For clarity only the protons from theN-methyl group and the amide bonds are shown

For clarity only the protons from theN-methyl group and the amide bonds are shown. a short review about the present clinical trials. The positive anti-angiogenic effects in cancer treatment can be further increased by combination with classical anti-cancer therapies. Several clinical trials in this direction are under HC-030031 investigation. Keywords:RGD peptides, integrin antagonists, glioblastoma, N-methylation, v3, conformational restriction, cyclization. == INTRODUCTION == Integrins are heterodimeric receptors that are important for cell-cell and cell-extracellular matrix (ECM) interactions and are composed of one and one -subunit [1,2]. These cell adhesion molecules act as transmembrane linkers between their extracellular ligands and the cytoskeleton, and modulate various signaling pathways essential in the biological functions of most cells. Integrins play a crucial role in processes such as cell migration, differentiation, and survival during embryogenesis, angiogenesis, wound healing, immune and non-immune defense mechanisms, hemostasis and oncogenic transformation [1]. The fact that many integrins are also linked with pathological conditions has converted them into very promising therapeutic targets [3]. In particular, integrins v3, v5 and 51 are involved in angiogenesis and metastasis of solid tumors, being excellent candidates for cancer therapy [4-7]. There are a number of different integrin subtypes which recognize and bind to the tripeptide sequence RGD (arginine, glycine, aspartic acid), which represents the most prominent recognition motif involved in cell adhesion. For example, the pro-angiogenic v3 integrin binds various RGD-containing proteins, including fibronectin (Fn), fibrinogen (Fg), vitronectin (Vn) and osteopontin [8]. It is therefore not surprising that this integrin has been targeted for cancer therapy and that Rabbit Polyclonal to ARHGEF5 RGD-containing peptides and peptidomimetics have been designed and synthesized aiming to selectively inhibit this receptor [9,10]. One classical strategy used in drug design is based on the knowledge about the structure of the receptor-binding pocket, preferably in complex with the natural ligand. However, this strategy, the so-called rational structure-based design, could not be applied in the field of integrin ligands since the first structures of integrins extracellular head groups were not described until 2001 for v3 [11] (one year later, in 2002 the structure of this integrin in complex with Cilengitide was also reported HC-030031 [12]) and 2004 for IIb3 [13]. Therefore, initial efforts in this field focused on a ligand-oriented design, which concentrated on optimizing RGD peptides by means of different chemical approaches in order to establish structure-activity relationships and identify suitable ligands. We focused our interest in finding ligands for v3 and based our approach on three chemical strategies pioneered in our group: 1) Reduction of the conformational space by cyclization; 2) Spatial screening of cyclic peptides; and 3)N-Methyl scan. The combination of these strategies lead to the discovery of the cyclic peptidec(RGDf(NMe)V) in 1995. This peptide showed subnanomolar antagonistic activity for the v3 receptor, nanomolar affinities for the closely related integrins v5 and 51, and high selectivity towards the platelet receptor IIb3. The peptide was patented together with Merck in 1997 (patent application submitted in 15.9.1995, opened in 20.3.1997) [14] and first presented with Mercks agreement at the European Peptide Symposium in Edinburgh (September 1996) [15]. The synthesis and activity of this molecule was finally published in 1999 [16]. This peptide is now developed by Merck-Serono, (Darmstadt, Germany) under HC-030031 the name “Cilengitide” and has recently entered Phase III clinical trials for HC-030031 treating glioblastoma [17]. The aim of this review is to describe the chemical development of Cilengitide in our laboratory, the biochemical background for its biological activity and to give a comprehensive summary of the clinical trials performed so far. == 1. DISCOVERY OF CILENGITIDE: DESIGN AND SYNTHESIS == == 1.1. The RGD-Binding Motif == Pioneering studies by Ruoslahti and HC-030031 Pierschbacher in the early 1980s.