Measuring the effects of radiotherapy on DNA methylation in colorectal cancer.

Abstract

e15089 Background: BCAT1 and IKZF1are methylated with high frequency in colorectal cancer (CRC). This study aimed to investigate the level of methylation in these two genes in tissue samples from CRC patients who had undergone radiotherapy. Methods: Tumor and adjacent non-tumor tissue was collected from 50 CRC patients, including 14 subjected to radiotherapy prior to surgical resection. DNA was extracted, bisulfite converted and the levels of methylated BCAT1 and IKZF1 DNA were expressed as the percentage of 5ng tissue DNA (normalized to ACTB levels). Results: In the 36 CRC patients who did not receive radiotherapy prior to resection, tumor tissues had high levels of methylated BCAT1 and IKZF1 compared with adjacent non-tumor tissues (p < 0.001, Table). The CRC tissues from the 14 patients who received radiotherapy pre-surgery had significantly lower levels of methylation compared to the levels in tumors from non-treated patients (p<0.01, Table). Radiotherapy did not appear to affect the methylated BCAT1/IKZF1DNA levels in adjacent non-cancer tissues (p > 0.05, Table). In this limited dataset, a correlation was observed with %methylation and response to radiotherapy measured based on tumor size relative to original size, with the lowest methylation in the tumors associated with the greatest downsizing. Conclusions: The high levels of methylated BCAT1 and IKZF1 in CRC tissue and the low levels in the surrounding non-cancer tissue suggest that the markers are tumor specific with no obvious field effect. In contrast, in the samples obtained from patients treated with radiotherapy prior to resection, the methylation levels in CRC tissues were similar to the levels measured in the adjacent non-tumor tissues. Further studies are necessary to determine the reason for this and whether it has implications for monitoring response to therapy based on blood levels of methylated BCAT1 and IKZF1. [Table: see text]