The development of effective theranostic pairs in nuclear medicine relies heavily on the chemical and biological compatibility between diagnostic and therapeutic radionuclides. Scandium-44 (44Sc) and lutetium-177 (177Lu) have emerged as promising candidates due to their favorable decay properties—44Sc for positron emission tomography (PET) imaging and 177Lu for targeted radiotherapy. Despite being considered close homologues, Sc(III) and Lu(III) exhibit distinct coordination behaviors due to differences in ionic size, Lewis acidity, and chemical hardness. This study investigates whether the bifunctional chelator picaga, derived from the ligand H3mpatcn, can enforce a structurally and chemically homologous environment for both metal ions, thereby enabling matched theranostic applications.EGF Antibody In Vivo
Using potentiometric titrations, variable temperature mass spectrometry (VT-MS), pair distribution function (PDF) analysis of X-ray scattering data, and computational modeling, we demonstrate that the picaga ligand induces nearly identical coordination geometries for Sc(III) and Lu(III).NME2 Antibody MedChemExpress The seven-coordinate complex structure is preserved across both metals, as evidenced by near-identical 1H NMR spectra and consistent bond lengths in DFT calculations. PDF analysis confirms that the local atomic environments of [Sc(mpatcn)] and [Lu(mpatcn)] are highly similar in solution, indicating minimal structural distortion despite differences in ionic radii. VT-MS reveals comparable hydration thermodynamics for both complexes, with Gibbs free energy values above the threshold for inner-sphere binding, suggesting second-sphere water interactions—consistent with high kinetic inertness.
Radiochemical labeling experiments confirm efficient complexation of both 47Sc and 177Lu at elevated temperatures, yielding >97% radiochemical purity after purification via solid-phase extraction. In vitro stability assessments show excellent resistance to dissociation in PBS and rat plasma over 168 hours, with >95% integrity retained. Binding affinity to PSMA, assessed using competitive displacement assays, yielded Ki values of 0.77 ± 0.12 nM for Lu(picaga)-DUPA and 1.PMID:34876482 6 ± 0.4 nM for Sc(picaga)-DUPA—comparable to clinically validated tracers like DCFPyL.
Biodistribution studies in PC-3 PiP tumor-bearing mice revealed high target uptake: 6.51 ± 3.83% ID/g for 177Lu(picaga)-DUPA and 12.74 ± 2.87% ID/g for 47Sc(picaga)-DUPA. Off-target accumulation was low, particularly in liver and kidneys, with no significant bone uptake observed—indicating exceptional in vivo inertness. Importantly, no statistically significant differences were found in tumor-to-background ratios between 44Sc-, 47Sc-, and 177Lu-labeled conjugates, confirming functional equivalence across isotopes.
These findings establish that the picaga chelator enables homologous structural and biological behavior for Sc(III) and Lu(III) complexes, making it a viable platform for developing true theranostic pairs. The rigid, constrictive ligand architecture effectively mitigates the inherent differences between these metals, offering a robust solution for future radiopharmaceutical applications involving scandium and lutetium isotopes.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
