Benchmarking of Human Dose Prediction for Inhaled Medicines from Preclinical In Vivo Data

Designing inhaled small molecule drugs for severe respiratory diseases: an overview of the challenges and opportunities

INTRODUCTION

Inhaled drugs offer advantages for the treatment of respiratory diseases over oral drugs by delivering the drug directly to the lung, thus improving the therapeutic index. There is an unmet medical need for novel therapies for lung diseases, exacerbated by a multitude of challenges for the design of inhaled small molecule drugs.

AREAS COVERED

The authors review the challenges and opportunities for the design of inhaled drugs for respiratory diseases with a focus on new target discovery, medicinal chemistry, and pharmacokinetic, pharmacodynamic, and toxicological evaluation of drug candidates.

EXPERT OPINION

Inhaled drug discovery is facing multiple unique challenges. Novel biological targets are scarce, as is the guidance for medicinal chemistry teams to design compounds with inhalation-compatible features. It is exceedingly difficult to establish a PK/PD relationship given the complexity of pulmonary PK and the impact of physical properties of the drug substance on PK. PK, PD and toxicology studies are technically challenging and require large amounts of drug substance. Despite the current challenges, the authors foresee that the design of inhaled drugs will be facilitated in the future by our increasing understanding of pathobiology, emerging medicinal chemistry guidelines, advances in drug formulation, PBPK models, and in vitro toxicology assays.

Optimization of Long-Acting Bronchodilator Dose Ratios Using Isolated Guinea Pig Tracheal Rings for Synergistic Combination Therapy in Asthma and COPD

The co-administration of a long-acting β2-agonist (LABA), and a long-acting muscarinic antagonist (LAMA), has been shown to be beneficial in the management of non-communicable chronic respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD). The resulting relaxation of the airways can be synergistically enhanced, reducing symptoms and optimizing lung function. This provides an insight into more effective treatments. In this study, the LABAs formoterol fumarate dihydrate (FOR) and indacaterol maleate (IND) were each associated with tiotropium bromide monohydrate (TIO) to assess their synergistic potential. This was done using an appropriate ex vivo model of isolated perfused guinea pig tracheal rings, and pharmacological models of drug interaction. Among the dose ratios studied for both types of combination, a higher synergistic potential was highlighted for FOR/TIO 2:1 (w/w). This was done through three steps by using multiple additions of drugs to the organ baths based on a non-constant dose ratio and then on a constant dose ratio, and by a single addition to the organ baths of specific amounts of drugs. In this way, the synergistic improvement of the relaxant effect on the airways was confirmed, providing a basis for improving therapeutic approaches in asthma and COPD. The synergy found at this dose ratio should now be confirmed on a preclinical model of asthma and COPD by assessing lung function.

Translating pharmacology models effectively to predict therapeutic benefit

Many in vitro and in vivo models are used in pharmacological research to evaluate the role of targeted proteins in a disease. Understanding the translational relevance and limitation of these models for analyzing the disposition, pharmacokinetic/pharmacodynamic (PK/PD) profile, mechanism, and efficacy of a drug, is essential when selecting the most appropriate model of the disease of interest and predicting clinically efficacious doses of the investigational drug. Here, we review selected animal models used in ophthalmology, infectious diseases, oncology, autoimmune diseases, and neuroscience. Each area has specific challenges around translatability and determination of an efficacious dose: new patient-specific dosing methods could help overcome these limitations.

Developing inhaled drugs for respiratory diseases: A medicinal chemistry perspective

Despite the devastating impact of many lung diseases on human health, there is still a significant unmet medical need in respiratory diseases, for which inhaled delivery represents a crucial strategy. More guidance on how to design and carry out multidisciplinary inhaled projects is needed. When designing inhaled drugs, the medicinal chemist must carefully balance the physicochemical properties of the molecule to achieve optimal target engagement in the lung. Although the medicinal chemistry strategy is unique for each project, and will change depending on multiple factors, such as the disease, target, systemic risk, delivery device, and formulation, general guidelines aiding inhaled drug design can be applied and are summarised in this review.

