Near-Infrared Optical Imaging of Integing αvβ3 in Human Tumor Xenografts

In vivo optical imaging is potentially useful for evaluating the presence of tumor markers that are targets of molecular medicine. Here we report the synthesis and characterization of integrin alpha v beta 3-targeted peptide cyclo(Lys-Arg-Gly-Asp-Phe) [c(KRGDf)] labeled with fluorescence dyes with wavelength spanning from the visible/near infrared (Cy5.5) to the true near infrared (IRDye800) for optical imaging. In vitro, the peptide-dye conjugates bound specifically to tumor cells expressing alpha v beta 3. When administered intravenously into mice at a dose of 6 nmol/mouse, the conjugates accumulated in tumors expressing alpha v beta 3. The tumor-to-background ratios for human KS1767 Kaposi's sarcoma in mice injected with Cy5.5c(KRGDf) and Cy5.5 were 5.5 and 1.5, respectively. Preinjection of c(KRGDf) blocked the uptake of Cy5.5-c(KRGDf) in tumors by 89%. In alpha v beta 3-positive M21 and -alpha v beta 3 negative M21-L human melanoma, fluorescence intensity in the tumor of mice injected with IRDye800-c(KRGDf) was 2.3 and 1.3 times that in normal tissue, respectively. Dynamic imaging revealed that Cy5.5-c(KRGDf) was rapidly taken up by KS1767 tumor immediately after bolus injection. The rate of its uptake in the tumor was reduced by preinjection of c(KRGDf) in an interval time-dependent manner. Our data suggest that near-infrared fluorescence imaging may be applied to the detection of tumors expressing integrin alpha v beta 3 and to the assessment of the optimal biological dose and schedule of targeted therapies. Mol Imaging (2004) 3, 343-351.