Stable expression of human aromatase complementary DNA in mammalian cells: a useful system for aromatase inhibitor screening.

A mammalian cell expression plasmid, pH beta-Aro, containing the human placenta aromatase complementary DNA was constructed. The prepared plasmid was used to transfect breast cancer cells (MCF-7), noncancerous breast cells (HBL-100), and Chinese hamster ovary cells by a stable expression method. While the maximum velocities for aromatase expressed in three types of cells were different (10-201 pmol of [3H2O] formed/h/mg) using [1 beta, 2 beta-3H]androst-4-ene-3,17-dione as the substrate, the apparent Michaelis-Menten constants were found to be similar (39.9-57.8 nM) and were within the range determined for the enzyme existing in human placenta. The expressed activities were inhibited by the known aromatase inhibitors, 4-hydroxyandrostenedione and aminoglutethimide, at concentrations that normally inhibit the human placental aromatase. However, it was found that the inhibition profiles were different for aromatase expressed in different types of cells, suggesting that other factors, such as the uptake of the inhibitor, may also play a role in determining the inhibition efficiency. These constructed aromatase expressing mammalian cell lines will be very useful tools for aromatase inhibitor screening.