Introduction: Ovarian cancer (OC), particularly high-grade serous carcinoma (HGSC), is a leading cause of gynecological cancer mortality due to late diagnosis and chemoresistance. About a third of patients do not respond to primary platinum-based (Pt-BM) chemotherapy treatment, and over time up to 80% of others develop chemoresistance, rendering recurrent disease incurable. There are currently no validated molecular predictive biomarkers for Pt resistance. Although studies of OC cell lines have shown that overexpression of the ATP7A membrane transporter correlates with resistance to Pt-BM and cross-resistance to copper (Cu), clinical evidence is lacking. The functionality of ceruloplasmin (CP), the main Cu-transporting protein in the blood, depends in part on ATP7A activity.
Methods: The research took place at the Department of Gynecology, Ljubljana University Medical Center, and at the Institute of Pharmacology and Experimental Toxicology at the Faculty of Medicine, University of Ljubljana. It was conducted at two levels. The first part was an in vitro study on selected cell lines, and the second part was a clinical study on ascites, blood, and tissue samples from HGSC patients treated at the Department of Gynecology. The in vitro study used two different cell lines, OAW28 and PEO1. After cell culture, measurements were made of the mean fluorescence intensity (MFI), which indicates the level of ATP7A expression and the percentage of ATP7A-positive cells in PEO1 and OAW28 cell lines using a flow cytometer. Furthermore, the clinical study included 28 HGSC patients that underwent neoadjuvant chemotherapy (NACT). ATP7A expression in ovarian and peritoneal tissues before NACT and in peritoneal and omental tissues after NACT was analyzed via qPCR, and CP levels in ascites and plasma were measured via ELISA before and after NACT.
Results: The in vitro analysis showed a statistically significant difference in MFI between PEO1 and OAW28 cell lines, indicating that OAW28 has significantly higher MFI values. The OAW28 cell line also had a slightly higher percentage of positive cells, which was also statistically significant. The clinical study investigated ATP7A expression and CP levels as potential biomarkers for predicting responses to PtBMs. In total, 54% of patients exhibited ATP7A expression in tissues before NACT (ovary and/or peritoneum), and 43% of patients exhibited ATP7A expression in tissue after NACT (peritoneum and/or omentum). A significant association was found between higher ATP7A expression in the peritoneum before NACT and an unfavorable CA-125 elimination rate constant K (KELIM) score. Patients with omental ATP7A expression had significantly higher plasma mean CP levels before NACT. Plasma CP levels decreased significantly after NACT, and higher CP levels after NACT were associated with a shorter platinum-free interval (PFI).
Conclusion: Based on the findings in this in vitro study, the ATP7A carrier plays a role in chemoresistance, as demonstrated in the OAW28 cell line, which shows higher ATP7A expression. Furthermore, together with the findings in the clinical study, it can be summed up that the ATP7A transporter and CP have the potential to serve as predictive markers of chemoresistance, but further research is needed to validate their clinical utility.
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