title: A polar substituent-containing acylation agent for the radioiodination of internalizing monoclonal antibodies: N-succinimidyl 4-guanidinomethyl-3-[131I]iodobenzoate ([131I]SGMIB).
abstract: The objective of this study was to develop an acylation agent for the radioiodination of monoclonal antibodies that would maximize retention of the label in tumor cells following receptor- or antigen-mediated internalization. The strategy taken was to add a polar substituent to the labeled aromatic ring to impede transport of labeled catabolites across lysosomal and cell membranes after antibody degradation. Preparation of unlabeled N-succinimidyl 4-guanidinomethyl-3-iodobenzoate (SGMIB) was achieved in six steps from 3-iodo-4-methylbenzoic acid. Preparation of 4-guanidinomethyl-3-[131I]iodobenzoic acid from the silicon precursor, 4-(N1,N2-bis-tert-butyloxycarbonyl)guanidinomethyl-3-trimethylsilylbenzoic acid proceeded in less than 5% radiochemical yield. A more successful approach was to prepare [131I]SGMIB directly from the tin precursor, N-succinimidyl 4-(N1,N2-bis-tert-butyloxycarbonyl)guanidinomethyl-3-trimethylstannylbenzoate, which was achieved in 60-65% radiochemical yield. A rapidly internalizing anti-epidermal growth factor receptor variant III antibody L8A4 was labeled using [131I]SGMIB in 65% conjugation efficiency and with preservation of immunoreactivity. Paired-label in vitro internalization assays demonstrated that the amount of radioactivity retained in cells after internalization for L8A4 labeled with [131I]SGMIB was 3-4-fold higher than that for L8A4 labeled with 125I using either Iodogen or [125I]SIPC. Catabolite assays documented that the increased retention of radioiodine in tumor cells for antibody labeled using [131I]SGMIB was due to positively charged, low molecular weight species. These results suggest that [131I]SGMIB warrants further evaluation as a reagent for labeling internalizing antibodies.
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710, USA. ganesan.v@duke.edu
authors.forename: G
authors.initials: G
authors.lastname: Vaidyanathan
authors.forename: D J
authors.initials: DJ
authors.lastname: Affleck
authors.forename: J
authors.initials: J
authors.lastname: Li
authors.forename: P
authors.initials: P
authors.lastname: Welsh
authors.forename: M R
authors.initials: MR
authors.lastname: Zalutsky
mesh_terms: D000215:Acylation; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000378:metabolism; D001565:Benzoates / Q000737:chemistry* / Q000493:pharmacokinetics; D001692:Biological Transport; D066246:ErbB Receptors / Q000276:immunology; D019791:Guanidine / Q000031:analogs & derivatives / Q000737:chemistry* / Q000493:pharmacokinetics; D006801:Humans; D018796:Immunoconjugates / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics*; D018189:Immunomagnetic Separation; D007457:Iodine Radioisotopes / Q000737:chemistry; D019275:Radiopharmaceuticals / Q000737:chemistry / Q000493:pharmacokinetics; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D001565:Benzoates; D018796:Immunoconjugates; D007457:Iodine Radioisotopes; C438937:N-succinimidyl 4-guanidinomethyl-3-iodobenzoate; D019275:Radiopharmaceuticals; D066246:ErbB Receptors; D019791:Guanidine