Preparation and preclinical evaluation of 177Lu-nimotuzumab targeting epidermal growth factor receptor overexpressing tumors

Objectives Nimotuzumab (h-R3) is a humanized monoclonal antibody (mAb) which recognizes the external domain of the epidermal growth factor receptor (EGFR) with high specificity. It was demonstrated that h-R3 has a unique clinical profile for immunotherapy of adult gliomas and pediatric pontine gliomas. The aim of this work was to evaluate the conjugate 177 Lu-h-R3 as a potential radioimmunoconjugate for radioimmunotherapy (RIT) of tumors overexpressing EGFR. Methods h-R3 was modified with the macrocylcic ligand S -2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid ( p -SCN-Bn-DOTA) and the acyclic ligand S -2-(4-Isothiocyanatobenzyl)-diethylenetriamine pentaacetic acid ( p -SCN-Bn-DTPA); the immunoconjugates were labeled with no-carried added 177 Lu. Specificity and affinity were tested using radioimmunoassays in a cell line overexpressing EGFR. Biodistribution in mice, healthy or bearing A431 epithelial carcinoma xenografts, was performed for 11 days. Tumor uptake, the influence of the nature of the chelate and the way of administration were studied. Absorbed dose in tumor and selected organs was calculated using the OLINDA/EXM software; the data from the animals was extrapolated to humans. Results 177 Lu-h-R3 conjugates were obtained with specific activity up to 915 MBq/mg without significant loss of immunoreactivity. The binding of 177 Lu-h-R3 conjugates to A431 cells showed to be EGFR specific, and the affinity was similar to native h-R3. Tumor uptake reached a maximum value of 22.4±3.1 %ID/g at 72 h and remained ∼20% ID/g over 1 week. Locoregional application showed better tumor/nontumor ratios than intravenous application. Conclusions 177 Lu-h-R3 should be considered for further evaluations as a potential radiopharmaceutical for RIT of tumors overexpressing EGFR.