Radiochemical and radiopharmacological characterization of a ⁶⁴Cu‐labeled α‐MSH analog conjugated with different chelators

Abstract

Radiolabeled α-melanocyte-stimulating hormone (α-MSH) derivatives have a high potential for diagnosis and treatment of melanoma, because of high specificity and binding affinity to the melanocortin-1 receptor (MC1R). Hence, the α-MSH-derived peptide NAP-NS1 with a β-Ala linker (ε-Ahx-β-Ala-Nle-Asp-His-D-Phe-Arg-Trp-Gly-NH 2 ) was conjugated to different chelators: either to NOTA (p-SCN-Bn-1,4,7-triazacyclononane-1,4,7-triacetic acid), to a hexadentate bispidine carbonate derivative (dimethyl-9-(((4-nitrophenoxy)carbonyl)oxy)-2,4-di(pyridin-2-yl)-3,7-bis(pyridin-2-ylmethyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate), or to DMPTACN (p-SCN-Ph-bis(2-pyridyl-methyl)-1,4,7triaza-cyclononane), labeled with 64 Cu, and investigated in terms of radiochemical and radiopharmacological properties. For the three 64 Cu-labeled conjugates negligible transchelation, suitable buffer and serum stability, as well as appropriate water solubility, was determined. The three conjugates exhibited high binding affinity (low nanomolar range) in murine B16F10, human MeWo, and human TXM13 cells. The B max values of [ 64 Cu]Cu-bispidine-NAP-NS1 ([ 64 Cu] Cu-2) and [ 64 Cu]Cu-DMPTACN-NAP-NS1 ([ 64 Cu]Cu-3) were higher than those of [ 64 Cu]Cu-NOTA-NAP-NS1 ([ 64 Cu]Cu-1), implying that different charged chelate units might have an impact on binding capacity. Preliminary in vivo biodistribution studies suggested the main excretion pathway of [ 64 Cu]Cu-1 and [ 64 Cu]Cu-3 to be renal, while that of [ 64 Cu]Cu-2 seemed to be both renal and hepatobiliary. An initial moderate uptake in the kidney decreased clearly after 60 minutes. All three 64 Cu-labeled conjugates should be considered for further in vivo investigations using a suitable xenograft mouse model. KEYWORDS α-MSH, copper chelators, malignant melanoma, melanocortin-1 receptor, molecular imaging, PET, radiopharmaceuticals, radiotracerThis manuscript is dedicated to Prof Jörg Steinbach on the occasion of his retirement in appreciation of his thoughtful and selfless leadership.

Enzymological Characterization of 64Cu-Labeled Neprilysin Substrates and Their Application for Modulating the Renal Clearance of Targeted Radiopharmaceuticals

“…The thiourea functionality at the N-terminus in both compounds might be causative for the observed results considering the phenomena of thione-thiol tautomerization , and potential Edman degradation. − Moreover, the occurrence of different isomers of 64 Cu-labeled NOTA-Bn-amine is known . In this context, similar radioactivity-detected HPLC chromatograms for [ 64 Cu]­Cu-NOTA-Bn-NCS-functionalized peptides were occasionally observed . It is worth noting that the HPLC analyses of the nonlabeled peptides 1a and 1b prior to radiolabeling revealed good purities (95% and 96%, respectively, Table ).…”

“…57 In this context, similar radioactivity-detected HPLC chromatograms for [ 64 Cu]Cu-NOTA-Bn-NCS-functionalized peptides were occasionally observed. 58 It is worth noting that the HPLC analyses of the nonlabeled peptides 1a and 1b prior to radiolabeling revealed good purities Facing the radiochemical challenges with NOTA-Bn-NCS, we decided to change the N-terminal group to NODAGA-PAMBA, which closely resembles the original structure but is attached via an amide bond instead of a thiourea functionality. A similar approach was recently followed by Bendre et al 44 for the introduction of cleavable linkers into PSMA ligands.…”

Cyclam with a phosphinate-bis(phosphonate) pendant arm is a bone-targeting carrier of copper radionuclides

“…This observation indicates the high stability of [ 64 Cu]Cu II -te1P BP and its resistance to in vivo trans-chelation to liver proteins (such as superoxide dismutase)a frequently observed metabolic fate of 64 Cu II -labeled compounds, particularly in rodents, which is accompanied by 64 Cu trapping in the liver. [51][52][53]…”

Neuroendocrine Factors in Melanoma Pathogenesis

“…Additionally, 18 F MSH derivates have successfully been used as PET imaging tracer substances for B16F10-luc melanoma in mice, with significant intratumor accumulation, clearly depicting small tumors [ 193 , 194 ]. Various 64 Cu-, 68 Ga-, and 203 Pb-labeled, as well as 3 and 4-arm DOTA α-MSH analogs are also explored for their MC1R affinities [ 193 , 195 , 196 , 197 , 198 ].…”