Structure-property correlations in a combinatorial library of degradable biomaterials

A combinatorial library of degradable polyarylates was prepared. These polymers are A-B-type copolymers consisting of an alternating sequence of a diphenol and a diacid. The library was prepared by copolymerizing, in all possible combinations, 14 different tyrosine-derived diphenols and eight different aliphatic diacids, resulting in 8 x 14 = 112 distinct polymers. This approach (a) increases the number of available polymeric candidate materials for medical applications, and (b) facilitates the identification of correlations between polymer structure and glass transition temperature, air-water contact angle, mechanical properties, and fibroblast proliferation. The pendent chain and backbone structures were systematically varied by (a) simple homologative variations in the number of methylene groups, (b) substitution of oxygen for methylene groups, and (c) introduction of branched and aromatic structures. The polymers contained within the library exhibited incremental variations in Tg (from 2 degrees C to 91 degrees C) and air-water contact angle (from 64 degrees to 101 degrees ). Fibroblast proliferation (in vitro, serum-containing media) ranged from approximating that measured on tissue culture polystyrene to complete absence of proliferation. Generally, decreased proliferation correlated linearly with increased surface hydrophobicity, except in those polymers derived from oxygen-containing diacids in their backbone which were uniformly good growth substrates even if their surfaces were very hydrophobic. In a selected subgroup of polymers, tensile strength of thin solvent cast films ranged from about 6 to 45 MPa, while Young's modulus (stiffness) ranged from about 0.3 to 1.7 GPa. Combinatorial biomaterial libraries such as these tyrosine-derived polyarylates permit the systematic study of material-dependent biological responses and provide the medical device designer with the option to choose a suitable material from a library of related polymers that encompasses a broad range of properties.

Modulation of wound healing during and after glaucoma surgery

Following all types of glaucoma filtration surgery (GFS), scarring still poses the major threat to long-term success. The healing and scarring determine the percentage of patients achieving low final intraocular pressures (IOPs) that are associated with virtually no glaucoma progression. The use of antifibrotic agents to inhibit scarring of trabeculectomy blebs is now a well-established clinical practice. Unfortunately, severe complications such as leakage, infection, hypotony, and endophthalmitis with complete loss of vision may occur. In addition, surgery still fails in some individuals despite maximal doses of current antifibrotics. Better therapeutic agents are needed. Many promising new agents are being evaluated clinically and in vitro. In this chapter, we will discuss our current understanding of the wound healing process after glaucoma surgery and promising new treatment modalities.

New strategies for polymer development in pharmaceutical science--a short review

We are developing synthetic polymers for pharmaceutical and medical applications. These applications can be broadly grouped on how the polymer will be utilized e.g. material, excipient or molecule. Our focus is to develop polymers with more defined structures that are based on biological, physicochemical and/or materials criteria. Strategies are being developed to more efficiently optimize structure-property correlations during preclinical development. We describe two examples of our research on pharmaceutical polymer development: narrow molecular weight distribution (MWD) homopolymeric precursors which can be functionalized to give families of narrow MWD homo- and co-polymers, and hydrolytically degradable polymers.

Combinatorial chemistry and biomedical polymer development

Polymers are ubiquitous components of products manufactured for medical and pharmaceutical applications. Widely used commodity polymers were the first polymers to be utilised in biomedical applications. These polymers were not developed with biocompatibility established at the onset and many speciality polymers have been developed in recent years to begin to meet the multifaceted demands for medical development, the optimisation of structure-property correlations and ultimately, clinical use. In the broader area of materials research, combinatorial or high throughput strategies used for drug development are recognised to have potential for discovery and process development. Much of the application of combinatorial chemistry in drugs research has been dependent on the use of polymeric reagents, substrates and supports. The chemistry of the reactions on polymers in solid and liquid phases have also played a major role in combinatorial drugs research. There is considerable interest in combinatorial materials research and this review outlines how this research may be applied for biomedical polymer development.

Storage stability of bevacizumab in polycarbonate and polypropylene syringes

PURPOSE

To compare and examine the storage stability of compounded bevacizumab in polycarbonate (PC) and polypropylene (PP) syringes over a 6-month period. PC syringes have been used in a recent clinical study and bevacizumab stability has not been reported for this type of syringe.

