Evolving landscape of detection and targeting miRNA/epigenetics for therapeutic strategies in ovarian cancer.

OC poses significant challenges in treatment, with platinum-based chemotherapy being the cornerstone of management. However, the emergence of platinum resistance necessitates the exploration of alternative therapeutic strategies. Herein, we discuss various therapeutic approaches, including targeted therapies, immunotherapies, epigenetic modulators, and novel combinations, to combat OC and overcome chemoresistance. Combination therapies have shown promise over monotherapies, as combining anticancer agents can produce synergistic effects and improve efficacy against OC [ 346 ]. For instance, Pujade-Lauraine et al. demonstrated that adding monoclonal antibodies targeting VEGF to chemotherapy enhances progression-free survival in platinum-resistant OC [ 347 ]. Similarly, cediranib, a VEGF receptor inhibitor, has proven effective in extending progression-free survival in relapsed OC, supporting angiogenesis inhibition as a beneficial approach [ 348 ]. Other studies, such as Wang et al.’s investigation of apatinib with pegylated liposomal doxorubicin, and the nanoparticle-drug conjugate CRLX-101 with bevacizumab, have shown therapeutic efficacy in recurrent OC [ 349 , 350 ]. In contrast, Richardson et al. reported limited benefit of combining pazopanib (small molecule inhibitor of multiple receptor tyrosine kinases), with paclitaxel in recurrent OC [ 351 ], while nivolumab combined with bevacizumab showed promising results in platinum-sensitive OC cases, indicating potential for immune checkpoint inhibitors [ 352 ]. Additionally, metformin showed favorable outcomes in advanced-stage epithelial OC patients [ 353 ]. We reported tumor growth inhibitory effect of gold nanoparticles by using an orthotopic patient-derived xenograft model of HGSOC [ 354 ]. Recently, poly (ADP-ribose) polymerase (PARP) inhibitors have emerged as a ground-breaking therapeutic approach in the management of OC, particularly in patients with BRCA1/2 mutations. These inhibitors exploit synthetic lethality, a phenomenon where cancer cells with defective DNA repair mechanisms, such as those harboring BRCA mutations, are selectively targeted [ 355 ]. While combinations such as pembrolizumab with bevacizumab and oral cyclophosphamide yielded benefits for platinum-resistant patients [ 356 ]. Additionally, combining of Aurora A kinase inhibitor alisertib with paclitaxel improved outcomes in recurrent OC [ 357 ]. While combinations such as pembrolizumab with bevacizumab and oral cyclophosphamide yielded benefits for recurrent OC patients [ 358 ]. Recently, we reported that higher expression of lysine-rich coiled-coil 1 (KRCC1) protein in HGSOC patients and OC cell lines is associated with drug resistance and poor overall survival. We confirmed that KRCC1 is a as a chromatin-bound protein associated with drug resistance and poor survival, with its silencing reducing tumor growth and enhancing response to treatment, suggesting KRCC1 could be a potent therapeutic target in OC [ 359 , 360 ]. Epigenetic modulators have shown promise in OC treatment by reversing resistance and enhancing chemotherapy efficacy. Bauman et al. combined the DNA methyltransferase inhibitor 5-azacytidine with erlotinib in OC, which was well-tolerated and produced positive outcomes [ 361 ]. Fu et al. suggested that hypomethylating agents may partially reverse platinum drug resistance in OC [ 362 ]. Fang et al. demonstrated that low-dose decitabine restored carboplatin sensitivity, extending progression-free survivalin OC patients [ 363 ]. New compounds, such as OSU-HDAC42, developed by Yang et al. and EZH2-targeting miR-298 regulation, are showing therapeutic potential, particularly in drug-resistant OC [ 364 , 365 ]. Vorinostat, a HDAC inhibitor, has shown efficacy with paclitaxel and carboplatin in platinum-sensitive recurrent OC patients, though treatment-related side effects were noted [ 366 ] and further research is necessary to fully understand their therapeutic benefits. miR therapeutics have gained significant interest in clinical trials for OC due to their potential to target specific molecular pathways involved in tumorigenesis and progression. Several miR-based therapies are currently being investigated in clinical trials for OC, aiming to either restore the expression of tumor suppressor miRs or inhibit the function of oncogenic miRs. MRX34 (miR-34 mimic) is a liposomal miR-34a mimic designed to restore the expression of miR-34a, a tumor suppressor miR that is frequently down-regulated in OC. A phase I clinical trial ( NCT01829971 ) evaluated the safety and efficacy of MRX34 in patients with advanced solid tumors, including OC. However, the trial was terminated early due to immune-related adverse events. Likewise, mesomiR-1 (miR-16 mimic) is a miR-16 mimic encapsulated in a liposomal nanoparticle formulation, designed to restore the expression of miR-16, a tumor suppressor miR that is often down-regulated in OC. A phase I/II clinical trial ( NCT02369198 ) is currently ongoing to evaluate the safety and efficacy of MesomiR-1 in patients with recurrent OC. Recently, Zhao et al. demonstrated that exosome-mediated delivery of miR-484 into a OC xenograft model, resulted in inhibited expression of VEGF-A in cancer cells and its receptors in endothelial cells, leading to improved vascular function which facilitated vascular normalization, and increased drug sensitivity [ 367 ]. In addition to these strategies, miR-regulated oncolytic virus therapies are currently under investigation. Oncolytic viruses can upgrade the delivery and efficacy of miR-based therapeutics [ 368 ]. Oncolytic viruses engineered to express tumor suppressor miRs or inhibit oncogenic miRs are being investigated as potential therapeutic agents for OC [ 369 ]. Emerging interest in natural antisense transcripts (NATs) highlights their potential role in regulating miRs and targeting cancer-relevant pathways (reviewed by Najafi et al. [ 370 ]). Kallikrein (KLK) serine protease family members KLK6 and KLK7 were reported to be elevated in OC cell lines as well as serum of the early stages of OC [ 371 ]. Kallikrein-related peptidases 4, 5, 6 and 7 (KLK4–7) induced the expression of moesin, keratin, type-I cytoskeletal 19 in OC which are positively correlated with the cancer progression [ 372 ]. High KLK7 level induces multicellular aggregates that promote cell survival and paclitaxel chemoresistance in OC [ 373 ]. Therefore, KLK4 inhibition may improve the drug-sensitivity and thus therapeutic applications in OC. Although reports are scanty but studies show few miRs can regulate KLKs in OC, like hsa-let-7a miR causes down-regulation of KLK6 in OC cell line. Additionally, hsa-let-7f, miR-224, miR-516a can target and decrease KLK10 level and therefore, these miRs can be useful for therapeutic developments in OC [ 374 , 375 ].

