Inhibitors of human leukocyte proteinase-3

Inhibitors and Antibody Fragments as Potential Anti-Inflammatory Therapeutics Targeting Neutrophil Proteinase 3 in Human Disease

Proteinase 3 (PR3) has received great scientific attention after its identification as the essential antigenic target of antineutrophil cytoplasm antibodies in Wegener's granulomatosis (now called granulomatosis with polyangiitis). Despite many structural and functional similarities between neutrophil elastase (NE) and PR3 during biosynthesis, storage, and extracellular release, unique properties and pathobiological functions have emerged from detailed studies in recent years. The development of highly sensitive substrates and inhibitors of human PR3 and the creation of PR3-selective single knockout mice led to the identification of nonredundant roles of PR3 in cell death induction via procaspase-3 activation in cell cultures and in mouse models. According to a study in knockout mice, PR3 shortens the lifespan of infiltrating neutrophils in tissues and accelerates the clearance of aged neutrophils in mice. Membrane exposure of active human PR3 on apoptotic neutrophils reprograms the response of macrophages to phagocytosed neutrophils, triggers secretion of proinflammatory cytokines, and undermines immune silencing and tissue regeneration. PR3-induced disruption of the anti-inflammatory effect of efferocytosis may be relevant for not only granulomatosis with polyangiitis but also for other autoimmune diseases with high neutrophil turnover. Inhibition of membrane-bound PR3 by endogenous inhibitors such as the α-1-protease inhibitor is comparatively weaker than that of NE, suggesting that the adverse effects of unopposed PR3 activity resurface earlier than those of NE in individuals with α-1-protease inhibitor deficiency. Effective coverage of PR3 by anti-inflammatory tools and simultaneous inhibition of both PR3 and NE should be most promising in the future.

Reversible ketomethylene-based inhibitors of human neutrophil proteinase 3

Neutrophil serine proteases, proteinase 3 (PR3) and human neutrophil elastase (HNE), are considered as targets for chronic inflammatory diseases. Despite sharing high sequence similarity, the two enzymes have different substrate specificities and functions. While a plethora of HNE inhibitors exist, PR3 specific inhibitors are still in their infancy. We have designed ketomethylene-based inhibitors for PR3 that show low micromolar IC50 values. Their synthesis was made possible by amending a previously reported synthesis of ketomethylene dipeptide isosteres to allow for the preparation of derivatives suitable for solid phase peptide synthesis. The best inhibitor (Abz-VADnV[Ψ](COCH2)ADYQ-EDDnp) was found to be selective for PR3 over HNE and to display a competitive and reversible inhibition mechanism. Molecular dynamics simulations show that the interactions between enzyme and ketomethylene-containing inhibitors are similar to those with the corresponding substrates. We also confirm that N- and C-terminal FRET groups are important for securing high inhibitory potency toward PR3.

Inhibitors of human neutrophil elastase based on a highly functionalized N-amino-4-imidazolidinone scaffold

A series of compounds based on the N-amino-4-imidazolidinone scaffold was synthesized and screened against human neutrophil elastase (HNE). These studies lead to the identification of a selective, low micromolar reversible competitive inhibitor of HNE.

Utilization of the 1,2,3,5-thiatriazolidin-3-one 1,1-dioxide scaffold in the design of potential inhibitors of human neutrophil proteinase 3

The S' subsites of human neutrophil proteinase 3 (Pr 3) were probed by constructing diverse libraries of compounds based on the 1,2,3,5-thiatriazolidin-3-one 1,1-dioxide using combinational and click chemistry methods. The multiple points of diversity embodied in the heterocyclic scaffold render it well-suited to the exploration of the S' subsites of Pr 3. Molecular modeling studies suggest that further exploration of the S' subsites of Pr 3 using the aforementioned heterocyclic scaffold may lead to the identification of highly selective, reversible competitive inhibitors of Pr 3.

Tablets of Functionalized Polystyrene Beads Alone and in Combination with Solid Reagents or Catalysts. Preparation and Applications in Parallel Solution and Solid Phase Synthesis

Pretreatment of polystyrene beads with a nonpolar organic solvent is the key for the generation of mechanically robust tablets consisting of neat functionalized polystyrene beads, both alone and in combination with solid reagents or catalysts. The novel dosing methodology provides accurately preweighed tablets in virtually any shape and size and with excellent disintegration properties, speeding up parallel solution and solid phase synthesis. The use of tablets is demonstrated in parallel Mitsunobu and acylation reactions.

