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  • Cysteine protease inhibitors representing several chemical s


    Cysteine protease inhibitors representing several chemical scaffold types are effective in halting parasite replication without toxicity to the host (Renslo and McKerrow, 2006). A vinyl sulfone cysteine protease inhibitor, K11777, is completing final Good Laboratory Practice (GLP) preclinical tests as a prelude to Phase I clinical trials against Chagas Disease. Several of the inhibitors we tested are direct analogs of the vinyl sulfone K11777, with a variety of substituents in the P1′, P1 and P3 positions. Our studies identified K11777 and related vinyl sulfone inhibitors that are effective inhibitors of the cysteine protease activity of N. fowleri. Three of the inhibitors tested in vitro were also cidal versus N. fowleri. Vinyl sulfone inhibitors can serve as the starting points to optimize compounds that inhibit N. fowleri as safe and effective drug candidates.
    Acknowledgements This work was supported by the National Institutes of Health grant 1KL2TR001444 (to AD) and funded by a Skaggs Scholarship from the UC San Diego Skaggs School of Pharmacy and Pharmaceutical Sciences (to IZ). F. S. thanks MINECO (Spain, CTQ14-60233-R) for financial support.
    Introduction Cysteine proteases are one of the major types of proteolytic enzymes. Their hallmark is the nucleophilic thiol group of the catalytic cysteine residue, which enables the hydrolysis of peptide bonds in various acamprosate calcium kinase (Brömme, 2001). The most abundant cysteine proteases share a structural fold with papain, a plant endopeptidase being accumulated in the latex of Carica papaya fruits. Therefore, they are grouped into the clan CA and named papain-like proteases, which comprise 38 families, with the most numerous C1 papain family (Brömme, 2001, Rawlings et al., 2012). Members of this family are widespread in nature, being found in almost every group of living organisms, including bacteria, fungi, protists, plants and animals (Rawlings et al., 2012). Animal cysteine proteases of the papain family, named cathepsins, localize predominantly to the lysosome, where they are involved in a number of physiological processes, such as intracellular protein turnover, proenzyme activation, prohormone maturation, bone remodeling, apoptosis and immune responses (phagocytosis, antigen presentation) (Berdowska, 2004, Müller et al., 2014). However, when the activity of cysteine cathepsins is upregulated, they may contribute to the development of different pathologies, including rheumatoid arthritis, osteoarthritis, osteoporosis, atherosclerosis, muscular dystrophy and cancer (Berdowska, 2004; Brömme, 2001). Therefore, these enzymes are considered as new diagnostic markers and promising drug targets to treat the aforementioned diseases (Berdowska, 2004). A number of selective cysteine cathepsin inhibitors, isolated from living organisms or synthesized in chemical laboratories, have been successfully used for the experimental treatment of many pathologies. Several of them have reached the stage of clinical trials, e.g., odanacatib (developed by Merck & Co., Inc.) as a potent and nontoxic inhibitor of cathepsin K to treat osteoporosis and bone metastasis (Gauthier et al., 2008). Different small-molecule inhibitors of cysteine cathepsins, isolated from cellular extracts or conditioned culture media of various microorganisms, have been applied in science, medical research and biotechnology. For instance, leupeptin and E-64, secreted by soil actinomycetes and Aspergillus japonicus, respectively, are common ingredients of commercially available protease inhibitor cocktails. These compounds and their derivatives have also been employed in the investigation of cysteine cathepsin biological functions, as well as in several therapeutic approaches. Additionally, saprophytic and pathogenic microbes may synthesize proteinaceous inhibitors of cysteine proteases in order to facilitate their adaptation to the host environment. Indeed, such inhibitors may regulate the activity of microbial endogenous proteases involved in host invasion, restrain the activity of host proteases produced as defense factors against infections or suppress both innate and adaptive immune responses of the host by inactivating lysosomal cathepsins (Kędzior et al., 2016).