Safety of inhaled proteins for therapeutic use

Biologics in Asthma: Emerging Biologics

Advances in our understanding of asthma pathophysiology have led to the advent of multiple targeted asthma therapies such as biologics. However, partial response to biologics occurs, indicating residual disease activity in some patients. Hence, there exists a need for new therapies that focus on novel pathways, alongside perhaps evaluation of combination biologic therapies and modulators of downstream cytokine activation. Therefore, although our current focus is on biologics; it is critical to take a more holistic approach including consideration for nonbiologic therapies that have the potential to significantly advance asthma care.

Barriers for orally inhaled therapeutic antibodies

INTRODUCTION

Respiratory diseases represent a worldwide health issue. The recent Sars-CoV-2 pandemic, the burden of lung cancer, and inflammatory respiratory diseases urged the development of innovative therapeutic solutions. In this context, therapeutic antibodies (Abs) offer a tremendous opportunity to benefit patients with respiratory diseases. Delivering Ab through the airways has been demonstrated to be relevant to improve their therapeutic index. However, few inhaled Abs are on the market.

AREAS COVERED

This review describes the different barriers that may alter the fate of inhaled therapeutic Abs in the lungs at steady state. It addresses both physical and biological barriers and discusses the importance of taking into consideration the pathological changes occurring during respiratory disease, which may reinforce these barriers.

EXPERT OPINION

The pulmonary route remains rare for delivering therapeutic Abs, with few approved inhaled molecules, despite promising evidence. Efforts must focus on the intertwined barriers associated with lung diseases to develop appropriate Ab-formulation-device combo, ensuring optimal Ab deposition in the respiratory tract. Finally, randomized controlled clinical trials should be carried out to establish inhaled Ab therapy as prominent against respiratory diseases.

Development of an Inhalation Dry Powder Preparation Method without Heat-drying Process

Biopharmaceuticals, including therapeutic genes and proteins, are characterized by highly-targeted, specific action and flexible pharmacological design and have a rapidly growing market share; however, because of high molecular weight and low stability, injection is the most common delivery route of biopharmaceuticals. Thus, pharmaceutical innovations are required to provide alternative delivery routes for biopharmaceuticals. Pulmonary drug delivery via inhalation is a promising approach, particularly for targeting local diseases of the lung, because it can exert therapeutic effects in small doses and can noninvasively and directly deliver drugs to airway surfaces. However, biopharmaceutical inhalers must ensure that the biopharmaceuticals maintain their integrity as they are subjected to several types of physicochemical stress, such as hydrolysis, ultrasound, and heating, at various stages during the process from manufacturing to administration. In this symposium, I present a novel dry powder inhaler (DPI) preparation method without heat-drying, with the goal of developing biopharmaceutical DPIs. Spray-freeze-drying is a nonthermal drying technique that produces a powder with porous shapes; this powder has suitable inhalation characteristics for DPI. A model drug, plasmid DNA (pDNA), was stably prepared as a DPI using the spray-freeze-drying process. Under dry conditions, the powders maintained high inhalation characteristics and maintained pDNA integrity for 12 months. The powder induced pDNA expression in mouse lungs that exceeded at higher levels than the solution did. This novel preparation method is suitable for DPI preparation for various drugs and may help expand the clinical application of DPIs.

Estimating inhalation bioavailability for peptides and proteins 1 to 10 kDa in size

Inhalation is a critical route for occupational exposure. To protect workers from adverse effects, health-based exposure limits (HBELs) are derived using chemical-specific information including inhalation bioavailability. Inhalation bioavailability of large proteins is well studied and generally accepted to be 1% or less. However, the inhalation bioavailability of peptides and proteins 1-10 kDa in size is not well defined. The goal of this study was to expand upon previous analyses and evaluate the inhalation bioavailability of small peptides. Inhalation bioavailability data for 72 peptides and protein samples ranging from 1.1 to 10.9 kDa in size were evaluated. The median inhalation bioavailability was 20%, which is in agreement with previously published analyses. Inhalation bioavailabilities for the vast majority were below 50%. Interestingly, species, peptide size, and peptide identity did not correlate with inhalation bioavailability. Other factors including inhalation dosimetry, peptide degradation, and chemical characteristics also decrease the amount of peptide available for absorption. Together, the median bioavailability of 20% is likely an appropriate estimate of systemic exposure and is sufficiently protective in most cases for the purposes of occupational exposure safety. Thus, in the absence of peptide-specific data or concerns, an inhalation bioavailability default of 20% is recommended for 1-10 kDa peptide and proteins.

Inhaled antibodies: Quality and performance considerations

The use of antibodies in the treatment of lung diseases is of increasing interest especially as the search for COVID-19 therapies has unfolded. Historically, the use of antibody therapy was based on multiple targets including receptors involved in local hyper-reactivity in asthma, viruses and micro-organisms involved in a variety of pulmonary infectious disease. Generally, protein therapeutics pose challenges with respect to formulation and delivery to retain activity and assure therapy. The specificity of antibodies amplifies the need for attention to molecular integrity not only in formulation but also during aerosol delivery for pulmonary administration. Drug product development can be viewed from considerations of route of administration, dosage form, quality, and performance measures. Nebulizers and dry powder inhalers have been used to deliver protein therapeutics and each has its advantages that should be matched to the needs of the drug and the disease. This review offers insight into quality and performance barriers and the opportunities that arise from meeting them effectively.

