In Celebration of Leslie Lars Iversen (1937 – 2020) by Thomas A. Ban
On July 30, 2020, Leslie Lars Iversen, a distinguished British pharmacologist psychiatrist, passed away.
Born and raised in the UK, Iversen received his PhD in Biochemistry and Pharmacology in 1964 from Trinity College, Cambridge. He spent a postdoctoral year with Julius Axelrod at the NIH and with S. Kuffler at the Harvard Medical School. From 1978 to 1983 he served as Director of the Neurochemical Pharmacology Unit of the UK Medical Research Council in Cambridge. In 1983 he joined the Neuroscience Research Center of Merck Sharp & Dohme Research Laboratories in Harlow, Essex, as Executive Director and in 1987 became Vice President of the Center.
Leslie Iversen’s research activities included the uptake, metabolism and turnover of tritiated NE, the inhibition by antipsychotic drugs of the DA sensitive adenylate cyclase in brain and the pharmacology of substance P. At Merck he was involved in studies of NMDA receptors, subunit selective GABA-A pharmacology and the regulation of neuropeptide release. Subsequently, Iversen’s research interests shifted to cannabis and studies on Alzheimer’s disease. He has written two books, The Uptake and Storage of Noradrenaline in Sympathetic Nerves and, together with his wife S.D. Iversen, Biochemical Pharmacology. He was a member of numerous prestigious societies, a Fellow of the Royal Society, a Foreign Honorary Member of the American Academy of Arts and Sciences and a Foreign Associate Member of the National Academy of Sciences, USA (Sulser 2011a,b).
A disciple of Julius Axelrod Iversen (1978) was first, in the 1960s, to demonstrate a calcium dependent release of GABA in crustaceans in response to stimulation of an inhibitory nerve (Osuka, Iversen, Hall and Kavitz 1966; Iversen, Mitchell and Srinivasan 1971). He was also first to demonstrate GABA uptake mechanisms in the mammalian brain (Iversen and Neel 1968). In the 1970s Iversen found that naloxone, an opiate antagonist, blocked morphine’s suppressant effect on the release of Substance P from the sensory nuclei of the brain and spinal cord (Dingledine, Iversen and Breiker 1976; Iversen, Jessel and Kanazawa 1976).
Leslie Lars Iversen was interviewed for the “oral history project” of the American College of Neuropsychopharmacology by Thomas A. Ban in San Juan, Puerto Rico, on December 9, 2009 at the Annual Meeting of the College.
TB: This is an interview with Dr. Leslie Iversen [born in Exeter, United Kingdom in 1937] for the Archives of the American College of Neuropsychopharmacology. We are at the Annual Meeting of the American College of Neuropsychopharmacology in San Juan, Puerto Rico. It is December 9, 2002. I’m Thomas Ban. Please tell us first where you were born and something about your education, and early interests. Then we would be interested to learn how you got involved in neuropsychopharmacology.
LI: It’s a privilege to be asked to join in this program. I was born in the West Country of England in Exeter, but my parents were Danish, so I’m a first generation immigrant. I was educated in Exeter at a grammar school and at the age of 18, I got a scholarship to go to Trinity College, Cambridge, which was a great privilege. But, meanwhile, I had to do two years military service. It was not optional and I joined the British navy, teaching ordinary seamen English and arithmetic. I was posted to the Mediterranean, where I spent two interesting years, learning how to snorkel, dive and sail the boats and forgetting all the science I’d ever known.
Then, I went to Cambridge in 1958 as an undergraduate to study botany, my boyhood passion. But after one term of botany I decided to change subjects because the teaching was very, very old fashioned, based on systematic classification of plants. They hadn’t even heard about biochemistry which I decided was much more exciting. So I switched to a three-year degree in biochemistry, which was, and still is, a very strong subject at Cambridge. The department was buzzing with excellent people and good teachers, so I had a very good education and ended up in final year doing nothing but biochemistry along with 14 other students. During that time, I became convinced I wanted to do research. I had read Aldous Huxley’s books, The Doors of Perception and Heaven and Hell, which influenced me greatly. It was, to a biochemist, an extraordinary story, that a chemical like mescaline or LSD, a few milligrams of a pure substance, could alter the state of consciousness and the whole way one sees the world in such a profound way. It was almost miraculous and I thought, scientists should try to understand this better. So, I became determined to do a PhD in brain biochemistry. The problem was, I also wanted to get married to my fellow-student Susan and we both wanted to stay in Cambridge to do our PhD’s, but I couldn’t find anyone who could teach me brain biochemistry. I was getting quite desperate until I met, by good fortune, my future supervisor Gordon Whitby. Gordon was a member of the faculty in the biochemistry department, but he’d been on leave in the States working with Julie Axelrod where he had been involved in the very first experiments with radiolabeled norepinephrine and the discovery, with Julie Axelrod and George Hertting, of what is now called the norepinephrine transporter. Gordon Whitby returned to Cambridge just at the time I wanted a PhD supervisor. So I became his student and was lucky to be exposed to the latest data from Julie Axelrod’s lab at NIH. We were the first people in the UK to have radioactively labeled norepinephrine. It was very early days for the subject and I was able to study the norepinephrine uptake process using the sympathetic nerves in rat heart as the model. I made a detailed study of the kinetics of the process and the many drugs that could inhibit it, including the synthetic phenethylamines, and psychotropic drugs, including the tricyclic antidepressants and cocaine. I was getting exposed to psychopharmacology and had a great time for three years. Largely because of Gordon Whitby’s contact with the Axelrod lab, I was able to meet Julie and to persuade him to take me as a post-doc. Then, I was fortunate to get the award of a Harkness Fellowship, a specialist fund, sponsoring Fellowships in both directions across the Atlantic, not only for scientists but for journalists and artists as well
TB: Are we in the early ‘60s?
