Cytotoxic metabolites from the aerial part of Onopordum heteracanthum growing in Saudi Arabia

Abstract

Six known metabolites: β-amyrin-3-O-stearate (1), taraxasterol acetate (2), lupeol (3), 27-nor-3β-hydroxy-25-oxocycloartane (4), stigmasterol (5), and scutellarein-6-methyl ether (6) were isolated from the CHCl₃ and EtOAc fractions of the aerial parts of Onopordum heteracanthum C.A. Mey (Asteraceae). Compounds 1 and 4 are reported for the first time from the genus Onopordum, while compounds 2, 3, 5, and 6 are reported for the first time from O. heteracanthum. Their chemical structures were established based on comprehensive spectroscopic analyses, together with comparison to literature data. The cytotoxic activity of these compounds was assessed against breast adenocarcinoma (MCF-7), human hepatocellular carcinoma (HepG2), and colorectal adenocarcinoma (HCT-116) tumor cell lines using the sulphorhodamine B assay (SRB). Compound 4 exhibited notable cytotoxic activity against MCF-7, HepG2, and HCT-116 cells (IC₅₀ values of 2.1 ± 0.06, 2.5 ± 0.06, and 2.9 ± 0.05 µM, respectively), compared with doxorubicin (IC₅₀s 0.2 ± 0.008, 0.6 ± 0.05, and 0.18 ± 0.005 µM, respectively). Compounds 1, 3, and 6 showed moderate activity, whereas compounds 2 and 5 were weak or inactive. These results highlighted the potential of O. heteracanthum as a source of bioactive triterpenoids with promising anticancer activities.

KEY WORDS: Onopordum heteracanthum, Triterpenes, Cycloartane, Flavonoid, Cytotoxicity

Bull. Chem. Soc. Ethiop. 2026, 40(10), 2069-2080.                                                     

DOI: https://dx.doi.org/10.4314/bcse.v40i10.2