Human Somatostatin SST4 Receptor Transgenic Mice: Construction and Brain Expression Pattern Characterization.

Somatostatin receptor subtype 4 (SST4) has been shown to mediate analgesic, antidepressant and anti-inflammatory functions without endocrine actions; therefore, it is proposed to be a novel target for drug development. To overcome the species differences of SST4 receptor expression and function between humans and mice, we generated an SST4 humanized mouse line to serve as a translational animal model for preclinical research. A transposon vector containing the hSSTR4 and reporter gene construct driven by the hSSTR4 regulatory elements were created. The vector was randomly inserted in Sstr4-deficient mice. hSSTR4 expression was detected by bioluminescent in vivo imaging of the luciferase reporter predominantly in the brain. RT-qPCR confirmed the expression of the human gene in the brain and various peripheral tissues consistent with the in vivo imaging. RNAscope in situ hybridization revealed the presence of hSSTR4 transcripts in glutamatergic excitatory neurons in the CA1 and CA2 regions of the hippocampus; in the GABAergic interneurons in the granular layer of the olfactory bulb and in both types of neurons in the primary somatosensory cortex, piriform cortex, prelimbic cortex and amygdala. This novel SST4 humanized mouse line might enable us to investigate the differences of human and mouse SST4 receptor expression and function and assess the effects of SST4 receptor agonist drug candidates.

Somatostatin Receptor as a Molecular Imaging Target in Human and Canine Cushing Disease.

OBJECTIVES: Fluorescence-guided surgery may improve completeness of resection in transsphenoidal surgery for Cushing disease (CD) by enabling visualization of residual tumor tissue at the margins. In this review we discuss somatostatin receptors (SSTRs) as targets for fluorescence-guided surgery and overview existing SSTR-specific imaging agents. We also compare SSTR expression in normal pituitary and corticotrophinoma tissues from human and canine CD patients to assess canines as a translational model for CD. METHODS: A PubMed literature search was conducted for publications containing the terms canine, somatostatin receptor, Cushing's disease, and corticotroph adenoma. SSTR expression data from each study was documented as the presence or absence of expression or, when possible, the number of tumors expressing a given SSTR subtype within a group of tumors being studied. Studies that used reverse transcription polymerase chain reaction to quantify SSTR expression were selected for additional comparative analysis. RESULTS: SSTR5 is strongly expressed in human corticotroph adenomas and weakly expressed in surrounding pituitary parenchyma, a pattern not conclusively observed in canine patients. SSTR2 mRNA expression is similar in human normal pituitary and corticotrophinoma cells but may be significantly higher in canine normal pituitary tissue than in corticotroph tumoral tissue. Limited data were available on SSTR subtypes 1, 3, and 4. CONCLUSIONS: Further studies must fill the knowledge gaps related to species-specific SSTR expression, so using canine CD as a translational model may be premature. We do conclude that the expression profile of SSTR5 (i.e., high local expression in pituitary adenomas relative to normal surrounding tissues) makes SSTR5 a promising molecular target for FGS.

Escitalopram as a modulator of proopiomelanocortin, kisspeptin, Kiss1R and MCHR1 gene expressions in the male rat brain.

Neuropeptides are important, multifunctional regulatory factors of the nervous system, being considered as a novel, atypical sites of antidepressants action. It has already been proven that some of them, such as selective serotonin reuptake inhibitors (SSRI), are able to affect peptidergic pathways in various brain regions. Despite these reports, there is so far no reports regarding the effect of treatment with SSRIs on brain proopiomelanocortin (POMC), kisspeptin, Kiss1R and MCHR1 gene expression. In the current study we examined POMC, kisspeptin, Kiss1R and MCHR1 mRNA expression in the selected brain structures (hypothalamus, hippocampus, amygdala, striatum, cerebellum and brainstem) of rats chronically treated with a 10 mg/kg dose of escitalopram using quantitative Real-Time PCR. Long-term treatment with escitalopram led to the upregulation of MCHR1 expression in the rat amygdala. Kisspeptin mRNA level was also increased in the amygdala, but Kiss1R mRNA expressions were elevated in the hippocampus, hypothalamus and cerebellum. POMC mRNA expressions were in turn decreased in the hippocampus, amygdala, cerebellum and brainstem. These results may support the hypothesis that these neuropeptides may be involved in the site-dependent actions of SSRI antidepressants. This is the first report of the effects of escitalopram on POMC, kisspeptin, Kiss1R and MCHR1 in animal brain. Our findings shed a new light on the pharmacology of SSRIs and may contribute to a better understanding of the alternative, neuropeptide-dependent modes of antidepressant action.