LI: I went to Julie Axelrod’s lab right after qualifying for my PhD, which was 1964.
TB: So in 1964, you went to the States.
LI: I got to Julie’s lab when Jacques Glowinski was there and he and I worked very closely on catecholamine metabolism in the brain. I became exposed to the CNS part of the monoamine story and having access to radiolabeled tracers, we were among the first to do studies with them. I had a very busy and productive year and was exposed to Julie Axelrod with his unique creativity, which I’m still a huge admirer of. Just a few weeks ago I went to Julie’s 90th birthday celebration at the NIH, having gone 10 years earlier to his 80th birthday. I was delighted to see him still in good spirits and intellectually sharp.
So, my postdoc year in his lab was a great time for me. My PhD mentor in Cambridge changed from Gordon Whitby to Arnold Burgen. Gordon Whitby left Cambridge about half way through my PhD. Arnold Burgen had come back from Montreal, Canada, to be head of pharmacology in Cambridge. He took me on for the last year and a half of my PhD and was an inspiring teacher. He was a friend and colleague of Steve Kuffler, the great neurobiologist at Harvard, and gave me an introduction there so I was able to do a second year of post-doc in the States at Harvard in the Department of Neurobiology. The whole concept of neuroscience was still very new and I think it was one of the first academic departments in the US that had a neuroscience program. That was, again, a period of great excitement. I worked with Ed Kravitz, the biochemist in the group but I also got to know many of the others: David Potter, Ed Furshpan and Steve Kuffler, who was another remarkable genius in neuroscience. This was a privileged time for me.
With Ed Kravitz I got to work on GABA. The group at Harvard had been working on GABA in the lobster where the peripheral muscles have both an excitatory nerve, which we now know releases glutamate, and an inhibitory nerve. Inhibition which occurs inside the central nervous system in mammals, occurs right down at the muscle level in crustaceans. GABA was suspected to be the transmitter for the inhibitory nerves, from a number of pieces of evidence the Harvard group had put together. My job was to make a final demonstration that, if you stimulated the inhibitory nerve, GABA was released. That might sound like a relatively simple thing to do, with a nice big muscle preparation from the lobster. We used the big crusher claw, which has a muscle that controls the finger in the inner part of the claw. The muscle, which weighed about a gram, was innervated by just one inhibitory nerve fiber, which we could expose and stimulate, while washing the muscle in sea water and measuring the released GABA. The problem was that trying to measure minute amounts of GABA in large volumes of seawater, which is a concentrated salt solution, proved technically very difficult. It took me and Ed Kravitz, together with a Japanese visitor Masanori Otsuka, two-thirds of my post-doc year to work out how to do this, and only in the last three months did we get some results. We showed that there was a calcium dependent release of GABA in response to stimulating an identified inhibitory nerve. This was the first real demonstration that GABA is released from inhibitory nerves. So, that was a fruitful period and a wonderful learning experience for me.
My two years in the United States from 1964 to 1966, were enormously influential both in learning how great laboratories work and in making friends and contacts in the US who have remained for the rest of my career. After that, I went back to Cambridge and rejoined the Department of Pharmacology, not as a faculty member but as a Research Fellow, sponsored initially by Trinity College and then by the Royal Society on one of their endowed Fellowships. A few years after I got back, I was appointed Director of a Medical Research Council Laboratory in Cambridge. We called it the “MRC Neurochemical Pharmacology Unit.”
TB: What year was that?
