Zhang, Peng

Abstract Single-stranded DNA (ssDNA) sequencing library method has shown to enrich shorter and degraded DNA fragments than double-stranded DNA (dsDNA) library. The goal of this study is to determine whether ssDNA libraries enriches more circulating tumor DNA (ctDNA) in plasma cell-free DNA (cfDNA). We used 2ng cfDNA to prepare dsDNA libraries and ssDNA libraries. We also prepare pure-ssDNA libraries by skipping the DNA denaturation step to capture the pre-existing ssDNA only. To calculate ctDNA content, we mapped fastq files to human genome and binned the mapped reads into 1 Mb genomic windows. We normalized the read counts using two unrelated healthy controls. The resulting ratios were transformed with log2 and adjusted for GC content. The fully normalized log2 ratios were subjected to segmentation using the copy number analysis method. After the segmentation, we selected the most significantly deleted genomic region with segment size >20 Mb in each library pair and calculated ctDNA content using formula: 100 × (1-2log2 ratio). We also calculated the plasma genomic abnormality (PGA) score (a composite score algorithm to reflect overall ctDNA burden in peripheral blood) to estimate ctDNA burden. Overall, we prepared and sequenced a total of 27 libraries including ten dsDNA libraries, ten ssDNA libraries and seven pure-ssDNA libraries, using ten cfDNAs from cancer patients. We received an average of 24264998 raw read sequences and 19495014 mappable reads per sequencing library. Duplicate rate in the ssDNA libraries (mean=0.057%, range=0.046-0.083%) and pure-ssDNA libraries (mean=0.06%, range= 0.054-0.065%) was significantly lower than in dsDNA libraries (mean=0.2%, range=0.14-0.249%) (p<0.001 and p<0.01, respectively), indicating that ssDNA-based library preparation method may better preserve the diversity and complexity of ctDNAs. Library insert size analysis showed that ssDNA libraries were on average 14bp shorter (range from 6 bp to 21 bp) than their matched dsDNA libraries. We also found the Ampure XP beads ratio influenced the library size. We observed consistently higher ctDNA content in ssDNA libraries than in matched dsDNA libraries (p<0.0005). Comparing ssDNA libraries (mean ctDNA content=34%) to their matched dsDNA libraries (mean ctDNA content=30.7%), the increased ctDNA content ranged from 1.3% to 6.4% (mean=3.3%). ctDNA content was also significantly higher in pure-ssDNA libraries than in their matched dsDNA libraries (p<0.005). The increased ctDNA content ranged from 1.0% to 6.9% (mean=3.6%). The PGA scores were always higher in the ssDNA libraries (p<0.0001) or pure-ssDNA libraries (p<0.005) compared to the matched dsDNA method. Our results demonstrate that ssDNA libraries enrich more ctDNA than dsDNA libraries do. Pre-existing ssDNA in plasma is abundant and provides sufficient resource for genomic analysis of ctDNA. Citation Format: Jing Zhu, Jingyong Huang, Peng Zhang, Manish Kohli, Chiang-Ching Huang, Liang Wang. Advantages of ssDNA over dsDNA library preparation for capturing cell-free tumor DNA in plasma [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 3536.

152 Background: Plasma cfDNA ARcopy number variations (CNV) have been suggested to have prognostic significance in mCRPC stage. We compared plasma AR amplification ( ARamp) with CTC counts (the only FDA approved prognostic marker in mCRPC stage) in a prospective trial of patients (pts) progressing on androgen deprivation therapy. Methods: Plasma and CTC counts were obtained concurrently as part of a prospective clinical trial in mCRPC stage pts initiating abiraterone acetate (NCT# 01953640). Plasma cfDNA was purified using DNA Blood Mini Kit (Qiagen, Valencia, CA) and AR CNVs were detected using QuantStudio3D digital PCR system (Life Technologies, Carlsbad, CA, USA). CTC enumeration was performed using the FDA cleared CellSearch platform. The distributions of overall survival (OS) time based on ARamp status and CTC counts ( < 5 vs ≥ 5 cells) were estimated using the Kaplan-Meier method. Log-rank tests were used to test association of ARamp status and CTC counts with overall survival (OS). Univariate and multivariate logistic regression models and ROC evaluated association of OS at 24 months by ARamp status and CTCs ≥ 5. Results: Between 05/2013 and 09/2015, 92 pts were enrolled of which complete CTC, plasma and outcome data was available for 70 pts. Median age of the cohort (range) was 72 yrs (39-91); Median PSA–16.2 ng/ml (range: 0.9-2026.0); Median CTC count was 2.0 (range: 0-372); 58/70 pts had bone metastases; 38/70 had high volume and 32/70 had low volume metastatic disease at the time of sample collection. The median (range) follow up time at the time of this analysis was: 26.5 (7.9-37.0) months at which time 28/70 patients had died. ARamp was present in 19/70 pts while 51/70 did not have amplification. 24/70 had CTCs ≥ 5. A significant association of increased ARamp status with OS (p < 0.0001, log-rank test; AUC: 0.66) as well as with CTC counts ≥ 5 (p = 0.001, log-rank test; AUC: 0.67) was observed. Combining CTC status and plasma ARamp status the AUC was 0.75. Conclusions: Plasma cfDNA ARamp status and CTC counts have comparable and clinically meaningful prognostic marker value in mCRPC stage patients.