The supply of plants for random screening programs

The use of plants in random screening must always involve a limited initial collection of material whether from an in-situ or ex-situ site. Depending on the success of the original sample a number of subsequent re-collections of much larger size may be necessary. McChesney (1992) suggests some numbers for the amounts of dried plant material necessary for completion of the following stages of drug development and marketing:

initial screening and isolation of lead compound: 5 kg of dried material, confirmatory screens and initial development: 50 kg, additional R&D through clinical testing: 200 tons,

'mass' collection or cultivation: as much as 200 thousand tons per year.4

If the commercial synthesis of a successful compound is feasible, then the ongoing 'mass' production of the species will, of course, not be required. Balandrin et al. (1985) suggest that as most natural product leads are secondary metabolites they will be difficult to synthesize and therefore will be costly. In this section the focus is on the initial collection of plant material that is required to confirm the classification of the biotic sample and to assess the biochemical activity in an initial screen. Although McChesney suggest 5 kg for this initial collection, 1 kg is the norm among most collectors. In fact, a much smaller amount of material is actually required for the sophisticated screens now available, but it is useful to have additional material on hand for use in other screens and to initiate pre-clinical development work.

As indicated earlier there are a number of types of information that may be used in selecting plant samples for primary screening. A full list includes:

collection information: date, location, site conditions, etc. taxonomic classification of the organism, ecological observations in the field that indicate biochemical activity, ethnobotanical information about traditional medicinal uses of plants, and

4 Note that these amounts are based on a worst-case scenario in which the active principle is present in concentrations of only 0.001%.

published reports of biochemical activity for a given species, genus or family.

The first two types of information must accompany all plant samples. This information is very important in ensuring the correct re-collection of further amounts of the same species for additional testing. Ecological observations and ethnobotanical information are optional and are typically gathered by the collector while in the field. The final type of information, published reports, is generated by drug researchers and used to direct the collecting process. The last three categories of information provide a means of 'prescreening' incoming material. In the case of random screening, these three types of information are not collected, thus lowering the initial costs of collection but potentially raising the number of species that need to be screened.

To fill demand for random screening programs pharmaceutical companies and public entities involved in drug research, such as NCI, depend on a range of collectors and intermediaries. The large botanic gardens and natural history museums in the USA and Europe are playing a major role, both in contracting out for the collection of samples and in conducting collecting expeditions, and in serving as an important source of taxonomic information for the purposes of species identification. In addition to the activities of these large institutions, individual collectors, often Northern academics, are often subcontracted to provide samples either to an intermediary such as a botanic garden or directly to a pharmaceutical company.

In the past few years, a number of innovative organizations have sprung up to provide pharmaceutical companies with alternative means of accessing the chemical diversity of the world's biodiversity. Biotics, a private British company, subcontracts the collection of samples to developing countries and carries out the initial processing, extraction of the sample, in its laboratories in the UK. Samples are then marketed directly to industry. Costa Rica's National Biodiversity Institute, a non-profit Costa Rican organization, has initiated a national inventory of biodiversity and has an active collecting program based on an agreement with the Costa Rican ministry responsible for the control of public wildlands.

To conclude the chapter a review of these two innovative institutions is provided in order to assess the potential of private companies and in-country national organizations in playing a significant role as brokers of tropical plants.

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