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Gadolinium-Diethylenetriamine pentaacetic acid-Leu-Ile-Lys-Lys-Pro-Phe

, PhD
National Center for Biotechnology Information, NLM, NIH

Created: ; Last Update: March 11, 2010.

Chemical name:Gadolinium-Diethylenetriamine pentaacetic acid-Leu-Ile-Lys-Lys-Pro-Phe
Abbreviated name:Gd-DTPA-g-R826
Agent category:Peptide
Target category:Acceptor
Method of detection:Magnetic resonance imaging (MRI)
Source of signal:Gadolinium, Gd
  • Checkbox In vitro
  • Checkbox Rodents
No structure is available in PubChem.



Magnetic resonance imaging (MRI) maps information about tissues spatially and functionally (1). Protons (hydrogen nuclei) are widely used to create images because of their abundance in water molecules, which comprise >80% of most soft tissues. The contrast of proton MRI images depends mainly on the density of nuclear proton spins, the relaxation times of the nuclear magnetization (T1, longitudinal; T2, transverse), the magnetic environment of the tissues, and the blood flow to the tissues. However, insufficient contrast between normal and diseased tissues requires the use of contrast agents. Most contrast agents affect the T1 and T2 relaxation of the surrounding nuclei, mainly the protons of water. T2* is the spin–spin relaxation time composed of variations from molecular interactions and intrinsic magnetic heterogeneities of tissues in the magnetic field (2). Cross-linked iron oxide (CLIO) and other iron oxide formulations affect T2 primarily and lead to a decreased signal. On the other hand, the paramagnetic T1 agents, such as gadolinium (Gd3+), and manganese (Mn2+), accelerate T1 relaxation and lead to brighter contrast images.

Apoptosis (programmed cell death) plays an important role in the pathophysiology of many diseases, such as cancer, neurodegenerative disorders, vascular disorders, and chronic hepatitis, as well as in the biology of normal cells like epithelial cells and immune cells (3). During apoptosis, there is rapid redistribution of phosphatidylserine from the inner membrane leaflet to the outer membrane leaflet, exposing the anionic head group of PS. PS is also accessible for annexin V binding in apoptosis and necrosis because of disruption of the plasma membrane. Annexin V binds to PS with high affinity (dissociation constant = 7 nM). Annexin V has been radiolabeled with 123I, 124I, and 99mTc for single-photon emission computed tomography imaging (4-6). Recently, annexin V was successfully labeled with 18F (7, 8), and 18F-labeled annexin V is being developed as a positron emission tomography agent for imaging apoptosis as well as necrosis. Cy5.5-annexin V and quantum dot (QD)-annexin V (9) have been evaluated as optical probes for near-infrared (NIR) imaging. Various bimodal annexin V–conjugated nanoparticles have been developed for imaging apoptosis, such as annexin V-CLIO-Cy5.5 and annexin V-QD-gadolinium for NIR and MRI imaging (10, 11).

A cyclic peptide, Cys-Leu-Ile-Lys-Lys-Pro-Phe-Cys, was identified with phage screening against PS (12). Leu-Ile-Lys-Lys-Pro-Phe (R826) was synthesized and conjugated to the 8-amino-3,6-dioxaoctanoyl linker to form g-R826, which was conjugated with 2-(4-isothiocyanatobenzyl)-diethylenetriamine pentaacetic acid (p-SCN-Bn-DTPA) to form DTPA-g-R826 for labeling with Gd for MRI of PS in apoptosis.



R826 peptide (with two Lys, protected with trifluoroacetic acid, and attached to 8-amino-3,6-dioxaoctanoyl at the N-terminus) was conjugated with two molar equivalents of p-SCN-Bn-DTPA for 48 h at room temperature (12). After removal of the protecting groups, DTPA-g-R826 was purified with dialysis and column chromatography. GdCl3 was added to a solution of DTPA-g-R826 and incubated for 24 h at room temperature. Gd-DTPA-g-R826 was purified with dialysis. The scrambled sequence of R826 (R826.Sc) was also conjugated to form Gd-DTPA-g-R826.Sc as a nonspecific control. The mass of Gd-DTPA-g-R826 was confirmed with mass spectroscopy. Longitudinal (r1) relaxivity values (nuclear magnetic resonance efficiency expressed in mM-1s-1) of Gd-DTPA-g-R826, Gd-DTPA-g-R826.Sc, and Gd-DTPA were 10.5, 10.5, and 3.8 measured at 0.3 T, respectively.

