Reagents for Astatination of Biomolecules. 4. Comparison of Maleimido-closo-Decaborate(2-) and meta-[~(211)At]Astatobenzoate Conjugates for Labeling anti-CD45 Antibodies with [~(211)At]Astatine

摘要

An investigation was conducted to compare the in vivo tissue distribution of a rat antimurine CD45 monoclonal antibody (30F11) and an irrelevant mAbs (CA12.10C12) labeled with ~(211)At using two different labeling methods. In the investigation, the mAbs were also labeled with ~(125)I to assess the in vivo stability of the labeling methods toward deastatination. One labeling method employed N-hydroxysuecinimidyl meta-[~(211)At]astatobenzoate, [~(211)At]lc, and N-hydroxysuccinimidyl meta-[~(125)I]iodobenzoate, [~(125)I]lb, in conjugation reactions to obtain the radiolabeled mAbs. The other labeling method involved conjugation of a maleimido-closo-deeaborate(2-) derivative, 2, with sulfhydryl groups on the mAbs, followed by labeling of the mAb-2 conjugates using Na[~(211)At]At or Na[~(125)I]I and chloramine-T. Concentrations of the ~(211)At/~(125)I pair of radiolabeled mAbs in selected tissues were examined in BALB/c mice at 1, 4, and 24 h post injection (pi). The co-injected anti-CD45 mAb, 30F11, labeled with [~(125)I]1b and [~(211)At]lc targeted the CD45-bearing cells in the spleen with the percent injected dose (%ID) of ~(125)I in that tissue being 13.31 ± 0.78; 17.43 ± 2.56; 5.23 ± 0.50; and ~(211)At being 6.56 ±0.40; 10.14 ±1.49; 7.52 ± 0.79 at 1, 4, and 24 h pi (respectively). However, better targeting (or retention) of the ~(125)1 and ~(211)At was obtained for 30F11 conjugated with the closo-decaborate(2-), 2. The %ID in the spleen of ~(125)I (i.e., [~(125)I]30F11-2) being 21.15 ± 1.33; 22.22 ±1.95; 12.41 ± 0.75; and ~(211)At (i.e., [~(211)At]30F11-2) being 22.78 ± 1.29; 25.05 ± 2.35; 17.30 ± 1.20 at 1, 4, and 24 h pi (respectively). In contrast, the irrelevant mAb, CA12.10C12, labeled with ~(125)I or ~(211)At by either method had less than 0.8% ID in the spleen at any time point, except for [~(211)At]CA12.10C12-1c, which had 1.62 ± 0.14%ID and 1.21 ± 0.08%ID at 1 and 4 h pi. The higher spleen: concentrations in that conjugate appear to be due to in vivo deastatination. Differences in ~(125)I and ~(211)At concentrations in lung, neck, and stomach indicate that the meta-[~(211)At]benzoyl conjugates underwent deastatination, whereas the ~(211)At-labeled closo-decaborate(2-) conjugates were very stable to in vivo deastatination. In summary, using the closo-decaborate(2-) ~(211)At labeling approach resulted in higher concentrations of ~(211) At in target tissue (spleen) and higher stability to in vivo deastatination in this model. These findings, along with the simpler and higher-yielding ~(211)At-labeling method, provide the basis for using the closo-decaborate(2-) labeling reagent, 2, in our continued studies of the application of ~(211)At-labeled mAbs for conditioning in hematopoietic cell transplantation.