Astatine-211 labeling of an antimelanoma antibody and its Fab fragment using N-succinimidyl p-[211At]astatobenzoate: comparisons in vivo with the p-[125I]iodobenzoyl conjugate

Abstract

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.

Astatinated trastuzumab, a putative agent for radionuclide immunotherapy of ErbB2-expressing tumours

“…This elevated uptake points to a probable in vivo deastatination of the antibody conjugate, since free astatine is known to accumulate in the thyroid and stomach (35). Other studies using different antibodies revealed the same effect, which means it is not trastuzumab-related (26). Treatment with perchlorate could alleviate this problem (35), but if this was impossible, loss of thyroid function can be alleviated by modern medicine to a large extent and could be deemed as an acceptable side effect of tumour treatment in some cases.…”

“…radiolysis. Indirect astatination of antibodies using succinimidyl ester of para-astatobenzoate is a wellestablished procedure, which usually produces a labelled antibody with preserved immunoreactivity (26,27). Such labelling modifies lysine residues, and its safety should be demonstrated for each antibody.…”

Biodistribution of 211At labeled HER-2 binding affibody molecules in mice

“…In most cases, the biodistribution of a protein radiolabeled with 125 I and 211 At are quite similar (11,15,16), but there have been previous reported exceptions (17,18), especially when smaller molecules, such as antibody fragments have been used. The results from these studies, with high uptake in stomach, lungs and spleen, indicate that free 211 At is released in vivo.…”

Production of [sup 211]At using the JSW BC3015 at the University of Pennsylvania

“…D-particles have been discussed as candidates for radiation therapy because of their high linear energy transfer (LET) 1,2,3 . With its halogen-like chemistry, 211 At, which emits D-particles, has the possibility of being used in a number of compounds.…”