Rational Design of Novel Anticancer Small-Molecule RNA m6A Demethylase ALKBH5 Inhibitors

Small molecules that regulate the N6-methyladenosine RNA modification as potential anti-cancer agents

Epitranscriptomics, the field of post-translational RNA modifications, is a burgeoning domain of research that has recently received significant attention for its role in multiple diseases, including cancer. N6-methyladenosine (m6A) is the most prominent post-translational RNA modification and plays a critical role in RNA transcription, processing, translation, and metabolism. The m6A modification is controlled by three protein classes known as writers (methyltransferases), erasers (demethylases), and readers (m6A-binding proteins). Each class of m6A regulatory proteins has been implicated in cancer initiation and progression. As such, many of these proteins have been identified as potential targets for anti-cancer chemotherapeutics. In this work, we provide an overview of the role m6A-regulating proteins play in cancer and discuss the current state of small molecule therapeutics targeting these proteins.

Methylation modifications in tRNA and associated disorders: Current research and potential therapeutic targets

High-throughput sequencing has sparked increased research interest in RNA modifications, particularly tRNA methylation, and its connection to various diseases. However, the precise mechanisms underpinning the development of these diseases remain largely elusive. This review sheds light on the roles of several tRNA methylations (m1A, m3C, m5C, m1G, m2G, m7G, m5U, and Nm) in diverse biological functions, including metabolic processing, stability, protein interactions, and mitochondrial activities. It further outlines diseases linked to aberrant tRNA modifications, related enzymes, and potential underlying mechanisms. Moreover, disruptions in tRNA regulation and abnormalities in tRNA-derived small RNAs (tsRNAs) contribute to disease pathogenesis, highlighting their potential as biomarkers for disease diagnosis. The review also delves into the exploration of drugs development targeting tRNA methylation enzymes, emphasizing the therapeutic prospects of modulating these processes. Continued research is imperative for a comprehensive comprehension and integration of these molecular mechanisms in disease diagnosis and treatment.

Regulations of m6A and other RNA modifications and their roles in cancer

RNA modification is an essential component of the epitranscriptome, regulating RNA metabolism and cellular functions. Several types of RNA modifications have been identified to date; they include N6-methyladenosine (m6A), N1-methyladenosine (m1A), 5-methylcytosine (m5C), N7-methylguanosine (m7G), N6,2'-O-dimethyladenosine (m6Am), N4-acetylcytidine (ac4C), etc. RNA modifications, mediated by regulators including writers, erasers, and readers, are associated with carcinogenesis, tumor microenvironment, metabolic reprogramming, immunosuppression, immunotherapy, chemotherapy, etc. A novel perspective indicates that regulatory subunits and post-translational modifications (PTMs) are involved in the regulation of writer, eraser, and reader functions in mediating RNA modifications, tumorigenesis, and anticancer therapy. In this review, we summarize the advances made in the knowledge of different RNA modifications (especially m6A) and focus on RNA modification regulators with functions modulated by a series of factors in cancer, including regulatory subunits (proteins, noncoding RNA or peptides encoded by long noncoding RNA) and PTMs (acetylation, SUMOylation, lactylation, phosphorylation, etc.). We also delineate the relationship between RNA modification regulator functions and carcinogenesis or cancer progression. Additionally, inhibitors that target RNA modification regulators for anticancer therapy and their synergistic effect combined with immunotherapy or chemotherapy are discussed.

Small molecule inhibitors targeting m6A regulators

As the most common form of epigenetic regulation by RNA, N6 methyladenosine (m6A) modification is closely involved in physiological processes, such as growth and development, stem cell renewal and differentiation, and DNA damage response. Meanwhile, its aberrant expression in cancer tissues promotes the development of malignant tumors, as well as plays important roles in proliferation, metastasis, drug resistance, immunity and prognosis. This close association between m6A and cancers has garnered substantial attention in recent years. An increasing number of small molecules have emerged as potential agents to target m6A regulators for cancer treatment. These molecules target the epigenetic level, enabling precise intervention in RNA modifications and efficiently disrupting the survival mechanisms of tumor cells, thus paving the way for novel approaches in cancer treatment. However, there is currently a lack of a comprehensive review on small molecules targeting m6A regulators for anti-tumor. Here, we have comprehensively summarized the classification and functions of m6A regulators, elucidating their interactions with the proliferation, metastasis, drug resistance, and immune responses in common cancers. Furthermore, we have provided a comprehensive overview on the development, mode of action, pharmacology and structure-activity relationships of small molecules targeting m6A regulators. Our aim is to offer insights for subsequent drug design and optimization, while also providing an outlook on future prospects for small molecule development targeting m6A.

Demethylases in tumors and the tumor microenvironment: Key modifiers of N6-methyladenosine methylation

RNA methylation modifications are widespread in eukaryotes and prokaryotes, with N6-methyladenosine (m6A) the most common among them. Demethylases, including Fat mass and obesity associated gene (FTO) and AlkB homolog 5 (ALKBH5), are important in maintaining the balance between RNA methylation and demethylation. Recent studies have clearly shown that demethylases affect the biological functions of tumors by regulating their m6A levels. However, their effects are complicated, and even opposite results have appeared in different articles. Here, we summarize the complex regulatory networks of demethylases, including the most important and common pathways, to clarify the role of demethylases in tumors. In addition, we describe the relationships between demethylases and the tumor microenvironment, and introduce their regulatory mechanisms. Finally, we discuss evaluation of demethylases for tumor diagnosis and prognosis, as well as the clinical application of demethylase inhibitors, providing a strong basis for their large-scale clinical application in the future.

A comprehensive review of m6A research in cervical cancer

Cervical cancer (CC) remains one of the most common malignancies among women worldwide, posing a serious threat to women's health. N6-methyladenosine (m6A) modification, as the most abundant type of RNA methylation modification, and has been found to play a crucial role in various cancers. Current research suggests a close association between RNA m6A modification and the occurrence and progression of CC, encompassing disruptions in m6A levels and its regulatory machinery. This review summarizes the current status of m6A modification research in CC, explores the mechanisms underlying m6A levels and regulators (methyltransferases, demethylases, reader proteins) in CC and examines the application of small-molecule inhibitors of m6A regulators in disease treatment. The findings provide new insights into the future treatment of CC.

A covalent compound selectively inhibits RNA demethylase ALKBH5 rather than FTO

N 6-Methyladenosine (m6A) is the most prevalent mRNA modification and is required for gene regulation in eukaryotes. ALKBH5, an m6A demethylase, is a promising target, particularly for anticancer drug discovery. However, the development of selective and potent inhibitors of ALKBH5 rather than FTO remains challenging. Herein, we used a targeted covalent inhibition strategy and identified a covalent inhibitor, TD19, which selectively inhibits ALKBH5 compared with FTO demethylase in protein-based and tumor cell-based assays. TD19 irreversibly modifies the residues C100 and C267, preventing ALKBH5 from binding to m6A-containing RNA. Moreover, TD19 displays good anticancer efficacy in acute myeloid leukemia and glioblastoma multiforme cell lines. Thus, the ALKBH5 inhibitor developed in this study, which selectively targets ALKBH5 compared with FTO, can potentially be used as a probe for investigating the biological functions of RNA demethylase and as a lead compound in anticancer research.

