Labeling internalizing anti-epidermal growth factor receptor variant III monoclonal antibody with (177)Lu: in vitro comparison of acyclic and macrocyclic ligands.

Abstract

INTRODUCTION:

The monoclonal antibody (mAb) L8A4, reactive with the epidermal growth factor receptor variant III (EGFRvIII), internalizes rapidly in glioma cells after receptor binding. Combining this tumor-specific mAb with the low-energy beta-emitter (177)Lu would be an attractive approach for brain tumor radioimmunotherapy, provided that trapping of the radionuclide in tumor cells after mAb intracellular processing could be maximized.

MATERIALS AND METHODS:

L8A4 mAb was labeled with (177)Lu using the acyclic ligands [(R)-2-amino-3-(4-isothiocyanatophenyl)propyl]-trans-(S,S)-cyclohexane-1,2-diamine-pentaacetic acid (CHX-A''-DTPA), 2-(4-isothiocyanatobenzyl)-diethylenetriaminepenta-acetic acid (pSCN-Bz-DTPA) and 2-(4-isothiocyanatobenzyl)-6-methyldiethylenetriaminepentaacetic acid (1B4M-DTPA), and the macrocyclic ligands S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane-tetraacetic acid (C-DOTA) and alpha-(5-isothiocyanato-2-methoxyphenyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (MeO-DOTA). Paired-label internalization and cellular processing assays were performed on EGFRvIII-expressing U87.DeltaEGFR glioma cells over 24 h to directly compare (177)Lu-labeled L8A4 to L8A4 labeled with (125)I using either iodogen or N-succinimidyl 4-guanidinomethyl-3-[(125)I]iodobenzoate ([(125)I]SGMIB). In order to facilitate comparison of labeling methods, the primary parameter evaluated was the ratio of (177)Lu to (125)I activity retained in U87.DeltaEGFR cells.

RESULTS:

All chelates demonstrated higher retention of internalized activity compared with mAb labeled using iodogen, with (177)Lu/(125)I ratios of >20 observed for the three DTPA chelates at 24 h. When compared to L8A4 labeled using SGMIB, except for MeO-DOTA, internalized activity for (125)I was higher than (177)Lu from 1-8 h with the opposite behavior observed thereafter. At 24 h, (177)Lu/(125)I ratios were between 1.5 and 3, with higher values observed for the three DTPA chelates.

CONCLUSIONS:

The nature of the chelate used to label this internalizing mAb with (177)Lu influenced intracellular retention in vitro, although at early time points, only MeO-DOTA provided more favorable results than radioiodination of the mAb via SGMIB.

• Authors: Marc Hens, Ganesan Vaidyanathan, Phil Welsh, Michael R Zalutsky
• Journal: Nuclear medicine and biology (Nucl Med Biol) Vol. 36 Issue 2 Pg. 117-28 (Feb 2009) ISSN: 0969-8051 [Print] United States
• PMID: 19217523 (Publication Type: Comparative Study, Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Antibodies, Monoclonal
• Chelating Agents
• Ligands
• Macrocyclic Compounds
• Radioisotopes
• Radiopharmaceuticals
• Lutetium
• ErbB Receptors

Topics

• Animals
• Antibodies, Monoclonal (chemistry, pharmacokinetics, therapeutic use)
• Brain Neoplasms (radiotherapy)
• Cell Line, Tumor
• Chelating Agents (chemistry)
• Chromatography, High Pressure Liquid
• ErbB Receptors (immunology)
• Glioma (radiotherapy)
• Isotope Labeling (methods)
• Ligands
• Lutetium (pharmacokinetics)
• Macrocyclic Compounds (chemistry)
• Mice
• Radioimmunotherapy
• Radioisotopes (chemistry, pharmacokinetics, therapeutic use)
• Radiopharmaceuticals (chemistry, pharmacokinetics, therapeutic use)