Comparative in vivo stability of copper-64-labeled cross-bridged and conventional tetraazamacrocyclic complexes.
The increased use of copper radioisotopes in radiopharmaceutical applications has created a need for bifunctional chelators (BFCs) that form stable radiocopper complexes and allow covalent attachment to biological molecules. The chelators most commonly utilized for labeling copper radionuclides to biomolecules are analogues of 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA); however, recent reports have communicated the instability of the radio-Cu(II)-TETA complexes in vivo. A class of bicyclic tetraazamacrocycles, the ethylene "cross-bridged" cyclam (CB-cyclam) derivatives, form highly kinetically stable complexes with Cu(II) and therefore may be less susceptible to transchelation than their nonbridged analogues in vivo. Herein we report results on the relative biological stabilities and identification of the resulting radiolabeled metabolites of a series of (64)Cu-labeled macrocyclic complexes. Metabolism studies in normal rat liver have revealed that the (64)Cu complex of 4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane ((64)Cu-CB-TE2A) resulted in significantly lower values of protein-associated (64)Cu than (64)Cu-TETA [13 +/- 6% vs 75 +/- 9% at 4 h]. A similar trend was observed for the corresponding cyclen derivatives, with the (64)Cu complex of 4,10-bis(carboxymethyl)-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane ((64)Cu-CB-DO2A) undergoing less transchelation than the (64)Cu complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid ((64)Cu-DOTA) [61 +/- 14% vs 90.3 +/- 0.5% protein associated (64)Cu at 4 h]. These data indicate that the structurally reinforcing cross-bridge enhances in vivo stability by reducing metal loss to protein in both the cyclam and cyclen cross-bridged (64)Cu complexes and that (64)Cu-CB-TE2A is superior to (64)Cu-CB-DO2A in that regard. These findings further suggest that a bifunctional chelator derivative of CB-TE2A is a highly desirable alternative for labeling copper radionuclides to biological molecules for diagnostic imaging and targeted radiotherapy.
Boswell
C Andrew
CA
Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA. andersoncj@mir.wustl.edu
Sun
Xiankai
X
Niu
Weijun
W
Weisman
Gary R
GR
Wong
Edward H
EH
Rheingold
Arnold L
AL
Anderson
Carolyn J
CJ
D000818:Animals; D001372:Aza Compounds / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D002614:Chelating Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D003301:Copper Radioisotopes; D018360:Crystallography, X-Ray; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006571:Heterocyclic Compounds / Q000378:metabolism; D006573:Heterocyclic Compounds, 1-Ring / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D015151:Immunoblotting; D008297:Male; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D011917:Rats, Inbred Lew; D017207:Rats, Sprague-Dawley; D013329:Structure-Activity Relationship; D013482:Superoxide Dismutase / Q000378:metabolism; D014018:Tissue Distribution
C483896:(4,10-bis(carboxymethyl)-1,4,7,10-tetraazabicyclo(5.5.2)tetradecane)copper(II); C483895:(4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo(6.6.2)hexadecane)copper(II); D001372:Aza Compounds; D002614:Chelating Agents; D003301:Copper Radioisotopes; D006571:Heterocyclic Compounds; D006573:Heterocyclic Compounds, 1-Ring; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; C113624:copper(II)-1,4,8,11-tetraazacyclotetradecane-N,N',N'',N'''-tetraacetic acid; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; D013482:Superoxide Dismutase