In vitro studies of radiobiological effects of boron neutron capture therapy (BNCT).

DAGROSA, MA; THOMASZ, L; PONTIGGIA, O; PERONA, M; THORP, S; SIMIAN, M; KAHL, S; JUVENAL, G; PISAREV, M

Rio de Janeiro, Brasil

Conferencia; 8th LOWRAD International Conference on” The effects of low and very low doses of ionizing radiation on human health and biotopes”.; 2009

Introduction: BNCT is an experimental ratiotherapeutic modality that uses the capacity of the isotope 10B to capture thermal neutrons leading to the production of 4He and 7Li, particles with high linear energy transfer (LET). BNCT showed to be effective to the treatment of different biological models of cancer. But little is known about the mechanisms of cellular response to the BNC reaction. Objectives: To evaluate in vitro the mechanisms of damage produce by the irradiation arising of BNCT and to compare them with biological effects of the low LET radiation. Methods: We measured in a cell line of colon cancer (HT-29) the survival cell fraction as a function of the absorbed total physical dose. We also analyzed the expression of p27/Kip1 and p53 by Western blotting. Exponentially growing cells were distributed into the following groups: 1) BPA (10 ppm 10B) + neutrons; 2) BOPP (2,4-bis (a,b-dihydroxyethyl)-deutero-porphyrin IX) (10 ppm 10B) + neutrons; 3) neutrons alone; 4) gamma-rays. A control group without irradiation for each treatment was added. The cells were irradiated in the thermal neutron beam of the RA-3 (flux= 7.5 109 n/cm2 sec) or with 60Co (1Gy/min) during different times in order to obtain total physical dose between 1-5 Gy (±10%). Results: A decrease in the survival fraction as a function of the physical dose was observed for all the treatments. We also observed that neutrons and neutrons + BOPP did not differ significantly and that BPA was the more effective boron compound. Protein extracts of irradiated cells (3Gy) were isolated at 24 h and 48 h post radiation exposure. The irradiation with neutrons in presence of 10BPA or 10BOPP produced an increase of p53 at 24 h maintained until 48 h compared to the control groups. On the contrary in the groups irradiated with neutrons alone or gamma the maximal increase of p53 was observed at 48 h. The level of expression of p27/Kip1 showed a reduction of this protein in all the irradiated groups, being more marked at 24 h and for the BNCT groups. Conclusions: These preliminary results suggest different radiobiological response for high (BNCT and neutrons) and low let (gamma) radiation. Future studies will allow establish the ratiosensitivity of the tumor associate to the cell cycle which will  contribute to the therapeutic improvement.