Role of Natural and Synthetic Flavonoids as Potential Aromatase Inhibitors in Breast Cancer: Structure-Activity Relationship Perspective.

World Health Organization categorized breast cancer as one of the leading cancer types in females worldwide, and its treatment remains challenging. Accumulated evidence suggested the role of estrogen and its metabolites in pre- and post-menopausal women. Upregulation of estrogen-dependent aromatase is significantly involved in the pathogenesis of breast cancer. Several aromatase inhibitors, such as exemestane, formestane, and letrozole, are being used clinically, owing to their estrogen suppression role. Apart from these drugs, several other molecules, such as natural and synthetic flavonoids, have been reported widely for a similar biological activity. However, some reasonable modifications are required for these structures to achieve desired efficacy and to alleviate toxicity. Designing a novel aromatase inhibitor will be possible if we can establish a rational correlation between the chemistry and biological features of the existing molecules. The benzopyranone-ring system, present in the flavonoid molecules, has been reported as a pharmacophore due to its inhibitory activity on aromatase, which helps repress breast cancer progression. This essential feature has been utilized to modify several natural flavonoids into 5 and 7 hydroxy/methoxy flavone, 4-imidazolyl/triazolyl flavone, 5,4'- diamino flavone, 7,8- benzo-4-imidazolyl flavone, α-naphthoflavone, and 2-azole/thiazolyl isoflavone derivatives. These scaffolds have been considered in this review for meticulous study in aspects of the structure-activity relationship for aromatase inhibitory activity, and it would likely pave the way for designing a potential lead candidate in the future.