N6-methyladenosine (m6A) modification in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the deadliest cancers of human, the tumor-related death of which ranks third among the common malignances. N6-methyladenosine (m6A) methylation, the most abundant internal modification of RNA in mammals, participates in the metabolism of mRNA and interrelates with ncRNAs. In this paper, we overviewed the complex function of m6A regulators in HCC, including regulating the tumorigenesis, progression, prognosis, stemness, metabolic reprogramming, autophagy, ferroptosis, drug resistance and tumor immune microenvironment (TIME). Furthermore, we elucidated the interplay between m6A modification and non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs). Finally, we summarized the potential of m6A regulators as diagnostic biomarkers. What's more, we reviewed the inhibitors targeting m6A enzymes as promising therapeutic targets of HCC. We aimed to help understand the function of m6A methylation in HCC systematically and comprehensively so that more effective strategies for HCC treatment will be developed.

RNA methylation-related inhibitors: Biological basis and therapeutic potential for cancer therapy

RNA methylation is widespread in nature. Abnormal expression of proteins associated with RNA methylation is strongly associated with a number of human diseases including cancer. Increasing evidence suggests that targeting RNA methylation holds promise for cancer treatment. This review specifically describes several common RNA modifications, such as the relatively well-studied N6-methyladenosine, as well as 5-methylcytosine and pseudouridine (Ψ). The regulatory factors involved in these modifications and their roles in RNA are also comprehensively discussed. We summarise the diverse regulatory functions of these modifications across different types of RNAs. Furthermore, we elucidate the structural characteristics of these modifications along with the development of specific inhibitors targeting them. Additionally, recent advancements in small molecule inhibitors targeting RNA modifications are presented to underscore their immense potential and clinical significance in enhancing therapeutic efficacy against cancer. KEY POINTS: In this paper, several important types of RNA modifications and their related regulatory factors are systematically summarised. Several regulatory factors related to RNA modification types were associated with cancer progression, and their relationships with cancer cell migration, invasion, drug resistance and immune environment were summarised. In this paper, the inhibitors targeting different regulators that have been proposed in recent studies are summarised in detail, which is of great significance for the development of RNA modification regulators and cancer treatment in the future.

RNA modifications in cellular metabolism: implications for metabolism-targeted therapy and immunotherapy

Cellular metabolism is an intricate network satisfying bioenergetic and biosynthesis requirements of cells. Relevant studies have been constantly making inroads in our understanding of pathophysiology, and inspiring development of therapeutics. As a crucial component of epigenetics at post-transcription level, RNA modification significantly determines RNA fates, further affecting various biological processes and cellular phenotypes. To be noted, immunometabolism defines the metabolic alterations occur on immune cells in different stages and immunological contexts. In this review, we characterize the distribution features, modifying mechanisms and biological functions of 8 RNA modifications, including N6-methyladenosine (m6A), N6,2'-O-dimethyladenosine (m6Am), N1-methyladenosine (m1A), 5-methylcytosine (m5C), N4-acetylcytosine (ac4C), N7-methylguanosine (m7G), Pseudouridine (Ψ), adenosine-to-inosine (A-to-I) editing, which are relatively the most studied types. Then regulatory roles of these RNA modification on metabolism in diverse health and disease contexts are comprehensively described, categorized as glucose, lipid, amino acid, and mitochondrial metabolism. And we highlight the regulation of RNA modifications on immunometabolism, further influencing immune responses. Above all, we provide a thorough discussion about clinical implications of RNA modification in metabolism-targeted therapy and immunotherapy, progression of RNA modification-targeted agents, and its potential in RNA-targeted therapeutics. Eventually, we give legitimate perspectives for future researches in this field from methodological requirements, mechanistic insights, to therapeutic applications.

Low expression of ZFP36L1 in osteosarcoma promotes lung metastasis by inhibiting the SDC4-TGF-β signaling feedback loop

ZFP36L1, which is a negative regulator of gene transcripts, has been proven to regulate the progression of several carcinomas. However, its role in sarcoma remains unknown. Here, by using data analyses and in vivo experiments, we found that ZFP36L1 inhibited the lung metastasis of osteosarcoma (OS). Knockdown of ZFP36L1 promoted OS cell migration by activating TGF-β signaling and increasing SDC4 expression. Intriguingly, we observed a positive feedback loop between SDC4 and TGF-β signaling. SDC4 protected TGFBR3 from matrix metalloproteinase (MMP)-mediated cleavage and therefore relieved the inhibition of TGF-β signaling by soluble TGFBR3, while TGF-β signaling positively regulated SDC4 transcription. We also proved that ZFP36L1 regulated SDC4 mRNA decay through adenylate-uridylate (AU)-rich elements (AREs) in its 3'UTR. Furthermore, treatment with SB431542 (a TGF-β receptor kinase inhibitor) and MK2 inhibitor III (a MAPKAPK2 inhibitor that increases the ability of ZFP36L1 to degrade mRNA) dramatically inhibited OS lung metastasis, suggesting a promising therapeutic approach for the treatment of OS lung metastasis.

Epitranscriptomic regulation in fasting hearts: implications for cardiac health

Cardiac tolerance to ischaemia can be increased by dietary interventions such as fasting, which is associated with significant changes in myocardial gene expression. Among the possible mechanisms of how gene expression may be altered are epigenetic modifications of RNA - epitranscriptomics. N6-methyladenosine (m6A) and N6,2'-O-dimethyladenosine (m6Am) are two of the most prevalent modifications in mRNA. These methylations are reversible and regulated by proteins called writers, erasers, readers, and m6A-repelled proteins. We analysed 33 of these epitranscriptomic regulators in rat hearts after cardioprotective 3-day fasting using RT-qPCR, Western blot, and targeted proteomic analysis. We found that the most of these regulators were changed on mRNA or protein levels in fasting hearts, including up-regulation of both demethylases - FTO and ALKBH5. In accordance, decreased methylation (m6A+m6Am) levels were detected in cardiac total RNA after fasting. We also identified altered methylation levels in Nox4 and Hdac1 transcripts, both of which play a role in the cytoprotective action of ketone bodies produced during fasting. Furthermore, we investigated the impact of inhibiting demethylases ALKBH5 and FTO in adult rat primary cardiomyocytes (AVCMs). Our findings indicate that inhibiting these demethylases reduced the hypoxic tolerance of AVCMs isolated from fasting rats. This study showed that the complex epitranscriptomic machinery around m6A and m6Am modifications is regulated in the fasting hearts and might play an important role in cardiac adaptation to fasting, a well-known cardioprotective intervention.