LI: It was 1970 when that started. The Unit was a self-contained laboratory in the Department of Pharmacology funded directly by Government Research Council funds. Looking back that was a dream job, because Medical Research Council funding was quite good, even if not enormously generous. It paid for staff, infrastructure, equipment and all the running costs and we were able to attract a number of talented post-docs and students locally and from overseas. We had a number of very able young scientists from USA, Canada, Australia and Europe. So, I spent 11 or 12 years doing that enormously satisfying and very exciting job and during those years some wonderful people came through the lab, like Ira Black, one of our post-docs, and Ian Hendry, one of our PhD students. Many, many people, who’ve later gone on to have their own independent and highly successful careers came through the lab. Tom Jessell was another, who is now doing very well in the field of developmental neurobiology. So, this was great..
TB: Did you continue your research with GABA?
LI: I continued to be interested in GABA and we collaborated with Jimmy Mitchell in the Department of Pharmacology. We were able to do some GABA release studies from the mammalian cortex using super-fusion techniques. We discovered the GABA uptake mechanism, which exists for amino acids as it does for monoamines. We discovered a glycine reuptake mechanism also. But, the two most notable events in that period in Cambridge were working on the mechanism of action of anti-schizophrenic drugs and, secondly, getting involved in the field of neuropeptides.
The anti-schizophrenic drug story was started by work done in Paul Greengard’s lab at Yale with his student, John Kebabian, who first described a dopamine stimulated adenylate cyclase in the pituitary. That was the first biochemical test tube model for a dopamine receptor, before ligand-binding studies came along. To me it was very exciting, because I’d already been interested in the idea, promulgated by Sol Snyder and others, that dopamine was at the heart of the story in schizophrenia. A lot of indirect lines of evidence were pointing towards a key role for dopamine and for blockade of dopamine receptors in the action of anti-schizophrenic drugs but the idea, until then, was based on indirect evidence. We thought maybe, we have, for the first time, the opportunity of testing this idea. Richard Miller, who was a very bright biochemistry student, joined the lab as my PhD student in 1974 or 1973, and started work on this mechanism, using the Kebabian-Greengard model, not in the pituitary, but in the basal ganglia of rat brain. He was able to show very quickly that a whole series of anti-schizophrenic drugs, the phenothiazines and the thioxanthenes, did indeed inhibit the dopamine stimulated cyclase system and did so in the rank order or potency you’d predict from their clinical potencies and known effects in animal models. We thought we had finally cracked the problem and this was how anti-schizophrenic drugs work. Richard published a number of papers. But there was a problem: certain classes of neuroleptic agents didn’t work in this model, notably the butyrophenones, such as haloperidol, which everyone knows to be a very potent neuroleptic, both in animal models and clinically. These drugs just didn’t work except at rather high concentrations. And, that was true for the whole class of sulpiride-type drugs also. So we knew we must have stumbled on only part of the story. A few years later Sol Snyder’s lab and Phil Seeman in Toronto finally nailed this down by showing what we’d been studying was the D1 receptor and it was probable that the D2 receptor, which they identified in radioligand binding studies, was more likely the target. And that’s what everyone believes today. But we had a lot of fun with the D1 research and I developed an interest in schizophrenia research, which has been with me ever since.
TB: Didn’t you get involved also in research with Substance P?
LI: While I was at Harvard, working with Ed Kravitz and Steve Kuffler, Masanori Otsuka from Japan was working on Substance P as a possible transmitter substance and he maintained a strong interest in this after returning to Tokyo. He and I remained in contact about this. My own interest in Substance P stemmed largely from Masanori’s very painstaking neurophysiological work, suggesting a role for Substance P as a sensory neurotransmitter. In the central nervous system, the work of Tomas Hökfelt and other Swedish histochemists mapping SP neuron groups was also important. Tomas was the first to publish a detailed map of Substance P pathways in peripheral nerves and in the many pathways within the brain. I got into this area knowing we had to generate antibodies and immunoassays to measure the peptide. But you couldn’t buy the peptide at that time.
TB: Are we in the 1970s now?
LI: We are talking about early 1970s when Susan Leeman in Boston had only just described the amino acid sequence of the peptide for the first time. I wrote to a contact at the Merck Institute in Raleigh, New Jersey. The head of chemistry there, at that time, was Ralph Hirschmann, who had made a batch of synthetic Substance P for Susan Leeman. He was very kind and gave me a 25 milligrams sample, which was a priceless treasure because 25 milligrams was enough to sustain the entire program at Cambridge for many years. We were able to generate antibodies and to devise our own immunoassays and immunostaining. Claudio Cuello, a visitor from Argentina made his own very detailed map of Substance P pathways in the CNS. Cuello later went to be head of pharmacology at McGill and still works in Canada. My student, Tom Jessell, was able to set up an in vitro brain slice SP release preparation using a sensitive immunoassay. He was the first to show that if you took slices of brain stem, sensory nuclei or spinal cord dorsal horn, the release of Substance P in the sensory areas was powerfully suppressed by opiates such as morphine, and that effect could be blocked by naloxone. So, we discovered one of the possible sites of action for opiate analgesics in the CNS at what we thought was one of the primary sensory relay stations, in which Substance P might be one of the pain transmitters. That was exciting and Substance P was also the subject of a collaborative study, between my lab and my wife’s laboratory in the Department of Experimental Psychology. She had developed her own psychopharmacology and behavioral psychology group. We were able to do collaborative studies in animals, using of one of our monoclonal SP antibodies, showing that if you infused a monoclonal antibody into the brain to neutralize Substance P, stress-induced release of dopamine no longer occurred. We believed we’d identified a possible Substance P link relevant to Substance P antagonists as antidepressants.
