Abstract
To label proteins with positron emitters with a half-life in the order of days, a method has been developed to label proteins with zirconium (Zr)-isotopes. Therefore, the bifunctional chelating agent desferal (Df) was coupled to albumins via a thioether bond. Labeling of the premodified proteins was easily performed by addition of these proteins to freeze-dried Zr-oxalate. This labeling was efficient (> 90%) and accomplished in several minutes. The conjugates showed a high in vitro stability. Biodistribution studies were performed with 88Zr-citrate, 88Zr-Df, and 88Zr-labeled mouse serum albumin ( 88Zr-Df-MSA), modified with different amounts of chelating groups. Whereas Zr-citrate was found to accumulate in bone, Zr-Df was cleared very fast by glomerular filtration. The 88Zr-Df-MSA showed similar blood clearance as did 123I-labeled MSA. The biodistribution pattern of 88Zr-Df-MSA differed only from 123I-MSA in that a higher accumulation of Zr in liver, kidney, and spleen was found. The absence of large amounts of 88Zr in bone indicated that in vivo the conjugates are also reasonably stable.
Highlights
Positron emission tomography (PET) LS a noninvasive imaging technique that provides quantitative data on the biodistribution of radiolabeled compounds
Its production must be simple and inexpensive, and it should not give off radionuclidic impurities
The radionuclide should by preference have a high percentage of positron emission as the only form of decay
Summary
Positron emission tomography (PET) LS a noninvasive imaging technique that provides quantitative data on the biodistribution of radiolabeled compounds. A method to label proteins with positron emitting nuclides might be valuable, considering the ubiquitousness of proteins and peptides and their role in many disease processes. The positron emitter must fulfill several requirements. Its production must be simple and inexpensive, and it should not give off radionuclidic impurities. The radionuclide should by preference have a high percentage of positron emission as the only form of decay. Protems have been labeled with several positron-emitting isotopes such as “F (tljz = 110 min; 7, 13,31), 68Ga (t’,* = 68 min; 31), 64Cu (t,,* = 12.7 h; 20, 25, 32), and 55Co (t,,* = 17.5 h; 22, 37)
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