Experimental and theoretical advances in functional understanding of flavonoids as anti-tumor agents.

The potential of flavonoids to act as anti-tumor agents has been recognized but not fully understood because flavonoids are acting at several stages in cancer progression with distinct structure-function relationships. A whole family of structurally different flavonoids is herein described by reviewing some critical aspects of their pro-oxidant behavior in vitro/vivo and in cell systems by which they may work as antioxidants. Different classes of flavonoids (chalcones, flavones, isoflavones, flavanols, flavanones and anthocyanins) are synthetically mimicked using natural product structure-antioxidant activity relationships that are relevant for their enhanced function against cancer as well as severe inflammation conditions under which an increased oxidative stress is often implicated. In the context of the common mechanisms of flavonoid action, clinical data on benefits of flavonoids in fighting against cancer are discussed. A structural basis needed to improve antioxidant activity of these agents is elaborated in more detail.