Gene Silencing Agents in Breast Cancer

MicroRNAs (miRs) are a class of non-coding RNAs, approximately 20–25 nucleotides long, discovered in the nematode, Caenorhabditis elegans, in 1993. There are two primary categories of non-coding RNA (ncRNA): (1) short interfering RNAs (siRNA) and (2) microRNAs (miRs). In general, miRs control protein production via partially complementary binding of the mRNA 3′UTRs. Both siRNAs and miRNAs are critical regulators of developmental and homeostatic processes as well as disease pathogenesis. While the treatment of advanced stage breast cancer presents several challenges, the development of therapeutic resistance contributes to a high mortality rate. Dysregulation of miR expression has been implicated in progression of breast cancer disease. Moreover, miRs have been found to play a role in the development of drug resistance. In this context, one of the therapeutic potentials of miRNAs is the correlation of circulating miR levels with breast cancer progression stages and disease phenotypes. Secondly, researchers are investigating novel delivery strategies for the substitution or silencing of ncRNAs involved in the disease. This chapter describes both the general miRNA mechanism of actions and the miRNAs related to breast cancer research. It is specifically designed for breast cancer researchers with expertise in gene delivery, clinicians, and clinical translational scientists

Duplicitous Dispositions of Micro-RNAs (miRs) in Breast Cancer

In 1993, a gene silencer known as lin-4 was first discovered in Caenorhabditis elegans and demonstrated to be critical for larval development. Lin-4 belongs to a family of signaling molecules known as non-protein coding microRNAs (miRNAs) which are not only highly conserved in humans, but also involved in the fundamental processes of oncogenesis. While miRNAs are not translated to proteins themselves, they are capable of regulating the expression and translation of other genes thus affecting a multitude of biological and pathological pathways as well as those essential to the malignant landscape. The aim of this chapter is to explore the diverse roles of miRNAs in the context of breast cancer. Following a brief overview of miRNA biogenesis, this chapter covers the production of miRNAs by tumor cells and stromal cells, onco-suppressor miRNAs, use as therapeutics, contribution to therapeutic resistance, and finally their emerging role as biomarkers

Metabolic Reprogramming of Triple-Negative Breast Cancer: The Role of miRNAs

MicroRNAs (miRNAs) are well known to influence the expression of the genes that regulate critical cellular functions. Various reports have suggested that they play critical roles in breast cancer metabolism through the regulation of various metabolic pathways, including the metabolism of glucose, lipids, glycolysis and the mitochondrial tricarboxylic acid cycle (TCA). miRNAs regulate the metabolic process by targeting key molecules (enzymes, kinases transporters) or by modifying the expression of key transcription molecules. In addition, miRNAs can indirectly regulate mRNA translation by targeting chromatin-remodeling enzymes. Furthermore, miRNAs influence the expression of both oncogenes and tumor suppressors and have a major impact on PI3K/AKT, HIF, and MYC signal transduction, which contributes to the metabolic phenotype in human cancer. Although human epidermal growth factor and endocrine therapies have been effective in treating breast cancer, for locally advanced and distant metastases mortality remains high. Drug resistance and recurrence remain major hurdles for advanced breast cancer therapy. Given the critical influence of metabolic reprogramming in the progression of neoplasm, tumorigenesis and metastasis, research should focus on novel targets of metabolic enzymes to reverse drug resistance and improve overall survival rates. Blocking the miRNAs that contribute to metabolic reprogramming or the use of exogenous miRNAs as antisense oligonucleotides, may be an effective way to treat aggressive, chemo-resistant cancers. This review summarizes current knowledge on the mechanism of action of miRNAs in altering the metabolism of cancer cells and presents possible therapeutic approaches to treating breast cancers that are resistant to current drugs

Robust Expression of Tumor Suppressor miRNA\u27s Let-7 and miR-195 Detected in Plasma of Saudi Female Breast Cancer Patients.

