Abstract 64: Tumor-tumor cooperation during osteosarcoma lung metastasis is driven by interactions between lung epithelia and niche-initiating anchor cells
Authors: Reinecke James B. , Saraf Amanda J. , Hinckley John M. , Gross Amy C. , Pommellette Helene Le , Vatelle Sophia , Cannon Matthew V. , Franz Emily , Cam Maren , Roberts Ryan D. 
Published: April 2023

Abstract
Metastasis remains the primary cause of morbidity in most solid tumors, yet the mechanisms by which tumors colonize distant tissues remain poorly understood. Osteosarcoma illustrates the need to address this knowledge gap—about 40% of patients diagnosed with osteosarcoma will die from their disease, almost always from complications associated with lung metastasis, which tend to be resistant to conventional treatments.
To identify interactions between tumor and stromal cells that facilitate the formation of metastatic lesions, we utilized a niche-labeling system to isolate tumor and tumor-associated cells from mice at four time points during metastatic lesion development. We performed single-cell RNA sequencing on the isolated samples and used the resulting data to identify critical tumor-host interactions and characterize the changes that occur in both tumor and stromal cell phenotypes over developmental time. We validated key pathways suggested by the bioinformatic analysis using cell culture, tumor-on-lung metastatic organoid systems, immunofluorescence of lung metastases from both mouse models and human patients, and single-cell RNA sequencing of primary tumors and lung metastases from human patients. We ultimately evaluated the functional relevance of key vulnerabilities using pharmacologic manipulation in murine models of metastatic osteosarcoma.
We found that osteosarcoma tumors exhibit significant transcriptional heterogeneity. This heterogeneity is conserved across cell lines, mouse models, and patient specimens and is preserved as cells colonize lung tissues, even as the process of colonization drives broad changes in the overall transcriptional phenotypes of both tumor and lung cells. A small subset of tumor cells engages the lung epithelium in a paracrine loop that drives feed-forward production of IL1, IL6, and CXCL8. These “anchor cells” survive initial dissemination to the lung, while other tumor cell subsets do not. Anchor cells express high levels of p21 and are hypo-proliferative. Their presence elicits a wound-healing response from the surrounding lung epithelium, causing the proliferation of type 2 epithelial cells and arrest of those cells in a fibrogenic transitional state, quite literally creating a non-healing wound. The IL6 and CXCL8 produced by established osteosarcoma cells act as chemo-attractants for circulating osteosarcoma cells that exhibit a growth/proliferative phenotype. Cells with this growth phenotype gradually replace the anchor cells as metastatic lesions develop. When established lesions are treated with conventional therapy, growth cells within lesions die while anchor cells survive. Disruption of the anchor-epithelial interaction using drugs that block IL1 signaling, IL6/CXCL8 signaling, or anti-fibrotic TKIs prevents metastatic colonization of the lung.
Citation Format: James B. Reinecke, Amanda J. Saraf, John M. Hinckley, Amy C. Gross, Helene Le Pommellette, Sophia Vatelle, Matthew V. Cannon, Emily Franz, Maren Cam, Ryan D. Roberts. Tumor-tumor cooperation during osteosarcoma lung metastasis is driven by interactions between lung epithelia and niche-initiating anchor cells [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 64.