Justin Grant

Synthesis and Physicochemical and Dynamic Mechanical Properties of a Water-Soluble Chitosan Derivative as a Biomaterial

The physicochemical and rheological properties of a water-soluble chitosan (WSC) derivative were characterized in order to facilitate its use as a novel material for biomedical applications. The WSC was prepared by conjugating glycidyltrimethylammonium chloride (GTMAC) onto chitosan chains. Varying the molar ratio of GTMAC to chitosan from 3:1 to 6:1 produced WSCs with a degree of substitution (DS) that ranged from 56% to 74%. The WSC with the highest DS was soluble in water up to concentrations of 25 g/dL at room temperature. An increase in the polymer concentration gradually increased both the pH and conductivity of the WSC solutions. The rheological properties of the WSC solutions were found to be dependent on the salt and polymer concentrations as well as the DS value. In the absence of salt, the rheological behavior of the WSC was found to be typical of that for a polyelectrolyte in the dilute solution regime. However, the addition of salt decreased the viscosity of the polymer solution due to the reduction of electrostatic repulsions by the positively charged trimethylated ammonium groups of the WSC. In the concentrated regime, the viscosity of the WSCs was found to follow a power-law expression. The lowest DS WSC had the more favorable viscoelastic properties that were attributed to its high molecular weight, as confirmed by the stress relaxation spectra and intrinsic viscosity measurements. The effect of DS on the degree of interaction between WSC and the lipid egg phosphatidylcholine was investigated by FTIR analysis. Overall, the lower DS WSC had enhanced rheological properties and was capable of engaging in stronger intermolecular physical interactions.

Predicting the Solubility of the Anti-Cancer Agent Docetaxel in Small Molecule Excipients using Computational Methods

PurposeTo develop an in silico model that provides an accurate prediction of the relative solubility of the lipophilic anticancer agent docetaxel in various excipients.Materials and MethodsThe in silico solubility of docetaxel in the excipients was estimated by means of the solubility (δ) and Flory-Huggins interaction (χFH) parameters. The δ values of docetaxel and excipients were calculated using semi-empirical methods and molecular dynamics (MD) simulations. Cerius2 software and COMPASS force-field were employed for the MD simulations. The χFH values for the binary mixtures of docetaxel and excipient were also estimated by MD simulations.ResultsThe values obtained from the MD simulations for the solubility of docetaxel in the various excipients were in good agreement with the experimentally determined values. The simulated values for solubility of docetaxel in tributyrin, tricaproin and vitamin E were within 2 to 6% of the experimental values. MD simulations predicted docetaxel to be insoluble in β-caryophyllene and this result correlated well with experimental studies.ConclusionsThe MD model proved to be a reliable tool for selecting suitable excipients for the solubilization of docetaxel.

Drug release mechanism of paclitaxel from a chitosan-lipid implant system: effect of swelling, degradation and morphology.

Localized and sustained delivery of anti-cancer agents to the tumor site has great potential for the treatment of solid tumors. A chitosan-egg phosphatidylcholine (chitosan-ePC) implant system containing PLA-b-PEG/PLA nanoparticles has been developed for the delivery of paclitaxel to treat ovarian cancer. Production of volumes of ascites fluid in the peritoneal cavity is a physical manifestation of ovarian cancer. In vitro release studies of paclitaxel from the implant were conducted in various fluids including human ascites fluid. A strong correlation (r2=0.977) was found between the release of paclitaxel in ascites fluid and PBS containing lysozyme (pH 7.4) at 37 degrees C. The drug release mechanism for this system was proposed based on swelling, degradation and morphology data. In addition, in vitro release of paclitaxel was found to be a good indicator of the in vivo release profile (correlation between release rates: r2=0.965). Release of paclitaxel was found to be sustained over a four-week period following implantation of the chitosan-ePC system into the peritoneal cavity of healthy Balb/C mice. Also, the concentrations of paclitaxel in both plasma and tissues (e.g. liver, kidney and small intestine) were found to be relatively constant.

Intermolecular interactions and morphology of aqueous polymer/surfactant mixtures containing cationic chitosan and nonionic sorbitan esters.

