A novel DCSTAMP antagonist impedes preosteoclast fusion via modulation of RAP1B-RAC1-mediated cytoskeletal remodeling.

DCSTAMP serves as a critical fusogenic protein orchestrating cell-cell fusion during osteoclastogenesis. The disruption of DCSTAMP functionality preserves preosteoclasts, thereby augmenting bone mass through both anabolic and anti-catabolic mechanisms. Despite its therapeutic potential, specific DCSTAMP inhibitors remain undiscovered. Here we used structure-based virtual screening utilizing AlphaFold predictions to identify a novel small molecule, E8431, which selectively targets the endoplasmic domain of DCSTAMP. In vitro investigations confirm E8431's capacity to impede preosteoclast fusion, concurrently inhibiting bone resorption while stimulating PDGFBB secretion, thus promoting osteogenic and angiogenic processes. We further elucidated a previously uncharacterized DCSTAMP signaling cascade involving DCSTAMP-RAP1B interaction, which activates RAP1-RAC1 signaling-dependent cytoskeletal reorganization. Notably, E8431 demonstrates potent inhibitory effects on this DCSTAMP-RAP1B molecular interface. Moreover, E8431 administration effectively attenuates ovariectomy-induced bone loss in murine models without apparent toxicity, underscoring its potential as a therapeutic agent for osteoporosis.