Localization and mRNA expression of somatostatin receptor subtypes in human prostatic tissue and prostate cancer cell lines

Somatostatin and Somatostatin Receptors in Tumour Biology

Somatostatin (SST), a growth hormone inhibitory peptide, is expressed in endocrine and non-endocrine tissues, immune cells and the central nervous system (CNS). Post-release from secretory or immune cells, the first most appreciated role that SST exhibits is the antiproliferative effect in target tissue that served as a potential therapeutic intervention in various tumours of different origins. The SST-mediated in vivo and/or in vitro antiproliferative effect in the tumour is considered direct via activation of five different somatostatin receptor subtypes (SSTR1-5), which are well expressed in most tumours and often more than one receptor in a single cell. Second, the indirect effect is associated with the regulation of growth factors. SSTR subtypes are crucial in tumour diagnosis and prognosis. In this review, with the recent development of new SST analogues and receptor-specific agonists with emerging functional consequences of signaling pathways are promising therapeutic avenues in tumours of different origins that are discussed.

The Role of Receptor-Ligand Interaction in Somatostatin Signaling Pathways: Implications for Neuroendocrine Tumors

Neuroendocrine tumors (NETs) arise from neuroendocrine cells and manifest in diverse organs. Key players in their regulation are somatostatin and its receptors (SSTR1-SSTR5). Understanding receptor-ligand interactions and signaling pathways is vital for elucidating their role in tumor development and therapeutic potential. This review highlights SSTR characteristics, localization, and expression in tissues, impacting physiological functions. Mechanisms of somatostatin and synthetic analogue binding to SSTRs, their selectivity, and their affinity were analyzed. Upon activation, somatostatin initiates intricate intracellular signaling, involving cAMP, PLC, and MAP kinases and influencing growth, differentiation, survival, and hormone secretion in NETs. This review explores SSTR expression in different tumor types, examining receptor activation effects on cancer cells. SSTRs' significance as therapeutic targets is discussed. Additionally, somatostatin and analogues' role in hormone secretion regulation, tumor growth, and survival is emphasized, presenting relevant therapeutic examples. In conclusion, this review advances the knowledge of receptor-ligand interactions and signaling pathways in somatostatin receptors, with potential for improved neuroendocrine tumor treatments.

Nanoparticles and phototherapy combination as therapeutic alternative in prostate cancer: A scoping review

Prostate cancer (CaP) is one of the most common types of cancers worldwide. Despite the existing surgical techniques, prostatectomy patients may experience tumor recurrence. In addition, castration-resistant cancers pose a challenge, especially given their lack of response to standard care. Thus, the development of more efficient therapies has become a field of great interest, and photothermal therapy (PTT) and photodynamic therapy (PDT) are promising alternatives, given their high capacity to cause cell injury and consequent tumor ablation. Phototherapy, along with chemotherapy, has also been shown to be more effective than pharmacotherapy alone. Free molecules used as photosensitizers are rapidly cleared from the body, do not accumulate in the tumor, and are primarily hydrophobic and require toxic solvents. Thus, the use of nanoparticles can be an effective strategy, given their ability to carry or bind to different molecules, protecting them from degradation and allowing their association with other surface ligands, which favors permeation and retention at the tumor site. Despite this, there is still a gap in the literature regarding the use of phototherapy in association with nanotechnology for the treatment of CaP. In this scoping review, it was found that most of the particles studied could act synergistically through PDT and PTT. In addition, fluorescent quenchers can act as diagnostic and therapeutic tools. However, future clinical studies should be performed to confirm the benefits and safety of the combination of nanoparticles and phototherapy for CaP.

Neuroendocrine cells of the prostate: Histology, biological functions, and molecular mechanisms

Prostate cancer (PCa) is a common cause of cancer-related mortality in men worldwide. Although most men are diagnosed with low grade, indolent tumors that are potentially curable, a significant subset develops advanced disease where hormone therapy is required to target the androgen receptor (AR). Despite its initial effect, hormone therapy eventually fails and the tumor progresses to lethal stages even through continued inhibition of AR. This review article focuses on the role of PCa cellular heterogeneity in therapy resistance and disease progression. Although AR-positive luminal-type cells represent the vast majority of PCa cells, there exists a minor component of AR-negative neuroendocrine (NE) cells that are resistant to hormonal therapy and are enriched by the treatment. In addition, it is now well accepted that a significant subset of hormonally treated tumors recur as small cell neuroendocrine carcinoma (SCNC), further highlighting the importance of targeting NE cells in addition to the more abundant luminal-type cancer cells. Although it has been long recognized that NE cells are present in PCa, their underlying function in benign prostate and molecular mechanisms contributing to PCa progression remains poorly understood. In this article, we review the morphology and function of NE cells in benign prostate and PCa as well as underlying molecular mechanisms. In addition, we review the major reported mechanisms for transformation from common adenocarcinoma histology to the highly lethal SCNC, a significant clinical challenge in the management of advanced PCa.

Evaluation of Somatostatin and CXCR4 Receptor Expression in a Large Set of Prostate Cancer Samples Using Tissue Microarrays and Well-Characterized Monoclonal Antibodies

BACKGROUND: Prostate cancer (PCa) is the most common type of cancer among men in Western countries. Despite numerous therapeutic options, few treatments are available for patients with end-stage disease. In the present study, different somatostatin receptors (SSTs) and the chemokine receptor CXCR4 were evaluated for their suitability as novel therapeutic targets in PCa. MATERIALS AND METHODS: The expression of SST subtypes 1, 2A, 3, and 5 and of CXCR4 was evaluated in 276 PCa tumor samples on a tissue microarray (TMA) in 23 whole-block tumor samples and in 3 PCa cell lines by immunohistochemistry using well-characterized monoclonal antibodies. RESULTS: Overall, the frequency and intensity of expression of SSTs and CXCR4 were very low among the PCa samples investigated. Specifically, SST5, SST2A, and SST3 were expressed, albeit at low intensity, in 10.5%, 9.1%, and 0.7% of the TMA samples, respectively. None of the TMA samples showed SST1 or CXCR4 expression. Only a single small-cell-type neuroendocrine carcinoma that was coincidentally included among the whole-block samples exhibited strong SST2A, SST5, and CXCR4 and moderate SST3 expression. Independent of the tumor cells, the tumor capillaries in many of the PCa samples were strongly positive for SST2A, SST3, SST5, or CXCR4 expression. SST expression in the tumor cells was associated with advanced tumor grade and stage. CONCLUSION: Overall, SST and CXCR4 expression levels are clearly of no therapeutic relevance in PCa. SST- or CXCR4-based therapy might be feasible, however, in rare cases of small-cell-type neuroendocrine carcinoma of the prostate.

