Abstract 5180: Enhanced and controlled chromatin extraction for chromatin-based epigenetic assays in FFPE tissues

Abstract

Abstract Background: Epigenetic dysregulation is involved in the etiology and progression of various human diseases. Formalin-fixed paraffin-embedded (FFPE) samples represent the gold standard for archiving pathology samples, and thus FFPE samples are a major resource of samples in clinical research. However, chromatin-based epigenetic assays in the clinical settings are limited to fresh or frozen samples and are hampered by low chromatin yield in FFPE samples due to the lack of reliable and efficient chromatin preparation methods. Here, we introduce a new chromatin extraction method from FFPE tissues (Chrom-EX PE) for chromatin-based epigenetic assays. Results: During rehydration of FFPE tissues, applying tissue-level cross-link reversal to the deparaffinized tissue at 65°C dramatically increased chromatin yield in the soluble fraction. We found the resulting chromatin to be compatible with ChIP-qPCR and ChIP-seq analysis of histone marks (H3K4me3, H3K27me3, and H3K27Ac) and RNA polymerase II. The chromatin prepared by Chrom-EX PE showed a gradual fragmentation pattern with varying incubation temperature. At temperatures below 37°C, the majority of soluble chromatin was over 1 kb in size. The soluble chromatin prepared at 45-60°C showed a typical nucleosomal pattern shown in cell lines and frozen tissues. The majority of the chromatin prepared at 65°C is close to mononucleosomal size. These observations indicate that chromatin preparation from FFPE samples can be controlled for downstream chromatin-based epigenetic assays. Conclusions: Our method achieves efficient extraction of high-quality chromatin from FFPE samples suitable for targeted and genome-wide epigenetic assays while minimizing degradation and damages. This approach provides a new platform for developing chromatin-based assays applicable to archived FFPE samples to circumvent the over-fixed nature of FFPE tissues. This work was supported, in part, by National Institutes of Health grant P01DK068055 and the Mayo Clinic Center for Individualized Medicine Epigenomics Program. Citation Format: Jian Zhong, Zhenqing Ye, Chad Clark, Samuel Lenz, Justin Nguyen, Huihuang Yan, Keith Robertson, Gianrico Farrugia, Zhiguo Zhang, Tamas Ordog, Jeong-Heon Lee. Enhanced and controlled chromatin extraction for chromatin-based epigenetic assays in FFPE tissues [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5180.