Science for Health
Chemistry as a discipline currently suffers from a poor public image. This seems to arise from the perception that it is a difficult subject to learn and from its association with topics such as pollution, nuclear science, and the treatment of crops and foodstuffs with potentially toxic pesticides. Partly as a result, a number of University chemistry departments are reporting falling student numbers and some departments have been closed completely. Nevertheless, chemistry holds a key place in science and society in the modern world. Each one of us living in a developed country is surrounded by the consequences of chemical research, for better or worse depending on one’s individual views. Anyone doubting this might briefly consider their own body and clothing which, from head to toe, are beneficiaries of (or targets for, depending on one’s mindset) aspects of chemistry. A very brief list includes hair dyes, skin creams, self-darkening sun glasses, toothpaste, all modern processed foods and preserved traditional ones, synthetic fibres, materials for replacement joints, batteries in pacemakers and very importantly, the huge range of prescribed medicines. Beyond our immediate selves, the petrochemical industry underpins our daily activities by providing fuel for transport of people, goods and services, and the reagents for the vast range of man-made materials on which we have become reliant. The semiconductor industry, which has brought computing into everyday use, depends on chemistry for the fabrication of more and more powerful microprocessing chips and storage devices. Of course, in common with essentially all human activities, the use of chemical technology can have adverse effects, and environmental pollution and global warming are likely to have profound consequences. Ameliorating these and other problems will also certainly require the skills of chemists. A current example is the replacement of ozone-depleting chlorofluorocarbons (CFCs) as refrigerants and aerosol propellants by less harmful substitutes.
Given this enormous importance of chemistry to our lives, and in particular to the development and production of medicines, it is not surprising that aspects of the subject have been a central topic of research at NIMR almost from the inception of the Institute some ninety years ago. It is notable that of five Nobel prizes awarded to scientists who have spent substantial parts of their careers at the Institute, two were for chemistry. During the 1920s and 1930s a plethora of important chemical discoveries were made at the Institute, some of which passed rapidly into clinical use while others were key wayposts of knowledge in particular areas. Sir Henry Dale isolated acetylcholine, one of a family of neurotransmitters that pass nerve impulses to other nerve or muscle cells. Ergometrine was isolated by H.W. Dudley, from the ergot fungus that infects rye, and is still used as a drug in obstetrics to control post-delivery hæmorrhage. Tubocurarine, a muscle relaxant, was identified and isolated by H. King from the curare toxin used in hunting by Amazonian Indians. As a direct consequence of this work, a series of synthetic compounds was developed by King and collaborators in the mid-1930s and these are still used as muscle relaxants in surgery, permitting lighter and hence safer levels of anæsthesia than would otherwise be required. One of these compounds, hexamethonium, was the first clinically-effective drug for treatment of high blood pressure. Also in the mid-1930s, calciferol, known to most of us as Vitamin D2, was prepared by R.K. Callow as the first pure, chemicallyidentified vitamin. In due course this work led to the effective elimination of rickets, previously a common and debilitating disease in the UK and elsewhere. This work and related studies of the molecular structure of cholesterol by O. Rosenheim and H. King carried out at about the same time, provide interesting insights into the dual competitive and collegiate nature of scientific research. On the one hand, NIMR chemists competed with the long-established chemical laboratories of German universities and industry, and on the other, like all of the scientists mentioned above, they depended on close collaboration with their biomedical colleagues at Mill Hill.
NIMR was the coordinating centre of the MRC Chemotherapy Committee, established in the years between the first and second World Wars to foster drug development in the public sector by supporting work in various chemical and biological laboratories. Chemotherapy had effectively begun only in 1910 with the use of salvarsan as a treatment for syphilis and by the late 1920s there were still very few effective drugs. Furthermore, those that were available were largely the products of the German chemical industry and there was concern that another war would cut off supplies. It was also felt that Britain, then at the height of its imperial power, should be making efforts to combat the tropical diseases prevalent in many of the territories over which it held sway. Much work at NIMR was directed at anti-parasitic therapies, particularly malaria and sleeping sickness, but effective drugs proved hard to find. One of the more enduring legacies is the drug pentamidine, which was produced very soon after similar compounds were developed at the Institute in a search for drugs active against trypanosomes, the parasites responsible for African sleeping sickness. Pentamidine was initially used to treat sleeping sickness but more recently has been reintroduced as a therapy for Pneumocystis carinii pneumonia that frequently affects patients with AIDS.
During the post-World War II period some very important developments were made by A.J.P. Martin and R.L.M. Synge in separation techniques known as chromatography that allowed the analysis and purification of complex mixtures of chemical substances. Martin moved to NIMR in 1948 and further developed these techniques, notably by the invention of gas-liquid chromatography (GLC) which is still an important analytical tool. Various modern methods based on this pioneering work are in everyday use in applications such as synthetic chemistry, forensic science, industrial quality control, environmental monitoring and the detection of illicit drugs in sport. Under Martin’s guidance, I.E. Bush made related advances in another separation technique, paper chromatography. This played an important role in work from the 1950s onwards on naturally-occurring substances such as steroids, particularly in the isolation and characterisation of the salt-regulating steroid aldosterone. The invention of the electron capture detector by J.E. Lovelock in 1957 greatly increased the sensitivity of GLC and ultimately had significant influence on the developing environmental movement in the 1960s through its ability to detect low levels of pesticide residues and chlorofluoro compounds. Lovelock left NIMR in 1961 and is now more widely known for his Gaia theory of the Earth as a self-regulating system, but the ramifications of his invention of the electron capture detector remain with us today.
