Sulfonated RAFT Copolymers as Heparin Mimetics: Synthesis, Reactivity Ratios, and Anticoagulant Activity

Investigation of physicochemical, morphological and biomedical properties of network hydrogels derived from arabinogalactan of acacia-tragacanth gum

Recently, significant progress has been made in the development of natural polysaccharide-derived functional copolymers for advanced biomedical uses. Herein, the main objective of the present research work was to explore the potential of gum acacia (GA) and tragacanth gum (TG) for developing network hydrogels to use in drug delivery (DD) applications. The copolymers were prepared by grafting of 3-sulfopropylacrlate (SPA) onto gum (GA-TG). FE-SEM, AFM, XRD, XPS, FTIR, 13C NMR and DSC techniques were applied for their characterizations and structural analysis. The physicochemical, morphological and biomedical properties of hydrogels were investigated. The optimized polymer network exhibited a mesh size (ξ) of 13.95 mm and a cross-linking density (ρ) of 6.44 × 10-5 mol/cm3. FE-SEM and AFM revealed heterogeneous morphology and rough topology of copolymer hydrogels. The XRD revealed the amorphous state of the copolymer. FTIR and 13C NMR confirmed the incorporation of poly(SPA) chains onto gums. Diffusion of meropenem drug occurred in a sustained manner with a non-Fickian diffusion mechanism. The release profile of the drug was best described by the First-order kinetic model. The results of polymer-blood interactions revealed their non-haemolytic & non-thrombogenic features. Copolymers exhibited antioxidant nature and illustrated 40.72 ± 2.08 % scavenging ability during DPPH assay. The hydrogel demonstrated a mucoadhesive nature and required 100 ± 10 mN forces to separate from mucous membrane. The meropenem impregnated hydrogel exhibited antibacterial activity against Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) bacteria, respectively. The results of various properties demonstrated the suitability of network hydrogels for DD uses.

Synthesis, Biological Evaluation and Reversal of Sulfonated Di- and Triblock Copolymers as Novel Parenteral Anticoagulants

Despite targeting different coagulation cascade sites, all Food and Drug Administration-approved anticoagulants present an elevated risk of bleeding, including potentially life-threatening intracranial hemorrhage. Existing studies have not thoroughly investigated the efficacy and safety of sulfonate polymers in animal models and fully elucidate the precise mechanisms by which these polymers act. The activity and safety of sulfonated di- and triblock copolymers containing poly(sodium styrenesulfonate) (PSSS), poly(sodium 2-acrylamido-2-methylpropanesulfonate) (PAMPS), poly(ethylene glycol) (PEG), poly(sodium methacrylate) (PMAAS), poly(acrylic acid) (PAA), and poly(sodium 11-acrylamidoundecanoate) (PAaU) blocks are synthesized and assessed. PSSS-based copolymers exhibit greater anticoagulant activity than PAMPS-based ones. Their activity is mainly affected by the total concentration of sulfonate groups and molecular weight. PEG-containing copolymers demonstrate a better safety profile than PAA-containing ones. The selected copolymer PEG47-PSSS32 exhibits potent anticoagulant activity in rodents after subcutaneous and intravenous administration. Heparin Binding Copolymer (HBC) completely reverses the anticoagulant activity of polymer in rat and human plasma. No interaction with platelets is observed. Selected copolymer targets mainly factor XII and fibrinogen, and to a lesser extent factors X, IX, VIII, and II, suggesting potential application in blood-contacting biomaterials for anticoagulation purposes. Further studies are needed to explore its therapeutic applications fully.

Antiviral Activities of Heparan Sulfate Mimetic RAFT Polymers Against Mosquito-borne Viruses

Mosquito-borne viruses are a major worldwide health problem associated with high morbidity and mortality rates and significant impacts on national healthcare budgets. The development of antiviral drugs for both the treatment and prophylaxis of these diseases is thus of considerable importance. To address the need for therapeutics with antiviral activity, a library of heparan sulfate mimetic polymers was screened against dengue virus (DENV), Yellow fever virus (YFV), Zika virus (ZIKV), and Ross River virus (RRV). The polymers were prepared by RAFT polymerization of various acidic monomers with a target MW of 20 kDa (average Mn ∼ 27 kDa by GPC). Among the polymers, poly(SS), a homopolymer of sodium styrenesulfonate, was identified as a broad spectrum antiviral with activity against all the tested viruses and particularly potent inhibition of YFV (IC50 = 310 pM). Our results further uncovered that poly(SS) exhibited a robust inhibition of ZIKV infection in both mosquito and human cell lines, which points out the potential functions of poly(SS) in preventing mosquito-borne viruses associated diseases by blocking viral transmission in their mosquito vectors and mitigating viral infection in patients.

