Carboxymethyl benzylamide dextran blocks angiogenesis of MDA-MB435 breast carcinoma xenografted in fat pad and its lung metastases in nude mice.

We previously showed that carboxymethyl benzylamide dextran (CMDB7) prevents tumor growth and tumor angiogenesis by binding to angiogenic growth factors, thereby preventing them from reaching their receptors on tumor or stromal cells (Bagheri-Yarmand et al. Br. J. Cancer, 78: 111-118, 1998; Bagheri-Yarmand et al. Cell Growth Differ., 9: 497-504, 1998). In this study, CMDB7 inhibited neovessel formation within the fibroblast growth factor 2-enriched matrigel in mice, and its anticancer effect was then tested in a metastatic breast cancer model. Human MDA-MB435 cells were injected into the mammary fat pad of nude mice, and breast tumors developed within 1 week; all of the mice had lung metastases at 12 weeks. CMDB7 treatment (50, 150, or 300 s.c. or 300 i.v. mg/kg/week for 10 weeks) reduced the incidence of lung metastases to 12%. Histological analysis showed markedly less tumor neovascularization in the CMDB7-treated mice. Pulmonary metastasis incidence was strongly dependent on the intratumoral neoangiogenesis in primary tumors.

Interactions of HIV-1 envelope glycoproteins with derivatized dextrans.

The present study demonstrates that derivatized dextrans, such as carboxylmethyl dextran benzylamide and carboxymethyl dextran benzylamide sulfonate, specifically interact with HIV-1 envelope glycoproteins (rgp160 and rgp41) with significantly higher affinities than those observed for dextran sulfate (MW 8 kDa). These results suggest the possible involvement in HIV infectivity of surface membrane molecules which may bind the virus at pre or post-CD4 binding steps. They also suggest the possible use of these compounds in anti-HIV therapy.

Temperature-responsive size-exclusion chromatography using poly(N-isopropylacrylamide) grafted silica.

Silica-based packing materials induce non-specific interactions with proteins in aqueous media because of the nature of their surface, mainly silanol groups. Therefore, the silica surface has to be modified in order to be used as stationary phase for the High Performance Size-Exclusion Chromatography (HPSEC) of proteins. For this purpose, porous silica beads were coated with hydrophilic polymer gels (dextrans of different molecular weights) carrying a calculated amount of diethyl-aminoethyl groups (DEAE). Actually, as shown by HPSEC, these dextran modified supports minimize non-specific adsorption for proteins and pullulans in aqueous solution. Then, in order to change the pore size in response to temperature, temperature responsive polymer of poly(N-isopropylacrylamide) (PIPAAm) was introduced into the surface of dextran-DEAE on porous silica beads. The structure of these supports before and after modification was alternately studied by Scanning Electronic Microscopy (SEM) and Scanning Force Microscopy (SFM). An adsorption of radiolabelled albumin was performed to complete our study. Silica modifications by dextran-DEAE and PIPAAm improve the neutrality of the support and minimize the non-specific interactions between the solid support and proteins in solution. At low temperature, the support having PIPAAm exhibits a high resolution domain in HPSEC and finally permits a better resolution of proteins and pullulans. At higher temperature, hydrophobic properties of PIPAAm produce interactions with some proteins and trigger off a slight delay of their elution time.

Antiviral activity of derivatized dextrans on HIV-1 infection of primary macrophages and blood lymphocytes.

The present study demonstrates at the molecular level that dextran derivatives carboxymethyl dextran benzylamine (CMDB) and carboxymethyl dextran benzylamine sulfonate (CMDBS), characterized by a statistical distribution of anionic carboxylic groups, hydrophobic benzylamide units, and/or sulfonate moieties, interact with HIV-1 LAI gp120 and V3 consensus clades B domain. Only limited interaction was observed with carboxy-methyl dextran (CMD) or dextran (D) under the same conditions. CMDBS and CMDB (1 microM) strongly inhibited HIV-1 infection of primary macrophages and primary CD4+ lymphocytes by macrophage-tropic and T lymphocyte-tropic strains, respectively, while D or CMD had more limited effects on M-tropic infection of primary macrophages and exert no inhibitory effect on M- or T-tropic infection of primary lymphocytes. CMDBS and CMDB (1 microM) had limited but significant effect on oligomerized soluble recombinant gp120 binding to primary macrophages while they clearly inhibit (> 50%) such binding to primary lymphocytes. In conclusion, the inhibitory effect of CMDB and the CMDBS, is observed for HIV M- and T-tropic strain infections of primary lymphocytes and macrophages which indicates that these compounds interfere with steps of HIV replicative cycle which neither depend on the virus nor on the cell.

