Development of inhaled liposomal antimicrobial formulations for treatment of chronic lung infection

Abstract

The lungs of people with cystic fibrosis are susceptible to bacterial infection which is difficult to eliminate; this results in repeated and prolonged antimicrobial treatment that is frequently associated with systemic side effects. Inhaled antimicrobial liposomal formulations could offer several benefits over systemic administration, including maximising drug concentrations in the airways, reducing systemic side effects and providing sustained drug release. In this thesis, liposomal formulations loaded with a number of different antimicrobials were prepared using spray drying as a platform for dry powder inhalers. Initially, a spray-dried azithromycin liposomal formulation was reproducibly prepared using different methods of liposomal preparation. The effect of increasing apramycin concentration on formulation characteristics and the stability profile and in vitro antimicrobial activity of an optimised apramycin formulation was also determined. In addition, a salt form of clofazimine was prepared to enhance solubility and improve the encapsulation efficiency of the clofazimine free base, followed by co-loading clofazimine mesylate and azithromycin into a single spray-dried liposomal formulation. Results showed that the reconstituted spray-dried liposomes containing azithromycin and apramycin were within the desired range: size < 140nm, particle size distribution (PdI) ≤ 0.3 with a zeta potential of > +60mV and encapsulation efficiency (EE%) of > 60%. The inclusion of 17% (w/v) trehalose and 0.5% (w/v) L-Leucine produced spray-dried powders with a glass transition temperature (Tg) of > 50°C, water content < 5%, and powder particle size ≤ 5μm. The organic solvent free method produced azithromycin liposomes with comparable properties to the thin film hydration method. Replacing clofazimine with clofazimine mesylate in the spray-dried liposomal formulation increased EE% and reduced powder particle size. Further enhancement in EE% of clofazimine mesylate was obtained upon co-loading clofazimine mesylate with azithromycin. A spray-dried apramycin formulation with high drug loading was efficiently prepared with a high EE% and desirable powder properties. The apramycin formulation remained stable for 24 weeks when stored at 20°C and 40°C in an enclosed container. Cationic liposomal loaded apramycin demonstrated lower minimum inhibitory concentrations than free apramycin against Pseudomonas aeruginosa and Mycobacterium abscessus clinical respiratory isolates grown planktonically and also showed a bactericidal effect at high concentrations in time-kill assays.This study has demonstrated that a spray-dried apramycin liposomal formulation may have the potential to be a promising new therapeutic option for treatment of cystic fibrosis lung infection.

Thesis embargoed until 31st July 2026

Date of Award	Jul 2023
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Michael Tunney (Supervisor) & Vicky Kett (Supervisor)