High-grade serous ovarian carcinoma (HGSOC), which predominantly affects postmenopausal women, represents the most common and most lethal form of ovarian cancer. In addition to surgical treatment, chemotherapy based on platinum compounds and taxanes is routinely employed. Although targeted maintenance therapies have recently been introduced, overall survival of patients with ovarian cancer has not improved substantially. Five years after the initial diagnosis, only approximately 47% of patients survive, largely due to the development of chemoresistance, highlighting an urgent need for novel therapeutic approaches. The development of ovarian cancer has been associated with excessive estrogen action, which is thought to promote tumor cell growth; however, the involvement of estrogens in the development of chemoresistance remains insufficiently explored. In hormone-dependent tumor tissue and surrounding local tissues, estrogens can be synthesized via the sulfatase or aromatase pathways. In this dissertation, the sulfatase pathway was investigated, in which estrogens are generated from estrone sulfate (E1S) through the action of steroid sulfatase (STS). The resulting estrone (E1) is subsequently reduced to estradiol (E2) or oxidized back to E1 by 17β-hydroxysteroid dehydrogenases. Conjugation of E1 and E2 to estrone sulfate (E1S) and estradiol sulfate (E2S) is catalyzed by estrogen sulfotransferase (SULT1E1). Cellular uptake of steroid precursors required for local estrogen biosynthesis is mediated by organic anion transporting polypeptides (SLCO/OATP) and organic anion transporters (SLC/OAT), whereas efflux from cells is facilitated by ATP-binding cassette (ABC) transporters. Biologically active estrogens (E1 and particularly E2) can activate intracellular receptors of the nuclear receptor superfamily (ERα and ERβ), which function as transcription factors regulating target gene expression, or engage membrane-associated receptors such as the G protein-coupled estrogen receptor (GPER), thereby triggering intracellular signaling pathways. Estrogens can induce DNA damage through oxidative metabolism by generating mutagenic adducts and reactive free radicals, which may lead to the acquisition of new mutations and represent one of the possible mechanisms underlying the development of chemoresistance. An additional mechanism potentially contributing to chemoresistance involves the activity of aldo–keto reductases (AKRs). AKRs participate in the metabolism of chemotherapeutic agents, reduce chemotherapy-induced cellular stress, and are also involved in the biosynthesis and metabolism of steroid hormones. Genes of the AKR1 family are overexpressed in various cancers, which may represent a mechanism underlying resistance to current therapeutic strategies and may further contribute to the growth of hormone-dependent tumors.
The aim of this study was to investigate the role of local estrogen biosynthesis and the contribution of AKR1C1–3 enzymes to chemoresistance in HGSOC. Through this approach, we sought to advance understanding of the involvement of estrogens and AKR1C enzymes in the mechanisms underlying chemoresistance in HGSOC and to identify novel targets for therapeutic intervention. Our results show that the expression of genes involved in estrogen transport, biosynthesis, metabolism, and signaling differs in platinum-resistant HGSOC patients and in platinum-resistant HGSOC cell lines. Genes implicated in estrogen biosynthesis, metabolism, and oxidative metabolism (HSD17B14, SULT1A1, CYP19A1, and NQO2) significantly influence survival outcomes in patients with HGSOC. Estrone sulfate (E1S) metabolism to active estrogens (E1 and E2) is more pronounced in carboplatin-sensitive HGSOC cell lines as compared to resistant cell lines, where it is redirected toward alternative, likely oxidative pathways. The steroid sulfatase inhibitor STX64 inhibits proliferation at nanomolar concentrations in ERα-positive HGSOC cells and induces apoptosis at higher micromolar concentrations in ERα-negative cells. STX64 shows limited synergy with carboplatin in HGSOC cells. The antiproliferative effects of estrogen receptor agonists equilin (EQ) and ethinylestradiol (EE2) are associated with the ESR1:ESR2 expression ratio, while E1S, EQ, and EE2 potentiate the inhibitory effect of carboplatin on HGSOC cell migration. Furthermore, analysis of AKR1C involvement indicates that AKR1C1–3 and NFE2L2, which encodes nuclear factor erythroid 2–related factor 2 (NRF2), may serve as prognostic biomarkers in serous ovarian cancer. The AKR1C inhibitors medroxyprogesterone acetate (MPA) and mefenamic acid (MEF) suppress proliferation and migration of HGSOC cells and synergistically enhance the effects of carboplatin. MPA and MEF primarily induce apoptotic cell death, whereas carboplatin induces necrosis; both compounds reduce the structural integrity and viability of HGSOC spheroids.
This doctoral thesis contributes to a deeper understanding of the role of estrogens, agonists and antagonists of estrogen receptors, as well as AKR1C enzymes and their inhibition in ovarian cancer chemoresistance. Furthermore, it highlights new opportunities for the development of targeted and personalized therapeutic strategies aimed at reducing treatment-related toxicity and improving survival outcomes in patients with advanced HGSOC.
|