n the late 1940s Sir John Cornforth joined NIMR and, with George Popjak, began an extensive and elegant series of studies that used radioisotopes to determine how cholesterol is made in the body. This work, for which he was ultimately awarded a Nobel Prize in 1975, is directly relevant to the modern statin drugs which are used to reduce cholesterol levels and thereby to diminish fatty deposits that otherwise restrict the flow in blood vessels. Statins act on an enzyme involved in cholesterol synthesis, one of the many enzymes studied in Cornforth’s steroid work. In another area of his work past and present research at NIMR are neatly linked, since Cornforth also published a method for the synthesis of N-acetylneuraminic acid. This compound is a component of the sugars that are attached to the outer membranes of animal cells and to which the influenza virus binds as the first step in its invasion of cells that ultimately results in an attack of flu. The structural details of this binding have been a major topic of recent and current research on influenza at NIMR. A former student of Cornforth’s, Roy Gigg was also a carbohydrate chemist engaged in the synthesis of inositol phosphates. These are important molecules that are used by cells as internal “messengers” to control various functions in response to outside stimuli. At the time, the actions of these compounds had only just been discovered and his work greatly assisted studies of their biological function.
Chemistry coupled to Biology has been a major influence on the success of the Institute’s research and not surprisingly, there are a number of current research programmes that depend on similar interactions. Two general areas have particular importance: fluorescent labelling of biological molecules, and the development of compounds that can be made biologically active in response to a brief flash of light.
Fluorescence is a property of some molecules that causes them to emit light when they are illuminated by light of a shorter wavelength. If a biological molecule can be altered, or labelled, to make it fluorescent then it can be detected when it is illuminated by light of the appropriate wavelength. Various sorts of information can become available, including the cellular environment of the molecule and its orientation with respect to, or its association with, other molecules. Fluorescence is a technique that is widely used in life science research generally but particular developments here have opened up new possibilities for tracking the metabolism of the biological molecule adenosine 5’-triphosphate (ATP). ATP is the immediate source of energy for muscle contraction and for many other functions within cells including the replication of nucleic acids and the movements of molecules and organelles within cells. In these activities, part of the ATP molecule is split off by a process called hydrolysis, generating an inorganic phosphate ion as a by-product. Thus measuring changes in inorganic phosphate ion production provides a way of following a biological process that involves hydrolysis of ATP. Unfortunately the methods to do this were tedious and did not permit measurements to be made in real time.
Seeking to improve on existing methods, the approach we took was to use a protein produced in nature by the common bacterium Escherichia coli. Each molecule of this protein binds one inorganic phosphate ion in a tight complex. Upon binding the phosphate ion, the protein was known to undergo a large change in shape from an open to a more compact structure, wrapped around the bound phosphate. It might be imagined to be like a Venus fly trap which lies open until an insect lands on it, whereupon the trap snaps shut. When we tagged the protein with a fluorescent label, this change of shape altered the environment of the label and as a consequence the fluorescence intensity was increased, an effect that is easy to monitor. By designing new fluorescent compounds precisely targeted to a specific region of the molecule we optimized its spectroscopic properties and the labelled protein is now being produced commercially to make it widely available to other research groups. These developments drew on a range of interacting skills in biochemistry, X-ray crystallography, and fluorescence spectroscopy but depended crucially on chemistry for synthesis and analysis.
The second major area of current chemistry research at NIMR involves attaching to a biomolecule a chemical group that prevents it from displaying its normal biological activity. The attached group is so designed that, when exposed to light of the right wavelength and intensity, it splits off from the molecule in a process called photolysis, generating the active biomolecule. These compounds are known as “caged compounds”, since the biomolecules are in a sense locked-up until they are released by the flash of light. We use the technique to study biological processes that take place in a few thousandths of a second or less. One particular area of interest is the rapid release of neurotransmitter molecules that carry signals between nerve cells. In normal physiological function an electrical impulse travelling down a nerve fibre comes to the end of that fibre and causes release of a chemical substance, the neurotransmitter. This substance diffuses across a gap between the two nerve cells to stimulate the next fibre, thereby propagating transmission of the signal from nerve cell to nerve cell. By being able to release known but variable concentrations of neurotransmitter independently of the incoming electrical impulse, the transmission process can be controlled, analysed and manipulated more readily, with the aim of developing better understanding of aspects of brain function. We prepared a range of caged compounds to optimize the efficiency and speed of neurotransmitter release compatible with photolysis in a water-based environment and therefore appropriate for studying live tissue. In the course of this work a new photochemical reaction was discovered and the nature and dynamics of several ion channels involved in nerve cell activation have been characterized. As a result of further improvements two of these caged compounds have been licensed for commercial production.
These projects and indeed the rich history of chemical work at NIMR demonstrate how important chemistry is in medical research and this can only increase as we approach an understanding of the mechanisms of biological activities. My participation in these multidisciplinary studies has been an extremely rewarding and enjoyable part of my career as a chemist. It is obvious that the continuing need for such teams will create opportunities for interesting chemistry far into the future. The importance and central position of chemistry in so many aspects of future science and industry demands the inspiration of education professionals and the chemistry community, and the interest and support of our politicians.
This essay was published in the Mill Hill Essays 2004
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