Current Drug Targets - Volume 14, Issue 10, 2013

MicroRNAs (miRNAs) are short non-coding RNAs that have been recognized to regulate the expression of uncountable number of genes. Their aberrant expression has been found to be linked to the pathology of many diseases including cancer. There is a drive to develop miRNA targeted therapeutics for different diseases especially cancer. Nevertheless, reining in these short non-coding RNAs is not as straightforward as originally thought. This is in view of the recent discoveries that miRNAs are under epigenetic regulations at multiple levels. Exportin 5 protein (XPO5) nuclear export mediated regulation of miRNAs is one such important epigenetic mechanism. XPO5 is responsible for exporting precursor miRNAs through the nuclear membrane to the cytoplasm, and is thus a critical step in miRNA biogenesis. A number of studies have shown that variations in components of the miRNA biogenesis pathways, particularly the aberrant expression of XPO5, increase the risk of developing cancer. In addition to XPO5, the Exportin 1 protein (XPO1) or chromosome region maintenance 1 (CRM1) can also carry miRNA export function. These findings are supported by pathway analyses that reveal certain miRNAs as direct interaction partners of CRM1. An in depth understanding of miRNA export mediated regulatory mechanisms is important for the successful design of clinically viable therapeutics. In this review, we describe the current knowledge on the mechanisms of miRNA nuclear transport mediated regulation and propose strategies to selectively block this important mechanism in cancer.

Pancreatic cancer (PC) is the fourth leading cause of cancer related deaths in the U.S., with a less than 6% fiveyear survival rate. Treatment is confounded by advanced stage of disease at presentation, frequent metastasis to distant organs at the time of diagnosis and resistance to conventional chemotherapy. In addition, the molecular pathogenesis of the disease is unclear. The extensive study of miRNAs over the past several years has revealed that miRNAs are frequently de-regulated in pancreatic cancer and contribute to the pathogenesis and aggressiveness of the disease. Several studies have tackled the practical difficulties in the application of miRNAs as viable therapeutic and diagnostic tools. Given that a single miRNA can affect a myriad of cellular processes, successful targeting of miRNAs as therapeutic agents could likely yield dramatic results. The current review attempts to summarize the advances in the field and assesses the prospects for miRNA profiling and targeting in aiding PC treatment.

The predominance of insulin resistance, T2D linked pancreatic cancer has increased throughout the world. The insulin/IGF signaling pathway related to insulin resistance, T2D and pancreatic cancer has been described. In this context, we have demonstrated the role of miRNAs in cancer progression and control of miRNAs in insulin/IGF signaling pathway, and pancreatic cancer. In this paper, an overview was depicted about the role of following miRNAs in pancreatic development and insulin secretion (miR-375, miR-7, miR-124a2, miR-195, miR-126, miR-9, miR-96, miR-34a); insulingrowth factor-1 receptor expression (miR-7, miR-139, miR-145, miR-1); the diabetes-associated pancreatic cancer pathway genes such as IRS, PI3K, AKT/PKB (miR-128a, miR-19a, miR-21, miR-29 a/b/c); mTOR protein regulation (miR- 99, miR-21, miR-126, and miR-146a) etc. At last, we have also explained the role of miRNAs in diagnostic marker (miR- 200, miR-21, miR-103, miR-107, and miR-155) and as a therapeutic modulator (miR-34, miR-21, miR-221, and miR-101) in pancreatic cancer.

Solar ultraviolet (UV) radiation, an ubiquitous environmental carcinogen, is classified depending on the wavelength, into three regions; short-wave UVC (200–280 nm), mid-wave UVB (280–320 nm), and long-wave UVA (320– 400 nm). The human skin, constantly exposed to UV radiation, particularly the UVB and UVA components, is vulnerable to its various deleterious effects such as erythema, photoaging, immunosuppression and cancer. To counteract these and for the maintenance of genomic integrity, cells have developed several protective mechanisms including DNA repair, cellcycle arrest and apoptosis. The network of damage sensors, signal transducers, mediators, and various effector proteins is regulated through changes in gene expression. MicroRNAs (miRNAs), a group of small non-coding RNAs, act as posttranscriptional regulators through binding to complementary sequences in the 3´-untranslated region of their target genes, resulting in either translational repression or target degradation. Recent studies show that miRNAs add an additional layer of complexity to the intricately controlled cellular responses to UV radiation. This review summarizes our current knowledge of the role of miRNAs in the regulation of the human skin response upon exposure to UV radiation.

