Innovations in Delivery of Biologics by Inhalation, Part 1

Naveen Kumar Reddy Yaragudi,¹ Sune Klint Andersen², Vivek Gupta³, Pavan Muttil⁴ and David Cipolla⁵

¹ Scientist, Janssen Drug Product Development and Supply,² Associate Director, Drug Product Development and Supply, Beerse, ³Associate Professor, College of Pharmacy, St. John’s University, ⁴Associate Professor, Department of Pharmaceutical Sciences, College of Pharmacy, University of New Mexico, ⁵Vice President, Research, Insmed Incorporated

This article is the first of a four-part series covering innovations in delivery of biologics by inhalation. For this series, the authors have liberally defined biologics (> 1 kDa molecular weight) to include anything that is not a small molecule. That is because inhalation delivery of traditional small molecules has gained increased understanding over time, whether delivered by metered dose inhalers (MDIs) or soft mist inhalers (SMIs) for potent drugs where the dose can be delivered in a few puffs, or in dry powder inhalers (DPIs) or nebulizers if larger doses are required for efficacy (Figure 1). In contrast, large molecule biologics often have a higher order structure, which is influenced by the amino acids in the primary structure. Depending on the number and type of amino acid residues, a biologic molecule can have a secondary, tertiary, or quaternary conformation. Thus, the biologic activity of the molecule may involve amino acid residues that are often distinct from each other on the linear amino acid sequence, and only when the protein folds into its higher order structure do these amino acids interact to form the active site. These higher order structures are often maintained by ionic and hydrophobic interactions, which can easily be perturbed when exposed to pharmaceutically relevant stresses such as shear or thermal excursions and this can cause proteins to aggregate. Therefore, prudent excipient selection is warranted during formulation development to preserve the native conformation.

This first article introduces aerosol delivery and describes aerosol delivery of liquid formulations. The second article will describe the requirements for development of biologic formulations in the solid-state (i.e., dried). The third article will cover various ways to produce solid-state formulations. Finally, the last article will describe the application of these inhaled aerosols as vaccines. 

Introduction

Most people have seen someone use an inhaler to deliver medication to treat their asthma or COPD symptoms. Some of you may also have seen the episode of House (Season 5, Episode 11 [1]) where a patient demonstrated to Hugh Laurie (aka House) how she used her inhaler; instead of inhaling from it, she sprayed it on her neck.

These devices appear simple to use but the dose of drug delivered to the airways can be compromised by poor compliance, poor inhaler-use technique, or misuse [2]. Variability in delivered dose can be a major impediment to the development of therapies that are expensive to manufacture and especially for those with narrow therapeutic windows, including most biologics.

For scientists developing an inhaled biologic therapy, key questions to consider are: which delivery format will be optimal, an MDI, DPI, SMI or nebulizer?; if selecting a propellent-based MDI, can an adequate dose be delivered and will the biologic be compatible with the non-aqueous solvents?; if selecting a DPI, can the biologic be converted into a solid-state formulation (i.e., dried) and maintain its functional attributes?; if selecting an SMI, does the molecule have adequate potency to be delivered in a reasonable number of inhalations and will it be compatible with the preservative?; if selecting a nebulizer, will the biologic retain its activity and integrity in response to the nebulization process?  

The list of inhaled biologics that have received regulatory approval by the FDA is not a long one, namely only nebulized rhDNase for treatment of cystic fibrosis and two DPI formulations of insulin to manage diabetes [3].  However, recently there has been a resurgence of interest in nasal or orally inhaled delivery of biologics, many in response to the COVID pandemic and the desire to develop medications to prevent or treat viral infections. In this series of articles, we review the formulation and manufacturing challenges as well as recent innovations that are spurring the development of inhaled biologic products.   

To orient the reader to the breadth of inhaled biologics that have been or are being considered, they include peptides (e.g., growth hormone, GLP-1 and parathyroid hormone), proteins (e.g., erythropoietin, interferon alpha and interferon beta), monoclonal antibodies, and more recently bacteriophage, gene therapy constructs, antisense oligonucleotides, and virus particles [4]. Since most biologics are typically incompatible with MDI formulations, the article will describe products utilizing both aqueous-based and solid-state formulation modalities with a particular emphasis on spray drying of biologics to produce respirable powders.  