Detecting OC at an early stage is particularly challenging due to the nature of its symptoms, which are often indistinct, nonspecific, and can easily be mistaken for other common conditions. Additionally, the biological behavior of OC contributes to the detection challenge. Ovarian tumors can grow and spread extensively within the pelvic and abdominal cavities before causing noticeable symptoms. This insidious growth pattern means that by the time symptoms prompt further investigation, the cancer is often already at an advanced stage [ 24 ]. Therefore, identifying biomarkers for early stage OC is utmost important. Biomarkers can be categorized into predictive, diagnostic, and prognostic types. Predictive biomarkers help tailor specific treatments and anticipate clinical outcomes. Diagnostic biomarkers precisely identify the disease, including its stage and subtype while prognostic biomarkers indicate overall prognosis and potential disease progression, regardless of the treatment [ 25 ]. An ideal biomarker should possess the characteristics of high sensitivity and specificity so that only those patients with a specific disease are detected. In addition, the detection should be non-invasive and ideally cost-effective. Despite advancements, existing serum biomarkers for OC lack specificity and sensitivity, highlighting the need for novel OC-specific biomarkers that can differentiate between its subtypes, stages. This underscores the need for the development of new biomarkers that are specific to OC. CA125 originates from a larger glycosylated transmembrane protein called Mucin 16 (MUC16) [ 26 ]. MUC16 contains a transmembrane domain, with its extensive extracellular portion, which includes CA125, extending into the surrounding environment. MUC16 is expressed in approximately 80% of OC cases, making CA125 a significant marker for OC. The N-glycans portion of the protein pairs with mesothelin and this is thought to be the primary contact site between tumor cells and the peritoneal surface; mesothelin-specific antibodies hinder adhesion of cancer cells to the mesothelium. Additionally, knockdown of CA125 leads to reduced OC invasion. CA125 is secreted into body fluids and serum threshold level is considered to be 35 U/mL in case of OC [ 27 ]. Recent findings suggest that CA125 might serve as a predictive marker for pre-invasive OC. Serum CA125 levels are frequently elevated months before clinical or symptomatic relapse in OC patients [ 28 ]. However, Rustin et al. did not find any survival benefit with early treatment based on increased CA125 concentrations compared with delayed treatment based on clinical recurrence [ 28 ]. However, serum CA125 is not only overexpressed in OC, but also in several other cancers, including pancreatic, hepatocellular carcinoma (HCC), and lung cancers. This makes it challenging to accurately diagnose cancer and determine its type at an early stage based on CA125 detection. Additionally, numerous nonmalignant conditions, such as idiopathic pulmonary fibrosis, rheumatoid arthritis-related interstitial lung disease, ovarian cysts, endometriosis, adenomyosis, uterine fibroid, pelvic inflammatory disease, cirrhosis, and cardio-renal failure, can also result in elevated serum CA125 levels [ 29 ]. Still, despite the limited sensitivity and specificity of circulating CA125, it is recommended as a clinical biomarker for screening of high-risk women with OC in the United States [ 30 ]. Although reports are scanty, but miR-200c can target the coding sequences and regulate the expression of mucin 16 in pancreatic cancer [ 31 ] which suggests possible involvement of miRs in biomarkers expression. HE4, a 25 kDa secretory protein, expressed in the reproductive and respiratory tract and reported to be secreted into the blood stream of OC patients. In the context of OC, the expression of HE4 is histotype specific, and mainly observed in serous and endometrial ovarian tumors [ 32 ]. Considering its disease association and expression, FDA approved HE4, in 2009 for early-stage detection and assessment of OC recurrence. Moreover, the combining of CA125 and HE4 has been shown to improve the efficacy of cancer prediction and making HE4 a promising biomarker for OC [ 33 ]. Additionally, studies indicate that HE4 can be regulated by miRs such as miR-149 that inhibits HE4 and sensitizes colorectal cancer to radiotherapy Similarly, miR-325–3p can also effectively target HE4 protein [ 34 , 35 ]. Therefore, assessing the miRs target for HE4, along with the expression profiling of both HE4 and miRs in OC, could provide valuable insights for disease diagnosis and therapy. Circulating tumor DNA (ctDNA) is an emerging biomarker with significant potential in cancer detection, monitoring, and prognosis. Comprising small DNA fragments released into the bloodstream as tumor cells undergo apoptosis or necrosis, ctDNA reflects the genetic makeup of the primary tumor, making it a valuable non-invasive tool for detecting cancer, evaluating treatment responses, and tracking disease progression or recurrence. To analyze ctDNA in patients, a minimally invasive liquid biopsy is performed. This approach enables real-time monitoring through repeated sampling, allowing for the capture of tumor dynamics over time. Liquid biopsy techniques focus on detecting both tumor cells and cell-free DNA (cfDNA) from primary, metastatic, or recurrent tumors circulating in the bloodstream, opening new avenues for early diagnosis, particularly for cancers that are challenging to detect through traditional methods [ 36 ]. For example, circulating tumor cells (CTCs), another component of liquid biopsies, have been detected in approximately 90% of newly diagnosed EOC cases, with an even higher prevalence in advanced disease stages. This finding underscores the potential of ctDNA and CTC analyses as critical tools for improving cancer detection and management [ 37 ]. Compared to conventional biomarkers like CA125—which can increase due to benign conditions and has a prolonged half-life of 9 to 44 days—ctDNA offers both higher specificity and a significantly shorter half-life of 16 minutes to 2.5 hours. This shorter half-life allows ctDNA levels to more accurately reflect the current tumor status, making it an ideal candidate for dynamic, real-time cancer monitoring and response assessment [ 38 , 39 ]. In summary, ctDNA holds promise as a sensitive and specific biomarker for cancer detection and management, particularly as technologies evolve to improve the accuracy and accessibility of liquid biopsy methods. With further standardization and validation, ctDNA analysis could soon become a cornerstone of personalized cancer care. In addition to the previously discussed biomarkers, mutations in tumor suppressor proteins, such as BRCA1 and BRCA2 significantly increase the risk of developing OC [ 40 ]. Research by Singh et al. revealed frequent methylation of the BRCA1 promoter in serous and mucinous OC, indicating its potential utility as a biomarker for risk assessment and treatment guidance [ 41 ]. Similarly, cell surface glycoprotein and tumor differentiation antigen mesothelin is reported to be overexpressed in OC and is correlated with shorter disease-free survival and worse overall survival of EOC patients [ 42 ]. This suggests that mesothelin could be effectively utilized alongside other biomarkers. Additionally, elevated levels of carbohydrate antigen 19–9 and carcinoembryonic antigen (CEA) have been observed in the serum of OC patients [ 43 ], highlighting their potential as complementary biomarkers when used in conjunction with others. Together, these findings underscore the importance of a multi-biomarker approach for enhancing diagnosis and treatment strategies in OC. Osteopontin, an extracellular matrix (ECM) glycoprotein produced and secreted into the ECM by endothelial and osteoblast cells, has been identified as being highly expressed in EOC. This protein is recognized as an early cancer biomarker in the blood, although research indicates that its expression does not significantly vary among different subtypes of OC. In HGSOC patients, osteopontin demonstrates approximately 90% sensitivity in blood and 98% in ascitic fluid. A meta-analysis suggested that osteopontin could serve as a valuable supplement to CA125 in OC screening [ 44 ]. Surfactant protein D, integral to the innate immune system, has been suggested as a useful biomarker in OC [ 45 ]. Additionally, Russell et al. used isobaric tags to identify 90 proteins with varying expression in OC, among which Protein Z emerged as an independent potential biomarker for early detection [ 46 ]. Recent research has shown that combining thymidine kinase 1 protein with serum-based biomarkers CA125 or HE4 enhance the detection efficacy in the early stages of cancer [ 47 ]. Programmed cell death protein 1 (PD-1) is a co-inhibitory molecule predominantly expressed in T cells, its ligand, PD-L1, interacts with PD-1 to suppress T-cell activation, leading to immune inhibition (reviewed by Abiko et al. [ 48 ]). Elevated levels of PD-1 and PD-L1 are associated with poor prognosis in OC [ 49 – 51 ] and studies show epigenetic regulation by DNA methylation, histone acetylation can alter the PD-L1 expression in various cancer (reviewed by Lin et al. [ 52 ]). PD-L1 expression has been positively associated with the stemness markers CD44 and LGR5 in OC [ 53 ]. Therefore, plasma PD-L1, PD-1 levels could