Somatostatin Receptor Type Research Articles

Phase I trial of molecularly targeted, radiolabeled somatostatin analog in children and young adults with recurrent or progressive solid tumors

10029 Background: Somatostatin receptors are highly expressed in several pediatric solid tumors, including neuroblastoma, medulloblastoma and neuroendocrine tumors. We hypothesize that molecularly targeted somatostatin analog, 90Y-DOTA- tyr3-Octreotide which binds with high affinity to somatostatin receptor type 2 (sst2), will be an effective therapy for pediatric malignancies that express sst2. Methods: A Phase I, dose/toxicity trial of 90Y-DOTA-tyr3-Octreotide was conducted at 30 (cohort 1), 40 (cohort2), and 50 (cohort 3) mCi/m2 with concomitant Aminosyn II infusion. Subjects received 3 cycles of treatment, 6 weeks apart. Eligibility criteria included: recurrent or progressive malignancy with at least one Octreoscan positive lesion; age 2–25 yrs; bone marrow cellularity >40%; GFR >80 ml/min/m2; no radiation therapy for 3 months; no chemotherapy for 30 days. Escalation was based on 3/3 or 4/6 subjects with no dose limiting toxicity. Additionally, subjects were limited to <21Gy calculated radiation dose to kidneys, including any previous external beam radiotherapy received prior to 90Y-DOTA-tyr3- Octreotide dosing. Results: Twelve subjects completed 3 cycles (5, 3 and 4 subjects in cohorts 1,2, 3, respectively). Diagnoses included gastrinoma (3), foregut carcinoid (3), neuroblastoma (2), paraganglioma (2), MENIIb, and anaplastic astrocytoma. Five subjects (38%) had a PR (>50% decrease in target lesion); four subjects had a positive response (>25%<50% decrease in target lesion); three subjects had stable disease for > 4 months; seven subjects remain alive without progression 2 months to 3.5 years after completion of therapy. Four subjects withdrew from the study after one cycle and had progressive disease within 6 weeks. No dose limiting toxicities were observed; specifically, no Grade III or greater renal or hematologic toxicity was observed. Conclusions: Based on intent to treat, 53% of children and young adults with recurrent, sst2 positive tumor had a positive response to 90Y-DOTA-tyr3- Octreotide. PR was obtained in at least one subject at each dose level. No dose limiting toxicities were observed with 50 mCi/m2, the recommended dose for Phase II studies. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration Molecular Insight Pharmaceuticals Milecular Insight Pharmaceuticals, Novartis Pharmaceuticals, Inc. Molecular Insight Pharmaceuticals

Bardet–Biedl syndrome proteins are required for the localization of G protein-coupled receptors to primary cilia

Primary cilia are ubiquitous cellular appendages that provide important yet not well understood sensory and signaling functions. Ciliary dysfunction underlies numerous human genetic disorders. However, the precise defects in cilia function and the basis of disease pathophysiology remain unclear. Here, we report that the proteins disrupted in the human ciliary disorder Bardet-Biedl syndrome (BBS) are required for the localization of G protein-coupled receptors to primary cilia on central neurons. We demonstrate a lack of ciliary localization of somatostatin receptor type 3 (Sstr3) and melanin-concentrating hormone receptor 1 (Mchr1) in neurons from mice lacking the Bbs2 or Bbs4 gene. Because Mchr1 is involved in the regulation of feeding behavior and BBS is associated with hyperphagia-induced obesity, our results suggest that altered signaling caused by mislocalization of ciliary signaling proteins underlies the BBS phenotypes. Our results also provide a potential molecular mechanism to link cilia defects with obesity.

Control of Gastric Acid Secretion in Somatostatin Receptor 2 Deficient Mice: Shift from Endocrine/Paracrine to Neurocrine Pathways

