Plasma miR-122-5p and miR-142-5p and their role in chemoresistance of colon cancer patients

Chemoresistance represents a major issue affecting cancer therapy efficacy. Because microRNAs (miRNAs) regulate gene expression on multiple levels, their role in chemoresistance development is reasonably certain. In our previous study, miR-122-5p and miR-142-5p were identified as diagnostic, prognostic, and predictive biomarkers for primary and metastatic rectal cancer. The aim of the present study was to investigate whether these miRNAs can also reflect the disease course of colon cancer (CC) patients. Further, we focused on a deeper understanding of their involvement in 5-fluorouracil (5-FU) chemoresistance development. The expression analysis of both miRNAs was analysed in repeated whole plasma samplings (n=3, approximately every 6 months) of CC patients (n=49) by RT-qPCR. Expression levels of both miRNAs were determined in the 5-FU sensitive and resistant CC cell lines. From RNA-seq profiles of both sensitive and 5-FU resistant DLD-1 cell lines, the expression levels of miR-122-5p and miR-142-5p validated target genes were detected and compared. Significant differences in the expression levels of both miRNAs between T0 and T1 or T2 samplings were observed. Further, an association between the occurrence of relapse and miR-122-5p expression levels was noticed. Patients who did not relapse had higher expression of miR-122-5p at T1 (p=0.01; 3.16-fold change) and T2 (p=0.04; 2.79-fold change) samplings in comparison with T0 sampling. Out of all miR-122-5p validated targets (n=102), 25 genes were significantly differentially expressed between sensitive and 5-FU-resistant cell lines. Our data suggest that miR-122-5p may represent a predictive marker of tumour relapse in CC patients. In vitro data suggests that this aspect may be linked to the potential therapeutic targets of miR-122-5p related to 5-FU-based chemoresistance. However, deeper mechanistic studies are still needed for progress toward personalized medicine.