Discovery of Pyrazolo[1,5-a]pyrimidine Derivative as a Novel and Selective ALKBH5 Inhibitor for the Treatment of AML

M6A (N6-methyladenosine) plays a significant role in regulating RNA processing, splicing, nucleation, translation, and stability. AlkB homologue 5 (ALKBH5) is an Fe(II)/2-oxoglutarate (2-OG)-dependent dioxygenase that demethylates mono- or dimethylated adenosines. ALKBH5 can be regarded as an oncogenic factor for various human cancers. However, the discovery of potent and selective ALKBH5 inhibitors remains a challenge. We identified DDO-2728 as a novel and selective inhibitor of ALKBH5 by structure-based virtual screening and optimization. DDO-2728 was not a 2-oxoglutarate analogue and could selectively inhibit the demethylase activity of ALKBH5 over FTO. DDO-2728 increased the abundance of m6A modifications in AML cells, reduced the mRNA stability of TACC3, and inhibited cell cycle progression. Furthermore, DDO-2728 significantly suppressed tumor growth in the MV4-11 xenograft mouse model and showed a favorable safety profile. Collectively, our results highlight the development of a selective probe for ALKBH5 that will pave the way for the further study of ALKBH5 targeting therapies.

EGFR promotes ALKBH5 nuclear retention to attenuate N6-methyladenosine and protect against ferroptosis in glioblastoma

Growth factor receptors rank among the most important oncogenic pathways, but pharmacologic inhibitors often demonstrate limited benefit as monotherapy. Here, we show that epidermal growth factor receptor (EGFR) signaling repressed N6-methyladenosine (m6A) levels in glioblastoma stem cells (GSCs), whereas genetic or pharmacologic EGFR targeting elevated m6A levels. Activated EGFR induced non-receptor tyrosine kinase SRC to phosphorylate the m6A demethylase, AlkB homolog 5 (ALKBH5), thereby inhibiting chromosomal maintenance 1 (CRM1)-mediated nuclear export of ALKBH5 to permit sustained mRNA m6A demethylation in the nucleus. ALKBH5 critically regulated ferroptosis through m6A modulation and YTH N6-methyladenosine RNA binding protein (YTHDF2)-mediated decay of the glutamate-cysteine ligase modifier subunit (GCLM). Pharmacologic targeting of ALKBH5 augmented the anti-tumor efficacy of EGFR and GCLM inhibitors, supporting an EGFR-ALKBH5-GCLM oncogenic axis. Collectively, EGFR reprograms the epitranscriptomic landscape through nuclear retention of the ALKBH5 demethylase to protect against ferroptosis, offering therapeutic paradigms for the treatment of lethal cancers.

The role of m6A demethylases in lung cancer: diagnostic and therapeutic implications

m6A is the most prevalent internal modification of eukaryotic mRNA, and plays a crucial role in tumorigenesis and various other biological processes. Lung cancer is a common primary malignant tumor of the lungs, which involves multiple factors in its occurrence and progression. Currently, only the demethylases FTO and ALKBH5 have been identified as associated with m6A modification. These demethylases play a crucial role in regulating the growth and invasion of lung cancer cells by removing methyl groups, thereby influencing stability and translation efficiency of mRNA. Furthermore, they participate in essential biological signaling pathways, making them potential targets for intervention in lung cancer treatment. Here we provides an overview of the involvement of m6A demethylase in lung cancer, as well as their potential application in the diagnosis, prognosis and treatment of the disease.

Dynamic alterations of the transcriptome-wide m6A methylome in cytogenetically normal acute myeloid leukaemia during initial diagnosis and relapse

Accumulating studies have indicated that N6-methyladenosine (m6A) plays an important role in acute myeloid leukaemia (AML). However, little is known about the m6A methylome at a transcriptome-wide scale in AML patients. We obtained three pairs of bone marrow (BM) samples from cytogenetically normal AML patients at the timepoints of diagnosis (AML) and relapse (R_AML) and three BM samples from healthy donors used as normal controls (NCs). Methylated RNA immunoprecipitation next-generation sequencing (MeRIP-Seq) was conducted to identify differences in the m6A methylomes between AML and NC and between R_AML and AML. We identified a total of 11,076 and 11,962 differential m6A peaks in AML and R_AML group, respectively. These dysregulated m6A peaks were detected on all chromosomes, especially chr1, chr19 and chr17, and were mainly enriched in 3' untranslated regions, stop codon and coding sequence regions. Moreover, GO and KEGG analyses indicated that m6A -modified genes were significantly enriched in cancer-related biological functions and pathways. Additionally, we identified a link between the m6A methylome and RNA transcriptome via combined analyses of MeRIP-seq and RNA-seq data. In addition, 5 genes, HSPG2, HOMER3, TSPO2, CXCL12 and FUT1 regulated by m6A modification potentially, were shown to be related to the prognosis of AML patients. Additionally, we detected the mRNA expression of major m6A regulators and potential target mRNA on the leukemogenesis and found that the expression of IGF2BP2, HSPG2 and HOMER3 were upregulated in AML at the time of diagnosis. Moreover, their expression became downregulated after remission and then elevated again at relapse. Our study provides the first data on the differential m6A methylome in AML patients during initial diagnosis and relapse. This study demonstrates a novel relationship between m6A modification and AML relapse and paves the way for further studies aimed at elucidating the epigenic mechanisms involved in the relapse of AML.

N6-methyladenosine (m6A) in cancer therapeutic resistance: Potential mechanisms and clinical implications

Cancer therapy resistance (CTR) is the development of cancer resistance to multiple therapeutic strategies, which severely affects clinical response and leads to cancer progression, recurrence, and metastasis. N6-methyladenosine (m6A) has been identified as the most common, abundant, and conserved internal transcriptional alterations of RNA modifications, regulating RNA splicing, translation, stabilization, degradation, and gene expression, and is involved in the development and progression of a variety of diseases, including cancer. Recent studies have shown that m6A modifications play a critical role in both cancer development and progression, especially in reversing CTR. Although m6A modifications have great potential in CTR, the specific molecular mechanisms are not fully elucidated. In this review, we summarize the potential molecular mechanisms of m6A modification in CTR. In addition, we update recent advances in natural products from Traditional Chinese Medicines (TCM) and small-molecule lead compounds targeting m6A modifications, and discuss the great potential and clinical implications of these inhibitors targeting m6A regulators and combinations with other therapies to improve clinical efficacy and overcome CTR.

RNA methylation, homologous recombination repair and therapeutic resistance

Homologous recombination (HR) repair of DNA double-strand breaks (DSBs) is critical for maintaining genomic integrity and stability. Defects in HR increase the risk of tumorigenesis. However, many human tumors exhibit enhanced HR repair capabilities, consequently endowing tumor cells with resistance to DNA-damaging chemotherapy and radiotherapy. This review summarizes the role of RNA methylation in HR repair and therapeutic resistance in human tumors. We also analyzed the interactions between RNA methylation and other HR-modulating modifications including histone acetylation, histone deacetylation, ubiquitination, deubiquitination, protein arginine methylation, and gene transcription. This review proposes that targeting RNA methylation is a promising approach to overcoming HR-mediated therapeutic resistance.