The use of heat to deliver fentanyl via pulmonary drug delivery

The golden standard to treat acute pain is by intravenous drug delivery of opioids such as fentanyl or morphine. Intravenous drug delivery requires the placement of an intravenous (IV) port, which can cause infections, dislodgments, and distress to the patients, and therefore a non-invasive method is desirable. Pulmonary drug delivery is a non-invasive method that has been shown to be a good alternative to intravenous administration. New devices have been investigated for treating acute pain by delivering fentanyl by heat. The pure drug, fentanyl, is applied onto a surface which is then heated up to 350 °C and inhaled, resulting in no formation of degradation products. Furthermore, forced degradation of fentanyl has been studied which showed that longer heating time and higher temperatures will result in the formation of degradation products. The evidence indicates that heat can be used to deliver drugs to the lungs where fast onset reaction can be obtained giving fast and non-invasive pain relief.

Protein and peptide delivery to lungs by using advanced targeted drug delivery

The challenges and difficulties associated with conventional drug delivery systems have led to the emergence of novel, advanced targeted drug delivery systems. Therapeutic drug delivery of proteins and peptides to the lungs is complicated owing to the large size and polar characteristics of the latter. Nevertheless, the pulmonary route has attracted great interest today among formulation scientists, as it has evolved into one of the important targeted drug delivery platforms for the delivery of peptides, and related compounds effectively to the lungs, primarily for the management and treatment of chronic lung diseases. In this review, we have discussed and summarized the current scenario and recent developments in targeted delivery of proteins and peptide-based drugs to the lungs. Moreover, we have also highlighted the advantages of pulmonary drug delivery over conventional drug delivery approaches for peptide-based drugs, in terms of efficacy, retention time and other important pharmacokinetic parameters. The review also highlights the future perspectives and the impact of targeted drug delivery on peptide-based drugs in the coming decade.

BSTP Review of 12 Case Studies Discussing the Challenges, Pathology, Immunogenicity, and Mechanisms of Inhaled Biologics

The inhalation route is a relatively novel drug delivery route for biotherapeutics and, as a result, there is a paucity of published data and experience within the toxicology/pathology community. In recent years, findings arising in toxicology studies with inhaled biologics have provoked concern and regulatory challenges due, in part, to the lack of understanding of the expected pathology, mechanisms, and adversity induced by this mode of delivery. In this manuscript, the authors describe 12 case studies, comprising 18 toxicology studies, using a range of inhaled biotherapeutics (monoclonal antibodies, fragment antigen-binding antibodies, domain antibodies, therapeutic proteins/peptides, and an oligonucleotide) in rodents, nonhuman primates (NHPs), and the rabbit in subacute (1 week) to chronic (26 weeks) toxicology studies. Analysis of the data revealed that many of these molecules were associated with a characteristic pattern of toxicity with high levels of immunogenicity. Microscopic changes in the airways consisted of a predominantly lymphoid perivascular/peribronchiolar (PV/PB) mononuclear inflammatory cell (MIC) infiltrate, whereas changes in the terminal airways/alveoli were characterized by simple ("uncomplicated") increases in macrophages or inflammatory cell infiltrates ranging from mixed inflammatory cell infiltration to inflammation. The PV/PB MIC changes were considered most likely secondary to immunogenicity, whereas simple increases in alveolar macrophages were most likely secondary to clearance mechanisms. Alveolar inflammatory cell infiltrates and inflammation were likely induced by immune modulation or stimulation through pharmacologic effects on target biology or type III hypersensitivity (immune complex disease). Finally, a group of experts provide introductory thoughts regarding the adversity of inhaled biotherapeutics and the basis for reasonable differences of opinion that might arise between toxicologists, pathologists, and regulators.

Preclinical Safety Assessment of 2 Inhaled Single-Domain Antibodies in the Cynomolgus Monkey

The safety of 2 single domain antibodies (dAbs) was evaluated by inhalation toxicology studies in the cynomolgus monkey. In the first case study, a 14-day repeat-dose study evaluating an anti-thymic stromal lymphopoietin (anti-TSLP) dAb resulted in minimal mononuclear inflammatory cell infiltrates in the lungs, increases in lymphocytes in bronchoalveolar lavage fluid, and development of antidrug antibodies (ADAs). In a 6-week inhalation study, there was an increase in incidence and/or severity of mononuclear cell infiltrates in the lung, increased cellularity in the tracheobronchial lymph node (TBLN), and development of ADA. The second case study evaluated a change in duration of inhalation dosing, a different route of exposure (intravenous or IV), and recovery following an off-dose period with an anti-tumor necrosis factor receptor 1 dAb. A 7-day repeat-dose inhalation study and a 14-day IV study produced no microscopic effects in the lung, whereas a 14-day inhalation study resulted in moderate increases in pulmonary perivascular/peribronchiolar/alveolar lymphocytic infiltrates and increased cellularity in the TBLN, with partial and full recovery, respectively, after 14 days. The lung and lymph node findings seen after inhalation of either dAb were considered secondary to the immunogenic response to a human protein and were considered nonadverse.

