecan in joint disease, the KS/mAb OA-1 ELISA may serve as a biomarker assay for evaluation of preclinical and clinical samples.

Design of selective and soluble inhibitors of tumor necrosis factor-alpha converting enzyme (TACE).

A program to improve upon the in vitro, in vivo, and physicochemical properties of N-hydroxyformamide TACE inhibitor GW 3333 (1) is described. Using the primary structure of pro-TNF-alpha, along with a homology model of the catalytic domain of TACE based on the X-ray diffraction coordinates of adamalysin, we synthesized N-hydroxyformamide TACE inhibitors containing a P2' arginine side chain. Introduction of nitro and sulfonyl electron-withdrawing groups covalently bound to the P2' guanidine moiety rendered the inhibitors electronically neutral at cellular pH and led to potent inhibition of TNF-alpha release from stimulated macrophages. Inhibitors containing these arginine mimetics were found to have increased solubility in simulated gastric fluid (SGF) relative to 1, allowing for the incorporation of lipophilic P1' side chains which had the effect of retaining potent TACE inhibition, but reducing potency against matrix metalloproteases (MMPs) thus increasing overall selectivity against MMP1, MMP3, and MMP9. Selected compounds showed good to excellent in vivo TNF inhibition when administered via subcutaneous injection. One inhibitor, 28a, with roughly 10x selectivity over MMP1 and MMP3 and high solubility in SGF, was evaluated in the rat zymosan-induced pleuisy model of inflammation and found to inhibit zymosan-stimulated pleural TNF-alpha elevation by 30%.

N-hydroxyformamide peptidomimetics as TACE/matrix metalloprotease inhibitors: oral activity via P1' isobutyl substitution.

N-Hydroxyformamide-class metalloprotease inhibitors were designed and synthesized, which have potent broad-spectrum activity versus matrix metalloproteases and TNF-alpha converting enzyme (TACE). Compound 13c possesses good oral and intravenous pharmacokinetics in the rat and dog.

Specific sequence elements are required for the expression of functional tumor necrosis factor-alpha-converting enzyme (TACE).

The tumor necrosis factor-alpha-converting enzyme (TACE) is a membrane-anchored zinc metalloprotease involved in precursor tumor necrosis factor-alpha secretion. We designed a series of constructs containing full-length human TACE and several truncate forms for overexpression in insect cells. Here, we demonstrate that full-length TACE is expressed in insect cells inefficiently: only minor amounts of this enzyme are converted from an inactive precursor to the mature, functional form. Removal of the cytoplasmic and transmembrane domains resulted in the efficient secretion of mature, active TACE. Further removal of the cysteine-rich domain located between the catalytic and transmembrane domains resulted in the secretion of mature catalytic domain in association with the precursor (pro) domain. This complex was inactive and function was only restored after dissociation of the complex by dilution or treatment with 4-aminophenylmercuric acetate. Therefore, the pro domain of TACE is an inhibitor of the catalytic domain, and the cysteine-rich domain appears to play a role in the release of the pro domain. Insect cells failed to secrete a deletion mutant encoding the catalytic domain but lacking the inhibitory pro domain. This truncate was inactive and extensively degraded intracellularly, suggesting that the pro domain is required for the secretion of functional TACE.

Cloning of a disintegrin metalloproteinase that processes precursor tumour-necrosis factor-alpha.

Tumour-necrosis factor-alpha (TNF-alpha) is a cytokine that contributes to a variety of inflammatory disease states. The protein exists as a membrane-bound precursor of relative molecular mass 26K which can be processed by a TNF-alpha-converting enzyme (TACE), to generate secreted 17K mature TNF-alpha. We have purified TACE and cloned its complementary DNA. TACE is a membrane-bound disintegrin metalloproteinase. Structural comparisons with other disintegrin-containing enzymes indicate that TACE is unique, with noteable sequence identity to MADM, an enzyme implicated in myelin degradation, and to KUZ, a Drosophila homologue of MADM important for neuronal development. The expression of recombinant TACE (rTACE) results in the production of functional enzyme that correctly processes precursor TNF-alpha to the mature form. The rTACE provides a readily available source of enzyme to help in the search for new anti-inflammatory agents that target the final processing stage of TNF-alpha production.

Phosphodiesterase type IV inhibition. Structure-activity relationships of 1,3-disubstituted pyrrolidines.

The synthesis of 1,3-disubstituted pyrrolidines 2 and their activities as type IV phosphodiesterase (PDE) inhibitors are described. Various groups were appended to the nitrogen of the pyrrolidine nucleus to enable structure-activity relationships to be assessed. Groups which render the pyrrolidine nitrogen of 2 nonbasic yielded potent PDE-IV inhibitors. Analogs of amides, carbamates, and ureas of 2 were synthesized to determine the effects that substitution on these functional groups had on PDE-IV inhibitor potency. The structural requirements for PDE-IV inhibitor potency differed among the three classes. A representative amide, carbamate, and urea (2c,d,h) were shown to be > 50-fold selective for inhibiting PDE-IV versus representative PDEs from families I-III and V. Furthermore, these same three inhibitors demonstrated potent functional activity (IC50 < 1 microM) by inhibiting tumor necrosis factor-alpha (TNF-alpha) release from lipopolysaccharide (LPS)-activated purified human peripheral blood monocytes and mouse peritoneal macrophages. These compounds were also tested orally in LPS-injected mice and demonstrated dose-dependent inhibition of serum TNF-alpha levels.

Two-dimensional diffusion of F1F0-ATP synthase and ADP/ATP translocator. Testing a hypothesis for ATP synthesis in the mitochondrial inner membrane.

We report here the first experimentally determined lateral diffusion coefficients of the F1F0-ATP synthase and the ADP/ATP translocator in isolated inner membranes of rat liver mitochondria. Rabbit IgG developed against the F1F0-ATP synthase isolated from rat liver mitochondria was determined to be immunospecific for the synthase subunits, notably the alpha-beta doublet, gamma and delta subunits of F1 and subunits two, three and four of F0. This IgG, conjugated with lissamine-rhodamine, was used as a fluorescent probe to monitor the diffusion of the synthase in the membrane. IgG to cytochrome bc1 complex, prepared and labeled similarly, was used as a fluorescent probe for diffusion of this redox component. Eosin maleimide was determined to specifically label the ADP/ATP translocator in the isolated inner membrane and was used as a specific probe for the diffusion of the translocator. Using fluorescence recovery after photobleaching, the experimental average lateral diffusion coefficient of the F1F0-ATP synthase was determined to be 8.4 x 10(-10) cm2/s or twice that of cytochrome bc1 complex while the diffusion coefficient of the ADP/ATP translocator was 1.7 x 10(-9) cm2/s or four times that of cytochrome bc1 complex suggesting that all three components are independent two-dimensional diffusants. Using these diffusion coefficients and applying a number of basic assumptions, we calculated the theoretical two-dimensional diffusion-controlled collision frequencies and derived collision efficiencies (protons transferred per collision) between each of the three proton-transferring redox complexes and both the F1F0-ATP synthase and ADP/ATP translocator by treating the redox components as proton donors and the synthase and translocator as proton acceptors. These collision efficiencies support the physical possibility of a diffusion-based, random collision process of proton transfer and ATP synthesis in the mitochondrial inner membrane.