Interferon-a-2 a Is a Potent Inhibitor of Hormone Secretion by Cultured Human Pituitary Adenomas

Interferon-a (IFNa) may exert direct inhibitory effects on cell proliferation and on the production of different peptide hormones. We investigated the effect of IFNa on hormone production by 15 GHsecreting pituitary adenomas, 4 clinically nonfunctioning or gonadotroph pituitary adenomas, and 4 prolactinomas in vitro. In the GHsecreting pituitary adenoma cultures, a short term (72-h) incubation with IFNa (50–100 U/mL) significantly inhibited GH secretion in 3 of 7 cases and PRL secretion in 6 of 7 cultures. During prolonged incubation (14 days) with IFNa, GH and/or PRL secretion was significantly inhibited in 7 of 8 cultures (GH, 17–78% inhibition; PRL, 39–88% inhibition). In the clinically nonfunctioning or gonadotroph cultures, incubation with IFNa resulted in inhibition of the secretion of gonadotropins and/or a-subunit in all cases (27–62%), whereas in the prolactinoma cultures PRL secretion was inhibited by IFNa in all cases (37–76%). The effect of IFNa was additive to the inhibitory effects of the dopamine agonist bromocriptine (10 nmol/L) or the somatostatin analog octreotide (10 nmol/L). The inhibition of hormone secretion by IFNa was accompanied by inhibition of the intracellular hormone concentrations. The effect of IFNa was dose dependent, with an IC50 for inhibition of hormone secretion of 2.3 6 0.3 U/mL (n 5 5), which is relatively low compared with the concentrations that are reached in patients treated with IFNa for various malignancies. In conclusion, the potent antihormonal effect of IFNa on cultured pituitary adenomas suggests that this drug might be of benefit in the treatment of selected patients with secreting pituitary adenomas. As treatment with IFNa is associated with considerable adverse reactions, studies with this drug should only be considered in inoperable, invasive aggressive, and dopamine agonistand/or somatostatin analog-resistant functioning pituitary macroadenomas. (J Clin Endocrinol Metab 84: 3336–3343, 1999) I (IFNs) are glycoproteins produced in response to viral and certain nonviral stimuli. Apart from having antiviral activity, IFNs are potent inhibitors of cell proliferation as well. Because of these properties IFNs have been approved for clinical use to treat certain viral diseases, autoimmune diseases, and malignancies (1). During the past 10 yr evidence has emerged that IFNs may play a regulatory role in pituitary hormone secretion as well. Both stimulatory and inhibitory effects of IFNs (IFNa and IFNg) on the secretion of ACTH, PRL, and GH have been reported (2–6). Apart from cells of the immune system, pituitary endocrine cells may also contain IFNa (7), providing further evidence for a local regulatory role for this group of proteins at the pituitary level. Moreover, Katahira et al. (8) recently showed that prolonged incubation with IFNa or IFNg induces a potent inhibitory effect on POMC gene expression in mouse AtT-20 pituitary tumor cells. Until now, IFNa has been used with variable success in the treatment of hormone-secreting gastroenteropancreatic tumors (mainly carcinoids). Treatment with IFNa may control tumor growth, but also reduces the secretion of tumor-related products in patients harboring these tumors, thereby improving clinical symptomatology (9–11). The decrease in the production of different peptide hormones is caused by its blocking effect on intracellular messenger ribonucleic acid formation (12) and appears to be signalled via the JAK (Janus kinase)-STAT (signal transducer and activator of transcription) pathway (13). Medical therapy of human pituitary adenomas comprises the use of dopamine (DA) agonists and somatostatin (SS) analogs. In patients with prolactinomas, treatment with DA agonists effectively reduces circulating PRL levels and tumor size in the majority of them, probably due to an inhibitory effect on PRL synthesis. However, a small subgroup of patients with prolactinomas is either resistant to DA agonist therapy or cannot be treated due to intolerance to therapy with DA agonists (14). In patients with acromegaly, good inhibition of circulating GH levels has been achieved using SS analogs such as octreotide, whereas tumor shrinkage is observed less frequently (15). This is probably due to the absence of an inhibitory effect of SS analogs on GH synthesis (16, 17). Finally, the effectiveness of the use of DA agonists and/or SS analogs in the medical treatment of clinically nonfunctioning pituitary adenomas (NFA) is still under discussion (18). The presence of IFNa in pituitary endocrine cells, its modulating effect on pituitary hormone secretion (and/or production), and the observations that IFNs act at the transcriptional level suggest that IFNs may also influence hormone secretion by pituitary adenomas. To further explore the possibilities of medical therapy of pituitary adenomas, we investigated in the present study the effect of IFNa-2a on hormone secretion by different types of cultured human pituitary adenoma cells. In addition, the interrelationship Received December 8, 1998. Revision received June 3, 1999. Accepted June 10, 1999. Address all correspondence and requests for reprints to: L. J. Hofland, Ph.D., Department of Internal Medicine III, University Hospital Dijkzigt, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands. E-mail: hofland@inw3.azr. nl. 0021-972X/99/$03.00/0 Vol. 84, No. 9 The Journal of Clinical Endocrinology & Metabolism Printed in U.S.A. Copyright © 1999 by The Endocrine Society