Production, quality control and biodistribiotion studies of 170Tm-DOTA-NHS-Cetuximab

Introduction: Antibodies with specificity towards tumour antigens can be labelled with radionuclides to enable diagnostic imaging (e.g. SPECT or PET) or to improve therapeutic efficiency. Combining beta-particle and gamma emission effect with therapeutic properties of C225 monoclonal antibody, Cetuximab (Erbitux, Merck Pharmaceuticals) was targeted in this study. Methods: The C225 antibody was labeled with 170Tm-Thulium chloride (100 MBq) after conjugation with in-house freshly prepared 1,4,7,10-tetraazacyclododecane-N,N,N,N-tetraacetic acid mono-(N-hydroxysuccinimidyl) ester (DOTA-NHS). Conjugated-cetuximab was obtained by the addition of 0.5 ml of a cetuximab pharmaceutical solution (1 mg, in phosphate buffer, pH = 8) to a glass tube precoated with freshly prepared DOTA-NHS (~5 mg) at 25°C. 170Tm-Thulium chloride was obtained by a thermal neutron flux (3-4 × 1013 n cm-2 s-1) of a natural thulium nitrate sample, dissolved in acidic media. Radiolabeling was performed in 2-3 hours by the addition of DOTA-NHS-Cetuximab conjugate at room temperature. Results: Radiochemical purity of 92% (ITLC, DTPA 1mM) was obtained for the final radioimmunoconjugate (specific activity = 72 TBq/mmol). Biodistribution studies in normal rats were performed to determine radioimmunoconjugate distribution up to 24 h. Stability of radiolabeled protein in presence of human serum was tested at 37 C for up to 72h and it was observed that the botained formulation is stable even up to one month after preparation. Conclusion: For [170Tm]-DOTA-NHS-Cetuximab, the radiochemical purity was 92% and the labeling and quality control took less than 1 h. The radiolabeled complex was stable in human serum for at least 72 h and no significant amount of free 170Tm as well as 170Tm-DOTA-NHS was observed. The final preparation was administered to normal rats and biodistribution of the radiopharmaceutical was checked 2-168 h later. The prepared radio-labeled cetuximab using 170Tm can be applied to improve the therapeutic potential of (epidermal growth factor receptor) EGFR -targeted drugs. The use of these selective labeled agents in nuclear medicine applications may facilitate in vivo EGFR-targeted drug efficacy.