serve as valuable biomarkers for OC prognosis and diagnosis [ 54 – 56 ] and targeting PD-1/PD-L1 pathway may offer promising immuno-therapeutic option in OC [ 48 ]. Urine-based peptidomic profiling has identified leucine-rich α -2 glycoprotein 1 (LRG-1) as a promising biomarker in OC [ 57 ]. Furthermore, Rockett et al. developed a low-cost, high throughput cluster-enhanced nanopore sensor capable of detecting two cysteine-containing peptides originating from LRG-1, making it a valuable tool for OC detection [ 58 ]. Conducting large-scale trials and comprehensive evaluations of these emerging biomarkers is crucial for improving the early and accurate detection of OC. Such studies can validate the biomarkers’ clinical utility, refine diagnostic accuracy, and could potentially enable earlier interventions, which are critical for improving patient outcomes. Additionally, integrating these biomarkers into multi-modal screening strategies could enhance sensitivity and specificity, addressing current limitations in early OC detection. RNA-based biomarkers are increasingly recognized as critical tools for the early detection and prognosis of OC. Their significance stems from the abundance of RNA copies within cells, making RNA detection feasible even in limited sample sizes [ 59 ]. The utility of RNA-based biomarkers extends further with studies identifying specific RNA expression patterns that differentiate between healthy individuals and those with EOC. For instance, Zalfa et al. identified an RNA expression signature of eight genes, ADGRG1, EPCAM, ESRP1, MAL2, MYH14, PRSS8, ST14 and WFDC2 that can differentiate between healthy individuals and those with EOC, exhibiting high sensitivity and specificity [ 60 ]. Pseudouridine synthase 7 (PUS7), an RNA modification gene, has also shown potential as a diagnostic marker for OC [ 61 ]. This highlights RNA’s potential as an ideal biomarker candidate in OC. Additionally, non-coding RNAs garnered interest due to their differential expression in various cancer types. El-Shal et al. identified increased expression of long non-coding RNA (lncRNA) RP5–837J1.2 in serum and cancer tissue samples, along with decreased serum level of miR-361–3p and pellino E3 ubiquitin protein ligase family member 3 (PELI3), supporting their roles in OC diagnosis [ 62 ]. The expression of the circular RNA circN4BP2L2, circBNC2 has been found to decrease in EOC, whereas circSETDB1 level was enhanced suggesting its potential as an OC biomarker [ 63 – 65 ]. Studies revealed that miRs display aberrant expression profiles in cancer cells compared to normal cells, alongside a tissue-specific expression pattern, making them promising diagnostic markers for certain cancer types. The stability of miRs within exosomes, vesicles, protein-bound state and lipoproteins in the bloodstream underscores their utility as reliable indicators for non-invasive cancer detection [ 66 ]. Moreover, inside the cell, after loading into the Argonaute (AGO) protein, the 5′ and 3′ termini of the miR remain inserted into the AGO middle and PIWI/AGO/Zwille domains which prevents exonucleolytic decay [ 67 ] and thus, miRs are very stable and their half-lives can extend from days to weeks in vivo , which manifests them as an ideal biomarker candidate [ 68 ]. MiR-146a-5p and miR-191–5p were found to be useful in discriminating CCOC and ovarian endometrioma and thus can be projected as early and non-invasive diagnostic biomarkers in CCOC [ 69 ]. In MOC, the miR-192/215 family, including miR-192, miR-194, and miR-215, is overexpressed and could serve as diagnostic biomarkers, as they are typically elevated in MOC but not in other OC subtypes or sex cord-stromal tumors [ 70 ]. As compared to healthy subjects the level of miR-1307 and miR-375 were found to be elevated in the serum exosomes of OC and these can be also used as potent serum biomarkers [ 71 ]. Additionally, miR-34a levels were found to be significantly up-regulated in serum exosomes of early-stage OC patients in comparison with advanced stages [ 72 ] and thus it is a potential biomarker of early-stage cancer detection. Wang et al. listed a panel of eight dysregulated miRs namely miR-1246, miR-1290, miR-483, miR-429, miR-34b-3p, miR-34c-5p, miR-145–5p, miR-449a that were consistently altered in both ascites and plasma of OC patients [ 73 ]. Chao et al. suggested that hsa-miR-130a can be a crucial serum biomarker for the evaluation of cancer recurrence [ 74 ]. Ongoing research continues to make significant progress in identifying RNA-based biomarkers, which hold promise for improving OC outcomes through earlier and more precise detection. In the following sections, we will delve deeper into the differential expressions of miRs in OC and probable proposition of various miRs as OC biomarkers and their role in drug resistance.

The evolving fields of miRs and epigenetics have attracted significant research interest, but their clinical applications remain in early stages. The identification of non-invasive, highly specific biomarkers for early diagnosis is a critical area of focus, with the potential to significantly improve outcomes. Profiling stage and histotype specific miR expression holds promise for developing diagnostic biomarkers, while therapeutic strategies targeting oncomiRs or restoring tumor-suppressing miRs holds promise for inhibiting cancer progression and metastasis. Further research is required to elucidate the roles of miRs in metastasis and to define optimal strategies for targeting chemoresistant OC. Regulatory network analyses of dysregulated miRs in OC reveal their influence on key signaling pathways, including P53, WNT/β-catenin, MAPK, TGF-β, mTOR, and VEGF. These pathways are integral to tumorigenesis and progression, highlighting the therapeutic potential of targeting miRs and their downstream effects. Experimental validation of these findings is essential to translate this knowledge into viable therapies. A comprehensive understanding of the molecular mechanisms driving chemoresistance and disease recurrence is equally critical. Epigenetic modulators such as DNMT and HDAC inhibitors have shown potential in reversing drug resistance, but their clinical efficacy, toxicity, and long-term safety require further investigation. Additionally, the development of efficient and targeted miR delivery systems for in vivo applications remains a key challenge. Given the heterogeneity in genetic backgrounds, lifestyle factors, and environmental influences among patients, large and diverse sample sizes are crucial for ensuring reproducibility and generalizability of research findings. This variability underscores the importance of personalized approaches to therapy. In conclusion, a multifaceted therapeutic strategy combining targeted therapies, immunotherapies, epigenetic modulators, and innovative combination treatments holds promise for improving outcomes in OC patients. Such approaches aim to address chemoresistance, reduce recurrence rates, and improve overall survival. Further clinical studies are essential to validate these strategies, refine therapeutic protocols, and pave the way for integrating these advancements into clinical practice.

MicroRNAs are small, non-coding RNA molecules, typically 18–24 nucleotides long, that play pivotal role in various biological functions including cell differentiation, proliferation, and apoptosis [ 75 ]. The process of miR maturation begins with their transcription from DNA into primary miRs (pri-miRs). These pri-miRs are then processed into precursor miRs (pre-miRs) and eventually into mature miRs. miRs regulate gene expression by binding to the 3′ untranslated regions (UTR) of their target mRNAs, leading either to the mRNA degradation or inhibition of protein synthesis [ 76 , 77 ]. The disruption of gene expression is mediated by the miRISC (RNA-induced silencing complex) and can be categorized into three primary processes: i) site-specific cleavage, ii) enhanced mRNA degradation, and iii) translation inhibition. These pathways have already been reviewed in detail by Jonas et al., Lorio et al. [ 78 , 79 ]. However, miRs can also bind to other regions, such as the 5′ UTR, coding sequences, and gene promoters, as reported in various studies. Interestingly, under certain conditions, miRs can also activate gene expression [ 80 ]. In mammals, miR genes often exhibit numerous isoforms, resulting from gene duplication [ 81 , 82 ]. Bioinformatics and laboratory-based studies suggest that a single miR can regulate more than 100 mRNAs, with over 60% of human protein-coding genes containing miR binding sites in their 3ʹ UTRs [ 83 ]. Recent studies have revealed miR-1914, miR-203, miR-135a-2, miR-149, miR-9–1, miR-20b, miR-301b, miR-545, miR-19b-1, and miR-1284 can be contributors to the high risk of OC recurrence [ 84 ]. Therefore, understanding the mechanisms of action of these miRs and their expression is essential for their potential use in therapeutic development. In the next part, we have focused on the altered expression of miRs and the role of miRs / epigenetics in OC progression. The deregulation of miRs through diverse genetic, epigenetic, and transcriptional mechanisms significantly contributes to the initiation and progression of cancer. Numerous regulatory steps control miR biogenesis at various stages, and alterations in these steps can impact miRNA-mediated gene expression, causing altered gene expression associated with