LidNA, a novel miRNA inhibitor constructed with unmodified DNA

Improvement of a miRNA inhibitor by intracellular selection

Sequences surrounding the miRNA binding domain of the miRNA inhibitor LidNA were selected intracellularly. The library was transfected into cells, and then, inhibitors that were associated with argonaute 2 were selected. The potent inhibitors were slowly degraded intracellularly, while the lower-activity inhibitors were rapidly degraded. A combination of the selected sequences surrounding the miRNA binding domain enhanced miRNA inhibitory activity.

ABBREVIATIONS

LidNA: DNA that puts a lid on miRNA function; LNA: locked nucleic acid; Ago2: argonaute 2; LNA: locked nucleic acid.

Structural improvement of LidNA: delta-type LidNA is a potent miRNA inhibitor constructed with unmodified DNA

Many miRNA inhibitors have been developed, including chemically modified oligonucleotides, such as 2'-O-methylated RNA and locked nucleic acid (LNA). Unmodified DNA has not yet been reported as a miRNA inhibitor due to relatively low DNA/miRNA binding affinity. We designed a structured DNA, LidNA, which was constructed with unmodified DNA, consisting of a complementary sequence to the target miRNA flanked by two structured DNA regions, such as double-stranded DNA. LidNA inhibited miRNA activity more potently than 2'-O-methylated RNA or LNA. To optimize LidNA, two double-stranded regions were joined, causing the molecule to assume a delta-like shape, which we termed delta-type LidNA. Delta-type LidNAs were developed to target endogenous and exogenous miRNAs, and exhibited potent miRNA inhibitory effects with a duration of at least 10 days. Delta-type LidNA-21, which targeted miR-21, inhibited the growth of cancer cell lines. This newly developed LidNA could contribute to miRNA studies across multiple fields.Abbreviations: LidNA: DNA that puts a lid on miRNA function; LNA: locked nucleic acid; 3'-UTR: 3'-untranslated regions; RISC: RNA-induced silencing complex; MBL: Molecular beacon-like LidNA; YMBL: Y-type molecular beacon-like LidNA; TDMD: target-directed microRNA degradation.

Improved cancer inhibition by miR-143 with a longer passenger strand than natural miR-143

We improved miR-143, which inhibits the growth of cancer cells, by the replacement of the passenger strand. As a result, new miR-143 variants were developed with a single mismatch at the 4th position from the 3'-terminal of the guide strand and an RNA passenger strand with a G-rich flanking DNA region. A reporter gene assay showed that the 80% inhibitory concentration of the new miR-143, long miR-143, was 69 pM, which was three times lower than that of natural miR-143. Long miR-143 inhibited the growth of two cancer cell lines, HeLa-S3 and MIAPaCa-2, more effectively than natural miR-143. This method could be applied to other miRNA families and should be useful for the development of miRNA drugs.

Potential Diagnostic, Prognostic and Therapeutic Targets of MicroRNAs in Human Gastric Cancer

Human gastric cancer (GC) is characterized by a high incidence and mortality rate, largely because it is normally not identified until a relatively advanced stage owing to a lack of early diagnostic biomarkers. Gastroscopy with biopsy is the routine method for screening, and gastrectomy is the major therapeutic strategy for GC. However, in more than 30% of GC surgical patients, cancer has progressed too far for effective medical resection. Thus, useful biomarkers for early screening or detection of GC are essential for improving patients’ survival rate. MicroRNAs (miRNAs) play an important role in tumorigenesis. They contribute to gastric carcinogenesis by altering the expression of oncogenes and tumor suppressors. Because of their stability in tissues, serum/plasma and other body fluids, miRNAs have been suggested as novel tumor biomarkers with suitable clinical potential. Recently, aberrantly expressed miRNAs have been identified and tested for clinical application in the management of GC. Aberrant miRNA expression profiles determined with miRNA microarrays, quantitative reverse transcription-polymerase chain reaction and next-generation sequencing approaches could be used to establish sample specificity and to identify tumor type. Here, we provide an up-to-date summary of tissue-based GC-associated miRNAs, describing their involvement and that of their downstream targets in tumorigenic and biological processes. We examine correlations among significant clinical parameters and prognostic indicators, and discuss recurrence monitoring and therapeutic options in GC. We also review plasma/serum-based, GC-associated, circulating miRNAs and their clinical applications, focusing especially on early diagnosis. By providing insights into the mechanisms of miRNA-related tumor progression, this review will hopefully aid in the identification of novel potential therapeutic targets.

MiRNA inhibition in tissue engineering and regenerative medicine

MicroRNAs (miRNAs) are noncoding RNAs that provide an endogenous negative feedback mechanism for translation of messenger RNA (mRNA) into protein. Single miRNAs can regulate hundreds of mRNAs, enabling miRNAs to orchestrate robust biological responses by simultaneously impacting multiple gene networks. MiRNAs can act as master regulators of normal and pathological tissue development, homeostasis, and repair, which has motivated expanding efforts toward the development of technologies for therapeutically modulating miRNA activity for regenerative medicine and tissue engineering applications. This review highlights the tools currently available for miRNA inhibition and their recent therapeutic applications for improving tissue repair.

Macro and small over micro: macromolecules and small molecules that regulate microRNAs

Given the correlation between the deregulation of specific miRNAs and disease onset, it is critical to identify miRNA regulators that effectively control miRNAs involved in the pathogenesis of target diseases. This review provides the latest update on oligonucleotide- and small-molecule-based miRNA regulators, and discusses assays developed to screen for small-molecule regulators.

Binding affinity of ssDNA is improved by attachment of dsDNA regions

LidNA, a microRNA inhibitor consisting of a microRNA binding ssDNA region sandwiched between dsDNA regions had higher affinity to target oligonucleotides than that without dsDNA region. This enhancement in affinity was found to be owing to the suppressed mobility of ssDNA region by the presence of dsDNA regions.

Clinical application of microRNA in gastric cancer in Eastern Asian area

Recent research has shown that microRNA (miRNA), which is involved in almost every step of gastric carcinogenesis, has broad prospective application in diagnosis and therapy of gastric carcinoma. Eastern Asia (South Korea, Japan and China) has the highest incidence of gastric cancer in the world. There were 988  000 new cases of gastric cancer worldwide and 736  000 deaths in 2008. Approximately 60% of the cases of gastric cancer are found in East Asia (mainly China). We herein provide a brief review of the clinical applications of miRNA, which include the following aspects: (1) miRNA may serve as a potential new generation of tumor markers; (2) a complete miRNA expression profile is highly specific, can reflect the evolutionary lineage and differentiation of tumors, and be used to carry out diversity analysis; (3) detecting specific miRNA expression in peripheral blood will become a new method for diagnosis of gastric cancer; (4) miRNA can predict prognosis of gastric cancer; (5) miRNA has predictive value in determining chemotherapy and radiotherapy resistance; and (6) miRNA could be a type of innovative drug. Finally, we focus on assessing the value of miRNA from laboratory to clinical application and the challenges it faces in East Asia.