Somatostatin receptor sst2 decreases cell viability and hormonal hypersecretion and reverses octreotide resistance of human pituitary adenomas.

In human somatotroph adenomas, growth hormone (GH) hypersecretion can be inhibited by somatostatin analogues such as octreotide. Unfortunately, serum GH levels reach normal values in only 60% of treated patients. The decreased sensitivity to octreotide is strongly related to a lower expression of somatostatin receptor sst2.

Efficacy of a dopamine-somatostatin chimeric molecule, BIM-23A760, in the control of cell growth from primary cultures of human non-functioning pituitary adenomas: a multi-center study.

Dopamine D2 and somatostatin receptors (sstrs) were reported to affect non-functioning pituitary adenoma (NFPA) proliferation in vitro. However, the reported results differ according to the experimental conditions used. We established an experimental protocol allowing reproducible evaluation of NFPA cell proliferation in vitro, to test and compare the antiproliferative effects of dopamine and somatostatin analogs (alone or in combination) with the activity of the dopamine-somatostatin chimeric molecule BIM-23A760.

Somatostatinergic ligands in dopamine-sensitive and -resistant prolactinomas.

Objective: Ten percent of patients with prolactinoma fail to respond with normalization of prolactin (PRL) and tumor shrinkage under dopamine agonist (DA) therapy. The resistance to treatment is linked to a loss of dopamine receptor 2 (D2DR). Prolactinomas express somatostatin (SST) receptor subtypes, SSTR1, 2, and 5.

The analysis of quantitative expression of somatostatin and dopamine receptors in gastro-entero-pancreatic tumours opens new therapeutic strategies.

Objective: Somatostatin (sst) are present in the majority of gastro-entero-pancreatic (GEP) tumours. Effects of somatostatin receptor (sst) analogues are partial and of limited duration. Cell lines derived from GEP express dopaminergic receptors D(2).

Somatostatin and dopamine-somatostatin multiple ligands directed towards somatostatin and dopamine receptors in pituitary adenomas.

Aim: 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.

Procedures: 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.

Involvement of the pituitary-specific transcription factor pit-1 in somatolactotrope cell growth and death: an approach using dominant-negative pit-1 mutants.

The anterior pituitary-specific transcription factor Pit-1 was initially identified and cloned as a transactivator of the prolactin (PRL) and GH genes and later as a regulator of the TSHb gene. It was found to be a major developmental regulator, because natural Pit-1 gene mutations cause a dwarf phenotype in mice and cause combined pituitary hormone deficiency associated with pituitary hypoplasia in humans. To further investigate the growth-promoting effects of Pit-1, we used a strategy based on the use of dominant-negative Pit-1 mutants as an alternative means of inactivating endogenous Pit-1 functions.

BIM-23A760, a chimeric molecule directed towards somatostatin and dopamine receptors, vs universal somatostatin receptors ligands in GH-secreting pituitary adenomas partial responders to octreotide.

We report the comparative efficacy of a somatostatin receptor 1 and 5 subtypes (SSTR2 and SSTR5), and dopamine D2 (DAD2) compound, BIM-23A760, in suppressing GH secretion, in cell culture from human GH-secreting tumors, from patients partially responsive to long-term treatments with octreotide or lanreotide. In 18 tumors tested, the SSTR2, SSTR5, and DAD2 mRNAs were coexpressed. The SSTR2-selective analog, BIM-23197, the SSTR5-selective analog, BIM-23268, and the dopamine (DA) analog, BIM-53097, produced a mean maximal suppression of GH secretion (24 +/- 3, 20 +/- 3, and 20 +/- 3%, respectively) that was similar to that obtained with octreotide (23 +/- 3%).

Efficacy of chimeric molecules directed towards multiple somatostatin and dopamine receptors on inhibition of GH and prolactin secretion from GH-secreting pituitary adenomas classified as partially responsive to somatostatin analog therapy.

Objective: This study compared the potency of a somatostatin receptor (sstr)2-sstr5 analog, BIM-23244, of an sstr2-dopamine D2 receptor (sstr2-DAD2) molecule, BIM-23A387 and of new somatostatin-dopamine chimeric molecules with differing, enhanced affinities for sstr2, sstr5 and DAD2, BIM-23A758, BIM-23A760 and BIM-23A761, to suppress GH and prolactin (PRL) from 18 human GH adenomas that are partially responsive to octreotide or lanreotide.

Materials And Methods: The sstr2, sstr5 and DAD2 mRNA levels were determined by RT-PCR. The effect of drugs was tested in cell cultures at various concentrations.

