A novel method for sensitive and specific detection of DNA methylation biomarkers based on DNA restriction during PCR cycling

Current status and future perspectives of circulating cell-free DNA methylation in clinical diagnostics

Aberrant DNA methylation is a hallmark of malignancies and can be detected in circulating cell-free DNA (ccfDNA) in bodily fluids, i.e. blood plasma, serum and urine. The availability of technologies that allow for an accurate and sensitive quantification of ccfDNA DNA methylation enables the precise monitoring of dynamic pathologic processes and pharmacodynamics. Recently, the first ccfDNA methylation biomarker

Diagnostic and prognostic value of SHOX2 and SEPT9 DNA methylation and cytology in benign, paramalignant and malignant pleural effusions

Pleural effusions (PE) are a common clinical problem. The discrimination between benign (BPE), malignant (MPE) and paramalignant (PPE) pleural effusions is highly important to ensure appropriate patient treatment. Today, cytology is the gold standard for diagnosing malignant pleural effusions. However, its sensitivity is limited due to the sometimes low abundance of tumor cells and the challenging assessment of cell morphology in cytological samples. This study aimed to develop and validate a diagnostic test, which allows for the highly specific detection of malignant cells in pleural effusions based on the DNA methylation biomarkers SHOX2 and SEPT9. A quantitative real-time PCR assay was developed which enabled the accurate and sensitive detection of SHOX2 and SEPT9 in PEs. Cytological and DNA methylation analyses were conducted in a case control study comprised of PEs from 114 patients (58 cases, 56 controls). Cytological analysis as well as SHOX2 and SEPT9 methylation resulted in 100% specificity. 21% of the cases were cytologically positive and 26% were SHOX2 or SEPT9 methylation positive. The combined analysis of cytology and DNA methylation resulted in an increase of 71% positively classified PEs from cancer patients as compared to cytological analysis alone. The absolute sensitivity of cytology and DNA methylation was not determinable due to the lack of an appropriate gold standard diagnostic for distinguishing between MPEs and PPEs. Therefore, it was unclear which PEs from cancer patients were malignant (containing tumor cells) and which PEs were paramalignant and resulted from benign conditions in cancer patients, respectively. Furthermore, DNA methylation analysis in PEs allowed the prognosis of the overall survival in cancer patients (Kaplan-Meier analysis, log rank test, p = 0.02 (SHOX2), p = 0.02 (SEPT9)). The developed test may be used as a diagnostic and prognostic adjunct to existing clinical and cytopathological investigations in patients with PEs of unclear etiology.

Improved PCR performance using template DNA from formalin-fixed and paraffin-embedded tissues by overcoming PCR inhibition

Formalin-fixed and paraffin-embedded (FFPE) tissues represent a valuable source for biomarker studies and clinical routine diagnostics. However, they suffer from degradation of nucleic acids due to the fixation process. Since genetic and epigenetic studies usually require PCR amplification, this degradation hampers its use significantly, impairing PCR robustness or necessitating short amplicons. In routine laboratory medicine a highly robust PCR performance is mandatory for the clinical utility of genetic and epigenetic biomarkers. Therefore, methods to improve PCR performance using DNA from FFPE tissue are highly desired and of wider interest. The effect of template DNA derived from FFPE tissues on PCR performance was investigated by means of qPCR and conventional PCR using PCR fragments of different sizes. DNA fragmentation was analyzed via agarose gel electrophoresis. This study showed that poor PCR amplification was partly caused by inhibition of the DNA polymerase by fragmented DNA from FFPE tissue and not only due to the absence of intact template molecules of sufficient integrity. This PCR inhibition was successfully minimized by increasing the polymerase concentration, dNTP concentration and PCR elongation time thereby allowing for the robust amplification of larger amplicons. This was shown for genomic template DNA as well as for bisulfite-converted template DNA required for DNA methylation analyses. In conclusion, PCR using DNA from FFPE tissue suffers from inhibition which can be alleviated by adaptation of the PCR conditions, therefore allowing for a significant improvement of PCR performance with regard to variability and the generation of larger amplicons. The presented solutions to overcome this PCR inhibition are of tremendous value for clinical chemistry and laboratory medicine.

Genome-wide screening for understanding the role of DNA methylation in colorectal cancer

DNA methylation analysis methods have undergone an impressive revolution over the past 15 years. Regarding colorectal cancer (CRC), the localization and distribution of several differently methylated genes have been determined by genome-wide DNA methylation assays. These genes do not just influence the pathogenesis of CRC, but can be used further as diagnostic or prognostic markers. Moreover, the identified four DNA methylation-based subgroups of CRC have important clinical and therapeutic merit. Since genome-wide DNA methylation analyzes result in a large amount of data, there is a need for complex bioinformatic and pathway analysis. Future challenges in epigenetic alterations of CRC include the demand for comprehensive identification and experimental validation of gene abnormalities. By introduction of genome-wide DNA methylation profiling into clinical practice not only the patients' risk stratification but development of targeted therapies will also be possible.

