p-NO2-Bn-H(4)neunpa and H(4)neunpa-Trastuzumab: Bifunctional Chelator for Radiometalpharmaceuticals and In-111 Immuno-Single Photon Emission Computed Tomography Imaging

Potentially nonadentate (N5O4) bifunctional chelator p-SCN-Bn-H(4)neunpa and its immunoconjugate H(4)neunpa-trastuzumab for In-111 radiolabeling are synthesized. The ability of p-SCN-Bn H(4)neunpa and H(4)neunpa-trastuzumab to quantitatively radiolabel (InCl3)-In-111 at an ambient temperature within 15 or 30 min, respectively, is presented. Thermodynamic stability determination with In3+, Bi3+, and La3+ resulted in high conditional stability constant (pM) values. In vitro human serum stability assays have demonstrated both In-111 complexes to have high stability over 5 days. Mouse biodistribution of {[}In-111]{[}In(p-NO2 Bn neunpa)](-), compared to that of {[}In-111]{[}In(p-NH2-Bn-CHX-A{''}-diethylenetriamine pentaacetic acid (DTPA))](2-), 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-111-CHX-A{''}-DTPA-trastuzumab demonstrate a similar distribution profile but with slightly lower tumor uptake of In-111-neunpa-trastuzumab compared to that of In-111-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-H(4)neunpa to be a promising chelator for In-111 (and other radiometals) with high in vitro stability and also show H(4)neunpa trastuzumab to be an excellent In-111 chelator with promising biodistribution in mice.