Preparation of sulfhydrylborane-dextran conjugates for boron neutron capture therapy

This study presents a carrier system for boron, potentially useful in boron neutron capture therapy (BNCT). Na2B12H11SH (BSH) was covalently coupled to dextran derivatives. This was accomplished in two ways. The first method comprises activation of dextran with 1-cyano-4-(dimethylamino)pyridine (CDAP) with subsequent coupling of 2-aminoethyl pyridyl disulfide (method A). The thiolated dextran could then couple BSH in a disulfide exchange reaction. In the second procedure, dextran was derivatized to a multially derivative (method B) which reacted with BSH in a free-radical-initiated addition reaction. The assessment of boron content of the conjugates was done by elemental analysis of sulfur and atomic spectroscopy of boron (ICP-AES). With method A, only limited numbers of boron cages could be coupled (10-20 cages per dextran chain). With method B, 100-125 boron cages per dextran chain was obtained, corresponding to 1200-1500 boron atoms per dextran chain. This result makes this derivative a promising template for use in the development of BNCT agents.