Journal
BIOCONJUGATE CHEMISTRY
Volume 26, Issue 12, Pages 2579-2591Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.bioconjchem.5b00572
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Funding
- NIH [P30 CA08748, 1F31CA180360-01]
- Molecular Design Institute at the Department of Chemistry of New York University
- CTSC of the National Center for Advancing Translational Sciences of the National Institutes of Health [TR000457]
- NSF [IGERT DGE 0965983]
- DOE [FG02-09ER16097, DE-SC0002184]
- National Institute on Minority Health and Health Disparities of the National Institutes of Health [MD007599]
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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 Zr-89(4+) cation is being released in vivo. Therefore, a more robust chelator for Zr-89 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 Zr-89(4+) 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 Zr-89. 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 Zr-89-HOPO-trastuzumab images. Biodistribution data confirmed the lower bone activity, measuring 17.0%ID/g in the bone at 336 h for Zr-89-DFO-trastuzumab while Zr-89-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 Zr-89. In vivo studies demonstrate the successful use of Zr-89-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 Zr-89-HOPO-trastuzumab suggests superior stability of the Zr-89-HOPO complex.
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