Demonstration of enhanced potency of a chimeric somatostatin-dopamine molecule, BIM-23A387, in suppressing growth hormone and prolactin secretion from human pituitary somatotroph adenoma cells.

In acromegaly, the combination of somatostatin (SS) and dopamine (DA) agonists has been shown to enhance suppression of GH secretion. In the present study, a new chimeric molecule, BIM-23A387, which selectively binds to the SS subtype 2 receptor (sst(2); K(i) = 0.10 nM) and to the DA D2 receptor (D2DR; K(i) = 22.

Pitx factors are involved in basal and hormone-regulated activity of the human prolactin promoter.

The pituitary-specific POU homeodomain factor Pit-1 likely interacts with other factors for cell-specific expression of prolactin. Here we identify the paired-like homeobox transcription factors Pitx1 and Pitx2 as factors functionally activating the proximal human prolactin promoter (hPRL-164luc). Using in vitro binding assays and a series of site-specific mutations of the proximal hPRL promoter, we mapped the B1 and B2 bicoid sites involved in Pitx-mediated transactivation of the hPRL-164luc construct.

Regulation of prolactin, GH, and Pit-1 gene expression in anterior pituitary by Pitx2: An approach using Pitx2 mutants.

The transcription factor Pitx2 is required for the morphogenesis of anterior structures such as the eye, teeth, and anterior pituitary. We investigated the functional properties of Pitx2 missense mutants previously reported in Axenfeld-Rieger syndrome, using reporter genes under the control of pituitary target gene [human (h)PRL, hGH, hPit-1] promoters transfected in nonpituitary and pituitary cell lines. The five mutants appeared to be transcriptionally defective despite conserved DNA-binding in CV1 cells.

Macroprolactinemia revisited: a study on 106 patients.

The predominance of high molecular weight PRL, or macroprolactinemia, has long been known in hyperprolactinemic patients with maintained fertility. Among 1,106 consecutive patients investigated for hyperprolactinemia in our center over a 10-yr period, serum PRL chromatography was performed in 368 cases because of discordant clinical, biological, or neuroradiological findings. We prospectively studied the 106 patients with macroprolactinemia (96 women, 6 men, 4 children) and compared them with the 262 hyperprolactinemic patients with a normal PRL elution pattern.

A luteinizing hormone-, alpha-subunit- and prolactin-secreting pituitary adenoma responsive to somatostatin analogs: in vivo and in vitro studies.

Objective: Evaluation of the efficiency of somatostatin analogues in the treatment of a mixed luteinizing hormone (LH)-, alpha-subunit-, prolactin (PRL)-secreting pituitary adenoma.

Design: 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.

Bim-23244, a somatostatin receptor subtype 2- and 5-selective analog with enhanced efficacy in suppressing growth hormone (GH) from octreotide-resistant human GH-secreting adenomas.

Although both somatostatin receptor subtype 2 (SSTR2) and SSTR5 messenger ribonucleic acid (mRNA) are consistently expressed in GH-secreting adenomas, SSTR2 has been believed to be the key modulator of somatostatin-mediated inhibition of GH release. The somatostatin agonists currently in clinical use, octreotide and lanreotide, are directed mainly to SSTR2 (IC(50) 12- to 18-fold higher than for SSTR5). Recently, however, it was demonstrated that an SSTR5 preferential agonist, BIM-23268, not only suppressed PRL release from prolactinomas and mixed GH-PRL adenomas, but also inhibited GH release in about half of GH adenomas.

Combined pituitary hormone deficiency due to the F135C human Pit-1 (pituitary-specific factor 1) gene mutation: functional and structural correlates.

The pituitary-specific transcription factor Pit-1 (pituitary-specific factor 1) is known to play a key role in the differentiation of PRL-, GH-, and TSH-secreting cells, and in the regulation of expression of the corresponding genes. In recent years, 12 distinct mutations of the Pit-1 gene have been shown to be responsible for a phenotype of multiple congenital pituitary hormone deficiency involving PRL, GH, and TSH. We had previously identified, in four siblings with GH, PRL, and TSH deficiencies, a mutation (F135C) resulting in a single amino acid change within the POU-specific binding domain of the Pit-1 molecule.

Human somatostatin receptor subtypes in acromegaly: distinct patterns of messenger ribonucleic acid expression and hormone suppression identify different tumoral phenotypes.

