No abstract

Integrins constitute an important class of cell adhesion receptors responsible not only for cell-matrix adhesion but also for signaling bidirectionally across the membrane. Integrins are involved in many biological processes such as angiogenesis, thrombosis, inflammation, osteoporosis and cancer. Integrins thus play a key role in many severe human diseases. In this review we will describe recent research and development of RGD-containing integrin ligands for medical applications including drug design, radiolabeling, drug targeting, as well as biomaterial research. Many ligands have been developed for targeting the avb3 integrin in order to block angiogenesis or osteoporosis, but there are also other integrins like avb5 and a5b1 which become more and more interesting for similar purposes. aIIbb3 constitutes a potent target in thrombosis therapy; but the search for suitable ligands is still ongoing. We will reconstruct the drug development process for these integrin subtypes considering selected examples with focus on structure based design. Different structural requirements are pointed out concerning integrin activity and particularly the selectivity towards the distinct integrin types. Furthermore, we will show recent progress in tumor and thrombosis imaging based on radiolabeled RGD-containing ligands binding avb3 or aIIbb3, respectively. Additionally further advances in biomaterial research are presented. We describe the coating of different implant materials with various avb3 recognizing ligands for the purpose of increasing cell attachment and biocompatibility.

Coating of surfaces by RGD peptides is well-known. Herein we describe the possibility to switch cell adhesion properties by changing the distance and orientation of the RGD peptides to the surface. A set of RGD peptides of the type cyclo(-RGDfK-) was synthesized containing the photoswitchable 4-[(4-aminophenyl)azo]benzocarbonyl central unit as spacer between the acrylamide anchor and the RGD peptide. PMMA (poly methyl methacrylate) surfaces were coated with these peptides. Control of adhesion stimulation by irradiation with 366 or 450 nm light could be achieved.

One key point for improving osseous integration of implants is to render them osteopromotive by specifically favoring the adhesion of osteoblasts. Mimicking the physiological adhesion process of osteoblasts to the extracellular matrix improves cell adhesion in vitro and results in improved and earlier osseous integration of implants in vivo. Our approach involves coating titanium implants with a tailor-made cyclic-RGD peptide, thus allowing them to bind to specific integrin receptors on the cell surface through multimeric phosphonates. The advantages of this very stable, new type of anchoring for practical application are presented.

Summary: A new 2‐oxazoline monomer with a Boc protected amino function, 2‐[N‐Boc‐5‐aminopentyl]‐2‐oxazoline; (Boc‐AmOx), was synthesized from commercially available compounds. With an initiator salt system (N‐methyl‐2‐methyl‐2‐oxazolinium triflate; MeOxOTf), the monomer could be converted via living cationic ring‐opening polymerization to well‐defined homopolymers with narrow molar mass distributions and targeted polymer chain length. After a quantitative deprotection, poly(2‐oxazoline)s with pendant amino functions were obtained. In order to vary the polymer functional group density and solubility of the polymer, copolymerization with different monomer ratios of Boc‐AmOx and 2‐ethyl‐2‐oxazoline (EtOx) was performed. Ex‐situ NMR spectroscopy studies verified the randomness of the cationic copolymerization. The accessibility of the pendant amino side functions was confirmed in polymer analog thiourea formation with different isothiocyanates, such as benzyl isothiocyanate (BzNCS), or a fluorescence dye, tetramethyl rhodamine isothiocyanate (TRITC). A cross‐linking reaction with a bifunctional isothiocyanate (Ph(NCS)2) resulted in poly(2‐oxazoline) hydrogels. magnified image