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

Abstract

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.

Novel Hybrid Benzoazacrown Ligand as a Chelator for Copper and Lead Cations: What Difference Does Pyridine Make

“…The lower overall basicity of H 2 BA2A1Py compared to H 3 BA3A induced a consequent decrease in the logβ of complexes with BA2A1Py 2− , although to a different degree: only 0.5 log for Cu 2+ , while 1.6 log for Pb 2+ ( Table 1 ), showing a preference towards Cu 2+ . This fact proves our suggestion about an increase in affinity for Cu 2+ of N-donor ligands and correlates with the described CuDOTAPy in vitro stability [ 9 ].…”

“…Given Cu 2+ is a transition metal cation, preferring softer N-donors along with O-donor atoms, it can be effectively bound by aromatic nitrogen that is known to be less basic than aliphatic amines. Moreover, it has been recently shown that H 4 DOTA derivatives with a pyridine arm can significantly improve copper binding [ 9 ].…”

“…To the best of our knowledge, protonation and complexation constants of such hybrid ligands with the simultaneous presence of acetic and pyridyl pendant groups have not been described in the literature yet. There are examples of substitutions of all (two or three) acetates in azacrowns by pyridines [ 3 , 6 , 10 , 11 ] and it has been shown that pyridine, as a pendant arm, can significantly improve the chelation ability and kinetics of binding towards Cu 2+ and Bi 3+ , including direct comparison with well-known H 4 DOTA [ 9 , 12 , 13 ].…”

Production, purification, and radiolabeling of the 203Pb/212Pb theranostic pair

“…All solvents and reagents were purchased from commercial suppliers (Sigma Aldrich, Fisher Scientific, VWR) and used as received, unless otherwise noted. (7,10-bis (pyridin-2-ylmethyl)-1,4,7,10-tetraazacyclododecane-1,4-diyl) diacetic acid) and DOTA-3Py (2-(4,7,10-tris (pyridin-2-ylmethyl)-1,4,7,10-tetraazacyclododecan-1-yl) acetic acid) were synthesized as previously described (Yang et al 2021). Instant thin layer chromatography paper impregnated with silicic acid (iTLC-SA) was purchased from Agilent Technologies (Santa Clara, CA).…”

“…We present the production of the 203 Pb and 212 Pb theranostic pair using TRIUMF's TR13 (13 MeV) and 500 MeV cyclotron, subsequent radiochemical purification and isotope characterization. The separated radioisotopes were evaluated alongside each other for radiolabeling a series of TRIUMF developed, pyridine based-DOTA analogues (Yang et al 2021) along with commercial standards DOTA and TCMC (Fig. 2), and the stability of each radiometal-complex was evaluated in vitro.…”