A Comprehensive Review on LncRNAs/miRNAs-DNMT1 Axis in Human Cancer: Mechanistic and Clinical Application.

DNMT1 , a considerable protein consisting of 1616 amino acids and featuring multiple domains, is intricately governed by intramolecular regulations that precisely restrict its functionality to hemimethylated DNA sites [ 30 ]. Notably, during DNA replication, DNMT1 plays a pivotal role in propagating DNA methylation. DNMT1 is classified as a class I methyltransferase family member, characterised by its possession of a conserved catalytic core known as the Rossmann fold. This core structure comprises a mixed seven‐stranded β‐sheet, bordered by three α‐helices on each side [ 31 ]. This enzyme facilitates the methylation reaction using an S‐adenosyl‐L‐methionine (AdoMet) —dependent mechanism. Within its catalytic core, it contains critical motifs responsible for both enzymatic catalysis and binding with the cofactor. An additional subdomain, the target recognition domain (TRD), is situated between the central β‐sheet and the final α‐helix of the catalytic core [ 32 , 33 ]. Furthermore, extensive research spanning several decades has examined the structure and function of DNMT1 . Kikuchi et al. explored the structural characteristics of human DNMT1 (amino acid residues: 351–1616) through cryogenic electron microscopy (cryo‐EM). Their investigation involved the stimulation of DNMT1 by the H3Ub2 tail and its formation of an intermediate complex alongside a hemimethylated DNA analogue. They present the cryo‐EM structure of the interaction between human DNMT1 and its native co‐activators, namely hemimethylated DNA and ubiquitinated histone H3. They discover a previously unexplored linker positioned between the Replication‐Foci Targeting Sequence (RFTS) and CXXC domains, which serve as a critical mediator for activation. Concurrent with this phenomenon, there is a substantial reconfiguration of the inhibitory RFTS and CXXC domains, facilitating the enzyme to attain its complete functional capacity. The findings offer a basis for understanding how DNMT1 is activated, which has implications for basic research and drug development [ 34 ]. Over the last 20 years, evidence has progressively linked the involvement and importance of DNMT1 in tumorigenesis, aggressiveness and treatment response of human cancers. In this context, Liu et al. revealed that in breast cancer (BC), DNMT1‐mediated hypermethylation of the FOXO3a promoter results in the suppression of FOXO3a expression . FOXO3a exhibits functional interrelation with the repression of FOXM1/SOX2 signalling, thereby leading to the consequential suppression of BCSC properties and tumorigenicity. Moreover, their investigation revealed that SOX2 exerts direct transactivation on DNMT1 expression, consequently inducing alterations in the methylation landscape. This, in turn, creates a feedback loop that leads to the inhibition of FOXO3a expression. Additionally, they unveiled that the suppression of DNMT activity resulted in the suppression of tumour growth by modulating the FOXO3a/FOXM1/SOX2 signalling axis in BC. From a clinical perspective, a notable and statistically significant inverse relationship was observed between the expression levels of FOXO3a and FOXM1/SOX2/DNMT1 . Furthermore, instances of diminished FOXO3a expression or elevated levels of FOXM1 , SOX2 and DNMT1 were indicative of an unfavourable prognosis in BC patients. Their findings present compelling evidence regarding the significant involvement of the DNMT1 / FOXO3a / FOXM1 / SOX2 pathway in regulating BCSC properties. This underscores the potential for identifying therapeutic targets for BC treatment based on these mechanistic insights [ 35 ]. Multiple studies have demonstrated that ncRNAs exhibit the ability to directly interact with DNMT1 , resulting in alterations within the cancer cell's epigenome. This has the potential to reveal a previously unknown mechanism that accounts for the substantial alterations in the epigenome observed across different types of tumours. In this regard, lncRNA KIF9‐AS1 is critical in regulating RAI2 expression, mainly through the recruitment of DNMT1 and subsequent modulation of RAI2 DNA methylation. Additionally, upregulation of RAI2 hindered the migration and proliferation while enhancing apoptosis in HCC cells. Further in vivo experimentation revealed that KIF9‐AS1 silencing inhibits subcutaneous tumour formation. Thereby, KIF9‐AS1 actively promotes HCC growth by facilitating DNMT1 ‐mediated promotion of RAI2 DNA methylation [ 36 ](Figure  2 ). A schematic representation of DNMT1 location, expression and functioning in human cancer. (A) Depiction of DNMT1 transcriptional processes followed by (B) translation leading to its expression. (C) Highlighting DNMT1's functional impact on chromatin structure regulation. (D) Illustrating the downstream effects of epigenetic changes mediated by DNMT1 on key biological features of cancer cells, encompassing proliferation, apoptosis resistance, angiogenesis and metastasis. This comprehensive portrayal underscores the pivotal involvement of DNMT1 across multiple stages of cancer development and progression.

