This review begins with an introduction to the basic skeleton and classes of flavonoids. Studies on flavonoids have shown that the presence or absence of their functional moieties is associated with enhanced cytotoxicity toward cancer cells. Functional moieties include the C2C3 double bond, C3 hydroxyl group, and 4-carbonyl group at ring C and the pattern of hydroxylation at ring B. Subsequently, the current knowledge on the chemistry, sources, pharmacology, and anticancer properties of diosmetin (DMT) and tamarixetin (TMT), two lesser-known methylated flavonoids with similar molecular structures, is updated. DMT is a methylated flavone with three hydroxyl groups, while TMT is a methylated flavonol with four hydroxyl groups. Both DMT and TMT display strong cytotoxic effects on cancer cell lines. Studies on the anticancer effects and molecular mechanisms of DMT included leukemia and breast, liver, prostate, lung, melanoma, colon, and renal cancer cells, while those of TMT have only been reported in leukemia and liver cancer cells. These findings suggest that flavones lacking the C3 hydroxyl group at ring C are more cytotoxic than flavonols having the C3 hydroxyl group. The in vitro and in vivo cytotoxic activities of DMT and TMT against cancer cells involve different molecular targets and signaling pathways. From this study, it is clear that little is known about the pharmacology and anticancer properties of DMT and TMT. The potentials for further research into these aspects of the two lesser-known methylated flavonoids are enormous.
Key words: Methylated flavonoids, diosmetin, tamarixetin, cytotoxic, anti-cancer effects
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