Abstract 3647: Prior DNA repair improves the read quality in next-generation sequencing of cell-free tumor DNA

Abstract

Abstract The cell-free tumor DNA (ctDNA) in patient's plasma is a noninvasive tumor biomarker. The detection of ctDNA is helpful to evaluate tumor progression, tumor response to the therapy, and subtyping of tumor cells. Targeting next-generation sequencing (NGS) technology provides a sensitive and specific technique for ctDNA detection. It can detect multiple tumor-related gene mutations. However, collection of high quality of cell-free DNA (cfDNA) may not be available in some cases. The quality of cfDNA in plasma is impacted by multiple factors, such as plasma collection and storage conditions, DNase activity in the blood, and the apoptotic and necrotic status of the tumor. These factors affect the integrity of cfDNA, leading to full or partial degradation of cfDNA, including double-strand DNA breaks and single strand DNA nicking. Lesions on cfDNA decrease the usability of ctDNA by digital PCR and targeted NGS. Due to amount limitation of cfDNA in some cases, the repair of damaged cfDNA could be a necessary rescue step in producing viable libraries for NGS. CfDNA was extracted from the plasma with Zymo Research's Quick-cfDNA Serum and Plasma kit and was quantified by realtime PCR with Alu primer sets. The size of cfDNA was about 160 base pairs, as estimated by Agilent Tapestation 2200 with the High Sensitivity DNA kit. The DNA repair of cfDNA was conducted with PreCR Repair Mix of New England BioLabs. The sequencing library was prepared with Accel-Amplicon 56G Oncology Panel of Swift Biosciences and sequenced in Illumina's MiSeq. The quality of sequencing data was determined with FastQC. Compared to PreCR Repair Mix treated cfDNA samples, fastQ data from some of untreated cfDNA samples showed failed per base sequencing quality, about 50% of sequencing cycles with the mean quality score below 30. The per sequencing quality score of these cfDNA samples failed also to pass the quality filter. The read size distribution analysis indicated that about 60 to 70% of read sized between 30 to 45 bases and about 75 to 80% of read was smaller than 75 bases. However, sequencing data from same cfDNA samples treated with PreCR Repair Mix show a greatly improved sequencing quality. Both per base sequencing quality and per sequencing quality score passed quality filter. The above 97% of reads sized over 92 bases, complying with the requirement of 56G Oncology Panel. In conclusion, the DNA repair process before library preparation is necessary to rescue damaged cfDNA for amplicon-based NGS. Citation Format: Hong Yin, Adam H. Greer, Glenn Mills. Prior DNA repair improves the read quality in next-generation sequencing of cell-free tumor DNA [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 3647.