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      Integrin Targeted Delivery of Chemotherapeutics

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          Abstract

          Targeted delivery of chemotherapeutics is defined in the sense, that is, to maximize the therapeutic index of a chemotherapeutic agent by strictly localizing its pharmacological activity to the site or tissue of action. Integrins are a family of heterodimeric transmembrane glycoproteins involved in a wide range of cell-to-extracellular matrix (ECM) and cell-to-cell interactions. As cell surface receptors, integrins readily interact with extracellular ligands and play a vital role in angiogenesis, leukocytes function and tumor development, which sets up integrins as an excellent target for chemotherapy treatment. The peptide ligands containing the arginine-glycine-aspartic acid (RGD), which displays a strong binding affinity and selectivity to integrins, particularly to integrin αvβ3, have been developed to conjugate with various conventional chemotherapeutic agents, such as small molecules, peptides and proteins, and nanoparticle-carried drugs for integtrin targeted therapeutic studies. This review highlights the recent advances in integrin targeted delivery of chemotherapeutic agents with emphasis on target of integrin αvβ3, and describes the considerations for the design of the diverse RGD peptide-chemotherapeutics conjugates and their major applications.

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          Most cited references95

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          A new concept for macromolecular therapeutics in cancer chemotherapy: mechanism of tumoritropic accumulation of proteins and the antitumor agent smancs.

          We previously found that a polymer conjugated to the anticancer protein neocarzinostatin, named smancs, accumulated more in tumor tissues than did neocarzinostatin. To determine the general mechanism of this tumoritropic accumulation of smancs and other proteins, we used radioactive (51Cr-labeled) proteins of various molecular sizes (Mr 12,000 to 160,000) and other properties. In addition, we used dye-complexed serum albumin to visualize the accumulation in tumors of tumor-bearing mice. Many proteins progressively accumulated in the tumor tissues of these mice, and a ratio of the protein concentration in the tumor to that in the blood of 5 was obtained within 19 to 72 h. A large protein like immunoglobulin G required a longer time to reach this value of 5. The protein concentration ratio in the tumor to that in the blood of neither 1 nor 5 was achieved with neocarzinostatin, a representative of a small protein (Mr 12,000) in all time. We speculate that the tumoritropic accumulation of these proteins resulted because of the hypervasculature, an enhanced permeability to even macromolecules, and little recovery through either blood vessels or lymphatic vessels. This accumulation of macromolecules in the tumor was also found after i.v. injection of an albumin-dye complex (Mr 69,000), as well as after injection into normal and tumor tissues. The complex was retained only by tumor tissue for prolonged periods. There was little lymphatic recovery of macromolecules from tumor tissue. The present finding is of potential value in macromolecular tumor therapeutics and diagnosis.
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            RGD and other recognition sequences for integrins.

            Proteins that contain the Arg-Gly-Asp (RGD) attachment site, together with the integrins that serve as receptors for them, constitute a major recognition system for cell adhesion. The RGD sequence is the cell attachment site of a large number of adhesive extracellular matrix, blood, and cell surface proteins, and nearly half of the over 20 known integrins recognize this sequence in their adhesion protein ligands. Some other integrins bind to related sequences in their ligands. The integrin-binding activity of adhesion proteins can be reproduced by short synthetic peptides containing the RGD sequence. Such peptides promote cell adhesion when insolubilized onto a surface, and inhibit it when presented to cells in solution. Reagents that bind selectively to only one or a few of the RGD-directed integrins can be designed by cyclizing peptides with selected sequences around the RGD and by synthesizing RGD mimics. As the integrin-mediated cell attachment influences and regulates cell migration, growth, differentiation, and apoptosis, the RGD peptides and mimics can be used to probe integrin functions in various biological systems. Drug design based on the RGD structure may provide new treatments for diseases such as thrombosis, osteoporosis, and cancer.
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              Crystal structure of the extracellular segment of integrin alpha Vbeta3 in complex with an Arg-Gly-Asp ligand.

              The structural basis for the divalent cation-dependent binding of heterodimeric alphabeta integrins to their ligands, which contain the prototypical Arg-Gly-Asp sequence, is unknown. Interaction with ligands triggers tertiary and quaternary structural rearrangements in integrins that are needed for cell signaling. Here we report the crystal structure of the extracellular segment of integrin alphaVbeta3 in complex with a cyclic peptide presenting the Arg-Gly-Asp sequence. The ligand binds at the major interface between the alphaV and beta3 subunits and makes extensive contacts with both. Both tertiary and quaternary changes are observed in the presence of ligand. The tertiary rearrangements take place in betaA, the ligand-binding domain of beta3; in the complex, betaA acquires two cations, one of which contacts the ligand Asp directly and the other stabilizes the ligand-binding surface. Ligand binding induces small changes in the orientation of alphaV relative to beta3.
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                Author and article information

                Journal
                Theranostics
                thno
                Theranostics
                Ivyspring International Publisher (Sydney )
                1838-7640
                2011
                17 February 2011
                : 1
                : 189-200
                Affiliations
                1. National Institute of Biomedical Imaging and Bioengineering (NIBIB), National Institutes of Health (NIH), Bethesda, MD;
                2. Molecular Imaging Center, Department of Radiology, Keck School of Medicine, University of Southern California, Los Angeles, CA
                Author notes
                ✉ Corresponding author: Dr. Xiaoyuan Chen, Laboratory of Molecular Imaging and Nanomedicine (LOMIN), National Institute of Biomedical Imaging and Bioengineering (NIBIB), National Institutes of Health (NIH), 31 Center Dr, 31/1C22, Bethesda, MD 20892, USA; Tel: 301-451-4246; Email: shawn.chen@ 123456nih.gov ; Dr. Kai Chen, Molecular Imaging Center, Department of Radiology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA; Tel: 323-442-3582; Email: chenkai@ 123456usc.edu

                Conflict of Interest: The authors have declared that no conflict of interest exists.

                Article
                thnov01p0189
                10.7150/thno/v01p0189
                3086622
                21547159
                a604135f-bc79-47ad-a3d6-ff4d601cd1d2
                © Ivyspring International Publisher. This is an open-access article distributed under the terms of the Creative Commons License (http://creativecommons.org/licenses/by-nc-nd/3.0/). Reproduction is permitted for personal, noncommercial use, provided that the article is in whole, unmodified, and properly cited.
                History
                Categories
                Review

                Molecular medicine
                integrin,targeted delivery,chemotherapeutics,rgd,bioconjugation.
                Molecular medicine
                integrin, targeted delivery, chemotherapeutics, rgd, bioconjugation.

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