In the early 1980s, along came a posse of people from US Merck Research Laboratories, led by Clem Stone, the head of the CNS Pharmacology at Merck. They were looking to build a basic neuroscience lab in England as part of the company’s global expansion. They wanted to be seen as a company doing research, not only in the USA and Canada, but in other parts of the world, in Japan and in Europe. They’d chosen England as one of the first targets, knowing that basic neuroscience and neuropharmacology were relatively strong subjects here. They came to Cambridge and asked would I be willing to advise them on the project. Of course, I said I’d be very happy to. So I advised them on the project, which was to build an entirely new neuroscience laboratory on a site halfway between Cambridge and London and staff it with up to 300 people, creating a major center for all basic and pre-clinical neuroscience for Merck worldwide. It was a multimillion dollar project. Of course, they were looking for someone to head the lab. I said initially not me, “I’ve got a perfectly good and secure job here in Cambridge working for the government, wonderful people come to work for me, I only have to write a progress report once every three years and I get a site visit once every six years.” In fact the good times for the Medical Research Council were about to come to an end. Things were getting a lot tougher in the 1980s than in the 1970s. Eventually, I saw that the Merck opportunity was just too good to miss. It was a once-in-a-career opportunity to do something much bigger than I’d done before, so I accepted the offer and started working for Merck Research in 1983. We started off in a temporary location and began recruiting people and that went well. In 1983 and 1984 there were a number of academic people looking for jobs and the pharmaceutical industry was not actively looking for people. So, we were able to hire some really excellent scientists. We had, quite rapidly, a head count of over 100 people within the first two years and by the time I’d finished, twelve years later, it was up to some 300 people working on science. It was a big operation and I learned what it was like to work for a big company which was different from working for the Medical Research Council in a number of ways.
TB: In what way was it different?
LI: First of all, we had a lot more money to spend and we could buy all the up-to-date equipment we wanted. I was fortunate to work for a company that was and is very science driven. Unlike many big pharma companies, which are dominated by accountants and marketing people, Merck has always been led by scientists and during my period there a scientist, Roy Vagelos, was appointed to be Chairman and Chief Executive, which was unheard of, but it worked very well. It was a period of expansion for neuroscience and a huge period of expansion for the pharmaceutical industry. It’s always nice to join an industry that is in a period of log growth! It was double digit growth every year and if it fell below 20% the Wall Street analysts would say something must be wrong. Of course, everybody knows in their heart that can’t go on forever, but in the 1980s it was expected.
During the period with Merck, I was able to set up a number of different projects in research. I learned the hard way about research and development in the pharmaceutical industry. When I joined, my mentor, Clem Stone, told me to expect that out of every 10 projects you start, you’d be lucky if one of them succeeded and became a product for the company. Being an arrogant academic, I thought the rules would be different for me, but they weren’t. Out of all the projects I started during the 12-year period I was there, only one of them made it to the market and that was Maxalt (rizatriptan), the anti-migraine compound. Rizatriptan is one of the sons of Sumatriptan, the 5HT1D agonist, which has proved to be a real breakthrough in the treatment of migraine headaches, with one of the first pharmacological mechanisms where you could treat the headache after it had started and stop it in its tracks. Sumatriptan from Glaxo was the first compound, but Sumatriptan had a number of deficiencies that we were able to improve on, notably, rather poor bioavailability when given orally and our compound was better absorbed orally and acted much faster. It has done quite well, particularly in the US.
I suppose one of our big challenges during my period at Merck was in the excitatory amino acid area. That was a field I’d never worked in before and we got into the area almost by accident. Merck had, before I came along, discovered a compound which was called MK-801 (dizocilpine) that had been selected by classical pharmacology screening in an animal test for anti-seizure activity and it proved to be active orally as an anti-convulsant. Merck had put it into development for epilepsy and wanted to know how they could make it better. So my lab was assigned to find out how MK-801 worked.
