Designing inhaled protein therapeutics for topical lung delivery: what are the next steps?

Challenges and opportunities for antiviral monoclonal antibodies as COVID-19 therapy

To address the COVID-19 pandemic, there has been an unprecedented global effort to advance potent neutralizing mAbs against SARS-CoV-2 as therapeutics. However, historical efforts to advance antiviral monoclonal antibodies (mAbs) for the treatment of other respiratory infections have been met with categorical failures in the clinic. By investigating the mechanism by which SARS-CoV-2 and similar viruses spread within the lung, along with available biodistribution data for systemically injected mAb, we highlight the challenges faced by current antiviral mAbs for COVID-19. We summarize some of the leading mAbs currently in development, and present the evidence supporting inhaled delivery of antiviral mAb as an early intervention against COVID-19 that could prevent important pulmonary morbidities associated with the infection.

Pharmacokinetic/pharmacodynamic approaches to drug delivery design for inhalation drugs

Introduction: Inhaled drugs are important in the treatment of many lung pathologies, but to be therapeutically effective they must reach unbound concentrations at their effect site in the lung that are adequate to interact with their pharmacodynamic properties (PD) and exert the pharmacological action over an appropriate dosing interval. Therefore, the evaluation of pharmacokinetic (PK)/PD relationship is critical to predict their possible therapeutic effect.Areas covered: We review the approaches used to assess the PK/PD relationship of the major classes of inhaled drugs that are prescribed to treat pulmonary pathologies.Expert opinion: There are still great difficulties in producing data on lung concentrations of inhaled drugs and interpreting them as to their ability to induce the desired therapeutic action. The structural complexity of the lungs, the multiplicity of processes involved simultaneously and the physical interactions between the lungs and drug make any PK/PD approach to drug delivery design for inhalation medications extremely challenging. New approaches/methods are increasing our understanding about what happens to inhaled drugs, but they are still not ready for regulatory purposes. Therefore, we must still rely on plasma concentrations based on the axiom that they reflect both the extent and the pattern of deposition within the lungs.

Inhalation delivery technology for genome-editing of respiratory diseases

The clustered regulatory interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9) system has significant therapeutic potentials for lung congenital diseases such as cystic fibrosis, as well as other pulmonary disorders like lung cancer and obstructive diseases. Local administration of CRISPR/Cas9 therapeutics through inhalation can achieve high drug concentration and minimise systemic exposure. While the field is advancing with better understanding on the biological functions achieved by CRISPR/Cas9 systems, the lack of progress in inhalation formulation and delivery of the molecule may impede their clinical translation efficiently. This forward-looking review discussed the current status of formulations and delivery for inhalation of relevant biologics such as genes (plasmids and mRNAs) and proteins, emphasising on their design strategies and preparation methods. By adapting and optimising formulation strategies used for genes and proteins, we envisage that development of inhalable CRISPR/Cas9 liquid or powder formulations for inhalation administration can potentially be fast-tracked in near future.

Computational Design of 25-mer Peptide Binders of SARS-CoV-2

SARS-CoV-2 is the novel coronavirus causing the COVID-19 pandemic. To enter human cells, the receptor-binding domain (RBD) of the S1 subunit of SARS-CoV-2 (SARS-CoV-2-RBD) initially binds to the peptidase domain of angiotensin-converting enzyme 2 receptor (ACE2-PD). Using peptides to inhibit SARS-CoV-2-RBD binding to ACE2 is a potential therapeutic solution for COVID-19. A previous study identified a 23-mer peptide (SBP1) that bound to SARS-CoV-2-RBD with comparable KD to ACE2. We employed computational protein design and molecular dynamics (MD) to design SARS-CoV-2-RBD 25-mer peptide binders (SPB25) with better predicted binding affinity than SBP1. Using residues 21-45 of the α1 helix of ACE2-PD as the template, our strategy is employing Rosetta to enhance SPB25 binding affinity to SARS-CoV-2-RBD and avoid disrupting existing favorable interactions by using residues that have not been reported to form favorable interactions with SARS-CoV-2-RBD as designed positions. Designed peptides with better predicted binding affinities, by Rosetta, than SPB25 were subjected to MD validation. The MD results show that five designed peptides (SPB25F8N, SPB25F8R, SPB25L25R, SPB25F8N/L25R, and SPB25F8R/L25R) have better predicted binding affinities, by the MM-GBSA method, than SPB25 and SBP1. This study developed an approach to design SARS-CoV-2-RBD peptide binders, and these peptides may be promising candidates as potential SARS-CoV-2 inhibitors.

