Somatostatin receptors in the gastrointestinal tract in health and disease.

The multiple actions of somatostatin are mediated by specific membrane-bound receptors present in all somatostatin target tissues, such as brain, pituitary, pancreas, and gastrointestinal tract. Three different types of tissues in the human gastrointestinal tract express somatostatin receptors: (1) the gastrointestinal mucosa, (2) the peripheral nervous system, and (3) the gut-associated lymphoid tissue, where the receptors are preferentially located in germinal centers. In all these cases, somatostatin binding is of high affinity and specific for bioactive somatostatin analogs. Somatostatin receptors are also expressed in pathological states, particularly in neuroendocrine tumors of the gastrointestinal tract. Ninety percent of the carcinoids and a majority of islet-cell carcinomas, including their metastases, usually have a high density of somatostatin receptors. Only 10 percent of the colorectal carcinomas and none of the exocrine pancreatic carcinomas, however, contain somatostatin receptors. The somatostatin receptors in tumors are identified with in vitro binding methods or with in vivo imaging techniques; the latter allow the precise localization of the tumors and their metastases in the patients. Since somatostatin receptors in gastroenteropancreatic tumors are functional, their identification can be used to assess the therapeutic efficacy of octreotide to inhibit excessive hormone release in the patients.     

Somatostatin receptors in normal and tumoral tissue

Somatostatin receptors have been visualized with autoradiography and characterised biochemically in various somatostatin target tissues, such as brain, pituitary, pancreas and gastrointestinal tract, where they are likely to mediate the somatostatin actions. With the same methods, somatostatin receptors have been detected also in tumors originating from somatostatin target tissues: high receptor incidence is found in GH-producing pituitary adenomas as well as in some hormone-producing gastrointestinal tumors. These tumors are often highly responsive to somatostatin analogs in vivo. Among brain tumors, meningiomas usually contain a high density of receptors, suggesting a novel function for somatostatin in the human meninges. Among other human tumors tested, prostate, ovarian and endometrial carcinomas were free of receptors whereas 3 out of 39 mammary tumors contained somatostatin receptors.     

Carcinoid tumor of the kidney: case report and review of the literature

Carcinoid tumors are low-grade malignant tumors that arise from neuroendocrine cells. Primary renal carcinoid tumors are extremely uncommon. They seem to be more indolent than renal cell carcinomas, although metastases to regional lymph nodes, liver, and bone have been described. The presence of metastases seems to indicate a more malignant course; however, even with metastases a patient might live for 3 or 4 years. Renal carcinoid tumors should be managed by radical or partial nephrectomy, and good outcomes have been obtained for organ-confined disease after radical excision. Conventional methods of imaging are inadequate for detecting smaller carcinoids, so somatostatin receptor scintigraphy should complement computed tomography and magnetic resonance imaging when searching for occult or metastatic disease. Close follow-up after surgery is necessary.     

Perspectives of new potential therapeutic applications of somatostatin analogs

At the present time only two long-acting somatostatin (SS) analogs, octreotide and lanreotide, are commonly used in the routine therapy. Both analogs have a high affinity mainly to a somatostatin receptor subtype 2 (SSTR2). The established indications for SS analogs treatment include acromegaly, neuroendocrine tumors of the pancreas and gastrointestinal tract, and some gastro-enterologic diseases (pancreatitis, gastrointestinal bleedings, refractory diarrheas, pancreatic and intestinal fistulas). The recent investigations allow to predict the enlargement of therapeutic applications of SS analogs. It concerns pituitary tumors other than somatotropinoma, tumors of other endocrine glands like thyroid and adrenal gland, as well as some non-endocrine tumors. The progress depends on the introduction of new SS analogs with high affinity for SS receptor subtypes other than SSTR2, because some tumors present the high expression of SSTR1 (e.g. prostatic cancers) or SSTR5 (e.g. colonic cancers). Great hopes are connected with the coupling of SS analogs with the radioactive isotopes or non-radioactive cytotoxic agents to destruct the neoplastic cells highly expressing the specific subtypes of SS receptors. The pre- or postoperative in vivo imaging of SS receptors by means of the receptor scintigraphy, as well as the post-operative identification of SS receptor subtypes in the excised tumor tissues using immunohistochemistry, should play an important role in the prediction of the effects of SS analog treatment. Beside oncology, new therapeutic applications of SS analogs could be presumed among others in ophthalmology; it concerns the treatment of progressive Graves-Basedow ophtalmopathy, diabetic retinopathy, glaucoma and corneal diseases connected with corneal vascularization.     