Glycopolymer-grafted nanoparticles as glycosaminoglycan mimics with cell proliferation and anti-tumor metastasis activities

Glycosaminoglycans (GAGs) are naturally existing extracellular components with a variety important biological functions. However, their heterogeneous chemical compositions and the challenges in purification have become the main disadvantages for clinical applications. Thus, various synthetic glycopolymers have been designed to mimic the structures and functions of natural GAGs. In the current study, glycopolymers from structurally simple glucose or N-acetylglucosamine monomers were synthesized, which were further subjected to sulfation of different degrees and grafting onto silica nanoparticles, leading to spherical-shaped nano-structures of uniform diameters. With the successively strengthened multivalent effect, the obtained glycopolymer nanoparticles not only showed excellent effects on promotion of cell proliferation by stabilizing growth factors, but also significantly inhibited tumor metastasis by weakening the adhesion between tumor cells and activated platelets. Among the prepared nanoparticles, S3-PGNAc@Si with N-acetylglucosamine segment and the highest sulfation degree exhibited the strongest bioactivities, which were even close to those of heparin. This work presents a novel approach for structural and functional mimicking of natural GAGs from simple and low-cost monosaccharides, holding great potential for a range of biomedical applications.

Enhancing BMP-2-mediated osteogenesis with a synthetic heparan sulfate mimetic

Bone morphogenetic protein 2 (BMP-2) is an osteoinductive protein and a potent inducers of bone formation, playing an essential role during bone fracture repair. Heparan sulfate (HS), a highly charged and linear polysaccharide, is known to interact with and enhance BMP-2 bioactivity. Despite showing potential as a potent adjuvant of the endogenous bone healing response, commercially available HS is derived from animal sources which are less desirable when considering translation into the clinic. In the present study, we screen twenty glycomimetics against BMP-2 to determine if fully synthetic analogues of HS can enhance the bioactivity of BMP-2 in vitro and bone healing in vivo. We found that a four-armed dendrimer harboring oversulfated maltose residues could bind BMP-2 with high affinity, enhance BMP-2 bioactivity in vitro and enhance bone regeneration in vivo. These data suggest fully synthetic glycomimetics are viable alternatives to naturally derived HS and offer an attractive alternative for clinical translation.

Supramolecular self-assembly of glycosaminoglycan mimetic nanostructures for cell proliferation and 3D cell culture application

Glycosaminoglycans (GAGs), such as heparin, heparan sulfate and chondroitin sulfate, are playing important roles in various biological processes. Due to the laborious work of organic or enzymatic total synthesis of GAGs, different approaches, including glycopolymers, dendrimers, etc., have been developed to mimic the structures and bioactivities of GAGs, but the syntheses can still be difficult. In the current study, a new format of GAG mimetic structure, supramolecularly assembled polymers, have been easily prepared by mixing fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) and sulfated glyco-modified fluorenylmethoxy derivatives (FGS and FG3S). The self-assembly behavior of these polymers into different structural formats of nanoparticles, nanofibers and macroscopic hydrogels upon adjusted concentrations and composite ratios have been detailed studied. The nanofibers modified with highly sulfated glycol groups (FG3S/Fmoc-FF) showed strong promotion effect for cell proliferation, which efficiency was even similar to that of natural heparin, higher than nanoparticles or non-/low-sulfated glyco-modified nanofibers. Moreover, the supramolecular polymers were further made into hydrogels that capable of 3D cell culture. This study provided a novel and efficient approach for GAG mimicking, showing great potential for tissue engineering related applications.

Heparin mimetics as potential intervention for COVID-19 and their bio-manufacturing

The COVID-19 pandemic has caused severe health problems worldwide and unprecedented decimation of the global economy. Moreover, after more than 2 years, many populations are still under pressure of infection. Thus, a broader perspective in developing antiviral strategies is still of great importance. Inspired by the observed multiple benefits of heparin in the treatment of thrombosis, the potential of low molecular weight heparin (LMWH) for the treatment of COVID-19 have been explored. Clinical applications found that LMWH decreased the level of inflammatory cytokines in COVID-19 patients, accordingly reducing lethality. Furthermore, several in vitro studies have demonstrated the important roles of heparan sulfate in SARS-CoV-2 infection and the inhibitory effects of heparin and heparin mimetics in viral infection. These clinical observations and designed studies argue for the potential to develop heparin mimetics as anti-SARS-CoV-2 drug candidates. In this review, we summarize the properties of heparin as an anticoagulant and the pharmaceutical possibilities for the treatment of virus infection, focusing on the perspectives of developing heparin mimetics via chemical synthesis, chemoenzymatic synthesis, and bioengineered production by microbial cell factories. The ultimate goal is to pave the eminent need for exploring novel compounds to treat coronavirus infection-caused diseases.

