Comparative Study of Mutations in Single Nucleotide Polymorphism

Comparative Study of Mutations in Single Nucleotide Polymorphism

ANTICANCER RESEARCH 37 : 651-658 (2017) doi:10.21873/anticanres.11360 Comparative Study of Mutations in Single Nucleotide Polymorphism Loci of KRAS and BRAF Genes in Patients Who Underwent Screening Colonoscopy, With and Without Premalignant Intestinal Polyps MICHAIL GALANOPOULOS 1, IOANNIS S. PAPANIKOLAOU 2, ELENI ZOGRAFOS 3, NIKOS VIAZIS 1, GEORGE PAPATHEODORIDIS 4, DIMITRIOS KARAMANOLIS 1, EVANGELOS MARINOS 3, GERASSIMOS J. MANTZARIS 1 and MARIA GAZOULI 3 1Department of Gastroenterology, Evangelismos, Ophthalmiatreion Athinon and Polyclinic Hospitals, Athens, Greece; 2Hepatogastroenterology Unit, Second Department of Internal Medicine and Research Institute, Attikon University General Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece; 3Laboratory of Biology, Department of Basic Medical Sciences, Medical School, National and Kapodistrian University of Athens, Athens, Greece; 4Academic Department of Gastroenterology, Laiko General Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece Abstract. Aim: Our aim was to perform a comparison the KRAS gene in samples of group B was significantly study of the mutation rate of V-Ki-ras2 Kirsten rat sarcoma higher than that in group A (p=0.013). Conclusion: Blood viral oncogene homolog (KRAS), and v-Raf murine sarcoma cfDNA may be a promising tool in CRC screening as it may viral oncogene homolog-B (BRAF) genes between blood- discriminate patients with CRC compared to healthy based cell-free DNA (cfDNA), and tissue sample biopsies in individuals and those with colonic polyps, even though it individuals undergoing screening colonoscopy. Materials does not appear useful in predicting the presence of colonic and Methods: All specimens were collected from January polyps. 2015 to January 2016. A total of 92 blood samples and colonic biopsy specimens were collected from healthy Colorectal cancer (CRC) is the third most common individuals with no polyps undergoing screening malignancy in the Western world and therefore is considered colonoscopy (group A, n=35), patients with colorectal a major public health issue (1). Approximately 1.4 million cancer (group B, n=27), and patients with neoplastic people worldwide were diagnosed with colorectal cancer in intestinal polyps (group C, n=30). Peripheral blood was 2012, whilst it is estimated that 693,900 people died from collected from each patient and a focal tissue biopsy was the disease in the same year (2). According to data obtained conducted. Results: We only found a limited statistically from the World Health Organization mortality database and significant difference (p=0.046) in the mutation analysis for Eurostat, nearly 173,400 EU citizens will have died of codon 12 of the KRAS gene when we compared tissue colorectal cancer in 2016 (3). The high mortality rate is due biopsies from patients in group B to those from group C. In to the fact that CRC usually remains undetected, until the the blood samples, only the rate of mutation in codon 12 of disease progresses up to a point that it becomes difficult to cure (4). The vast majority of colon cancers evolve from precancerous colorectal lesions called adenomas (5). Therefore, early detection and diagnosis could have a Correspondence to: Maria Gazouli, Ph.D., Department of Basic significant impact on the reduction of mortality from CRC. Medical Sciences, Laboratory of Biology, Medical School, National A new non-invasive method of detecting and monitoring and Kapodistrian University of Athens, Michalakopoulou 176, CRC has attracted researchers’ interest recently: the molecular 11527 Athens, Greece. Tel/Fax: +30 2107462231, e-mail: [email protected] characterization of circulating free DNA (cfDNA) in blood circulation. Identification of cf DNA was first reported more Key Words: Colorectal cancer, cell-free DNA, KRAS , BRAF , single than half a century ago (6). These extracellular nucleic acids nucleotide polymorphism, biomarkers. are active products of apoptosis and necrosis of both normal 651 ANTICANCER RESEARCH 37 : 651-658 (2017) and dead cells; they can also be released via complex surgery/treatment. Moreover, repeated biopsies are not interactions between tumor and adjacent healthy cells (7, 8). recommended, since they are deemed unethical and Outside the peripheral circulation (plasma, serum), cf DNA impractical. Therefore, the use of cfDNA for the detection of may also be found in other body fluids (9). What is these tumor-specific genomic alterations may become a essentially novel is that reports in the recent literature showed promising option for targeted-therapies selection. that cfDNA has a prognostic value in patients with CRC (10- The aim of our study was to evaluate the frequency of 