Cytotoxic phytochemicals from the crude extract of Tetrapleura tetraptera fruits towards multi-factorial drug resistant cancer cells

Ethnopharmacological relevance: Tetrapleura tetraptera is an African medicinal spice used in traditional medicine to treat several ailments including cancer. Aim of the study: The present study was designed to evaluate the cytotoxicity of the dichloromethane-methanol (1:1) extract of the fruits of Tetrapleura tetraptera (TTF) and its constituents: (3R, 4S)-3,4-dimethyloxetan-2-one (1), luteolin (2), stigmasterol (4), 3-O-[6'-O-undecanoyl-/3-D-glucopyranosyl]stigmasterol (6), olean-12-en-3/3-O-D-glucopyranoside (7), 3-O-/3-D-glucopyranosyl-(1 -> 6)-/3-D-glucopyranosylurs-12-en-28-oic acid (8), 3-O/3-D-glucopyranosyl-(1 -> 3)-/3-D-glucopyranosyl-27-hydroxyolean-12-ene-28-oic acid (9), methyl-O-/3-D-glucopyranoside (10), /3-D-fructofuranosyl-(2 -> 1)-/3-D-glucopyranoside (11) towards a panel of cancer cell lines including MDR phenotypes. The cellular mode of induction of apoptosis by TTF and compound 7 was further investigated. Materials and methods: The resazurin reduction assay (RRA) was applied to determine the cytotoxicity of the studied samples. The cell cycle (PI staining), apoptosis (annexin V/PI staining), mitochondrial membrane potential (MMP; JC-1) and reactive oxygen species (ROS; H2DCFH-DA) were measured by flow cytometry. Column chromatography was used for the purification of TTF, whilst nuclear magnetic resonance (NMR) spectroscopic analysis was applied for structural elucidation. Results: The botanical, TTF and the phytochemicals, 2, 7, 8 and 9 as well as doxorubicin exerted cytotoxicity against 9 cancer cell lines including drug-sensitive and drug resistant phenotypes. TTF, compound 7 and doxorubicin were the most active samples, and displayed IC50 values ranging from 10.27 mu g/mL (in CCRF-CEM leukemia cells) to 23.61 mu g/mL (against HCT116 p53(-/-) colon adenocarcinoma cells) for TTF, from 4.76 mu M (against CCRF-CEM cells) to 12.92 mu M (against HepG2 hepatocarcinoma cells) for compound 7, and from 0.02 mu M (against CCRF-CEM cells) to 122.96 mu M (against CEM/ADR5000 cells) for doxorubicin. TTF induced apoptosis in CCRF-CEM cells through MMP alteration and increased ROS production while compound 7 induced apoptosis mediated by caspases activation, MMP alteration and increased ROS production. Conclusion: Tetrapleura tetraptera and some of its constituents, mostly compound 7 are good cytotoxic natural products that should be explored in depth to develop new drugs to fight cancers.