Improvement of limit of detection in primer extension-based multiplexed mutation assay using capillary electrophoresis.

One of the challenges in liquid biopsy for early cancer detection is ascribed to the fact that mutation DNA often represents an extremely small ratio of less than 1% compared to wild-type genes in blood. However, in conventional fragment analysis with capillary electrophoresis (CE), the detectable allele frequency could be about 5%. In this work, we developed an original reagent-based fragment analysis with single base extension (SBE) reactions for cancer-associated mutation assay using a commercially available CE device, and investigated on a possibility of improvement of limit of detection (LOD) for genetic mutation. First, after adjustment of reagent conditions for the SBE reactions, the linear relationship between gene template concentration and fluorescence intensity was obtained from 1 to 100 fmol of target genes. Next, from the results of an experiment to detect mutation EGFR L858R at abundance ratios of mutant type to wild type (100-fmol template) of 0, 1, 5, and 10%, it was shown that the target gene can be detected with LOD of 0.33%. This high sensitivity was realized in part by separating fluorescently labeled substrates into an individual tube for an each-colored SBE reaction. Moreover, mutations EGFR L858R and KRAS G12V were simultaneously detected at sensitivities equivalent to LODs of 0.57 and 0.47%, respectively. These results indicate that < 1% of mutations in multiplex gene mutations can be simultaneously detected, and that possibility suggests that the developed method can be used in clinical practice for detecting cancers.