Cathepsin S inhibitor

Ki: 0.185 nM

Cathepsin S is a lysosomal cysteine protease, playing an important role in antigen presentation. The inhibition of Cathepsin S is expected to result in immunosuppression, which makes this enzyme an attractive target to potentially treat autoimmune and inflammatory diseases. Cathepsin S inhibitor is a novel Cathepsin S inhibitor.

In vitro: Cathepsin S inhibitor was a slow, tight-binding reversible inhibitor of recombinant cathepsin S, exhibiting greater selectivity for cathepsin S compared to cathepsin B [1].

In vivo: No animal in vivo data available currently

Clinical trial: Oral Cathepsin S inhibitor that blocked MHCII antigen presentation could result in a T-cell-selective immunosuppressant agent with improved safety over the current standard of care for the treatment of rheumatoid arthritis, psoriasis, multiple sclerosis and other autoimmune-based inflammatory diseases [2].

References:
[1] Wiener JJ, Sun S, Thurmond RL.  Recent advances in the design of cathepsin S inhibitors. Curr Top Med Chem. 2010;10(7):717-32.
[2] Lee-Dutra A, Wiener DK, Sun S.  Cathepsin S inhibitors: 2004-2010. Expert Opin Ther Pat. 2011;21(3):311-37.

Antimicrobial Peptide LL-37 Is Both a Substrate of Cathepsins S and K and a Selective Inhibitor of Cathepsin L.[Pubmed:25884905]

Biochemistry. 2015 May 5;54(17):2785-98.

Lung cysteine cathepsins B, K, L, and S contribute to physiological and pathological processes including degradation of antimicrobial peptides/proteins (AMPs) such as surfactant protein SP-A, lactoferrin, secretory leukocyte peptidase inhibitor, and beta-defensins-2 and -3. Substantial amounts of uncleaved LL-37, a 37-mer cationic AMP, were observed in the sputum of patients with cystic fibrosis (CF). Nevertheless LL-37 was degraded after prolonged incubation in CF sputum, and the hydrolysis was blocked by E-64, a selective inhibitor of cysteine proteases. Cathepsins K and S, expressed in human alveolar macrophages, thoroughly hydrolyzed LL-37 in vitro, whereas it competitively inhibited cathepsin L (Ki = 150 nM). Cleavage of LL-37 by cathepsins S and K impaired its antimicrobial activity against Pseudomonas aeruginosa and Staphylococcus aureus, in a time- and concentration-dependent manner. The exchange of residues 67 and 205 in the S2 pockets of cathepsins L (Leu67Tyr/Ala205Leu) and K (Tyr67Leu/Leu205Ala) switched the specificity of these mutants toward LL-37. Molecular modeling suggested that LL-37 interacted with the active site of cathepsin L in both forward (i.e., substrate-like) and reverse orientations with similar binding energies. Our data support the hypothesis that cysteine cathepsins modulate the innate immunity response by degrading distinct and representative members of the AMP family.

Differential cathepsin responses to inhibitor-induced feedback: E-64 and cystatin C elevate active cathepsin S and suppress active cathepsin L in breast cancer cells.[Pubmed:27592448]

Int J Biochem Cell Biol. 2016 Oct;79:199-208.

Cathepsins are powerful proteases, once referred to as the lysosomal cysteine proteases, that have been implicated in breast cancer invasion and metastasis, but pharmaceutical inhibitors have suffered failures in clinical trials due to adverse side effects. Scientific advancement from lysosomotropic to cell impermeable cathepsin inhibitors have improved efficacy in treating disease, but off-target effects have still been problematic, motivating a need to better understand cellular feedback and responses to treatment with cathepsin inhibitors. To address this need, we investigated effects of E-64 and cystatin C, two broad spectrum cathepsin inhibitors, on cathepsin levels intra- and extracellularly in MDA-MB-231 breast cancer cells. Cathepsins S and L had opposing responses to both E-64 and cystatin C inhibitor treatments with paradoxically elevated amounts of active cathepsin S, but decreased amounts of active cathepsin L, as determined by multiplex cathepsin zymography. This indicated cellular feedback to selectively sustain the amounts of active cathepsin S even in the presence of inhibitors with subnanomolar inhibitory constant values. These differences were identified in cellular locations of cathepsins L and S, trafficking for secretion, co-localization with endocytosed inhibitors, and longer protein turnover time for cathepsin S compared to cathepsin L. Together, this work demonstrates that previously underappreciated cellular compensation and compartmentalization mechanisms may sustain elevated amounts of some active cathepsins while diminishing others after inhibitor treatment. This can confound predictions based solely on inhibitor kinetics, and must be better understood to effectively deploy therapies and dosing strategies that target cathepsins to prevent cancer progression.