The gastrin-enterochromaffin-like (ECL) cell-parietal cell axis is known to play an important role in the regulation of gastric acid secretion. Somatostatin, acting on somatostatin receptor type 2 (SSTR(2)), interferes with this axis by suppressing the activity of the gastrin cells, ECL cells, and parietal cells. Surprisingly, however, freely fed SSTR(2) knockout mice seem to display normal circulating gastrin concentration and unchanged acid output. In the present study, we compared the control of acid secretion in these mutant mice with that in wild-type mice. In SSTR(2) knockout mice, the number of gastrin cells was unchanged; whereas the numbers of somatostatin cells were reduced in the antrum (-55%) and increased in the oxyntic mucosa (35%). The ECL cells displayed a reduced expression of histidine decarboxylase and vesicle monoamine transport type 2 (determined by immunohistochemistry), and an impaired transformation of the granules to secretory vesicles (determined by electron microscopic analysis), suggesting low activity of the ECL cells. These changes were accompanied by an increased expression of galanin receptor type 1 in the oxyntic mucosa. The parietal cells were found to respond to pentagastrin or to vagal stimulation (evoked by pylorus ligation) with increased acid production. In conclusion, the inhibitory galanin-galanin receptor type 1 pathway is up-regulated in the ECL cells, and the direct stimulatory action of gastrin and vagal excitation is enhanced on the parietal cells in SSTR(2) knockout mice. We suggest that there is a remodeling of the neuroendocrine mechanisms that regulate acid secretion in these mutant mice.

Somatostatin receptor type 2A immunohistochemistry in neuroendocrine tumors: a proposal of scoring system correlated with somatostatin receptor scintigraphy

Typing somatostatin receptor expression in neuroendocrine tumors is of relevance to target somatostatin analogue-based diagnostic approach and treatment. The expanding use of immunohistochemistry to detect somatostatin receptors is to date not paralleled by an accurate methodological setting and standardized interpretation of the results. A multicentric study was designed to compare somatostatin receptor immunohistochemical expression with in vivo scintigraphic data and verify its usefulness in the clinical management of neuroendocrine tumors. After methodological setting by testing different somatostatin receptor antibodies, 107 cases of neuroendocrine tumors with available somatostatin receptor scintigraphy data and pathological material were retrospectively analyzed for somatostatin receptor types 2A, 3 and 5 immunohistochemical expression, and compared with scintigraphic images and, whenever available, with the clinical response to somatostatin analogue treatment. Restricting ‘positive cases' to the presence of a membrane pattern of staining, an overall somatostatin receptor type 2A immunohistochemistry/somatostatin receptor scintigraphy agreement of 77% (χ2 test P<0.0001) was reached. Lower concordance ratios were detected in preoperative and metastatic tumor samples, possibly as a consequence of somatostatin receptor expression heterogeneity. Pure somatostatin receptor type 2A cytoplasmic staining showed poor correlation with somatostatin receptor scintigraphy (54% concordance rate). The immunohistochemical detection of somatostatin receptor types 3 and 5, which showed almost exclusively a cytoplasmic pattern, did not improve the concordance with scintigraphic data. In a pilot series, somatostatin receptor type 2A immunohistochemistry correlated with clinical response in 75% of cases. In conclusion, we propose a scoring system for somatostatin receptor type 2A immunohistochemistry in neuroendocrine tumors correlated with in vivo data, based on the evidence that only membrane (rather that cytoplasmic) staining should be considered for a reliable, standardized and clinically relevant report.

Signaling Can Be Uncoupled from Imaging of the Somatostatin Receptor Type 2

Endogenous and exogenous somatostatin receptors are commonly targeted for imaging using radiopharmaceutical analogues of somatostatin. Ligand binding activates receptor-mediated signaling. We assessed whether somatostatin receptor type 2A (SSTR2A) imaging can be uncoupled from signal transduction. In both human fibrosarcoma (HT1080) and human embryonic kidney (HEK293) cells, reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay found similar levels of expression of hemagglutinin A tagged SSTR2A (HA-SSTR2A) or the same fusion protein with a deletion of the C-terminus beyond amino acid 314 (HA-SSTR2Delta314). Scatchard analysis demonstrated similar degrees of ligand binding by the wild-type or mutant receptor to (111)In-octreotide in both cell pairs. Cyclic guanosine monophosphate (cGMP) production and inhibition of forskolin-induced cylic adenosine monophosphate (cAMP) production were evaluated at the signaling level, and growth inhibition was evaluated at the cellular level before and after stimulation. Unlike wild-type receptor, HA-SSTR2Delta314 was deficient in inhibiting forskolin-induced cAMP production (p < .05) and in inciting cGMP (p < .05) production; furthermore, at the cellular level, HA-SSTR2Delta314 was deficient in inhibiting cell proliferation (p < .05). Yet tumors expressing HA-SSTR2Delta314 could be imaged in vivo. Thus, in vivo imaging of SSTR2 can be uncoupled from cAMP and cGMP signaling as well as growth inhibition.

