Growing vascular endothelial cells express somatostatin subtype 2 receptors

The Role of Somatostatin in the Gastrointestinal Tract

The gastrointestinal (GI) tract is responsible for food digestion and host protection from harmful stimuli; however, its function as an endocrine organ is also well documented. Somatostatin (SST) was first discovered in the hypothalamus, but the GI tract is its main producer and target organ. SST is a potent inhibitor of many GI functions, including peristalsis, hormone secretion, and gastric acid production, while its anti-inflammatory effects contribute to the integrity of the intestinal barrier. These data make SST and its analogs useful agents in clinical practice. As our understanding of SST metabolism and function evolves, their use in a wide variety of medical conditions can improve patient care.

The Investigation of Somatostatin Receptors as a Potential Target in Breast Phyllodes Tumours

BACKGROUND

Somatostatin receptors (SSTRs) are expressed in most neuroendocrine neoplasms, particularly in gastroenteropancreatic neuroendocrine tumours, and have been utilised as diagnostic markers and therapeutic targets. The radioiodinated somatostatin analogue 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid- Tyr3-octreotate (DOTATATE) has been employed for SSTR targeting for either diagnostic or therapeutic purposes depending on the labelling with 68Gallium or 177Lutetium, respectively. SSTR expression is reported in a subset of breast adenocarcinoma and breast neuroendocrine carcinomas; however, minimal knowledge exists regarding their expression in fibroepithelial (biphasic) breast lesions such as fibroadenoma and phyllodes tumours. Aggressive ends of the spectrum, i.e., "cystosarcoma phyllodes", may present a management challenge with recurrences and metastases, and SSTRs could be a promising therapeutic target for these types of tumours.

METHODS

Gene and protein expressions of SSTRs in primary human fibroepithelial lesions of the breast are investigated using RT-PCR and immunoblotting. Localisation of the SSTR-positive cells was determined with immunohistochemistry and immunofluorescence.

RESULTS AND CONCLUSIONS

Both fibroadenoma and phyllodes tumours express SSTRs. Immunohistochemical analyses suggested that this expression is in the stromal, not epithelial, component by demonstrating that SSTR stained in the areas overlapping with α-smooth muscle actin-positive myoepithelial cells around blood vessels and capillary structures. This study is the first in the literature to demonstrate SSTR positivity in mammary fibroepithelial neoplasms. Once validated, these findings may also have significant implications for managing the treatment of these tumours.

Somatostatin receptor 2A expression in von Hippel-Lindau-related hemangioblastomas

BACKGROUND

Central nervous system hemangioblastomas are the most prevalent manifestation of von Hippel-Lindau (VHL) disease and remain the main cause of mortality. Surgical resection is the primary treatment strategy, but is not always possible, and should be used as restrictively as possible. There is an unmet need for less invasive treatment strategies, such as targeted therapy. Expression of somatostatin receptor 2A (SSTR2A) in VHL-related hemangioblastomas has been described earlier, but the extent of expression in a larger population has yet to be determined. The authors hypothesize that a substantial subset of VHL-related hemangioblastomas show SSTR2A expression, which may serve as a potential new treatment target.

METHODS

Patients who were surgically treated for a VHL-related hemangioblastoma from 1990 until 2021 at the UMC Utrecht were included. Clinical data was derived from a clinical database. Tissue samples were histopathologically examined with use of hematoxylin and eosin staining, and immunohistochemical analysis of SSTR2A expression was performed.

RESULTS

Forty-three tissue samples were obtained from 26 patients. Nine showed strong positivity for SSTR2A expression, whereas 13 showed moderate and 15 sparse expression. Three samples showed no expression of SSTR2A. The distribution showed right-skewedness favoring a strong expression. SSTR2A expression colocalized with endothelial markers and not with stromal cells. Additionally, within-patient variability for SSTR2A expression was described in 14 patients.

