In-DTPA-Bz-NH-SA-K(IR-783-S-Ph-CO)-c(CGRRAGGSC)NH

Optical fluorescence imaging is increasingly used to monitor biological functions of specific targets (1-3). However, the intrinsic fluorescence of biomolecules poses a problem when fluorophores that absorb visible light (350–700 nm) are used. Near-infrared (NIR) fluorescence (700–1,000 nm) detection avoids the background fluorescence interference of natural biomolecules, providing a high contrast between target and background tissues in small animals. NIR fluorophores have a wider dynamic range and minimal fluorescence background as a result of reduced scattering compared with visible fluorescence detection. They also have high sensitivity because of low fluorescence background, as well as 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 becoming a non-invasive alternative to radionuclide imaging in small animals (4, 5). Interleukin-11 (IL-11) is a multifunctional growth factor for blood cells and their precursors (6). IL-11 receptor high-affinity binding complex consists of a low-affinity IL-11 ligand-binding α-chain (IL-11Rα) and a signal-transduction β-chain (gp 130). IL-11 and IL-11Rα are involved in breast cancer development and progression (7, 8). Arap et al. (9) reported that the cyclic nonapeptide c(CGRRAGGSC) was capable of binding specifically to IL-11Rα. Wang et al. (10) reported the development of a multimodality imaging agent, In-DTPA-Bz-NH-SA-K(IR-783-S-Ph-CO)-c(CGRRAGGSC)NH (In-DLIA-IL11Rα), for imaging IL-11Rα expression on breast tumors: single-photon emission computed tomography (SPECT) used In-DTPA-Bz-NH-SA and NIR imaging used IR-783-S-Ph-CO.