Design and Synthesis of Tri-Ring P₃ Benzamide-Containing Aminonitriles as Potent, Selective, Orally Effective Inhibitors of Cathepsin K

Abstract

We have prepared a series of achiral aminoacetonitriles, bearing tri-ring benzamide moieties and an aminocyclohexanecarboxylate residue at P2. This combination of binding elements resulted in sub-250 pM, reversible, selective, and orally bioavailable cathepsin K inhibitors. Lead compounds displayed single digit nanomolar inhibition in vitro (of rabbit osteoclast-mediated degradation of bovine bone). The best compound in this series, 39n (CRA-013783/L-006235), was orally bioavailable in rats, with a terminal half-life of over 3 h. 39n was dosed orally in ovariectomized rhesus monkeys once per day for 7 days. Collagen breakdown products were reduced by up to 76% dose-dependently. Plasma concentrations of 39n above the bone resorption IC50 after 24 h indicated a correlation between functional cellular and in vivo assays. Inhibition of collagen breakdown by cathepsin K inhibitors suggests this mechanism of action may be useful in osteoporosis and other indications involving bone resorption.

Efficacy of a Cathepsin K Inhibitor in a Preclinical Model for Prevention and Treatment of Breast Cancer Bone Metastasis

“…Structure, potency, and selectivity profile of the cathepsin K inhibitor L-006,235 has previously been reported (17). L-235 [N-(1-((cyanomethyl)carbamoyl)cyclohexyl)-4-(2-(4-methylpiperazin-1-yl)thiazol-4-yl)benzamide] and zoledronic acid [1-hydroxy-2-(1H-imidazole-1-yl)ethylidene-bisphophonic acid] was synthesized by Merck Res.…”

“…This CatKi potently inhibited the breast cancer Matrigel invasion with an IC 50 of 3.2 nmol/L (data not shown) as compared with its activity in blocking osteoclastic bone resorption (IC 50 ¼ 5 nmol/L; ref. 17). Therefore, the ability of the intratibially injected MDA-MB-231 cells to invade to sites distant from the original injected site was characterized in vivo by immunohistochemically staining the sections from injected tibia for cytokeratin, a marker of the breast cancer cells (Fig.…”

“…Efficacy of L-235 as a bone resorption inhibitor has been well established in rabbits, it inhibits rabbit CatK (IC 50 ¼ 0.5 nmol/L) and bone resorption in vitro by rabbit OCs (IC 50 ¼ 5 nmol/L; ref. 17). When dosed orally once-daily for 27 weeks in OVX-rabbits, L-235 at 10 mg/kg prevented estrogen deficiency-induced osteopenia (21).…”

“…To further our understanding on the potential benefits and mechanisms of the CatK inhibitors compared with the bisphosphonates for the treatment of MBD, we selected L-006235 (L-235) as a proof-of-concept CatKi for evaluation in various rodent models of metastatic disease. The reversible CatKi, L-235, is structurally related to ODN (17,18). This compound inhibits human CatK with a Ki of 0.25 nmol/L, and is >4,000-fold selective against other human cathepsins L, B, and S (17).…”

New Cathepsin Inhibitors to Explore the Fluorophilic Properties of the S2 Pocket of Cathepsin B: Design, Synthesis, and Biological Evaluation

“…Compounds 4 were reacted with n-tetrabutyl ammonium fluoride (TBAF) [12] and the resulting amino acids were coupled, without purification, with aminoacetonitrile hydrochloride, under standard conditions, to obtain the desired fluorinated dipeptidomimetics 5 (Table 1). [13] The non-fluorinated reference compounds 6 a-6 d (for structures, see Table 2) were synthesized (see the Supporting Information, Figure S1) following the sequence described for the homocycloleucine derivatives [8,13] .…”