Abstract

Background: To improve prognosis of patients with colorectal cancer, powerful blood-based biomarkers enabling for early detection are needed. As genome-wide DNA hypomethylation is associated with carcinogenesis, and cell-free DNA, thought to be of tumor origin, is found in the circulation of patients with cancer, we investigated the relevance of 5-methylcytosine-modified DNA present in cell-free circulating nucleosomes as a serum biomarker using a convenient enzyme-linked immunosorbent assay (ELISA) technique. Materials and Methods: Serum samples from 90 individuals [24 with colorectal cancer (CRC), 10 with benign colorectal diseases (BCD) and 56 healthy controls (HC)] were tested for the differential diagnostic performance of a novel ELISA for nucleosome-bound methylated DNA. Methodical features, including intra- and interassay imprecision, were tested using serum pools. To minimize interassay variability, values were transformed to adjusted optical densities and robust statistics were applied for clinical evaluation. Findings were later re-evaluated on a set of 113 patients (49 CRC, 26 BCD and 38 HC). Results: Intra- and interassay reproducibility were 3.4% and 15.3%, respectively. Levels of circulating methylated DNA were significantly decreased in CRC and BCD when compared to HC (p<0.05), although there was no difference between BCD and CRC. For discrimination of CRC from HC, the area under the curve in receiver operating characteristic curve was 0.78 and sensitivities were 33% at 95% specificity and 75% at 70% specificity, respectively. The findings were generally confirmed when validated in the second set of patients. Conclusion: Reduced methylation of DNA on circulating nucleosomes detected by ELISA can potentially serve as a diagnostic tool in patients with CRC.