MicroRNA and brain tumors: a cause and a cure?

Cerebrospinal Fluid Liquid Biopsies in the Evaluation of Adult Gliomas

PURPOSE OF REVIEW

This review aims to discuss recent research regarding the biomolecules explored in liquid biopsies and their potential clinical uses for adult-type diffuse gliomas.

RECENT FINDINGS

Evaluation of tumor biomolecules via cerebrospinal fluid (CSF) is an emerging technology in neuro-oncology. Studies to date have already identified various circulating tumor DNA, extracellular vesicle, micro-messenger RNA and protein biomarkers of interest. These biomarkers show potential to assist in multiple avenues of central nervous system (CNS) tumor evaluation, including tumor differentiation and diagnosis, treatment selection, response assessment, detection of tumor progression, and prognosis. In addition, CSF liquid biopsies have the potential to better characterize tumor heterogeneity compared to conventional tissue collection and CNS imaging. Current imaging modalities are not sufficient to establish a definitive glioma diagnosis and repeated tissue sampling via conventional biopsy is risky, therefore, there is a great need to improve non-invasive and minimally invasive sampling methods. CSF liquid biopsies represent a promising, minimally invasive adjunct to current approaches which can provide diagnostic and prognostic information as well as aid in response assessment.

Discerning the Prospects of miRNAs as a Multi-Target Therapeutic and Diagnostic for Alzheimer's Disease

Although over the last few decades, numerous attempts have been made to halt Alzheimer's disease (AD) progression and mitigate its symptoms, only a few have been proven beneficial. Most medications available, still only cater to the symptoms of the disease rather than fixing the cause at the root level. A novel approach involving the use of miRNAs, which work on the principle of gene silencing, is being explored by scientists. Naturally present miRNAs in the biological system help to regulate various genes than may be implicated in AD-like BACE-1 and APP. One miRNA thus, holds the power to keep a check on several genes, conferring it the ability to be used as a multi-target therapeutic. With aging and the onset of diseased pathology, dysregulation of these miRNAs is observed. This flawed miRNA expression is responsible for the unusual buildup of amyloid proteins, fibrillation of tau proteins in the brain, neuronal death and other hallmarks leading to AD. The use of miRNA mimics and miRNA inhibitors provides an attractive perspective for fixing the upregulation and downregulation of miRNAs that led to abnormal cellular activities. Furthermore, the detection of miRNAs in the CSF and serum of diseased patients might be considered an earlier biomarker for the disease. While most of the therapies designed around AD have not succeeded completely, the targeting of dysregulated miRNAs in AD patients might give a new direction to scholars to develop an effective treatment for Alzheimer's disease.

Overview of miR-106a Regulatory Roles: from Cancer to Aging

MicroRNAs (miRNAs) comprise a class of non-coding RNA with extensive regulatory functions within cells. MiR-106a is recognized for its super-regulatory roles in vital processes. Hence, the analysis of its expression in association with diseases has attracted considerable attention for molecular diagnosis and drug development. Numerous studies have investigated miR-106 target genes and shown that this miRNA regulates the expression of some critical cell cycle and apoptosis factors, suggesting miR-106a as an ideal diagnostic and prognostic biomarker with therapeutic potential. Furthermore, the reported correlation between miR-106a expression level and cancer drug resistance has demonstrated the complexity of its functions within different tissues. In this study, we have conducted a comprehensive review on the expression levels of miR-106a in various cancers and other diseases, emphasizing its target genes. The promising findings surrounding miR-106a suggest its potential as a valuable biomolecule. However, further validation assessments and overcoming existing limitations are crucial steps before its clinical implementation can be realized.

MicroRNA as a Potential Therapeutic Molecule in Cancer

Small noncoding RNAs, as post-translational regulators of many target genes, are not only markers of neoplastic disease initiation and progression, but also markers of response to anticancer therapy. Hundreds of miRNAs have been identified as biomarkers of drug resistance, and many have demonstrated the potential to sensitize cancer cells to therapy. Their properties of modulating the response of cells to therapy have made them a promising target for overcoming drug resistance. Several methods have been developed for the delivery of miRNAs to cancer cells, including introducing synthetic miRNA mimics, DNA plasmids containing miRNAs, and small molecules that epigenetically alter endogenous miRNA expression. The results of studies in animal models and preclinical studies for solid cancers and hematological malignancies have confirmed the effectiveness of treatment protocols using microRNA. Nevertheless, the use of miRNAs in anticancer therapy is not without limitations, including the development of a stable nanoconstruct, delivery method choices, and biodistribution. The aim of this review was to summarize the role of miRNAs in cancer treatment and to present new therapeutic concepts for these molecules. Supporting anticancer therapy with microRNA molecules has been verified in numerous clinical trials, which shows great potential in the treatment of cancer.

