Astatine-211 labeling of an antimelanoma antibody and its Fab fragment using N-succinimidyl p-astatobenzoate: comparisons in vivo with the p-[125I]iodobenzoyl conjugate.
Astatine-211 labeling of an antimelanoma antibody, NR-ML-05, and its Fab fragment with N-succinimidyl p-[211At]astatobenzoate (2a) has been described. Preparation of the astatinated intermediate 2a was accomplished by distilling astatine-211 from an irradiated bismuth target directly into a reaction mixture containing an organometallic compound, N-succinimidyl p-(tri-n-butylstannyl)benzoate (1), and an oxidant, N-chlorosuccinimide, in 5% HOAc/MeOH. Trapping of distilled astatine as 2a was found to be efficient, resulting in 70-90% yields based on the amount of astatine-211 in the reaction mixture. The dry distillation technique employed gave recoveries of astatine-211 which ranged from 20% to 75%. Conjugation of 2a to NR-ML-05 and its Fab fragment was accomplished in 40-60% yields. The [211At]astatobenzoyl-conjugated antibodies were found to be stable in vitro when challenged by strong denaturants and nucleophilic reagents. Coinjected dual-labeled studies of the 2a astatinated antibodies and the same antibodies labeled with N-succinimidyl p-[125I]iodobenzoate (2b) in athymic mice bearing the human tumor xenograft A375 Met/Mix demonstrated that both radiolabeled antibodies had equivalent tumor localization. Data from the dual-labeled biodistribution of the intact antibody suggests that the astatine is stably attached. Data from the dual-labeled Fab fragment suggests that a portion of the astatine label is released as astatide, either from the astatinated Fab or from a catabolite.
University of Washington Medical Center, Seattle 98195.
S W
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Hadley
D S
DS
Wilbur
M A
MA
Gray
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Atcher
D000818:Animals; D000912:Antibodies, Neoplasm / Q000737:chemistry*; D001246:Astatine / Q000494:pharmacology; D005260:Female; D006801:Humans; D007128:Immunoglobulin Fragments / Q000737:chemistry*; D000922:Immunotoxins; D007457:Iodine Radioisotopes; D007463:Iodobenzoates / Q000737:chemistry*; D007553:Isotope Labeling / Q000379:methods*; D008297:Male; D008545:Melanoma / Q000276:immunology*; D051379:Mice; D008819:Mice, Nude; D014018:Tissue Distribution
D000912:Antibodies, Neoplasm; D007128:Immunoglobulin Fragments; D000922:Immunotoxins; D007457:Iodine Radioisotopes; D007463:Iodobenzoates; D001246:Astatine