Development and characterisation of dry powder formulations of biopharmaceuticals for inhalation delivery

Abstract

Since the inception of biologics, there has been a far-reaching movement towards noninvasive administration of biomacromolecules. Indeed, pulmonary delivery has historically benefited the management of respiratory conditions such as asthma and chronic obstructive pulmonary disease. However, the gap between the number of approved biologics and their inhaled counterparts is widening, and no therapeutic antibody administered via the inhalation route exists in the market. One of the advantages of dry powder inhalers is that the drug product can be stored and administered in the solid state at room temperature which insures against instability of labile biologics.

In this work, two established particle engineering techniques – spray drying and spray freeze drying – were used to generate powder formulations of biologics intended for inhalation. Due to the stresses associated with the atomisation and dehydration steps, stabilising excipients are necessary. Here, 2-hydroxypropyl-beta-cyclodextrin (2HPβCD), a cyclic oligosaccharide, was employed because of its favourable safety profile, protein-stabilising ability, and amorphous nature. A factorial study design was conducted to investigate the spray-drying parameters that could produce particles that are within the size range suitable for deep lung deposition. The aerosol performance was evaluated using a Next Generation Impactor and the particle morphology was visualised by scanning electron microscopy.

The optimised spray-drying variables were applied to produce powder formulations of a monoclonal antibody directed against interleukin-4 receptor alpha (IL-4Rα), a proinflammatory cytokine implicated in the pathophysiology of severe asthma. The antibody and its antigen-binding fragment were included at concentrations ranging from 5% to 50% w/w. Although the antibody was reasonably stabilised – as evidenced by the minimal aggregation detected using size-exclusion chromatography – the spray-dried powder formulations were hindered by suboptimal dispersibility, with the emitted fraction not exceeding 63%. Thermogravimetric analysis revealed that the residual water content was high (> 5%) across all the formulations. Efforts were then made to reduce the moisture by spray drying at higher temperatures, albeit the attempt was not fruitful. This prompted an alternative strategy of incorporating hydrophobic amino acids. To this end, cysteine and leucine were tested as candidates given that adequate aerosol characteristics and protein stabilisation had been observed with them in other studies.

A series of dual-excipient formulation platforms were prepared by co-spray drying 2HPβCD with either amino acid at different weight ratios, from which 2HPβCD-leucine at a 1:1 ratio emerged as the formulation platform with the most desirable aerodynamic properties. Hence, subsequent antibody formulations were based upon this excipient combination. The residual moisture content of these leucine-containing formulations was low, between 1% and 3%. This presumably contributed to the enhanced aerosolisation and fine particle fraction. The antigen-binding ability, examined by enzyme-linked immunosorbent assay, and the antiproliferative potency of the processed antibody in TF-1 cells were preserved relative to the untreated antibody controls.

Beyond the anti-IL-4Rα antibody, spray-freeze-dried intranasal vaccines and spray-dried formulations of a SARS-CoV-2 neutralising antibody for COVID-19 were also explored. The powder vaccines highlight the potential to augment mucosal responses in those already intramuscularly immunised, while the latter demonstrates the translatability of the earlier results obtained to another antibody.