[Show abstract][Hide abstract] ABSTRACT: Heparin and heparan sulfate (HS) glycosaminoglycans (HSGAGs) are sulfated polysaccharides that play important roles in fundamental biological processes by binding to proteins. The prototypic example of HSGAG-protein interactions is that with the fibroblast growth factors (FGFs), specifically FGF1 and FGF2. Structural and biochemical studies have shown that the chain length, sulfation pattern, and conformation of HSGAGs play a critical role in FGF binding and activity. Previously, we showed that a tetrasaccharide of the form A(NS,6X)-I(2S)-A(NS,6X)-I(2S)-OPr (where X is OH or O-sulfate and Pr is propyl) with at least one of the A(NS,6X) residues having a 6-O sulfate group was the minimum binding motif for FGF1 [Guerrini, M., Agulles, T., Bisio, A., Hricovini, M., Lay, L., Naggi, A., Poletti, L., Sturiale, L., Torri, G., and Casu, B. (2002) Biochem. Biophys. Res. Commun. 292, 222-230]. We report NMR structural analysis using two-dimensional NOE spectroscopy (2D-NOESY) and transferred NOESY (trNOESY) on a non-6-O-sulfated synthetic tetrasaccharide TETRA (A(NS)-I(2S)-A(NS)-I(2S)-OPr) both in its free state and bound to FGF2. This tetrasaccharide comprises both the structural trisaccharide motif A(NS)-I(2S)-A(NS) that forms "kinks" in longer heparin chains induced by FGF binding [Raman, R., Venkataraman, G., Ernst, S., Sasisekharan, V., and Sasisekharan, R. (2003) Proc. Natl. Acad. Sci. U.S.A. 100, 2357-2362] and the common binding motif I(2S)-A(NS)-I(2S) present in octasaccharides that exhibited strong FGF2 binding [Kreuger, J., Salmivirta, M., Sturiale, L., Gimenez-Gallego, G., and Lindahl, U. (2001) J. Biol. Chem. 276, 30744-30752]. These data suggest that TETRA could be the shortest HSGAG oligosaccharide that binds to FGF2. Furthermore, our study confirms that both the IdoA residues in TETRA adopt the chair (1)C(4) conformation upon FGF2 binding to provide the best molecular fit in contrast to an analogous 6-O-sulfated tetrasaccharide motif observed in the FGF2-HSGAG cocrystal structure where one of the IdoAs adopts skew-boat (2)S(O) conformation. Thus, our study highlights the fact that the conformational plurality of IdoA is able to accommodate the changes in the sulfation pattern to provide the necessary specificity for protein binding.
[Show abstract][Hide abstract] ABSTRACT: The antithrombotic activity of low molecular weight heparins (LMWHs) is largely associated with the antithrombin (AT)-binding pentasaccharide sequence AGA(*)IA (GlcN(NAc/NS,6S)-GlcA-GlcN(NS,3,6S)-IdoUA(2S)-GlcN(NS,6S)). The location of the AGA(*)IA sequences along the LMWH chains is also expected to influence binding to AT. This study was aimed at investigating the role of the structure and molecular conformation of different disaccharide extensions on both sides of the AGA(*)IA sequence in modulating the affinity for AT. Four high purity octasaccharides isolated by size exclusion chromatography, high pressure liquid chromatography, and AT-affinity chromatography from the LMWH enoxaparin were selected for the study. All the four octasaccharides terminate at their nonreducing end with 4,5-unsaturated uronic acid residues (DeltaU). In two octasaccharides, AGA(*)IA was elongated at the reducing end by units IdoUA(2S)-GlcN(NS,6S) (OCTA-1) or IdoUA-GlcN(NAc,6S) (OCTA-2). In the other two octasaccharides (OCTA-3 and OCTA-4), AGA(*)IA was elongated at the nonreducing side by units GlcN(NS,6S)-IdoUA and GlcN(NS,6S)-GlcA, respectively. Extensions increased the affinity for AT of octasaccharides with respect to pentasaccharide AGA(*)IA, as also confirmed by fluorescence titration. Two-dimensional NMR and docking studies clearly indicated that, although elongation of the AGA(*)IA sequence does not substantially modify the bound conformation of the AGA(*)IA segment, extensions promote additional contacts with the protein. It should be noted that, as not previously reported, the unusual GlcA residue that precedes the AGA(*)IA sequence in OCTA-4 induced an unexpected 1 order of magnitude increase in the affinity to AT with respect to its IdoUA-containing homolog OCTA-3. Such a residue was found to orientate its two hydroxyl groups at close distance to residues of the protein. Besides the well established ionic interactions, nonionic interactions may thus contribute to strengthen oligosaccharide-AT complexes.
