Targeting Epigenetics in Cancer

Installation of a cancer promoting WNT/SIX1 signaling axis by the oncofusion protein MLL-AF9

BACKGROUND

Chromosomal translocation-induced expression of the chromatin modifying oncofusion protein MLL-AF9 promotes acute myelocytic leukemia (AML). Whereas WNT/β-catenin signaling has previously been shown to support MLL-AF9-driven leukemogenesis, the mechanism underlying this relationship remains unclear.

METHODS

We used two novel small molecules targeting WNT signaling as well as a genetically modified mouse model that allow targeted deletion of the WNT protein chaperone Wntless (WLS) to evaluate the role of WNT signaling in AML progression. ATAC-seq and transcriptome profiling were deployed to understand the cellular consequences of disrupting a WNT signaling in leukemic initiating cells (LICs).

FINDINGS

We identified Six1 to be a WNT-controlled target gene in MLL-AF9-transformed leukemic initiating cells (LICs). MLL-AF9 alters the accessibility of Six1 DNA to the transcriptional effector TCF7L2, a transducer of WNT/β-catenin gene expression changes. Disruption of WNT/SIX1 signaling using inhibitors of the Wnt signaling delays the development of AML.

INTERPRETATION

By rendering TCF/LEF-binding elements controlling Six1 accessible to TCF7L2, MLL-AF9 promotes WNT/β-catenin-dependent growth of LICs. Small molecules disrupting WNT/β-catenin signaling block Six1 expression thereby disrupting leukemia driven by MLL fusion proteins.

Function of BRD4 in the pathogenesis of high glucose‑induced cardiac hypertrophy

Diabetic cardiomyopathy is one of the major complications of diabetes, and due to the increasing number of patients with diabetes it is a growing concern. Diabetes-induced cardiomyopathy has a complex pathogenesis and histone deacetylase-mediated epigenetic processes are of prominent importance. The olfactory bromodomain-containing protein 4 (BRD4) is a protein that recognizes and binds acetylated lysine. It has been reported that the high expression of BRD4 is involved in the process of cardiac hypertrophy. The aim of the present study was to investigate the function of BRD4 in the process of high glucose (HG)-induced cardiac hypertrophy, and to clarify whether epigenetic regulation involving BRD4 is an important mechanism. It was revealed that BRD4 expression levels were increased in H9C2 cells following 48 h of HG stimulation. This result was also observed in a diabetic rat model. Furthermore, HG stimulation resulted in the upregulation of the myocardial hypertrophy marker, atrial natriuretic peptide, the cytoskeletal protein α-actin and fibrosis-associated genes including transforming growth factor-β, SMAD family member 3, connective tissue growth factor and collagen, type 1, α1. However, administration of the specific BRD4 inhibitor JQ1 (250 nM) for 48 h reversed this phenomenon. Furthermore, protein kinase B (AKT) phosphorylation was activated by HG stimulation and suppressed by JQ1. In conclusion, BRD4 serves an important role in the pathogenesis of HG-induced cardiomyocyte hypertrophy through the AKT pathway.

Enzalutamide therapy for advanced prostate cancer: efficacy, resistance and beyond

The androgen receptor drives the growth of metastatic castration-resistant prostate cancer. This has led to the development of multiple novel drugs targeting this hormone-regulated transcription factor, such as enzalutamide – a potent androgen receptor antagonist. Despite the plethora of possible treatment options, the absolute survival benefit of each treatment separately is limited to a few months. Therefore, current research efforts are directed to determine the optimal sequence of therapies, discover novel drugs effective in metastatic castration-resistant prostate cancer and define patient subpopulations that ultimately benefit from these treatments. Molecular studies provide evidence on which pathways mediate treatment resistance and may lead to improved treatment for metastatic castration-resistant prostate cancer. This review provides, firstly a concise overview of the clinical development, use and effectiveness of enzalutamide in the treatment of advanced prostate cancer, secondly it describes translational research addressing enzalutamide response vs resistance and lastly highlights novel potential treatment strategies in the enzalutamide-resistant setting.

Epigenetic Crosstalk between the Tumor Microenvironment and Ovarian Cancer Cells: A Therapeutic Road Less Traveled

Metastatic dissemination of epithelial ovarian cancer (EOC) predominantly occurs through direct cell shedding from the primary tumor into the intra-abdominal cavity that is filled with malignant ascitic effusions. Facilitated by the fluid flow, cells distribute throughout the cavity, broadly seed and invade through peritoneal lining, and resume secondary tumor growth in abdominal and pelvic organs. At all steps of this unique metastatic process, cancer cells exist within a multidimensional tumor microenvironment consisting of intraperitoneally residing cancer-reprogramed fibroblasts, adipose, immune, mesenchymal stem, mesothelial, and vascular cells that exert miscellaneous bioactive molecules into malignant ascites and contribute to EOC progression and metastasis via distinct molecular mechanisms and epigenetic dysregulation. This review outlines basic epigenetic mechanisms, including DNA methylation, histone modifications, chromatin remodeling, and non-coding RNA regulators, and summarizes current knowledge on reciprocal interactions between each participant of the EOC cellular milieu and tumor cells in the context of aberrant epigenetic crosstalk. Promising research directions and potential therapeutic strategies that may encompass epigenetic tailoring as a component of complex EOC treatment are discussed.

