This Article Abstract Full Text (PDF) Submit a related Letter to the Editor Purchase Article View Shopping Cart Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Saveanu, A. Articles by Jaquet, P. Search for Related Content PubMed PubMed Citation Articles by Saveanu, A. Articles by Jaquet, P.

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 Adenomas¹

Interactions Cellulaires Neuroendocriniennes, Unité Mixte de Recherche 6544, Centre National de la Recherche Scientifique (A.S., G.G., A.E., P.J.), and Laboratoire de Transfert d’Oncologie Biologique-Assistance Publique-Hôpitaux de Marseilles (L.O., F.F.), Institut Fédératif Jean Roche, Faculté de Médecine Nord, 13916 Marseilles, France; Service de Neurochirurgie, Centre Hospitalier de Marseilles, Hôpital de la Timone (H.D.), 13005 Marseilles, France; Service d’Endocrinologie de Toulouse (P.C.), 31403 Toulouse, France; and Biomeasure, Inc. (M.D.C., J.P.M.), Milford, Massachusetts 01757

Address all correspondence and requests for reprints to: Dr. Philippe Jaquet, Interactions Cellulaires Neuroendocriniennes-Unité Mixte de Recherche 6544, Centre National de la Recherche Scientifique, Institut Fédératif Jean Roche, Faculté de Médecine Nord, boulevard Pierre Dramard, 13916 Marseilles Cedex 20, France.

	Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
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 (IC₅₀ 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. In addition, the SSTR5-preferring analog showed a slight additive effect when used in combination with SSTR2 preferential drugs at submaximal concentrations in octreotide partially sensitive adenomas. In the present study we quantified SSTR2 and SSTR5 mRNA expression and the GH-suppressive effects of somatostatin-14; octreotide; a SSTR2-preferential compound, BIM-23197; a SSTR5-preferential compound, BIM-23268; and a new SSTR2- and SSTR5-bispecific compound, BIM-23244, in GH-secreting tumors classified as either full responders to octreotide (n = 5) or partially sensitive to octreotide (n = 5). The octreotide-sensitive GH secretory adenomas presented with a high level of both SSTR2 and SSTR5 mRNA expression [222 ± 61 and 327 ± 136 pg/pg glyceraldehyde-3-phosphate dehydrogenase (GAPDH), respectively]. In these tumors the suppression of GH release was similarly achieved at picomolar ranges by octreotide, BIM-23197, and BIM-23244 (EC₅₀ = 25 ± 15, 3 ± 2, and 3 ± 3 pmol/L, respectively). The compounds preferential for only SSTR5 were unable to inhibit GH release in such tumors. Among the octreotide partially responsive tumors, SSTR2 mRNA expression was 9-fold lower than in the octreotide-sensitive tumors (25 ± 12 vs. 222 ± 61 pg/pg GAPDH; P < 0.015), whereas SSTR5 mRNA expression was approximately 7-fold higher than in the octreotide-sensitive tumors (2271 ± 1197 pg/pg GAPDH). In these octreotide partially responsive tumors, the SSTR5-preferential compound, BIM-23268, and the SSTR2- and SSTR5-bispecific compound, BIM-23244, were quite effective in suppressing GH secretion (EC₅₀ = 25 ± 13 and 50 ± 31 pmol/L, respectively). Similarly, BIM-23244, was able to suppress by 51 ± 5% PRL release from five mixed GH- and PRL-secreting adenomas. These data indicate that due to heterogeneous expression of SSTR2 and SSTR5 receptor subtypes, in GH-secreting tumors, a bispecific analog, such as BIM-23244, that can activate both receptors could achieve better control of GH hypersecretion in a larger number of acromegalic patients.

	Introduction

Top Abstract Introduction Subjects and Methods Results Discussion References

 
THE SOMATOSTATIN (SRIF) agonists, octreotide and lanreotide, have been widely used in the treatment of acromegalic patients. Worldwide experience with long-term treatments using these SRIF analogs has resulted in normalized GH and insulin-like growth factor I (IGF-I) levels in about 50% of patients (1, 2, 3). To explain the lack of full efficacy of such drugs in half of the acromegalic patients, a loss of SRIF receptor binding capacity was proposed in two different studies (4, 5). In fact, decreased efficacy of SRIF agonists associated with a significant decrease in SRIF receptors represents in these series less than 20% of the cases. Somatostatin exerts its biological effects via five distinct high affinity receptor (SSTR) subtypes that belong to the family of G protein-coupled receptors (6). Recent studies using subtype-selective SRIF analogs demonstrated the involvement of both SSTR2 and SSTR5 receptor subtypes in regulating GH secretion from human pituitary adenomas (7, 8). As octreotide and lanreotide both have 12- to 18-fold lower binding affinities for SSTR5 than for SSTR2 (9), it is possible that their partial efficacy on the control of GH secretion in some acromegalic patients could be the consequence of their lower affinity for the SSTR5 subtype.