Seyed Mohsen Aghaei‐Zarch: conceptualization (lead), supervision (lead), visualization (equal), writing – original draft (equal), writing – review and editing (equal). Ali Esmaeili: conceptualization (supporting), validation (supporting), visualization (equal), writing – original draft (equal), writing – review and editing (equal). Saeid Bagheri‐Mohammadi: conceptualization (equal), supervision (equal), validation (equal), writing – original draft (equal), writing – review and editing (equal).

The authors have nothing to report.

Recent developments in gene editing technology have demonstrated promising approaches for precise and targeted DNA modification. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9, initially identified in Escherichia coli , provides a powerful tool for precise genome editing. By utilising base complementary pairing, the CRISPR/Cas9 system offers a highly specific DNA modification. Recently developed CRISPR/Cas9‐based tools, namely CRISPR interference (CRISPRi), employ a catalytically dead Cas9 (dCas9) protein complexed with a transcriptional effector and a single guide RNA (sgRNA). This variant of dCas9 is unable to trigger DNA cleavage, yet it maintains its capacity for sequence‐specific DNA binding. The binding of a dCas9/sgRNA complex to a target gene sequence modulates transcriptional activity [ 176 ]. Another variant of the CRISPR system, known as CRISPR activation (CRISPRa), can be utilised to enhance the expression of lncRNA genes. Recent studies have highlighted the potential of CRISPRa in activating DANCR, which in turn promotes chondrogenic differentiation and improves calvarial bone healing [ 177 ]. So, applying CRISPR/Cas9 technology could restore the expression of downregulated ncRNAs, leading to epigenetic reprogramming in various diseases, such as cancer. In this manner, CRISPR‐based targeted activation of ncRNAs such as miRNAs and lncRNAs may provide an alternative therapeutic approach for cancers.

Stem cells possess two pivotal characteristics, specifically the capacity for self‐renewal and the potential to undergo differentiation into various cell lineages endowed with distinct functional roles. These inherent attributes are also exhibited by cancer stem cells (CSCs). These cells have been identified in various cancer types, contributing to tumour formation. A recent study revealed that the axis involving ncRNA and DNMT1 plays a crucial role in regulating the activity of CSCs. Therefore, in the following section, we explain the effects of the ncRNA‐ DNMT1 axis on CSC activity and their impact on tumorigenesis [ 153 ]. LCSCs displayed increased DNMT1 activity and expression, reduced miR‐34a expression accompanied by enhanced promoter methylation, and heightened stemness properties compared to the original liver cancer cells. Also, DNMT1 silencing resulted in the repression of DNMT1 itself, accompanied by an increase in miR‐34a levels through demethylation of its promoter region. This inhibition also led to a reduction in stemness characteristics within LCSCs. Furthermore, overexpression of miR‐34a resulted in the repression of stemness properties, while silencing miR‐34a exert opposite effects. Furthermore, overexpression of miR‐34a successfully mitigated the impact of elevated DNMT1 levels on the stem cell characteristics of LCSCs while leaving DNMT1 expression unaffected. Ultimately, FOXM1 serve as a direct target of miR‐34a within LCSCs. Therefore, DNMT1's abnormal activity results in promoter methylation and subsequent repression of miR‐34a, thereby leading to FoxM1 overexpression through the promotion of LCSC stemness. Thereby, inhibition of DNMT1/miR‐34a ‐mediated FOXM1 overexpression could potentially suppress liver cancer by selectively targeting LCSCs [ 154 ]. Also, DNMT1/miR‐34a axis plays a crucial role in regulating osteosarcoma cancer stem‐like cells (OSLCs). In this regard, higher DNMT1 levels, primarily through the induction of methylation in the miR‐34a promoter, significantly reduce its expression and are associated with increased stemness of OSLCs. Moreover, silencing DNMT1 is associated with demethylation of the miR‐34a promoter and upregulation of miR‐34a expression, which leads to the suppression of stemness in OSLCs in a dose‐dependent manner. Thereby, abnormal activation of DNMT1 induces promoter methylation of miR‐34a , resulting in its downregulation, thereby enhancing and maintaining the stemness characteristics of OSLCs [ 155 ]. According to recent experimentation, high SALL4 expression is associated with lower progression‐free survival (PFS) rates, and SALL4 inhibition led to diminished capabilities of colony formation, proliferation, drug resistance and migration in vitro. Furthermore, there is a direct and inverse relationship between miR‐497‐5p and SALL4 . Moreover, suppression of miR‐497‐5p led to the enhancement of stem‐like properties in choriocarcinoma CSLCs. In addition, increased expression of SALL4 and miR‐497‐5p reduction facilitates the progression of choriocarcinoma within an in vivo. Notably, DNMT1 / 3B overexpression, facilitated by the upregulation of SALL4 , hindered the expression of miR‐497‐5p by promoting hypermethylation. Thus, the miR‐497‐5p/SALL4/DNMT1/3B