Prognostic impact of somatostatin receptor expression in advanced bladder cancer.

INTRODUCTION AND OBJECTIVES: Somatostatin receptors (SSTR) recently have been identified as potential targets for treatment of solid tumors. Furthermore, they have been shown to be of high relevance for tumor biology and prognosis in various types of cancer. However, there is a lack of clinical data for SSTR in bladder cancer (BC). Aim of this study was to determine the expression of all relevant somatostatin receptor subtypes in benign urothelium and tumor tissue of patients with muscle invasive BC. Furthermore, their potential role as prognostic factor for cancer-specific survival (CSS) and overall survival (OS) was evaluated. METHODS: The collective included BC and benign urothelium tissue of 103 patients (Median age 69; range 32-84, 79 male, 24 female) who underwent a radical cystectomy. A tissue microarray with subsequent immunohistochemical staining was used to assess membranous expression of SSTR1-5. Results were correlated to clinical and histopathological data as well as CSS and OS. RESULTS: Expressions of SSTR1-4 were significantly decreased in BC compared to benign urothelium (P < 0.002 each), whereas SSTR5 expression was increased (P = 0.0017). Expression of SSTR1 was associated with organ-confined disease (≤pT2) (P = 0.0477). No correlation between SSTR1-5 expression and N- and M-stage was observed. Univariate analyses showed a significantly longer CSS and OS in patients with high expression of SSTR3 (P = 0.0316 and 0.0044). Multivariate analyses confirmed SSTR3 expression as independent marker of improved CSS and OS (P = 0.0324 and 0.0076). CONCLUSIONS: The majority of somatostatin receptor subtypes exhibit decreased expression in BC compared to benign bladder tissue. Expression of SSTR3 is an indicator for favorable prognosis in patients with muscle-invasive BC. These results support preclinical investigations using somatostatin receptor analogues such as octreotide to influence BC growth.

Ciliary melanin-concentrating hormone receptor 1 (MCHR1) is widely distributed in the murine CNS in a sex-independent manner.

Melanin-concentrating hormone (MCH) is a ubiquitous vertebrate neuropeptide predominantly synthesized by neurons of the diencephalon that can act through two G protein-coupled receptors, called MCHR1 and MCHR2. The expression of Mchr1 has been investigated in both rats and mice, but its synthesis remains poorly described. After identifying an antibody that detects MCHR1 with high specificity, we employed immunohistochemistry to map the distribution of MCHR1 in the CNS of rats and mice. Multiple neurochemical markers were also employed to characterize some of the neuronal populations that synthesize MCHR1. Our results show that MCHR1 is abundantly found in a subcellular structure called the primary cilium, which has been associated, among other functions, with the detection of free neurochemical messengers present in the extracellular space. Ciliary MCHR1 was found in a wide range of areas, including the olfactory bulb, cortical mantle, striatum, hippocampal formation, amygdala, midline thalamic nuclei, periventricular hypothalamic nuclei, midbrain areas, and in the spinal cord. No differences were observed between male and female mice, and interspecies differences were found in the caudate-putamen nucleus and the subgranular zone. Ciliary MCHR1 was found in close association with several neurochemical markers, including tyrosine hydroxylase, calretinin, kisspeptin, estrogen receptor, oxytocin, vasopressin, and corticotropin-releasing factor. Given the role of neuronal primary cilia in sensing free neurochemical messengers in the extracellular fluid, the widespread distribution of ciliary MCHR1, and the diverse neurochemical populations who synthesize MCHR1, our data indicate that nonsynaptic communication plays a prominent role in the normal function of the MCH system.

