Design and development of a series of borocycles as selective, covalent kallikrein 5 inhibitors.

The connection between Netherton syndrome and overactivation of epidermal/dermal proteases, particularly Kallikrein 5 (KLK5) has been well established and it is expected that a KLK5 inhibitor would improve the dermal barrier and also reduce the pain and itch that afflict Netherton syndrome patients. One of the challenges of covalent protease inhibitors has been achieving selectivity over closely related targets. In this paper we describe the use of structural insight to design and develop a selective and highly potent reversibly covalent KLK5 inhibitor from an initial weakly binding fragment.

Evaluation of a crystallographic surrogate for kallikrein 5 in the discovery of novel inhibitors for Netherton syndrome.

The inhibition of kallikrein 5 (KLK5) has been identified as a potential strategy for treatment of the genetic skin disorder Netherton syndrome, in which loss-of-function mutations in the SPINK5 gene lead to down-regulation of the endogenous inhibitor LEKTI-1 and profound skin-barrier defects with severe allergic manifestations. To aid in the development of a medicine for this target, an X-ray crystallographic system was developed to facilitate fragment-guided chemistry and knowledge-based drug-discovery approaches. Here, the development of a surrogate crystallographic system in place of KLK5, which proved to be challenging to crystallize, is described. The biochemical robustness of the crystallographic surrogate and the suitability of the system for the study of small nonpeptidic fragments and lead-like molecules are demonstrated.

Structure guided drug design to develop kallikrein 5 inhibitors to treat Netherton syndrome.

The connection between Netherton syndrome and overactivation of epidermal/dermal proteases particularly KLK5 has been well established. To treat sufferers of this severe condition we wished to develop a topical KLK5 inhibitor in order to normalise epidermal shedding and reduce the associated inflammation and itching. In this paper we describe structure-based optimisation of a series of brightly coloured weak KLK5 inhibitors into colourless, non-irritant molecules with good KLK5 activity and selectivity over a range of serine proteases.

Kallikrein 5 inhibitors identified through structure based drug design in search for a treatment for Netherton Syndrome.

Netherton syndrome (NS) is a rare and debilitating severe autosomal recessive genetic skin disease with high mortality rates particularly in neonates. NS is caused by loss-of-function SPINK5 mutations leading to unregulated kallikrein 5 (KLK5) and kallikrein 7 (KLK7) activity. Furthermore, KLK5 inhibition has been proposed as a potential therapeutic treatment for NS. Identification of potent and selective KLK5 inhibitors would enable further exploration of the disease biology and could ultimately lead to a treatment for NS. This publication describes how fragmentation of known trypsin-like serine protease (TLSP) inhibitors resulted in the identification of a series of phenolic amidine-based KLK5 inhibitors 1. X-ray crystallography was used to find alternatives to the phenol interaction leading to identification of carbonyl analogues such as lactam 13 and benzimidazole 15. These reversible inhibitors, with selectivity over KLK1 (10-100 fold), provided novel starting points for the guided growth towards suitable tool molecules for the exploration of KLK5 biology.

The γδTCR combines innate immunity with adaptive immunity by utilizing spatially distinct regions for agonist selection and antigen responsiveness.

T lymphocytes expressing γδ T cell antigen receptors (TCRs) comprise evolutionarily conserved cells with paradoxical features. On the one hand, clonally expanded γδ T cells with unique specificities typify adaptive immunity. Conversely, large compartments of γδTCR+ intraepithelial lymphocytes (γδ IELs) exhibit limited TCR diversity and effect rapid, innate-like tissue surveillance. The development of several γδ IEL compartments depends on epithelial expression of genes encoding butyrophilin-like (Btnl (mouse) or BTNL (human)) members of the B7 superfamily of T cell co-stimulators. Here we found that responsiveness to Btnl or BTNL proteins was mediated by germline-encoded motifs within the cognate TCR variable γ-chains (Vγ chains) of mouse and human γδ IELs. This was in contrast to diverse antigen recognition by clonally restricted complementarity-determining regions CDR1-CDR3 of the same γδTCRs. Hence, the γδTCR intrinsically combines innate immunity and adaptive immunity by using spatially distinct regions to discriminate non-clonal agonist-selecting elements from clone-specific ligands. The broader implications for antigen-receptor biology are considered.

