Peptides radiolabelled

The number of technetium and rhenium tricarbonyl compounds in preclinical evaluation is remarkable. These efforts comprise small molecules as well as macromolecules useful in diagnostic and/or therapeutic nuclear medicine. There are also clinical data available with tumor affine peptides such as neurotensin receptor- and somatostatin receptor-targeting peptides radiolabeled with the Tc(CO)3 core. 

Zinn KR, Buchsbaum DJ, Chaudhuri T, Mountz JM, Kirkman RL, Rogers BE. Non-invasive monitoring of gene transfer using a reporter receptor imaged with a high affinity peptide radiolabeled with Tc or Re. J Nucl Med 2000 41 887-895. 

Peptide radiolabeling has been investigated by Sutcliffe et al. using conjugation of a... 

One of the first practical applications for these fluorescent labelled heparins was to examine the heparin binding behavior of different proteins and peptides under study in our laboratories. To this end we used a modification of the dot-blot assay described by Hirose and colleagues (13). F-D labelled heparin (-1 fluorescein/heparin) was radiolabelled with 125Iodine using iodobeads, to a specific activity of approximately 0.5 x 106 cpm/pg. Solutions of proteins with known heparin-binding capacities were dotted on nitrocellulose paper. A series of replicates... 

DTPA has also been used in the peptide-based " in-DTPA-octreotide. Octreotide is a shortened peptide analog of somatostatin designed to be more stable in vivo. Radiolabeling of octreotide for diagnostic imaging applications with radioisotopes for PET or SPECT has been investigated,... 

The immobilized immunoprecipitates are washed twice with lysis buffer containing 0.5 MNaCl and twice with buffer A. The beads are resuspended in 20 /il of kinase buffer also containing the appropriate concentration of the specific peptide. Reactions should also be set up without peptide as a negative control for nonspecific or self-incorporation of radiolabel. To start the reactions, 5 /il of ATP is added (final concentration 0.1 mM unlabeled ATP, 1 /iCi [7 -32P]ATP (per assay) in kinase buffer). The assays are allowed to proceed for 15 to 30 min at 30° with constant shaking at 900 rpm, and stopped by spotting 20 /il of the sample (slurry) onto a square (1.5 X 1.5 cm) of phosphocellulose (P81) paper. The P81 papers are immediately immersed in 500 ml of 1% (v/v) orthophosphoric acid, and then washed 3 times with the same solution (to remove the excess ATP). The washes therefore contain almost all of the radiolabel and must be handled carefully and disposed of appropriately. The papers are briefly rinsed in ethanol and air-dried. The incorporation of 32P-label is measured by Cerenkov counting. 

Each bead can iodinate up to 500 pg of tyrosine-containing protein or peptide. This translates into an oxidative capacity of about 0.55 pmol per bead. The rate of reaction can be controlled by changing the number of beads that are used and altering the sodium iodide concentration added to the reaction. Reaction volumes of 100-1,000 pi are possible per bead. The following protocol is suggested for iodinating proteins. Optimization should be done to determine the best incorporation level to obtain good radiolabel incorporation with retention of protein activity. 

Li, M., and Meares, C.F. (1993) Synthesis, metal chelate stability studies, and enzyme digestion of a peptide-liked DOTA derivatives and its corresponding radiolabeled immunoconjugates. Bioconjugate Chem. 4, 275-283. 

Peptide-derivatization of radionuclides has been used extensively, the advantages of these systems include their high affinity for the target, low toxicity, small size, hydrophilicity, and favorable pharmacokinetics, in addition to easy synthesis (and radiolabeling) routes. 

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