Mechanisms of temozolomide resistance in glioblastoma - a comprehensive review

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults and has an exceedingly low median overall survival of only 15 months. Current standard-of-care for GBM consists of gross total surgical resection followed by radiation with concurrent and adjuvant chemotherapy. Temozolomide (TMZ) is the first-choice chemotherapeutic agent in GBM; however, the development of resistance to TMZ often becomes the limiting factor in effective treatment. While O6-methylguanine-DNA methyltransferase repair activity and uniquely resistant populations of glioma stem cells are the most well-known contributors to TMZ resistance, many other molecular mechanisms have come to light in recent years. Key emerging mechanisms include the involvement of other DNA repair systems, aberrant signaling pathways, autophagy, epigenetic modifications, microRNAs, and extracellular vesicle production. This review aims to provide a comprehensive overview of the clinically relevant molecular mechanisms and their extensive interconnections to better inform efforts to combat TMZ resistance.

MicroRNA based theranostics for brain cancer: basic principles

BACKGROUND

Because of the complexity of the blood-brain barrier (BBB), brain tumors, especially the most common and aggressive primary malignant tumor type arising from the central nervous system (CNS), glioblastoma, remain an essential challenge regarding diagnostic and treatment. There are no approved circulating diagnostic or prognostic biomarkers, nor novel therapies like immune checkpoint inhibitors for glioblastoma, and chemotherapy brings only minimal survival benefits. The development of molecular biology led to the discovery of new potential diagnostic tools and therapeutic targets, offering the premise to detect patients at earlier stages and overcome the current poor prognosis.

MAIN BODY

One potential diagnostic and therapeutic breakthrough might come from microRNAs (miRNAs). It is well-known that miRNAs play a role in the initiation and development of various types of cancer, including glioblastoma. The review aims to answer the following questions concerning the role of RNA theranostics for brain tumors: (1) which miRNAs are the best candidates to become early diagnostic and prognostic circulating biomarkers?; (2) how to deliver the therapeutic agents in the CNS to overcome the BBB?; (3) which are the best methods to restore/inhibit miRNAs?

CONCLUSIONS

Because of the proven roles played by miRNAs in gliomagenesis and of their capacity to pass from the CNS tissue into the blood or cerebrospinal fluid (CSF), we propose miRNAs as ideal diagnostic and prognostic biomarkers. Moreover, recent advances in direct miRNA restoration (miRNA mimics) and miRNA inhibition therapy (antisense oligonucleotides, antagomirs, locked nucleic acid anti-miRNA, small molecule miRNA inhibitors) make miRNAs perfect candidates for entering clinical trials for glioblastoma treatment.

MicroRNA-10b-5p downregulation inhibits the invasion of glioma cells via modulating homeobox B3 expression

MicroRNA-10b (miR-10b) has been reported to be specifically upregulated in glioma tissues and cell lines. The aim of the present study was to investigate the effect of miR-10b-5p on the proliferation and invasion of glioma cells, and the possible underlying molecular mechanism. Cell viability was evaluated using an MTT assay, and flow cytometry was performed for cell cycle analysis. The effects of miR-10b-5p on glioma cell migration and invasion were assessed using wound healing and Transwell assays, respectively. The activity of matrix metalloproteinase 2 (MMP2) was also determined using zymography. Furthermore, homeobox B3 (HOXB3) mRNA expression in glioma cells was examined using quantitative polymerase chain reaction analysis. The protein expression levels of HOXB3, high mobility group box 1 (HMGB1) and Ras homolog family member C (RhoC) were further measured using western blotting. It was observed that glioma cells transfected with miR-10b-5p inhibitor exhibited significantly decreased proliferation. The wound healing and Transwell assays demonstrated that the miR-10b-5p inhibitor reduced the ability of glioma cells to migrate and invade, while transfection with miR-10b-5p mimic exhibited the opposite effect. HOXB3 was downregulated by miR-10b-5p at both the mRNA and protein levels. In addition, the expression of proteins associated with migration and invasion, including HMGB1, RhoC and MMP2, was upregulated in glioma cells transfected with miR-10b-5p mimic, while these proteins were downregulated in cells transfected with miR-10b-5p inhibitor. Taken together, the findings of the present study indicated that miR-10b-5p downregulation suppressed glioma cell proliferation and invasion, possibly by modulating HOXB3, which may provide a novel bio-target for glioma therapy.

