Therapeutic potential of non-peptide chymase inhibitors

Discovery and Preclinical Characterization of Fulacimstat (BAY 1142524), a Potent and Selective Chymase Inhibitor As a New Profibrinolytic Approach for Safe Thrombus Resolution

Chymase is a serine-protease produced by mast cells. In the past few decades, its role in fibrotic diseases triggered the search for orally available chymase inhibitors. Aiming at reducing adverse cardiac remodeling after myocardial infarction, our research efforts resulted in the discovery of fulacimstat (BAY 1142524). While clinical trials did not demonstrate efficacy in this indication, the recent discovery of a new unexpected biological role of chymase spurred a revival of interest in chymase inhibition: chymase was shown to inactivate plasmin within fibrin-rich clots. Chymase inhibitors are now considered as potential profibrinolytic drugs with low bleeding risk and therefore exceptional safety for the treatment of acute thrombosis settings such as stroke, pulmonary embolism, or venous thrombosis. This article describes the chemical optimization journey from a screening hit to the discovery of fulacimstat (BAY 1142524), a selective chymase inhibitor with a good safety profile, as well as its preclinical in vitro and in vivo characterization.

Binding Loop Substitutions in the Cyclic Peptide SFTI-1 Generate Potent and Selective Chymase Inhibitors

Chymase is a serine protease that is predominantly expressed by mast cells and has key roles in immune defense and the cardiovascular system. This enzyme has also emerged as a therapeutic target for cardiovascular disease due to its ability to remodel cardiac tissue and generate angiotensin II. Here, we used the nature-derived cyclic peptide sunflower trypsin inhibitor-1 (SFTI-1) as a template for designing novel chymase inhibitors. The key binding contacts of SFTI-1 were optimized by combining a peptide substrate library screen with structure-based design, which yielded several variants with potent activity. The lead variant was further modified by replacing the P1 Tyr residue with para-substituted Phe derivatives, generating new inhibitors with improved potency (K_i = 1.8 nM) and higher selectivity over closely related enzymes. Several variants were shown to block angiotensin I cleavage in vitro, highlighting their potential for further development and future evaluation as pharmaceutical leads.

In Vitro Modulation of Renin-Angiotensin System Enzymes by Amaranth (Amaranthus hypochondriacus) Protein-Derived Peptides: Alternative Mechanisms Different from ACE Inhibition

Among the factors affecting the development of cardiovascular diseases, hypertension is one of the most important. Research done on amaranth proteins has demonstrated their hypotensive capacity in vivo and in vitro; nevertheless, the mechanism underlying this effect remains unclear. The aim of this study was to analyze in vitro the inhibition of peptides derived from an amaranth hydrolysate (AHH) on other RAS enzymes other than ACE. The chymase and renin activities were studied. AHH was not able to inhibit chymase activity, although a dose-response effect was found on renin activity (IC₅₀ 0.6 mg/mL). To provide an approach to the renin inhibition mechanism, we analyzed AHH renin inhibition kinetics and performed a structural characterization of the peptides involved in the effect in terms of molecular size and hydrophobicity. Results suggest that amaranth peptides exhibit renin competitive inhibition behavior. Renin inhibition potency was directly related to peptide hydrophobicity. RP-HPLC separation of AHH and subsequent analysis of the peptide sequences showed 6 peptides belonging to 11S globulin (that can be grouped into 3 families) that would be responsible for renin inhibition. These results demonstrate that Amaranthus hypochondriacus seeds are an adequate source of peptides with renin inhibitory properties that could be used in functional food formulations.

Chymase inhibition as a pharmacological target: a role in inflammatory and functional gastrointestinal disorders?

Chymase has been extensively studied with respect to its role in the pathophysiology of cardiovascular disease, and is notable for its role in the generation of angiotensin II, a mediator crucial in vascular remodelling. However, in more recent years, an association between chymase and several inflammatory diseases, including gastrointestinal (GI) disorders such as inflammatory bowel diseases (IBD) have been described. Such studies, to date, with respect to IBD at least, are descriptive in the clinical context; nonetheless, preclinical studies implicate chymase in the pathogenesis of gut inflammation. However, studies to elucidate the role of chymase in functional bowel disease are in their infancy, but suggest a plausible role for chymase in contributing to some of the phenotypic changes observed in such disorders, namely increased epithelial permeability. In this short review, we have summarized the current knowledge on the pathophysiological role of chymase and its inhibition with reference to inflammation and tissue injury outside of the GI tract and discussed its potential role in GI disorders. We speculate that chymase may be a novel therapeutic target in the GI tract, and as such, inhibitors of chymase warrant preclinical investigation in GI diseases.