Convenient Synthesis and Evaluation of Heptadentate Bifunctional Ligand for Radioimmunotherapy Applications

Design and synthesis of a new bifunctional chelating agent: Application for Al 18F/177Lu complexation

Theranostic and personalized medicine are blooming strategies to improve oncologic patients' health care and facilitate early treatment. While 18F-radiochemistry for theranostic application is attractive due to its imaging properties, combining diagnosis by positron emission tomography (PET) via aluminum-fluoride-18 and β- therapy with lutetium-177 is relevant. Nevertheless, it requires the use of two different chelating agents, which are NOTA and DOTA for aluminum-fluoride-18 and lutetium-177 radiolabeling, respectively. To overcome this issue, we propose herein the synthesis of a new hybrid chelating agent named NO2A-AHM, which can be labeled with different types of emitters (β+, β- and γ) using the mismatched Al18F/177Lu pair. NO2A-AHM, is based on a hydrazine moiety functionalized by a NOTA cycle, a chelating arm, and a linker with a maleimide function. This design is chosen to increase the flexibility and allow the formation of 5 up to 7 coordination bonds with metal ions. Moreover, this agent can be coupled to targeting moieties containing a thiol function, such as peptides, to increase selectivity towards specific cancer cells. Experimental complexation and computational chemistry studies are performed to confirm the capacity of our chelating agent to label both aluminum-fluoride and lutetium using molecular modeling approaches at Density Functional Theory (DFT) level. The proof of concept of the ability of NO2A-AHM to complex both aluminum-fluoride-18, for PET imaging applications, and lutetium-177 for radiotherapy has shown encouraging results which is prominent for the development of a fully consistent theranostic approach.

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 β-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.

Ultrasensitive electrochemical immunoassay for surface array protein, a Bacillus anthracis biomarker using Au-Pd nanocrystals loaded on boron-nitride nanosheets as catalytic labels

Bacillus anthracis, the causative agent of anthrax, is a well known bioterrorism agent. The determination of surface array protein (Sap), a unique biomarker for B. anthracis can offer an opportunity for specific detection of B. anthracis in culture broth. In this study, we designed a new catalytic bionanolabel and fabricated a novel electrochemical immunosensor for ultrasensitive detection of B. anthracis Sap antigen. Bimetallic gold-palladium nanoparticles were in-situ grown on poly (diallyldimethylammonium chloride) functionalized boron nitride nanosheets (Au-Pd NPs@BNNSs) and conjugated with the mouse anti-B. anthracis Sap antibodies (Ab2); named Au-Pd NPs@BNNSs/Ab2. The resulting Au-Pd NPs@BNNSs/Ab2 bionanolabel demonstrated high catalytic activity towards reduction of 4-nitrophenol. The sensitivity of the electrochemical immunosensor along with redox cycling of 4-aminophenol to 4-quinoneimine was improved to a great extent. Under optimal conditions, the proposed immunosensor exhibited a wide working range from 5 pg/mL to 100 ng/mL with a minimum detection limit of 1 pg/mL B. anthracis Sap antigen. The practical applicability of the immunosensor was demonstrated by specific detection of Sap secreted by the B. anthracis in culture broth just after 1h of growth. These labels open a new direction for the ultrasensitive detection of different biological warfare agents and their markers in different matrices.

Transferrin conjugates of triazacyclononane-based bifunctional NE3TA chelates for PET imaging: Synthesis, Cu-64 radiolabeling, and in vitro and in vivo evaluation

Three different polyaminocarboxylate-based bifunctional NE3TA (7-[2-[carboxymethyl)amino]ethyl]-1,4,7-triazacyclononane-1,4-diacetic acid) chelating agents were synthesized for potential use in copper 64-PET imaging applications. The bifunctional chelates were comparatively evaluated using transferrin (Tf) as a model targeting vector that binds to the transferrin receptor overexpressed in many different cancer cells. The transferrin conjugates of the NE3TA-based bifunctional chelates were evaluated for radiolabeling with (64)Cu. In vitro stability and cellular uptake of (64)Cu-radiolabeled conjugates were evaluated in human serum and prostate (PC-3) cancer cells, respectively. Among the three NE3TA-Tf conjugates tested, N-NE3TA-Tf was identified as the best conjugate for radiolabeling with (64)Cu. N-NE3TA-Tf rapidly bound to (64)Cu (>98% radiolabeling efficiency, 1min, RT), and (64)Cu-N-NE3TA-Tf remained stable in human serum for 2days and demonstrated high uptake in PC-3 cancer cells. (64)Cu-N-NE3TA-Tf was shown to have rapid blood clearance and increasing tumor uptake in PC-3 tumor bearing mice over a 24h period. This bifunctional chelate presents highly efficient chelation chemistry with (64)Cu under mild condition that can be applied for radiolabeling of various tumor-specific biomolecules with (64)Cu for potential use in 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 β-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.