Case Studies Discussing the Pathology, Immunogenicity, and Proposed Mechanism of Toxicity of an Inhaled Anti-TGFβ Humanized Fab Antibody in Non-Human Primates and Mice

Treatment of nonhuman primates and mice with a humanized antigen-binding fragment (Fab) antibody (UCBFab) inhibiting transforming growth factor β via daily inhalation for up to 13 weeks resulted in low systemic exposure but high local exposure in the lung. Target engagement was demonstrated by reduced levels of signal transducers, phosphoSMAD and plasminogen activator inhibitor-1 in the bronchoalveolar lavage fluid (BALF). Treatment was associated with a high frequency and titer of antidrug antibodies, indicating high local immunogenicity, and local pathology within the lung and draining lymph nodes. Microscopic changes were characterized by perivascular (PV) and peribronchiolar (PB) mononuclear inflammatory cell (MIC) infiltrates that were principally lymphocytic in nature and mixed inflammatory cell infiltrates and/or inflammation within the alveoli. Immunohistochemical investigation revealed a predominantly CD68-positive macrophage and CD3- and CD8>CD4-positive T-cell response in the alveoli, whereas within the airways, there was a variable mixture of CD3-positive T cells, CD20-positive B cells, and CD68-positive macrophages. Increased cellularity of the draining lymph nodes was also noted, indicating the presence of an immune response to the inhaled test article. Morphologic changes did not progress over time, and all changes partially recovered. Increased leukocytes (principally macrophages) in BALF cytology correlated with the changes seen by histopathology.

Post-inhalation cough with therapeutic aerosols: Formulation considerations

This review provides an assessment of post-inhalation cough with therapeutic aerosols. Factors that increase cough may be mitigated through design of the drug, formulation, and device. The incidence of cough is typically less than 5% for drugs with a nominal dose less than 1 mg, including asthma and COPD therapeutics. Cough increases markedly as the dose approaches 100 mg. This is due to changes in the composition of epithelial lining fluid (e.g., increases in osmolality, proton concentration). Whether an individual exhibits cough depends on their degree of sensitization to mechanical and chemical stimuli. Hypersensitivity is increased when the drug, formulation or disease result in increases in lung inflammation. Cough related to changes in epithelial lining fluid composition can be limited by using insoluble neutral forms of drugs and excipients.

The History of Therapeutic Aerosols: A Chronological Review

In 1956, Riker Laboratories, Inc., (now 3 M Drug Delivery Systems) introduced the first pressurized metered dose inhaler (MDI). In many respects, the introduction of the MDI marked the beginning of the modern pharmaceutical aerosol industry. The MDI was the first truly portable and convenient inhaler that effectively delivered drug to the lung and quickly gained widespread acceptance. Since 1956, the pharmaceutical aerosol industry has experienced dramatic growth. The signing of the Montreal Protocol in 1987 led to a surge in innovation that resulted in the diversification of inhaler technologies with significantly enhanced delivery efficiency, including modern MDIs, dry powder inhalers, and nebulizer systems. The innovative inhalers and drugs discovered by the pharmaceutical aerosol industry, particularly since 1956, have improved the quality of life of literally hundreds of millions of people. Yet, the delivery of therapeutic aerosols has a surprisingly rich history dating back more than 3500 years to ancient Egypt. The delivery of atropine and related compounds has been a crucial inhalation therapy throughout this period and the delivery of associated structural analogs remains an important therapy today. Over the centuries, discoveries from many cultures have advanced the delivery of therapeutic aerosols. For thousands of years, therapeutic aerosols were prepared by the patient or a physician with direct oversight of the patient using custom-made delivery systems. However, starting with the Industrial Revolution, advancements in manufacturing resulted in the bulk production of therapeutic aerosol delivery systems produced by people completely disconnected from contact with the patient. This trend continued and accelerated in the 20th century with the mass commercialization of modern pharmaceutical inhaler products. In this article, we will provide a summary of therapeutic aerosol delivery from ancient times to the present along with a look to the future. We hope that you will find this chronological summary intriguing and informative.

Toxicology Studies for Inhaled and Nasal Delivery

This review examines issues related to the toxicological testing of pharmaceuticals delivered by the inhalation or nasal route. The purpose of the toxicology studies is to conduct studies in animals that will aid the assessment of the safety of these agents delivered to patients. Inhalation toxicology studies present some unique issues because the dosing method differs from more standard administration methods such as oral or injection administration. Also, dose determination issues are more complex, particularly for inhalation administration since it is often difficult to determine the amount of material delivered to the lung both for patients and in animal toxicology studies.

