Sussex Drug Discovery Centre (SDDC)

Respiratory Diseases

Respiratory diseases including COPD, cystic fibrosis and severe asthma remain areas of high unmet medical need and significant health burden. Although disparate in the underlying initiating factor(s) for the disease (eg. CF is a monogenetic disease whilst COPD and asthma are commonly polygenic), these diseases share some common symptomologies, most notably large amounts of mucus, reduced airway hydration and impaired mucociliary clearance (MCC) leading to the plugging of the small airways. To date there are no registered therapies for effective mucus management in broad respiratory disease populations, arguably the result of a lack of complex disease relevant screening systems to identify targets.

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Chronic levels of mucus leading to airway obstruction are a key feature of several respiratory diseases associated with high unmet medical need. Figure shows histological cross section of an airway from a healthy individual with a clear open airway lumen; this contrasts heavily with the airways from patients with cystic fibrosis and chronic bronchitis. The mucus plug expectorated from a severe asthmatic is several centimetres in length.

MCC is a key component of pulmonary innate (non-immune) defence and is the process by which ‘sticky’ mucus captures noxious particles and removes them from the airways. This process is highly dependent upon the balance between two specialised epithelial cell subtypes (goblet and ciliated cells) and additionally their ability to transport water into the airway.

Mucus clearance is governed by the co-ordinated balance between mucus containing goblet cells, ciliated cells and the volume of airway surface liquid available to effectively hydrate the mucus. In a number of respiratory diseases the balance is disturbed due to increased number of mucus producing goblets cells and/or reduction in the volume of airway surface liquid which is determined by ion channel activity

 

Our current respiratory discovery efforts are focussed in two areas:

Ion channel modulation

The ion flux pathways that control airway hydration have been defined in the main by the study of human genetics. Human loss of function mutations in CFTR (a cAMP regulated chloride channel) and the epithelial sodium channel (ENaC) precipitate two pathologies – cystic fibrosis (CF) and type II pseudohypoaldosteronism (PHA). CF is characterised by airway dehydration and impaired MCC, whilst conversely PHA patients have excess fluid in the airway lumen and display a MCC rate 3-4 time faster than normal. Despite our developed understanding of the ion channels controlling airway hydration these have not yet been fully or effectively pharmacologically exploited offering the potential to deliver novel therapies for respiratory disease.

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The airway lumen phenotypes of healthy individuals and patients with CF and PHA. Healthy individuals have well hydrated mucus (3% w/v solids) and effective MCC, the result of the co-ordinated balance between secretory (CFTR) and absorptive (ENaC) ion flux pathway. In CF patients the secretory pathway is dysfunctional leading to airway dessication, viscous mucus (10% w/v solids) and failed MCC. In contrast PHA patients with ENaC loss of function have excess hydration which leads to more effective MCC.

Epithelial cell fate and function

Understanding how the respiratory epithelium forms and responds to a variety of disease relevant insults provides the opportunity for the identification of new drug targets and associated therapies. In vitro assays which fully recapitulate airway epithelial architecture and function using human bronchial epithelial cells (HBECs), have been available for many years but are low throughput, resource intensive and costly. Culturing cells in a 3D matrix can generate fully differentiated cultures in a high throughput (384 well) fashion. These cultures, termed ‘bronchospheres’, require few cells per well and recapitulate the native airway responses thus facilitating investigation into a basic understanding of disease relevant pathways and approaches for pharmacological and therapeutic intervention in respiratory diseases.

Human bronchial epithelial ‘bronchosphere’ cultures. Left. Single well of a 384 well plate showing multiple bronchospheres; Middle. Bronchosphere formed from normal HBEC with staining showing the presence of a pseudostratified epithelium with ciliated cells and mucus (MUC5AC); Right. Bronchospheres treated with disease relevant inflammatory cytokine (IL-13) inducing a hypersecretory phenotype as evidence by loss of ciliated cells and increased mucus secretion.