Abstract
Ovarian Cancer (OC) is the most lethal gynecological malignancy in France nowadays and the 8th most-frequent cause of cancer-related death among women worldwide. OC progresses without clinical signs or symptoms in most of cases, leading to a late stage diagnosis (stage III/IV) when it has spread into the peritoneal cavity under the form of peritoneal carcinomatosis (PC). The treatments available do not show substantial returns, as disease will reoccur in 70-90% of patients. Conversely to external radiotherapy, with high-risk ofdamaging the surrounding healthy tissues, Targeted Radionuclide Therapy (TRT) specifically irradiates tumors while sparing healthy tissues, offering an attractive therapeutic option. Here, we investigated the radiosensitizing effects of AGuIX® nanoparticles (NP) on OC combined with 177Lu-Trastuzumab. We expect the high LET Auger electrons emitted by the irradiated NPsto overcome OC treatment resistance.In vivo, using female nude mice bearing intraperitoneal (IP) xenografts from SKOV3-luc cells, we report the enhanced therapeutic efficacy of the combination TRT + AGuIX®, which strongly delayed tumor growth and increased mice median survival compared to controls (****p<0.0001) and TRT alone group (*p=0.016). SPECT/CT imaging highlighted thespecific targeting of PC tumor nodules after IP injection of the radiolabeled antibody and the NP, opening a new opportunity to optimize this theranostic strategy for the management of OC.The combination efficacy was supported by in vitro data, showing synergistic effects between AGuIX® and TRT, as measured by clonogenic survival assay using SKOV3, OVCAR3 and A431 cells. Fluorescence and Transmission Electron Microscopy (TEM) imaging showed a co-localization of the NP with cell lysosomes, organelles charged with transition metals as iron, essential for hydroxyl radical production through the Fenton reaction. Consequently, andcompared to TRT alone, TRT + AGuIX® significantly increased Reactive Oxygen Species (ROS) production and lipid peroxidation, suggesting a potential role of ferroptosis in AGuIX®-mediated toxicity. We acknowledge a decreased number of lysosomes in treated cells associated with cytoplasmic pH decrease, suggesting a lysosomal disruption. Autophagosome accumulation, a striking cytoplasmic vacualization, mitochondrial depolarization, apoptosisandmicronuclei formation were a signature of the combination, which can be reversed by iron chelation.We provide strong evidence of AGuIX® radiosensitizing effect when combined, for the first time, with a radiolabeled antibody for the treatment of OC-derived PC. At a cellular level, we report a high dependence on iron-derived hydroxyl radical production, leading to a lysosomal–mediated cell disruption. The later radiosensitization allows reducing the activity injected in mice while keeping a high therapeutic efficacy, reducing potential treatment- related toxicites. As AGuIX® NPs are already combined with external radiotherapy in clinical trials, the present study opens perspectives to translation in TRT for the treatment of OC-derived PC.