Development of [¹⁸F]AG-120 as radiotracer for the detection by positron emission tomography (PET) of the mutant isocitrate dehydrogenase 1 in glioma:

Background: Mutations of isocitrate dehydrogenase (IDH) enzymes are frequent alterations in glioma - the most common being the IDH1R132H - and their identification has become essential for patient stratification. Here, we propose a transdisciplinary approach to develop an ¹⁸F-labeled ligand to detect the IDH1R132H protein directly and non-invasively by PET.
Material and Methods: Radiosynthesis was performed using the TRACERlab FX2 N automated radiosynthesizer. In vitro evaluation of inhibitory potency, binding affinity, and cell uptake of [¹⁸F]AG-120 was performed using U251 human glioblastoma cells stably transfected with IDH1 or IDH1R132H. In vivo metabolism was investigated in CD-1 mice, and dynamic PET scans (NanoScan®PET/CT) were performed in nude rats bearing U251-IDH1 or U251-IDH1R132H glioblastoma.
Results: AG-120 shows a high inhibitory potency toward IDH1R132H (IC50=5.11 nM). Diastereomerically pure [¹⁸F]AG-120 was produced by an automated copper-mediated radiofluorination. Internalization studies showed a higher uptake of [18F]AG-120 in U251-IDH1R132H cells compared to that in U251-IDH1 cells (0.4 vs. 0.013% ID/μg protein at 120 min), which was suppressed by self-blocking (0.009% ID/μg protein at 120 min). Excellent metabolic stability in vivo was demonstrated (parent fractions in plasma and brain at 30 min p.i.: 85% and 91%, respectively). Low initial uptake in tumors of both models (TAC-peak value ~0.4 SUV) was observed. A slightly higher retention in IDH1R132H- compared to IDH1-tumors (Tumor-to-Background Ratio[30-60min]: ~1.6 vs. ~1.1) was detected.
Conclusion: We have successfully automated the production of [¹⁸F]AG-120 and gained valuable insights into its interactions with IDH1 and IDH1R132H. [¹⁸F]AG-120 will serve as a reference compound for future evaluations of mIDH inhibitors/radioligands and may have applications in peripheral tumors, such as chondrosarcoma.
Acknowledgements: This work was funded by the the European-Regional-Development-Fund and the Sächsische-Aufbaubank (project no. 100364142). We thank Dr. Jacqueline Kessler and Prof. Dirk Vordermark, Department of Radiotherapy, Martin Luther University Halle-Wittenberg, Halle, Germany, for providing the cells.