Liposome-based delivery of a boron-containing cholesteryl ester for high-LET particle-induced damage of prostate cancer cells: A boron neutron capture therapy study

Purpose: The efficacy of a boron-containing cholesteryl ester compound (BCH) as a boron neutron capture therapy (BNCT) agent for the targeted irradiation of PC-3 human prostate cancer cells was examined. Materials and methods: Liposome-based delivery of BCH was quantified with inductively coupled plasma-mass spectrometry (ICP-MS) and high-performance liquid chromatography (HPLC). Cytotoxicity of the BCH-containing liposomes was evaluated with neutral red, 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS), and lactate dehydrogenase assays. Colony formation assays were utilized to evaluate the decrease in cell survival due to high-linear energy transfer (LET) particles resulting from 10 B thermal neutron capture. Results: BCH delivery by means of encapsulation in a lipid bilayer resulted in a boron uptake of 35.2 +/- 4.3 mu g/10(9) cells, with minimal cytotoxic effects. PC-3 cells treated with BCH and exposed to a 9.4 x 10(11) n/cm(2) thermal neutron fluence yielded a 20-25% decrease in clonogenic capacity. The decreased survival is attributed to the generation of high-LET alpha particles and Li-7 nuclei that deposit energy in densely ionizing radiation tracks. Conclusion: Liposome-based delivery of BCH is capable of introducing sufficient boron to PC-3 cells for BNCT. High-LET a particles and Li-7 nuclei generated from B-10 thermal neutron capture significantly decrease colony formation ability in the targeted PC-3 cells.