Detailed biodistribution of liposomes prepared with polyborane instead of cholesterol for BNCT: effects of PEGylation

Various drug delivery systems for boron neutron capture therapy (BNCT) have been developed. To selectively destroy cancer cells, the high accumulation and selective delivery of 10 B into tumor tissue are required. In this study, a polyborane for BNCT with enhanced hydrophobicity was synthesized from decaborane as a boron carrier, and embedded into bare and PEGylated liposomes. These liposomes having diameters of 40–43 nm were injected into tail vein of tumor-bearing mice to evaluate their biodistribution. Boron concentrations in tumor and tumor/blood ratios of the liposomes were reached over 30 μg/g of tissue and over 5 at 8–24 h, respectively. At 12 h after injection, PEGylated liposomes were found in tumor with high boron level (130.0 μg/g of tissue). This result showed that the PEGylated liposomes with a diameter of 40 nm were able to achieve efficient intratumoral 10 B amount without replacing the 11 B with 10 B.