Abstract B013: Activin’s influence on the tumor microenvironment in colon cancer

Abstract Background and aims: Activin A (activin) is a key molecule that regulates cell specific and context dependent signaling in tumor growth and metastasis as well as local and systemic inflammatory responses. Understanding the link between tumor-promotive and inflammatory effects may provide a novel opportunity for targeted therapy in colorectal cancer (CRC). We have previously shown that activin signaling promotes epithelial to mesenchymal transition, tumor migration, and that serum activin correlates with advanced stage in CRC patients. Recently, activin has been implicated in enhancing CD4+ to CD8+ communications to promote cytotoxic elimination of tumor cells. We now hypothesize that activin exerts cell-specific effects in the tumor microenvironment (TME) to both promote anti-tumoral activity of immune cells and pro-metastatic behavior of tumor cells in a context-dependent manner. Methods: Western blot and transwell migration assays with and without activin were performed in human epithelial colon cancer cells with varying expression levels of ACVR2 and in human colonic fibroblasts. The influence of the canonical Smad4 pathway was elucidated in a Ts4-Cre;Apcflox;Smad4flox mouse model for CRC. We analyzed a TMA of 1055 stage II and III CRC patients from the QUASAR2 cohort to correlate activin and CD4+ expression with outcome. The TMAs were also analyzed via Digital Spatial Profiling (DSP, NanoString) to determine the immune cell heterogeneity and cell signaling patterns within the tumor microenvironment relative to activin. Results: The non-canonical pAkt pathway is activated in ACVR2-restored but not ACVR2-mutated HCT116+chr2 colon cancer cells, which leads to tumor cell migration in a PI3K-dependent manner. In vivo, ablation of downstream canonical SMAD signaling is associated with elevated activin, alpha-SMA and pAkt and increases in tissue dysplasia, intestinal stromal disorganization, and animal mortality. While there are direct pro-metastatic effects of activin on tumor cells, activin expression in the TME of stage II or III CRC patients is associated with elevated CD4 and survival benefit (High activin/high CD4: 1.665 hazard ratio, 95% Cl of ratio 1.379 to 2.010). DSP analysis confirmed co-localization of activin with immune cells in the TME which influences cell signaling patterns found in these regions. Conclusion: In colon cancer cells, activin leads to preferential prometastatic PI3K/Akt pathway activation. Within the TME, high levels of activin in the presence of CD4+ T-cells is associated with better outcomes in CRC patients. This work lays the foundation to further study context-dependent activin signaling as an adjunct or target in CRC. Citation Format: Mark B. Wiley, Jessica Bauer, Kunaal Mehrotra, David N. Church, Rachel S. Kerr, David J. Kerr, Paul Grippo, Barbara Jung. Activin’s influence on the tumor microenvironment in colon cancer [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer; 2022 Oct 1-4; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_1):Abstract nr B013.