Differential Responses of Several Chemicals including Boron-Enriched Compounds in Gamma Ray-Exposed Gliomas

Despite many developments in neurosurgical and pharmacological techniques, a malignant glioma is one of the most deadly cancers and to date lacks an effective treatment in humans. Boron neutron capture therapy (BNCT) has been regarded as a promising treatment for the malignant gliomas. BNCT is a two step radiotherapy in which a selective radiation effects on tumor cells is achieved by first targeting the tumor with 10B and then exposing it to low energy neutrons. The stable 10B isotope has a large cross-sectional area for the capture of thermal neutrons. The reaction yields intensively ionizing particles, 4He2+ (α particles) and recoiling 7Li3+ nuclei. These highly cytotoxic nuclear fragments destroyed the tumor cells. For the successful BNCT, high amount boron molecules must be carried into the target tumor cells selectively. Borocaptate sodium (BSH) is a low molecular weight substance originally tested for the BNCT. Clinical trials using BSH for the BNCT of brain tumors reported significant outcomes with long-term survivals in patients with malignant gliomas. Boronated amino acid analogs, p-boronophenylalanine (BPA), are used in the BNCT for the treatment of malignant melanomas. Recently, BPA has been reported to be preferentially taken up by glioma cells. These boron-enriched compounds should be kept low to minimize the damage to normal tissues. Therefore, the preliminary study for the enhancement of selective delivery of boron atoms to tumor cells has been reported. Also, several investigators proposed abilities of boron compounds as a radioprotector against gamma ray-exposed condition. The present study tested the comparative effect of boron compounds and known radioprotectant agents in the gamma-irradiated gliomas