Journal
BIOCHIMICA ET BIOPHYSICA ACTA-GENERAL SUBJECTS
Volume 1830, Issue 3, Pages 2562-2573Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.bbagen.2012.12.007
Keywords
Positron emission tomography; Molecular imaging; Annexin A5; Carbon-11; Cell death; Sel-tag
Categories
Funding
- Swedish Foundation for Strategic Research (SSF) [RBa08-0067]
- Governmental Agency for Innovation Systems (VINNOVA) [2009-00179]
- Swedish Cancer Society (Cancerfonden) [2009/739]
- Swedish Research Council [2008-2654, 2004-5104, 2008-3186]
- Karolinska Institutet
- Swedish Foundation for Strategic Research (SSF) [RBa08-0067] Funding Source: Swedish Foundation for Strategic Research (SSF)
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Background: Radiolabeled annexin A5 (AnxA5) is widely used for detecting phosphatidylserine exposed on cell surfaces during apoptosis. We describe here a new method for labeling AnxA5 and a size-matched control protein with short-lived carbon-11, for probing the specificity of in vivo cell death monitoring using positron emission tomography (PET) imaging. Methods: AnxA5 and the control protein were recombinantly expressed with a C-terminal Sel-tag, the tetrapeptide -Gly-Cys-Sec-Gly-COOH. The proteins were then labeled either fluorescently for in vitro corroborations of binding behaviors or with C-11 for dynamic in vivo PET studies. Results: AnxA5 demonstrated retained calcium-dependent binding to apoptotic cells after the C-terminus modification. The control protein showed no functional binding. The C-11-ligands demonstrated similar in vivo pharmacokinetic behavior in healthy mice except for higher uptake in kidney and higher intact elimination to urine of AnxA5. After inducing hepatic apoptosis, however, the uptake of labeled AnxA5 in the targeted tissue increased compared to baseline levels while that of the control protein tended to decrease. Conclusions: These data suggest that the combined use of these two tracers can facilitate differentiating specific AnxA5 binding and its changes caused by induced cell death from uptake due to non-specific permeability and retention effects at baseline or after therapy. General significance: The Sel-tag enables rapid and mild reactions with electrophilic agents giving site-specifically labeled proteins for multi-probe analyses. The combined use of C-11-labeled AnxA5 and a size-matched control protein with dynamic PET can be useful for evaluating drug effects on target as well as off-target tissues. (C) 2013 Elsevier B.V. All rights reserved.
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