p‑SCN-Bn-HOPO: A Superior Bifunctional Chelator for 89Zr ImmunoPET

• Published in: Bioconjugate chemistry Vol. 26; no. 12; pp. 2579 - 2591
• Main Authors: Deri, Melissa A, Ponnala, Shashikanth, Kozlowski, Paul, Burton-Pye, Benjamin P, Cicek, Huseyin T, Hu, Chunhua, Lewis, Jason S, Francesconi, Lynn C
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 16.12.2015
• Subjects: RADIOLOGY AND NUCLEAR MEDICINE
• ISSN: 1043-1802; 1520-4812
• DOI: 10.1021/acs.bioconjchem.5b00572

Zirconium-89 has an ideal half-life for use in antibody-based PET imaging; however, when used with the chelator DFO, there is an accumulation of radioactivity in the bone, suggesting that the 89Zr4+ cation is being released in vivo. Therefore, a more robust chelator for 89Zr could reduce the in vivo release and the dose to nontarget tissues. Evaluation of the ligand 3,4,3-(LI-1,2-HOPO) demonstrated efficient binding of 89Zr4+ and high stability; therefore, we developed a bifunctional derivative, p-SCN-Bn-HOPO, for conjugation to an antibody. A Zr-HOPO crystal structure was obtained showing that the Zr is fully coordinated by the octadentate HOPO ligand, as expected, forming a stable complex. p-SCN-Bn-HOPO was synthesized through a novel pathway. Both p-SCN-Bn-HOPO and p-SCN-Bn-DFO were conjugated to trastuzumab and radiolabeled with 89Zr. Both complexes labeled efficiently and achieved specific activities of approximately 2 mCi/mg. PET imaging studies in nude mice with BT474 tumors (n = 4) showed good tumor uptake for both compounds, but with a marked decrease in bone uptake for the 89Zr-HOPO-trastuzumab images. Biodistribution data confirmed the lower bone activity, measuring 17.0%ID/g in the bone at 336 h for 89Zr-DFO-trastuzumab while 89Zr-HOPO-trastuzumab only had 2.4%ID/g. We successfully synthesized p-SCN-Bn-HOPO, a bifunctional derivative of 3,4,3-(LI-1,2-HOPO) as a potential chelator for 89Zr. In vivo studies demonstrate the successful use of 89Zr-HOPO-trastuzumab to image BT474 breast cancer with low background, good tumor to organ contrast, and, importantly, very low bone uptake. The reduced bone uptake seen with 89Zr-HOPO-trastuzumab suggests superior stability of the 89Zr-HOPO complex.