Highly sensitive detection of rare mutant alleles by combining argonaute-based enrichment and XNA-PCR.

e14605 Background: Characterization of disease-associated, cell-free nucleic acids (liquid biopsy) provides a powerful, minimally-invasive means for early disease detection, genotyping, and personalized therapy. Detection of alleles of clinical interest is often challenged by their low concentration and sequence homology with the much more abundant wildtype nucleic acids. Methods: Argonuate (Ago) from the thermophilic bacterium Thermus thermophilus ( TtAgo) utilizes short DNA guides to specifically cleave complementary DNA and RNA targets. We found that under optimized conditions, TtAgo cleaves DNA and RNA complementary to the guide DNA with high efficiency, but spares nucleic acids with a single nucleotide mismatch at and around its catalytic site with high sensitivity. Based on these findings, we designed a new multiplexed enrichment assay, dubbed NAVIGATER (Nucleic Acid enrichment Via DNA Guided Argonaute from Thermus thermophilus), that utilizes TtAgo, to specifically cleave perfectly complementary DNA and RNA while sparing alleles of interest. Results: NAVIGATER greatly increases the fractions of rare mutant alleles with single nucleotide precision enhancing the sensitivity of downstream detection methods such as XNA-PCR. We demonstrate 60-fold enrichment of KRAS G12D in blood samples from pancreatic cancer patients and over ten-fold improved sensitivity of XNA-PCR, enabling multiplex detection of KRAS and EGFR mutants at 0.01% fractions. Conclusions: NAVIGATER has important advantages over other mutant allele enrichment assays such as the ones based on CRISPR-Cas. It does not require the target to contain a protospacer-adjacent motif; is a true (turnover) catalyst; can cleave both DNA and associated exosomal RNA targets, improving sensitivity; and can operate at elevated temperatures for higher selectivity and compatibility with detection schemes.