Professor Brenda Costell (head of school of pharmacy, University of Bradford) gave a warm welcome to participants at the meeting. She referred to pharmacognosy's "long and pleasant history" at Bradford and said that the subject was a growing area that the school did not intend to allow to be under-represented.
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Ethnobotanist interviewing an indigenous healer in Soteapan, Mexico |
Professor Michael Heinrich (chair in pharmacognosy, centre for pharmacognosy and phytotherapy, School of Pharmacy, University of London) discussed ethnobotany and its role in drug discovery.
He referred to the "enormous botanical diversity" of Mexico and described some of the work that his group had done with communities there. Several approaches had been used in field studies, including carrying out interviews with traditional healers to gather information on plants they used to treat different illnesses, and the use of travelling herbaria which were presented to healers and teachers in order to gather more information about the traditional uses of different plants. Field studies, which usually took around 15 months, also included preparing voucher specimens, and observing what indigenous peoples did at healing ceremonies and how recipes were prepared.
Field studies with Mayan communities in the Yucatan, Mexico, the Nahua (Veracruz) and Zapotec (Oaxaca) had been completed. Total numbers of species described in these studies were 320, 203 and 445, respectively. Professor Heinrich's group had also counted the "total number of use reports" (ie, individual reports on the use of a certain species). These data could be used to obtain "parallel use reports" which gave an idea of the inter- and intra-cultural importance of different species. Other studies involving the Washambaa, the main ethnic population of the Western Usambara mountains in Tanzania, had described 328 plant taxa with 2,260 use reports. Gastrointestinal disorders represented the disease category for which there had been the highest proportion of use reports for plants.
Professor Heinrich also drew attention to the importance of protecting and respecting the rights of indigenous peoples in carrying out ethnobotanical research and in ensuring that they were appropriately rewarded for the use of their resources.
Professor Peter Houghton gave a summary of the use of bioassays - the use of a biological system to detect properties of a mixture or a pure chemical - in natural product drug discovery.
Bioassays could involve the use of in vivo systems (clinical trials, whole animal experiments), ex vivo systems (isolated tissues and organs) or in vitro systems (eg, cultured cells). Collection of material for testing in bioassays could either be random collection of samples or directed collection, ie, from plants known to be used traditionally.
Bioassays were often linked with the processes of fractionation and isolation, known as bioassay-guided fractionation. According to Professor Houghton, there was often a reduction in or loss of activity after fractionation. There might be several explanations for this: for example, it might be due to the breakdown of compounds as a result of the fractionation process, or because of a loss of synergy when individual constituents of a plant extract were separated.
There were several other problems with bioassays as a method of novel drug discovery:
Professor Houghton also outlined the advantages and disadvantages of in vivo and in vitro studies. In vivo studies were relevant to clinical conditions and also provided toxicity data, but costs, complex designs, patient recruitment and the difficulty in determining mode of action were among their disadvantages. In vitro studies were faster and used relatively small amounts of materials, but activity might be missed, for example, where a metabolite rather than the parent substance was the active component.
Dr Daryl Rees (Phytopharm Ltd) said a botanical had been defined as "a standardised extract of medicinal plants in which the chemical composition is not fully specified" and described how the conventional pharmaceutical approach to drug discovery and development could be applied to botanical products.
In the early clinical evaluation of botanicals, promising leads were judged according to medical and commercial criteria. Promising clinical leads triggered full development programmes, and data based on effects in humans were used to guide mode of action studies. Referring to the quality of botanical products, Dr Rees emphasised that specialised knowledge was needed to be able to control quality - good agricultural practice needed to be linked with good manufacturing practice.
Dr Rees described several plant extracts in development with Phytopharm. P7 was a three-plant product that had shown encouraging results in studies in canine atopy. P54 was made from extracts of two plants, one of which was turmeric (Curcuma longa).
According to Dr Rees, C longa had anti-inflammatory activity associated with gastroprotective effects, and might have potential in the treatment of Crohn's disease.
Summing up, Dr Rees said that the botanical paradigm combined drug discovery with drug development. One of the advantages of this approach was that it could reduce the risk of late failure of a product.
The prestige lecture was delivered by Professor Douglas Kinghorn (University of Illinois at Chicago, United States) who commended the "sterling efforts" of some of the pioneers in pharmacognosy.
