High-affinity Somatostatin Receptors Research Articles

The Inhibitory Effect of a Novel Cytotoxic Somatostatin Analogue AN-162 on Experimental Glioblastoma

Glioblastoma multiforme is the most common and most aggressive type of high grade tumor with a poor prognosis upon discovery. Based on earlier promising results earned with AN-162, a doxorubicin molecule linked to somatostatin (SST) analogue RC-160, it was our aim to determine the effect of AN-162 on DBTRG-05 glioblastoma cell line, and to test its efficacy in experimental brain tumors. We detected the expression of mRNA for somatostatin receptor (SSTR) subtypes 2 and 3 in DBTRG-05 cells with RT-PCR. Using ligand competition assay, specific high affinity receptors for somatostatin were found. The MTT assay showed that both AN-162 and doxorubicin (DOX) significantly inhibited cell proliferation and that there was no significant difference between the effects in vitro. Nude mice were xenografted with DBTRG-05 glioblastoma tumors. AN-162 showed a significant inhibition of tumor growth compared with the control group and the groups treated with equimolar doses of doxorubicin, somatostatin analogue RC-160, or the unconjugated mixture of doxorubicin plus RC-160. The tumor doubling time in the group of animals treated with AN-162 was extended and was significantly different from doubling times in the control group and in the other treatment groups. Our study clearly demonstrates a potent inhibitory effect of AN-162 in experimental glioblastoma, thus suggesting the possibility of its utilization in patients suffering from malignant brain cancer.

Somatostatin receptor expression, tumour response, and quality of life in patients with advanced hepatocellular carcinoma treated with long-acting octreotide

Octreotide may extend survival in hepatocellular carcinoma (HCC). Forty-one per cent of HCCs have high-affinity somatostatin receptors. We aimed to determine the feasibility, safety, and activity of long-acting octreotide in advanced HCC; to identify the best method for assessing somatostatin receptor expression; to relate receptor expression to clinical outcomes; and to evaluate toxicity. Sixty-three patients with advanced HCC received intramuscular long-acting octreotide 20 mg monthly until progression or toxicity. Median age was 67 years (range 28–81 years), male 81%, Child–Pugh A 83%, and B 17%. The aetiologies of chronic liver disease were alcohol (22%), viral hepatitis (44%), and haemochromatosis (6%). Prior treatments for HCC included surgery (8%), chemotherapy (2%), local ablation (11%), and chemoembolisation (6%). One patient had an objective partial tumour response (2%, 95% CI 0–9%). Serum alpha-fetoprotein levels decreased more than 50% in four (6%). Median survival was 8 months. Thirty four of 61 patients (56%) had receptor expression detected by scintigraphy; no clear relationship with clinical outcomes was identified. There were few grade 3 or 4 toxicities: hyperglycaemia (8%), hypoglycaemia (2%), diarrhoea (5%), and anorexia (2%). Patients reported improvements in some symptoms, but no major changes in quality of life were detected. Long-acting octreotide is safe in advanced HCC. We found little evidence of anticancer activity. A definitive randomised trial would identify whether patients benefit from this treatment in other ways.

Radiothérapie métabolique des tumeurs endocrines gastro-entéro-pancréatiques par les analogues radio-marqués de la somatostatine

Surgery is the only curative treatment of gastro-entero-pancreatic endocrine tumors. In inoperable or metastasized forms, therapeutic options are limited. The metabolic or systemic radiotherapy, using radiolabeled somatostatin analogs, constitutes a new therapeutic alternative, currently in development which requires the presence of high affinity somatostatin receptors on tumoral cells. Using (111)In-pentetreotide, the main result is a symptomatic effect. With new somatostatin analogs coupled to B- emitters, such as Octreother or (177)Lu-DOTA-Octreotate, 10 to 30% of objective tumoral responses are observed in progressive patients, unresponsive to conventional treatments. Such results are explained by the high affinity for somatostatin receptors and the large emission diameter of these radiolabeled compounds. Renal toxicity is limited by amino-acid infusion whereas changes in blood count are usually moderate and transient. Multicentric prospective studies are necessary to identify the predictive factors of tumoral response and toxicity. The prospects are related to the development of new radiopharmaceuticals, even more specific of somatostatin receptors sub-types and to the use of other peptide analogues whose applications will overflow the framework of endocrine tumours.

