bim-23268 and Pituitary-Neoplasms

We report the comparative efficacy of octreotide, cabergoline and multiple ligands directed towards the different somatostatin subtypes (ssts), such as BIM-23A779 and SOM-230, and of chimeric analogs which bind both somatostatin and the dopamine D2 receptors (D2R), such as BIM-23A760 and BIM-23A781, in cell cultures from human growth hormone (GH)-secreting pituitary adenomas.. RT-PCR analysis of the quantitative expression of the different ssts and D2R mRNAs was performed on tumor fragments of 22 GH-secreting adenomas collected after surgery. Pharmacological studies, using the different ligands, were performed on cell cultures of such tumors.. sst2, sst5 and D2R were constantly coexpressed in all tumors, in variable amounts. The levels of expression of sst2 and D2R mRNAs were significantly correlated with the maximal GH suppression by either octreotide or cabergoline (p < 0.001). In each tumor tested, 3 patterns of response, in terms of GH suppression, were observed. GH secretion was preferentially inhibited by the sst2 preferential compound octreotide in 61% of the tumors. In 19% of the tumors, the maximal inhibition of GH release was achieved with the sst5 preferential compound BIM-23268. The dopamine analog cabergoline was the most effective inhibitor of GH secretion in 21% of cases. Among the compounds tested, the most potent inhibitors of GH secretion were the sst2, sst5, D2R chimeric compound BIM-23A760, followed by the sst universal ligand SOM-230.. The variable patterns of response to sst2, sst5 and dopamine D2 analogs may explain the greater efficacy of drugs which bind to the 3 receptors in suppressing GH secretion. The biological potency (EC50) and efficacy of the chimeric compound BIM-23A760 on GH secretion can be partly explained by its high affinity for sst2. The effect of multiple receptor activation on the functions of other pituitary tumor types, such as prolactinomas and corticotropinomas, is not presently analyzed, and the efficacy of multireceptor ligands remains to be elucidated.

Topics: Adenoma; Adult; Antineoplastic Agents, Hormonal; Cabergoline; Dopamine; Drug Screening Assays, Antitumor; Ergolines; Female; Human Growth Hormone; Humans; Ligands; Male; Octreotide; Pituitary Neoplasms; Receptors, Dopamine D2; Receptors, Somatostatin; Recombinant Fusion Proteins; RNA, Messenger; Somatostatin; Tumor Cells, Cultured

Somatostatin (SST) receptors, specially sst2 and sst5, provide a valuable target to inhibit excessive hormone release and cell growth in pituitary tumors by using SST analogs (SSAs). Unfortunately, an appreciable proportion of tumors fail to respond to SSA despite expressing high levels of one or more ssts. Recently we identified two novel truncated sst5 variants, sst5TMD5, and sst5TMD4, absent in normal pituitary but expressed in pituitary tumors.. We aimed at exploring the potential role of sst5TMD5 and sst5TMD4 in the poor response of some tumors to SSA in vivo and in vitro. Specifically, 25 somatotropinomas showing different responses to octreotide in vivo and sst2 (BIM-23197)- and sst5(BIM-23268)-selective compounds in vitro were screened for sst5TMD5/sst5TMD4 expression by real-time PCR. Relationships between ssts expression and in vivo and in vitro secretory response of the corresponding pituitary samples were assessed.. sst5TMD5 was absent in all samples analyzed. sst5TMD4 was found in 85% of tumors, and its expression was positively correlated to that of sst5 (R(2) = 0.79, P < 0.001). Expression of sst5TMD4 was negatively correlated with the ability of octreotide to reduce GH levels in vivo and partially negatively correlated with inhibition of GH secretion by an sst5 selective agonist (BIM-23268) in vitro.. These results indicate that sst5TMD4 is related to the reduced ability of octreotide at normalizing hormone secretion in poorly responsive tumors in vivo. Further studies will help to evaluate the potential use of sst5TMD4 expression in surgically removed pituitary adenomas as a predictor of the subsequent response of different pituitary tumors to SSA therapy.