[Show abstract][Hide abstract] ABSTRACT: Recently, certain lots of heparin have been associated with an acute, rapid onset of serious side effects indicative of an allergic-type reaction. To identify potential causes for this sudden rise in side effects, we examined lots of heparin that correlated with adverse events using orthogonal high-resolution analytical techniques. Through detailed structural analysis, the contaminant was found to contain a disaccharide repeat unit of glucuronic acid linked beta1-->3 to a beta-N-acetylgalactosamine. The disaccharide unit has an unusual sulfation pattern and is sulfated at the 2-O and 3-O positions of the glucuronic acid as well as at the 4-O and 6-O positions of the galactosamine. Given the nature of this contaminant, traditional screening tests cannot differentiate between affected and unaffected lots. Our analysis suggests effective screening methods that can be used to determine whether or not heparin lots contain the contaminant reported here.
[Show abstract][Hide abstract] ABSTRACT: Low-molecular-weight heparins (LMWH) appear to prolong survival of patients with cancer. Such a beneficial effect is thought to be associated with interruption of molecular mechanisms involving the heparan sulfate (HS) chains of cell surface and extracellular matrix proteoglycans (HSPGs), growth factors and their receptors, heparanase, and selectins. The beneficial effects of heparin species could also be associated with their ability to release tissue factor pathway inhibitor from endothelium. The utility of heparin and LMWH as anticancer drugs is limited due to their anticoagulant properties. Non-anticoagulant heparins can be obtained either by removing chains containing the antithrombin-binding sequence, or by inactivating critical functional groups or units of this sequence. The non-anticoagulant heparins most extensively studied are regioselectively desulfated heparins and 'glycol-split' heparins. Some modified heparins of both types are potent inhibitors of heparanase. A number of them also attenuate metastasis in experimental models. With cancer cells overexpressing selectins, heparin-mediated inhibition of tumor cells-platelets aggregation and tumor cell interaction with the vascular endothelium appears to be the prevalent mechanism of attenuation of early stages of metastasis. The structural requirements for inhibition of growth factors, heparanase, and selectins by heparin derivatives are somewhat different for the different activities. An N-acetylated, glycol-split heparin provides an example of application of a non-anticoagulant heparin that inhibits cancer in animal models without unwanted side effects. Delivery of this compound to mice bearing established myeloma tumors dramatically blocked tumor growth and progression.
Pathophysiology of Haemostasis and Thrombosis 02/2008; 36(3-4):195-203. DOI:10.1159/000175157 · 2.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Vascular cell adhesion molecules, P- and L-selectins, facilitate metastasis of cancer cells in mice by mediating interactions with platelets, endothelium, and leukocytes. Heparanase is an endoglycosidase that degrades heparan sulfate of extracellular matrix, thereby promoting tumor invasion and metastasis. Heparin is known to efficiently attenuate metastasis in different tumor models. Here we identified modified, nonanticoagulant species of heparin that specifically inhibit selectin-mediated cell-cell interactions, heparanase enzymatic activity, or both. We show that selective inhibition of selectin interactions or heparanase with specific heparin derivatives in mouse models of MC-38 colon carcinoma and B16-BL6 melanoma attenuates metastasis. Selectin-specific heparin derivatives attenuated metastasis of MC-38 carcinoma, but heparanase-specific derivatives had no effect, in accordance with the virtual absence of heparanase activity in these cells. Heparin derivatives had no further effect on metastasis in mice deficient in P- and L-selectin, indicating that selectins are the primary targets of heparin antimetastatic activity. Selectin-specific and heparanase-specific derivatives attenuated metastasis of B16-BL6 melanomas to a similar extent. When mice were injected with a derivative containing both heparanase and selectin inhibitory activity, no additional attenuation of metastasis could be observed. Thus, selectin-specific heparin derivatives efficiently attenuated metastasis of both tumor cell types whereas inhibition of heparanase led to reduction of metastasis only in tumor cells producing heparanase.