Bioavailability of therapeutic proteins by inhalation--worker safety aspects

A literature review and analysis of inhalation bioavailability data for large therapeutic proteins was conducted in order to develop a practical estimate of the inhalation bioavailability of these drugs. This value is incorporated into equations used to derive occupational exposure limits(OELs) to protect biopharmaceutical manufacturing workers from systemic effects. Descriptive statistics implies that a value of 0.05, or 5% is an accurate estimate for large therapeutic proteins (molecular weight ≥ 40kDa). This estimate is confirmed by pharmacokinetic modeling of data from a human daily repeat-dose inhalation study of immunoglobulin G. In conclusion, we recommend using 5% bioavailability by inhalation when developing OELs for large therapeutic proteins.

Inhaled biopharmaceutical drug development: nonclinical considerations and case studies

Biopharmaceuticals are complex molecules often manufactured from living systems and their specificity and novelty holds great promise for the treatment of chronic diseases for which there are currently no cures. The inhalation route of biopharmaceutical drug delivery is attractive because the large surface area of the lung, and close proximity of the alveolar and vascular systems, maximizes the potential for drug delivery to the lung and/or systemic circulation. In addition, costs of delivery to the patient are potentially much reduced, in comparison with parental administration, since inhalation is non-invasive and likely to promote patient compliance. However, in comparison with small molecule drug development, developing an inhaled biopharmaceutical that is effective and safe for human use is associated with many challenges. This review considers some general principles of drug delivery to lung and issues associated with the translation of proof of concept studies to toxicology safety studies (e.g. aerosol generation, species selection, exaggerated pharmacology, and immunogenicity). This review also presents a summary of nonclinical and clinical data from inhaled biopharmaceuticals which are either marketed for human use or in Phase II clinical trials (e.g. DNase, insulin, human growth hormone, vaccines, therapeutic plasmid DNA complexes).

Novel devices for individualized controlled inhalation can optimize aerosol therapy in efficacy, patient care and power of clinical trials

In the treatment of pulmonary diseases the inhalation of aerosols plays a key role - it is the preferred route of drug delivery in asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis. But, in contrast to oral and intravenous administration drug delivery to the lungs is controlled by additional parameters. Beside its pharmacology the active agent is furthermore determined by its aerosol characteristics as particle diameter, particle density, hygroscopicity and electrical charge. The patient related factors like age and stage of pulmonary disease will be additionally affected by the individual breathing pattern and morphometry of the lower airways. A number of these parameters with essential impact on the pulmonary drug deposition can be influenced by the performance of the inhalation system. Therefore, the optimization of nebulisation technology was a major part of aerosol science in the last decade. At this time the control of inspiration volume and air flow as well as the administration of a defined aerosol bolus was in the main focus. Up to date a more efficient and a more targeted pulmonary drug deposition - e.g., in the alveoli - will be provided by novel devices which also allow shorter treatment times and a better reproducibility of the administered lung doses. By such means of precise dosing and drug targeting the efficacy of inhalation therapy can be upgraded, e.g., the continuous inhalation of budesonide in asthma. From a patients' perspective an optimized inhalation manoeuvre means less side effects, e.g., in cystic fibrosis therapy the reduced oropharyngeal tobramycin exposure causes fewer bronchial irritations. Respecting to shorter treatment times also, this result in an improved quality of life and compliance. For clinical trials the scaling down of dose variability in combination with enhanced pulmonary deposition reduces the number of patients to be included and the requirement of pharmaceutical compounds. This review summarises principles and advances of individualised controlled inhalation (ICI) as offered by the AKITA inhalation system.

Inhaled insulin: overview of a novel route of insulin administration

Diabetes is a chronic disease characterized by inadequate insulin secretion with resulting hyperglycemia. Diabetes complications include both microvascular and macrovascular disease, both of which are affected by optimal diabetes control. Many individuals with diabetes rely on subcutaneous insulin administration by injection or continuous infusion to control glucose levels. Novel routes of insulin administration are an area of interest in the diabetes field, given that insulin injection therapy is burdensome for many patients. This review will discuss pulmonary delivery of insulin via inhalation. The safety of inhaled insulin as well as the efficacy in comparison to subcutaneous insulin in the various populations with diabetes are covered. In addition, the experience and pitfalls that face the development and marketing of inhaled insulin are discussed.

Therapeutic application of peptides and proteins: parenteral forever?

Varied therapeutic peptides and proteins represent a rapidly growing part of marketed drugs and have an undisputed place alongside other established therapies. Nevertheless, such biodrugs have several drawbacks that hinder their therapeutic application. These are undesirable physicochemical properties, such as variable solubility, low bioavailability and limited stability. These issues can be overcome by addition of stabilizing agents and directed injectable administration, which can however result in low patient compliance. Hence, there is a drive in the biotechnology industry to produce needle-free and more user-friendly drugs, and this has led to the growth of nano-enabled drug delivery systems in the last decade. As discussed here, nanobiotechnology is becoming a commercially feasible and promising opportunity for oral, pulmonary and transdermal administration routes.

