Abstract 2822: Maximizing radiotherapy impact: a novel pre-clinical platform for screening of radiosensitizing agents in patient-derived tumor organoids
Authors: Wijler Liza , Garcia Jara , Abdulrahman Muntaser , van Seters Linda , Nguyen My , Staes Annelot , Herpers Bram , Price Leo , Putker Marrit 
Published: April 2023

Abstract
Introduction: Radiotherapy (RT) is widely used for various cancer types, however, radiotoxicity in healthy neighbouring tissues remains challenging. To optimize effectiveness of current therapeutic regimens, there is a clinical need to enhance radiotherapy-mediated killing by radiosensitizing agents. Radiosensitizers show great potential by accelerating DNA damage, production of free radicals and disturbing cell cycle processes by induction of cytostatic and -toxic effects, but pre-clinical drug efficacy testing methods are limited. Patient-derived organoids (PDOs) have emerged as clinically relevant in vitro screening tools to enable drug discovery for specific mutational and molecular subtypes of many cancer indications. Although some radiosensitizing agents have been identified, potential radiosensitizing effects of standard of care as well as novel anti-cancer drugs remain largely unknown. Here, we present a unique screening platform that enables radiosensitizer discovery by showing in-depth insight in cytostatic-and toxic changes and RT-drug synergy.
Methods: Twelve PDO models from colorectal, pancreas, breast, lung, melanoma, cervical and ovarian tumors were screened for responsiveness to potential radiosensitizing agents using our organoid screening platforms. PDOs were seeded in 384-wells format in suspension or 3D gel (for cell-titer-glo (CTG) or imaging purposes) and compound exposure (three concentrations) was performed prior to irradiation (0, 2, 4, 6, 10 Gy). Cell viability data was obtained using both CTG-based assays and high content imaging (HCI)-based assay. Assay robustness and reproducibility were ensured (Z-scores &lt;0.6, reproducible IC50 values). To assess radiosensitizing effects, data was normalized to non-irradiated control conditions. Morphological changes were assessed using HCI.
Results: Clear differences in radiosensitivity were observed, with six out of twelve PDOs showing sensitivity to 10 Gy RT (&lt;30% viability), one breast, two melanoma and two lung PDOs showing limited sensitivity (47-86% viability) and one ovarian PDO showing no response to RT (98% viability). A wide range of responses to the chemo-irradiation treatments were observed, with oxaliplatin exhibiting radiosensitizing effects in cervical and colorectal PDOs, gemcitabine in cervical PDOs and docetaxel showing radioprotective properties in melanoma PDO.
Conclusion and Discussion: Our novel platform for testing potential radiosensitizing anti-cancer agents holds great promise for advanced drug discovery in a clinically relevant and readily available PDO panel, harbouring a wide range of RT-sensitive to insensitive models. CTG and HCI read-outs offer both fast and in-depth assessment of cytotoxic and cytostatic effects and organoid morphology, creating omnipotent potential for tailored compound screening of radiosensitizers.
Citation Format: Liza Wijler, Jara Garcia, Muntaser Abdulrahman, Linda van Seters, My Nguyen, Annelot Staes, Bram Herpers, Leo Price, Marrit Putker. Maximizing radiotherapy impact: a novel pre-clinical platform for screening of radiosensitizing agents in patient-derived tumor organoids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2822.