Inhibition of serine proteases by functionalized sulfonamides coupled to the 1,2,5-thiadiazolidin-3-one 1,1 dioxide scaffold

A challenge associated with drug design is the development of selective inhibitors of proteases (serine or cysteine) that exhibit the same primary substrate specificity, that is, show a preference for the same P(1) residue. While these proteases have similar active sites, nevertheless there are subtle differences in their S and S' subsites which can be exploited. We describe herein for the first time the use of functionalized sulfonamides as a design and diversity element which, when coupled to the 1,2,5-thiadiazolidin-3-one 1,1 dioxide scaffold yields potent, time-dependent inhibitors of the serine proteases human leukocyte elastase (HLE), proteinase 3 (PR 3) and cathepsin G(Cat G). Our preliminary findings suggest that (a) appending to the 1,2,5-thiadiazolidin-3-one 1,1 dioxide scaffold recognition and diversity elements that interact with both the S and S' subsites of a target protease may result in optimal enzyme selectivity and potency and, (b) functionalized sulfonamides constitute a powerful design and diversity element with low intrinsic chemical reactivity and potentially wide applicability.

Studies on 2-benzyloxy-4H-3,1-benzoxazin-4-ones as serine protease inhibitors

The class of 3,1-benzoxazin-4-ones includes potent inhibitors of various serine proteases. Structural investigation on three 2-benzyloxy-4H-3,1-benzoxazin-4-ones (1-3) are described with respect to their reactivity to alkaline hydrolysis. The 13C NMR data of 2-benzyloxy-5-methyl-4H-3,1-benzoxazin-4-one 3 are discussed. This peri substituted compound was subjected to a crystal structure analysis. The heterocyclic skeleton together with the carbonyl oxygen and the methyl carbon is planar, and only small angle distortions occurred. The inhibition of neutrophil serine proteases by 1-3 is reported. The different reactivity of the 5-methyl derivative 3 towards serine proteases is mainly influenced by specific interactions within the active sites. Thus, 3 was found to rapidly acylate human leukocyte proteinase 3 and exhibited a Ki value of 1.8 nM.

3-(Alkylthio)-N-hydroxysuccinimide derivatives: potent inhibitors of human leukocyte elastase

A series of 3-(alkylthio)-N-hydroxysuccinimide derivatives was synthesized and their inhibitory activity towards human leukocyte elastase (HLE) was investigated. The interaction of the compounds having a 3-alkylthioether side chain (compounds 1 and 2) with HLE was found to involve rapid acylation of the enzyme, followed by total regain of enzymatic activity within 3 h. Interestingly, compounds 3-8, having an oxidized thioether side chain, were found to be highly effective, time-dependent, irreversible inhibitors of the enzyme. The k(obs)/I values for compounds 3-8 ranged between 890 and 24,000 M-1 s-1. These findings demonstrate that, unlike the physiological inhibitor of HLE (alpha-1-proteinase inhibitor), which is inactivated upon oxidation, low-molecular-weight compounds retain and/or show enhanced inhibitory activity towards HLE upon oxidation of the thioether side chain and lay the groundwork for the development of compounds that embody proteinase inhibitory and antioxidant activity.

Human neutrophil proteinase 3: mapping of the substrate binding site using peptidyl thiobenzyl esters

A series of peptidyl thiobenzyl esters was used to map the active site of human leukocyte proteinase 3. The steady-state kinetics parameters reveal the following features regarding the substrate specificity of proteinase 3 and its putative active site: (a) the preferred P1 residue is a small hydrophobic amino acid such as aminobutyric acid, norvaline, valine or alanine (in decreasing order of preference); (b) the enzyme has an extended active site; and (c) its active site is similar to that of the related serine proteinases leukocyte elastase and leukocyte cathepsin G.

Inhibitors of human neutrophil cathepsin G: structural and biochemical studies

The interaction of a series of sulfonate and phosphate esters derived from N-hydroxysuccinimide with human leukocyte cathepsin G was investigated. The synthesized compounds were found to be time-dependent inhibitors of the enzyme. The composite interplay of steric and electronic effects leads to the formation of acyl enzymes of variable stability, ultimately resulting in partial or full recovery of enzymatic activity. Compounds acting via phosphorylation of the active site serine inactivated the enzyme rapidly and irreversibly.

Substrate and inhibitor studies on proteinase 3

Various amino acid and peptide thioesters were tested as substrates for human proteinase 3 and the best substrate is Boc-Ala-Ala-Nva-SBzl with a kcat/Km value of 1.0 x 10(6) M-1.s-1. Boc-Ala-Ala-AA-SBzl (AA = Val, Ala, or Met) are also good substrates with kcat/Km values of (1-4) x 10(5) M-1.s-1. Substituted isocoumarins are potent inhibitors of proteinase 3 and the best inhibitors are 7-amino-4-chloro-3-(2-bromoethoxy)isocoumarin and 3,4-dichloroisocoumarin (DCI) with kobs/[I] values of 4700 and 2600 M-1.s-1, respectively. Substituted isocoumarins, peptide phosphonates and chloromethyl ketones inhibited proteinase 3 less potently than human neutrophil elastase (HNE) by 1-2 orders of magnitude.