In the present study we used in vivo data to select a series of tumors from acromegalic patients considered either full octreotide responders or partial responders. In these cases a portion of the tumor tissue obtained after transsphenoidal surgery was analyzed in terms of SSTR2 and SSTR5 messenger ribonucleic acid (mRNA) expression. The remainder of the tumor tissue was used for cell culture experiments in which the GH- and PRL-suppressive effects of SRIF-14 and of different SRIF analogs that are selective for the SSTR2-, SSTR5-, and SSTR2- plus -5 subtypes were analyzed. The main objectives in the present work were to characterize the quantitative mRNA expression of GH tumors from octreotide poorly responders and to extend in this group the preliminary observations (7, 8) showing a better suppressive effect on GH suppression of somatostatin analogs preferential for both SSTR2 and SSTR5 subtypes.

	Subjects and Methods

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Patients

The present study was undertaken after obtaining informed consent from each patient. Ten acromegalic patients (seven women and three men), aged 26–62 yr, presenting with macroadenoma were studied. Their endocrine status and the neuroradiological characterization of the pituitary adenomas were documented before treatment. Basal GH levels were the mean of three random samples obtained between 0800–0900 h. The basal IGF-I value was evaluated under fasting conditions between 0800–0900 h. Magnetic resonance imaging revealed adenomas with a maximal 11- to 42-mm diameter. SRIF agonist sensitivity was assessed by an acute test using a single 200-µg injection of octreotide (Sandostatin, Novartis, Basel, Switzerland). Sensitivity to somatostatin analogs was expressed as the percent decrease in GH from the basal value to the mean GH values 2–6 h after octreotide injection. According to the test results, five patients were considered full octreotide responders (mean GH suppression, 79 ± 7%), whereas the other five cases were considered partial octreotide responders (mean GH suppression, 33 ± 6%). All patients underwent transsphenoidal surgery. The clinical endocrine and tumoral status of each patient is summarized in Table 1.

GH and PRL were measured using commercial immunoradiometric kits (Immunotech, Marseilles, France). Normal GH values ranged from 0.2–2.4 µg/L; normal PRL values ranged from 1–24 µg/L in women and from 1–17 µg/L in men. After an ethanol-acid extraction, the plasma IGF-I assay was performed using the IGF-I RIA kit from Nichols Institute Diagnostics (San Juan Capistrano, CA). The normal ranges, according to sex and age, were established by our laboratory.

Detection of SSTRs

Total RNA was extracted from 30–60 mg tissue from each tumor using the SV total RNA isolation system (Promega Corp., Lyon, France). The RNA samples were subsequently treated with 30 U ribonuclease-free deoxyribonuclease I (Roche, Mannheim, Germany). Total RNA was reverse transcribed into complementary DNA using 1 µg hexamers (Pharmacia Biotech, Orsay, France) and Moloney murine leukemia virus reverse transcriptase, as described by the manufacturer.

The 5'-exonuclease (Taq Man) assay, which produces a direct proportional readout for the progression of PCR reactions, was used to quantify the SSTRs mRNA (10). The details of reaction conditions, the primers used, and the quantification calculation for SSTR2 and SSTR5 mRNA were described previously (8). The results were expressed as picograms of SSTR per pg glyceraldehyde-3-phosphate dehydrogenase (GAPDH).

Cell culture studies

A portion of each tumor obtained at surgery was dissociated by mechanical and enzymatic methods. Depending on the tumor, 4–90 x 10⁶ isolated cells were obtained. Tumor cells were initially cultured in DMEM supplemented with 10% FCS for 3 days. On day 3, the cells were washed and plated in multiwell culture dishes (Costar 3524, Brumath, France) coated with extracellular matrix from bovine endothelial corneal cells as previously described (11) at a density of 2 x 10⁴ cells/well. When they were attached to the matrix on days 5–8, depending on the culture, the medium was removed and replaced with DMEM supplemented with 2% FCS, antibiotics, transferrin, and selenium as previously described (11). The effects of various doses of SRIF-14; octreotide; a SSTR2-preferential compound, BIM-23197; a SSTR5-preferential compound BIM-23268; and the SSTR2- and SSTR5-selective compound, BIM-23244, on the inhibition of GH and PRL release were measured over an 8-h period between days 5–8 of culture. Each drug concentration was tested in quadruplicate.

Products

SRIF-14 was purchased from Sigma (Saint-Quentin Fallavier, France). Octreotide was supplied by Novartis (Basel, Switzerland). The BIM compounds were provided by Biomeasure, Inc. (Milford, MA). The human SSTR affinities (IC₅₀; nanomoles per L) of each compound, determined by radioligand receptor binding assays to membranes from transfected CHO-K1 cells expressing the different human SSTR subtypes, are summarized in Table 2. The native SRIF and SRIF analogs were dissolved in 0.01 mol/L acetic acid containing 0.1% purified serum albumin (Life Technologies, Inc., Cergy-Pontoise, France). The drugs were stored at -80 C as 10^-3 mol/L solutions. For each experiment, fresh working solutions were prepared from a new aliquot.

The results are presented as the mean ± SEM. Statistical significance between two unpaired groups was determined by the Mann-Whitney test. To measure the strength of association between the pairs of variables without specifying dependencies, Spearman order correlations were used. P < 0.05 was considered significant for all tests.

