The Medicinal Value of Biodiversity: New Hits to Fight Cancer

Natural products are produced by a wide range of different organisms. Microorganisms, plants, marine species, and animals employ such compounds for several purposes such as building blocks, coenzymes and cofactors, host-defense against microbial infection and predators, protection of ecological niches, communication between and within species, pigments, cellular signaling, gene expression, and homeostasis maintenance. Currently, many key therapeutic classes of drugs in use are derived from natural products, such as the antimalarial drug artemisinin, several anticancer agents, the lipid-lowering statins and immunosuppressors used to prevent the rejection of tissue grafts (Harvey, 2010). Since ancient times, natural products represent the main source of compounds employed in drug discovery and development. Still now, nature provides the mankind with a diversity of small bioactive compounds, opening promising avenues for the treatment of a great variety of diseases. Indeed, through millions of years, natural products have evolved to encompass a broad spectrum of chemical and functional diversity that enables them to target of a nearly limitless number of biological macromolecules in a highly selective manner. In contrast, synthetic molecules generated by combinatorial chemistry show lower chemical diversity and selective action than their natural counterparts. Because of these characteristics, natural products, mostly plant secondary metabolites, have seen great success as therapeutic agents. In fact, about 50% of the drugs introduced in the market during the last 20 years were derived directly or indirectly from bioactive compounds. Interestingly, of the approximately 1,200 new medicines approved by the FDA in the 25-year period up to 2006, only around one-third of the small molecules were completely synthetic in origin, with the remaining being natural products, direct derivatives of natural products or synthetic compounds inspired by a natural product lead (Vuorelaa et al., 2004; Newman & Cragg, 2009; Harvey, 2010). Besides the known diversity of bioactive compounds, it is certain that a great number of novel nature-based molecular structural models, with novel biological activities, remain to be discovered. It is currently estimated that approximately 420,000 plant species exist in