In vitro applications of radiolabelled antibodies

The principle in vitro types of application are for radioimmuno- (or related) assay and pre-clinical development studies prior to future in vivo use, but antibodies may also be labelled for use as probes in immunocytochemistiy. Western blots, or for immunoprecipitation. The choice of radionuclide will depend upon such factors as ease of tracer preparation, ease and efficiency of detection (counting or autoradiography), shelf-life of radiotracer, cost, and safety. A list of some of the most common radionuclides which might be employed for preparation of radiotracers with applications in vitro, together with their physical decay properties is shown in Table 1. 

While the soft beta emitters, tritium, carbon-14, and sulfur-35 are widely used for synthesis of radiotracers by commercial sources, they are not commonly used for the preparation of tracers in academic laboratories. Although antibodies can be labelled with these isotopes, the main advantage of these radionuclides is their high resolution for autoradiographic studies, and, while 

Radionuclide Type of decay Eneigy (MeV) pmax Ev Half-life 

The radiolabelling grade of radioiodine purchased from commercial suppliers will be in the form of sodium iodide. It will be essentially carrier free (i.e. uncontaminated ty stable iodine-127) and is normally dissolved in sodium hydroxide solution (typically O.Ol-O.OOl M) at concentrations of about 100 mCi (3.7 GBq)/ml. The function of the hydroxide ions are to maintain the chemical state of the iodide and prevent formation of volatile radioiodine molecules. Freshly prepared and purchased solutions of radioiodine will invariably give the best labelling efficiencies but with time, radiolysis produces free radicals which react with the iodide ions to produce non-reactive by-products. Nevertheless radioiodine solutions stored (at room temperature) for one to two months will normally give acceptable results. 

Radfoiodination with iodine-125 using Chloramine-T as oxidant 

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