cancer progression [ 85 ]. Interestingly, Calin et al. showed that approximately 50% of miRs are located at fragile sites (cancer susceptibility loci), which harbor genes or genetic variants associated with an increased risk of specific cancer types [ 86 ]. Mutations in miR seed sequence can disrupt target repression by tumor-suppressive miRs or lead to alterations in target selection, thereby promoting oncogenesis. Additionally, sequence variations such as SNPs, have been shown to influence miR targeting [ 87 , 88 ]. Mutations in the miR biogenesis pathway for example, partial deletion of Dicer and Drosha, two vital miR processing enzymes, has been shown to expedite tumorigenesis in vitro and in vivo [ 89 ]. Research indicates that conditional deletion of one Dicer1 allele accelerates the growth of adenocarcinomas [ 90 ]. To investigate genome-wide miR DNA copy number abnormalities in OC, Zhang et al. [ 91 ] performed high-resolution array-based comparative genomic hybridization, discovering DNA copy number variation in 37.1% of genomic loci containing miRNA genes. Additionally, cytogenetic analysis of patients with HGSOC revealed focal somatic copy number amplifications at several chromosome 19 regions: 19p13.2, 19p13.12, 19p13.11, 19q12, 19q13.12, and 19q13.2 [ 92 ]. Certain transcription factors regulate miR expression by recruiting chromatin remodeling enzymes to miR loci, as demonstrated by the silencing of miR-223 by AML1/ETO [ 93 ]. Oncogenic transcription factors like Myc bind to miR promoter regions and down-regulate miRs with anti-proliferative and tumor-suppressive roles, such as miR-15a/16–1, miR-26a, miR-29, and members of the miR-34 family [ 94 – 97 ]. The transcription factor p53, frequently mutated in over 50% of human cancers, also regulates several miRs involved in cell cycle control and apoptosis, including miR-107 and miR-1249, which inhibit angiogenesis and epithelial-mesenchymal transition (EMT) [ 98 – 100 ]. Moreover, miR-339–5p, miR-509–5p directly target 3’ UTR of MDM2, a primary negative regulator of p53, adding regulatory complexity to the p53-MDM2 feedback loop [ 101 – 103 ]. Based on the target genes, some miRs can act as a tumor suppressor in OC. For example, miR-337–3p suppresses cell proliferation and induces apoptosis by targeting and down-regulating PI3K/AKT pathway proteins PIK3CA and PIK3CB, which correlates with lower pathological grades in OC patients [ 104 ]. Similarly, miR-145 also acts as a tumor suppressor in OC by directly targeting the oncoprotein high-mobility group A2 (HMGA2) hence reducing cell proliferation and migration while promoting apoptosis. Down-regulation of miR-145 in OC leads to increased expression of HMGA2, which is associated with advanced disease stages and distant metastasis [ 105 ]. Likely, the level of miR-193a-5p was observed to be lower in serum samples of OC patients and cancer cell lines. This miR-193a-5p suppress OC cell proliferation and metastasis by regulating RB binding protein 6, ubiquitin ligase [ 106 ]. Expression level of another miRNA miR-148a was also found to be lower in OC patient samples and this miR inhibits proliferation, migration and invasion of OC [ 107 ]. miR-574–3p suppressed the activation of AKT, FAK, c-Src and MMP-9 expression by targeting EGFR and ultimately leads to inhibition of OC metastasis [ 108 ]. Additional studies indicate that miR-138 and miR-708 play roles in inhibiting OC metastasis through mechanisms such as targeting SOX4, HIF-1α, and Rap1B [ 109 ]. Lower level of miR-708 and higher Rap1B are reported in late-state ovarian tumors and Lin et al. showed glucocorticoid treatments enhanced the expression of miR-708, which subsequently inhibited Rap1B, integrin-mediated focal adhesion formation and thus inhibition of cancer cell migration/invasion and impaired abdominal metastasis in an orthotopic xenograft mouse [ 110 ]. Dysregulation of let-7A-3/let-7b, observed in around 44% of OC cases and has been shown to inhibit tumor growth upon restoration [ 111 ]. Additionally, Bai et al. reported that decreased expression of miR-532/miR-3064 correlates with reduced patient survival in OC, which was attributed to inhibition of hTERT [ 112 ]. Research has identified that epigenetic regulation of various tumor suppressor genes and miRNAs, including RSK4, SPARC, PROM1, and SFRP2, is associated with non-serous OC development [ 113 ]. Hypermethylation and thus subsequent reduced expression of miR-129–2, miR-137, miR-193A, miR -203A, miR-339, miR-375 were found in OC patients and these were associated with the metastatic progression to lymph nodes, peritoneum, and other distant organs [ 114 ]. In addition to the epigenetic regulation, tumor microenvironment can also modulate and down-regulate miRNAs such as miR-193b which resultant into OC metastasis [ 115 ]. Contrary to these, few miRs can act as an oncogene for example, studies of Wang et al. revealed that miR-1246 and miR-1290 in malignant ascites-derived extracellular vesicles promote invasion and migration of OC cells by regulating a common target retinoid orphan receptor alpha (RORα) [ 73 ]. Other oncogenic miRNAs, miR-216a accelerates EMT and OC metastasis via suppressing PTEN/AKT pathway [ 116 ]. miR-181a drives TGF-β-mediated EMT in OC by suppressing its functional target, Smad7 [ 117 ] ( Fig. 2 ). Similar to this, miR-135a play crucial roles in OC progression, metastasis and down-regulation of miR-135a has been shown to inhibit N-cadherin expression, potentially impeding EMT [ 118 ]. Members of the miR-200 family (miR-200a, miR-200b, miR-200c, miR-141, and miR-429) are essential in regulating OC invasion and metastasis by modulating EMT regulators like ZEB1 and ZEB2 [ 119 – 121 ]. This family of miRs may serve as a molecular marker for OC invasion, metastasis, and prognosis ( Table 1 , 2 ). However, contradictory reports exist regarding their expression profiles in OC patients as Fitriawan et al. found up-regulation of miR-141 in the plasma of EOC patients [ 122 ]. In a similar fashion, miR-9 exhibits context-dependent behavior, acting as a tumor suppressor in some cases by targeting ERK1/2 and MMP-9, while in other contexts its opposite and promotes EMT and metastasis by modulating pathways such as Wnt-β catenin and AKT1 [ 123 – 125 ]. Though research on miR dysregulation in CCOC remains limited, initial findings indicate elevation of miR-146a-5p, miR-191–5p in CCOC patients serum [ 69 ]. Histotype-specific miR profiling, as observed in higher expression of miR-30a in clear cell histotype and miR-192/194 in mucinous histotype, requires further attention for understanding disease origin and progression [ 126 ]. Gene ontology analyses also suggest miR-1914 targets numerous genes involved in essential cellular processes, although its role in OC requires further study [ 84 ]. MicroRNAs are versatile regulators of gene expression and can target multiple RNAs that share the same miRNA response elements (MREs). This competition among RNAs for binding to a limited pool of miRs supports the competing endogenous RNA (ceRNA) hypothesis, where ceRNAs—acting as miR sponges—affect gene expression and play crucial roles in pathological conditions, including cancer [ 127 ]. In OC also, ceRNA networks contribute to tumor growth, metastasis, and chemotherapy resistance, often involving intricate epigenetic modifications that influence miR regulation. In a recent study, Huang et al. [ 128 ] developed a mathematical model to explore how epigenetic modifications, such as promoter methylation and histone modification, integrate with the ceRNA network to regulate OC progression. Their findings demonstrated that miRNA-targeted mRNAs’ behavior is affected by both ceRNA competition mechanisms and epigenetic modifications of miRs. Through estrogen receptor (ER) signaling pathways, they showed that epigenetic repression of miR-193a by E2F6 is associated with the up-regulation of c-KIT and PBX1, two oncogenes in OC. This repression results from the recruitment of the histone methyltransferase EZH2 to the miR-193a promoter, leading to its hypermethylation and decreased expression. Further experimentation revealed that estrogen treatment in immortalized ovarian surface epithelial cells increased E2F6 and c-KIT expression while down-regulating miR-193a [ 129 ]. These results suggest that disrupting E2F6 silencing through DNMT and EZH2 inhibitors, along with modulating estrogen receptor signaling, could potentially reduce OC stemness and provide a new avenue for therapeutic development. Recent studies have identified several circRNAs with pivotal roles in OC development and progression. CircRNA051239, for example, is up-regulated in EOC tissues and patient plasma exosomes, where it acts as a sponge for miR-509–5p, leading to increased expression of serine protease 3 (PRSS3) and thereby promoting OC growth and metastasis [ 130 ]. Another circRNA, circ_0061140, functions by sponging miR-370, which enhances OC cell proliferation and metastasis and holds potential as a therapeutic target and predictive biomarker [ 131 ]. CircCELSR1 facilitates OC cell proliferation and metastasis by sponging miR-598, which up-regulates the oncogenic BRD4 [ 132 ]. Similarly, circFGFR3 contributes to OC progression by sponging miR-29a-3p, enhancing the expression of E2F1, a transcription factor known to promote EMT [ 133 ]. Likewise, CiRS-7 acts as a ceRNA, sponging miR-641, which leads to increased expression of