Anti‐Cancer Drug Discovery and Development in Brazil: Targeted Plant Collection as a Rational Strategy to Acquire Candidate Anti‐Cancer Compounds

Throughout medical history, plant products have been shown to be valuable sources of novel anti‐cancer drugs. Examples are the Vinca alkaloids, the taxanes, and the camptothecins, derived from the Madagscan periwinkle plant Catharantus roseus , the Pacific yew Taxus brevifolia , and the Chinese tree Camptotheca acuminata , respectively. For this reason, the South‐American Office for Anti‐Cancer Drug Development has implemented a large‐scale project of acquisition and testing of compounds isolated from South American medicinal plants. The species are selected on the basis of a potentially useful phytochemical composition by consulting ethnopharmacological, chemosystemic, and ecological information. The collected samples are dried and first extracted with an organic solvent, then with distilled water. These crude extracts are evaluated at a concentration of 50 μg/ml for antiproliferative activity against one cell line. Extracts that significantly inhibit the growth of the cells (≥50%) at relatively low concentrations (≤50 μg/ml) are submitted to the more comprehensive disease‐oriented screen of the U.S. National Cancer Institute. In parallel, these samples are further purified by bioassay‐guided purification, involving repeated fractionation by diverse chromatography methods. If the active substance is expected to represent a novel structure, it is identified by appropriate chemical techniques, mechanistic studies are performed with a wide diversity of tumor models and laboratory techniques, and efforts are undertaken for the synthesis of potentially more useful analogs.