18F-Labelled inhibitors for targeting of IDH1 mutant gliomas
Neumaier, Bernd (Corresponding author)
Cologni, Roberta / Holschbach, Marcus / Bier, Dirk / Carloni, Paolo
Computational Biomedicine; INM-9
Nuklearchemie; INM-5
2023
25th International Symposium on Radiopharmaceutical Sciences, Honolulu, USA (USA), 2023-05-22 - 2023-05-26
Conference Presentation
Neuroimaging


Objectives: Low grade diffuse gliomas are primary brain tumorscharacterized by the presence of mutations in isocitrate dehydrogen-ase 1 (IDH1), which equip the enzyme with a neomorphic activity thatincreases production of 2-hydroxyglutarate [1]. High concentrations ofthis oncometabolite are thought to interfere with histone methylationand cellular differentiation, thereby promoting gliomagenesis. Inaddition, mutated IDH1 (mIDH1) has been recognized as a keybiomarker for differential diagnosis, since it is not present in themore aggressive glioblastomas. While current approaches for detec-tion of mIDH1 require invasive tissue sampling, positron emissiontomography (PET) with mIDH1-selective probes could allow for non-invasive assessment of the IDH status. Here, we describe thepreparation, radiofluorination and preliminary biological evaluationof two candidate PET tracers derived from the mIDH1-selectiveinhibitor Olutasidenib.Methods: The boronic acid pinacol ester precursor for coppermediated radiofluorination was prepared using para bromoaniline asthe starting material and Ellman’s sulfinamide as chiral auxiliary forthe formation of the desired S-enantiomer. However, due to significantproduction of the undesired R-enantiomer, we ultimately decided toprepare and radiolabel both R- and S-enantiomer in order to comparethem in cellular uptake assays. For radiofluorination, [ 18 F]fluoride wasloaded onto an anion exchange cartridge and eluted with TEAB inMeOH followed by removal of MeOH. An equimolar solution ofradiolabeling precursor and copper mediator in 1,3-dimethyl-2-imidazolidinone was then added and the mixture was stirred in airat 100 °C for 15 minutes, followed by deprotection with 0.3 M NaOH inH2 O at 80°C for 3 minutes. After HPLC-purification and formulation inphysiological saline solution, the radiotracers were subjected to apreliminary evaluation in wildtype and mIDH1-transfected U-87 MGglioma cell lines.Results: The protected (S) and (R) radiolabeling precursors wereproduced in 15 steps and the 18F-labeled R,S-enantiomers 2 and 3 werefurnished in radiochemical yields of 60 ± 11%, radiochemical purities of>99% and molar activities of 102–237 GBq/μmol. Tracers lipophilicity(logD7.4 ) was found to be 2.53 if measured in PBS buffer but negativewhen measured in water (logP). No degradation was observed duringincubation in rat blood plasma at 37°C over 60 minutes. In contrast ifthe tracer was spotted onto silica plates full degradation was observed.Cell uptake experiments revealed a significantly higher uptake intransfected rather than wild type cells for both [ 18F]1 and S-[18 F]2 butwhile 90% of the first could reach the cytoplasm, the latter mostlyremained in the medium, suggesting that it may only partially cross thecellular membrane.Conclusion: Three 18F-labelled mIDH1-selective inhibitors havebeen successfully prepared and shown to exhibit significantly higheruptake into mIDH1-expressing compared to wildtype glioma cells. Apreclinical evaluation will be performed on [ 18 F]1, while furtherexperiments will be conducted on [ 18 F]2 to explain the unexpectedresults and subsequently compare them with the results of [ 18F]3.