Design,Synthesis And Preliminary Activity Evaluation Of Hydroxamic Acid HDAC Inhibitors

The occurrence of cancer is related to many factors,including genetic changes and epigenetic abnormalities.The acetylation of N terminal in histone lysine is the most common epigenetic disorder in cancer,which is closely related to the occurrence and development of numerous cancers.Therefore,enzymes involved in the acetylation of lysine have become important targets for the development of small molecule anti-tumor drugs.Histone deacetylase is abnormally highly expressed in many tumor cells,leading to low expression or inactivation of tumor suppressor genes,and ultimately inducing tumorigenesis.By regulating acetylation state in tumor cells,histone deacetylase inhibitors(HDACIs)can not only play a direct anti-tumor effect by inducing cell apoptosis,blocking cell cycle progression,promoting senescence,inducing cellular differentiation and DNA damage,improving immunogenicity,antiangiogenesis and inducing autophagy,also can overcome the acquired drug resistance to conventional therapy by influencing other signal pathways,such as inhibiting DNA damage repair,up-regulating the expression of metastasis suppressor factors,reducing the invasion ability of drug-resistant tumor cells.To date,only six HD AC inhibitors have been approved for clinical use and only one drug was marketed in China.Except for Chidamide,which was appro ved for the treatment of breast cancer,other HDACI drugs are used for hematological tumors.To discover new HDACIs with potent anti-tumor activity,we selected hydroxamic acid as the zinc binding group,introducing a urea group,which has good water solubility property and can act as hydrogen bond donor and acceptor,together with a thiazole or phenyl group as the linker,and introducing different substituents as the cap unit to design thiazole hydroxamic acids(A series)and phenyl hydroxamic acids(B series,para-or meta-substituted)HDACIs.The amino-substituted methyl benzoate or methyl thiazole formate was reacted with triphosgene to form isocyanate-substituted methyl benzoate or methyl thiazole formate intermediates,and then reacted with different amines to afford the urea intermediates.Finally,the methyl ester intermediates were reacted with hydroxylamine to give the target thiazole hydroxamic acid derivatives and the phenyl hydroxamic acid derivatives.The chemical structures of target compounds were determined by ESI-MS.1H NMR and 13C NMR spectroscopies.All compounds were tested for the inhibition activities against HDACs(Hela cell nuclear extracts,containing pan-HDACs)and in vitro antiproliferative activities against several tumor cell lines.The results showed that thiazole hydroxamic acid derivatives in A series exhibited poor inhibitory effect on HD ACs,only AY-4 showed good inhibitory activity with an inhibitory rate of 79.4%at 10 μM concentration,and with an IC50 value of 620 nM.Most of the para-substituted phenyl hydroxamic acid derivatives in B series showed potent inhibitory activity against HD ACs.The inhibitory rates of representative compounds BY-5 and BY-6 at 10 μM were 87.7%and 78.9%,respectively,and with IC50 values of 430 nM and 860 nM,respectively.Meta-substituted phenyl hydroxamic acid derivatives in B series displayed poor inhibitory effect on HDACs.In vitro tumor cell proliferation inhibition experiments showed that para-substituted phenyl hydroxamic acid derivatives in B series showed moderate inhibitory activities against HepG2 and K562 cells,Among all tested compounds,BY-3 and BY-9 showed the best antiproliferative activity against K562 cells,with IC50 values of 7.85 pM and 5.47 μM,respectively.While BY-7 and BY-8 displayed the best effect on HepG2 cells,with IC50 values of 3.10 μM and 5.79 μM,respectively.Thiazole hydroxamic acid derivatives in A series and meta-substituted phenyl hydroxamic acid derivatives in B series showed poor proliferation inhibitory activity on the tested tumor cells.Overall,the inhibitory effect of these compounds on HepG2 cells is slightly better than that on K562 cells.BY-7,the most potent compound,its inbibitory effect on HepG2 cells is comparable to that of the control drug SAHA.In conclusion,we designed and synthesized two series of HDACIs containing a urea-based linker,and evaluated the inhibitory effects of these compounds on HDACs and on the proliferation of hepatocarcinoma HepG2 and leukemia K562 cells.Although several compounds showed good effect on HDACs and on the tested tumor cells,further structural optimization is still needed to improve their inhibitory activities.