Somatostatin controls Kaposi's sarcoma tumor growth through inhibition of angiogenesis.

Somatostatin and its analogs are active in the inhibition of SST receptor-positive endocrine neoplasms, but their activity and mechanism in nonendocrine tumors is not clear. Somatostatin potently inhibited growth of a Kaposi's sarcoma xenograft in nude mice, yet in vitro the tumor cells did not express any known somatostatin receptors and were not growth inhibited by somatostatin. Histological examination revealed limited vascularization in the somatostatin-treated tumors as compared with the controls. Somatostatin was a potent inhibitor of angiogenesis in an in vivo assay. In vitro, somatostatin inhibited endothelial cell growth and invasion. Migration of monocytes, important mediators of the angiogenic cascade, was also inhibited by somatostatin. Both cells types expressed somatostatin receptor mRNAs. These data demonstrate that somatostatin is a potent antitumor angiogenesis compound directly affecting both endothelial and monocytic cells. The debated function of somatostatin in tumor treatment and the design of therapeutic protocols should be reexamined considering these data.     

The incidence of somatostatin receptors in human neoplasms in the light of ex vivo-in vitro studies

Human neoplastic cells express and often even over-express the somatostatin receptors (sstr). It concerns not only pituitary tumors and the so-called neuroendocrine tumors of the gut, but many other neoplasms, including the non-endocrine cancers. The incidence of sstr is important because it determines the possibility of treatment with SST (somatostatin) analogs. The examination of sstr is possible under the in vivo conditions, by means of the receptor scintigraphy using the radiolabeled SST analogs. The receptors can be also examined under the ex vivo-in vitro conditions, using the post-surgical or biopsy specimens. Among the in vitro (ex vivo) methods, the immunohistochemical investigation with specific anti-receptor antibodies seems to be particularly useful for routine clinical diagnostics. This review presents the data, obtained by means of different in vitro techniques, on the incidence of five sstr subtypes in the different human tumors, deriving from endocrine glands, diffuse neuroendocrine cells as well as in neoplasms considered as non-endocrine.     

Multimodality imaging of somatostatin receptor-positive tumors with nuclear and bioluminescence imaging

Multimodal bioluminescence (BLI) and single-photon emission computed tomography/computed tomography (SPECT/CT) imaging were investigated as means to monitor somatostatin receptor subtype 2 (SST2)-positive neuroendocrine tumors as both a subcutaneously implanted and a liver metastasis animal model in mice and rats. Ultimately, such a model will be of use for studying SST2-targeted peptide receptor radionuclide therapy (PRRT). CA20948 cells were transfected with a green fluorescent protein/luciferase plasmid construct. Cells were inoculated subcutaneously in the shoulder of nude mice: nontransfected cells in the left shoulder and transfected cells in the right shoulder. BLI, SPECT/CT imaging, biodistribution analysis, and ex vivo autoradiography of the tumors were performed. BLI and SPECT/CT imaging were also performed on an intrahepatic tumor model in the rat. Caliper volume measurement of transfected tumors could be correlated with BLI measurements (R2 = .76). SPECT/CT imaging showed high levels of accumulation of 111In-DTPA-octreotide in control and transfected tumors, which was confirmed by biodistribution analysis and autoradiography. Subcapsular inoculation of transfected cells in rat liver resulted in an intrahepatic tumor, which could be visualized by both SPECT/CT and BLI. Transfection of CA20948 tumor cells did not alter the growth properties of the cell line or the expression of SST2. Transfected tumors could be clearly visualized by BLI and SPECT/CT imaging. The transfected SST2-positive tumor cell line could represent a novel preclinical model for tumor monitoring in studies that aim at further optimizing PRRT for neuroendocrine tumors.     