Somatostatin Receptor Imaging In Vivo by Planar Scintigraphy Facilitates the Diagnosis of Canine Insulinomas

Somatostatin receptors expressed by insulinomas in 5 dogs were imaged in vivo by means of indium In 111 pentetreotide (OctreoScan) scintigraphy. The diagnosis in each dog was supported by the presence of hypoglycemia ( 20 μIU/mL), and histopathologic review of neoplastic tissue. All insulinomas expressed high-affinity somatostatin receptors of subtype sst2, as shown by receptor autoradiography in vitro using 1 2 5 I-[tyrosine 3 ]-octreotide and 1 2 5 I-[leucine 8 , D-tryptophan 2 2 , tyrosine 2 5 ]-somatostatin-28 with an sst2 subtype-selective analogue. Scintigrams were obtained at 1, 4, 12, and 24 hours after the IV administration of 74-222 MBq of OctreoScan to each patient. Abnormal foci of activity were 1st observed from I hour after administration of the radioligand in dog 3, to 24 hours after its administration in dog 4; in dogs I and 2, abnormal foci of activity were visible from 12 hours. Dog 5 showed a questionable abnormal focus of activity at 12 hours, but not at 24 hours. Scintigraphy enabled accurate prediction of the anatomical location of the primary tumor in 1 of 4 dogs, but was unable to differentiate a right- from a left- pancreatic lobe tumor, or vice versa, in 3 dogs; the 5th dog had equivocal results. 1 1 1 In-pentetreotide scintigraphy is a useful diagnostic adjunct to the clinical evaluation of the insulinoma patient, but is unable to localize the tumor in some cases.

Expression of somatostatin receptor subtypes (SSTR1–5) in Alzheimer’s disease brain: An immunohistochemical analysis

Somatostatin, widely distributed in human cortical brain regions, acts through specific high affinity somatostatin receptors (SSTR1-5) to exert profound effects on motor, sensory, behavioral, cognitive and autonomic functions. Somatostatin levels are consistently decreased in the cortex of Alzheimer's disease (AD) brain and in cerebrospinal fluid, and have become reproducible markers of this disease. In the present study, the distributional pattern of SSTR1-5 antigens in the frontal cortex of AD and age-matched control brains was studied using antipeptide polyclonal rabbit antibodies directed against the five human somatostatin receptor subtypes. All five SSTRs were differentially expressed as membrane and cytoplasmic proteins in cortical neurons with significant variations in control vs. AD brain. In AD cortical brain region, somatostatin and neuropeptide-Y-positive neurons decreased (>70%), and glial fibrillary acidic protein-positive astrocytes significantly increased (>130%) in comparison to control brain. SSTR2 and 4 were the predominant subtypes followed by SSTR1, 3 and 5. AD cortex showed a marked reduction in neuronal expression of SSTR4 and 5 and a modest decrease in SSTR2-like immunoreactivity without any changes in SSTR1 immunoreactive neurons. In contrast, SSTR3 was the only receptor subtype that increased in AD cortex. In AD cortex, SSTR1-, 3- and 4-like immunoreactivities were strongly expressed in glial cells but not SSTR2 and 5. These findings suggest the differential loss of immunoreactivity of SSTR2, 4 and 5 but not SSTR1, and increased SSTR3 in frontal cortex of AD brain as well as subtype-selective glial expression in AD brain. In summary, subtype-selective changes in the expression of SSTRs at protein levels in AD cortical regions suggest that somatostatin and SSTR-containing neurons are pathologically involved in AD and could possibly be used as markers of this disease.

Somatostatin Receptor Imaging In Vivo by Planar Scintigraphy Facilitates the Diagnosis of Canine Insulinomas

