Metabolomic Profiling of Kigelia africana Extracts with Anti-Cancer Activity by High Resolution Tandem Mass Spectroscopy

Background: Kigelia africana is an African tree with a wide distribution across southern, central and western Africa. It has a history of therapeutic usage by multiple African ethnic groupings which inhabit the areas in which it grows. Amongst these groups there is a myriad of medicinal uses in the treatment of a wide variety of bacterial, fungal and protozoal infections, as well as in the treatment of inflammation and cancers. This study was undertaken to further examine K. africana fruit extracts for the ability to inhibit cancer cell growth, and to use an unbiased metabolomic profiling approach to detect and putatively identify as many individual components as possible, with the aim of developing a database of identified compounds. Materials and Methods: K. africana fruit powder was extracted and tested for inhibitory activity against the Jeg-3 choriocarcinoma cell line using a colorimetric cell proliferation assay. Toxicity was evaluated using an Artemia franciscana nauplii bioassay. Non-targeted HPLC separation of crude extracts coupled to high resolution time-of-flight (TOF) mass spectroscopy with screening against 3 compound databases was used for the identification and characterisation of individual components in crude plant extracts. Results: The methanol, water and ethyl acetate K. africana fruit extracts displayed significant anti- proliferative activity against Jeg-3 choriocarcinoma cells. The methanol and water extracts displayed the strongest anti-proliferative activity, inhibiting Jeg-3 growth to 42% and 46% of the untreated cell growth respectively. The ethyl acetate extract also significantly inhibited Jeg-3 cell proliferation, with decreases to 62% of the untreated control value. Neither the chloroform or hexane extracts had any effect on Jeg-3 cell proliferation. With the exception of the water extract (which displayed moderate toxicity), all extracts were non-toxic or of low toxicity. HPLC-MS/MS TOF analysis identified 356 unique mass signals in the extracts. The putative identities of 227 of these compounds are reported here. Conclusion: This report extends previous studies into the anti-cancer affects of K. africana fruit extracts. The generation of a database of the detected compounds will allow for rapid differentiation of compound profiles between active and less active extracts in future studies. This is expected to assist in the identification of the most important compounds for further separation and bioactivity studies.