Development of a High-Throughput Screening Strategy for Upregulators of the OPG/RANKL Ratio with the Potential for Antiosteoporosis Effects

The ratio between osteoprotegerin (OPG) and the receptor activator of NF-B ligand (RANKL) in the bone microenvironment indicates the level of osteoclastogenesis, and upregulation of this ratio would improve osteoporosis. In this study, we established a novel high-throughput screening (HTS) system using two stably transfected monoclonal cell lines that either express firefly luciferase under the OPG promoter control or concurrently express firefly and renilla luciferases under control of the OPG and RANKL promoters, respectively. With this system, we can conveniently and rapidly detect the effects of compounds on the expression of OPG and RANKL through changes in firefly and renilla luciferase activities. A total of 8160 compounds were screened using this system, yielding five compounds without previously reported activity. The compound with greatest potential is E05657 with high activity and low effective concentration in the HTS system. It increases the OPG/RANKL ratio and OPG secretion, decreases the NFATc1 expression, and reduces osteoclastogenesis in vitro. These results indicate that this novel HTS system can be used to identify small molecules with potential antiosteoporosis effects, and E05657 is a promising lead compound as a novel antiosteoporosis drug.