Application of supercritical fluid to preparation of powders of high-molecular weight drugs for inhalation

The application of supercritical carbon dioxide to particle design has recently emerged as a promising way to produce powders of macromolecules such as proteins and genes. Recently, an insulin powder for inhalation was approved by authorities in Europe and the USA. Other macromolecules for inhalation therapy will follow. In the 1990s proteins were precipitated with supercritical CO(2) from solutions in an organic solvent such as dimethylsulfoxide, which caused significant unfolding of protein. Since 2000, aqueous solutions of proteins and genes have generally been used with a cosolvent such as ethanol to precipitate in CO(2). Operating conditions such as temperature, pressure, flow rates, and concentration of ingredients affect the particle size and integrity of proteins or genes. By optimizing these conditions, the precipitation of proteins and genes with supercritical CO(2) is a promising way to produce protein and gene particles for inhalation.

Inhaled insulin

Inhaled insulin has attractive pharmacodynamic properties with a fast onset of action which should lead to improved postprandial blood glucose concentrations. Comparisons with regular subcutaneous (sc) insulin in clinical studies, however, showed lower fasting blood glucose concentrations. Overall, clinical efficacy of inhaled insulin was comparable to that of regular sc insulin. Treatment with inhaled insulin was safe and well tolerated, with slight and reversible changes in lung function parameters and a rise in insulin antibodies (not associated with any clinical or safety parameters) as main adverse effects. Treatment satisfaction in open-label studies was higher with inhaled than with sc insulin, indicating that inhaled insulin might help to overcome one of the major hurdles of diabetes therapy, i.e. a timely initiation of insulin therapy. The first inhaled insulin formulation was approved in the US and Europe in January 2006, but some countries granted reimbursement only for selected patients, or did not reimburse treatment with inhaled insulin at all because of the high treatment costs. These are due to the rather low bioavailability of approximately 8-15%. Therefore, further research is needed to improve the bioavailability of inhaled insulin: e.g. through optimization of the inhaler, the insulin formulation, or the inhalation technique. In view of the potential for further improvement, inhaled insulin may become a very attractive alternative to sc insulin, in particular in patients in whom insulin therapy has to be initiated and/or intensified.

Effect of upper respiratory tract infection on AIR inhaled insulin pharmacokinetics and glucodynamics in healthy subjects

The suitability of employing AIR Inhaled Insulin (AIR Insulin; AIR is a registered trademark of Alkermes) during acute upper respiratory tract infection (URI) has not been determined. Twenty-one healthy, non-diabetic subjects were enrolled in a single-sequence, two-period, euglycemic clamp study. Subjects received a single 12 U-equivalent dose of AIR Insulin before rhinovirus (RV16) inoculation and during symptomatic infection. Spirometry was used to evaluate pulmonary safety. AIR Insulin exposure (the area under the immunoreactive insulin (IRI) concentration vs time curve from time zero until the IRI concentrations returned to the predose baseline value (AUC(0-t'))) and glucodynamic response (total amount of glucose infused (G(tot))) were comparable before and during RV infection (AUC(0-t') 46,300 vs 52,600 pmol min/l, P=0.21; G(tot) 61,800 vs 68,700 mg, P=0.42, respectively). Variability of pharmacokinetic and pharmacodynamic parameters did not change during URI; either did the number or intensity of adverse events. No significant change in forced expiratory volume or forced vital capacity was observed following AIR Insulin administration or during URI. The AIR Insulin system provides similar pharmacokinetic and glucodynamic responses under conditions of an experimentally induced RV infection and is regarded as suitable for use in diabetic patients during URIs.

Inhalation, deposition, and fate of insulin and other therapeutic proteins

In contrast to other interfaces between the outer and inner environment, such as the skin and gastrointestinal tract, the lungs are ideally suited for the delivery of polypeptides and proteins to the systemic circulation. There is a wealth of experience from aerosol physics and lung biology to support the idea that insulin delivery via the lungs is an effective strategy. The elaborate branching network of airways, the extensive surface area of the deep lung, and the thin air-blood barrier make it possible to deliver insulin and other proteins to the parenchyma, where it can be absorbed into the pulmonary circulation and become available throughout the body. Protein-containing aerosols in inspired air deposit throughout the respiratory tract because of the following forces: gravity, diffusion, and inertial impaction. Lung anatomy, breathing pattern, and particle size determine the influence of these forces. Once deposited in the lungs, most protein-containing formulations quickly dissolve in airway or alveolar lining fluid. Then, a significant fraction of insulin is transported across the air-blood barrier into the blood, where it continues to be biologically active. A substantial fraction--usually the majority--is cleared from the lungs or degraded within the lungs.

Inhaled insulin delivery--where are we now?

Since 1925, when the concept of treating diabetes with inhaled insulin (INH) was originally published, a number of clinical challenges have been resolved through technological advancements. Efforts by pharmaceutical partnerships or individual companies have resulted in the development of both injection-free devices and novel insulin formulations. Four different INH systems are now in phase 3 of clinical development, and several other INH systems are in earlier stages of clinical study. Clinical data consistently demonstrate that INH therapy is comparable to subcutaneous (SC) therapy in improving glycaemic control in patients with either type 1 or type 2 diabetes, generally without greater risk of overall hypoglycaemia. INH is generally well tolerated and appears to be safe. Adverse-event profiles for INH therapies are similar to SC insulin therapy, with the majority of events being reported as being mild to moderate. Long-term safety studies are ongoing, with emphasis on evaluating the impact of INH therapy on pulmonary function and immune responses. Although small, reversible decreases in pulmonary diffusion capacity (DL(co)) and FEV1 have been reported in response to INH, pulmonary function and structure do not appear to be affected in any clinically significant way. While insulin antibodies are increased in INH therapy, these antibodies have not been correlated with haemoglobin A1c (HbA1c), insulin dosage, hypoglycaemia, pulmonary function or adverse events. Nevertheless, properly controlled, long-term studies will best answer any remaining concerns. From the patient's perspective, INH therapy is preferred by the majority of patients over conventional SC insulin therapy. Studies have shown that patients prefer INH therapy, because it provides greater lifestyle flexibility and social acceptability while at the same time avoiding the pain associated with injection. Thus, after more than 80 years during which the injection route has been the only means of administering insulin, patients and physicians may soon avail themselves of another valuable tool in management of diabetes.