Molecular and cellular biology of neuroendocrine lung tumors: Evidence for separate biological entities

Pulmonary neuroendocrine tumors (NETs) are traditionally described as comprising a spectrum of neoplasms, ranging from low grade typical carcinoids (TCs) via the intermediate grade atypical carcinoids (ACs) to the highly malignant small cell lung cancers (SCLCs) and large cell neuroendocrine carcinomas (LCNECs). Recent data, however, suggests that two categories can be distinguished on basis of molecular and clinical data, i.e. the high grade neuroendocrine (NE) carcinomas and the carcinoid tumors. Bronchial carcinoids and SCLCs may originate from the same pulmonary NE precursor cells, but a precursor lesion has only been observed in association with carcinoids, termed diffuse idiopathic pulmonary neuroendocrine cell hyperplasia. The occurrence of mixed tumors exclusively comprising high grade NE carcinomas also supports a different carcinogenesis for these two groups. Histopathologically, high grade NE lung tumors are characterized by high mitotic and proliferative indices, while carcinoids are defined by maximally 10 mitoses per 2mm(2) (10 high-power fields) and rarely have Ki67-proliferative indices over 10%. High grade NE carcinomas are chemosensitive tumors, although they usually relapse. Surgery is often not an option due to extensive disease at presentation and early metastasis, especially in SCLC. Conversely, carcinoids are often insensitive to chemo- and radiation therapy, but cure can usually be achieved by surgery. A meta-analysis of comparative genomic hybridization studies performed for this review, as well as gene expression profiling data indicates separate clustering of carcinoids and carcinomas. Chromosomal aberrations are much more frequent in carcinomas, except for deletion of 11q, which is involved in the whole spectrum of NE lung tumors. Deletions of chromosome 3p are rare in carcinoids but are a hallmark of the high grade pulmonary NE carcinomas. On the contrary, mutations of the multiple endocrine neoplasia type 1 (MEN1) gene are restricted to carcinoid tumors. Many of the differences between carcinoids and high grade lung NETs can be ascribed to tobacco consumption, which is strongly linked to the occurrence of high grade NE carcinomas. Smoking causes p53 mutations, very frequently present in SCLCs and LCNECs, but rarely in carcinoids. It further results in other early genetic events in SCLCs and LCNECs, such as 3p and 17p deletions. Smoking induces downregulation of E-cadherin and associated epithelial to mesenchymal transition. Also, high grade lung NETs display higher frequencies of aberrations of the Rb pathway, and of the intrinsic and extrinsic apoptotic routes. Carcinoid biology on the other hand is not depending on cigarette smoke intake but rather characterized by aberrations of other specific genetic events, probably including Menin or its targets and interaction partners. This results in a gradual evolution, most likely from proliferating pulmonary NE cells via hyperplasia and tumorlets towards classical carcinoid tumors. We conclude that carcinoids and high grade NE lung carcinomas are separate biological entities and do not comprise one spectrum of pulmonary NETs. This implies the need to reconsider both diagnostic as well as therapeutic approaches for these different groups of malignancies.     

Pharmacological characterization of a recombinant, fluorescent somatostatin receptor agonist

Somatostatin (SST) is a peptide neurotransmitter/hormone found in several mammalian tissue types. Apart from its natural importance, labeled SST/analogues are utilized in clinical applications such as targeting/diagnosis of neuroendocrine tumors. We report on the development and characterization of a novel, recombinant, fluorescent somatostatin analogue that has potential to elucidate somatostatin-activated cell signaling. SST was genetically fused with a monomeric-red fluorescent protein (mRFP) as the fluorescent label. The attachment of SST to mRFP had no detectable effect on its fluorescent properties. This analogue's potency to activate the endogenous and transfected somatostatin receptors was characterized using assays of membrane potential and Ca(2+) mobilization and immunocytochemistry. SST-mRFP was found to be an effective somatostatin receptor agonist, able to trigger the membrane hyperpolarization, mobilization of the intracellular Ca(2+) and receptor-ligand internalization in cells expressing somatostatin receptors. This complex represents a novel optical reporter due to its red emission spectral band suitable for in vivo imaging and tracking of the somatostatin receptor signaling pathways, affording higher resolution and sensitivity than those of the state-of-the-art radiolabeling bioassays.     

