Preparation and anti-HIV activity of O-acylated heparin and dermatan sulfate derivatives with low anticoagulant effect

Chemical Modification of Glycosaminoglycan Polysaccharides

The linear anionic class of polysaccharides, glycosaminoglycans (GAGs), are critical throughout the animal kingdom for developmental processes and the maintenance of healthy tissues. They are also of interest as a means of influencing biochemical processes. One member of the GAG family, heparin, is exploited globally as a major anticoagulant pharmaceutical and there is a growing interest in the potential of other GAGs for diverse applications ranging from skin care to the treatment of neurodegenerative conditions, and from the treatment and prevention of microbial infection to biotechnology. To realize the potential of GAGs, however, it is necessary to develop effective tools that are able to exploit the chemical manipulations to which GAGs are susceptible. Here, the current knowledge concerning the chemical modification of GAGs, one of the principal approaches for the study of the structure-function relationships in these molecules, is reviewed. Some additional methods that were applied successfully to the analysis and/or processing of other carbohydrates, but which could be suitable in GAG chemistry, are also discussed.

Identification of Heparin Modifications and Polysaccharide Inhibitors of Plasmodium falciparum Merozoite Invasion That Have Potential for Novel Drug Development

Despite recent successful control efforts, malaria remains a leading global health burden. Alarmingly, resistance to current antimalarials is increasing and the development of new drug families is needed to maintain malaria control. Current antimalarials target the intraerythrocytic developmental stage of the Plasmodium falciparum life cycle. However, the invasive extracellular parasite form, the merozoite, is also an attractive target for drug development. We have previously demonstrated that heparin-like molecules, including those with low molecular weights and low anticoagulant activities, are potent and specific inhibitors of merozoite invasion and blood-stage replication. Here we tested a large panel of heparin-like molecules and sulfated polysaccharides together with various modified chemical forms for their inhibitory activity against P. falciparum merozoite invasion. We identified chemical modifications that improve inhibitory activity and identified several additional sulfated polysaccharides with strong inhibitory activity. These studies have important implications for the further development of heparin-like molecules as antimalarial drugs and for understanding merozoite invasion.

Sulfated Glycans and Related Digestive Enzymes in the Zika Virus Infectivity: Potential Mechanisms of Virus-Host Interaction and Perspectives in Drug Discovery

As broadly reported, there is an ongoing Zika virus (ZIKV) outbreak in countries of Latin America. Recent findings have demonstrated that ZIKV causes severe defects on the neural development in fetuses in utero and newborns. Very little is known about the molecular mechanisms involved in the ZIKV infectivity. Potential therapeutic agents are also under investigation. In this report, the possible mechanisms of action played by glycosaminoglycans (GAGs) displayed at the surface proteoglycans of host cells, and likely in charge of interactions with surface proteins of the ZIKV, are highlighted. As is common for the most viruses, these sulfated glycans serve as receptors for virus attachment onto the host cells and consequential entry during infection. The applications of (1) exogenous sulfated glycans of different origins and chemical structures capable of competing with the virus attachment receptors (supposedly GAGs) and (2) GAG-degrading enzymes able to digest the virus attachment receptors on the cells may be therapeutically beneficial as anti-ZIKV. This communication attempts, therefore, to offer some guidance for the future research programs aimed to unveil the molecular mechanisms underlying the ZIKV infectivity and to develop therapeutics capable of decreasing the devastating consequences caused by ZIKV outbreak in the Americas.

Antiviral Portrait Series: 4. Polysuifates as Inhibitors of HIV and Other Enveloped Viruses

Polysulfates are highly potent and selective inhibitors of the in vitro replication of HIV and other enveloped viruses. They not only inhibit the cytopathic effect of HIV, but also prevent HIV-induced syncytium (giant cell) formation. They also act synergistically with other anti-HIV drugs. The anti-HIV activity of polysulfates is a result of their shielding of the positively charged sites in the V3 loop of the viral envelope glycoprotein gp120. When polysulfates were administered intravenously to rabbits, their half-life was approximately 2h. Although they are very poorly absorbed following oral administration, they can be made orally bioavailable with the appropriate chemical modifications. Also, polysulfates may lose (much of) their anticoagulant activity upon chemical modification without giving up their anti-HIV activity. Their efficacy in the therapy and/or prophylaxis of retroviral infections remains to be demonstrated both in animal models and in humans.

