New Insights into the Metabolic Profile and Cytotoxic Activity of Kigelia africana Stem Bark

Ultra-high-performance liquid chromatography coupled to Orbitrap high-resolution mass spectrometry (UHPLC-HRMS) was recently employed in many fields to obtain a rapid characterization of plant extracts. <i>Kigelia africana</i> (family Bignoniaceae) is a quintessential African herbal medicinal plant with immense indigenous medicinal and non-medicinal applications. The aim of the present research was to obtain an in-depth metabolite profiling of the <i>K. africana</i> stem bark extract using UHPLC-HRMS and to conduct a preliminary screening of its anticancer activity against a panel of malignant human cell lines of different origin. The UHPLC-HRMS analysis revealed 63 secondary metabolites including phenolic acids, gallo- and ellagitannins, iridoids, naphthoquinones, and anthraquinones. A total of 34 of all annotated compounds are reported for the first time in <i>K. africana</i> stem bark. The studied profile was dominated by trimethylellagic acid, dimethylellagic acid isomers, and ellagic acid. In all tumor models, we established a pronounced inhibition of cell growth in a mostly dose-dependent manner, with IC₅₀ values ranging near and well below (4-30 µg/mL) the lowest treatment concentration of 25 µg/mL. The established cytotoxicity profile of the <i>K. africana</i> extract, highly biased toward malignantly transformed but not normal cells, suggests specific modulation of defined molecular tumor targets. This study revealed <i>K. africana</i> stem bark as a new source of gallo- and ellagitannins, and highlighted the studied herbal drug as an antiproliferative agent with potential pharmaceutical application.