Poly(triazolyl methacrylate) glycopolymers as potential targeted unimolecular nanocarriers

Synthetic glycopolymers are increasingly investigated as multivalent ligands for a range of biological and biomedical applications. This study indicates that glycopolymers with a fine-tuned balance between hydrophilic sugar pendant units and relatively hydrophobic polymer backbones can act as single-chain targeted nanocarriers for low molecular weight hydrophobic molecules. Non-covalent complexes formed from poly(triazolyl methacrylate) glycopolymers and low molecular weight hydrophobic guest molecules were characterised through a range of analytical techniques - DLS, SLS, TDA, fluorescence spectroscopy, surface tension analysis - and molecular dynamics (MD) modelling simulations provided further information on the macromolecular characteristics of these single chain complexes. Finally, we show that these nanocarriers can be utilised to deliver a hydrophobic guest molecule, Nile red, to both soluble and surface-immobilised concanavalin A (Con A) and peanut agglutinin (PNA) model lectins with high specificity, showing the potential of non-covalent complexation with specific glycopolymers in targeted guest-molecule delivery.

Synthetic glycopolymers as modulators of protein aggregation: influences of chemical composition, topology and concentration

Synthetic glycopolymers with a variable macromolecular architecture and carbohydrate moieties are utilised to modulate stress-induced aggregation of monoclonal antibodies.

Selective, non-covalent conjugation of synthetic peptides with recombinant proteins mediated by host-guest chemistry

The combination of potent chemical moieties with biologically active proteins is key to some of today's most innovative therapeutic drugs. In order to obviate any chemical modification of the proteins, we present a novel and powerful strategy for the selective conjugation of recombinant protein domains with synthetically derived peptides via a cucurbit[8]uril host-guest chemistry approach.

The role of electrostatics in protein-protein interactions of a monoclonal antibody

Understanding how protein-protein interactions depend on the choice of buffer, salt, ionic strength, and pH is needed to have better control over protein solution behavior. Here, we have characterized the pH and ionic strength dependence of protein-protein interactions in terms of an interaction parameter kD obtained from dynamic light scattering and the osmotic second virial coefficient B22 measured by static light scattering. A simplified protein-protein interaction model based on a Baxter adhesive potential and an electric double layer force is used to separate out the contributions of longer-ranged electrostatic interactions from short-ranged attractive forces. The ionic strength dependence of protein-protein interactions for solutions at pH 6.5 and below can be accurately captured using a Deryaguin-Landau-Verwey-Overbeek (DLVO) potential to describe the double layer forces. In solutions at pH 9, attractive electrostatics occur over the ionic strength range of 5-275 mM. At intermediate pH values (7.25 to 8.5), there is a crossover effect characterized by a nonmonotonic ionic strength dependence of protein-protein interactions, which can be rationalized by the competing effects of long-ranged repulsive double layer forces at low ionic strength and a shorter ranged electrostatic attraction, which dominates above a critical ionic strength. The change of interactions from repulsive to attractive indicates a concomitant change in the angular dependence of protein-protein interaction from isotropic to anisotropic. In the second part of the paper, we show how the Baxter adhesive potential can be used to predict values of kD from fitting to B22 measurements, thus providing a molecular basis for the linear correlation between the two protein-protein interaction parameters.

Microemulsions for oral delivery of insulin: design, development and evaluation in streptozotocin induced diabetic rats

Insulin loaded microemulsions were developed adopting a low shear reverse micellar approach using didoceyldimethylammonium bromide (DMAB) as the surfactant, propylene glycol (PG) as the co-surfactant, triacetin (TA) as the oil phase and insulin solution as the aqueous phase. A ternary phase diagram was constructed based on multiple cloud point titration to highlight the reverse micellar region. The droplet sizes of the microemulsions were 161.7±24.7nm with PDI of 0.447±0.076 and insulin entrapment of ∼85%. Transmission electron microscopy (TEM) revealed the spherical nature and size homogeneity of the microemulsion droplets. The conformational stability of the entrapped insulin within microemulsions was confirmed by fluorescence spectroscopy and circular dichroism. The microemulsions displayed a 10-fold enhancement in bioavailability compared with plain insulin solution administered per oral in healthy rats. The short-term in vivo efficacy in STZ induced diabetic rats provided the proof of concept by a modest glucose reduction at a dose of 20IU/kg. Together this preliminary data indicate the promise of microemulsions for oral delivery of insulin.

