Cancer epigenetics: a perspective on the role of DNA methylation in acquired endocrine resistance

Prediction of circRNAs Based on the DNA Methylation-Mediated Feature Sponge Function in Breast Cancer

Several studies have found that DNA methylation is associated with transcriptional regulation and affect sponge regulation of non-coding RNAs in cancer. The integration of circRNA, miRNA, DNA methylation and gene expression data to identify sponge circRNAs is important for revealing the role of DNA methylation-mediated regulation of sponge circRNAs in cancer progression. We established a DNA methylation-mediated circRNA crosstalk network by integrating gene expression, DNA methylation and non-coding RNA data of breast cancer in TCGA. Four modules (26 candidate circRNAs) were mined. Next, 10 DNA methylation-mediated sponge circRNAs (sp_circRNAs) and five sponge driver genes (sp_driver genes) in breast cancer were identified in the CMD network using a computational process. Among the identified genes, ERBB2 was associated with six sponge circRNAs, which illustrates its better sponge regulatory function. Survival analysis showed that DNA methylations of 10 sponge circRNA host genes are potential prognostic biomarkers in the TCGA dataset (p = 0.0239) and GSE78754 dataset (p = 0.0377). In addition, the DNA methylation of two sponge circRNA host genes showed a significant negative correlation with their driver gene expressions. We developed a strategy to predict sponge circRNAs by DNA methylation mediated with playing the role of regulating breast cancer sponge driver genes.

Treatment for the endocrine resistant breast cancer: Current options and future perspectives

Endocrine resistance remains a challenge and an unmet need for managing hormone receptor-positive breast cancer. The mechanisms of endocrine resistance are multifaceted and are likely to evolve over time following various single or combination therapies. The purpose of this review article is to provide general understanding of molecular basis of endocrine resistance of breast cancer and to offer comprehensive review on current treatment options and potential new treatment strategies for endocrine resistant breast cancers. Last but not the least, we discuss current challenges and future directions for management of endocrine resistant breast cancers.

Targeting Intracellular Calcium Signaling ([Ca2+]i) to Overcome Acquired Multidrug Resistance of Cancer Cells: A Mini-Overview

Cancer is a main public health problem all over the world. It affects millions of humans no matter their age, gender, education, or social status. Although chemotherapy is the main strategy for the treatment of cancer, a major problem limiting its success is the intrinsic or acquired drug resistance. Therefore, cancer drug resistance is a major impediment in medical oncology resulting in a failure of a successful cancer treatment. This mini-overview focuses on the interdependent relationship between intracellular calcium ([Ca²⁺]_i) signaling and multidrug resistance of cancer cells, acquired upon treatment of tumors with anticancer drugs. We propose that [Ca²⁺]_i signaling modulates gene expression of multidrug resistant (MDR) genes which in turn can be modulated by epigenetic factors which in turn leads to modified protein expression in drug resistant tumor cells. A precise knowledge of these mechanisms will help to develop new therapeutic strategies for drug resistant tumors and will improve current chemotherapy.

Adenovirus siMDM2 and NDRG2 Gene Therapy Inhibits Cell Proliferation and Induces Apoptosis of Squamous Cell Carcinoma

Squamous cell carcinoma (SCC) is one of the most common skin cancers. In the present study, we explored the effects of depletion of murine double minute gene 2 (MDM2) together with overexpression of N-myc downstream-regulated gene 2 (NDRG2) on cutaneous SCC. In order to achieve high efficiency of gene knockdown and overexpression in SCC-13 cells, recombinant adenovirus carrying siMDM2 and NDRG2 expression construct was produced. We found Ad-siMDM2, Ad-NDRG2, and Ad-siMDM2-NDRG2 infections inhibit the growth of SCC-13 cells in vitro, and Ad-siMDM2-NDRG2 infection has the highest inhibitory effect. Subcutaneous injections of Ad-siMDM2, Ad-NDRG2, and Ad-siMDM2-NDRG2 into SCC-13 xenograft nude mice resulted in the reduction of tumor volume. Moreover, we found that apoptosis protein caspase 3 was up-regulated in the Ad-siMDM2-, Ad-NDRG2-, and Ad-siMDM2-NDRG2-treated groups. Our data indicate that the adenovirus-mediated MDM2 silencing and NDRG2 overexpression can synergistically inhibit local cancer cell proliferation, induce apoptosis, and further prevent metastases of SCC. Our study provides a promising method that can be further developed as a new therapeutic approach against SCC.