DNA methylation of the homeobox genes PITX2 and SHOX2 predicts outcome in non-small-cell lung cancer patients

Biomarkers that facilitate prediction of disease progression in lung cancer patients might be clinically valuable in optimizing individualized therapy. In this study, the ability of the DNA methylation biomarkers PITX2 and SHOX2 to predict disease outcome in lung cancer patients has been evaluated. Quantitative, methylation-specific (HeavyMethyl), real-time polymerase chain reaction assays were used to measure DNA methylation of PITX2 and SHOX2 in bisulfite-converted DNA from formalin-fixed, paraffin-embedded tissues from 474 non-small-cell lung cancer patients. In univariate Cox Proportional Hazard analysis, high methylation of SHOX2 and PITX2 was a significant predictor of progression-free survival [SHOX2: n=465, hazard ratio (HR)=1.395 (1.130 to 1.721), P=0.002; PITX2: n=445, HR=1.312 (1.059 to 1.625), P=0.013]. Patients with low methylation of either PITX2 and/or SHOX2 (n=319) showed a significantly higher risk of disease progression as compared with patients with higher methylation of both genes [n=126; HR=1.555 (1.210 to 1.999), P=0.001]. This was particularly true for the subgroup of patients receiving no adjuvant radiotherapy or chemotherapy [n=258, HR=1.838 (1.252 to 2.698), P=0.002]. In multivariate analysis, both biomarkers added significant independent prognostic information to pT, pN, pM, and grade. Another interesting finding of this study was that SHOX2 and PITX2 DNA methylation was shown to be inversely correlated with TTF1 (also known as NKX2-1) expression (PITX2: P=0.018, SHOX2: P<0.001). TFF1 expression was previously found to be associated with improved survival in the same patient cohort. DNA methylation of PITX2 and SHOX2 is an independent prognostic biomarker for disease progression in non-small-cell lung cancer patients.

SHOX2 DNA methylation is a biomarker for the diagnosis of lung cancer in plasma

INTRODUCTION

Recently, analysis of DNA methylation of the SHOX2 locus was shown to reliably identify lung cancer in bronchial aspirates of patients with disease. As a plasma-based assay would expand the possible applications of the SHOX2 biomarker, this study aimed to develop a modified SHOX2 assay for use in a blood-based test and to analyze the performance of this optimized SHOX2 methylation assay in plasma.

METHODS

Quantitative real-time polymerase chain reaction was used to analyze DNA methylation of SHOX2 in plasma samples from 411 individuals. A training study (20 stage IV patients with lung cancer and 20 controls) was performed to show the feasibility of detecting the SHOX2 biomarker in blood and to determine a methylation cutoff for patient classification. The resulting cutoff was verified in a testing study composed of 371 plasma samples from patients with lung cancer and controls.

RESULTS

DNA methylation of SHOX2 could be used as a biomarker to distinguish between malignant lung disease and controls at a sensitivity of 60% (95% confidence interval: 53-67%) and a specificity of 90% (95% confidence interval: 84-94%). Cancer in patients with stages II (72%), III (55%), and IV (83%) was detected at a higher sensitivity when compared with stage I patients. Small cell lung cancer (80%) and squamous cell carcinoma (63%) were detected at the highest sensitivity when compared with adenocarcinomas.

CONCLUSIONS

SHOX2 DNA methylation is a biomarker for detecting the presence of malignant lung disease in blood plasma from patients with lung cancer.

Restriction enzyme-mediated enhanced detection of circulating cell-free fetal DNA in maternal plasma

A universal method confirming the presence of circulating cell-free fetal (ccff) DNA in maternal plasma is important in the field of noninvasive prenatal diagnostics. Restriction endonuclease digestion of one allele of a single-nucleotide polymorphism (SNP) was used to allow detection of paternal alleles in maternal plasma DNA. Multiplexed genotyping of 92 panethnic high-frequency SNPs predicted >0.99 probability of detecting at least four informative loci per sample. Child-maternal paired DNA samples were used to confirm detection of 2% child's heterozygous DNA in a background of maternal DNA homozygous for the digestible allele. By restriction endonuclease digestion of DNA in a PCR cocktail before thermal cycling, 10 genomic copies of a paternal SNP allele were detectable in a background of 990 maternal SNP alleles. A comparison of 154 pregnant and nonpregnant female plasma DNA samples demonstrated enhanced detection of nondigestible SNP alleles in maternal plasma. Receiver operating characteristic curve analysis showed an optimal detection threshold of four nondigestible SNP alleles in plasma for the confirmation of ccff DNA and 98% sensitivity and 96% specificity at a 95% confidence level. Our study demonstrates the ability of this technique to confirm the presence of paternal alleles from ccff DNA in maternal plasma.