Inhaled cytokines and cytokine antagonists

Cytokine and cytokine antagonist have provided novel and effective therapies for many human diseases. A number of approved cytokines including the interferons (alpha, beta and gamma), interleukin-2 (IL-2), granulocyte macrophage colony stimulating factor (GM-CSF) as well as novel cytokine antagonists have been administered by the pulmonary route for both local lung disease and as a non-invasive method for systemic delivery. We review the published clinical experience of inhaled cytokines and cytokine antagonists. We discuss the limitations of the existing data and the type of clinical data desired to establish the advantages and safety of inhaled cytokines and cytokine antagonists.

Clinical evaluation of inhaled insulin

Diabetes affects over 18.2 million individuals in the United States alone. Current therapy to treat type 1 diabetes relies on subcutaneous insulin administration either by injection or continuous infusion. In addition, patients with type 2 diabetes who fail lifestyle intervention and oral therapy require subcutaneous insulin. Optimal injection protocols to achieve tight metabolic control often prove burdensome to patients. Thus, development of pulmonary insulin delivery to supplement and/or replace subcutaneous insulin injections may be an effective alternative, allowing patients to achieve intensive diabetes management. This review will discuss the devices in development for the delivery of inhaled insulin. In addition, the efficacy of inhaled insulin in both type 1 and type 2 diabetic populations will be discussed. Finally, the available safety data with respect to the unique pulmonary effects of inhaled insulin will be covered.

Clinical perspectives on pulmonary systemic and macromolecular delivery

The large epithelial surface area, the high organ vascularization, the thin nature of the alveolar epithelium and the immense capacity for solute exchange are factors that led the lung to serve as an ideal administration route for the application of drugs for treatment of systemic disorders. However, the deposition behaviour of aerosol particles in the respiratory tract depends on a number of physical (e.g. properties of the particle), chemical (e.g. properties of the drug) and physiological (e.g. breathing pattern, pulmonary diseases) factors. If these are not considered, it will not be possible to deposit a reproducible and sufficient amount of drug in a predefined lung region by means of aerosol inhalation. The lack of consideration of such issues led to many problems in inhalation drug therapy for many years mainly because physiological background of aerosol inhalation was not fully understood. However, over the last 20 years, there has been considerable progress in aerosol research and in the understanding of the underlying mechanisms of particle inhalation and pulmonary particle deposition. As a consequence, an increasing number of studies have been performed for the lung administration of drugs using a variety of different inhalation techniques. This review describes the physical and in part some of the physiological requirements that need to be considered for the optimization of pulmonary drug delivery to target certain lung regions.

Systemic Delivery of Drugs to Humans via Inhalation

Unwanted systemic absorption of drugs delivered for the local treatment of respiratory disease is well documented. Methods to minimize this now exist, especially for reduction of oropharyngeal deposition. While small molecules appear to be absorbed also from the airways, it is the alveolated regions that provide a large absorptive surface. Lung has been used as a portal for systemic delivery of substances such as anesthetics, nicotine and a number of illicit drugs. Much research has lead to the solutions of the fundamental technical hurdles of practicable delivery of systemic therapeutic drugs in milligram quantities to the lung efficiently and reproducibly. Commercial manufacturing processes exist for production of delivery systems suitable for this purpose. Generally, the deposition of small molecules in the "deep lung" leads to high absorption rates, making the inhalation delivery attractive for drugs with intended rapid onset of action. Many therapeutics, especially peptides and proteins, that cannot be delivered systemically non-invasively, are absorbed with various degrees of systemic bioavailability via inhalation. The critical factor for efficient and reproducible systemic delivery is lung deposition which depends on the properties of drug particles (size, shape, density, hygroscopicity, velocity, charge) and the state of the respiratory system (including the individual's anatomy, age, sex, disease, lung volume). While concerns exist about the potential adverse reactions of the immune system to therapeutic proteins and peptides delivered to and through the lung, there is not much data on the immune response or its link to any safety issues with inhaled biologics. Desirable systemic immune effects have been demonstrated by cytokine delivery to the lung.