Influence of 17q gain and promoter polymorphisms on mRNA expression of somatostatin receptor type 2 in neuroblastoma

BackgroundNeuroblastoma, the most frequent solid extracranial tumor in children, is characterized by a wide spectrum of clinical behaviours. We previously reported that high expression of somatostatin receptor type-2 (sst2) mRNA is associated to increased overall and event free survival. Several genetic abnormalities are detected in neuroblastomas, frequently involving balanced and/or unbalanced gain on the long arm on chromosome 17, the same region containing sst2 gene. MethodsIn this study we detected balanced and/or unbalanced 17q gain in 50 neuroblastomas. Since two polymorphisms in sst2 promoter (−57 C>G and −83 A>G) were previously described as responsible for an in vitro reduction of sst2 mRNA expression, promoter sequencing was also performed in the same samples. The results were compared to sst2 mRNA expression, measured by real-time RT-PCR. ResultsThe frequency of 17q gain (14/50 neuroblastomas) was significantly associated to sst2 mRNA over-expression (Fischer's exact test: p=0.0012). The sst2 expression was significant higher both in balance and unbalance 17q amplifications (ANOVA: p=0.04). Conversely, we found a reduction of sst2 mRNA in neuroblastomas with −57 C>G promoter polymorphism (ANOVA: p=0.03). ConclusionWe highlighted that 17q gain and promoter polymorphisms can play a role into the regulation of sst2 expression in neuroblastomas.

Lack of concordance between I-111 pentreotide (PEN) status and immuno-histochemistry (IHC) status for somatostatin receptors type 1, 2, and 3 in neuroendocrine tumors (NET)

15060 Background: The use of somatostatin analogues (ST) in the treatment of NET is recommended for functional and non- function slow progressing tumors that present with positive PEN. The goal of the study was to determine if expression of ST receptors type 2, 3 and 1 in NET tumors by IHC predict the PEN status and response to ST. Methods: Retrospective analysis of paraffin blocs from primary or metastatic sites and PEN imaging from 39 patients with a diagnosis of NET confirmed by independent pathology review. IHC analysis was performed in a central laboratory using antibody ST receptor type 1 from Neomarkers and type 2 and 3 from Affinity Bio Reagents. Status for each receptor type was reported as positive or negative, diffuse or focal and by % of positive cells. All slides were reviewed by the same pathologist. PEN images were submitted to an independent radiology review and reported as positive or negative and the signal intensity was graded from 1 to 4. Investigators were blinded to receptor and PEN status. This concordance analysis study was designed with a power to detect at least 60% correlation between receptor and PEN status with type I error of 5% and a type II error of 20%. Results: There was no correlation between receptor and PEN status ( Table ). Furthermore, there was no significant correlation between PEN and receptor types 3 and 1 in receptor type 2 negative patients (p=0,54, p=0,14, respectively). There was no correlation between receptor type status and PEN positive intensity. No independent or multivariate characteristics by IHC can correlate to PEN status in this cohort. Conclusions: Commonly used antibodies for IHC detection of receptors type 2, 3 and 1 used in this study failed to correlate with PEN. These results do not support the use of IHC as a substitute for PEN with respect to prediction of ST activity in NET. [Table: see text] No significant financial relationships to disclose.

Comparison of the binding modes of TT-232 in somatostatin receptors type 1 and 4

The somatostatin analogue cyclopeptide TT-232 was docked to homology models of somatostatin receptors type 1 and 4. Calculations have been performed by applying H-bonding (subtype 1: Asp137-Lys5, Gln291- DPhe1, Gln291-Cys2; subtype 4: Asp122-Lys5) and distance (subtype 4: His294-Thr7) constraints with the GOLD docking procedure. Docking showed overlapping TT-232 backbone residues. Differences were found, however, in the position of aromatic amino acids DTrp4, DPhe1 and Tyr3 of TT-232, allowing for different binding modes and functions to be performed by somatostatin receptors type 1 and 4. In accordance, TT-232 did not affect basal GABA release associated with somatostatin receptor type 1 function.

