Abstract 1302: BDNF methylation and expression is associated with stage and CMS classification in colorectal cancer
Authors: Lopez Jaime , Demond Hannah , Gutierrez Alvaro , Buchegger Kurt , Vivallo Aleida , Carrillo Diego , Quezada Claudia , Brebi Priscilla , Ili Carmen Gloria 
Published: June 2023

Abstract
Colorectal cancer (CRC) is an important public health problem worldwide. The incidence and mortality of this cancer have been increased, becoming the third most frequent cancer and the second more deathly neoplasia in the world. It is remarkable the impact of epigenetics in the colon carcinogenesis, classification, diagnosis and prognosis. DNA methylation is the most studied and important epigenetic modification in CRC. This phenomenon occurs early in the carcinogenesis with a global hypomethylation and hypermethylation of gene promoter regions, especially of tumor suppressor genes, downregulating its expression. Previously, we performed genome-wide methylation sequencing of paired samples from CRC patients: normal adjacent tissue, primary tumor and lymph node metastasis. BDNF (Brain-derived neurotrophic factor) hypermethylation was found associated with poor prognosis. BDNF has been associated with colon cancer before. However, the importance of BDNF methylation in colorectal cancer and metastasis has not been described yet. We aim to validate the methylation and expression of BDNF, related to stage and molecular classification.
Colorectal cancer dataset from The Cancer Genome Atlas (TCGA) was used to validate the methylation findings reported in our previous report (374 primary tumor samples and 74 normal adjacent samples). RT-qPCR analysis for BDNF mRNA was performed in six cell lines, using normal colon tissue as baseline and beta-actin gene as normalizer. In addition, we evaluated the mRNA expression of BDNF of 29 paired-samples of primary colorectal tumors (Stages IIB-IVA) and its normal adjacent (NAT) counterpart.
TCGA dataset showed that BDNF methylation in primary tumor is significantly higher than normal samples (P&lt;0.001). In addition, we found differential methylation levels between CMS stages (P&lt;0.001). In vitro results showed low expression of BDNF cell lines CMS1 and CMS4 compared to CMS2 and CMS3 (P&lt;0.001). In patients, we found that BDNF was downregulated in primary tumor compared to NAT (p&lt;0.01). Furthermore, we found that, BDNF was downregulated in TNM stages II-III, meanwhile TNM stage IV overexpress BDNF (P&lt;0.01). When we analyze BDNF expression related with CMS classification in patients, we found higher levels of BDNF in CMS3 compared to CMS1 (P&lt;0.001).
We propose that BDNF is being regulated by methylation in colorectal cancer and metastasis. This methylation would be a dynamic process that allow to inhibit or activate BDNF gene expression according tumor stage, CMS and metastasis phenotype. Further studies should be conducted to prove this hypothesis, however, the methylation and/or expression would be useful as prognostic biomarker.
Citation Format: Jaime Lopez, Hannah Demond, Alvaro Gutierrez, Kurt Buchegger, Aleida Vivallo, Diego Carrillo, Claudia Quezada, Priscilla Brebi, Carmen Gloria Ili. BDNF methylation and expression is associated with stage and CMS classification in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1302.