Aerosol Delivery of Liquid Formulations

From a formulation standpoint, a nebulizer or SMI may appear to be a sensible choice for delivery of a biologic, especially for those that are produced by cell culture and thus remain in an aqueous milieu after purification. However, many biologics can undergo hydrolysis reactions or aggregation in solution and the generation of degradants or aggregates has the potential to induce unwanted immunogenicity or compromise efficacy in the host [5,6]. This has been a long-standing concern for injectable or infusion biologic products but should also be avoided in inhaled products. Thus, to ensure adequate long-term stability, an inhaled biologic product may require specialized formulation (e.g., addition of a buffer tailored to maintain the optimum pH and addition of a particular surfactant or other excipient(s) to reduce aggregation) and proper cold chain storage.

If a biologic has adequate stability in solution, there is still the possibility that shear stress may degrade it during nebulization. There are two main categories of nebulizers, jet nebulizers and mesh nebulizers. Jet nebulizers rely upon a compressed air source to create the aerosol. During that process, the liquid formulation is exposed to mechanical shear forces that generate the aerosol; however, only a small fraction of the aerosol exits the mouthpiece with the vast majority redepositing within the nebulizer to be repeatedly exposed to the shear stress [7]. In contrast, for mesh nebulizers, there is generally less potential for degradation as the formulation passes only once through the aerosol-generating mesh. Soft mist inhalers are more akin to mesh nebulizers in that the liquid is exposed to shear only once to create the aerosol [8].

For SMIs and both jet and mesh nebulizers, substantial air-liquid interface is generated during droplet formation, and this can lead to formation of protein aggregates [7]. Typically, the protein’s hydrophobic amino acid residues prefer to be associated with other hydrophobic residues internally within the folded protein. As indicated earlier, the higher order structure can be impacted (transient unfolding) under shearing conditions such as nebulization which generates droplets and enormous interfacial area. Proteins are surface active, and they compete with other excipients for interface. Accumulation of transiently unfolded proteins at interface may lead to formation of soluble protein aggregates and, in the extreme scenario, insoluble protein particulates. Appropriately selected surfactants may be a good choice of excipient to preserve proteins from interfacial stress.

The only approved biologic given by nebulization, Pulmozyme rhDNase [9], is a refrigerated product that is stored in sterile, single-use ampoules that allows the patient to dispense the 2.5 mL directly into the nebulizer (Figure 2). During development, and prior to approval in 1993, rhDNase was shown to retain its secondary and tertiary structure after nebulization, with complete retention of enzymatic activity and no formation of protein aggregates [9]. In the last few years, many biologic candidates in preclinical or clinical evaluation have used nebulizers as the means of delivery. We look forward to hearing about those that show promise after entering clinical development. 

References:

1.       House, Season 5, episode 11

2.       Melani AS. Inhaler technique in asthma and COPD: challenges and unmet knowledge that can contribute to suboptimal use in real life. Expert Rev Clin Pharmacol. 2021 Aug;14(8):991-1003. doi: 10.1080/17512433.2021.1929922.

3.       Anderson S, et al. Inhaled Medicines: Past, Present and Future. Pharmacol Rev. 2022;74(1):1-85.

4.       Cipolla D. Will pulmonary drug delivery for systemic application ever fulfill its rich promise? Expert Opin Drug Deliv. 2016;13(10):1337-1340. doi: 10.1080/17425247.2016.1218466

5.       Singh SK, et al. An industry perspective on the monitoring of subvisible particles as a quality attribute for protein therapeutics. J Pharm Sci. 2010 Aug;99(8):3302-21.

6.       Rosenberg AS. Effects of protein aggregates: an immunologic perspective. AAPS J. 2006 Aug 4;8(3):E501-7.

7.       Maa YF, Hsu CC. Protein denaturation by combined effect of shear and air-liquid interface. Biotechnol Bioeng. 1997 Jun 20;54(6):503-12.

8.       Leiner S, et al. Soft Mist Inhalers. In: Pharmaceutical Inhalation Aerosol Technology, Third Edition. CRC Press. AJ. Hickey, SR. da Rocha (eds). 2019;21:493-507.

9.       Cipolla D, Gonda I, Shire SJ.  Characterization of Aerosols of Human Recombinant Deoxyribonuclease I (rhDNase) Generated by Jet Nebulizers. Pharm Res. 1994;11(4):491-497.