Preparation and characterization of O-acylated fucosylated chondroitin sulfate from sea cucumber

Fucosylated chondroitin sulfate (FuCS), a kind of complex glycosaminoglycan from sea cucumber, has potent anticoagulant activity. In order to understand the relationship between structures and activity, the depolymerized FuCS (dFuCS) was chosen to prepare its derivates by selective substitution at OH groups. Its O-acylation was carried out in a homogeneous way using carboxylic acid anhydrides. The structures of O-acylated derivatives were characterized by NMR. The results indicated that the 4-O-sulfated fucose residues may be easier to be acylated than the other ones in the sulfated fucose branches. But the O-acylation was always accompanied by the β-elimination, and the degree of elimination was higher as that of acylation was higher. The results of clotting assay indicated that the effect of partial O-acylation of the dFuCS on their anticoagulant potency was not significant and the O-acylation of 2-OH groups of 4-O-sulfated fucose units did not affect the anticoagulant activity.

Case study: contamination of heparin with oversulfated chondroitin sulfate

In late 2007 and early 2008, a cluster of adverse events in patients receiving Heparin Sodium Injection occurred in the United States and in some countries in Europe. The adverse events were reported as being "allergic type" reactions, chiefly characterized by acute hypotension, nausea, and shortness of breath. The root cause of the cluster of adverse events was determined to be a contamination of the heparin by oversulfated chondroitin sulfate. The isolation and structure determination of this contaminant was accomplished by an FDA-led consortium of academic and government laboratories and independently by Baxter Healthcare, whose vial products were first identified in the USA as being associated with the adverse events. Oversulfated chondroitin sulfate was shown to produce acute hypotension in animal models, demonstrating that it was most likely the causative agent responsible for certain of the reported adverse events in patients receiving the contaminated heparin products.

HFT-T, a targeting nanoparticle, enhances specific delivery of paclitaxel to folate receptor-positive tumors

Nonspecific distribution of chemotherapeutic drugs (such as paclitaxel) is a major factor contributing to side effects and poor clinical outcomes in the treatment of human head and neck cancer. To develop novel drug delivery systems with enhanced efficacy and minimized adverse effects, we synthesized a ternary conjugate heparin-folic acid-paclitaxel (HFT), loaded with additional paclitaxel (T). The resulting nanoparticle, HFT-T, is expected to retain the antitumor activity of paclitaxel and specifically target folate receptor (FR)-expressing tumors, thereby increasing the bioavailability and efficacy of paclitaxel. In vitro experiments found that HFT-T selectively recognizes FR-positive human head and neck cancer cell line KB-3-1, displaying higher cytotoxicity compared to the free form of paclitaxel. In a subcutaneous KB-3-1 xenograft model, HFT-T administration enhanced the specific delivery of paclitaxel into tumor tissues and remarkably improved antitumor efficacy of paclitaxel. The average tumor volume in the HFT-T treatment group was 92.9 +/- 78.2 mm(3) vs 1670.3 +/- 286.1 mm(3) in the mice treated with free paclitaxel. Furthermore, paclitaxel tumors showed a resurgence of growth after several weeks of treatment, but this was not observed with HFT-T. This indicates that HFT-T could be more effective in preventing tumors from developing drug resistance. No significant acute in vivo toxicity was observed. These results indicate that specific delivery of paclitaxel with a ternary structured nanoparticle (HFT-T) targeting FR-positive tumor is a promising strategy to enhance chemotherapy efficacy and minimize adverse effects.

