Epithelial ovarian cancer (OC) is the most lethal gynecologic malignancy. The majority of advanced stage patients develop uniformly fatal resistance to standard platinum-based treatments. Epigenetic changes, particularly DNA methylation aberrations have been implicated in acquired resistance to platinum in OC. The goal of the current study was to identify methylation changes associated with the development of acquired resistance to platinum-based chemotherapy. We hypothesized that OC tumors harboring an aberrant DNA methylome could be reversed by DNMTi and re-sensitized to platinum treatment. To achieve our objective, we generated and compared tumor DNA methylation profiles from patients with recurrent platinum-resistant OC treated on a clinical trial with a DNA methyl transferase inhibitor, guadecitabine, before (n=65) and after (n=19) treatment (NCT01696032), and patients with primary (platinum-naïve) OC (n=20). Human ovarian surface epithelial cells (HOSE) were used as controls (n=5). We examined methylation levels across the genome using the Infinium Human Methylation 450 Bead Chip (Illumina). By comparing the methylome of platinum naive and platinum resistant ovarian tumors, normalized to HOSE, we identified 444 CpG island-containing gene promoters that became hypermethylated in resistant tumors. Of those, 45 gene promoters were hypermethylated at an FDR<0.05 and 19 genes at an FDR<0.05 and Δβ>0.1. Among those significantly hypermethylated genes, acquired promoter CpG island methylation of Ras Association Domain Family 1A (RASSF1A; a tumor suppressor gene in multiple cancer types) was observed. Of the 444 hypermethylated promoters in tumor resistant samples, 93 CpG islands became hypomethylated after guadecitabine treatment, suggesting that these promoters may be associated with reversal of resistance. Of those were the IFNA8 promoter, a gene known to be associated with anti-tumor effects in ovarian and other solid malignancies, and DEFB124, which is involved in the innate immune response. Pathways associated with immune reactivation were highly enriched by guadecitabine treatment, including IL-12 signaling and production of macrophages and MAPK and apoptosis signaling. Together, these results support that aberrant DNA methylation affecting gene networks associate with immune response plays a role in platinum resistant development and could be a therapeutic target.

Citation Format: Fang Fang, Horacio Cardenas, Guanglong Jiang, Susan M. Perkins, Chi Zhang, Harold Keer, Yunlong Liu, Daniela Matei, Kenneth Nephew. Epigenomic signatures of acquired platinum resistance in high grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2997.