The FASEB Journal 12/2007; 21(13):3562-72. DOI:10.1096/fj.07-8450com · 5.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The heparan sulfate proteoglycan syndecan-1 is expressed by myeloma cells and shed into the myeloma microenvironment. High levels of shed syndecan-1 in myeloma patient sera correlate with poor prognosis and studies in animal models indicate that shed syndecan-1 is a potent stimulator of myeloma tumor growth and metastasis. Overexpression of extracellular endosulfatases, enzymes which remove 6-O sulfate groups from heparan sulfate chains, diminishes myeloma tumor growth in vivo. Together, these findings identify syndecan-1 as a potential target for myeloma therapy. Here, 3 different strategies were tested in animal models of myeloma with the following results: (1) treatment with bacterial heparinase III, an enzyme that degrades heparan sulfate chains, dramatically inhibited the growth of primary tumors in the human severe combined immunodeficient (SCID-hu) model of myeloma; (2) treatment with an inhibitor of human heparanase, an enzyme that synergizes with syndecan-1 in promoting myeloma progression, blocked the growth of myeloma in vivo; and (3) knockdown of syndecan-1 expression by RNAi diminished and delayed myeloma tumor development in vivo. These results confirm the importance of syndecan-1 in myeloma pathobiology and provide strong evidence that disruption of the normal function or amount of syndecan-1 or its heparan sulfate chains is a valid therapeutic approach for this cancer.
[Show abstract][Hide abstract] ABSTRACT: Heparin-like polysaccharides possess the capacity to inhibit cancer cell proliferation, angiogenesis, heparanase-mediated cancer cell invasion, and cancer cell adhesion to vascular endothelia via adhesion receptors, such as selectins. The clinical applicability of the antitumor effect of such polysaccharides, however, is compromised by their anticoagulant activity. We have compared the potential of chemically O-sulfated and N,O-sulfated bacterial polysaccharide (capsular polysaccharide from E. COLI K5 [K5PS]) species to inhibit metastasis of mouse B16-BL6 melanoma cells and human MDA-MB-231 breast cancer cells in two in vivo models. We demonstrate that in both settings, O-sulfated K5PS was a potent inhibitor of metastasis. Reducing the molecular weight of the polysaccharide, however, resulted in lower antimetastatic capacity. Furthermore, we show that O-sulfated K5PS efficiently inhibited the invasion of B16-BL6 cells through Matrigel and also inhibited the in vitro activity of heparanase. Moreover, treatment with O-sulfated K5PS lowered the ability of B16-BL6 cells to adhere to endothelial cells, intercellular adhesion molecule-1, and P-selectin, but not to E-selectin. Importantly, O-sulfated K5PSs were largely devoid of anticoagulant activity. These findings indicate that O-sulfated K5PS polysaccharide should be considered as a potential antimetastatic agent.
Seminars in Thrombosis and Hemostasis 08/2007; 33(5):547-56. DOI:10.1055/s-2007-982087 · 3.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Heparanase is an endo-beta-D-glucuronidase that cleaves the heparan sulfate chains of heparan sulfate proteoglycans and is implicated in angiogenesis and metastasis. With the aim of establishing a simple and reliable method for studying the susceptibility of heparin/heparan sulfate oligosaccharides to be cleaved by heparanase, an on-line ion pair reversed-phase high-performance liquid chromatographic/electrospray ionization mass spectrometric method was set up. The method works in the micromolar range of concentration and does not require derivatization of the substrate or of the products. It is based on mass identification of oligosaccharide fragments generated by heparanase and their quantification with reference to an internal heparin disaccharide standard. Substrates were (1) the synthetic pentasaccharides GlcN (NS,6S) - GlcA - GlcN (NS,3S,6S) - IdoA (2S) - GlcN (NS,6S) - OMe (AGA*IA (M)) and GlcN (NS,6S) - GlcA - GlcN (NS,6S) - IdoA (2S) - GlcN (NS,6S) - OMe (AGAIA (M)), corresponding to the heparin/heparan sulfate active site for antithrombin, and to the same sequence devoid of the 3- O-sulfate group in the central glucosamine, respectively; and (2) two natural heparin octasaccharides containing the AGA*IA sequence in different locations along the chain. The two pentasaccharides exhibited a higher susceptibility to heparanase cleavage with respect to the octasaccharides. The commercial availability of AGA*IA (M) makes it an ideal substrate to determine the specific activity of heparanase preparations. The present method could also be used for rapid screening of potential heparanase inhibitors.
