Cytotoxic alkaloids from the roots of Tabernaemontan elegans

Tabernaemontana elegans is a traditional medicinal plant used in Mozambique to treat several diseases including cancer. The Dragendorff's reagent lead chromatographic fractionation of the methanolic extract of Tabernaemontana elegans yielded seven monoterpene indole and bisindole alkaloids. Their structures were established mainly by 1D and 2D NMR data. The cytotoxicity of alkaloids was evaluated in HCT116 colon carcinoma cells by the CellTiter 96® AQueous Non-Radioactive Cell Proliferation Assay employing 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS), and phenazine methosulfate (PMS) as electron coupling reagent. Conversion of MTS into aqueous soluble formazan was accomplished by dehydrogenase enzymes in metabolically active cells, and absorbance was directly proportional to the number of viable cells in culture. After 48h of compound incubation, the absorbance of soluble formazan product was measured directly from 96-well plates without additional processing, at 490nm, using a microplate reader (Bio-Rad). Bisindole monoterpene indole alkaloids were cytotoxic to HCT cells, showing comparable results to positive control, 5-fluorouracil