CONCLUSION

SSTR2A is expressed in varying degrees in the majority of VHL-related hemangioblastomas. Future treatment with somatostatin analogues or even peptide receptor radionuclide treatment may be considered for SSTR2A-positive cases.

The State-of-the-Art Mechanisms and Antitumor Effects of Somatostatin in Colorectal Cancer: A Review

Somatostatin, a somatotropin release inhibiting factor (SST, SRIF), is a widely distributed multifunctional cyclic peptide and acts through a transmembrane G protein-coupled receptor (SST1-SST5). Over the past decades, research has begun to reveal the molecular mechanisms underlying the anticancer activity of this hormonal peptide. Among gastrointestinal tract (GIT) tumors, direct and indirect antitumor effects of SST have been documented best in gastroenteropancreatic neuroendocrine tumors (GEP-NETs) and less well in non-endocrine cancers, including sporadic colorectal cancer (CRC). In the latter, the signaling pathways involved in the antitumor function of SST are primarily MAPK/ERK/AKT and Wnt/β-catenin. Direct (involving the MAPK pathway) and indirect (VEGF production) antiangiogenic effects of SST in CRC have also been described. The anti-inflammatory role of SST in CRC is emphasized, but detailed molecular mechanisms are still being explored. The role of SST in tumor genome/tumor microenvironment (TME)/host's gut microbiome interactions is only partially known. The results of SST analogues (SSAs)' treatment of sporadic CRC in monotherapy in vivo are not spectacular. The current review aims to present the state-of-the-art mechanisms and antitumor activity of endogenous SST and its synthetic analogues in CRC, with particular emphasis on sporadic CRC.

False-Positive Uptake in Splenic Hemangioma on 68 Ga-DOTATATE PET/CT

ABSTRACT

Somatostatin receptor imaging using 68 Ga-DOTATATE PET is widely popular for evaluation of neuroendocrine tumors. 68 Ga-DOTATATE PET/CT shows highest physiologic uptake in spleen followed by other organs such as kidneys, adrenal glands, and liver. Hemangiomas, although rare, are the most common primary benign neoplasm of the spleen, composed of endothelial-lined vascular channels. We present a case of 77-year-old man who underwent 68 Ga-DOTATATE PET/CT scan for evaluation of pancreatic neuroendocrine tumor and incidentally demonstrated intense radiotracer uptake in splenic hemangiomata.

Unusual 68 Ga-DOTATATE Uptake in Primary Nodal Hemangioma of Axillary Lymph Node

ABSTRACT

68 Ga-DOTATATE PET/CT is a well-known modality in diagnosis, staging, and in predicting therapy response of neuroendocrine tumors. We present a case of 63-year-old woman with diagnosis of pancreas neuroendocrine tumor showing 68 Ga-DOTATATE uptake in a lymph node in left axilla. It was diagnosed as capillary hemangioma after biopsy. 68 Ga-DOTATATE uptake in bone hemangiomas is well-known; however, its uptake in a nodal hemangioma is worth to know as it might change the clinical perspective.

Evolving role of seneca valley virus and its biomarker TEM8/ANTXR1 in cancer therapeutics

Oncolytic viruses have made a significant inroad in cancer drug development. Numerous clinical trials are currently investigating oncolytic viruses both as single agents or in combination with various immunomodulators. Oncolytic viruses (OV) are an integral pillar of immuno-oncology and hold potential for not only delivering durable anti-tumor responses but also converting “cold” tumors to “hot” tumors. In this review we will discuss one such promising oncolytic virus called Seneca Valley Virus (SVV-001) and its therapeutic implications. SVV development has seen seismic evolution over the past decade and now boasts of being the only OV with a practically applicable biomarker for viral tropism. We discuss relevant preclinical and clinical data involving SVV and how bio-selecting for TEM8/ANTXR1, a negative tumor prognosticator can lead to first of its kind biomarker driven oncolytic viral cancer therapy.