Granulocyte-macrophage colony-stimulating factor inhalation therapy for patients with idiopathic pulmonary alveolar proteinosis: a pilot study; and long-term treatment with aerosolized granulocyte-macrophage colony-stimulating factor: a case report

Idiopathic pulmonary alveolar proteinosis (IPAP) is considered to be caused by an autoantibody to the granulocyte-macrophage colony-stimulating factor (GM-CSF), which neutralizes GM-CSF and therefore impairs the differentiation of alveolar macrophages. The authors have previously characterized the BAL fluid and alveolar macrophages obtained from three IPAP patients who were successfully treated with aerosolized GM-CSF and demonstrated restoration of the cell number, expression of surface marker, and phagocytic ability of the alveolar macrophages as well as a decrease in the autoantibody levels in the BAL fluid. The condition recurred in one of the patients after 20 months. This patient underwent a second and third course of GM-CSF inhalation therapy with the same dose and schedule as the first one. Since the second therapeutic intervention did not succeed in producing any improvement in the symptoms and disease markers, the authors used a new nebulizer and a liquid preparation of the drug instead of the lyophilized preparation for the third therapeutic session and this restored the respiratory function considerably. A 6-month maintenance therapeutic regimen with a lower GM-CSF inhalation frequency brought about a further improvement in the disease markers. The results suggest that the efficacy of GM-CSF inhalation therapy might be related to the drug preparation mode, choice of nebulizer, and duration of treatment.

Antibody response to inhaled insulin in patients with type 1 or type 2 diabetes. An analysis of initial phase II and III inhaled insulin (Exubera) trials and a two-year extension trial

OBJECTIVE

To compare antibody responses to inhaled human insulin vs. sc human insulin and to determine whether insulin antibody binding is associated with adverse clinical consequences.

RESEARCH DESIGN AND METHODS

Insulin antibody data from initial phase II/III trials were analyzed comparing the efficacy and safety of inhaled insulin with various agents, including sc insulin. Additionally, data from a 24-month extension of the phase III studies were examined. Data were pooled into the following three groups based on insulin treatment status at baseline: patients with type 1 diabetes, and patients with type 2 diabetes using insulin and not using insulin at baseline. Ig class analysis was also performed on randomly selected sera from type 1 patients at the end of the initial trials.

RESULTS

In the initial trials, greater insulin antibody binding was observed in patients receiving inhaled insulin vs. sc insulin. The greatest antibody responses to inhaled insulin were observed in patients with type 1 diabetes [nonparametric comparison of medians at the end of the study, 22.0% binding (unadjusted 95% confidence interval: 19.5, 24.5)], and the lowest responses were observed in non-insulin-using patients with type 2 diabetes in which there was no difference in median values at the end of the study. There were no correlations between antibody binding and glycemic control (measured using glycosylated hemoglobin), insulin dose requirements, hypoglycemic events, or pulmonary function (measured by changes in forced expiratory volume in 1 sec and diffusion capacity of carbon monoxide). Antibody responses were IgG in type. Differences in antibody levels observed in patients with type 1 vs. type 2 diabetes were maintained over the 24-month extension trials. Peak antibody levels across all groups were generally observed after 6-12 months of insulin therapy. Inhaled insulin therapy was not associated with a greater incidence of allergy or other hypersensitivity reactions.

CONCLUSION

Inhaled insulin was observed to produce a larger antibody response than sc insulin. Insulin antibody binding has not been associated with adverse clinical consequences in trials to date.

Renal-selective delivery and angiotensin-converting enzyme inhibition by subcutaneously administered captopril-lysozyme

In previous studies, we have demonstrated that the low molecular weight protein lysozyme can be used as a renal-selective drug carrier for delivery of the angiotensin-converting enzyme (ACE) inhibitor captopril. Typically, such macromolecular drug-targeting preparations are administered intravenously. In the present study, we investigated the fate of captopril-lysozyme following subcutaneous administration, a convenient route for long-term treatment. The absorption from the subcutaneous injection site and renal uptake of lysozyme were determined by gamma scintigraphy in rats. Bioavailability, renal accumulation, and stability of the captopril-lysozyme conjugate were evaluated by high performance liquid chromatography analysis and by ACE activity measurements. Lysozyme was absorbed gradually and completely from the subcutaneous injection site within 24 h and accumulated specifically in kidneys. After subcutaneous injection of the captopril-lysozyme conjugate, higher renal captopril levels and lower captopril-lysozyme levels in urine indicated the improved renal accumulation in comparison with intravenous administration of the conjugate, as well as its stability at the injection site. After both treatments, captopril-lysozyme conjugate effectuated renal ACE inhibition, whereas plasma ACE was not inhibited. In conclusion, our results demonstrate that we can use the subcutaneous route to administer drug delivery preparations like the captopril-lysozyme conjugate.

