HDAC inhibitors induce tumor-cell-selective pro-apoptotic transcriptional responses

Abstract

The identification of recurrent somatic mutations in genes encoding epigenetic enzymes has provided a strong rationale for the development of compounds that target the epigenome for the treatment of cancer. This notion is supported by biochemical studies demonstrating aberrant recruitment of epigenetic enzymes such as histone deacetylases (HDACs) and histone methyltransferases to promoter regions through association with oncogenic fusion proteins such as PML-RARα and AML1-ETO. HDAC inhibitors (HDACi) are potent inducers of tumor cell apoptosis; however, it remains unclear why tumor cells are more sensitive to HDACi-induced cell death than normal cells. Herein, we assessed the biological and molecular responses of isogenic normal and transformed cells to the FDA-approved HDACi vorinostat and romidepsin. Both HDACi selectively killed cells of diverse tissue origin that had been transformed through the serial introduction of different oncogenes. Time-course microarray expression profiling revealed that normal and transformed cells transcriptionally responded to vorinostat treatment. Over 4200 genes responded differently to vorinostat in normal and transformed cells and gene ontology and pathway analyses identified a tumor-cell-selective pro-apoptotic gene-expression signature that consisted of BCL2 family genes. In particular, HDACi induced tumor-cell-selective upregulation of the pro-apoptotic gene BMF and downregulation of the pro-survival gene BCL2A1 encoding BFL-1. Maintenance of BFL-1 levels in transformed cells through forced expression conferred vorinostat resistance, indicating that specific and selective engagement of the intrinsic apoptotic pathway underlies the tumor-cell-selective apoptotic activities of these agents. The ability of HDACi to affect the growth and survival of tumor cells whilst leaving normal cells relatively unharmed is fundamental to their successful clinical application. This study provides new insight into the transcriptional effects of HDACi in human donor-matched normal and transformed cells, and implicates specific molecules and pathways in the tumor-selective cytotoxic activity of these compounds.

Manipulation of B-cell responses with histone deacetylase inhibitors

“…Although the reasons for the observed differences in sensitivity to panobinostat are unclear, perhaps the distinct transcriptional responses of lymphocyte subsets, progenitor populations and malignant cells instill particular resistance or sensitivity to HDACi. Indeed, we have observed that isogenic matched normal and tumour cells display subtle differences in transcriptional responses to HDACi resulting in profound differential biological responses 53 .…”

Belinostat and vincristine demonstrate mutually synergistic cytotoxicity associated with mitotic arrest and inhibition of polyploidy in a preclinical model of aggressive diffuse large B cell lymphoma

“…[5][6][7] HDACi are largely ineffective as monotherapy against DLBCL as well as solid tumors, therefore, research focus has shifted to combining HDACi with other therapeutics for treatment of a variety of cancers. [8][9][10] A confounding issue in identifying effective HDACi-containing drug combinations is that a multitude of mechanisms have been attributed to the anti-cancer effects of HDACi including: alteration of gene expression, activation of pro-apoptotic pathways, induction of tumor cell differentiation, inhibition of angiogenesis, and modulation of cell cycle progression.…”

“…[8][9][10] A confounding issue in identifying effective HDACi-containing drug combinations is that a multitude of mechanisms have been attributed to the anti-cancer effects of HDACi including: alteration of gene expression, activation of pro-apoptotic pathways, induction of tumor cell differentiation, inhibition of angiogenesis, and modulation of cell cycle progression. 5,7,[11][12][13][14] Taking a mechanistic approach to understand the molecular effects of HDACi specifically in the DLBCL context, we developed a cell-based model of sensitivity and resistance to HDACi. The mechanistic knowledge gained from this system can be used to rationally select therapeutics which can be effectively combined with HDACi.…”

A genome scale RNAi screen identifies GLI1 as a novel gene regulating vorinostat sensitivity

“…GLI2 is a more potent activator of BCL2 expression than GLI1, 55 which may explain the subtle transcription repression observed (1.6-fold). Bolden et al 5 previously described a tumor-cellselective pro-apoptosis gene expression signature upon vorinostat treatment of paired normal and tumorigenic human fibroblasts. Vorinostat treatment of BJ LTSTERas fibroblasts resulted in repression of BCL2L1 (BCLXL) and BCL2L2 (BCLW), which was also observed in the vorinostat-treated HCT116-VR cells in this study, indicating a potentially conserved transcriptional response to vorinostat treatment in transformed cells.…”

“…2 In addition, we and others have demonstrated that overexpression of prosurvival Bcl-2-family proteins protects cells against HDACi-induced apoptosis. [3][4][5][6] HR23B has also been implicated in vorinostat resistance as a protein through which vorinostat induces apoptosis via impaired proteasome function. [7][8][9] As the identification of these mechanisms of resistance has not yet impacted the clinical use of HDACi through the generation of combination therapy approaches or clinical biomarkers, a genome-wide study was conducted to identify further mechanisms of resistance to HDACis that may improve the clinical application of these agents.…”