	Results

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Correlation between octreotide sensitivity and SSTR2 and SSTR5 subtype mRNA expression in acromegaly

The degree of GH inhibition by SRIF-14 in vitro and the levels of SSTR2 mRNA expression have been previously shown to be highly correlated (8). In the present series the degree of GH inhibition in patients, as evaluated by acute octreotide test, was also highly correlated to the level of SSTR2 mRNA expression (P < 0.009; Table 1).

In five adenomas (A1–A5) highly sensitive to octreotide, the mean SSTR2 expression was 222 ± 61 pg/pg GAPDH. When the same analysis was made in four of five (A7–A10) adenomas from partial octreotide responders, the mean SSTR2 mRNA expression was much lower (25 ± 12 pg/pg GAPDH). As shown in Fig. 1, the five adenomas from octreotide-responsive patients expressed SSTR5 mRNA at an equivalent level (SSTR2/SSTR5 mRNA ratio, 0.9 ± 0.3). In contrast, adenomas from the four partial octreotide responders with low SSTR2 mRNA expression expressed high levels of SSTR5 mRNA (2271 ± 1197 pg/pg GAPDH). Thus, these data establish two patterns of mRNA expression in the GH-secreting tumors. The octreotide-sensitive adenomas equally express both SSTR2 and SSTR5 mRNA, whereas in the adenomas that were poorly responsive to octreotide, the loss of SSTR2 mRNA contrasted with a 30-fold higher expression of SSTR5 vs. SSTR2 mRNA.

View larger version (16K): [in this window] [in a new window]   Figure 1. Quantitative RT-PCR expression of SSTR2 and SSTR5 mRNAs in 9 of 10 GH-secreting adenomas. The 9 analyses were ranked according to in vivo sensitivity to octreotide (see Table 1). Results are expressed as picograms per pg GAPDH. The percent GH suppression by octreotide challenge is defined in Materials and Methods.

Effects of SSTR2- and SSTR5-preferential agonists on GH secretion (Fig. 2)

In this series of experiments, the dose-response inhibition of GH release was examined with 10^-13–10^-8 mol/L concentrations of SRIF-14; the SSTR2-preferential compound, BIM-23197; and the SSTR5 preferential compound, BIM-23268. Among the 10 adenoma cell cultures, 2 patterns of responses to SSTR2- and SSTR5-preferential analogs were observed. In cultures from the 5 octreotide-sensitive tumors (A1–A5), the SSTR2-preferential compound, BIM-23197, produced a maximal 41 ± 7% mean GH suppression at a 0.1 nmol/L concentration, with an EC₅₀ of 3 ± 2 pmol/L. A similar dose-response inhibition of GH release was obtained with SRIF-14. In contrast, the SSTR5-preferential compound, BIM-23268, produced a maximal inhibition of GH release only at 10 nmol/L (EC₅₀ = 800 ± 350 pmol/L). This discrepancy between the results obtained with BIM-23197 and BIM-23268 can be explained on the basis of the binding affinities of BIM-23268, which is preferential for SSTR5, but at high concentrations behaves as a weak SSTR2 agonist. Thus, in the tumor cells from full octreotide responders, the GH-suppressive effect of somatostatin was mediated through only the SSTR2 subtype. In the second class of GH-secreting tumors that were partially responsive to octreotide (A6–A10), maximal GH suppression was equally achieved by SRIF-14 and the SSTR5-preferential agonist, BIM-23268. In these 5 adenoma cell cultures, BIM-23197 was slightly less potent than BIM-23268 (maximal GH suppression, 31 ± 5% and 38 ± 7%, respectively). The EC₅₀ values achieved with BIM-23268 and BIM-23197 were 25 ± 13 and 47 ± 18 pmol/L, respectively. These data indicate that in tumor cells that are partially responsive to octreotide, the GH-suppressive effect of SRIF is mediated through both the SSTR5 and SSTR2 subtypes.

View larger version (26K): [in this window] [in a new window]   Figure 2. Mean dose-response GH suppression curves obtained with SRIF-14; the SSTR2- preferential compound, BIM-23197; and the SSTR5-preferential compound, BIM-23268, in cell cultures from 10 GH adenomas. Results are expressed as the mean ± SEM percent GH suppression vs. that with medium alone (c, control). The subclasses of octreotide responders (n = 5) or partial responders (n = 5) were defined by in vivo octreotide sensitivity, as shown in Table 1, for each tumor.

BIM-23244 vs. octreotide in the octreotide-sensitive and octreotide partially sensitive tumors (Fig. 3)

In the five octreotide-sensitive tumors in which the GH-suppressive effect of SRIF was mediated through the SSTR2 subtype, the effects of the SSTR2- plus SSTR5-selective analog, BIM-23244, and octreotide on GH secretion were examined using 10^-3–10^-8 mol/L of each compound. The dose-response inhibition curves of GH release induced by BIM-23244 and octreotide were parallel (EC₅₀ = 3 ± 3 and 55 ± 15 pmol/L, respectively). At nanomolar concentrations, the mean maximal GH suppressions induced by BIM-23244 and octreotide were 44 ± 5% and 36 ± 7%, respectively. These results show that when the GH-suppressive effect is mediated through the SSTR2 subtype, native SRIF and BIM-23244 are similarly efficacious in suppressing GH secretion. As expected from the binding affinities for SSTR2 (Table 2), BIM-23244 was slightly more potent than octreotide.

