Biological evaluation of these HDAC inhibitors indicated that benzothiazole analogue 9b exerted the most potent anti-proliferative activity (IC50 = 2.01 μM) against human neuroblastoma SH-SY5Y cell line, slightly better than the clinically approved HDAC inhibitor, SAHA (IC50 = 2.90 μM). The gene discussed is HDAC9; the disease is neuroblastoma.