A bioavailable cathepsin S nitrile inhibitor abrogates tumor development.[Pubmed:27097645]

Mol Cancer. 2016 Apr 21;15:29.

BACKGROUND: Cathepsin S has been implicated in a variety of malignancies with genetic ablation studies demonstrating a key role in tumor invasion and neo-angiogenesis. Thus, the application of Cathepsin S inhibitors may have clinical utility in the treatment of cancer. In this investigation, we applied a cell-permeable dipeptidyl nitrile inhibitor of cathepsin S, originally developed to target cathepsin S in inflammatory diseases, in both in vitro and in vivo tumor models. METHODS: Validation of cathepsin S selectivity was carried out by assaying fluorogenic substrate turnover using recombinant cathepsin protease. Complete kinetic analysis was carried out and true K i values calculated. Abrogation of tumour invasion using murine MC38 and human MCF7 cell lines were carried out in vitro using a transwell migration assay. Effect on endothelial tube formation was evaluated using primary HUVEC cells. The effect of inhibitor in vivo on MC38 and MCF7 tumor progression was evaluated using cells propagated in C57BL/6 and BALB/c mice respectively. Subsequent immunohistochemical staining of proliferation (Ki67) and apoptosis (TUNEL) was carried out on MCF7 tumors. RESULTS: We confirmed that this inhibitor was able to selectively target cathepsin S over family members K, V, L and B. The inhibitor also significantly reduced MC38 and MCF7 cell invasion and furthermore, significantly reduced HUVEC endothelial tubule formation in vitro. In vivo analysis revealed that the compound could significantly reduce tumor volume in murine MC38 syngeneic and MCF7 xenograft models. Immunohistochemical analysis of MCF7 tumors revealed Cathepsin S inhibitor treatment significantly reduced proliferation and increased apoptosis. CONCLUSIONS: In summary, these results highlight the characterisation of this nitrile Cathepsin S inhibitor using in vitro and in vivo tumor models, presenting a compound which may be used to further dissect the role of cathepsin S in cancer progression and may hold therapeutic potential.

Insights from molecular modeling into the selective inhibition of cathepsin S by its inhibitor.[Pubmed:28236030]

J Mol Model. 2017 Mar;23(3):92.

Cathepsin S has been demonstrated to play a crucial role in the remodeling of extracellular matrix proteins such as elastin and collagen, which in turn contribute to the structural integrity of the cardiovascular wall. Atherosclerotic lesions, aneurysm formation, plaque rupture, thrombosis, and calcification are some of the cardiovascular disorders related to cathepsin S. A highly selective inhibitor of human as well as animal cathepsin S, RO5444101, was recently reported to attenuate the progression of atherosclerotic lesions. Here, we attempted to gain insight into the molecular mechanism of action of RO5444101 on cathepsin S by performing molecular docking and molecular dynamics (MD) simulation studies. The results of our studies correlate well with relevant reported experimental data and potentially explain the selectivity of this inhibitor for cathepsin S rather than cathepsin L1/L, cathepsin L2/V, and cathepsin K, which share conserved catalytic sites and have sequence similarities of 49%, 50%, and 55%, respectively, with respect to cathepsin S. In contrast to those closely related cathepsins, 20 ns MD simulation data reveal that the overall interaction of cathepsin S with RO5444101 is more stable and involves more protein-molecule interactions than the interactions of the inhibitor with the other cathepsins. This study therefore considerably improves our understanding of the molecular mechanism responsible for cathepsin S inhibition and facilitates the identification of potential novel selective inhibitors of cathepsin S.

LY 3000328 is a potent and selective Cathepsin S (Cat S) inhibitor with IC50s of 7.7 and 1.67 nM for hCat S and mCat S, respectively.

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