Anion Carriers for Channel Replacement Therapy

The common, life-shortening inherited disease cystic fibrosis (CF) is characterised by defective anion transport across cell membranes. The proposed research aims to develop chemicals which are capable of transporting anions across cell membranes, and are ready for testing in humans after safety studies are completed.

Almost 11,000 people live with CF in the UK and >70,000 worldwide. The disease is caused by malfunction of a protein, the cystic fibrosis transmembrane conductance regulator (termed CFTR), which allows the transport of anions (e.g. chloride and bicarbonate) across cell membranes. When CFTR is faulty or missing from the cell membrane, ducts and tubes in the body 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.

A novel approach to treat the root cause of CF is "CFTR replacement therapy" using anionophores (anion carriers). Anionophores are synthetic small molecules which are designed to replace the action of CFTR, by picking up anions on one side of the membrane, carrying them across, and releasing them on the far side. After their delivery to the lungs by inhalation and insertion into cell membranes, anionophores could rescue normal levels of anion transport and, through a chain of effects, restore the healthy mucus which is easily cleared from the lungs.

In earlier work, we and others have shown that it is indeed possible to design small molecules which insert into membranes and mediate transmembrane anion transport. Some of our systems are capable of very high activity approaching that of CFTR. Importantly, a few anionophores, with drug-like properties, are capable of efficient delivery to cell membranes, where they work for prolonged periods, transporting anions into and out of cells, without signs of toxicity.

Based on our previous results, there is good reason to believe that anionophores could be used to treat CF. This project will take critical steps towards realising this goal. The work will be performed by a collaboration involving chemists and physiologists in Bristol, and a chemistry group in Sydney, Australia (funded separately). Initially we will work towards optimising activity in cells, identifying the best candidates for closer examination. We will then apply a series of tests on tissues lining ducts and tubes (as opposed to individual cells) designed to validate our hypothesis that anionophores can restore normal function in CF patients. Meanwhile we will perform in-depth studies on anionophore behaviour, in both synthetic and natural membranes, so that biomedical development can rest on firm foundations. This will include selectivity and mechanistic investigations, as well as fluorescence microscopy to ascertain anionophore distribution in cells. We will also test new delivery systems which could be used to help anionophores reach cell membranes. At the end of the project we will have set the stage for clinical studies, potentially leading to treatments for CF.

Anion transporters (anionophores) are actively studied by supramolecular chemists, with the aim of discovering useful biological effects. In particular, it is hoped that anionophores might be used to bypass the malfunctioning anion channels which underlie "channelopathies" such as cystic fibrosis (CF). However, while much progress has been made on anion transport across synthetic membranes, the effects of anionophores on cells is less well studied. This proposal involves a collaboration between two supramolecular chemists (A.P. Davis and P.A. Gale) and a biophysicist (D.N. Sheppard) which aims to fulfil the biological potential of anionophores, with particular focus on the treatment of CF. In a project funded through EPSRC, we explored a range of anionophore architectures, demonstrating very high activities. We also developed an assay for anion transport in cells, finding that some agents were both highly effective and non-cytotoxic. Here we aim to progress our work to the point where clinical studies can be justified.

The research will involve: (a) Identifying optimal candidates for clinical development through synthesis and testing in cells, employing a variant of the previously-developed assay; (b) Testing candidates in polarised epithelia, including the demonstration that anionophores can restore function to CF airway epithelia and promote the recovery of mucociliary transport; (c) Mechanistic studies that will lead to an improved understanding of anionophore activity in membranes, as well as distribution in cells; (d) The design, synthesis and study of anionophores with optimised selectivity, especially for chloride vs. OH-/H+; (e) The development of delivery systems that allow a greater range of agents to be studied in cells.

As well as providing a platform for clinical development, the above work will serve to develop and characterise a set of selective anion transporters which can be offered to the biomedical community for use as research tools.

This project will impact society in four respects.

First, Health Research and Medicine. Individuals afflicted by cystic fibrosis (CF) will be the major beneficiaries of the proposed research. We aim to develop an innovative approach to treat patients suffering from this common, life-shortening inherited disease. Our therapeutic strategy tackles the root cause of the disease, defective anion transport, which leads to ducts and tubes throughout the body becoming blocked by thick, sticky mucus. By tackling the cause of CF, rather than its symptoms, our approach has the potential to enhance the quality of life and longevity of individuals with CF. Because other lung diseases (e.g. chronic obstructive pulmonary disease, a leading cause of death globally) have symptoms resembling those of CF, new therapies for CF have the potential to benefit many more individuals than those with the disease. In addition, by providing a new tools for membrane research, we will contribute to progress in a range of medically-relevant research programmes.

Second, the Economy. The development of an innovative new therapy for CF has economic implications. CF is the most common rare genetic disease affecting >70,000 people worldwide, representing a significant market. A number of pharmaceutical companies, including large multi-nationals, SMEs and new start-ups, are actively developing transformational new therapies that target the root cause of CF. On completion of the proposed research, we expect to have developed an anionophore for clinical testing. Commercial exploitation of this small molecule is therefore a realistic possibility.

Third, Training. The PDRAs undertaking the research will gain valuable insight into drug development. Not only will they acquire skill and expertise in synthetic chemistry, membrane biophysics and cell biology, 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 careers fairs to learn about employment opportunities.

Fourth, Public Understanding of Science. Our approach to treat CF serves as an excellent example of how intervention at a molecular level, with rationally designed agents, can be used to address a major medical problem. This is an excellent story, which we know has wide appeal. We will disseminate it to the public through outreach activities and when appropriate press releases. Those affected by CF (patients, their families and supporters) will be especially interested as will school students considering careers in chemistry and biomedical research. We will therefore make particular efforts to reach these key audiences.