Somatostatin receptors expressed by insulinomas in 5 dogs were imaged in vivo by means of indium in 111 pentetreotide (OctreoScan) scintigraphy. The diagnosis in each dog was supported by the presence of hypoglycemia (<60 mg/dL), hyperinsulinemia (>20 microU/mL), and histopathologic review of neoplastic tissue. All insulinomas expressed high-affinity somatostatin receptors of subtype sst2, as shown by receptor autoradiography in vitro using 125I-[tyrosine3]-octreotide and 125I-[leucine8, Dtryptophan22, tyrosine25]-somatostatin-28 with an sst2 subtype-selective analogue. Scintigrams were obtained at 1, 4, 12, and 24 hours after the i.v. administration of 74-222 MBq of OctreoScan to each patient. Abnormal foci of activity were 1st observed from 1 hour after administration of the radioligand in dog 3, to 24 hours after its administration in dog 4; in dogs 1 and 2, abnormal foci of activity were visible from 12 hours. Dog 5 showed a questionable abnormal focus of activity at 12 hours, but not at 24 hours. Scintigraphy enabled accurate prediction of the anatomical location of the primary tumor in 1 of 4 dogs, but was unable to differentiate a right- from a left-pancreatic lobe tumor, or vice versa, in 3 dogs; the 5th dog had equivocal results. 111In-pentetreotide scintigraphy is a useful diagnostic adjunct to the clinical evaluation of the insulinoma patient, but is unable to localize the tumor in some cases.

Inhibition of Human Epithelial Ovarian Cancer Cell Growth in vitro by Somatostatin Analog RC-160

In this study, we investigated the effects of somatostatin analog RC-160 on the growth of the OV-1063 human epithelial ovarian cancer cell line in vitro. RC-160 inhibited cell proliferation, as measured by cell number, and [³H]thymidine incorporation into DNA at 10^–9–10^–5M. In OV-1063 cells, ¹²⁵I-labeled RC-160 was bound to one class of specific, saturable binding sites with high affinity (K_d = 0.2 ± 0.03 nM) and low capacity (5,500 binding sites per cell). ¹²⁵I-labeled RC-160 could be displaced by unlabeled RC-160. Ligand binding was dependent on time and temperature. Receptor internalization assay showed that the ligand-receptor complex was internalized at 37°C, which indicates the presence of biologically active somatostatin receptors on OV-1063 cells. These results suggest that somatostatin analog RC-160 can suppress the growth of OV-1063 human epithelial ovarian cancer cells by a direct action and that the inhibitory effect of somatostatin analog is mediated through the high-affinity somatostatin receptors.

Two-Dimensional Fluorescence Intensity Distribution Analysis: Theory and Applications

A method of sample analysis is presented which is based on fitting a joint distribution of photon count numbers. In experiments, fluorescence from a microscopic volume containing a fluctuating number of molecules is monitored by two detectors, using a confocal microscope. The two detectors may have different polarizational or spectral responses. Concentrations of fluorescent species together with two specific brightness values per species are determined. The two-dimensional fluorescence intensity distribution analysis (2D-FIDA), if used with a polarization cube, is a tool that is able to distinguish fluorescent species with different specific polarization ratios. As an example of polarization studies by 2D-FIDA, binding of 5′-(6-carboxytetramethylrhodamine) (TAMRA)-labeled theophylline to an anti-theophylline antibody has been studied. Alternatively, if two-color equipment is used, 2D-FIDA can determine concentrations and specific brightness values of fluorescent species corresponding to individual labels alone and their complex. As an example of two-color 2D-FIDA, binding of TAMRA-labeled somatostatin-14 to the human type-2 high-affinity somatostatin receptors present in stained vesicles has been studied. The presented method is unusually accurate among fluorescence fluctuation methods. It is well suited for monitoring a variety of molecular interactions, including receptors and ligands or antibodies and antigens.

The significance of somatostatin analogues in the antiproliferative treatment of carcinomas.

Somatostatin is a cyclic tetradecapeptide hormone. It was initially isolated from bovine hypothalami. Somatostatin inhibits endocrine and exocrine secretion, as well as tumor cell growth, by binding to specific cell-surface receptors. Its potent inhibitory activity is limited, however, by its rapid enzymatic degradation and the consequently short plasma half-life. Octreotide is a short somatostatin analogue with increased duration of action compared with somatostatin. Preclinical studies have focused on the anticancer effects of octreotide and the related somatostatin analogues. In vitro, at nanomolar concentrations, these analogues inhibit the growth of tumor cells that express high-affinity somatostatin receptors. Accordingly, such analogues potently inhibit the growth of somatostatin receptor-positive tumors in various rodent models. The range of cancers susceptible to octreotide and related somatostatin analogues includes mammary, pancreatic, gastric, colorectal, prostate, thyroid, and lung carcinomas. Moreover, an indirect antiproliferative effect of somatostatin analogues is achievable in somatostatin receptor-negative tumors whose growth is driven by factors (e.g., gastrin, insulin-like growth factor-1) that become down-regulated by somatostatin. The clinical effect of somatostatin analogues in terms of tumor response in cancer patients is a subject of controversy, however. Most responses have been seen in patients with pancreatic cancers.

