p-NO-Bn-Hneunpa and Hneunpa-Trastuzumab: Bifunctional Chelator for Radiometalpharmaceuticals and In Immuno-Single Photon Emission Computed Tomography Imaging.

Potentially nonadentate (NO) bifunctional chelator p-SCN-Bn-Hneunpa and its immunoconjugate Hneunpa-trastuzumab for In radiolabeling are synthesized. The ability of p-SCN-Bn-Hneunpa and Hneunpa-trastuzumab to quantitatively radiolabel InCl at an ambient temperature within 15 or 30 min, respectively, is presented. Thermodynamic stability determination with In, Bi, and La resulted in high conditional stability constant (pM) values. In vitro human serum stability assays have demonstrated both In complexes to have high stability over 5 days. Mouse biodistribution of [In][In(p-NO-Bn-neunpa)], compared to that of [In][In(p-NH-Bn-CHX-A″-diethylenetriamine pentaacetic acid (DTPA))], at 1, 4, and 24 h shows fast clearance of both complexes from the mice within 24 h. In a second mouse biodistribution study, the immunoconjugates In-neunpa-trastuzumab and In-CHX-A″-DTPA-trastuzumab demonstrate a similar distribution profile but with slightly lower tumor uptake of In-neunpa-trastuzumab compared to that of In-CHX-A″-DTPA-trastuzumab. These results were also confirmed by immuno-single photon emission computed tomography (immuno-SPECT) imaging in vivo. These initial investigations reveal the acyclic bifunctional chelator p-SCN-Bn-Hneunpa to be a promising chelator for In (and other radiometals) with high in vitro stability and also show Hneunpa-trastuzumab to be an excellent In chelator with promising biodistribution in mice.