Current Pharmaceutical Design - Volume 13, Issue 20, 2007

In the first contribution to this special issue of Current Pharmaceutical Design dedicated to topics on angiogenesis and anti-angiogenesis, Presta and co-workers [1] describe the FGF/FGFR as a target for anti-angiogenesis therapy, starting from the experimental evidence that the FGF family is involved in angiogenesis and angioproliferative diseases. On this basis, they summarize different approaches aimed at impairing FGF/FGFR activity and their possible involvement in therapeutic protocols. In the same context, Guerrini and co-workers [2] review on conformational aspects of heparin sequences involved in the interaction with FGF. For this purpose, results from both experimental (X-ray crystallography and NMR) and theoretical (molecular modeling simulations) studies are reported for heparin oligosaccharides of variable length, as well as for heparins bearing “glycol-split” residues. Glicol-split heparins are also reported by Casu and co-workers [3] as potent inhibitors of heparanase and, most interestingly, as antiangiogenic and antimetastatic drug candidates. Moreover, they also allow to distinguish antiangiogenic effects caused by heparanase inhibition from those deriving from direct inhibition of growth factors. The next contribution describes compounds with antiangiogenic activity. Peptides derived from endogenous proteins (i.e., thrombospondin, laminin, endostatin, decorin, and parathyroid hormone) are examples of antiangiogenic agents reported by Ge and co-workers [4]. They could be obtained following phage-display library screening and combinatorial chemistry, with physico-chemical profiles appropriately set up to increase their potency and stability. However, application of such compounds into clinical practice is not obvious, but critical problems are to be solved before. Rossello and co-workers [5] report a survey on inhibitors of matrix metalloproteinases (MMPi), focusing attention on compounds with improved potency and selectivity. Improvement of binding to the catalytic zinc atom, design of no-zinc binding inhibitors and dimeric inhibitors are the new and major challenges in the field of MMPi. In the contribution from Hiraki and co-workers [6], a couple of type II transmembrane glycoproteins (namely, chondromodulin-I and tenomodulin) are described as inhibitors of angiogenesis and anti-tumorigenic agents. Details on structure, biological activity and localization are also reported. Miura and co-workers [7] discuss on the regulation of angiogenesis and angiogenic factors by cardiovascular medications (such as statins, angiotensin II receptor blockers, ACE inhibitors, and calcium channel blockers) in the context of coronary artery disease (CAD). The development of coronary collateral circulation is reported to have a critical role for treating patients with CAD. Schenone and co-workers [8] report on Src inhibitors able to interfere directly with angiogenic processes, while Angelucci and his group [9] describe the role of the Focal Adhesion Kinase (FAK) and the Proline-rich tYrosine Kinase-2 (PYK-2) in angiogenesis. These two topics are becoming very important in the studies on modulation of angiogenesis and represent a new avenue for the search of antiangiogenic small molecules. References [1] Rusnati M, Presta M. Fibroblast growth factors/fibroblast growth factor receptors as targets for the development of anti-angiogenesis strategies. Curr Pharm Des 2007; 13(20): 2025-2044. [2] Guerrini M, Hricovini M, Torri G. Interaction of heparins with fibroblast growth factors. Conformational aspects. Curr Pharm Des 2007; 13(20): 2045-2056. [3] Vlodavsky I, Ilan N, Naggi A, Casu B. Heparanase: Structure, biological functions, and inhibition by heparin-derived mimetics of heparan sulfate. Curr Pharm Des 2007; 13(20): 2057-2073. [4] Sulochana KN, Ge R. Developing antiangiogenic peptide drugs for angiogenesis-related diseases. Curr Pharm Des 2007; 13(20): 2074-2086. [5] Nuti E, Tuccinardi T, Rossello A. Matrix metalloproteinase inhibitors: New challenges in the era of post broad-spectrum inhibitors. Curr Pharm Des 2007; 13(20): 2087-2100.....

Angiogenesis, the process of new blood vessel formation from pre-existing ones, plays a key role in various physiological and pathological conditions, including embryonic development, wound repair, inflammation, and tumor growth. The 1980s saw for the first time the identification, purification, and sequencing of the two prototypic heparin-binding angiogenic fibroblast growth factors (FGF) 1 and 2. Since then, 22 structurally-related members of the FGF family and differenent classes of FGF receptors have been identified. Several experimental evidences point to a role for various FGFs in the neovascularization process that takes place in inflammation, angioproliferative diseases, and tumor growth. Thus, the FGF/FGF receptor system represents a target for the development of antiangiogenic therapies. Purpose of this review is to summarize the different modalities that have been approached to impair the proangiogenic activity of the FGF/FGF receptor system and discuss their possible therapeutic implications.