Inhibition of complement activation by natural sulfated polysaccharides (fucans) from brown seaweed.

In the present study, we demonstrate that natural sulfated polysaccharides (fucans) isolated from brown seaweed are potent inhibitors of human complement activation. A fucan fraction of chromatographic molecular weight 22,600, termed BS8, was found to inhibit classical and alternative pathway activation in whole serum in a dose-dependent fashion. Fucan BS8 inhibited formation of the classical pathway C3 convertase by interfering with C1 activation or by inhibiting C4 cleavage and the interaction between C4b and C2. The fucan also inhibited formation/function of the alternative pathway C3 convertase by suppressing the binding of B to C3b and by interfering with the stabilizing function of Properdin. The inhibitory effect of fucans on formation of the C3 convertases was dependent on the molecular weight of the polysaccharide for compounds of chromatographic molecular weight below 16,600. Fucan had no effect on the function of the terminal complex. Since fucans were more efficient than heparin in inhibiting activation of the classical pathway in whole serum and exhibited a lesser specific anticoagulant activity on a molar basis, our results suggest that these natural sulfated polysaccharides have a potential for use as anti-complementary and anti-inflammatory agents.

Sulfonated dextran inhibits complement activation and complement-dependent cytotoxicity in an in vitro model of hyperacute xenograft rejection.

In the present study, we demonstrate that a substituted soluble dextran derivative bearing 73% carboxylic groups and 15% benzylamide sulfonate groups, termed CMDBS25, inhibits complement activation and complement-mediated damage in an in vitro model of xenogeneic rejection. Incubation of porcine aortic endothelial cells with normal human serum resulted in time-dependent complement consumption as assessed by C3a generation in the fluid phase and deposition of activated complement fragments C3, C5 and of C5b-9 on target cells. The presence of C5b-9 membrane attack complex was associated with 51Cr release from prelabelled endothelial cells. The addition of 5-25 mg of CMDBS25/ml under the experimental conditions used, inhibited complement activation and C3a generation in a dose-dependent fashion. CMDBS25 (25 mg/ml) totally suppressed iC3b, C5 and C5b-9 cytolytic complex deposition on cells and inhibits by 42% lysis of target endothelial cells. Native dextran had no effect. Our observations document the anti-complementary properties of sulfonated dextran derivatives and their potential as therapeutic agents for the prevention of complement-dependent hyperacute xenograft rejection.

Fucans, sulfated polysaccharides extracted from brown seaweeds, inhibit vascular smooth muscle cell proliferation. I. Comparison with heparin for antiproliferative activity, binding and internalization.

Smooth muscle cell (SMC) proliferation is inhibited both in vivo and in vitro by heparin. However, the precise mechanisms of action are still not understood. The analogy between two sulfated polysaccharides, heparin and fucan, has led us to compare in detail their effects on SMC growth. We have prepared and characterized a 19 kDa fucan fraction from brown seaweed, Ascophyllum nodosum. Fucan affects the growth of SMCs in a time- and dose-dependent, reversible and non-toxic fashion. As determined by cell counting, [3H]thymidine incorporation, and microcytofluorimetry analysis, heparin was less active than fucan in inhibiting SMC growth. Fucan and heparin act by preferential blocking of G0/G1, thus decreasing the G0/S transition. Binding experiments with [125I]fucan indicated saturable, unlabeled-fucan displaceable binding sites with an apparent Kd of 30 nM. Moreover, displacement experiments performed with various polysaccharides revealed that antiproliferative compounds interacted with these membrane sites, but non-antiproliferative polysaccharides (dextran, chondroitin sulfate) did not, providing evidence of a correlation between binding to SMCs and their antiproliferative activity. When cells were exposed at 37 degrees C to a fluorescent 5-([4,6-dichlorotriazin-2-yl]-amino)fluorescein (DTAF)-fucan, internalization occurred and punctate vesicles were observed which accumulated rapidly in the perinuclear region as previously reported for heparin. Nuclear preparations (membranes + contents) of cultured SMCs previously incubated with radiolabeled heparin or fucan indicated the presence of radioactivity, suggesting an antiproliferative action of both polysaccharides at the nuclear level. Collectively, these observations indicated that fucan and heparin share some similar mechanisms of action, such as SMC growth inhibition, binding, and internalization. In the accompanying paper (Logeart et al., Eur. J. Cell Biol. 74, 1997, this issue), we describe the effect of fucans of different molecular weights and conclude that there is no direct link between polysaccharide degradation and the antiproliferative effect on SMCs.

