Coordination chemistry of [Y(pypa)]− and comparison immuno-PET imaging of [44Sc]Sc- and [86Y]Y-pypa-phenyl-TRC105. Issue 17 (9th April 2020)

• Record Type: Journal Article
• Authors: Li, Lily; de Guadalupe Jaraquemada-Peláez, María; Aluicio-Sarduy, Eduardo; Wang, Xiaozhu; Barnhart, Todd E.; Cai, Weibo; Radchenko, Valery; Schaffer, Paul; Engle, Jonathan W.; Orvig, Chris
• Is Part Of: Dalton transactions. Volume 49:Issue 17(2020)
• Page Start: 5547
• Page End: 5562
• Publication Date: 2020-04-09
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d0dt00437e
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : H4 pypa was conjugated to an antibody via a newly synthesized H4 pypa-phenyl-NCS; promising immuno-PET imaging with 44Sc was demonstrated. Abstract : Both scandium-44 and yttrium-86 are popular PET isotopes with appropriate half-lives for immuno-positron emission tomography (immuno-PET) imaging. Herein, a new bifunctional H4 pypa ligand, H4 pypa-phenyl-NCS, is synthesized, conjugated to a monoclonal antibody, TRC105, and labeled with both radionuclides to investigate the long-term in vivo stability of each complex. While the 44 Sc-labeled radiotracer exhibited promising pharmacokinetics and stability in 4T1-xenograft mice ( n = 3) even upon prolonged interactions with blood serum proteins, the progressive bone uptake of the 86 Y-counterpart indicated in vivo demetallation, obviating H4 pypa as a suitable chelator for Y 3+ ion in vivo . The solution chemistry of [ nat Y(pypa)] − was studied in detail and the complex found to be thermodynamically stable in solution with a pM value 22.0, ≥3 units higher than those of the analogous DOTA- and CHX-A′′-DTPA-complexes; the 86 Y-result in vivo was therefore most unexpected. To explore further this in vivo lability, Density Functional Theory (DFT) calculation was performed to predict the geometry of [Y(pypa)] − and the results were compared with those for the analogous Sc- and Lu-complexes; all three adopted the same coordination geometry ( i.e. distorted capped square antiprism), but the metal-ligand bonds were much longer in [Y(pypa)] − than in [Lu(pypa)] − and [Sc(pypa)] −, which could indicate that the size of the binding cavity is too small for the Y 3+ ion, but suitable for both the Lu 3+ and Sc 3+ ions. Considered along with results from [ 86 Y][Y(pypa-phenyl-TRC105)], it is noted that when matching chelators with radionuclides, chemical data such as the thermodynamic stability and in vitro inertness, albeit useful and necessary, do not always translate to in vivo inertness, especially with the prolonged blood circulation of the radiotracer bound to a monoclonal antibody. Although H4 pypa is a nonadentate chelator, which theoretically matches the coordination number of the Y 3+ ion, we show herein that its binding cavity, in fact, favors smaller metal ions such as Sc 3+ and Lu 3+ and further exploitation of the Sc-pypa combination is desired.