Of interest to anyone who wants to know more about the molecular entities that comprise life saving drugs…..For the chemist. it will provide the fundamental knowledge…. For the nonscientist, it is illuminating and easy to read.

― Journal of Natural Products, 70(4), 711-712, 8 March 2007 (Romila D Charan)

I recommend this book very strongly to all, whether chemists or biologists, who need to know about the biology of nitric oxide……of value not only to undergraduate students, and their teachers, but also to research workers.

― Biochemical Society, 27 July 2005 (Stuart Ferguson)

A fascinating read….. should be on the recommended reading list for those entering the medical profession or a subject allied to medicine.

― Chemistry & Industry, Issue 18, 19th September 2005 (Dr Sally Freeman)

This is an essential book for the library – both personal and departmental.

― Education in Chemistry, September 2005 Issue (Simon Cotton)

Life Saving Drugs will be beneficial to undergraduates, not as a core text but to broaden their perspectives and to show them that pharmacology adn history are never dull.

― The Times Higher Educational Supplement, February 24, 2006 (Keith Hillier)

Useful for anyone withan interest in medicines, from good A-level students to postgraduates, it certainly deserves a place in the teacher’s personal library.

― Journal of Biological Education, Vol 40, No.2, Spring 2006 (Gill Hickman)

Life Saving Drugs

The Elusive Magic Bullet

By John Mann

The Royal Society of Chemistry

Copyright © 2004 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-0-85404-634-8

Contents

Chapter 1 The Elusive Magic Bullet: Introduction, 1,
Chapter 2 Fighting Bacteria, 11,
Chapter 3 Antiviral Treatments, 85,
Chapter 4 Cancer: The Disease and its Treatment, 141,
Chapter 5 Magic Bullets: Still Elusive After all These Years, 223,
Further Reading, 233,
Subject Index, 241,

CHAPTER 1

The Elusive Magic Bullet: Introduction

Theophrastus Philippus Aureolus Bombastus von Hohenheim would not have been surprised that arsenic was a major component of the first effective treatment for syphilis. This 16th-century alchemist and physician, better known as Paracelsus, is reputed to have acquired his skills from barber surgeons, alchemists and gypsies, although he acquired notoriety after his appointment as Professor of Medicine in Basel. He was renowned for his use of mercury, arsenic, antimony and tin salts for the treatment of syphilis, intestinal worms and sundry other conditions endemic in mediaeval Europe – although it is probable that he killed more patients than he cured with these very toxic metal salts. Four hundred years later, Paul Ehrlich discovered the arsenic-containing drug ‘606’ (later called Salvarsan), the first true anti-syphilitic and immediately hailed as a ‘magic bullet.’ It was to remain the mainstay of treatment until the arrival of another ‘wonder drug’ of the 20th century – penicillin.

Paracelsus rejected the druglore (mainly plant-based) laid down by the famous Greek physicians Dioscorides and Galen, and believed instead in the so-called ‘Doctrine of Signatures.’ The main belief was that the shape of a plant revealed the disease or organ that would benefit from therapy involving extracts of that particular plant. Thus, the tooth-shaped seeds of henbane were given for toothache, brain-shaped walnuts for headache and liverwort for liver complaints. His prescribing also owed much to the Arab preference for sulfur, mercury and common salt – the essence of combustibility, fluidity and earthiness – coupled with a firm belief in magic, necromancy and astrology.

These strange ideas (at least in contemporary terms) should not, however, overshadow his major contribution to medicine, which was his forthright belief that each disease had a specific cause and its own remedy. There is an interesting congruence between this belief and the later triumphs of Paul Ehrlich, who invented just such a treatment for syphilis caused by the organism Treponema pallidum.

Paul Ehrlich was born in March 1854 and was brought up in Upper Silesia, in the town of Strehlen. The son of an innkeeper, he received a major part of his education at the University of Breslau. Here, he developed a fascination for the properties of aniline dyes, then a very important product of the German fine chemicals industry. Even in early experiments, he was able to show how certain dyes could help in the identification of cells and for the definition of their fine structure. His secretary of many years, Martha Marquardt, records in her excellent biography of Ehrlich that he was visited in his laboratory one day by Robert Koch, who had become famous through his studies on the causative organisms of anthrax, tuberculosis, diphtheria and several other common diseases. Ehrlich’s teacher apparently introduced him to this honoured guest with the words: “That is ‘little Ehrlich’. He is very good at staining, but he will never pass his examinations.”