Fucans, sulfated polysaccharides extracted from brown seaweeds, inhibit vascular smooth muscle cell proliferation. II. Degradation and molecular weight effect.

Fucan, a sulfated polysaccharide extracted from brown seaweeds, inhibits smooth muscle cell (SMC) proliferation with a higher antiproliferative activity than heparin (Logeart et al., Eur. J. Cell Biol. 74, 1997, this issue). In order to investigate the structure-activity relationship of fucan on SMC growth, we have prepared by size exclusion chromatography fucan fractions of various molecular masses ranging from 5.5 to 556 kDa. Our experiments showed that the antiproliferative activity is dependent on the molecular weight of the polysaccharide. The molecular weight threshold indicated that about 30 saccharidic units on fucan were necessary to give the antiproliferative activity on SMCs. A kinetics study of DNA synthesis using tritiated thymidine uptake was also performed with different molecular weight fucan fractions. Although all tested fractions acted as soon as the cells enter the first cell cycle, the duration and potency of action varied. Moreover, displacement experiments of iodinated fucan revealed that the low molecular fucan fraction interacted weakly with the binding sites. Finally, gel permeation chromatography of internalized radiolabeled heparin and fucans was performed with SMCs. A rapid degradation of internalized heparin was observed, whereas only low molecular weight fucan fractions were partially degraded by SMCs. Together, these results indicate the significance of molecular weight on the antiproliferative activity of fucans on SMCs, and might help to understand their mechanism of action. In addition, the degradation experiments with internalized heparin and fucans ruled out a direct link between polysaccharide degradation and the antiproliferative effect on SMCs.

Derivatized dextrans modulate collagen synthesis in aortic smooth muscle cells.

The effect of specifically derivatized dextrans, with or without antiproliferative activity on smooth muscle cells (SMC), was investigated on type I and type III collagen biosynthesis and mRNA levels in post-confluent SMC cultures. Our results indicate that dextran derivatives decreased total protein and collagen synthesis independently of their antiproliferative activities. However, the most substituted dextran, the one exhibiting the strongest antiproliferative activity towards SMC, was the most active in modulating type III collagen expression. In addition, only the two dextran derivatives bearing benzylamide groups inhibited collagen excretion.

Effects of the binding of a dextran derivative on fibroblast growth factor 2: secondary structure and receptor-binding studies.

CMDB (carboxymethyldextran-benzylamide) are dextrans statistically substituted with carboxymethyl and benzylamide groups which can mimick some of the biological properties of heparin. It has previously been shown that CMDB inhibit autocrine growth of breast tumor cells (Bagheri-Yarmand et al., Biochem. Biophys. Res. Commun. 239: 424-428, 1997) and selectively displace fibroblast growth factor 2 (FGF-2) from its receptor. Here, we used circular dichroism and fluorescence anisotropy measurements to show that the conformation of FGF-2 was significantly altered upon its binding to CMDB and to short CMDB fragments prepared within this study. CMDB and fragments formed a stable 1:1 complex with FGF-2, with affinities being estimated as 20+/-10 nM from fluorescence anisotropy analysis. No such a complex was formed with insulin-like growth factor (IGF-1) or epidermal growth factor (EGF). CMDB competed with the FGF-2 receptor for binding to FGF-2 but did not disturb the binding of IGF-1 and EGF to their receptors. Thus, our results highlight the selectivity of CMDB and their fragments towards FGF-2. Heparin, however, competes with CMDB and their fragments for binding to FGF-2. The carboxymethyl and benzylamide groups of these molecules likely interact directly with a heparin-binding region of FGF-2. The resulting change in conformation disturbs the binding of FGF-2 to its receptor and consecutively its mitogenic activity.

