Heterogeneity of Binding Sites and Bioeffects of Raloxifene on the Human Leukemic Cell Line FLG 29.1

The benzothiophene divarative raloxifene is known to mimic estrogen in human bone remodeling. To investigate the “in vitro” properties of raloxifene on osteoclast precursors, the human leukemic cell line FLG 29.1, which differentiates toward the osteoclastic phenotype, was examined for raloxifene binding and for evidence of its bioeffects. Scatchard and Hill analysis of binding data with the tritiated raloxifene demonstrated the presence of two classes of binding sites in both nuclear and cytosol fractions with Kd values of ∼ 1 nM and ∼ 5 nM, respectively. In addition, analysis of binding data using tritiated 17βE2as ligand at high concentrations (10 - 40 nM) and either unlabeled 17βE2or raloxifene as competitors gave similar results demonstrating the presence of type II EBS in these cells. Picomolar concentrations of raloxifene significantly (p