High-affinity glycopolymer binding to human DC-SIGN and disruption of DC-SIGN interactions with HIV envelope glycoprotein

Noncovalent interactions between complex carbohydrates and proteins drive many fundamental processes within biological systems, including human immunity. In this report we aimed to investigate the potential of mannose-containing glycopolymers to interact with human DC-SIGN and the ability of these glycopolymers to inhibit the interactions between DC-SIGN and the HIV envelope glycoprotein gp120. We used a library of glycopolymers that are prepared via combination of copper-mediated living radical polymerization and azide-alkyne [3+2] Huisgen cycloaddition reaction. We demonstrate that a relatively simple glycopolymer can effectively prevent the interactions between a human dendritic cell associated lectin (DC-SIGN) and the viral envelope glycoprotein gp120. This approach may give rise to novel insights into the mechanisms of HIV infection and provide potential new therapeutics.

Antibacterial effects of poly(2-(dimethylamino ethyl)methacrylate) against selected gram-positive and gram-negative bacteria

Antimicrobial coatings can reduce the occurrence of medical device-related bacterial infections. Poly(2-(dimethylamino ethyl)methacrylate) (pDMAEMA) is one such polymer that is being researched in this regard. The aims of this study were to (1) elucidate pDMAEMA's antimicrobial activity against a range of Gram-positive and Gram-negative bacteria and (2) to investigate its antimicrobial mode of action. The methods used include determination of minimum inhibitory concentration (MIC) values against various bacteria and the effect of pH and temperature on antimicrobial activity. The ability of pDMAEMA to permeabilise bacterial membranes was determined using the dyes 1-N-phenyl-naphthylamine and calcein-AM. Flow cytometry was used to investigate pDMAEMA's capacity to be internalized by bacteria and to determine effects on bacterial cell cycling. pDMAEMA was bacteriostatic against Gram-negative bacteria with MIC values between 0.1-1 mg/mL. MIC values against Gram-positive bacteria were variable. pDMAEMA was active against Gram-positive bacteria around its pK(a) and at lower pH values, while it was active against Gram-negative bacteria around its pK(a) and at higher pH values. pDMAEMA inhibited bacterial growth by binding to the outside of the bacteria, permeabilizing the outer membrane and disrupting the cytoplasmic membrane. By incorporating pDMAEMA with erythromycin, it was found that the efficacy of the latter was increased against Gram-negative bacteria. Together, the results illustrate that pDMAEMA acts in a similar fashion to other cationic biocides.

Modification of thiol functionalized aptamers by conjugation of synthetic polymers

Aptamers are known for their short in vivo circulating half-life and rapid renal clearance. Their conjugation to poly(ethylene glycol) (PEG) is a way to improve their residence in the body. Two aptamers (AptD and AptF), having a disulfide protected thiol modification on the 3' end, have been conjugated to maleimide activated PEGs of various molecular weights and structures (linear PEG20; branched PEG20 and 40; PolyPEG17, 40, and 60 kDa). The high yield coupling (70-80% in most of the cases) could be achieved using immobilized tris[2-carboxyethyl]phosphine hydrochloride (TCEP) as reducing agent at pH 4. The affinity of PEGylated AptD for its target was reduced by conjugation to linear PEG20 and branched PEG40, but not to branched PEG20 and PolyPEGs. This work demonstrates an alternative approach to PEGylation of aptamers, and that the effect of PEG on the affinity for the target varies according to the structure and conformation of the synthetic polymer.

Phosphine-mediated one-pot thiol-ene "click" approach to polymer-protein conjugates

We employ water-soluble organic phosphines as key reagents in a one-pot synthetic protocol where a (poly)peptide disulfide bridge is first reduced followed by subsequent reaction of the two thiols in situ with poly(monomethoxy ethylene glycol)(meth)acrylates (p(mPEG)(M)A); we use salmon calcitonin (sCT) as a disulfide bridge-containing peptide, which contains a disulfide bridge-Cys1-Cys7-that can be reduced to give two sulfhydryl units available for thiol functionalisation; bioactivity is retained.

Conjugation of salmon calcitonin to a combed-shaped end functionalized poly(poly(ethylene glycol) methyl ether methacrylate) yields a bioactive stable conjugate

Salmon calcitonin (sCT) was conjugated via its N-terminal cysteine to a comb-shaped end-functionalized poly(poly(ethylene glycol) methyl ether methacrylate) (PolyPEG, 6.5 kDa), and to linear PEG (5 kDa). Conjugate molecular weight and purity was assessed by SEC-HPLC and MALDI-TOF MS. Bioactivity of conjugates was measured by cyclic AMP assay in T47D cells. Calcium and calcitonin levels were measured in rats following intravenous injections. Stability of conjugates was tested against serine proteases, intestinal and liver homogenates and serum. Cytotoxicity of conjugates was assessed by lactate dehydrogenase (LDH) assay and by haemolytic assay of rat red blood cells. Results showed that the two conjugates were of high purity with molecular weights similar to predictions. Both conjugates retained more than 85% bioactivity in vitro and had nanomolar EC(50) values similar to sCT. While both sCT-PolyPEG(6.5 K) and sCT-PEG(5 K) were resistant to metabolism by serine proteases, homogenates and serum, PolyPEG (6.5 K) was more so. Although both conjugates reduced serum calcium to levels similar to those achieved with sCT, PolyPEG(6.5 K) extended the T(1/2) and AUC of serum sCT over values achieved with sCT-PEG and sCT itself. None of PolyPEG, PEG or methacrylic acid displayed significant cytotoxicity. PolyPEG may therefore have potential to improve pharmacokinetic profiles of injected peptides.

Dexamethasone-pDMAEMA polymeric conjugates reduce inflammatory biomarkers in human intestinal epithelial monolayers

The mucoadhesive polymer, poly(dimethylamino)ethyl methacrylate, (pDMAEMA), was synthesised by living radical polymerisation and subsequently conjugated by quaternisation reaction to a functionalised anti-inflammatory corticosteroid dexamethasone, to separately yield two conjugates with either 9:1 or 18:1 molar ratios of dexamethasone:polymer respectively. The hypothesis was to test whether the active agent maintained in vitro bioactivity when exposed to the apical side of human intestinal epithelial monolayers, Caco-2 and mucus-covered HT29-MTX-E12 (E12). HPLC analysis indicated high conjugate purity. Similar to pDMAEMA, fluorescently-labelled dexamethasone-pDMAEMA conjugates were bioadhesive to Caco-2 and mucoadhesive to E12. Apical addition of conjugates suppressed mRNA expression of the inflammatory markers, NURR1 and ICAM-1 in E12 following stimulation by PGE(2) and TNF-alpha, respectively. Conjugates also suppressed TNF-alpha stimulated cytokine secretion to the basolateral side of Caco-2 monolayers. Measurement of dexamethasone permeability from conjugates across monolayers suggested that conjugation reduced permeability compared to free dexamethasone. LDH assay indicated that conjugates were not cytotoxic to monolayers. Anti-inflammatory agents can therefore be successfully conjugated to polymers and they retain adhesion and bioactivity and have potential to be formulated for topical administration.