FoxD2-AS1 is a prognostic factor in glioma and promotes temozolomide resistance in a O6-methylguanine-DNA methyltransferase-dependent manner

Targeting epigenetic mechanisms of resistance to chemotherapy in gliomas

Glioma, an aggressive type of brain tumors of glial origin is highly heterogeneous, posing significant treatment challenges due to its intrinsic resistance to conventional therapeutic schemes. It is characterized by an interplay between epigenetic and genetic alterations in key signaling pathways which further endorse their resistance potential. Aberrant DNA methylation patterns, histone modifications and non-coding RNAs may alter the expression of genes associated with drug response and cell survival, induce gene silencing or deregulate key pathways contributing to glioma resistance. There is evidence that epigenetic plasticity enables glioma cells to adapt dynamically to therapeutic schemes and allow the formation of drug-resistant subpopulations. Furthermore, the tumor microenvironment adds an extra input on epigenetic regulation, increasing the complexity of resistance mechanisms. Herein, we discuss epigenetic changes conferring to drug resistance mechanisms in gliomas in order to delineate novel therapeutic targets and potential approaches that will enable personalized treatment.

Dual role of microRNA-31 in human cancers; focusing on cancer pathogenesis and signaling pathways

Widespread changes in the expression of microRNAs in cancer result in abnormal gene expression for the miRNAs that control those genes, which in turn causes changes to entire molecular networks and pathways. The frequently altered miR-31, which is found in a wide range of cancers, is one cancer-related miRNA that is particularly intriguing. MiR-31 has a very complicated set of biological functions, and depending on the type of tumor, it may act both as a tumor suppressor and an oncogene. The endogenous expression levels of miR-31 appear to be a key determinant of the phenotype brought on by aberrant expression. Varied expression levels of miR-31 could affect cell growth, metastasis, drug resistance, and other process by several mechanisms like targeting BRCA1-associated protein-1 (BAP1), large tumor suppressor kinase 1 (LATS1) and protein phosphatase 2 (PP2A). This review highlights the current understanding of the genes that miR-31 targets while summarizing the complex expression patterns of miR-31 in human cancers and the diverse phenotypes brought on by altered miR-31 expression.

A review on the role of FOXD2-AS1 in human disorders

FOXD2 adjacent opposite strand RNA 1 (FOXD2-AS1) is a long non-coding RNA being transcribed from a locus on chromosome 1p33. This transcript has been found to be up-regulated in tumor samples of almost all types of malignancies in association with a significant increase in malignant features. FOXD2-AS1 can affect activity of PI3K/AKT, AKT/mTOR, Hippo/YAP, Notch, NRf2, Wnt/β-catenin, NF-ƙB and ERK/MAPK pathways. Furthermore, it can enhance stem cell properties in cancer cells and prompt epithelial-mesenchymal transition. It is also involved in induction of resistance to a variety of anticancer agents such as adriamycin, cisplatin, 5-fluorouracil, temozolomide and gemcitabine. This article summarizes the impact of FOXD2-AS1 in diverse human disorders.

Modulating glioblastoma chemotherapy response: Evaluating long non-coding RNA effects on DNA damage response, glioma stem cell function, and hypoxic processes

Glioblastoma (GBM) is the most common and aggressive primary adult brain tumor, with an estimated annual incidence of 17 000 new cases in the United States. Current treatments for GBM include chemotherapy, surgical resection, radiation therapy, and antiangiogenic therapy. However, despite the various therapeutic options, the 5-year survival rate remains at a dismal 5%. Temozolomide (TMZ) is the first-line chemotherapy drug for GBM; however, poor TMZ response is one of the main contributors to the dismal prognosis. Long non-coding RNAs (lncRNAs) are nonprotein coding transcripts greater than 200 nucleotides that have been implicated to mediate various GBM pathologies, including chemoresistance. In this review, we aim to frame the TMZ response in GBM via exploration of the lncRNAs mediating three major mechanisms of TMZ resistance: (1) regulation of the DNA damage response, (2) maintenance of glioma stem cell identity, and (3) exploitation of hypoxia-associated responses.

Subtyping and grading of lower-grade gliomas using integrated feature selection and support vector machine

Classifying lower-grade gliomas (LGGs) is a crucial step for accurate therapeutic intervention. The histopathological classification of various subtypes of LGG, including astrocytoma, oligodendroglioma and oligoastrocytoma, suffers from intraobserver and interobserver variability leading to inaccurate classification and greater risk to patient health. We designed an efficient machine learning-based classification framework to diagnose LGG subtypes and grades using transcriptome data. First, we developed an integrated feature selection method based on correlation and support vector machine (SVM) recursive feature elimination. Then, implementation of the SVM classifier achieved superior accuracy compared with other machine learning frameworks. Most importantly, we found that the accuracy of subtype classification is always high (>90%) in a specific grade rather than in mixed grade (~80%) cancer. Differential co-expression analysis revealed higher heterogeneity in mixed grade cancer, resulting in reduced prediction accuracy. Our findings suggest that it is necessary to identify cancer grades and subtypes to attain a higher classification accuracy. Our six-class classification model efficiently predicts the grades and subtypes with an average accuracy of 91% (±0.02). Furthermore, we identify several predictive biomarkers using co-expression, gene set enrichment and survival analysis, indicating our framework is biologically interpretable and can potentially support the clinician.