Ehrlich did pass his exams and then completed his studies at the University of Leipzig, graduating in 1878 (aged 24) with a doctorate in Medicine. His thesis was, perhaps not surprisingly, entitled: ‘Contributions to the Theory and Practice of Histological Staining. Part I. The Chemical Conception of Staining. Part II. The Aniline Dyes from Chemical, Technological and Histological Aspects’. In it, he emphasised the value of an understanding of the chemistry involved in staining organisms, in particular, the specificity of these processes. This search for specific binding (and killing) agents for microorganisms was the central theme for the rest of his research career.

But before research once again dominated his life, he had to make a living and for several years he worked as a house physician in various hospitals. By all accounts, he was a kind and effective clinician, although his research on dyes was never far from his mind. He developed a diagnostic test for the acute phase of typhoid fever, but his major triumph in 1882 was a specific stain for the tubercle bacillus – recently identified by Robert Koch as the cause of tuberculosis – thus facilitating detection of the organism in sputum (saliva) samples. This research undoubtedly led to his own infection by the organism, and in 1887, he began to exhibit the classic symptoms of pulmonary tuberculosis. His illness was not life-threatening but necessitated a two-year sojourn in Egypt, away from the stresses and harsh winters of Germany.

He returned in 1889, completely recovered, and accepted an appointment at the Institute for Infectious Diseases in Berlin directed by Robert Koch. Ehrlich continued to develop his ideas about the specificity of chemicals for particular cells and for their structural components, but he also became heavily involved in the development of methods for the accurate measurement of the potency of diphtheria antitoxin. This seminal work is often overlooked owing to the subsequent excitement over Salvarsan, but it can be viewed as a key part of the evolution of his ideas about chemotherapy.

The bacteriologist Emil von Behring had discovered specific antitoxins in the blood serum of animals infected with sub-lethal doses of diphtheria bacilli, but he was unable to produce samples with reproducible levels of activity. Ehrlich not only showed how to raise high concentrations of antitoxins in horses by successive injections of diphtheria bacilli but also developed the methods necessary for the measurement of the potency of the individual serum samples. The treatment of patients then became both safe and effective, and the fact that his methods are still in use today provides a cogent testimony to his skill and ingenuity.

These studies reinforced his belief in what he termed the side-chain theory of interactions. He believed that within each cell, there were large amounts of ‘protoplasm’ with projections (the ‘side-chains’), whose normal physiological function was to interact with the essential chemicals involved in various life processes. These same side-chains could also have a specific affinity for toxins, and once these had been attached, the side-chain lost its capacity to function normally. To compensate, the cell now produced extra copies of the whole side-chain, which were released into the bloodstream and could act as antitoxins. He initially called the combining moiety on the side-chain a haptophore and the toxin was the toxophore, but later used the expression receptor to describe the site at which a foreign organism or drug interacted with the cell. This term is now central to pharmacological terminology. His views on what we would now call immunotherapy and chemotherapy are probably best summarised in his own words:

“What makes serum therapy so extraordinarily active is the fact that the protecting substances of the body are products of the organism themself, and that they act purely parasitotropically and not organotropically (i.e., against the body). Here we may speak of magic bullets which aim exclusively at the dangerous intruding parasites, strangers to the organism, but do not touch the organism itself and its cells. … But we know of a number of infectious diseases … where serum therapy either does not work at all. … I call attention especially to malaria, to the diseases caused by trypanosomes. … In these cases chemical substances must come to aid the treatment. Instead of serum therapy, chemotherapy must be used.”