Feedback control of thyrotropin secretion in the chicken: Thyroid hormones increase the expression of hypophyseal somatostatin receptor types 2 and 5

We have studied the involvement of the somatostatin receptor type 5 (SSTR5) in the control of thyrotropin (TSH) release in the chicken. Hypothalamic somatostatin (SS-14) is known to inhibit both thyrotropin-releasing hormone (TRH)- and corticotropin-releasing hormone (CRH)-induced TSH secretion. Studies using receptor-specific agonists have indicated that the inhibitory effect of SS-14 on TRH-induced TSH release is mediated by SSTR2 and SSTR5. Using the same agonists, we were able to demonstrate the involvement of SSTR5 in the inhibition of the in vitro CRH-induced TSH secretion by SS-14. Subsequently, we determined hypophyseal SSTR5 mRNA expression during the last week of embryonic development using real-time PCR. SSTR5 mRNA levels were low until day 19 of incubation, but between day 19 and hatching SSTR5 mRNA expression increased 3-fold. Since this increase coincides with the increasing plasma T 3 levels towards hatching, and a similar ontogenetic expression pattern was found for SSTR2, we quantified hypophyseal SSTR2 and SSTR5 mRNA expression levels in chicken embryos treated with thyroid hormones. Injection of thyroid hormones was indeed found to increase the expression of both mRNAs significantly. We hypothesize that the negative feedback exerted by the increasing plasma T 3 levels towards hatching is at least in part mediated by an increased expression of SSTR2 and SSTR5.

Expression of Type 5 Somatostatin Receptor in TSH-secreting Pituitary Adenomas: A Possible Marker for Predicting Long-term Response to Octreotide Therapy

In TSH-secreting pituitary adenomas (TSHoma), octreotide (OCT) therapy reduces tumor size and TSH secretion in some cases but not in others. As OCT acts through various types of somatostatin receptors (SSTRs), the different responses of TSHoma to OCT might be explained by the differences of SSTR expression. We therefore studied the expression of subtype-specific SSTR mRNA transcripts in tumor tissues by RT-PCR. Type 2 (SSTR2) mRNA transcripts were detected in all 8 tumors but those of SSTR3 and SSTR5 were demonstrated only in 5 of them. Serum TSH levels were decreased by OCT administration test in all patients but OCT therapy was effective in two patients out of three. SSTR5 mRNA was detected in two tumors from the responder, but not in one tumor that was resistant to OCT. These observations suggest that the temporal decrease of TSH by OCT may be mediated by SSTR2, and that the long term response to OCT therapy may be related with the expression of SSTR5. Therefore, the expression of SSTR5 in TSHoma may be a useful marker for predicting the outcome of the therapy, but further studies with larger numbers of patients are necessary.

Glucose inhibits glucagon secretion by a direct effect on mouse pancreatic alpha cells

The mechanisms by which glucose regulates glucagon release are poorly understood. The present study aimed to clarify the direct effects of glucose on the glucagon-releasing alpha cells and those effects mediated by paracrine islet factors. Glucagon, insulin and somatostatin release were measured from incubated mouse pancreatic islets and the cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) recorded in isolated mouse alpha cells. Glucose inhibited glucagon release with maximal effect at 7 mmol/l. Since this concentration corresponded to threshold stimulation of insulin secretion, it is unlikely that inhibition of glucagon secretion is mediated by beta cell factors. Although somatostatin secretion data seemed consistent with a role of this hormone in glucose-inhibited glucagon release, a somatostatin receptor type 2 antagonist stimulated glucagon release without diminishing the inhibitory effect of glucose. In islets exposed to tolbutamide plus 8 mmol/l K(+), glucose inhibited glucagon secretion without stimulating the release of insulin and somatostatin, indicating a direct inhibitory effect on the alpha cells that was independent of ATP-sensitive K(+) channels. Glucose lowered [Ca(2+)](i) of individual alpha cells independently of somatostatin and beta cell factors (insulin, Zn(2+) and gamma-aminobutyric acid). Glucose suppression of glucagon release was prevented by inhibitors of the sarco(endo)plasmic reticulum Ca(2+)-ATPase, which abolished the [Ca(2+)](i)-lowering effect of glucose on isolated alpha cells. Beta cell factors or somatostatin do not seem to mediate glucose inhibition of glucagon secretion. We instead propose that glucose has a direct inhibitory effect on mouse alpha cells by suppressing a depolarising Ca(2+) store-operated current.

