Serum microRNA expression during neoadjuvant chemoradiation for rectal cancer.

Abstract

e15081 Background: Changes in microRNA (miRNA) expression during treatment for locally advanced rectal cancer (LARC) may provide insight into disease biology and potentially act as predictive biomarkers. We investigated 112 miRNAs in serum during neoadjuvant chemoradiation for LARC. Methods: Serum was collected at baseline, week 3 and at completion of chemoradiation from 40 prospectively recruited patients with LARC. Responders were classed as tumour regression grade (AJCC classification) 0 or 1 and non-responders as 2 or 3. Serum was also collected from 20 healthy controls. RNA extraction was performed using the Norgen total RNA purification kit. Reverse transcription and pre-amplification were performed according to Taqman OpenArray MicroRNA Panels manufacturer's instructions. QuantStudio12K platform was used for miRNA array qPCR. The delta-delta-Ct method was used to identifiy differentially expressed miRNAs, normalised against U6 snRNA. Analysis was performed in R using paired t-statistics and the Benjamini-Hochberg False Discovery Rate for multiple hypothesis testing adjustment, with q < 0.05 for significance. Enriched KEGG pathways were identified using DIANA, based on verified gene targets of each miRNA from Tarbase. Results: Four miRNAs (miR-125b-1, miR-1183, miR-130a, miR-375) were differentially expressed in baseline patient samples compared to controls. From baseline to completion of treatment, three of these - miR-125b-1, miR-1183, miR-130a were downregulated by more than 2-fold. Comparing responders and non-responders, miR-130a was significantly downregulated in the non-responders only. Conclusions: miR-125b-1, miR-1183 and miR-130a are significantly downregulated in patients with LARC during chemoradiation. These miRNAs are known to target key colorectal cancer genes such as ATM and CHEK1, which have been implicated in chemoradiation resistance. miR-130a warrants further investigation as a predictive biomarker, being downregulated in patients with a poor response to therapy. Work is ongoing, investigating these miRNA targets in the solid tissue in these patients. To our knowledge, this is the first study to profile potentially predictive miRNA changes during chemoradiation in LARC.