A potent small molecule, nonpeptide inhibitor of cathepsin K (SB 331750) prevents bone matrix resorption in the ovariectomized rat.

Abstract

Inhibition of the cyteine proteinase, cathepsin K (E.C. 3.4.22.38) has been postulated as a means to control osteoclast-mediated bone resorption. The preferred animal models for evaluation of antiresorptive activity are in the rat. However, the development of compounds that inhibit rat cathepsin K has proven difficult because the human and rat enzymes differ in key residues in the active site. In this study, a potent, nonpeptide inhibitor of rat cathepsin K (K(i) = 4.7 nmol/L), 5-(2-morpholin-4-yl-ethoxy)-benzofuran-2-carboxylic acid ((S)-3-methyl-1-(3-oxo-1-[2-(3-pyridin-2-yl-phenyl)-ethenoyl]-azepan-4-ylcarbanoyl)-butyl)-amide (SB 331750), is described, which is efficacious in rat models of bone resorption. SB 331750 potently inhibited human cathepsin K activity in vitro (K(i) = 0.0048 nmol/L) and was selective for human cathepsin K vs. cathepsins B (K(i) = 100 nmol/L), L (0.48 nmol/L), or S (K(i) = 14.3 nmol/L). In an in situ enzyme assay, SB 331750 inhibited osteoclast-associated cathepsin activity in tissue sections containing human osteoclasts (IC(50) approximately 60 nmol/L) and this translated into potent inhibition of human osteoclast-mediated bone resorption in vitro (IC(50) approximately 30 nmol/L). In vitro, SB 331750 partially, but dose-dependently, prevented the parathyroid hormone-induced hypercalcemia in an acute rat model of bone resorption. To evaluate the ability of SB 331750 to inhibit bone matrix degradation in vivo, it was administered for 4 weeks at 3, 10, or 30 mg/kg, intraperitoneally (i.p.), u.i.d. in the ovariectomized (ovx) rat. Both 10 and 30 mg/kg doses of compound prevented the ovx-induced elevation in urinary deoxypyridinoline and prevented the ovx-induced increase in percent eroded perimeter. Histological evaluation of the bones from compound-treated animals indicated that SB 331750 retarded bone matrix degradation in vivo at all three doses. The inhibition of bone resorption at the 10 and 30 mg/kg doses resulted in prevention of the ovx-induced reduction in percent trabecular area, trabecular number, and increase in trabecular spacing. These effects on bone resorption were also reflected in inhibition of the ovx-induced loss in trabecular bone volume as assessed using microcomputerized tomography (microCT; approximately 60% at 30 mg/kg). Together, these data indicate that the cathepsin K inhibitor, SB 331750, prevented bone resorption in vivo and this inhibition resulted in prevention of ovariectomy-induced loss in trabecular structure.

• Authors: Michael W Lark, G B Stroup, I E James, R A Dodds, S M Hwang, S M Blake, B A Lechowska, S J Hoffman, B R Smith, R Kapadia, X Liang, K Erhard, Y Ru, X Dong, R W Marquis, D Veber, M Gowen
• Journal: Bone (Bone) Vol. 30 Issue 5 Pg. 746-53 (May 2002) ISSN: 8756-3282 [Print] United States
• PMID: 11996914 (Publication Type: Journal Article)

Chemical References

• Benzofurans
• Cysteine Proteinase Inhibitors
• Pyridines
• SB 331750
• Cathepsins
• CTSK protein, human
• Cathepsin K
• Ctsk protein, rat

Topics

• Animals
• Benzofurans (pharmacology)
• Binding Sites (drug effects)
• Bone Resorption (drug therapy, prevention & control)
• Cathepsin K
• Cathepsins (antagonists & inhibitors, chemistry, metabolism)
• Cysteine Proteinase Inhibitors (chemistry, pharmacology)
• Disease Models, Animal
• Female
• Humans
• In Vitro Techniques
• Male
• Osteoclasts (cytology, drug effects)
• Ovariectomy
• Parathyroidectomy
• Pyridines (pharmacology)
• Rats
• Rats, Sprague-Dawley
• Thyroidectomy