New mechanisms of adrenostatic compounds in a human adrenocortical cancer cell line

Background Adrenostatic compounds are frequently used in the treatment of p atients with Gushing's syndrome and act via direct inhibition of steroidoge nic enzymes. However, additional mechanisms may be involved in the blockade of adrenal steroid secretion. We therefore investigated the effects of ami noglutethimide (AG), metyrapone (MTP) and etomidate (ETO) in the human NCI- h295 adrenocortical carcinoma cell line. Materials and methods Cells were incubated with increasing doses of the adr enostatic compounds. Steroid hormone secretion (cortisol, 17-OH-progesteron e, DHEA-S) and cAMP synthesis were determined and Northern blot analysis an d cell proliferation experiments were performed. Results ETO was the most potent adrenostatic compound inhibiting P450c11 hy droxylase at low concentrations (IC50 15 nM), and also blocking P450 side-c hain cleavage (scc) enzyme (IC50 400 nM) at higher concentrations. The patt ern of enzyme inhibition was similar for MTP with an IC50 of 3.5 muM for P4 50c11 and 17 muM for P450scc, while AG blocked P450scc with an IC50 of 10 m uM. AG significantly suppressed the baseline ACTH-R mRNA expression in a do se-dependent fashion (300 muM AG: 5% +/- 1%; 30 muM AG: 64% +/- 1%; 3 muM A G: 108% +/- 19% compared with control cells: 100% +/- 11%) but increased gl ucocorticoid receptor mRNA. The reduced ACTH-R mRNA was paralleled by low A CTH-induced cAMP accumulation indicating reduced expression of ACTH-R prote in. The simultaneous incubation of hydrocortisone together with AG reversed the inhibitory effect of AG on the ACTH-R expression. AG and ETO inhibited cell proliferation in the NCI-h295 cells, but ETO was much more potent and showed antiproliferative effects at concentrations of 6 muM. The growth in hibition was not reversed by administration of hydrocortisone. Conclusions Our data demonstrate that adrenostatic compounds not only act b y suppression of steroidogenic enzymes but can also influence both ACTH-R e xpression and cell proliferation in adrenal cells. As these effects occur i n vitro at concentrations that are reached during treatment with theses dru gs in patients, they are probably also of clinical relevance. Particularly the antiproliferative activity of ETO may be useful in Gushing's syndrome d ue to adrenocortical cancer. The interaction of steroidogenesis, ACTH-R and glucocorticoid receptor expression as well as cell proliferation provides a new concept of the intra-adrenal response to stress in humans.