In vitro activity: Anastrozole has high intrinsic potency in vitro and inhibits human placental aromatase with an IC50 of 15 nM. Anastrozole it is 200 times as potent as AG, twice as potent as 4-OHA and one third as potent as fadrozole. Anastrozole inhibits aromatase by binding competitively to the hem group of the CYP unit of the enzyme thereby reducing estrogen biosynthesis in the periphery and the breast. Anastrozole has little or no effect on other steroid hormones.

Kinase Assay: Aromatase inhibition is measured using human placental microsomes and the method of Thompson and Siiteri with Testosterone (0.5 μM) as substrate. 11-hydroxylase inhibition is determined by measuring the conversion of [1,2,6,7-3H]-ll-deoxy- cortisol to cortisol using freshly prepared mitochondria from guinea pig, dog and cow adrenal glands. Reaction products are extracted into chloroform and separated by thin layer chromatography.

Cell Assay: Anastrozole is a comparatively simple, achiral benzyltriazole derivative, that inhibits human placental aromatase with an IC50 of 15 nM. In the same assay it is 200 times as potent as aminoglutethimide (AG), twice as potent as 4-OHA and one third as potent as Fadrozole.