Peptide and peptide-based inhibitors of SARS-CoV-2 entry

To date, no effective vaccines or therapies are available against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative pandemic agent of the coronavirus disease 2019 (COVID-19). Due to their safety, efficacy and specificity, peptide inhibitors hold great promise for the treatment of newly emerging viral pathogens. Based on the known structures of viral proteins and their cellular targets, antiviral peptides can be rationally designed and optimized. The resulting peptides may be highly specific for their respective targets and particular viral pathogens or exert broad antiviral activity. Here, we summarize the current status of peptides inhibiting SARS-CoV-2 entry and outline the strategies used to design peptides targeting the ACE2 receptor or the viral spike protein and its activating proteases furin, transmembrane serine protease 2 (TMPRSS2), or cathepsin L. In addition, we present approaches used against related viruses such as SARS-CoV-1 that might be implemented for inhibition of SARS-CoV-2 infection.

Developing inhaled protein therapeutics for lung diseases

Biologic therapeutics such as protein/polypeptide drugs are conventionally administered systemically via intravenous injection for the treatment of diseases including lung diseases, although this approach leads to low target site accumulation and the potential risk for systemic side effects. In comparison, topical delivery of protein drugs to the lung via inhalation is deemed to be a more effective approach for lung diseases, as proteins would directly reach the target in the lung while exhibiting poor diffusion into the systemic circulation, leading to higher lung drug retention and efficacy while minimising toxicity to other organs. This review examines the important considerations and challenges in designing an inhaled protein therapeutics for local lung delivery: the choice of inhalation device, structural changes affecting drug deposition in diseased lungs, clearance mechanisms affecting an inhaled protein drug’s lung accumulation, protein stability, and immunogenicity. Possible approaches to overcoming these issues will also be discussed.

Airway Delivery of Anti-influenza Monoclonal Antibodies Results in Enhanced Antiviral Activities and Enables Broad-Coverage Combination Therapies

Influenza causes widespread illness in humans and can result in morbidity and death, especially in the very young and elderly populations. Because influenza vaccination can be poorly effective some years, and the immune systems of the most susceptible populations are often compromised, passive immunization treatments using broadly neutralizing antibodies is a promising therapeutic approach. However, large amounts of a single antibody are required for effectiveness when delivered through systemic administration (typically intravenous infusion), precluding the feasible dosing of antibody combinations via this route. The significance of our research is the demonstration that effective therapeutic treatments of multiple relevant influenza types (H1N1, H3N2, and B) can be achieved by airway administration of a single combination of relatively small amounts of three anti-influenza antibodies. This advance exploits the discovery that airway delivery is a more potent way of administering anti-influenza antibodies compared to systemic delivery, making this a feasible and cost-effective therapeutic approach.

