Azepanone-Based Inhibitors of Human and Rat Cathepsin K

Abstract

The synthesis, in vitro activities, and pharmacokinetics of a series of azepanone-based inhibitors of the cysteine protease cathepsin K (EC 3.4.22.38) are described. These compounds show improved configurational stability of the C-4 diastereomeric center relative to the previously published five- and six-membered ring ketone-based inhibitor series. Studies in this series have led to the identification of 20, a potent, selective inhibitor of human cathepsin K (K(i) = 0.16 nM) as well as 24, a potent inhibitor of both human (K(i) = 0.0048 nM) and rat (K(i,app) = 4.8 nM) cathepsin K. Small-molecule X-ray crystallographic analysis of 20 established the C-4 S stereochemistry as being critical for potent inhibition and that unbound 20 adopted the expected equatorial conformation for the C-4 substituent. Molecular modeling studies predicted the higher energy axial orientation at C-4 of 20 when bound within the active site of cathepsin K, a feature subsequently confirmed by X-ray crystallography. Pharmacokinetic studies in the rat show 20 to be 42% orally bioavailable. Comparison of the transport of the cyclic and acyclic analogues through CaCo-2 cells suggests that oral bioavailability of the acyclic derivatives is limited by a P-glycoprotein-mediated efflux mechanism. It is concluded that the introduction of a conformational constraint has served the dual purpose of increasing inhibitor potency by locking in a bioactive conformation as well as locking out available conformations which may serve as substrates for enzyme systems that limit oral bioavailability.

P-Glycoprotein Recognition of Substrates and Circumvention through Rational Drug Design

“…A series of azepanone-based inhibitors of cathepsin K were studied in Caco-2 cell monolayers and rat oral bioavailability. 145 The analogues had similar molecular weights, hydrophobicities, and H-bonding capacities. The acyclic derivatives were P-gp substrates, and conformational constraint via cyclization overcame this ( Figure 18A).…”

Emerging Roles of Cysteine Cathepsins in Disease and their Potential as Drug Targets

“…Although the amino acid sequences of rodent and human cathepsin K are highly homologous, there are important differences in several critical residues in the active site cleft, involved in substrate and/or inhibitor binding. Consequently, the compounds developed against human enzyme, would have substantially lower biological activity in a rodent disease model [178]. Two major ways to overcome this problem have been described in literature.…”

Optimization of peptidyl allyl sulfones as clan CA cysteine protease inhibitors

“…More generally, cathepsins have been linked to rheumatoid arthritis, osteoarthritis, neurological disorders and lysosomal storage diseases 14,15 . Because of their role in these diseases, cathepsins have been targets for drug development [16][17][18][19][20][21][22] . Continued investigation of new cathepsin inhibitors provides a route for expanding treatment of these diseases.…”