This work in the newly emerging area of immunology occupied Ehrlich for more than a decade, and as a consequence, his research on drug design did not begin in earnest until the turn of the century. At that time, the only drug that had curative properties against a disease (malaria) was quinine and this had been in use since the 17th century, generally in the form of Jesuits’ powder, an extract of the bark of the cinchona tree. Ehrlich had been involved with one study (in 1891) of the effect of the dye methylene blue on malaria, and this had been encouraging, in that some amelioration of the symptoms characteristic of the disease had been observed. This positive result seems to have encouraged him to try other dyes on a variety of trypanosomes, the microorganisms responsible for such diseases as African sleeping sickness and Chagas’ disease in South America. Laveran and Mesmil, of the Pasteur Institute in Paris, had greatly facilitated such studies when they showed that trypanosomes could be transferred between animals, and these host animals could then be used as a convenient source of the parasites. Ehrlich and his Japanese collaborator Kiyoshi Shiga, showed that Trypan red was effective against trypanosomal infections in mice but had no effect on larger mammals including humans. Their attention was diverted to the use of arsenic compounds when Laveran and Mesnil demonstrated that Trypan red was much more effective if administered in conjunction with arsenious acid. In addition, they became aware of the work of H. W. Thomas of the Liverpool Institute of Hygiene and Tropical Medicine, who had demonstrated the efficacy of the arsenic-containing drug Atoxyl in the treatment of animals infected with trypanosomes. This drug (sodium arsanilate) had been synthesised by Bechamp in 1863 and was about 20 times less toxic than Fowler’s solution (mentioned below). Ehrlich and Shiga had earlier tried Atoxyl on cultures of trypanosomes but without success.

That they should have tried arsenic derivatives was not at all unreasonable, since these had been used not only by Paracelsus but also by many physicians in the form of Fowler’s solution. The inventor, the Staffordshire physician Thomas Fowler, had extolled the virtues of his solution (mainly potassium arsenite) in 1786 in a report entitled ‘Medical Report of the Effects of Arsenic in Cases of Agues, Remittent Fevers and Residual Headaches.’ The Scottish missionary and explorer David Livingstone was amongst the first to extoll the virtues of Fowler’s solution for alleviation of the symptoms of sleeping sickness. Ehrlich was further influenced in his choice of drug by the studies by, amongst others, his mentor Robert Koch, on the efficacy of the Atoxyl in trypanosomal infections in animals. This particular arsenic derivative had been prepared, as a possible replacement for Fowler’s solution, but in 1906, its chemical structure was still not known with certainty, and Ehrlich’s first experiments concerned an attempt to confirm its structure. He had received no formal chemical training but seems have to have spent much of his spare time performing test-tube-scale experiments in a laboratory cluttered with unlabelled bottles and jars, and he soon concluded from his observations that the suggested chemical structure was wrong. In particular, it reacted with nitrous acid to form a diazonium salt; hence, he proposed that Atoxyl contained a free amino group. This would make it chemically reactive and would thus be a good starting material for the construction of numerous structural analogues. His chemical collaborators disagreed with him and a furious row ensued . His secretary Martha Marquardt reported the following exchange:

“Atoxyl is not an anilide of arsenic acid. On the contrary, it contains a free amino-group … (and in consequence). … I have deliberately asked for the most simple derivatives to be worked out first. I must ask you to follow my orders strictly. You cannot judge whether this is right or wrong.” To which one of the chemists Dr. von Braun replied:

“We cannot accept your directions, and must work according to the classic formula of Bechamp (the discoverer of Atoxyl).” Ehrlich then stormed out of the laboratory with the words: “I adhere to my orders and leave it to you to take the consequences.” Two of the three chemists, von Braun and Schmitz, resigned on the spot, but the third, Alfred Bertheim, stayed and worked on the preparation of the compounds decreed by Ehrlich. This research was funded by Casella Dyworks, which was subsequently acquired by the Hoechst Dyeworks. Their synthetic work quickly revealed the accuracy of Ehrlich’s proposed structure, and several hundred analogues were prepared and evaluated for biological activity. Compound number 418, later called arsenophenyl-glycine, for which they proposed a structure containing an arsenic-arsenic double bond was particularly effective against trypanosomes both in laboratory tests and in animals, and was administered to humans after 1907. But the major triumph came when the group moved on to test their compounds against the spirochaete responsible for syphilis, Treponema pallidum.

