Synthesis of polyglutamide-based metal-chelating polymers and their site-specific conjugation to trastuzumab for auger electron radioimmunotherapy.

Three types of metal-chelating polymers (MCPs) with hydrazide end groups were synthesized. (1) The first set of polymers (the F-series) was synthesized with a furan end group, and all of the pendant groups along the chain carried only a diethylenetriaminepentaacetic acid (DTPA) metal-chelating functionality. The hydrazide was introduced via a Diels-Alder reaction between the furan and 3,3'-N-[ε-maleimidocaproic acid] hydrazide (EMCH). (2) The P-series polymers was designed to carry several copies of a nuclear-localization peptide sequence (NLS peptides, CGYGPKKKRKVGG, harboring the NLS from the simian virus 40 large T-antigen) in addition to the DTPA metal-chelating groups. (3) The third type of polymer (the P-Py series) was a variation of the P-series polymers but with the introduction of a small number of pyrene chromophores along the backbone to allow for UV measurement of the incorporation of the MCPs into trastuzumab (tmab). These hydrazide-terminated polymers were site-specifically conjugated to aldehyde groups generated by NaIO4 oxidation of the pendant glycan in the Fc domain of tmab. The immunoconjugates were radiolabeled with (111)In and analyzed by SE-HPLC to confirm the attachment of the polymer to the antibody. HER2 binding assays demonstrated that neither the MCPs nor the presence of the NLS peptides interfered with specific antigen recognition on SK-Br-3 cells, although nonspecific binding was increased by polymer conjugation. Our results suggest that MCPs can be site-specifically attached to antibodies via oxidized glycans in the Fc domain and labeled with (111)In to construct radioimmunoconjugates with preserved immunoreactivity.