Abstract 704: Targeting hypoxic survival pathways to overcome radiotherapy-related treatment resistance

Abstract Tumor cells undergo biological adaptations in order to survive stress conditions, such as hypoxia and nutrient deprivation. These biological adaptations include the activation of hypoxic survival pathways that play an important role in acquiring radioresistance which becomes most challenging with treatment regimens using high doses of radiation/fraction (e. g. , hypofractionated radiotherapy). Therefore, inhibiting key regulators within these pathways and thereby exploiting these survival mechanisms, gives rise to new potential drug targets for combined treatment modalities. This novel strategy investigated in our laboratory relies on the concept of biological cooperation: while ionizing radiation kills primarily well-oxygenated cells, such inhibitors of survival kinases will drive quiescent tumor cells under hypoxia and/or nutrient deprivation either directly into cell death or into re-entry into a proliferative and thereby more ionizing radiation-sensitive state. One of the survival kinases we are investigating in combination with ionizing radiation (IR) is DYRK1B (dual-specificity tyrosine regulated kinase 1B). We demonstrated that the expression of DYRK1B was upregulated under serum-starvation and hypoxia, but not in response to IR. The small molecule DYRK1B inhibitor AZ191 and shRNA-mediated DYRK1B knockdown significantly reduced proliferative activity and clonogenicity of SW620 tumor cells alone and in combination with IR under serum-starved conditions, which correlated with increased ROS levels and DNA damage. Furthermore, AZ191 successfully targeted the hypoxic core of tumor spheroids while IR preferentially targeted normoxic cells in the rim of the spheroids. A combined treatment effect was also observed in patient-derived colorectal carcinoma organoids but not in healthy tissue organoids. This data shows that inhibition of DYRK1B in quiescent tumor cells could drive tumor cells on their own into crisis or into a more radiosensitive cell cycle phase and thus supports our strategy of biological cooperation. In the continuation of this project, we have performed a drug-screen with approx. 3’000 clinically relevant compounds in colorectal tumor cells lines under normoxic and hypoxic conditions in order to explore additional hypoxia-mediated survival pathways contributing to radioresistance. Thereby we aim to identify novel combined treatment modalities to overcome radiotherapy-induced hypoxia and hypoxia-related resistance mechanisms. Citation Format: Claire Beckers, Lazaros Vasilikos, Alba Sanchez-Fernandez, Lorena Moor, Martin Pruschy. Targeting hypoxic survival pathways to overcome radiotherapy-related treatment resistance abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 704.