Differential antiviral activity of derivatized dextrans.

The antiviral activity of water-soluble dextrans derivatized with varying percentages of carboxymethyl, benzylamide, and sulfonate groups was evaluated. Several of the polymers exhibited potent antiviral activity against a variety of enveloped viruses, but not against non-enveloped viruses, and only when present during virus adsorption. The mechanism of activity against retroviruses [i.e. human immunodeficiency virus (HIV)] and herpes viruses (i.e. human cytomegalovirus) could be ascribed to inhibition of virus binding to the cells. An absolute requirement for anti-HSV activity appeared to be a sufficiently high percentage of benzylamide and benzylamide sulfonate groups. This did not, however, apply for human cytomegalovirus, respiratory syncytial virus, and HIV. The sensitivity of the latter viruses appeared to be influenced by factors other than the global chemical composition, which leads us to assume that physical factors such as the distribution and sequence of the substituents on the sugar backbone play an important role in the antiviral activity of the derivatized dextrans.

Anticoagulant activity of dextran derivatives. Part I: Synthesis and characterization.

Substituted dextrans bearing carboxymethyl and benzylsulphonate groups have been prepared. These materials exhibit an antithrombic activity correlated with the ratio of each substituent. The highest activity is obtained when the dextran derivative contains more than 50% of carboxylic acid groups and simultaneously about 15% of benzylsulphonate functions.

Randomness and biospecificity: random copolymers are capable of biospecific molecular recognition in living systems.

Biospecific molecular recognition in living systems is known to be based on the lock and key principle as proposed by Emil Fischer. Based on this concept, biospecific polymers have been produced synthetically by attaching biospecific 'keys' to the polymer chain. We postulate that biospecificity can be achieved by alternative means, namely random substitution of a preformed polymer with suitable chemical groups or random copolymerization of suitable functional monomers. Such polymers, we suggest, will contain arrangements of the chemical functions which mimic natural biospecific sites and the probability of occurrence of such arrangements will depend on the average composition of the polymer. In support of this principle, we have developed several functional random copolymer systems which possess a variety of biological properties depending on the type of chemical function. Examples are: polymers possessing anticoagulant properties similar to those of heparin; polymers which interact specifically with components of the immune system; and polymers which, in contact with cells, affect their growth and metabolism. In the case of statistical copolymers possessing 'DNA-like' properties obtained by phosphorylation of hydroxylated polystyrene derivatives, Monte Carlo simulations were used to determine the distribution of phosphodiester (PDE) groups along the chains and to compute the probabilities of occurrence of particular arrangements of PDE found in the 'DNA-like' sites. The results showed that these sites are made up of PDE groups separated by distances that closely match those between the same groups along a generatrix of the DNA double-helix cylinder. These findings offer the prospect of manufacturing polymeric biomaterials endowed with biomimetic character. Moreover, they provide the basis for a hypothesis regarding the appearance of biospecificity at the origin of life, suggesting that biospecific structures may have evolved by natural selection from purely random copolymers. It is likely therefore that biospecificity is a continuous function of randomness, arising from purely statistical distributions of reactivity and evolving into precisely defined structures such as those involved in ligand-receptor interactions.

Antithrombic activity of some polysaccharide resins.

Crosslinked dextrans (Sephadex) bearing essentially carboxymethyl, benzylsulphonate and alpha-amino acid groups have been synthesized. The antithrombic activity of the resins may be the result of a cooperative effect between the functional groups. The binding of benzylsulphonate to carboxymethylated Sephadex endows these materials with activity. However the highest activity is obtained when the resins contain simultaneously benzylsulphonate, alpha-amino acid and carboxylic acid groups.

Anticoagulant hydrogels derived from crosslinked dextran. Part I: Synthesis, characterization and antithrombic activity.

