HDAC9 and cancer: Regarding the phenomenon in which OTX015/WT-161 can arrest the cell cycle in the G1/S phase, it has been previously reported that BET inhibitors can arrest the cell cycle in the G1 phase of a variety of malignant tumours [28, 35]; HDAC inhibitors induced apoptosis and blocked cells in the G1 phase [36], which was consistent with the effect of OTX015/WT-161 on the cell cycle of OS in this study.