Growth Inhibition of Lung Cancer Cells by Histone Deacetylase Inhibitors

[[abstract]]Purpose: Recent studies have shown that overexpression and/or increased activity of histone deacetylases (HDACs) are observed in solid and hematologic tumors. It makes the HDACs as the attractive novel therapeutic target for cancer treatment. Therefore, we evaluated whether novel HDAC inhibitors (HDACIs) such as HDAC-44 and HTPB can be anti-cancer drugs in lung cancer and investigated their molecular mechanisms on inhibition of cancer cell growth. Materials and Methods: The cytotoxicity of HDAC-44 and HTPB alone or in combination with cisplatin in normal and lung caner cells were determined by trypan blue exclusion. Changes in cell cycle distribution by HDACIs were examined by flow cytometry. HDACIs-induced cell apoptosis was tested by DNA ladder assay. Alteration of cytoskeleton structure of the treated cells was examined by immunocytochemical analysis. RT-PCR and Western blot analysis were used to observe whether HDACIs alter mRNA and protein expressions and protein acetylation. In addition, we used Chromatin immunoprecipitation (ChIP) and ChIP-on-chip to search for more target genes that are influenced by HDACIs. Results: Novel HDACIs facilitated acetylation of histone H3, H4, and p53 proteins. In addition, novel HDACIs induced p21WAF1/Cip1 and Tissue inhibitor of metalloproteinase-3 (TIMP-3) transcriptional activation. Novel HDACIs (HDAC-44 and HTPB) induced lung cancer cell death (The IC50 of HDAC 44 in H1299 is 1.09 μM, HDAC44 in A549 is 0.64 μM, HDAC44 in CL1-1 is 0.67 μM, HTPB in H1299 is 2.99 μM, HTPB in A549 is 1.60 μM、HTPB in CL1-1 is 2.78 μM, SAHA in H1299 is 4.59 μM, SAHA in A549 is 1.89 μM, SAHA in CL1-1 is 2.86 μM) without showing apparent cytotoxicity towards normal lung cells. Combined treatment of HDAC-44 and cisplatin showed a synergistically cytotoxic effect in lung cancer cells. HDAC-44 and HTPB induced G2/M arrest and cell apoptosis such as DNA ladder and anti-apoptotic Bcl-2 protein down-regulation in different lung cancer cell lines. HDAC-44 may lead to a-tubulin abnormal distribution and cancer cell cytokinesis inhibition. ChIP-on-chip analysis indicated that histones on a subset of CpG islands were commonly acetylated by HDACIs in A549, H1299, CL1-1 tested. The genes containing these CpG islands will be used as targets for further mechanistic studies of HDACIs. Conclusion: The current studies and our data suggest that HDAC-44 and HTPB could be potential therapeutic drugs in lung cancer. Their effects toward other types of cancer are worthy of further analysis.