Reveromycin A, an agent for osteoporosis, inhibits bone resorption by inducing apoptosis specifically in osteoclasts

Abstract

Mature bone-resorbing osteoclasts (OCs) mediate excessive bone loss seen in several bone disorders, including osteoporosis. Here, we showed that reveromycin A (RM-A), a small natural product with three carboxylic groups in its structure, induced apoptosis specifically in OCs, but not in OC progenitors, nonfunctional osteoclasts, or osteoblasts. RM-A inhibited protein synthesis in OCs by selectively blocking enzymatic activity of isoleucyl-tRNA synthetase. The proapoptotic effect of RM-A was inhibited by neutralization or disruption of the acidic microenvironment, a prominent characteristic of OCs. RM-A was incorporated in OCs but not in nonfunctional osteoclasts and OC progenitors in neutral culture medium. Effects of RM-A on OC apoptosis increased under acidic culture conditions. RM-A not only was incorporated, but also induced apoptosis in OC progenitors in acidic culture medium. RM-A inhibited osteoclastic pit formation, decreased prelabeled 45 Ca release in organ cultures, and antagonized increased bone resorption in ovariectomized mice. These results suggested that preventive effects of RM-A on bone resorption in vitro and in vivo were caused by apoptosis through inhibition of isoleucyl-tRNA synthetase in OCs and that specific sensitivity of OCs to RM-A was due to the acidic microenvironment, which increased cell permeability of RM-A by suppressing dissociation of protons from carboxylic acid moieties, making them less polar. This unique mechanism suggested that RM-A might represent a type of therapeutic agent for treating bone disorders associated with increased bone loss.isoleucyl-tRNA synthetase ͉ inhibitor ͉ antiresorptive agent M ature osteoclasts resorb bone and mediate excessive bone loss seen in several bone disorders, including osteoporosis, arthritis, periodontitis, bone metastasis, and corticosteroidinduced bone loss (1-4). Mature bone-resorbing osteoclasts (OCs) exhibit highly specialized morphological structures, such as actin rings, clear zones, and ruffled borders, which are functional markers of OCs (2-5). These structures permit OCs to establish an isolated acidic microenvironment between themselves and the bone surface. The acidic microenvironment formed by V-ATPase on the ruffled borders of OCs allows dissolution of bone minerals and degradation of the bone matrix by proteases (6, 7). Therefore, these specialized features in OCs represent major potential targets for reducing OC activity and, consequently, could be useful for treatment of bone disorders. In addition, recent studies showed that receptor activator of NF-B ligand (RANKL), which is an essential factor for OC differentiation and activation, was one of the major targets of antiresorptive agents (2).Two types of antiresorptive drugs targeting OCs, i.e., bisphosphonates (BPPs) and calcitonin (CT), are used for clinical treatment of osteoporosis. BPPs, the most effective class of antiresorptive drugs available, inhibit bone resorption by suppressing functions of OCs and by shortening their lifespan (8 -10). Because of targeting of ...

Inhibition of Hsp90 activates osteoclast c-Src signaling and promotes growth of prostate carcinoma cells in bone

“…As a result, and in direct contrast to its antitumor activity in vitro and in a s.c. xenograft model, 17-AAG indirectly stimulates the intraosseous growth of PC-3M prostate cancer cells. However, this can be counteracted by three mechanistically distinct inhibitors of osteoclastogenesis, a Src kinase inhibitor (23), a bisphosphonate (24), and the osteoclast-specific apoptosis inducer reveromycin A (25). This study emphasizes the importance of obtaining a more complete understanding of the complex role played by Hsp90 in regulating normal tissue homeostasis, and how these events impact tumor growth and response to targeted therapy.…”

Osteoclast‐targeting small molecules for the treatment of neoplastic bone metastases

“…We recently found a unique biological activity: RM-A-induced cell death occurred specifically in osteoclasts with a several hundred-fold lesser concentration of RM-A than that which inhibited the cell growth of various other cells, including osteoblastic cells and osteoclast precursor cells. (43) It is unlikely that such selectivity is due to the target molecule of RM-A. Chemical analysis of RM-A showed that it is an acidic compound with three carboxylic groups in its structure (Fig.…”

“…CAII, carbonic anhydrase II; Cath K, cathepsin K; M-CSF, macrophage-colony stimulating factor; MMP-9, matrix metalloproteinase-9; PDGF, platelet-derived growth factor. (9) Alendronate, Zoledronate FPP synthase Marketed (9) MK-0822, AAE581 Cathepsin K Clinical (12) AZD0530, CGP76030 c-Src Clinical, Preclinical (19) L-000845704, SB265123 a V b 3 integrin Clinical, Preclinical (23,57) FR202126, Iejimalide A, B V-ATPase Preclinical (26,30) NS3736 ClC-7 Cl ) channel Preclinical (32) KN-93 CaMKIV Preclinical (33) LFM-A13 Btk ⁄ Tec Preclinical (34) (-)-DHMEQ, PDTC NF-jB Preclinical (35,36) Reveromycin A IleRS Preclinical (43,44) CaMKIV, Ca 2+ ⁄ calmodulin-dependent kinase IV; (-)-DHMEQ, (-)-dehydroxymethylepoxyquinomicin; FPP, farnesyl pyrophosphate; IleRS, isoleucyl-tRNA synthetase; PDTC, pyrrolidine dithiocarbamate.…”

Structure-Function Analyses of Cytochrome P450revI Involved in Reveromycin A Biosynthesis and Evaluation of the Biological Activity of Its Substrate, Reveromycin T

“…Reveromycin A (RM-A) 3 (3), which is a spiroacetal polyketide compound produced by Streptomyces sp. SN-593, inhibits bone resorption by specifically inducing apoptosis in osteoclasts (4). It has been demonstrated that RM-A inhibited bone metastasis of lung and prostate cancer cells through anti-osteoclastic activity (5-7).…”