A model ternary heparin conjugate by direct covalent bond strategy applied to drug delivery system

A model ternary heparin conjugate by direct covalent bond strategy has been developed, in which modified heparin using active mix anhydride as intermediate conjugates with model drug molecule and model specific ligand, respectively. Designed ester bonds between model drug and heparin facilitate hydrolysis kinetics research. The strategy can be extended to design and synthesize a targeted drug delivery system. The key point is to use mixed anhydride groups as activating intermediates to mediate the synthesis of the ternary heparin conjugate. Formation of mixed anhydride is detected by the conductimetry experiment. The ternary heparin conjugate is characterized by (13)C NMR, FT-IR and GPC, respectively. The decreased trend on degree of substitution (DS) is consistent with that of introduced anticancer drug and specific ligand in drug delivery system. Moreover, their anticoagulant activity is evaluated by measuring activated partial thromboplastin time (APTT) and anti-factor Xa activity. The results show that model ternary heparin conjugate with reduced anticoagulant activity may avoid the risk of severe hemorrhagic complication during the administration and is potential to develop a safe and effective drug delivery system on anticancer research.

Semi-synthetic heparin derivatives: chemical modifications of heparin beyond chain length, sulfate substitution pattern and N-sulfo/N-acetyl groups

The glycosaminoglycan heparin is a polyanionic polysaccharide most recognized for its anticoagulant activity. Heparin binds to cationic regions in hundreds of prokaryotic and eukaryotic proteins, termed heparin-binding proteins. The endogenous ligand for many of these heparin-binding proteins is a structurally similar glycosaminoglycan, heparan sulfate (HS). Chemical and biosynthetic modifications of heparin and HS have been employed to discern specific sequences and charge-substitution patterns required for these polysaccharides to bind specific proteins, with the goal of understanding structural requirements for protein binding well enough to elucidate the function of the saccharide-protein interactions and/or to develop new or improved heparin-based pharmaceuticals. The most common modifications to heparin structure have been alteration of sulfate substitution patterns, carboxyl reduction, replacement N-sulfo groups with N-acetyl groups, and chain fragmentation. However, an accumulation of reports over the past 50 years describe semi-synthetic heparin derivatives obtained by incorporating aliphatic, aryl, and heteroaryl moieties into the heparin structure. A primary goal in many of these reports has been to identify heparin-derived structures as new or improved heparin-based therapeutics. Presented here is a perspective on the introduction of non-anionic structural motifs into heparin structure, with a focus on such modifications as a strategy to generate novel reduced-charge heparin-based bind-and-block antagonists of HS-protein interactions. The chemical methods employed to synthesize such derivatives, as well as other unique heparin conjugates, are reviewed.

Diversity-oriented chemical modification of heparin: Identification of charge-reduced N-acyl heparin derivatives having increased selectivity for heparin-binding proteins

The diversity-oriented chemical modification of heparin is shown to afford charge-reduced heparin derivatives that possess increased selectivity for binding heparin-binding proteins. Variable N-desulfonation of heparin was employed to afford heparin fractions possessing varied levels of free amine. These N-desulfonated heparin fractions were selectively N-acylated with structurally diverse carboxylic acids using a parallel synthesis protocol to generate a library of 133 heparin-derived structures. Screening library members to compare affinity for heparin-binding proteins revealed unique heparin-derived structures possessing increased affinity and selectivity for individual heparin-binding proteins. Moreover, N-sulfo groups in heparin previously shown to be required for heparin to bind specific proteins have been replaced with structurally diverse non-anionic moieties to afford identification of charge-reduced heparin derivatives that bind these proteins with equivalent or increased affinity compared to unmodified heparin. The methods described here outline a process that we feel will be applicable to the systematic chemical modification of natural polyanionic polysaccharides and the preparation of synthetic oligosaccharides to identify charge-reduced high affinity ligands for heparin-binding proteins.

