This is the fourth paper in a series describing an inhalation biopharmaceutics classification system (iBCS), an initiative supported by the Product Quality Research Institute. The paper examines the application of the inhalation Biopharmaceutics Classification System (iBCS) through the drug discovery, development, and postapproval phases for orally inhaled drug products (OIDP) and for the development of generic OIDPs. We consider the implication of the iBCS class in terms of product performance and identify the practical gaps that must be filled to enable the classification system to be adopted into day-to-day practice. Consideration is given to the critical experimental data required and the methods for their generation with a focus on: (i) dose to the lungs, (ii) drug solubility in relevant media and methods to model the dissolution of respirable formulations, and (iii) pulmonary drug permeability. As described in three prior publications, the iBCS was developed to classify inhaled drugs based on physicochemical and biorelevant product attributes in a manner that will allow formulators and discovery chemists to identify and mitigate product development risks. It was not established to enable in vitro determination of bioequivalence between orally inhaled drug products. However, once analytical methods are in place to correctly classify inhaled drugs, the system has the potential to provide an understanding of the development risks associated with both establishing bioequivalence between two drug products and enabling postapproval changes based on product iBCS class.

In this article, we specify for the first time a quantitative biopharmaceutics classification system for orally inhaled drugs. To date, orally inhaled drug product developers have lacked a biopharmaceutics classification system like the one developed to navigate the development of immediate release of oral medicines. Guideposts for respiratory drug discovery chemists and inhalation product formulators have been elusive and difficult to identify due to the complexity of pulmonary physiology, the intricacies of drug deposition and disposition in the lungs, and the influence of the inhalation delivery device used to deliver the drug as a respirable aerosol. The development of an inhalation biopharmaceutics classification system (iBCS) was an initiative supported by the Product Quality Research Institute (PQRI). The goal of the PQRI iBCS working group was to generate a qualitative biopharmaceutics classification system that can be utilized by inhalation scientists as a "rule of thumb" to identify desirable molecular properties and recognize and manage CMC product development risks based on physicochemical properties of the drug and the deposited lung dose. Herein, we define the iBCS classes quantitatively according to the dose number and permeability. The proposed iBCS was evaluated for its ability to categorize marketed inhaled drugs using data from the literature. The appropriateness of the classification of each drug was assessed based on published development, clinical and nonclinical data, and mechanistic physiologically based biopharmaceutics modeling. The inhaled drug product development challenges for each iBCS classification are discussed and illustrated for different classes of marketed inhaled drugs. Finally, it is recognized that discriminatory laboratory methods to characterize regional lung deposition, dissolution, and permeability will be key to fully realizing the benefits of an iBCS to streamline and derisk inhaled drug development.

For oral drugs, the formulator and discovery chemist have a tool available to them that can be used to navigate the risks associated with the selection and development of immediate release oral drugs and drug products. This tool is the biopharmaceutics classification system (giBCS). Unfortunately, no such classification system exists for inhaled drugs. The perspective outlined in this manuscript provides the foundational principles and framework for a classification system for inhaled drugs. The proposed classification system, an inhalation-based biopharmaceutics classification system (iBCS), is based on fundamental biopharmaceutics principles adapted to an inhalation route of administration framework. It is envisioned that a classification system for orally inhaled drugs will facilitate an understanding of the technical challenges associated with the development of new chemical entities and their associated new drug products (device and drug formulation combinations). Similar to the giBCS, the iBCS will be based on key attributes describing the drug substance (solubility and permeability) and the drug product (dose and dissolution). This manuscript provides the foundational aspects of an iBCS, including the proposed scientific principles and framework upon which such a system can be developed.

This work is the second in a series of publications outlining the fundamental principles and proposed design of a biopharmaceutics classifications system for inhaled drugs and drug products (the iBCS). Here, a mechanistic computer-based model has been used to explore the sensitivity of the primary biopharmaceutics functional output parameters: (i) pulmonary fraction dose absorbed (Fabs) and (ii) drug half-life in lumen (t1/2) to biopharmaceutics-relevant input attributes including dose number (Do) and effective permeability (Peff). Results show the nonlinear sensitivity of primary functional outputs to variations in these attributes. Drugs with Do < 1 and Peff > 1 × 10-6 cm/s show rapid (t1/2 < 20 min) and complete (Fabs > 85%) absorption from lung lumen into lung tissue. At Do > 1, dissolution becomes a critical drug product attribute and Fabs becomes dependent on regional lung deposition. The input attributes used here, Do and Peff, thus enabled the classification of inhaled drugs into parameter spaces with distinctly different biopharmaceutic risks. The implications of these findings with respect to the design of an inhalation-based biopharmaceutics classification system (iBCS) and to the need for experimental methodologies to classify drugs need to be further explored.

The Janus family of tyrosine kinases (JAK1, JAK2, JAK3, and TYK2) play an essential role in the receptor signaling of cytokines that have been implicated in the pathogenesis of severe asthma, and there is emerging interest in the development of small-molecule-inhaled JAK inhibitors as treatments. Here, we describe the optimization of a quinazoline series of JAK inhibitors and the results of mouse lung pharmacokinetic (PK) studies where only low concentrations of parent compound were observed. Subsequent investigations revealed that the low exposure was due to metabolism by aldehyde oxidase (AO), so we sought to identify quinazolines that were not metabolized by AO. We found that specific substituents at the quinazoline 2-position prevented AO metabolism and this was rationalized through computational docking studies in the AO binding site, but they compromised kinome selectivity. Results presented here highlight that AO metabolism is a potential issue in the lung.