Somatostatin in neuroblastoma and ganglioneuroma.

Neuroblastoma, a childhood tumour of the sympathetic nervous system, may in some cases differentiate to a benign ganglioneuroma or regress due to apoptosis. Somatostatin may inhibit neuroblastoma growth and induce apoptosis in vitro and was therefore investigated. Using a radioimmunoassay, we found that all ganglioneuromas contained high somatostatin concentrations (> 16 pmol/g), significantly higher than neuroblastomas (n = 117, median 2.8 pmol/g), healthy adrenals, Wilms' tumours, phaeochromocytomas and other neuroendocrine tumours (P < 0.001). Neuroblastomas contained more somatostatin than control tumours (P < 0.001-0.05). Neuroblastomas amplified for the MYCN oncogene contained less somatostatin than non-amplified tumours (1.2 pmol/g versus 4.0 pmol/g, respectively; P = 0.026). In a clinically unfavourable neuroblastoma subset (age > 12 months, stage 3 or 4) 16 children with high concentrations of somatostatin in primary tumours had a better prognosis than 23 with low somatostatin (46.7% versus 0% survival at 5 years, P < 0.005). Scintigraphy using 111In-pentetreotide identified tumours expressing high-affinity somatostatin receptors in vivo. However, no significant correlation was found between somatostatin receptor expression and peptide content in 15 tumours. Similarly, human SH-SY5Y neuroblastoma xenografts grown in nude rats showed low somatostatin concentrations, but were positive for somatostatin receptor scintigraphy. Treatment of these rats with the somatostatin analogue octreotide seemed to upregulate in vivo receptor expression of somatostatin and vasoactive intestinal peptide more effectively than 13-cis retinoic acid. In conclusion, somatostatin in neuroblastoma is associated with differentiation to benign ganglioneuromas in vivo and favourable outcome in advanced tumours. Furthermore, somatostatin receptor scintigraphy may identify tumours with high-affinity receptors in children that might benefit from targeted therapy using synthetic somatostatin analogues.

Somatostatin receptor scintigraphy in patients with pituitary adenoma.

Presence of high-affinity somatostatin (SST) receptors in most endocrine tumor cells allow in vivo scintigraphic visualization of these neoplasms after intravenous administration of a radionuclide-labeled somatostatin analog. 111In-octreotide is at present the most often used substance for imaging of the SST receptor expression in vivo. The aim of this study is to investigate the correlation between presence of in vivo scintigraphically detectable SST receptors in pituitary tumors and clinical parameters such as patients' age, tumor size, hormonal hypersecretion, and response to octreotide therapy. Forty-two-consecutive patients were enrolled in this trial. Twenty-five of them had nonsecreting pituitary tumors, 11 were acromegalic, and 6 had macro- or microprolactinoma. Scintigraphic images of the head were obtained at 10 min and 24 hours after injection of the radionuclide. In 23 patients, no specific binding of 111In-octreotide was found. Five patients showed a weak positive, 5 had a positive, and 9 a strong positive signal in the region of interest. Uptake of octreotide was significantly correlated with tumor size and age (p < 0.01). Small-size pituitary adenomas were most likely to be scintigraphically receptor-negative, while large suprasellar tumors tended to exhibit a rather strong receptor positivity. Statistical analysis of the data could not confirm the hypothesized correlation between endocrine activity of the pituitary tumors and the scintigraphically proven SST receptor expression in vivo. A positive Octreoscan was not predictive for the result of octreotide therapy.

