Abstract
BACKGROUND: Synovial sarcoma (SS) is a rare but aggressive soft tissue malignancy characterized by a high rate of pulmonary metastasis and limited response to conventional therapies. Hypoxia, a common feature of tumor microenvironment, has been implicated in cancer progression, yet its specific contribution to metastatic dissemination in SS remains insufficiently characterized. METHODS: We investigated the effects of hypoxia on metastatic behavior in two SS cell lines: SYO-1 (SS18-SSX2 fusion-positive) and SW982 (fusion-negative). Cells were cultured under hypoxic (O₂ < 1%) and normoxic (21% O₂) conditions, followed by reoxygenation. Expression of hypoxia-responsive and metastasis-related genes (e.g., HIF-1α, CA9, VEGF, IGF2, ADM, YB-1, TGF-β1) was assessed via qRT-PCR. To evaluate in vivo metastatic potential, a lung colonization model was established by injecting pretreated cells into the tail veins of immunodeficient (NMRI nu/nu) mice. RESULTS: Hypoxia significantly upregulated canonical HIF-1α targets in both cell lines, with SYO-1 showing stronger and more sustained induction, particularly of CA9 and VEGF. In vivo, SYO-1 cells formed significantly more micrometastatic lung lesions compared to SW982, with distinct perivascular clustering and signs of early intravasation. SW982 cells exhibited limited, diffuse infiltration and lower hypoxia-induced gene activation. These differences suggest that the SS18-SSX fusion may synergize with hypoxia signaling to enhance metastatic potential. Notably, HIF-1α, CA9, and IGF2 expression correlated with metastatic capacity, while TGF-β1 expression declined under hypoxia, indicating a dynamic regulation of prometastatic pathways. CONCLUSION: Our findings demonstrate that hypoxia promotes SS metastasis through activation of HIF-1α and related pathways. Fusion-positive SS cells appear particularly responsive to hypoxic cues, suggesting that targeting hypoxia-induced signaling could be a promising strategy to inhibit metastasis in SS. These results provide mechanistic insight into SS progression and support the integration of hypoxia-targeted therapies into future treatment strategies.