Systematic Review: Targeted Molecular Imaging of Angiogenesis and Its Mediators in Rheumatoid Arthritis

Extensive angiogenesis is a characteristic feature in the synovial tissue of rheumatoid arthritis (RA) from a very early stage of the disease onward and constitutes a crucial event for the development of the proliferative synovium. This process is markedly intensified in patients with prolonged disease duration, high disease activity, disease severity, and significant inflammatory cell infiltration. Angiogenesis is therefore an interesting target for the development of new therapeutic approaches as well as disease monitoring strategies in RA. To this end, nuclear imaging modalities represent valuable non-invasive tools that can selectively target molecular markers of angiogenesis and accurately and quantitatively track molecular changes in multiple joints simultaneously. This systematic review summarizes the imaging markers used for single photon emission computed tomography (SPECT) and/or positron emission tomography (PET) approaches, targeting pathways and mediators involved in synovial neo-angiogenesis in RA.

Structural insights into the activation of somatostatin receptor 2 by cyclic SST analogues

The endogenous cyclic tetradecapeptide SST14 was reported to stimulate all five somatostatin receptors (SSTR1-5) for hormone release, neurotransmission, cell growth arrest and cancer suppression. Two SST14-derived short cyclic SST analogues (lanreotide or octreotide) with improved stability and longer lifetime were developed as drugs to preferentially activate SSTR2 and treat acromegalia and neuroendocrine tumors. Here, cryo-EM structures of the human SSTR2-Gi complex bound with SST14, octreotide or lanreotide were determined at resolutions of 2.85 Å, 2.97 Å, and 2.87 Å, respectively. Structural and functional analysis revealed that interactions between β-turn residues in SST analogues and transmembrane SSTR2 residues in the ligand-binding pocket are crucial for receptor binding and functional stimulation of the two SST14-derived cyclic octapeptides. Additionally, Q1022.63, N2766.55, and F2947.35 could be responsible for the selectivity of lanreotide or octreotide for SSTR2 over SSTR1 or SSTR4. These results provide valuable insights into further rational development of SST analogue drugs targeting SSTR2.

Suspicious cold thyroid nodule with intense focal 68Ga-DOTATATE uptake: a case report

A 51-year-old male was found with bilateral thyroid nodules on ultrasonography neck imaging. The largest nodule, measuring 23 × 26 × 35 mm, was located in the left lobe and was classified as EU-TIRADS 4. Thyroid function tests were normal, as were serum levels of parathormone, Chromogranin A, carcinoembryonic antigen and calcitonin. The nodule was cold on thyroid scintigraphy. Fine-needle aspiration of the nodule did not demonstrate cellular atypia. High focal uptake was found on both ¹¹¹In-DTPA-octreotide scintigraphy and ⁶⁸Ga-DOTATATE PET/CT. Histopathological analysis showed a microfollicular adenoma without malignancy. Immunohistochemical staining did not suggest neuroendocrine neoplasia or C cell hyperplasia. However, high expression of somatostatin receptor 2 (SSTR2) was observed in the microfollicular adenoma compared to the surrounding healthy tissue, with predominant localization in the endothelial cells and at the secretory pole of the thyroid epithelial cells in contact with blood vessels. High focal thyroid uptake on ⁶⁸Ga-DOTATATE PET/CT can be observed in benign thyroid nodules due to an overexpression of SSTR by endothelial cells. However, incidental focal thyroid uptake on SSTR imaging requires further investigations to rule out thyroid malignancy.

68 Ga DOTANOC PET/CT Scan in Primary Juvenile Nasopharyngeal Angiofibroma - A Pilot Study

OBJECTIVES/HYPOTHESIS

Somatostatin receptors (SSTRs) are highly expressed in neuroendocrine tumors and is exploited for its imaging and treatment. SSTRs expression is also demonstrated in diverse benign and malignant tumor cell types and proliferating peri-tumoral vessels. Similarly, Juvenile Nasopharyngeal Angiofibroma (JNA) expresses different SSTRs and may be utilized for its imaging and treatment using DOTA, 1-Nal3-octreotide (DOTANOC)-PET/CT scan.