Is Somatostatin Receptor and Dopamine Receptor profiling useful in the management of silent somatotroph tumors?

Silent somatotroph tumors (sSTs) are pituitary neuroendocrine tumors (PitNETs) which do not give rise to the clinical syndrome of acromegaly. Differently to their functioning counterparts, the adjuvant medical treatment with somatostatin analogues (SSAs) or dopamine receptors agonists (DAs) has been scarcely addressed in these tumors. As preliminary results of an ongoing research on silencing mechanisms involved in the pathogenesis of sSTs, we have characterized by qRT-PCR the expression of SSTRs and DRDs in a large series of 18 silent and 68 functioning STs. Although the expression of SSTR2 and SSTR5 was lower in sSTs than in functioning ones, we found a negative correlation between SSTR2 and the tumor size of the sSTs. Additionally, levels of expression of DRD2 were similar between the two subtypes suggesting a possible basis for the treatment of these tumors with SSAs and DAs.

Somatostatin and cannabinoid receptors crosstalk in protection of huntingtin knock-in striatal neuronal cells in response to quinolinic acid.

In the present study, we describe the status of somatostatin receptor 2 and 5 (SSTR2 and SSTR5) as well as cannabinoid type 1 receptor (CB1R) in Huntingtin (Htt) knock-in striatal neuronal cells. In mutant Htt (mHtt) knock-in (STHdhQ111/111) and wild type (STHdhQ7/7) striatal neuronal cells, SSTRs and CB1R exhibit prominent cytoplasmic expression and respond to agonist in a receptor specific manner. In response to quinolinic acid (QUIN)-induced toxicity, STHdhQ111/111 cells are more vulnerable and display suppressed cell survival signaling pathways. Receptor-specific agonists protect cells from QUIN-induced toxicity and activate ERK1/2 in both STHdh cells. Co-activation of SSTRs and CB1R resulted in loss of protective effects, delayed ERK1/2 phosphorylation and altered receptor complex composition. These results provide firsthand evidence in support of the protective role of SSTRs in STHdh cells and the possible crosstalk between SSTRs and CB1R in the modulation of excitotoxicity in Huntington's disease.

Somatostatin Receptor 2 Expression in Canine Meningioma.

The neuropeptide somatostatin (SST) plays an important regulatory role in the proliferation of normal and neoplastic cells. Five subtypes of somatostatin receptors (SSTRs), SSTR1-SSTR5, have been identified in human tumours. The SSTR2 subtype is identified most commonly in meningiomas. Long half-life SST analogues are now recommended for the systemic treatment of unresectable or radiation-refractory recurrent human meningiomas. In this study, SSTR2 expression was evaluated in 46 canine meningiomas; in 21 cases this was by immunohistochemistry and in 25 cases by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR). In addition, SSTR2 expression was evaluated by immunocytochemistry, western blotting and RT-qPCR on primary cell cultures prepared from two canine meningiomas. SSTR2 immunohistochemical expression was observed in 17/21 cases (81%), and SSTR2 mRNA expression was detected in 14/25 cases (56%). SSTR2 protein and gene expression were not significantly correlated with the tumour histological subtype or grade. Overall, meningothelial meningiomas showed constant and diffuse SSTR2 immunohistochemical expression and the highest SSTR2 gene expression level compared with other subtypes. A tendency for loss of SSTR2 in high-grade meningiomas was observed in both immunohistochemical and RT-qPCR studies. About 90% of cultured canine meningioma cells showed SSTR2 expression. In both of the meningioma cell cultures, SSTR2 expression was also detected by western blotting and RT-qPCR. This study demonstrates for the first time that canine meningioma expresses SSTR2 and that this expression is maintained in vitro. Our results, while preliminary, provide encouragement for further studies aimed at finding novel medical treatment strategies for canine meningioma, especially for tumours that are not surgically accessible.

