the other cancer types also has a low Dm, implying HDACs are 1624117-53-8 important for parafollicular thyroid cancer cells. PXD101 inhibits a broad spectrum of HDACs, including prevents to conclude which HDAC is more important in the survival of thyroid cancers. One therapeutic mechanism of HDAC inhibitors in treating malignancy is through the induction of apoptosis. PXD101 caused apoptotic effects in a dose-and time-dependent manner in BHP7-13, WRO82-1 and 8505C, suggesting that this mechanism accounts for therapeutic efficacy of PXD101. Prior reports show HDAC inhibitors reduce thioredoxin activity, accumulate ROS and lead to apoptosis in transformed cells, but not in normal cells. Therefore, ROS accumulation in malignant cells may be a mechanism of cancer-specificity cytotoxicity of HDAC inhibitors. In this study, PXD101 accumulated ROS in a dose-dependent fashion in WRO82-1 and 8505C, but not in the resistant cell line BHP7-13. These observations are consistent with this mechanism of susceptibility to HDAC inhibitors. RAS/RAF/ERK and PI3K/AKT/mTOR signaling pathways are important in thyroid cancer tumorigenesis, progression and survival. The interruption of these signaling pathways is one strategy to treat thyroid malignancy. In this study, PXD101 inhibited these pathways in the sensitive cell line 8505C, but not in WRO82-1 and BHP7-13. The data imply that the ability of PXD101 to inhibit RAS/RAF/ERK and PI3K/AKT/ mTOR pathways may confer sensitivity. 1123838-51-6 distributor p-H2AX is a classic marker of DSBs, a serious type of DNA damage. PXD101 significantly induced p-H2AX in three thyroid cancer cell lines, supporting DSBs as one mechanism accounting for the cytotoxicity of PXD101. We show that PXD101 decreases DSBs repair proteins in the NHEJ and HR pathways. For NHEJ, the KU70-KU80 heterodimer recognizes DSBs, and recruits a DNA protein kinase complex. The decreased expression of KU70 or KU80 can impair the NHEJ repair pathway. For HR, RAD51 binds to the resected end of single-stranded DNA, allowing for synthesisdependent strand annealing for DSB repair. An analysis of the extent of the contribution of individual HR proteins to DNA repair and found that depletion of RAD51 induces the most significant HR defect. The SSA pathway is an alternative mechanism for DSBs repair when NHEJ and HR are defective. PXD101 increased RAD52 and
