Fluorescent Probes for Subcellular Localization during Osteclast Formation.

Labeling of a small bioactive molecule with fluorescent probe has been becoming an essential tool in cell biology to reveal the subcellular distribution and the location of a molecular target. QOA-8a is a novel molecule with potent antiosteoporotic effect in vivo. To investigate the molecular mechanism of QOA-8a, novel fluorescence-tagged chemical probes as bioactive as their parent molecule were designed and synthesized. The fluorescent compound 12 showed a more potent inhibitory activity on RANKL-induced osteoclastogenesis at 2 μM compared with that of QOA-8a. Microscopy experiments revealed that almost all of probe 12 accumulated in the fusing region, with little in the osteoclast precursors or the mature osteoclasts during osteoclast formation. The result suggests the location of the binding target of QOA-8a, which might greatly narrow down the search field of the target protein(s).