The origins of syphilis are still a subject of debate, but it seems clear that spirochaetes of the Treponema type have always been endemic in Europe and were responsible for a relatively mild form of syphilis. However, the arrival of Columbus and his men in the Caribbean provided the opportunity for exposure of Europeans to the more potent organism Treponema pallidum. Their sexual exploits with the local Indians ensured that these adventurers imported the organism into Europe. Here, it almost certainly underwent genetic change to produce a highly contagious and ravaging form of syphilis. This swept Europe at the end of the 15th century in the wake of the marauding French army as it waged war with the Italians. The fall of Naples in 1495 heralded a period of unbridled licentiousness and the inevitable spread of the disease, which is believed to have claimed 10 million lives between 1495 and 1510. The first manifestations of infection were genital sores and the disease usually progressed inexorably to involve the bones and cartilage. The condition was known variously as the ‘French disease,’ the ‘Spanish disease,’ the ‘English disease’ or the ‘Great Pox,’ and has remained a serious problem, in certain parts of the world, to this day. The original remedy introduced by Paracelsus involved the use of mercury salts and this was still the main treatment well into the 20th century, although the relatively water-insoluble salts like the very toxic mercurous chloride (Calomel) had been largely replaced with the more soluble salts of benzoic acid and salicylic acid, which were less toxic. Mercury compounds can cause all kinds of neurological problems like loss of memory and mental concentration, numbness of the extremities (paraesthesia), trembling and eventually blindness and death. Set against these problems was the desperate need to provide a treatment for a disease that even today has an incidence of around 20 million cases per year, and was then of much greater incidence.

For his new work with Treponema, Ehrlich was joined in 1909 by another Japanese collaborator, Sahachiro Hata, an expert on syphilis, who had been the first researcher to succeed in infecting rabbits with the disease. He retested all the arsenic derivatives against Treponemapallidum and identified compound 606 as a particularly potent analogue, which possessed curative activity for infected rabbits. Compound 606 had been prepared in 1907, but it had not exhibited any activity against trypanosomes, and Ehrlich subsequently claimed that this had been due to the incompetence of a former collaborator. This lapse and the problems with hypersensitivity reactions seen in some patients receiving arsenophenylglycine persuaded Ehrlich to proceed with great caution. As a result, very extensive animal tests were carried out before 606 was released to selected hospitals for clinical trials.

Ehrlich was well-served by his chosen clinicians, many of whom carried out further animal tests as well as treatment of patients. Excellent results were obtained from hospitals in Pavia, St. Petersburg, Zurich, Altmark and Magdeburg (Germany) and Sarajevo. Samples were also used in England, and the studies at St. Mary’s Hospital, Paddington were carried out by a young bacteriologist named Alexander Fleming (soon to be famous for his work on penicillin) and his assistant Leonard Colebrook (later famous for his work on the sulfonamides). In the edition of the Lancet of June 17, 1911, they described the use of anew apparatus for the intravenous injection of 606 and gave the following conclusions about its efficacy: “Whether the new drug will displace mercury in the treatment of syphilis remains to be seen. … It, however, has a remarkable effect in causing the lesions to disappear, and especially is this seen in some cases which have resisted mercurial treatment. Much has been made of the dangers inherent in the administration of the drug, but so far as we have gone we have not seen the slightest trace of the evil effects which have been written about in any case which has been injected intravenously.”

Encouraged by these successful clinical trials, Ehrlich announced the results at the International Congress for Internal Medicine at Weisbaden on April 19, 1910. The world’s press responded to this new treatment with predictable excitement. Ehrlich was inundated with requests for samples of the drug and during the period June to December 1910, an incredible 65,000 doses of the drug were supplied free of charge to any physician who requested it. Not surprisingly, there was some careless administration. Solutions of the sodium salt of the drug were made with tap water rather than with distilled water, and because the instability of the compound had not been appreciated, many of the samples had decomposed prior to administration. Ehrlich took a great personal interest in these further clinical trials and was much distressed whenever patients suffered as a result of these problems. He subsequently issued very precise instructions for the care and preparation of the drugs.

The demand for 606 soon outstripped the supply capabilities of Ehrlich’s laboratory, and he elicited the support of the Hoechst Chemical Works for the manufacture of the drug, now patented under the name Salvarsan. In contrast to the enthusiastic reception accorded to Salvarsan in Europe, in the USA, the reception was mixed. In America, venereal disease carried a much greater stigma than in Europe. Patients with syphilis were not allowed to be treated in hospitals or dispensaries – the one exception being members of the armed forces. So it was the US Naval Hospital on Mare Island, California, that received the first doses of Salvarsan in October 1910, and 10 patients were treated with at least some dramatic results. As word spread of the efficacy of the drug, some American physicians warned that this remedy might encourage greater sexual promiscuity. One suspects that at least some feared this new quick-acting treatment would reduce the lucrative fees that they received for the long-term treatment of their syphilitic private patients.

(Continues…)Excerpted from Life Saving Drugs by John Mann. Copyright © 2004 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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