Poster presented at the 11th International Symposium on the Synthesis and Applications of Isotopes and Isotopically Labelled Compounds (IIS 2012) in Heidelberg, 9-13 September, 2012.Isotopically labeled therapeutic proteins are used in in vivo studies where either sensitive assays are necessary or it is desirable to distinguish a pulse dose of therapeutic protein from endogenous material. Traditionally isotopes of choice are those with the relatively short half-life (eg 125I, t½ 60.25 days) necessary to achieve the high specific activities that drives assay sensitivity.
However, use of these isotopes limits the experimental timeframe and raises safety issues. These problems can be overcome by 14C-labeling proteins and using the ultra-sensitive isotope ratio measurement technology of accelerator mass spectrometry (AMS). AMS utilizes a high-voltage accelerator to efficiently separate and measure individual isotopic ions, thereby achieving sensitivities in the attomole range  whilst enabling much reduced amounts of radioactivity to be used. Here we describe methods for the labeling of proteins with 14C for AMS analysis and approaches to the subsequent analysis of samples to achieve high sensitivity and specificity.
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