Importance of Immunohistochemical Detection of Somatostatin Receptors.

The long-acting somatostatin analogs represent important weapons in treatment protocols of patients with neuroendocrine tumors. Because these peptides preferentially bind to the specific somatostatin receptors, the targeted therapy requires detection of them. As one of the national consulting centers, here we present the results of the immunohistochemically positive neuroendocrine neoplasms diagnosed between 2010 and 2014. Twenty-four paraffin-embedded cases (14 females 10 men, 21-79 years) from different localizations were found to express somatostatin-receptor type 2 (SSTR2). None of the patients has received previous hormonal therapy. The immune reactions have shown membranous, cytoplasmic or mixed patterns. There was no correlation between the expression and the chromogranin A levels, the grades or the hormonal activity/inactivity of the given neoplasms. Our results show that the immunohistochemical detection of SSTR2 is a quick, reliable and effective tool that provides useful information to the oncologists for the therapeutic decision. Because the incidence of the neuroendocrine tumors is still low, centralized pathological units are needed to perform such technique.

Somatostatin receptor SSTR2A and SSTR5 expression in neuroendocrine breast cancer.

Neuroendocrine breast cancer (NEBC) is a group of rare tumors, which could benefit from therapy targeting the somatostatin receptors (SSTRs). In particular, SSTR2A and SSTR5 are potential targets given their consistent expression in gastrointestinal and pancreatic primary and metastatic neuroendocrine cancers. Currently, there are no studies describing the expression of SSTRs in NEBC. The purpose of our study was to characterize the immunohistochemical expression of SSTR2A and SSTR5 in a cohort of NEBC. Thirty-one primary NEBC cases were analyzed, and SSTR2A and SSTR5 immunohistochemistry performed and scored using the modified immunoreactive score proposed by Remmele and Stanger. All patients were females with a mean age of 66.6 years (SD = 14). 77% of cases were histological grade 2. SSTR2A showed a weak positivity in 11 cases (35.5%), moderate positivity in 6 cases (19.4%) and strong positivity in 5 cases (16.1%). Nine cases were negative for SSTR2A (29%). SSTR5 showed a weak positivity in 16 cases (51.6%), moderate positivity in 6 cases (19.4%), while no cases showed strong positivity. Nine cases were negative for SSTR5 (29%). Five cases were negative for both SSTR2A and SSTR5. A weak to moderate SSTR2A and SSTR5 expression was observed in 50-70% of the cases. A subset of NEBCs with strong SSR2A expression may benefit from SSTRs targeted therapy. These results need further validation in a larger series including metastatic NEBC, to provide potential therapeutic targets for patients with advanced disease.

Intraindividual comparison of 68Ga-DOTATATE PET / CT vs 11C-Choline PET / CT in patients with prostate cancer in biochemical relapse: in vivo evaluation of the expression of somatostatin receptors. / Comparación intraindividual de la PET/TC con 68Ga-DOTATATE vs. PET/TC con 11C-colina en pacientes con cáncer de próstata en recaída bioquímica: evaluación in vivo de la expresión de receptores de la somatostatina.

