Flavonoids are part of a large family of polyphenols that are found extensively in fruits and vegetables. This class of compounds has been of considerable medical interest due to their anti-inflammatory and anti-cancer activities. Although extensive effort has been made to identify the biological effects responsible for the chemopreventive activity of these compounds, the exact molecular mechanisms involved are not fully understood. In this study, we focused on the cytotoxic effects of fourteen different flavonoids against a series of breast cancer cell lines and evaluated the induction of cell cycle arrest at G1 or G2/M phase as result of such treatment. We also assessed a possible structure-function relationship for cellular cytotoxicity based on the various chemical structures of flavonoids. The results showed that several flavonoids were cytotoxic in all cell lines even in the absence of certain signaling pathways. In addition, only some flavonoids were able to induce cell cycle arrest, suggesting their cytotoxic potential may be independent of their ability to block cells at G1 or G2/M phases. Our results enabled identification of certain structural properties that are important for the anticancer activity of flavonoids. Finally, these results suggested that cytotoxicity does not depend on a particular signaling pathway