Presenting data from six countries on the organisation of pharmacognosy (see Table), Professor Kinghorn said: "I urge policy makers in the United Kingdom to consider this position so that we can get numbers approaching this." He referred to the "staggering output" from Japan and said that the country was leading the way in pharmacognosy in the new millennium. Japan, with 53 papers, was top of the list of countries with papers co-authored by individuals from schools and colleges of pharmacy published in the 1999 issues of the Journal of Natural Products (of which Professor Kinghorn was editor-in-chief). By contrast, the UK was 16th in the list with three such papers.
The organisation of pharmacognosy (data presented by Professor Douglas Kinghorn) |
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| Number of: | Country | |||||
| US | Japan | Germany | France | Italy | Turkey | |
| Colleges/faculties/institutes of pharmacy | 81 | 45 | 22 | 23 | 32 | 8 |
| Pharmacognosy laboratories | 30 | 46 | 22 | 14 | NS | 8 |
| Full professors | 45 | 68 | 25 | 35 | 13 | 25 |
| Members of national pharmacognosy organisations | >1,100 | 1,400 | 1,000 | 100 | 150 | NS |
Professor Kinghorn referred to the major increase in the use of botanicals in dietary supplements by the US public as having a major influence on research opportunities in pharmacognosy/natural products - "I can't emphasise enough how important this is," he said. The US National Institutes of Health had provided over US$50m of funding for research into complementary and alternative medicine.
Other important initiatives were the creation of the Association of Natural Products Pharmacists, the inclusion of new botanical monographs in the US Pharmacopoeia, and the establishment of new chairs in pharmacognosy. "Pharmacists don't know much [about botanicals], but we have now put botanicals back into the curriculum." Professor Kinghorn remarked: "There is an inherent interest [in this area] from the students."
Professor Kinghorn went on to describe some of the major grants and research programmes that were being undertaken at the University of Illinois at Chicago. One of these, a collaborative project with the Research Triangle Institute and Bristol-Myers Squibb and funded by the National Cancer Institute, was concerned with the discovery and development of novel plant-derived anticancer agents. Several strategies were being used, including literature searches, collection of rainforest specimens and bioassay-guided fractionation. Out of this work, betulinic acid from the stem bark of Ziziphus mauritiana had been shown to be selectively cytotoxic for a human melanoma cell line and had also demonstrated inhibitory activity against tumour growth in mice.
Concluding, Professor Kinghorn said: "As we enter the new millennium, worldwide interest in pharmacognosy and natural products is at an all-time high. . . . Pharmacognosy remains a major part of the pharmacy curriculum in many countries, and it should be." In his view, the increasing interest in botanical products would create additional research opportunities in pharmacognosy.
The second day of the meeting, chaired by Dr Melanie O'Neill (Glaxo Wellcome) focused on biologically active compounds from natural sources other than plants. Dr O'Neill said that, in 1999, eight of the 30 top-selling medicines were natural products or were derived from natural products. These eight included the cholesterol-lowering statins (simvastatin, pravastatin), antibiotics (amoxycillin and clavulanic acid, clarithromycin, azithromycin, ceftriaxone), an immunosuppressant (cyclosporin) and an anticancer agent (paclitaxel), which together totalled US$16bn in sales.
Professor Gerald Blunden (school of pharmacy, University of Portsmouth) noted that marine organisms were a tremendous source of new compounds. Some compounds had a negative value, for example, shellfish toxins. Saxitoxin and neosaxitoxin were very common causative compounds involved in paralytic shellfish toxicity, which was characterised by muscle cramps and could be fatal. Saxitoxin was being developed as an agent for use in pharmacological models of paralysis. In amnesic shellfish toxicity, which could also be fatal, domoic acid was a causative compound. Other shellfish toxins, such as okadaic acid, caused nausea and diarrhoea but were not fatal.
Antimicrobial and antiviral agents had also been isolated from marine organisms. Cephalosporin C had first been isolated from a marine organism. Antiviral compounds, such as the didemnins, avarol and avarone, had been isolated from sponges. Bryostatins, such as bryostatin 1, were examples of antitumour compounds that had been isolated primarily from Bugula neritina. Cyclic and linear peptides and depsipeptides, collectively known as dolastatins, had been isolated from a sea hare species, Dolabella auricularia. These compounds had been shown to be inhibitors of cell growth in vitro; dolastatin-10 was highly antineoplastic.
Summing up, Professor Blunden told the meeting that a vast array of different structures had been isolated from marine organisms, including some with completely new ring structures.
Professor Bob Hider (school of pharmacy, King's College London) discussed physiologically active compounds from venoms. Venoms were, he said, incredibly subtle mixtures of compounds, and were a "virtually untapped" source for drug discovery. There were eight million species of insect, yet fewer than one million had been described. Similarly, only 10 per cent of the 750,000 species of arachnid had been described.