The role of N6-methyladenosine modification in rodent models of neuropathic pain: from the mechanism to therapeutic potential

Neuropathic pain (NP) is a common chronic pain condition resulted from lesions or diseases of somatosensory nervous system, but the pathogenesis remains unclear. A growing body of evidence supports the relationship between pathogenesis and N6-methyladenosine (m6A) modifications of RNA. However, studies on the role of m6A modifications in NP are still at an early stage. Elucidating different etiologies is important for understanding the specific pathogenesis of NP. This article provides a comprehensive review on the role of m6A methylation modifications including methyltransferases ("writers"), demethylases ("erasers"), and m6A binding proteins ("readers") in NP models. Further analysis of the pathogenic mechanism relationship between m6A and NP provided novel theoretical and practical significance for clinical treatment of NP.

The role of N6-methyladenosine (m6A) in kidney diseases

Chemical modifications are a specific and efficient way to regulate the function of biological macromolecules. Among them, RNA molecules exhibit a variety of modifications that play important regulatory roles in various biological processes. More than 170 modifications have been identified in RNA molecules, among which the most common internal modifications include N6-methyladenine (m6A), n1-methyladenosine (m1A), 5-methylcytosine (m5C), and 7-methylguanine nucleotide (m7G). The most widely affected RNA modification is m6A, whose writers, readers, and erasers all have regulatory effects on RNA localization, splicing, translation, and degradation. These functions, in turn, affect RNA functionality and disease development. RNA modifications, especially m6A, play a unique role in renal cell carcinoma disease. In this manuscript, we will focus on the biological roles of m6A in renal diseases such as acute kidney injury, chronic kidney disease, lupus nephritis, diabetic kidney disease, and renal cancer.

Regulation of m6A modification on ferroptosis and its potential significance in radiosensitization

Radiotherapy is often used to treat various types of cancers, but radioresistance greatly limits the clinical efficiency. Recent studies have shown that radiotherapy can lead to ferroptotic cancer cell deaths. Ferroptosis is a new type of programmed cell death caused by excessive lipid peroxidation. The induction of ferroptosis provides a potential therapeutic strategy for radioresistance. As the most common post-transcriptional modification of mRNA, m6A methylation is widely involved in the regulation of various physiopathological processes by regulating RNA function. Dynamic m6A modification controlled by m6A regulatory factors also affects the susceptibility of cells to ferroptosis, thereby determining the radiosensitivity of tumor cells to radiotherapy. In this review, we summarize the mechanism and significance of radiotherapy induced ferroptosis, analyze the regulatory characteristics of m6A modification on ferroptosis, and discuss the possibility of radiosensitization by enhancing m6A-mediated ferroptosis. Clarifying the regulation of m6A modification on ferroptosis and its significance in the response of tumor cells to radiotherapy will help us identify novel targets to improve the efficacy of radiotherapy and reduce or overcome radioresistance.

The roles and implications of RNA m6A modification in cancer

N6-Methyladenosine (m6A), the most prevalent internal modification in eukaryotic mRNA, has been extensively and increasingly studied over the past decade. Dysregulation of RNA m6A modification and its associated machinery, including writers, erasers and readers, is frequently observed in various cancer types, and the dysregulation profiles might serve as diagnostic, prognostic and/or predictive biomarkers. Dysregulated m6A modifiers have been shown to function as oncoproteins or tumour suppressors with essential roles in cancer initiation, progression, metastasis, metabolism, therapy resistance and immune evasion as well as in cancer stem cell self-renewal and the tumour microenvironment, highlighting the therapeutic potential of targeting the dysregulated m6A machinery for cancer treatment. In this Review, we discuss the mechanisms by which m6A modifiers determine the fate of target RNAs and thereby influence protein expression, molecular pathways and cell phenotypes. We also describe the state-of-the-art methodologies for mapping global m6A epitranscriptomes in cancer. We further summarize discoveries regarding the dysregulation of m6A modifiers and modifications in cancer, their pathological roles, and the underlying molecular mechanisms. Finally, we discuss m6A-related prognostic and predictive molecular biomarkers in cancer as well as the development of small-molecule inhibitors targeting oncogenic m6A modifiers and their activity in preclinical models.

Advances in targeting RNA modifications for anticancer therapy

Numerous strategies are employed by cancer cells to control gene expression and facilitate tumorigenesis. In the study of epitranscriptomics, a diverse set of modifications to RNA represent a new player of gene regulation in disease and in development. N6-methyladenosine (m6A) is the most common modification on mammalian messenger RNA and tends to be aberrantly placed in cancer. Recognized by a series of reader proteins that dictate the fate of the RNA, m6A-modified RNA could promote tumorigenesis by driving protumor gene expression signatures and altering the immunologic response to tumors. Preclinical evidence suggests m6A writer, reader, and eraser proteins are attractive therapeutic targets. First-in-human studies are currently testing small molecule inhibition against the methyltransferase-like 3 (METTL3)/methyltransferase-like 14 (METTL14) methyltransferase complex. Additional modifications to RNA are adopted by cancers to drive tumor development and are under investigation.

The Regulation of m6A Modification in Glioblastoma: Functional Mechanisms and Therapeutic Approaches

Glioblastoma is the most prevalent primary brain tumour and invariably confers a poor prognosis. The immense intra-tumoral heterogeneity of glioblastoma and its ability to rapidly develop treatment resistance are key barriers to successful therapy. As such, there is an urgent need for the greater understanding of the tumour biology in order to guide the development of novel therapeutics in this field. N6-methyladenosine (m6A) is the most abundant of the RNA modifications in eukaryotes. Studies have demonstrated that the regulation of this RNA modification is altered in glioblastoma and may serve to regulate diverse mechanisms including glioma stem-cell self-renewal, tumorigenesis, invasion and treatment evasion. However, the precise mechanisms by which m6A modifications exert their functional effects are poorly understood. This review summarises the evidence for the disordered regulation of m6A in glioblastoma and discusses the downstream functional effects of m6A modification on RNA fate. The wide-ranging biological consequences of m6A modification raises the hope that novel cancer therapies can be targeted against this mechanism.

RBM33: A new regulator of N-6-methyladenosine (m6A) methylation

In this issue of Molecular Cell, Yu et al.¹ identify RBM33 as a previously unrecognized m⁶A (N-6-methyladenosine) RNA binding protein that plays a critical role in ALKBH5-mediated m⁶A demethylation of a subset of mRNA transcripts by forming a complex with ALKBH5.