axis emerged as a critical factor in fostering the stemness phenotype of choriocarcinoma [ 156 ]. Pancreatic CSCs, irrespective of their heterogeneity or polyclonality within the analysed tumours, exhibit elevated levels of DNMT1 activity and DNA methylation. Moreover, applying pharmacological or genetic methods to target DNMT1 in CSCs specifically decreased their self‐renewal and in vivo tumour formation capacity. These findings establish DNMT1 as a promising therapeutic target for CSCs. Further, the miR‐17‐92 cluster, which consists of six individual members ( miR‐17 , 18a , 19a , 19b , 20a and 92a ), exhibited hypermethylation in CSCs compared to non‐CSCs. Additionally, miR‐17‐92 upregulation decreased CSC self‐renewal potential, in vivo tumour formation ability, and resistance to chemotherapy. Furthermore, suppression of the miR‐17‐92 cluster in differentiated cells resulted in a contrasting outcome, inducing non‐CSCs to exhibit characteristics resembling CSCs. In this manner, DNMT1 primarily functions by repressing the miR‐17‐92 cluster, significantly influencing PDAC CSCs maintenance. These results highlight the DNMT1 / miR‐17‐92 cluster axis as a critical regulator of biological processes in CSCs and offer a compelling basis for developing epigenetic modifiers to target CSC plasticity [ 157 ]. There is a notable upregulation of BCL11A in TNBC, while the expression of miR ‐ 137 is significantly decreased in both TNBC tissues and cell lines. The expression of BCL11A is downregulated at both the mRNA and protein levels by miR‐137 through direct targeting of its 3′ UTR. Additionally, upregulation of miR‐137 or silencing of BCL11A resulted in a decrease in the number of tumorspheres and the proportion of CSCs in both MDA‐MB‐231 and SUM149 cell lines, while also exerting an inhibitory effect on tumour growth in vivo. Additionally, an interaction exists between BCL11A and DNMT1 within TNBC cells. Notably, the inhibition of either DNMT1 or BCL11A results in a compromised capacity for cancer stemness and tumorigenesis in TNBC, which is achieved through the suppression of ISL1 expression both in vivo and in vitro. Furthermore, miR‐137 disrupts the interaction between BCL11A and DNMT1 , reducing cancer stemness and inhibiting tumour progression in TNBC [ 158 ]. Ding et al. explored the impact of the miR‐126/DNMT1 axis on the proliferation and growth of leukaemia stem cell (LSC) lines, including MOLM13‐LSCs and KG‐1a‐LSCs. They firstly indicated a notable upregulation of miR‐126 expression in both CD34+ cells and the aforementioned LSC lines. They observed that miR‐126 silencing in MOLM13‐LSCs and KG‐1a‐LSCs impeded cellular proliferation while enhancing apoptosis. They further substantiated that miR‐126 directly interacts with DNMT1 and exerts negative regulatory control over its expression. Thereby, miR‐126 enhances the proliferative capacity of LSCs by regulating DNMT1 [ 159 ](Figure  4 ). A schematic representation of miRNAs/DNMT1 axis in cancer stem cells.

Human Genome Project Completion has unveiled that approximately 1.5% of the human genome is constituted by protein‐coding genes [ 13 ]. Indeed, the Encyclopaedia of DNA Elements (ENCODE) and the Functional Annotation of the Mammalian Genome (FANTOM), two prominent collaborative initiatives, have provided evidence indicating that a significant portion of the genome undergoes transcription and generates a diverse array of ncRNAs [ 14 ]. Presently, there is a prevailing belief that the level of intricacy exhibited by a species demonstrates a stronger correlation with the quantity of ncRNAs rather than the number of protein‐coding genes [ 15 ]. NcRNAs are indispensable agents in regulating essential cellular functions spanning all biological kingdoms. They actively govern diverse aspects of gene expression, including transcription and translation processes, thereby profoundly influencing genome organisation and stability [ 16 ]. Mounting evidence suggests that ncRNAs exert a diverse range of mechanisms, such as transcriptional processes, stability of messenger RNA (mRNA), post‐translational modifications, modulation of chromosome structure and RNA splicing. Notably, miRNA, lncRNA and circular RNA (circRNA) are among the extensively investigated ncRNAs. The subsequent section provides a more comprehensive elucidation of these well‐studied ncRNA types. MiRNAs represent a class of diminutive RNA molecules, typically about 22 nucleotides in length, which can exert negative post‐transcriptional regulation over their target gene expression [ 17 ]. RNA polymerase II (Pol II) transcribes these miRNAs into primary transcripts, which undergo processing within the cellular nucleus by the RNase III Drosha and DGCR8 (microprocessor complex) to form precursor miRNAs [ 18 ]. Precursor miRNAs exhibit a configuration characterised by imperfect stem loops and undergo translocation to the cytoplasm facilitated by Exportin‐5 [ 19 ]. Within the cytoplasmic compartment, these precursor miRNAs undergo additional processing by the RNase III Dicer to attain their ultimate functional mature miRNA form. MiRNAs exert their regulatory function by forming complexes with their target mRNAs, resulting in the downregulation