METHODS

Repackaged bevacizumab was obtained from Moorfields Pharmaceuticals in PC and PP syringes. Bevacizumab from the stored syringes was analysed at monthly time points for a 6-month period and compared with bevacizumab from a freshly opened vial at each time point. SDS-PAGE electrophoresis and size-exclusion chromatography (SEC) was used to observe aggregation and degradation. Dynamic light scattering (DLS) provided information about the hydrodynamic size and particle size distribution of bevacizumab in solution. VEGF binding and the active concentration of bevacizumab was determined by surface plasmon resonance (SPR) using Biacore.

RESULTS

SDS-PAGE and SEC analysis did not show any changes in the presence of higher molecular weight species (HMWS) or degradation products in PC and PP syringes from T0 to T6 compared with bevacizumab sampled from a freshly opened vial. The hydrodynamic diameter of bevacizumab in the PC syringe after 6 months of storage was not significantly different to bevacizumab taken from a freshly opened vial. Using SPR, the VEGF binding activity of bevacizumab in the PC syringe was comparable to bevacizumab taken from a freshly opened vial.

CONCLUSION

No significant difference over a 6-month period was observed in the quality of bevacizumab repackaged into prefilled polycarbonate and polypropylene syringes when compared with bevacizumab that is supplied from the vial.

N-(2-hydroxypropyl)methacrylamide copolymer-6-(3-aminopropyl)-ellipticine conjugates. Synthesis, in vitro, and preliminary in vivo evaluation

Ellipticine derivatives have potential as anticancer drugs. Their clinical use has been limited, however, by poor solubility and host toxicity. As N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-anticancer conjugates are showing promise in early clinical trials, a series of novel HPMA copolymer conjugates have been prepared containing the 6-(3-aminopropyl)-ellipticine derivative (APE, NSC176328). Drug was linked to the polymer via GFLG or GG peptide side chains. To optimize biological behavior, HPMA copolymer-GFLG-APE conjugates with different drug loading (total APE: 2.3-7% w/w; free APE: <0.1% w/w) were synthesized. Conjugation of APE to HPMA copolymers considerably increased its aqueous solubility (>10-fold). HPMA copolymer-GG-APE did not liberate drug in the presence of isolated lysosomal enzymes (tritosomes), but HPMA copolymer-GFLG-APE released APE to a maximum of 60% after 5 h. The rate of drug release was influenced by drug loading; lower loading led to greater release. Whereas free APE (35 microg/mL) caused significant hemolysis (50% after 1 h), HPMA copolymer-APE conjugates were not hemolytic up to 300 microg/mL (APE-equiv). As would be expected from its cellular pharmacokinetics, HPMA copolymer-GFLG-APE was >75 times less cytotoxic than free drug (IC(50) approximately 0.4 microg/mL) against B16F10 melanoma in vitro. However, in vivo when tested in mice bearing s.c. B16F10 melanoma, HPMA copolymer-GFLG-APE (1-10 mg/kg single dose, APE-equiv) given i.p. was somewhat more active (highest T/C value of 143%) than free APE (1 mg/kg) (T/C =127%). HPMA copolymer-APE conjugates warrant further evaluation as potential anticancer agents.

The control of conjunctival fibrosis as a paradigm for the prevention of ocular fibrosis-related blindness. "Fibrosis has many friends"

The processes involved in ocular fibrosis after disease or ocular tissue injury, including surgery play an important part in the development or failure of treatment of most blinding diseases. Ocular fibrosis is one of the biggest areas of unmet need in ophthalmology. Effective anti-scarring therapies could potentially revolutionise the management of many diseases like glaucoma worldwide. The response of a quiescent or activated conjunctiva to glaucoma surgery and aqueous flow with different stimulatory components and the response to different interventions and future therapeutics is a paradigm for scarring prevention in other parts of the eye and orbit. Evolution in our understanding of molecular and cellular mechanisms in ocular fibrosis is leading to the introduction of new and re-purposed therapeutic agents, targeting a wide range of key processes. This review provides current and futures perspectives on different approaches to conjunctival fibrosis following glaucoma surgery and highlights the challenges faced in implementing these therapies with maximal effect and minimal side effects.