Seminars in Thrombosis and Hemostasis 08/2007; 33(5):488-95. DOI:10.1055/s-2007-982079 · 3.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Heparanase is an endoglycosidase which cleaves heparan sulfate (HS) and hence participates in degradation and remodeling of the extracellular matrix (ECM). The enzyme also releases angiogenic factors from the ECM and thereby induces an angiogenic response in vivo. Heparanase is preferentially expressed in human tumors and its over-expression in tumor cells confers an accelerated growth and invasive phenotype in experimental animals. In contrast, heparanase gene silencing is associated with a marked inhibition of tumor progression. Heparanase upregulation correlates with increased tumor vascularity and poor postoperative survival of cancer patients. Studies on relationships between structure and the heparanase-inhibiting activity of nonanticogulant heparins systematically differing in their O-sulfation patterns, degrees of N-acetylation, and glycol-splitting of nonsulfated uronic acid residues, have permitted to select effective inhibitors of the enzymatic activity of heparanase. N-acetylated, glycol-split heparins emerged as highly effective and specific inhibitors of heparanase and tumor growth and metastasis. Several observations support the involvement of heparanase in haemostasis. A marked induction of tissue factor (TF) was noted in response to heparanase over-expression in tumor-derived cell lines and heparanase over-expressing transgenic mice. A direct correlation was also found between heparanase and TF expression levels in leukemia patients. TF induction was even more pronounced upon exogenous addition of heparanase to primary endothelial cells that do not normally express TF, and this induction was associated with enhanced coagulation. These and other results indicate that pro-heparanase is rapidly tethered on cell surfaces, partially depending on cell surface heparan sulfate, generating a local procoagulant effect. In addition, pro-heparanase can reverse the anti-coagulant effect of unfractionated heparin and the Factor Xa inhibitory activity of low molecular weight heparin (LMWH). These effects were also demonstrated in plasma derived from patients treated with LMWH. The pro-coagulant effects of pro-heparanase were also exerted by a peptide corresponding to its major functional heparin-binding domain. Heparanase pro-coagulant activities suggest its possible role as a natural regulator of heparinoid anti-coagulant activities, and point to a possible use of this molecule or its heparin binding domain as antidote for heparinoid therapies.
[Show abstract][Hide abstract] ABSTRACT: 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 (L-iduronic 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.
Current pharmaceutical design 02/2007; 13(20):2057-73. DOI:10.2174/138161207781039742 · 3.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Heparan sulfate (HS) proteoglycans play a key role in the self-assembly, insolubility and barrier properties of the extracellular matrix (ECM). Cleavage of HS therefore affects the integrity of tissues and hence normal and pathological phenomena involving cell migration and response to changes in the ECM. Mammalian heparanase, HS-degrading endoglycosidase,is synthesized as a latent 65 kDa precursor that undergoes proteolytic cleavage, yielding 8 kDa and 50 kDa subunits that heterodimerize to form a highly active enzyme. Heparanase is preferentially expressed in human tumors and its over-expression in tumor cells confers an invasive phenotype in experimental animals. Heparanase also releases angiogenic factors from the ECM and tumor micro environment and thereby induces an angiogenic response in vivo. Enhanced heparanase expression correlates with metastatic potential, tumor vascularity and reduced postoperative survival of cancer patients. Heparanase also promotes cell adhesion, survival and signaling events, independent of its enzymatic activity. These observations, the anti-cancerous effect of heparanase gene silencing and of heparanase inhibiting molecules as well as the unexpected identification of a predominant functional heparanase, suggest that the enzyme is a promising target for anti-cancer drug development. Here, we summarize recent progress in molecular and cellular aspects of heparanase, emphasizing its causal involvement in cancer metastasis and angiogenesis, and discuss the development of heparin-like heparanase inhibitors.