of mRNA stabilities and translation. In cases where the miRNA exhibits complete complementarity with its target mRNA, it can initiate the degradation of the targeted mRNA molecule. MiRNAs can also engage with their targets through partial complementarity, frequently observed in the 3′ UTR regions of mRNAs. This interaction results in the translational suppression of the target genes by a partially understood mechanism that necessitates further investigation for complete elucidation [ 20 ]. Using post‐transcriptional gene silencing (PTGS) and mRNA degradation, miRNAs can govern the epigenome, thereby inducing downregulation of critical epigenetic modifiers and orchestrating alterations in the chromatin landscape [ 21 ]. Prominent instances of epigenetic factors engaging with miRNAs encompass histone deacetylases ( HDACs ), histone methyltransferases ( HMTs ) and DNA methyltransferases ( DNMTs ). Apart from the miRNAs that hold the capacity to regulate the epigenome, it is noteworthy that the expression of these miRNAs can, in turn, be subject to regulation through epigenetic modifications. For instance, CpG islands, typically prevalent at gene promoters, are likewise present in around half of all miRNA genes, rendering them susceptible to abnormal DNA methylation and consequent dysregulation of gene expression [ 22 ]. These epigenetic modifications can induce either the downregulation or upregulation of miRNA expressions and, these altered expression patterns have been linked to various stages of tumorigenesis. In this regard, Hu et al. conducted qRT‐PCR and genomic bisulfite sequencing to examine the epigenetic silencing of miR‐484 in CC. They observed that the insufficiency of DNMT1 , which EZH2 recruits, led to a decline in CpG methylation within the promoter region miR‐484, elevating miR‐484 expression levels. They concluded that miR‐484 was reduced due to DNMT1 ‐mediated hypermethylation occurring in its promoter region, and this molecular event contributes to its role as a tumour suppressor in CC [ 23 ]. These findings demonstrated a reciprocal relationship between DNMT1 and miRNAs in human cancer (Figure  1 ). A schematic representation of the direct relationship between DNMT1 and miRNAs. The illustration portrays how specific miRNAs target DNMT1 mRNA, leading to the inhibition of its transcriptional activity. Conversely, DNMT1 exerts control by methylating the genes encoding these miRNAs, thereby impeding their own transcription. This bidirectional modulation highlights the intricate regulatory crosstalk between DNMT1 and miRNAs in epigenetic regulation. LncRNAs, encompassing sequences exceeding 200 nucleotides, participate in many physiological and pathological processes, emphasising their significant involvement in cancer development [ 24 ]. LncRNAs exert regulatory control over tumour progression by actively engaging in gene expression, drug resistance and metastasis [ 25 ]. Remarkably, contemporary investigations have unveiled the multifaceted capacity of lncRNAs in orchestrating DNA methylation processes [ 12 ]. While the prevalence of this model remains uncertain in the present era, a diverse array of lncRNAs has been documented to engage DNMTs and govern the expression of target genes, thus assuming pivotal functions in various biological processes, including but not limited to osteoarthritis, neural differentiation, cardiovascular diseases, adipogenesis, mesoderm commitment, mental disorders, muscle regeneration and different cancer types [ 26 ]. Furthermore, certain lncRNAs have been demonstrated to act as sequestering agents for DNMT , thereby exerting a negative regulatory influence on DNA methylation. In this regard, nuclear paraspeckle assembly transcript 1 ( NEAT1 ) directly interacts with DNMT1 , leading to the subsequent suppression of P53 and cyclic GMP‐AMP synthase stimulator of interferon genes ( cGAS / STING ) expression in lung cancer. So, NEAT1 , by interacting with DNMT1, inhibits the cGAS/STING pathway, thereby regulating cytotoxic T cell infiltration in lung cancer [ 27 ]. Furthermore, a recent functional investigation also substantiated the interaction between lncRNA ATB and DNMT1 , stabilising DNMT1 expression. Furthermore, ATB facilitated the association of DNMT1 with p53 . Importantly, heightened expression of lncRNA ATB expedited the proliferative and migratory capabilities of renal cell carcinoma (RCC) cells while concurrently hindering cell apoptosis. This effect is attributed to the p53 reduction, which is facilitated by the binding of ATB to DNMT1 [ 28 ]. Importantly, substantial evidence demonstrates that lncRNAs exert control over the expression of DNMTs and Ten‐Eleven Translocation enzymes ( TETs ) at various regulatory levels to modulate DNA methylation processes. Studies have reported that lncRNAs can suppress or promote DNMT expression, thus assuming crucial roles in cancer development. In this regard, lncRNA GAS5 directly interacts with EZH2 , consequently facilitating the assembly of the polycomb repressive complex 2 ( PRC2 ). This molecular event, in turn, leads to the transcriptional suppression of DNMT1 [ 29 ]. Therefore, lncRNAs, by regulating DNMT1 , are involved in the epigenetic process.