Antitumor effects of analogs of LH-RH and somatostatin: Experimental and clinical studies

Many clinical approaches for the treatment of hormone-sensitive tumors are being developed based on analogs of LH-RH and somatostatin. Inhibition of the pituitary-gonadal axis forms the basis for oncological applications of LH-RH agonists like [ -Trp⁶]-LH-RH and new LH-RH antagonists free of edematogenic effects such as [Ac- -Nal(2)¹- -Phe(4Cl)²- -Pal(3)³, -Cit⁶, -Ala¹⁰]-LH-RH (SB-75). Agonists and antagonists of LH-RH have been used in patients with prostate cancer and might be also beneficial for the treatment of breast cancer and ovarian, endometrial and pancreatic carcinomas. Some of the effects of LH-RH analogs can be due to direct action since LH-RH receptors have been found in these cancers. The use of sustained delivery systems based on microcapsules of PLG, makes the treatment more efficacious. Octaeptide analogs of somatostatin such as -P s-Trp-NH₂ (RC-160) and related analogs were designed specifically for antitumor activity. These somatostatin analogs, by virtue of having a wide spectrum of activities appear to inhibit various tumors through multiple mechanisms. Direct antiproliferative actions of somatostatin analogs appear to be mediated by specific receptors located on tumor cells. High affinity binding sites for RC-160 and related analogs have been found in human pancreatic, prostate, breast and ovarian cancers and brain tumors such as meningiomas. In vivo administration of analog RC-160 inhibits the growth of Dunning R-3327 prostate cancers in rats, MXT mammary tumors in mice and BOP-induced ductal pancreatic cancers in hamsters. Combination of microcapsules of RC-160 with [ -Trp⁶]-LH-RH results in synergistic potentiation of the inhibition of these cancers. Somatostatin analog RC-160 and LH-RH antagonist SB-75 are the object of further experimental studies and clinical trials aimed at the exploration of their inhibitory effects on the processes of malignant growth.     

Biomarkers and molecular imaging in gastroenteropancreatic neuroendocrine tumors

Neuroendocrine gastrointestinal and pancreatic tumors (GEP-NETs) are a heterogenous group of cancers with various clinical expressions. All tumors produce and secret various amines and peptides, which can be used as tissue and circulating markers. Chromogranin A (CgA) is a general tumor marker stored in secretory granules within the tumor cell and released upon stimulation. CgA is the best general tumor marker at the moment, expressed in 80-90% in all patients with GEP-NETs. CgA and NSE are used as tissue markers for the delineation of the neuroendocrine features of the tumors, but recently also the proliferation marker Ki-67 has been included in the standard procedure for evaluation of the proliferation. GEP-NETs are classified into well differentiated neuroendocrine tumors (Ki-67<2%), well-differentiated neuroendocrine carcinoma (Ki-67 2-20%), poorly differentiated neuroendocrine carcinoma (Ki-67>20%). The molecular imaging of NETs is based on the ability of these tumor cells to express somatostatin receptors as well as the APUD features. Octreoscan has been applied for imaging and staging of the disease for more than 2 decades and will nowadays be replaced by 68Ga-DOTA-Octreotate, with higher specificity and sensitivity. 18Fluoro-DOPA and 11C-5HTP are specific tracers for NETs with high specificity and selectivity. A new potential biomarker is auto-antibodies to paraneoplastic antigen MA2, which might indicate early recurrence of carcinoids after surgery with a curative intent. Circulating tumor cells (CTC) have been applied in GEP-NETs quite recently. There is still an unmet need for new markers.     

