Synthesis and preclinical characterization of [64Cu]NODAGA-MAL-exendin-4 with a Nε-maleoyl-L-lysyl-glycine linkage.
BACKGROUND
Renal localization of high radioactivity levels during targeted imaging compromises tissue visualization in the kidney region and limits diagnostic accuracy. Radioiodinated antibody fragments with a renal enzyme-cleavable N(ε)-maleoyl-L-lysyl-glycine (MAL) linkage demonstrated low renal radioactivity levels in mice, from early postinjection times. This study tested the hypothesis whether a (64)Cu-labeled NODAGA-exendin-4 peptide with a MAL linkage ([(64)Cu]NODAGA-MAL-exendin-4) could decrease kidney radioactivity levels in rats, compared to a [(64)Cu]NODAGA-exendin-4 reference, without impairing the radioactivity levels in the target tissue.


METHODS
NODAGA-MAL-exendin-4 was synthesized in a two-phase approach using solid support to prepare maleoyl-derivatized NODAGA followed by Michael addition to cysteine-derivatized exendin-4 in solution. Radiolabeling was performed in buffered aqua with [(64)Cu]CuCl2, which was produced via the (64)Ni(p,n)(64)Cu nuclear reaction. The in vitro and in vivo stability, lipophilicity, and distribution kinetics in major rat organs for [(64)Cu]NODAGA-MAL-exendin-4 were studied and compared to [(64)Cu]NODAGA-exendin-4. Labeling of pancreatic islets was assessed using autoradiography.


RESULTS
NODAGA-MAL-exendin-4 was synthesized, with an overall yield of 9%, and radiolabeled with (64)Cu with high specific radioactivity. Serum incubation studies showed high stability for [(64)Cu]NODAGA-MAL-exendin-4. Similar tissue distribution kinetics was observed for [(64)Cu]NODAGA-MAL-exendin-4 and [(64)Cu]NODAGA-exendin-4, with high kidney radioactivity levels.


CONCLUSIONS
The incorporated MAL linkage in [(64)Cu]NODAGA-MAL-exendin-4 was unable to reduce kidney radioactivity levels, compared to [(64)Cu]NODAGA-exendin-4. The applicability of metabolizable linkages in the design of kidney-saving exendin-4 analogs requires further investigation.
Turku PET Centre, University of Turku and Turku University Central Hospital, FI-20520 Turku, Finland; Department of Organic Chemistry, University of Turku, FI-20014 Turku, Finland. Electronic address: chbiyi@utu.fi.
Cheng-Bin
CB
Yim
Kirsi
K
Mikkola
Veronica
V
Fagerholm
Viki-Veikko
VV
Elomaa
Tamiko
T
Ishizu
Johan
J
Rajander
Joern
J
Schlesinger
Anne
A
Roivainen
Pirjo
P
Nuutila
Olof
O
Solin
D000085:Acetates / Q000097:blood / Q000138:chemical synthesis* / Q000493:pharmacokinetics; D000818:Animals; D001345:Autoradiography; D060326:Chemistry Techniques, Synthetic; D004355:Drug Stability; D000077270:Exenatide; D005998:Glycine / Q000737:chemistry*; D006573:Heterocyclic Compounds, 1-Ring / Q000097:blood / Q000138:chemical synthesis* / Q000493:pharmacokinetics; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007553:Isotope Labeling; D007700:Kinetics; D008297:Male; D010455:Peptides / Q000737:chemistry*; D049268:Positron-Emission Tomography; D051381:Rats; D014688:Venoms / Q000737:chemistry*
C572723:1-(1,3-carboxypropyl)-4,7-carboxymethyl-1,4,7-triazacyclononane; D000085:Acetates; D006573:Heterocyclic Compounds, 1-Ring; D010455:Peptides; D014688:Venoms; D000077270:Exenatide; D005998:Glycine
Copper-64; Exendin; GLP-1 receptor; NODAGA; Renal brush border membrane