Despite the notable progress made in diagnosis and treatment over recent decades, human cancer continues to pose a significant clinical obstacle owing to the lack of advancements in long‐term survival rates. Besides genetic change, disruption of epigenetic processes can also lead to altered gene function and malignant cellular transformation. Epigenetic enzymes such as DNMT1 could lead to transcription repression by catalysing genomic DNA methylation and are usually aberrantly expressed in human tumours. Moreover, dysregulation of ncRNAs is linked to epigenetic reprogramming throughout tumour advancement, primarily attributable to their capacity to engage with DNMTs, notably DNMT1 . In the current work, we noticed a reciprocal relationship between ncRNAs and DNMT1 . Some miRNAs, including miR‐185 , miR‐139‐5p and miR‐377 , could directly target DNMT1 , whereas others, such as miR‐378 , miR‐30b, miR‐34a , miR‐497 and miR‐142 could be hypermethylated by DNMT1 and downregulated. This dual regulatory mechanism further emphasises the complexity of miRNA‐ DNMT1 interactions and their relevance in cancer pathogenesis. Notably, the ncRNA‐ DNMT1 axis plays a critical role in mediating resistance to various chemotherapy agents, including cisplatin, doxorubicin and TMZ, by regulating the expression of essential miRNAs and promoting aberrant DNA methylation that impacts tumour cell sensitivity. In addition, the ncRNA‐ DNMT1 axis plays a crucial role in regulating CSCs activity, with multiple microRNAs, such as miR‐34a and miR‐126 , modulating DNMT1 expression to influence stemness characteristics and tumour progression across various cancers. Additionally, various therapeutic strategies, including herbal medicine, synthetic RNA molecules, DNC and miRNA replacement, have been implemented to modulate the ncRNA/ DNMT1 axis as part of cancer therapy approaches. However, one limitation of the current review article is that we mainly focused on two mechanisms by which lncRNAs regulate DNMT1 function: first, by acting as molecular sponges for miRNAs, leading to increased DNMT1 expression, and second, by functioning as scaffolds to recruit DNMT1 to target miRNAs, resulting in their hypermethylation and suppression. However, lncRNAs can also operate through other approaches. For example, lncRNAs can interact with DNA and co‐transcriptionally form RNA–DNA hybrids, such as R‐loops, which are recognised by chromatin modifiers to either activate or inhibit target gene transcription, or by transcription factors. This mechanism, however, has not yet been studied in relation to DNMT1 . Thus, one of the major limitations of the current work is that we did not cover all regulatory pathways related to lncRNAs in the regulation of DNMT1 .

Recent empirical evidence indicated the role of the ncRNA/ DNMT1 axis in advancing malignant tumours. Consequently, this axis holds significant promise as a viable target for therapeutic intervention in managing human neoplastic conditions. Multiple ncRNA/ DNMT1 axis regulators have been formulated as potential interventions in cancer therapy. In the subsequent section, we delve into the significance of the ncRNA/ DNMT1 axis as a focal point for various remedies to combat malignancies in human beings. There has been a growing global acceptance of herbal medicines in recent years, leading pharmaceutical companies to actively explore them as valuable reservoirs for exploring novel drugs [ 160 ]. Empirical investigations have revealed that herbal medicine exhibits the potential to regulate various ncRNAs and the DNMT1 axis, which are closely associated with cancer. Consequently, this modulation mechanism holds promise in impeding the onset and progression of cancer. The genus Vitex encompasses 250 shrubs and trees, distributed predominantly across the tropical and subtropical regions, while several species inhabit temperate zones. Traditionally, Vitex species have been historically employed to alleviate various health conditions, including premenstrual issues, migraines, malignancies, diarrhoea, respiratory infections, rheumatic pain, GI ailments, sprains and inflammatory responses. Casticin (3′, 5‐dihydroxy‐3, 4′, 6, 7 tetramethoxyflavone), a flavonoid compound possessing a molecular formula of C19H18O8 and a molecular weight of 374.34, holds significance in this regard. A commercially accessible variant of casticin (98% purity) derived from V. trifolia is readily obtainable in an analytically graded form. Casticin, a bioactive compound, has been extracted from different plant tissues within the Vitex genus, including the fruits and leaves of V. trifolia , aerial parts and seeds of V. agnus‐castus , and leaves of V. negundo . Recent studies demonstrated that casticin displays apoptosis and antiproliferation activity. This compound has shown effectiveness against numerous cancer cell lines through diverse molecular mechanisms [ 161 ]. CAS exhibited a selective decrease in the viability of HCC cells while having no discernible effect on L02 cells. Additionally, CAS demonstrated the ability to impede the stemness characteristics within HCC cells. CAS could suppress the activity and expression of DNMT1 while simultaneously upregulating the levels of miR‐148a‐3p. Furthermore, the influence of CAS on stemness traits was nullified when DNMT1 was stably overexpressed, whereas miR‐148a‐3p upregulation augmented the diminishing effect of CAS on stemness features. Further, DNMT1 upregulation facilitated hypermethylation of the miR‐148a‐3p promoter, subsequently suppressing its