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M Fassnacht, F Beuschlein, S Vay, P Mora, B Allolio, and M Reincke

The adrenostatic compound aminoglutethimide (AG), a potent inhibitor of the P450 side chain cleavage enzyme, is used in the treatment of ACTH-dependent or adrenal Cushing's syndrome. Recently, AG has been shown to inhibit ACTH receptor (ACTH-R) mRNA expression in ovine adrenocortical cells in a time-dependent fashion. To investigate whether ACTH-R down-regulation will also be induced in tumor cells, we studied the effect of AG on ACTH-R expression in the human NCI-h295 adrenocortical carcinoma cell line, which expresses functional ACTH receptors and produces steroids of the glucocorticoid, mineralocorticoid and androgen pathway. The cells were incubated in triplicate with increasing doses of AG (3, 30, 300 microM) which suppressed steroid secretion dose-dependently. After 48 h, cells were harvested, and total RNA was extracted, electrophoresed, blotted and hybridized with a human ACTH-R cDNA probe. In parallel experiments, after preincubation with AG the cells were stimulated with ACTH (10 nM) for 10 min and the intracellular cAMP accumulation was determined by RIA. AG significantly suppressed the baseline ACTH-R mRNA expression in a dose-dependent fashion (300 microM AG, 5+/-1%; 30 microM AG, 64+/-1%; 3 microM AG, 108+/-19% compared with control cells, 100+/-11%). The reduced ACTH-R mRNA expression was paralleled by low ACTH-induced cAMP accumulation indicating reduced expression of the ACTH-R protein. The adrenostatic compound metyrapone, an inhibitor of 11beta-hydroxylase activity, also suppressed ACTH-R mRNA expression in a similar fashion. Stimulation of the protein kinase A pathway by simultaneous incubation of ACTH (10 nM) or forskolin (10 microM) together with AG was not able to overcome the steroid biosynthesis blockade, but reversed the inhibitory effects of AG on the ACTH-R mRNA expression. Also, cortisol (12 microM) reversed the AG-induced ACTH-R mRNA expression. We conclude that AG induces profound ACTH-R down-regulation in the NCI-h295 cell line either by affecting the gene expression or by decreasing transcript accumulation via an effect on RNA stability. This novel action of AG can be reversed by stimulation of the cAMP pathway and of the glucocorticoid-mediated signal transduction cascade. As the down-regulation occurs in vitro at concentrations which are reached during treatment with AG in humans it may contribute to its therapeutic activity in adrenal disease.

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M Fassnacht, A Franke, A Dettling, S Hahner, M Zink, S Wudy, and B Allolio

Bisphosphonates (BPs), specific inhibitors of osteoclasts, are well established in the management of skeletal metastases in breast cancer. Recent studies have suggested that these compounds may also directly influence tumor cell proliferation. As adrenocortical cancer frequently leads to bone metastases, we investigated the effects of clodronate (CLO) in the human adrenocortical cancer cell line NCI-H295 and in primary cultures of bovine adrenocortical cells. Both the non-amino BP CLO and the amino BP pamidronate (PAM) exhibited a dose-dependent antiproliferative effect in both cell types (cell viability in NCI-H295 cells: 100 microM CLO: 98+/-8%; 500 microM CLO 76+/-6%; 1000 microM CLO 53+/-2; 10 microM PAM 96+/-3%; 50 microM PAM 46+/-6%; 100 microM PAM 11+/-1% vs untreated control cells: 100+/-10%; P<0.01). FACS analysis in NCI-H295 cells treated with either CLO or PAM demonstrated both apoptotic and necrotic cell death. However, while during PAM treatment cell number and hormone secretion decreased in parallel, we observed specific impairment of steroidogenesis in the presence of CLO with a dose-dependent increase in the 17-OH-progesterone/cortisol ratio (100 microM CLO 134+/-30%; 500 microM CLO 284+/-10%; 1000 microM CLO 545+/-130% vs 100+/-20% in control cells; P<0.01). Further analysis in ACTH-stimulated bovine adrenal cells using stable isotope dilution/gas chromatography-mass spectrometry demonstrated CLO-induced inhibition of adrenal 21-hydroxylase (P450c21) activity leading to a dose-dependent increase in the 17-OH-progesterone/11-deoxycortisol ratio. In conclusion, we demonstrate a dose-dependent antiproliferative effect of CLO and PAM in adrenocortical cells. In addition, for the first time, we describe a suppressive effect of CLO on steroidogenesis via inhibition of adrenal 21-hydroxylase (P450c21) activity.

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Anthony P Coll, Martin Fassnacht, Steffen Klammer, Stephanie Hahner, Dominik M Schulte, Sarah Piper, Y C Loraine Tung, Benjamin G Challis, Yacob Weinstein, Bruno Allolio, Stephen O’Rahilly, and Felix Beuschlein

Pro-opiomelanocortin (POMC) is a polypeptide precursor that undergoes extensive processing to yield a range of peptides with biologically diverse functions. POMC-derived ACTH is vital for normal adrenal function and the melanocortin α-MSH plays a key role in appetite control and energy homeostasis. However, the roles of peptide fragments derived from the highly conserved N-terminal region of POMC are less well characterized. We have used mice with a null mutation in the Pomc gene (Pomc −/−) to determine the in vivo effects of synthetic N-terminal 1–28 POMC, which has been shown previously to possess adrenal mitogenic activity. 1–28 POMC (20 μg) given s.c. for 10 days had no effect on the adrenal cortex of Pomc −/− mice, with resultant cortical morphology and plasma corticosterone levels being indistinguishable from sham treatment. Concurrent administration of 1–28 POMC and 1–24 ACTH (30 μg/day) resulted in changes identical to 1–24 ACTH treatment alone, which consisted of upregulation of steroidogenic enzymes, elevation of corticosterone levels, hypertrophy of the zona fasciculate, and regression of the X-zone. However, treatment of corticosterone-depleted Pomc −/− mice with 1–28 POMC reduced cumulative food intake and total body weight. These anorexigenic effects were ameliorated when the peptide was administered to Pomc −/− mice with circulating corticosterone restored either to a low physiological level by corticosterone-supplemented drinking water (CORT) or to a supraphysiological level by concurrent 1–24 ACTH administration. Further, i.c.v. administration of 1–28 POMC to CORT-treated Pomc −/− mice had no effect on food intake or body weight. In wild-type mice, the effects of 1–28 POMC upon food intake and body weight were identical to sham treatment, but 1–28 POMC was able to ameliorate the hyperphagia induced by concurrent 1–24 ACTH treatment. In a mouse model which lacks all endogenous POMC peptides, s.c. treatment with synthetic 1–28 POMC alone can reduce food intake and body weight, but has no impact upon adrenal growth or steroidogenesis.