Targeted therapies through microRNAs: pulp or fiction?

Breast cancer: miRNAs monitoring chemoresistance and systemic therapy

With a high mortality rate that accounts for millions of cancer-related deaths each year, breast cancer is the second most common malignancy in women. Chemotherapy has significant potential in the prevention and spreading of breast cancer; however, drug resistance often hinders therapy in breast cancer patients. The identification and the use of novel molecular biomarkers, which can predict response to chemotherapy, might lead to tailoring breast cancer treatment. In this context, accumulating research has reported microRNAs (miRNAs) as potential biomarkers for early cancer detection, and are conducive to designing a more specific treatment plan by helping analyze drug resistance and sensitivity in breast cancer treatment. In this review, miRNAs are discussed in two alternative ways-as tumor suppressors to be used in miRNA replacement therapy to reduce oncogenesis and as oncomirs to lessen the translation of the target miRNA. Different miRNAs like miR-638, miR-17, miR-20b, miR-342, miR-484, miR-21, miR-24, miR-27, miR-23 and miR-200 are involved in the regulation of chemoresistance through diverse genetic targets. For instance, tumor-suppressing miRNAs like miR-342, miR-16, miR-214, and miR-128 and tumor-promoting miRNAs like miR101 and miR-106-25 cluster regulate the cell cycle, apoptosis, epithelial to mesenchymal transition and other pathways to impart breast cancer drug resistance. Hence, in this review, we have discussed the significance of miRNA biomarkers that could assist in providing novel therapeutic targets to overcome potential chemotherapy resistance to systemic therapy and further facilitate the design of tailored therapy for enhanced efficacy against breast cancer.

Neuroendocrine microRNAs linked to energy homeostasis: future therapeutic potential

The brain orchestrates whole-body metabolism through an intricate system involving interneuronal crosstalk and communication. Specifically, a key player in this complex circuitry is the hypothalamus that controls feeding behaviour, energy expenditure, body weight and metabolism, whereby hypothalamic neurons sense and respond to circulating hormones, nutrients, and chemicals. Dysregulation of these neurons contributes to the development of metabolic disorders, such as obesity and type 2 diabetes. The involvement of hypothalamic microRNAs, post-transcriptional regulators of gene expression, in the central regulation of energy homeostasis has become increasingly apparent, although not completely delineated. This review summarizes current evidence demonstrating the regulation of feeding-related neuropeptides by brain-derived microRNAs as well as the regulation of specific miRNAs by nutrients and other peripheral signals. Moreover, the involvement of microRNAs in the central nervous system control of insulin, leptin, and estrogen signal transduction is examined. Finally, the therapeutic and diagnostic potential of microRNAs for metabolic disorders will be discussed and the regulation of brain-derived microRNAs by nutrients and other peripheral signals is considered. Demonstrating a critical role of microRNAs in hypothalamic regulation of energy homeostasis is an innovative route to uncover novel biomarkers and therapeutic candidates for metabolic disorders.

MicroRNA Expression Profiles and Breast Cancer Chemotherapy

Breast cancer is the most common malignancy diagnosed in women. Traditionally, radical surgical resection was the cornerstone of breast cancer management, with limited exceptions. In recent times, our enhanced appreciation of the biomolecular characteristics of breast cancer has transformed the treatment paradigm to include prescription of chemotherapeutical agents, radiotherapies, targeted therapies, as well as more refined surgical approaches. While treatments with such modalities have enhanced clinico-oncological outcomes for breast cancer patients, the efforts of oncological and translational research have concentrated on the identification of novel biomarkers which may successfully inform prognosis and response to therapies, improve current therapeutic strategies, and enhance prognostication. Mi(cro)RNAs are small, non-coding molecules which are known to play regulatory roles in governing gene expression and cellular activity. Measurement of miRNA expression profiles have been illustrated to inform the response to therapies, such as conventional chemotherapy, and are currently undergoing assessment as means of enhancing treatment strategies with these cytotoxic agents. Herein, this review outlines how chemotherapy prescription has revolutionised breast cancer treatment and illustrates the novel role of miRNAs as biomarkers capable of enhancing current therapeutic strategies using chemotherapy in patients being treated with curative intent for breast cancer.

