Aromatase in the human choriocarcinoma JEG-3: inhibition by R 76 713 in cultured cells and in tumors grown in nude mice.
The aromatase enzyme and its inhibition by R 76 713 were characterized in the JEG-3 choriocarcinoma cell line in culture and in JEG-3 tumors grown in nude mice. Optimal cell culture parameters and enzyme reaction conditions for the determination of aromatase activity were established. Under these conditions, in vitro JEG-3 aromatase was inhibited by R 76 713 with IC50-values of 7.6 +/- 0.5 nM and 2.7 +/- 1.1 nM using 500 nM of androstenedione and testosterone as substrate respectively. The Km-value of the aromatase enzyme with androstenedione as substrate was 62 +/- 19 nM; with testosterone as substrate, a value of 166 +/- 27 nM was found. In the presence of increasing concentrations of R 76 713, the Km-values increased while the Vmax remained unchanged. Using androstenedione and testosterone as substrate Lineweaver-Burk analysis of the data showed Ki-values for R 76 713 of 0.43 +/- 0.06 nM and 0.47 +/- 0.39 nM respectively. R 76 713 appeared to competitively inhibit the JEG-3 aromatase. Aromatase could easily be measured in homogenates of JEG-3 tumors grown in nude mice and showed Km-values similar to those found for JEG-3 cells in vitro. IC50-values for inhibition of tumor aromatase by R 76 713 were also similar to those found in cultured cells. Tumor aromatase measured ex vivo, 2 h after a single oral administration of R 76 713 was dose-dependently inhibited. An ED50-value of 0.05 mg/kg was calculated. The JEG-3 choriocarcinoma proved to be a useful aromatase model enabling the comparative study of aromatase inhibition in vitro and in vivo.
Krekels
M D
MD
Department of Endocrinology and Oncology, Janssen Research Foundation, Beerse, Belgium.
Wouters
W
W
De Coster
R
R
Van Ginckel
R
R
Leonaers
A
A
Janssen
P A
PA
D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D001141:Aromatase / Q000378:metabolism; D047072:Aromatase Inhibitors; D001667:Binding, Competitive; D002822:Choriocarcinoma / Q000201:enzymology*; D005260:Female; D006801:Humans; D007700:Kinetics; D051379:Mice; D008819:Mice, Nude; D013379:Substrate Specificity; D013739:Testosterone / Q000378:metabolism; D014230:Triazoles / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D047072:Aromatase Inhibitors; D014230:Triazoles; C060523:vorozole; D013739:Testosterone; D000735:Androstenedione; D001141:Aromatase