Correlation of SHOX2 gene amplification and DNA methylation in lung cancer tumors

BACKGROUND

DNA methylation in the SHOX2 locus was previously used to reliably detect lung cancer in a group of critical controls, including 'cytologically negative' samples with no visible tumor cell content, at a high specificity based on the analysis of bronchial lavage samples. This study aimed to investigate, if the methylation correlates with SHOX2 gene expression and/or copy number alterations. An amplification of the SHOX2 gene locus together with the observed tumor-specific hypermethylation might explain the good performance of this marker in bronchial lavage samples.

METHODS

SHOX2 expression, gene copy number and DNA methylation were determined in lung tumor tissues and matched morphologically normal adjacent tissues (NAT) from 55 lung cancer patients. Quantitative HeavyMethyl (HM) real-time PCR was used to detect SHOX2 DNA methylation levels. SHOX2 expression was assayed with quantitative real-time PCR, and copy numbers alterations were measured with conventional real-time PCR and array CGH.

RESULTS

A hypermethylation of the SHOX2 locus in tumor tissue as compared to the matched NAT from the same patient was detected in 96% of tumors from a group of 55 lung cancer patients. This correlated highly significantly with the frequent occurrence of copy number amplification (p < 0.0001), while the expression of the SHOX2 gene showed no difference.

CONCLUSIONS

Frequent gene amplification correlated with hypermethylation of the SHOX2 gene locus. This concerted effect qualifies SHOX2 DNA methylation as a biomarker for lung cancer diagnosis, especially when sensitive detection is needed, i.e. in bronchial lavage or blood samples.

SHOX2 DNA methylation is a biomarker for the diagnosis of lung cancer based on bronchial aspirates

BACKGROUND

This study aimed to show that SHOX2 DNA methylation is a tumor marker in patients with suspected lung cancer by using bronchial fluid aspirated during bronchoscopy. Such a biomarker would be clinically valuable, especially when, following the first bronchoscopy, a final diagnosis cannot be established by histology or cytology. A test with a low false positive rate can reduce the need for further invasive and costly procedures and ensure early treatment.

METHODS

Marker discovery was carried out by differential methylation hybridization (DMH) and real-time PCR. The real-time PCR based HeavyMethyl technology was used for quantitative analysis of DNA methylation of SHOX2 using bronchial aspirates from two clinical centres in a case-control study. Fresh-frozen and Saccomanno-fixed samples were used to show the tumor marker performance in different sample types of clinical relevance.

RESULTS

Valid measurements were obtained from a total of 523 patient samples (242 controls, 281 cases). DNA methylation of SHOX2 allowed to distinguish between malignant and benign lung disease, i.e. abscesses, infections, obstructive lung diseases, sarcoidosis, scleroderma, stenoses, at high specificity (68% sensitivity [95% CI 62-73%], 95% specificity [95% CI 91-97%]).

CONCLUSIONS

Hypermethylation of SHOX2 in bronchial aspirates appears to be a clinically useful tumor marker for identifying subjects with lung carcinoma, especially if histological and cytological findings after bronchoscopy are ambiguous.

A combined HM-PCR/SNuPE method for high sensitive detection of rare DNA methylation

Background

DNA methylation changes are widely used as early molecular markers in cancer detection. Sensitive detection and classification of rare methylation changes in DNA extracted from circulating body fluids or complex tissue samples is crucial for the understanding of tumor etiology, clinical diagnosis and treatment. In this paper, we describe a combined method to monitor the presence of methylated tumor DNA in an excess of unmethylated background DNA of non-tumorous cells. The method combines heavy methyl-PCR, which favors preferential amplification of methylated marker sequence from bisulfite-treated DNA with a methylation-specific single nucleotide primer extension monitored by ion-pair, reversed-phase, high-performance liquid chromatography separation.

Results

This combined method allows detection of 14 pg (that is, four to five genomic copies) of methylated chromosomal DNA in a 2000-fold excess (that is, 50 ng) of unmethylated chromosomal background, with an analytical sensitivity of > 90%. We outline a detailed protocol for the combined assay on two examples of known cancer markers (SEPT9 and TMEFF2) and discuss general aspects of assay design and data interpretation. Finally, we provide an application example for rapid testing on tumor methylation in plasma DNA derived from a small cohort of patients with colorectal cancer.

Conclusion

The method allows unambiguous detection of rare DNA methylation, for example in body fluid or DNA isolates from cells or tissues, with very high sensitivity and accuracy. The application combines standard technologies and can easily be adapted to any target region of interest. It does not require costly reagents and can be used for routine screening of many samples.