This work is part of a larger screening program, which seeks to discover new antitumor plants and compounds from the Brazilian Amazon. In a prescreen of stem and leaf extracts of Tachia grandiflora Maguire & Weaver (Gentianaceae) based on the SRB method, leaf methanol and ethanol extracts showed appreciable cytotoxicity in human breast (MCF-7) and colon (HCT-8) tumor cell lines. Liquid-liquid partitioning of the leaf ethanol extract yielded hexane, chloroform, butanol, and water-methanol fractions. Only the hexane and chloroform fractions were active, inhibiting murine melanoma (B-16) and HCT-8 cells. The chloroform fraction suffered sequential column chromatography on silica gel using different eluent systems and yielded a number of very active subfractions. In all, 25 fractions and subfractions were tested, and 10 exhibited high growth inhibition of HCT-8, and two of these presented strong inhibition of murine melanoma (B-16) cells. The most active subfractions were tested against five tumor cell lines (leukemia CEM and HL-60, as well as the three used previously) using the MTT assay, and four fractions demonstrated significant cytotoxicity based on IC50. Cell lysis was discarded as a possible mechanism for in vitro cytotoxicity given that these fractions did not exhibit hemolytic activity. The greatest antiproliferative potential was found in the second (two samples) and third generation (two samples) chromatographic subfractions of the chloroform fraction (obtained from partitioning of the ethanol extract). These subfractions proved to be complex mixtures from which no pure substance could be isolated after further chromatographic separations. © 2007 Informa Healthcare.
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