Epigenetic regulation in the tumor microenvironment: molecular mechanisms and therapeutic targets

Over decades, researchers have focused on the epigenetic control of DNA-templated processes. Histone modification, DNA methylation, chromatin remodeling, RNA modification, and noncoding RNAs modulate many biological processes that are crucial to the development of cancers. Dysregulation of the epigenome drives aberrant transcriptional programs. A growing body of evidence suggests that the mechanisms of epigenetic modification are dysregulated in human cancers and might be excellent targets for tumor treatment. Epigenetics has also been shown to influence tumor immunogenicity and immune cells involved in antitumor responses. Thus, the development and application of epigenetic therapy and cancer immunotherapy and their combinations may have important implications for cancer treatment. Here, we present an up-to-date and thorough description of how epigenetic modifications in tumor cells influence immune cell responses in the tumor microenvironment (TME) and how epigenetics influence immune cells internally to modify the TME. Additionally, we highlight the therapeutic potential of targeting epigenetic regulators for cancer immunotherapy. Harnessing the complex interplay between epigenetics and cancer immunology to develop therapeutics that combine thereof is challenging but could yield significant benefits. The purpose of this review is to assist researchers in understanding how epigenetics impact immune responses in the TME, so that better cancer immunotherapies can be developed.

Aberrant RNA m6A modification in gastrointestinal malignancies: versatile regulators of cancer hallmarks and novel therapeutic opportunities

Gastrointestinal (GI) cancer is one of the most common malignancies, and a leading cause of cancer-related death worldwide. However, molecular targeted therapies are still lacking, leading to poor treatment efficacies. As an important layer of epigenetic regulation, RNA N6-Methyladenosine (m⁶A) modification is recently linked to various biological hallmarks of cancer by orchestrating RNA metabolism, including RNA splicing, export, translation, and decay, which is partially involved in a novel biological process termed phase separation. Through these regulatory mechanisms, m⁶A dictates gene expression in a dynamic and reversible manner and may play oncogenic, tumor suppressive or context-dependent roles in GI tumorigenesis. Therefore, regulators and effectors of m⁶A, as well as their modified substrates, represent a novel class of molecular targets for cancer treatments. In this review, we comprehensively summarize recent advances in this field and highlight research findings that documented key roles of RNA m⁶A modification in governing hallmarks of GI cancers. From a historical perspective, milestone findings in m⁶A machinery are integrated with a timeline of developing m⁶A targeting compounds. These available chemical compounds, as well as other approaches that target core components of the RNA m⁶A pathway hold promises for clinical translational to treat human GI cancers. Further investigation on several outstanding issues, e.g. how oncogenic insults may disrupt m⁶A homeostasis, and how m⁶A modification impacts on the tumor microenvironment, may dissect novel mechanisms underlying human tumorigenesis and identifies next-generation anti-cancer therapeutics. In this review, we discuss advances in our understanding of m⁶A RNA modification since its discovery in the 1970s to the latest progress in defining its potential clinic relevance. We summarize the molecular basis and roles of m⁶A regulators in the hallmarks of GI cancer and discuss their context-dependent functions. Furthermore, the identification and characterization of inhibitors or activators of m⁶A regulators and their potential anti-cancer effects are discussed. With the rapid growth in this field there is significant potential for developing m⁶A targeted therapy in GI cancers.

The potential role of m6A modifications on immune cells and immunotherapy

N6-methyladenosine (m6A), is the most prevalent and reversible post-transcriptional epigenetic modification of RNA in mammals. Dysregulation of m6A modifications impacts RNA procession, degradation, translocation, and translation, disrupting immune cell homeostasis and promoting tumor initiation and development. Here, we discuss an -up-to-date summary of the mechanisms by which m6A modifications regulate immune cell anti-tumor as well as self-homeostasis. We also present how the dysregulation of m6A modifications intrinsic to tumor cells regulates the function of immune cells in the tumor microenvironment. Meanwhile, we described some specific inhibitors targeting m6A modulators and discussed their potential use in cancer treatments.

RNA modifications in hematological malignancies

RNA modifications play an important role in various cancers including blood cancers by controlling gene expression programs critical for survival, proliferation and differentiation of cancer cells. While hundreds of RNA modifications have been identified, many have not been functionally characterized. With development of enabling technologies to identify and map RNA modifications, tremendous advancement has been made in our understanding of the biological functions of these molecular markers in diverse cellular contexts. In the last 5 years, N⁶-methyladenosine (m⁶A), the most prevalent internal mRNA modification, has been extensively implicated in many facets of leukemogenesis. Other types of RNA modifications are also involved in the regulation of cell fate decisions and tumorigenesis. Here, we summarize existing knowledge and recent discoveries regarding the role of RNA modifications in leukemia. We choose to highlight cutting-edge techniques to characterize and profile RNA modifications while discussing critical functions of key modifiers and regulatory mechanisms in the pathogenesis of hematological malignancies and touch on therapeutic strategies targeting RNA modifications. These important advancements in the field will continue to foster a strong foundation for the development of innovative treatments for hematological malignancies.

The regulation of N6-methyladenosine modification in PD-L1-induced anti-tumor immunity

There is growing evidence that programmed death ligand-1 (PD-L1) has exciting therapeutic efficacy in hematological malignancy and partial solid tumors. However, many patients still face failure with the treatment of immune checkpoint blockade because of PD-L1 expression regulation during transcription and post-transcription processes, including N6-methyladenosine (m6A). Similar to the epigenetic regulation in DNA and histones, recent research has revealed the essential regulation of m6A modification in RNA nuclear export, metabolism and translation. Recent studies have shown that m6A-induced PD-L1 expression emerges as one of the main reasons for the immunological alteration in this process and contributes to the failure of T cell-induced anti-tumor immunity. The results of preclinical studies demonstrate the potential of m6A-targeted therapy in combination with immune checkpoint blockade. The comprehensive expression of m6A-related genes also provided the possibility to indicate the prognosis and to optimize the treatment for patients of various cancer types. In this review, we focus on the m6A modification in PD-L1 mRNA as well as the regulation of PD-L1 expression in cancer cells and summarize its clinical value in anti-PD-L1 cancer immune therapy.

Promotion of the resistance of human oral epithelial cells to herpes simplex virus type I infection via N6-methyladenosine modification

OBJECTIVE

This study aimed to explore the mechanism behind N6-methyladenosine (m6A) modification of the total ribonucleic acid (RNA) involved in the resistance to herpes simplex virus type I (HSV-1) infection in oral epithelial cells.

METHOD

The variation in m6A modification level on messenger RNA following HSV-1 infection was determined using the RNA dot blot method. The expression levels of alpha-ketoglutarate-dependent dioxygenase lab homolog 5 (ALKBH5) protein and fatty mass and obesity-associated genes (FTO) were determined using real-time fluorescence quantification polymerase chain reaction and the western blot technique, respectively. Next, after suppressing the expression of ALKBH5 or FTO via small interfering RNA, human immortalised oral epithelial cells (HIOECs) were infected with HSV-1, followed by measurement of the viral load or expression level of type I interferon (I-IFN) and interferon-stimulated genes (ISGs).

RESULTS

The m6A modification level was significantly increased following HSV-1 infection of the HIOECs (P < 0.05), while the expression of ALKBH5 and FTO genes was reduced (P < 0.01). Moreover, the suppression of ALKBH5 or FTO increased the production of I-IFN and ISGs during the HSV-1 infection of the HIOECs (P < 0.01), and the viral load was significantly reduced (P < 0.01).

CONCLUSION

During oral HSV-1 infection, the m6A level was increased through the down-regulation of ALBHK5 and FTO expression, increasing I-IFN production and the promotion of HSV-1 clearing in HIOECs.

