Changing the selectivity profile - from substrate analog inhibitors of thrombin and factor Xa to potent matriptase inhibitors.

The type II transmembrane serine protease matriptase is a potential target for anticancer therapy and might be involved in cartilage degradation in osteoarthritis or inflammatory skin disorders. Starting from previously described nonspecific thrombin and factor Xa inhibitors we have prepared new noncovalent substrate-analogs with superior potency against matriptase. The most suitable compound 35 (H-d-hTyr-Ala-4-amidinobenzylamide) binds to matriptase with an inhibition constant of 26 nM and has more than 10-fold reduced activity against thrombin and factor Xa. The crystal structure of inhibitor 35 was determined in the surrogate protease trypsin, the obtained complex was used to model the binding mode of inhibitor 35 in the active site of matriptase. The methylene insertion in d-hTyr and d-hPhe increases the flexibility of the P3 side chain compared to their d-Phe analogs, which enables an improved binding of these inhibitors in the well-defined S3/4 pocket of matriptase. Inhibitor 35 can be used for further biochemical studies with matriptase.

Matriptase, HAT, and TMPRSS2 activate the hemagglutinin of H9N2 influenza A viruses.

Influenza A viruses of the subtype H9N2 circulate worldwide and have become highly prevalent in poultry in many countries. Moreover, they are occasionally transmitted to humans, raising concern about their pandemic potential. Influenza virus infectivity requires cleavage of the surface glycoprotein hemagglutinin (HA) at a distinct cleavage site by host cell proteases. H9N2 viruses vary remarkably in the amino acid sequence at the cleavage site, and many isolates from Asia and the Middle East possess the multibasic motifs R-S-S-R and R-S-R-R, but are not activated by furin. Here, we investigated proteolytic activation of the early H9N2 isolate A/turkey/Wisconsin/1/66 (H9-Wisc) and two recent Asian isolates, A/quail/Shantou/782/00 (H9-782) and A/quail/Shantou/2061/00 (H9-2061), containing mono-, di-, and tribasic HA cleavage sites, respectively. All H9N2 isolates were activated by human proteases TMPRSS2 (transmembrane protease, serine S1 member 2) and HAT (human airway trypsin-like protease). Interestingly, H9-782 and H9-2061 were also activated by matriptase, a protease widely expressed in most epithelia with high expression levels in the kidney. Nephrotropism of H9N2 viruses has been observed in chickens, and here we found that H9-782 and H9-2061 were proteolytically activated in canine kidney (MDCK-II) and chicken embryo kidney (CEK) cells, whereas H9-Wisc was not. Virus activation was inhibited by peptide-mimetic inhibitors of matriptase, strongly suggesting that matriptase is responsible for HA cleavage in these kidney cells. Our data demonstrate that H9N2 viruses with R-S-S-R or R-S-R-R cleavage sites are activated by matriptase in addition to HAT and TMPRSS2 and, therefore, can be activated in a wide range of tissues what may affect virus spread, tissue tropism and pathogenicity.

Identification of the first synthetic inhibitors of the type II transmembrane serine protease TMPRSS2 suitable for inhibition of influenza virus activation.

TMPRSS2 (transmembrane serine proteinase 2) is a multidomain type II transmembrane serine protease that cleaves the surface glycoprotein HA (haemagglutinin) of influenza viruses with a monobasic cleavage site, which is a prerequisite for virus fusion and propagation. Furthermore, it activates the fusion protein F of the human metapneumovirus and the spike protein S of the SARS-CoV (severe acute respiratory syndrome coronavirus). Increased TMPRSS2 expression was also described in several tumour entities. Therefore TMPRSS2 emerged as a potential target for drug design. The catalytic domain of TMPRSS2 was expressed in Escherichia coli and used for an inhibitor screen with previously synthesized inhibitors of various trypsin-like serine proteases. Two inhibitor types were identified which inhibit TMPRSS2 in the nanomolar range. The first series comprises substrate analogue inhibitors containing a 4-amidinobenzylamide moiety at the P1 position, whereby some of these analogues possess inhibition constants of approximately 20 nM. An improved potency was found for a second type derived from sulfonylated 3-amindinophenylalanylamide derivatives. The most potent derivative of this series inhibits TMPRSS2 with a K(i) value of 0.9 nM and showed an efficient blockage of influenza virus propagation in human airway epithelial cells. On the basis of the inhibitor studies, a series of new fluorogenic substrates containing a D-arginine residue at the P3 position was synthesized, some of them were efficiently cleaved by TMPRSS2.

