Noncancerous PTGS2 DNA fragments of apoptotic origin in sera of prostate cancer patients qualify as diagnostic and prognostic indicators

Abstract

Our study was designed to evaluate Cell-Free DNA in sera of prostate cancer (PCA) patients as a useful biomarker. Real-time PCR was used to amplify a <200 bp PTGS2 DNA fragment that biochemically characterizes apoptosis and a larger >250 bp Reprimo DNA fragment that defines mostly other cell death entities. The apoptosis index (AI) expresses the ratio of PTGS2 to Reprimo DNA fragments. GSTP1 hypermethylation was assessed to evaluate the amount of tumor-derived DNA. We analyzed serum of 216 patients (168 PCA; 5 incidental PCA; 42 benign prostatic hyperplasia (BPH); 11 healthy individuals). Distinctly elevated concentrations of PTGS2 fragments were detected in PCA compared to BPH and healthy individuals (median: 70.2, 10.5 and 7.1 ng/ml, respectively; p < 0.0001). The AI was significantly increased in PCA vs. BPH patients and healthy individuals (6.01 vs. 1.54 and 0.84 respectively; p = 0.002-0.0001). GSTP1 hypermethylation was only present in a small percentage (mean 1.92%) of circulating DNA. Concentrations of apoptotic PTGS2 fragments discriminated sensitively (88%) and specifically (64%) between BPH and PCA, whereas the AI was more specific (82%) but less sensitive (70%). The AI correlated with histological grading (p = 0.044). Kaplan-Meier analysis for a subset of 124 patients revealed a significant correlation between apoptotic PTGS2 fragments or the AI and PSA recurrence following radical prostatectomy (p = 0.0395-0.0482). In conclusion, circulating PTGS2 fragments of apoptotic origin and the AI are promising serum biomarkers for the diagnosis and prognosis of PCA. We suggest that cancer-induced apoptosis of peripheral noncancerous tissues is relevant in many malignancies.