Helen M. Burt

Development of amphiphilic diblock copolymers as micellar carriers of taxol

Diblock copolymers of poly(DL-lactide)-block-methoxy polyethylene glycol were synthesized from monomers of DL-lactide (DLLA) and methoxy polyethylene glycol (MePEG) by a ring opening bulk polymerization in the presence of stannous octoate. The copolymer molecular weight and composition were controlled by changing the monomer weight ratio. The copolymers dissolved in water to form polymeric micelles with a hydrophobic poly(DL-lactide) (PDLLA) core and a water soluble MePEG shell. The critical micelle concentrations (CMC), measured by fluorescence techniques, depended on copolymer molecular weight and ranged from millimolar to micromolar. The PDLLA core of the micelle was in a highly viscous state since the 1H-NMR peaks of PDLLA in the copolymers presented in CDC13 and disappeared in D2O due to the restriction of PDLLA chain mobility. Up to 25% taxol could be loaded into matrices of PDLLA-MePEG (MePEG molecular weight: 2000; DL-lactide/MePEG compositions: 40:60 or 50:50) using the solution casting method. Dissolution of the taxol/copolymer matrices in water, 0.9% NaC1, or 5% dextrose solutions resulted in complete solubilization of taxol within the copolymer micelles. Evidence of strong association or binding of taxol to the PDLLA block of the copolymer even below the polymer CMC is presented.

Polyether-polyester diblock copolymers for the preparation of paclitaxel loaded polymeric micelle formulations.

A number of hypersensitivity reactions have been attributed to the presence of Cremophor((R)) EL in the current formulation for paclitaxel. This has led to the development of formulations for paclitaxel employing polyether-polyester diblock copolymers as micelle forming carriers. Diblock copolymers of methoxypolyethylene glycol-block-poly(D,L-lactide) (MePEG:PDLLA) were synthesized from monomers of D,L-lactide and MePEG by a ring opening bulk polymerization in the presence of stannous octoate. Up to 25% paclitaxel could be loaded into matrices of MePEG:PDLLA (60:40, MePEG molecular weight of 2000) using the solution casting method. Dissolution of paclitaxel/copolymer matrices in aqueous media resulted in complete solubilization of paclitaxel within the hydrophobic PDLLA core of the micelles. This review article describes the synthetic reaction conditions influencing the degree of conversion of monomer to copolymer, thermal properties, critical micelle concentrations of copolymers, methods of incorporation of paclitaxel into copolymer matrices and subsequent constitution in aqueous media and biological evaluations of micellar paclitaxel.

The use of nanocrystalline cellulose for the binding and controlled release of drugs

The objective of this work was to investigate the use of nanocrystalline cellulose (NCC) as a drug delivery excipient. NCC crystallites, prepared by an acid hydrolysis method, were shown to have nanoscopic dimensions and exhibit a high degree of crystallinity. These crystallites bound significant quantities of the water soluble, ionizable drugs tetratcycline and doxorubicin, which were released rapidly over a 1-day period. Cetyl trimethylammonium bromide (CTAB) was bound to the surface of NCC and increased the zeta potential in a concentration-dependent manner from −55 to 0 mV. NCC crystallites with CTAB-modified surfaces bound significant quantities of the hydrophobic anticancer drugs docetaxel, paclitaxel, and etoposide. These drugs were released in a controlled manner over a 2-day period. The NCC-CTAB complexes were found to bind to KU-7 cells, and evidence of cellular uptake was observed.

Solubility and stability of taxol: effects of buffers and cyclodextrins

Abstract The degradation kinetics of taxol in aqueous solutions were investigated at 37°C over a pH range of 1–9. The hydrolysis rates followed pseudo first-order kinetics with respect to residual taxol concentration. The pH-rate profile at 37°C showed that a maximum stability of taxol occurred in the pH 3–5 region. The effect of γ-cyclodextrin (γCD), hydroxypropyl-γ-cyclodextrin (HPγCD) and hydroxypropyl-β-cyclodextrin (HPβCD) on the solubility and stability of taxol was also investigated. Taxol was more stable in cyclodextrin solution than in buffer solution of comparable pH. The solubility of taxol in water increased in the presence of cyclodextrins with HPβCD giving the greatest increase in taxol solubility. Taxol (as received) was anhydrous and on suspension in water, it dissolved to form a supersaturated solution which recrystallized as a hydrate of lower solubility. Taxol formed predominantly second order complexes with the cyclodextrins. Complexes of taxol with HPβCD were more stable than those of HPγCD or γCD. Further increase in the solubility of taxol was observed when ethanol was added as a co-solvent.

Determination of surfactant critical micelle concentration by a novel fluorescence depolarization technique

A novel method using fluorescence depolarization to determine the critical micelle concentrations (CMC) of surfactants was developed. Fluorescence anisotropies of Triton X-100, sodium dodecyl sulfate, and sodium cholate were measured using 1,6-diphenyl-1,3, 5-hexatriene as a fluorescence probe. Fluorescence anisotropy decreased with increasing surfactant concentrations below the CMC and leveled off above the CMC. The depolarization method does not depend on the concentration of DPH and is largely immune to light-scattering problems encountered in turbid aqueous systems.

An investigation of the antitumour activity and biodistribution of polymeric micellar paclitaxel.

