Kaye, Richard Simon; (2008) Development of Microparticulate Formulations for the Delivery of Therapeutic Antibodies to the Respiratory Tract. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Background: Antibodies are immune proteins that have been developed into therapeutic agents due to their highly specific targeting capabilities. The respiratory delivery of antibodies targeted against inhaled pathogens is desirable, since this would reduce the quantity and inconvenience of dosing that would be required by injection, given that antibodies are not orally bioavailable. Microparticulate formulations have been developed to encapsulate antibodies in order to achieve the stability, modified-release (MR) and the aerodynamic properties required for pulmonary and nasal delivery. Method: Antibody (IgG)-loaded microparticles were manufactured by the spray-drying of a W/O/W double-emulsion, which contained the bio-compatible, poly(lactide-co-glycolide) (PLGA) as the MR polymer, and the lung delivery-approved excipients dipalmitoylphosphatidylcholine (DPPC) and lactose, for emulsion stability and thermal protection, respectively, having found that these excipients gave an improved encapsulation efficiency (EE) and reduced initial burst-release compared to poly(vinyl alcohol). This IgG formulation was optimised by factorial experimental design, primarily in terms of yield, encapsulation efficiency and initial burst-release. The optimised microparticulate IgG formulation was characterised in terms of particle diameter and morphology by laser diffraction, photon correlation spectroscopy, and both scanning and transmission electron microscopy. The antibody release profile was measured in both pH 7.4 and pH 2.5 release media, comparing various types of PLGA polymers. The released antibody stability was investigated by gel electrophoresis, enzyme-linked immunosorbent assay and field-flow fractionation. The 3-(4,5-dimethyl- thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay was performed with an in vitro epithelial cell line to assess any potential toxicity of the formulation. The powder dispersibility, aerodynamic diameter (MMAD) and fine particle fraction (FPF) of the IgG formulation, with or without 1% m/m additions of leucine and magnesium stearate, were measured by laser diffraction with a 'RODOS' dry-powder feeder, and using an 'Andersen' cascade impactor (ACI), using an Aerolizer ® dry-powder inhaler. An intraperitoneal in vivo model was used to assess the efficacy of formulated therapeutic F1+V antibodies for the potential treatment of Yersinia pestis (plague). Separately, a spray-dried, water-soluble IgG formulation was developed for nasal delivery, using sugars, albumin and sodium chloride as excipients. This formulation, and variations of it containing leucine, Aerosil® and magnesium stearate, were evaluated in terms of nasal deposition by actuating from Uni-Dose DP™ devices into a nasal cast model. Results: The 'dry' particle median diameter (D50%) of the pulmonary formulation, as measured in cyclohexane, was ~4 μm, and the particles were spherical. However, when measured in water, the lactose component dissolved, producing nanoparticles (~400 nm), which were anticipated to be small enough to avoid phagocytosis within alveoli. The IgG encapsulation efficiency (using a theoretical loading of 3.5% m/m) was close to 100%, with ~30% immediate burst-release. After 35 days ~90% cumulative IgG was achieved using pH 2.5 release media. The IgG released after 2 h was found to be stable in terms of molecular weight and biological activity. The formulation did not affect the viability of in vitro epithelial cells, relative to positive and negative controls. The MMAD calculated from the ACI deposition data was ~3-4 μm. The addition of leucine and magnesium stearate to the formulation was found to increase powder dispersibility. Use of these excipients achieved FPFs of up to ~60%. The therapeutic F1+V antibodies were successfully incorporated into the formulation, although, in preliminary in vivo studies, the formulated antibody was found not to confer protection against infection. The best of the nasal formulations achieved ~45% dose deposition beyond the nasal vestibule of the cast model.

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