MSACL 2024 Abstract

Introduction: Glioma is the most common neoplasm in the central nervous system with tumor resection as the primary treatment option and total tumor resection being associated with better patient outcomes. However, gross total resection is difficult to achieve due to the infiltrative nature of glioma. Thus, rapid detection of molecular features with high sensitivity and minimal to no sample preparation is crucial for intraoperative diagnosis. Isocitrate dehydrogenase (IDH) mutation status plays a critical role in the diagnosis and prognosis as patients with IDH-mutant glioma exhibit higher survival rates. However, IDH mutations are commonly determined by immunohistochemistry (IHC) and genetic testing, methods that are incompatible with intraoperative evaluation. Mutations in IDH enzymes lead to the accumulation of an oncometabolite, 2-hydroxyglutarate (2HG), which is the product of α-ketoglutaric acid reduction in a nicotinamide adenine dinucleotide phosphate (NADPH)-dependent manner. Consequently, elevated concentrations of 2HG are associated with IDH-mutant glioma, which can play a significant role in the assessment of IDH mutation status in glioma. Desorption electrospray ionization mass spectrometry (DESI-MS) enables rapid and sensitive detection of 2HG in glioma biopsies. Cystathionine, a key intermediate in the transsulfuration pathway, has been found in high concentrations in glioma tumors, and it too can be detected by DESI-MS and targeted as a potential biomarker in glioma samples.

Objectives: In this study, DESI-MS is used for intraoperative assessment of IDH mutation status in glioma patients by measuring relative 2HG concentration in less than two minutes.
Methods: Adult patients undergoing glioma resection were recruited and their biopsied tissues were analyzed during surgery by DESI-MS. Tumor biopsies were smeared on glass slides and analyzed by DESI-MS with no subsequent sample treatment. Measurements were done in MS/MS mode to improve specificity and minimize matrix interferences. Signals for 2HG fragment ions were measured relative to those of glutamate (Glu), as the endogenous reference molecule.

Results: The DESI-MS predictions of IDH mutation status made on 129 core samples from 34 patients agreed with IHC and/or polymerase chain reaction (PCR) results (sensitivity, specificity, and accuracy all 100%). In addition, 2HG was observed in 80% of the margin biopsies indicating that the tumor infiltrates beyond the surgical margins. Initial offline studies of cystathionine revealed high concentrations in IDH-mutant and IDH-wildtype tumors compared to the normal mouse brain.

Conclusions:
IDH mutation status was assessed correctly through direct analysis of brain biopsies by DESI-MS in less than two minutes. IDH-mutant glioma samples were strongly associated with high concentrations of 2HG. Elevated concentrations of 2HG in margin biopsies show that tumor infiltration beyond surgical margins is common. The results show the value of DESI-MS as a rapid and sensitive tool for intraoperative evaluation of glioma with the potential for achieving better patient outcomes.