Regulatory network of competitively interacting RNAs and effectiveness of rectal tumors radiotherapy.

Background: Currently, rectal tumors radiotherapy effectiveness reaches an acceptable level only in a small number of patients (they have a complete clinical response), which is associated with the formation of malignant cells radioresistance. A comprehensive study that integrates various epigenetic parameters would explain a number of molecular mechanisms of rectal tumor cells radioresistance and identify new bio-markers. In the last decade, using high-through-put sequencing, the competitively interacting RNAs regulatory network (long non-coding RNAs, miRNAs and mRNAs) has been shown.

Purpose: The aim of the study was to analyze the features of competitively interacting RNAs regulatory network functioning in patients with rectal cancer who are radioresistant and sensitive to radiotherapy. The study was performed on 500 patients with dia-gnosed rectal cancer. Radiotherapy was performed on a Novalis TX linear particle accelerator according to the standard protocol (single focal dose 2.4 Gy, total focal dose 54.0 Gy). Total RNA preparations were isolated from paired bio-psy fragments of tumor and non-tumor tissues of the rectum (obtained by video-colonoscopy). The relative abundance of mRNA, miRNA and lncRNA transcripts was assessed by the RT-qPCR method. Using bio-informatic analysis, the probability of potential interactions between the investigated mRNA, miRNA and lncRNA was determined. It has been shown that the effectiveness of radiotherapy depends on the level of miRNA (miRNA-195-5p; miRNA-4257; miRNA-5187-5p; miRNA-149-5p; miRNA-138 -1-3p; miRNA-6798-5p; miRNA-6819-5p; miRNA-4728-5p; miRNA-1249-5p; miRNA-557; miRNA-1273h-5p; miRNA-6737-5p; miRNA-6808-5p; miRNA-3202; miRNA-5195-3p; miRNA-130b-3p) and lncRNA (XIST, HELLPAR, NEAT1, AC008124. 1, LINC01089, LINC01547, and VASH1-AS1) expression, which regulate the DNA repair system (H2AX, RBBP8) and apoptosis (BCL2).

Conclusion: A comprehensive study of competitively interacting RNAs regulatory network and radiotherapy effectiveness of rectal tumors made it possible to establish the mechanisms of radioresistance formation and its bio-markers.