Effects of microRNAs and long non-coding RNAs on chemotherapy response in glioma

Glioma is the most prevalent invasive primary tumor of the central nervous system. Glioma cells can spread and infiltrate into normal surrounding brain tissues. Despite the standard use of chemotherapy and radiotherapy after surgery in glioma patients, treatment resistance is still a problem, as the underlying mechanisms are still not fully understood. Non-coding RNAs are widely involved in tumor progression and treatment resistance mechanisms. In the present review, we discuss the pathways by which microRNAs and long non-coding RNAs can affect resistance to chemotherapy and radiotherapy, as well as offer potential therapeutic options for future glioma treatment.

Curcumol inhibits malignant biological behaviors and TMZ-resistance in glioma cells by inhibiting long noncoding RNA FOXD2-As1-promoted EZH2 activation

Currently, conventional treatment is not sufficient to improve the survival of glioma patients. Hence, adopting novel personalized treatment programs is imperative. Curcumol, a Chinese herbal medicine extract from the roots of Rhizoma Curcumae, has attracted significant interest due to its beneficial pharmacological activities. The current study revealed that curcumol inhibited the proliferation, metastasis, self-renewal ability, and TMZ resistance in glioma cells in vitro and in vivo. Next, the potential molecular mechanisms of curcumol in inhibiting glioma were investigated. We found that the long non-coding RNA (lncRNA) FOXD2-As1 might contribute to the effects of curcumol on glioma cells. Enforced expression of FOXD2-As1 attenuated the curcumol-induced reduction in glioma cell proliferation, metastasis, self-renewal ability, and TMZ resistance. Moreover, the forced expression of FOXD2-As1 reversed the inhibitory effect of curcumol on the binding ability of EZH2 and H3K27me3 modification in the promoter regions of anti-oncogenes. Our results showed for the first time that curcumol is effective in inhibiting malignant biological behaviors and TMZ-resistance of glioma cells by suppressing FOXD2-As1-mediated EZH2 activation. Our study offers the possibility of exploiting curcumol as a promising therapeutic agent for glioma treatment and may provide an option for the clinical application of this natural herbal medicine.

The regulatory role of antisense lncRNAs in cancer

Antisense long non-coding RNAs (antisense lncRNAs), transcribed from the opposite strand of genes with either protein coding or non-coding function, were reported recently to play a crucial role in the process of tumor onset and development. Functionally, antisense lncRNAs either promote or suppress cancer cell proliferation, migration, invasion, and chemoradiosensitivity. Mechanistically, they exert their regulatory functions through epigenetic, transcriptional, post-transcriptional, and translational modulations. Simultaneously, because of nucleotide sequence complementarity, antisense lncRNAs have a special role on its corresponding sense gene. We highlight the functions and molecular mechanisms of antisense lncRNAs in cancer tumorigenesis and progression. We also discuss the potential of antisense lncRNAs to become cancer diagnostic biomarkers and targets for tumor treatment.

The Impact of Epigenetic Modifications on Adaptive Resistance Evolution in Glioblastoma

Glioblastoma (GBM) is a highly lethal cancer that is universally refractory to the standard multimodal therapies of surgical resection, radiation, and chemotherapy treatment. Temozolomide (TMZ) is currently the best chemotherapy agent for GBM, but the durability of response is epigenetically dependent and often short-lived secondary to tumor resistance. Therapies that can provide synergy to chemoradiation are desperately needed in GBM. There is accumulating evidence that adaptive resistance evolution in GBM is facilitated through treatment-induced epigenetic modifications. Epigenetic alterations of DNA methylation, histone modifications, and chromatin remodeling have all been implicated as mechanisms that enhance accessibility for transcriptional activation of genes that play critical roles in GBM resistance and lethality. Hence, understanding and targeting epigenetic modifications associated with GBM resistance is of utmost priority. In this review, we summarize the latest updates on the impact of epigenetic modifications on adaptive resistance evolution in GBM to therapy.