Somatostatin receptors in malignant tissues

High affinity somatostatin receptors (SS-R) have been identified in membrane homogenates or tissue sections from several hundred human tumors. SS-R were found in most tumors originating from SS target tissues, i.e. GH- and TSH-producing pituitary tumors, endocrine gastroenteropancreatic (GEP) tumors (including metastases) and brain tumors, including gliomas and neuroblastomas. SS-R were also expressed in several tumors originating from various other tissues, i.e. breast and small cell lung carcinomas, some colorectal cancers, and medullary tyroid carcinomas. In general, most of the SS-R+ tumors are well-differentiated and/or have neuroendocrine features. They often have low or absent epidermal growth factor receptor (EGF-R) expression. In some tumors (i.e. breast tumors) SS-R are not homogeneously distributed, making SS-R autoradiography a particularly useful tool for assessing SS-R status. SS-R are functional in pituitary and GEP tumors where they mediate hormone secretion inhibition. In these and in the other SS-R+ tumors, SS-R may also mediate antiproliferative effects of SS, as evidenced, in animals where growth of SS-R+ tumor xenografts is inhibited by SS analogs. For diagnosis, SS-R+ tumors and metastases can be localized in vivo by scanning techniques after ¹²³I-labelled SS analog injection.     

La radiothérapie interne vectorisée par les analogues de la somatostatine,en pratique,en 2019

Somatostatin receptors are overexpressed in differentiated gastroenteropancreatic neuroendocrine tumors (GEP-NET). Radiolabeled somatostatin analogs have been used for a few decades for imaging and more recently for peptide receptor radionuclide therapy (PRRT) in a theranostic approach. Medical access to PRRT has long been limited to a few European specialized medical centers despite promising results in large cohorts of patients. NETTER-1, a phase 3 randomized trial, has demonstrated a drastic improvement of midgut NET patients progression-free survival in PRRT arm as compared to somatostatin analogs, leading to marketing authorizations in USA and Europe. PRRT clinical availability is growing in France, with around 20 medical centers offering this innovative treatment for GEP-NET patients care in 2019. PPRT success-story should lead to improvements of radionuclide therapy developments, which will reshape our medical specialty to a more “clinically” practice. This review aims to detail PRRT in clinical practice in France in 2019, with emphasize on treatment indications, planning and practical aspects. Radioprotection aspects and future optimization perspectives will also be discussed.     

Somatostatin receptor imaging in vivo localization of tumors with a radiolabeled somatostatin analog

This paper presents the results of the visualization of somatostatin (SS) receptor positive tumors in man after the i.v. administration of the SS analog Tyr³-octreotide coupled to ¹²³I. It is an easy, quick and harmless procedure which allows imaging of primary and (often unexpected) secondary deposits and/or multiple localizations of the majority of endocrine pancreatic tumors, metastatic carcinoids and pituitary tumors, as well as of a multitude of humors with neuroendocrine characteristics and well-differentiated brain tumors and meningiomas. In the case of hormone-secreting tumors a positive scan in most instances also predicts the subsequent successful therapy with octreotide.     

NPY receptors in human cancer: a review of current knowledge

Many peptide hormone receptors are over-expressed in human cancer, permitting an in vivo targeting of tumors for diagnostic and therapeutic purposes. NPY receptors are novel and promising candidates in this field. Using in vitro receptor autoradiography, Y1 and Y2 receptors have been found to be expressed in breast carcinomas, adrenal gland and related tumors, renal cell carcinomas, and ovarian cancers in both tumor cells and tumor-associated blood vessels. Pathophysiologically, tumoral NPY receptors may be activated by endogenous NPY released from intratumoral nerve fibers or tumor cells themselves, and mediate NPY effects on tumor cell proliferation and tumoral blood supply. Clinically, tumoral NPY receptors may be targeted with NPY analogs coupled with adequate radionuclides or cytotoxic agents for a scintigraphic tumor imaging and/or tumor therapy.     

