In this study a novel bone-targeting agent containing elements of the tricarbonylmethane system of ring A of tetracycline was developed and was shown to bind to the mineral constituent of bone, hydroxyapatite. Conjugation of this bone-targeting agent to estradiol resulted in a bone-targeted estrogen (BTE2-A1) with an enhanced ability to bind to hydroxyapatite. In an ovariectomized rat model of osteoporosis a partial separation of the ...