Design,Synthesis And Anti-tumor Activity Evaluation Of Novel 5-cyano-6-arylpyrimidine HDAC6 Inhibitors

Histone deacetylase 6(HDAC6)is a class Ⅱb HDAC subtype,which is highly expressed in breast cancer,gastric cancer,ovarian cancer,colorectal cancer,lung cancer and other cancer cells.HDAC6 not only participates in the process of histone deacetylation,but also targets various non-histone substrates,such as α-tubulin and heat shock protein 90(HSP90).to regulate the proliferation,metastasis and invasion of cancer cells.However,the currently reported HDAC6 inhibitors still face problems including weak subtype selectivity and low tumor response rate.Hence,the work of developing HDAC6 inhibitors with high potence and selectivity is of great significance for the treatment and prognosis of tumors.Nitrogen-containing heterocyclic ring,as an important pharmacophore,has demonstrated a variety of biological functions such as anti-cancer,anti-virus and antibacterial.The lead compound 9a with potential inhibitory activity against HDAC6 was screened out in the early stage of this paper,following work was focused on synthesizing a series of novel 5-cyano-6-arylpyrimidines through structural modification of 9a.Then,the enzymatic evaluation and preliminary anti-tumor activity study were carried out.The details are as follows:1.In this study,through the screening of HDAC6 inhibitory activity in the nitrogen-containing heterocyclic compound library,compound 9a containing 5-cyano6-phenylpyrimidine skeleton was found to have a potential selective inhibitory effect on HDAC6.Subsequently,fifty-eight novel pyrimidine derivatives were designed and synthesized by modifying the C-4 and C-6 positions of the Cap,Linker and ZBG regions,respectively.2.All targeted compounds were tested their inhibitory activities towards HDAC6.The structure-activity relationship analysis showed that:1)When the C-4 position of the pyrimidine in the Cap region was an aliphatic substituent,the compounds showed superior HDAC6 inhibition and selectivity,among which N-methylpiperazine substituent was the best:At the same time,it was found that when the C-4 position was substituted by mercaptotetrazolium,the compound showed obvious inhibitory effect on both HDAC6 and HDAC1,which might provide a certain reference for the design of dual-targeting HDAC6/1 compounds.In addition,when the pyrimidine C-6 position was modified by aryl,the compounds showed good functional group tolerance;2)The modification of Linker showed that alkyl chains of different lengths and styryl groups were not conducive to the improvement of activity;3)The modification of ZBG showed that hydroxamic acid was better than benzamide and carboxyl.Among them,compound 9ab displayed the best inhibitory activity with IC50 value of 28.61 nM,which was 25.2-fold higher than the inhibitory effect on HDAC1.Molecular docking further showed that compound 9ab could fully bind to the HDAC6 catalytic pocket and form some intermolecular interactions with the nearby residues.In vitro antitumor activity evaluation showed that compound 9ab could inhibit the proliferation and induce apoptosis of MGC-803 cells in a concentration-dependent manner.In conclusion,a total of 58 pyrimidine derivatives with novel structures were synthesized using target-based drug design strategies in this study,and their inhibitory activities against HDAC6 were preliminarily evaluated.Combined with the structureactivity relationship analysis,compound 9ab showed the optimal inhibitory effect on HDAC6(IC50=28.61 nM).Moreover,9ab could inhibit MGC-803 cells proliferation and induce apoptosis in a concentration-dependent manner.In conclusion,the discovery of these 5-cyano-6-arylpyrimidine-based HDAC6 inhibitors not only enriches the pyrimidine-derived compound library,but also provides a useful guiding for the subsequent design and synthesis of HDAC 6 inhibitors with stronger anti-tumor effects.