Pathophysiology of Haemostasis and Thrombosis 02/2006; 35(1-2):116-27. DOI:10.1159/000093553 · 2.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Heparanase is an endo-beta-glucuronidase that cleaves heparan sulfate (HS) chains of heparan sulfate proteoglycans on cell surfaces and in the extracellular matrix (ECM). Heparanase, overexpressed by most cancer cells, facilitates extravasation of blood-borne tumor cells and causes release of growth factors sequestered by HS chains, thus accelerating tumor growth and metastasis. Inhibition of heparanase with HS mimics is a promising target for a novel strategy in cancer therapy. In this study, in vitro inhibition of recombinant heparanase was determined for heparin derivatives differing in degrees of 2-O- and 6-O-sulfation, N-acetylation, and glycol splitting of nonsulfated uronic acid residues. The contemporaneous presence of sulfate groups at O-2 of IdoA and at O-6 of GlcN was found to be non-essential for effective inhibition of heparanase activity provided that one of the two positions retains a high degree of sulfation. N-Desulfation/ N-acetylation involved a marked decrease in the inhibitory activity for degrees of N-acetylation higher than 50%, suggesting that at least one NSO3 group per disaccharide unit is involved in interaction with the enzyme. On the other hand, glycol splitting of preexisting or of both preexisting and chemically generated nonsulfated uronic acids dramatically increased the heparanase-inhibiting activity irrespective of the degree of N-acetylation. Indeed N-acetylated heparins in their glycol-split forms inhibited heparanase as effectively as the corresponding N-sulfated derivatives. Whereas heparin and N-acetylheparins containing unmodified D-glucuronic acid residues inhibited heparanase by acting, at least in part, as substrates, their glycol-split derivatives were no more susceptible to cleavage by heparanase. Glycol-split N-acetylheparins did not release basic fibroblast growth factor from ECM and failed to stimulate its mitogenic activity. The combination of high inhibition of heparanase and low release/potentiation of ECM-bound growth factor indicates that N-acetylated, glycol-split heparins are potential antiangiogenic and antimetastatic agents that are more effective than their counterparts with unmodified backbones.
[Show abstract][Hide abstract] ABSTRACT: Vascular endothelial growth factor (VEGF) represents a target for antiangiogenic therapies in a wide spectrum of diseases, including cancer. As a novel strategy to generate nonanticoagulant antiangiogenic substances exploiting binding to VEGF while preventing receptor engagement, we assessed the VEGF-antagonist activity of a low-molecular-weight (LMW) compound (ST2184, Mw = 5800) generated by depolymerization of an undersulfated glycol-split heparin derivative. The parental compound was obtained by introducing regular sulfation gaps along the prevalently N-sulfated heparin regions, followed by glycol-splitting of all nonsulfated uronic acid residues (approximately 50% of total uronic acid residues). ST2184 was endowed with a negligible anticoagulant activity after S.C. injection in mice. ST2184 binds VEGF165 as evaluated by its capacity to retard 125I-VEGF165 electrophoretic migration in a gel mobility shift assay and to prevent VEGF165 interaction with heparin immobilized onto a BIAcore sensor chip. Unlike heparin, ST2184 was unable to present 125I-VEGF165 to its high-affinity receptors in endothelial cells and inhibited VEGF165-induced neovascularization in the chick embryo chorioallantoic membrane. Undersulfated, LMW glycol-split heparins may therefore provide the basis for the design of novel nonanticoagulant angiostatic compounds.