Background Female breast cancer is frequently diagnosed at a later stage and the leading cause of cancer deaths world-wide. Levels of cell-free circulating microRNAs (miRNAs) can potentially be used as biomarkers to measure disease progression in breast cancer patients in a non-invasive way and are therefore of high clinical value. Methods Using quantitative RT-PCR, circulating miRNAs were measured in blood samples collected from disease-free individuals (n = 34), triple-negative breast tumours (TNBC) (n = 36) and luminal tumours (n = 57). In addition to intergroup comparisons, plasma miRNA expression levels of all groups were analyzed against RNASeq data from cancerous breast tissue via The Cancer Genome Atlas (TCGA). Results A differential set of 18 miRNAs were identified in the plasma of breast cancer patients and 10 miRNAs were uniquely identified based on ROC analysis. The most striking findings revealed elevated tumor suppressor let-7 miRNA in luminal breast cancer patients, irrespective of subtype, and elevated miR-195 in plasma of TNBC breast cancer patients. In contrast, hsa-miR-195 and let-7 miRNAs were absent from cancerous TCGA tissue and strongly expressed in surrounding non-tumor tissue indicating that cancerous cells may selectively export tumor suppressor hsa-miR-195 and let-7 miRNAs in order to maintain oncogenesis. Conclusions While studies have indicated that the restoration of let-7 and miR-195 may be a potential therapy for cancer, these results suggested that tumor cells may selectively export hsa-miR-195 and let-7 miRNAs thereby neutralizing their potential therapeutic effect. However, in order to facilitate earlier detection of breast cancer, blood based screening of hsa-miR-195 and let-7 may be beneficial in a female patient cohort

Novel miRNA Targets and Therapies in the Triple-Negative Breast Cancer Microenvironment: An Emerging Hope for a Challenging Disease.

Treatment of triple-negative breast cancer (TNBC) remains challenging because of the heterogeneity of the disease and lack of single targetable driving mutations. TNBC does not rely on estrogen, progesterone or epidermal growth factor receptors and is associated with aggressive disease progression and poor prognosis. TNBC is also characterized by resistance to chemotherapeutics, and response to immunotherapies is limited despite promising results in a subset of TNBC patients. MicroRNAs (miRNAs) have emerged as significant drivers of tumorigenesis and tumor progression in triple-negative breast cancer (TNBC) and present unique opportunities to target various components of the TNBC microenvironment for improved efficacy against this difficult to treat cancer. Effects of miRNAs on multiple targets may improve response rates in the context of this genetically and biologically heterogeneous disease. In this review, we offer a comprehensive view of miRNA regulation in TNBC, treatment challenges presented by TNBC in the context of the tumor microenvironment and stem cell subpopulations, and current and emerging miRNA-based therapeutic strategies targeting various components of the TNBC microenvironment. In addition, we offer insight into novel targets that have potential for treating TNBC through multiple mechanisms in the tumor microenvironment simultaneously and those that may be synergistic with standard chemotherapies

Clinical Identification of Dysregulated Circulating microRNAs and Their Implication in Drug Response in Triple Negative Breast Cancer (TNBC) by Target Gene Network and Meta-Analysis

