A selective inhibitor of the osteoclastic V-H(+)-ATPase prevents bone loss in both thyroparathyroidectomized and
L Visentin1, R A Dodds, M Valente
1SmithKline Beecham S.p.A, Milano, Italy. SmithKline Beecham Pharmaceuticals, Bone and Cartilage Biology, King of Prussia, Pennsylvania, USA.
Abstract:
A potent and selective inhibitor of the osteoclastic V-H(+)-ATPase, (2Z,4E)-5-(5,6-dichloro-2-indolyl)-2-methoxy-N-(1,2,2,6, 6-pentamethylpiperidin-4-yl)-2,4-pentadienamide (SB 242784), was evaluated in two animal models of bone resorption. SB 242784 completely prevented retinoid-induced hypercalcemia in thyroparathyroidectomized (TPTX) rats when administered orally at 10 mg/kg. SB 242784 was highly efficacious in the prevention of ovariectomy-induced bone loss in the rat when administered orally for 6 months at 10 mg/kg/d and was partially effective at 5 mg/kg/d. Its activity was demonstrated by measurement of bone mineral density (BMD), biochemical markers of bone resorption, and histomorphometry. SB 242784 was at least as effective in preventing bone loss as an optimal dose of estrogen. There were no adverse effects of compound administration and no effects on kidney function or urinary acidity. Selectivity of the inhibitor was further studied using an in situ cytochemical assay for bafilomycin-sensitive V-H(+)-ATPase using sections of osteoclastoma and numerous other tissues. SB 242784 inhibited the osteoclast enzyme at 1,000-fold lower concentrations than enzymes in any of the other tissues evaluated. SB 242784 demonstrates the utility of selective inhibition of the osteoclast V-H(+)-ATPase as a novel approach to the prevention of bone loss in humans.
Insights
SB 242784, a selective V-H(+)-ATPase inhibitor, effectively prevented bone loss and hypercalcemia in animal models. This compound shows promise for treating bone resorption diseases without adverse effects.
Area of Science:
- Pharmacology
- Bone Biology
- Biochemistry
Background:
- Osteoclastic V-H(+)-ATPase is a key target for managing bone resorption.
- Selective inhibition of this enzyme offers a potential therapeutic strategy for bone loss.
Purpose of the Study:
- To evaluate the efficacy and selectivity of SB 242784, a novel V-H(+)-ATPase inhibitor, in animal models of bone resorption.
Main Methods:
- SB 242784 was tested in retinoid-induced hypercalcemia and ovariectomy-induced bone loss models in rats.
- Bone mineral density, biochemical markers, and histomorphometry were used to assess efficacy.
- In situ cytochemical assays evaluated enzyme selectivity across various tissues.
Main Results:
- SB 242784 completely prevented hypercalcemia and significantly reduced ovariectomy-induced bone loss.
- Efficacy was dose-dependent, with no adverse effects or impact on kidney function.
- The compound demonstrated high selectivity, inhibiting osteoclast V-H(+)-ATPase at much lower concentrations than other tissues.
Conclusions:
- Selective inhibition of osteoclast V-H(+)-ATPase by SB 242784 is a viable approach for preventing bone loss.
- SB 242784 represents a novel therapeutic strategy for conditions characterized by excessive bone resorption.
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