Controlled-release formulations, in the form of micro- or nanoparticles, are increasingly attractive to the pharmaceutical industry for drug delivery. For respiratory illnesses, controlled-release microparticle formulations provide an opportunity to deliver a higher percentage of an inhaled medicament dose to the lung, thus potentially reducing the therapeutic dose, frequency of dosing, and minimising side-effects. We describe the use of a multimodal approach consisting of MALDI MS imaging, 3D depth profiling TOF-SIMS analysis, and histopathology to monitor the distribution of drug and excipients in sections taken from excised rat lungs following an inhaled administration of drug-laden microparticles. Following a single dose, the administered drug was detected in the lung via both MALDI MS and TOF-SIMS over a range of time points. Both imaging techniques enabled the characterisation of the distribution and retention of drug particles and identified differences in the capabilities of both imaging modalities. Histochemical staining of consecutive sections was used to provide biological context to the findings and will also be discussed in this presentation. We demonstrate how this multimodal approach could be used to help increase our understanding of the use of controlled release microparticles.

An alternative approach has been developed to estimate the clinical dose of new drug molecules at an early stage in the drug discovery process. This approach has been compared to traditional methods using the clinical dose as indicated on the drug label of 136 marketed drugs. At the early stages of drug discovery only in silico predictions or some initial in vitro screening data are normally available, typically parameters such as affinity/potency (pXC50)from isolated enzymes or receptors, measured albumin and phospholipid binding using biomimetic HPLC measurements, and in vitro clearance using P450 enzymes or liver microsomes. The combination of the biomimetic HPLC phospholipid and protein binding provides a drug efficiency max parameter described previously (HPLC DEmax), and in vitro potency makes it possible to estimate a clinical dose that would result in an efficacious steady state free concentration at the site of action. The influence of the potential discrepancies between the in vitro and a later stage in vivo DEmax, the whole blood potency, volume of distribution and clearance on the dose estimation has been investigated, using data from a GSK programme profiled during lead optimisation. It was found that drug potency had the greatest influence on estimating the clinical dose. When the estimated dose is low, the impact of other parameters such as the volume of distribution and clearance was much less significant and typically did not affect compound ranking.

The drug discovery process can be accelerated by chromatographic profiling of the analogs to model in vivo distribution and the major non-specific binding. A balanced potency and chromatographically determined membrane and protein binding (IAM MB/PB) data enable selecting drug discovery compounds for further analysis that have the highest probability to show the desired in vivo distribution behavior for efficacy and reduced chance for toxicity. Although the basic principles of the technology have already appeared in numerous publications, the lack of standardized procedures limited its widespread applications especially in academia and small drug discovery biotech companies. In this paper, the standardized procedures are described that has been trademarked as Regis IAM MB/PB Technology®. Comparison between the Drug Efficiency Index (DEI=pIC50-logVdu+2) and generally used Ligand Lipophilicity Efficiency (LLE) has been made, demonstrating the advantage of measured IAM and HSA binding over calculated log P. The power of the proposed chromatographic technology is demonstrated using the data of marketed drugs.

Using X-ray crystallographic screening, fragments 4 and 6 were identified as inhibitors of hematopoietic prostaglandin D2 synthase (H-PGDS). Both fragments induced a small protein movement in the X-ray crystal structure relative to the apo structure, where the highly polar nature of the ligand complemented the induced protein conformation. The manuscript describes the fragment optimisation of 4 and 6 followed by fragment growth to lead molecule 10. This showed favourable physicochemical properties and evidence of oral activity in blocking PGD2 generation in vivo.

Dengue is the most prevalent mosquito‐borne viral disease, posing a public health threat to 2.5 billion people worldwide. No clinically approved vaccine or antiviral therapy is currently available. Toward the development of antivirals for the treatment of dengue virus, we have established and applied various cell‐based phenotypic assays to screen large compound libraries. Our screening effort has led to the identification of inhibitors of dengue virus with distinct modes of action. This chapter reviews (i) the overall approaches for anti‐dengue drug discovery, (ii) the current status of cellular phenotypic screening assays for dengue virus and (iii) characterization of three classes of small inhibitors identified from the phenotypic screening. It remains to be determined whether these inhibitors could be further developed into clinical candidates for the treatment of dengue virus infection. However, considering the success of cell‐based screening in the development of antivirals for human immunodeficiency virus and hepatitis C virus, we expect that phenotypic screening should ultimately yield clinical candidates for dengue virus in the near future.

Novel indole-3-thio-, 3-sulfonyl- and 3-oxy-aryl-1-acetic acids are reported which are potent, selective antagonists of the chemoattractant receptor-homologous expressed on Th2 lymphocytes receptor (CRTh2 or DP2). Optimization required maintenance of high CRTh2 potency whilst achieving a concomitant reduction in rates of metabolism, removal of cyp p450 inhibition and minimization of aldose reductase and aldehyde reductase activity. High quality compounds suitable for in vivo studies are highlighted, culminating in the discovery of AZD1981 (22).

The design and synthesis of a new series of c-Jun N-terminal kinase inhibitors are reported. The novel series of substituted amino indazoles were designed based on a combination of hits from high-throughput screening and X-ray crystal structure information of the compounds crystallised into the JNK-1 ATP binding site.