Developing Novel Therapies for the Treatment of Respiratory Diseases

We recently had the pleasure of speaking with Martin Gosling, Enterprise Therapeutics’ CSO and Professor of Molecular Pharmacology at the University of Sussex. Martin highlights the respiratory diseases Enterprise Therapeutics primarily focus on and the new disease modifying therapies they have in development.

Laura Lansdowne (LL): Could you tell us more about Enterprise Therapeutics’ scientific strategy to treating respiratory diseases? Are there particular diseases you primarily focus on?

Martin Gosling (MG): Each day we inhale around 11,000 liters of air which contains potentially harmful dust and microbes, such as viruses and bacteria. Mucus clearance is key to effectively removing these agents from the airways to preserve lung health. One of the most important determinants of the efficiency of mucus clearance is its hydration state. Mucus is initially produced in a dehydrated form within goblet cells which line the airway. Once secreted, mucus absorbs water to become a sticky but low viscosity gel. In healthy individuals, it’s 97% water. So, the ratio between the amount of mucus and amount of fluid available to hydrate it is incredibly important. An increase in the number of goblet cells and/or a reduction in the amount of airway fluid results in poorly hydrated, thick and sticky mucus which is difficult to clear and can consequently damage the lungs. In severe situations, the mucus can plug the airway completely, leading to a significant loss ofairway function. Enterprise Therapeutics is discovering and developing new therapies that target ion channels TMEM16A and ENaC to increase the hydration and clearance of mucus. Enterprise has also identified novel targets and compounds that reduce mucus production, an approach that complements mucus hydration therapies.

Mucus obstruction is a characteristic of many respiratory diseases including severe asthma, chronic obstructive pulmonary disease and chronic bronchitis, but is most severe in cystic fibrosis (CF), which is our primary disease focus. CF is a devastating genetic disease with an incidence of 1:2500 births and a current life expectancy of only 40 years. CF patients have a significant reduction in the hydration of their mucus (it’s only 85% water) leading to failed clearance, a high incidence of infections and rapid decline in lung function.

LL: Could you elaborate on the compounds featured in your development pipeline? Can you provide us some insight into their therapeutic targets and mechanism of action?

MG: Enterprise currently has three active drug discovery programs, two aimed at increasing mucus hydration and one aimed at reducing the amount of mucus itself.

The hydration status of the airways is controlled by ion channels. In airway epithelial cells, the flux of ions is followed by osmotically obligated water, therefore ion channels are pivotal to controlling the amount of water in the airways available to hydrate mucus. A key secretory pathway for the flow of fluid into the airways is the cystic fibrosis transmembrane conductance regulator (CFTR). This channel allows anions (chloride and bicarbonate) to flow into the airways and is the channel that is dysfunctional in CF, leading to the dehydrated, thickened mucus. There is however another anion channel present in airway epithelial cells, called TMEM16A. Enterprise has discovered first-in-class “potentiator” compounds which enhance the activity of TMEM16A. By doing so, these compounds increase anion and fluid flow into the airways, thinning the mucus and increasing its clearance. Our data show TMEM16A potentiation can minimally achieve equivalent pre-clinical efficacy to that of CFTR repair, and is independent of the mutational status of CFTR, making the approach applicable to all CF patients, and patients with non-CF lung disease.

There is also an ion channel that leads to fluid absorption from the airways – this channel, the epithelial sodium channel (ENaC), allows the influx of sodium ions and hence fluid out of the airways. Interestingly there are patients that have genetic loss of function mutations in ENaC – these patients have an increase in airway surface liquid and clear mucus at a rate about four times faster than individuals with normal ENaC function. Enterprise has identified proprietary compounds which inhibit the activity of ENaC, thus inhibiting the removal of fluid from the airways. These compounds are favorably retained in the lung, and therefore expected to provide a superior efficacy and safety profile compared to other ENaC drug candidates.

Our third program is aimed at reducing the number of mucus producing goblet cells. In addition to goblet cells there are several other cell types lining the airways, including ciliated cells, which are functionally responsible for moving mucus along and out of the airways. Although goblet and ciliated cells are very different, they arise from the same progenitor cell, an airway stem cell called the basal cell. The high plasticity of the basal cell means its surrounding environment will influence whether it chooses to differentiate into a ciliated or goblet cell. This plasticity is important to the lung as it allows it to adapt to changing conditions. For example, if the lung becomes infected with a virus or bacteria the number of goblet cells can be easily upregulated, increasing the amount of mucus available to clear the infection. However, in multiple respiratory diseases this process becomes unbalanced and the ratio between ciliated and goblet cells strongly favors goblet cells. At Enterprise, we have identified a drug target that can influence the basal cells to preferentially differentiate into ciliated cells, both reducing the number of mucus producing cells and increasing the number of mucus transporting cells.

LL: Could you tell us more about the drug discovery approaches used for the creation of these compounds?

MG: Our projects have employed a combination of conventional and more innovative approaches to deliver the portfolio. For example, with the TMEM16A project we already knew the target but needed to find a chemical starting point for the program. Somewhat conventionally we took the route of medium/high throughput screening with low molecular weight compound libraries. However, the assay formats we used included the automated high throughput electrophysiology. We felt it was important to use an assay that had direct measurement of ion flow through the channel, accurate control of the factors known to open the channel (intracellular calcium & voltage), and a high signal to noise ratio to detect low activity compounds. In the end the output of all of our screening efforts went through the automated electrophysiology assay.

In contrast, for our goblet cell reduction program we first had to identify an appropriate target. There are a number of ways to identify new drug targets, each with their advantages and disadvantages. Within Enterprise we place a great deal of emphasis upon human cell-based systems as we feel these have the highest translational value into the clinical setting. So, we used a primary human bronchial epithelial (HBE) cell-based screen. HBE cells are a precious and limited resource, requiring substantial effort to culture and maintain. Conventionally they are grown on filters at an air liquid interface (ALI) to mimic the airway setting. Culturing enough filters to undertake even a small screen is challenging, so we used a state-of-the-art high throughput phenotypic assay pioneered by one of Enterprise’s founders, Henry Danahay. In this assay the HBEs are seeded into a 3D gel matrix where they form “bronchospheres”. Bronchospheres are fluid filled spheres that contain goblet and ciliated cells, recapitulating much of the airway cell architecture. The big advantage for us was that they can be grown in 384 well plates and require significantly lower cell numbers and resources than the ALI filters. Once we had used the bronchospheres to identify a drug target, it was a case of executing a traditional discovery program.

LL: What impact could these drugs have for patients in the future?

MG: Aspirationally, we hope that our drugs will deliver a significant impact for patients with CF and potentially those with other respiratory diseases. The current focus for CF approved therapeutics is on CFTR repair. Drugs which restore function to CFTR have been launched recently, the first being Kalydeco (Ivacaftor) by Vertex in 2012. These drugs are having an impressive impact on the lung function of many CF patients, however this approach does not treat the ≥10% of CF patients with nonsense mutations, and does not cure CF or reduce the decline in lung function to levels associated with normal health. As our approaches are not dependent upon CFTR they should be suited to all patients with CF. Additionally we anticipate that they will deliver benefit in combination with CFTR repair drugs, further improving the lung health of patients.

Martin Gosling was speaking to Laura Elizabeth Lansdowne, Science Writer for Technology Networks.