Meth-DOP-PCR: an assay for the methylation profiling of trace amounts of DNA extracted from bodily fluids

Cancer cells release their DNA into the patient's bodily fluids and cancer-specific signatures can be recognized in the circulating DNA. The aberrant methylation of CpG-rich regions in gene promoter sequences is an early marker of cell transformation whose specificity and optimal sensitivity can be achieved by assessing the methylation status of multiple genes ('methylation profiling'). Most of the current technologies for methylation analysis rely upon the combination of chemical conversion of the DNA and PCR analysis for the detection of methylated and unmethylated alleles. However, the small amount of circulating DNA, and its fragmentation, dramatically reduces the template DNA molecules making difficult the methylation profiling. To overcome this limitation, we have developed the Meth-DOP-PCR assay, a combination between a modified degenerate oligonucleotide primed PCR (DOP-PCR) and methylation-specific PCR (MSP), for the high-throughput methylation analysis of trace-amount of circulating DNA. We have demonstrated the concordance between Meth-DOP-PCR and MSP and shown the application of this technique for the methylation analysis of DNA extracted from the serum of lung cancer patients. We have estimated that through this procedure it is possible to obtain at least a 25-fold increase of the number of determinations allowing the methylation profiling from less than 1 ml of serum. Thus, Meth-DOP-PCR appears as a simple, cost-effective and efficient technique, for the development of novel methylation-based diagnostic assays.