Polysulfated sialic acid derivatives as anti-human immunodeficiency virus

We report the synthesis of a novel alkyl polysulfated sialic acid derivative denoted as NMSO3. NMSO3 exhibited potent inhibition against both laboratory and clinical human immunodeficiency virus type 1 (HIV-1). The anti-viral activity of this compound (1 uM) was compared to dextran sulfate (3 uM), and was found to be more potent against HIV-1IIIb than AZT (10 uM). The anti-coagulation time was more than 15-fold shorter than that of dextran sulfate. An in vivo anti-viral study of NMSO3 in NOD-SCID-PBL mice HIV model showed complete protection of the animals from virus challenge at the concentration of 10 mg/kg. This suggests that NMSO3 can be effective in the treatment of HIV-infected individuals.

Antiviral Activities of Polysaccharides from Natural Sources

The ever increasing resistance of human pathogens to current anti-infective agents is a serious medical problem, leading to the need to develop novel antibiotic prototype molecules. In the case of viruses, the search for antiviral agents involves additional difficulties, particularly due to the nature of the infectious viral agents. Thus, many compounds that may cause the death of viruses are also very likely to injure the host cell that harbours them. Natural products are increasingly appreciated as leads for drug discovery and development. Screening studies have been carried out in order to find antiviral agents from natural sources, and the occurrence of antiviral activity in extracts of plants, marine organisms and fungi is frequent. The evidence indicates that there may be numerous potentially useful antiviral phytochemicals in nature, waiting to be evaluated and exploited. In addition, other plants, not previously utilized medicinally, may also reveal antivirals. Among natural antiviral agents, recent investigations have reconsidered the interest of phyto-polysaccharides, which act as potent inhibitors of different viruses. This chapter will illustrate a variety of antiviral polysaccharides from natural sources since 1990, with the aim of making this matter more accessible to drug development

Isolation and NMR characterization of rosacelose, a novel sulfated polysaccharide from the sponge Mixylla rosacea

Rosacelose, a new anti-HIV polysaccharide composed of glucose and fucose sulfate, has been isolated from an aqueous extract of the marine sponge Mixylla rosacea. Extensive use of 1H and 13C multidimensional NMR spectroscopy, combined with chemical analysis were used to establish a linear polysaccharide structure composed mainly of 4,6-disulfated 3-O-glycosylated alpha-D-glucopyranosyl and 2,4-disulfated 3-O-glycosylated alpha-L-fucopyranosyl residues (in a 3:1 molar ratio).

Preparation and characterization of 'heparinocytes': erythrocytes with covalently bound low molecular weight heparin

In an attempt to create the possibility of stable, long acting, intravascular anticoagulation, low molecular weight heparin was modified by introducing a sulfhydryl group into the molecule (LMWH-SH). Human erythrocytes were covalently grafted with LMWH-SH by the use of a heterobifunctional coupling reagent which reacts with the SH group of LMWH-SH and surface exposed amino groups of erythrocytes now called 'heparinocytes' (HC). HC were morphologically indistinguishable from untreated erythrocytes and displayed identical osmotic resistance. The functionality of HC was analyzed by classical coagulation tests in which they dose dependently inhibited clot formation. HC were also functional in recalcified whole blood inhibiting thrombin formation as assessed by the cleavage of the chromogenic substrate S-2238. The system appears applicable as a potential autologous, long-term anticoagulant treatment or prophylaxis.

A novel strategy to generate biologically active neo-glycosaminoglycan conjugates

Heparin and heparan sulfate are structurally related polysaccharides with a variety of biological effects/functions. Most of these effects are due to interactions, of varying specificity, between the negatively charged polysaccharide chains and proteins. While such interactions generally involve a single saccharide domain of decasaccharide size or less, ternary complexes of two protein molecules binding to separate domains on a single polysaccharide chain are known to occur. To facilitate studies on domain organization and its importance for biological function a strategy was developed to chemically conjugate defined heparin oligomers in linear and chemoselective fashion. The procedure requires that the oligosaccharide to provide the reducing-terminal domain of the conjugate is generated by lyase degradation of a parent polysaccharide, whereas the nonreducing-terminal domain is obtained through deaminative cleavage with nitrous acid. The applicability of the method was demonstrated by constructing a conjugate composed of two heparin 12-mers, of which the reducing-terminal component contained the antithrombin-binding region, whereas the nonreducing-terminal domain did not. Contrary to any of the unconjugated oligomers, the product was found to efficiently promote the inactivation of thrombin by antithrombin.