Effective and reliable anti-influenza treatments are acutely needed and passive immunizations using broadly neutralizing anti-influenza monoclonal antibodies (bNAbs) are a promising emerging approach. Because influenza infections are initiated in and localized to the pulmonary tract, and newly formed viral particles egress from the apical side of the lung epithelium, we compared the effectiveness of hemagglutinin (HA) stalk-binding bNAbs administered through the airway (intranasal or via nebulization) versus the systemic route (intraperitoneal or intravenous). Airway deliveries of various bNAbs were 10- to 50-fold more effective than systemic deliveries of the same bNAbs in treating H1N1, H3N2, B/Victoria-, and B/Yamagata-lineage influenza viral infections in mouse models. The potency of airway-delivered anti-HA bNAbs was highly dependent on antiviral neutralization activity, with little dependence on the effector function of the antibody. In contrast, the effectiveness of systemically delivered anti-HA bNAbs was not dependent on antiviral neutralization, but critically dependent on antibody effector functions. Concurrent administration of a neutralizing/effector function-positive bNAb via the airway and systemic routes showed increased effectiveness. The small amount of airway-delivered bNAbs needed for effective influenza treatment creates the opportunity to combine potent bNAbs with different anti-influenza specificities to generate a cost-effective antiviral therapy that provides broad coverage against all circulating influenza strains infecting humans. A 3 mg/kg dose of the novel triple antibody combination CF-404 (i.e., 1 mg/kg of each component bNAb) delivered to the airway was shown to effectively prevent weight loss and death in mice challenged with ten 50% lethal dose (LD₅₀) inoculums of either H1N1, H3N2, B/Victoria-lineage, or B/Yamagata-lineage influenza viruses.

IMPORTANCE Influenza causes widespread illness in humans and can result in morbidity and death, especially in the very young and elderly populations. Because influenza vaccination can be poorly effective some years, and the immune systems of the most susceptible populations are often compromised, passive immunization treatments using broadly neutralizing antibodies is a promising therapeutic approach. However, large amounts of a single antibody are required for effectiveness when delivered through systemic administration (typically intravenous infusion), precluding the feasible dosing of antibody combinations via this route. The significance of our research is the demonstration that effective therapeutic treatments of multiple relevant influenza types (H1N1, H3N2, and B) can be achieved by airway administration of a single combination of relatively small amounts of three anti-influenza antibodies. This advance exploits the discovery that airway delivery is a more potent way of administering anti-influenza antibodies compared to systemic delivery, making this a feasible and cost-effective therapeutic approach.

Pulmonary Delivery of Biological Drugs

In the last decade, biological drugs have rapidly proliferated and have now become an important therapeutic modality. This is because of their high potency, high specificity and desirable safety profile. The majority of biological drugs are peptide- and protein-based therapeutics with poor oral bioavailability. They are normally administered by parenteral injection (with a very few exceptions). Pulmonary delivery is an attractive non-invasive alternative route of administration for local and systemic delivery of biologics with immense potential to treat various diseases, including diabetes, cystic fibrosis, respiratory viral infection and asthma, etc. The massive surface area and extensive vascularisation in the lungs enable rapid absorption and fast onset of action. Despite the benefits of pulmonary delivery, development of inhalable biological drug is a challenging task. There are various anatomical, physiological and immunological barriers that affect the therapeutic efficacy of inhaled formulations. This review assesses the characteristics of biological drugs and the barriers to pulmonary drug delivery. The main challenges in the formulation and inhalation devices are discussed, together with the possible strategies that can be applied to address these challenges. Current clinical developments in inhaled biological drugs for both local and systemic applications are also discussed to provide an insight for further research.

Biodistribution and elimination pathways of PEGylated recombinant human deoxyribonuclease I after pulmonary delivery in mice

Conjugation of recombinant human deoxyribonuclease I (rhDNase) to polyethylene glycol (PEG) of 20 to 40 kDa was previously shown to prolong the residence time of rhDNase in the lungs of mice after pulmonary delivery while preserving its full enzymatic activity. This work aimed to study the fate of native and PEGylated rhDNase in the lungs and to elucidate their biodistribution and elimination pathways after intratracheal instillation in mice. In vivo fluorescence imaging revealed that PEG30 kDa-conjugated rhDNase (PEG30-rhDNase) was retained in mouse lungs for a significantly longer period of time than native rhDNase (12 days vs 5 days). Confocal microscopy confirmed the presence of PEGylated rhDNase in lung airspaces for at least 7 days. In contrast, the unconjugated rhDNase was cleared from the lung lumina within 24 h and was only found in lung parenchyma and alveolar macrophages thereafter. Systemic absorption of intact rhDNase and PEG30-rhDNase was observed. However, this was significantly lower for the latter. Catabolism, primarily in the lungs and secondarily systemically followed by renal excretion of byproducts were the predominant elimination pathways for both native and PEGylated rhDNase. Catabolism was nevertheless more extensive for the native protein. On the other hand, mucociliary clearance appeared to play a less prominent role in the clearance of those proteins after pulmonary delivery. The prolonged presence of PEGylated rhDNase in lung airspaces appears ideal for its mucolytic action in patients with cystic fibrosis.

