Biodistribution of BPA and BSH after single, repeated and simultaneous administrations for neutron-capture therapy of cancer.

The effect of administration mode of L-BPA and BSH on the biodistribution in the melanoma-bearing hamsters was investigated. In single intravenous (i.v.) administration, BSH (100 mg BSH/kg) showed no significant retention of (10)B in all the tissues, including tumors, while long-term retention of (10)B in the tumor, muscle and brain was observed with L-BPA (500 mg BPA/kg). The dose escalation of L-BPA and the simultaneous single administration of L-BPA and BSH were not so effective at increasing boron accumulation in tumor after bolus i.v. injection. The boron concentration in tumor was 41 microg B/g after single bolus i.v. injection even at the dose of 1000 mg BPA/kg. In contrast, two sequential bolus i.v. injections of l-BPA with the dose of 500 mg BPA/kg each was found to be effective at increasing (10)B accumulation in the tumor; the maximum (10)B concentration in the tumor reached 52 microg B/g at 3 h after the second i.v. injection.