ZEB1 and MDM2, promoting EMT and metastasis in OC [ 134 ]. CircPLEKHM3, in contrast, sponges miR-9, acting as a ceRNA to suppress cell proliferation, EMT, and OC progression [ 135 ]. Circ_100395, often found down-regulated in OC tissues, correlates with reduced miR-1228 levels, a relationship that supports OC progression; however, its over-expression has been shown to have anti-proliferative, anti-migratory, and anti-invasive effects in OC cells [ 136 ]. Taken together, these studies underscore the interplay between ceRNA networks and miRNA-mediated epigenetic control in OC. Through sponging miRNAs, circRNAs and other ceRNAs influence gene expression programs crucial for OC progression, metastasis, and therapy resistance. Moreover, this interplay is often regulated by epigenetic modifications such as DNA methylation and histone modification, which alter miR availability and activity. Targeting these ceRNA and epigenetic interactions offers promising new approaches for therapeutic development in OC, with the potential to disrupt key pathways involved in cancer cell survival, proliferation, and metastasis. In conclusion, the field of miR research remains dynamic and continues to expand, with numerous studies highlighting the diverse roles of miRs in cancer progression. However, discrepancies often arise due to variations in experimental methodologies and differing findings reported by research groups for specific miRs. Achieving a reliable understanding of miRNA functions necessitates rigorous evaluation of data, including careful scrutiny of experimental designs, sample sources, and analytical methods. By integrating these diverse findings through systematic analysis, we can identify promising candidate miRs for further exploration, prioritizing those supported by consistent and reproducible evidence. In this context, we have compiled and tabulated data on the differential expression of miRs in OC patients and cell lines reported over the past 15 years, with information curated from PubMed ( Tables 1 , 2 ). This comprehensive dataset provides a valuable resource for advancing miR research and its translational potential in OC. To further elucidate the regulatory interactions between these dysregulated miRs (both up-regulated and down-regulated in OC, Tables 1 , 2 ) and their target genes, a network analysis was conducted using the miRNet 2.0 web tool ( https://www.mirnet.ca , accessed in November, 2024). Using degree (cutoff 10) and betweenness (cutoff 10) centrality parameters for down-regulated, and degree (cutoff 15) and betweenness (cutoff 15) for up-regulated miRs a network was constructed ( Fig. 3 ), following our previous work [ 3 ]. The most commonly targeted genes by down-regulated miRs included MYC, CDK6, NUFIP2, CDK4, KLHL15, IGF1R, CCND2, CCND1, PTEN, VEGFA, among others. Conversely, the up-regulated miRs targeted genes such as NUFIP2, PTEN, FRS2, XIAP, GATA6, KPNA6, TP53, ZNF460, KLHL15, BCL2L11, PLAGL2, CCND1, SMAD4, MDM2 and more. Pathway enrichment analysis using KEGG revealed that down-regulated miRs predominantly target genes involved in key signaling pathways critical to OC development, including P53, WNT-β catenin, MAPK, TGF-β, mTOR, VEGF, ErbB, JAK-STAT, and mTOR signaling. Up-regulated miRs were found to regulate overlapping pathways, such as P53, WNT-β catenin, and mTOR signaling, highlighting their pivotal roles in cancer progression.

Ovarian cancer (OC) is the third most common gynecologic malignancy, following cervical and uterine cancers [ 1 ]. However, it has the highest mortality rate among all gynecologic cancers. The American Cancer Society estimates that in 2024, around 19,680 women in the U.S. will be diagnosed with OC and nearly 12,740 will lose their lives to the disease [ 2 ]. The high mortality of OC is attributed to multiple factors, one of which is its late detection often at an advanced stage due to its being frequently asymptomatic in nature [ 3 ]. Other factors contributing to the severity of OC include its high metastatic potential and acquired drug resistance, where cancer cells develop resistance to the therapeutic drugs, they were initially sensitive to. Due to its high metastatic potential, the impact of OC extends aggressively beyond the ovary leading to the advancement of the disease in terms of stages, ultimately manifesting as a heterogeneous collection of malignancies [ 4 ]. For instance, Stage I, the cancer is confined to the ovaries, or the fallopian tubes; in Stage II the cancer has spread other pelvic organs, such as the uterus, bladder, colon, or rectum; Stage III represents a more advanced phase, where the cancer has metastasized to the retroperitoneal lymph nodes and the peritoneum outside the pelvis; and in Stage IV the cancer has spread to lymph nodes and organs beyond the abdomen, including the liver, lungs, spleen, bones, and potentially the brain [ 5 ] ( Fig. 1 ). In addition to the delayed detection, acquired drug resistance and high metastatic potential have made the scenario worst. Based on histopathological evaluation and molecular genetic changes, OC is classified into five principal types: high-grade serous ovarian carcinoma (HGSOC) (75%), endometrioid ovarian carcinoma (EnOC) (5–10%), clear cell ovarian carcinoma (CCOC) (10%), mucinous ovarian carcinoma (MOC) (3%), and low-grade serous ovarian carcinoma (LGSOC) (<5%). Each type represents a distinct disease with unique characteristics in terms of epidemiological factors, genetic risk factors, precursor lesions, spread patterns, molecular events in cancer development, chemotherapy responses, and overall prognosis [ 6 ]. HGSOC is often hard to detect in the early stages because of ambiguous symptoms such as abdominal pain, constipation, bloating, and fatigue. As a result, it is frequently diagnosed at stage III (51% of cases) and stage IV (29% of cases), with a five-year survival rate below 30% [ 7 , 8 ]. Treatment options for HGSOC include surgical debulking followed by platinum or paclitaxel-based chemotherapy but many patients, though respond initially, develop chemoresistance and face cancer recurrence, leading to reduced survival [ 9 , 10 ]. The highly immunosuppressive HGSOC tumor microenvironment limits effective immunotherapy [ 11 ]. EnOC is the second most common type after HGSOC and several factors are associated with the development of EnOC, including endometriosis itself, gene mutations, familial cancer syndromes, alterations in reproductive system microbiota, delayed menopause, menopausal hormone replacement therapy, body mass index (BMI), and obesity [ 12 ]. CCOC, a rare subtype of epithelial OC, is associated with endometriosis and predominantly affects perimenopausal women [ 13 ]. LGSOC is wilms tumor gene 1 (WT1) and estrogen receptor (ER) positive and reported to express progesterone receptor (PR) in many cases. Serous borderline tumors are often considered the common precursor lesion of LGSOC [ 14 ]. Unlike HGSOC, this type does not confer such a level of genomic instability and fewer mutations. This subtype is mostly encountered in women of median age 46–48 years. While LGSOC represents nearly 5% of all OC, most cases are found at a late stage with ~80% diagnosed at stage III, <10% at Stage I/II and ~20% in stage IV [ 15 , 16 ]. LGSOC is intrinsically highly chemoresistant [ 17 ] and thus development of treatment strategy is a major clinical challenge. MOC is a rare type of OC that originates from ovarian teratomas, or transitional cell neoplasms. It is typically WT1 and Napsin A negative, with mutant p53 present in ~60% of cases. MOC represents <5% of OC diagnoses and most cases (~80%) are diagnosed at Stage I and the rest of them in Stage II-IV [ 18 , 19 ]. It is highly resistant to treatment although the risk of cancer recurrence after surgery is very less [ 20 , 21 ]. Throughout the history of cancer investigation, it has been widely acknowledged that various phenotypes such as proliferation, invasion, metastasis, and drug resistance are controlled by numerous intricate mechanisms and their interactions. Among these regulatory processes, extensive research has identified epigenetic regulations especially microRNAs (miRNAs or miRs) as significant players in a wide array of biological activities, particularly those that facilitate the initiation, development and progression of tumors [ 22 ]. OC has been associated with intricate alterations within the genome, involving the expression and functionality of various miRs [ 23 ]. Recent reports support key role of miR in epigenetic regulation which has not been discussed so well previously. In this present review, we have elaborated the contributions of epigenetic involvements with emphasis on the role and regulation of miRs in several crucial aspects of OC, including cancer progression and drug resistance mechanisms. In this process, we have also discussed expressional vicissitudes in terms of key proteins, epigenetic regulations including miRs associated as molecular signature with different types of OCs. Additionally, since late detection is a bottle neck in countering OC, we have discussed how epigenetic signatures including miRs can be considered as biomarkers. By exploring these interconnected facets, we aim to provide a meticulous comprehension of the molecular dynamics in OC, its detection, highlighting the potential emerging avenues for miRs and epigenetics-based therapeutic intervention and management strategies.

