Digital Loop-Mediated Isothermal Amplification-Based Absolute Methylation Quantification Revealed Hypermethylated DAPK1 in Cervical Cancer Patients

The aberrant methylation of many genes has been reported to be associated with various carcinomas. Accurate detection of the methylation level could provide critical insights into the diagnostic analysis of diseases. Here, a sensitive HpaII-edited absolute droplet loop-mediated isothermal amplification (HEADLAMP) method based on methylation-sensitive restriction enzyme (MSRE) HpaII was developed for the digital quantification of DNA methylation. Methylation levels of the death-associated protein kinase 1 (DAPK1) gene that is associated with many cancers were studied using β-actin as an internal reference. DAPK1 (2.5 pM) with 0.01% methylation (250 aM) can be detected with the conventional HpaII-edited LAMP assay. Using HEADLAMP, as low as 1% methylation level can be distinguished with an estimated limit of detection of 5 aM (ca. 3 copies/μL). Moreover, HEADLAMP can detect low levels of methylated DAPK1 in normal L-02 cells, while the conventional assay cannot. Finally, HEADLAMP was applied to the detection of DAPK1 methylation in 20 clinical tissue samples, which revealed hypermethylated DAPK1 in cervical cancer patients. We envisage potential applications of this robust, specific, and sensitive HEADLAMP assay in epigenetic studies and early clinical diagnosis.