expression. Additionally, miR‐148a‐3p effectively restrained DNMT1 expression by selectively binding to the 3′‐UTR of DNMT1 mRNA. In the context of in vivo nude mouse xenograft experiments, agomir‐148a‐3p and CAS exhibited substantial efficacy in inhibiting tumour growth, surpassing the individual activities of either molecule. In this manner, CAS could impede stemness properties in HCC cells through its disruption of the mutual negative modulation between miR‐148a‐3p and DNMT1 [ 162 ]. Importantly, the botanical remedy known as Rhizoma of Paris polyphyllin, a component of Traditional Chinese Medicine, has gained significant recognition among herbal healthcare professionals for its extensive use in treating various tumour types, such as those affecting the liver, urinary bladder and pancreas. Polyphyllin I (PPI), a steroidal saponin, has been extensively investigated as a prominent active constituent of Rhizoma of Paris. It has demonstrated noteworthy antitumor properties across various cancer types by impeding tumour cell proliferation, suppressing metastasis and eliciting cell cycle arrest and apoptosis via the mitochondrial pathway [ 163 ]. PPI exerted a substantial inhibitory effect on the proliferation and migration capabilities of CRPC cells while also inducing cell cycle arrest. Mechanistically, PPI led to a reduction in the expression of HOTAIR , DNMT1 and EZH2 . Intriguingly, HOTAIR silencing resulted in decreased protein expressions of EZH2 and DNMT1 . Conversely, the introduction of exogenous HOTAIR counteracted the inhibitory effects of PPI on EZH2 and DNMT1 protein expressions, as well as EZH2 promoter activity and cell growth. Moreover, in vivo findings demonstrated that PPI triggers inhibition of tumour growth, HOTAIR and the protein expressions of DNMT1 and EZH2 . Therefore, PPI impedes the proliferation of CRPC cells by suppressing HOTAIR expression, subsequently leading to the repression of DNMT1 and EZH2 expressions. In this manner, the overall responses of PPI are influenced by the intricate interplay between DNMT1 , HOTAIR and EZH2 , characterised by their mutual regulation and reciprocal effects [ 164 ]. Curcumin, derived from the rhizome of the Curcuma longa plant and belonging to the polyphenolic class, has traditionally been utilised in medicinal practices as an agent with antioxidant and anti‐inflammatory properties [ 165 ]. However, the hydrophobic characteristics inherent to this phytochemical impose significant constraints on its ability to be effectively absorbed by cells and exert its biological effects. To surmount this challenge, a potentially efficacious strategy involves the incorporation of curcumin within dendrosome nanoparticles, which has recently been devised as dendrosomal nano‐curcumin (DNC) [ 166 ]. Chamani et al. explored the impact of DNC on the mir‐34 family member's expression in two HCC cell lines, Huh7 and HepG2. They demonstrated that DNC treatment induced upregulation of mir34a, mir34b and mir34c expression while concurrently downregulating the expression of DNMT1, DNMT3A and DNMT3B in both Huh7 and HepG2 cell lines. Also, the viability of Huh7 and HepG2 cells diminished by DNC administration, primarily by facilitating the reestablishment of miR‐34 s expression. So, DNC exerted its effect by downregulating DNMTs, thereby reactivating the epigenetically suppressed miR‐34 family. In this manner, DNC could be a promising candidate for epigenetic therapy in HCC [ 167 ]. Over the past 2 years, endeavours in synthetic biology have yielded innovative synthetic RNA constituents that can modulate gene expression within living organisms [ 168 ]. These advancements have laid the foundation for achieving scalable and customizable cellular functionality. The primary obstacles that need to be addressed in this nascent discipline involve elucidating strategies for effectively integrating computational and directed‐evolution techniques to enhance the intricacy of engineered RNA systems [ 169 ]. Additionally, there is a pressing need to explore avenues for the widespread application of these systems within mammalian contexts. PAS1‐30 nt‐RNA represents a chemically engineered PAS1 segment artificially created to incorporate enhancements in 2′‐O‐methylation and 5′‐cholesterol, specifically facilitating in vivo RNA transportation. In BC, DNMT1 acts as a suppressor of PAS1 expression, and subsequent DNMT1 silencing resulted in a noticeable increase in PAS1 levels. Additionally, protein PAS1 interacts with the RNA‐binding protein vigilin, preserving its overall stability. Furthermore, PAS1 facilitates the binding of H3K9me3 at the PH20 promoter through its interaction with SUV39H1, resulting in the repression of PH20. Importantly, in vivo and in vitro analysis revealed that PAS1 upregulation effectively impeded BC cell proliferation and metastasis. Combining decitabine with PAS1‐30 nt‐RNA significantly displays enhanced anti‐tumour effects, surpassing the efficacy observed with decitabine as a standalone treatment. The observed effectiveness of the combination is contingent not only upon the collaborative impacts of the DNMT inhibitor and PAS1‐30 nt‐RNA but also on the augmented expression of PAS1 instigated by the DNMT inhibitor. In this manner, in future BC treatment, a potential approach could involve the concurrent administration of decitabine and PAS1‐30 nt‐RNA, primarily targeting the modulation of DNMT1 / PAS1 / PH20 interactions [ 170 ]. MicroRNA molecules play a pivotal role in cancer progression and are progressively being implemented in clinical settings as