• Mi Youn Seol, Seo Hee Choi, Ik Jae Lee, Hyung Soon Park, Hye Ryun Kim, Sang Kyum Kim, and Hong In Yoon.
• Department of Radiation Oncology, Yonsei Cancer Center, Heavy Ion Therapy Research Institute, Yonsei University College of Medicine, Seoul, Korea.
• Yonsei Med. J. 2023 Feb 1; 64 (2): 139147139-147.

PurposeGlioblastoma (GBM) is a malignant brain tumor with poor prognosis. Radioresistance is a major challenge in the treatment of brain tumors. The development of several types of tumors, including GBM, involves the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway. Upon activation, this pathway induces radioresistance. In this study, we investigated whether additional use of selective inhibitors of PI3K isoforms would enhance radiosensitivity in GBM.Materials And MethodsWe evaluated whether radiation combined with PI3K isoform selective inhibitors can suppress radioresistance in GBM. Glioma 261 expressing luciferase (GL261-luc) and LN229 were used to confirm the effect of combination of radiation and PI3K isoform inhibitors in vitro. Cell viability was confirmed by clonogenic assay, and inhibition of PI3K/AKT signaling activation was observed by Western blot. To confirm radiosensitivity, the expression of phospho-γ-H2AX was observed by immunofluorescence. In addition, to identify the effect of a combination of radiation and PI3K-α isoform inhibitor in vivo, an intracranial mouse model was established by implanting GL261-luc. Tumor growth was observed by IVIS imaging, and survival was analyzed using Kaplan-Meier survival curves.ResultsSuppression of the PI3K/AKT signaling pathway increased radiosensitivity, and PI3K-α inhibition had similar effects on PI3K-pan inhibition in vitro. The combination of radiotherapy and PI3K-α isoform inhibitor suppressed tumor growth and extended survival in vivo.ConclusionThis study verified that PI3K-α isoform inhibition improves radiosensitivity, resulting in tumor growth suppression and extended survival in GBM mice.© Copyright: Yonsei University College of Medicine 2023.

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