Background

[PubMed]

Optical fluorescence imaging is increasingly used to obtain biological functions of specific targets (1, 2). 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. NIR fluorophores have a wider dynamic range and minimal background interference as a result of reduced scattering compared with visible fluorescence detection. They also have high sensitivity as a result of low infrared background interference, 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 becoming a non-invasive alternative to radionuclide imaging.

Integrins are a family of cell-surface heterodimeric glycoproteins that mediate diverse biological events involving cell–cell and cell–matrix interactions (3). They consist of an α and a β subunit. They are important for cell adhesion and signal transduction. The α₃β₁ integrin plays an important role in normal lung, kidney, cerebral cortical, and epithelial development (4). On the other hand, it affects tumor growth, tumor invasiveness, and metastasis as the α₃β₁ integrin is strongly expressed on tumor cells (5, 6). D-Cys-D-Asp-Gly-HCit-Gly-Pro-Gln-D-Cys (OA02) was identified to bind to the α₃ integrin on human ovarian cancer cells using one-bead-one-compound combinatorial libraries (7, 8). OA02 was conjugated with Cy5.5 to study in vivo biodistribution of the tracer in tumor-bearing mice (9). Cy5.5 is a NIR fluorescent dye with an absorbance maximum at 675 nm and emission maximum at 694 nm with a high extinction coefficient of 250,000 (mol/L)^-1cm^-1. OA02-Cy5.5 was found to have a high specific accumulation in α₃β₁-positve ES-2 human ovarian tumor cells in nude mice.

Synthesis

[PubMed]

Cy5.5 monofunctional N-hydroxysuccinimide (NHS) ester was used to conjugate D-Cys-D-Asp-Gly-HCit-Gly-Pro-Gln-D-Cys-Ebes-Ebes-Lys using solid-phase synthesis to form OA02-Cy5.5 (9). The NHS ester of Cy5.5 reacted with the ε-amino group of the lysine. The peak containing the OA02-Cy5.5 conjugate was analyzed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. The measured mass was m/z 2,457.2, which was ~1 Cy5.5/OA02. The chemical purity was >90%.

In Vitro Studies: Testing in Cells and Tissues

[PubMed]

Receptor-mediated endocytosis of OA02-biotin in SKOV-3 human ovarian tumor cells (α₃-positive) was observed by fluorescent microscopy (9). The staining was confined to the cell membrane and cytoplasm. On the other hand, Raji B-cell lymphomas (α₃-negative) did not show any staining.

Animal Studies

Human Studies

[PubMed]

No publication is currently available.

NIH Support

R33 CA89706, 5-T32-RR07038

References

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Albelda S.M. , Mette S.A. , Elder D.E. , Stewart R. , Damjanovich L. , Herlyn M. , Buck C.A. Integrin distribution in malignant melanoma: association of the beta 3 subunit with tumor progression. Cancer Res. 1990; 50 (20):6757–64. [PubMed: 2208139]

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Aina O.H. , Liu R. , Sutcliffe J.L. , Marik J. , Pan C.X. , Lam K.S. and From Combinatorial Chemistry to Cancer-Targeting Peptides. Mol Pharm. 2007 [PubMed: 17880166]

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Aina O.H. , Marik J. , Liu R. , Lau D.H. , Lam K.S. Identification of novel targeting peptides for human ovarian cancer cells using "one-bead one-compound" combinatorial libraries. Mol Cancer Ther. 2005; 4 (5):806–13. [PubMed: 15897245]

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Aina O.H. , Marik J. , Gandour-Edwards R. , Lam K.S. Near-infrared optical imaging of ovarian cancer xenografts with novel alpha 3-integrin binding peptide "OA02". Mol Imaging. 2005; 4 (4):439–47. [PubMed: 16285906]