Pyridine-containing octadentate ligand NE3TA-PY for formation of neutral complex with 177Lu(III) and 90Y(III) for radiopharmaceutical applications: Synthesis, DFT calculation, radiolabeling, and in vitro complex stability.

Targeted radionuclide therapy is a developing therapeutic modality for cancer and employs a cytotoxic radionuclide bound to a chelating agent and a bioactive molecule with high binding affinity for a specific biomarker in tumors. An optimal chelator is one of the critical components to control therapeutic efficacy and toxicity of targeted radionuclide therapy. We designed a new octadentate ligand NE3TA-PY (7-[2-[(carboxymethyl)(2-pyridylmethyl)amino]ethyl]-1,4,7-triazacyclononane-1,4-diacetic acid) for ß-particle-emitting 177Lu and 90Y with targeted radionuclide therapy applications. The pyridine-containing polyaminocarboxylate ligand was proposed to form a neutral complex with Lu(III) and Y(III). The new chelator NE3TA-PY was synthesized and experimentally and theorectically studied for complexation with 177Lu(III) and 90Y(III). DFT-optimized structures of Y(III)-NE3TA-PY and Lu(III)-NE3TA-PY complexes were predicted. NE3TA-PY displayed excellent radiolabeling efficiency with both 177Lu and 90Y. The new chelator (NE3TA-PY) bound to 177Lu was more stable in human serum and better tolerated when challenged by EDTA than 90Y-labeled NE3TA-PY. Our findings suggest that the new chelator (NE3TA-PY) produced excellent Lu-177 radiolabeling and in vitro complex stability profiles.

New Bifunctional Chelator 3p-C-NEPA for Potential Applications in Lu(III) and Y(III) Radionuclide Therapy and Imaging.

We have developed structurally unique bifunctional chelators in the NETA, NE3TA, and DEPA series for potential radiopharmaceutical applications. As part of our continued research efforts to generate efficient bifunctional chelators for targeted radionuclide therapy and imaging of various diseases, we designed a scorpion-like chelator that is proposed to completely saturate the coordination spheres of Y(III) and Lu(III). We herein report the synthesis and evaluation of a new chelator (3p-C-NEPA) with 10 donor groups for complexation with ß-emitting radionuclides 90Y(III), 86Y(III), and 177Lu(III). The chelator was synthesized and evaluated for radiolabeling kinetics with the readily available radioisotopes 90Y and 177Lu, and the corresponding 90Y or 177Lu-radiolabeled complexes were evaluated for in vitro stability in human serum and in vivo complex stability in mice. The new chelator rapidly bound 90Y or 177Lu and formed a stable complex with the radionuclides. The new chelator 3p-C-NEPA radiolabeled with either 90Y or 177Lu remains stable in human serum without dissociation for 10 days. 177Lu-labeled 3p-C-NEPA produced a favorable in vivo biodistribution profile in normal mice.

Promising bifunctional chelators for copper 64-PET imaging: practical (64)Cu radiolabeling and high in vitro and in vivo complex stability.

Positron emission tomography (PET) using copper-64 is a sensitive and non-invasive imaging technique for diagnosis and staging of cancer. A bifunctional chelator that can present rapid radiolabeling kinetics and high complex stability with (64)Cu is a critical component for targeted PET imaging. Bifunctional chelates 3p-C-NE3TA, 3p-C-NOTA, and 3p-C-DE4TA were evaluated for complexation kinetics and stability with (64)Cu in vitro and in vivo. Hexadentate 3p-C-NOTA and heptadentate 3p-C-NE3TA possess a smaller TACN-based macrocyclic backbone, while nonadentate 3p-C-DE4TA is constructed on a larger CYCLEN-based ring. The frequently explored chelates of (64)Cu, octadentate C-DOTA and hexadentate C-NOTA were also comparatively evaluated. Radiolabeling kinetics of bifunctional chelators with (64)Cu was assessed under mild conditions. All bifunctional chelates instantly bound to (64)Cu in excellent radiolabeling efficiency at room temperature. C-DOTA was less efficient in binding (64)Cu than all other chelates. All (64)Cu-radiolabeled bifunctional chelates remained stable in human serum without any loss of (64)Cu for 2 days. When challenged by an excess amount of EDTA, (64)Cu complexes of C-NOTA, 3p-C-NE3TA and 3p-C-NOTA were shown to be more stable than (64)Cu-C-DOTA and (64)Cu-3p-C-DE4TA. (64)Cu complexes of the new chelates 3p-C-NE3TA and 3p-C-NOTA displayed comparable in vitro and in vivo complex stability to (64)Cu-C-NOTA. In vivo biodistribution result indicates that the (64)Cu-radiolabeled complexes of 3p-C-NOTA and 3p-C-NE3TA possess excellent in vivo complex stability, while (64)Cu-3p-C-DE4TA was dissociated as evidenced by high renal and liver retention in mice. The results of in vitro and in vivo studies suggest that the bifunctional chelates 3p-C-NE3TA and 3p-C-NOTA offer excellent chelation chemistry with (64)Cu for potential PET imaging applications.