Neuroendocrine Differentiation in Prostate Cancer: Emerging Biology, Models, and Therapies

Although a de novo clinical presentation of small cell neuroendocrine carcinoma of the prostate is rare, a subset of patients previously diagnosed with prostate adenocarcinoma may develop neuroendocrine features in later stages of castration-resistant prostate cancer (CRPC) progression as a result of treatment resistance. Despite sharing clinical, histologic, and some molecular features with other neuroendocrine carcinomas, including small cell lung cancer, castration-resistant neuroendocrine prostate cancer (CRPC-NE) is clonally derived from prostate adenocarcinoma. CRPC-NE therefore retains early prostate cancer genomic alterations and acquires new molecular changes making them resistant to traditional CRPC therapies. This review focuses on recent advances in our understanding of CRPC-NE biology, the transdifferentiation/plasticity process, and development and characterization of relevant CRPC-NE preclinical models.

Non-coding and coding genomic variants distinguish prostate cancer, castration-resistant prostate cancer, familial prostate cancer, and metastatic castration-resistant prostate cancer from each other

A considerable number of deposited variants has provided new possibilities for knowledge discovery in different types of prostate cancer. Here, we analyzed variants located on 3'UTR, 5'UTR, CDs, Intergenic, and Intronic regions in castration-resistant prostate cancer (8496 variants), familial prostate cancer (3241 variants), metastatic castration-resistant prostate cancer (3693 variants), and prostate cancer (16599 variants). Chromosome regions 10p15-p14 and 2p13 were highly enriched (P < 0.00001) for variants located in 3'UTR, 5'UTR, CDs, intergenic, and intronic regions in castration-resistant prostate cancer. In contrast, 10p15-p14, 10q23.3, 12q13.11, 13q12.3, 1q25, and 8p22 regions were enriched (P < 0.001) in familial prostate cancer. In metastatic castration-resistant prostate cancer, 10p15-p14, 10q23.3, 11q22-q23, 14q21.1, and 14q32.13 were highly variant regions (P < 0.001). Chromosome 2 and chromosome 1 hosted many enriched variant regions. AKR1C3, BRCA1, BRCA2, CHGA, CYP19A1, HOXB13, KLK3, and PTEN contained the highest number of 3'UTR, 5'UTR, CDs, Intergenic, and Intronic variants. Network analysis showed that these genes are upstream of important functions including prostate gland development, tumor recurrence, prostate cancer-specific survival, tumor progression, cancer mortality, long-term survival, cancer recurrence, angiogenesis, and AR. Interestingly, all of EGFR, JAK2, NR3C1, PDZD2, and SEMA3C genes had single nucleotide polymorphisms (SNP) in castration-resistant prostate cancer, consistent with high selection pressure on these genes during drug treatment and consequent resistance. High occurrence of variants in 3'UTRs suggests the importance of regulatory variants in different types of prostate cancer; an area that has been neglected compared with coding variants. This study provides a comprehensive overview of genomic regions contributing to different types of prostate cancer.

Is There a Standard Chemotherapeutic Regimen for Hormone-Refractory Prostate Cancer? Present and Future Approaches in the Management of the Disease

Prostate cancer that no longer responds to hormonal manipulation can be defined as hormone-refractory prostate cancer. Until recently, there has been no standard chemotherapeutic approach for hormone-refractory prostate cancer. The major benefits of chemotherapy in the treatment of the disease are palliative in nature, in terms of reduction of pain and use of analgesics and improvement of performance status, as followed in the most recent trials. Phase III studies are necessary to better evaluate the efficacy of the different regimens, because several old studies suffer for methodological deficits. There is a promising activity of new drug combinations, such as vinca alkaloids and taxanes. Phase I and II trial are testing combinations of classic chemotherapeutic agents and biologic drugs, and the first results appear interesting. In this article, recent advances in the treatment of hormone-refractory prostate cancer using chemotherapeutic regimens are critically reviewed.

The elements of life and medicines

Which elements are essential for human life? Here we make an element-by-element journey through the periodic table and attempt to assess whether elements are essential or not, and if they are, whether there is a relevant code for them in the human genome. There are many difficulties such as the human biochemistry of several so-called essential elements is not well understood, and it is not clear how we should classify elements that are involved in the destruction of invading microorganisms, or elements which are essential for microorganisms with which we live in symbiosis. In general, genes do not code for the elements themselves, but for specific chemical species, i.e. for the element, its oxidation state, type and number of coordinated ligands, and the coordination geometry. Today, the biological periodic table is in a position somewhat similar to Mendeleev's chemical periodic table of 1869: there are gaps and we need to do more research to fill them. The periodic table also offers potential for novel therapeutic and diagnostic agents, based on not only essential elements, but also non-essential elements, and on radionuclides. Although the potential for inorganic chemistry in medicine was realized more than 2000 years ago, this area of research is still in its infancy. Future advances in the design of inorganic drugs require more knowledge of their mechanism of action, including target sites and metabolism. Temporal speciation of elements in their biological environments at the atomic level is a major challenge, for which new methods are urgently needed.

