Functional Imaging of Oxidative Stress with a Novel PET Imaging Agent, ¹⁸F-5-Fluoro-l-Aminosuberic Acid

2-step radiosynthesis and identification of ¹⁸F-FASu. HPLC of final product with γ detector demonstrates more than 98% radiochemical purity. HPLC of ¹⁹F-FASu standard with evaporative light scattering detector (ELSD) shows that differences in retention time of peaks matches 0.27-min (16-s) delay between the 2 detectors.

In vitro system x_c^- inhibition, uptake, and specificity studies in diethylmaleate-treated SKOV-3 cells. (A) Competitive inhibition of test agents on ³H-l-Glu uptake during 30-min incubation. l-Asp, l-Glu, l-aminoadipic acid, dl-aminopimelic acid, l-ASu, l-AAz, and l-aminosebacic acid are all anionic amino acids from 4 to 10 carbons (C₄–C₁₀) in length, respectively. Values are normalized to uptake of ³H-l-Glu in phosphate-buffered saline alone (mean ± SD, n = 3). (B) Comparison of direct cell uptake of ³H-l-ASu and ³H-l-Glu. ³H-l-ASu and ³H-l-Glu were matched for specific activity and radiation dose per sample. Uptake values are expressed as percentage of total activity used per well (mean ± SD, n = 3). (C) Comparison of ³H-l-Glu, ³H-l-ASu, and ³H-l-Leu uptake in presence of selected amino acid transporter inhibitors for 30 min. ³H-l-Glu, ³H-l-ASu, and ³H-l-Leu were matched for specific activity and radiation dose per sample. Values are normalized to uptake of each agent in phosphate-buffered saline alone (mean ± SD, n = 3). SSZ = sulfasalazine.

Uptake of HPLC-purified ¹⁸F-FASu in EL4 and SKOV-3 cells in vitro. (A) EL4 cells were evaluated for uptake of ³H-l-ASu and ¹⁸F-FASu in absence or presence of 1 mM l-Glu or l-ASu for 30 min. Uptake and inhibition profiles were similar for both radiolabeled compounds. Values are normalized to uptake of each agent in phosphate-buffered-saline-alone control (mean ± SD, n = 4). (B) ¹⁸F-FASu uptake in SKOV-3 cells in absence and presence of 0.5 mM sulfasalazine was evaluated with 5-, 20-, 40-, and 60-min incubations. Uptake values are raw CPM values per sample (mean ± SD, n = 3). SSZ = sulfasalazine.

In vivo biodistribution in CD-1 nude mice bearing EL4 xenograft tumors with HPLC-purified ¹⁸F-FASu. (A) ¹⁸F-FASu retention in clearance organs at 5, 30, 60, 120, and 240 min after injection are shown in %ID/organ. (B) ¹⁸F-FASu retention in tumor, blood, muscle, bone, brain, and liver. Data are %ID/g (mean ± SD, n ≥ 4).

¹⁸F-FASu PET imaging in CD-1 nude mice bearing SKOV-3 xenograft tumors 1 h after injection. Maximum-intensity-projection image of 1 of 2 SKOV-3 tumor–bearing nude mice imaged in this study; tumor is indicated by green arrow. ¹⁸F-FASu was HPLC-purified. On necropsy, it was determined that weight of this tumor was 31 mg.