A tetravalent RGD ligand for integrin-mediated cell adhesion

Monovalent RGD (arginine-glycine-aspartic acid) peptides or polymers furnished with RGD in random distributions are employed as cell-scaffolds and gene delivery vehicles. However, integrin binding to RGD is dependent on the spatial distribution (clustering) of the ligand and intrinsic integrin affinity via conformational changes (avidity). Here we have designed and expressed a polypeptide consisting of a tetrameric coiled coil and spacer facilitating polyvalent (clustered) display of integrin ligands; the RGD motif was used as proof of principle. Size-exclusion chromatography and circular dichroism showed that the polypeptide self assembled as a tetramer in solution with a defined secondary structure. Cell adhesion to surfaces coated with the polypeptide was up to 3-fold greater than that for (monovalent) RGDS peptide at equivalent concentrations. Moreover, the polypeptide in solution at concentrations ≥1μM inhibited cell adhesion to fibronectin-coated surfaces, while RGDS peptide in solution at concentrations up to 500μM did not. These cell data demonstrate that the polypeptide bound integrin receptors in a polyvalent manner. The polypeptide will therefore be of use in the engineering of tissue-culture scaffolds with increased cell adhesion activity, or to targeted gene delivery vehicles, and could incorporate protein ligands in place of the RGD motif.

A freeze-dried formulation of bacteriophage encapsulated in biodegradable microspheres

With the emergence of widespread antibiotic resistance, there has been renewed interest in the use of bacteriophages. While their potency, safety and specificity have underpinned their clinical potential, to date, little work has been focussed on their formulation with respect to controlled release and/or passive targeting. Here, we show that bacteriophages selective for Staphylococcus aureus or Pseudomonas aeruginosa can be encapsulated into biodegradable polyester microspheres via a modified w/o/w double emulsion-solvent extraction protocol with only a partial loss of lytic activity. Loss of lytic activity could be attributed to the exposure of the bacteriophages to the water-dichloromethane interface, with the lyophilization process itself having little effect. The microspheres were engineered to have an appropriate size and density to facilitate inhalation via a dry-powder inhaler and fluorescently labeled bacteriophages were distributed entirely within the internal porous matrix. The release profile showed a burst release phase (55-63% release within 30 min), followed by a sustained release till around 6h, as appropriate for pulmonary delivery. Despite the poor shelf-life of the formulation, the work is proof-of-concept for the formulation and controlled delivery of bacteriophages, as suitable for the treatment of bacterial lung infections.

Interdomain mobility and conformational stability of type III fibronectin domain pairs control surface adsorption, desorption and unfolding

The 9th-10th type III fibronectin domain pair (9-10FNIII) has found widespread use as a biomimetic surface for cell adhesion. However, the effect of mutations to 9-10FNIII on its surface adsorption characteristics have not been investigated. Here we address this issue using total internal reflection fluorescence (TIRF) and circular dichroism spectroscopy, comparing two conformationally stable 9-10FNIII mutants against the wild type. Desorption of the 9-10FNIII mutants from the silica surface was minimal in comparison to desorption of 9-10FNIII. The extent and rate of protein desorption from silica was empirically matched by loss of secondary structure upon adsorption, with only the spectrum for 9-10FNIII showing extensive loss of the beta-sandwich fold. For the proteins adsorbed to hydrophobic surfaces, only the CD spectra for the 9-10FNIII mutant constrained via an interdomain disulphide bridge showed similarity with the corresponding solution structure. Since the binding of 9-10FNIII to integrin alpha5beta1 is highly dependent on the relative spatial arrangement of the two domains, we suggest that the observed differences in cell adhesion and spreading on wild type 9-10FNIII and mutants may in part be attributed to the extent of protein desorption and unfolding at the surface.

