XPO1-Inhibitor Selinexor Induces MGMT Expression by Activating PKA-CREB Signaling in IDH wildtype Glioblastoma

Josephine A Mapunda¹Yuta Suzuki¹Danielle Burgenske²Paul A Decker³Lin Zhang⁴Jeanette E Eckel-Passow³Jann N Sarkaria²Gaspar Kitange^1*

• ¹Division of Neuro-Oncology Research, The Hormel Institute, University of Minnesota Twin Cities, Austin, MN, United States
• ²Department of Radiation Oncology, Mayo Clinic Minnesota, Rochester, United States
• ³Department of Quantitative Health Sciences, Mayo Clinic Minnesota, Rochester, United States
• ⁴Department of Public Health, University of Minnesota Twin Cities, Minneapolis, United States

Purpose The temozolomide (TMZ) resistance mechanisms in MGMT-promoter methylated IDH wildtype glioblastoma (GBM) tumors are poorly known. This study aimed to identify potential modulators of TMZ resistance in methylated GBM cells. Methods A genome-wide shRNA library screen was conducted to identify genes modulating resistance in a TMZ-resistant model of MGMT-methylated U251 GBM cells. The Incucyte Device was used for live cell growth monitoring, and DNA damage was assessed by foci staining. Results Exportin (XPO1) was among the identified candidate TMZ-resistant genes, and the XPO1 inhibitor Selinexor was selected for further investigations. The MGMT-unmethylated GBM6 cells were sensitive to Selinexor alone, without additional sensitization when combined with TMZ. In contrast, MGMT-methylated GBM22 cells were relatively sensitive to Selinexor alone and were significantly sensitized to the Selinexor/TMZ combination. Interestingly, silencing MGMT sensitized GBM6 cells to the combined Selinexor/TMZ treatment, while forced exogenous MGMT expression blocked the sensitivity of U251 cells to the combined Selinexor/TMZ treatment. Selinexor treatment induced MGMT expression concurrently with increased phosphorylation of serine 133 of CREB protein (pCREBS133) in GBM6 and other MGMT-promoter unmethylated GBM cells. Finally, Selinexor-induced MGMT expression and pCREBS133 were blocked by the protein kinase A inhibitor H89, suggesting a role for PKA-CREB signaling in this process. Conclusions This study demonstrates XPO1 as a mediator TMZ resistance in MGMT-methylated GBM cells, and that MGMT expression status is a potential determinant of sensitivity to Selinexor/TMZ treatment in GBM cells. These findings also uncover a novel mechanism linking Selinexor with PKA-CREB-mediated MGMT expression, suggesting that Selinexor may enhance MGMT-dependent TMZ resistance in GBM.