Metabolism of High-Grade Serous Ovarian Carcinoma (HGSOC) Cells

Academic Background

High-Grade Serous Ovarian Carcinoma (HGSOC) is the most common and aggressive subtype of epithelial ovarian cancer. Most patients are diagnosed at stage III or IV, with a 5-year survival rate ranging from 20% to 40%. Treatment for HGSOC typically involves surgical removal of the tumor, followed by multiple cycles of chemotherapy (such as paclitaxel and carboplatin). For BRCA1/2 mutation carriers, PARP inhibitors may be used. Despite these treatments, the survival rate of HGSOC has shown little improvement since the 1970s.

Recent studies have shown that the response of HGSOC to chemotherapy is closely related to its metabolic phenotype. Specifically, HGSOC cells that prioritize oxidative phosphorylation (OXPHOS) over aerobic glycolysis exhibit better responses to chemotherapy. However, previous research has primarily been based on HGSOC cell lines, proposing the hypothesis that HGSOC cells can be divided into two distinct metabolic phenotypes: high OXPHOS and low OXPHOS. It was further suggested that these two phenotypes respond differently to glucose and glutamine deprivation. However, this hypothesis has not yet been validated in primary HGSOC cells.

Therefore, this study aimed to validate this hypothesis by isolating and culturing primary cancer cells from HGSOC patients, and to explore the metabolic flexibility of HGSOC cells and their responses to glucose and glutamine deprivation.

Source of the Paper

This paper was co-authored by Daniela Šimčíková, Dominik Gardáš, Petr Heneberg, and others, with the research team coming from multiple institutions, including the Third Faculty of Medicine at Charles University in Prague and Masaryk University. The paper was published in 2024 in the journal Cancer & Metabolism, titled Metabolism of primary high-grade serous ovarian carcinoma (HGSOC) cells under limited glutamine or glucose availability.

Research Process and Results

1. Acquisition and Cultivation of Research Subjects

The research team isolated primary cancer cells from 45 HGSOC patients and non-transformed ovarian fibroblasts from the surrounding ovarian tissue of the same patients as controls. These cells were cultured under 2D conditions for 2 to 6 weeks, and their purity was confirmed through flow cytometry and immunohistochemistry. The study also analyzed the expression of endoplasmic reticulum (ER) stress markers through immunohistochemistry.

2. Metabolic Flexibility Testing

The research team tested the metabolic flexibility of primary cancer cells under conditions of glucose and glutamine deprivation. By measuring extracellular acidification rate (ECAR) and oxygen consumption rate (OCR), the glycolytic and oxidative phosphorylation activities of the cells were assessed. The results showed that HGSOC cells did not form two distinct groups of high OXPHOS and low OXPHOS, but instead exhibited a continuum of OXPHOS phenotypes. Most tumor cells showed mild responses to glucose or glutamine deprivation, and these responses were correlated with those of non-transformed ovarian fibroblasts from the same patients.

3. Gene and Protein Expression Analysis

The research team analyzed the expression of 14 genes related to metabolic pathways, particularly those involved in glycolysis and glutamine metabolism. The results showed that the proliferation of tumor cells under glucose-free conditions was positively correlated with the expression of the lipid trafficking regulator FABP4, and negatively correlated with the expression of HK2 and HK1. Additionally, the correlation between the expression of electron transport chain (ETC) proteins and OCR or ECAR was weak.

4. Endoplasmic Reticulum Stress and Autophagy

The study found that all analyzed HGSOC tumor cells exhibited high levels of ER stress markers (such as BIP, PERK, and eIF2α). By using ER stress inducers (such as tunicamycin) and relievers (such as TUDCA), the research team further modulated the levels of ER stress. The results showed that tunicamycin significantly increased autophagy in tumor cells, while copper(II)-phenanthroline complexes (C0 and C1) did not significantly affect BIP levels.

5. Drug Sensitivity Testing

The research team tested the effects of various metabolic modulators (such as metformin and Erastin) on tumor cells. The results showed that metformin significantly inhibited the proliferation of tumor cells under glucose-free conditions, while Erastin exhibited cytotoxicity in some tumor cells. Additionally, the study found that the fatty acid oxidation inhibitor Etomoxir had a synergistic effect with glutamine deprivation, significantly reducing the ATP levels of tumor cells.

Conclusions and Significance

This study refuted the previously proposed hypothesis based on HGSOC cell lines that there are two distinct metabolic phenotypes: high OXPHOS and low OXPHOS. The research revealed that HGSOC cells exhibit a continuum of OXPHOS phenotypes, and their metabolic flexibility is complex and diverse. The study also highlighted the important role of ER stress in HGSOC cells and provided potential therapeutic strategies involving various metabolic modulators.

Research Highlights

1. Refuting the Classic Hypothesis: This study is the first to validate the continuum of metabolic phenotypes in primary HGSOC cells, refuting the previously proposed dichotomy of high OXPHOS and low OXPHOS based on cell lines.
2. Regulation of ER Stress: The study found that HGSOC cells universally exhibit high levels of ER stress and revealed the roles of tunicamycin and TUDCA in modulating ER stress and autophagy.
3. Drug Sensitivity Testing: The research provided potential applications for various metabolic modulators (such as metformin and Erastin) in HGSOC treatment, particularly their significant effects under glucose-free conditions.

Research Value

This study offers new perspectives on the metabolism of HGSOC, revealing the metabolic complexity of primary HGSOC cells. The findings not only contribute to understanding the metabolic mechanisms of HGSOC but also provide a theoretical basis for developing personalized treatment strategies targeting metabolic pathways. Additionally, the study emphasized the importance of ER stress in HGSOC, offering new targets for future drug development.

Other Valuable Information

The research team also found that the metabolic phenotypes of HGSOC cells were correlated with clinical parameters of the patients (such as FIGO stage and BRCA1/2 mutations). For example, tumor cells from BRCA1 mutation carriers exhibited lower HK1 expression, while patients with higher FIGO stages showed lower IDO1 and FABP4 expression. These findings provide new biomarkers for the prognosis of HGSOC.

Through systematic experimental design and detailed data analysis, this study provides important scientific evidence for the metabolism of HGSOC and offers new insights for future clinical treatments.