Metformin Upregulates Circadian Gene PER2 to Inhibit Growth and Enhance the Sensitivity of Glioblastoma Cell Lines to Radiotherapy Via SIRT2/G6PD Pathway

Hailiang Li ^1,2 Zheng Ma ³ Wanfu Yang ⁴ Yifan Zhang ⁵ Jinping Sun ⁶ Haifeng Jiang ⁶ Faxuan Wang ⁷ Li Hou ^3* Hechun Xia ^2,5*

• ¹ Department of Surgical Oncology, General hospital of Ningxia Medical University, Ningxia, China
• ² Key Laboratory of Craniocerebral Diseases, Ningxia Medical University, Yinchuan, Ningxia, China
• ³ Department of Otolaryngology and Head and Neck Surgery, General Hospital of Ningxia Medical University, Yinchuan, Henan Province, China
• ⁴ Department of Radiation Oncology, General Hospital of Ningxia Medical University, Ningxia, China
• ⁵ Department of Neurosurgery, General Hospital of Ningxia Medical University, Yichuan, China
• ⁶ Department of Pathology, General Hospital of Ningxia Medical University, Yinchuan, Ningxia, China
• ⁷ School of Public Health and Management, Ningxia Medical University, Yinchuan, Ningxia Hui Region, China

Glioblastoma multiform (GBM) is considered the deadliest brain cancer. Standard therapies are followed by poor patient's survival outcomes, so novel and more efficacious therapeutic strategies are imperative to tackle this scourge. Metformin has been reported to have anti-cancer effects. However, the precise mechanism underlying these effects remains elusive. A better understanding of its underlying mechanism will inform future experimental designs exploring metformin as a potential adjuvant therapy for GMB. This research aimed to elucidate the potential molecular mechanism of metformin in GMB by integrating proteomics and transcriptomics. We found that differential expressional genes and proteins relating to circadian rhythm were enriched in proteomic or transcriptomic. The expression of PER2, the key circadian gene, was up-regulated in GMB cell lines when treated with metformin. Furthermore, the expression of silent information regulator 2(SIRT2) was down-regulated, while the expression of the G6PD protein just slightly increased in GMB cell lines. Meanwhile, NADPH + production and G6PDH enzyme activity significantly decreased. Further study validated that metformin inhibited the cell growth of GBM cell lines through up-regulating PER2 and inhibited SIRT2/G6PD signaling pathway, enhancing radiotherapy sensitivity. We also found that the inhibition of SIRT2 caused by metformin is mediated by PER2. We found the pivotal role of metformin as a effective circadian rhythm regulator. Targeting circadian clock gene to modify and rescue the dysfunctional circadian clock of GBM cells at molecular level might be an innovative way to administer cancer chronotherapy and maintain metabolic homeostasis in real world practice.