Solution formulation and lyophilisation of a recombinant fibronectin fragment

The 9th-10th type III fibronectin domain pair shows promise in tissue engineering and tumour vasculature targeting. Calorimetry and structure-function analysis were used to investigate the effects of solution formulation and lyophilisation of a mutant ((9-10)FNIII-P). A single endothermic transition for (9-10)FNIII-P in solution was observed at pH<8, irrespective of addition of sucrose or PEG. The temperature at the maximum heat capacity (T(m)) and enthalpy (deltaH) of the transition increased for increasing sucrose concentrations but decreased for increasing PEG concentrations. The transition was fitted to a single two-state unfolding mechanism (in contrast to unfolding in guanidine. x HCl) and was partially reversible only at pH 4, with increasing concentrations of sucrose causing a marked fall in deltaH between scans. Circular dichroism spectra for the thermal unfolding of (9-10)FNIII-P at pH 4 showed loss of native beta-sheet structure and loss of aromatic contributions to the peak centred around 226 nm yielding an intermediate conformation, which in the presence of sucrose was more disordered. Despite a glass transition (T(g)') for (9-10)FNIII-P(aq) of -70 degrees C, primary drying at -30 degrees C did not perturb its conformation upon reconstitution or its biological activity following lyophilisation; the addition of sucrose or PEG had no influence on structure or activity. The main consideration in the formulation of (9-10)FNIII-P was therefore pH.

Physical ageing and thermal analysis of PLGA microspheres encapsulating protein or DNA

PLGA microspheres undergo physical ageing but their ageing kinetics have not been reported, nor the effect of encapsulated protein or plasmid DNA on any associated changes to the glass transition. Differential scanning calorimetry (DSC) was used to measure the rate of ageing of various PLGA microsphere formulations, with temperature-modulated DSC used to accurately measure the associated glass transition. The Cowie-Ferguson model was applied to determine the parameters describing the enthalpy relaxation kinetics. We show that encapsulated proteins had no significant effect on the glass transition of the microspheres, whereas DNA and PVA were mild antiplasticising agents, particularly with high Mw PLGA. Physical ageing occurred through a range of enthalpy relaxation times (or modes) and was independent of both encapsulated protein and surfactant used during microsphere preparation. Analysis of accelerated ageing at 35 degrees C gave calculated enthalpy relaxation times to thermal equilibrium of 280-400 h. No ageing was observed < or = 10 degrees C and at 25 degrees C estimated relaxation times were at least one order of magnitude greater than at 35 degrees C. Ageing of PLGA microspheres therefore occurs at temperatures >10 degrees C, but relaxation will be far from equilibrium unless storage times and/or temperatures are prolonged or nearing the glass transition, respectively.

Tight junction modulation and biochemical characterisation of the zonula occludens toxin C-and N-termini

The ZOT N-terminal domain was expressed and refolded, yielding a soluble protein with defined secondary structure. Although distantly related to protein I of filamentous phages, no evidence of ATPase activity was found. It is therefore unlikely that the ZOT N-terminal domain is involved in cholera toxin phage packaging in Vibrio cholerae. The ZOT C-terminal domain caused delocalisation of occludin and ZO-1 from Caco-2 cell-cell contacts, irrespective of disulfide bridge formation in its putative binding domain. However, the C-terminal domain did not cause actin reorganisation and this may explain the absence of a concomitant reduction in the transepithelial electrical resistance across cell monolayers.

The Influence of Surfactant on PLGA Microsphere Glass Transition and Water Sorption: Remodeling the Surface Morphology to Attenuate the Burst Release

PURPOSE

The stability of protein unloaded and loaded poly(lactic-co-glycolic acid) (PLGA) microspheres fabricated with surfactant was challenged through exposure to environmental conditions of different relative humidity.