Drug resistance is a significant barrier in the effective treatment of OC, and it can be classified as either intrinsic or acquired. Intrinsic resistance is present from the onset of diagnosis, where cancer cells are inherently unresponsive to chemotherapy. Acquired resistance, on the other hand, develops after initial exposure to chemotherapy, allowing tumor cells to survive and proliferate despite ongoing treatment. The primary chemotherapy treatment for OC involves the platinum and paclitaxel. Although initial treatment effectively controls disease progression, resistance often develops through multiple mechanisms, leading to frequent recurrence. This acquired resistance frequently causes cross-resistance to various drugs, known as multidrug resistance (MDR) [ 188 ], complicating treatment and significantly contributing to cancer-related mortality. MDR mechanisms in mammalian cells encompass both cellular and noncellular pathways. Noncellular mechanisms include changes in the tumor microenvironment, such as production of lactic acid by hypoxic tumor cells. This acidification reduces the efficacy of drugs that rely on the pH gradient across the cell membrane for uptake [ 189 ]. Cellular mechanisms, however, involve more direct alterations in the biochemical and genetic properties of cancer cells. One key cellular mechanism is the inactivation of chemotherapeutic drugs by enzymes such as metallothioneins or glutathione S-transferase (GST). These enzymes can neutralize drugs before they exert their cytotoxic effects, leading to either non-classical MDR phenotypes or classical transport-dependent phenotypes. Another major pathway involves the overexpression of ATP-binding cassette (ABC) transporters, particularly P-glycoprotein (P-gp/ABCB1/MDR1). This transporter actively effluxes chemotherapeutic agents out of the cells, reducing their intracellular concentrations to sub-therapeutic levels, thus making the treatment ineffective [ 190 – 192 ]. Other mechanisms contributing to drug resistance include reduced drug uptake, altered drug metabolism or inactivation, target gene mutations, and changes in signaling cascade [ 193 , 194 ]. The factors associated with drug resistance are discussed in greater detail in the following subsections. The effectiveness of chemotherapy in treating OC heavily depends on the retention of drugs within cancer cells, which is primarily regulated by the activities of efflux and influx transporter [ 195 ]. A significant reduction in drug accumulation, particularly platinum-based drugs like cisplatin, has been observed in resistant cancer cells. For instance, studies have shown a 50% reduction in platinum accumulation in cisplatin resistant cancer cells which correlates with a 3–4-fold increase in drug efflux [ 196 ]. ATP-binding cassette (ABC) protein transporters, including P-glycoprotein or P-gp (ABCB1), MRP1 (ABCC1) and MXR, BCRP (ABCG2) are known for transporting various substances such as drugs, sugar, amino acids, lipids and nucleotides and functioning primarily as an efflux pump [ 197 , 198 ]. Many studies have linked their overexpression to drug resistance [ 199 ]. Moreover, recent research indicates that the activation of signaling pathways like FOXO3a, PI3K/Akt, Hedgehog, and NF-κB is correlated with an increase in ABC transporter expression, enhancing drug efflux [ 199 ]. In OC, the expression of these transporters is found to be regulated by miRs and thus epigenetically. In doxorubicin-treated OC cells ABCG2 level was found to be increased and further studies revealed this up-regulation was promoted by hyperacetylation of histones due to weaker histone deacetylase 1 and ABCG2 promoter association. Loss of histone deacetylase 1 and stronger binding of RNA pol II to the proximal promoter resultant into elevated level of ABCG2 and thus occurrence of drug resistance [ 200 ]. Epigenetic suppression of miR-490 by promoter hypermethylation reduces drug sensitivity in OC by up-regulating miR-490’s target ABCC2 [ 157 ]. Whereas intratumoral administration of miR-873 enhanced cisplatin sensitivity by suppressing tumor growth in vivo via targeting ABCB1 [ 201 ]. Given the central role of these transporters in mediating drug resistance, developing non-toxic inhibitors that specifically target ABC transporters in cancer cells and in-depth study of epigenetic modifications can be very crucial for improving the efficacy of chemotherapy. On the influx side, copper transporters, particularly CTR1, are involved in the cellular uptake of platinum-based drugs. Reduced expression of CTR1 can lead to lower cisplatin uptake and thus potential drug resistance [ 202 ]. Additionally, Lv et al. demonstrated that the core fucosylation of CTR1, which regulates cisplatin uptake is significantly increased in the sera of cisplatin treated EOC patients, suggesting a link between core fucosylation of CTR1 and cisplatin resistance in EOC [ 203 ]. This core fucosylation of CTR1 may be crucial for the proper conformation of its platinum-binding ectodomain, which is necessary for effective cisplatin recognition and uptake. Contrary to CTR1, CTR2 acts as a platinum efflux transporters and its overexpression is associated with drug resistance in OC [ 204 ]. Furthermore, the Cu-exporting ATPases ATP7A and ATP7B have been positively associated with resistance to platinum-based medications in OC [ 205 ]. The expression of other influx transporters, such as OATP1B3, a member of the organic anion transporting proteins (OATPs) family, has also been found to be associated with drug sensitivity [ 206 ]. These findings underscore the complexity of drug resistance mechanisms in OC and highlight the critical role of both efflux and influx transporters in this process. The intricate balance between these transporters significantly influences drug retention within cancer cells, which is essential for the success of chemotherapy. Therefore, targeting these transporters either by inhibiting efflux pumps that expel drugs from the cells or by enhancing drug uptake through specific activators or modulators represents a promising therapeutic strategy. Further research into the detailed mechanisms underlying transporter activation and regulation is crucial for developing more effective treatments. By unravelling these mechanisms, it may be possible to devise novel strategies that overcome drug resistance in OC, ultimately improving patient outcomes. In OC, the increased expression of drug-metabolizing enzymes, such as cytochrome P450 (CYP450) and glutathione-S transferase (GST) plays a critical role in diminishing intracellular activity of chemotherapeutic agents ( Fig. 4 ) [ 207 , 208 ]. For instance, elevated levels of P450 enzymes, particularly CYP1B1, are linked to increased drug sequestration and inactivation of anticancer drugs [ 209 ] like docetaxel [ 207 ]. This overexpression is directly associated with drug resistance, leading to reduced chemotherapy effectiveness. The overexpression of MDR1 and GST enzymes, particularly glutathione S-transferase-π, and glycogen synthase kinase-3β (GSK3 β) tended to be more resistant to chemotherapy [ 210 , 211 ], down-regulation of these genes were observed in chemotherapy-sensitive patients, suggesting their aberrant expression is associated with chemotherapy resistance and a reduced three-year survival rate. In cancer cells, the up-regulation of glutathione-S transferase leads to the direct inactivation of anticancer drugs by their conjugating activity and contributes to enhanced resistance to apoptosis (reviewed in detail by Townsend et al., Allocati et al. [ 212 , 213 ]). In OC, particularly, the expression of glutathione S-transferase-π, is significantly increased, showing a correlation with drug resistance [ 214 ]. Though the mechanisms by which the expression of GST enzymes are regulated in OC is not known, studies on other solid tumors have revealed association of epigenetic regulation by DNA methylation and histone modification in cancer cells. A study on colon cancer reported higher level of GSTP-1 due to promoter hypomethylation [ 215 ]. Likewise, hypermethylation of GST-M2 was associated with reduced expression of the enzyme in lung cancer [ 216 ]. The expression of histone methyltrasferase G9a correlates with poor survival in OC patients [ 217 ]. This G9a induces the expression of CYP450 by regulating H3K4 and H3K27 methylation of the promoter [ 218 ]. These results point to the possibility of exploring chromatin changes driving differential expression of GST enzymes in OC. Additionally, intracellular elevated glutathione level is associated with drug resistance [ 219 ] while, treatment with buthionine sulfoximine (BSO), a glutathione biosynthesis inhibitor, resulted in approximately 90% decrease in cellular glutathione and increase in cisplatin cytotoxicity [ 220 , 221 ]. These findings underscore the importance of exploring strategies that target these metabolic pathways to overcome drug resistance and improve treatment outcomes in OC. Anticancer drugs such as cisplatin exerts its effect by