[Show abstract][Hide abstract] ABSTRACT: Orchestration of the rapid formation and reorganization of new tissue observed in wound healing involves not only cells and polypeptides but also the extracellular matrix (ECM) microenvironment. The ability of heparan sulfate (HS) to interact with major components of the ECM suggests a key role for HS in maintaining the structural integrity of the ECM. Heparanase, an endoglycosidase-degrading HS in the ECM and cell surface, is involved in the enzymatic machinery that enables cellular invasion and release of HS-bound polypeptides residing in the ECM. Bioavailabilty and activation of multitude mediators capable of promoting cell migration, proliferation, and neovascularization are of particular importance in the complex setting of wound healing. We provide evidence that heparanase is normally expressed in skin and in the wound granulation tissue. Heparanase stimulated keratinocyte cell migration and wound closure in vitro. Topical application of recombinant heparanase significantly accelerated wound healing in a flap/punch model and markedly improved flap survival. These heparanase effects were associated with enhanced wound epithelialization and blood vessel maturation. Similarly, a marked elevation in wound angiogenesis, evaluated by MRI analysis and histological analyses, was observed in heparanase-overexpressing transgenic mice. This effect was blocked by a novel, newly developed, heparanase-inhibiting glycol-split fragment of heparin. These results clearly indicate that elevation of heparanase levels in healing wounds markedly accelerates tissue repair and skin survival that are mediated primarily by an enhanced angiogenic response.-Zcharia, E., Zilka, R., Yaar, A., Yacoby-Zeevi, O., Zetser, A., Metzger, S., Sarid, R., Naggi, A., Casu, B., Ilan, N., Vlodavsky, I., Abramovitch, R. Heparanase accelerates wound angiogenesis and wound healing in mouse and rat models.
The FASEB Journal 03/2005; 19(2):211-21. DOI:10.1096/fj.04-1970com · 5.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Heparin remains a major drug in prevention of thromboembolic disease. Concerns related to its animal source have prompted search for heparin analogues. The anticoagulant activity of heparin depends on a specific pentasaccharide sequence that binds antithrombin. We report the generation of a product with antithrombin-binding, anticoagulant, and antithrombotic properties similar to those of heparin, through combined chemical and enzymatic modification of a bacterial (E. coli K5) polysaccharide. The process is readily applicable to large-scale production.
[Show abstract][Hide abstract] ABSTRACT: Heparin (HP) is a linear polysaccharide that is made up of alternating disaccharide sequences of a uronic acid and an aminosugar. The length of repeating trisulfated disaccharide (TSD) units along the HP chains has been assessed only in statistical terms and for a limited number of HP types. It has been accessed mainly through size profiling of oligosaccharides generated by cleavage of heparins oxidized with periodate at the level of nonsulfated uronic acids. The molecular conformation of glycosaminoglycans (GAGs), especially of those containing IdoA, such as heparin, HS, and dermatan sulfate, has long been a matter of controversy. Modeling of 3D structures of polysaccharides in a solution involves the assumption of the conformation of individual residues and building up the polymer chains with these residues in a way that minimizes the overall conformational energy.
Chemistry and Biology of Heparin and Heparan Sulfate, 01/2005: pages 1-28; , ISBN: 9780080448596
[Show abstract][Hide abstract] ABSTRACT: Tumor neovascularization (angiogenesis) is regarded as a promising target for anticancer drugs. Heparin binds to fibroblast growth factor-2 (FGF2) and promotes the formation of ternary complexes with endothelial cell surface receptors, inducing an angiogenic response. As a novel strategy to generate antiangiogenic substances exploiting binding to FGF2 while preventing FGF receptor (FGFR) activation, sulfation gaps were generated along the heparin chains by controlled alkali-catalyzed removal of sulfate groups of iduronic acid 2-O-sulfate residues, giving rise to the corresponding epoxide derivatives. A new class of heparin derivatives was then obtained by opening the epoxide rings followed by oxidative glycol-splitting of the newly formed (and the preexisting) nonsulfated uronic acid residues. In vitro these heparin derivatives prevent the formation of FGFR/FGF2/heparan sulfate proteoglycan ternary complexes and inhibit FGF2-stimulated endothelial cell proliferation. They exert an antiangiogenic activity in the chick embryo chorioallantoic membrane assay, where the parent heparin is inactive. Low and very low molecular weight derivatives of a prototype compound, as well as its glycine and taurine derivatives obtained by reductive amination of glycol-split residues, retained the angiostatic activity. A significant relationship was found between the extent of glycol-splitting and the FGF2-antagonist/angiostatic activities of these heparin derivatives. Molecular dynamics calculations support the assumption that glycol-split residues act as flexible joints that, while favoring 1:1 binding to FGF2, disrupt the linearity of heparin chains necessary for formation of active complexes with FGFRs.