Effects of octreotide and insulin on colon cancer cellular proliferation and correlation with hTERT activity

Peptide hormone somatostatin and its receptors have a wide range of physiological functions and play a role in the treatment of numerous human diseases, including colorectal cancer. Octreotide, a synthetic somatostatin-analog peptide, inhibits growth of colonic cancer cells primarily by binding to G-protein coupled receptors and elicits cellular responses through second-messenger systems. Insulin also initiates mitogenic signals in certain cell types. The objective of the present study was to explore the effects of octreotide with or without insulin treatment, on Caco-2 and HT-29 human colon-cancer cell proliferation and to correlate their effects with the activation of telomerase reverse transcriptase (hTERT). The involvement of protein tyrosine phosphatases in the regulation of the anti-proliferative effect of octreotide was also evaluated. Sodium orthovanadate was used to reverse the anti- proliferative effect of octreotide. Telomerase activity was determined for each time point under octreotide and/or insulin treatment. Elevated expression of sst1, sst2 and sst5 was confirmed in both cell lines by RT-PCR. Immunocytochemistry detected sst1, sst2A, sst2B, sst3, sst4 and sst5 protein expression in the membranes of both cell lines. Octreotide inhibited the proliferation of Caco-2 and HT-29 cells in a time and dose-dependent manner. Insulin exerted proliferative effects in Caco-2 cells and octreotide reversed its effect in both cell lines. Sodium orthovanadate suppressed the anti-proliferative effect of octreotide both in Caco-2 and HT-29 cells. Telomerase activity was significantly reduced when Caco-2 cells were exposed to octreotide, under serum-free cultured medium. On the other hand, telomerase attenuation after octreotide treatment could not counteract the actions of insulin on both cells. Our data indicate that the use of octreotide could provide a possible therapeutic approach to the management of certain patients who suffer from colon cancer.

PET and PET/CT with 68gallium-labeled somatostatin analogues in Non GEP-NETs Tumors

Somatostatin (SST) is a 28-amino-acid cyclic neuropeptide mainly secreted by neurons and endocrine cells. A major interest for SST receptors (SSTR) as target for in vivo diagnostic and therapeutic purposes was born since a series of stable synthetic SST-analouges PET became available, being the native somatostatin non feasible for clinical use due to the very low metabolic stability. The rationale for the employment of SST-analogues to image cancer is both based on the expression of SSTR by tumor and on the high affinity of these compounds for SSTR. The primary indication of SST-analogues imaging is for neuroendocrine tumors (NETs), which usually express a high density of SSTR, so they can be effectively targeted and visualized with radiolabeled SST-analogues in vivo. Particularly, SST-analogues imaging has been widely employed in gastroenteropancreatic (GEP) NETs. Nevertheless, a variety of tumors other than NETs expresses SSTR thus SST-analogues imaging can also be used in these tumors, particularly if treatment with radiolabeled therapeutic SST-analouges PET is being considered. The aim of this paper is to provide a concise overview of the role of positron emission tomography/computed tomography (PET/CT) with (68)Ga-radiolabeled SST-analouges PET in tumors other than GEP-NETs.

Peptide receptor targeting in cancer: the somatostatin paradigm

Peptide receptors involved in pathophysiological processes represent promising therapeutic targets. Neuropeptide somatostatin (SST) is produced by specialized cells in a large number of human organs and tissues. SST primarily acts as inhibitor of endocrine and exocrine secretion via the activation of five G-protein-coupled receptors, named sst1–5, while in central nervous system, SST acts as a neurotransmitter/neuromodulator, regulating locomotory and cognitive functions. Critical points of SST/SST receptor biology, such as signaling pathways of individual receptor subtypes, homo- and heterodimerization, trafficking, and cross-talk with growth factor receptors, have been extensively studied, although functions associated with several pathological conditions, including cancer, are still not completely unraveled. Importantly, SST exerts antiproliferative and antiangiogenic effects on cancer cells in vitro, and on experimental tumors in vivo. Moreover, SST agonists are clinically effective as antitumor agents for pituitary adenomas and gastro-pancreatic neuroendocrine tumors. However, SST receptors being expressed by tumor cells of various tumor histotypes, their pharmacological use is potentially extendible to other cancer types, although to date no significant results have been obtained. In this paper the most recent findings on the expression and functional roles of SST and SST receptors in tumor cells are discussed.

Italian Society of Endocrinology Career Award Lecture: from somatostatin to…somatomedin

Somatostatin plays different parts in hormonal regulation through 5 specific receptors in human body. It has two interesting actions such as an antisecretory activity, mostly on the gastrointestinal system and pituitary level, and an antiproliferative action on tumor cells. Many synthetic somatostatin analogues, more stable than the natural one, have been developed and two are already used in different clinical settings, including endocrine oncology. The inhibitory action on tumor growth may result from both indirect actions, namely the suppression of growth factors and growth-promoting hormones (e.g., GH/IGF-I axis) and inhibition of angiogenesis, as well as modulation of the immune system, and direct actions, such as activation of anti-growth activities (e.g., apoptosis). Recently, the development of specific polyclonal antibodies allowed the precise identification of the 5 specific somatostatin receptors and their localization in different cell species. Somatostatin receptor subtypes belong to the G protein-coupled receptor family, share a common molecular topology, and can traffic not only in vitro within different cell types but also in vivo. A picture of the pathways and proteins involved in these processes is beginning to emerge. Moreover, the process of homo- and/or heterodimerization of G-protein coupled receptors and receptor tyrosine kinase families are crucial for implicating the fundamental properties of receptor proteins including receptor expression, trafficking, and desensitization, as well as signal transduction. Furthermore, functional consequences of such an interaction in modulation of signaling pathways linked to pathological conditions specifically in cancer are discussed.

GPCRs and cancer

G-protein-coupled receptors (GPCRs), which represent the largest gene family in the human genome, play a crucial role in multiple physiological functions as well as in tumor growth and metastasis. For instance, various molecules like hormones, lipids, peptides and neurotransmitters exert their biological effects by binding to these seven-transmembrane receptors coupled to heterotrimeric G-proteins, which are highly specialized transducers able to modulate diverse signaling pathways. Furthermore, numerous responses mediated by GPCRs are not dependent on a single biochemical route, but result from the integration of an intricate network of transduction cascades involved in many physiological activities and tumor development. This review highlights the emerging information on the various responses mediated by a selected choice of GPCRs and the molecular mechanisms by which these receptors exert a primary action in cancer progression. These findings provide a broad overview on the biological activity elicited by GPCRs in tumor cells and contribute to the identification of novel pharmacological approaches for cancer patients.

