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Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.

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Molecular Imaging and Contrast Agent Database (MICAD) [Internet].

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, PhD
National Center for Biotechnology Information, NLM, NIH
Corresponding author.

Created: ; Last Update: November 12, 2008.

Chemical name:Cy7-Bis-dipicolylamine-zincimage 56269464 in the ncbi pubchem database
Abbreviated name:Cy7-DPA-Zn, Zn-DPA-Cy7
Synonym:PSS-794, PSVue 794, Probe 1, Probe 2
Agent category:Compound
Target category:Phospholipid
Method of detection:Optical near-infrared (NIR) fluorescence
Source of signal/contrast:Cy7
  • Checkbox In vitro
  • Checkbox Rodents
Click on the above structure for additional information in PubChem.



Optical fluorescence imaging is increasingly being used to obtain images of biological functions of specific targets in vitro and in small animals (1, 2). Near-infrared (NIR) fluorescence (700–900 nm) detection avoids the background fluorescence interference of natural biomolecules, providing a high contrast between target and background tissues. NIR fluorescence imaging is becoming a non-invasive alternative to radionuclide imaging in vitro and in small animals.

Apoptosis (programmed cell death) plays an important role in the pathophysiology of many diseases, such as cancer, neurodegenerative disorders, vascular disorders, atherosclerosis, 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 (PS) (3) from the inner membrane leaflet to the outer membrane leaflet, exposing the anionic head group of PS. PS is also accessible for annexin V (or annexin A5) binding in necrosis because of disruption of the plasma membrane. Annexin V, a 36-kDa protein, binds to PS with high affinity (Kd = 7 nM). Annexin V has been radiolabeled with 123I 124I, and 99mTc for imaging of cell death (4-6). Annexin V was successfully labeled with 18F (18F-labeled annexin V (4-[18F]FBA)) and is currently being developed as a positron emission tomography agent for imaging apoptosis as well as necrosis (7, 8). Cy5.5-Annexin V has been evaluated as an optical probe in small animals.

Gram-negative bacterium (e.g., Escherichia coli) and Gram-positive bacterium (e.g., Staphylococcus aureus) contain negatively charged molecules such as phosphatidylglycerol and phosphates in their cell membranes (9), whereas healthy mammalian cells primarily contain phospholipids of nearly neutral charge (10). Bis-dipicolylamine-zinc (DPA-Zn) showed selective affinity for anionic phospholipids (11, 12) on the surface of apoptotic bacteria and inflammatory neutrophils. Cy7, a NIR carbocyanine dye, was conjugated to DPA-Zn to form Cy7-DPA-Zn for in vivo NIR imaging of bacterial infection in mice (13, 14). Cy7-DPA-Zn was also able to detect apoptotic and necrotic cells (15-17).



The synthesis of Cy7-DPA-Zn was described by Leevy et al. (14). Cy7 was conjugated to bis-dipicolylamine via a reaction with 4-hydroxybenzoic acid to form Cy7-bis-dipicolylamine (Cy7-DPA). Zinc nitrate was added to Cy7-DPA in ethanol. After 30 min of incubation, the solution was evaporated to provide Cy7-DPA-Zn. The extinction coefficient of Cy7-DPA-Zn is 110,000 cm-1M-1, and the quantum yield is 0.14. The absorption maximum of Cy7-DPA-Zn is 794 nm, and the emission maximum is 810 nm.

In Vitro Studies: Testing in Cells and Tissues


Leevy et al. (13) showed that incubation of Cy7-DPA-Zn with S. aureus in culture for 10 min effectively stained the periphery of the bacteria as observed with fluorescence microscopy. Leevy et al. (12) also showed that bacteria were clearly stained in preference to the membrane surface of human epithelial cells isolated from human saliva. Hanshaw et al. (11) showed that phosphatidylserine on the membrane surface of apoptotic cells (Jurkat, CHO, HeLa) were clearly stained in preference to the membrane surface of the counterpart healthy cells. Thakur et al. (18) showed that Cy7-DPA-Zn bound to apoptotic S. aureus and neutrophils and not to their normal counterparts with confocal microscopy.

Animal Studies



Leevy et al. (13) performed in vivo fluorescence imaging in nude mice (n = 4) with an in vivo leg infection model in which 5 × 107S. aureus colony-forming units were injected intramuscularly into the muscles overlaying the tibia bone. Cy7-DPA-Zn (0.075 mmol) was injected intravenously at 6 h after infection. The target/muscle ratio was 4.0 at 3 h and decreased slightly to 3.9 at 21 h. On the other hand, the target/liver ratio was 1.5 at 3 h and gradually increased to 2.7 at 21 h. Ex vivo imaging showed that the infected leg exhibited four-fold greater intensity than the liver and kidneys. Histoimmunochemical studies of frozen tissue sections confirmed the colocalization of Cy7-DPA-Zn with S. aureus in the infected leg. In another study, Thakur et al. (18) showed that the bacteria infection foci exhibited one-fold greater intensity than those in inflammation (turpentine-induced). No blocking experiment was performed.

Smith et al. (15) performed in vivo NIR fluorescence imaging studies of Cy7-DPA-Zn (3 mg/kg) in rats (n = 3) bearing rat PAIII prostate tumors. Whole-body images were obtained at every 3 h for 24 h after intravenous injection. The tumor was clearly visualized at 6 h after injection with tumor/non-tumor ratio of 2.5, which decreased to 2.2 at 24 h. The tumor/non-tumor ratios were 1.2 with injection of Cy7 at the time points studied. Ex vivo imaging at 24 h after injection confirmed the high tumor fluorescence intensity of Cy7-DPA-Zn with ~35-fold higher than Cy7. The highest fluorescence intensities were observed in the core of the tumor sections. The fluorescence intensity levels of Cy7-DPA-Zn in the liver, kidney and lung were ~50% lower than that of the tumor, whereas Cy7 exhibited little accumulation in the normal organs. Microscopic analysis showed that the fluorescence signal from Cy7-DPA-Zn colocalized with tumor’s necrotic regions. Smith et al. also performed various in vivo NIR fluorescence imaging studies of cell death in the thymus, muscle, and PAIII tumors of rodents treated with dexamethasone, chemicals (ionophore, ethanol, and ketamine), and radiation (16, 17), respectively. Cy7-DPA-Zn exhibited higher fluorescence intensities as compared with untreated controls. No blocking experiments were performed.

Other Non-Primate Mammals


No publication is currently available.

Non-Human Primates


No publication is currently available.

Human Studies


No publication is currently available.

NIH Support

R01 GM059078, T32 GM075762, P50 CA94056, R01 GM36262


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