Cancer chemopreventive in vitro activities of isoflavones isolated from Iris germanica.

Six known isoflavones were isolated from the rhizomes of Iris germanica, and were established by UV, MS and NMR techniques as irisolidone (1), irisolidone 7-O-alpha-D-glucoside (1a), irigenin (2), irilone (3), iriflogenin (4), and iriskashmirianin (5). These compounds were examined for their cancer chemopreventive potential. They were shown to be potent inhibitors of cytochrome P450 1A activity with IC 50 values in the range 0.25-4.9 microM. The isoflavones 2, 3 and 5 displayed moderate activity as inducers of NAD(P)H:quinone reductase (QR) in cultured mouse Hepa 1c1c7 cells, with CD values (concentration required to double the specific activity of QR) of 3.5-16.7 microM, whereas weak activity was observed with compounds 4 and 5 in the radical (DPPH) scavenging bioassay (IC 50 values 89.6 and 120.3 microM, respectively). With respect to anti-tumor promoting potential based on anti-inflammatory mechanisms, none of the compounds demonstrated significant activity in the concentration range tested.