12). According to these data, cfDNA can be used both as a KRAS and BRAF mutations in cfDNA extracted from the diagnostic tool and as a prognostic marker, and it can also be blood of three groups of patients: Group A: healthy used in the detection of tumor-specific mutations in the individuals undergoing screening colonoscopy and in whom bloodstream of patients with CRC (13). no polyps were found; group B: patients with CRC; and It is well known that the adenoma–carcinoma sequence group C: patients with neoplastic intestinal polyps, in constitutes a basic pathway of CRC carcinogenesis (14). The comparison to their respective biopsy samples from commonest mutations presenting in CRC tumor cells are of intestinal tissue. V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS ). However, the clinical importance of KRAS mutation Materials and Methods in CRC is debatable; a number of studies reported no association with survival (15, 16), whereas other studies Participants and specimens. All specimens were collected at the suggested that patients with CRC with KRAS mutation have Department of Gastroenterology, Evangelismos Hospital, Athens, poorer outcome (17-19). KRAS and v-Raf murine sarcoma Greece, from January 2015 to January 2016. A total of 92 blood viral oncogene homolog-B ( BRAF ) mutations lead to the samples and 92 colon biopsy specimens were collected from healthy individuals undergoing screening colonoscopy with no polyps constitutive activation of endothelial growth factor receptor (group A, n=35), patients with CRC (group B, n=27), and patients (EGFR) signaling through the oncogenic RAS/RAF/MEK/ with neoplastic intestinal polyps (group C, n=30). Detailed data are ERK pathway. Due to these mutations, CRC cells develop listed in Table I. Peripheral blood was collected from each patient resistance to monoclonal antibodies to EGFR, as well as to and focal tissue biopsies were conducted. All specimens were stored widely used targeted EGFR therapies (20). In order to at −80˚C for further analysis. Patients with a family history of prevent this potential effect, it is advised that prior to their familial adenomas and polyps or hereditary nonpolyposis colorectal treatments, all patients eligible for anti-EGFR regimens cancer (HNPCC) were excluded from this study. Our study was performed in accordance with the guidelines of the Hospital Ethics KRAS should be tested for mutations in the gene. Committee. Informed consent was obtained from all participants. Concurrently, BRAF V600E point mutations should be identified, since they are found in 9% of cases and may Genotype analysis. DNA from biopsy samples was extracted using potentially interfere with the targeted therapies (21). BRAF a commercial kit (Nucleospin Tissue; Macherey-Nagel, Düren is found downstream of KRAS and contributes to the Germany). cfDNA was isolated from plasma samples using High activation of the same intracellular pathways. According to Pure Viral Nucleic Acid Kit (Roche Diagnostics, Mannheim, several reports, the majority of KRAS and BRAF mutations Germany) according to the manufacturer’s instructions. The concentration of DNA was determined in a Nanodrop ND-100 found are mutually exclusive (22). A mutation in BRAF is spectrophotometer (Nanodrop Technologies, Wilmington, DE, considered a negative prognostic factor (23). Still, because USA). The presence of a mutation at codon 12 and codon 13 of of conflicting reports, BRAF mutational status has not been KRAS was determined by an enriched polymerase chain reaction yet included in standard CRC treatment guidelines as a guide followed by restriction fragment length polymorphism (PCR-RFLP) for anti-EGFR treatment (24-27). as previously described (30, 31). In summary, a mismatched Various methods are currently used in the analysis of the upstream primer for codon 12 amplification, and a mismatched KRAS mutational status of a patients with CRC. In fact, the downstream primer for codon 13 amplification which introduced a BstNI , and a HaeIII restriction site in the wild-type allele, method of determining it from tumor sections of each respectively, were used. The primers used were as follows: individual patient is presented as one of the first examples KRAS12F: 5’-ACTGAATATAAACTTGTGGTAGTTGGACCT-3’, of personalized medicine in the field of oncology (28). KRAS12R: 5’-CTGTATCAAAGAATGGTCCTGCACCAGTA-3’, Detection of BRAF mutations is included in the screening of and KRAS13F: 5’-GTACTGGTGGAGTATTTGATAGTGTATTAA- patients without KRAS mutations identified, in accordance 3’, KRAS13R: 5’-GTATCGTCAAGGCACTCTTGCCTAGG-3’. with standard guidelines (29). The underlined bases represent mismatches. The expected sizes of It is important to point out that although the molecular the PCR products are 162 bp and 159 bp for codon

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