New Lyophilized Kit for Rapid Radiofluorination of Peptides

Radio labeling compounds with positron-emitting radionuclides often involves a time-consuming, customized process. Herein, we report a simple lyophilized kit formulation for labeling peptides with F-18, based on the aluminum-fluoride procedure. The prototype kit contains IMP485, a NODA (1,4,7-triazacyclononane-1,4-diacetate)-MPAA (methyl phenylacetic acid)-di-HSG (histaminesuccinyl-glycine) hapten-peptide, [NODA-MPAA-D-Lys(HSG)-D-Tyr-D-Lys(HSG)-NH2], used for pretargeting, but we also examined a similar kit formulation for a somatostatin-binding peptide [IMP466, NOTA-D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Throl] bearing a NOTA ligand to determine if the benefits of using a kit can be extended to other AlF-binding peptides. The NODA-MPAA ligand forms a single stable complex with (AlF)(2+) in high yields. In order to establish suitable conditions for a facile kit, the formulation was optimized for pH, peptide to Al3+ ratio, bulking agent, radioprotectant, and the buffer. For optimal labeling, the kit was reconstituted with an aqueous solution of F-18(-) and ethanol (1:1), heated at 100-110 degrees C for 15 min, and then simply and rapidly purified using one of two equally effective solid-phase extraction (SPE) methods. (AlF)-F-18-IMP485 was isolated as a single isomer complex, in high yield (45-97%) and high specific activity (up to 223 GBq/mu mol), within 20 min. The labeled product was stable in human serum at 37 degrees C for 4 h and in vivo, urine samples showed the intact product was eliminated. Tumor targeting of the (AlF)-F-18-IMP485 in nude mice bearing human colon cancer xenografts pretargeted with an anti-CEACAM5 bispecific antibody showed very low uptake (0.06% +/- 0.02 ID/g) in bone, further illustrating its stability. At 1 h, pretargeted animals had high (AlF)-F-18-IMP485 tumor uptake (28.1% +/- 4.5 ID/g), with ratios of 9 +/- 4, 123 +/- 38, 110 +/- 43, and 120 +/- 108 for kidney, liver, blood and bone, respectively. Tumor uptake remained high at 3 h postinjection, with increased tumor/nontumor ratios. The NOTA-somatostatin-binding peptide also was fluorinated with good yield and high specific activity in the same kit formulation. However, yields were somewhat lower than those achieved with IMP485 containing the NODA-MPAA ligand, likely reflecting this ligand's superior binding properties over the simple NOTA These studies indicate that F-18-labeled peptides can be reproducibly prepared as stable Al-F complexes with good radiochemical yield and high specific activity using a simple, one-step, lyophilized kit followed by a rapid purification by SPE that provides the F-18-peptide ready for patient injection within 30 min.