A new method for the labelling of proteins with radioactive arsenic isotopes

Radioarsenic labelled radiopharmaceuticals could be a valuable asset to positron emission tomography. In particular, the long half-lives of As-72 (T-1/2 = 26 h) and As-74 (T-1/2 = 17.8 d) allow to investigate slow physiological or metabolical processes, like the enrichment and distribution of monoclonal antibodies (mab) in tumour tissue. In this work, a new method for the labelling of proteins with various radioactive arsenic isotopes was developed. For this purpose, two proteins, namely a chimeric IgG(3) monoclonal antibody, ch3G4, directed against anionic phospholipids, and Rituxan (Rituximab), were labelled as a proof of principle with no-carrier-added radioarsenic isotopes (As-74 and As-77). The developed labelling chemistry gives high yields (> 99.9%), is reliable and could easily be transferred to automated labelling systems in a clinical environment. At least for the mab used in this work, this route of radioarsenic labelling does not affect the immunoreactivity of the product. The arsenic label stays stable for up to 72 h at the molecular mass of the monoclonal antibody, which is in particular relevant to follow the pharmacology and pharmacokinetics of the labelled mab for several days. (c) 2006 Elsevier B.V. All rights reserved.