Overexpression of oncomiR-21 has been observed in most cancer types, such as leukemia. This miR has been implicated in a number of cellular processes, including chemoresistance, possibly by directly modulating the expression of several apoptotic related proteins. It was recently shown to directly target Bcl-2 mRNA and upregulate Bcl-2 protein expression. Nevertheless, the possible effect of miR-21 in autophagy has never been addressed. This study investigates the effects of targeting miR-21 with antimiRs on chronic myeloid leukemia cellular autophagy and on associated drug sensitivity. We observed that miR-21 downregulation decreased cellular viability and proliferation, although no changes to the normal cell cycle profile were observed. miR-21 downregulation also caused increased programmed cell death and a decrease in the expression levels of Bcl-2 protein, although PARP cleavage was not affected, indicating that apoptosis was not the relevant mechanism underlying the observed results. Treatment with antimiR-21 caused an increase in the autophagy related proteins Beclin-1, Vps34 and LC3-II. Accordingly, autophagic vacuoles were visualized both by monodansylcadaverine (MDC) and acridine orange (AO) staining and also by transmission electron microscopy (TEM). Additionally, miR-21 downregulation increased K562 and KYO-1 cellular sensitivity to etoposide or doxorubicin. This chemosensitivity was reverted by pre-treating cells with 3-MA, an autophagy inhibitor. Finally, serum starvation (an autophagy inducer) also increased sensitivity to these drugs, confirming that autophagy sensitized these cells to the effect of these drugs. To the best of our knowledge, this is the first description of autophagy induction via miR-21 targeting and its involvement in drug sensitivity.

The progress in the understanding of biological events underlying multiple myeloma (MM) development and progression has allowed the design of molecularly targeted therapies (MTTs) for this disease and several new compounds are presently under investigation in the preclinical and clinical settings. The recent discovery that miRNAs, and short non coding RNAs in general, are involved in the pathogenesis of cancer has raised the issue whether a novel therapeutic approach should be provided by selective interference with miRNA network. This review will focus on the rationale of miRNA-based therapeutics, providing the most relevant information on biogenesis and technical issues in miRNA analysis. Finally, a detailed overview of the recent findings on miRNA therapeutics of MM will be discussed.

Although genistein has been shown to inhibit tumorigenesis in a variety of human cancers including pancreatic cancer (PC), the exact molecular mechanism of its anti-cancer effects has not yet been fully elucidated. Recently, microRNAs (miRNAs) have been reported to regulate multiple aspects of tumor development and progression, indicating that targeting miRNAs could be a novel strategy to treat human cancers. In the current study, we investigated whether a natural compound genistein could down-regulate onco-miR-223, resulting in the inhibition of cell growth and invasion, and induction of apoptosis in PC cells. We found that genistein treatment significantly inhibited miR-223 expression and up-regulated Fbw7, one of the targets of miR-223. Moreover, down-regulation of miR-223 inhibited cell growth and induced apoptosis in PC cells. These findings suggest that genistein exerts its anti-tumor activity partly through downregulation of miR-223 in PC cells.

The Notch signaling plays a key role in cell differentiation, survival, and proliferation through diverse mechanisms. Thus, alterations of the Notch signaling can lead to a variety of disorders including human malignancies. Of considerable interest, recent evidence indicates that there is a significant cross-talk between Notch and microRNAs. As a key component of the Notch-mediated transcription complex, Notch can regulate expression of a number of microRNAs; at the same time, Notch ligands, Notch receptor or Notch effectors are also subject to regulation by microRNAs. Thus, a better understanding of how Notch signaling interacts with microRNAs in the context of cancer will help identify novel biomarkers and therapeutic targets. In this review, we update on recent findings on microRNAs interacting with Notch signaling at various levels, leading to tumorigenesis or chemoresistance. We also highlight the therapeutic potential of targeting Notch signaling and related microRNAs.

MicroRNAs (miRNAs) are small single-strand non-coding endogenous RNAs that regulate gene expression by multiple mechanisms. Recent evidence suggests that miRNAs are critically involved in the pathogenesis, evolution, and progression of cancer. The miRNAs are also crucial for the regulation of cancer stem cells (CSCs). In addition, miRNAs are known to control the processes of Epithelial-to-Mesenchymal Transition (EMT) of cancer cells. This evidence suggests that miRNAs could serve as targets in cancer treatment, and as such manipulating miRNAs could be useful for the killing CSCs or reversal of EMT phenotype of cancer cells. Hence, targeting miRNAs, which are deregulated in cancer, could be a promising strategy for cancer therapy. Recently, the regulation of miRNAs by natural, nontoxic chemopreventive agents including curcumin, resveratrol, isoflavones, (-)-epigallocatechin-3-gallate (EGCG), lycopene, 3,3’- diindolylmethane (DIM), and indole-3-carbinol (I3C) has been described. Therefore, natural agents could inhibit cancer progression, increase drug sensitivity, reverse EMT, and prevent metastasis though modulation of miRNAs, which will provide a newer therapeutic approach for cancer treatment especially when combined with conventional therapeutics.

