TP53 mutations in circulating free DNA from Egyptian patients with non-Hodgkin's lymphoma

P53 protein plays important role in the maintenance of genome stability in mammalian cells; it acts in many processes including cell-cycle checkpoint, DNA repair, apoptosis, and angiogenesis. Mutations of P53 have been reported as common mutations in solid tumours, including non-Hodgkin lymphoma, NHL, and have been implicated in drug resistance, aggression and poor prognosis. Chronic infection with hepatitis C, HCV, has been associated in some studies with increased risk of NHL. HCV is a widespread infection in the Egyptian population. Circulating free DNA (CFDNA) has been shown to be a good source of liver tissue-derived DNA in African and Asian patients with chronic liver disease or hepatocellular carcinoma, HCC. Our previous results have shown TP53 mutations in 5% of CFDNA and 10% of tumours of HCC, with underlying HCV.

Since previous studies have shown p53 mutations in the DNAs extracted from the NH lymphoid tumours, we have assessed the presence of p53 mutations from exons 5 to 9 in CFDNA in patients with NHL, from Alexandria, Egypt, where HCV is highly prevalent, in a first attempt case-control preliminary study.

CFDNA was extracted from sera of 20 cases with NHL and 20 negative control individuals. The retrieved serum DNAs were screened for TP53 mutations from exons 5 to 9 using direct sequencing and a PCR-restriction digestion analysis (RFLP). Concentrations of CFDNA were measured using Fluorometric assay.

Concentrations of CFDNA were significantly higher among NHL patients compared to the negative control individuals indicating a very high release or turn-over of DNA from the tumour into the blood stream among NHL patients. Mutations of p53 determined in NHL cases (30%) were of Arg-176 (1/20: 5%), Phe-238 (1/20: 5%), Ser-249 (2/20; 10%), Lys-249 (1/20: 5%) and Phe-250 (1/20: 5%). No mutations were detected among controls. However, Arg-213 polymorphism was found in 2 cases of NHL (10%) and in 1 case of controls (5%).

Our findings of higher DNA concentrations with some p53 mutations in CFDNA from patients with NHL that match the previous reported p53 mutations from tumour DNA may hold promises that CFDNA may serve as a convenient source of tumour-derived DNA to serve as a promising tool of a non-invasive, low-cost new strategy for earlier detection, diagnosis and follow up of the disease. A large-scale prospective study utilizing CFDNA and DNA from tumours of NHL patients will be required to validate this first trial of utilizing CFDNA from NHL patients.