Drivers of absolute systemic bioavailability after oral pulmonary inhalation in humans

There are few studies in humans dealing with the relationship between physico-chemical properties of drugs and their systemic bioavailability after administration via oral inhalation route (Fpulm). Getting further insight in the determinants of Fpulm after oral pulmonary inhalation could be of value for drugs considered for a systemic delivery as a result of poor oral bioavailability, as well as for drugs considered for a local delivery to anticipate their undesirable systemic effects. To better delineate the parameters influencing the systemic delivery after oral pulmonary inhalation in humans, we studied the influence of physico-chemical and permeability properties obtained in silico on the rate and extent of Fpulm in a series of 77 compounds with or without marketing approval for pulmonary delivery, and intended either for local or for systemic delivery. Principal component analysis (PCA) showed mainly that Fpulm was positively correlated with Papp and negatively correlated with %TPSA, without a significant influence of solubility and ionization fraction, and no apparent link with lipophilicity and drug size parameters. As a result of the small sample set, the performance of the different models as predictive of Fpulm were quite average with random forest algorithm displaying the best performance. As a whole, the different models captured between 50 and 60% of the variability with a prediction error of less than 20%. Tmax data suggested a significant positive influence of lipophilicity on absorption rate while charge apparently had no influence. A significant linear relationship between Cmax and dose (R² = "0.79) highlighted that Cmax was primarily dependent on dose and absorption rate and could be used to estimate Cmax in humans for new inhaled drugs.

In vitro and in vivo antitubercular activity of benzothiazinone-loaded human serum albumin nanocarriers designed for inhalation

The aim of this study was to investigate the potential of human serum albumin (HSA) as a solubilising agent/drug delivery vehicle for pulmonary administration of antimycobacterial benzothiazinone (BTZ) compounds. The solubility of four novel BTZ compounds (IR 20, IF 274, FG 2, AR 112) was enhanced 2 to 140-fold by incubation with albumin (0.38-134 μg/mL). Tryptophan 213 residue quenching studies indicated moderate binding strength to Sudlow's site I. Nanoparticle manufacture achieved 37-60% encapsulation efficiency in HSA particles (169 nm, zeta potential -31 mV). Drug release was triggered by proteases with >50% released in 4 h. The antimycobacterial activity of IR 20 and FG 2 loaded in HSA nanoparticles was enhanced compared to DMSO/phosphate buffered saline (PBS) or albumin/PBS solutions in an in vitro M. tuberculosis-infected macrophage model. Intranasal instillation was used to achieve pulmonary delivery daily over 10 days to M. tuberculosis infected mice for FG2 HSA nanoparticles (0.4 mg/kg), FG 2 DMSO/saline (0.4 and 8 mg/kg) and a reference compound, BTZ043, DMSO/saline (0.4 and 8 mg/kg). A lower lung M. tuberculosis burden was apparent for all BTZ cohorts, but only significant for BTZ043 at both doses. In conclusion, mechanisms of HSA nanoparticle loading and release of BTZ compounds were demonstrated, enhanced antimycobacterial activity of the nanoparticle formulations was demonstrated in a biorelevant in vitro bioassay and the effectiveness of BTZ by pulmonary delivery in vivo was established with pilot evidence for effectiveness when delivered by HSA nanoparticles. Finally, the feasibility of developing an inhaled nanoparticle-in-microparticle powder formulation was ascertained.