PyA-cluster system for the detection and imaging of miRNAs in living cells through double-three-way junction formation

Herein, we describe an extended version of a fluorescence probe for detecting miRNAs through the novel application of a ^PyA-cluster system. By testing various (CG)_n sequences in the middle of the oligonucleotide strand of the probe, we obtained an optimal sequence that formed a double-three-way-junction structure, with two ^PyA units positioned close together, in the presence of the target miRNA. This system readily detected the locations of target miRNAs in living cells and allowed visualization of structural changes through variations in the color of the fluorescence.

Overexpression of tissue microRNA10b may help predict glioma prognosis

We investigated the relationship between microRNA-10b (miR-10b) expression and prognosis in human glioma patients. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis was used to characterize the expression patterns of miR-10b in 128 glioma and 20 normal brain tissues. Clinical information - age, sex, Karnofsky Performance Status (KPS) and World Health Organization (WHO) grade - were also collected. The associations between miR-10b expression and the clinicopathological factors and outcome of glioma patients were statistically analyzed. Expression levels of miR-10b in glioma tissue were significantly higher than in normal brain tissue (P<0.001). High-grade glioma (WHO grade III and IV) had much higher miR-10b expression levels than low-grade tumors (WHO grade I and II). Additionally, the increased miR-10b expression in the glioma tissues was significantly associated with a low KPS (P=0.03). Kaplan-Meier survival curves and Cox regression analyses showed that overexpression of miR-10b (P=0.01) and high grade (P=0.02) were independent factors predicting poor outcome for glioma patients. Furthermore, subgroup analyses showed that the miR-10b expression level was significantly associated with poor overall survival in glioma patients with high grades (P<0.001). Up-regulation of miR-10b may have value in predicting clinical outcome in glioma patients, particularly for those with high pathological grades.

Hepatocellular carcinoma and microRNA: new perspectives on therapeutics and diagnostics

Hepatocellular carcinoma (HCC) remains one of the most lethal forms of cancer in the world. In this arena, utilities of microRNA (miRNA) as a sophisticated tool, in therapeutics and diagnostics, remains a prime focus among the leading researchers. It is well known that viral hepatitis, chronic alcoholism and metabolic syndrome are the prime causes of HCCs. Nevertheless, HCCs are usually diagnosed at late stages by using current serum biomarkers. Most epidemiological studies have found the survival rate in HCC cases to be relatively low. Therefore, development of effective noninvasive biomarkers for early detention of HCC and new strategies for HCC treatment remains a high priority research area on the shoulders of liver oncologists. Accumulating evidence in cancer diagnostics and therapeutics indicates that miRNAs involve in HCC progression, which may serve as sensitive biomarkers for detecting carcinogenesis and monitoring therapies of HCC. This review focuses on the role of miRNAs in the diagnostics and therapeutics of HCC.

Function and mechanism of tumor suppressor gene LRRC4/NGL-2

LRRC4/NGL-2 (Leucine rich repeat containing 4/Netrin-G ligand-2), a relatively specific expressed gene in brain tissue, is a member of the LRRC4/ NGL (netrin-G ligand) family and belongs to the superfamily of LRR proteins. LRRC4/NGL-2 regulates neurite outgrowth and lamina-specific dendritic segmentation, suggesting that LRRC4/NGL-2 is important for the development of the nervous system. In addition, LRRC4/NGL-2 has been identified as a tumor suppressor gene. The overexpression of LRRC4/NGL-2 suppresses glioma cell growth, angiogenesis and invasion through complicated signaling regulation networks. LRRC4/NGL-2 also has the ability to form multiphase loops with miRNA, transcription factors and gene methylation modification; the loss of LRRC4/NGL-2 function may be an important event in multiple biological processes in gliomas. In summary, LRRC4/NGL-2 is a critical gene in the normal development and tumorigenesis of the nervous system.