Inhibition of PAD4 activity is sufficient to disrupt mouse and human NET formation.

PAD4 has been strongly implicated in the pathogenesis of autoimmune, cardiovascular and oncological diseases through clinical genetics and gene disruption in mice. New selective PAD4 inhibitors binding a calcium-deficient form of the PAD4 enzyme have validated the critical enzymatic role of human and mouse PAD4 in both histone citrullination and neutrophil extracellular trap formation for, to our knowledge, the first time. The therapeutic potential of PAD4 inhibitors can now be explored.

Discovery of novel irreversible inhibitors of interleukin (IL)-2-inducible tyrosine kinase (Itk) by targeting cysteine 442 in the ATP pocket.

IL-2-inducible tyrosine kinase (Itk) plays a key role in antigen receptor signaling in T cells and is considered an important target for anti-inflammatory drug discovery. In order to generate inhibitors with the necessary potency and selectivity, a compound that targeted cysteine 442 in the ATP binding pocket and with an envisaged irreversible mode of action was designed. We incorporated a high degree of molecular recognition and specific design features making the compound suitable for inhaled delivery. This study confirms the irreversible covalent binding of the inhibitor to the kinase by x-ray crystallography and enzymology while demonstrating potency, selectivity, and prolonged duration of action in in vitro biological assays. The biosynthetic turnover of the kinase was also examined as a critical factor when designing irreversible inhibitors for extended duration of action. The exemplified Itk inhibitor demonstrated inhibition of both TH1 and TH2 cytokines, was additive with fluticasone propionate, and inhibited cytokine release from human lung fragments. Finally, we describe an in vivo pharmacodynamic assay that allows rapid preclinical development without animal efficacy models.

Identification of novel interacting partners of Sirtuin6.

SIRT6 is a member of the Sirtuin family of histone deacetylases that has been implicated in inflammatory, aging and metabolic pathways. Some of its actions have been suggested to be via physical interaction with NFκB and HIF1α and transcriptional regulation through its histone deacetylase activity. Our previous studies have investigated the histone deacetylase activity of SIRT6 and explored its ability to regulate the transcriptional responses to an inflammatory stimulus such as TNFα. In order to develop a greater understanding of SIRT6 function we have sought to identify SIRT6 interacting proteins by both yeast-2-hybrid and co-immunoprecipitation studies. We report a number of interacting partners which strengthen previous findings that SIRT6 functions in base excision repair (BER), and novel interactors which suggest a role in nucleosome and chromatin remodeling, the cell cycle and NFκB biology.

Over expression of wild type or a catalytically dead mutant of Sirtuin 6 does not influence NFκB responses.

SIRT6 is involved in inflammation, aging and metabolism potentially by modulating the functions of both NFκB and HIF1α. Since it is possible to make small molecule activators and inhibitors of Sirtuins we wished to establish biochemical and cellular assays both to assist in drug discovery efforts and to validate whether SIRT6 represents a valid drug target for these indications. We confirmed in cellular assays that SIRT6 can deacetylate acetylated-histone H3 lysine 9 (H3K9Ac), however this deacetylase activity is unusually low in biochemical assays. In an effort to develop alternative assay formats we observed that SIRT6 overexpression had no influence on TNFα induced nuclear translocation of NFκB, nor did it have an effect on nuclear mobility of RelA/p65. In an effort to identify a gene expression profile that could be used to identify a SIRT6 readout we conducted genome-wide expression studies. We observed that overexpression of SIRT6 had little influence on NFκB-dependent genes, but overexpression of the catalytically inactive mutant affected gene expression in developmental pathways.

Both Ca2+ and Zn2+ are essential for S100A12 protein oligomerization and function.

