Radiosynthesis and biological evaluation of [¹⁸F]AG-120 for PET imaging of the mutant isocitrate dehydrogenase 1 in gliomas

Gliomas are clinically challenging tumors due to their location and invasiveness nature, which often hinder complete surgical resection. The evaluation of the isocitrate dehydrogenase mutation status has become crucial for effective patient stratification. Through a transdisciplinary approach, we have developed an 18F-labeled ligand for non-invasive assessment of the IDH1R132H variant by using positron emission tomography (PET) imaging. In this study, we successfully prepared diastereomerically pure [¹⁸F]AG-120 with a copper-mediated radiofluorination approach of the stannyl precursor 6 without azeotropic drying on a TRACERlab FX2 N radiosynthesis module. In vitro internalization studies demonstrated significantly higher uptake of [¹⁸F]AG-120 in mutant IDH1R132H-U251 human high-grade glioma cells compared to wild-type IDH1-U251 cells (0.4 vs. 0.013% applied dose/μg protein at 120 min). In vivo studies conducted in mice, exhibited the excellent metabolic stability of [¹⁸F]AG-120, with parent fractions of 85% and 91% in plasma and brain at 30 min p.i., respectively. Dynamic PET studies with [¹⁸F]AG-120 in naïve mice and orthotopic glioma rat model reveal limited blood-brain barrier permeation along with a low uptake in the brain tumor. Interestingly, there was no significant difference in uptake between mutant IDH1R132H- and wild-type IDH1-tumors (tumor-to-blood ratio [40-60min]: ~1.7 vs. ~1.3). In conclusion, our preclinical evaluation demonstrated a target-specific internalization of [¹⁸F]AG-120 in vitro, a high metabolic stability in vivo in mice, and a slightly higher accumulation of activity in IDH1R132H-glioma compared to IDH1-glioma. Overall, our findings contribute to advancing the field of molecular imaging and encourage the evaluation of [¹⁸F]AG-120 to improve diagnosis and management of gliomas and other IDH1R132H-related tumors.