A potent small molecule, nonpeptide inhibitor of cathepsin K (SB 331750) prevents bone matrix resorption in the ovariectomized rat.
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.
Lark
Michael W
MW
Department of Bone and Cartilage Biology, SmithKline Beecham Pharmaceuticals, 709 Swedeland Road, PO Box 1539, King of Prussia, PA 19406, USA. michael_lark-1@gsk.com
Stroup
G B
GB
James
I E
IE
Dodds
R A
RA
Hwang
S M
SM
Blake
S M
SM
Lechowska
B A
BA
Hoffman
S J
SJ
Smith
B R
BR
Kapadia
R
R
Liang
X
X
Erhard
K
K
Ru
Y
Y
Dong
X
X
Marquis
R W
RW
Veber
D
D
Gowen
M
M
D000818:Animals; D001572:Benzofurans / Q000494:pharmacology*; D001665:Binding Sites / Q000187:drug effects; D001862:Bone Resorption / Q000188:drug therapy* / Q000517:prevention & control*; D056657:Cathepsin K; D002403:Cathepsins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D004195:Disease Models, Animal; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects*; D010052:Ovariectomy; D016105:Parathyroidectomy; D011725:Pyridines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013965:Thyroidectomy
D001572:Benzofurans; D015853:Cysteine Proteinase Inhibitors; D011725:Pyridines; C467690:SB 331750; D002403:Cathepsins; C534130:CTSK protein, human; D056657:Cathepsin K; C534133:Ctsk protein, rat