Modulation of human aromatase gene expression by specific antisense oligodeoxynucleotides

Abstract

The presence of estrogen is considered to play a crucial role for the development of hormone-dependent tumors. Estrogens are generated by an endomembrane-bound cytochrome P450 termed aromatase. This ratelimiting enzyme converts androgens into estrogens by a series of three sequential hydroxylations that results in loss of the angular C-19 methyl group and concomitantly in aromatization of ring A of the steroid ring system. To improve specificity of clinically applied aromatase inhibitors which exclusively are designed to act on enzyme protein, a novel strategy of inhibition was examined: inhibition at the nucleic acid level. An antisense oligodeoxynucleotide complementary to the translation start region of human aromatase transcripts (antisense-arom) was synthesized and employed to inhibit cyclic AMP-triggered aromatase gene expression in cultured human choriocarcinoma cells (JEG-3). Appearance of transcripts following induction by hCG or the membrane permeating dibutyryl cyclic AMP was significantly inhibited (reaching 70% and 60% inhibition, respectively) accompanied by accelerated mRNA degradation. The inhibition at nucleic acid level was paralleled by a decrease of both the aromatase protein and the microsomal aromatase activity. The data appear to indicate the antisense strategy to be a most promising approach for the development of a novel type of specific aromatase inhibitor.