A Review on Anticancer Profile of Flavonoids: Sources, Chemistry, Mechanisms, Structure-activity Relationship and Anticancer Activity.

Background: Epidemiological studies have suggested that a regular intake of flavonoids is beneficial for cellular homeostasis and in the prevention of the transformation of normal cells into cancerous cells. Because of their multiple biological targets, flavonoids have been studied and investigated as phytoconstituents with potential anticancer properties. Flavonoids interfere in the development of cancerous cells by inhibition of topoisomerases, protein kinases, angiogenesis, induction of apoptosis, cell cycle arrest, modulation of multidrug resistance, and improvement in anti-oxidative activities. The current review summarizes the anticancer properties of flavonoids along with the key structural features and their mechanisms. The present study provides a detailed analysis of anticancer activities with previously published data on different flavonoids. The review highlighted the structural aspects and mechanism of action of flavonoids with their potential target sites. Flavonoids induce anticancer activity by protein kinases inhibition, P-gp modulation, antiangiogenesis, topoisomerases inhibition, etc. Open ring C, the double bond between C2-C3, the oxo group at C4, and the position of ring B are crucial determinants for their anticancer activity. Flavonoids act by multiple mechanisms but further studies on target selectivity and specificity of flavonoids are necessary to establish them as anticancer therapeutics. The presence of a C2-C3 double bond and oxo group at C4 (also known as an enone moiety) or -OH in the neighbour of a double bond that can transform easily into an enone are common features present in flavonoids. Thus, it can be concluded that enone moiety or its precursor groups are mainly responsible for the anticancer activities of flavonoids via different mechanisms of action.