Targeting RNA N6-methyladenosine to synergize with immune checkpoint therapy

Cancer immunotherapy, especially immune checkpoint therapy, has revolutionized therapeutic options by reactivating the host immune system. However, the efficacy varies, and only a small portion of patients develop sustained antitumor responses. Hence, illustrating novel strategies that improve the clinical outcome of immune checkpoint therapy is urgently needed. N6-methyladenosine (m⁶A) has been proved to be an efficient and dynamic posttranscriptional modification process. It is involved in numerous RNA processing, such as splicing, trafficking, translation and degradation. Compelling evidence emphasizes the paramount role of m⁶A modification in the regulation of immune response. These findings may provide a foundation for the rational combination of targeting m⁶A modification and immune checkpoints in cancer treatment. In the present review, we summarize the current landscape of m⁶A modification in RNA biology, and highlight the latest findings on the complex mechanisms by which m⁶A modification governs immune checkpoint molecules. Furthermore, given the critical role of m⁶A modification in antitumor immunity, we discuss the clinical significance of targeting m⁶A modification to improve the efficacy of immune checkpoint therapy for cancer control.

Emerging roles of m6A RNA modification in cancer therapeutic resistance

Marvelous advancements have been made in cancer therapies to improve clinical outcomes over the years. However, therapeutic resistance has always been a major difficulty in cancer therapy, with extremely complicated mechanisms remain elusive. N6-methyladenosine (m6A) RNA modification, a hotspot in epigenetics, has gained growing attention as a potential determinant of therapeutic resistance. As the most prevalent RNA modification, m6A is involved in every links of RNA metabolism, including RNA splicing, nuclear export, translation and stability. Three kinds of regulators, "writer" (methyltransferase), "eraser" (demethylase) and "reader" (m6A binding proteins), together orchestrate the dynamic and reversible process of m6A modification. Herein, we primarily reviewed the regulatory mechanisms of m6A in therapeutic resistance, including chemotherapy, targeted therapy, radiotherapy and immunotherapy. Then we discussed the clinical potential of m6A modification to overcome resistance and optimize cancer therapy. Additionally, we proposed existing problems in current research and prospects for future research.

METTL3 from Target Validation to the First Small-Molecule Inhibitors: A Medicinal Chemistry Journey

RNA methylation is a critical mechanism for regulating the transcription and translation of specific sequences or for eliminating unnecessary sequences during RNA maturation. METTL3, an RNA methyltransferase that catalyzes the transfer of a methyl group to the N⁶-adenosine of RNA, is one of the key mediators of this process. METTL3 dysregulation may result in the emergence of a variety of diseases ranging from cancer to cardiovascular and neurological disorders beyond contributing to viral infections. Hence, the discovery of METTL3 inhibitors may assist in furthering the understanding of the biological roles of this enzyme, in addition to contributing to the development of novel therapeutics. Through this work, we will examine the existing correlations between METTL3 and diseases. We will also analyze the development, mode of action, pharmacology, and structure-activity relationships of the currently known METTL3 inhibitors. They include both nucleoside and non-nucleoside compounds, with the latter comprising both competitive and allosteric inhibitors.

Genetic and epigenetic defects of the RNA modification machinery in cancer

Cancer was initially considered to be an exclusively genetic disease, but an interplay of dysregulated genetic and epigenetic mechanisms is now known to contribute to the cancer phenotype. More recently, chemical modifications of RNA molecules - the so-called epitranscriptome - have been found to regulate various aspects of RNA function and homeostasis. Specific enzymes, known as RNA-modifying proteins (RMPs), are responsible for depositing, removing, and reading chemical modifications in RNA. Intensive investigations in the epitranscriptomic field in recent years, in conjunction with great technological advances, have revealed the critical role of RNA modifications in regulating numerous cellular pathways. Furthermore, growing evidence has revealed that RNA modification machinery is often altered in human cancers, highlighting the enormous potential of RMPs as pharmacological targets or diagnostic markers.

Recent Advances of RNA m6A Modifications in Cancer Immunoediting and Immunotherapy

Cancer immunotherapy, which modulates immune responses against tumors using immune-checkpoint inhibitors or adoptive cell transfer, has emerged as a novel and promising therapy for tumors. However, only a minority of patients demonstrate durable responses, while the majority of patients are resistant to immunotherapy. The immune system can paradoxically constrain and promote tumor development and progression. This process is referred to as cancer immunoediting. The mechanisms of resistance to immunotherapy seem to be that cancer cells undergo immunoediting to evade recognition and elimination by the immune system. RNA modifications, specifically N6-methyladenosine (m6A) methylation, have emerged as a key regulator of various post-transcriptional gene regulatory processes, such as RNA export, splicing, stability, and degradation, which play unappreciated roles in various physiological and pathological processes, including immune system development and cancer pathogenesis. Therefore, a deeper understanding of the mechanisms by which RNA modifications impact the cancer immunoediting process can provide insight into the mechanisms of resistance to immunotherapies and the strategies that can be used to overcome such resistance. In this chapter, we briefly introduce the background of cancer immunoediting and immunotherapy. We also review and discuss the roles and mechanisms of RNA m6A modifications in fine-tuning the innate and adaptive immune responses, as well as in regulating tumor escape from immunosurveillance. Finally, we summarize the current strategies targeting m6A regulators for cancer immunotherapy.

m6A modification on the fate of colorectal cancer: functions and mechanisms of cell proliferation and tumorigenesis

N6-methyladenosine (m6A) is the most pervasive RNA modification in eukaryotic cells. The dynamic and reversible m6A modification of RNA plays a critical role in the occurrence and progression of tumors by regulating RNA metabolism, including translocation, mRNA stability or decay, pre-mRNA splicing, and lncRNA processing. Numerous studies have shown that m6A modification is involved in the development of various cancers. This review aims to summarize the significant role of m6A modification in the proliferation and tumorigenesis of CRC, as well as the potential of modulating m6A modification for tumor treatment. These findings may offer new therapeutic strategies for clinical implementation of m6A modification in CRC in the near future.

RNA m6 A methylation in cancer

N⁶ -methyladenosine (m⁶ A) is one of the most abundant internal modifications in eukaryotic messenger RNAs (mRNAs) and non-coding RNAs (ncRNAs). It is a reversible and dynamic RNA modification that has been observed in both internal coding segments and untranslated regions. Studies indicate that m⁶ A modifications play important roles in translation, RNA splicing, export, degradation and ncRNA processing control. In this review, we focus on the profiles and biological functions of RNA m⁶ A methylation on both mRNAs and ncRNAs. The dynamic modification of m⁶ A and its potential roles in cancer development are discussed. Moreover, we discuss the possibility of m⁶ A modifications serving as potential biomarkers for cancer diagnosis and targets for therapy.