We tried a lot of different things. First, we set up a radioligand binding assay. Eric Wong, a talented young biochemist, did that using tritium-labeled MK-801. We could then screen the entire Sigma catalog to see whether we could find anything to interact with that binding site and we found that pentazocine and phencyclidine were moderately active competitive antagonists for MK-801 binding. That didn’t tell us very much, because these were opiates of obscure mechanisms. We really didn’t understand it. But then, we learned of David Lodge’s neurophysiology experiments in which he described in vivo neuropharmacology experiments where phencyclidine and pentazocine were NMDA receptor antagonists. That gave us a clue that MK-801 might be an NMDA receptor antagonist. John Kemp and Geoff Woodruff and others in our neurophysiology lab at Merck were very quickly able to show that MK-801 was indeed a potent non-competitive NMDA receptor antagonist. It was an open channel antagonist. In other words, the agonist had to be present for the antagonist to work. We were then able to show, in a number of animal studies, that this compound had a number of properties expected from glutamate antagonists behaviorally. Notably MK-801 was a neuroprotective agent. We were keen on the idea that in stroke or other cerebral ischemia injuries, glutamate release might contribute to the damage. There were a number of animal models of ischemia, involving ligature of the middle cerebral artery or other insults to the brain to deprive it of blood flow and oxygen, and we worked with Jim McCulloch in Glasgow with those models. He was one of the experts in this area and he generated a number of examples where MK-801, given in vivo, was a very powerful protector against damage that would otherwise occur when these stroke models were performed. We could rescue up to two-thirds or more of the damage that would normally occur by giving MK-801, so we got quite excited about that. We wanted to get into the clinic and test this in stroke patients. But then, we hit a problem.
John Olney at Washington University, St. Louis, who had been one of the pioneers of the whole idea about glutamate as an excitotoxic chemical in brain, published a paper in Science, reporting that in rats given a high dose of MK-801, one could see various signs of neuropathology in certain areas of the brain, notably, in the limbic areas in the cingulate cortex. What he observed was that some of the large neurons in those areas of the brain developed a pale structure with a large number of fluid filled vacuoles and looked pretty sick within a few hours after MK-801 administration. We rushed into the lab, repeated his findings and found that the great majority of those neurons recovered to normal when the drug was no longer there. However, we had to admit there were a small number of nerve cells that apparently died in those particular areas of the brain. That became a very hot issue with the Food and Drug Administration, who called a halt to all companies working with NMDA antagonists until this issue had been resolved. And, they set down a number of experiments they’d like to see done in primates and other animals before anything went into the clinic. Merck took a look at some other data that suggested a possibility MK-801 might prove to be a hallucinogenic molecule and decided to give up on clinical development. We were of course very disappointed by that; although in retrospect we now see all the other companies that tested NMDA antagonists in stroke failed miserably.
TB: What else did you do?
LI: We continued to be interested in the NMDA receptor and we were able to start developing cell models in which different sub-units of the NMDA receptor were expressed. We began to look at some types of selective drugs to be worked with in future glutamate pharmacology. We did the same thing for the GABA-A receptors, an epic project in retrospect, which started in the 1980s and, only 20 years later, is beginning to show some fruits for the Merck Research Labs. The GABA-A receptor has α, β, γ subunits each of which is encoded by multiple genes. So, the number of possible permutations of GABA-A receptors is absolutely enormous, but we figured probably most of these don’t exist in brain and by making antibodies selective to the different sub-units we were able to work out that in the mammalian brain, there are not more than 20 or so of the thousands of permutations. So we were able to set the foundations for sub-unit selective GABA-A pharmacology, which is continuing to this day, and Merck Research now has compounds in the development pipeline which stemmed from that research.
The other big focus for the Merck lab was neuropeptides. We had inherited, again, from previous work at Merck, a series of compounds that were pure, very selective, non-peptide drugs working at cholecystokinin (CCK) receptors in the central nervous system and the gut. CCK is one of the gut-brain peptides. In the gut CCK affects gut motility, pancreatic secretions, gall bladder secretions, and in the stomach, the closely related peptide gastrin, is a stimulator of gastric acid secretion. But, in the brain, CCK acts in multiple pathways. Its function is not yet understood, but satiety may be one of the systems involved.
The particular focus we had was the curious phenomenon that CCK can cause panic in human volunteers. This was based on studies by the Danish scientist Jens Rehfeld and, then, by Claude de Montigny and his colleagues at McGill, Kelly and Bradwejn, who had shown that if you give very small doses of CCK4 to human subjects by IV bolus injection, you get an almost immediate panic reaction in a dose-dependent manner. It is a remarkable piece of psychopharmacology. With clinical colleagues at Merck and by working with Bradwejn and de Montigny and colleagues in Canada, we were able to show that if you gave the Merck CCK antagonist drug L-365,260, orally, one hour before giving the CCK4 injection, you could block the CCK induced panic. That showed our drug worked in the right place and at the right time.