BACKGROUND AND OBJECTIVES: To prospectively compare the detection rate of 68Ga-DOTATATE versus 11C-choline PET/CT in patients with prostate cancer in biochemical relapse, and to evaluate somatostatin receptor expression in vivo to plan targeted therapies (177Lu-DOTATATE). MATERIAL AND METHODS: We prospectively analysed 64 patients with biochemical relapse (median PSA: 4.25 ng/mL). A PET/CT was performed with 11C-choline, and another with 68Ga-DOTATATE. The SUVmax was measured in all lesions. The correlative images, histopathology and/or clinical and biochemical follow-up were taken as the reference standard. RESULTS: The overall detection rate per patient was 48.43% for 68Ga-DOTATATE and 46.87% for 11C-choline. The results were concordant in 53 cases (82.81%). The maximum SUV of 11C-choline was significantly higher than that of 68Ga-DOTATATE for all the concordant lesions (n=130): 6.17 (1.7-15.5) versus 4.38 (1.37-26.7), median (range) for each radiotracer, respectively (p < .0001). The sensitivity and specificity values per patient were the same for both techniques: 0.82 (0.65-0.93) and 0.9 (0.73-0.98), respectively. Although the difference was not significant, the sensitivity was lower in patients with lower PSA levels: 0.63 vs. 0.89; p=.13. A significant correlation was found between the SUVmax of both tracers (r = 0.41, n = 130, p <.0001). CONCLUSIONS: 68Ga-DOTATATE PET/CT and 11C-choline PET/CT seem to have a high capacity to detect pathological lesions in the assessment of patients with prostate cancer with biochemical relapse. Further studies are required to test the potential complementary value of these PET/CT techniques, and to evaluate the potential role of 8Ga-DOTATATE for planning somostatin receptor-mediated therapies (177Lu-DOTATATE).

Neuroendocrine Breast Carcinomas Share Prognostic Factors with Gastroenteropancreatic Neuroendocrine Tumors: A Putative Prognostic Role of Menin, p27, and SSTR-2A.

OBJECTIVES: Due to the rarity of breast carcinomas with neuroendocrine features (NEBC), the knowledge on their biology is very limited but the identification of their biology and prognostic factors is essential to evaluate both pathogenesis and possible targeted treatment options. We assessed the expression of the well-characterized prognostic factors of gastroenteropancreatic neuroendocrine tumors (GEP-NET) in NEBC. METHODS: We assessed the immunohistochemical expression of neuron-specific enolase (NSE), thymidylate synthase (TS), p27, CD56, menin, and somatostatin receptor type 2A (SSTR-2A) in a series of 36 NEBC and 45 invasive ductal carcinomas (IDC). RESULTS: Nuclear and cytoplasmic TS, nuclear and cytoplasmic NSE, and nuclear p27 had significant overexpression in NEBC compared with IDC (for all, p < 0.01). In NEBC, cytoplasmic SSTR-2A expression was associated with excellent distant disease-free survival (p = 0.013), cytoplasmic menin expression with poorer relapse-free survival (p = 0.022), and nuclear p27 with longer breast cancer-specific survival (p = 0.022). CONCLUSIONS: There is a striking similarity in GEP-NET and NEBC regarding prognostic factors. GEP-NET and NEBC also appear to show similar expression patterns of the studied markers, while there are notable differences compared to IDC. Due to the wide expression of SSTR-2A, the treatment option with somatostatin analogs in NEBC should be evaluated.

SSTR2a Is a Useful Diagnostic Marker for Follicular Dendritic Cells and Their Related Tumors.

SSTR2a, a member of the somatostatin receptor family, has been used as a diagnostic marker of meningioma. However, the expression of SSTR2a in follicular dendritic cells (FDCs) and their related tumors has been poorly characterized. This study aimed to assess the potential diagnostic utility of measuring SSTR2a immunohistochemically in FDCs and their related tumors. We evaluated whole-tissue sections from 182 cases including 83 lymphoid reactive follicular hyperplasias, 17 follicular lymphomas, 18 follicular dendritic cell sarcomas (FDCSs), 6 inflammatory pseudotumor-like FDCSs, and 58 other histologic mimics. Immunohistochemistry for SSTR2a and other FDC markers (CD21, CD23, CD35, clusterin, and podoplanin) were performed in all 182 cases. Diffuse membrane immunoreactivity for SSTR2a in FDCs was observed in 100% of follicular lymphoma and FDCS cases and in 96.4% of the reactive follicular hyperplasias cases. Notably, the positive rate of SSTR2a in FDCSs was higher than that of CD21 (88.9%), CD23 (77.8%), CD35 (94.4%), clusterin (55.6%), and podoplanin (94.4%). All inflammatory pseudotumor-like FDCSs were negative for SSTR2a. The histologic mimics were negative for SSTR2a, except for 1 leiomyosarcoma case that showed focal (~10%) positive expression for SSTR2a. Overall, our findings indicate that SSTR2a is a highly sensitive and diagnostically useful marker for FDCs and FDCSs. Furthermore, immunohistochemistry for SSTR2a may be helpful to distinguish FDCSs from inflammatory pseudotumor-like FDCSs and other histologic mimics. Moreover, our findings suggest that SSTR2a may be a potential therapeutic target for treatment of FDCSs.