Structure-function relations of heparin-mimetic sulfated xylan oligosaccharides: inhibition of human immunodeficiency virus-1 infectivity in vitro

Heparins/heparan sulfates modulate the function of proteins and cell membranes in numerous biological systems including normal and disease processes in humans. Heparin has been used for many years as an anticoagulant, and anticoagulant heparin-mimetics were developed several decades ago by chemical sulfation of non-mammalian polysaccharides, e.g., an antithrombotic sulfated xylan. This pharmaceutical, which comprises a mixture of sulfated oligoxylans, also mimics most other biological actions of natural heparins in vitro, including inhibition of the human immunodeficiency virus, but the molecular basis for these actions has been unclear. Here, numerous Components of the sulfated oligoxylan mixture were isolated and when bioassayed in the case of anti-HIV-1 infectivity revealed that a structural specificity underlines the capacity of sulfated xylan to inhibit HIV-1, rather than a non-specific mechanism. Components were isolated by chromatographic fractionation through Bio-Gel P10 in 0.5 M ammonium bicarbonate. This fractionation revealed an elution range associated with apparent molecular weights of approximately 22000 to <1500 relative to standard heparin and heparan sulfates and newly prepared sulfated oligosaccharide standards. Components were characterized by metachromatic absorption spectroscopy, ultracentrifugation, GlcA analysis, and potency against HIV-1 infectivity, both in the tetrazolium cytotoxicity assay and in syncytium-forming assays, in CD4-lymphocytes. Structural specificity was indicated by the differential potencies exhibited by the Components: Highest activity (cytotoxicity) was exhibited by Components in the chromatographic region > or = approximately 5500 in mass (50% effective (inhibitory) concentration = 0.5-0.7 microg ml(-1) in the first fractionation series, and 0.1-0.5 microg ml(-1) in a second series). The potency declined sharply below approximately 5400 in mass, but with an exception; a second structure exhibiting relatively high potency eluted among low-mass oligosaccharides which had an average size of approximately a nonomer. Components displayed differential potencies also against the syncytium-forming infectivity of HIV-1. The high potency against syncytium-formation was retained by Components down to a minimum size of about 4500 in mass, smaller than the > or = approximately 5400 required above. One in ten of the beta1,4-linked xyloses in the native xylan are substituted with a monomeric alpha1,2 DGlcA branch. We have speculated that pharmaceutical actions of sulfated xylan might be related to structures involving the alpha-D linked substituents and this was examined using a space-filling model of a sulfated octaxylan and by analyses of Components for GlcA content. Understanding structure/function relations in the heparin-like actions of these agents would be of general significance for the careful examination of their potential clinical usefulness in many human processes modulated by heparins, including AIDS.

Heparin accelerates the inhibition of cathepsin G by mucus proteinase inhibitor: potent effect of O-butyrylated heparin

Heparin tightly binds cathepsin G and so protects the enzyme from inhibition by alpha1-antichymotrypsin, alpha1-proteinase inhibitor and eglin c, three proteins which do not bind heparin [Ermolieff J., Boudier C., Laine A., Meyer B. and Bieth J.G. (1994) J. Biol. Chem. 269, 29502-29508]. Here we show that heparin no longer protects cathepsin G from inhibition when the enzyme is reacted with mucus proteinase inhibitor (MPI), a heparin-binding protein. Heparin fragments of Mr=4500 and 8100 and O-butyrylated heparin of Mr=8000 form tight complexes with cathepsin G (Kd=0.5-2.2 nM) and MPI (Kd=0. 4-0.8 muM) and accelerate the MPI-promoted inhibition of cathepsin G by a factor of 17-26. They also accelerate the inhibition of neutrophil elastase and pancreatic chymotrypsin. The rate acceleration is due to the binding of heparin to MPI. Butyrylation of heparin slightly decreases its affinity for cathepsin G and MPI but sharply decreases the ionic interactions between the positively charged proteins and the negatively charged polyanion. The butyrylated heparin derivative is the best rate accelerator: it increases the rate constant for the MPI-induced inhibition of cathepsin G and elastase by factors of 26 and 23, respectively. This, together with the fact that it has a good bioavailability and a very low anticoagulant activity, suggests that it might be an adjuvant of MPI-based therapy of cystic fibrosis.