View larger version (24K): [in this window] [in a new window]   Figure 3. Mean dose-response GH suppression curves obtained with octreotide and the SSTR2- and SSTR5-bispecific compound, BIM-23244 (10-13–10-8 mol/L). Results are expressed as the mean ± SEM percent GH suppression vs. the control value (medium alone). The subclasses of octreotide responders (n = 5) or partial responders (n = 5) were defined by in vivo octreotide sensitivity, as shown in the Table 1, for each tumor.

Comparison between BIM-23244 and the combination of SSTR2- and SSTR5-preferential agonists (Fig. 4)

In the five cell cultures from adenomas equally sensitive to the SSTR2- and SSTR5- preferential agonists (octreotide partial responders), the dose-response inhibition of GH release by BIM-23244 was compared with that induced by a combination of the SSTR2 preferential agonist, BIM-23197, and the SSTR5 preferential agonist, BIM-23268, at equimolar doses. Similar maximal levels of GH suppression (44 ± 5%) were achieved by BIM-23244 and the combination of BIM-23197 and BIM-23268. The dose-response inhibitions of GH release induced by the two treatments were parallel. As expected from their respective IC₅₀ values for both the SSTR2 and SSTR5 subtypes, the combination of BIM-23197 and BIM-23268 was slightly more potent in suppressing GH secretion than the biselective agonist BIM-23244.

View larger version (18K): [in this window] [in a new window]   Figure 4. Mean GH suppression dose-response curves with BIM-23244 alone and BIM-23197 in combination with BIM-23268 (10-13–10-8 mol/L). Results are expressed as the mean ± SEM GH suppression vs. the control value (medium alone) in five SSTR2- and SSTR5-responsive adenomas.

Effect of BIM-23244 vs. octreotide on PRL release (Fig. 5)

In five tumor cell cultures (A1, A2, A7, A9, and A10), both PRL and GH were secreted into the culture medium. A dose-response inhibition of PRL secretion by SRIF-14 and by the different SRIF analogs was observed in all tumors, with a significant maximal inhibition of PRL release. As shown in Fig. 5A, the dose-related inhibition of PRL release was similarly achieved with increasing concentrations of SRIF-14 and the SSTR5-preferring compound, BIM-23268. The SSTR2-preferring compound, BIM-23197, was partially effective in suppressing PRL suppression (mean maximal PRL inhibition, 34 ± 5% vs. 52 ± 6%, respectively, for BIM-23197 and BIM-23268). Compared with octreotide, the biselective analog, BIM-23244, was more effective in suppressing PRL secretion (Fig. 5B). The mean maximal PRL suppressions at 10 nmol/L BIM-23244 and octreotide were 51 ± 5% and 34 ± 7%, respectively (P = 0.045). These results in mixed GH-/PRL-secreting tumors indicate a better PRL-suppressive effect of either the SSTR5-preferring compound or the bispecific SSTR2 and SSTR5 compound compared with the agonists preferential for SSTR2 alone.

View larger version (24K): [in this window] [in a new window]   Figure 5. Mean dose-response PRL suppression curves in five mixed GH- and PRL-secreting adenomas. A, With SRIF-14 and the SSTR2- and SSTR5-preferential compounds, BIM-23197 and BIM-23268, respectively. B, With octreotide and BIM-23244 (10-8–10-13 mol/L). Results are expressed as the mean ± SEM percent PRL suppression vs. the control value (medium alone).

	Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

From our data, two classes of tumors emerged among the GH-secreting adenomas. The first was a series of tumors characterized by high sensitivity to SRIF-14 and SSTR2-preferential agonists. These tumors presented the highest level of SSTR2 mRNA expression and had the highest GH-suppressive effect with octreotide. Why, despite equivalent SSTR5 mRNA expression, the SSTR5 preferential analog did not suppress GH release in such tumors remains unknown. In the second class of tumors, the level of SSTR2 mRNA was low, and octreotide produced only partial inhibition of GH release. SRIF-14 was nevertheless able to suppress GH release, with a maximal suppressive effect similar to that of the first class of tumors, but at a 10-fold higher concentration. The presence of high levels of SSTR5 mRNA was associated with a potent suppressive effect of BIM-23268 on GH release, more efficacious than that of the SSTR2 analogs. In these tumors, the bispecific SSTR2 and SSTR5 compound, BIM-23244, induced a suppression of GH release identical to that achieved by native SRIF. These data suggest that in tumors deficient in the SSTR2 subtype presenting with a high SSTR5/SSTR2 ratio there may be a rescue through the SSTR5 subtype that mediates the suppression of GH release.

