Introduction

Ovarian cancer is the fifth most lethal gynecologic malignancy in women globally, mainly affecting women aged 55 to 74 years [1, 2]. It has varied heterogeneity on the molecular, histopathological, and clinical levels, and is linked with the highest fatality rates [3]. According to the American Cancer Society, a total of 19,710 new cases and 13,270 deaths have been recorded in 2023 [4]. There is a strong correlation between survival rate and stage of epithelial ovarian cancer. Early detection of ovarian cancer results in an elevated 5-year survival probability of up to 93%. However, due to the asymptomatic nature of the disease at the early stage (I/II), high recurrence rate, and lack of improved early diagnosis methods, the disease is diagnosed at an advanced stage (stage III/IV) leading to a 5-year survival rate lesser than 35% [5].

At present, the current strategies for ovarian cancer detection involve pelvic examination, transvaginal ultrasonography, and imagining techniques like MRI and PET scans. The drawback of these methods is their limited sensitivity and specificity therefore, they are combined with other serum biomarkers like CA125 and HE4 [6]. Clinically, CA125 is an FDA-approved serum biomarker routinely used for monitoring treatment and disease recurrence with a sensitivity of 50–55% and specificity of 90% [7]. Nevertheless, this sensitivity and specificity are not efficient for early-stage diagnosis and moreover CA125 is found to be elevated in benign conditions and in other non-ovarian malignancies during pregnancy. Due to the lack of early detection methods and less specificity of imaging techniques, there is an urgent need to identify a set of more valuable and reliable molecular markers and to study their role in molecular mechanisms implicated in the development and progression of ovarian cancer, which could further aid in the diagnosis of ovarian cancer.

DNA methylation is one of the most common and well-studied epigenetic modifications. Hypermethylation at the tumor suppressor gene promoters plays a key role in the onset and progression of cancer. Its high stability and occurrence in the early stage of tumorigenesis make it a promising biomarker for early detection [8]. The first direct involvement of altered DNA methylation patterns in carcinogenesis was established in 1994 by Herman et al., in cases of renal carcinoma demonstrating promoter hypermethylation as a factor responsible for the silencing of tumor suppressor gene VHL [9]. Following that, other similar investigations were undertaken, with abnormal methylation at CpG islands in the promoter region as a probable mechanism in the transcriptional suppression of tumor suppressor genes such as RASSF1a, BRCA1, CDH1, DAPK, and OPCML in a variety of cancers [10,Functional and pathway enrichment analysis

An online biological information database known as the Database for Annotation, Visualisation, and Integrated Discovery (DAVID, version 6.8; http://david.ncifcrf.gov) was utilized to examine the gene ontology of DMGs [21]. This offers functional analysis according to three categories: Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analysis, Cellular Components (CC), Molecular Functions (MF), and Biological Processes (BP). P-value < 0.05 was used as the cut-off criterion for statistical significance.

PPI network construction

Search Tool for the Retrieval of Interacting Genes (STRING) (http://string-db.org/; version 11.0) is an online database for identifying the interaction between different proteins based on information fetched from sources like text mining, experiments, databases, and predictive bioinformatics data [68,69,70,71,72]. Peng et al. showed that STK4 methylation mediated downregulation consequently facilitate the progression of thyroid carcinoma by activating the Hippo signaling pathway [73]. Promoter hypermethylation of STK4 was also reported in in human sarcomas and pancreatic cancer [74, 75].

Our study presents hypermethylated CGI of POLR3B, GIGYF2, and PLXND1 with the H3k27 mark. Our preliminary results highlight targets (PLXND1, POLR3B, CRKL, GIGYF2, BMP2, and STK4) showing a negative correlation between promoter methylation gene expression. We also reported significant downregulation of these hypermethylated genes when analyzed through two GEO datasets (GSE5388 and GSE38666) and RNA-seq data (GSE212991).

Conclusion

This investigation showcased a comprehensive genome-wide methylation profile of epithelial ovarian cancer (EOC) and identified six hypermethylated/downregulated genes, (POLR3B, PLXND1, GIGYF2, CRKL, STK4, and BMP2) as potential diagnostic targets. The study also emphasized the potential of non-CpG sites to discriminate ovarian cancer from the disease-free normal sample. Network analysis highlighted the pathways crucial to cancer development, including the focal adhesion, Ras signaling pathway, and MAPK signaling pathway. POLR3B and GIGYF2, identified as novel hypermethylated genes, might serve as promising biomarkers for diagnosing and predicting the prognosis of ovarian cancer. These newly identified hypermethylated/downregulated genes warrant further investigations regarding their potential as therapeutic targets.