Cy7-Bis-dipicolylamine-zinc

Excerpt

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 (K_d = 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).