Failure of conventional as well as target-based therapy against the advanced metastatic cancers is a significant clinical problem. While some cancers, such as pancreatic cancer, respond poorly to any kind of therapies, tumor relapse is often observed in many other cancer types after initial therapeutic response. Hence, significant research is being conducted to understand the mechanisms underlying therapeutic refractoriness of cancer. During the past decade, cancer stem cell (CSC) hypothesis has gained significant experimental and clinical support, and CSCs have emerged as potentially useful pharmacologic targets. MicroRNAs (miRNAs) are a group of small (˜18–25 nucleotides) non-protein encoding RNAs that are now established as important regulators of gene expression. They can function as tumor promoters (oncomirs) or suppressors (anti-oncomirs) and thus hold profound implications for cancer therapy. Recent studies have identified several miRNAs to be differentially expressed in CSCs and established their role in targeting genes and pathways supporting cancer stemness properties. Here, we discuss these findings and review recent advances in miRNA-based strategies to exploit therapeutic potential of miRNAs in cancer treatment.

Recently, microRNAs (miRNAs) including miR-34 family have been found to play a critical role in tumorigenesis through regulating the expression of its target genes, which are involved in many cellular processes such as cell proliferation, survival, apoptosis, migration, invasion and angiogenesis. Thus, this review described the role of miR-34 family and how its deregulation is involved in the development and progression of human malignances. Moreover, we described the potential role of miR-34 as a novel biomarker for tumor diagnosis. Furthermore, we summarized that miR-34 family could be up-regulated by natural compounds in human cancers. Therefore, targeting miR-34 family could be a novel strategy for achieving better treatment outcome of cancer patients in the future.

The transcription factor Forkhead box protein M1 (FOXM1) is overexpressed in the majority of cancer patients. This overexpression is implicated to play a role in the pathogenesis, progression, and metastasis of cancer. This important role of FOXM1 demonstrates its significance to cancer therapy. MicroRNAs (miRNAs) are small noncoding, endogenous, single-stranded RNAs that are pivotal posttranscriptional gene expression regulators. MiRNAs aberrantly expressed in cancer cells have important roles in tumorigenesis and progression. Currently, miRNAs are being studied as diagnostic and prognostic biomarkers and therapeutic tools for cancer. The rapid discovery of many target miRNAs and their relevant pathways has contributed to the development of miRNA-based therapeutics for cancer. In this review, we summarize the latest and most significant findings on FOXM1 and miRNA involvement in cancer development and describe the role/roles of miRNA/FOXM1 signaling pathways in cancer initiation and progression. Targeting FOXM1 via regulation of miRNA expression may have a role in cancer treatment, although the miRNA delivery method remains the key challenge to the establishment of this novel therapy.

The nociceptin system, which consists of endogenous nociceptin/orphanin FQ and NOP receptors, is present in the central nervous system (CNS), as well as respiratory, cardiovascular, urogenital and gastrointestinal (GI) tissues. It is critically involved in nociception and pain signaling, as well as modulation of hormone and neurotransmitter release, stress responses and reversal of stress-induced analgesia. In the GI tract, the nociceptin system participates in the maintenance of homeostasis by affecting secretion and motility. Here we give an overview on the nociceptin system in the GI tract. The nociceptin system is an attractive target for novel drugs, which may be effective in the treatment of inflammatory or functional GI disorders, such as inflammatory bowel diseases (IBD) and irritable bowel syndrome (IBS).

Curcumin, a natural polyphenolic compound present in turmeric, exhibited multiple pharmacological activities. Extensive studies in last two decade suggested that curcumin possesses anti-inflammatory, anticancer, antiviral, anti-amyloid, antiarthritic and antioxidant properties. The mechanism for these effects involves modulation of several signaling transduction pathways. Various clinical studies have suggested that curcumin might be a potential candidate for the prevention and/or treatment of a variety of colonic diseases such as ulcerative colitis, Crohn’s disease and colonic cancer. However, several evidences suggested the role of curcumin in multiple diseases, but the major challenge is to obtain optimum therapeutic levels of curcumin due to its low solubility and poor bioavailability. Improved absorption and cellular uptake of curcumin can be achieved through alteration in formulation properties and novel approaches in delivery systems. This review presents an overview of the background of curcumin, pharmacology, pharmacokinetics, clinical evidence in chemoprevention of bowel diseases and recent approaches to deliver curcumin for improved cellular uptake and bioavailability.