Synthesis of DOTA-pyridine chelates for 64Cu coordination and radiolabeling of αMSH peptide

Background 64Cu is one of the few radioisotopes that can be used for both imaging and therapy, enabling theranostics with identical chemical composition. Development of stable chelators is essential to harness the potential of this isotope, challenged by the presence of endogenous copper chelators. Pyridyl type chelators show good coordination ability with copper, prompting the present study of a series of chelates DOTA-xPy (x = 1–4) that sequentially substitute carboxyl moieties with pyridyl moieties on a DOTA backbone. Results We found that the presence of pyridyl groups significantly increases 64Cu labeling conversion yield, with DOTA-2Py, −3Py and -4Py quantitatively complexing 64Cu at room temperature within 5 min (1 × 10− 4 M). [64Cu]Cu-DOTA-xPy (x = 2–4) exhibited good stability in human serum up to 24 h. When challenged with 1000 eq. of NOTA, no transmetallation was observed for all three 64Cu complexes. DOTA-xPy (x = 1–3) were conjugated to a cyclized α-melanocyte-stimulating hormone (αMSH) peptide by using one of the pendant carboxyl groups as a bifunctional handle. [64Cu]Cu-DOTA-xPy-αMSH retained good serum stability (> 96% in 24 h) and showed high binding affinity (Ki = 2.1–3.7 nM) towards the melanocortin 1 receptor. Conclusion DOTA-xPy (x = 1–3) are promising chelators for 64Cu. Further in vivo evaluation is necessary to assess the full potential of these chelators as a tool to enable further theranostic radiopharmaceutical development.

Using bioorthogonally catalyzed lethality strategy to generate mitochondria-targeting antitumor metallodrugs in vitro and in vivo

Synthetic lethality was proposed nearly a century ago by geneticists and recently applied to develop precision anticancer therapies. To exploit the synthetic lethality concept in the design of chemical anticancer agents, we developed a bioorthogonally catalyzed lethality (BCL) strategy to generate targeting antitumor metallodrugs both in vitro and in vivo. Metallodrug Ru-rhein was generated from two nontoxic species Ru-N3 and rhein-alkyne via exclusive endogenous copper-catalyzed azide alkyne cycloaddition (CuAAC) reaction without the need of an external copper catalyst. The nontoxic species Ru-arene complex Ru-N3 and rhein-alkyne were designed to perform this strategy, and the mitochondrial targeting product Ru-rhein was generated in high yield (> 83%) and showed high antitumor efficacy in vitro. This BCL strategy achieved a remarkable tumor suppression effect on the tumor-bearing mice models. It is interesting that the combination of metal-arene complexes with rhein via CuAAC reaction could transform two nontoxic species into a targeting anticancer metallodrug both in vitro and in vivo, while the product Ru-rhein was nontoxic towards normal cells. This is the first example that exclusive endogenous copper was used to generate metal-based anticancer drugs for cancer treatment. The anticancer mechanism of Ru-rhein was studied and autophagy was induced by increased reactive oxygen species and mitochondrial damage. The generality of this BCL strategy was also studied and it could be extended to other metal complexes such as Os-arene and Ir-arene complexes. Compared with the traditional methods for cancer treatment, this work presented a new approach to generate targeting metallodrugs in vivo via the BCL strategy from nontoxic species in the metal-based chemotherapy.

Synthesis of DOTA-Pyridine Chelates for 64Cu Coordination and Radiolabeling of αMSH Peptide

Background : 64Cu is one of the few radioisotopes that can be used for both imaging and therapy, enabling theranostics with identical chemical composition. Development of stable chelators is essential to harness the potential of this isotope, challenged by the presence of endogenous copper chelators. Pyridyl type chelators show good coordination ability with copper, prompting the present study of a series of chelates DOTA-xPy (x=1-4) that sequentially substitute carboxyl moieties with pyridyl moieties on a DOTA backbone. Results: We found that the presence of pyridyl groups significantly increases 64 Cu labeling yield, with DOTA-2Py, -3Py and -4Py quantitatively complexing 64 Cu at room temperature within 5 min (10 -4 M). [ 64 Cu]Cu-DOTA-xPy (x=2-4) exhibited good stability in human serum up to 24 hours. When challenged with 1000 eq. of NOTA, no transmetallation was observed for all three 64 Cu complexes. DOTA-xPy (x=1-3) were conjugated to a cyclized α-melanocyte-stimulating hormone (αMSH) peptide by using one of the pendant carboxyl groups as a bifunctional handle. [ 64 Cu]Cu-DOTA-xPy-αMSH retained good serum stability (>96% in 24 hours) and showed high binding affinity (Ki=2.1-3.7 nM) towards the melanocortin 1 receptor. Conclusion : DOTA-xPy (x=1-3) are promising chelators for 64 Cu. Further in vivo evaluation is necessary to assess the full potential of these chelators as a tool to enable further theranostic radiopharmaceutical development.

Anatomical redistribution of endogenous copper in embryonic mice overexpressing SOD1

Detailed quantitative in situ imaging of embryonic mice reveals overt Cu redistribution associated with SOD1-overexpression.