The system of sulfated alpha-(1-->3)-linked D-mannans from the red seaweed Nothogenia fastigiata: structures, antiherpetic and anticoagulant properties

Structural analysis of two xylomannans extracted from Nothogenia fastigiata was carried out. The results are consistent with the general pattern previously reported for other xylo-mannans of the same system, alpha-(1-->3)-linked D-mannans 2- and 6-sulfated and having single stubs of beta-(1-->2)-linked D-xylose, but one of the new samples contains a significant amount of 2,6-disulfated units. Both xylomannans studied are obtained as complexes with a beta-D-(1-->3)-, alpha-L-(1-->4)-galactan and a beta-D-(1-->3)-, beta-D-(1-->4)-'mixed linkage' xylan co-existing in the seaweed, a fact that limits the accuracy of the data determined. The structures of the galactan and the xylan are similar to those previously informed for this seaweed. The antiviral activity against four different herpes simplex viral strains and the anticoagulant properties of all the xylo-mannans of the system are reported.

The potential for heparin and its derivatives in the therapy and prevention of HIV-1 infection

Heparin is one of several sulphated polysaccharides which potently inhibit replication of the human immunodeficiency virus type 1 (HIV-1) in cultures of CD4+ve human cells. The EC50 value is around 5 microg ml(-1). We have demonstrated that heparin binds to recombinant gp120, the envelope glycoprotein of HIV-1, at a site termed the V3 loop, or principle neutralizing domain, which consists of a disulphide-bridged loop of 32-35 amino acids particularly enriched with basic residues. Using a series of chemically modified heparins we have shown that there is structural specificity in the anti-HIV activity of heparin. Heparin is routinely used clinically as an anticoagulant, and has proved essentially non-toxic and well tolerated. Low anticoagulant derivatives of heparin which retain high anti-HIV-1 activities in vitro may be generated by several routes. Such preparations are ideal candidates for clinical investigation as potential novel therapeutic agents for use in combination with other drugs in the management of AIDS and HIV infection.

Antiherpetic and anticoagulant properties of carrageenans from the red seaweed Gigartina skottsbergii and their cyclized derivatives: correlation between structure and biological activity

The antiviral activity against herpes simplex virus types 1 and 2 of kappa/l-, partially cyclized mu/v-, and lambda-carrageenans isolated from the red seaweed Gigartina skottsbergii and their cyclized derivatives was analyzed. lambda-Carrageenans and the partially cyclized mu/v-carrageenan were the most potent inhibitors of herpes viruses (including acyclovir-resistant variants and clinical isolates), with IC50 values lower than 1 microgram ml-1 against both serotypes and selectivity indices higher than 10(3). kappa/l-Carrageenans were slightly less effective than the other two types with IC50 values in the range 1.6-4.1 micrograms ml-1. Antiherpetic activity was directly correlated to the amount of alpha-D-galactose 2,6-disulfate residues in the natural carrageenans. The cyclization of the alpha-D-galactose 6-sulfate and 2,6-disulfate units into 3,6-anhydro-alpha-D-galactose and 3,6-anhydro-alpha-D-galactose 2-sulfate residues in these polysaccharides, in general, lowers the antiherpetic activity of the derivatives with respect to the natural carrageenans. Some carrageenans showed a very reduced anticoagulant activity only at concentrations that were considerably higher than the IC50, whereas others were totally devoid of anticoagulant properties. Among natural carrageenans, the mu/v-type IC3 shows the best relationship between antiviral efficacy and lack of anticoagulant action, resulting a very promising compound.

