Comparison of 64Cu-Complexing Bifunctional Chelators for Radioimmunoconjugation: Labeling Efficiency, Specific Activity, and in Vitro/in Vivo Stability

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• 作者：Maggie S. Cooper ; Michelle T. Ma ; Kavitha Sunassee ; Karen P. Shaw ; Jennifer D. Williams ; Rowena L. Paul ; Paul S. Donnelly ; Philip J. Blower
• 刊名：Bioconjugate Chemistry
• 出版年：2012
• 出版时间：May 16, 2012
• 年：2012
• 卷：23
• 期：5
• 页码：1029-1039
• 全文大小：446K
• 年卷期：v.23,no.5(May 16, 2012)
• ISSN：1520-4812

文摘

High radiolabeling efficiency, preferably to high specific activity, and good stability of the radioimmunoconjugate are essential features for a successful immunoconjugate for imaging or therapy. In this study, the radiolabeling efficiency, in vitro stability, and biodistribution of immunoconjugates with eight different bifunctional chelators labeled with ⁶⁴Cu were compared. The anti-CD20 antibody, rituximab, was conjugated to four macrocyclic bifunctional chelators (p-SCN-Bn-DOTA, p-SCN-Bn-Oxo-DO3A, p-SCN-NOTA, and p-SCN-PCTA), three DTPA derivatives (p-SCN-Bn-DTPA, p-SCN-CHX-A鈥?DTPA, and ITC-2B3M-DTPA), and a macrobicyclic hexamine (sarcophagine) chelator (sar-CO₂H) = (1-NH₂-8-NHCO(CH₂)₃CO₂H)sar where sar = sarcophagine = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane). Radiolabeling efficiency under various conditions, in vitro stability in serum at 37 掳C, and in vivo biodistribution and imaging in normal mice over 48 h were studied. All chelators except sar-CO₂H were conjugated to rituximab by thiourea bond formation with an average of 4.9 卤 0.9 chelators per antibody molecule. Sar-CO₂H was conjugated to rituximab by amide bond formation with 0.5 chelators per antibody molecule. Efficiencies of ⁶⁴Cu radiolabeling were dependent on the concentration of immunoconjugate. Notably, the ⁶⁴Cu-NOTA-rituximab conjugate demonstrated the highest radiochemical yield (95%) under very dilute conditions (31 nM NOTA-rituximab conjugate). Similarly, sar-CO-rituximab, containing 1/10th the number of chelators per antibody compared to that of other conjugates, retained high labeling efficiency (98%) at an antibody concentration of 250 nM. In contrast to the radioimmunoconjugates containing DTPA derivatives, which demonstrated poor serum stability, all macrocyclic radioimmunoconjugates were very stable in serum with <6% dissociation of ⁶⁴Cu over 48 h. In vivo biodistribution profiles in normal female Balb/C mice were similar for all the macrocyclic radioimmunoconjugates with most of the activity remaining in the blood pool up to 48 h. While all the macrocyclic bifunctional chelators are suitable for molecular imaging using ⁶⁴Cu-labeled antibody conjugates, NOTA and sar-CO₂H show significant advantages over the others in that they can be radiolabeled rapidly at room temperature, under dilute conditions, resulting in high specific activity.