Radiosynthesis and biological evaluation of [¹ ⁸F]AG-120 as imaging agent for the detection of the mutant isocitrate dehydrogenase 1 in glioma by PET

Introduction: Glioma are clinically challenging tumors due to their location and invasiveness, limiting their complete surgical resection. Mutated isocitrate dehydrogenase enzymes (IDH) are frequent alterations - the most common being the IDH1R132H - expressed only in glioma but not in healthy brain, correlating with prognosis. Hence, the evaluation of the IDH mutation status has become essential in clinical patient stratification. Currently, the IDH mutations are determined either directly by invasive biopsies or indirectly by magnetic resonance spectroscopy. Here, we propose a transdisciplinary approach to develop an 18F-labeled ligand to detect the IDH1R132H protein directly and non-invasively by positron emission tomography (PET) imaging. Such an imaging tool could improve the selection of cancer patients who are most likely to benefit from precision medicine. In the present study, we performed the radiofluorination of AG-120 (Ivosidenib), an FDA-approved small molecule inhibitor of mutant-IDH. Methods: The stannyl precursor (HL174) was synthetized according to the published synthesis of AG-120 [1] with minor modifications. The radiosynthesis was performed by copper-mediated radiofluorination of HL174 (Fig. 1) using a TRACERlab FX2 N synthesis module. The inhibitory potency of AG-120 was measured with a diaphorase/resazurin coupled assay using recombinant IDH1R132H or IDH1 (n=2). Internalization of [18F]AG-120 were determined in vitro using U251 human glioblastoma cells stably transfected with IDH1 or IDH1R132H [2]. In vivo metabolism was investigated in healthy CD-1 mice (n=3) by radio-chromatographic analyses of plasma and brain tissue. Dynamic PET (Mediso, nanoScan® PET/CT) imaging studies were performed in nude rats bearing U251-IDH1 (n=2) or U251-IDH1R132H (n=2) glioblastoma. Results: For the first time, diastereomerically pure [18F]AG-120 was prepared by an automated copper-mediated radiolabelling approach without azeotropic drying starting from the stanny