Radiobiological Studies in a Human Cell Line of Undifferentiated Thyroid Cancer (UTC) for BNCT.

DAGROSA, MA; CRIVELLO, M; THORP, S; PERONA, M; POZZI, E; CASAL, M; CABRINI, R; KAHL, SB; JUVENAL, GJ; PISAREV, M A

Florencia, Italia

Congreso; 13th International Congress on Neutron Capture Therapy, “A new option against cancer”; 2008

In previous studies we demonstrated the efficacy of BNCT for the treatment of UTC using 10BPA (p-borophenylalanine) alone and combined with 10BOPP (2,4-bis (a,b-dihydroxyethyl)-deutero-porphyrin IX). Inthe present work we evaluated in vitro the mechanisms of damage induced by BNCT by cytokinesis blockmicronuclei assay (CBMN) and by the cell fraction survival using a colorimetric assay of viability (MTT). We also calculated the relative biological effectiveness factor (RBE) of the neutron beam and the compound biological effectiveness (CBE) values for BPA and BOPP. Exponentially growing human cells of UTC (ARO) were distributed into the following groups: 1) BPA (10 ppm 10B) + neutrons; 2) BOPP (10 ppm 10B) + neutrons; 3) neutrons alone; 4) gamma-rays (60Co). The cells were irradiated in the thermal neutron beam of the RA-3 (flux= 7.5 109 n/cm2 sec). The irradiations were performed during different times in order to obtain total physical doses between 1-5 Gy (±10%). The frequency of micronucleated binucleated UTC cells and the number of MN per micronucleated binucleated cells showed a dependent dose relationship until around 2 Gy. The response to gamma rays was significantly less than the other treatments. The irradiation with neutrons alone and neutrons + BOPP showed curves that didn’t differ significantly and showed less DNA damage than neutrons + BPA. 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 is the more effective compound. The RBE and CBE factors calculated from CBMN and MTT assays, respectively, gave the following values: beam RBE: 4.4 ± 1.1 and 2.4 ± 0.6; CBE for BOPP: 8.0 + 2.2 and 2.0 + 1; CBE for BPA: 19.6 + 3.7 and 3.6 + 1.3. These values represent the first experimental values obtained for the RA-3 in a biological model and will be useful for future dosimetric experimental studies of the application of BNCT to UTC.