Topics: Acromegaly; Antineoplastic Agents, Hormonal; Genetic Variation; Humans; Octreotide; Oligopeptides; Piperazines; Pituitary Neoplasms; Polymerase Chain Reaction; Receptors, Somatostatin; Sequence Deletion; Somatostatin

In a series of human corticotroph adenomas, we recently found predominant mRNA expression of somatostatin (SS) receptor subtype 5 (sst5). After 72 h, the multiligand SS analog SOM230, which has a very high sst5 binding affinity, but not Octreotide (OCT), significantly inhibited basal ACTH release. To further explore the role of sst5 in the regulation of ACTH release, we conducted additional studies with mouse AtT-20 cells. SOM230 showed a 7-fold higher ligand binding affinity and a 19-fold higher potency in stimulating guanosine 5'-O-(3-thiotriphosphate) binding in AtT-20 cell membranes compared with OCT. SOM230 potently suppressed CRH-induced ACTH release, which was not affected by 48-h dexamethasone (DEX) pretreatment. However, DEX attenuated the inhibitory effects of OCT on ACTH release, whereas it increased the inhibitory potency of BIM-23268, an sst5-specific analog, on ACTH release. Quantitative PCR analysis showed that DEX lowered sst(2A+2B) mRNA expression significantly after 24 and 48 h, whereas sst5 mRNA levels were not significantly affected by DEX treatment. Moreover, Scatchard analyses showed that DEX suppressed maximum binding capacity (B(max)) by 72% when 125I-Tyr3-labeled OCT was used as radioligand, whereas B(max) declined only by 17% when AtT-20 cells were treated with [125I-Tyr11]SS-14. These data suggest that the sst5 protein, compared with sst2, is more resistant to glucocorticoids. Finally, after SS analog preincubation, compared with OCT both SOM230 and BIM-23268 showed a significantly higher inhibitory effect on CRH-induced ACTH release. In conclusion, our data support the concept that the sst5 receptor might be a target for new therapeutic agents to treat Cushing's disease.

Topics: Adrenocorticotropic Hormone; Animals; Corticotropin-Releasing Hormone; Dose-Response Relationship, Drug; Down-Regulation; Glucocorticoids; Mice; Octreotide; Pituitary Gland; Pituitary Neoplasms; Receptors, Somatostatin; RNA, Messenger; Somatostatin; Stimulation, Chemical; Tumor Cells, Cultured

Somatostatin (SRIH), a cyclic tetradecapeptide hormone originally isolated from mammalian hypothalamus, is a potent suppressor of pituitary growth hormone (GH) secretion. SRIH acts through a family of G-protein-coupled membrane receptors containing seven transmembrane domains. Five genes encoding distinct SRIH receptor (SSTR) subtypes have so far been cloned in human and other species and termed SSTR1-5. In human somatotrophe pituitary adenomas GH secretion is controlled by both SSTR2 and SSTR5. However, in clinical practice only somatostatin analogs selective for SSTR2 (octreotide and lanreotide) are available. This may explain why clinical and in vitro responses to these analogs in acromegaly are only partial. In this study, we investigated the inhibitory effect of two new SRIH analogs with high selectivity for SSTR2 (NC-4-28B) and SSTR5 (BIM-23268) and compared it to that of native somatostatin (SRIH-14) on a large number of GH-secreting adenomas obtained by transphenoidal neurosurgery. Tissues from 16 adenomas were enzymatically dispersed and plated in 24-well dishes at 50,000 cells/well. After 3 days, groups of three wells were incubated for 4 h with medium alone, SRIH-14 or analogs NC-4-28B or BIM-23268, at the concentrations of 0.01, 0.1 and 1 microM. Our results show that 9 out of 16 adenomas were responsive (GH suppression: 20-40% vs. control, p < 0.05) to SRIH. In this group only 4 adenomas showed similar responses to both selective analogs, with 2 nonresponders (expression of other SRIH receptor subtypes) and 2 responders (concomitant expression of SSTR2 and SSTR5) to both analogs. GH release was selectively inhibited by NC-4-28B in 3 adenomas and by BIM-23268 in the remaining 2 adenomas, suggesting predominant expression of SSTR2 and SSTR5, respectively. SRIH failed to inhibit GH release in 7 adenomas (43%). Interestingly, in that group a better inhibitory effect was obtained with BIM-23268 (5 out of 7 adenomas) than with NC-4-28B, suggesting expression of a few SSTR5 receptors only, or of both SSTR2 and SSTR5, respectively. We conclude that the availability of somatostatin analogs selective for SSTR5 will enhance the treatment potency and spectrum in acromegaly.