Exploring circulating micro-RNA in the neoadjuvant treatment of breast cancer

Breast cancer is the most frequently diagnosed malignancy amongst females worldwide. In recent years the management of this disease has transformed considerably, including the administration of chemotherapy in the neoadjuvant setting. Aside from increasing rates of breast conserving surgery and enabling surgery via tumour burden reduction, use of chemotherapy in the neoadjuvant setting allows monitoring of in vivo tumour response to chemotherapeutics. Currently, there is no effective means of identifying chemotherapeutic responders from non‐responders. Whilst some patients achieve complete pathological response (pCR) to chemotherapy, a good prognostic index, a proportion of patients derive little or no benefit, being exposed to the deleterious effects of systemic treatment without any knowledge of whether they will receive benefit. The identification of predictive and prognostic biomarkers could confer multiple benefits in this setting, specifically the individualization of breast cancer management and more effective administration of chemotherapeutics. In addition, biomarkers could potentially expedite the identification of novel chemotherapeutic agents or increase their efficacy. Micro‐RNAs (miRNAs) are small non‐coding RNA molecules. With their tissue‐specific expression, correlation with clinicopathological prognostic indices and known dysregulation in breast cancer, miRNAs have quickly become an important avenue in the search for novel breast cancer biomarkers. We provide a brief history of breast cancer chemotherapeutics and explore the emerging field of circulating (blood‐borne) miRNAs as breast cancer biomarkers for the neoadjuvant treatment of breast cancer. Established molecular markers of breast cancer are outlined, while the potential role of circulating miRNAs as chemotherapeutic response predictors, prognosticators or potential therapeutic targets is discussed.

MicroRNA-141-3p and miR-200a-3p regulate insulin-like growth factor 2 during mouse placental development

Insulin-like growth factor 2 (IGF2) plays a vital role in fetal and placental development throughout gestation. Placental expression of IGF2 decreases substantially in intra-uterine growth restriction (IUGR) and Igf2 null mice develop small placentas. In this report, we examined the role of microRNAs in regulating Igf2 gene expression during mouse placental development. Using bioinformatic analysis, we have identified microRNAs that have conserved binding sites in the 3'-UTR of Igf2. Using luciferase reporter assay, we demonstrated that miR141-3p and miR-200a-3p mimics substantially down regulated relative luciferase activity by binding to 3'-UTR of Igf2, which was reversed by using miR141-3p and miR-200a-3p inhibitors. Furthermore, in a similar assay, use of Igf2 3'-UTR that lacked the binding site for the microRNAs did not have any effect on luceiferase activity. Interestingly, the expression of miR141-3p and miR-200a-3p were inversely and temporally correlated to the expression of IGF2 during mouse placental development. Overexpression of miR141-3p and miR-200a-3p in mouse trophoblast stem cells suppressed endogenous expression of IGF2. Consequently, IGF2 silencing by miR141-3p and miR-200a-3p diminished Akt activation in mouse trophoblast stem cells. Our study provides evidence for regulation of Igf2 by microRNAs and further elucidates the role of miR141-3p and miR-200a-3p in the mouse placental development.

MicroRNAs and metabolism crosstalk in energy homeostasis

In record time, microRNAs (miRNAs) have acquired the respected stature of important natural regulators of global gene expression. Multiple studies have demonstrated that a large number of miRNAs are under the control of various metabolic stimuli, including nutrients, hormones, and cytokines. Conversely, it is now well recognized that miRNAs control metabolism, thereby generating a bidirectional functional link, which perturbs energy homeostasis in case of disconnection in the miRNA-metabolism interplay. A challenging road lies ahead for defining the role of miRNAs in the pathogenesis of diseases such as diabetes and for establishing their usefulness as new medications and clinically reliable biomarkers.

Circulating microRNAs in hematological diseases: principles, challenges, and perspectives

The complex microRNA (miRNA) network plays an important role in the regulation of cellular processes such as development, differentiation, and apoptosis. Recently, the presence of cell-free miRNAs that circulate in body fluids was discovered. The ability of these circulating miRNAs to mirror physiological and pathophysiological conditions as well as their high stability in stored patient samples underlines the potential of these molecules to serve as biomarkers for various diseases. In this review, we describe recent findings in miRNA-mediated cell-to-cell communication and the functions of circulating miRNAs in the field of hematology. Furthermore, we discuss current approaches to design biomarker studies with circulating miRNAs. This article critically reviews the novel field of circulating miRNAs and highlights their suitability for clinical and basic research in addition to their potential as a novel class of biomarkers.