Somatostatin expression in human renal cortex and mesangial cells

Somatostatin modulates important physiologic functions of the kidney, including mesangial cell contraction, glomerular prostaglandin synthesis, and phosphate, water and sodium excretion. In diabetic nephropathy, somatostatin inhibits renal hypertrophy. High affinity somatostatin receptors are expressed in the kidney. Circulating somatostatin concentrations, however, are generally well below the affinity constants of known somatostatin receptors. Thus, we hypothesized that somatostatin is produced in the kidney and released locally to act in an autocrine/paracrine manner. Using reverse transcriptase and polymerase chain reaction (RT-PCR) analysis, we found that fresh human renal cortex and cultured human mesangial cells express somatostatin mRNA. Restriction enzyme and Southern blot analysis confirmed that RT-PCR cDNA products were derived from somatostatin mRNA. Radioimmunoassay of mesangial cell culture supernatants demonstrated SS-immunoreactive peptide (87±30 pg/ml compared to 19±9 pg/ml in medium not exposed to cells; P<0.05). In contrast, renal cells did not transcribe detectable levels of vasoactive intestinal peptide (VIP) or neuropeptide Y (NPY) mRNA, nor did they synthesize measurable peptide. Our results demonstrate that renal cells produce somatostatin and suggest that kidney-derived somatostatin may regulate renal function in an autocrine/paracrine manner. Characterization of this pathway may lead to novel methods to alter the course of diabetic nephropathy and other renal diseases.

Somatostatin analog RC-160 inhibits the growth of human osteosarcomas in nude mice

We investigated the effects of the potent somatostatin analog RC-160 on the growth of human osteosarcoma cell lines SK-ES-1 and MNNG/HOS, transplanted into nude mice or cultured in vitro. Growth of SK-ES-1 and MNNG/HOS tumors in nude mice was significantly inhibited after 4 weeks of treatment with daily s.c. injections of 100 micrograms RC-160, as measured by a reduction in tumor volume and weight. Histologically, the number of mitotic cells was decreased in the groups treated with RC-160. In mice bearing either tumor model, administration of RC-160 significantly decreased serum growth hormone and insulin-like growth factor I (IGF-I) levels. Specific high-affinity receptors for somatostatin and epidermal growth factor were found on membranes of MNNG/HOS tumors but not on SK-ES-1 tumors. Receptor analyses also demonstrated high-affinity binding sites for IGF-I on membranes of both tumors. In cell cultures, the proliferation rate of MNNG/HOS cells, but not of SK-ES-1, was significantly suppressed by RC-160. Our findings demonstrate that RC-160 can significantly inhibit the growth of SK-ES-1 and MNNG/HOS osteosarcomas in mice.

Cellular localisation and co-expression of somatostatin receptor messenger RNAs in the human brain.

Genes for five high affinity somatostatin receptors, named sst1-5, have been cloned recently. In this study we describe the tissue distribution and cellular localisation of mRNA encoding sst1, sst3 and sst4 receptors in the human cerebellum, frontal cortex (Brodmann's area 11) and hippocampus. RT-PCR and in situ hybridisation studies indicated a distinct, but partially overlapping pattern of expression of the receptor mRNAs. In situ hybridisation studies using co-expression techniques with probes for sst1, sst3 and sst4 receptor mRNA on paraffin sections revealed the presence of neurones expressing more than one somatostatin receptor mRNA type in both the hippocampus and pyramidal cells of layer V of the frontal cortex.

Intraoperative detection and resection of occult neuroblastoma: A technique exploiting somatostatin receptor expression

Tumor cell expression of specific high-affinity somatostatin receptors has been associated with a favorable prognosis in children with neuroblastoma. The purpose of this study was (1) to document intraoperatively the in vivo binding of the somatostatin analogue 125I-tyr 3-octreotide to highaffinity somatostatin receptors expressed on human neuroblastoma, using a hand-held gamma detector; (2) to determine whether gamma-probe detection of radioligand binding to tumor receptors could identify occult malignancy; and (3) to determine the safety and biodistribution of 125I-tyr 3-octreotide in children. Six children with stage III or IV neuroblastoma received an intravenous injection of 125I-tyr 3-octreotide and underwent operative exploration using gamma-probe detection of radioligand binding to tumor somatostatin receptors. Tissue that demonstrated in vivo binding of 125I-tyr 3-octreotide, or that was suspicious for tumor, was extirpated and analyzed by histopathology, immunohistochemistry, and microautoradiography. The biodistribution of 125I-tyr 3-octreotide was recorded intraoperatively over time. Tumor tissue from each child also was assayed in vitro for somatostatin receptor expression by competitive binding studies using 125I-tyr 3-octreotide. In vivo binding of 125I-tyr 3-octreotide to malignant tissue was documented in the five children with a known tumor burden. Seventeen sites of radioreceptor binding were amenable to resection. Histopathological analysis confirmed neuroblastoma in 15 of these specimens. Four of the 15 proven tumor foci were occult malignancies. Every site of histologically proven neuroblastoma demonstrated in vivo binding of 125I-tyr 3-octreotide. Five of seven sites histologically negative for neuroblastoma also were negative for in vivo radioreceptor binding. Microautoradiography confirmed in vivo binding of 125I-tyr 3-octreotide to tumor cells. Uptake of 125I-tyr 3-octreotide in abdominal organs occurred within 15 minutes of injection, was highest in the liver and gallbladder, and decreased over 24 hours. The conclusions were as follows. (1) 125I-tyr 3-octreotide binds, in vivo, to somatostatin receptors on neuroblastoma, with 100% sensitivity and 71% specificity. (2) Occult neuroblastoma is found through gammaproble detection of radioligand binding to receptors. (3) The biodistribution of 125I-tyr 3-octreotide reflects the hepatobiliary clearance of this radionuclide. (4) Radioreceptor-guided surgery may safely provide more complete operative staging and cytoreduction of neuroblastoma.

