It was found that the proportion of microRNA genes inactivated by methylation of regulatory CpG islands is several times higher than the genes encoding proteins, which increases their attractiveness as promising markers of cancer. The aim of this work is to evaluate the clinical significance of methylation of 13 tumor-associated microRNA genes (MIR-124a-2, MIR-124a-3, MIR-125-B1, MIR-127, MIR-129-2, MIR-132, MIR-137, MIR-203a, MIR-34b/c, MIR-375, MIR-9-1, MIR-9-3, MIR-339) in 26 patients with ovarian cancer. Methylation level was evaluated by the method of methylation-specific PCR in real time. The data obtained in primary tumors (26), histologically unchanged ovarian tissues (15) and peritoneal metastases (19) were compared using a number of statistical programs. For all 13 genes, an increase in the level of methylation was revealed during the transition from unchanged tissue to primary tumors and further from primary tumors to peritoneal metastases; moreover, in the genes MIR-203a, MIR-375 and MIR-339, the level of methylation in metastases increased most significantly (in 2 and more times). A correlation was observed for the first time, showing a consistency between the increase in methylation level in some miRNA pairs, for example, MIR-129-2/MIR-132 (rs> 0,7; p<0,0001), both in primary tumors and in metastases. An analysis of microRNA gene methylation in clinical samples of ovarian cancer showed a correlation between the observed molecular changes both with the initial stages of tumor formation and with the progression and dissemination of ovarian cancer, with the presence of metastases in a large omentum and with the appearance of ascites. The revealed dependencies deepen the understanding of the mechanism of peritoneal metastasis and can be used to select new diagnostic and prognostic markers of ovarian cancer.
Keywords: miRNA gene methylation; ovarian cancer.