Org 33201: a new highly selective orally active aromatase inhibitor.

Org 33201 has been selected as a very potent aromatase inhibitor. The compound is an enantiomer of a SC2H5 substituted imidazoylethylphenalene. Org 33201 inhibited human aromatase activity for 50% at a concentration of 2.2 x 10(9) mol/l. More than 200-fold higher concentrations were needed for the inhibition of other cytochrome P-450 enzymes. In vivo the compound was active in rats (ED50 = 0.035 mg/kg) and dogs (1 mg/kg gave 70% inhibition) after oral administration. It can be concluded that Org 33201 is a potent and highly selective orally active aromatase inhibitor.