Heparin and heparin-like oligo- and polysaccharides bind to fibroblast growth factors (FGFs) and modulate their ability to form active ternary complexes with FGF receptors (FGFRs). Considerable efforts have been made in recent years to identify the minimal heparin and heparan sulfate (HS) sequences that bind and activate individual FGFs. Heparin sequences involved in interaction with FGFs invariably contain at least one residue of 2-O-sulfated iduronic acid (IdoA2S), which adopts either the 1C4 chair conformation or the equienergetic skew-boat 2S0. In solution and in the absence of a binding protein, both these conformations are present in a dynamic equilibrium. In oligosaccharide-protein co-crystals, the protein selects those conformers that provide optimal contacts. The crystalline structure of a heparin hexasaccharide/FGF complex exhibits one of the two IdoA2S residues in the active site of the growth factor in 1C4 conformation and the other (outside the active site) in 2S0 conformation. NMR studies suggest that active conformations of heparin/HS oligosaccharides in solution could be distinct from those adopted in crystals. Heparin tetrasaccharides in the presence of FGF1 and FGF2 have both their IdoA2S residues prevalently in the 1C4 form. Current NMR and molecular modelling studies are being extended to longer heparin oligosaccharides as well as to heparins with “glycol-split” residues along their chains.

Heparanase is an endoglycosidase which cleaves heparan sulfate (HS) and hence participates in degradation and remodeling of the extracellular matrix (ECM). Heparanase is preferentially expressed in human tumors and its over-expression in tumor cells confers an invasive phenotype in experimental animals. The enzyme also releases angiogenic factors from the ECM and thereby induces an angiogenic response in vivo. Heparanase upregulation correlates with increased tumor vascularity and poor postoperative survival of cancer patients. Heparanase is synthesized as a 65 kDa inactive precursor that undergoes proteolytic cleavage, yielding 8 kDa and 50 kDa protein subunits that heterodimerize to form an active enzyme. Heparanase exhibits also non-enzymatic activities, independent of its involvement in ECM degradation. Among these, are the enhancement of Akt signaling, stimulation of PI3K- and p38-dependent endothelial cell migration, and up regulation of VEGF, all contributing to its potent pro-angiogenic activity. Studies on relationships between structure and heparanase inhibition activity of nonanticogulant heparins systematically differing in their O-sulfation patterns, degrees of N-acetylation, and glycol-splitting of both pre-existing nonsulfated uronic acid residues (prevalently D-glucuronic) and/or those (Liduronic acid/L-galacturonic acid) generated by graded 2-O-desulfation, have permitted to select effective inhibitors of the enzymatic activity of heparanase. N-acetylated, glycol-split heparins emerged as especially strong inhibitors of heparanase, exerting little or no release of growth factors from ECM. N-acetylated glycol-split species of heparin, as well as heparanase gene silencing inhibit tumor metastasis, angiogenesis and inflammation in experimental animal models. These observations and the unexpected identification of a single functional heparanase, suggest that the enzyme is a promising target for anti-cancer and anti-inflammatory drug development.

Angiogenesis is regulated by stimulators and inhibitors and involve multiple biological processes including endothelial cell proliferation, migration, cell-cell and cell-matrix adhesion, assembly into tube structures as well as apoptosis. Designing and developing peptides for therapeutic application to inhibit angiogenesis is an important area in antiangiogenic drug development. Small peptides have advantages over proteins for therapeutic application, due to their stability, solubility, increased bio-availability and lack of immune response in the host cell. Endogenous protein angiogenesis stimulators and inhibitors hold vital information for designing antiangiogenic peptides for drug development. These proteins function through their interaction with extracellualr matrix molecules, cell surface receptors, proteases, as well as growth factors and cytokines. Conserved domains such as thrombospondin type 1 repeats (TSRs), kringle domains as well as critical amino acid residues present in these domains are involved in their functions. By exploiting these properties, several small peptides have been designed, synthetically made and being tested for therapeutic efficacy. Peptides derived from type 1 repeat of thrombospondin, alpha 4 and beta 1 chains of laminin, arginine rich N terminus of endostatin, leucine rich repeat 5 of decorin, pigment epithelium derived factor and N terminal of parathyroid hormone are examples of small antiangiogenic peptides derived from endogenous proteins. Such bioactive peptides are further modified physico-chemically to increase their potency and stability. In addition, phage-display library screening and combinatorial approach are also in use to identify novel antiangiogenic peptides targeting tumour and various proteins. This review will provide a comprehensive summary of the current status of the antiangiogenic peptides and their relevance for drug designing and development. Several critical issues that need to be resolved in translating this concept into clinical practice are also discussed.

