Isochondodendrine and 2′-norcocsuline: additional alkaloids from Triclisia subcordata induce cytotoxicity and apoptosis in ovarian cancer cell lines

Triclisia subcordata Oliv (Menispermeaceae) is used in herbal medicine for the treatment of cancer and other diseases in Africa. This study aims to isolate minor alkaloids present in this plant and assay their cytotoxic activities. Isochondodendrine and 2′-norcocsuline as two minor alkaloids together with the abundant cycleanine were isolated and identified by mass spectrometry and NMR spectroscopy. Both isochondodendrine and 2′-norcocsuline exhibited in vitro cytotoxicity in four ovarian cancer cell lines (A2780, IGROV-1, OVCAR-8, and OVCAR-4) with IC 50 ranges of 3.5–17 μM and 0.8–6.2 μM respectively. These alkaloids showed mostly slightly weaker potencies when tested using normal human ovarian epithelial cells, IC 50 = 10.5 ± 1.2 μM and 8.0 ± 0.2 μM for isochondodendrine and 2′-norcocsuline, respectively. The alkaloids induced apoptosis in ovarian cancer cells because they activated caspases 3/7, induced cleavage of PARP, increased the subG 1 population in cell cycle analysis and increased Annexin V/propidium iodide staining. These observations suggest that isochondodendrine and 2′-norcocsuline contributing to the cytotoxic activity of T. subcordata may be suitable starting points for the future development of novel therapeutics to treat ovarian cancer.