BACKGROUND: Human S100A12 is a member of the S100 family of EF-hand calcium-modulated proteins that are associated with many diseases including cancer, chronic inflammation and neurological disorders. S100A12 is an important factor in host/parasite defenses and in the inflammatory response. Like several other S100 proteins, it binds zinc and copper in addition to calcium. Mechanisms of zinc regulation have been proposed for a number of S100 proteins e.g. S100B, S100A2, S100A7, S100A8/9. The interaction of S100 proteins with their targets is strongly dependent on cellular microenvironment. RESULTS: The aim of the study was to explore the factors that influence S100A12 oligomerization and target interaction. A comprehensive series of biochemical and biophysical experiments indicated that changes in the concentration of calcium and zinc led to changes in the oligomeric state of S100A12. Surface plasmon resonance confirmed that the presence of both calcium and zinc is essential for the interaction of S100A12 with one of its extracellular targets, RAGE--the Receptor for Advanced Glycation End products. By using a single-molecule approach we have shown that the presence of zinc in tissue culture medium favors both the oligomerization of exogenous S100A12 protein and its interaction with targets on the cell surface. CONCLUSION: We have shown that oligomerization and target recognition by S100A12 is regulated by both zinc and calcium. Our present work highlighted the potential role of calcium-binding S100 proteins in zinc metabolism and, in particular, the role of S100A12 in the cross talk between zinc and calcium in cell signaling.

Proteolysis of prion protein by cathepsin S generates a soluble beta-structured intermediate oligomeric form, with potential implications for neurotoxic mechanisms.

Formation of PrP aggregates is considered to be a characteristic event in the pathogenesis of TSE diseases, accompanied by brain inflammation and neurodegeneration. Factors identified as contributing to aggregate formation are of interest as potential therapeutic targets. We report that in vitro proteolysis of ovine PrP(94-233) (at neutral pH and in the absence of denaturants) by the protease cathepsin S, a cellular enzyme that also shows enhanced expression in pathogenic conditions, occurs selectively in the region 135-156. This results in an unusually efficient, concentration-dependent conformational conversion of a large subfragment of PrP(94-233) into a soluble beta-structured oligomeric intermediate species, that readily forms a thioflavin-T-positive aggregate. N-terminal sequencing of the proteolysis fragments shows the aggregating species have marked sequence similarities to truncated PrP variants known to confer unusually severe pathogenicity when transgenically expressed in PrP(o/o) mice. Circular dichroism analysis shows that PrP fragments 138-233, 144-233 and 156-233 are significantly less stable than PrP(94-233). This implies an important structural contribution of the beta1 sequence within the globular domain of PrP. We propose that the removal or detachment of the beta1 sequence enhances beta-oligomer formation from the globular domain, leading to aggregation. The cellular implications are that specific proteases may have an important role in the generation of membrane-bound, potentially toxic, beta-oligomeric PrP species in pre-amyloid states of prion diseases. Such species may induce cell death by lysis, and also contribute to the transport of PrP to neuronal targets with subsequent amplification of pathogenic effects.

Misfolded forms of glyceraldehyde-3-phosphate dehydrogenase interact with GroEL and inhibit chaperonin-assisted folding of the wild-type enzyme.

We studied the interaction of chaperonin GroEL with different misfolded forms of tetrameric phosphorylating glyceraldehyde-3-phosphate dehydrogenase (GAPDH): (1) GAPDH from rabbit muscles with all SH-groups modified by 5,5'-dithiobis(2-nitrobenzoate); (2) O-R-type dimers of mutant GAPDH from Bacillus stearothermophilus with amino acid substitutions Y283V, D282G, and Y283V/W84F, and (3) O-P-type dimers of mutant GAPDH from B. stearothermophilus with amino acid substitutions Y46G/S48G and Y46G/R52G. It was shown that chemically modified GAPDH and the O-R-type mutant dimers bound to GroEL with 1:1 stoichiometry and dissociation constants K(d) of 0.4 and 0.9 muM, respectively. A striking feature of the resulting complexes with GroEL was their stability in the presence of Mg-ATP. Chemically modified GAPDH and the O-R-type mutant dimers inhibited GroEL-assisted refolding of urea-denatured wild-type GAPDH from B. stearothermophilus but did not affect its spontaneous reactivation. In contrast to the O-R-dimers, the O-P-type mutant dimers neither bound nor affected GroEL-assisted refolding of the wild-type GAPDH. Thus, we suggest that interaction of GroEL with certain types of misfolded proteins can result in the formation of stable complexes and the impairment of chaperonin activity.