Aromatase inhibition by 4-thiosubstituted-4-androstene-3,17-dione derivatives

The synthesis and evaluation of 4-thiosubstituted-4-androstenedione analogs as inhibitors of estrogen synthetase (aromatase) is described. All compounds were prepared by the addition of various thiol reagents to 4β,5β-epoxyandrostanedione. Inhibitory activity of synthesized compounds was assessed using a human placental microsomal preparation as the enzyme source and [1β-³H]4-androstene-3,17-dione as substrate. Synthesized compounds exhibiting high inhibitory activity were further evaluated under initial velocity conditions to determine apparent K_i values. Several compounds were effective competitive inhibitors, and have apparent K_i values ranging from 34 to 52 nM, with the apparent K_m for androstenedione being 54 nM. The results of these studies demonstrate a tightly fitted enzyme pocket that can accommodate bulky substituents at the C-4 position of androstenedione not to exceed 4.3 Å in width and 5.5 Å in length.