Then, our clinical colleagues went on and did a clinical trial in patients with recurrent panic attacks. It was a six-week placebo controlled trial with 40 patients and showed absolutely nothing. The drug did not work; it did not reduce the frequency of panic attacks or their intensity. It was a very clear negative finding. And, if you think about it, the logic was very weak. The logic says, “CCK causes panic therefore panic is due to CCK.” Of course, the last part is a non sequitur. Management at Merck decided, quite rightly, that this whole program was not going anywhere and they cancelled the drug development. Despite the fact our lab in England had made a number of attractive looking second generation compounds we had to give up that whole thing. But, that’s the way it goes in the business of developing drugs.
We had another neuropeptide in the lab, which was still going strongly at Merck after my departure. That was Substance P. Substance P has been one of my interests since my days at Cambridge in the 1970s. At Merck, we tried to find drugs that worked as Substance P antagonists. We had the belief they might act in the spinal cord or brain stem, and represent a novel generation of analgesics, working in the central nervous system by non-opioid mechanisms. That was the objective.
We didn’t know how to find a non-peptide drug working on a peptide receptor, so we tackled this in two ways. We tried rational drug development, using the peptide itself as a model, making peptide analogues by cyclizing some peptide analogues of Substance P. That chemistry program yielded some antagonist compounds but these were not bioavailable. They didn’t get into the brain, being peptides, and they were not absorbed orally, so they didn’t really go anywhere from an in vivo pharmacology point of view. We also tried natural product screening to see if we could find a lead. That was how the cholecystokinin program had started at Merck some years earlier. We tried to do the same with Substance P. We plugged our assays into a large lab in Spain doing such screenings for Merck and we ran screening, which we thought at that time was on quite a large scale, about 50,000 tests a year for two years. Nowadays, you do that in one week. At the end we had absolutely nothing, so we had to pull that program. By the late 1980s we had to admit that we hadn’t got anywhere at all with our Substance P program and were about to give it up.
But then the first real breakthrough came in this area, the Pfizer SP antagonist was presented in a paper published in January 1991. This was a non-peptide antagonist molecule with sub-nanomolar affinity for the NK1 receptor relevant to the action of Substance P. The whole field broke open from that discovery. We discovered, along with many other companies, that if we searched the Merck chemical library using the Pfizer pharmacophore we could pull out other compounds that had reasonable activity at the Substance P receptor, and could develop our own chemical series. We went into this in a very big way, with chemistry on both sides of the Atlantic, and generated multiple series of NK1-selective Substance P antagonists. We tested them in a number of animal tests, thinking naively, that once you had the Substance P antagonist, you’d be able to understand what Substance P was all about very quickly. And, of course, life isn’t so simple. We found that in pain models these compounds were not particularly good analgesics. In fact, in most acute pain tests, in which morphine works well, the Substance P antagonists didn’t work at all. Only in chronic models of pain did the SP antagonists appear to have some beneficial effects. More than 12 clinical trials have been reported by Merck and others for different types of clinical pain in which the SP antagonists have not been found to be effective pain relievers. Our original idea just didn’t work but by the time I left Merck, we’d developed another idea.
TB: When did you leave Merck?
LI: I left in 1995. By that time, we had picked up on the idea that the vagus nerve has a large proportion of SP-containing sensory fibers and one of the functions of these fibers is in the vomiting reflex. The vagal nerves go to the nucleus tractus solitarius and then to the nearby area prostema and that’s the vomiting reflex circuitry. We showed in animal models that Substance P antagonists were very potent antiemetic agents and they worked against a wider range of emetic stimuli than the classical 5HT3 antagonist drugs, then the clinical gold standard. They also worked in the “secondary phase” of vomiting seen in cancer chemotherapy with agents such as Cisplatin (cis-diamminedichloroplatinum) that can go on for several days and is relatively unresponsive to 5-HT3 compounds. The Merck development compound “Emend®,” a Substance P antagonist, went into clinical trial just after I left the company and was, indeed, very effective as an antiemetic against the secondary phase nausea in cancer therapy. It was subsequently approved and marketed.
The other discovery made after that was what I call a “rainy afternoon experiment” by one of our scientists. When you finish your week’s work on a Friday afternoon, particularly if it’s raining, and do an experiment because you have a good idea, that is what I call a “rainy afternoon experiment.”
Nadia Rupniak in the behavioral lab at Merck did something like that. She did a Substance P antagonist study using an animal model predictive of anxiolytic-antidepressant activity. In the model the infant pup is separated from the guinea pig mother and the pup emits distress by vocalization than can be picked up and recorded. If the animals are treated with antidepressants, such as fluoxetine, or with anxiolytics, such as diazepam, this phenomenon can be prevented or reversed. Nadia showed that the Substance P antagonist she had available did so in a very potent way. Then, she went on to show similar activity in a number of other of these compounds.