Ectopic ACTH syndrome

Ectopic ACTH syndrome represents a cancer-induced amplification of a property [proopiomelanocortin (POMC) peptides production] normally present in the cells from which the cancer originated but with aberrant posttranslational processing of POMC resulting in a greatly elevated secretion of ACTH precursors. The classic ectopic ACTH-producing tumors described in the 1960s were highly malignant but more recently slowly growing tumors such as carcinoids are reported with increasing frequency. Clinical features of patients with ectopic ACTH were analyzed, including biochemical abnormalities, plasma ACTH, cortisol and urinary steroids. Dynamic tests such as high-dose dexamethasone suppression, metyrapone and ovine-CRH (oCRH) stimulation were explored, as well as inferior petrosal sinus ACTH sampling before and after oCRH. Among the tumor markers examined, elevation of ACTH precursors was uniformly present followed by increased output of calcitonin, gut hormones, oncofetal and placental hormones in decreasing order. Since more than 90% of ectopic ACTH tumors are neuroendocrine in nature exhibiting APUD characteristics, their 2 markers, neuron-specific enolase and chromogranins are very useful. The imaging procedures for localization of the tumor ranged from chest X-rays to computed tomography and magnetic resonance of the chest and abdomen. Abdominal ultrasonography was also useful. Finally somatostatin receptor scintigraphy permitted demonstration of unrecognized tumors and/or metastases, even when the tumors were occult. The ACTH content, immunostaining for APUD markers and altered POMC processing were evaluated in ectopic tumors and/or metastases. Occult ectopic ACTH syndrome of more than 4–6 months of symptoms without the emergence of an obvious source was reviewed. Since the tumors are often clinically and biochemically undistinguishable from pituitary-dependent Cushing's disease, inferior petrosal sinus sampling for ACTH after oCRH stimulation established the diagnosis in over 90% of the cases. 60% of the occult tumors were thoracic carcinoids (3/4 bronchial carcinoids), followed by small cell lung cancer and pancreatic neuroendocrine tumors. In 12% the primary etiology was not detected. The rare syndrome of ectopic CRH syndrome (6 published cases) leading to excessive stimulation of the pituitary which became hyperplastic and secreted excessive amounts of ACTH is discussed. Finally, the 12 published cases and 1 unreported patient with ectopic CRH-ACTH tumors were reviewed, the majority being metastatic small cell lung carcinomas, bronchial and thymic carcinoids.     

Preclinical evaluation of 68Ga-DOTA-minigastrin for the detection of cholecystokinin-2/gastrin receptor-positive tumors

In comparison to somatostatin receptor scintigraphy, gastrin receptor scintigraphy using 111In-DTPA-minigastrin (MG0) showed added value in diagnosing neuroendocrine tumors. We investigated whether the 68Ga-labeled gastrin analogue DOTA-MG0 is suited for positron emission tomography (PET), which could improve image quality. Targeting of cholecystokinin-2 (CCK2)/gastrin receptor-positive tumor cells with DOTA-MG0 labeled with either 111In or 68Ga in vitro was investigated using the AR42J rat tumor cell line. Biodistribution was examined in BALB/c nude mice with a subcutaneous AR42J tumor. In vivo PET imaging was performed using a preclinical PET-computed tomographic scanner. DOTA-MG0 showed high receptor affinity in vitro. Biodistribution studies revealed high tumor uptake of 68Ga-DOTA-MG0: 4.4 ± 1.3 %ID/g at 1 hour postinjection. Coadministration of an excess unlabeled peptide blocked the tumor uptake (0.7 ± 0.1 %ID/g), indicating CCK2/gastrin receptor-mediated uptake (p = .0005). The biodistribution of 68Ga-DOTA-MG0 was similar to that of 111In-DOTA-MG0. Subcutaneous and intraperitoneal tumors were clearly visualized by small-animal PET imaging with 5 MBq 68Ga-DOTA-MG0. 111In- and 68Ga-labeled DOTA-MG0 specifically accumulate in CCK2/gastrin receptor-positive AR42J tumors with similar biodistribution apart from the kidneys. AR42J tumors were clearly visualized by microPET. Therefore, 68Ga-DOTA-MG0 is a promising tracer for PET imaging of CCK2/gastrin receptor-positive tumors in humans.     

Somatostatin receptor imaging in vivo localization of tumors with a radiolabeled somatostatin analog

This paper presents the results of the visualization of somatostatin (SS) receptor positive tumors in man after the i.v. administration of the SS analog Tyr³-octreotide coupled to ¹²³I. It is an easy, quick and harmless procedure which allows imaging of primary and (often unexpected) secondary deposits and/or multiple localizations of the majority of endocrine pancreatic tumors, metastatic carcinoids and pituitary tumors, as well as of a multitude of humors with neuroendocrine characteristics and well-differentiated brain tumors and meningiomas. In the case of hormone-secreting tumors a positive scan in most instances also predicts the subsequent successful therapy with octreotide.     