Topics: Adenoma; Adult; Aged; Dose-Response Relationship, Drug; Female; Human Growth Hormone; Humans; Male; Middle Aged; Pituitary Neoplasms; Receptors, Somatostatin; Somatostatin

Evaluation of the efficiency of somatostatin analogues in the treatment of a mixed luteinizing hormone (LH)-, alpha-subunit-, prolactin (PRL)-secreting pituitary adenoma.. A 30-year-old woman, with amenorrhaea-galactorrhaea, presented with a pituitary macroadenoma. The endocrine evaluation showed high plasma levels of PRL, LH, and alpha-subunit inhibited by 65%, 65% and 33% respectively under octreotide test (200 microg, s.c.). Long-term treatment with slow release (SR) lanreotide (30 mg/10 days, i.m.) restored menstrual cycles and normalized PRL values. Due to persisting supranormal levels of LH and alpha-subunit, and to the absence of tumoral shrinkage, the adenoma was resected by the transsphenoidal route.. In vitro characterization of the somatostatin receptor subtypes (SSTR) expression and functionality. Real-time polymerase chain reaction was performed to quantify the expression of SSTR mRNAs and functionality of the SSTRs was assessed in cell culture studies with various concentrations of native somatostatin (SRIF-14) and of analogues preferential for SSTR2 or SSTR5.. This adenoma presented with high levels of SSTR2, SSTR3 and SSTR5 mRNAs, as compared with a series of gonadotroph adenomas. In cell culture studies, PRL, LH and alpha-subunit were inhibited by 60%, 47% and 33% respectively by SRIF-14 at a concentration of 10 nmol/l. The SSTR2 (BIM-23197, lanreotide) and SSTR5 (BIM-23268) preferential analogues both produced a partial 21-38% inhibition of PRL, LH, and alpha-subunit release.. In this plurihormonal-secreting adenoma, the high efficacy of somatostatin analogues to inhibit PRL, LH and alpha-subunit secretion in vivo may be explained by the unusually high level of expression and by the functionality of both SSTR2 and SSTR5 receptor subtypes.

Topics: Adult; Aminoquinolines; Antineoplastic Agents; Dopamine Agonists; Female; Glycoprotein Hormones, alpha Subunit; Humans; Oligopeptides; Peptides, Cyclic; Piperazines; Pituitary Neoplasms; Prolactin; Prolactinoma; Receptors, Somatostatin; Reverse Transcriptase Polymerase Chain Reaction; RNA, Neoplasm; Somatostatin

Recently, it was demonstrated that somatostatin analogs preferential for the SSTR5 subtype suppress PRL release from prolactinoma cell cultures by 30-40%. These data supported the idea of somatostatin receptor subtype-specific control of PRL secretion in such tumors. The present study examines the quantitative profile of SSTRs messenger ribonucleic acid (mRNA) in 10 PRL-secreting tumors and correlates the expression with the ability of native somatostatins (SS14 and SS28), SSTR2 preferential analogs (octreotide and BIM-23197), and the SSTR5 preferential analog BIM-23268 to suppress PRL secretion. RT-PCR quantitative analysis showed a large predominance of SSTR5 mRNA [5648 +/- 1918 pg/pg glyceraldehyde-3-phosphate dehydrogenase (GAPDH)] vs. SSTR2 mRNA (148 +/- 83 pg/pg GAPDH). The SSTR1 transcript was also highly expressed in prolactinomas (1296 +/- 669 pg/pg GAPDH). SSTR5 mRNA expression correlated with PRL inhibition induced by both SRIF14 and SRIF28. Among the different analogs tested, only BIM-23268 produced inhibition of PRL release similar to that achieved with the native peptides. Its EC50 for PRL suppression was 0.28 +/- 0.10 nmol/L. No additive effects on PRL suppression were achieved by cotreatment of the tumor cells with SSTR2 and SSTR5 preferential analogs. In the same tumor cell cultures, quinagolide, a potent dopamine agonist, produced a dose-dependent inhibition of PRL with an EC50 at least 10 times lower than that of BIM-23268. Coincubation of quinagolide and BIM-23268, particularly in tumor cells resistant to dopamine agonist treatment, did not produce additive effects on PRL suppression. In conclusion, prolactinomas have a specific pattern of SSTR subtype mRNA expression (SSTR5 and SSTR1). SSTR5 expression is correlated to PRL regulation. These inhibitory effects are superimposable, at a higher concentration, to those of the dopamine agonists, but are not additive, particularly in the adenomas resistant to dopaminergic suppression of PRL release.

Topics: Adult; Aminoquinolines; Dopamine Agonists; Female; Gene Expression; Hormones; Humans; Male; Middle Aged; Octreotide; Oligopeptides; Piperazines; Pituitary Neoplasms; Prolactin; Prolactinoma; Receptors, Somatostatin; RNA, Messenger; Somatostatin; Tumor Cells, Cultured