Chromatin and Metabolism

Chromatin is a mighty consumer of cellular energy generated by metabolism. Metabolic status is efficiently coordinated with transcription and translation, which also feed back to regulate metabolism. Conversely, suppression of energy utilization by chromatin processes may serve to preserve energy resources for cell survival. Most of the reactions involved in chromatin modification require metabolites as their cofactors or coenzymes. Therefore, the metabolic status of the cell can influence the spectra of posttranslational histone modifications and the structure, density and location of nucleosomes, impacting epigenetic processes. Thus, transcription, translation, and DNA/RNA biogenesis adapt to cellular metabolism. In addition to dysfunctions of metabolic enzymes, imbalances between metabolism and chromatin activities trigger metabolic disease and life span alteration. Here, we review the synthesis of the metabolites and the relationships between metabolism and chromatin function. Furthermore, we discuss how the chromatin response feeds back to metabolic regulation in biological processes.

Immune checkpoint therapy in liver cancer

Immune checkpoints include stimulatory and inhibitory checkpoint molecules. In recent years, inhibitory checkpoints, including cytotoxic T lymphocyte–associated antigen 4 (CTLA-4), programmed cell death protein-1 (PD-1), and programmed cell death ligand 1 (PD-L1), have been identified to suppress anti-tumor immune responses in solid tumors. Novel drugs targeting immune checkpoints have succeeded in cancer treatment. Specific PD-1 blockades were approved for treatment of melanoma in 2014 and for treatment of non-small-cell lung cancer in 2015 in the United States, European Union, and Japan. Preclinical and clinical studies show immune checkpoint therapy provides survival benefit for greater numbers of patients with liver cancer, including hepatocellular carcinoma and cholangiocarcinoma, two main primary liver cancers. The combination of anti-PD-1/PD-L1 with anti-CTLA-4 antibodies is being evaluated in phase 1, 2 or 3 trials, and the results suggest that an anti-PD-1 antibody combined with locoregional therapy or other molecular targeted agents is an effective treatment strategy for HCC. In addition, studies on activating co-stimulatory receptors to enhance anti-tumor immune responses have increased our understanding regarding this immunotherapy in liver cancer. Epigenetic modulations of checkpoints for improving the tumor microenvironment also expand our knowledge of potential therapeutic targets in improving the tumor microenvironment and restoring immune recognition and immunogenicity. In this review, we summarize current knowledge and recent developments in immune checkpoint-based therapies for the treatment of hepatocellular carcinoma and cholangiocarcinoma and attempt to clarify the mechanisms underlying its effects.

Clinically Applicable Inhibitors Impacting Genome Stability

Advances in technology have facilitated the molecular profiling (genomic and transcriptomic) of tumours, and has led to improved stratification of patients and the individualisation of treatment regimes. To fully realize the potential of truly personalised treatment options, we need targeted therapies that precisely disrupt the compensatory pathways identified by profiling which allow tumours to survive or gain resistance to treatments. Here, we discuss recent advances in novel therapies that impact the genome (chromosomes and chromatin), pathways targeted and the stage of the pathways targeted. The current state of research will be discussed, with a focus on compounds that have advanced into trials (clinical and pre-clinical). We will discuss inhibitors of specific DNA damage responses and other genome stability pathways, including those in development, which are likely to synergistically combine with current therapeutic options. Tumour profiling data, combined with the knowledge of new treatments that affect the regulation of essential tumour signalling pathways, is revealing fundamental insights into cancer progression and resistance mechanisms. This is the forefront of the next evolution of advanced oncology medicine that will ultimately lead to improved survival and may, one day, result in many cancers becoming chronic conditions, rather than fatal diseases.

Moonlighting with WDR5: A Cellular Multitasker

WDR5 is a highly conserved WD40 repeat-containing protein that is essential for proper regulation of multiple cellular processes. WDR5 is best characterized as a core scaffolding component of histone methyltransferase complexes, but emerging evidence demonstrates that it does much more, ranging from expanded functions in the nucleus through to controlling the integrity of cell division. The purpose of this review is to describe the current molecular understandings of WDR5, discuss how it participates in diverse cellular processes, and highlight drug discovery efforts around WDR5 that may form the basis of new anti-cancer therapies.

Introduction to the Theme "New Approaches for Studying Drug and Toxicant Action: Applications to Drug Discovery and Development"

The theme "New Approaches for Studying Drug and Toxicant Action: Applications to Drug Discovery and Development" links 13 articles in this volume of the Annual Review of Pharmacology and Toxicology (ARPT). The engaging prefatory articles by Arthur Cho and Robert Lefkowitz set the stage for this theme and for the reviews that insightfully describe new approaches that advance research and discovery in pharmacology and toxicology. Examples include the progress being made in developing Organs-on-Chips/microphysiological systems and human induced pluripotent stem cell-derived cells to aid in understanding cell and tissue pharmacokinetics, action, and toxicity; the recognition of the importance of circadian rhythm, the microbiome, and epigenetics in drug and toxicant responses; and the application of results from new types of patient-derived information to create personalized/precision medicine, including therapeutics for pain, which may perhaps provide help in dealing with the opioid epidemic in the United States. Such new information energizes discovery efforts in pharmacology and toxicology that seek to improve the efficacy and safety of drugs in patients and to minimize the consequences of exposure to toxins.