Histone Deacetylase Inhibitors Trigger a G2 Checkpoint in Normal Cells That Is Defective in Tumor Cells

Abstract

Important aspects of cell cycle regulation are the checkpoints, which respond to a variety of cellular stresses to inhibit cell cycle progression and act as protective mechanisms to ensure genomic integrity. An increasing number of tumor suppressors are being demonstrated to have roles in checkpoint mechanisms, implying that checkpoint dysfunction is likely to be a common feature of cancers. Here we report that histone deacetylase inhibitors, in particular azelaic bishydroxamic acid, triggers a G2 phase cell cycle checkpoint response in normal human cells, and this checkpoint is defective in a range of tumor cell lines. Loss of this G2 checkpoint results in the tumor cells undergoing an aberrant mitosis resulting in fractured multinuclei and micronuclei and eventually cell death. This histone deacetylase inhibitor-sensitive checkpoint appears to be distinct from G2/M checkpoints activated by genotoxins and microtubule poisons and may be the human homologue of a yeast G2 checkpoint, which responds to aberrant histone acetylation states. Azelaic bishydroxamic acid may represent a new class of anticancer drugs with selective toxicity based on its ability to target a dysfunctional checkpoint mechanism in tumor cells.

Histone Hyperacetylation in Mitosis Prevents Sister Chromatid Separation and Produces Chromosome Segregation Defects

“…The frequency of mitotic cells was reduced by 30% already at 200 ng/ml TSA ( Figure 1A), when cells were kept in the presence of the drug during prophase or during synthesis of late-replicating heterochromatic regions (1 or 7 h before fixation, respectively), in accordance with available data showing a G2 checkpoint induction by deacetylase inhibitors in normal cells (Qiu et al, 2000). For 1-h TSA treatment, a further 30% decrease of the mitotic index was observed in cells treated with 500 ng/ml TSA and no further reduction was observed at 1000 ng/ml, indicating that inhibition of deacetylation and biological effects were fully accomplished with 500 ng/ml TSA.…”

Histone deacetylase inhibitors and the promise of epigenetic (and more) treatments for cancer

“…The second is the mitotic-spindle checkpoint, which normally detects aberrant mitosis and blocks mitotic exit until the defect is rectified. The disruption of both checkpoints results in the premature exit of tumour cells from an abortive mitosis and the subsequent induction of apoptosis 88,89 . One model of action for HDACi derived from these studies, and those on the effects of HDACi on DNA repair, is that HDACi should lead to an increased accumulation of DNA damage (by endogenous stress or by drug treatment) in sensitive cells.…”

Histone deacetylase inhibitors: molecular mechanisms of action

“…Normal cells are relatively resistant to HDACi-induced cell death (Burgess et al, 2004;Insinga et al, 2005;Ungerstedt et al, 2005). The cell death pathways identified in mediating HDACiinduced transformed cell death include apoptosis (Rosato and Grant, 2005;Bolden et al, 2006;Minucci and Pelicci, 2006) by the intrinsic (Ruefli et al, 2001) and extrinsic pathways, mitotic catastrophe/cell death (Qiu et al, 2000;Dowling et al, 2005;Xu et al, 2005), autophagic cell death (Shao et al, 2004), senescence and reactive oxygen species (ROS)-facilitated cell death (Rosato and Grant, 2005;Ungerstedt et al, 2005). The response to HDACi appears to depend, in part at least, on the nature of HDACi, concentration and time of exposure, and importantly, the cell context.…”

“…Histone acetylation interferes with histone phosphorylation and disrupts the function of mitotic spindle checkpoint proteins, such as BubR1, hBUB1, CENP-F and CENP-E (Dowling et al, 2005;Robbins et al, 2005). As a result, the cells show a transient arrest at prometaphase, followed with aberrant mitosis such as missegregation and loss of chromosomes, resulting in cell death by either apoptosis or, mitotic cell death/ catastrophe (Qiu et al, 2000;Cimini et al, 2003;Xu et al, 2005). HDACi-induced a-tubulin acetylation does not affect mitosis, although a-tubulin is a component of mitotic spindle that mediates mitosis.…”