Optimization of boron neutron capture therapy (BNCT) for the treatment of thyroid cancer by using the histone deacetylase inhibitor sodium butyrate

PERONA, M; RODRIGUEZ , C; CARPANO, M; THORP, S; PISAREV , M; JUVENAL, G; DAGROSA, MA

Hsinchu

Encuentro; 6th Young Researchers Boron Neutron Capture Therapy Meeting (6th YBNCT); 2011

National Tsing Hua University

In previous studies we have shown that boron neutron capture therapy (BNCT) could be an alternative therapy for the treatment of poorly differentiated thyroid carcinoma (DTC). Histone deacetylase inhibitors (HDAC-I) like sodium butyrate (NaB), are agents that cause hyperacetylation of histone proteins and, as a consequence they can induce growth arrest, differentiation, apoptotic cell death and altered transcription of a finite number of genes in different tumour cells. It has also been recently described their capacity to increase the effect of gamma irradiation on cell lines and animals bearing different carcinomas. The purpose of this study was to evaluate the effect of the NaB as a radiosensitizer of the BNC reaction for the treatment of DTC. Methodology: Follicular thyroid carcinoma (WRO) cells were incubated with increasing concentrations of NaB to test citotoxicity during different lengths of time. Exponentially growing cells were incubated with 1 mM NaB during 24 hr before irradiation and then distributed into the following groups: 1) BPA (10 µg10B/mL) + neutrons; 2) BOPP 2, 4-bis (a,b-dihydroxyethyl)-deutero-porphyrin IX) (10 µg10B/mL) + neutrons; 3) neutrons alone.  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) in order to obtain total physical doses ranging between  1-5 Gy (±10%). Cell survival was evaluated with the 3-(4, 5-dimethylthiazol-2-yl)-2, 5 diphenyltetrazoliumbromide (MTT) colorimetric assay on day 4 after irradiation. Cell death and cell cycle distribution were evaluated 24 and 48 hr post irradiation. Results: A significant concentration-dependent reduction of cell growth was observed when cell were incubated for 48 and 72 hr (p<0.01) with NaB. Cell survival after irradiation decreased in all the treatments as a function of the physical absorbed dose. This effect was greater in both BNCT groups. Moreover, the addition of NaB significantly increased this effect on cell viability (p<0.05). The analysis of the mechanisms of radiation-induced cell death showed that 24 and 48 hr post irradiation the frequency of apoptosis and cell necrosis increased in all the irradiated groups compared with control groups. The NaB increased the percentage of necrotic cells in the groups irradiated with both boron compounds (BPA and BOPP) at 24 hr (p<0.05). It was observed an accumulation of cells in G2/M phase at 24 hr for all the irradiated groups, independently of the addition of the radiosensitizer. Conclusions: sodium butyrate could be used as a radiosensitizer for the BNCT treatment.