Noncovalent complexation of amphotericin-B with Poly(α-glutamic acid)

A noncovalent complex of amphotericin B (AmB) and poly(α-glutamic acid) (PGA) was prepared to develop a safe and stable formulation for the treatment of leishmaniasis. The loading of AmB in the complex was in the range of ∼20-50%. AmB was in a highly aggregated state with an aggregation ratio often above 2.0. This complex (AmB-PGA) was shown to be stable and to have reduced toxicity to human red blood cells and KB cells compared to the parent compound; cell viability was not affected at an AmB concentration as high as 50 and 200 μg/mL respectively. This AmB-PGA complex retained AmB activity against intracellular Leishmania major amastigotes in the differentiated THP-1 cells with an EC50 of 0.07 ± 0.03-0.08 ± 0.01 μg/mL, which is similar to Fungizone (EC50 of 0.06 ± 0.01 μg/mL). The in vitro antileishmanial activity of the complex against Leishmania donovani was retained after storage at 37 °C for 7 days in the form of a solution (EC50 of 0.27 ± 0.03 to 0.35 ± 0.04 μg/mL) and for 30 days as a solid (EC50 of 0.41 ± 0.07 to 0.63 ± 0.25 μg/mL). These encouraging results indicate that the AmB-PGA complex has the potential for further development.

Competitive Reactions During Amine Addition to cis-Aconityl Anhydride

Amine addition to cis-aconityl anhydride has been used to prepare monomers needed to make water-soluble polymers that are being developed for biomedical applications. Unfortunately competitive decarboxylation, double bond isomerization, and hydrolysis reactions of cis-aconityl anhydride have been observed during monomer synthesis. Since cis-aconityl anhydride has also been used for bioconjugation applications, these deleterious side reactions should be accounted for. Reactions and product profiles of cis-aconityl anhydride with amines and amino acids in aqueous and organic media are described. The side reactions could be avoided with weakly nucleophilic aromatic amines and by the interfacial reaction of glycine with cis-aconityl anhydride.

The study of water uptake in degradable polymers by thermally stimulated depolarization currents

Poly(DTH succinate) is a new, degradable polymer with potential applications as a medical implant material. This polymer can be classified as an alternating copolymer of succinic acid and desaminotyrosyl-tyrosine hexyl ester (DTH), a diphenolic monomer derived from the natural amino acid L-tyrosine. In this study, the effects of water uptake (hydration) on the secondary relaxations of poly(DTH succinate) were investigated using the technique of thermally stimulated depolarization currents (TDSC). Four relaxation peaks were precisely characterized by means of Gaussian activation energy distributions. Drying and rehydration treatments show that only small amounts of water, at most 0.5% (w/w), are necessary to hydrate two of the four polar moieties in poly(DTH succinate): the pendent chain ester carbonyls and the amide carbonyls in the polymer backbone. Water appeared to be more tightly bound to the amide carbonyl group and more loosely bound to the ester carbonyl group in the pendent chain. Even at a high state of hydration (1.2% w/w), TDSC indicated that no water was associated with the phenyl ester bond in the polymer backbone. This finding may explain the unexpectedly high stability of this polymer toward hydrolysis under physiological conditions. Polymer packing was also affected by hydration. In an intermediate hydration state (water content: 0.5% w/w) polymer packing was less dense than in the wet state (water content: 1.2% w/w). This study represents the first application of the TDSC technique to the study of hydration in a degradable biomedical polymer. The results obtained indicate that the TDSC technique may be useful to assist in the understanding of the mechanisms of hydration and subsequent hydrolytic degradation in degradable biomaterials.

