Preparation of DOTA-dendron Cetuximab bioconjugates for radioimmunotherapy using ⁹⁰Y, ¹⁷⁷Lu and ⁶⁷Cu

In order to improve the efficiency of radioimmunotherapy by augmenting the specific activity of the radiolabeled bioconjugates while preserving their immunoreactivity, we prepared a water-soluble dendron bearing four 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid moieties by solidphase peptide synthesis. An N-hydoxysuccinimide ester of the dendron was synthesized and the dendron conjugated to lysine amino groups of the therapeutic monoclonal antibody Cetuximab which is specific for the epidermal growth factor receptor and overexpressed by various tumours. Dendron-bearing Cetuximab is thus used for treatment of colon, head, and neck cancer, so as to combine high specific activities brought by multilabeling to achieve a more effective targeted radionuclide therapy as it has been shown for Zevalin and Rituximab. The dendron to antibody ratio was determined by MALDI-TOF MS. These new conjugates have been radiolabeled by ⁶⁴Cu and ⁹⁰Y and higher specific activities have been obtained compared to monochelator- labeled antibody. positron emission tomography imaging in mice showed a significant tumour accumulation. Here we discuss the relationships between dendron to antibody ratio, antigen affinity and specific activity of monochelator and dendron-labeled Cetuximab conjugates.