Electrochemical behavior and determination of tumor inhibiting or promoting activities of flavonoids.

This paper deals with determination of the tumor inhibiting or promoting activities of 11 flavonoids performed by DC polarography. Flavonoids were tested in the presence of polyaromatic carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) or in combination with DMBA and 12-O-tetradecanoylphorbol-13-acetate (TPA), which is known as a specific tumor promoter for epidermal carcinogenesis. We found that in this experimental system the promotory or inhibitory activities of studied flavonoids depend on the number and position of hydroxyl groups in their chemical structures and are related to the polarographic behavior of these compounds. Flavonoids, which are hydroxylated at the ring B, are reduced in anhydrous DMF on a mercury dropping electrode in two one-electron steps. Absence of the hydroxyl groups in these positions caused their reduction in three one-electron steps. Similarly, flavonoids with hydroxyl groups at the ring B have been shown to inhibit the activities of DMBA (2.7-45.9%) and of DMBA + TPA (47.2-78.2%). Missing hydroxyl groups caused weaker inhibitory activity against DMBA + TPA (19.01-38.74%) and the enhancement of DMBA activity (31.08-66.21%). Presented data demonstrated that the electrochemical method--DC polarography is very sensitive, simple technique for determination of the tumor inhibiting or promoting activities of the studied compounds.