Introduction: Metastasis in high-grade serous ovarian cancer (HGSOC) is confined to the peritoneal cavity, where cancer cells form multicellular clumps known as spheroids. Spheroids enter dormancy by stopping growth and can go undetected during surgical debulking and persist after chemotherapy. Spheroids are the primary source of residual disease relapse in patients with HGSOC. We identified Netrin signaling as crucial for dormant spheroid survival. Netrins are a family of secreted molecules that guide nervous system development. Although previously linked to various cancers, their role in HGSOC pathobiology remains unexplored.

Methods: We showed that overexpression of Netrin-1 or -3 ligands enhanced spheroid formation in vitro. Xenograft experiments in mice revealed that overexpressing Netrin-1 and -3 leads to increased metastatic dissemination in vivo. In contrast, inhibition of Netrin signaling through genetic deletion of UNC5 receptors showed significantly prolonged disease-free survival in xenografted mice compared to the control group.

Results: MEK and ERK emerged as downstream targets of Netrin-mediated cell survival in dormant conditions. The viability of HGSOC dormant spheroids was greatly compromised by MEK inhibitors. Similarly, knockout of UNC5 family of receptors blocked ERK activation and inhibited Netrin-mediated survival of spheroids. These results indicate that Netrins signal through UNC5 receptors to activate ERK to support dormant cell survival. Moreover, treatment of xenografted mice with the MEK inhibitor Trametinib resulted in reduced metastasis and significantly fewer spheroids recovered from the peritoneum compared to the vehicle-treated group.

Significance: Understanding spheroid dormancy is key to preventing ovarian cancer recurrence. Our findings indicate Netrin signaling has a central role in metastatic dissemination of dormant HGSOC spheroids and is a promising target for the development of more effective treatment strategies for patients.