Abstract 5456: Identifying the role of tissue factor in osteosarcoma metastasis

Abstract Patients with osteosarcoma who develop metastasis face very poor prognoses. Even when treated with the most effective medical and surgical interventions available, about forty percent of osteosarcoma patients will eventually succumb to lung metastasis. Despite the relevance of metastasis to clinical outcomes, we understand little about the mechanisms that drive these tumor cells into the lung and facilitate their metastatic growth. Consequently, there are no approved antimetastatic agents for osteosarcoma and outcomes have not improved in more than 40 years. Tissue factor is a tightly regulated physiologic initiator of coagulation with functions in inflammation, cytokinesis, angiogenesis, apoptosis, and growth factor secretion. These functions are divided between two separate pathways: initiation of the coagulation cascade via activation of factors VII and X, and propagation of cell signaling pathways via PAR activation. It is aberrantly expressed in many cancers and has been associated with metastatic behavior and inferior outcomes by affecting metastatic vascularity, growth, and migration. Osteosarcoma has been shown to also aberrantly express tissue factor, with descriptive studies suggesting similar effects on metastatic behavior. We hypothesized that tissue factor expressed on the surface of disseminated osteosarcoma cells activates procoagulant pathways and PAR signaling, and that both facilitate pulmonary metastasis. To test this, we first established and quantified expression of tissue factor across six osteosarcoma cell lines using Western blot, flow cytometry, and confocal microscopy in both monoculture and in coculture with human bronchial epithelial cells. PAR1 and PAR2 were also discovered to be expressed in osteosarcoma cells. RNA sequencing performed suggests that both tissue factor and PAR1 expression in osteosarcoma increase over the metastatic period, as does FVII expression by alveolar macrophages; this implies that tissue factor activation during metastasis is dynamic and dependent on host interactions. Ongoing work includes functional assays of osteosarcoma tissue factor and PARs activity as well as preclinical testing of tissue factor inhibition in a murine xenograft model of osteosarcoma. To define how tissue factor propagates metastasis, we are separately inhibiting its coagulant and cell signaling pathways after murine tail vein injection using apixaban or pathway-specific antibodies. We will also use an inducible F3 knockout to alter tumor expression of tissue factor. If we find that manipulation of tissue factor expression changes metastatic behavior across cell lines, this will suggest that tissue factor plays a crucial, mechanistic role in osteosarcoma metastasis. Varying effectiveness of coagulation or signaling pathway inhibition on metastasis will implicate tissue factor’s mechanism of metastatic propagation. Citation Format: Charles C. Treinen, Amy Gross, Maren Cam, Bryce Kerlin, Ryan Roberts. Identifying the role of tissue factor in osteosarcoma metastasis [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(6_Suppl):Abstract nr 5456.