Octreotide promotes apoptosis in human somatotroph tumor cells by activating somatostatin receptor type 2

Somatostatin analogs currently used in the treatment of acromegaly and other neuroendocrine tumors inhibit hormone secretion and cell proliferation by binding to somatostatin receptor type (SST) 2 and 5. The antiproliferative pathways coupled to these receptors have been only partially characterized. The aim of this study was to evaluate the effect of octreotide and super selective SST2 (BIM23120) and SST5 (BIM23206) analogs on apoptotic activity and apoptotic gene expression in human somatotroph tumor cells. Eight somatotroph tumors expressing similar levels of SST2 and SST5 evaluated by real-time PCR and western blot analyses were included in the study. In cultured cells obtained from these tumors, octreotide induced a dose-dependent increase of caspase-3 activity (160+/-20% vs basal at 10 nM) and cleaved cytokeratin 18 levels (172+/-25% vs basal) at concentrations higher than 0.1 nM. This effect was due to SST2 activation since BIM23120 elicited comparable responses, while BIM23206 was ineffective. BIM23120-stimulated apoptosis was dependent on phosphatases, since it was abrogated by the inhibitor orthovanadate, and independent from the induction of apoptosis-related genes, such as p53, p63, p73, Bcl-2, Bax, BID, BIK, TNFSF8, and FADD. In somatotroph tumors, both BIM23120 and BIM2306 caused growth arrest as indicated by the increase in p27 and decrease in cyclin D1 expression. In conclusion, the present study showed that octreotide-induced apoptosis in human somatotroph tumor cells by activating SST2. This effect, together with the cytostatic action exerted by both SST2 and SST5 analogs, might account for the tumor shrinkage observed in acromegalic patients treated with long-acting somatostatin analogs.

Advanced Generation Adenoviral Virotherapy Agents Embody Enhanced Potency Based upon CAR-Independent Tropism

In this current issue of Clinical Cancer Research , Reddy et al. ([1][1]) constructed an adenoviral virotherapy agent that uses the human E2F-1 gene promoter to regulate the adenoviral E1A gene. The E2F transcription factor plays an important role in cell proliferation and is repressed by the

Mapping of somatostatin receptor types in GH or/and PRL producing pituitary adenomas

Background: Somatostatin is a tetradecapeptide exerting inhibitory action on endocrine and exocrine cell secretion and proliferation. Somatostatin receptors (SST) are widely expressed in various neoplasms including endocrine tumours. Using immunohistochemistry,...

Inhibition of metastatic progression of SSTR2 gene transfection mediated by adenovirus in human pancreatic carcinoma cells

The inhibition of metastatic progression of Somatostatin receptor type 2 (SSTR2) gene transfection mediated by adenovirus in human pancreatic carcinoma cells and the mechanisms involved in this effect were studied. The full-length human SSTR2 cDNA was introduced into the pancreatic cancer cell line BXPC-3 by adenovirus-mediated transfection. Stable expression of mRNAs and protein of SSTR2 was detected by RT-PCR and Western-blot. The Matrigel-coated Transwell was used to detect the migratory and invasive ability of SSTR2-expressing cells, Adv-GFP control cells and mock control cells. Furthermore, the expression of matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of metalloproteinase-2 (TIMP-2) was detected by RT-PCR in these cells. The stable expression of SSTR2 was detected in BXPC-3 transfected by Adv-GFP-SSTR2. A dramatic decrease of BXPC-3 expressing sst2 cells migrating through a Matrigel-coated filter was observed, as compared with Adv-GFP control and mock control cells (P < 0.01). Moreover, the expression of MMP-2 mRNA was significantly reduced in the SSTR2-expressing cells and conversely the expression of TIMP-2 mRNA was significantly increased in the SSTR2-expressing cells when compared with the Adv-GFP control and mock control (P < 0.01). The expression of reintroduced human SSTR2 gene in BXPC-3 cells by Adv-GFP-SSTR2 had the anti-migratory and anti-invasive effects, and the mechanisms involved in this effect may be due to the down-regulated expression of MMP-2 and up-regulated expression of TIMP-2.