Resistance to therapy is a persistent problem that leads to mortality in breast cancer, particularly triple-negative breast cancer (TNBC). MiRNAs have become a focus of investigation as tissue-specific regulators of gene networks related to drug resistance. Circulating miRNAs are readily accessible non-invasive potential biomarkers for TNBC diagnosis, prognosis, and drug-response. Our aim was to use systems biology, meta-analysis, and network approaches to delineate the drug resistance pathways and clinical outcomes associated with circulating miRNAs in TNBC patients. MiRNA expression analysis was used to investigate differentially regulated circulating miRNAs in TNBC patients, and integrated pathway regulation, gene ontology, and pharmacogenomic network analyses were used to identify target genes, miRNAs, and drug interaction networks. Herein, we identified significant differentially expressed circulating miRNAs in TNBC patients (miR-19a/b-3p, miR-25-3p, miR-22-3p, miR-210-3p, miR-93-5p, and miR-199a-3p) that regulate several molecular pathways (PAM (PI3K/Akt/mTOR), HIF-1, TNF, FoxO, Wnt, and JAK/STAT, PD-1/PD-L1 pathways and EGFR tyrosine kinase inhibitor resistance (TKIs)) involved in drug resistance. Through meta-analysis, we demonstrated an association of upregulated miR-93, miR-210, miR-19a, and miR-19b with poor overall survival outcomes in TNBC patients. These results identify miRNA-regulated mechanisms of drug resistance and potential targets for combination with chemotherapy to overcome drug resistance in TNBC. We demonstrate that integrated analysis of multi-dimensional data can unravel mechanisms of drug-resistance related to circulating miRNAs, particularly in TNBC. These circulating miRNAs may be useful as markers of drug response and resistance in the guidance of personalized medicine for TNBC

Genomic Alterations Affecting Competitive Endogenous RNAs (ceRNAs) and Regulatory Networks (ceRNETs) with Clinical Implications in Triple-Negative Breast Cancer (TNBC)

The concept of competitive endogenous RNA regulation has brought on a change in the way we think about transcriptional regulation by miRNA–mRNA interactions. Rather than the relatively simple idea of miRNAs negatively regulating mRNA transcripts, mRNAs and other non-coding RNAs can regulate miRNAs and, therefore, broad networks of gene products through competitive interactions. While this concept is not new, its significant roles in and implications on cancer have just recently come to light. The field is now ripe for the extrapolation of technologies with a substantial clinical impact on cancer. With the majority of the genome consisting of non-coding regions encoding regulatory RNAs, genomic alterations in cancer have considerable effects on these networks that have been previously unappreciated. Triple-negative breast cancer (TNBC) is characterized by high mutational burden, genomic instability and heterogeneity, making this aggressive breast cancer subtype particularly relevant to these changes. In the past few years, much has been learned about the roles of competitive endogenous RNA network regulation in tumorigenesis, disease progression and drug response in triple-negative breast cancer. In this review, we present a comprehensive view of the new knowledge and future perspectives on competitive endogenous RNA networks affected by genomic alterations in triple-negative breast cancer. An overview of the competitive endogenous RNA (ceRNA) hypothesis and its bearing on cellular function and disease is provided, followed by a thorough review of the literature surrounding key competitive endogenous RNAs in triple-negative breast cancer, the genomic alterations affecting them, key disease-relevant molecular and functional pathways regulated by them and the clinical implications and significance of their dysregulation. New knowledge of the roles of these regulatory mechanisms and the current acceleration of research in the field promises to generate insights into the diagnosis, classification and treatment of triple-negative breast cancer through the elucidation of new molecular mechanisms, therapeutic targets and biomarkers

Translational Implications of Dysregulated Pathways and microRNA Regulation in Quadruple-Negative Breast Cancer

Triple-negative breast cancers (HER2−, ER−, PR−) continue to present a unique treatment challenge and carry unfavorable prognoses. The elucidation of novel therapeutic targets has necessitated the re-evaluation of stratification approaches to best predict prognosis, treatment response and theranostic and prognostic markers. Androgen receptor expression and function have important implications on proliferation, tumor progression, immunity and molecular signaling in breast cancer. Accordingly, there has been increasing support for classification of androgen receptor-negative triple-negative breast cancer or quadruple-negative breast cancer (QNBC). QNBC has unique molecular, signaling and expression regulation profiles, particularly those affected by microRNA regulatory networks. microRNAs are now known to regulate AR-related targets and pathways that are dysregulated in QNBC, including immune checkpoint inhibitors (ICIs), SKP2, EN1, ACSL4 and EGFR. In this review, we explore and define the QNBC tumor subtype, its molecular and clinical distinctions from other subtypes, miRNA dysregulation and function in QNBC, and knowledge gaps in the field. Potential insights into clinical and translational implications of these dysregulated networks in QNBC are discussed