Current Cancer Drug Targets - Volume 18, Issue 1, 2018

The efficacy of cancer immunotherapy relies on the ability of the host immune system to recognise the cancer as non-self and eliminate it from the body. Whilst this is an extremely fertile area of medical research, with positive clinical trials showing durable responses, attention must be paid to the subset of patients that do not respond to these treatments. Immune surveillance and immunoediting by the host could itself select for immune-evasive tumour cells during tumour development leading to immunotherapy resistance. One such mechanism of non-efficacy or resistance is the epigenetic silencing of a specific gene required in the immunotherapy response pathway. Epigenetics is the study of the control of expression patterns in a cell via mechanisms not involving a change in DNA sequence. All tumour types show aberrant epigenetic regulation of genes involved in all the hallmarks of cancer, including immunomodulation. Inhibition of key enzymes involved in maintenance of epigenetic states is another important area of research for new treatment strategies for cancer. Could epigenetic therapies be used to successfully enhance the action of immunomodulatory agents in cancer, and are they acting in the way we imagine? An understanding of the effects of epigenetic therapies on immunological pathways in both the tumour and host cells, especially the tumour microenvironment, will be essential to further develop such combination approaches.

Lung cancer remains the major cause of human mortality among all the cancer types despite the colossal amount of efforts to prevent the cancer onset and to provide the appropriate cure. Recent reports have identified that important contributors of lung cancer-related mortality are the drug resistance and aggressive tumor relapse, the characteristics contributed by the presence of lung cancer stem cells (CSCs). The identification of lung CSCs is inherently complex due to the quiescent nature of lung epithelium, which makes the distinction between the normal lung epithelium and lung CSCs difficult. Recently, multiple researches have helped in the identification of lung CSCs based on the presence or absence of certain specific types of stem cell markers. Maintenance of lung CSCs is chiefly mediated through the epigenetic modifications of their genome. In this review, we will discuss about the origin of lung CSCs and the role of epigenetic modifications in their maintenance. We will also discuss in brief the major lung CSC markers and the therapeutic approaches to selectively target this population of cells.

Cancer is considered one of the leading causes of death in the United States. Although preventive strategies, early detection, and improved treatment options have been developed, novel targets and therapeutics are still needed. Since concluding that cancer is mediated by genetic and epigenetic alterations of the cell, many research groups are now focusing on other means of prevention and therapy via nutrition, epigenetic mechanisms, and non-coding RNAs which have been shown to control gene expression and have many different functions at the cellular level. With the advent of high-throughput sequencing in human cancer, the potential to identify novel biomarkers and therapeutic targets of disease has increased tremendously and led to the identification of many non-coding RNAs that are dysregulated in various cancers. Gene expression and regulation is important in maintaining the homeostasis of normal tissues and cells. Not uncommonly, up- or down-regulation of particular genes are associated with cancer as a result of increased or decreased expression of transcriptional targets. This review focuses on the role of nutrition in cancer and the dysregulation of non-coding RNAs with particular emphasis on long non-coding RNAs and microRNAs in different cancer types.

Histone deacetylases (HDACs) play a significant role in the proliferation and dissemination of cancer and represent promising epigenetic drug targets. The HDAC inhibitor vorinostat featuring a zinc-binding hydroxamate fragment was already clinically approved. However, HDAC inhibitors containing hydroxamic acids are often hampered by acquired or intrinsic drug resistance and may lead to enhanced tumor aggressiveness. In order to overcome these drawbacks of hydroxamate HDAC inhibitors, a series of multimodal derivatives of this compound class, including such with different zinc-binding groups, was recently developed and showed promising anticancer activity. This review provides an overview of the chemistry and pleiotropic anticancer modes of action of these conceptually new HDAC inhibitors.

