Highly sensitive detection of sentinel lymph node metastasis of breast cancer by digital PCR for RASSF1A methylation

Highly Sensitive and Diversified Electrochemiluminescence DNA Methylation Biosensing Platform Based on Self-Assembly of Nanotags

This work proposes a highly sensitive, simple, and reliable electrochemiluminescence (ECL) DNA methylation biosensing platform by employing DNA-functionalized magnetic beads (DNA-MBs) for target capture and nanotag self-assembly aggregation for signal amplification. The target methylated DNA was first captured on DNA-MBs through base pairing recognition, and then its methylation sites were recognized by antibody-5mC (Ab-5mC). Afterward, a pair of antibodies functionalized [Ru(byp)3]2+-doped silica nanoparticles (Ab2-Ru@SiO2 and Ab3-Ru@SiO2) was layer-by-layer assembled on Ab-5mC for amplified signal transduction. The sensing beads could be transferred to screen-printed carbon electrodes (SPCEs) for ECL curve detection via photomultiplier tube or to gold-coated indium tin oxide (Au/ITO) arrays for high-throughput imaging detection. As the nanotag assembly layers increased from 1 to 3, the detection sensitivities of SPCE-based curve detection and Au/ITO-based imaging detection were enhanced 7-fold and 3-fold, achieving detection limits down to 0.8 pM and 0.9 fM, respectively. The nanotags showed good stability, with storage times of 300 days for Ru@SiO2 and 60 days for Ab-Ru@SiO2, respectively. This method is universal and could be applied to detect different methylated DNAs by using their corresponding DNA-MBs. The proposed ECL biosensing platform possessed advantages of high sensitivity, good diversity, and practicality, showing potential for high-throughput DNA methylation detection in clinical diagnosis.

Evaluation of RASSF1A methylation in the lysate of sentinel lymph nodes for detecting breast cancer metastasis: A diagnostic accuracy study

The restriction enzyme-based digital methylation-specific polymerase chain reaction (RE-dMSP) assay is useful for diagnosing sentinel lymph node (SN) metastasis in patients with breast cancer, by detecting tumor-derived methylated Ras association domain-containing protein 1 (RASSF1A). In addition, this assay has high concordance (95.0%) with one-step nucleic acid amplification (OSNA). The present study aimed to perform RE-dMSP using OSNA lysate from more patients and to re-evaluate its clinical usage. Overall, 418 SNs from 347 patients were evaluated using both OSNA and RE-dMSP. The concordance rate was 83.3% (348/418). RASSF1A methylation of the primary tumors was negative in 36 patients. When these patients were excluded, the concordance rate improved to 88.2% (330/374). Of the 79 OSNA-negative cases, 19 were RE-dMSP-positive, although all were positive for cytokeratin 19 expression in the primary tumor, suggesting that RE-dMSP can detect tumor-derived DNA with a higher sensitivity. The percent of methylated reference of the breast tumors showed a wide variety in the 16 OSNA-positive/RE-dMSP-negative cases, and such variability of methylation could have affected the results in these patients. In conclusion, although RE-dMSP can diagnose SN metastasis with high sensitivity and accuracy, and can be a supplementary tool to OSNA in breast cancer, RE-dMSP showed certain discordance with OSNA and critically depended on the absence or heterogeneity of DNA methylation in breast tumors. Further research is expected to develop an assay targeting other DNA alterations, such as mutations.

Endonuclease-Assisted PAM-free Recombinase Polymerase Amplification Coupling with CRISPR/Cas12a (E-PfRPA/Cas) for Sensitive Detection of DNA Methylation

DNA methylation is considered as a potential cancer biomarker. The evaluation of DNA methylation level will contribute to the prognosis and diagnosis of cancer. Herein, we propose a novel assay based on endonuclease-assisted protospacer adjacent motif (PAM)-free recombinase polymerase amplification coupling with CRISPR/Cas12a (E-PfRPA/Cas) for sensitive detection of DNA methylation. The methylation-sensitive restriction enzyme (MSRE) is first used to selectively digest unmethylated DNA, while the methylated target remains structurally intact. Therefore, the methylated target can initiate the RPA reaction to generate a large amount of double-stranded DNA (dsDNA). To avoid the dependence of PAM site of CRISPR/Cas12a, one of the RPA primers is designed with 5'-phosphate terminuses. After treating with Lambda, the sequence with 5'-phosphate modification will be degraded, leaving the single-stranded DNA (ssDNA). The CRISPR/Cas12a can accurately locate ssDNA without PAM, then initiating its trans-cleavage activity for further signal amplification. Meanwhile, non-specific amplification can be also avoided under Lambda, effectively filtering the detection background. Benefiting from the specificity of MSRE, the high amplification efficiency of Lambda-assisted RPA, and the self-amplification effect of CRISPR/Cas, the E-PfRPA/Cas assay shows outstanding sensitivity and selectivity, and as low as 0.05% of methylated DNA can be distinguished. Moreover, the lateral flow assay is also introduced to exploit the point-of-care diagnostic platform. Most importantly, the proposed method shows high sensitivity for determination of genomic DNA methylation from cancer cells, indicating its great potential for tumor-specific gene analysis.

