Design And Synthesis Of HDAC Inhibitors Based On L-2-amino-7-bromoheptanoic Acid

Epigenetic changes are mediated by regulation of gene expression and are crucial to the onset and progression of many diseases, including cancer and various neurodegenerative diseases. There are many ways of post-translational modifications, and the histone acetylation is one of the most important modifications. Two types of enzymes, histone acetyl transferases (HATs) and histone deacetylase (HDACs) play important roles in the acetylation of lysines. HDACs catalyze the removal of ε-amino groups of lysine residues in histones, leading to chromatin condensation and transcriptional repression. Therefore, HDACs play an important role in the regulation of gene expression, cell growth and proliferation and act a novel class of cancer chemotherapeutics in clinical development.HDACs inhibitors (HDACIs) target HDACs enzymatic activity thereby inducing hyperacetylation of HDACs substrates, and result in altering chromatin structure and tumor suppressing gene expression. The crystallographic studies for the design of valuable HDACIs have pointed out three structural requirements:a cap group that provides interaction with the rim of the active site; a zinc binding group (ZBG) that binds to the zinc ion at the bottom of the active site; and a hydrophobic linker that fits the tube-like portion of the binding pocket.Based on the binding mode between HDACs and HDACIs, nine kinds of L-2-amino-7-bromoheptanoic acid (L-Ab7) derivatives with thioesters were designed and synthesized, introduced hydrophobic group in the carboxy-terminal of L-Ab7as a surface recognition area, which formed hydrophobic interactions with the activity surface; a thioacetyl as metal binding group, which could be hydrolyzed in the cells and transformed into a mercapto group, which bound with zinc ion firmly; and5methylene of L-Ab7as a connecting region, to ensure inhibitors able to enter the narrow active pocket. Compounds purity was greater than97%by HPLC, and the structure of compounds was detected by HR-MS and NMR.We used the HDACs fluorescent kits for detecting inhibitory activity of the target products. The results exhibited that most of our target compounds exhibited nanomolar inhibitory activities. Within this series,4b and4g were even more potent than the other target compounds, and IC50were56nM and34nM respectively. Among these inhibitors,4g still exhibited maximum inhibitory activity in HDAC1assay, and IC50were84nM. In the detection of HDAC6, the target compound did not show high inhibitory activity as same as HDAC and HDAC1, but exhibited micromolar inhibitory activities yet, and the ICs0of4i is92nM.The anti-proliferation activity of all compounds was determined against MCF-7(Breast cancer). HeLa (Cervical cancer), hepG2(Hepatic carcinoma) and SMMC-7721(Hepatic carcinoma). The result showed that compounds4b and4g brought about60%and78%cells growth inhibition respectively against MCF-7cell line in100μM doses. However, unlike MS-275, all compounds were able to inhibit cells growth potently in HeLa cancer cell line (>60%). and most of them were more effective than TSA. In the detection of HepG2and SMMC-7721, the inhibitory effect of inhibitors on HepG2cells was significantly better than SMMC-7721.We used the AutoDock4.2software on docking of the target compounds. Molecular docking studies indicated that2-amino-4-phenylthiazol group connected with the active surface of HDAC2closely, resulting in the inhibitor entering the pocket smoothly. Mercapto as zinc ion binding group entered HDAH active pocket smoothy, and connected with Zn2+.