Development of alkylated hydrazides as highly potent and selective class I HDAC inhibitors with T cell modulatory properties

Histone deacetylases (HDACs) are modulators of epigenetic gene regulation and additionally control the activity of non-histone protein substrates by removing acyl or acetyl groups from modified lysine residues. We recently demonstrated that pharmacological inhibition of the HDAC8 enzyme belonging to class I of HDACs and overexpressed in a variety of human cancers controls histone H3 lysine 27 (H3K27)-acetylation and reduces hepatocellular carcinoma tumorigenicity in a T cell-dependent manner. Here, we present a new chemotype of alkylated hydrazide-based class I HDAC inhibitors in which the n-hexyl side chain attached to the hydrazide moiety show HDAC8 selectivity in vitro. An enzymatic assay provided important structure-activity relationships for this new series of alkyl hydrazides. Analysis of the mode of inhibition of the alkyl hydrazides against HDAC8 revealed a substrate-competitive binding mode. The most promising compound 7d marked induced acetylation of the HDAC8 substrates H3K27 and SMC3 at 10 μM but not tubulin in CD4+ T lymphocytes, and significantly upregulated gene expressions for memory and effector functions. Furthermore, intraperitoneal injection administration of 7d (10 mg/kg) in C57BL/6 mice increased interleukin-2 expression in CD4+ T cells and CD8+ T cell proportion with no apparent toxicity. This study expands a novel chemotype of highly potent class I HDAC inhibitors with T cell modulatory properties for future therapeutic applications.