Airway Epithelial Lining Fluid and Plasma Pharmacokinetics of Inhaled Fluticasone Propionate and Salmeterol Xinafoate in Mechanically Ventilated Pigs

Background: The lower respiratory tract of the landrace pig has close anatomical and physiological similarities with that of the human, and hence, for inhalation studies this species is well suited for biopharmaceutical research. Methods: The objective of this study was to evaluate pharmacokinetics in pigs following one dose of Diskus™ Seretide™ forte device, labeled 500/50 fluticasone propionate (FP) and salmeterol xinafoate (SX), respectively. The PreciseInhale™ (PI) instrument was used to actuate the inhaler for in vitro testing and aerosol dosing to pigs. In vitro, the aerosol was characterized with a cascade impactor with respect to mass median aerodynamic diameter, geometric standard deviation, and fine particle dose. In vivo, dry powder inhalation exposure was delivered as a short bolus dose, to anesthetized and mechanically ventilated landrace pigs. In addition to plasma PK, PK assessment of airway epithelial lining fluid (ELF) was used in this study. ELF of the depth of three to fourth airway generation of the right lung was accessed using standard bronchoscopy and a synthetic absorptive matrix. Results and Conclusions: Dry powder inhalation exposures with good consistency and well characterized aerosols to the pig lung were achieved by the use of the PreciseInhale™ instrument. Drug concentrations of ELF for both FP and SX were demonstrated to be four to five orders of magnitude higher than its corresponding systemic plasma drug concentrations. Clinical PK following inhalation of the same dose was used as benchmark, and the clinical study did demonstrate similar plasma PK profiles and drug exposures of both FP and SX as the current pig study. Two factors explain the close similarity of PK (1) similiar physiology between species and (2) the consistency of dosing to animals. To conclude, our study demonstrated the utility and translational potential of conducting PK studies in pigs in the development of inhaled pharmaceuticals.

Contemporary Formulation Development for Inhaled Pharmaceuticals

Pulmonary delivery has gained increased interests over the past few decades. For respiratory conditions, targeted drug delivery directly to the site of action can achieve a high local concentration for efficacy with reduced systemic exposure and adverse effects. For systemic conditions, the unique physiology of the lung evolutionarily designed for rapid gaseous exchange presents an entry route for systemic drug delivery. Although the development of inhaled formulations has come a long way over the last few decades, many aspects of it remain to be elucidated. In particular, a reliable and well-understood method for in vitro-in vivo correlations remains to be established. With the rapid and ongoing advancement of technology, there is much potential to better utilise computational methods including different types of modelling and simulation approaches to support inhaled formulation development. This review intends to provide an introduction on some fundamental concepts in pulmonary drug delivery and inhaled formulation development followed by discussions on some challenges and opportunities in the translation of inhaled pharmaceuticals from preclinical studies to clinical development. The review concludes with some recent advancements in modelling and simulation approaches that could play an increasingly important role in modern formulation development of inhaled pharmaceuticals.

Dosing considerations for inhaled biologics

The number of biologics in the therapeutic development pipeline is increasing including those delivered though inhalation (Morales, 2017; Fathe, 2016). Biologics comprise a broad variety of complex macromolecules with unique physicochemical characteristics. These distinctive characteristics control their pharmacological mechanisms of action, stability, and ultimately affect their processing, formulation, and delivery requirements. This review systematically covers crucial aspects of biologic powders formulations and dry powder inhalers which need to be taken into consideration to establish the drug loading and the payload to be delivered to reach the desired clinical dose.

Translational model to predict pulmonary pharmacokinetics and efficacy in man for inhaled bronchodilators

Translational pharmacokinetic (PK) models are needed to describe and predict drug concentration‐time profiles in lung tissue at the site of action to enable animal‐to‐man translation and prediction of efficacy in humans for inhaled medicines. Current pulmonary PK models are generally descriptive rather than predictive, drug/compound specific, and fail to show successful cross‐species translation. The objective of this work was to develop a robust compartmental modeling approach that captures key features of lung and systemic PK after pulmonary administration of a set of 12 soluble drugs containing single basic, dibasic, or cationic functional groups. The model is shown to allow translation between animal species and predicts drug concentrations in human lungs that correlate with the forced expiratory volume for different classes of bronchodilators. Thus, the pulmonary modeling approach has potential to be a key component in the prediction of human PK, efficacy, and safety for future inhaled medicines.