A new tripodal tris(hydroxypyridinone) bifunctional chelator for gallium allows easy production of (68)Ga-labelled proteins rapidly under mild conditions in high yields at exceptionally high specific activity and low concentration.

High radiolabeling efficiency, preferably to high specific activity, and good stability of the radioimmunoconjugate are essential features for a successful immunoconjugate for imaging or therapy. In this study, the radiolabeling efficiency, in vitro stability and biodistribution of immunoconjugates with eight different bifunctional chelators labeled with 64 Cu were compared. The anti-CD20 antibody, rituximab, was conjugated to four macrocyclic bifunctional chelators (p-SCN-Bn-DOTA, p- , three DTPA derivatives (p-SCN-Bn-DTPA, p-SCN-CHX-A"-DTPA and ITC-2B3M-DTPA) and a macrobicyclic hexamine ("sarcophagine") chelator (sar-CO 2 H) = (1-NH 2 -8-NHCO(CH 2 ) 3 CO 2 H)sar where sar = sarcophagine = 3, 6,10,13,16,19-hexaazabicyclo[6.6.6]icosane). Radiolabeling efficiency under various conditions, in vitro stability in serum at 37°C and in vivo biodistribution and imaging in normal mice over 48 h were studied. All chelators except sar-CO 2 H were conjugated to rituximab by thiourea bond formation with an average of 4.9 +/− 0.9 chelators per antibody molecule. Sar-CO 2 H was conjugated to rituximab by amide bond formation with 0.5 chelators per antibody molecule. Efficiencies of 64 Cu radiolabeling were dependent on the concentration of immunoconjugate. Notably, the 64 Cu-NOTA-rituximab conjugate demonstrated highest radiochemical yield (95%) under very dilute conditions (31 nM NOTA-rituximab conjugate). Similarly, sar-CO-rituximab, containing 1/10 th the number of chelators per antibody compared to other conjugates retained high labeling efficiency (98 %) at an antibody concentration of 250 nM. In contrast to the radioimmunoconjugates containing DTPA derivatives, which demonstrated poor serum stability, all macrocyclic radioimmunoconjugates were very stable in serum with <6 % dissociation of 64 Cu over 48 h. In vivo biodistribution profiles in normal female Balb/C mice were similar for all the macrocyclic radioimmunoconjugates with most of the activity remaining in the blood pool up to 48 h. Whilst all the macrocyclic bifunctional chelators are suitable for molecular imaging using 64 Cu-labeled antibody conjugates, NOTA and sar-CO 2 H show significant advantages over the others in that they can be radiolabeled rapidly at room temperature, under dilute conditions resulting in high specific activity. Europe PMC Funders Group

PurposeThe human sodium/iodide symporter (hNIS) is a well-established target in thyroid disease and reporter gene imaging using gamma emitters 123I-iodide, 131I-iodide and 99mTc-pertechnetate. However, no PET imaging agent is routinely available. The aim of this study was to prepare and evaluate 18F-labelled tetrafluoroborate ([18F]TFB) for PET imaging of hNIS.Methods[18F]TFB was prepared by isotopic exchange of BF4− with [18F]fluoride in hot hydrochloric acid and purified using an alumina column. Its identity, purity and stability in serum were determined by HPLC, thin-layer chromatography (TLC) and mass spectrometry. Its interaction with NIS was assessed in vitro using FRTL-5 rat thyroid cells, with and without stimulation by thyroid-stimulating hormone (TSH), in the presence and absence of perchlorate. Biodistribution and PET imaging studies were performed using BALB/c mice, with and without perchlorate inhibition.Results[18F]TFB was readily prepared with specific activity of 10 GBq/mg. It showed rapid accumulation in FRTL-5 cells that was stimulated by TSH and inhibited by perchlorate, and rapid specific accumulation in vivo in thyroid (SUV = 72 after 1 h) and stomach that was inhibited 95% by perchlorate.Conclusion[18F]TFB is an easily prepared PET imaging agent for rodent NIS and should be evaluated for hNIS PET imaging in humans.Electronic supplementary materialThe online version of this article (doi:10.1007/s00259-010-1523-0) contains supplementary material, which is available to authorized users.