In Vitro Studies: Testing in Cells and Tissues


Burtea et al. (12) performed in vitro binding of Gd-DTPA-g-R826 (0.4 mM) to apoptotic Jurkat T cells. Gd concentrations were 400 and 140 nmol Gd per gram of cells for the apoptotic cells and control cells, respectively. Less than 5 nM Gd/g was observed in the apoptotic cells and control cells for Gd-DTPA-g-R826.Sc and Gd-DTPA. Caspase-3 activity was approximately nine times higher in the apoptotic cells than in the control cells. R826 exhibited a 50% inhibition concentration value of 14.8 nM using biotinylated annexin V with the apoptotic cells.

Animal Studies



Burtea et al. (12) performed in vivo MRI in apolipoprotein E–deficient (apoE-/-) mice after injection with 0.06 mmol/kg Gd-DTPA-g-R826 (n = 11), Gd-DTPA-g-R826.Sc (n = 4), or Gd-DTPA (n = 5). There was 132% enhancement in MRI signal intensity (ΔSNR) in the aortic wall at 10 min after injection. The ΔSNR remained constant (111%) for up to 61 min of imaging. Gd-DTPA-g-R826.Sc exhibited ΔSNR of 93% and 68% at 25 and 60 min, respectively. Gd-DTPA produced ΔSNR of 89% and 45% at 10 and 60 min, respectively. Immunohistological staining of the aorta sections of apoE-/- mice confirmed the presence of atherosclerotic lesions with extensive expression of PS. In mice with liver apoptosis induced with anti-Fas antibody, Gd-DTPA-g-R826 (n = 11) showed ΔSNR of 94% at 60 min and 60% at 90 min after injection, whereas healthy liver (n = 7) showed ΔSNR of 38% during the first 8 min, which decreased to <5% at 60 min after injection. Pretreatment with 0.1 mmol/kg R826 (10 min before Gd-DTPA-g-R826 injection) reduced the ΔSNR to <30% from 10–60 min after injection (n = 6). Gd-DTPA-g-R826.Sc (n = 8) showed ΔSNR of <40% at 10–60 min after injection in apoptotic and normal livers. Gd-DTPA (n = 7) showed ΔSNR of 20–30% R832 at 10 min and decreased to <5% at 60 min after injection. Immunohistological staining of the apoptotic liver sections confirmed the presence of extensive expression of PS.

Other Non-Primate Mammals


No publication is currently available.

Non-Human Primates


No publication is currently available.

Human Studies


No publication is currently available.


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Prinzen L., Miserus R.J., Dirksen A., Hackeng T.M., Deckers N., Bitsch N.J., Megens R.T., Douma K., Heemskerk J.W., Kooi M.E., Frederik P.M., Slaaf D.W., van Zandvoort M.A., Reutelingsperger C.P. Optical and magnetic resonance imaging of cell death and platelet activation using annexin a5-functionalized quantum dots. Nano Lett. 2007;7(1):93–100. [PubMed: 17212446]
van Tilborg G.A., Mulder W.J., Chin P.T., Storm G., Reutelingsperger C.P., Nicolay K., Strijkers G.J. Annexin A5-conjugated quantum dots with a paramagnetic lipidic coating for the multimodal detection of apoptotic cells. Bioconjug Chem. 2006;17(4):865–8. [PubMed: 16848390]
Burtea C., Laurent S., Lancelot E., Ballet S., Murariu O., Rousseaux O., Port M., Vander Elst L., Corot C., Muller R.N. Peptidic targeting of phosphatidylserine for the MRI detection of apoptosis in atherosclerotic plaques. Mol Pharm. 2009;6(6):1903–19. [PubMed: 19743879]
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