Selective binding to monoamine oxidase a : in vitro and in vivo evaluation of f-18-labeled beta-carboline derivatives

In this study we synthesized four different F-18-labeling precursors for the visualization of the monoamino oxidase A using harmol derivatives. Whereas two are for prosthetic group labeling using [F-18]fluoro-d(2)-methyl tosylate and 2-[F-18]fluoroethyl-tosylate, the other three precursors are for direct nucleophilic F-18-labeling. Additionally the corresponding reference compounds were synthesized. The syntheses of [F-18]fluoro-d(2)-methyl-harmol and 2-[F-18] fluoroethyl-harmol were carried out using harmol as starting material. For direct nucleophilic F-18-labeling of the tracers carrying oligoethyled spacers (PEG), a toluenesulfonyl leaving group was employed. The radiolabeling, purification and formulation for each tracer was optimized and evaluated in vitro and in vivo. Stability tests in human serum showed that all tracers were stable over the observation period of 60 min. mu PET studies using of the synthesized tracers revealed that the tracers carrying PEG spacers showed no sufficient brain uptake. Consequently, the F-18-fuoro alkylated tracers [F-18] fluoro-d2-methyl-harmol and 2-[F-18]fluoroethyl-harmol were further evaluated showing SUVs in the brain of 1.0 +/- 0.2 g/mL and 3.4 +/- 0.5 g/mL after 45 min, respectively. In blockade studies the selectivity and specificity of both tracers were demonstrated. However, for [F-18]fluoro-d(2)-methyl-harmol a rapid washout from the brain was also observed. In vitro binding assays revealed that 2-[F-18] fluoroethyl-harmol (IC50 = 0.54 +/- 0.06 nM) has a higher affinity than the F-18-fluoro-d(2)-methylated ligand (IC50 = 12.2 +/- 0.6 nM), making 2-[F-18] fluoroethyl-harmol superior to the other evaluated compounds and a promising tracer for PET imaging of the MAO A

Tryptophan metabolism is inversely regulated in the tumor and blood of patients with glioblastoma

Tryptophan (Trp)-catabolic enzymes (TCEs) produce metabolites that activate the aryl hydrocarbon receptor (AHR) and promote tumor progression and immunosuppression in glioblastoma. As therapies targeting TCEs or AHR become available, a better understanding of Trp metabolism is required. Methods: The combination of LC-MS/MS with chemical isobaric labeling enabled the simultaneous quantitative comparison of Trp and its amino group-bearing metabolites in multiple samples. We applied this method to the sera of a cohort of 43 recurrent glioblastoma patients and 43 age- and sex-matched healthy controls. Tumor volumes were measured in MRI data using an artificial neural network-based approach. MALDI MSI visualized Trp and its direct metabolite N-formylkynurenine (FK) in glioblastoma tissue. Analysis of scRNA-seq data was used to detect the presence of Trp metabolism and AHR activity in different cell types in glioblastoma. Results: Compared to healthy controls, glioblastoma patients showed decreased serum Trp levels. Surprisingly, the levels of Trp metabolites were also reduced. The decrease became smaller with more enzymatic steps between Trp and its metabolites, suggesting that Trp availability controls the levels of its systemic metabolites. High tumor volume associated with low systemic metabolite levels and low systemic kynurenine levels associated with worse overall survival. MALDI MSI demonstrated heterogeneity of Trp catabolism across glioblastoma tissues. Analysis of scRNA-seq data revealed that genes involved in Trp metabolism were expressed in almost all the cell types in glioblastoma and that most cell types, in particular macrophages and T cells, exhibited AHR activation. Moreover, high AHR activity associated with reduced overall survival in the glioblastoma TCGA dataset.Conclusion: The novel techniques we developed could support the identification of patients that may benefit from therapies targeting TCEs or AHR activatio