In vitro evaluation of two polyhedral boron anion derivatives as linkers for attachment of radioiodine to the anti-HER2 monoclonal antibody trastuzumab.

Improving intracellular retention is important for the use of radiohalogens in radionuclide therapy using internalizing antibodies. Two putative linkers for residualization of radioiodine labels, 7-(4-isothiocyanato-phenyl)undecahydro-7,8-dicarba-nido-undecaborate(1-) ion (NBI) and (4-isothiocyanato-benzylammonio)undecahydro-closo-dodecaborate(1-) (DABI), were analyzed. The anti-HER-2 antibody, trastuzumab, was labeled with iodine-125 using NBI and DABI linkers, and, for comparison, with the para-[(125)I]iodobenzoate (PIB), and Chloramine-T((R)) (CAT) methods. The different labels were tested for residualizing properties using the HER-2 overexpressing SKBR-3 cells. The cellular radioactivity retention showed that DABI provided a 55% better retention than CAT and was 42% better than PIB after 20 hours. NBI did not improve retention. Accumulation tests up to 21 hours showed that the HER-2-specific accumulation of radioactivity delivered with DABI was, on average, 33% higher than with the use of PIB. These DABI-dependent improvements could, with high probability, be attributed to the good residualizing properties of DABI. The affinity of DABI-labeled trastuzumab to SKBR-3 cells was not better than the affinity of the PIB labeled (3.2 +/- 1.9 nM and 0.77 +/- 0.39 nM, respectively). In conclusion, the use of the DABI linker improved intracellular retention in vitro in comparison with the other labeling methods.

Radiobromination of anti-HER2/neu/ErbB-2 monoclonal antibody using the p-isothiocyanatobenzene derivative of the [76Br]undecahydro-bromo-7,8-dicarba-nido-undecaborate(1-) ion.

The monoclonal humanized anti-HER2 antibody trastuzumab was radiolabeled with the positron emitter (76)Br (T(1/2) =16.2 h). Indirect labeling was performed using the p-isothiocyanatobenzene derivative of the [(76)Br]undecahydro-bromo-7,8-dicarba-nido-undecaborate(1-) ((76)Br-NBI) as a precursor molecule. (76)Br-NBI was prepared by bromination of the 7-(p-isothiocyanato-phenyl)dodecahydro-7,8-dicarba-nido-undecaborate(1-) ion (NBI) with a yield of 93-95% using Chloramine-T (CAT) as an oxidant. Coupling of radiobrominated NBI to antibody was performed without intermediate purification, in an "one pot" reaction. An overall labeling yield of 55.7 +/- 4.8% (mean +/- maximum error) was achieved when 300 microg of antibody was labeled. The label was stable in vitro in physiological and denaturing conditions. In a cell binding test, trastuzumab remained immunoreactive after labeling.

Palladium-catalyzed Heck reactions of styrene derivatives and 2-iodo-p-carborane.

p-Carborane has been vinylated on the 2-B-atom in high yields using the Heck reaction. Thus, the reaction between 2-iodo-p-carborane and various styrenes [4-H-, 4-C(6)H(4)-, 4-Cl-, 4-Br-, 4-NO(2)-, 4-CH(3)O-, and 4-CH(3)-] resulted in the production of the corresponding trans-beta-(2-B-p-carboranyl)styrene in DMF solution when reacted in the presence of silver phosphate and the palladacycle Herrmann's catalyst.