HDAC Inhibitors Act with 5-aza-2′-Deoxycytidine to Inhibit Cell Proliferation by Suppressing Removal of Incorporated Abases in Lung Cancer Cells

Abstract

5-aza-2′-deoxycytidine (5-aza-CdR) is used extensively as a demethylating agent and acts in concert with histone deacetylase inhibitors (HDACI) to induce apoptosis or inhibition of cell proliferation in human cancer cells. Whether the action of 5-aza-CdR in this synergistic effect results from demethylation by this agent is not yet clear. In this study we found that inhibition of cell proliferation was not observed when cells with knockdown of DNA methyltransferase 1 (DNMT1), or double knock down of DNMT1-DNMT3A or DNMT1-DNMT3B were treated with HDACI, implying that the demethylating function of 5-aza-CdR may be not involved in this synergistic effect. Further study showed that there was a causal relationship between 5-aza-CdR induced DNA damage and the amount of [3H]-5-aza-CdR incorporated in DNA. However, incorporated [3H]-5-aza-CdR gradually decreased when cells were incubated in [3H]-5-aza-CdR free medium, indicating that 5-aza-CdR, which is an abnormal base, may be excluded by the cell repair system. It was of interest that HDACI significantly postponed the removal of the incorporated [3H]-5-aza-CdR from DNA. Moreover, HDAC inhibitor showed selective synergy with nucleoside analog-induced DNA damage to inhibit cell proliferation, but showed no such effect with other DNA damage stresses such as γ-ray and UV, etoposide or cisplatin. This study demonstrates that HDACI synergistically inhibits cell proliferation with nucleoside analogs by suppressing removal of incorporated harmful nucleotide analogs from DNA.

Combinations of DNA Methyltransferase and Histone Deacetylase Inhibitors Induce DNA Damage in Small Cell Lung Cancer Cells: Correlation of Resistance with IFN-Stimulated Gene Expression

“…This in turn can result in the induction of tumor cell differentiation, cell cycle arrest, DNA damage, and apoptosis (9)(10)(11)(12). Acetylation of histones affects the transcription of genes by modification of chromatin structure and is dependent on the contrasting actions of histone acetyltransferase and HDAC (13).…”

“…Sequential treatment of lung cancer cells with 5-AZA-dC and the HDAC inhibitors depsipeptide or trichostatin A markedly enhanced apoptosis induced by HDAC inhibitors (21). 5-AZA-dC can also initiate cytotoxicity by its incorporation into DNA with the induction of DNA damage (10,22,23). When incorporated into DNA, 5-AZA-dC covalently links with DNMT causing DNA damage either by structural instability at its incorporation site or by obstructing DNA synthesis (23).…”

Histone deacetylase modulators provided by Mother Nature

“…Consequently, it would be more appropriate to call HATs and HDACs lysine acetyltransferases (KATs) and lysine deacetyltransferases (KDACs), respectively. Furthermore, HDACi, from a chemosensitization point of view, seem particularly attractive when combined with either conventional chemotherapeutic drugs inducing apoptosis (e.g., doxorubicin or etoposide) and/or with other epigenetically active drugs, such as the DNA demethylating agent 5-aza-2 0 -deoxycytidine, to restore epigenetically mediated gene silencing (Chai et al 2008;Schnekenburger et al 2011;Yoon et al 2010). Hence, it seems that HDACi offer promising alternatives for anticancer therapies.…”

“…Isothiocyanates such as phenethyl isothiocyanate (PEI-TC) from cruciferous vegetables (e.g., broccoli) show inhibitory activities against HDACs and induce an increase in histone acetylation, particularly at promoters of genes encoding p21 and Bax, which are involved in the cell cycle and apoptosis, respectively (Wang et al 2008). Indole-3-carbinol from broccoli and cauliflower is metabolized to 3,3 0 -diindolylmethane (DIM) and induces the proteasomal degradation of class I HDACs (1, 2, 3 and 8), thereby inhibiting the anti-apoptotic protein survivin.…”

“…The activators resveratrol and quercetin are polyphenols isolated from grapes and citrus fruits, respectively. These molecules induce SIRT1 activity, which in turn deacetylates survivin and subsequently triggers apoptosis (Wang et al 2008). However, it has been reported that inhibition of class III HDACs might favor tumor suppression.…”