Pharmacological transglutaminase 2 inhibition enhances temozolomide response in patient-derived glioblastoma tumorspheres

Abstract

Purpose Glioblastoma (GBM) is the most common and aggressive primary malignant brain tumor, with a median survival of less than two years despite standard therapy. Transglutaminase 2 (TGM2) contributes to tumor progression and poor clinical outcomes. This study evaluated the therapeutic potential of combining streptonigrin (SN), a TGM2 inhibitor, with temozolomide (TMZ), the standard chemotherapeutic agent for GBM. Methods Two patient-derived GBM tumorspheres (TSs; TS15-88, proneural subtype; TS19-156, classical subtype) were treated with SN, TMZ, or their combination. Cell viability and ATP production were measured to assess cell proliferation, and synergy was quantified using the Bliss synergy score. Apoptosis was analyzed by flow cytometry. Stemness and invasiveness were evaluated using neurosphere formation and three-dimensional invasion assays. Protein and mRNA expression levels were assessed by western blotting and RNA sequencing. In vivo efficacy was evaluated using a mouse orthotopic xenograft model. Results The combination of SN and TMZ significantly reduced cell viability and ATP levels and induced apoptosis more effectively than either agent alone. Moreover, combination treatment effectively reduced stemness and invasiveness in GBM TSs, along with the expression of related proteins and mRNAs. In vivo, combination therapy prolonged survival in mice and reduced the expression of invasion-related proteins, as demonstrated by immunohistochemistry. Conclusion These findings suggest that targeting TGM2 with SN enhances the therapeutic efficacy of TMZ in GBM. The combination of SN and TMZ may represent one potential therapeutic approach for GBM and warrants further mechanistic and translational investigation.