Matriptase Induction of Metalloproteinase-Dependent Aggrecanolysis In Vitro and In Vivo: Promotion of Osteoarthritic Cartilage Damage by Multiple Mechanisms.

OBJECTIVE: To assess the ability of matriptase, a type II transmembrane serine proteinase, to promote aggrecan loss from the cartilage of patients with osteoarthritis (OA) and to determine whether its inhibition can prevent aggrecan loss and cartilage damage in experimental OA. METHODS: Aggrecan release from human OA cartilage explants and human stem cell-derived cartilage discs was evaluated, and cartilage-conditioned media were used for Western blotting. Gene expression was analyzed by real-time polymerase chain reaction. Murine OA was induced by surgical destabilization of the medial meniscus, and matriptase inhibitors were administered via osmotic minipump or intraarticular injection. Cartilage damage was scored histologically and aggrecan cleavage was visualized immunohistochemically using specific neoepitope antibodies. RESULTS: The addition of soluble recombinant matriptase promoted a time-dependent release of aggrecan (and collagen) from OA cartilage, which was sensitive to metalloproteinase inhibition and protease-activated receptor 2 antagonism. Although engineered human (normal) cartilage discs failed to release aggrecan following matriptase addition, both matrix metalloproteinase- and aggrecanase-mediated cleavages of aggrecan were detected in human OA cartilage. Additionally, while matriptase did not directly degrade aggrecan, it promoted the accumulation of low-density lipoprotein receptor-related protein 1 (LRP-1) in conditioned media of the OA cartilage explants. Matriptase inhibition via neutralizing antibody or small molecule inhibitor significantly reduced cartilage damage scores in murine OA, which was associated with reduced generation of metalloproteinase-mediated aggrecan cleavage. CONCLUSION: Matriptase potently induces the release of metalloproteinase-generated aggrecan fragments as well as soluble LRP-1 from OA cartilage. Therapeutic targeting of matriptase proteolytic activity reduces metalloproteinase activity, further suggesting that this serine proteinase may have potential as a disease-modifying therapy in OA.

Development and characterization of new peptidomimetic inhibitors of the West Nile virus NS2B-NS3 protease.

A series of new substrate analogue inhibitors of the WNV NS2B-NS3 protease containing decarboxylated arginine mimetics at the P1 position was developed. Among the various analogues, trans-(4-guanidino)cyclohexylmethylamide (GCMA) was identified as the most suitable P1 residue. In combination with dichloro-substituted phenylacetyl groups at the P4 position, three inhibitors with inhibition constants of <0.2 µM were obtained. These GCMA inhibitors have a better selectivity profile than the previously described agmatine analogues, and possess negligible affinity for the trypsin-like serine proteases thrombin, factor Xa, and matriptase. A crystal structure in complex with the WNV protease was determined for one of the most potent inhibitors, 3,4-dichlorophenylacetyl-Lys-Lys-GCMA (K(i)=0.13 µM). The inhibitor adopts a horseshoe-like conformation, most likely due to a hydrophobic contact between the P4 phenyl ring and the P1 cyclohexyl group, which is further stabilized by an intramolecular hydrogen bond between the P1 guanidino group and the P4 carbonyl oxygen atom. These inhibitors are stable, readily accessible, and have a noncovalent binding mode. Therefore, they may serve as suitable lead structures for further development.

Identification of the first low-molecular-weight inhibitors of matriptase-2.

As recently discovered, matriptase-2, a type II transmembrane serine protease, plays a crucial role in body iron homeostasis by down-regulating hepcidin expression, which results in increased iron levels. Thus, matriptase-2 represents a novel target for the development of enzyme inhibitors potentially useful for the treatment of systemic iron overload (hemochromatosis). A comparative three-dimensional model of the catalytic domain of matriptase-2 was generated and utilized for structure-based virtual screening in combination with similarity searching and knowledge-based compound design. Two N-protected dipeptide amides containing a 4-amidinobenzylamide as P1 residue (compounds 1 and 3) were identified as the first small molecule inhibitors of matriptase-2 with K(i) values of 170 and 460 nM, respectively. An inhibitor of the closely related protease matriptase (compound 2, K(i) = 220 nM), with more than 50-fold selectivity over matriptase-2, was also identified.