Abstract 6827: Myocardin and myocardin-related transcription factor as potential drivers of the myofibroblastic cancer-associated fibroblast phenotype in colorectal cancer

Abstract Background: Cancer-associated fibroblasts (CAFs) play a key role in modifying the tumor microenvironment (TME) and could be a future target for treatment. CAFs are typically categorized based on function: myofibroblastic CAFs (myCAFs) amplify extracellular matrix production that blocks therapy and immune cell infiltration while inflammatory CAFs (iCAFs) produce immuno-suppressive cytokines and chemokines. Here we sought to better understand the role and mechanisms of myCAFs in altering the TME by identifying their unique markers and potential drivers. Methods: Z-scores of ACTA2/TAGLN or ICAM1/PDPN were used to create datasets high in myCAF and iCAF markers, respectively, from TCGA data. A gene set enrichment analysis (GSEA) was performed on the resulting differential expression. Samples of patients were collected to create a cohort of colorectal cancers that were stained via immunohistochemistry (IHC) for alpha-smooth muscle actin (αSMA), transgelin (TAGLN), myocardin (MYOCD) and myocardin-related transcription factor A (MRTFA). Slides were evaluated for collagen using Masson’s trichrome stain. MYOCD and MRTFA nuclear expression was expressed as positively stained nuclei per high powered field (HPF; 400x). TAGLN, αSMA, and collagen were scored on a scale of 0-3+. Results: Of the 592 TCGA patients compiled across all disease stages, 23 (median age 63) formed the myCAF-high group (7 males, 16 females). Within this group, GSEA indicated an upregulation of myogenesis (q 0. 001) with the following genes positively associated with myCAF markers: MYLK (q 0. 001, log2 fold change FC 1. 52), DES (q 0. 001, 5. 32), and MYH11 (q 0. 001, 3. 57). The following were also upregulated in the myCAF high cohort: CNN1 (q 0. 001, 2. 95) and MYOCD (q 0. 001, 2. 27). These genes are targets of MYOCD and MRTFA transcription factors potentially driving the myCAF phenotype. To assess this potential relationship, we evaluated 306 tumor samples from 153 patients with CRC. The cohort consisted of 56 female patients and 97 male patients aged 13-90 years old across all disease stages. High amounts of nuclear MRTFA were associated with high scores for myCAF markers aSMA (average score 1. 54 when MRTFA+ nuclei 5 per HPF vs 2. 06 when MRTFA + nuclei 5 per HPF, p0. 001, Wilcoxon Rank Sum Test), TAGLN (1. 37 vs 1. 62, p = 0. 043), and collagen (1. 73 vs 2. 10, p = 0. 009). Likewise, for MYOCD, αSMA (1. 79 vs 2. 14, p = 0. 001) and collagen (1. 87 vs 2. 15, p = 0. 017) were positively correlated. Conclusions: Increased nuclear expression of MYOCD and MRTFA in stromal cells of CRC are positively correlated with myCAF gene expression, supporting our initial hypothesis of these being drivers of the phenotype. Our findings now motivate further analysis as to whether the inhibition of these transcription factors could lead to a reduction in the immune regulatory myCAF phenotype. Citation Format: Alec B. Cornelio, Katherine A. Johnson, Yousef Gadalla, Sharanya Nath, Cheri A. Pasch, Wei Zhang, Kristina A. Matkowskyj, Dustin A. Deming. Myocardin and myocardin-related transcription factor as potential drivers of the myofibroblastic cancer-associated fibroblast phenotype in colorectal cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6827.