Somatostatinergic phenotype markers in the human neuroblastoma cell-line LA-N-2

We have characterized somatostatinergic phenotype markers of the human neuroblastoma, LA-N-2. A single mRNA-transcript (∼850bp) and two cellular somatostatin immunoreactivity forms, a high molecular weight form ( M r 15,000) and a fragment corresponding to somatostatin-28 was found, while the somatostatin-14 peptide was absent. Saturation binding experiments demonstrated a single class of high-affinity somatostatin receptors with K d and B max of 0.27 ± 0.03 nM and 45 ± 1 fmol/mg protein. Partial G-protein uncoupling (30%) was demonstrated, using GTPγS, with an affinity of 9.7 nM. The LA-N-2 cell line, previously shown to be cholinergic, may serve as a simplified system to elucidate heterologous neurotransmittor interactions. Such studies are of interest since dysfunctions of the cholinergic basal forebrain neurons and somatostatin immunoreactive interneurons have been consistently observed in Alzheimer's disease.

Expression of somatostatin receptors in childhood neuroblastoma.

Somatostatin receptors are expressed on certain neural crest-derived tumors, including pancreatic islet cell and carcinoid tumors, medullary thyroid carcinomas, pheochromocytomas, and paragangliomas. The authors evaluated the expression of high affinity somatostatin receptors in childhood neuroblastoma using autoradiography techniques with the somatostatin analogue 125I-octreotide or 125I-[Leu8,D-Trp22,Tyr25]-SS-28 as the radioligand. Thirty tumors from 30 children with neuroblastoma were analyzed. Twenty-three of 30 tumors that were tested expressed somatostatin receptors. Correlation of somatostatin receptor expression with survival was statistically significant. The survival of those patients whose tumors expressed somatostatin receptors was of longer duration than that of patients whose tumors did not. This was an independent prognostic factor. Somatostatin receptors were expressed more frequently in tumor tissue from patients with lower stages of disease and in those with no evidence of N-myc amplification. Tumoral somatostatin receptors are expressed in a subgroup of patients with childhood neuroblastoma. Survival analysis in this group of patients indicates that somatostatin receptor expression is a favorable prognostic factor. This finding may have important implications for the therapy of children with this malignancy.

Effects of somatostatin analogue RC-160 and bombesin/gastrin-releasing peptide antagonists on the growth of human small-cell and non-small-cell lung carcinomas in nude mice