The Lord of the NanoRings: Cyclodextrins and the battle against SARS-CoV-2

A handful of singular structures and laws can be observed in nature. They are not always evident but, once discovered, it seems obvious how to take advantage of them. In chemistry, the discovery of reproducible patterns stimulates the imagination to develop new functional materials and technological or medical applications. Two clear examples are helical structures at different levels in biological polymers as well as ring and spherical structures of different size and composition. Rings are intuitively observed as holes able to thread elongated structures. A large number of real and fictional stories have rings as inanimate protagonists. The design, development or just discovering of a special ring has often been taken as a symbol of power or success. Several examples are the Piscatory Ring wore by the Pope of the Catholic Church, the NBA Championship ring and the One Ring created by the Dark Lord Sauron in the epic story The Lord of the Rings. In this work, we reveal the power of another extremely powerful kind of rings to fight against the pandemic which is currently affecting the whole world. These rings are as small as ~1 nm of diameter and so versatile that they are able to participate in the attack of viruses, and specifically SARS-CoV-2, in a large range of different ways. This includes the encapsulation and transport of specific drugs, as adjuvants to stabilize proteins, vaccines or other molecules involved in the infection, as cholesterol trappers to destabilize the virus envelope, as carriers for RNA therapies, as direct antiviral drugs and even to rescue blood coagulation upon heparin treatment.

“One ring to rule them all. One ring to find them. One ring to bring them all and in the darkness bind them.” J. R. R. Tolkien.

Fibrinolytic abnormalities in acute respiratory distress syndrome (ARDS) and versatility of thrombolytic drugs to treat COVID-19

The global pandemic of coronavirus disease 2019 (COVID-19) is associated with the development of acute respiratory distress syndrome (ARDS), which requires ventilation in critically ill patients. The pathophysiology of ARDS results from acute inflammation within the alveolar space and prevention of normal gas exchange. The increase in proinflammatory cytokines within the lung leads to recruitment of leukocytes, further propagating the local inflammatory response. A consistent finding in ARDS is the deposition of fibrin in the air spaces and lung parenchyma. COVID-19 patients show elevated D-dimers and fibrinogen. Fibrin deposits are found in the lungs of patients due to the dysregulation of the coagulation and fibrinolytic systems. Tissue factor (TF) is exposed on damaged alveolar endothelial cells and on the surface of leukocytes promoting fibrin deposition, while significantly elevated levels of plasminogen activator inhibitor 1 (PAI-1) from lung epithelium and endothelial cells create a hypofibrinolytic state. Prophylaxis treatment of COVID-19 patients with low molecular weight heparin (LMWH) is important to limit coagulopathy. However, to degrade pre-existing fibrin in the lung it is essential to promote local fibrinolysis. In this review, we discuss the repurposing of fibrinolytic drugs, namely tissue-type plasminogen activator (tPA), to treat COVID-19 associated ARDS. tPA is an approved intravenous thrombolytic treatment, and the nebulizer form has been shown to be effective in plastic bronchitis and is currently in Phase II clinical trial. Nebulizer plasminogen activators may provide a targeted approach in COVID-19 patients to degrade fibrin and improving oxygenation in critically ill patients.

