Metastasis is the leading cause of cancer-related deaths. However, the mechanisms behind the metastatic cascade remain poorly understood. Tumor’s metastatic potential is strongly influenced by microenvironmental cues such as low oxygen (hypoxia). Our published work reported that lung metastases in sarcoma are associated with increased primary tumor expression of the hypoxia-inducible collagen-modifying lysyl hydroxylase, Plod2; in multiple subtypes of sarcoma, excessive collagen lysyl hydroxylation results in secretion of immature collagen aggregates able to physically associate with tumor cells and promote both intravasation and extravasation. In the current study, we observed that Plod2 is colocalized with collagen VI and is important for its extracellular network structure, suggesting that collagen VI is a putative substrate of Plod2. Using an impedance sensing assay and a zebrafish intravital microinjection model, we demonstrated that tumoral Plod2 and collagen VI weaken the endothelial barrier and promote extravasation. With a tail vein injection mouse model, we determined that collagen VI is essential for lung metastasis. Clinically, we detected high levels of collagen VI in metastatic sarcoma in surgically resected patient lungs. Furthermore, by analyzing patient data in The Cancer Genome Atlas (TCGA), we found a strong correlation between the expression of both PLOD2 and collagen VI with disease outcomes. Together, our study identifies a novel mechanism of sarcoma lung metastasis, opening up opportunities for therapeutic intervention. Citation Format: Ying Liu, Ashley M. Fuller, Ileana Murazzi, Ann Devine, Nicolas Skuli. Tumor-secreted collagen VI weakens endothelium and promotes metastasis [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr B017.

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CD8+ T cell dysfunction is a critical barrier to anti-tumor immunity, but molecular mechanisms underlying the regulation of T cell dysfunction in solid tumors are diverse and complex. Extracellular matrix (ECM) composition facilitates solid tumor progression in part by inhibiting T cell migration/infiltration; however, the impact of individual ECM molecules on T cell function in the tumor microenvironment (TME) is virtually unknown. Moreover, upstream regulators of aberrant ECM deposition/organization in solid tumors are poorly defined. Therefore, we investigated the regulation and effects of ECM composition on CD8+ T cell function in undifferentiated pleomorphic sarcoma (UPS). This immunologically "hot" soft-tissue sarcoma exhibits durable responses to checkpoint therapy in some human patients, suggesting it may provide insights into strategies for optimizing T cell function and improving immunotherapy efficacy. Using an autochthonous model of UPS and data from multiple human patient cohorts, we discovered a multi-pronged mechanism wherein oncogene-induced remodeling of the TME promotes CD8+ T cell dysfunction, suppresses T cell-mediated cytolysis, and enhances immune evasion. Specifically, we observed that the transcriptional co-activator Yap1, which we previously linked to UPS progression, promotes the aberrant deposition of collagen VI in the UPS TME. In turn, collagen VI induces CD8+ T cell dysfunction by inhibiting T cell autophagic flux and remodeling fibrillar collagen architecture in the TME. Furthermore, collagen type I opposed ColVI in this setting, acting as tumor suppressor. Thus, our findings reveal that CD8+ T cell-mediated anti-tumor immunity in solid cancers is dependent upon oncogene-mediated ECM composition and remodeling in the TME.

Only a small percentage of disseminating tumor cells are capable of forming lethal metastatic foci. Though advances in sequencing and genomics have dramatically enhanced our understanding of primary tumor biology and novel target identification, these techniques alone have not proven sufficient to identify the factors that permit metastasis of this small cellular fraction. For example, we observed that in some tumors the major molecular predictor of metastatic potential is HIF1α protein stabilization in response to low intratumoral O2 tension (hypoxia). These observations clearly show that in-depth understanding of environmental signals and subsequent cellular responses is necessary to fully characterize metastatic potential. Consistent with our earlier observations, we discovered that the collagen-modifying enzyme PLOD2, a direct transcriptional target of HIF1α, dramatically enhances both early (cell migration/invasion) and late (extravasation/lung colonization) steps of the metastatic cascade. We previously reported the role of PLOD2 in modulating the primary tumor microenvironment to facilitate cell migration and intravasation. However, the mechanisms by which PLOD2 and tumor associated collagen impact later metastatic stages (i.e., endothelial adherence, extravasation) are unknown- in part because these processes are particularly difficult to simulate in vitro and to visualize in vivo. Therefore, we have developed new models and tools including a zebrafish embryo xenograft system to image migrating and extravasating tumor cells in vivo. This approach allows us to investigate the late metastatic cascade and define the microenvironmental cues that promote tumor cell dissemination. We also observed that PLOD2-modified collagen is secreted into the extracellular milieu during dissemination and weakens endothelial barrier function. We are investigating the role of tumor collagen and PLOD2 in endothelial adherence and extravasation for the purpose of therapeutically targeting the molecular underpinnings of metastases. Our work focuses on soft tissue sarcomas. However, recent studies by other groups have linked PLOD2 and modified collagen to carcinoma metastasis as well, suggesting a broader applicability for our work. Ultimately, we believe these studies will transform our ability to treat and even prevent metastasis, a unique possibility in sarcoma patients due to the relatively long interval between primary tumor diagnosis and metastatic outgrowth in some patients (5-10 years). The tools we have developed and the mechanisms we are pursuing will open new avenues of research that were once inaccessible and lead to novel therapeutic opportunities for the treatment of metastatic disease in multiple cancer contexts. Citation Format: T.S. Karin Eisinger, Ying Liu, Ileana Murazzi. Identification of a “hypoxic secretome” and its role in metastasis [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr IA024.