Stimulatory effect of SOM230 on human and rat adrenal corticosteroid secretion in vitro.

SOM230 (pasireotide, Signifor), a recently developed somatostatin analog, has been tested in ACTH-secreting pituitary tumors with promising results. No study has yet evaluated whether this analog also directly affects adrenal steroid production. The aim of the current study was to evaluate whether SOM230 modulates corticosteroid secretion by normal adrenals in vitro. Primary cultures from normal human and rat adrenals were incubated with 10-100 nM SOM230 with and without 10nM ACTH. Dose-response studies with 1 nM-1 µM SOM230 were performed on rat adrenals. Cortisol/corticosterone levels in medium were measured after 4 and 24h. SOM230 (10nM) significantly increased corticosteroid levels after 24h incubation in both human (36.4 ± 0.43 ng/well vs 27.7 ± 3.17 ng/well, p<0.05) and rat (16.2 ± 1.16 ng/well vs 11.6 ± 0.92 ng/well p<0.05) adrenals; lesser effects were observed with 100 nM SOM (33.4 ± 2.59 ng/well vs 27.7 ± 3.17 ng/well p<0.05; 13.4 ± 0.82 ng/well vs 11.6 ± 0.92 ng/well, N.S. vs baseline secretion for human and rat adrenals, respectively). Dose-response curves confirmed maximal effect at 10nM SOM230. The corticosteroid secretory response to ACTH was unaffected by SOM230 co-incubation. In conclusion, SOM230 exerts a moderate stimulatory effect on adrenal corticosteroid secretion in vitro. This argues against a direct adrenal involvement in the clinical efficacy of SOM230 in patients with ACTH-secreting pituitary tumors and widens the known range of action of SOM230.

Responses to corticotrophin-releasing hormone and dexamethasone in a large series of human adrenocorticotrophic hormone-secreting pituitary adenomas in vitro reveal manifold corticotroph tumoural phenotypes.

Patients with Cushing's disease are known to present a variable secretory response to stimulatory and inhibitory challenges. Evaluation of the secretory behaviour of pituitary adrenocorticotrophic hormone (ACTH)-secreting adenomas in vitro aids in the comprehension of its behaviour in vivo; however, given the small size of these tumours and the consequent paucity of material available to in vitro studies, a comprehensive study on the secretory behaviour of human corticotroph tumours has not yet been performed. The present study aimed to assess the spectrum of responses to the two main corticotroph modulators, corticotrophin-releasing hormone (CRH) and dexamethasone, in a large series of human ACTH-secreting pituitary tumours. Seventy-two ACTH-secreting pituitary tumours were collected during surgery and established in culture. Specimens were incubated with 10 nm CRH and/or 10 nm dexamethasone for 4 h and 24 h. Secretion in unstimulated, control wells was set at 100% and changes in ACTH concentrations by at least 20% were considered as responses. Parallel experiments in 12 rat anterior pituitary primary cultures were evaluated. A marked ACTH increase was observed during incubation with CRH in 70% of tumoural specimens at 4 h (range 124-3500% of control wells) and in 57% at 24 h (range 122-3323%). Dexamethasone reduced ACTH secretion in almost 50% of tumours (range 78-2% of control at 4 h; 76-3% at 24 h), whereas it did not affect ACTH medium levels in 30% of specimens and induced a paradoxical ACTH increase in 20% of tumours (range 130-327% of control at 4 h; 156-348% at 24 h). By comparison, CRH uniformly increased ACTH levels in rat anterior pituitary primary cultures (mean 745 ± 84% at 4 h; 347 ± 25% at 24 h), whereas dexamethasone decreased ACTH levels by 40-50% in all experiments. In conclusion, the present study of a large series of human ACTH-secreting pituitary tumours in vitro revealed a considerable variability in the responses to CRH and dexamethasone. This finding indicates the existence of multiple corticotroph tumoural phenotypes and may account for the different responses to physiological and pharmacological modulators in vivo.

Insulin analogues differently activate insulin receptor isoforms and post-receptor signalling.

AIMS/HYPOTHESIS: Five insulin analogues, with modified insulin-like molecular structures, are currently approved for treating diabetic patients. They activate cell signalling and biological responses via insulin receptor isoforms (IR-A and IR-B), each having specific characteristics for eliciting cell responses. The molecular and biological effects of these analogues on receptor isoforms in comparison to native insulin are not well defined, and their effects on the IGF1 receptor (IGF1R) are controversial. The characterisation of these effects was the aim of the present study. METHODS: Short-acting (insulin lispro [B28Lys,B29Pro human insulin], insulin aspart [B28Asp human insulin], insulin glulisine [B3Lys,B29Glu human insulin]) and long-acting (insulin glargine [A21Gly,B31Arg,B32Arg human insulin], insulin detemir [B29Lys(epsilon-tetradecanoyl),desB30 human insulin]) insulin analogues were studied in three engineered cell models (R(-), IGF1R-deprived mouse fibroblasts transfected with either only human IR-A or IR-B or IGF1R). Receptor binding and phosphorylation, AKT and extracellular signal-regulated kinase (ERK) activation, cell proliferation and colony formation were evaluated after exposing the cells to each analogue and were compared with insulin, IGF1 and the carcinogenic analogue B10Asp. RESULTS: All short-acting insulin analogues produced molecular and biological effects similar but not identical to those of insulin. Relative to insulin, long-acting analogues more strongly activated the ERK pathway via both IR-A and IGF1R as well as increased cell proliferation. At the concentration tested, no analogue (except B10Asp via IR-A) had increased transforming activity. CONCLUSIONS/INTERPRETATION: Cell models that permit comparisons of the activity of insulin to that of insulin analogues via each receptor individually indicate that only minor differences exist between insulin and short-acting analogues. By contrast, long-acting analogues activate the mitogenic signalling pathway more effectively than insulin and cause increased cell proliferation.