Synthesis and comparative biological evaluation of bifunctional ligands for radiotherapy applications of (90)Y and (177)Lu.

Zevalin® is an antibody-drug conjugate radiolabeled with a cytotoxic radioisotope ((90)Y) that was approved for radioimmunotherapy (RIT) of B-cell non-Hodgkin's lymphoma. A bifunctional ligand that displays favorable complexation kinetics and in vivo stability is required for effective RIT. New bifunctional ligands 3p-C-DE4TA and 3p-C-NE3TA for potential use in RIT were efficiently prepared by the synthetic route based on regiospecific ring opening of aziridinium ions with prealkylated triaza- or tetraaza-backboned macrocycles. The new bifunctional ligands 3p-C-DE4TA and 3p-C-NE3TA along with the known bimodal ligands 3p-C-NETA and 3p-C-DEPA were comparatively evaluated for potential use in targeted radiotherapy using ß-emitting radionuclides (90)Y and (177)Lu. The bifunctional ligands were evaluated for radiolabeling kinetics with (90)Y and (177)Lu, and the corresponding (90)Y or (177)Lu-radiolabeled complexes were studied for in vitro stability in human serum and in vivo biodistribution in mice. The results of the comparative complexation kinetic and stability studies indicate that size of macrocyclic cavity, ligand denticity, and bimodality of donor groups have a substantial impact on complexation of the bifunctional ligands with the radiolanthanides. The new promising bifunctional chelates in the DE4TA and NE3TA series were rapid in binding (90)Y and (177)Lu, and the corresponding (90)Y- and (177)Lu-radiolabeled complexes remained inert in human serum or in mice. The in vitro and in vivo data show that 3p-C-DE4TA and 3p-C-NE3TA are promising bifunctional ligands for targeted radiotherapy applications of (90)Y and (177)Lu.

Novel hexadentate and pentadentate chelators for 64Cu-based targeted PET imaging.

A series of new hexadentate and pentadentate chelators were designed and synthesized as chelators of (64)Cu. The new pentadentate and hexadentate chelators contain different types of donor groups and are expected to form neutral complexes with Cu(II). The new chelators were evaluated for complex kinetics and stability with (64)Cu. The new chelators instantly bound to (64)Cu with high labeling efficiency and maximum specific activity. All (64)Cu-radiolabeled complexes in human serum remained intact for 2 days. The (64)Cu-radiolabeled complexes were further challenged by EDTA in a 100-fold molar excess. Among the (64)Cu-radiolabeled complexes evaluated, (64)Cu-complex of the new chelator E was well tolerated with a minimal transfer of (64)Cu to EDTA. (64)Cu-radiolabeled complex of the new chelator E was further evaluated for biodistribution studies using mice and displayed rapid blood clearance and low organ uptake. (64)Cu-chelator E produced a favorable in vitro and in vivo complex stability profiles comparable to (64)Cu complex of the known hexadentate NOTA chelator. The in vitro and in vivo data highlight strong potential of the new chelator E for targeted PET imaging application.

Efficient synthesis of functionalized aziridinium salts.

Various aziridinium salts were efficiently prepared from bromination of a series of backbone substituted N,N-bisubstituted beta-amino alcohols and isolated via flash column chromatography. The effect of C-substitution, N-substitution, solvent, leaving group, and counteranions on formation of the isolable aziridinium salts was investigated.