Browsing by Subject "Radioiodine"

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    Radiolabeled inhibitors as probes for imaging mutant IDH1 expression in gliomas: Synthesis and preliminary evaluation of labeled butyl-phenyl sulfonamide analogs.
    (Eur J Med Chem, 2016-08-25) Chitneni, Satish K; Reitman, Zachary J; Gooden, David M; Yan, Hai; Zalutsky, Michael R
    INTRODUCTION: Malignant gliomas frequently harbor mutations in the isocitrate dehydrogenase 1 (IDH1) gene. Studies suggest that IDH mutation contributes to tumor pathogenesis through mechanisms that are mediated by the neomorphic metabolite of the mutant IDH1 enzyme, 2-hydroxyglutarate (2-HG). The aim of this work was to synthesize and evaluate radiolabeled compounds that bind to the mutant IDH1 enzyme with the goal of enabling noninvasive imaging of mutant IDH1 expression in gliomas by positron emission tomography (PET). METHODS: A small library of nonradioactive analogs were designed and synthesized based on the chemical structure of reported butyl-phenyl sulfonamide inhibitors of mutant IDH1. Enzyme inhibition assays were conducted using purified mutant IDH1 enzyme, IDH1-R132H, to determine the IC50 and the maximal inhibitory efficiency of the synthesized compounds. Selected compounds, 1 and 4, were labeled with radioiodine ((125)I) and/or (18)F using bromo- and phenol precursors, respectively. In vivo behavior of the labeled inhibitors was studied by conducting tissue distribution studies with [(125)I]1 in normal mice. Cell uptake studies were conducted using an isogenic astrocytoma cell line that carried a native IDH1-R132H mutation to evaluate the potential uptake of the labeled inhibitors in IDH1-mutated tumor cells. RESULTS: Enzyme inhibition assays showed good inhibitory potency for compounds that have iodine or a fluoroethoxy substituent at the ortho position of the phenyl ring in compounds 1 and 4 with IC50 values of 1.7 μM and 2.3 μM, respectively. Compounds 1 and 4 inhibited mutant IDH1 activity and decreased the production of 2-HG in an IDH1-mutated astrocytoma cell line. Radiolabeling of 1 and 4 was achieved with an average radiochemical yield of 56.6 ± 20.1% for [(125)I]1 (n = 4) and 67.5 ± 6.6% for [(18)F]4 (n = 3). [(125)I]1 exhibited favorable biodistribution characteristics in normal mice, with rapid clearance from the blood and elimination via the hepatobiliary system by 4 h after injection. The uptake of [(125)I]1 in tumor cells positive for IDH1-R132H was significantly higher compared to isogenic WT-IDH1 controls, with a maximal uptake ratio of 1.67 at 3 h post injection. Co-incubation of the labeled inhibitors with the corresponding nonradioactive analogs, and decreasing the normal concentrations of FBS (10%) in the incubation media substantially increased the uptake of the labeled inhibitors in both the IDH1-mutant and WT-IDH1 tumor cell lines, suggesting significant non-specific binding of the synthesized labeled butyl-phenyl sulfonamide inhibitors. CONCLUSIONS: These data demonstrate the feasibility of developing radiolabeled probes for the mutant IDH1 enzyme based on enzyme inhibitors. Further optimization of the labeled inhibitors by modifying the chemical structure to decrease the lipophilicity and to increase potency may yield compounds with improved characteristics as probes for imaging mutant IDH1 expression in tumors.
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    Stapled peptides as scaffolds for developing radiotracers for intracellular targets: Preliminary evaluation of a radioiodinated MDM2-binding stapled peptide in the SJSA-1 osteosarcoma model.
    (Bioorganic & medicinal chemistry letters, 2022-04-15) Zhou, Zhengyuan; Zalutsky, Michael R; Chitneni, Satish K
    Stapled peptides are promising scaffolds for inhibiting protein-protein interactions in cells, including between the intracellular oncoprotein MDM2 and p53. Herein, we have investigated the potential utility of a stapled peptide, VIP116, for developing radiolabeled agents targeting MDM2. VIP116 was radioiodinated using the prosthetic agent N-succinimidyl-3-[*I]iodobenzoate ([*I]SIB). The resulting labeled peptide [*I]SIB-VIP116 exhibited high uptake (165.3 ± 27.7%/mg protein) and specificity in SJSA-1 tumor cells. Tissue distribution studies of [*I]SIB-VIP116 revealed a peak tumor uptake of 2.19 ± 0.56 percent injected dose per gram (%ID/g) in SJSA-1 xenografts at 2 h post-injection, which was stable until 6 h. [*I]SIB-VIP116 exhibited high activity (8.33 ± 1.18%ID/g) in the blood pool but had high tumor-to-muscle ratios (12.0 ± 5.7), at 30 min. Metabolic stability studies in mice indicated that about 80% of the activity in plasma was intact [*I]SIB-VIP116 at 4 h. Our results confirm the cell permeability and specific binding of [*I]SIB-VIP116 to MDM2 and the suitability of the VIP116 scaffold for radiolabeled probe development.