More than two decades have been spent to develop many families of synthetic matrix metalloproteinases inhibitors (MMPI) as therapeutical agents for serious pathologies. Unfortunately, clinical trials conducted on broad-spectrum inhibitors have yielded disappointing results, especially in the cancer pathology area. Despite these outcomes, some small synthetic MMPI are in advanced trials or launched in clinical ones for cancer, arthritis, periodontal diseases. Today many groups are developing intensive efforts to find new classes of inhibitors characterized by improved potency and, above all, high selectivity against the specific MMP involved in each targeted pathology. The new challenges include the development of new MMPI bearing more effective ZBGs and the development of new allosteric non-zinc binding inhibitors, devoid of ZBGs. An analysis of more recent results in this field reported on journals and patents will be developed, to consider some of the more interesting new highly selective synthetic MMPI, their SARs, the new theoretical approaches used for modelling and the results of their biological evaluations.

The negative regulation of angiogenesis may provide a promising therapeutic target for a number of lifestyle-related diseases, as the switch to an angiogenic phenotype in many tissues represents a critical step during the progression of such disorders. Cartilage is avascular and shows resistance to vascular invasion from the surrounding well-vascularized mesenchyme. Using guanidine extracts of fetal bovine cartilage, we have identified and purified chondromodulin-I (ChM-I) as an angiogenesis inhibitor. The cDNA sequence of this factor has revealed that the ChM-I precursor protein is a type II transmembrane glycoprotein (334 amino acids) and that mature ChM-I is encoded in the C-terminal region of the precursor. After cleavage of the ChM-I precursor at its processing site, mature ChM-I (120 amino acids) is secreted from chondrocytes into the extracellular matrix. Following on from the identification of ChM-I as an angiogenesis inhibitor in cartilage, we have also cloned both mouse and human tenomodulin (TeM), which share significant homology with ChM-I at their C-termini. Moreover, exogenous expression experiments in COS cells suggests that TeM is a type II transmembrane glycoprotein (317 amino acids). When overexpressed in HUVECs, the C-terminal domain (116 amino acids) of the TeM protein shows both anti-angiogenic and anti-tumorigenic activities at equivalent levels to mature ChM-I. In our present review, we discuss the structure, biological activities and localization of these anti-angiogenic molecules..

Coronary artery disease (CAD) is the most important cause of death in the industrialized world. After experimental myocardial infarction, numerous dilated vessels appear in the border zone between the infarct and noninfarct areas. Angiogenic therapy has been widely regarded as an attractive approach for both treating CAD and enhancing arterioprotective functions of the endothelium. In this report, we critically review the evidence supporting the regulation of angiogenesis and angiogenic factors by cardiovascular medications such as statins, cholesterol ester transfer protein inhibitor, angiotensin II type 1 receptor blocker, angiotensin-converting enzyme inhibitor and calcium channel blocker, etc. Furthermore, in patients with CAD, vascular growth (vasculogenesis), capillary network growth (angiogenesis) and collateral artery growth (arteriogenesis), may be important. Current evidence from clinical trials on these therapies suggests that the development of coronary collateral circulation is likely to be a viable therapeutic strategy for CAD, while adaptation to chronic coronary stenosis can proceed. Many studies have suggested that newly developed strategies which include the administration of angiogenic growth factors and the transplantation of bone marrow-derived angioblasts are beneficial for the ischemic heart. Our assessment of the evidence in this review leads us to conclude that the development of collateral circulation using conventional cardiovascular medications may also play a critical role and needs to be reconsidered in the treatment of patients with CAD.