Reliability and Discriminant Validity of HER2 Gene Quantification and Chromosome 17 Aneusomy Analysis by Real-Time PCR in Primary Breast Cancer

There is an increasing demand for the evaluation of HER2 status in breast cancer. In this study, sections from fixed tissues and triton extracts of tissue homogenates were obtained from 163 malignant breast tumors and analyzed in parallel using immunohistochemistry combined with fluorescence in situ hybridization, as gold standard tests, and an ELISA test (c-erbB2/c-neu Rapid Format ELISA, Oncogene Research Products, USA). Tumor DNA was employed to evaluate two quantitative PCR methods: the HER2/neu DNA Quantification Kit (Roche Diagnostics GmbH, Germany), which uses the gastrin chromosome 17 reference gene, and our recently developed Oncolab qPCR assay, where both a chromosome 17 gene (somatostatin receptor type II (SSTR2)) and a non-chromosome 17 reference gene (glyceraldehyde-3-phosphate deshydrogenase (GAPDH)) were used to detect an increase in HER2 gene copy number and to evaluate the aneusomy of chromosome 17, respectively. By IHC/FISH and ELISA, HER2 was overexpressed in 27 (16.6%) and 24 (14.7%) samples, respectively. With the Roche and Oncolab qPCR assays, 29 (17.8%) samples showed a ratio of HER2/gastrin > or = 2.0 and 26 (16.0%) showed a ratio of HER2/SSTR2 > or = 2.0, respectively. In samples presenting HER2/SSTR2 <2.0 and HER2/GAPDH > or = 2.0, which was indicative of a chromosome 17 polysomy, we observed a modest increase in HER2 protein expression. Complete agreement between the four methods for HER2 status determination was obtained for 154 (94.5%) samples. Overall, these results demonstrate that quantitative PCR is a reliable method for analyzing HER2 status and chromosome 17 polysomy.

Reliability and discriminant validity of HER2 gene quantification and chromosome 17 aneusomy analysis by real-time PCR in primary breast cancer

There is an increasing demand for the evaluation of HER2 status in breast cancer. In this study, sections from fixed tissues and triton extracts of tissue homogenates were obtained from 163 malignant breast tumors and analyzed in parallel using immunohistochemistry combined with fluorescence in situ hybridization, as gold standard tests, and an ELISA test (c-erbB2/c-neu Rapid Format ELISA, Oncogene Research Products, USA). Tumor DNA was employed to evaluate two quantitative PCR methods: the HER2/neu DNA Quantification Kit (Roche Diagnostics GmbH, Germany), which uses the gastrin chromosome 17 reference gene, and our recently developed Oncolab qPCR assay, where both a chromosome 17 gene (somatostatin receptor type II (SSTR2)) and a non-chromosome 17 reference gene (glyceraldehyde-3-phosphate deshydrogenase (GAPDH)) were used to detect an increase in HER2 gene copy number and to evaluate the aneusomy of chromosome 17, respectively. By IHC/FISH and ELISA, HER2 was overexpressed in 27 (16.6%) and 24 (14.7%) samples, respectively. With the Roche and Oncolab qPCR assays, 29 (17.8%) samples showed a ratio of HER2/gastrin > or = 2.0 and 26 (16.0%) showed a ratio of HER2/SSTR2 > or = 2.0, respectively. In samples presenting HER2/SSTR2 <2.0 and HER2/GAPDH > or = 2.0, which was indicative of a chromosome 17 polysomy, we observed a modest increase in HER2 protein expression. Complete agreement between the four methods for HER2 status determination was obtained for 154 (94.5%) samples. Overall, these results demonstrate that quantitative PCR is a reliable method for analyzing HER2 status and chromosome 17 polysomy.