Fibroblast-Derived STC-1 Modulates Tumor-Associated Macrophages and Lung Adenocarcinoma Development

The tumor microenvironment (TME) consists of different cell types, including tumor-associated macrophages (TAMs) and tumor-associated fibroblasts (TAFs). How these cells interact and contribute to lung carcinogenesis remains elusive. Using G12DKRAS- and V600EBRAF-driven mouse lung models, we identify the pleiotropic glycoprotein stanniocalcin-1 (STC1) as a regulator of TAM-TAF interactions. STC1 is secreted by TAFs and suppresses TAM differentiation, at least in part, by sequestering the binding of GRP94, an autocrine macrophage-differentiation-inducing factor, to its cognate scavenger receptors. The accumulation of mature TAMs in the Stc1-deficient lung leads to enhanced secretion of TGF-β1 and, thus, TAF accumulation in the TME. Consistent with the mouse data, in human lung adenocarcinoma, STC1 expression is restricted to myofibroblasts, and a significant increase of naive macrophages is detected in STC1-high compared with STC1-low cases. This work increases our understanding of lung adenocarcinoma development and suggests new approaches for therapeutic targeting of the TME.

Pharmacokinetic Analysis of Epithelial/Endothelial Cell Barriers in Microfluidic Bilayer Devices with an Air-Liquid Interface

As the range of applications of organs-on-chips is broadening, the evaluation of aerosol-based therapies using a lung-on-a-chip model has become an attractive approach. Inhalation therapies are not only minimally invasive but also provide optimal pharmacokinetic conditions for drug absorption. As drug development evolves, it is likely that better screening through use of organs-on-chips can significantly save time and cost. In this work, bio-aerosols of various compounds including insulin were generated using a jet nebulizer. The aerosol flows were driven through microfluidic bilayer devices establishing an air–liquid interface to mimic the blood–air barrier in human small airways. The aerosol flow in the microfluidic devices has been characterized and adjusted to closely match physiological values. The permeability of several compounds, including paracellular and transcellular biomarkers, across epithelial/endothelial cell barriers was measured. Concentration–time plots were established in microfluidic devices with and without cells; the curves were then utilized to extract standard pharmacokinetic parameters such as the area under the curve, maximum concentration, and time to maximum concentration. The cell barrier significantly affected the measured pharmacokinetic parameters, as compound absorption through the barrier decreases with its increasing molecular size. Aerosolizing insulin can lead to the formation of fibrils, prior to its entry to the microfluidic device, with a substantially larger apparent molecular size effectively blocking its paracellular transport. The results demonstrate the advantage of using lung-on-a-chip for drug discovery with applications such as development of novel inhaled therapies.

Computational Design of ACE2-Based Peptide Inhibitors of SARS-CoV-2

Peptide inhibitors against the SARS-CoV-2 coronavirus, currently causing a worldwide pandemic, are designed and simulated. The inhibitors are mostly formed by two sequential self-supporting α-helices (bundle) extracted from the protease domain (PD) of angiotensin-converting enzyme 2 (ACE2), which bind to the SARS-CoV-2 receptor binding domains. Molecular dynamics simulations revealed that the α-helical peptides maintain their secondary structure and provide a highly specific and stable binding (blocking) to SARS-CoV-2. To provide a multivalent binding to the SARS-CoV-2 receptors, many such peptides could be attached to the surfaces of nanoparticle carriers. The proposed peptide inhibitors could provide simple and efficient therapeutics against the COVID-19 disease.

High frequency acoustic nebulization for pulmonary delivery of antibiotic alternatives against Staphylococcus aureus

