Background: High grade serous carcinoma (HGSC), the most common form of ovarian cancer, often metastasizes transperitoneally via shedding the of cancer cells as aggregates (cancer spheroids), allowing it to disseminate throughout the peritoneal cavity. Overexpression of transmembrane protein podocalyxin (PODXL) has been associated with poor prognosis of several epithelial cancers including HGSC, and PODXL surface localisation in HGSC has been associated with a significant decrease in disease-free survival.
Aims: To examine PODXL expression in HGSC tissues, ovarian cancer cell lines and ascites-derived primary tumour cells, and to determine the impact of PODXL on HGSC spheroid morphology and compactness.
Methods: PODXL expression was examined by immunohistochemistry in tissues, and by RT-PCR and immunofluorescence (ICC) in cell lines and ascites-derived primary cells. Kuramochi cells, a HGSC cell line with high PODXL expression, were used as a model and PODXL was knocked out (KO) using CRISPR technology. Spheroids of control and PODXL-KO Kuramochi cells were compared to determine the effect of PODXL on spheroid morphology and hardiness.
Results: All HGSC tissues showed positive PODXL staining with varying intensity. Tissues with high levels of PODXL showed strong apical staining in cluster-like patterns. PODXL was expressed by many ovarian cancer cell lines, and ICC showed PODXL localisation on the surface of cancer spheroids. Spheroids formed with PODXL-KO Kuramochi cells were less compact, more fragile and broke apart more easily under external force than the control. Among ascites-derived primary cancer cells (n=6 patients) examined so far, 2 showed low whereas 4 displayed moderate-high levels of PODXL expression; when spheroids were generated from these cells, those with high PODXL expression were more compact than those with low PODXL.
Conclusions: PODXL may promote the formation of compact and hardy spheroids in HGSC for cancer metastasis and thus may represent a potential therapeutic target for HGSC treatment.