The emerging therapeutic target of dynamic and reversible N6-methyladenosine modification during cancer development

As a reversible and dynamic epigenetic modification, N6-methyladenosine (m6A) modification is ubiquitous in eukaryotic cells. m6A methylation is prevalent in almost all RNA metabolism processes that affect the fate of cells, including cancer development. As indicated by the available evidence, targeting m6A regulators may play a crucial role in tumor therapy and multidrug resistance. Currently, many questions remain uncovered. Here, we review recent studies on m6A modification in various aspects of tumor progression, tumor immunity, multidrug resistance, and therapeutic targets to provide new insight into the m6A methylation process.

Emerging roles of the RNA modifications N6-methyladenosine and adenosine-to-inosine in cardiovascular diseases

Cardiovascular diseases lead the mortality and morbidity disease metrics worldwide. A multitude of chemical base modifications in ribonucleic acids (RNAs) have been linked with key events of cardiovascular diseases and metabolic disorders. Named either RNA epigenetics or epitranscriptomics, the post-transcriptional RNA modifications, their regulatory pathways, components, and downstream effects substantially contribute to the ways our genetic code is interpreted. Here we review the accumulated discoveries to date regarding the roles of the two most common epitranscriptomic modifications, N⁶-methyl-adenosine (m⁶A) and adenosine-to-inosine (A-to-I) editing, in cardiovascular disease.

Physio-pathological effects of N6-methyladenosine and its therapeutic implications in leukemia

N6-methyladenosine (m6A), the most prevalent epigenetic modification of RNA in mammals, has become a hot topic throughout recent years. m6A is involved with every links of the RNA fate, including RNA splicing, nuclear export, translation and stability. Due to the reversible and dynamic regulatory network composed of ‘writers’ (methylase), ‘erasers’ (demethylase) and ‘readers’ (m6A binding proteins), m6A has been deemed as an essential modulator in vast physiological and pathological processes. Previous studies have shown that aberrant expression and dysfunction of these regulators are implicated in diverse tumors, exemplified by hematological malignancies. However, we should hold a dialectic perspective towards the influence of m6A modification on leukemogenesis. Given that m6A itself is neither pro-oncogenic nor anti-oncogenic, whether the modifications promote hematological homeostasis or malignancies occurrence and progression is dependent on the specific targets it regulates. Ample evidence supports the role of m6A in maintaining normal hematopoiesis and leukemogenesis, thereby highlighting the therapeutic potential of intervention in m6A modification process for battling leukemia. In this review, we introduce the advances of m6A modification and summarize the biological functions of m6A in RNA metabolism. Then we discuss the significance of several well-studied m6A regulators in modulating normal and malignant hematopoiesis, with focus on the therapeutic potentials of targeting these regulators for battling hematopoietic malignancies.

Discovery of two novel ALKBH5 selective inhibitors that exhibit uncompetitive or competitive type and suppress the growth activity of glioblastoma multiforme

A group of RNA methylation enzymes is currently of interest as a new target for cancer therapy. Alpha-ketoglutarate-dependent dioxygenase B (AlkB) homolog 5 (ALKBH5) is an N⁶ -methyladenosine (m⁶ A) demethylation enzyme, and by high-throughput screening from pure small molecule compounds, we identified two novel inhibitors, Ena15 and Ena21, against it. Each compound showed either uncompetitive or competitive inhibition for 2-oxoglutarate (2OG). In addition, Ena21 had little inhibitory activity for fat mass and obesity-associated protein (FTO), which is another N⁶ -methyladenosine demethylation enzyme, while Ena15 enhanced the demethylase activity of FTO. The predicted binding poses of both compounds with the crystal structure of ALKBH5 (PDB ID: 4NRO) were comparable with these observations pertaining to the interaction of the 2OG catalytic site in this enzyme kinetics. Furthermore, either knockdown of ALKBH5 or inhibition with Ena15 or Ena21 inhibited cell proliferation of glioblastoma multiforme-derived cell lines, decreased cell population in the synthesis phase of the cell cycle, increased m⁶ A RNA level, and stabilized FOXM1 mRNA. Based on these results, Ena15 and Ena21 were found to be potential candidates that might help in further research into the biological function of ALKBH5.

One Stone, Two Birds: N6-Methyladenosine RNA Modification in Leukemia Stem Cells and the Tumor Immune Microenvironment in Acute Myeloid Leukemia

Acute myeloid leukemia is the most common acute leukemia in adults, with accumulation of abundant blasts and impairment of hematogenic function. Despite great advances in diagnosis and therapy, the overall survival of patients with acute myeloid leukemia remains poor. Leukemia stem cells are the root cause of relapse and chemoresistance in acute myeloid leukemia. The tumor immune microenvironment is another trigger to induce recurrence and drug resistance. Understanding the underlying factors influencing leukemia stem cells and the tumor immune microenvironment is an urgent and unmet need. Intriguingly, N6-methyladenosine, the most widespread internal mRNA modification in eukaryotes, is found to regulate both leukemia stem cells and the tumor immune microenvironment. Methyltransferases and demethylases cooperatively make N6-methyladenosine modification reversible and dynamic. Increasing evidence demonstrates that N6-methyladenosine modification extensively participates in tumorigenesis and progression in various cancers, including acute myeloid leukemia. In this review, we summarize the current progress in studies on the functions of N6-methyladenosine modification in acute myeloid leukemia, especially in leukemia stem cells and the tumor immune microenvironment. We generalize the landscape of N6-methyladenosine modification in self-renewal of leukemia stem cells and immune microenvironment regulation, as well as in the initiation, growth, proliferation, differentiation, and apoptosis of leukemia cells. In addition, we further explore the clinical application of N6-methyladenosine modification in diagnosis, prognostic stratification, and effect evaluation. Considering the roles of N6-methyladenosine modification in leukemia stem cells and the tumor immune microenvironment, we propose targeting N6-methyladenosine regulators as one stone to kill two birds for acute myeloid leukemia treatment.

Cancer epitranscriptomics in a nutshell

Remarkable technological progress has led to breakthrough discoveries in epitranscriptomics, reshaping our understanding of modifications decorating RNA. The past decade has seen a tremendous endeavor to describe the nature, functions, and biological roles of messenger RNA (mRNA) modifications, positioning epitranscriptomics as a crucial pillar in tumor biology. Like DNA and histone modifications, mRNA marks have been increasingly linked to cancer pathogenesis. Here, we summarize the latest research in cancer epitranscriptomics with emphasis on N6-methyladenosine, untangling its contribution to five prime oncogenic features: tumor growth, activating invasion and metastasis, stemness, metabolic reprogramming, and tumor microenvironment. We discuss mRNA-modifying enzymes, their impact on biological processes, and contribution to cancer hallmarks. We spotlight epitranscriptomics as a promising bonanza for forthcoming targeting approaches in cancer therapy.