Merck senior management took the bold move of going straight into the clinic for a trial in depression, doing a head-to-head comparison study with paroxetine, one of the SSRI antidepressants, and showed that the Substance P antagonist used in that study was as effective as paroxetine and lacked the sexual dysfunction side effect that seemed to affect a high proportion of SSRI treated patients. That compound went on to further development and Merck management learned some of the rules about antidepressant drugs, namely, that they don’t always work in clinical trials. They were very disappointed by a second study done in 650 patients, a dose- ranging study, using fluoxetine as the positive comparator. Fluoxetine didn’t work and the Merck compound didn’t work and the probable explanation is that the patients included in the study were suffering from mild depression and the placebo effect, which is well known to be greatest in mild depression, killed the outcome. Having worked with neuropeptide pharmacology for 30 years, it was gratifying to see some practical outcome with “Emend®” from all that.
Those are some of the highlights of my time at Merck. Some of the other things that could have happened, but didn’t happen, might be worth mentioning. When I first joined in the early 1980s Merck had just completed a large scale clinical trial in the USA and Canada with one of the first SSRI’s, zimelidine. Zimelidine was developed by Arvid Carlsson and the Astra Company in Sweden, and by that time it was already on the market as an antidepressant in Europe. The findings in the Merck clinical trials with zimelidine looked wonderful, with very good clinical data. I think it was a 4,000 patient, very large scale, Phase 3 study. I was there at the Clinical Neuroscience Group at Merck when they were packing up all the papers that go from floor to ceiling for the FDA NDA submission. They hired a truck to take the papers to Washington. Merck could have been first in the U.S. market with an SSRI, but the compound developed serious complications. In Europe there were some Guillian-Barre Syndrome episodes and Astra rightly decided to pull the compound off the market. So, it never got to the market in America. Merck had another shot at this a few years later with another SSRI, fluvoxamine, licensed from Duphar, a Dutch company. That went into early stage clinical trials and caused nausea, vomiting in a large proportion of patients and Merck stopped further development.
I’ve been enormously privileged to work in world class labs in the US and to work for a world class company, which has been a huge learning experience for me. A great deal of good science has come from the Merck lab and I was given a great deal of autonomy in the scientific direction of an entirely new program of neuroscience projects.
TB: What did you do after you left Merck?
LI: I’ll just add a couple of notes about my interests since leaving Merck. Since leaving Merck, I have developed quite a strong interest in cannabis pharmacology. Again, as with many things in life, partly by accident, I was recruited by the UK Government’s House of Lords’ inquiry into the medicinal use of cannabis about five years ago and had to advise their Lordships on what questions to ask and what witnesses to call on this issue. I had to learn quickly about the field myself, which I hadn’t worked in before. I became very interested in the subject and the House of Lords produced a report suggesting there may be some grounds for the medicinal use of cannabis in certain conditions, particularly, multiple sclerosis, and left it at that. The government of the day, in 1998, said we don’t want to know about that because we know we’re not going to do anything on this issue. They looked at the medicinal use of cannabis as a gateway into legalizing the drug and didn’t want to take this up. This was in 1998. And, it is interesting to see how the field has developed with the discovery of cannabis receptors, endogenous cannabinoids and the prospects of a whole new pharmacology evolving.
The potential for developing new medicinal agents in this area is very great. Attitudes to the medicinal use of cannabinoids have changed quite markedly just in the last two or three years. The Medical Research Council in Britain sponsored two quite large scale trials of oral cannabis extract vs. pure tetrahydrocannabinol vs. placebo in patients with multiple sclerosis, a 600-patient study, and in patients with chronic pain, which is a 200-patient study. This is, for the first time, a proper scale clinical study on whether cannabis works or not. There’s also a commercial company in Britain, G. W. Pharmaceuticals, who are doing their own clinical trials of a herbal cannabis extract in MS and pain and a number of other indications. Our government has said that if adequate clinical data can be produced to the regulatory agencies, they will declare cannabis no longer to be an illegal drug for medicinal use and they will sanction and license it. That will be, if it happens, a large advance. On our side of the Atlantic, things are happening. Even politicians are getting the message that the way in which we’re waging war on drugs is not working. We try to convey to young people that cannabis is a poisonous, deadly drug. This is something that is counter-intuitive to them, because they see their peers and even their parents smoking cannabis without harm. So, they just don’t believe the government message.
TB: What are you working on right now?
LI: In my present job, I’m a part-time academic at King’s College, London. In the merged medical school of Guy’s and St. Thomas hospitals at Kings College we’re building a new research center for age related disease on the Guy’s campus. Indeed, we have already built the center, courtesy of a large charity grant from Lord Wolfson and his Foundation. I’m trying to help them build that into a world class center for Alzheimer’s disease research, a topic which is very much neglected in Europe.