Somatostatin receptors in non-neuroendocrine malignancies: the potential role of somatostatin analogs in solid tumors

Somatostatin receptors (sstrs) are G-protein-coupled receptors that mediate various physiological effects when activated by the neuropeptide somatostatin or its synthetic analogs. In addition to the well-documented antisecretory effects of sstr2-preferential somatostatin analogs octreotide and lanreotide, ligand binding to sstr initiates an inhibitory action on tumor growth. This effect may result from both indirect actions (suppression of growth factors and growth-promoting hormones [e.g., GH/IGF-1 axis] and inhibition of angiogenesis) and direct actions (activation of antigrowth activities [e.g., apoptosis]). As solid tumor cells express multiple sstrs, there is a rationale to evaluate the potential antitumor effects of pasireotide (SOM230), a multireceptor-targeted somatostatin analog with high binding affinity for sstr1–3 and sstr5. Pasireotide reduces systemic IGF-1 levels more potently than currently available somatostatin analogs and has been well tolerated in clinical trials.

[Neuroendocrine target therapies for prostate cancer]

It is important to determine whether an increase in Chromogranin A levels and neuroendocrine (NE) cell activation are associated with progression towards on hormone-independent prostate-cancer. We proposed a combination of estrogens and somatostatin analogues as therapy of NE activation in hormone-independent prostate cancer. The combined therapy with ethinyl estradiol and lanreotide offered objective and symptomatic responses in patients with limited treatment options and refractoriness to conventional hormonal therapy strategies; in particular, it offered a median overall survival that was superior to the 10-month median survival in patients with hormone refractory disease. This combined therapy also sustains the new concept in cancer treatment in which therapies may target not only cancer cells but also its microenvironment, which can yield protection against apoptosis.

Immunohistochemical expression and localization of somatostatin receptor subtypes in androgen ablated prostate cancer

OBJECTIVE

The aim was to examine the expression and localization of the five somatostatin receptors (termed SSTR1 to 5) in radical prostatectomies (RPs) from patients with prostatic adenocarcinoma (PCa) under complete androgen ablation (CAA) before operation.

MATERIAL

The five SSTRs were evaluated in the epithelial, smooth muscle and endothelial cells of normal-looking epithelium (Nep), high-grade prostatic intraepithelial neoplasia (HGPIN) and PCa in 20 RPs with clinically detected PCa from patients under CAA. Twenty RPs with clinically detected PCa from hormonally untreated patients were used as control group.

RESULTS

Concerning the secretory cells (i) Membrane staining was seen for SSTR3 and SSTR4; the mean percentages of positive cells, higher in SSTR3 than in SSTR4, decreased sharply in HGPIN and PCa compared with Nep; the mean percentages in the androgen ablated group were 30% to 90% lower than in the untreated; (ii) Cytoplasmic staining was seen for all five SSTRs; the mean percentages of positive cells in Nep, HGPIN and PCa of the untreated group were similar, and in general as high as 80% or more; in the treated group, the Nep values were similar to those in the untreated, whereas the values in HGPIN and PCa were lower for SSTR1, three and five, with a decrease of 30% for SSTR1; (iii) Nuclear staining was seen with SSTR4 and SSTR5, the mean percentages for the former being much lower than for the latter; treatment affected both HGPIN and PCa, whose proportions of stained cells were 30% to 55% lower than in the untreated group. Cytoplasmic staining in the basal cells was seen for all five SSTRs, both in Nep and HGPIN. The values in the treated group were lower than in the other, the difference between the two group being in general comprised between 10% and 40%. Treatment did not affect SSTR staining in the smooth muscle and endothelial cells.

CONCLUSIONS

The present study expands our knowledge on the expression and localization of the five SSTRs in the prostate following CAA.

Androgen-responsive and -unresponsive prostate cancer cell lines respond differently to stimuli inducing neuroendocrine differentiation

The treatment of advanced prostate cancer (CaP) with androgen deprivation therapy inevitably renders the tumours castration resistant and incurable. Under these conditions, neuroendocrine differentiation (NED) of CaP cells occurs and neuropeptides released by neuroendocrine cells facilitate tumour progression. Pharmacological strategies aiming to prevent or delay NED during androgen ablation could, therefore, increase the effectiveness of the therapy. Mechanisms and pathways inducing NED in CaP are poorly understood and data are often discordant. In the present study, we used several CaP cell lines (androgen-responsive: LNCaP, PC3-AR, 22RV1 and -irresponsive: DU145 and PC3) to evaluate NED after androgen deprivation or treatment with epidermal growth factor (EGF). NED was determined by neuron-specific enolase and chromogranin A expression and by the occurrence of morphological changes in the cells. Androgen-deprivation conditions induced NED in LNCaP and PC3-AR, but not in 22Rv1, PC3 and DU145 cells. LNCaP and PC3-AR cells also became resistant to thapsigargin-induced apoptosis. In all the AR-positive cell lines, androgen deprivation caused a decrease in androgen receptor expression indicating that it is downregulated irrespective of NED induction. Treatment with EGF induced NED in DU145 cells and the EGF receptor inhibitor gefinitib prevented the process. On the contrary, no effect of EGF was demonstrated in LNCaP or 22Rv1 cells. CaP cell lines did not respond univocally to treatments inducing NED, suggesting that studies on this topic should be performed in a wide spectrum of cell models which can be more indicative of the tumour variability in vivo.

Somatostatin receptor subtypes in hormone-refractory (castration-resistant) prostatic carcinoma

The aim of this study was to examine the tissue expression and localisation of the somatostatin receptors (SSTRs) in hormone-refractory (HR) prostate cancer (PCa). Five SSTRs were evaluated immunohistochemically in 20 radical prostatectomies (RPs) with Gleason score (GS) 3+3=6 PCa, in 20 RPs with GS 4+4=8 and 4+5=9 PCa, and 20 transurethral resection of the prostate specimens with HR PCa. The mean values in the cytoplasm (all five SSTRs were expressed), membrane (only SSTR3 and SSTR4 were expressed) and nuclei (only SSTR4 and SSTR5 were expressed) of the glands in HR PCa were 20-70% lower than in the other two groups, the differences being statistically significant. All five SSTRs were expressed in the smooth muscle and endothelial cells of HR PCa, the mean values being lower than in the other two groups. In conclusion, this study expands our knowledge on the expression and localisation of five SSTRs in the various tissue components in the HR PCa compared with hormone-sensitive PCa.

