A comparison of human H295R and rat R2C cell lines as in vitro screening tools for effects on aromatase.

In this study we evaluated the rat Leydig cell carcinoma cell line R2C and the human adrenocorticocarcinoma cell line H295R for their suitability as in vitro screening tools for potential interference of xenobiotics with aromatase activity. A 24h exposure to prochloraz (PRO), fadrozole (FAD) and epoxyconazole (EPO) resulted in complete catalytic inhibition in H295R and R2C cells. In H295R cells, PRO and FAD were mixed-type inhibitors with apparent K(i) values of 0.04 and 0.03 microM, and apparent K(i)' values of 0.33 and 0.06 microM, respectively. EPO was a competitive inhibitor with an apparent K(i) value of 0.51microM. In R2C, all three compounds showed mixed type inhibition kinetics, with apparent K(i) values (microM) of 0.004, 0.003 and 0.07, and apparent K(i)' values (microM) of 0.41, 0.01 and 2.42, respectively. Exposure for 24h of H295R cells to 8-bromo-cyclic adenosine monophosphate (8-Br-cAMP), prostaglandin E2 (PGE2), phorbol 12-myristate 13-acetate (PMA), or dexamethasone (DEX) resulted in 4.0, 2.8, 3.6 or 3.6-fold induction of aromatase activity, respectively, as well as in an increase of several human aromatase transcripts with promoter-specific 5'-ends (pII and I.3). In R2C cells, only PMA slightly induced aromatase activity. A 24h exposure of H295R cells to atrazine (ATR), resulted in a three-fold induction of aromatase activity and a slight increase in pII and I.3 aromatase transcripts. However, ATR did not induce aromatase activity in R2C cells. We conclude that the H295R cell line contains aromatase promoter regions, which are responsive to the respective stimulants. They play a role in aromatase regulation in various tissues such as brain, placenta, healthy and diseased gonadal and breast tissue and therefore, they may play an important role in tumor genesis, development, behavior and reproduction. The H295R cell line may therefore be a relevant and useful tool in risk assessment of xenobiotics. The R2C cell line, although not suitable for studying induction, appears to be a more sensitive cell line for studying inhibitory effects of xenobiotics on aromatase activity.