Iodination radiolabeling

Stein R, Govindan S V, Mattes M J, et al. (2003). Improved iodine radiolabels for monoclonal antibody therapy. Cancer Res. 63 111-118. 

Stein R, Goldenberg D M, Thorpe S R, et al. (1995). Effects of radiolabeling monoclonal antibodies with a residualizing iodine radiolabel in the accretion of radioisotope in tumors. Cancer Res. 55 3132-3139. 

The mechanism of iodination radiolabeling involves reactive iodine, generated by enzymatic or chemical oxidation of isotopic sodium iodide, reacting as an... 

Radiolabel 55 nmol of SASD using IODO-GEN (Thermo Fisher) and 40 pCi Na 125I for 30 seconds. Do not use chloramine-T, since termination of the iodination reaction with this reagent involves addition of a reducing agent which may cleave the disulfide bonds of the crosslinker. 

These factors make 125I the iodine label of choice for radiolabeling biological molecules. Its commercial availability from a number of suppliers at relatively low cost further adds to its popularity. Even though it has lower specific activity than 131I, iodine-125 still provides much greater sensitivity than 14C, 32P, 35S, or 3H in labeling biomolecules. In fact, the use of a radioactive iodine label can create probes that have 150-fold more sensitivity than tritiated molecules and as much as 35,000 times the detectability of 14C-labeled molecules (Bolton and Hunter, 1986). 

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. 

The following procedure describes the iodination process for the Bolton-Hunter reagent and its subsequent use for the radiolabeling of protein molecules. Modification of other macromolecules can be done using the same general method. For particular labeling applications, optimization of the level of iodine incorporation may have to be done to obtain the best specific radioactivity with retention of biological activity. 

Hnatowich, D. J. (1990) Recent developments in the radiolabeling of antibodies with iodine, indium, and technetium. Sem. Nuclear. Med. 20, 80-91. 

An allied application of radiolabelled anti-tumour monoclonal antibodies is that of diagnostic imaging (immunoscintigraphy). In this case, the radioisotope employed must be a y-emitter (such that the radioactivity can penetrate outward through the body for detection purposes). Although various radioisotopes of iodine have been evaluated, (technetium) is the one... 

E.G. Robins, F. Brady, S.K. Luthra, Hypervalent iodine reagents as precursors for radiolabelling pyrimidines using n.c.a. [ F]fluoride, J. Label. Compds Radiopharm. 48 (2005) SI45. 

Polymer precursors of radiolabeled 4-13 iodine benzoic, (I), and amide derivatives were previously prepared by the authors (4) as illustrated in Eq. (3). 

The following sparingly soluble chloroamide together with I will also iodinate tyrosine and can be used to incorporate radiolabeled iodine into proteins.285,286... 

Polystyrene-bound alkenes react with alcohols or amines in the presence of mercury(II) trifluoroacetate to yield 2-alkoxy- or 2-aminoethylmercury compounds [30]. The C-Hg bond can be reduced to a C-H bond by treatment with LiBH4, or converted into a C-I bond by treatment with iodine [30]. Organomercury compounds have been immobilized with polystyrene-bound carboxylates [31]. The resulting product was used as starting material for the preparation of radiolabelled 6-iodo DOPA (Figure 4.4). 

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