The increasing prevalence of multidrug resistant bacteria has warranted the search for new antimicrobial agents as existing antibiotics lose their potency. Among these, bacteriophage therapy, as well as the administration of specific bacteriolysis agents, i.e., lytic enzymes, have emerged as attractive alternatives. Nebulizers offer the possibility for delivering these therapeutics directly to the lung, which is particularly advantageous as a non-invasive and direct route to treat bacterial lung infections. Nevertheless, nebulizers can often result in significant degradation of the bacteriophage or protein, both structurally and functionally, due to the large stresses the aerosolization process imposes on these entities. In this work, we assess the capability of a novel low-cost and portable hybrid surface and bulk acoustic wave platform (HYDRA) to nebulize a Myoviridae bacteriophage (phage K) and lytic enzyme (lysostaphin) that specifically targets Staphylococcus aureus. Besides its efficiency in producing phage or protein-laden aerosols within the 1-5 μm respirable range for optimum delivery to the lower respiratory tract where lung infections commonly take place, we observe that the HYDRA platform-owing to the efficiency of driving the aerosolization process at relatively low powers and high frequencies (approximately 10 MHz)-does not result in appreciable denaturation of the phages or proteins, such that the loss of antimicrobial activity following nebulization is minimized. Specifically, a low (0.1 log₁₀ (pfu/ml)) titer loss was obtained with the phages, resulting in a high viable respirable fraction of approximately 90%. Similarly, minimal loss of antimicrobial activity was obtained with lysostaphin upon nebulization wherein its minimum inhibitory concentration (0.5 μg/ml) remained unaltered as compared with the non-nebulized control. These results therefore demonstrate the potential of the HYDRA nebulization platform as a promising strategy for pulmonary administration of alternative antimicrobial agents to antibiotics for the treatment of lung diseases caused by pathogenic bacteria.

Recent progress in drug delivery

Drug delivery systems (DDS) are defined as methods by which drugs are delivered to desired tissues, organs, cells and subcellular organs for drug release and absorption through a variety of drug carriers. Its usual purpose to improve the pharmacological activities of therapeutic drugs and to overcome problems such as limited solubility, drug aggregation, low bioavailability, poor biodistribution, lack of selectivity, or to reduce the side effects of therapeutic drugs. During 2015-2018, significant progress in the research on drug delivery systems has been achieved along with advances in related fields, such as pharmaceutical sciences, material sciences and biomedical sciences. This review provides a concise overview of current progress in this research area through its focus on the delivery strategies, construction techniques and specific examples. It is a valuable reference for pharmaceutical scientists who want to learn more about the design of drug delivery systems.

Monoclonal antibodies for severe asthma: Pharmacokinetic profiles

Several monoclonal antibodies (mAbs) (omalizumab, mepolizumab, reslizumab, benralizumab, and dupilumab) are currently approved for the treatment of severe asthma. They have complex pharmacokinetic profiles. These profiles are unique in that they are dependent on their structure as well as can be markedly influenced by the biology of their target antigen, but their general behaviour can still be considered a class property, similar to their endogenous IgG counterpart. They cannot be administered by oral route, have a slow distribution into tissue, are metabolized to peptides and amino acids in several tissues but are protected from degradation by binding to protective receptors (the FcRn), which explains their long elimination half-lives. Their clearance is nonlinear because of the saturation of the target-mediated elimination. Also anti-drug antibody (ADA) response and off-target binding, as well as their glycosylation pattern, can influence the pharmacokinetics of mAbs.

Pulmonary delivery of therapeutic proteins based on zwitterionic chitosan-based nanocarriers for treatment on bleomycin-induced pulmonary fibrosis

Nanoparticle-based pulmonary delivery of protein therapeutics provides a promising approach for improving protein bioavailability to treat either local or systemic diseases, however high-efficient nanocarrier is a great challenge. Here, biomimetic phosphorylcholine-chitosan nanoparticles (PCCs-NPs) taking advantages of both zwitterionic phosphorylcholine and chitosan were developed as a pulmonary protein delivery platform. msFGFR2c, a potential therapeutic protein for lung fibrosis as model was loaded into PCCs-NPs via ionic gelation. The obtained msFGFR2c/PCCs-NPs inhibited α-SMA expression in fibroblasts induced by TGF-β1, slightly more effective than naked msFGFR2c. After orotracheal administration to bleomycin-induced pulmonary fibrosis model rats, msFGFR2c/PCCs-NPs resulted in a significant antifibrotic efficacy, with reduction in inflammatory cytokines and α-SMA expression, remarkable attenuation of lung fibrosis score and collagen deposition, and significant increase in survival rate, while naked msFGFR2c exhibited a poor efficacy. The in vitro and in vivo results strongly indicated that PCCs-NPs may be a promising nanocarrier for pulmonary protein delivery.