Methoxylated flavones, a superior cancer chemopreventive flavonoid subclass?

Dietary flavonoids and other polyphenols show great potential as cancer chemopreventive agents in cell culture studies. This does not translate well into in vivo activity, because of extensive conjugative metabolism of these compounds in the intestine and liver. This paper presents a review of a flavonoid subclass in which all hydroxyl groups are capped by methylation. This results in dramatically increased metabolic stability and membrane transport in the intestine/liver, thus improving oral bioavailability. The methoxyflavones also show increased cancer chemopreventive properties. At the cancer initiation stage, bioactivation of polyaromatic hydrocarbon carcinogens and binding to DNA are markedly diminished through effects on CYP1A1/1B1 transcription but also through direct interactions with the proteins. At the cancer promotion stage, the proliferation of cancer cells, but not normal cells, is inhibited with greater potency than with the unmethylated flavones. Limited mechanistic experiments, such as of effects on cell cycle regulation, indicate that the mechanisms of methoxyflavone activities are unique, including aromatase inhibition. The cancer preventive effects and mechanisms of the polymethoxyflavones, such as tangeretin and nobiletin, are discussed in comparison. It is concluded that the methoxyflavones have properties that may make them particularly useful as cancer chemopreventive agents.