Such changes in the intensity of GH suppression as a function of the specificity of the SRIF agonists are in keeping with recent experimental data demonstrating ligand- induced SSTR subtype dimerization in CHO-K1 transfected cells (26). This study showed that the ligands (SRIF or SRIF agonist) could produce a homo- or heterodimerization of the SSTR receptor subtypes. Such a ligand-induced dimerization process resulted in increased binding affinity and modified SSTR functionality. Furthermore the ability of the ligands to homodimerize SSTR5 was highly dependent on the quantity of SSTR5 transfected into CHO-K1 cells. In our GH-secreting tumors presenting with high expression of SSTR2 mRNA, it could be that octreotide as well as ligands with high affinity to SSTR2 are inducing preferential SSTR2 homodimerization, mediating profound GH suppression in the picomolar range of these agonists. In the octreotide partially sensitive tumors, such a SSTR2 homodimerization could not be fully effective due to poor SSTR2 expression. In these cases, SSTR5 expressed at high levels could transduce GH inhibition by SRIF agonists with high affinity to SSTR5. Whether the SSTR5 preferential compounds act through homodimerization of SSTR5 subtypes or through SSTR5-SSTR2 receptor subtype heterodimerization remains speculative. Therefore, in octreotide partial responders in which the SSTR2 receptor is poorly efficient, the SSTR5-mediated pathway could compensate and transduce the inhibition of GH release in the presence of SSTR5 preferential compounds. The better efficacy of bipreferential SSTR2 and SSTR5, such as BIM-23244 and SRIF-14, compared with that of octreotide could support the hypothesis of a more efficient induced GH inhibition through SSTR5-SSTR2 heterodimerization.

In conclusion, the bispecific SRIF agonist, BIM-23244, targeting SSTR2 and SSTR5, was demonstrated to induce a greater GH- and PRL-suppressive effect in tumors considered partial octreotide responders. Such data, although significant in our cell culture studies, have to be extended by in vivo studies. Indeed, such an SSTR2- and SSTR5-bispecific agonist may also act upon other target cells bearing the SSTR5 subtype. Recent data (27) showed a preferential localization of SSTR1 and SSTR5 on pancreatic ß-cells as well as a preferential inhibition of insulin release by the SSTR5 preferential compound, BIM-23268 (28, 29). It is thus mandatory, particularly in acromegalic patients, to assess in vivo the inhibition of insulin secretion that can be produced by administration of a SSTR2- and SSTR5-bispecific agonist.

	Acknowledgments

 
We are grateful to Dr. P. M. Martin for using a Taq Man technology for real-time quantitative PCR in the Assistance Publique Hopitaux de Marseilles laboratory and to N. Peralez and Dr. D. Morando for technical assistance. The skillful help of Mrs. C. Taverna in the redaction of the manuscript was greatly appreciated.

	Footnotes

 
¹ This work was supported in part by a grant from Biomeasure, Inc., and a grant from Ligue Nationale contre le Cancer.

Received July 18, 2000.

Revised September 13, 2000.

Accepted September 14, 2000.

	References

Top Abstract Introduction Subjects and Methods Results Discussion References

 