Affinity partitioning of plasmid DNA with a zinc finger protein

The affinity isolation of pre-purified plasmid DNA (pDNA) from model buffer solutions using native and poly(ethylene glycol) (PEG) derivatized zinc finger-GST (Glutathione-S-Transferase) fusion protein was examined in PEG-dextran (DEX) aqueous two-phase systems (ATPSs). In the absence of pDNA, partitioning of unbound PEGylated fusion protein into the PEG-rich phase was confirmed with 97.5% of the PEGylated fusion protein being detected in the PEG phase of a PEG 600-DEX 40 ATPS. This represents a 1322-fold increase in the protein partition coefficient in comparison to the non-PEGylated protein (Kc = 0.013). In the presence of pDNA containing a specific oligonucleotide recognition sequence, the zinc finger moiety of the PEGylated fusion protein bound to the plasmid and steered the complex to the PEG-rich phase. An increase in the proportion of pDNA that partitioned to the PEG-rich phase was observed as the concentration of PEGylated fusion protein was increased. Partitioning of the bound complex occurred to such an extent that no DNA was detected by the picogreen assay in the dextran phase. It was also possible to partition pDNA using a non-PEGylated (native) zinc finger-GST fusion protein in a PEG 1000-DEX 500 ATPS. In this case the native ligand accumulated mainly in the PEG phase. These results indicate good prospects for the design of new plasmid DNA purification methods using fusion proteins as affinity ligands.

Antileishmanial activity, uptake, and biodistribution of an amphotericin B and poly(α-Glutamic Acid) complex

A noncovalent, water-soluble complex of amphotericin B (AMB) and poly(α-glutamic acid) (PGA), with AMB loadings ranging from 25 to 55% (wt/wt) using PGA with a molecular weight range of 50,000 to 70,000, was prepared as a potential new treatment for visceral leishmaniasis (VL). The AMB-PGA complex was shown to be as active as Fungizone (AMB deoxycholate) against intracellular Leishmania donovani amastigotes in differentiated THP-1 cells. The in vitro uptake of the AMB-PGA complex by differentiated THP-1 cells was similar to that of Fungizone and higher than that of AmBisome (liposomal AMB). The AMB-PGA complex also displayed a dose-response profile similar to that of AmBisome in vivo in BALB/c mice against L. donovani, with 50% effective doses (ED50s) of 0.24 ± 0.03 mg/kg of body weight for the AMB-PGA complex and 0.24 ± 0.06 mg/kg for AmBisome. A biodistribution study with mice indicated that the AMB-PGA complex cleared more rapidly from plasma than AmBisome, with a comparable low level of distribution to the kidneys.

Fc-fusion mimetics

The Fc-fusion mimetic RpR 2̲ was prepared by disulfide bridging conjugation using PEG in the place of the Fc.

Characterization of combinatorially designed polyarylates by time-of-flight secondary ion mass spectrometry

A series of 16 polyarylates, with well-controlled and systematically varying chemistry, has been characterized by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The polymers are structurally identical except for the incremental additions of C2H4 units to the backbone and sidechain. From the spectra, peaks characteristic of all polyarylates are identified. Furthermore, evaluation of the spectra and identification of unique signals allow classification of the polyarylates according to sidechain and backbone chemistry.

Poly-glutamic dendrimer-based conjugates for cancer vaccination - a computational design for targeted delivery of antigens

Computational techniques are useful to predict interaction models and molecular properties for the design of drug delivery systems, such as dendrimers. This work evaluated the impact of surface modifications of mannosamine-conjugated multifunctional poly(glutamic acid) (PG)-dendrimers as nanocarriers of the tumour associated antigens (TAA) MART-1, gp100:44 and gp100:209. Molecular dynamics simulations and docking studies were performed. Nitrobenzoxadiazole (NBD)-PG-G4-dendrimer displayed 64 carboxylic groups, however, the Frontier Molecular Orbital Theory study evidenced that only 32 of those were available to form covalent bonds. When the number of mannosamines conjugated to dendrimer was increased from 16 to 32, the dendrimer interacted with the receptor with higher affinity. However, 16 mannosamines-NBD-PG-G4-dendrimer was chosen to conjugate TAA for added functionality as no carboxylic end groups were available for further conjugation in the 32 mannosamines-dendrimer. Docking results showed that the majority of TAA-conjugated NBD-PG-G4-dendrimer demonstrated a favourable interaction with mannosamine binding site on mannose receptor, thus constituting a promising tool for TAA targeted delivery. Our in silico approach effectively narrows down the selection of the best candidates for the synthesis of functionalised PG-dendrimers with desired functionalities. These results will significantly reduce the time and efforts required to experimentally synthesise modified dendrimers for optimal antigen delivery.