Design, synthesis, and biological evaluation of novel estradiol-bisphosphonate conjugates as bone-specific estrogens.

Bone deficiency causes osteoporosis and often decreases quality of life in patients with rheumatoid arthritis. Estrogens are known to protect elderly women from bone loss. Synthesis of new estradiol-bisphosphonate conjugates (E(2)-BPs) was accomplished and their in vivo activity as bone-specific estrogens were examined. Among them, MCC-565 showed selective estrogenic activity in bones; but it showed little estrogenic activity in the uterus. We also found that the linker moiety in E(2)-BPs was essential for the absorption and specificity of the conjugates.