Unknown,Transcriptomics,Genomics,Proteomics

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Whole genome characterisation of chemoresistant ovarian cancer [Illumina_450K_Methylation]

ABSTRACT: Patients with high-grade serous ovarian cancer (HGSC) have experienced little improvement in overall survival, and standard treatment has not advanced beyond platinum-based combination chemotherapy, during the past 30 years. To understand the drivers of clinical phenotypes better, here we use whole-genome sequencing of tumour and germline DNA samples from 92 patients with primary refractory, resistant, sensitive and matched acquired resistant disease. We show that gene breakage commonly inactivates the tumour suppressors RB1, NF1, RAD51B and PTEN in HGSC, and contributes to acquired chemotherapy resistance. CCNE1 amplification was common in primary resistant and refractory disease. We observed several molecular events associated with acquired resistance, including multiple independent reversions of germline BRCA1 or BRCA2 mutations in individual patients, loss of BRCA1 promoter methylation, an alteration in molecular subtype, and recurrent promoter fusion associated with overexpression of the drug efflux pump MDR1. Genomic DNA (500ng) was bisulfite converted using EZ DNA methylation Kit (Zimo Research) following the manufacturer’s protocol with modification for Illumina Infinium Methyaltion arrays. Samples were hybridized to Infinium Human Methylation 450K BeadChips (Illumina) according to the manufacturer’s protocol. Arrays were scanned on Iscan (Illumina). Data was background corrected, normalized to internal controls and QC was performed at the probe and sample level. COMBAT was used to remove batch effects (Johnson et al., 2007). Contributor: The Australian Ovarian Cancer Study Group

ORGANISM(S): Homo sapiens

SUBMITTER: Ann-Marie Patch

PROVIDER: E-GEOD-65820 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Multiple DNA methylation changes have been associated with the acquisition of drug resistance; however it remains uncertain how many of these changes may represent critical DNA methylation drivers of chemoresistance. Using genome-wide DNA methylation profiling across 27,578 CpG sites on Illumina HumanMethylation27 bead array we identified loci at 4092 genes becoming hypermethylated in the chemoresistant A2780/cp70 ovarian tumour cell line compared to the parental sensitive A2780 line. Hypermethylation at CpG islands (CGI) is often associated with transcriptional silencing, however only 245 of these hypermethylated genes become down-regulated in A2780/cp70 as measured by microarray expression profiling. Treatment with the demethylating agent Decitabine induces re-sensitisation to cisplatin and resulted in re-expression of 41 of the down-regulated genes in cisplatin-resistant cells at the time point when re-sensitisation occurs. 13 of the 41 genes were consistently hypermethylated in two further independent cisplatin-resistant A2780 cell derivatives. Nine out of the 13 genes (ARHGDIB, ARMCX2, COL1A, FLNA, FLNC, MEST, MLH1, NTS, PSMB9) acquired methylation at CpG sites in ovarian tumours at relapse following chemotherapy or chemoresistant cell lines derived at the time of patient relapse. Furthermore, 5/13 candidate genes acquired methylation in drug-resistant in vivo-derived ovarian cancer sustaining (side population) cells. Therefore, this small set of genes are potential key drivers of chemoresistance and should be further evaluated as predictive biomarkers, both to existing chemotherapies, but also to epigenetic therapies used to modulate drug resistance. Array-based methylation profiling was performed using the Infinium HumanMethylation27 BeadChip in two cisplatin sensitive cell lines and three cisplatin resistant cell lines derived in vitro, four pairs of cisplatin sensitive and resistant cell lines derived in vivo, 7 pairs of tumour tissues obtained from patients before chemotherapy and at disease relapse, 2 pairs of IGROV1 SP and NSP cells. The reproducibility of the Infinium HumanMethylation27 BeadChips was evaluated using biological and technical replicates of matched chemosensitive/chemoresistant ovarian cancer cell lines PEO1/PEO4. Differential methylation cutoff was estimated from two biological replicates by bootstrap resampling.

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Whole genome characterisation of chemoresistant ovarian cancer [Illumina_450K_Methylation]

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