A Bystander Effect Observed in Boron Neutron Capture Therapy: A Study of the Induction of Mutations in the HPRT Locus

Abstract

To investigate bystander mutagenic effects induced by alpha-particles during boron neutron capture therapy, we mixed cells that were electroporated with borocaptate sodium (BSH), which led to the accumulation of (10)B inside the cells, and cells that did not contain the boron compound. The BSH-containing cells were irradiated with alpha-particles produced by the 10B(n,alpha)7Li reaction, whereas cells without boron were affected only by the 1H(n,gamma)2H and 14N(n,rho)14C reactions. The lethality and mutagenicity measured by the frequency of mutations induced in the hypoxanthine-guanine phosphoribosyltransferase locus were examined in Chinese hamster ovary cells irradiated with neutrons (Kyoto University Research Reactor: 5 MW). Neutron irradiation of 1:1 mixtures of cells with and without BSH resulted in a survival fraction of 0.1, and the cells that did not contain BSH made up 99.4% of the resulting cell population. The molecular structures of the mutations were determined using multiplex polymerase chain reactions. Because of the bystander effect, the frequency of mutations increased in the cells located nearby the BSH-containing cells compared with control cells. Molecular structural analysis indicated that most of the mutations induced by the bystander effect were point mutations and that the frequencies of total and partial deletions induced by the bystander effect were less than those induced by the original neutron irradiation. These results suggested that in boron neutron capture therapy, the mutations caused by the bystander effect and those caused by the original neutron irradiation are induced by different mechanisms.