Integrin receptors are critical cell surface proteins involved in cell adhesion and are important in tumor progression. Inhibitors of integrin receptors can be effective anti-cancer agents because they can prevent tumor adhesion and abolish integrin functions which are important for cancer survival and metastasis. The receptors are composed of two subunits, alpha (a) and beta (a), and consist of an extracellular head portion that binds ligand and two long tails that anchor the receptor in the cell membrane. Structural studies have shown that integrin receptors can exist in several conformational states, an inactive "bent" form that has low affinity for known ligands and an "extended" active form that has high affinity for ligands. It has been shown that the conformational change from the "bent" to the "extended" form is essential for integrin ligand binding. Thus, approaches to identify novel drugs that prevent transition of the inactive to the active form of this receptor could be useful in inhibiting integrin functions. One receptor that has been extensively studied is the aVa3 integrin, a receptor important for migration and invasion of the tumor cells, as well as cell proliferation and tumor-induced angiogenesis. In this grant we propose to develop a unique technology to measure ligand binding to aVa3 that could be employed to discover drugs targeting this as well as other integrin receptors. Biodesy LLC has developed second-harmonic generation (SHG), a nonlinear optical technique that can be used to probe conformational changes in proteins. The technology is highly sensitive to small structural shifts in a molecule, making it an excellent means of detecting conformational changes in integrin receptors. As a consequence, SHG could provide a unique approach to identify drugs that selectively bind to either the inactive or the active form of aVa3. To develop SHG to measure ligand binding to aVa3, we will label soluble aVa3 with a second-harmonic-active fluorophore, attach the labeled receptor to a solid surface and measure its interaction with cRGD, a peptide integrin ligand. Once this SHG assay format has been developed, we will validate its utility and determine the specificity of the assay by testing whether physiologic ligands and activating antibodies that are known to bind to aVa3 produce the expected SHG response. These studies will provide the foundation for future work to develop SHG into a technology to identify selective inhibitors of aVa3 as well as other integrin receptors that can be used to treat cancer.
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