Development of intracellular targeting liposomes for boron neutron-capture therapy

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The successful treatment of cancer by BNCT requires the selective concentration of ^<10>B within malignant tumor cells. Intracellular targeting ability and cytotoxic effects of ^<10>B entrapped TF-PEG-liposomes, in which TF is covalently linked to the distal terminal of PEG chains on the external surface of PEG-liposomes, were examined in Colon 26 tumor-bearing mice. TF-PEG-liposomes readily bound to tumor cells in vitro, and were internalized by receptor-mediated endocytosis. ^<10>B-PEG-liposomes and ^<10>B-TF-liposomes showed prolonged residence time in the circulation and low RES uptake in tumor-bearing mice, resulting in enhanced extravasation of the liposomes into the solid tumor tissue and reached high level of ^<10>B content in tumor. After thermal neutron irradiation of mice injected with ^<10>B-PEG-liposomes or ^<10>B-TF-liposomes, tumor growth was suppressed relative to controls. These results suggest that intravenous injection of ^<10>B TF-PEG-liposome can increase the intracellular retention of ^<10>B atoms, which were introduced by receptor mediated endocytosis after binding, causing tumor growth suppression in vivo upon thermal neutron irradiation.