Immunohistochemical expression and localization of somatostatin receptor subtypes in prostate cancer with neuroendocrine differentiation

The aim of the study is to examine the tissue expression and localization of the somatostatin receptors (SSTRs) in prostate cancer (PCa) with neuroendocrine (NE) differentiation. The five SSTR subtypes (SSTR1 to 5) were evaluated immunohistochemically in the secretory cells of normal-looking epithelium (Nep), high-grade prostatic intraepithelial neoplasia (HGPIN) and PCa in 20 radical prostatectomies (RPs) with Gleason score 3+3=6 acinar PCa; 20 RPs with GS 4+4=8 and 4+5=9 PCa; and 20 RPs with PCa with NE differentiation. The basal cells were evaluated in Nep and HGPIN. In all groups the stromal smooth muscle and endothelial cells were also analyzed. Concerning the secretory cells, (i) the greatest mean proportions of cells with strong cytoplasmic staining in PCa were seen for SSTR2, mainly in the group of RP with NE differentiation, and for SSTR4 in all three groups; the mean values in HGPIN were intermediate between Nep and PCa; (ii) Membrane staining was seen for SSTR3 and SSTR4; the mean percentages of positive cells, higher in SSTR3 than in SSTR4, decreased from Nep to HGPIN and PCa in all three RP groups; in the latter two, the mean percentages were similar; and (iii) Nuclear staining was seen with SSTR4 and SSTR5; for SSTR4, the mean percentages in the PCa of the three groups were higher than in HGPIN and Nep, the highest proportion being with PCa with NE differentiation. Concerning the basal cells, in Nep the mean proportions of cells with strong staining intensity were greater for SSTR1 and SSTR3 than for the other subtypes, the lowest being with SSTR2; in HGPIN the highest mean propositions of positive cells was with SSTR3, the proportions in the three RP groups being similar. Concerning the stromal smooth muscle and endothelial cells, the highest mean values being in SSTR1 and the lowest in SSTR5; for the former subtype the highest proportion of endothelial cells with strong intensity was seen in the RP NE group. In conclusion, this immunohistochemical study expands our knowledge on the expression and localization of five SSTRs in the various tissue components in the prostate with PCa with NE differentiation, compared with conventional PCa. Typing somatostatin receptor expression in NE tumours could be of relevance to target somatostatin analogue-based diagnostic approach and treatment.

Regulation of prostate cancer cell proliferation by somatostatin receptor activation

Although some evidence supports the antitumoral effects of somatostatin (SRIF) and related agonists, the available data in prostate cancer (PCa) model systems and clinical studies are few, conflicting and not conclusive. This study investigated the effects of lanreotide and new mono- and bi-specific SRIF agonists on proliferation, ligand-driven SRIF receptor (sst) dimerization and secretory pattern of the IGF system in LNCaP cells, a model of androgen-dependent PCa. LNCaP expressed all sst(s), but sst(4). Among them, sst(1) and sst(3) were inversely regulated by serum concentration. sst(1)/sst(2) and sst(2)/sst(5) dimers were constitutively present and further stabilized by treatment with BIM-23704 (sst(1)/sst(2)) and BIM-23244 (sst(2)/sst(5)), respectively. Dose-response studies showed that lanreotide and BIM-23244 were significantly more potent in inhibiting LNCaP cell proliferation than BIM-23120 (sst(2)) and BIM-23206 (sst(5)) alone or in combination. Treatment with BIM-23926 [corrected] (sst(1)) markedly reduced cell proliferation, whereas exposure to BIM-23704 resulted in a lower cell growth inhibition. The antiproliferative effects of BIM-23244, lanreotide and BIM-23704 were unchanged, reduced and abolished by the sst(2) antagonist BIM-23627, respectively. All SRIF analogs caused a significant induction in p27(KipI) and p21 and down-regulation of protein expression of cyclin E, as well as reduced IGF-I and IGF-II secretion. In particular, the administration of exogenous IGF-I, at variance to IGF-II, counteracted the inhibitory effect on cell proliferation of these compounds. Moreover, SRIF agonists reduced endogenous IGFBP-3 proteolysis. These results show that, in LNCaP cells, activation of sst(1) and sst(2)/sst(5) results in relevant antiproliferative/antisecretive actions.

Emerging drugs for prostate cancer

Prostate cancer mortality usually occurs as a result of castrate resistant disease. Many approaches are currently being evaluated to improve the treatment of this condition. These include drugs that induce androgen deprivation, that is, LHRH antagonists; more active or less toxic chemotherapy agents; immunologic approaches, including passive and active immunization; drugs that target the androgen receptor and/or androgen synthesis; drugs that target specific pathways, including tyrosine kinase inhibitors, angiogenesis inhibitors, endothelin antagonists and matrix metalloproteinase inhibitors; and antioxidants and cell cycle inhibitors. Many of these agents seem promising. The rationale, biologic activity and therapeutic results of these emerging drugs are reviewed.

Visualization of somatostatin receptors in prostate cancer and its bone metastases with Ga-68-DOTATOC PET/CT

PURPOSE

To assess DOTATOC-affine somatostatin receptor expression in advanced prostate cancer and its bone metastases with regard to DOTATOC-mediated receptor therapies, using a Ga-68-DOTATOC PET/CT.

PROCEDURES

Twenty consecutive patients with advanced prostate cancer underwent bone scintigraphy, followed by Ga-68-DOTATOC PET/CT within 3 weeks. Through side-by-side comparison with bone scintigraphy, the number of visible bone metastases on PET was determined. In addition, in cases of visible metastases, the maximum standard uptake value (SUV(max)) of Ga-68-DOTATOC was measured in the metastases and in normal bone. In patients who did not undergo a prostatectomy (n = 12), the SUV(max) was additionally measured in the prostate and in adjacent tissue. For focal lesions, the difference in SUV(max) (Delta SUV(max)) between the metastases and normal bone was calculated. For patients still having their prostate, a Delta SUV(max) between the prostate and its adjacent tissue was calculated.