Central nervous system (CNS) tumors represent the second most prevalent group of cancers in children and adolescents, yet account for the majority of childhood cancer-related deaths and considerable morbidity among survivors, due to high-intensity non-selective standard therapies delivered to immature nervous system structures undergoing development. These tumors arise at different ages –not infrequently very early in life-, in different locations and cellular contexts, have varied cell types of origin, and have heterogeneous responses to the “classic” current therapeutic approaches. Demographic, radiologic and morphological characterization have several limitations, putting into the “classic boxes” heterogeneous tumors that are diverse in their genetic and epigenetic background and that will likely behave biologically different. Given that, epigenetic disruption (i.e. DNA methylation, histone modification and chromatin remodeling) is a common feature identified more and more frequently in pediatric cancer, it is logical to speculate that interrogating epigenetic marks may help to further define the molecular profile, and therefore tumor biology, evolution and treatment of these tumors. An integrated approach that incorporates traditional features complemented with genetic and epigenenetic specific markers offers tremendous promise to “risk-group” stratification and better prognostication. Also, it will help unveil the key driver pathways for tumor formation and for the discovery of targeted therapy for neoplasms that appear in the developing brain, facilitating early identification of therapy responders and track accurately disease progression. In this paper, we reviewed the most representative pediatric brain tumors where epigenetic alterations have been identified as initiating or driving events in tumor development, maintenance or progression.

The incidence of gastric cancer has been declining globally in the last decades. Despite the improvements in the diagnostic procedures, most cases are still detected at advanced stages due to lack of specific symptoms associated with early phases of tumour development. Consequently, gastric cancer poses a major health burden worldwide due to high mortality rates. Continuing advances in high-throughput technologies are revealing an intricate network of genetic and epigenetic changes associated with carcinogenesis. In addition, several risk factors, both environmental and genetic, have been recognized, which promote accumulation of diverse alterations affecting the expression of oncogenes, tumour suppressor genes, DNA repair genes, and other genes, implicated in normal gastric cell functions. A plethora of aberrant molecular events found in patients with this disease and intragenic heterogeneity of tumours from individuals are delaying the development of targeted biological therapies. Frequent occurrence of characteristic CpG island methylator phenotypes (CIMP phenotypes) in gastric cancers, particularly in association with Helicobacter pylori or EBV infection, could lead to introduction of epigenetic modulators into standard treatment regimens used against early and advanced forms of adenocarcinomas. This review highlights aberrant DNA methylation events in the development of gastric tumours and addresses the different aspects associated with the application of therapeutic epigenetic modulation in the management of the disease.

Lung cancer remains the most diagnosed cancer in the world, with a high mortality rate and fewer therapeutic options. The most common lung cancer is non-small cell, consisting of adenocarcinoma, squamous cell carcinoma and large cell lung carcinoma. As per all solid tumours, the changes that occur for the initiation and metastasis of lung cancer can be described using the EMT (epithelial mesenchymal transition). Cells progressing through EMT lose their epithelial cell characteristics, expressing more mesenchymal markers and are phenotypically different. The transition can be controlled by changes in various pathways, such as TGF-β, PI3K, MAPK, Hedgehog and Wnt. The changes in those pathways can be controlled epigenetically, via DNA methylation, histone modifications or changes in small/non-coding RNA. We will describe the epigenetic changes that occur in these pathways and how we can consider novel methods to generate a synthetic lethality target in an epigenetically regulated pathway in EMT.

Background: Epigenetic modulations such as histone modifications are becoming increasingly valued for their ability to modify genes without altering the DNA sequence. Many bioactive compounds have been shown to alter genetic and epigenetic profiles in various cancers. Sulforaphane (SFN), an isothiocyanate found in cruciferous vegetables such as kale, cabbage and broccoli sprouts, is one of the most potent histone deacetylase inhibitors (HDACis) to date. Recently, it has been identified that HDACis may play a vital role in regulating microRNAs (miRs) and human telomerase reverse transcriptase (hTERT). Objective: The aim of our study was to identify if aberrant HDAC, hTERT and miR levels could be regulated through novel dietary-based approaches in colorectal cancer (CRC) cells. Methods: We evaluated the in vitro epigenetic effects of SFN on CRC cells by MTT assay, cellular density assay, real-time reverse transcriptase-polymerase chain reaction (RT-PCR), cell cycle analysis, western-blot assay, HDAC activity assay and teloTAGGG telomerase PCR Elisa assay. Results: We demonstrated the inhibitory effects of physiologically relevant concentrations of SFN in both HCT116 and RKO CRC cells, and showed for the first time that SFN treatment decreased cell density, significantly inhibited cell viability and induced apoptosis in CRC cells. We also found that practical doses of SFN significantly down-regulated oncogenic miR-21, HDAC and hTERT mRNA, protein and enzymatic levels in CRC cells. Conclusion: Our studies suggest that the regulation of HDAC, hTERT and miR-21 is a promising approach for delaying and/or preventing CRC and may be accomplished via the consumption of SFN in cruciferous vegetables.