targets and agents for therapeutic purposes [ 171 ]. A novel intervention strategy known as miRNA replacement has been recently devised, aiming to address the therapeutic potential of miRNAs. The rationale for advancing miRNA therapeutics is founded on the principle that rectifying these deficiencies in miRNAs through either antagonistic or restorative measures holds the potential to yield therapeutic advantages [ 172 ]. Therefore, we presented the most recent inquiries into the therapeutic approaches concerning the delivery of miRNAs. Specifically, Ding et al. examined the impact of miR‐200 family constituents and epigenetic alterations on preserving the mesenchymal/metastatic phenotype subsequent to EMT in HCC. They observed that mesenchymal cells following EMT exhibit significant upregulation of E‐box repressors Zeb2 and Zeb1 , alongside a simultaneous decrease in the expression of four members of the miR‐200 family (namely, miR‐200a , miR‐200b , miR‐200c and miR‐429 ). Their further experimentation revealed the methylation of multiple CpG sites present within the E‐cadherin promoter region in mesenchymal cells. They also showed that miR‐200b enforced expression in these cells led to a noteworthy enhancement in E‐cadherin levels and a concurrent decrease in cell migration in vitro. On the contrary, their in vivo investigations demonstrated the absence of notable alterations in metastatic capacity after miR‐200b overexpression. Their subsequent experimentation unveiled that the combined administration of a DNMT inhibitor and miR‐200b overexpression led to a considerable reduction in the invasive characteristics and complete elimination of metastatic potential in mesenchymal cells. Additionally, it was revealed that the specific application of short hairpin RNA to target E‐cadherin directly did not lead to the restoration of metastatic capability following DNMT silencing and re‐expression of miR‐200b . Furthermore, they disclosed that E‐cadherin restoration in primary mesenchymal cells proved insufficient in impeding metastatic potential. A practical approach to address liver cancer metastasis may involve a combined therapeutic strategy involving the modulation of miR‐200b expression and DNMT silencing without necessarily relying on E‐cadherin restoration [ 173 ]. Furthermore, Cai et al. examined the combined therapeutic impact of sorafenib and gold nanoparticles carrying anti‐ miR‐221 on HCC cell lines. Their investigation revealed that the administration of sorafenib in HepG2 and Huh7 cells triggered miR‐221 signalling pathway activation, resulting in significant upregulation of miR‐221 expression. They additionally validated the decrease in p27 expression due to sorafenib treatment while observing a corresponding increase in DNMT1 levels. They observed that increasing concentrations of AuNPs‐anti‐miR221 inhibited cell growth in both Huh7 and HepG2 cells. Moreover, the combined treatment of AuNPs‐anti‐miR221 and sorafenib led to a significant enhancement in cell growth inhibition. Additionally, they found that AuNPs‐anti‐miR221 exhibited a synergistic effect, further enhancing the inhibitory action of sorafenib. Their further experimentation disclosed that the administration of sorafenib in combination with AuNPs‐anti‐miR221 triggers elevated levels of p27 expression and reduced levels of DNMT1 expression. This signifies that AuNPs‐anti‐miR221 exhibits chemosensitizing properties when used in conjunction with sorafenib. Thereby, AuNPs‐anti‐miR‐221 could effectively augment the inhibitory impact of sorafenib on cell proliferation by deactivating the miR‐221/p27/DNMT1 signalling pathway. Hence, it is plausible to consider AuNPs‐anti‐miR221 as a viable chemosensitizer in treating HCC when used with sorafenib [ 174 ]. Importantly, Indoleamine 2, 3‐dioxygenase (IDO) is an intracellular enzyme whose increased activity demonstrates a negative correlation with the presence of tumour‐infiltrating lymphocytes (TILs) in cases of oesophageal and endometrial cancers. Zhou et al. explored the impact of cancer‐secreted exosomal miR‐142‐5p on the immune status of cervical squamous cell carcinoma (CSCC). They initially demonstrated a positive association between elevated levels of miR‐142‐5p and indoleamine 2, 3‐dioxygenase (IDO) expression in lymphatic vessels associated with advanced CSCC. They observed that miR‐142‐5p is conveyed from CSCC‐secreted exosomes to lymphatic endothelial cells (LECs), leading to the depletion of CD8 + T cells through the enhancement of lymphatic indoleamine 2, 3‐dioxygenase (IDO) expression. This effect was negated when an IDO inhibitor was administered. Their mechanistic analysis demonstrated that miR‐142‐5p directly inhibits the expression of lymphatic AT‐rich interactive domain‐containing protein 2 ( ARID2 ). Furthermore, it hinders the recruitment of DNMT1 to the interferon ( IFN)‐γ promoter and amplifies the transcription of IFN‐γ by suppressing promoter methylation. Consequently, this cascade of events culminates in heightened IDO activity. They additionally observed a positive association between elevated levels of serum exosomal miR‐142‐5p and the advancement of CSCC, along with parallel increases in IDO activity. Therefore, CSCC cells release exosomes containing miR‐142‐5p , which subsequently promote IDO expression in LECs through the ARID2‐DNMT1‐IFN‐γ signalling pathway, resulting in the suppression and depletion of CD8 + T cells [ 175 ](Table  2 ). An overview of different compounds targeting non‐coding RNAs and their potential influence on DNMT1 activity.

