Abstract A035: A real-time PCR method for the detection of cancer-specific methylation patterns in cfDNA

Abstract

Abstract Non-invasive liquid biopsy tests are proving to be the next frontier in cancer diagnostics with methylation emerging as a reliable biomarker for low levels of circulating tumor DNA (ctDNA). There is a rising interest in sensitive, low-cost liquid biopsy assays to detect low copies of hypermethylated ctDNA in an excess background of non-cancer-associated hypomethylated cell- free DNA (cfDNA). Real-time quantitative methylation-specific PCR (qMSP) allows for the detection of low abundance methylated fragments. qMSP approaches have previously been developed but are predominantly designed to target a specific CpG site. To date we are not aware of any qMSP approaches that target pan-cancer-associated methylation patterns across multiple CpG sites. Harbinger Health has developed a qMSP method with locked nucleic acid (LNA) blockers that target methylation haplotypes, allowing for multiplex enrichment and quantification of cancer-specific methylation patterns. Using targeted bisulfite sequencing, we identified ten pan-cancer-informative CpG-dense regions which showed consistent contiguous elevated methylation states in cancer cfDNA and low levels of methylation in non-cancer cfDNA. We designed qMSP assays for these regions and LNA blockers which bind to unmethylated target CpG sites, outcompeting the hydrolysis probe through a high Tm differential. This prevented non-specific probe hybridization. The qMSP-LNA assays were evaluated in simplex and multiplex using cell line DNA in a titration of hypermethylated “ctDNA” spiked into hypomethylated “cfDNA” to simulate varying ctDNA levels, and then validated with cancer and non-cancer cfDNA samples at 5 ng input, equivalent to 1450 haploid copies. The percentage of methylated DNA was estimated by the ratio of methylated copies (qMSP-LNA) to total copies (internal reference), which were quantified by standard curves. The qMSP-LNA assays detected low abundance methylated DNA fragments down to 23 target copies. LNA blockers completely depleted background signal originating from unmethylated DNA with high specificity, showing no inhibition of methylated DNA detection. When tested in cfDNA samples which varied in conversion efficiency, discordant methylation states, and methylation abundance, the assays reproducibly amplified and detected highly methylated fragments which correspond to cancer signal. Harbinger Health has developed qMSP-LNA assays for contiguous CpG biomarkers which differentiate cancer and non-cancer samples from only ten pan-cancer-informative regions. The qMSP-LNA method detected low abundance fragments with specific methylation patterns with high specificity and sensitivity. The assay reproducibly detected methylated DNA in cfDNA samples that represent a clinically relevant range of methylation signal and will be further validated in a larger cohort of cancer and non-cancer cfDNA samples. Due to the high specificity and sensitivity, this cost-effective PCR method may provide utility and improve access for early cancer detection and monitoring. Citation Format: Emily Neaga, Caitlin Gilley, Sarah Falotico, Mayur Gurnani, Zhenyu Zhang, Jocelyn Charlton, Miguel Williams, Anthony Shuber. A real-time PCR method for the detection of cancer-specific methylation patterns in cfDNA [abstract]. In: Proceedings of the AACR Special Conference: Liquid Biopsy: From Discovery to Clinical Implementation; 2024 Nov 13-16; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(21_Suppl):Abstract nr A035.