Methyl-binding DNA capture Sequencing for Patient Tissues

Methylation is one of the essential epigenetic modifications to the DNA, which is responsible for the precise regulation of genes required for stable development and differentiation of different tissue types. Dysregulation of this process is often the hallmark of various diseases like cancer. Here, we outline one of the recent sequencing techniques, Methyl-Binding DNA Capture sequencing (MBDCap-seq), used to quantify methylation in various normal and disease tissues for large patient cohorts. We describe a detailed protocol of this affinity enrichment approach along with a bioinformatics pipeline to achieve optimal quantification. This technique has been used to sequence hundreds of patients across various cancer types as a part of the 1,000 methylome project (Cancer Methylome System).

Estrogen Receptor Expression Is Associated with DNA Repair Capacity in Breast Cancer

Estrogen-receptor-positive (ER+) tumors employ complex signaling that engages in crosstalk with multiple pathways through genomic and non-genomic regulation. A greater understanding of these pathways is important for developing improved biomarkers that can better determine treatment choices, risk of recurrence and cancer progression. Deficiencies in DNA repair capacity (DRC) is a hallmark of breast cancer (BC); therefore, in this work we tested whether ER signaling influences DRC. We analyzed the association between ER positivity (% receptor activation) and DRC in 270 BC patients, then further stratified our analysis by HER2 receptor status. Our results show that among HER2 negative, the likelihood of having low DRC values among ER- women is 1.92 (95% CI: 1.03, 3.57) times the likelihood of having low DRC values among ER+ women, even adjusting for different potential confounders (p<0.05); however, a contrary pattern was observed among HER2 positives women. In conclusion, there is an association between DRC levels and ER status, and this association is modified by HER2 receptor status. Adding a DNA repair capacity test to hormone receptor testing may provide new information on defective DNA repair phenotypes, which could better stratify BC patients who have ER+ tumors. ER+/HER2- tumors are heterogeneous, incompletely defined, and clinically challenging to treat; the addition of a DRC test could better characterize and classify these patients as well as help clinicians select optimal therapies, which could improve outcomes and reduce recurrences.

Endocrine Resistance in Breast Cancer

Around 70% of all breast cancers are estrogen receptor alpha positive and hence their development is highly dependent on estradiol. While the invention of endocrine therapies has revolusioned the treatment of the disease, resistance to therapy eventually occurs in a large number of patients. This paper seeks to illustrate and discuss the complexity and heterogeneity of the mechanisms which underlie resistance and the approaches proposed to combat them. It will also focus on the use and development of methods for predicting which patients are likely to develop resistance.

Mechanisms of resistance to endocrine therapy in breast cancer: focus on signaling pathways, miRNAs and genetically based resistance

Breast cancer is the most frequent malignancy diagnosed in women. Approximately 70% of breast tumors express the estrogen receptor (ER). Tamoxifen and aromatase inhibitors (AIs) are the most common and effective therapies for patients with ERα-positive breast cancer. Alone or combined with chemotherapy, tamoxifen significantly reduces disease progression and is associated with more favorable impact on survival in patients. Unfortunately, endocrine resistance occurs, either de novo or acquired during the course of the treatment. The mechanisms that contribute to hormonal resistance include loss or modification in the ERα expression, regulation of signal transduction pathways, altered expression of specific microRNAs, balance of co-regulatory proteins, and genetic polymorphisms involved in tamoxifen metabolic activity. Because of the clinical consequences of endocrine resistance, new treatment strategies are arising to make the cells sensitive to tamoxifen. Here, we will review the current knowledge on mechanisms of endocrine resistance in breast cancer cells. In addition, we will discuss novel therapeutic strategies to overcome such resistance. Undoubtedly, circumventing endocrine resistance should help to improve therapy for the benefit of breast cancer patients.

The development of endocrine therapy for women with breast cancer

The development of endocrine therapies has transformed the treatment of patients with breast cancer. The shift from ablative surgery and aggressive chemotherapies to more targeted, better tolerated therapy has improved both mortality and quality of life for patients with hormone-responsive disease. During the 1970s, the selective oestrogen-receptor modulator, tamoxifen, emerged as a new treatment for women with advanced breast cancer. The subsequent development of numerous and diverse selective endocrine therapies such as luteinising hormone-releasing hormone agonists, aromatase inhibitors and oestrogen-receptor antagonists have added further treatment options. Furthermore, with well-tolerated and effective endocrine therapy, adjuvant treatment became an option for patients with early breast cancer. Tamoxifen emerged as the gold standard adjuvant therapy in the 1980s; however, later trials in postmenopausal women showed the aromatase inhibitors offer advantages over tamoxifen. In addition to AIs being indicated as adjuvant therapy, some are also being evaluated for use as a preventative measure in high-risk women. This chronological account outlines key milestones in the evolution of endocrine therapies over the last 40 years, highlighting each class of agent and the key trials that have led to changes in clinical practice. The advances in endocrine therapies outlined here, coupled with advances in breast cancer management and diagnostics, will likely lead to more patient-tailored therapy, resulting in greater clinical benefits and more cost-effective treatment strategies.