We investigated the effects of our synthetic bombesin/gastrin-releasing peptide (GRP) antagonists and somatostatin analogue RC-160 on the growth of human small-cell lung carcinoma (SCLC) and non-small-cell lung carcinoma (non-SCLC) lines in nude mice. Athymic nude mice bearing xenografts of the SCLC NCl-H69 line or non-SCLC NCl-H157 line were treated for 5 and 4 weeks, respectively, with somatostatin analogue RC-160 or various bombesin/GRP antagonists. RC-160, administered s.c. peritumorally at a dose of 100 micrograms per animal per day, inhibited the growth of H69 SCLC xenografts as shown by more than 70% reduction in tumour volumes and weights, as compared with the control group. Bombesin/GRP antagonists, RC-3440, RC-3095 and RC-3950-II, given s.c. peritumorally at a dose of 20 micrograms per animal per day, also inhibited the growth of H69 SCLC tumours. RC-3950-II had the greatest inhibitory effect and decreased tumour volume and weights by more than 80%. The growth of H-157 non-SCLC xenografts was significantly reduced by treatment with RC-160, but not with bombesin/GRP antagonist RC-3095. In mice bearing either tumour model, administration of RC-160 significantly decreased serum growth hormone and gastrin levels. Specific high-affinity receptors for bombesin and somatostatin were found on membranes of SCLC H69 tumours, but not on non-SCLC H157 tumours. Receptor analyses demonstrated high-affinity binding sites for epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) on the membranes of H69 and H157 tumours. EGF receptors were down-regulated on H69 tumours after treatment with RC-160 and bombesin/GRP antagonists. The concentration of binding sites for EGF and IGF-I on the H157 tumours was decreased after treatment with RC-160, but bombesin/GRP antagonist RC-3095 had no effect. These results demonstrate that bombesin/GRP antagonists inhibit the growth of H-69 SCLC, but not of H-157 non-SCLC xenografts in nude mice, whereas somatostatin analogue RC-160 is effective in both tumour models. This raises the possibility that these peptide analogues could be used selectively in the treatment of various subclasses of lung cancer.

Somatostatin-receptor scintigraphy in gastroenteropancreatic tumors. An overview of European results.

Somatostatin has been demonstrated in high concentrations in the hypothalamus, the cerebral cortex, the brain stem, the gastrointestinal tract, and the pancreas. In the central nervous system, it acts as a neurotransmitter, whereas its hormonal activities include the inhibition of the release of growth hormone, insulin, glucagon, and gastrin (for a review, see ref. 1). Also, antiproliferative effects have been reported, both in vitro on tumor cell lines, and in vivo on neuroendocrine human tumors. High-affinity somatostatin receptors have been identified in the brain and on many cells of neuroendocrine origin, like the somatotroph cells of the anterior pituitary and the pancreatic islet cell^.^.^ Also, cells not known classically as neuroendocrine, such as lymphocytes, may possess these receptor^.^ Besides, somatostatin receptors have been demonstrated on a variety of human tumors by classical biochemical binding techniques, as well as by in vitro autoradiography. These tumors include those with APUD (amine precursor uptake and decarboxylation) characteristics (pituitary tumors, endocrine pancreatic tumors, carcinoids, paragangliomas, small cell lung cancers, medullary thyroid carcinomas, pheochromocytomas} as well as meningiomas, well-differentiated brain tumors (astrocytomas), neuroblastomas, and some human breast cancers. Because of the short plasma half-life of somatostatin (2-4 min), analogues more suitable for medical treatment have been developed. The somatostatin analogue, octreotide, has been shown to bind to somatostatin receptors on both tumorous and nontumorous tissues. An 'In-labeled somatostatin analogue ([DTPA-D-Phe'l-octreotide] was developed for its use in scintigraphy. [DTPA-D-Phe'l-octreotide was shown to bind 'In efficiently in a single-step labeling procedure. The binding as well as the biological

Persistent lack of somatostatin receptors in gastric mucosa of healing ulcers in rats

Background/Aims: Growth factors and their receptors play a role in healing ulcers of the rat. Somatostatin is a putative growth factor in the gastric mucosa with multiple functions mediated by specific receptors. Therefore, the distribution of somatostatin receptors was evaluated in the gastric mucosa of healing ulcers. Methods: Somatostatin receptors were measured in the gastric mucosa of healthy rats and of rats with cryoulcers and acetic acid-induced ulcers, using somatostatin receptor autoradiography with 125I-[Tyr3]-octreotide or 125I-[Leu8, D-Trp22, Tyr25]-somatostatin-28 as radioligands. Epidermal growth factor receptors were measured on adjacent sections with 125I-epidermal growth factor. Results: High-affinity Somatostatin receptors are present in the gastric fundic mucosa of healthy rats. In contrast, in healing ulcers, the somatostatin receptors are almost lacking in the ulcer edge or scar at 3, 7, 28, 49, and even 84 days after ulcer induction (83%–91% reduction). Similar results are obtained with cryoulcers and with acetic acid-induced ulcers. For comparison, the number of epidermal growth factor receptors are increased in the same healing ulcers. Conclusions: The persistent absence of somatostatin receptors for several months after ulcer induction may be of pathophysiological significance in ulcer repair and healing.