Homogeneous boron targeting of heterogeneous tumors for boron neutron capture therapy (BNCT): Chemical analyses in the hamster cheek pouch oral cancer model

Objective: BNCT is a tumour cell targeted radiation therapy. Uniform targeting of heterogeneous turnours with therapeutically effective boron carriers would contribute to a therapeutic effect on all tumour cell populations and avoid radioresistant fractions. This remains an unresolved challenge. The aim of the present study was to evaluate the degree of variation in boron content delivered by boronophenylalanine (BPA), GB-10 ((Na2B10H10)-B-10) and the combined administration of (BPA + GB-10) in different portions of tumour, precancerous tissue around tumour and normal pouch tissue in the hamster cheek pouch oral cancer model. Materials and methods: Samples of different areas of tumour, precancerous tissue and normal pouch tissue were taken from tumour-bearing hamsters, 3 h post-administration of i.p. BPA(15.5 mg B/kg b.w.), or i.v. GB-10(50 mg B/kg b.w.), or 3 h and 1.5 h post-ad ministration respectively of i.v. GB-10 (34.5 mg B/b.w.) and sequential i.p. injections of BPA (total dose 31 mg B/kg b.w.) given jointly. Boron content was evaluated by inductively coupled plasma optical emission spectroscopy (ICP-OES). The degree of homogeneity in boron targeting was assessed in terms of the coefficient of variation (V: [S.D./mean] x 100) of boron values. Statistical analysis of the results was performed by one-way ANOVA and the least significant difference test. Results: GB-10 and GB-10 plus BPA achieved respectively a statistically significant 1.8- and 3.3-fold increase in targeting homogeneity over BPA. Conclusions: The combined boron compound administration protocol contributes to homogeneous targeting of heterogeneous tumours; and would be expected to increase therapeutic efficacy of BNCT. (c) 2006 Elsevier Ltd. All rights reserved.