1. Newman CB, Melmed S, Snyder PJ, et al. 1995 Safety and efficacy of long term octreotide therapy of acromegaly: results of a multicenter trial in 103 patients. A clinical research center study. J Clin Endocrinol Metab. 80:2768–2775.[Abstract]
2. Ezzat S, Kontogeorgos G, Redelmeier DA, Horvath E, Harris AG, Kovacs K. 1995 In vivo responsiveness of morphological variants of growth hormone-producing pituitary adenomas to octreotide. Eur J Endocrinol. 133:686–690.[Abstract]
3. Sassolas G, Harris AG, James-Deidier A, French SMS201–995 Acromegaly Study Group. 1990 Long term effect of incremental doses of the somatostatin analog SMS 201–995 in 58 acromegalic patients. J Clin Endocrinol Metab. 71:391–397.[Abstract]
4. Ikuyama S, Nawata H, Kato K, Karashima T, Ibayashi H, Nakagaki H. 1985 Specific somatostatin receptors on human pituitary adenoma cell membranes. J Clin Endocrinol Metab. 61:666–671.[Abstract]
5. Reubi JC, Landolt AM. 1989 The growth hormone responses to octreotide in acromegaly correlate with adenoma somatostatin receptor status. J Clin Endocrinol Metab. 68:844–850.[Abstract]
6. Patel YC, Srikant CB. 1994 Subtype selectivity of peptide analogs for all five cloned human somatostatin receptors (hsstr1–5). Endocrinology. 135:2814–2817.[Abstract]
7. Shimon I, Yan X, Taylor JE, Weiss MH, Culler MD, Melmed S. 1997 Somatostatin receptor (SSTR) subtype-selective analogs differentially suppress in vitro growth hormone and prolactin in human pituitary adenomas. Novel potential therapy for functional pituitary tumors. J Clin Invest. 100:2386–2392.[Medline]
8. Jaquet P, Saveanu A, Gunz G, et al. 2000 Human somatostatin receptor subtypes in acromegaly: distinct patterns of mRNA expression and of GH and PRL suppression identify tumoral phenotypes. J Clin Endocrinol Metab. 85:781–792.[Abstract/Free Full Text]
9. Shimon I, Taylor JE, Dong JZ, et al. 1997 Somatostatin receptor subtype specificity in human fetal pituitary cultures. Differential role of SSTR2 and SSTR5 for growth hormone, thyroid-stimulating hormone, and prolactin regulation. J Clin Invest. 4:789–798.
10. Perkin-Elmer. 1995 (Taq Man TM) probe design, synthesis, and purification. Foster City: Applied Biosystems.
11. Jaquet P, Gunz G, Grisoli F. 1985 Hormonal regulation of prolactin release by human prolactinoma cells cultured in serum-free conditions. Horm Res. 22:153–163.[Medline]
12. Ezzat S, Snyder PJ, Young WF, et al. 1992 Octreotide treatment of acromegaly. A randomized, multicenter study. Ann Intern Med. 117:711–718.
13. Flogstad AK, Halse J, Bakke S, et al. 1997 Sandostatin LAR in acromegalic patients: long-term treatment. J Clin Endocrinol Metab. 82:23–28.[Abstract/Free Full Text]
14. Caron P, Morange-Ramos I, Cogne M, Jaquet P. 1997 Three year follow-up of acromegalic patients treated with intramuscular slow-release lanreotide. J Clin Endocrinol Metab. 82:18–22.[Abstract/Free Full Text]
15. al-Maskari M, Gebbie J, Kendall-Taylor P. 1996 The effect of a new slow-release, long-acting somatostatin analogue, lanreotide, in acromegaly. Clin Endocrinol (Oxf). 45:415–421.[CrossRef][Medline]
16. Bertherat J, Chanson P, Dewailly D, et al. 1993 Somatostatin receptors, adenylate cyclase activity, and growth hormone (GH) response to octreotide in GH-secreting adenomas. J Clin Endocrinol Metab 77:1577–1583.
17. Eden PA, Taylor JE. 1993 Somatostatin receptor subtype gene expression in human and rodent tumors. Life Sci. 53:85–90.[CrossRef][Medline]
18. Schaer JC, Waser B, Mengod G, Reubi JC. 1997 Somatostatin receptor subtypes sst₁, sst₂, sst₃ and sst₅ expression in human pituitary, gastroentero-pancreatic and mammary tumors: comparison of mRNA analysis with receptor autoradiography. Int J Cancer. 70:530–537.[CrossRef][Medline]
19. Greenman Y, Melmed S. 1994 Heterogeneous expression of two somatostatinreceptor subtypes in pituitary tumors. J Clin Endocrinol Metab. 78:398–403.[Abstract]
20. Greenman Y, Melmed S. 1994 Expression of three somatostatin receptor subtypes in pituitary adenomas: evidence for preferential SSTR5 expression in the mammosomatotroph lineage. J Clin Endocrinol Metab. 79:724–729.[Abstract]
21. Miller GM, Alexander JM, Bikkal HA, Katznelson L, Zervas NT, Klibanski A. 1995 Somatostatin receptor subtype gene expression in pituitary adenomas. J Clin Endocrinol Metab. 4:1386–1392.
22. Murabe H, Shimatsu A, Ihara C, et al. 1996 Expression of somatostatin receptor (SSTR) subtypes in pituitary adenomas: quantitative analysis of SSTR2 mRNA by reverse transcription-polymerase chain reaction. J Neuroendocrinol. 8:605–610.[CrossRef][Medline]
23. Nielsen S, Mellemkjaer S, Rasmussen LM, et al. 1998 Gene transcription of receptors for growth hormone-releasing peptide and somatostatin in human pituitary adenomas. J Clin Endocrinol Metab. 83:2997–3000.[Abstract/Free Full Text]
24. Panetta R, Patel YC. 1995 Expression of mRNAfor all five human somatostatin receptors (hSSTR1–5) in pituitary tumors. Life Sci. 56:333–342.[CrossRef][Medline]
25. Reubi JC, Schaer JC, Waser B, Mengod G. 1994 Expression and localization of somatostatin receptor SSTR1, SSTR2 and SSTR3 messenger RNAs in primary human tumors using in situ hybridization. Cancer Res. 54:3455–3459.[Abstract/Free Full Text]
26. Rocheville M, Lange DC, Kumar U, Sasi R, Patel RC, Patel YC. 2000 Subtypes of the somatostatin receptor assemble as functional homo- and heterodimers. J Biol Chem. 275:7862–7869.[Abstract/Free Full Text]
27. Kumar U, Sasi R, Suresh S, et al. 1999 Subtype-selective expression of the five somatostatin receptors (hSSTR1–5) in human pancreatic islet cells. Diabetes. 48:78–85.
28. Zambre Y, Ling Z, Chen MC, et al. 1999 Inhibition of human pancreatic islet insulin release by receptor-selective somatostatin analogs directed to somatostatin receptor subtype 5. Biochem Pharmacol. 57:1159–1164.[CrossRef][Medline]
29. Strowski MZ, Parmar RM, Blake AD, Schaeffer JM. 2000 Somatostatin inhibits insulin and glucagon secretion via two receptor subtypes: an in vitro study of pancreatic islets from somatostatin receptor 2 knockout mice. Endocrinology141 :111–117.