RESULTS

Sixty four of 216 metastases (30%) were visible in 13 patients with focal metastases. Of six patients with diffuse metastases (superscan), one showed diffuse metastases, three showed a total of ten focal metastases, and two showed no correlate on PET. One patient with a neuroendocrine prostate cancer showed no correlate on PET. The maximum Delta SUV(max) between metastases and normal bone was 4.9 (mean = 1.6 +/- 0.9) and between the prostate and adjacent tissue 5.9 (mean = 2.8 +/- 1.6).

CONCLUSIONS

In prostate cancer and its bone metastases, DOTATOC-affine somatostatin receptors (subtype 2 and 5) can be visualized with Ga-68-DOTATOC PET/CT. But their expression is so weak that other conjugates should be tested for receptor-mediated therapies which are better at addressing the prostate cancer-specific somatostatin receptor subtypes 1 and 4-or even other receptors.

Interaction of the human somatostatin receptor 3 with the multiple PDZ domain protein MUPP1 enables somatostatin to control permeability of epithelial tight junctions

The presence of heterotrimeric G-proteins at epithelial tight junctions suggests that these cellular junctions are regulated by so far unknown G-protein coupled receptors. We identify here an interaction between the human somatostatin receptor 3 (hSSTR3) and the multiple PDZ protein MUPP1. MUPP1 is a tight junction scaffold protein in epithelial cells, and as a result of the interaction with MUPP1 the hSSTR3 is targeted to tight junctions. Interaction with MUPP1 enables the receptor to regulate transepithelial permeability in a pertussis toxin sensitive manner, suggesting that hSSTR3 can activate G-proteins locally at tight junctions.

Putative tissue markers in prostate cancer

A variety of putative prostate cancer markers have been described in human serum, urine, seminal fluid, and histological specimens. These markers exhibit varying capacities to detect prostate cancer and to predict disease course. In order to be considered markers for diagnosis or prognosis of disease course, and to be brought forward for large-scale clinical evaluation, they should fulfill several criteria. Firstly, there should be a biological or therapeutic rationale for choosing the marker, or at least a consistent association with disease presence, disease characteristics such as stage, or disease aggressiveness. Secondly, there should be an assessment of the strength of marker association with disease outcome. Thirdly, the marker should be assessed as an independent predictor in a multivariate analysis.

Somatostatin, cortistatin and their receptors in tumours

Somatostatin (SS) and its synthetic analogs have a role in the treatment of neuroendocrine tumours both in terms of symptoms control and antiproliferative activities. These effects are mediated by five SS receptors, widely expressed in both human neuroendocrine and non-neuroendocrine tumours, which were demonstrated to be diagnostically and therapeutically valuable targets. Cortistatin (CST), a brain cortex peptide, partially homologous to SS and having similar functions is also expressed in peripheral tissues and tumours. CST binds all SS receptors, and, differently from SS, also the ghrelin receptor GHSR1a and the CST specific receptor MrgX2. The expression profile of CST is mostly restricted to neuroendocrine tumours (gastrointestinal, pancreas, lung, parathyroid, thyroid, adrenal). In these tumours, CST probably acts via the SS or ghrelin receptor, the MrgX2 receptor being absent. Thus, in comparison to SS analogs, CST synthetic analogs may represent additional diagnostic/therapeutic tools in those tumours expressing the receptors for SS, for ghrelin or for both peptides.

Somatostatin receptor scintigraphy in thoracic diseases

Somatostatin (SS) receptor scintigraphy is useful for the diagnosis of lesions with high density of SS receptors, and above all neuroendocrine tumors. For several years, only indium-labeled octreotide has been applied to visualise in vivo tissues with SS receptor overexpression. Radiolabeled octreotide became the gold standard for the detection of neuroendocrine tumors. More recently, however, several new SS analogues with varying affinity for SS receptor subtypes have been developed, and different radionuclides as radiolabels have been introduced. Moreover, significant improvements have been made by the introduction of hybrid machines, such as single photon emission computed tomography/ computed tomography (SPECT/CT) or positron emission tomography (PET)/CT that enable to perform whole-body imaging quickly and with high anatomical resolution in several body areas, including the chest. The development of more specific radiopharmaceuticals, together with the modern technique of imaging, may provide excellent quality images with high contrast, allowing to depict very small lesions and making them easy to interpret. Indeed, in the management of SS receptor-positive lesions, the contribution of nuclear medicine is essential in several clinical settings, such as initial diagnosis, disease staging, follow-up, treatment planning, and treatment monitoring. In addition, the tracer uptake might be used as a prognostic parameter and as a predictor of treatment response. In the chest, apart in (neuro)endocrine tumors, SS receptors have been demonstrated in granulomatous diseases, like sarcoidosis and other immune-mediated disorders, such as anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis. In this paper we review and discuss the role of SS receptor scintigraphy in diagnosis, staging or follow- up of thoracic SS receptor-positive lesions.

New perspective in the management of neuroendocrine differentiation in prostate adenocarcinoma

In this review, we will present some of the information that is known about neuroendocrine (NE) cells and differentiation in the prostate. We will then speculate on the potential role that NE differentiation in prostate carcinoma may play and how this differentiation may be clinically analysed and treated. The androgen-independent growth of prostate cancer can be caused by different mechanisms; one of these is receptor-specific paracrine or autocrine growth modulation of human prostatic cancer cells by neuropeptides secreted by NE cells. Our results affirm that different methods of androgen deprivation can influence the serum chromogranin A (CgA) levels to different extents in prostate cancer. In particular, bicalutamide produces a significantly lower increase in serum CgA compared with castration therapy. In the light of other evidence that supports a significant relationship between serum CgA levels, tissue CgA expression and NE activity, we hypothesise that bicalutamide may reduce the risk of NE cell hyperactivation in prostate cancer. It is important to determine whether increases in CgA levels and NE cell activation are associated with progression towards hormone-independent prostate cancer. We recently proposed as therapy of NE activation in hormone-independent prostate cancer, a combination of oestrogens and somatostatin analogues. The combination of ethinyl estradiol and lanreotide had a favourable toxicity profile, offered objective and symptomatic responses in patients with limited treatment options and refractoriness to conventional hormonal therapy strategies and, in particular, offered a median overall survival that was superior to the 10-month median survival in patients with hormone refractory disease. This combination therapy also sustains the novel concept in cancer treatment in which therapies may target not only cancer cells but also its microenvironment in combination, which can confer protection from apoptosis.

