The development and validation of a novel targeted methylation sequencing technology detecting 0.003 percent tumor signal in early-stage cancer plasma.

Abstract

4092 Background: Methylation analysis in cell-free DNA holds great potential for early cancer detection. In the plasma of early stage cancer patient, the tumor content is estimated to be less than 0.1%, therefore demands a highly sensitive assay. Targeted Methylation Sequencing (TMS) is the most promising approach; however, the current sensitivity and specificity are compromised by low efficiency and low recovery of target enrichment, and further hampered by background noise associated with large panels. The ideal solution would be an in-depth analysis using a focused small cancer-specific methylation biomarker panel, but is not supported by existing technologies. Methods: Here we present a new technology designed for TMS analysis in cfDNA: Point-n-Seq, featuring an enrichment of target molecules directly from cfDNA before bisulfite conversion and amplification. Particularly, this technology enables small focused panel that interrogates the methylation status of 1 to ~1000 markers. We designed a CRC panel covering 100 methylation markers in 3 steps: identify ~1000 CRC-specific markers from public databases; eliminate makers with high background signal in baseline cfDNA of healthy population; finalize the list with the most differentiating markers between patient and healthy cfDNA. Results: The capture of Point-n-Seq CRC panel is highly efficient resulting in high uniformity (94% > 0.5X) and on-target rate ( > 80%). For 20 ng cfDNA input, more than 1000 deduped informative reads were obtained for each marker on average, despite the high GC content ( > 80%). The output of informative reads was linear to the cfDNA input ranging from 1 ng to 40 ng. In titration studies, 0.6 pg (0.2X genome equivalent) methylated DNA in 20 ng cfDNA (0.003%) was reliably detected over cfDNA background. Using plasma samples from patients with CRC - early stage (I, n = 7; II, n = 7), late stage (III, n = 11; IV, n = 3), and control individuals (n = 105), the average fractions of methylated signal are 0.0034%, 0.013%, 0.09%, 0.17%, 0.29% for control, stage I, II, III, IV accordingly. With a simple cut-off using methylation fraction, Point-n Seq CRC panel achieved a sensitivity of 86% for stage I, 100% for stage (II-IV) at a specificity of 91%, with AUC = 0.96. Conclusions: Point-n-Seq TMS is the first hybridization based NGS technology enables the small focused methylation panel (e.g. 100 markers) sequencing using cfDNA, and it will greatly facilitate the development of practical and cost-effective methylation assays for clinical use.