p53 wild-type/low c-Myc-expressing ONS76 pediatric medulloblastoma cells become senescent after gamma-irradiation and can be eliminated by senolytic substances

Abstract Craniospinal irradiation (CSI) is an indispensable part of oncological treatment for pediatric medulloblastoma. However, despite significantly improving oncological outcome, it is also associated with severe short- and long-term side effects such as inflammation and impaired neurocognition. The presence of senescent cells has been identified as a potential contributing factor to these issues. In our study, we demonstrate that p53 wild-type and c-Myc-low-expressing ONS76 medulloblastoma cells underwent senescence, a terminal and stable cell cycle arrest, after exposure to gamma irradiation (γIR). In contrast, p53-mutated UW228-3 cells exhibited apoptosis following the same treatment. ONS76 cells displayed typical senescence properties, including cell and nuclei enlargement, an active DNA damage response with stabilization of p53 and increased expression of its target gene, the CDK inhibitor p21 WAF1/CIP1 , as well as elevated senescence-associated beta-galactosidase activity and lipofuscin accumulation. Knockdown of p53 or p21 expression with siRNAs abolished γIR-mediated senescence. Furthermore, overexpression of c-Myc resulted in a partial shift from senescence to cell death induction after γIR treatment, which was inhibited by using the caspase-inhibitor q-VD-OPh. The γIR-exposed ONS76 cells showed susceptibility to senolytic substances, such as the BCL-2 family inhibitor Navitoclax and the PI3K-inhibitors PX-866 and BAY80-6946, which specifically target senescent cells. In conclusion, employing senolytics on irradiated medulloblastoma cells with wild-type p53 and low c-Myc expression may lead to reduced therapeutic side effects as well as attenuate tumor relapse and potentially minimize CSI doses required for effective tumor cell elimination.