Abstract 960: Improved cfDNA methylation profiling through correction of misrepaired jagged-ends
Authors: Wang Rui , Hamilton Emily G. , Almanza Diego , Hui Angela , Diehn Maximilian , Alizadeh Ash A. 
Published: March 2024

Background: Profiling cfDNA methylation enables early cancer detection and classification, but challenges arise from "jagged ends" (JEs) for ~90% of cfDNA molecules, as well as for FFPE samples and partially degraded genomic DNA. Repair of these jagged ends introduces erroneous methylation signals, especially in shorter cfDNA fragments enriched for tumor derived molecules. Separately, DNA conversions during 5mC profiling hamper accurate simultaneous ctDNA genotyping of somatic mutations. To meet these needs, we developed a method preserving double-stranded cfDNA molecules without error-prone end-repair at jagged ends. This enables superior methylation profiling including hemimethylation detection, and simultaneous ctDNA SNV genotyping.

Methods: We present JEEPERS (Jagged-End Error Polishing of Enzymatically misRepaired Sequences), a novel method for correcting errors in double-stranded library preparation for methylation profiling. JEEPERS detects and quantifies enzymatic repair errors at JEs, correcting them in silico. Leveraging duplex UMIs, it utilizes complementary strands and sibling reads from cfDNA families without jagged ends. The method exploits the 5' to 3' polarity of ER-associated errors and JE length profiles for correction. JEEPERS introduces anchor CpGs for precise correction of rare signals and enables accurate SNV calling at non CpG sites, addressing the challenge of differentiating true SNVs from conversion artifacts leading to C&gt;T/G&gt;A changes in sequencing data.

Results: Analyzing 248 cfDNA samples (139 NSCLC patients, 109 healthy controls) by methylation profiling (EM-Seq) and ctDNA mutation genotyping (CAPP-Seq), JEEPERS correction efficiently addressed distortions, even at low tumor concentrations. Limiting dilution experiments demonstrated JEEPERS achieving a LOD95 of ~0.2% with 95% specificity (n=300). Despite ~50% lower molecular depth, JEEPERS-corrected cfDNA EM-Seq enabled accurate simultaneous methylation profiling and ctDNA genotyping, correlating strongly with CAPP-Seq genotypes (R=0.998, n=30). As expected, mutant ctDNA molecules were shorter than wild-type in both CAPP-Seq and EM-Seq data. cfDNA methylation patterns varied by oncogene vs. tumor suppressor status; EGFR mutants showed increased methylation (p&lt;0.01), while TP53 mutants had lower methylation levels (p&lt;0.05).

Conclusions: Our method effectively corrects cfDNA methylation data, even at low tumor concentration, ensuring enhanced methylation signal accuracy and proficient SNV calling capabilities. This integrated approach offers a powerful means for investigating the link between SNVs and DNA methylation, significantly enhancing the accuracy of cancer detection using cfDNA, especially for early-stage tumors. This paves the way for a deeper understanding of the molecular mechanisms driving cancer initiation and progression.

Citation Format: Rui Wang, Emily G. Hamilton, Diego Almanza, Angela Hui, Maximilian Diehn, Ash A. Alizadeh. Improved cfDNA methylation profiling through correction of misrepaired jagged-ends [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 960.