Differential somatostatin, CXCR4 chemokine and endothelin A receptor expression in WHO grade I-IV astrocytic brain tumors.

PURPOSE: Glioblastomas represent the most common primary malignant tumor of the nervous system and the most frequent type of astrocytic tumors. Despite improved therapeutic options, prognosis has remained exceptionally poor over the last two decades. Therefore, new treatment approaches are urgently needed. An overexpression of somatostatin (SST) as well as chemokine CXCR4 and endothelin A (ETA) receptors has been shown for many types of cancer. Respective expression data for astrocytic brain tumors, however, are scarce and contradictory. METHODS: SST subtype, CXCR4 and ETA expression was comparatively evaluated in a total of 57 grade I-IV astrocytic tumor samples by immunohistochemistry using well-characterized monoclonal antibodies. RESULTS: Overall, receptor expression on the tumor cells was only very low. SST5 was the most prominently expressed receptor, followed by SST3, ETA, SST2 and CXCR4. In contrast, tumor capillaries displayed strong SST2, SST3, SST5, CXCR4 and ETA expression. Presence of SST5, CXCR4 and ETA on tumor cells and of SST3, CXCR4 and ETA on microvessels gradually increased from grade II to grade IV tumors. Ki-67 values correlated significantly with CXCR4 expression on tumor cells and with vascular SST3, CXCR4 or ETA positivity. SST5 or CXCR4 positivity of tumor cells and vascular SST3 or CXCR4 expression negatively correlated with patient outcome. CONCLUSIONS: Though having some prognostic value, SST, CXCR4 or ETA expression on astrocytic tumor cells is clearly of no therapeutic relevance. Indirect targeting of these highly vascularized tumors via SST3, SST5, CXCR4 or ETA on the microvessels, in contrast, may represent a promising additional therapeutic strategy.

Octreotide modulates the expression of somatostatin receptor subtypes in inflamed rat jejunum induced by Cryptosporidium parvum.

Somatostatins are proteins that are involved in gastrointestinal function. However, little is known with regard to somatostatin receptor subtype (SSTR) expression changes that occur in the jejunum during low-grade inflammation and during subsequent octreotide treatment. The aim of the present study was to investigate the expression of SSTRs in the jejunums of Cryptosporidium parvum (C. parvum)-infected rats by immunohistochemisty, reverse transcription (RT) PCR and quantitative real-time RT-PCR assays. Five-day-old suckling Sprague-Dawley rats (n = 15 for each group) were orally gavaged with 105 Nouzilly isolate (NoI) oocysts. Rats then received 50 µg/kg/day of octreotide by intraperitoneal injection from day 10 to day 17 post-infection. Animals were sacrificed on days 7 and 14 post-infection for immunohistochemical analysis and on days 14, 35 and 50 for mRNA expression analysis of SSTR subtypes. Histological analysis of jejunum tissues demonstrated infection of C. parvum along the villus brush border on day 7 post-infection and infection clearance by day 14 post-infection. Real-time PCR analysis indicated that in the inflamed jejunum, a significant increase in SSTR1 and SSTR2 expression was observed on day 14 post-infection. Octreotide therapy down-regulated the expression of SSTR2 on day 37 post-infection but significantly increased expression of SSTR1, SSTR2 and SSTR3 on day 50 post-infection. The results indicate that specific SSTRs may regulate the inflammatory pathway in the rat intestinal inflammation model.

