Synthetic Anionophores with Therapeutic Potential - a Coordinated Two-Centre Approach

The common life-shortening inherited disease cystic fibrosis (CF) is characterised by defective anion transport across cell borders (or membranes) lining ducts and tubes throughout the body. The proposed research aims to develop chemicals capable of transporting anions across cell membranes. These synthetic transporters might be used to develop a therapy that restores anion transport to CF tissues. They should also have value as tools for biomedical research.

CF affects over 8,500 individuals in the UK of whom 60% are less than 20 years old. In CF, malfunction of a particular protein, the cystic fibrosis transmembrane conductance regulator (termed CFTR) causes ducts and tubes throughout the body to become blocked by thick, sticky mucus. In the lungs, this triggers a vicious cycle of infection and inflammation that destroys lung tissue, leading to breathing difficulties, poor quality of life and premature death.

CFTR is normally found on the surface of cells lining ducts and tubes, where it acts as a passive gated pathway for the movement of anions, such as chloride and bicarbonate. By controlling chloride and hence salt and water movements, CFTR lubricates ducts and tubes, while bicarbonate is critical for normal mucus formation and movement.

A novel approach to CF treatment is "CFTR replacement therapy" with anionophores (ion transporters selective for anions). Anionophores are small molecules that mimic the actions of anion channels by transferring anions across the barrier presented by biological membranes. Following their delivery to the lungs by inhalation, anionophores could insert into the cell membrane, replace missing CFTR activity and restore, for a period, normal mucus transport. To test the feasibility of this approach suitable anionophores must be developed. In particular, activities must be high (so that small amounts can be used), and the molecules must have proven effectiveness in live cells (as opposed to synthetic model membranes).

Working independently the teams at Bristol and Southampton have made significant contributions to this problem, producing and studying anionophores which are among the most active available. In the proposed work they will join forces to bridge the gap between "proof-of-principle" and meaningful, potentially therapeutic, biological activity.

To develop novel anionophores for CFTR bypass therapy, we seek chemicals which bind anions strongly, insert easily into cell membranes and which satisfy rules for drug-like molecules. We will create such small molecules by fusing elements of the Bristol and Southampton anionophores to form novel anion carriers. We will determine how tightly the anionophores bind chloride and bicarbonate and how easily they pass these anions across synthetic model membranes. For selected chemicals, we will perform tests in model membranes using sophisticated electrical methods to establish their exact mechanism of action.

To identify anionophores that are effective in live cells, we will use cells engineered to express an anion-sensitive fluorescent protein to screen large numbers of molecules for transport activity. Compounds that demonstrate optimal deliverability and anion transport activity will be subjected to further biological testing using cells that line the air passages of CF lungs. First, we will investigate whether anionophores restore salt and water transport to these cells. Then, we will determine whether anionophores promote mucus transport. Finally, we will perform preliminary tests for toxicity and other properties to assess whether the anionophores are likely to succeed as drugs. If results are favourable our studies will yield a persuasive case for anionophore-based CFTR replacement therapy, paving the way for a programme of drug development in collaboration with medical and industrial partners.

This project will impact on society in the following ways.

Health Research and Medicine: In the ideal scenario, sufferers from cystic fibrosis (CF) will be the major beneficiaries of this research. We aim to develop a novel approach to treat individuals afflicted by this common, life-shortening inherited disease. Our therapeutic strategy tackles the root cause of the condition - defective anion transport across the surface of cells lining ducts and tubes throughout the body. By tackling the cause of CF, our strategy has the potential to enhance the quality of life and longevity of individuals with the disease. Because other diseases [e.g. myotonia (muscle stiffness) and nephrolithiasis (kidney stones)] are caused by loss of anion transport, our therapeutic strategy will likely have benefit in a larger group than CF patients alone. The project will also have a more generalised impact on health research. Molecules which carry ions across membranes are important tools for research into cell biology, but thus far only cation-transporting agents have been available. By providing anion-transporting counterparts, we will make a valuable addition to the toolbox for biomedical research. This extra capability will facilitate the understanding of biological systems and thus the development of new treatments in many areas.

Economy: The relevance of the project to medicine (especially CF), and also to health research, has economic implications. CF is the commonest rare genetic disease, with some 70,000 sufferers in the developed world, constituting a significant market. Indeed several pharmaceutical companies (>10) are now seeking new approaches to treatment. If our anionophores are successful, commercial exploitation is a very realistic prospect.

Training: The PDRAs undertaking the research will gain valuable insight into drug development. Not only will they acquire skills and expertise in synthetic chemistry and biological screening, but they will also learn about project management and effective communication of research findings. We will mentor actively our PDRAs, providing them with advice on career development and encouraging them to attend appropriate training courses to refine transferable skills and career fairs to learn about employment opportunities.

Public Understanding of Science: Our approach to treating CF serves as an excellent example of how intervention at a molecular level, with rationally designed agents, can be used to address major medical problems. This is a good story which we will disseminate to the public through outreach activities, press releases etc. Those affected by the condition (sufferers and parents) will be especially interested, and we will make particular efforts to reach this audience.