Aim: The aim of this study was to investigate the in vivo and in vitro properties of 99mTc labelled monoclonal antibody, IOR CEA 1 when radiolabelled by different methods.
Methods: To achieve that purpose IOR CEA was directly radiolabelled via 2-mercaptoethanol (2-Me) and stannous ion (SnCl2) reduction and indirectly via the 2-iminothiolane (2-Im) conjugation. The resulting 99mTc-MoAbs were analysed for number of free sulfhydryl groups, chemical and radiochemical purity (checked by HPLC and SDS PAGE), immunoreactivity and biological distribution in mice.
Results: Experimental results indicated a similar radiochemical purity and immunoreactivity for direct labelling methods and a decrease of both for 2-Im method. 2-Me antibody reduction led to a high antibody fragmentation as indicated by non-denaturing SDS PAGE analysis. Nevertheless SnCl2 and 2-Im labels revealed lower in vivo stability.
Conclusion: 99mTc-(2-Me) IOR CEA presented favorable in vitro and in vivo properties. Therefore this label was compared to 99mTc-monoclonal antibody BW 431/26. Similar characteristics were found. Clinical studies also revealed identical biodistribution profile.