Identification and imaging of miR-155 in the early screening of lung cancer by targeted delivery of octreotide-conjugated chitosan-molecular beacon nanoparticles.

Lung cancer is still the most common cancer globally. Early screening remains the key to improve the prognosis of patients. There is currently a lack of specific and sensitive methods for early screening of lung cancer. In recent years, studies have found that microRNA plays an important role in the occurrence and development of lung cancer and become a biological target in the early diagnosis of lung cancer. In this study, lung cancer cells, subcutaneous xenografts of lung cancer in nude mice, and Lox-Stop-lox K-ras G12D transgenic mice were used as models. The transgenic mice displayed the dynamic processes from normal lung tissue to atypical hyperplasia, adenomas, carcinoma in situ and lung adenocarcinoma. It was found that miR-155 and somatostatin receptor 2 (SSTR2) were expressed in all the disease stages of transgenic mice. Through molecular beacon (MB) technology and nanotechnology, chitosan-molecular beacon (CS-MB) nanoparticles and targeted octreotide (OCT) were conjugated and synthesized. The octreotide-conjugated chitosan-molecular beacon nanoparticles (CS-MB-OCT) can specifically bind to SSTR2 expressed by the lung cancer cells to achieve the goal of identification of lung cancer cells and imaging miR-155 in vivo and in vitro. Fluorescence imaging at different disease stages of lung cancer in Lox-Stop-lox K-ras G12D transgenic mice was performed, and could dynamically monitor the occurrence and development of lung cancer by different fluorescence intensity ranges. The current research, in turn, provides new idea, new method, and new technology for the early screening of lung cancer.

Somatostatin receptor subtype 1 as a potential diagnostic marker and therapeutic target in prostate cancer.

BACKGROUND: Prostate cancer (PCa) is a highly prevalent neoplasia that is strongly influenced by the endocrine system. Somatostatin (SST) and its five receptors (sst1-5 encoded by SSTR1-5 genes) comprise a pleiotropic system present in most endocrine-related cancers, some of which are successfully treated with SST analogs. Interestingly, it has been reported that SSTR1 is overexpressed in PCa, but its regulation, functional role, and clinical implications are still poorly known. METHODS: PCa specimens (n = 52) from biopsies and control prostates from cystoprostatectomies (n = 12), as well as in silico databases were used to evaluate SSTR1 and miRNAs expression. In vitro studies in 22Rv1 PCa cells were implemented to explore the regulation of SSTR1/sst1 by different miRNAs, and to evaluate the consequences of SSTR1/sst1 overexpression, silencing and/or activation [with the specific BIM-23926 sst1 agonist (IPSEN)] on cell-proliferation, migration, signaling-pathways, and androgen-signaling. RESULTS: We found that SSTR1 is overexpressed in multiple cohorts of PCa samples, as compared with normal prostate tissues, wherein it correlates with androgen receptor (AR) expression, and appears to be associated with aggressiveness (metastasis). Furthermore, our data revealed that SSTR1/sst1 expression might be regulated by specific miRNAs in PCa, including miR-24, which is downregulated in PCa samples and correlates inversely with SSTR1 expression. In vitro studies indicated that treatment with the BIM-23926 sst1 agonist, as well as SSTR1 overexpression, decreased, whereas SSTR1 silencing increased, cell-proliferation in 22Rv1 cells, likely through the regulation of PI3K/AKT-CCND3 signaling-pathway. Importantly, sst1 action was also able to modulate androgen/AR activity, and reduced PSA secretion from PCa cell lines. CONCLUSIONS: Altogether, our results indicate that SSTR1 is overexpressed in PCa, where it can exert a relevant pathophysiological role by decreasing cell-proliferation and PSA secretion. Therefore, sst1, possibly in combination with miR-24, could be used as a novel tool to explore therapeutic targets in PCa.