RASSF1A methylation as a biomarker for detection of colorectal cancer and hepatocellular carcinoma

BACKGROUND

Studies have validated the potential of methylated cell-free DNA as a biomarker in various tumors, and methylated DNA in plasma may be a potential biomarker for cancer.

AIM

To evaluate the diagnostic value of RASSF1A methylation in plasma for colorectal cancer (CRC) and hepatocellular carcinoma (HCC).

METHODS

A total of 92 CRC patients, 67 colorectal polyp (CRP) patients, 63 HCC patients, and 66 liver cirrhosis (LC) patients were enrolled. The plasma DNA was subjected to DNA extraction, double-strand DNA concentration determination, bisulfite conversion, purification, single-strand DNA concentration determination, and digital polymerase chain reaction (PCR) detection. The methylation rate was calculated. The diagnostic value was evaluated by the area under the curve (AUC).

RESULTS

The age and sex in the CRC and CRP groups and the HCC and LC groups were also matched. The DNA methylation rate of RASSF1A in plasma in the CRC group was 2.87 ± 1.80, and that in the CRP group was 1.50 ± 0.64. DNA methylation of RASSF1A in plasma showed a significant difference between the CRC and CRP groups. The AUC of RASSF1A methylation for discriminating the CRC and CRP groups was 0.82 (0.76-0.88). The AUCs of T1, T2, T3 and T4 CRC and CRP were 0.83 (0.72-0.95), 0.87 (0.78-0.95), 0.86 (0.77-0.95), and 0.75 (0.64-0.85), respectively. The DNA methylation rate of RASSF1A in plasma in the HCC group was 4.45 ± 2.93, and that in the LC group was 2.46 ± 2.07. DNA methylation of RASSF1A in plasma for the HCC and LC groups showed a significant difference. The AUC of RASSF1A methylation for discriminating the HCC and LC groups was 0.70 (0.60-0.79). The AUCs of T1, T2, T3 and T4 HCC and LC were 0.80 (0.61, 1.00), 0.74 (0.59-0.88), 0.60 (0.42-0.79), and 0.68 (0.53-0.82), respectively.

CONCLUSION

RASSF1A methylation in plasma detected by digital PCR may be a potential biomarker for CRC and HCC.

Dual Methylation-Sensitive Restriction Endonucleases Coupling with an RPA-Assisted CRISPR/Cas13a System (DESCS) for Highly Sensitive Analysis of DNA Methylation and Its Application for Point-of-Care Detection

High-performance detection of DNA methylation possesses great significance for the diagnosis and therapy of cancer. Herein, for the first time, we present a digestion strategy based on dual methylation-sensitive restriction endonucleases coupling with a recombinase polymerase amplification (RPA)-assisted CRISPR/Cas13a system (DESCS) for accurate and sensitive determination of site-specific DNA methylation. This dual methylation-sensitive restriction endonuclease system selectively digests the unmethylated target but exhibits no response to methylated DNA. Therefore, the intact methylated DNA target triggers the RPA reaction for rapid signal amplification. In contrast, the digested unmethylated target initiates no RPA reaction. RPA products with a T7 promoter can execute the T7 transcription in the presence of T7 RNA polymerase to generate a large number of single-stranded RNA (ssRNA). This ssRNA can be recognized by CRISPR/Cas13a to induce the ssRNase activity of Cas13a, showing the indiscriminate cleavage of the collateral FQ reporter to release the fluorescence signal. With such a design, by combining the unique features of dual methylation-sensitive restriction endonucleases with RPA-assisted CRISPR/Cas13a, the DESCS system not only presents the rapid and powerful signal amplification for the determination of methylated DNA with ultrahigh sensitivity but also effectively eliminates the false positive influences from incomplete digestion of the unmethylated target. More importantly, 0.01% methylation level can be effectively distinguished with the existence of excess unmethylated DNA. In addition, the DESCS assay is integrated into the lateral flow biosensor (LFB) for the point-of-care determination of DNA methylation. In view of the superiorities in high sensitivity, outstanding selectivity, and ease of operation, the DESCS system will provide a reliable assay for site-specific analysis of methylation.

Quantification of DNA methylation independent of sodium bisulfite conversion using methylation-sensitive restriction enzymes and digital PCR

Epigenetic regulation is important in human health and disease, but the exact mechanisms remain largely enigmatic. DNA methylation represents one epigenetic aspect but is challenging to quantify. In this study, we introduce a digital approach for the quantification of the amount and density of DNA methylation. We designed an experimental setup combining efficient methylation‐sensitive restriction enzymes with digital polymerase chain reaction (PCR) to quantify a targeted density of DNA methylation independent of bisulfite conversion. By using a stable reference and comparing experiments treated and untreated with these enzymes, copy number instability could be properly normalized. In silico simulations demonstrated the mathematical validity of the setup and showed that the measurement precision depends on the amount of input DNA and the fraction methylated alleles. This uncertainty could be successfully estimated by the confidence intervals. Quantification of RASSF1 promoter methylation in a variety of healthy and malignant samples and in a calibration curve confirmed the high accuracy of our approach, even in minute amounts of DNA. Overall, our results indicate the possibility of quantifying DNA methylation with digital PCR, independent of bisulfite conversion. Moreover, as the context‐density of methylation can also be determined, biological mechanisms can now be quantitatively assessed.