Abstract 5247: The effect of aspirin on the transcriptional landscape of the colon
Authors: Downie Jonathan M. , Geraghty Connor M. , Stappenbeck Thaddeus S. , Yilmaz Ömer H. , Drew David A. , Chan Andrew T. 
Published: June 2023

Colorectal cancer (CRC) remains the second leading cause of cancer mortality in the United States. Aspirin is the most promising CRC prevention agent with significant data supporting long-term use with a reduction in the incidence of adenomatous polyps and colorectal cancer. The adoption of aspirin as a preventive agent has been limited by an incomplete understanding of aspirin’s mode of action in humans. To elucidate the mechanism of aspirin prevention, we sought to identify aspirin-associated transcriptional changes within the colon. To accomplish this objective, we performed RNA sequencing of biopsy-derived colonic epithelial cells from participants enrolled (N=180) in our ongoing aspirin randomized placebo-control trial (RCT) program, “ASPirin Intervention for the REDuction of colorectal cancer risk” (ASPIRED). Individuals with a recent resection of an adenoma were eligible. Participants for whom epithelial cells from rectosigmoid mucosal biopsies were successfully obtained at both pre- and post-treatment timepoints (n=130) were included in this analysis. Participants were randomized to once-daily placebo (n=45), low-dose aspirin (81 mg) (n=46), or standard-dose aspirin (325 mg) (n=39) for 8-12 weeks. For each timepoint, we performed Illumina RNA 100-bp paired-end sequencing of 4,000 fluorescence-activated cell-sorted (FACS) colonic epithelial cells (CD45-; EpCAM+). Transcriptomic read alignment and read counts per gene were obtained using STAR and Salmon. Quality control measures removed 52 participants (20 placebo, 18 low-dose aspirin, and 14 standard-dose aspirin) from the analysis. No significant differences in age, gender, ethnicity, or BMI were observed between placebo and aspirin-treated participants. We then identified genes whose expression is modulated by aspirin exposure (low and standard dose aspirin) while controlling for baseline gene expression differences between placebo and aspirin-exposed patients and for intra-sample gene expression variability using Dream. We found 57 genes were significantly differentially expressed in aspirin-treated participants at an FDR &lt; 0.10. AGR2, which is a CRC oncogene that is upregulated by prostaglandin E2 (PGE2), was significantly downregulated by aspirin treatment suggesting aspirin modules the expression of PGE2 responsive genes in the colonic epithelium. Gene enrichment analysis found aspirin significantly downregulated scaffold proteins (e.g. KRT8, KRT18, and ACTB) and structural ribosomal RNA binding proteins. These pathways are critical processes in epithelial cell differentiation. This finding supports previous in vitro evidence that aspirin results in cell composition changes within the colonic epithelium favoring stem-like cell states, which may underlie its preventive effect.

Citation Format: Jonathan M. Downie, Connor M. Geraghty, Thaddeus S. Stappenbeck, Ömer H. Yilmaz, David A. Drew, Andrew T. Chan. The effect of aspirin on the transcriptional landscape of the colon. [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 5247.