Long Non-Coding RNAs in Diagnosis, Treatment, Prognosis, and Progression of Glioma: A State-of-the-Art Review

Glioma is the most common malignant central nervous system tumor with significant mortality and morbidity. Despite considerable advances, the exact molecular pathways involved in tumor progression are not fully elucidated, and patients commonly face a poor prognosis. Long non-coding RNAs (lncRNAs) have recently drawn extra attention for their potential roles in different types of cancer as well as non-malignant diseases. More than 200 lncRNAs have been reported to be associated with glioma. We aimed to assess the roles of the most investigated lncRNAs in different stages of tumor progression and the mediating molecular pathways in addition to their clinical applications. lncRNAs are involved in different stages of tumor formation, invasion, and progression, including regulating the cell cycle, apoptosis, autophagy, epithelial-to-mesenchymal transition, tumor stemness, angiogenesis, the integrity of the blood-tumor-brain barrier, tumor metabolism, and immunological responses. The well-known oncogenic lncRNAs, which are upregulated in glioma, are H19, HOTAIR, PVT1, UCA1, XIST, CRNDE, FOXD2-AS1, ANRIL, HOXA11-AS, TP73-AS1, and DANCR. On the other hand, MEG3, GAS5, CCASC2, and TUSC7 are tumor suppressor lncRNAs, which are downregulated. While most studies reported oncogenic effects for MALAT1, TUG1, and NEAT1, there are some controversies regarding these lncRNAs. Expression levels of lncRNAs can be associated with tumor grade, survival, treatment response (chemotherapy drugs or radiotherapy), and overall prognosis. Moreover, circulatory levels of lncRNAs, such as MALAT1, H19, HOTAIR, NEAT1, TUG1, GAS5, LINK-A, and TUSC7, can provide non-invasive diagnostic and prognostic tools. Modulation of expression of lncRNAs using antisense oligonucleotides can lead to novel therapeutics. Notably, a profound understanding of the underlying molecular pathways involved in the function of lncRNAs is required to develop novel therapeutic targets. More investigations with large sample sizes and increased focus on in-vivo models are required to expand our understanding of the potential roles and application of lncRNAs in glioma.

The Roles Played by Long Non-Coding RNAs in Glioma Resistance

Glioma originates in the central nervous system and is classified based on both histological features and molecular genetic characteristics. Long non-coding RNAs (lncRNAs) are longer than 200 nucleotides and are known to regulate tumorigenesis and tumor progression, and even confer therapeutic resistance to glioma cells. Since oncogenic lncRNAs have been frequently upregulated to promote cell proliferation, migration, and invasion in glioma cells, while tumor-suppressive lncRNAs responsible for the inhibition of apoptosis and decrease in therapeutic sensitivity in glioma cells have been generally downregulated, the dysregulation of lncRNAs affects many features of glioma patients, and the expression profiles associated with these lncRNAs are needed to diagnose the disease stage and to determine suitable therapeutic strategies. Accumulating studies show that the orchestrations of oncogenic lncRNAs and tumor-suppressive lncRNAs in glioma cells result in signaling pathways that influence the pathogenesis and progression of glioma. Furthermore, several lncRNAs are related to the regulation of therapeutic sensitivity in existing anticancer therapies, including radiotherapy, chemotherapy and immunotherapy. Consequently, we undertook this review to improve the understanding of signaling pathways influenced by lncRNAs in glioma and how lncRNAs affect therapeutic resistance.

Long Non-Coding RNAs in Multidrug Resistance of Glioblastoma

Glioblastoma, also known as glioblastoma multiforme, is the most aggressive brain tumor in adults. Despite the huge advance in developing novel therapeutic strategies for patients with glioblastoma, the appearance of multidrug resistance (MDR) against the common chemotherapeutic agents, including temozolomide, is considered as one of the important causes for the failure of glioblastoma treatment. On the other hand, recent studies have demonstrated the critical roles of long non-coding RNAs (lncRNAs), particularly in the development of MDR in glioblastoma. Therefore, this article aimed to review lncRNA's contribution to the regulation of MDR and elucidate the underlying mechanisms in glioblastoma, which will open up new lines of inquiry in the treatment of glioblastoma.

The DNA methylation-regulated MCTP1 activates the drug-resistance of esophageal cancer cells

Accumulating studies have demonstrated that drug-resistance remains a great obstacle for the effective treatment of cancers. Esophageal cancer is still one of the most common cancers worldwide, which also suffers from the drug-resistance during clinical treatment. Here we performed drug-resistance profiling assays and identified several drug-resistant and drug-sensitive esophageal cancer cell lines. The following methylation sequencing showed that the MCTP1 gene is hypermethylated in the drug-resistant esophageal cancer cells. As a result, the expression of MCTP1 is down-regulated in the drug-resistant esophageal cancer cells. Down-regulation of MCTP1 also affects the migration and apoptosis of esophageal cancer cells, as revealed by the wound-healing and apoptosis assays. Further investigations proposed two signaling pathways that might involve in the MCTP1-mediated drug-resistance of esophageal cancer cells. All these results suggested that MCTP1 activates the drug-resistance of esophageal cancer cells, which has implications for further design of new biomarker of esophageal cancer treatment.