TB: So, that’s what you have been doing these years?
LI: In addition, I have been advising small companies how to get off the ground in the biotech pharmaceutical area. I work with a small company in California, one in Germany and one in Denmark. I have my own small company in England. I advise venture capital funding in Denmark. I do various things, which tap into my experience over the years as a scientist and as a pharmaceutical industry executive.
TB: You have been involved in neuropsychopharmacology for a long time. When did you attend the first meeting of the ACNP?
LI: I think in the 1970s. I was invited to one of the catecholamine sessions, but I wasn’t a member until the mid 1980s. Since then I’ve been a fairly regular attendee. I find it very beneficial to hear what’s going on in the field. It’s one of the best places for finding out what’s going on.
TB: You mentioned that you had been working with your wife, who’s a psychologist.
LI: Yes, Susan joined the Merck labs shortly after I moved there and she headed a substantial group of behavioral pharmacology scientists for about nine years and left to take a Chair of Psychology at Oxford, which is where she is now.
TB: Didn’t you write a book with her?
LI: Yes, in the 1970s. Susan wrote most of this short textbook on behavioral pharmacology, which we felt there was a need for at the time.
TB: It was a very successful book.
LI: Yes, as textbooks go. More recently, with my cannabis interest, I’ve written a book on The Science of Marijuana, also for Oxford University Press, which I enjoyed doing. It was an attempt to bring a neutral scientific analysis of the evidence, pro and con, to a general well-educated but not a scientific readership. That book did quite well, going into paperback, and had a second updated edition later.
TB: When did you publish your first paper?
TB: Wasn’t it on norepinephrine uptake?
LI: Yes, the very first study we did was repeating some of the work done at NIH in Julie Axelrod’s lab. It was on what happens when you inject radiolabeled norepinephrine intravenously into a mouse. When you inject a catecholamine intravenously, after a certain period of time, it will disappear. But that was not actually what was happening. When you inject the radiolabeled norepinephrine in a low dose and follow it over time, a lot of it disappears in the first few minutes but almost half remains in the animal for many hours What happens is that some the injected NE goes to the liver and gets metabolized rapidly by COMT and monoamine oxidase, but some gets taken up by peripheral synthetic nerve endings and stays until it gets released and eventually disappears. And this takes hours. We were able to show that epinephrine was somewhat less vulnerable to uptake and retention than NE.
TB: Where was it published?
LI: British Journal of Pharmacology.
TB: What was your most recent paper?
LI: If you count reviews, the one I’m most proud of is a large review on Cannabis. It was published in the journal, Brain, a distinguished neurology journal. It is unlike the book I wrote on the subject, a much more detailed academic review.
TB: What would you think is your most important contribution to the field? You moved in your research from uptake mechanisms to Alzheimer’s disease.
LI: I think my contributions to schizophrenia were, at the time, quite important, but rapidly superseded by more important events. In the neuropeptide field, I’m pleased to have been one of the pioneers of the field, who kept with it for many years. Tomas Hökfelt and I now sit down together and remember we stayed with this for 30 years and we’re finally seeing some results from it. So, that’s incredible. We can’t claim to be the ones that produced all the results, but we were there in a pioneering field, popularizing the idea. That was important.
TB: What would you like to see happen in the future in the field?
LI: I would like to see a better way of conducting clinical studies in Alzheimer’s disease, which, I think, is urgently needed. It’s very gratifying to see the enormous basic research and pharmaceutical company effort in this area, not just treating the symptom but the illness itself, understanding the molecular and genetic basis. We’ve made really big advances, but I think clinicians will admit they’re still very poorly equipped to identify the right patients to treat at the right time. If we find a new drug that interferes with the process of Alzheimer’s disease, we need to identify patients in an early stage of their disease. By the time you get clinical symptoms, you’ve probably lost a significant amount of brain tissue and there’s no pharmacologist in the world who’s going to put that back. The challenge in this aspect of psychopharmacology is to find better ways of looking into the human brain, seeing how to visualize the amyloid, which is beginning to happen, having better diagnostic imaging and neuropsychological tests.
TB: Is there anything else we should have on the record?
LI: I’m delighted to see, in the field of schizophrenia, we finally, in the year 2002, are beginning to see the payoff from the human genome project. We’re beginning to see the first real insights into the genetic basis of psychiatric illness. Schizophrenia may be one of the first and that’s tremendously exciting. It’s a whole new era of fresh targets and pharmacology.
TB: I think we should conclude this interview on that note. Thank you very much.
LI: It was my pleasure, thank you.
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January 7, 2021