Purpose: We have previously reported that human glioblastoma cells are sensitized to radiation-induced
death after their exposure to trichostatin A (TSA), a histone deacetylase inhibitor (HDAC-I), prior to the
irradiation. We aimed to measure the magnitude of the radiosensitizing effect of TSA in human head and
neck cancer cell lines. Materials and Methods: Human head and neck cancer cell lines, HN-3 and HN-9, were exposed to 0,50, 100, and 200 nM TSA for 18 hr prior to irradiation. Then, the TSA-treated cells were irradiated with 0, 2, 4, 6, and 8 Gy, and cell survival was measured by clonogenic assay. Results: Pre-irradiation exposure to TSA was found to radiosensitize HN-3 and HN-9 cell lines. In HN-9 cells, the fraction surviving after 2 Gy (SF2) was significantly reduced by treatment of TSA at concentration as low as 50 nM. However, a treatment with 200 nM TSA was required to significantly decrease SF2 in the HN-3 cell line. SER of pre-irradiation treatment with 200 nM TSA was 1.84 in HN-3 and 7.24 in HN-9, respectively. Conclusions: Our results clearly showed that human head and neck cancer cell lines can be sensitized to ionizing radiation by pre-irradiation inhibition of histone deacetylase (HDAC) using TSA, and that this potentiation might well be a general phenomenon.