Bioenergetics and gene silencing approaches for unraveling nucleotide recognition by the human EIF2C2/Ago2 PAZ domain

Gene silencing and RNA interference are major cellular processes that control gene expression via the cleavage of target mRNA. Eukaryotic translation initiation factor 2C2 (EIF2C2, Argonaute protein 2, Ago2) is considered to be the major player of RNAi as it is the core component of RISC complexes. While a considerable amount of research has focused on RNA interference and its associated mechanisms, the nature and mechanisms of nucleotide recognition by the PAZ domain of EIF2C2/Ago2 have not yet been characterized. Here, we demonstrate that the EIF2C2/Ago2 PAZ domain has an inherent lack of binding to adenine nucleotides, a feature that highlights the poor binding of 3′-adenylated RNAs with the PAZ domain as well as the selective high trimming of the 3′-ends of miRNA containing adenine nucleotides. We further show that the PAZ domain selectively binds all ribonucleotides (except adenosine), whereas it poorly recognizes deoxyribonucleotides. In this context, the modification of dTMP to its ribonucleotide analogue gave a drastic improvement of binding enthalpy and, hence, binding affinity. Additionally, higher in vivo gene silencing efficacy was correlated with the stronger PAZ domain binders. These findings provide new insights into the nature of the interactions of the EIF2C2/Ago2 PAZ domain.

TGF-β-induced miR10a/b expression promotes human glioma cell migration by targeting PTEN

Human gliomas are associated with high rates of morbidity and mortality. In the brain, increased mRNA levels of transforming growth factor β (TGF-β) correlate with the degree of malignancy of human gliomas. miR10a/10b expression has been demonstrated to be associated with TGF-β expression in brain tumors, and it is reported that TGF-β induces miR10 expression. Therefore, miR10a/10b expression may be induced by TGF-β expression and may be involved in the TGF-β-induced migration of brain tumor cells. The present study examined the expression of TGF-β and miR10a/10b in the tissues of 10 patients with brain tumors using quantitative PCR (qPCR), and the correlation between TGF-β and miR10a or miR10b expression was analyzed. Additionally, U251 and SHG-44 cells were treated with TGF-β and the expression of miR10a/10b was examined. Further, cell migration was analyzed following transfection of U251 cells with miR10a/10b and the association between miR10a/10b and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) was investigated. U251 cells were transfected with miR10a/10b inhibitors and a PTEN expression plasmid prior to TGF-β treatment and then cell migration was assessed. A significant correlation was identified between TGF-β and miR10a expression (r2=0.6936, P=0.007) and between TGF-β and miR10b expression (r2=0.5876, P=0.02) in the tissues of patients with brain tumors. The results also showed that TGF-β induces miR10a/10b expression and that TGF-β-induced miR10a/10b expression promotes cell migration through the suppression of PTEN. In conclusion, TGF-β-induced miR10a/10b promotes brain tumor migration. This study may provide a number of suggestions for the clinical treatment of brain tumors.

Co-inhibition of microRNA-10b and microRNA-21 exerts synergistic inhibition on the proliferation and invasion of human glioma cells

MicroRNAs (miRNAs) are small non-coding RNAs that function as negative gene regulators. Alterations in the expression of miRNAs have been implicated in the pathogenesis and development of most human malignancies. Recent data indicate that microRNA-21 and microRNA-10b are significantly elevated in glioblastoma multiforme (GBM) suggesting their role in the regulation of multiple genes associated with cancer. In this study, U87MG human glioblastoma cells were treated with miRNA inhibitors targeting miR-10b and miR-21, alone or in combination. The results showed that the miR-21 inhibitor additively interacted with miR-10b inhibitor on U87MG cells. The 50% inhibitory concentration values were dramatically decreased in cells treated with the combination of miR-10b and miR-21 inhibitors. Furthermore, inhibitors synergistically combined, enhanced apoptosis significantly and reduced invasion ability assessed by flow cytometry and Transwell migration assay. Thus, the miR-21 inhibitor may interrupt the activity of EGFR pathways, increasing PDCD4 and TPM1 expression and reducing MMP activities, independently of PTEN status. Meanwhile, miR-10b inhibitor reduced by Twist proceeds to inhibit translation of the mRNA encoding HOXD10 leading to the increase of the expression of the well-characterized pro-metastatic gene RHOC. Taken together, these data strongly suggest that a combination of miR-21 inhibitor and miR-10b inhibitor could be an effective therapeutic strategy for controlling the growth of GBM by inhibiting oncogene expression and overexpressing tumor suppressor genes. Moreover, a regulatory strategy based on the combination of miRNA inhibitors may provide insights into the mechanisms of the modulation of signaling genes involved in tumor cell apoptosis and invasiveness.