Until recently, a problem with investigating venom from smaller species had been that it was not possible to obtain enough venom. Now, however, using cloning and expression techniques, it was possible to make sufficient quantities - it was only necessary initially to obtain about 5ng of toxin and subsequently to isolate messenger RNA and incorporate it into bacteria for production of peptides and proteins.
According to Professor Hider, peptides were the main class of compounds found in venoms. Peptides were extremely versatile structures - there were 1013 different ways of building a decapeptide; for a 60mer, this figure was 1078. In his view, peptide and protein products were going to be increasingly important as pharmaceuticals.
Some work had been done on venoms from larger species, such as the black widow spider. However, the chemistry of invertebrate venoms in the insect and arachnid world was an area that needed further investigation, Professor Hider concluded.
Professor Chris Shaw (pharmaceutical biotechnology research group, University of Ulster at Coleraine) discussed antimicrobial compounds in amphibian defensive skin secretions. There were about 5,000 species of amphibian but, according to Professor Shaw, frog populations were disappearing. "Here is a resource we need to work on rapidly," he said.
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The red-eyed tree frog (Agalychnis callidryas) source of caerulein |
The most complex frog venoms found contained 1,200 to 1,400 compounds. Examples of peptides that had been isolated from frog venoms were caerulein (which mimicked cholecystokinin and was used in radiography procedures to contract the gall bladder) isolated from the red-eyed tree frog Agalychnis callidryas, bombesin (a 14-amino acid peptide isolated from the European fire-bellied frog) and sauvagine (analogues of which had anxiolytic activity), which was also found in the venom of A callidryas.
Antimicrobial compounds, such as bombinins from the Oriental fire-bellied toad Bombina orientalis, had also been identified. Bombinin, a 27-amino acid peptide had broad spectrum antimicrobial activity but was highly haemolytic. Another broad spectrum antimicrobial, magainin from Xenopus laevis, had low haemolytic activity compared with the bombinins. "We are getting closer to something that might be a lead for pharmaceuticals," Professor Shaw commented.
It was generally believed that magainin and other peptides functioned as defensive shields against surface infection. However, Professor Shaw questioned whether this was correct since the peptides were cytolysins and were, in his view, "spears not shields". The secretion from another species, Rana palustris, contained a range of peptides including esculentins (43 amino acids), brevinins (24 amino acids) and temporins (13 amino acids). In this species, the secretory glands were in stripes on the frog's back, not on the belly, and were again likely to function as spears not as a shield.
Temporin-1, a peptide from the garden frog Rana temporaria, was almost identical with one found in wasp venom. Similarly, another protein from a frog species showed 94 per cent homology with one from the venom of the black mamba snake. According to Professor Shaw, there were other examples of commonalities between frog, insect and snake venoms. "There's some message here," he remarked. "These are ancient defensive chemicals with a well-established function."
Summing up, Professor Shaw said that compounds isolated from frog venoms had demonstrable broad-spectrum antimicrobial activity, including activity against multidrug-resistant organisms, and that structure-activity studies were now required. He predicted that the discovery of these compounds would lead to a new generation of antimicrobials within the next five years. He ended with a quote from Shakespeare: "The toad, ugly and venomous, wears yet a precious jewel in his crown."
Professor David Hawksworth gave an overview of the range of bioactive compounds that could be found in lichens. Lichens were a symbiotic association of a fungus with an algal partner. They had a "sandwich-type" structure with a fungal layer on top and a bottom layer of fungal hyphae that attached the structure to rock or bark. About 13,250 species of lichen were known worldwide, although there might be up to 18,000 species in total.
A vast range of types of compound were produced by the fungal component, such as depsides and depsidones. These compounds were among those that gave rise to the colour of lichens. In many cases, crystals and secondary metabolites were found on the surface of lichens and were, therefore, easy to extract. Crystal formation could also be used in the identification of lichens.
Lichens had several modern-day uses. They were used in perfumes to stop the evaporation of volatile components, and Iceland moss (Cetraria islandica) was used in cough pastilles. Usnic acid, a dibenzofuran, was an antibacterial compound from the lichen Alectoria sarmentosa which had traditionally been used in wound dressings. According to Professor Hawksworth, there were many other leads that could be obtained from medicinal uses and folklore. "However, it is an area that needs more research. Lichens have not had that much attention from mycologists," he said.
Poster sessions
Thirty one posters were presented at the meeting covering subjects from phytochemistry to clinical uses of plant extracts.
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