(P 19) SERUM EXOSOMES IDENTIFY AN ABERRANT PROTEOMIC SIGNATURE IN CANINE OSTEOSARCOMA PRECEDING METASTATIC PROGRESSION

Objective: Osteosarcoma (OS) is an aggressive bone cancer affecting both dogs and humans, often associated with treatment resistance and metastasis. Exosomes, small extracellular vesicles, play a critical role in facilitating cellular interactions that drive key hallmarks of cancer, including therapy resistance, invasion, and metastasis. To determine how exosomal cargo evolves over the treatment course of OS, we characterized longitudinal changes in protein cargo from circulating exosomes collected from a cohort of canine OS patients who underwent amputation and received adjuvant chemotherapy preceding metastatic progression.

Methods: Exosomes were isolated from serum of 14 canine OS patients prior to and after amputation, prior to metastatic progression, and at the time of radiographic detection of pulmonary metastasis. Mass spectrometry proteomic analysis followed by pathway and protein-protein interaction (PPI) network analysis were performed to identify differentially abundant proteins and key pathways associated with proteomic signatures.

Results: The median disease-free interval between amputation and metastatic progression was 130 days (range: 56-933 days). A unique proteomic signature (97 DAPs) was identified in exosomes at the pre-metastatic time point, which ranged between 30-150 days prior to radiographic evidence of metastatic disease (median 120 days). Pathway analysis identified enrichment in fibrinolysis, coagulation, and complement systems. PPI analyses identified 13 hub proteins. Integration of biological pathways (WikiPathways) and the fold change of differential protein abundance at the pre-metastatic stage suggests a state of reduced complement and fibrinolysis activity and elevated kallikrein-kinin pathway activity preceding metastatic progression.

Conclusion: Circulating exosomal protein cargo from canine OS patients reveals systemic dysregulation of complement, fibrinolysis, and kallikrein-kinin systems that precedes metastatic progression in OS. These findings provide insight into how key biologic pathways evolve over time and may support metastatic progression in OS.