A novel synthetic triazolotriazepine derivative JTT-606 inhibits bone resorption by down-regulation of action and production of bone resorptive factors

In the search for a nem class of bone-sparing agents, we have conducted ran dom screening of the domestic chemical library using Ca-45 release assay fr om prelabeled cultured neonatal mouse calvariae and identified a novel synt hetic triazolotriazepine JTT-606 as a candidate fur a potent inhibitor of b one resorption, JTT-606 inhibited Ca-45 release dose dependently not only i n the control calvarial culture but also in the stimulated cultures by inte rleukin-1 alpha (IL-1 alpha), fibroblast growth factor 2 (FGF-2), and parat hyroid hormone (PTH), JTT-606 also inhibited both basal and stimulated oste oclast-like (OCL) cell formation in the coculture of mouse osteoblastic cel ls and bone marrow cells dose dependently, indicating its inhibitory effect on osteoclast: differentiation. Ex vivo OCL cell formation by cultured bon e marrow cells collected from, ovariectomized (OVX) mice also was decreased dose dependently by in vivo application of JTT-606 to a level similar to t hat from sham-operated mice, Furthermore, JTT-606 inhibited resorbed pit fo rmation by isolated mature osteoclasts as well as by unfractionated bone ce lls derived from rabbit long bones in the control and FGF-2-stimulated cult ures dose dependently, indicating both the direct and the indirect actions of JTT-606 on mature osteoclast function, In addition, JTT-606 reduced prod uction of IL-1 alpha, tumor necrosis factor alpha (TNF-alpha), IL-6;, and g ranulocyte-macrophage colony-stimulating factor (GM-CSP) in the human perip heral blood mononuclear cell culture, In vivo analyses of mature OVX rats r evealed that the application of JTT-606 for 12 weeks increased the BMD of t he lumbar spine and decreased the levels of serum osteocalcin and urine deo xypyridinoline to levels similar to those of 17 beta-estradiol-treated OVX rats. We propose that JTT-606 may inhibit both osteoclast differentiation a nd function by down-regulating both the action and the production of bone r esorptive factors. It is speculated that JTT-606 could be a potent agent fo r the treatment of osteopenic disorders with elevated osteoclastic bone res orption.