Isoalantolactone, a sesquiterpene lactone from Artemisia afra Jacq. ex Willd and its in vitro mechanism of induced cell death in HeLa cells

• A sesquiterpene lactone, isoalantolactone, is isolated from A. afra.
• Isoalantolactone significantly contributes to the cytotoxicity of A. afra.
• Isoalantolactone induces the intrinsic mode of apoptosis in a caspase-dependent manner
• G2/M arrest is induced by isoalantolactone, which may cause mitotic catastrophe

Isoalantolactone is a sesquiterpene lactone (SL) that has not yet been isolated from Artemisia afra, a South African plant that is commonly used in the Eastern Cape Province as a traditional remedy for inflammation and respiratory ailments. Recently, an ethanol extract of A. afra has shown to induce caspase-dependent apoptosis in a mitochondrial-dependent manner. In the current study, bio-assay guided fractionation was used to isolate isoalantolactone from A. afra. Structural elucidation was done by IR, 1D and 2D NMR, CD and mass spectrometry. HeLa cancer cells were treated with isoalantolactone and cytotoxicity was exhibited in a dose-dependent manner. A low IC50 value of 8.15 ± 1.16 μM was achieved. In this study, we show that after 24 h of treatment of HeLa cells with 8.62 μM isoalantolactone, a delay in G2/M phase of the cell cycle was evident accompanied by a decrease in mitochondrial membrane potential. Apoptosis was confirmed using the TUNEL assay to detect DNA fragmentation and phosphatidylserine translocation was detected using Annexin-V/FITC staining after 24 h of exposure to this compound. In summary, we show that cytotoxic isoalantolactone isolated from A. afra induces apoptosis in a mitochondrial and caspase-dependent manner and thus contributes to cytotoxicity induced by A. afra.