Preklinische evaluatie van nieuwe behandelingsmethoden voor eierstokkanker

High-grade serous ovarian cancer (HGSOC), the most common histological subtype of ovarian cancer, is often termed a 'silent killer' due to its vague symptoms, late-stage diagnosis and poor survival outcomes. Most patients present with peritoneal metastases at diagnosis. Standard treatment consists of a cytoreductive surgery combined with platinum-based chemotherapy. Additionally, three targeted therapies, anti-vascular endothelial growth factor (VEGF), poly (ADP-ribose) polymerase inhibitors (PARPi) and mirvetuximab soravtansine targeting the folate receptor alpha (FRα), have been approved in certain indications. Despite the introduction of these targeted treatments and the overall good response observed after standard-of-care therapy, over 70% of patients relapse after first-line treatment, of which many subsequently develop treatment resistance. As a result, the five-year survival rate for HGSOC patients remains about 30%. Immunotherapies, specifically immune checkpoint inhibitors (ICI), have transformed treatment strategies across multiple malignancies including non-small cell lung cancer and melanoma. However, ICIs have shown limited success in HGSOC, likely due to the highly immunosuppressive tumor microenvironment (TME), which fosters immune evasion and stimulates uncontrolled disease progression. In particular, the accumulation of myeloid-derived suppressor cells (MDSCs) has been correlated with a more advanced disease stage and a reduced progression-free survival in HGSOC patients. In this PhD project, the objective was therefore to explore novel therapeutic approaches for HGSOC, focusing on both direct cytotoxic targeting of the tumor cells and the modulation of the immunosuppressive TME to enhance anti-tumor immunity. In part 1 of this PhD project, novel treatment modalities directly targeting the cancer cells were investigated. Herein, we first explored Tumor Treating Fields (TTFields), consisting of alternating electrical fields applied through electrode arrays placed on the patients' skin, in combination with already approved treatments for HGSOC and immunotherapy. Firstly, in our in vitro experiments, TTFields enhanced carboplatin sensitivity, especially in platinum-resistant HSGOC cells, indicating that TTFields can help mitigate drug resistance. Secondly, application of TTFields also induced a homologous recombination deficient (HRD)-like phenotype ("BRCAness") in homologous recombination proficient (HRP) ovarian cancer cells in vitro, resulting in increased sensitivity of these cells to DNA damage. Moreover, synthetic lethality was observed in vitro upon combination with PARPi, due to the dual inhibition of DNA damage repair pathways. This synergistic effect translated in vivo into prolonged survival in HRP ovarian cancer-bearing mice. Furthermore, as both TTFields and PARPi treatment have been reported to induce immunogenic cell death (ICD), we assessed their combination with ICI treatment in mice bearing HRP metastatic ovarian cancer, although this did not improve survival outcomes. As second treatment directly targeting the cancer cells, we investigated targeted alpha therapy (TAT) using lead-212 conjugated to PTK7-targeting antibodies ([²¹²Pb]Pb-TCMC-chOI-1). Overexpression of PTK7 has been correlated with worse prognosis and enhanced epithelial-to-mesenchymal transition in HGSOC patients. Moreover, due to its high linear energy transfer resulting in DNA damage in a short range, TAT is considered a promising approach for eradicating micro-metastases, which are often related to high relapse rates in HGSOC. Our TAT studies demonstrated effective tumor targeting and a significant prolongation of survival in HGSOC-bearing mice after intraperitoneal administration of [²¹²Pb]Pb-TCMC-chOI-1. In part 2 of this PhD project, immunotherapeutic strategies tackling the abundant immunosuppression in ovarian cancer were explored. We first reviewed the preclinical evidence for combining widely used ICIs and chemotherapy in literature. This review highlighted the importance of the combination order of treatments, since it influenced the survival of cancer bearing mice. Rationally designing combination treatment strategies in order to find the optimal therapeutic regimen through proper preclinical studies appears crucial. We next focused on the manipulation of the abundant immunosuppressive MDSC, taking the rational design and order of treatments into account. Although most studies have been focusing on anti-PD1/PD-L1 or anti-CTLA4 ICIs, we investigated anti-TIM3 checkpoint blockade, given its broader expression on multiple immune cells, including innate immune cells, which are otherwise overlooked. However, anti-TIM3 monotherapy or combination with carboplatin-paclitaxel chemotherapy failed to improve survival in ovarian cancer-bearing mice. Interestingly, a significant difference in survival outcomes was observed when altering the administration schedule of anti-TIM3 and carboplatin-paclitaxel. Specifically, sequential administration in which mice received chemotherapy followed by anti-TIM3 resulted in reduced survival compared to concurrent treatment, underscoring the importance of the administration schedule on the therapeutic outcome. Lastly, we investigated drug repurposing to inhibit MDSC-induced immunosuppression. This approach holds much promise, due to the prior knowledge on safety and pharmacokinetics which can result in a faster and less costly clinical translation. From a review of available literature, 17 drug repurposing candidates were identified of which the four most promising were selected based on their evidence and clinical applicability, namely, 5-azacytidine, metformin, celecoxib and lurbinectedin. In vitro, 5-azacytidine failed to reverse MDSC-induced suppression on T-cell proliferation, while metformin and celecoxib elevated their suppressive effect. Subsequent in vivo studies testing metformin and celecoxib monotherapy suggested modest survival benefit, although no improvement was observed with addition of concomitant carboplatin-paclitaxel chemotherapy. The drug repurposing candidate lurbinectedin, a chemotherapeutic agent, significantly prolonged survival in HGSOC-bearing mice. However, attempts to enhance this effect by combining with metformin and/or celecoxib, both targeting the MDSC function, were unsuccessful. Lurbinectedin's reported ability of inhibiting MDSC recruitment to the TME was confirmed in an immune modulation experiment using anti-GR1 and clodronate liposomes. In conclusion, this PhD project provides preclinical evidence towards several promising treatment approaches for HGSOC. TTFields can sensitize platinum-resistant cancer cells and induce HRD-like states in HRP tumors, enhancing PARPi efficacy. PTK7-targeted 212Pb-based TAT effectively prolongs survival in HGSOC-bearing mice. Immunosuppression was not sufficiently abrogated by TIM3 checkpoint inhibition but may be influenced by drug repurposing candidates targeting MDSC. Several of our experiments, underscored by a literature review, reveal that the order of combined treatments is important and can drastically alter outcomes. Further research is required to identify optimal combination regimens which both relieve immunosuppression and promote anti-tumor immune responses.