A Novel Class of Nonpeptidic Biaryl Inhibitors of Human Cathepsin K

Abstract

A novel series of nonpeptidic biaryl compounds was identified as potent and reversible inhibitors of cathepsin K. The P2-P3 amide bond of a known amino acetonitrile dipeptide 1 was replaced with a phenyl ring, thereby giving rise to this biaryl series that retained potency vs cathepsin K and showed an improved selectivity profile against other cathepsins. Structural modification within this series resulted in the identification of compound (R)-2, a potent human cathepsin K inhibitor (IC(50) = 3 nM) that is selective versus cathepsins B (IC(50) = 3950 nM), L (IC(50) = 3725 nM), and S (IC(50) = 2010 nM). In an in vitro assay involving rabbit osteoclasts and bovine bone, compound (R)-2 inhibited bone resorption with an IC(50) of 95 nM. It was shown that, unlike some peptidic nitrile inhibitors of cysteine proteases, the nitrile moiety of (R)-2 is not converted to the corresponding amide 3 by cathepsin K. This indicates that this class of nonpeptidic nitrile inhibitors is unlikely to be hydrolyzed by cysteine proteases. Furthermore, the inhibition of cathepsin K by compound (R)-2 was shown to be fully reversible and not observably time-dependent. To demonstrate the efficacy of compound (R)-2 in vivo, it was administered to ovariectomized (OVX) rhesus monkeys at 20 mg/kg, po once daily for 8 days, and a urinary marker of bone turnover, N-telopeptide of type I collagen (uNTx), was measured. During the eight-day dosing period, the mean reduction by compound (R)-2 in uNTx was 80% (p < 0.001). This demonstrates that inhibition of cathepsin K leads to an inhibition of this bone resorption marker in OVX rhesus monkeys and strongly suggests that inhibition of cathepsin K is a viable therapeutic approach for the treatment of osteoporosis.

Effect of Cathepsin K Inhibitor Basicity on in Vivo Off-Target Activities

“…Recombinant humanized rabbit, rat, and mouse Cat K and human Cat L and S were provided by Celera (Rockville, MD) (Robichaud et al, 2003). Human liver Cat B was from Sigma (St. Louis, MO).…”

An activity-based probe for the determination of cysteine cathepsin protease activities in whole cells

“…Recombinant rabbit Cat K and human Cat F, L, S, and V were prepared as previously described [9,12,13]. Human liver Cat B was from Sigma, while recombinant human Cat C and Z were from R&D Systems.…”

“…The cysteine cathepsins are made up of 11 members in humans, of which catalytic activity has been identiWed for 9 of them [7]. Current interest in cysteine cathepsin biology has increased as cathepsins B (Cat B), K, and S are potential targets for the pharmacological treatment of cancer, arthritis, and liver diseases [8], osteoporosis [9], and autoimmune diseases [10], respectively. When developing pharmacological inhibitors, potencies versus the target and antitargets are generally determined using puriWed recombinant enzymes.…”

Discovery of Biphenylacetamide-Derived Inhibitors of BACE1 Using de Novo Structure-Based Molecular Design

“…31,32 Subsequent hydrolysis of 31a, followed by Suzuki coupling of the resultant phenylacetic acid 32a with phenylboronic acid using tetrabutylammonium bromide (TBAB), 33 attained the biaryl scaffold 33a in 50% yield. Similarly, the 3-methoxy-4-phenyl substituted scaffold 33b was obtained following the same procedure using methyl 4-iodo-3-methoxybenzoate 29b, which the preparation followed the synthetic route described by Baret et al Intermediates 35 and 36 were synthesized from the conversion of 4-biphenylacetic acid 28 to the methyl ester 34 followed by alkylation at the alpha-C position using procedures reported by Robichaud et al 35 The alkylated intermediates were subsequently hydrolyzed to give the corresponding biphenylacetic acid intermediates 35 and 36 (Scheme 5). Aryl halide intermediates 38 and 39 were prepared by coupling 4-bromophenylacetic acid 37 with benzylamine and 27 respectively, which the products were coupled to the appropriately substituted aryl boronic acid under Suzuki coupling conditions to furnish the corresponding biaryl scaffolds.…”