Effects of Somatostatin Analogs on a Growth Hormone-Releasing Hormone Secreting Bronchial Carcinoid,in Vivoandin VitroStudies

Abstract

A 56-yr-old woman presented with acromegaly, a pulmonary mass, and elevated levels of GHRH, GH, and IGF-I. Histological examination revealed a bronchial carcinoid with positive staining for GHRH. Somatostatin analogs (SAs) can play an important role in the treatment of neuroendocrine tumors, dependent on the somatostatin receptor subtype (sst) expression pattern. The sst pattern in bronchial carcinoids and effects of SAs have not been extensively investigated, particularly not for the recently developed universal SA SOM230 (Pasireotide) that has high affinity for sst1, 2, 3, and 5. Our objective was to investigate the in vivo response of a GHRH-producing bronchial carcinoid to octreotide (OCT), its sst-expression profile, and in vitro responses to different SAs, including SOM230. In vivo, 50 microg OCT was administered, and plasma GH and GHRH responses were determined. In vitro, the expression of ssts was analyzed by quantitative PCR. Furthermore, the effects of SOM230 and OCT on GHRH secretion were evaluated in primary cell cultures of the carcinoid tissue. In vivo, OCT administration fully suppressed GH and GHRH levels. In vitro, sst1 mRNA was most abundant, followed by sst2 and sst5. Both SOM230 and OCT inhibited GHRH production dose dependently (SOM230 100 nm vs. control, P = 0.01; OCT 110 nm vs. control, P = 0.05). In this case of a GHRH-producing bronchial carcinoid, we demonstrated that SOM230 was a potent inhibitor of GHRH production in vitro and was at least equally potent compared with OCT. Therefore, SOM230 may be a potential therapeutic agent to control GHRH secretion in ectopic acromegaly.