Discovery of cytokine mimics using cell-based systems

Radiolabeled multimeric cyclic RGD peptides as integrin alphavbeta3 targeted radiotracers for tumor imaging

Integrin alphavbeta3 plays a significant role in tumor angiogenesis and is a receptor for the extracellular matrix proteins with the exposed arginine-glycine-aspartic (RGD) tripeptide sequence. These include vitronectin, fibronectin, fibrinogen, lamin, collagen, Von Willibrand's factor, osteoponin, and adenovirus particles. Integrin alphavbeta3 is expressed at low levels on epithelial cells and mature endothelial cells, but it is overexpressed on the activated endothelial cells of tumor neovasculature and some tumor cells. The highly restricted expression of integrin alphavbeta3 during tumor growth, invasion, and metastasis presents an interesting molecular target for both early detection and treatment of rapidly growing solid tumors. In the past decade, many radiolabeled linear and cyclic RGD peptide antagonists have been evaluated as the integrin alphavbeta3 targeted radiotracers. Significant progress has been made on their use for imaging tumors of different origin by single photon emission computed tomography (SPECT) or positron emission tomography (PET) in several tumor-bearing animal models. [18F]Galacto-RGD is under clinical investigation as the first integrin alphavbeta3 targeted radiotracer for noninvasive visualization of the activated integrin alphavbeta3 in cancer patients. This review will focus on the radiolabeled multimeric cyclic RGD peptides (dimers and tetramers) useful as radiotracers to image the tumor integrin alphavbeta3 expression by SPECT and PET, and some fundamental aspects for the development of integrin alphavbeta3 targeted radiotracers. These include the choice of radionuclide and bifunctional chelators, selection of targeting biomolecules, and factors influencing the integrin alphavbeta3 binding affinity and tumor uptake, as well as different approaches for modification of radiotracer pharmacokinetics.

Towards erythropoietin mimicking small molecules

Small molecules potentially mimicking the hormone erythropoietin have been discovered by screening of a library of rationally designed multicomponent reaction molecules in a functional cell-based assay.

Conformational analysis of an alpha3beta1 integrin-binding peptide from thrombospondin-1: implications for antiangiogenic drug design

The integrin alpha3beta1 plays important roles in development, angiogenesis, and the pathogenesis of cancer, suggesting potential therapeutic uses for antagonists of this receptor. Recently, an alpha3beta1 integrin-binding site was mapped to residues 190-201 (FQGVLQNVRFVF) of the N-terminal domain of the secreted protein thrombospondin-1 (TSP1). This sequence displays diverse biological activities in vitro and inhibits angiogenesis in vivo. Herein we describe the NMR solution conformation of this segment in both water and dodecylphosphocholine micelles. While essentially unstructured in water, a more well-defined conformation is populated in micelles, particularly in the C-terminal half of the peptide and correlated with increased biological activity of the micellar peptide. The data suggested that the residues that are critical for biological activity are contained in a structurally well-defined segment of the peptide. These data support the role of the NVR motif as a required element of full-length TSP1 for specific molecular recognition by the alpha3beta1 integrin.

Novel and selective alpha(v)beta3 receptor peptide antagonist: design, synthesis, and biological behavior

Among RGD-dependent integrins, the alpha(v)beta3 receptor has recently received increasing attention as a therapeutic target because of its critical role in tumor-induced angiogenesis and metastasis formation. Here, we describe a new peptide antagonist of alpha(v)beta3 receptor, designed on the basis of the crystal structure of integrin alpha(v)beta3 in complex with c(RGDf[NMe]V) and the NMR structure of echistatin. Cell adhesion assays have demonstrated that the peptide is a potent and selective antagonist of the alpha(v)beta3 receptor.

Combining pharmacophore search, automated docking, and molecular dynamics simulations as a novel strategy for flexible docking. Proof of concept: docking of arginine-glycine-aspartic acid-like compounds into the alphavbeta3 binding site

A novel and highly efficient flexible docking approach is presented where the conformations (internal degrees of freedom) and orientations (external degrees of freedom) of the ligands are successively considered. This hybrid method takes advantage of the synergistic effects of structure-based and ligand-based drug design techniques. Preliminary antagonist-derived pharmacophore determination provides the postulated bioactive conformation. Subsequent docking of this pharmacophore to the receptor crystal structure results in a postulated pharmacophore/receptor binding mode. Pharmacophore-oriented docking of antagonists is subsequently achieved by matching ligand interacting groups with pharmacophore points. Molecular dynamics in water refines the proposed complexes. To validate the method, arginine-glycine-aspartic acid (RGD) containing peptides, pseudopeptides, and RGD-like antagonists were docked to the crystal structure of alphavbeta3 holoprotein and apoprotein. The proposed directed docking was found to be more accurate, faster, and less biased with respect to the protein structure (holo and apoprotein) than DOCK, Autodock, and FlexX docking methods. The successful docking of an antagonist recently cocrystallized with the receptor to both apo and holoprotein is particularly appealing. The results summarized in this report illustrated the efficiency of our light CoMFA/rigid body docking hybrid method.