Design of Potent, Selective, and Orally Bioavailable Inhibitors of Cysteine Protease Cathepsin K

Abstract

Osteoclast-mediated bone matrix resorption has been attributed to cathepsin K, a cysteine protease of the papain family that is abundantly and selectively expressed in osteoclast. Inhibition of cathepsin K could potentially be an effective method to prevent osteoporosis. Structure-activity studies on a series of reversible ketoamides based inhibitors of cathepsin K have led to identification of potent and selective compounds. Crystallographic studies have given insights into the mode of binding of these inhibitors. A series of ketoamides with varying P1 moieties were first synthesized to find an optimum group that would fit into the S1 subsite of the cysteine protease, cathepsin K. With a desired P1 group in place a variety of heterocyclic analogues in the P' region were synthesized to study their steric and electronic effects. In the process of exploring these P' heterocyclic variations, excellent selectivity was gained over other highly homologous cysteine proteases, including cathepsins L, S, and V. The favorable pharmacokinetic properties of some of these cathepsin K inhibitors in rats make them suitable for evaluation in rodent osteoporosis models. A representative cathepsin K inhibitor was shown to attenuate PTH-stimulated hypercalcemia in the TPTX rat model. These inhibitors provide a viable lead series in the discovery of new therapies for the prevention and treatment of osteoporosis

Application of EMBM to Structure‐Based Design of Warheads for Protease Inhibitors

“…Reversible covalent ketoamide inhibitors of cathepsin K with varied substituent X in the CS of inhibitors. [14] Figure 8. Cathepsin K. Correlations of experimental vs. calculated pK i 's, generated on the training set (gray) and examined on the test set (black).…”

“…Thermodynamic stabilization of the corresponding tetrahedral complex (TC) formed between the inhibitor and the attacking nucleophile [11] is exploited for the design of reversible enzyme mechanism based inhibitos. [2,6,[12][13][14][15] Depending on the protease family, the nucleophile could be either an oxygen or a sulfur atom. The sulfhydryl anion of Cys has significantly lower potential to stabilize an anionic TC in comparison with the hydroxide anion because of the larger extent of electron back-donation from the HOMO of the electrophilic CS of the inhibitor to the LUMO of the attacking Cys nucleophile.…”

A review of recent progress (2002-2012) on the biological activities of pyrazoles

“…91 Phenylpyrazole 94 was discovered in an HTS approach as a dual BcL-2/ BcL-xL inhibitor, proteins of the BcL (B-cell Lymphoma) family which regulates apoptosis. 92 Dipeptide derivatives 95 93,94 and 96 95 have been disclosed as Cathepsin K (Cat K) inhibitors potentially useful for the treatment of osteoporosis. They are potent inhibitors but have poor selectivity over off-target cathepsins.…”

Peptidomimetic 2-cyanopyrrolidines as potent selective cathepsin L inhibitors

“…Phenylalanine derivatives (26 -29) did not inhibit cathepsin B and showed only a weak affinity towards cathepsin L. Leucine derivatives (22 -25) were also inactive as cathepsin B inhibitors but showed improved potency towards cathepsin L. Among the compounds (22 -25) a -phenylcinnamic derivative (24) showed the highest affinity for the enzyme cathepsin L. Looking at the activity profiles of these compounds it seems that a bulky moiety at P 3 should be able to provide more potent inhibitors. In compounds (22) and (23) the hydrophobic phenyl groups were tethered too far from the P 2 -P 3 amide linkage to fit optimally at S 3 pocket of the enzyme which is reflected in their lower degree of binding affinity for the enzyme as compared to compound (25), which has a phenyl group attached directly to the amidic linkage.…”

“…Till recently, most of the reported cysteine protease inhibitors have been irreversible inhibitors like fluromethyl ketones [21], vinylsulfones [22] or epoxysuccinates [23]. Numerous warheads [24] have been utilized in designing of reversible inhibitors of cysteine proteases including peptidic aldehydes [25], nitriles [26], cyclopropanones [27], diamino ketones [28] and a-ketoamides [29]. There has also been a report on the use of non-covalent amides as cathepsin K inhibitors [30].…”