Abstract By Aikaterini Skorda

High-grade serous ovarian cancer is the most aggressive histotype of the epithelial ovarian cancer neoplasms and the most lethal among the gynecological malignancies. The disease is characterized by a median latency of more than ten years and obscure clinical symptoms, meaning that detection occurs at an already advanced disease stage. By that time, HGSC extensive dissemination into the abdominal space through the contiguous peritoneal surfaces, ascites fluid, and lymphatics hinders the effectiveness of cytoreductive surgery. An essentially elevated proportion of patients develop resistance to the first-line treatment, which is based on combination therapy of platinum with taxane, and to the follow-up targeted treatments, ultimately leading to a chronic disease with progressive relapses. HGSC extensive inter- and intra-patient heterogeneity dictates dissemination, development of drug resistance and significantly challenges the establishment of effective long-lasting treatment modalities and personalized treatment approaches. Hence, novel therapeutic strategies and clinically meaningful patient
stratification need to be established, alongside a deeper understanding of the mechanisms underlying the progression of this disease. To address those unmet needs, we established a personalized patient-derived HGSC organoid platform from multisite and longitudinal tissue samples to study drug response and functionality.

Firstly, we evaluated organoid response to an FDA-approved, well-tolerated antihistamine that induces off-target, lysosome-dependent cell death. In line with preclinical and epidemiological studies, we showed a putative antitumor effect for this antihistamine for a subset of organoid cultures. Additionally, we defined a resistant to the drug group of organoids and suggested possible mechanisms of underlying resistance based on both tumor tissue RNA sequencing and organoid experimental data. Next, we investigated HGSC tumor evolution prior to treatment based on estimation of HGSC spatial and
temporal heterogeneity of tumor samples. We identified three HGSC evolutionary states, characterized of distinct morphological features, genomic profiles and evolutionary trajectories. We identified patient subtypes with differences in progression-free and overall survival rates. We demonstrated that worse prognosis was associated with significant enrichment of the PI3K/AKT pathway, the functionality of which we evaluated in vitro in organoid cultures. We targeted the pathway with the FDA-approved
PI3Kα inhibitor, alpelisib, and we demonstrated partial dependency on the pathway for organoid survival.

Conclusively, we propose two potentially effective treatments for a subset of HGSC patients, which could inform future personalized clinical approaches. Additionally, we provide valuable insights in HGSC tumor evolution. We emphasize the importance of integrating multi-omics sequencing data with functional testing in preclinical models that reliably recapitulate the complex heterogeneity of HGSC, to deepen our understanding of the disease and suggest effective treatment modalities.