Methylation status of eight tumor suppressors in neuroendocrine pancreatic tumors.

Abstract

e16197 Background: Aberrant DNA methylation is a characteristic feature of cancer, affecting gene expression and tumor phenotype. In this study, we quantified the methylation of promoters of eight tumor suppressor genes in pancreatic neuroendocrine tumors (Pan-NET). Methods: The method of pyrosequencing was used to quantity level (Met,%) of methylation of gene promoters - tumor suppressors AHRR, APC1A, DAPK, MGMT, MLH1, P16, RASSF1A, RUNX3 in tumor samples from 55 patients with pancreatic NET (G1-G3) and in the blood of 10 healthy donors. Met for each sample was calculated as the median methylation of CpG sites in triplicate. Results: Hypermethylation was observed for AHRR (75%), APC1A (25%), RASSF1A (30%). In contrast, DAPK, MGMT, MLH1, P16, RUNX3 had low methylation levels ( < 20%). The median of methylation in the blood of healthy donors for AHRR was 91% (76-98); for all other loci it did not exceed 6%. A high incidence of methylation in excess of blood levels in healthy donors was identified for RASSF1A (0.96); AHRR (0.75); MGMT (0.65); RUNX3 (0.41), APC1A (0.25). For tumor suppressor P16, only one case of increased methylation was recorded (Met = 15%), despite the fact that this phenomenon is not uncommon for NETs of other localizations. In 66% of pancreatic NET cases, hypermethylation of more than two promoters of tumor suppressor genes was noted. An association tendency was found between the presence of MEN1 mutations and the RASSF1A methylation level (p = 0.08). Correlation analysis revealed a significant level of negative association between changes in methylation of MLH1 and AHRR (p < 0.01); for the latter, the prognostic value of a high methylation status and a better prognosis for many malignant neoplasms were described. Conclusions: In the present study, significant methylation of the promoters of the APC1A, DAPK, MGMT, RASSF1A, and RUNX3 genes in well-differentiated pancreatic NETs was identified with a high frequency. At the same time, isolated cases of hypermethylation were noted for the well-known tumor suppressors MLH1 and P16.