crosslinking with DNA bases. It causes DNA damage and interfere with the DNA repair mechanisms and ultimately leads to induction of apoptosis [ 222 ]. Increased DNA damage tolerance and enhanced repair mechanisms are key contributors to chemotherapy resistance in OC. Resistant cancer cells have been shown to repair DNA damage at a rate 2–4 times higher than their drug-sensitive counterparts, enabling them to survive the genotoxic stress imposed by chemotherapy [ 221 , 223 ]. Interestingly, more than 50% of HGSOC are reported to be homologous recombination-deficient (HRD), on the other hand, in non-HRD cases, 20% confer CCNE1 gene amplification which codes for cell cycle regulator cyclin E1 [ 224 , 225 ]. Another cell cycle regulator cyclin-dependent kinase CDK6 was found to stabilize transcription factor FOXO3, transcriptional induction of ATR kinase which regulates DNA damage response, thus causes drug-resistant and inhibition of this pathway leads to increased apoptosis following platinum treatment [ 226 ]. Therefore, use of cell cycle inhibitors such as CHK1 and CHK2 inhibitor prexasertib [ 227 ] may be helpful. To decipher the mechanisms underlying resistance to platinum-based drugs, Li et al. demonstrated a positive correlation between the total number of hypermethylated CpG-islands and increased drug resistance in A2780 EOC cells and therefore epigenetic involvements [ 228 ]. BRCA1 hypermethylation was observed in OC patients, correlating with resistance to platinum-based chemotherapy [ 229 ]. Combinatorial use of prexasertib and PARP inhibitor olaparib showed synergistic cytotoxic effects against BRCA wild type OC [ 230 ]. They showed that while prexasertib treatment enhanced cell cycle replication stress, olaparib inhibited Rad51 foci formation and thus caused DNA damage. miRs are also found to be involved in this process, like, miR-9 found to cause down-regulation of BRCA1, prevents DNA damage repair and enhances drug sensitivity in OC [ 231 ]. Similarly, miR-506 directly targets and decreases DNA double strand break repair gene RAD51 level and increases cisplatin and olaparib sensitivity in OC [ 232 ]. However, miR-622 was found to cause drug resistance by targeting Ku complex and restore HR-mediated double strand break repair in OC [ 233 ]. In addition to these, there are some other proteins like Y-box binding protein 1 (YBX1) is associated with drug resistance in OC and its level was found to be elevated in cisplatin-resistant patient-derived organoids. Meng et al. revealed that YBX1 recognizes m5C modifications of chromodomain-helicase-DNA-binding protein 3 (CDH3) which helps in DNA damage repair and maintains CDH3 mRNA stability by recruiting PABPC1 protein. This regulatory process enhances efficiency of homologous recombination repair and makes the OC cells to withstand platinum-induced stress. Inhibition of YBX1 increases drug sensitivity in subcutaneous and PDO orthotopic xenograft models [ 234 ]. Collectively, these studies highlight the role of epigenetic control in DNA damage and drug resistance, warranting further detailed investigation. In OC, drug resistance poses a significant barrier to effective treatment. Two cellular processes, autophagy and apoptosis, play pivotal roles in determining whether cancer cells survive or succumb to chemotherapy. Autophagy is a survival mechanism through which cells recycle damaged components to withstand stress, while apoptosis is the process of programmed cell death. However, when autophagy becomes overactive in cancer cells, it can shield them from chemotherapy-induced apoptosis, thereby contributing to drug resistance [ 235 , 236 ]. Several miRs that are under-expressed in OC are known to contribute to drug resistance through this mechanism. However, their re-expression has been shown to trigger apoptosis and increase drug sensitivity, countering the survival mechanisms of cancer cells. Key examples include miR-30a, which counteracts cisplatin-induced autophagy by modulating SMAD4 and TGF-β expression. By inhibiting autophagy, miR-30a shifts the cell toward apoptosis, increasing the sensitivity of OC cells to cisplatin, a commonly used chemotherapy drug [ 237 ]. Similarly, miR-152 blocks cisplatin-induced autophagy, making OC cells more susceptible to apoptosis [ 238 ]. miR-29c-3p suppresses autophagy by targeting FOXP1 and disrupting the FOXP1/ATG14 pathway [ 239 ]. Similarly, miR-20a-5p inhibits autophagy and OC progression by regulating DNMT3B-mediated DNA methylation of RBP1, a protein affecting cancer cell behavior [ 240 ]. By targeting HMGA2, miR-219–5p disrupts the autophagy pathway [ 241 ], boosting cisplatin sensitivity and promoting apoptotic cell death in OC cells. In contrast, some miRNAs contribute to drug resistance by enhancing autophagy. For example, miR-1251–5p promotes cancer progression by targeting tubulin-binding cofactors that regulate apoptosis, thereby increasing cell survival and autophagy [ 242 ]. Non-coding RNAs, such as lncRNAs and circRNAs, play a significant role in autophagy-related drug resistance in OC by functioning as ceRNAs that sequester miRNAs and regulate key autophagy-related genes. For instance, circMUC16 promotes autophagy by binding to miR-199a that results in the increased levels of Beclin1 and RUNX1, facilitating cancer cell survival [ 243 ]. Similarly, circRAB11FIP1 sponges miR-129, activating autophagy and enhancing drug resistance [ 244 ]. Among lncRNAs, HOXA11-AS is up-regulated in cisplatin-resistant OC cells, and its silencing induces apoptosis, highlighting its role in chemoresistance [ 245 ]. Additionally, TMEM147-AS1, up-regulated by a feedback loop involving Aurora Kinase A (AURKA) and DEAD-box helicase 5 (DDX5), sponges hsa-let-7b/7c-5p, leading to cisplatin resistance through lipophagy activation [ 246 ]. Targeting these RNAs and associated pathways offers potential therapeutic strategies to overcome drug resistance in OC. Several natural compounds have shown potential in targeting autophagy and apoptosis in OC, enhancing the effectiveness of chemotherapy and promoting cancer cell death. Resveratrol, a polyphenol found in grapes and berries, inhibits miR-1305 and utilizes the ARH-I pathway to induce a dormant state in OC cells, improving chemotherapy sensitivity [ 247 ]. Luteolin, another polyphenol, induces apoptosis in cisplatin-resistant OC cells by down-regulating the anti-apoptotic protein Bcl2 [ 248 ], while salinomycin targets OC stem cells, reducing their resilience [ 249 ]. Oridonin from Rabdosia rubescens inhibits proteins involved in cell invasion and promotes apoptosis in drug-resistant OC cells [ 250 ]. Emodin, a traditional Chinese medicine compound, increases sensitivity to paclitaxel by down-regulating drug resistance-associated proteins [ 251 ]. In addition to these, some other proteins are also reported to be associated with OC drug resistance, for example overexpression of anti-apoptotic gene CLN3 were observed in OC and knockdown of this gene induced apoptosis by increasing Bax, cleaved-caspase 8, cleaved-caspase 3 and cleaved-RARP in cisplatin resistant OC cells [ 252 ]. Higher expression of E3 ligase CRL4 is connected with OC cisplatin resistance and silencing of these genes reported to suppress the apoptotic inhibitor BIRC3 and resultant into occurrence of apoptosis [ 253 ]. Serine/threonine kinase doublecortin-like kinase 1 (DCLK1) is reported to be associated with cisplatin resistance and inhibition of DCLK1 altered TGF-β signaling and increased drug sensitivity in OC [ 254 ]. Emerging research also suggests that CSCs and the EMT process also contributors to drug resistance in OC. CSCs are a subset of cancer cells with self-renewal capabilities and a strong resistance to chemotherapy, making them particularly difficult to eliminate. The EMT process, often associated with increased invasiveness and resistance, enables cancer cells to transition to a more aggressive, stem-like state. Targeting CSCs and EMT-related pathways may help overcome drug resistance by eliminating these resilient cells and preventing the cellular changes that allow OC cells to evade chemotherapy. DNA methylation, a key epigenetic modification, involves the addition of a methyl group (–CH 3 ) to the 5-C position of cytosine by DNA methyltransferase enzymes. This process often results in promoter hypermethylation, typically leading to transcriptional repression [ 255 ]. While the role of epigenetic regulation in OC drug resistance is still emerging, studies have begun to establish a link. For instance, the hypermethylation of genes such as TGFβI , hMLH1 , DVL1 , NFATC3 , HSulf-1 , RGS10–1 has been associated with poor responses to chemotherapeutic agents [ 256 – 260 ]. In a similar vein, Lum et al. investigated epigenetic factors in advanced OC patients and found that the suppression of docking protein 2 led to carboplatin resistance via inhibition of apoptosis [ 261 ]. Additionally, Dai et al. reported that epigenetic regulation through promoter methylation and down-regulation of FZD4 , DVL1 , and ROCK1 is indicative of