Background: Gliomas represent the most common form of primary malignant brain tumors, with temozolomide (TMZ) being a widely established standard chemotherapeutic agent for its treatment. Interestingly, a common mutation in the isocitrate dehydrogenase 1 (IDH1) gene among glioma patients has shown to be a major molecular determinant influencing prognosis and therapeutic responsiveness to TMZ. Despite such clinical relevance, understanding the molecular mechanism behind the effect of IDH1 in the progression of disease still remains unclear.
 
Objectives: In this study, an integrative analysis of transcriptome, global proteome and phosphoproteome was performed to identify cellular pathways regulated by IDH1 mutation and their key regulatory molecules in glioma.
 
Methods: CRISPR-Cas9 genome editing was employed to generate IDH1R132H/WT mutated U-87 MG GBM cell-lines. WT and IDH1 mutant cells were subjected to mRNA sequencing as well as MS-based global and phosphoproteome profiling. For proteomic analyses, a modified filter-aided sample preparation method (FASP) was applied along with isobaric labeling, and a DO-NCFC-RP/RP LC system was combined with an Orbitrap HF-X mass spectrometer. Public transcriptomic data from TCGA GBM cohort and TMZ treated patient samples were also taken for analysis. Across all datasets, differentially expressed genes/proteins (DEGs/DEPs) were identified to obtain molecular candidates affected from IDH1 mutation.
 
Results: Based on our findings, we proposed a network model suggesting a suppression effect of TGF-β signaling from the IDH1-CAV1-TGFBR axis resulting in reduction of CTSK-collagen module. This molecular cascade may underlie the favorable outcome observed in IDH1-mutant gliomas. In-vivo models demonstrated the inhibition of CTSK with odanacatib can significantly enhance TMZ efficacy.
 
Conclusion/implications for practice or policy: Collectively, our findings suggest a molecular mechanism centering the suppression of TGF-β signaling in effect of the IDH1 mutation highlighting downregulation of CTSK as a key contributor. From these results, we suggest co-treatment of CTSK inhibitor with TMZ as a potential treatment strategy for aggressive or TMZ-resistant glioma patients.