Molecular signatures of progression and chemoresistance in epithelial ovarian carcinoma

Abstract

Epithelial ovarian carcinoma (EOC) is a heterogeneous disease generally classified into five histopathological subtypes; low- and high-grade serous, endometrioid, clear cell and mucinous carcinomas. Although each subtype has distinct clinical and molecular characteristics, they are all treated with surgery and platinum/ taxane chemotherapy. Despite initial responsiveness a majority of patients relapse into platinum-resistant and disseminated disease. This, together with often late diagnosis, makes EOC the most lethal gynecological cancer. Dissemination is mainly abdominal, via exfoliated tumor cells in peritoneal ascitic fluid. The origin and phenotype of cells in malignant ascites is poorly understood. Tumor progression of carcinomas towards metastasis includes epithelial-to-mesenchymal-transition (EMT), where epithelial cells gain a mesenchymal morphology to facilitate invasion. Progression and chemoresistance have also been attributed to a small population of highly tumorigenic and chemoresistant cancer stem cells, or tumor-initiating cells (TICs). In addition, altered cellular energetics is a hallmark of cancer wherefore tumor-specific metabolic features are potential targets for overcoming chemoresistance.

In Paper I cell populations in malignant ascites were found to differ significantly with respect to protein expression levels of EMT and TIC markers. We identified two potential TIC profiles, highlighting a biological heterogeneity in ascitic tumor cell populations. The indicated presence of cancer-associated fibroblasts (CAFs) may further contribute to malignant properties. We found that CAF marker α-SMA expression was increased in clinical stage IV, compared to stage IIIC.

Paper II reveals that long-term repeated cisplatin treatment can select for and/or induce a multiresistant cell population with EMT and TIC features. Resistance could be linked to upregulation of VDAC and HK-II, which form an anti-apoptotic complex on mitochondria. Multiresistant cells were sensitive to the lactate/ pyruvate analogue 3-BP that dissociates this complex, and particularly sensitive to 3-BP when combined with cisplatin in low doses.

In Paper III expression of mitochondrial regulators PGC1α and TFAM was found to vary between EOC subtypes. For clear cell carcinomas (CCC) a profile consisting of low or undetectable levels of PGC1α, TFAM, ERα and low Ki-67 index was identified. This CCC profile, and also glycogen accumulation, was further linked to chemoresistance development in vitro.

In Paper IV we used 1H NMR-based metabolomics to identify significant differences in the intracellular polar metabolome of parental and multiresistant EOC cell lines. Furthermore, we developed a tailored and reliable protocol for metabolic profiling of adherent cells, suitable for further characterization of metabolic alterations in EOC and other pathological conditions.

Taken together, this thesis identifies signatures of progression and chemoresistance in EOC and highlights the need for subtype-specific treatment.