Chidamide, a Novel Histone Deacetylase Inhibitor, Displays Potent Antitumor Activity Against MDS Cells Mainly through JAK2/STAT3 Signaling Inhibition

Background:

Many studies have indicated that histone deacetylases (HDAC) activity is always increased in a lot of human tumors, and inhibition of HDAC activity are promising new strategies in the treatment of cancers. Chidamide (CS055/HBI-8000), a novel histone deacetylases inhibitor (HDACi) of the benzamide class, is currently under clinical trials. Despite emerging information on the effect of chidamide in multiple cancers, little is yet known about mechanism of action, and there were few reports about this drug's effects on myelodysplastic syndromes (MDS). In this study, we aimed to investigate the antitumor activities of chidamide on MDS cell line SKM-1 and to explore the possible mechanism.

Methods:

We treated MDS cells with different concentrations of chidamide. The effect of chidamide on HDAC activity of MDS cells was studied by using a HDAC Fluorometric Activity Assay Kit. The induction of histone acetylation was confirmed by detecting acetylated histone H3 and H4 using Western blot analysis. The effect of chidamide on the proliferation of MDS cells was analyzed by Cell Counting Kit (CCK-8) assay. Apoptosis were detected by Annexin V/propidium iodide (PI) double-labeled cytometry. Cell cycle was analyzed by a PI method. The acetylation levels of genes promoterassociated histone H3 and H4 were examined by chromatin immunoprecipitation (ChIP) and quantitative real-time PCR. Quantitativereal-time PCR and Western blot were used to detect the expression of signaling pathway factors (SOCS3, JAK2, STAT3,Bcl-XL,Bcl-2 and Mcl-1).

Results:

Our results demonstrated chidamide suppressed MDS cells growth in a time- and dose-dependent manner, and induced cell apoptosis and cell cycle arrest at G0/G1phase. Chidamide was able to significantly inhibit the HDAC activity and increase the acetylated histoneH3 and H4 of MDS cells. ChIP analysis further indicated that chidamide induced acetylated histones accumulation in the promoter of SOCS3.Moreover, chidamide upregulated the mRNA and protein expression ofSOCS3, and also significantly downregulated JAK2/STAT3 signaling. Further, we identified reduced expression of STAT3 downstream targets with treatment of chidamide, including Bcl-XL, Bcl-2 and Mcl-1, which may explain the cytotoxic effects of chidamide on MDS cells.

Conclusion:

These results demonstrate that chidamide possesses significant cytotoxic effects on MDS cells mainly through histone modifications of SOCS3 and consequently JAK2/STAT3 signaling inhibition. Therefore, Our data provide rationale for clinical investigation of chidamide in MDS.