Histological and biochemical analysis of DNA damage after BNCT in rat model.

To understand the mechanism of tumor cell death induced by boron neutron capture therapy (BNCT) and to optimize BNCT condition, we used rat tumor graft models and histological and biochemical analyses were carried out focusing on DNA damage response. Rat lymphosarcoma cells were grafted subcutaneously into male Wister rats. The rats with developed tumors were then treated with neutron beam irradiation 45min after injection of 330mg/kg bodyweight boronophenylalanine ((10)BPA) (+BPA) or saline control (-BPA). BNCT was carried out in the National Nuclear Center of the Republic of Kazakhstan (neutron flux: 1×10(9)nvt/s, fluence: 6×10(11)nvt) with the presence of background γ-irradiation of 33Gy. 6 and 20h after BNCT treatment, tumors were resected, fixed and subjected to immunohistochemistry and biochemical analyses. Immunostaining of nuclei showed that double strand break (DSB) marker gamma H2AX staining was high in 20h/+BPA sample but not in 20h/-BPA samples. Poly(ADP-ribose), DSB and single strand break markers of DNA, also demonstrated this tendency. These two markers were observed at low levels in unirradiated tissues or 6h after BNCT either under -BPA and +BPA conditions. HMGB1 level increased in 6h/+BPA but not in 6h/-BPA or 20h/+BPA samples. The persistent staining of γH2AX and poly(ADP-ribose) in +BPA group suggests accumulated DSB damage after BNCT. The early HMGB1 upregulation and γH2AX and poly(ADP-ribose) observed later might be the markers for monitoring the DNA damage induced by BNCT.