Synthesis and in vitro characterization of a tissue-selective fullerene: vectoring C(60)(OH)(16)AMBP to mineralized bone

A tissue-vectored bisphosphonate fullerene, C(60)(OH)(16)AMBP 4,4-bisphosphono-2-(polyhydroxyl-1,2-dihydro-1,2-methanofullerene60]-61-carboxamido)butyric acid], designed to target bone tissue has been synthesized and evaluated in vitro. An amide bisphosphonate addend, in conjunction with multiple hydroxyl groups, confers a strong affinity for the calcium phosphate mineral hydroxyapatite of bone. Constant composition crystal growth studies indicate that C(60)(OH)(16)AMBP reduces hydroxyapatite mineralization by 50% at a concentration of 1 microM, following a non-Langmuirian mechanism. Parallel studies with C(60)(OH)(30) also indicate an affinity for hydroxyapatite, but at a reduced level (28% crystal growth rate reduction at 1 microM) compared with C(60)(OH)(16)AMBP. This study is the first to demonstrate that a fullerene-based material can be successfully targeted to a selected tissue as a step toward the development of such materials for medical purposes, in general.