Mechanism for enhanced 5-aminolevulinic acid fluorescence in isocitrate dehydrogenase 1 mutant malignant gliomas

Abstract

Fluorescence-guided surgery using 5-aminolevulinic acid (5-ALA) has become main modality in the treatment of malignant gliomas. However unlike glioblastomas, there are inconsistent result about fluorescence status in WHO grade III gliomas. Here, we have shown that mutational status of IDH1 is bind to 5-ALA fluorescence, and investigated its mechanism. Using genetically engineered malignant glioma cells harboring wild type (U87MG-IDH1WT, U87MG-IDH2WT) or mutant (U87MG-IDH1R132H, U87MG-IDH2R132K) versions of IDH1 and IDH2, we confirmed a lag in 5-ALA metabolism and a temporary accumulation of protoporphyrin IX (PpIX) in U87MG-IDH1R132H and U87MG-IDH2R132K cells. To investigate the metabolic aspects of the mechanism responsible, we used liquid chromatography?mass spectrometry (LC-MS) to screen for tricarboxylic acid (TCA) cycle-related metabolite changes resulting from 5-ALA exposure. We observed low baseline levels of NADPH, an essential cofactor for the rate-limiting step of heme degradation, in U87MG-IDH1R132H cells. Abundant levels of NADPH are required to metabolize excessive 5-ALA, giving a plausible reason for the temporary enhanced 5-ALA fluorescence in mutant IDH1 cells. This hypothesis was supported by the results of metabolic screening in human malignant glioma samples. In conclusion, we have discovered a relationship between enhanced 5-ALA fluorescence and IDH1 mutations in WHO grade III gliomas. Low baseline levels of NADPH in tumors with mutated IDH1 is responsible for the enhanced fluorescence from the metabolic aspects of the mechanism.