Interaction of hsa-miR-381 and glioma suppressor LRRC4 is involved in glioma growth

LRRC4 is not only a brain-specific gene, but it has also been identified as a tumor suppressor gene for glioma. Promoter methylation of LRRC4 is frequently involved in the inactivation in glioma. MiRNA-mediated gene regulation has recently been demonstrated to play an important role in multiple biological processes related to cancer, including glioma. In this study, we demonstrated that a small regulatory microRNA, hsa-miR-381, an "oncomir", had a major role in glioma progression and that LRRC4 was a target of hsa-miR-381. By regulating LRRC4, hsa-miR-381 increased the in vitro and in vivo proliferation of glioma cells, and this action was associated with decreased inhibition of MEK/ERK and AKT signaling. Conversely, LRRC4, as a glioma suppressor, inhibited the endogenous expression of hsa-miR-381 and decreased cell proliferation and tumor growth. The interaction of hsa-miR-381 and LRRC4 is involved in the pathogenesis of glioma. In addition, the stable expression of hsa-miR-381 in blood provides a novel and promising diagnostic biomarker, and anti-hsa-miR-381 "antagomir" may be an ideal target for glioma therapy.

MicroRNA-10b is overexpressed in malignant glioma and associated with tumor invasive factors, uPAR and RhoC

MicroRNAs (miRNAs) are effective post-transcriptional regulators of gene expression and are important in many biological processes. Although the oncogenic and tumor suppressive functions of several miRNAs have been characterized, the role of miRNAs in mediating tumor invasion and migration remains largely unexplored. Recently, miR-10b was identified as an miRNA highly expressed in metastatic breast cancer, promoting cell migration and invasion. Here, we performed real-time reverse transcriptase polymerase chain reaction (RT-PCR) assays on 43 glioma samples (17 glioblastoma, 6 anaplastic astrocytoma, 10 low-grade astrocytoma, 6 oligodendroglioma and 4 ependymoma) and 6 glioma cell lines. We found that miR-10b expression was upregulated in all glioma samples compared to non-neoplastic brain tissues. The expression levels of miR-10b were associated with higher grade glioma. In addition, mRNA expressions of RhoC and urokinase-type plasminogen activator receptor (uPAR), which were thought to be regulated by miR-10b via HOXD10, were statistically significantly correlated with the expression of miR-10b (p < 0.001, p = 0.001, respectively). Also, protein expression levels of RhoC and uPAR were associated with expression levels of miR-10b (p = 0.009, p = 0.014, respectively). Finally, multifocal lesions on enhanced MRI of 7 malignant gliomas were associated with higher expression levels of miR-10b (p = 0.02). Our data indicated that miR-10b might play some role in the invasion of glioma cells.

Delivery of small-interfering RNA (siRNA) to the brain

BACKGROUND

Two fundamental difficulties in the delivery of drugs to treat central nervous system (CNS) diseases are the systemic delivery of therapeutics across the bloodbrain-barrier (BBB), and the targeting of drugs to specific tissues or cells within the brain. With the advent and promise of RNA-based therapeutics that utilize RNA interference (RNAi) to trigger specific silencing of genes within diseased tissues, the necessity to surmount such obstacles has become even more urgent.

OBJECTIVE

Most pre-clinical and clinical studies on delivery of RNAi to the CNS have utilized invasive, intra-cerebral delivery of RNA to the targeted tissue. Thus, methods need to be developed to facilitate delivery of therapeutically significant quantities of RNA to the CNS via the systemic route, and to elicit clinically significant RNAi effects within the CNS tissues.

METHODS

Cell-penetrating-peptides (CPPs) are 'molecular delivery vehicles' that can traverse cell membranes and co-transport peptides or polynucleotides. The present invention examines 1) the utility of CPP-RNA duplexes for delivery of RNA to CNS tissues and, 2) cell-mediated release of the RNA payload once the CPP-RNA duplex is internalized by the CNS cells.

CONCLUSIONS

The invention and embodiments listed therein outline molecular tools that can be adapted for non-invasive, systemic delivery of therapeutic RNA to the CNS in a future clinical setting.