Chemotherapy of human immunodeficiency virus (HIV) infection: anti-HIV agents targeted at early stages in the virus replicative cycle

Several compounds have been identified that inhibit an early stage in the replicative cycle of the human immunodeficiency virus (HIV): i) virus adsorption: polysulfates, polysulfonates, polycarboxylates, polyphosphates, and polyoxometalates; or ii) virus-cell fusion: plant lectins, negatively charged albumins and betulinic acid derivatives; iii) virus fusion/uncoating: bicyclam derivatives; iv) reverse transcription: dideoxynucleoside analogues, acyclic nucleoside phosphonates and non-nucleoside reverse transcriptase inhibitors. In principle, HIV may develop resistance to any of these specific anti-HIV agents. However, virus breakthrough can be completely prevented if these agents, alone or in combination, are added to the HIV-infected cells from the beginning at sufficiently high ('knock-out') concentrations.

Inhibition of human immunodeficiency virus infection by heparin derivatives

Heparin (Hep) and sulfated polysaccharides (SPs) have been reported to inhibit HIV infection in vitro. In vivo, anticoagulant activity and reduced bioavailability were found to limit the antiviral effects of Hep. In this investigation, three nonanticoagulant N-acylated Hep conjugates [OI1:3Hep, Pal1:5Hep, and Pal1:5Hep(SO4)] were compared to Hep for their ability to interact with HIV replication in CD4-positive cell lines and PBMCs. Resulfated palmitoyl-Hep [Pal1:5Hep(SO4)] exhibited the strongest anti-HIV effects. For instance, no provirus HIV DNA was detected in the genome of HIV-1-LAI-infected PBMCs treated with this heparin derivative. Cell-to-cell fusion and RT activity were explored to explain these differences. Hep and Pal1:5Hep(SO4) derivative exerted identical effects on cell-to-cell fusion. On the other hand, Pal1:5Hep(SO4) displayed the strongest inhibitory effects in the acellular RT inhibition assay. This suggests that RT might be a second target for N-acylated Hep, even though SP uptake and the preferential effects of SPs on RT as opposed to DNA polymerase have not yet been demonstrated. Nevertheless, considering the anticoagulant, antiviral, and antiinflammatory effects of N-acylated Hep, the N-acylated Hep derivatives might be excellent candidates as new anti-HIV pharmacological tools.

Antiviral therapy for human immunodeficiency virus infections

Depending on the stage of their intervention with the viral replicative cycle, human immunodeficiency virus inhibitors could be divided into the following groups: (i) adsorption inhibitors (i.e., CD4 constructs, polysulfates, polysulfonates, polycarboxylates, and polyoxometalates), (ii) fusion inhibitors (i.e., plant lectins, succinylated or aconitylated albumins, and betulinic acid derivatives), (iii) uncoating inhibitors (i.e., bicyclams), (iv) reverse transcription inhibitors acting either competitively with the substrate binding site (i.e., dideoxynucleoside analogs and acyclic nucleoside phosphonates) or allosterically with a nonsubstrate binding site (i.e., non-nucleoside reverse transcriptase inhibitors), (v) integration inhibitors, (vi) DNA replication inhibitors, (vii) transcription inhibitors (i.e., antisense oligodeoxynucleotides and Tat antagonists), (viii) translation inhibitors (i.e., antisense oligodeoxynucleotides and ribozymes), (ix) maturation inhibitors (i.e., protease inhibitors, myristoylation inhibitors, and glycosylation inhibitors), and finally, (x) budding (assembly/release) inhibitors. Current knowledge, including the therapeutic potential, of these various inhibitors is discussed. In view of their potential clinical the utility, the problem of virus-drug resistance and possible strategies to circumvent this problem are also addressed.