Cy7-Tyr-d-Glu-Cys-Hyp-Tyr(3-Cl)-Gly-Leu-Cys-Tyr-Ile-Gln-NH

Optical fluorescence imaging is increasingly used to monitor biological functions of specific targets in small animals (1-4). However, the intrinsic fluorescence of biomolecules poses a problem when fluorophores that absorb visible light (350–650 nm) are used. Near-infrared (NIR) fluorescence (650–1,000 nm) detection avoids the natural background fluorescence interference of biomolecules, providing a high contrast between target and background tissues in small animals. NIR fluorophores have a wider dynamic range and minimal background fluorescence as a result of reduced scattering compared with visible fluorescence detection. NIR fluorophores also have high sensitivity, attributable to low background fluorescence, and high extinction coefficients, which provide high quantum yields. The NIR region is also compatible with solid-state optical components, such as diode lasers and silicon detectors. NIR fluorescence imaging is a noninvasive alternative to radionuclide imaging in small animals (4, 5). Extracellular matrix adhesion molecules consist of a complex network of fibronectins, collagens, chondroitins, laminins, glycoproteins, heparin sulfate, tenascins, and proteoglycans that surround connective tissue cells, and they are mainly secreted by fibroblasts, chondroblasts, and osteoblasts (6). Cell substrate adhesion molecules are considered essential regulators of cell migration, differentiation, and tissue integrity and remodeling. These molecules play a role in inflammation and atherogenesis, but they also participate in the process of invasion and metastasis of malignant cells in the host tissue (7). A meshwork of clotted plasma protein was present in the tumor stroma but not in normal tissues, providing a functional matrix for angiogenesis, cell migration, and tumor cell invasion (8). There are high levels of collagens, fibronectin, and fibrin in the tumor connective tissues. Thrombosis plays a major role in many cardiovascular diseases such as myocardial infarction, pulmonary embolism, deep venous thrombosis, and cerebral venous thrombosis (9). Thrombosis occurs by an activation process of thrombin (F2 coagulation factor II), which then converts fibrinogen into fibrin. Thrombin initiates the cross-linking of the polymerized fibrin the activation of a transglutamase enzyme called coagulation factor XIII (FXIIIa indicates activated factor XIII) (10). Atherosclerotic lesions often contain microthrombi and fibrin on their surface. Fibrin is associated with a variety of malignant tumors. Fibrin is essential for stroma formation in the tumor with deposition of fibrin, which leads to tumor angiogenesis and metastasis. Hara et al. (11) prepared Cy7-Tyr-d-Glu-Cys-Hyp-Tyr(3-Cl)-Gly-Leu-Cys-Tyr-Ile-Gln-NH (Cy7-FTP11) for use with NIR fluorescence imaging of fibrin in thrombi in mice using high-resolution intravital fluorescence microscopy and fluorescence molecular tomography.