early-disease relapse in EOC patients [ 260 ]. Up-regulation of transmembrane protein TMEM88 has been associated with platinum resistance in OC mediated by promoter hypomethylation. TMEM88 contributes to drug resistance by inhibiting Wnt signaling pathway, a critical pathway in cancer progression and chemoresistance [ 262 ]. Similarly, the regulatory role of DNA methylation extends to miRs, as many miR loci contain CpG islands, making them susceptible to epigenetic modifications. For instance, promoter methylation-induced suppression of miR-103a-3p has been linked to carboplatin-induced acquisition of a mesenchymal-like phenotype, increasing OC cell invasiveness [ 263 ]. However, Wilczyński et al. did not find significant clinical correlations or changes in miR-103 expression in OC patient samples, suggesting context-specific roles of miR-103a-3p. Notably, miR-103a-3p is also regulated by the lncRNA EPB41L4A-AS2, which enhances RUNX1T1 expression, further driving OC progression. These findings underscore the complex interplay between DNA methylation, non-coding RNAs, and signaling pathways in mediating drug resistance and tumor progression in OC [ 264 , 265 ]. This miR-103a is also found to be regulated by LncRNA EPB41L4A-AS2 which enhances RUNX1T1 expression and leads to the OC progression [ 266 ]. These studies underscore the potential of targeting DNA methylation enzymes as a promising strategy for overcoming chemotherapy resistance in OC. In the upcoming section we have discussed the role and regulation of miRs in drug resistance. Histone proteins undergo post-translational modifications (PTMs), which are covalent changes comprising methylation, acetylation, phosphorylation, ubiquitination, ADP-ribosylation, SUMOylation, glycosylation, ADP-ribosylation and deamination. These modifications occur mainly in the N or C terminal tails of histones and play crucial roles in regulating chromatin structure and gene expression [ 267 ]. As key epigenetic markers, PTMs influence various cellular processes, including DNA repair, transcription, and cellular response to external stimuli, such as chemotherapy. In OC, various histone acetylation has been shown to be involved including SIRT2, HDAC1, HDAC4, HDAC11, NCOA3, BRD4, OGA [ 268 ]. One of the most studied epigenetic modifications in cancer is histone acetylation, particularly the role of lysine deacetylases. The sirtuin 1 (SIRT1) enzyme, a NAD+-dependent deacetylase, is involved in deacetylating histone proteins, such as H3K9, leading to chromatin compaction and transcriptional repression [ 269 ]. In OC, SIRT1 has been implicated in chemotherapy resistance [ 270 ]. Overexpression of SIRT1 has been linked to a variety of mechanisms that help tumor cells evade the cytotoxic effects of chemotherapy. SIRT1 can modulate the tumor microenvironment, enhance drug efflux, promote DNA repair, and even facilitate the acquisition of mutations that confer resistance to treatment [ 271 – 275 ]. By maintaining genomic stability, SIRT1 supports cancer cell proliferation and promotes the stem-like properties of cancer cells [ 276 ]. Additionally, SIRT1 up-regulates multiple antioxidant pathways, contributing to both cancer cell survival and chemoresistance [ 277 ]. Targeting SIRT1 with specific inhibitors such as MHY2245 and EX-527 has shown promising results in inducing caspase-mediated cell death in OC cells, suggesting that SIRT1 inhibitors may serve as a potential therapeutic strategy to overcome chemotherapy resistance in OC [ 278 ]. Further studies have highlighted the role of histone methylation in chemotherapy resistance. For example, H3K27me3 (trimethylation of histone H3 at lysine 27), a mark associated with transcriptional repression, was found to be reduced in chemoresistant OC cell lines compared to chemosensitive counterparts, suggesting that modifications at this locus may contribute to drug resistance [ 279 ]. In addition, EZH2 (Enhancer of Zeste Homologue 2), a H3K27 methyltransferase, is frequently up-regulated in cisplatin-resistant OC cells [ 280 ]. This up-regulation enhances the repression of tumor suppressor genes, which facilitates chemotherapy resistance by reducing drug-induced apoptosis. The microRNA miR-101 has been shown to target EZH2, leading to the epigenetic silencing of its target genes and promoting cancer metastasis [ 281 ]. In conclusion, histone modifications, including acetylation and methylation, play pivotal roles in the development of chemotherapy resistance in OC. Therefore, targeting histone modifications presents a novel approach in the therapeutic development for OC, which has been discussed in the section 5 . MicroRNAs play significant roles in mediating OC drug resistance [ 282 ] by regulating various cellular pathways associated with chemoresistance. Our previous research demonstrated that miR-15a, miR-16, and miR-195 are significantly underexpressed in OC. Our findings confirm that the combined delivery of miR-15a and miR-16 can effectively suppress the growth of cisplatin-resistant OC in a preclinical mouse model [ 165 , 283 ]. Similarly, studies on non-coding RNAs revealed that linc00161 modulates the miR-128/MAPK1 pathway, playing a key role in drug resistance in OC [ 284 ]. Additionally, Jang et al. revealed that the angiogenic factor Vascular Endothelial Growth Factor A (VEGFA) induced SRC enhances DNA methyltransferase 3A activity, leading to the methylation of miR-128–2. This process promotes the enrichment of OC stem-like cells, thereby exacerbating chemoresistance [ 285 ]. Likewise, overexpression of miR-21 correlates with cisplatin resistance, as miR-21 inhibition can trigger apoptosis and increase drug sensitivity [ 286 ] ( Table 3 ). miR-199a-3p plays a role in OC chemoresistance by regulating discoidin domain receptor tyrosine kinase 1 (DDR1) expression, while promoter hypermethylation of DDR1 is linked to OC progression [ 287 ]. On the contrary, miR-484 up-regulation is associated with decreased expression of angiogenic factors VEGFB and VEGF Receptor 2 (VEGFR2), resulting in enhanced sensitivity to binary platinum plus taxane chemotherapy [ 150 ]. Elevated miR-378 levels have been observed in the platinum-sensitive OC patients compared to resistant stage III patients [ 288 ]. Similarly, miR-561–5p is also associated with drug sensitivity as silencing miR-561–5p increases glyoxalase I expression, contributing to greater chemoresistance in advanced-stage (III/IV) OC patients [ 289 ]. miR-489, conversely, enhances cisplatin sensitivity and suppresses proliferation by down-regulating Akt3 [ 290 , 291 ]. While miR-149 targets MSI2 via PI3K/AKT, X-linked apoptosis inhibitory factor and Forkhead Box M1 (FOXM1) and increased cancer cells sensitivity to cisplatin [ 292 – 294 ]. The miR-200 family is closely associated with OC recurrence [ 295 ], progression, and response to chemotherapy. Down-regulation of miR-200c has been linked to paclitaxel resistance in OC cell lines, with miR-200c restoration shown to enhance sensitivity to paclitaxel by targeting the TUBB3 gene, which regulates chemoresistance [ 296 ]. miR-200b and miR-200c are also involved in cisplatin sensitivity through direct targeting of DNA methyltransferases DNMT3A, DNMT3B, and indirectly DNMT1 via specificity protein 1 (Sp1) [ 297 ]. The transcription factor grainyhead-like 2 (GRHL2) supports the epithelial phenotype and positively regulates miR-200b/a expression, with loss of GRHL2 shown to increase H3K27me3 histone marks on the promoters of miR-200b/a and E-cadherin, illustrating an interaction between EMT transcription factors and epigenetic regulators [ 298 ]. miR-200b/c has been shown to target mortalin, a member of the heat shock protein 70 family, which is implicated in OC cell proliferation, migration, and cisplatin resistance, thereby increasing drug sensitivity when mortalin expression is down-regulated [ 299 ]. Finally, overexpression of the receptor neuropilin 1 (NRP1) is associated with multidrug resistance and poor prognosis in OC, while miR-200c targets NRP1 to enhance sensitivity to olaparib, an important drug in OC treatment [ 300 ]. While some studies support a tumor-suppressive role for miR-199a, with hypermethylation leading to its reduced expression in OC, other studies have shown that silencing miR-199a increases cisplatin resistance in SKOV3 cells [ 301 ]. Petrillo et al. observed that OC patients with a platinum-free interval (PFI) of less than six months show higher expression of miR-181a-5p, miR-199a-5p, and miR-199a-3p than those with a PFI between six and twelve months, highlighting their potential as markers for chemotherapy response [ 302 ]. We have compiled details of miRs, and their targets associated with OC drug resistance in Table 3 . In summary, miRs play a multifaceted role in OC, influencing gene expression and contributing to drug resistance and disease progression. Continued research into miR regulation and function in OC is essential for the development of effective therapeutic interventions that target these small but powerful regulators.