Glycosaminoglycan Mimetic Precision Glycomacromolecules with Sequence-Defined Sulfation and Rigidity Patterns

Sulfated glycosaminoglycans (sGAGs) such as heparan sulfate (HS) are structurally diverse linear polysaccharides that are involved in many biological processes and have gained interest as antiviral compounds. Their recognition is driven by a complex orchestra of structural parameters that are still under intense investigation. One distinct characteristic is the incorporation of sulfation patterns including highly sulfated and non-sulfated sequences that provide variations in flexibility and conformation, which in turn impact the biological function of sGAGs. However, these distinct features have not yet been fully realized in the synthetic preparation of sGAG mimetics. Here, we present the synthesis of three groups of sulfated glycomacromolecules as sGAG mimetics: (i) globally sulfated glycooligomers, (ii) glycooligomers with sequence-defined sulfation patterns, and (iii) a globally sulfated glycooligomer-oligo-L-proline hybrid structure. The complete synthesis, including chemical sulfation, was conducted on solid support, enabled by the introduction of a commercially available photocleavable linker allowing for the preservation of sensitive sulfates during cleavage of the products. Structures were obtained in good purity and with high degrees of sulfation demonstrating the wide applicability of this methodology to prepare tailor-made sulfated glycomacromolecules and similar sGAG mimetics. Structures were tested for their anticoagulant properties showing activity similar to their natural HS counterpart and significantly lower than HP.

From Cancer to COVID-19: A Perspective on Targeting Heparan Sulfate-Protein Interactions

Heparan sulfate (HS) is a complex, polyanionic polysaccharide ubiquitously expressed on cell surfaces and in the extracellular matrix. HS interacts with numerous proteins to mediate a vast array of biological and pathological processes. Inhibition of HS-protein interactions is thus an attractive approach for new therapeutic development for cancer and infectious diseases, including COVID-19; however, synthesis of well-defined native HS oligosaccharides remains challenging. This has aroused significant interest in the development of HS mimetics which are more synthetically tractable and have fewer side effects, such as undesired anticoagulant activity. This account provides a perspective on the design and synthesis of different classes of HS mimetics with useful properties, and the development of various assays and molecular modelling tools to progress our understanding of their interactions with HS-binding proteins.

Inhibition of Tumor-Host Cell Interactions Using Synthetic Heparin Mimetics

Low-molecular-weight heparin (LMWH) is the guideline-based drug for antithrombotic treatment of cancer patients, while its direct antitumor effects are a matter of ongoing debate. Although therapeutically established for decades, LMWH has several drawbacks mainly associated with its origin from animal sources. Aiming to overcome these limitations, a library of synthetic heparin mimetic polymers consisting of homo- and copolymers of sulfonated and carboxylated noncarbohydrate monomers has recently been synthesized via reversible addition-fragmentation chain transfer polymerization. These heparin mimetics were investigated for their capacities to interfere with simulated steps of tumor cell metastasis. Among them, homo- and copolymers from sodium 4-styrenesulfonate (poly(SSS)) with acrylic acid (poly(SSS-co-AA)) with an MW between 5 and 50 kDa efficiently attenuated cancer cell-induced coagulation and thus platelet activation and degranulation similar to or even better than LMWH. Furthermore, independent of anticoagulant activities, these polymers affected other metastasis-relevant targets with impressive affinities. Hence, they blocked heparanase enzymatic activity outmatching commercial heparins or a glycosidic drug candidate. Furthermore, these polymers bind P-selectin and the integrin VLA-4 similar to or even better than heparin, indicated by a biosensor approach and thus efficiently blocked melanoma cell binding to endothelium under blood flow conditions. This is the first report on the prospects of synthetic heparin mimetics as promising nontoxic compounds in oncology to potentially substitute heparin as an anticoagulant and to better understand its role as an antimetastatic drug.