title: In vivo inhibition of serine protease processing requires a high fractional inhibition of cathepsin C.
abstract: Inhibition of cathepsin C, a dipeptidyl peptidase that activates many serine proteases, represents an attractive therapeutic strategy for inflammatory diseases with a high neutrophil burden. We recently showed the feasibility of blocking the activation of neutrophil elastase, cathepsin G, and proteinase-3 with a single cathepsin C selective inhibitor in cultured cells. Here we measured the fractional inhibition of cathepsin C that is required for blockade of downstream serine protease processing, in cell-based assays and in vivo. Using a radiolabeled active site probe and U937 cells, a 50% reduction of cathepsin G processing required approximately 50% of cathepsin C active sites to be occupied by an inhibitor. In EcoM-G cells, inhibition of 50% of neutrophil elastase activity required approximately 80% occupancy. Both of these serine proteases were fully inhibited at full cathepsin C active site occupancy, whereas granzyme B processing in TALL-104 cells was partially inhibited, despite complete occupancy. In vivo, leukocytes from cathepsin C(+/-) mice exhibited comparable levels of neutrophil elastase activity to wild-type animals, even though their cathepsin C activity was reduced by half. The long-term administration of a cathepsin C inhibitor to rats, at doses that resulted in the nearly complete blockade of cathepsin C active sites in bone marrow, caused significant reductions of neutrophil elastase, cathepsin G and proteinase-3 activities. Our results demonstrate that the inhibition of cathepsin C leads to a decrease of activity of multiple serine proteases involved in inflammation but also suggest that high fractional inhibition is necessary to reach therapeutically significant effects.
authors.affiliation: Department of Biochemistry and Molecular Biology, Merck Frosst Centre for Therapeutic Research, Kirkland, Quebec, Canada.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Méthot
authors.forename: Daniel
authors.initials: D
authors.lastname: Guay
authors.forename: Joel
authors.initials: J
authors.lastname: Rubin
authors.forename: Diane
authors.initials: D
authors.lastname: Ethier
authors.forename: Karen
authors.initials: K
authors.lastname: Ortega
authors.forename: Simon
authors.initials: S
authors.lastname: Wong
authors.forename: Denis
authors.initials: D
authors.lastname: Normandin
authors.forename: Christian
authors.initials: C
authors.lastname: Beaulieu
authors.forename: T Jagadeeswar
authors.initials: TJ
authors.lastname: Reddy
authors.forename: Denis
authors.initials: D
authors.lastname: Riendeau
authors.forename: M David
authors.initials: MD
authors.lastname: Percival
mesh_terms: D000818:Animals; D020789:Cathepsin C / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008297:Male; D011480:Protease Inhibitors / Q000737:chemistry / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D020298:U937 Cells
chemical_list: D011480:Protease Inhibitors; D020789:Cathepsin C; D012697:Serine Endopeptidases