Somatostatin Receptor Type 2 Undergoes Plastic Changes in the Human Epileptic Dentate Gyrus

Temporal lobe epilepsy (TLE) is characterized by hippocampal sclerosis together with profound losses and phenotypic changes of different classes of interneurons, including those expressing somatostatin (SRIF). To understand the functional significance of the plasticity of SRIF transmission in TLE, unraveling the status of SRIF receptors is, however, a prerequisite. To address this issue, we characterized expression and distribution of the major SRIF receptor, the sst2 subtype, in hippocampal tissue resected in patients with TLE using complementary neuroanatomic approaches. In patients with hippocampal sclerosis, the number of cells expressing sst2 receptor mRNA as well as sst2 receptor-binding sites and immunoreactivity decreased significantly in the CA1-3, reflecting neuronal loss. By contrast, in the dentate gyrus, sst2 receptor mRNA expression was strongly increased in the granule cell layer, and sst2 receptor-binding sites and immunoreactivity was preserved in the inner but decreased significantly in the outer molecular layer. In this latter region, pronounced changes in SRIF terminal fields were observed. Decreased receptor density in the distal dendrites of granule cells is likely to reflect downregulation of sst2 receptors in response to physiopathologic release of SRIF. Because sst2 receptors have anticonvulsant and antiepileptogenic properties, this phenomenon may contribute to the etiology of TLE seizures.

Exogenous Gene Expression in Tumors: Noninvasive Quantification with Functional and Anatomic Imaging in a Mouse Model

To assess whether a combination of functional (planar imaging and single photon emission computed tomography [SPECT]) and anatomic (magnetic resonance [MR] imaging) imaging techniques can be used to noninvasively quantify tumor expression of a somatostatin receptor type 2A (SSTR2A) gene chimera in vivo. All animal experiments were approved by the institutional animal care and use committee. Expression of the SSTR2A gene chimera was quantified in vitro, in vivo, and ex vivo. The epitope tag of the fusion protein was detected through an antibody, and the receptor portion was detected by using the Food and Drug Administration-approved radiopharmaceutical indium 111 octreotide. Six mice were injected with cells transfected with vector and with two clonal cell lines that each expressed different amounts of the gene chimera. With a dedicated small-animal gamma camera, planar imaging and SPECT were used for quantification of radiopharmaceutical uptake in vivo; 4.7-T MR imaging was used to derive tumor weight. After imaging, excised tumors were evaluated for uptake and weight. For statistical analysis, linear regression analysis, Wilcoxon rank sum test, and Kruskal-Wallis test were employed. Different expression levels of the chimeric gene were confirmed in vitro. Radiopharmaceutical uptake assessed in excised tumors and that derived from in vivo planar (r = 0.94, P < .05, n = 18) or SPECT (r = 0.90, P < .05, n = 18) images correlated. Weight of excised tumors and that derived from MR images (r = 0.98, P < .05, n = 18) correlated. MR images also allowed morphologic assessment. The biodistribution parameter of percentage of injected dose per gram of excised tumors correlated with the same measure derived from a combination of planar (r = 0.90, P < .05, n = 18) or SPECT (r = 0.87, P < .05, n = 18) images and MR images. A combination of noninvasive functional and anatomic imaging can be used in vivo to quantify gene transfer in tumors.

Octreotide inhibits growth factor–induced and basal proliferation of lens epithelial cells in vitro

To evaluate whether a synthetic analog of somatostatin, octreotide, has an inhibitory effect on lens epithelial cell (LEC) proliferation induced by basal and basic fibroblast growth factor as well as insulin-like growth factor 1. Confluent LEC cultures were kept in serum-free defined medium containing [(3)H]-thymidine in the presence of octreotide alone at the concentration range of 10(-7) M to 10(-10) M or in combination with either basic fibroblast growth factor or insulin-like growth factor 1. Additionally, the expression of somatostatin receptors (1-5) in LECs were analyzed by reverse transcription-polymerase chain reaction. Octreotide decreased the proliferation of human LECs in a dose-dependent manner, exhibiting a maximal inhibitory concentration at 10(-9) M (P<.03). Moreover, octreotide (10(-9) M) potently inhibited basic fibroblast growth factor- and insulin-like growth factor 1-induced bovine lens epithelial cell proliferation (P<.0001). The respective products of all 5 subtypes of somatostatin receptors were found in human LECs and somatostatin receptor type 2 in bovine LECs. The data show that, depending on the concentration, octreotide is able to decrease proliferative responses of LECs. Moreover, the cell proliferation induced by growth factors was potently inhibited by octreotide. Therefore, octreotide could be a potential drug after cataract surgery in prevention of growth factor-dependent proliferative disorders such as posterior capsule opacification and anterior capsule contraction in diabetic patients.