Considerations for Developing Inhaled and Nasally Delivered Biologics

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Inhalable drug formulations show much promise for improving biopharmaceutical delivery. But as Ashleigh Wake (director of business development at Intertek) explained to Ask the Expert attendees in September 2021, such formulations necessitate development of complex quality control (QC) analytical methods. Wake highlighted special considerations for characterizing and controlling the stability and potency of inhaled and nasally delivered biologics.

Wake’s Presentation
Wake emphasized that nasal and inhaled biological products necessitate QC strategies to control both a protein product and its delivery system. Suitable devices and formulations must be selected, and core analytical methods must be established to characterize a drug product’s chemical, physical (e.g., particle size, leak rate, and moisture content), microbiological (sterility), and performance-related (particle or droplet size, spray pattern, and plume geometry) features. Although such methods can be difficult to set up, their requirements are well understood, and regulatory guidance (e.g., USP <601> and <1601>) provides clear instruction about assessing product release and stability.

When establishing QC methods for a biologic drug substance, analysts must consider the product’s aggregation potential, degradation mechanisms, and relative potency. Wake noted that regulatory agencies are coming to expect orthogonal assessment of such quality attributes considering the inherent difficulty of assaying biologics.

Because protein structures are based on weak binding interactions, analysts must ensure that a formulation and manufacturing process will maintain a therapeutic protein’s structure. Assessing a nasal or inhaled biologic’s degradation potential involves testing for charge variants, oxidation products, and other such species. Methods for such studies include capillary electrophoresis and anion-exchange or hydrophilic-interaction chromatography. Although such methods can be difficult to establish, they are well understood.

By contrast, testing for aggregation propensity is demanding and complex. Regulators often expect application of both a stationary and a dynamic assay method — e.g., size-exclusion chromatography (SEC) alongside a dynamic light scattering technique. Part of the rationale for orthogonal assessment relates to the disadvantages of relevant assays. For instance, SEC is a standard laboratory method that produces quantitative results with acceptable accuracy and precision, yet its materials can interact with target proteins in ways that form aggregates and diminish recovery, skewing results. In such cases, analytical ultracentrifugation and related separation methods are applied to evaluate an assay’s propensity for inducing aggregation and underestimating recovery.

Accurate assessment of downstream recovery is important to quantifying a dose’s protein content. Typically, concentration is determined using a nonspecific, total-protein assay (e.g., absorbance at 280 nm). However, if a suitable quantitative method is in place (e.g., enzyme-linked immunosorbent assay), then sponsors must consider how protein adherence to assay components influences testing accuracy. Using specialized, low-binding materials is advisable, as is precoating assay-component surfaces with surfactants or blocking proteins. Surfactants or glycerols can be added to extraction solvents, and changes to an extraction buffer such as an increase in organic content or a decrease in pH can improve assay accuracy. Proteins also can be lysed enzymatically from surfaces.

Wake noted that measuring the protein content in a delivered dose is insufficient; analysts must establish that a protein product’s potency has not changed during delivery. Related assays are complex to establish, particularly concerning acceptance criteria. Wake encouraged attendees, however, to remember that formulation for nasal delivery or nebulization preserves protein-product potency.

Questions and Answers
How is dose-delivery reproducibility ascertained?
Analysts collect what material is dispensed during device actuation, then quantify its protein content. Minimally, 10 replicates are performed and compared for variability. Because inhaled and nasal drug products are delivered in high volumes, detection limits can be difficult to manage for some methods, necessitating movement away from conventional UV-based to more sophisticated approaches (e.g., chromatography methods).

What advances have come in assaying protein-product recovery?
Recovery can be aided by adapting a formulation’s diluents, recovery solutions, solvents, salts, and inorganic ions. Determining an ideal product-recovery method can take time and effort, but recoveries >90% often can be achieved.

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