Positively charged templates for labeling internalizing antibodies: comparison of N-succinimidyl 5-Iodo-3-pyridinecarboxylate and the D-amino acid peptide KRYRR

Receptor-mediated internalization of monoclonal antibodies (mAbs), such as those specific for the epidermal growth factor receptor variant III (EGFRvI II), can lead to rapid loss of radioactivity from the target cell. In the c urrent study, the anti-EGFRvIII mAb L8A4 was radioiodinated using two metho ds -N-succinimidyl 5-iodo-3-pyridinecarboxylate (SIPC) and via a D-amino ac id peptide LysArgTyrArgArg (D-KRYRR). Paired-label internalization assays p erformed on EGFRvIII-expressing U87 Delta EGFR cells in vitro demonstrated that labeling L8A4 using D-KRYRR resulted in significantly higher retention of radioiodine in the intracellular compartment. In athymic mice with D256 human glioma xenografts, tumor uptake was similar for both labeling method s through 24 hr. However, an up to fourfold higher tumor retention was obse rved for mAb labeled with the D-amino acid peptide at later time points. Ra diation absorbed dose calculations based on these biodistribution data indi cated that L8A4 labeled using D-KRYRR exhibited better tumor-to-normal-orga n radiation dose ratios, suggesting that this labeling method may be of par ticular value for labeling internalizing mAbs. (C) 2001 Elsevier Science In c. All rights reserved.