Recently, studies using somatostatin (SRIF) analogs preferential for either the SRIF receptor 2 (SSTR2) or the SSTR5 subtype demonstrated a variable suppression of GH and PRL release from GH-secreting human adenomas. These data suggested the concept of SSTR subtype specificity in such tumors. In the present study the quantitative expression of messenger ribonucleic acid (mRNA) for the 5 SSTR subtypes and the inhibitory effects of SRIF14; SRIF28; octreotide; the SSTR2-preferential analog, BIM-23197; and the SSTR5-preferential analog, BIM-23268, on GH and PRL secretion were analyzed in cells cultured from 15 acromegalic tumors.

Quantitative and functional expression of somatostatin receptor subtypes in human prolactinomas.

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.

Expression of functional growth hormone secretagogue receptors in human pituitary adenomas: polymerase chain reaction, triple in-situ hybridization and cell culture studies.

We examined the expression of functional growth hormone secretagogue receptors (GHS-R) in a series of 30 human pituitary adenomas-six secreting GH, three GH-PRL, six prolactin (PRL), five adrenocorticotrophic hormone (ACTH), one thyroid stimulating hormone (TSH), four gonadotroph and five non-secreting adenomas. By reverse transcriptase polymerase chain reaction (RT-PCR), the coexpression of the two GHS-R isoforms (Ia and Ib) was found in all the GH-, GH-PRL- and PRL-secreting adenomas, and only in two out of three corticotroph, two out of four gonadotroph and one out of five non-secreting tumours. They were absent in the TSH-secreting adenoma.

Impact of gsp oncogene on the expression of genes coding for Gsalpha, Pit-1, Gi2alpha, and somatostatin receptor 2 in human somatotroph adenomas: involvement in octreotide sensitivity.

The impact of the gsp oncogene on the expression of genes engaged in the somatotroph cell phenotype remains poorly understood in human somatotroph adenomas. As the gsp oncogene is associated with an increased octreotide (somatostatin agonist) sensitivity, a group of 8 somatotroph adenomas bearing the gsp mutation (gsp+) and another group of 16 adenomas without the mutation (gsp-) were analyzed, all of them presenting variable octreotide sensitivities. The expressions of genes encoding for G(s)alpha, Pit-1, G(i2)alpha, and SSTR2, involved in the regulation of secretory activity in somatotroph cells, were assessed by Northern blot.

Expression of the members of the Ptx family of transcription factors in human pituitary adenomas.

A number of putative transcription factors described in the pituitary have been implicated as key elements in the processes that direct pituitary development. Three recently described proteins, Ptx1, Ptx2, and Ptx3, define a new family of transcription factors, the Ptx subfamily, within the paired-like class of homeodomain factors. In mice, Ptx1 and Ptx2 gene expression has been detected in the area of the pituitary primordium and is maintained throughout development in Rathke pouch and adult pituitary.

Pronostic and therapeutic consequences of Gs alpha mutations in somatotroph adenomas.

Human pituitary somatotroph adenomas can be associated with mutations of the s alpha-subunit of G proteins. However, the impact of the gsp mutations on the tumoral phenotype is not well understood at present. This study aims to determine whether the detection of this mutation could impact on the management of acromegalic patients.

[Homeoproteins and pituitary adenoma].

Several transactivating factors specifically involved in the differentiation and proliferation of anterior pituitary cell types have been recently identified. Among them Pit-1 a member of the POU-domain transcription factors family is specific of anterior pituitary cells, and was initially identified and cloned as a transactivator of the GH and PRL genes and as a regulator of the TSH beta gene. Pit-1 play a key role during embryogenesis in the differentiation and proliferation of somatotrophs, lactotrophs and thyreotrophs.

Pit-1 gene expression in human pituitary adenomas.

The anterior pituitary-specific transcription factor Pit-1 (also known as GHF-1) was initially identified and cloned as a transactivator of the GH and PRL genes, and later as a regulator of the TSH beta gene. Analysis of Pit-1 expression during mouse embryogenesis revealed that initiation of its expression correlates both temporally and spatially with activation of its target genes. Immunocytochemical studies revealed a high expression of Pit-1 protein in the nuclei of only three cell types: somatotropes, lactotropes and thyrotropes.

Abnormal transduction mechanisms in pituitary adenomas.

Pituitary adenomas are differentiated tumors expressing their appropriate mature hormone. Tumoral cells sometimes present with a defective physiological inhibitory or stimulatory control, resulting in paradoxical responses or nonresponsiveness to regulatory neurohormones. These abnormalities can be explained by defects at the intracellular transduction mechanism level.