Abstract Purpose: To evaluate in vitro cytotoxicity, in vivo antitumour activity and biodistribution of a novel polymeric (poly(DL-lactide)-block-methoxy polyethylene glycol) micellar paclitaxel. Methods: Hs578T breast, SKMES non-small-cell lung, and HT-29 colon human tumour cells were exposed, either for 1 h or continuously, to conventionally formulated paclitaxel (Cremophor paclitaxel) or polymeric micellar paclitaxel. After a period of incubation, cytotoxicity was measured using a radiometric system. In the in vivo antitumour study, B6D2F1 mice, bearing P388 leukaemia tumour intraperitoneally (i.p.), were treated with polymeric micellar paclitaxel or Cremophor paclitaxel by i.p. injection. The number of deaths and body weights were recorded. In the biodistribution study, CD-1 mice were given micellar paclitaxel i.p. at a dose of 100 mg/kg. The mice were sacrificed after a given time and the organs were harvested. Paclitaxel in the organs was extracted by acetonitrile and analysed using HPLC. Results: The polymeric micellar paclitaxel showed similar in vitro cytotoxicity to Cremophor paclitaxel against the tumour cell lines. The polymeric micellar formulation of paclitaxel produced a fivefold increase in the maximum tolerated dose (MTD) as compared with Cremophor paclitaxel when administered i.p. In addition, micellar paclitaxel was more efficacious in vivo when tested in the murine P388 leukaemia model of malignancy than Cremophor paclitaxel when both were administered i.p. at their MTDs. Micellar paclitaxel-treated animals had an increased survival time and, importantly, long-term survivors (20% of those tested) were obtained only in the polymeric paclitaxel formulation group. Biodistribution studies indicated that a significant amount of paclitaxel could be detected in blood, liver, kidney, spleen, lung and heart of mice after i.p. dosing of the polymeric micellar paclitaxel formulation. Conclusion: These preliminary results indicate that polymeric micellar paclitaxel could be a clinically useful chemotherapeutic formulation.

Polymeric drug delivery of platinum-based anticancer agents.

Platinum-based anticancer agents such as cisplatin and carboplatin are in widespread clinical use but associated with many side effects. Improving the delivery of cytotoxic platinum compounds may lead to reduced side effects and achieve greater efficacy at lower doses. Polymer-based therapeutics have been investigated as potential drug delivery vehicles for platinum-based drugs. Against a background of the chemistry and pharmacology of cytotoxic platinum compounds, this review discusses the formation and properties of platinum-polymer complexes, dendrimers, micelles, and microparticulates.

The antioxidants curcumin and quercetin inhibit inflammatory processes associated with arthritis

Abstract.ObjectiveCurcumin and quercetin are antioxidant molecules with anti-proliferative, anti-inflammatory and immunosuppressive activities. The objective of this study was to investigate the inhibitory activity of these agents using four assays of inflammatory aspects of arthritis.MethodsCrystal-induced neutrophil activation was measured by luminol-dependent chemiluminescence. Synoviocyte proliferation was measured by an MTS assay using HIG-82 rabbit synoviocytes in cell culture. Chondrocyte (cultured primary cells) expression of the matrix metalloproteinases collagenase and stromelysin was measured by Northern Blot analysis. Angiogenesis was measured using the chorioallantoic membrane of the chick embryo.ResultsBoth agents inhibited neutrophil activation, synoviocyte proliferation and angiogenesis. Curcumin strongly inhibited collagenase and stromelysin expression at micromolar concentrations whereas quercetin had no effect in this assay.ConclusionThese studies suggest that curcumin and to a lesser extent quercetin may offer therapeutic potential for the treatment of crystal-induced arthritis or rheumatoid arthritis.

Development of a Polymeric Surgical Paste Formulation for Taxol

AbstractPurpose. To develop and characterize a biodegradable polymeric sustained release surgical paste formulation for taxol. Methods. Taxol was incorporated into poly(ε-caprolactone) (PCL) or blends of PCL with methoxypolyethylene glycol, MW 350 (MePEG). The surgical pastes were characterized using gel permeation chromatography, thermal analysis, scanning electron microscopy, and a tensile strength tester. In vitro release data for taxol from the surgical paste formulations was carried out at 37°C in phosphate buffered saline, pH 7.4, using an HPLC assay for taxol. Antiangiogenic activity of the formulations were assessed using a chick chorioallantoic membrane assay (CAM). Results. The addition of up to 30% MePEG in PCL decreased the melting point of PCL by 5°C and the tensile strength by 152.7 N/cm2 to 26.7 N/cm2 but increased the degree of PCL crystallinity from 42% to 51%. Taxol showed a biphasic in vitro release profile composed of a burst phase lasting 1 or 2 days followed by a period of slow sustained drug release. There was no significant difference in the release profiles of taxol from two different sources of PCL. The addition of MePEG increased the amount of water taken up by the polymer blends but decreased the rate of taxol release. The formulations were shown to have antiangiogenic activity by the CAM assay at levels as low as 0.1% taxol using 3 mg surgical paste pellets. Conclusions. Our surgical paste formulations for taxol give sustained release while having physical properties which can be adjusted using additives.

Taxol encapsulation in poly(ɛ-caprolactone) microspheres

Poly(ɛ-caprolactone) (PCL) microspheres containing taxol were prepared by the solvent evaporation method and tested for angiogenesis inhibition using the chick chorioallantoic membrane (CAM) model. Very high encapsulation efficiencies (95%) for taxol in PCL microspheres were obtained. In vitro release studies showed about 25% of the loaded drug was released in 6 weeks from microspheres containing 5% taxol. Studies with the CAM showed that taxol released from the microspheres induced vascular regression and inhibited angiogenesis.