Selective cytotoxic effects on human breast carcinoma of new methoxylated flavonoids from Euryops arabicus grown in Saudi Arabia.

The chloroform-methanol extract of Euryops arabicus, collected from Saudi provenance, yielded a new kaurane diterpene (1) and seven methoxylated flavones (2-8), two of which are new (2 and 3). Structures of the compounds were elucidated through interpretation of spectral data of NMR, MS and comparison with literature values. All compounds were evaluated for their anti-tumor activities, employing four different cancer cell lines (WI-38, VERO, HepG2 and MCF-7), ABTS free radical scavenging and immunemodulatory effects. All metabolites had considerable antioxidant and immunestimulatory effects. All compounds showed anticancer activity with IC₅₀ in range 10-125 μM, whilst 2 and 6 showed significant anti-proliferative activity against HepG2 (IC₅₀ = 20 and 15 μM) and MCF-7 (IC₅₀ = 15 and 10 μM), respectively. This effect was attributed to significant S-phase cell cycle arrest.