State of insulin self-association does not affect its absorption from the pulmonary route

This study is designed to compare and contrast the pulmonary absorption profiles of monomeric and hexameric insulin in the presence or absence of ethylene diamine tetraacetic acid (EDTA) or n-tetradecyl-beta-d-maltoside (TDM). The pulmonary absorption of two forms of insulin was studied by monitoring the changes in plasma insulin and glucose levels after intratracheal administration of monomeric or hexameric insulin into anesthetized rodents. EDTA or TDM was added to the formulation in order to evaluate if either of these agents has effects on the rate and extent of pulmonary absorption of monomeric and hexameric insulin. The biochemical changes that may occur after acute administration of TDM-based formulation have also been investigated by estimating lung injury markers in bronchoalveolar lavage fluid. A dose-dependent increase in the plasma insulin and decrease in plasma glucose levels was observed when increasing concentrations of hexameric or monomeric insulin were administered via the pulmonary route. Pulmonary administration of monomeric and hexameric insulin produced comparable absorption profiles in the presence or absence of EDTA or TDM. The bronchoalveolar lavage fluid analysis did not show differences in the levels of injury markers produced in TDM-treated rats and that produced in saline-treated rats, indicating no evidence for adverse effects of TDM in these short-term studies. Overall, in terms of rapidity of action and efficacy to reduce blood sugar, monomeric insulin did not provide advantages over hexameric insulin when administered via the pulmonary route.

Carrier-based strategies for targeting protein and peptide drugs to the lungs

With greater interest in delivery of protein and peptide-based drugs to the lungs for topical and systemic activity, a range of new devices and formulations are being investigated. While a great deal of recent research has focused on the development of novel devices, attention must now be paid to the formulation of these macromolecular drugs. The emphasis in this review will be on targeting of protein/peptide drugs by inhalation using carriers and ligands.

Waiting to inhale: noninjectable insulin, are we there yet?

Subcutaneous injection has been the only route of insulin administration for patients with type 1 or type 2 diabetes for the past 80 years. Although research and development in this time has improved the insulin treatments themselves, it is only now that alternative routes of insulin administration are becoming viable. Many avenues of insulin administration have been explored, including oral, buccal, and pulmonary routes. However, these methods of noninvasive insulin delivery are not free from difficulties and only preliminary data are available for oral insulin pills and buccal insulin sprays. The most promising alternative route of delivery appears to be inhaled insulin and two devices are already in phase III testing. Nevertheless, inhaled insulin devices will still have to overcome some problems and recent studies show that these challenges are currently being confronted. It appears that years of research into noninvasive methods of insulin administration are close to fruition and this review outlines the most recent findings in this area.

Impact of formulation and methods of pulmonary delivery on absorption of parathyroid hormone (1–34) from rat lungs

The aim of this work was to optimize the absorption of parathyroid hormone 1-34 (PTH) from the lungs by determining factors favoring its transport from the air spaces into the bloodstream. We simultaneously conducted pharmacokinetic and regional lung deposition studies in vivo in the rat following intratracheal administration of PTH in solution or dry powder form. Dry powders of PTH or albumin were prepared by spray-drying using lactose and dipalmitoylphosphatidylcholine (DPPC). Deposition in the trachea, peripheral, and central lobe sections was assessed after tissue grinding using albumin as a marker. The method of intratracheal instillation had a significant impact on PTH absorption from the lungs, and the deeper the deposition within the respiratory tract, the higher the absorption. Inhalation of the PTH powder resulted in high systemic bioavailability despite deposition of the formulation principally in upper airways. We demonstrated that the increased absorption resulted from DPPC that had permeation enhancer properties even though it was abundantly present locally in pulmonary surfactant. Optimization of PTH absorption from the lungs could be attained by targeting the peripheral lungs as well as codelivering DPPC.

Absorption enhancers in pulmonary protein delivery

Extensive research efforts have been directed towards the systemic administration of therapeutic proteins and poorly absorbed macromolecules via various nontraditional, injection-free administration sites such as the lung. As a portal for noninvasive delivery, pulmonary administration possesses several attractive features including a large surface area for drug absorption. Nevertheless, achieving substantial bioavailability of proteins and macromolecules by this route has remained a challenge, chiefly due to poor absorption across the epithelium. The lungs are relatively impermeable to most drugs when formulated without an absorption enhancer/promoter. In an attempt to circumvent this problem, many novel absorption promoters have been tested for enhancing the systemic availability of drugs from the lungs. Various protease inhibitors, surfactants, lipids, polymers and agents from other classes have been tested for their efficacy in improving the systemic availability of protein and macromolecular drugs after pulmonary administration. The purpose of this article is to provide the reader with a summary of recent advances made in the field of pulmonary protein delivery utilizing absorption enhancers. This report reviews the various agents used to increase the bioavailability of these drugs from the lungs, their mechanisms of action and effectiveness, and their potential for toxicity.

Alveolar macrophages are a primary barrier to pulmonary absorption of macromolecules

We demonstrate that a primary source of elimination of inhaled macromolecules after delivery to the lungs and before absorption into the systemic circulation owes to clearance by alveolar macrophages (AM). Depletion of AM by liposome-encapsulated dichloromethylene diphosphonate is shown to cause severalfold enhancement in systemic absorption of IgG and human chorionic gonadotropin after intratracheal instillation in rats. Lowering the doses of IgG delivered to the lungs alleviates local degradation and results in a dramatic increase in systemic absorption of the protein as well. Chemical and physical means of minimizing uptake of macromolecules by AM are proposed as novel methods for enhancing protein absorption from the lungs. Such strategies may have important ramifications on the development of inhalation as an attractive mode of administration of therapeutic proteins to the bloodstream.