In this study, the impact of surfactant molecular composition (saturated sorbitan monolaurate or unsaturated sorbitan monooleate) on polymer/surfactant assemblies was examined. Specifically, the associations between the cationic chitosan and the uncharged surfactants were monitored by surface tension, turbidity, and conductivity measurements. Bright field, confocal laser scanning, and transmission electron microscopy revealed that nanometer-sized chitosan/surfactant aggregates comprised of a chitosan-rich shell and a chitosan-poor core agglomerate at high surfactant concentrations to yield micrometer-scaled supramolecular structures with highly ordered internal structure. The size and architecture of these chitosan/surfactant assemblies were dependent on the structure and concentration of the surfactant employed. The association mechanism among chitosan, surfactant, and the chitosan/surfactant aggregates was discussed in terms of the semirigid polyelectrolyte character of chitosan and the hydrophobic character of sorbitan esters. This study provides important insight into the structural and physical parameters of surfactant that govern the formation of multicompartment polymer/surfactant assemblies.

Efficacy assessment of sustained intraperitoneal paclitaxel therapy in a murine model of ovarian cancer using bioluminescent imaging

We evaluated the pre-clinical efficacy of a novel intraperitoneal (i.p.) sustained-release paclitaxel formulation (PTXePC) using bioluminescent imaging (BLI) in the treatment of ovarian cancer. Human ovarian carcinoma cells stably expressing the firefly luciferase gene (SKOV3Luc) were injected i.p. into SCID mice. Tumour growth was evaluated during sustained or intermittent courses of i.p. treatment with paclitaxel (PTX). In vitro bioluminescence strongly correlated with cell survival and cytotoxicity. Bioluminescent imaging detected tumours before their macroscopic appearance and strongly correlated with tumour weight and survival. As compared with intermittent therapy with Taxol®, sustained PTXePC therapy resulted in significant reduction of tumour proliferation, weight and BLI signal intensity, enhanced apoptosis and increased survival times. Our results demonstrate that BLI is a useful tool in the pre-clinical evaluation of therapeutic interventions for ovarian cancer. Moreover, these results provide evidence of enhanced therapeutic efficacy with the sustained PTXePC implant system, which could potentially translate into successful clinical outcomes.

Influence of molecular organization and interactions on drug release for an injectable polymer-lipid blend.

An injectable blend composed of a water soluble chitosan (WSC) derivative, egg phosphatidylcholine (ePC), and fatty acid chlorides (FACl) was explored for localized delivery of anticancer agents. The composition-property relationships of the injectable WSC-FACl-ePC blend were determined by investigating the physico-chemical and performance properties of the blend as a function of the ratio of the components, as well as the acyl chain length of the FACl (C10-C16) employed. Thermal and rheological measurements revealed that the melting transitions and viscosities of the blends increased as a function of FACl acyl chain length. FTIR analysis demonstrated that the stability of the blends was attributed to the specific interactions among the molecules. In addition, confocal laser scanning microscopy revealed that the incorporation of C10-C16 FACl altered the molecular organization of ePC and WSC within the blends, which resulted in distinct physico-chemical properties. Specifically, the formation of micro-domains within the blends increased the stability, as well as delayed the release of paclitaxel from the formulation under physiologically relevant conditions. Overall, the interactions identified among the components, and the relationships established between the composition and properties of the blend can be used as a tool to develop advanced injectable drug delivery systems for pharmaceutical applications.

Thermosensitive Depot-Forming Injectable Phosphatidylcholine Blends Tailored for Localized Drug Delivery

A thermosensitive depot-forming system was developed for sustained and localized delivery of the anticancer drug, paclitaxel. The formulation is injectable as a melt slightly above the body temperature and forms a solid depot upon cooling to 37°C. The thermosensitive system was prepared by blending various combinations of phosphatidylcholines at specific weight ratios solubilized in laurinaldehyde. Of the blends investigated, distearoyl-phosphatidylcholine (DSPC) and egg-phosphatidylcholine (ePC) were found to be most miscible. A liquid-to-gel phase transition temperature (TC ) of 39°C was observed for the 70:30 (w/w) DSPC-ePC blend and a TC of 38.4°C with the addition of paclitaxel. Blends containing higher concentrations of ePC had a greater degree of swelling and weight loss. Furthermore, microscopy revealed an increase in porosity and erosion as the amount of ePC was increased in blends incubated in biologically relevant media. DSPC-ePC blends provided sustained release of paclitaxel over a 30-day period and the rate of drug release increased as the amount of ePC increased. Overall, the relationships established between the composition and properties of the blend may be employed to tailor the thermosensitive injectable formulation for localized chemotherapy of solid tumors.