Hydrogels have been prepared by binding various amino acids to Sephadex derivatives bearing carboxymethyl and sulphonated benzylamide groups. Depending on the chemical nature and content of the amino acid substituent, these insoluble strongly hydrophilic materials may absorb 7 to 19 volumes of buffer per volume of dry material. These hydrogels present antithrombic activity in relation to their swelling ratio. The adsorption of thrombin might partially explain the anticoagulant effect as shown by the evaluated affinity constants between the hydrogels and the enzyme i.e. 1 to 2 X 10(6) I/M.

Adsorption of thrombin from buffer and modified plasma to polystyrene resins containing sulphonate and sulphamide arginyl methyl ester groups.

The adsorption of albumin and thrombin to insoluble modified polystyrene resins bearing sulphonate (PSSO3) and L-arginyl methyl ester groups (PAOM) was investigated in both purified and plasma systems. Radioiodinated proteins were used to follow adsorption in a 'minicolumn' experiment. Albumin adsorption was found to follow the Langmuir model and specific surface areas of the various resins were evaluated from plateau albumin adsorption data. The adsorption isotherms of thrombin both in buffer and in antithrombin III/fibrinogen-free plasma were also found to be Langmuir-like, and the quantities adsorbed at the isotherm plateaux are in the monolayer range. Analysis of the isotherms at 4 degrees and 37 degrees C for the purified system shows that adsorption is endothermic. Adsorption capacities in plasma remain high (30-50% of those in the purified system) despite competition from the other plasma proteins. These data confirm the strong affinity and selectivity of these resins for thrombin.

Anticoagulant hydrogels derived from crosslinked dextran. Part II: Mechanism of thrombin inactivation.

Sephadex derivatives bearing carboxymethyl, sulphonated benzylamine and amino acid groups exhibit heparin-like behaviour as demonstrated by the kinetic study of the thrombin inactivation in the presence of antithrombin III. Furthermore, whatever the chemical composition of these hydrogels, the diffusion coefficient of thrombin remained approximately constant and could not be connected with the variation of the antithrombin activity of the resins. Hence, in the heparin-like mechanism, the diffusion rate of thrombin inside the beads of hydrogels was not the limiting step. In fact, the swelling ratio (varying according to the chemical composition of these biomaterials) was involved in the anticoagulant properties of the resins.

Anticomplementary activity of dextran derivatives.

Substitution with carboxylic and benzylamine sulphonated groups conferred on dextran both antithrombic activity and the capacity to inhibit formation of the amplification C3 convertase of complement. In dextrans substituted with carboxylic groups (greater than 40%), a high content of sulphonate (greater than 10%) resulted in both anticomplementary and antithrombic properties whereas a lower content of sulphonate resulted in high anticomplementary but weak antithrombic activity. The anticomplementary activity of highly substituted dextrans was similar to that of heparin, although anticoagulant activity was much lower than in heparin, confirming independent structural requirements for both activities in the heparin molecule.

Anticoagulant activity of dextran derivatives. Part II: Mechanism of thrombin inactivation.

The mechanism of anticoagulant activity of dextrans substituted with carboxylic and benzylamide sulphonate groups is studied by various coagulation tests. These derivatives exhibit a heparin-like antithrombic activity which requires the presence of antithrombin III; however they are less effective than heparin on a weight basis. They also exert a direct antithrombic activity by an antithrombic III independent pathway; but this action is negligible compared to the thrombin inhibition observed in the presence of antithrombin III. Dextran derivatives have been prepared with antithrombic properties similar to those of heparin.

Enzymatic degradation and immunogenic properties of derivatized dextrans.

Dextran T40 was modified with carboxylic, benzylamide and benzylamine-sulphonated groups (samples 1-10). The polymers were incubated with dextranase and the decrease of molecular weight was determined by high performance size exclusion chromatography. It was shown that the higher the substitution of dextrans, the lower their degradability. Modification of dextran with benzylamine and benzylamine-sulphonated groups appeared to hinder the formation of the enzyme-substrate complex more than the same quantity of carboxylic groups. The immunogenicity of one of the modified dextrans, containing 54% of carboxylic groups and 19.5% of benzylamine-sulphonated groups, was determined after subcutaneous and intravenous administration into Balb/c mice. The antibody titre was very low even if administered in complete Freund's adjuvant and did not depend on the injected dose. On the average, the titres of antibodies were lower by five orders of magnitude compared to bovine gamma globulin.