The role of IL-6/STAT3 signaling in CIC-DUX4 fusion sarcoma metastasis and immunosuppression - ABSTRACT CIC-DUX4 fusion-positive sarcomas (CDS) are an aggressive and understudied subset of small round cell sarcomas that primarily affect children and adolescents/young adults. Due to a lack of mechanistic understanding of how the CIC-DUX4 fusion oncoprotein drives CDS disease progression and metastasis, patient outcomes remain dismal, and CDS is universally lethal in the metastatic setting. Therefore, there is an urgent need to determine the mechanisms by which CIC-DUX4 fusion drives CDS metastasis. Our preliminary data demonstrate that the CIC-DUX4 fusion oncoprotein activates IL-6/STAT3 signaling, leading to elevated expression of cancer stem cell markers and reprogrammed lipid metabolism. Both cancer stem cells and altered lipid metabolism have important role in tumor cell survival and metastasis in various cancers. In addition to these tumor cell-intrinsic factors, during tumor growth in vivo, the CIC-DUX4 fusion mediates dramatic recruitment of tumor-associated macrophages (TAMs), which produce multiple immunosuppressive/metastatic chemokines and cytokines shown to be downstream of IL-6/STAT3 in other cancers. Moreover, CIC-DUX4 fusion-expressing tumors show significantly increased Foxp3+PD1+CTLA4+ immunosuppressive CD4+ T cells. These findings suggest that the CIC-DUX4 fusion also facilitates CDS tumor progression and metastasis through recruiting and regulating immune cells. Despite these findings, a key remaining question is whether targeting IL-6/STAT3 signaling will effectively block CIC-DUX4 fusion oncoprotein-driven tumor growth, metastasis, and immunosuppression. It is also unclear whether targeting IL- 6/STAT3 signaling can alleviate CICDUX4 fusion-induced immunosuppression to enable effective treatments by immune checkpoint blockades. Therefore, we propose to define the critical role of IL-6/STAT3 signaling intrinsic to tumor cells in CDS growth and metastasis, to define the dependency on IL- 6/STAT3 signaling in CIC-DUX4-induced TAM recruitment and TAM-mediated immunosuppression and metastasis, and to therapeutically exploit CIC-DUX4 fusion-mediated IL-6/STAT3 signaling-induced immunosuppression as a prelude to a clinical trial. The mechanistic insights and information gained from the proposed studies will lead to the development of a new rational therapy for this understudied patient population.
