Synthesis and in vitro characterization of a bone-vectored carbon(60) derivative

Abstract

The first tissue-vectored fullerene derivative, C60 (OH)16AMBP (4,4-bisphosphono-2-(polyhydroxyl-1,2-dihydro-1,2-methanofullerene[60]-61-carboxamido)-butyric acid), designed to target bone tissue, has been synthesized, characterized and evaluated. An amide bisphosphonate addend, in conjunction with multiple hydroxyl groups, confers strong affinity for the bone mineral hydroxyapatite (HAP) in vitro. Constant composition crystal growth inhibition studies conducted with a 35 muM concentration of the inhibitor, show that C60(OH)16AMBP reduces the rate of HAP crystal growth by 87% via a non-Langmuirian mechanism, with an affinity constant KL of 3.40 x 106 L mol-1 (R 2 = 0.99). Surprisingly, C60(OH)16AMBP is also paramagnetic, forming an apparently stable radical under ambient conditions. Evans' NMR method in aqueous solution implies an S = 1/2 system, which is also suggested by solid-state magnetometry measurements. Parallel studies with C60(OH)30 · 2 H2O also confirm a strong affinity for HAP (58% crystal growth rate reduction; KL = 4.14 x 105 L mol-1 (R2 = 0.97)) and suggest a similar paramagnetic ground state for this "non-vectored" fullerol molecule, as well. These results, along with ongoing studies involving noble gas-doped endohedral fullerol derivatives, have set the stage for the first studies of tissue-directed fullerene-based materials in vivo