Mass spectrometry characterization of DOTA-Nimotuzumab conjugate as precursor of an innovative β- tracer suitable in radio-guided surgery.

The aim of the present work has been the mass spectrometry characterization of the Nimotuzumab (NIM) antibody chemically modified with the bifunctional chelating agent para-S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraaza cyclododecanetetraacetic acid (p-SCN-Bn-DOTA). The conjugate, upon labeling with the pure β--emitter 90Y3+, could represent a promising candidate as radiotracer for an innovative radio-guided surgery (RGS) technique, developed and patented by researchers of our group, which uses a probe system for intraoperative detection of tumor residues exploiting the selective uptake of β--emitting tracers. The results reported in this study show that multiple DOTA molecules bind to lysine residues of both light and heavy chains of the antibody and, probably, some of them are linked to the variable region of antibody. Moreover, the new mass spectrometric analysis highlights the presence of unreacted NIM in the final product. The information obtained by this work is of fundamental importance in the perspective to utilize this conjugate as a radiocompound after its labeling with 90Y3+ radioisotope. Indeed, the conjugation efficiency and the presence of unreacted NIM affect the specific activity of the final radiotracer which binds specific receptor.