Cancer, in its essence, encompasses more than 100 distinct malignant diseases that manifest in different tissues throughout the human body [ 1 , 2 ]. The elevated mortality rates linked to cancer are, in part, attributable to deficient early detection modalities and imprecise diagnostic instruments. Therefore, precise cancer diagnosis and prognosis estimation are crucial to improving patient survival rates. The prevailing cancer biomarkers, predominantly comprised of protein or peptide‐based entities like glycoproteins, often demonstrate fluctuations in their tissue or blood levels, serving as potential indicators for disease progression, including cancer [ 3 ]. An increasing body of research has substantiated the pivotal role of epigenetic alterations in tumorigenesis and cancer progression. Epigenetic processes are crucial for maintaining proper growth, development and gene control in various body systems [ 4 ]. When these mechanisms become disrupted, they can alter gene function, leading to pathological conditions such as cancer. So, tumorigenesis cannot be solely attributed to genetic modifications, as it also encompasses epigenetic transformations, including DNA methylation [ 5 ]. This covalent alteration can impede gene transcription by either obstructing the interaction between a transcription factor and its corresponding binding sites or recruiting methylated binding domain proteins that facilitate the suppression of gene expression [ 6 ]. DNMT1 is an enzymatic catalyst that establishes DNA methylation patterns throughout cellular differentiation and development. UHRF1 is a cofactor of DNMT1 and binds directly to DNMT1 via its N‐terminal ubiquitin‐like domain (UBL). UHRF1 RING domain catalysed the binding of DNMT1 to ubiquitinated histone H3, ensuring subnuclear localization of DNMT1 and maintenance of DNA methylation [ 7 ]. Multiple investigations have demonstrated its pivotal contribution to the pathogenesis of cancer [ 8 ]. In this regard, Zhang et al. examined the correlation between DNMT1 and aberrant methylation patterns of tumour suppressor genes (TSGs) and their association with the malignant phenotype observed in cervical cancer (CC). Their findings disclosed that the DNMT1 methylation status could impact the activity of various crucial TSGs during the development of cervical tumours. Consequently, targeting DNMT1 methylation holds promise as a viable therapeutic approach for treating CC [ 9 ]. Furthermore, DNMT1 ‐mediated effects in carcinogenesis may occur through the regulation of cell cycle‐ and apoptosis‐related genes. Notably, DNMT1 silencing has been shown to increase Bax expression while decreasing Bcl‐2 and CCND1 / 2 in AN3CA cells, suggesting the potential of DNMT1 in endometrial carcinoma (EC) therapy [ 10 ]. Thereby, among the numerous epigenetic regulators associated with cancer, DNMT1 has been identified as a key enzyme, owing to its fundamental role in maintaining cellular methyltransferase activity, regulating both global and gene‐specific demethylation, and the reactivation of TSGs in human cancer cells [ 11 ]. In this manner, exploring the function of DNMT1 in cancer presents a valuable opportunity to increase our understanding of tumour biology and to identify potential therapeutic targets. Recent extensive research emphasises the importance of ncRNA molecules in governing the function of DNMT1 . In this regard, DACOR1, a long non‐coding RNA (lncRNA), has been shown to activate tumour‐suppressor pathways and function as a regulator of cellular growth suppression. In terms of mechanism, DACOR1 markedly reduced the expression of cystathionine β‐synthase, a critical methyl donor in DNA methylation. Collectively, dysregulation of DNMT1‐associated lncRNAs plays a critical role in driving abnormal DNA methylation patterns and gene expression in colon tumorigenesis [ 12 ]. Furthermore, recent investigations offer valuable insights into the intercommunication and mechanisms involved in regulating DNMT1 by ncRNA. This observation underscores the extensive engagement of ncRNAs and their interplay with crucial epigenetic modifiers, such as DNMT1 , governing the expression of numerous target genes.

The authors declare no conflicts of interest.