Recent Advances of m6A Demethylases Inhibitors and Their Biological Functions in Human Diseases

N6-methyladenosine (m6A) is a post-transcriptional RNA modification and one of the most abundant types of RNA chemical modifications. m6A functions as a molecular switch and is involved in a range of biomedical aspects, including cardiovascular diseases, the central nervous system, and cancers. Conceptually, m6A methylation can be dynamically and reversibly modulated by RNA methylation regulatory proteins, resulting in diverse fates of mRNAs. This review focuses on m6A demethylases fat-mass- and obesity-associated protein (FTO) and alkB homolog 5 (ALKBH5), which especially erase m6A modification from target mRNAs. Recent advances have highlighted that FTO and ALKBH5 play an oncogenic role in various cancers, such as acute myeloid leukemias (AML), glioblastoma, and breast cancer. Moreover, studies in vitro and in mouse models confirmed that FTO-specific inhibitors exhibited anti-tumor effects in several cancers. Accumulating evidence has suggested the possibility of FTO and ALKBH5 as therapeutic targets for specific diseases. In this review, we aim to illustrate the structural properties of these two m6A demethylases and the development of their specific inhibitors. Additionally, this review will summarize the biological functions of these two m6A demethylases in various types of cancers and other human diseases.

Discovery of a potent, selective and cell active inhibitor of m6A demethylase ALKBH5

AlkB homolog 5 (ALKBH5) is an RNA m⁶A demethylase involved in the regulation of genes transcription, translation and metabolism and has been considered as a promising therapeutic target for various human diseases, especially cancers. However, there is still a lack of potent and selective ALKBH5 inhibitors. Herein, we report a new class of ALKBH5 inhibitors containing the 1-aryl-1H-pyrazole scaffold, which were obtained through fluorescence polarization-based screening, structural optimization and structure-activity relationship analysis. Among these compounds, 20m was the most potent one, which showed an IC₅₀ value of 0.021 μM in fluorescence polarization assay. Compound 20m exhibited high selectivity towards ALKBH5 versus FTO as well as other AlkB subfamily members, indicating good selectivity for ALKBH5. Cellular thermal shift assay (CETSA) analysis showed that 20m could efficiently stabilize ALKBH5 in HepG2 cells. Dot blot assay demonstrated that 20m could increase m⁶A level in intact cells. Collectively, 20m is a potent, selective and cell active ALKBH5 inhibitor and could be used as a versatile chemical probe to explore the biological function of ALKBH5.

Mechanisms of substrate recognition and N6-methyladenosine demethylation revealed by crystal structures of ALKBH5-RNA complexes

AlkB homologue 5 (ALKBH5) is a ferrous iron and 2-oxoglutarate dependent oxygenase that demethylates RNA N6-methyladenosine (m6A), a post-transcriptional RNA modification with an emerging set of regulatory roles. Along with the fat mass and obesity-associated protein (FTO), ALKBH5 is one of only two identified human m6A RNA oxidizing enzymes and is a potential target for cancer treatment. Unlike FTO, ALKBH5 efficiently catalyzes fragmentation of its proposed nascent hemiaminal intermediate to give formaldehyde and a demethylated nucleoside. A detailed analysis of the molecular mechanisms used by ALKBH5 for substrate recognition and m6A demethylation is lacking. We report three crystal structures of ALKBH5 in complex with an m6A-ssRNA 8-mer substrate and supporting biochemical analyses. Strikingly, the single-stranded RNA substrate binds to the active site of ALKBH5 in a 5'-3' orientation that is opposite to single-stranded or double-stranded DNA substrates observed for other AlkB subfamily members, including single-stranded DNA bound to FTO. The combined structural and biochemical results provide insight into the preference of ALKBH5 for substrates containing a (A/G)m6AC consensus sequence motif. The results support a mechanism involving formation of an m6A hemiaminal intermediate, followed by efficient ALKBH5 catalyzed demethylation, enabled by a proton shuttle network involving Lys132 and Tyr139.

The Roles and Regulation of m6A Modification in Glioblastoma Stem Cells and Tumorigenesis

Glioblastoma is the most common and most lethal primary malignant brain tumor. N6-methyladenosine (m6A) is a widespread and abundant internal messenger RNA (mRNA) modification found in eukaryotes. Accumulated evidence demonstrates that m6A modification is aberrantly activated in human cancers and is critical for tumorigenesis and metastasis. m6A modification is also strongly involved in key signaling pathways and is associated with prognosis in glioblastoma. Here, we briefly outline the functions of m6A and its regulatory proteins, including m6A writers, erasers, and readers of the fate of RNA. We also summarize the latest breakthroughs in this field, describe the underlying molecular mechanisms that contribute to the tumorigenesis and progression, and highlight the inhibitors targeting the factors in m6A modification in glioblastoma. Further studies focusing on the specific pathways of m6A modification could help identify biomarkers and therapeutic targets that might prevent and treat glioblastoma.

Roles of RNA Modifications in Diverse Cellular Functions

Chemical modifications of RNA molecules regulate both RNA metabolism and fate. The deposition and function of these modifications are mediated by the actions of writer, reader, and eraser proteins. At the cellular level, RNA modifications regulate several cellular processes including cell death, proliferation, senescence, differentiation, migration, metabolism, autophagy, the DNA damage response, and liquid-liquid phase separation. Emerging evidence demonstrates that RNA modifications play active roles in the physiology and etiology of multiple diseases due to their pervasive roles in cellular functions. Here, we will summarize recent advances in the regulatory and functional role of RNA modifications in these cellular functions, emphasizing the context-specific roles of RNA modifications in mammalian systems. As m⁶A is the best studied RNA modification in biological processes, this review will summarize the emerging advances on the diverse roles of m⁶A in cellular functions. In addition, we will also provide an overview for the cellular functions of other RNA modifications, including m⁵C and m¹A. Furthermore, we will also discuss the roles of RNA modifications within the context of disease etiologies and highlight recent advances in the development of therapeutics that target RNA modifications. Elucidating these context-specific functions will increase our understanding of how these modifications become dysregulated during disease pathogenesis and may provide new opportunities for improving disease prevention and therapy by targeting these pathways.

RNA-binding proteins and cancer metastasis

RNA-binding proteins (RBPs) can regulate gene expression through post-transcriptionally influencing all manner of RNA biology, including alternative splicing (AS), polyadenylation, stability, and translation of mRNAs, as well as microRNAs (miRNAs) and circular RNAs (circRNAs) processing. There is accumulating evidence reinforcing the perception that dysregulation or dysfunction of RBPs can lead to various human diseases, including cancers. RBPs influence diverse cancer-associated cellular phenotypes, such as proliferation, apoptosis, senescence, migration, invasion, and angiogenesis, contributing to the initiation and development of tumors, as well as clinical prognosis. Metastasis is the leading cause of cancer-related recurrence and death. Therefore, it is necessary to elucidate the molecular mechanisms behind tumor metastasis. In fact, a growing body of published research has proved that RBPs play pivotal roles in cancer metastasis. In this review, we will summarize the recent advances for helping us understand the role of RBPs in tumor metastasis, and discuss dysfunctions and dysregulations of RBPs affecting metastasis-associated processes including epithelial-mesenchymal transition (EMT), migration, and invasion of cancer cells. Furthermore, we will discuss emerging RBP-based strategy for the treatment of cancer metastasis.