Preclinical study of selective thermal neutron capture treatment of pigs having spontaneous melanoma using melanin productive activity

Four pigs having spontaneous melanoma were irradiated with 0.5 - 2 x 1013 n/cm2 of thermal neutron under remote anesthesia. Compounds of 10B used in this experiment were 10B12-chlorpromazine (10B12-CPZ), 10B-dopa, and 10B1-para-boronophenylalanine (10B1-BPA), and they were injected into melanoma or regions around melanoma. After irradiation of thermal neutron, melanoma tended to reduce in four pigs, and melanoma cells in white fur and hair bulb disappeared in 3 of 4 pigs. Hematological examinations and blood chemistry tests did not show any changes in blood findings both before and after the irradiation, and white blood cell counts were within a normal range. Dermatitis following the irradiation disappeared one week later. Histological changes one month after the irradiation indicated that many melanophages feeding melanosome replaced melanoma cells, which suggested disintegration of melanoma cells. Marked effectiveness of this treatment was recognized in each pig. 10B-BPA.HCI was injected into one pig twice, and its accumulation in melanoma and normal regions around melanoma was expressed as boron concentrations. As a result, the accumulation in melanoma (6.6 μg/g wet tissue) was 3.1 times as much as that in normal regions around melanoma (2.1 μg/g wet tissue). (Tsunoda, M.)