Somatostatin receptor gene expression in neuroblastoma

Somatostatin receptor expression is a favorable prognostic factor in human neuroblastoma. Somatostatin receptors have been demonstrated in vitro by pharmacologic analysis of tumor tissue and in vivo by diagnostic radioreceptor scintigraphy. However, which receptor subtypes (sst(1), sst(2), sst(3), sst(4), and sst(5)) are expressed in these tumors has not yet been delineated. We used RT-PCR to analyze expression of the five somatostatin receptor genes in 32 neuroblastoma tumor specimens. All 32 tumor specimens expressed mRNA for c-abl and sst(1); sst(2) mRNA was detected in 27/32 samples and somatostatin mRNA was detected in 30/32 tumor specimens. The remaining receptor subtypes, sst(3), sst(4), and sst(5) were variably expressed. Receptor protein for sst(1) and sst(2) was visualized in tumor neuroblasts as well as in endothelial cells of tumor vessels using immunostaining with specific anti-receptor antibodies. The effect of high expression of somatostatin receptors on cell proliferation was examined in SKNSH neuroblastoma cells transfected with sst(1) and sst(2). SS(14) binding to wild-type SKNSH cells was undetectable; but the native peptide bound with high affinity to the SKNSH/sst(1) and SKNSH/sst(2) neuroblastoma cell lines. Pharmacologic analysis of binding with two long-acting analogues, CH275 and octreotide, confirmed selective expression of sst(1) and sst(2) in stably transfected SKNSH cells. Formation of neuroblastoma xenograft tumors in nude mice was significantly delayed for both SKNSH/sst(1) (P<0.001) and SKNSH/sst(2) (P<0.05) cells compared to wild-type SKNSH. We conclude that: (1) Somatostatin receptors, sst(1) and sst(2), are expressed in the majority of neuroblastomas at diagnosis; and (2) upregulation of functional sst(1) or sst(2) in neuroblastoma cell lines suppresses tumorigenicity in a xenograft model. These observations suggest that somatostatin receptors may be a useful therapeutic target in neuroblastoma.     

Immunohistochemical evaluation of ras oncogene expression in pulmonary and pleural neoplasms

We undertook an immunohistochemical analysis of human bronchopulmonary epithelial neoplasms and pleural mesotheliomas using a monoclonal antibody which recognizes ras oncogene products (p21ras). The monoclonal antibody, RAP-5, recognizes both unaltered and certain mutated p21ras. Formalin fixed and paraffin embedded tissue samples of 187 lung epithelial tumors and 27 pleural mesotheliomas were investigated; normal and bronchiectatic lungs were similarly studied. Normal lung and pleural tissue did not immunostain except for occasional type II pneumocytes. Reactive type II pneumocytes adjacent to carcinomas and bronchiectasis immunostained consistently. Twenty four/34 (71%) squamous carcinomas immunostained. Only 8/50 (16%) adenocarcinomas immunostained focally and weakly whereas 19/24 (79%) bronchioloalveolar carcinomas immunostained. Eleven/18 (61%) large cell carcinomas immunostained with variable intensity. Eleven/13 (85%) carcinoids, 6/7 (85%) well differentiated neuroendocrine carcinomas, and 18/21 (86%) intermediate cell neuroendocrine carcinomas immunostained while none of 20 small cell neuroendocrine carcinomas immunostained. Only a few mesotheliomas were immunostained focally. Two/14 (14%) epithelial type and 1/9 (11%) biphasic type mesotheliomas immunostained weakly; none of 4 spindle cell mesotheliomas immunostained. We conclude that while at least occasional cases of most types of pulmonary epithelial neoplasms express p21ras, the frequency and intensity of the expression are distinctly greater in certain tumor types such as squamous, bronchioloalveolar, and neuroendocrine neoplasm except for the small cell type. Contrary to these lung epithelial neoplasms, most mesotheliomas did not immunostain for p21ras. Whether the enhanced p21ras expression may point to a different mechanism of transformation or may merely reflect differentiation features remains undetermined.