This article has been cited by other articles:

				U. Plockinger, S. Albrecht, C. Mawrin, W. Saeger, M. Buchfelder, S. Petersenn, and S. Schulz Selective Loss of Somatostatin Receptor 2 in Octreotide-Resistant Growth Hormone-Secreting Adenomas J. Clin. Endocrinol. Metab., April 1, 2008; 93(4): 1203 - 1210. [Abstract] [Full Text] [PDF]

				D. Ferone, W. W. de Herder, R. Pivonello, J. M. Kros, P. M. van Koetsveld, T. de Jong, F. Minuto, A. Colao, S. W. J. Lamberts, and L. J. Hofland Correlation of in Vitro and in Vivo Somatotropic Adenoma Responsiveness to Somatostatin Analogs and Dopamine Agonists with Immunohistochemical Evaluation of Somatostatin and Dopamine Receptors and Electron Microscopy J. Clin. Endocrinol. Metab., April 1, 2008; 93(4): 1412 - 1417. [Abstract] [Full Text] [PDF]

				S. L. Fougner, J. Bollerslev, F. Latif, J. K. Hald, T. Lund, J. Ramm-Pettersen, and J. P. Berg Low Levels of Raf Kinase Inhibitory Protein in Growth Hormone-Secreting Pituitary Adenomas Correlate with Poor Response to Octreotide Treatment J. Clin. Endocrinol. Metab., April 1, 2008; 93(4): 1211 - 1216. [Abstract] [Full Text] [PDF]

				G. F Taboada, R. M Luque, L. V. Neto, E. d. O Machado, B. C Sbaffi, R. C Domingues, J. B Marcondes, L. M C Chimelli, R. Fontes, P. Niemeyer, et al. Quantitative analysis of somatostatin receptor subtypes (1-5) gene expression levels in somatotropinomas and correlation to in vivo hormonal and tumor volume responses to treatment with octreotide LAR Eur. J. Endocrinol., March 1, 2008; 158(3): 295 - 303. [Abstract] [Full Text] [PDF]

				E. Resmini, P. Dadati, J.-L. Ravetti, G. Zona, R. Spaziante, A. Saveanu, P. Jaquet, M. D. Culler, F. Bianchi, A. Rebora, et al. Rapid Pituitary Tumor Shrinkage with Dissociation between Antiproliferative and Antisecretory Effects of a Long-Acting Octreotide in an Acromegalic Patient J. Clin. Endocrinol. Metab., May 1, 2007; 92(5): 1592 - 1599. [Abstract] [Full Text] [PDF]

				D. Ferone, A. Saveanu, M. D Culler, M. Arvigo, A. Rebora, F. Gatto, F. Minuto, and P. Jaquet Novel chimeric somatostatin analogs: facts and perspectives Eur. J. Endocrinol., April 1, 2007; 156(suppl_1): S23 - S28. [Abstract] [Full Text] [PDF]

				J. van der Hoek, S. W J Lamberts, and L. J Hofland Preclinical and clinical experiences with the role of somatostatin receptors in the treatment of pituitary adenomas Eur. J. Endocrinol., April 1, 2007; 156(suppl_1): S45 - S51. [Abstract] [Full Text] [PDF]

				G. F Taboada, R. M Luque, W. Bastos, R. F C Guimaraes, J. B Marcondes, L. M C Chimelli, R. Fontes, P. J P Mata, P. N. Filho, D. P Carvalho, et al. Quantitative analysis of somatostatin receptor subtype (SSTR1-5) gene expression levels in somatotropinomas and non-functioning pituitary adenomas Eur. J. Endocrinol., January 1, 2007; 156(1): 65 - 74. [Abstract] [Full Text] [PDF]

				M. Duran-Prado, C. Bucharles, B. J. Gonzalez, R. Vazquez-Martinez, A. J. Martinez-Fuentes, S. Garcia-Navarro, S. J. Rhodes, H. Vaudry, M. M. Malagon, and J. P. Castano Porcine Somatostatin Receptor 2 Displays Typical Pharmacological sst2 Features but Unique Dynamics of Homodimerization and Internalization Endocrinology, January 1, 2007; 148(1): 411 - 421. [Abstract] [Full Text] [PDF]

				D. O'Toole, A. Saveanu, A. Couvelard, G. Gunz, A. Enjalbert, P. Jaquet, P. Ruszniewski, and A. Barlier The analysis of quantitative expression of somatostatin and dopamine receptors in gastro-entero-pancreatic tumours opens new therapeutic strategies Eur. J. Endocrinol., December 1, 2006; 155(6): 849 - 857. [Abstract] [Full Text] [PDF]

				C Susini and L Buscail Rationale for the use of somatostatin analogs as antitumor agents Ann. Onc., December 1, 2006; 17(12): 1733 - 1742. [Abstract] [Full Text] [PDF]

				R. Cescato, S. Schulz, B. Waser, V. Eltschinger, J. E. Rivier, H.-J. Wester, M. Culler, M. Ginj, Q. Liu, A. Schonbrunn, et al. Internalization of sst2, sst3, and sst5 Receptors: Effects of Somatostatin Agonists and Antagonists J. Nucl. Med., March 1, 2006; 47(3): 502 - 511. [Abstract] [Full Text] [PDF]

				E Thodou, G Kontogeorgos, D Theodossiou, and M Pateraki Mapping of somatostatin receptor types in GH or/and PRL producing pituitary adenomas. J. Clin. Pathol., March 1, 2006; 59(3): 274 - 279. [Abstract] [Full Text] [PDF]

