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Plants represent a gigantic source of active molecules of plant origin, and the resources of the flora are far from being totally inventoried. Around the world, we continue to search for plants that can be used as a basis for new treatments. Relatively recent, this systematic search for plant therapeutic resources opens up extremely promising prospects.

The world’s flora includes several hundred thousand different species, of which about 250,000 have been described and listed.But only 2,000 to 3,000 of them have been the subject of scientific, chemical or pharmacological studies. In addition, some of these relatively old studies deserve to be repeated in the light of current knowledge. Because, from now on, one is no longer satisfied to isolate the active principles of the plants or to determine their indications.

By synthetic chemistry, one can reproduce the molecules, modify them more or less importantly, and thus obtain derived substances with specific properties. A method ultimately less hazardous than that which would be to create ex nihilo an artificial molecule capable of acting in the human body.

A huge collection work remains to be done if we want to benefit from all the plant biodiversity and the therapeutic potential of the plants. Many species, indeed, are still unknown to us, especially those growing in the forests of Equatorial Africa, Southeast Asia, South America, or the Pacific Islands. It is also necessary to collect from the indigenous populations, all possible information on their traditional uses, in order to inventory the “healing plants” and to be able to identify them.

The search for new plants is entrusted to teams of ethnobotanists and ethnopharmacologists. The survey starts on the ground, and she can use different procedures. The collection, large and systematic, performed at random, allows to bring back a maximum of samples, which will then go through the analysis robots. In some laboratories of large pharmaceutical companies, there are machines capable of testing up to 100,000 samples per day! Nevertheless, this method remains laborious and its results are very random.

We can also systematically search for species of a family known to contain specific active substances. Thus, for example, many Rutaceae or Rubiaceae are sources of alkaloids: it is therefore plants of these families that we will first try to collect to find these substances. But most often, the ethnobotanist begins his survey by questioning the indigenous people, especially the healers and the people who are known to know the powers of the plants. He then selects the plants that seem interesting, note the name given to them in the local dialect, the parts used, their usual use and the virtues attributed to them.

Once the samples have been identified and collected in sufficient quantity, it is up to the chemists to play.

They make extracts of the raw material in order to isolate chemical constituents of the plant, pure or mixed. These extracts are tested – in vitro and in vivo – to first determine a possible toxicity and then to define their biological activity. The selection is severe: it is considered that at this stage a single molecule is retained for 10,000 compounds analyzed!

Clinical studies, generally very long, are then carried out: first on the animal, then on human volunteers. If the results are positive, the galenic work itself can begin: it is to give the active substance the drug form (capsules, tablets, liquid solutions …) under which it will be used and marketed. The last step, crucial for the pharmaceutical laboratory, is the application for marketing authorization (or AMM), made to government authorities. In total, it usually takes 12 to 15 years or more between forest collection and commercialization of the drug.

Prospecting projects for plant resources are developing around the world. But there are significant threats to biodiversity, and therefore to the capital of new medicinal molecules. If deforestation continues at the current rate, one-fourth of the tropical forest that exists today will have disappeared in 2025 and, with it, probably around 10% of the world’s plant species.

Hence the urgency to make an inventory as comprehensive as possible, and the need to ensure the preservation of local flora. This is reflected in the agreements signed between some governments and pharmaceutical companies: in exchange for access to genetic resources of native flora, the laboratory pays a fraction of the profits to national research and conservation organizations. the flora. Last but not least, bioprospecting must respect the rights of indigenous peoples to their medicinal plants.

Dr. Kimberly Seltzer

Postdoctoral Scholar, UC Berkeley Research Assistant, MIT

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