Somatostatin, Somatostatin Receptors, and Pancreatic Cancer

Somatostatin may play an important role in the regulation of cancer growth including pancreatic cancer by interaction with somatostatin receptors (SSTRs) on the cell surface. Five SSTRs were cloned, and the function of these SSTRs is addressed in this review. SSTR-2, SSTR-5, and SSTR-1 are thought to play major roles in inhibiting pancreatic cancer growth both in vitro and in vivo. SSTR-3 may be involved in mediating apoptosis, but the role of SSTR-4 is not clear. In most pancreatic cancers, functional SSTRs are absent. Reintroduction of SSTR genes has been shown to inhibit pancreatic cancer growth in cell cultures and animal models.

SOMATOSTATIN ANALOGUES AND ESTROGENS IN THE TREATMENT OF ANDROGEN ABLATION REFRACTORY PROSTATE ADENOCARCINOMA

PURPOSE

Prostate cancer progression to androgen ablation refractory stage D3 corresponds to cancer cell escape from androgen withdrawal induced apoptosis. Of note, salvage chemotherapy can extend the median survival of approximately 10 months in patients with stage D3. Therefore, novel therapeutic strategies that target the molecular basis of androgen resistance are required.

MATERIALS AND METHODS

The MEDLINE and Current Content databases were used to find studies of the use of estrogens and somatostatin analogues for D3 prostate adenocarcinoma. We also analyzed the rationale and clinical results of our combination therapy using lanreotide and ethinylestradiol.

RESULTS

Negative experiences have been reported with somatostatin analogues as monotherapy. On the other hand, the median progression-free survival reported in our experience using lanreotide acetate plus ethinylestradiol clearly surpassed the 10-month survival historically described in stage D3 cases.

CONCLUSIONS

The use of somatostatin analogues in combination therapy for D3 prostate cancer sustains the novel concept in cancer treatment in which therapies may target not only cancer cells, but also the microenvironment in combination, which can confer protection from apoptosis.

Characterization of somatostatin receptor expression in human pancreatic cancer using real-time RT-PCR

BACKGROUND

Somatostatin inhibits cell proliferation and may act as a tumor suppressor by interacting with five different somatostatin receptors (SSTRs). We hypothesized that SSTR expression is down-regulated in human pancreatic cancer. In the current study, we used a powerful real-time RT-PCR technique to examine the mRNA expression levels of all five SSTR subtypes in human pancreatic cancer.

MATERIALS AND METHODS

Total RNA was extracted from three pancreatic cancer cell lines (Panc-1, MIA PaCa-2, and Hs 766T), three surgical specimens of pancreatic cancer, and adjacent pancreatic tissue, and a pancreatic cancer cell line transfected with the SSTR-2 gene. Specific primers were designed and mRNA levels for the five SSTRs were analyzed with real-time quantitative RT-PCR using a Bio-Rad iCycler system.

RESULTS

The pancreatic tumor specimens had a 2.5- and 4.3-fold reduction of SSTR-2 and SSTR-5 mRNA levels, respectively, as compared to their adjacent normal pancreatic tissues. SSTR-1 and SSTR-3 were also detected in both the cancer specimens and the adjacent tissues, but SSTR-4 was absent. Human pancreatic cancer cell lines also expressed SSTR-2 and SSTR-5 mRNA, but not SSTR-1, SSTR-3, and SSTR-4. Up-regulation of SSTR-2 mRNA by 2.2 x 10(4)-fold in Panc-1 cells resulted in receptor expression and growth inhibition.

CONCLUSION

Expression of SSTR-2 and SSTR-5 could be important in the growth inhibitory effect of somatostatin in human pancreatic cancer. Down-regulation of SSTR transcription or SSTR mRNA instability may result in loss of a tumor suppressive effect of SSTRs in human pancreatic cancer.

Expression of serotonin receptors and role of serotonin in human prostate cancer tissue and cell lines

BACKGROUND

Increase in the number of serotonin (5-HT) releasing neuroendocrine (NE) cells has been shown to be correlated with tumor progression, loss of androgen dependence, and poor prognosis. Serotonin is a well-known mitogen which mediates a wide variety of physiological effects via multiple receptors, of which receptor subtype 1 (5-HTR1) has been identified in prostate cancer (PC) cell lines. Recently, 5-HT has been found to show growth-promoting activity and to be functionally related to oncogenes.

MATERIALS AND METHODS

Localization, protein content, and mRNA expression of 5-HTR subtype 1A, 1B, and 1D was studied in prostatic tissue (35 patients), metastases, PC cell lines, a benign prostatic stromal cell line (human prostate cell preparation (hPCP)), and xenografts of PC-3 cells by immunohistochemistry (IHC), Western blotting, and RT-PCR, respectively. The growth-inhibition effect of a 5-HT1A antagonist (NAN-190) on PC cell lines was studied using a bromodeoxyuridine (BrdU) assay.

RESULTS

A strong immunoreaction of 5-HTR1A and 1B was demonstrated in high-grade tumor cells (35/35) and a small number of BPH cells, whereas 5-HTR1D was confined to vascular endothelial cells. 5-HTR1A was also demonstrated in PC cells metastasized to lymph node and bone, PC-3, DU145, LNCaP, and in xenografts of PC-3 cells and hPCP. Western blot analysis gave strong bands from PC tissue extracts compared to BPH tissue. Using RT-PCR, 5-HTR1A mRNA was demonstrated in all PC cell lines. An antagonist of 5-HTR1A (NAN-190) inhibited the growth of PC-3, DU145, and LNCaP cells but not of hPCP cells.

