A naturally occurring phenanthrene from Pleione bulbocodioides inhibits osteoclast formation by directly targeting Src kinase.

Elevated bone resorption resulting from osteoclast (OC) overactivation is a primary factor contributing to osteoporosis progression, suggesting plant-derived antiresorptive agents targeting osteoclast formation and function are effective strategies for managing osteoporosis. To date, no natural phenanthrenes with anti-OC activity have been reported. Herein, a structure-based virtual screening was employed to identify Src kinase binders from a natural phenanthrene library, which revealed dihydrophenanthrene PPb from Pleione bulbocodioides as a potent Src inhibitor. PPb could bind to the kinase structural domain of Src, and the hydrogen bonds formed with GLN278 and GLU313 are crucial for their binding. Further pharmacological evidence suggested that the identified PPb significantly inhibited RANKL-induced OC formation, decreased the expression of OC-specific genes and proteins, and inhibited the F-acting rings and bone resorption. Moreover, PPb administration significantly attenuated glucocorticoid-induced bone loss in osteoporotic zebrafish. Mechanistic studies showed that in the early stage of OC differentiation, PPb directly targeted Src kinase to suppress the activation of Src and its downstream MAPK and PI3K/AKT signaling pathways. In the later stage of differentiation, PPb further diminished the expression of Src protein, contributing to the sustained inhibition of Src signaling. Through the regulation of Src signaling, PPb significantly impeded OC differentiation, maturation, and bone resorption function, ultimately alleviating osteoporosis symptoms resulting from OC overactivity. These findings offer compelling support for the potential therapeutic application of PPb as a potent Src inhibitor for managing osteoporosis and also provide valuable insights for the future exploration of novel anti-resorptive agents from the natural phenanthrene library.