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Histone deacetylase 6 (HDAC6) has emerged as a critical regulator of many cellular pathways in tumors due to its unique structure basis and abundant substrate types. Over the past few decades, the role played by HDAC6 inhibitors as anticancer agents has sparked great interest of biochemists worldwide. However, they were less reported for gastric cancer therapy. In this paper, with the help of bioisosteric replacement, in-house library screening, and lead optimization strategies, we designed, synthesized and verified a series of 1,3-diaryl-1,2,4-triazole-capped HDAC6 inhibitors with promising anti-gastric cancer activities. Amongst, compound 9r displayed the best inhibitory activity towards HDAC6 (IC 50 = 30.6 nM), with 128-fold selectivity over HDAC1. Further BLI and CETSA assay proved the high affinity of 9r to HDAC6. In addition, 9r could dose-dependently upregulate the levels of acetylated α-tubulin, without significant effect on acetylated histone H3 in MGC803 cells. Besides, 9r exhibited potent antiproliferative effect on MGC803 cells, and promoted apoptosis and suppressed the metastasis without obvious toxicity, suggesting 9r would serve as a potential lead compound for the development of novel therapeutic agents of gastric cancer. [Display omitted] ● A novel series of 1,3-diaryl-1,2,4-triazole-capped HDAC6 inhibitors were designed and synthesized by the strategies of bioisosteric replacement, in-house library screening, and lead optimization. ● Compound 9r exhibited the best potency to HDAC6 (IC 50 = 30.6 nM), with 128-fold selectivity over HDAC1. ● Compound 9r displayed promising anti-gastric cancer activity without obvious toxicity. [ABSTRACT FROM AUTHOR]

In this paper, a series of thiosemicarbazone derivatives containing different aromatic heterocyclic groups were synthesized and the tridentate donor system of the lead compound was optimized. Most of the target compounds showed improved antiproliferative activity against MGC803 cells. SAR studies revealed that compound 5d displayed significant advantages in inhibition effect with an IC 50 value of 0.031 μM, and better selectivity between cancer and normal cells than 3-AP and DpC (about 15- and 5-fold improved respectively). Besides, compound 5d showed selective antiproliferative activity in not only other cancer cells but also different gastric cancer cell lines. In-depth mechanism studies showed that compound 5d could induce mitochondria-related apoptosis which might be related to the elevation of intracellular ROS level, and cause cell cycle arrest at S phase. Moreover, 5d could evidently suppress the cell migration and invasion by blocking the EMT (epithelial–mesenchymal transition) process. Consequently, our studies provided a lead optimization strategy of thiosemicarbazone derivatives which would contribute to discover high-efficiency and low-toxicity agents for the treatment of gastric cancer. Image 1 • The design and synthesis were based on lead optimization strategy. • 5d showed higher antiproliferative activity and lower toxicity than 3-AP and DpC. • 5d could induce cell apoptosis, and inhibit the migration and invasion of MGC803 cells. [ABSTRACT FROM AUTHOR]