CONCLUSIONS

This is the first study demonstrating an overexpression of 5-HTR subtypes 1A and 1B in PC cells, especially in high-grade tumors. Moreover, 5-HT stimulates proliferation of PC cells and 5-HTR1A antagonists inhibit proliferation. Thus, we propose that 5-HT has an important role in tumor progression, especially in the androgen-independent state of the disease. The design of specific antagonists for this type of receptor might be useful for the growth control of androgen-independent tumors.

Cortistatin production by HepG2 human hepatocellular carcinoma cell line and distribution of somatostatin receptors

BACKGROUND/AIMS

Recently, trials of octreotide have shown a significant survival benefit in the treatment of advanced hepatocellular carcinoma but new data are controversial. We, therefore, examined the production of somatostatin and cortistatin, the expression and distribution of somatostatin receptors (sst) in HepG2 human hepatocellular carcinoma cells, and the possible antiproliferative effect of octreotide on these cells.

METHODS

Radioimmunoassay and RT-PCR studies were performed for the detection of somatostatin and cortistatin. RT-PCR, radioligand binding and immunocytochemistry assays were employed for the detection of the ssts. Growth and viability of cells were measured by the tetrazolium salt assay.

RESULTS

HepG2 cells were found to express sst(2), sst(3) and sst(5) receptors. Immunocytochemistry revealed a mainly intracellular distribution of all ssts with unique patterns for each of them. Membrane binding sites for somatostatin were mainly of the sst(3) (39+/-8%) and sst(5) (59+/-5%) types, while only minor sst(2) binding could be detected (5+/-12%). Octreotide was found to inhibit the proliferation of HepG2 cells (IC(50) 1.25 x 10(-9)M) via protein tyrosine phosphatases. HepG2 cells produced cortistatin while somatostatin expression was not detected.

CONCLUSIONS

In conclusion, HepG2 cells express cortistatin, which regulates somatostatin receptors. Cell proliferation was reduced by octreotide via a protein tyrosine phosphatase dependent mechanism.

Somatostatin receptors: from basic science to clinical approach. Unlabeled somatostatin analogues-1: Prostate cancer

Neuroendocrine cells have been found in all the stages of prostate cancer, but their clinical significance is not completely understood. Neuroendocrine cells are androgen receptor- and prostate-specific antigen-negative, do not proliferate, and secrete many neuropeptides, such as chromogranin A. Neuroendocrine differentiation of prostate cancer correlates with an advancing tumour stage, poor prognosis and tumour progression after androgen deprivation. Furthermore, neuroendocrine phenotype is associated with the increased expression of neo-angiogenesis and vascular endothelial growth factor and with an over-expression of survivin, a new anti-apoptosis protein. Chromogranin A is the quantitatively major secretory protein of the vesicles inside neuroendocrine prostate cells and it is the marker most frequently used to detect neuroendocrine features, both in tissues and in general circulation. Tumours displaying neuroendocrine phenotype tend to be more aggressive and resistant to hormone-therapy. Neuroendocrine differentiation seems to be a dynamic phenomenon: in vitro and in vivo data suggest that it can be induced by androgen suppression. Moreover, the differences in the expression of somatostatin receptors between primary and hormone-refractory prostate cancer are likely to be related to the changes in neuroendocrine phenotype during androgen deprivation. Circulating chromogranin A levels seem to be scarcely affected by endocrine- and chemotherapy, while they significantly decreased after treatment with somatostatin analogs.

Somatostatin receptors and their interest in diagnostic pathology

Since the discovery of somatostatin (SS) and of its interactions with a family of specific somatostatin receptors (sst), a wide body of evidence has been reported on its biological activities. Those activities include inhibition of hormone secretion, neuromodulatory properties in the central nervous system, cell growth control, and induction of apoptosis. At the same time, the distribution of sst has been analyzed in both normal and pathological tissues and sst subtype selective SS-analogs, able to mimic most SS functions, have been developed. The results have been fundamental insights into sst physiology and potent clinical implications in a variety of neoplastic and non neoplastic diseases. Neuroendocrine tumors have been particular targets of investigation. Alternative methods have been validated and are available to analyze the presence and functionality of sst at the level of either mRNA or protein. These methods include RT-PCR, Northern blot, in situ hybridization, immunohistochemistry, autoradiography, and in vivo scintigraphy. Tissue localization techniques are now accessible to many pathology laboratories worldwide and the role of the pathologist in typing the different sst present in a given sample is becoming more and more crucial. This is particularly, but not exclusively, the case in the field of neuroendocrine oncology, where sst typing may affect the clinical management of patients with sst-positive tumors.

Expression of somatostatin receptor subtypes 2 and 4 in human benign prostatic hyperplasia and prostatic cancer

BACKGROUND

The presence of receptor subtypes for the inhibitory peptide somatostatin in prostatic tissue has been a controversial issue with conflicting reports. To elucidate whether prostatic epithelial cells express mRNA for somatostatin receptor (SSTR) subtype 2 and 4, we have investigated the localization of SSTR2 and SSTR4 transcripts in prostatic tissues by in situ hybridization.

METHODS

Nonradioactive in situ hybridization was performed with specific fluorescein-labeled SSTR2 and SSTR4 riboprobes on consecutive sections of benign prostatic hyperplasia (BPH) and prostate cancer tissues.

RESULTS

We report, for the first time, tissue localization of SSTR2 and SSTR4 mRNA in BPH and malignant cells of human prostate. Hybridization signals for SSTR4 mRNA transcripts were confined to the prostatic epithelium (12 of 16 BPH cases, and in 12 of 13 carcinoma cases), whereas SSTR2 transcripts were predominantly localized in the stromal compartment but also were detectable in epithelial cells in a significant number of specimens (11 of 17 BPH cases, and in 12 of 14 carcinoma cases). Furthermore, the staining intensity for SSTR2 and SSTR4 transcripts is stronger in malignant cells compared with adjacent BPH epithelium.

CONCLUSION

The data presented suggest that the expression of SSTR2 and SSTR4 transcripts is up-regulated in malignant cells and that not only SSTR2 agonists, but also compounds targeting the SSTR4 subtype may have a potential role in the treatment of prostate cancer.