Delivery of sodium borocaptate (BSH) to oral cancer by transferrin-PEG-liposome, for boron neutron capture therapy (BNCT)

Sodium borocaptate (BSH) is boron compound used in clinical Boron Neutron Capture Therapy (BNCT). BSH is accumulated in cancer tissues in concentrations proportional to its blood concentration, but it is rarely actively taken up by itself. Therefore, a novel drug delivery system (DDS) is required. Here, we devised a method to accumulate BSH selectively in tumors in mice, using transferrin-conjugated polyethylene glycol liposome (Tf-PEG-liposome). The tumor-bearing mice were intravenously injected with one of the three boron compounds (Bare BSH, PEG-liposome-BSH, Tf-PEG-liposome-BSH). After 24, 48, 72 h, the boron concentration was measured by inductively coupled plasma-atomic emission spectrometry. Blood levels of boron were high in the PEG-liposome-BSH group and Tf-PEG-liposome-BSH group (Tf group) in comparison with the Bare BSH group at 24 h after. But, at 48 h after blood levels of boron were reduced in all three groups. Boron concentrations in tongue tissue were low in all treatment groups. The Tf group exhibited higher boron concentrations in tumor tissues compared to the other groups at 24 and 48 h. The Tf-PEG-liposome increased the boron concentration of tumor selectively and, furthermore, extended retention time. These results suggest that Tf-PEG-liposome has the potential to improve tumor boron delivery in BNCT. (author)