				D. Ferone, M. Arvigo, C. Semino, P. Jaquet, A. Saveanu, J. E. Taylor, J.-P. Moreau, M. D. Culler, M. Albertelli, F. Minuto, et al. Somatostatin and dopamine receptor expression in lung carcinoma cells and effects of chimeric somatostatin-dopamine molecules on cell proliferation Am J Physiol Endocrinol Metab, December 1, 2005; 289(6): E1044 - E1050. [Abstract] [Full Text] [PDF]

				M C Zatelli, D Piccin, F Tagliati, A Bottoni, M R Ambrosio, A Margutti, M Scanarini, M Bondanelli, M D Culler, and E C d. Uberti Dopamine receptor subtype 2 and somatostatin receptor subtype 5 expression influences somatostatin analogs effects on human somatotroph pituitary adenomas in vitro J. Mol. Endocrinol., October 1, 2005; 35(2): 333 - 341. [Abstract] [Full Text] [PDF]

				M. Filopanti, C. Ronchi, E. Ballare, S. Bondioni, A. G. Lania, M. Losa, S. Gelmini, A. Peri, C. Orlando, P. Beck-Peccoz, et al. Analysis of Somatostatin Receptors 2 and 5 Polymorphisms in Patients with Acromegaly J. Clin. Endocrinol. Metab., August 1, 2005; 90(8): 4824 - 4828. [Abstract] [Full Text] [PDF]

				P Jaquet, G Gunz, A Saveanu, H Dufour, J Taylor, J Dong, S Kim, J-P Moreau, A Enjalbert, and M D Culler 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 Eur. J. Endocrinol., July 1, 2005; 153(1): 135 - 141. [Abstract] [Full Text] [PDF]

				M. C. Zatelli, D. Piccin, A. Bottoni, M. R. Ambrosio, A. Margutti, R. Padovani, M. Scanarini, J. E. Taylor, M. D. Culler, L. Cavazzini, et al. Evidence for Differential Effects of Selective Somatostatin Receptor Subtype Agonists on {alpha}-Subunit and Chromogranin A Secretion and on Cell Viability in Human Nonfunctioning Pituitary Adenomas in Vitro J. Clin. Endocrinol. Metab., October 1, 2004; 89(10): 5181 - 5188. [Abstract] [Full Text] [PDF]

				R. D. Murray, K. Kim, S.-G. Ren, I. Lewis, G. Weckbecker, C. Bruns, and S. Melmed The Novel Somatostatin Ligand (SOM230) Regulates Human and Rat Anterior Pituitary Hormone Secretion J. Clin. Endocrinol. Metab., June 1, 2004; 89(6): 3027 - 3032. [Abstract] [Full Text] [PDF]

				L. J. Hofland, J. van der Hoek, P. M. van Koetsveld, W. W. de Herder, M. Waaijers, D. Sprij-Mooij, C. Bruns, G. Weckbecker, R. Feelders, A.-J. van der Lely, et al. The Novel Somatostatin Analog SOM230 Is a Potent Inhibitor of Hormone Release by Growth Hormone- and Prolactin-Secreting Pituitary Adenomas in Vitro J. Clin. Endocrinol. Metab., April 1, 2004; 89(4): 1577 - 1585. [Abstract] [Full Text] [PDF]

				J. van der Hoek, W. W. de Herder, R. A. Feelders, A.-J. van der Lely, P. Uitterlinden, V. Boerlin, C. Bruns, K. W. Poon, I. Lewis, G. Weckbecker, et al. A Single-Dose Comparison of the Acute Effects between the New Somatostatin Analog SOM230 and Octreotide in Acromegalic Patients J. Clin. Endocrinol. Metab., February 1, 2004; 89(2): 638 - 645. [Abstract] [Full Text] [PDF]

				S.-G. Ren, J. Taylor, J. Dong, R. Yu, M. D. Culler, and S. Melmed Functional Association of Somatostatin Receptor Subtypes 2 and 5 in Inhibiting Human Growth Hormone Secretion J. Clin. Endocrinol. Metab., September 1, 2003; 88(9): 4239 - 4245. [Abstract] [Full Text] [PDF]

				J. C. Reubi Peptide Receptors as Molecular Targets for Cancer Diagnosis and Therapy Endocr. Rev., August 1, 2003; 24(4): 389 - 427. [Abstract] [Full Text] [PDF]

				M. C. Zatelli, D. Piccin, F. Tagliati, M. R. Ambrosio, A. Margutti, R. Padovani, M. Scanarini, M. D. Culler, and E. C. degli Uberti Somatostatin Receptor Subtype 1 Selective Activation in Human Growth Hormone (GH)- and Prolactin (PRL)-Secreting Pituitary Adenomas: Effects on Cell Viability, GH, and PRL Secretion J. Clin. Endocrinol. Metab., June 1, 2003; 88(6): 2797 - 2802. [Abstract] [Full Text] [PDF]

				L. J. Hofland and S. W. J. Lamberts The Pathophysiological Consequences of Somatostatin Receptor Internalization and Resistance Endocr. Rev., February 1, 2003; 24(1): 28 - 47. [Abstract] [Full Text] [PDF]

G. Weckbecker, U. Briner, I. Lewis, and C. Bruns SOM230: A New Somatostatin Peptidomimetic