METHODS

Polyvinyl alcohol (PVA) or Triton X-100 was added to the primary emulsion of the double-emulsion solvent evaporation technique. After storage at ambient humidity and 75% relative humidity, the mechanical stability of the polymer was tested to reveal PLGA chain mobility using differential scanning calorimetry. Subsequent surface modifications were examined by atomic force microscopy (AFM), and protein release profiles were collected.

RESULTS

Residual amounts of PVA and particularly Triton X-100 raised the hydrophilicity of the microspheres. When exposed to ambient humidity or 75% relative humidity, PVA and Triton X-100 had, respectively, an antiplasticizing and a plasticizing effect upon PLGA, and both led to physical aging. The high-resolution AFM imaging of microspheres containing model protein and Triton X-100 showed that the depth of the surface pores was reduced when exposed to 75% relative humidity, and the initial burst release subsequently decreased.

CONCLUSION

These studies suggested that the mechanical stability of PLGA was influenced by the addition of surfactants, which, depending on the formulation, led to surface pore remodeling under high humidity, reducing the initial burst release while maintaining the spherical integrity of the microsphere.

The eighth FIII domain of human fibronectin promotes integrin alpha5beta1 binding via stabilization of the ninth FIII domain

Binding of the extracellular matrix molecule fibronectin to the integrin receptor alpha(5)beta(1) elicits downstream signaling pathways that modulate cell function. Fibronectin-alpha(5)beta(1) interaction occurs via the conserved RGD sequence in the tenth FIII (FIII10) domain of fibronectin. A synergistic site containing the sequence PHSRN in the adjacent FIII9 domain has also been identified. Here we investigate the function of the eighth FIII domain in integrin-mediated cell adhesion using a wide range of methods, including biochemical, biological, and biophysical assays of integrin binding, cell adhesion, and protein denaturation. Mutation of the FIII9 synergistic site (PHSRN to PHAAA) in FIII9-10 reduced the binding activity for integrin alpha(5)beta(1) to levels observed for FIII10 alone, but the corresponding mutant in FIII8-9-10 showed no loss of binding activity. Cell adhesion assays also demonstrated enhanced functional activity of constructs containing FIII8. Equilibrium chemical denaturation studies indicated that FIII8 confers conformational stability upon FIII9, but only if the exposed loops, PHSRN and VKNEED on FIII9 and FIII8, respectively, are intact. These results demonstrate that the loss of integrin binding activity, observed upon alteration of the PHSRN synergistic site of FIII9-10, results partly from a loss of conformational stability of FIII9. Our data suggest a mechanism for integrin alpha(5)beta(1)-fibronectin interaction, which in addition to the primary RGD binding event, involves a conformation-sensitive scanning by the integrin for accessible sites on the ligand, whereupon full activation of downstream signaling occurs.

Investigations of structural requirements for endothelin antagonism

Following the isolation of the vasoactive peptide, endothelin (ET), considerable effort has been expended in the development of ET antagonists, some of which have recently been proved to be promising therapeutic agents. Their clinical potential, however, is often limited because of a peptidic nature or a non-selective ETA/ETB receptor antagonism. While many non-peptide ET antagonists are optimised ad hoc from a lead compound found during a compound screening program, directing the development of a molecule towards a selectivity for the ETA or ETB receptor rests upon the elucidation of the respective receptor-binding conformation of ET-1 and ET-3, or a template structure derived from a peptide antagonist whose structure/activity relationship is well characterised. This review focuses on peptide ET antagonists whose structure/activity relationships are well characterised and so provides some insight to the conformational criteria required of putative ETA or ETB receptor selective antagonists. Although the conformation of ET has been previously reported in depth on many occasions a brief summary is provided here in order to relate the structure/activity relationships of the ET antagonists to the structure of ET. The list of ET antagonists discussed here is not comprehensive, since the emphasis for the review has been to focus on studies where structural data were obtained which shed light on the receptor binding conformation(s) of endothelin.