STUDY DESIGN

Prospective cohort.

METHODS

Nineteen clinico-radiologically diagnosed primary JNA patients underwent a 68 Ga-DOTANOC PET-CT scan. Using a dedicated PET/CT scanner, a low-dose head and neck spot CT scan was performed after 45 to 60 minutes of intravenous injection of 2 to 3 mCi(74-111 MBq) of DOTANOC. The primary objective was to assess the intensity and pattern of DOTANOC uptake in these patients.

RESULTS

DOTANOC expression was noted in all cases (n = 19) of primary JNA (100%). The mean (SD) DOTANOC SUVmax ratio of tumor and background was 6.9+/-1.4(range, 3.8-9.5). Intra-cranial extension in all 13/19 patients was prominently visualized due to the absence of DOTANOC uptake in the brain. Compared to the background all stages of JNA showed significant DOTANOC uptake (P < .0001). No difference in uptake between advanced-stage tumors and early tumors was noted (P = .47). A statistically non-significant negative trend was noted for decreasing uptake with increasing age (Spearman correlation coefficient, r = -0.19).

CONCLUSIONS

This first study of 68 Ga-DOTANOC-PET/CT scan in JNA demonstrates consistent and reliable uptake activity in all patients irrespective of age and stage. This opens up possibilities to physiological diagnostic imaging with a promise of greater specificity and sensitivity and may have applications in ambivalent diagnostic situations such as the detection of recurrence.

LEVEL OF EVIDENCE

3 Laryngoscope, 131:1509-1515, 2021.

The impact of SST2 trafficking and signaling in the treatment of pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (Pan-NETs), are heterogeneous neoplasms, whose incidence and prevalence are increasing worldwide. Pan-NETs are characterized by the expression of somatostatin receptors (SSTs). In particular, SST2 is the most widely distributed SST in NETs, thus representing the main molecular target for somatostatin analogs (SSAs). SSAs are currently approved for the treatment of well-differentiated NETs, and radionuclide-labeled SSAs are used for diagnostic and treatment purposes. SSAs, by binding to SSTs, have been shown to inhibit hormone secretion and thus provide control of hypersecretion symptoms, when present, and inhibit tumor proliferation. After SSA binding to SST2, the fate of the receptor is determined by trafficking mechanisms, crucial for the response to endogenous or pharmacological ligands. Although SST2 acts mostly through G protein-dependent mechanism, receptor-ligand complex endocytosis and receptor trafficking further regulate its function. SST2 mediates the decrease of hormone secretion via a G protein-dependent mechanism, culminating with the inhibition of adenylyl cyclase and calcium channels; it also inhibits cell proliferation and increases apoptosis through the modulation of protein tyrosine phosphatases. Moreover, SST2 inhibits angiogenesis and cell migration. In this respect, the cross-talk between SST2 and its interacting proteins, including Filamin A (FLNA) and aryl hydrocarbon receptor-interacting protein (AIP), plays a crucial role for SST2 signaling and responsiveness to SSAs. This review will focus on recent studies from our and other groups that have investigated the trafficking and signaling of SST2 in Pan-NETs, in order to provide insights into the mechanisms underlying tumor responsiveness to pharmacological treatments.

Pharmacokinetic analysis of [68Ga]Ga-DOTA-TOC PET in meningiomas for assessment of in vivo somatostatin receptor subtype 2

PURPOSE

DOTA-D-Phe¹-Tyr³-octreotide with gallium-68 ([⁶⁸Ga]Ga-DOTA-TOC) is one of the PET tracers that forms the basis for peptide receptor radionuclide therapy based on somatostatin receptor subtype 2 (SSTR2) expression in meningiomas. Yet, the quantitative relationship between [⁶⁸Ga]Ga-DOTA-TOC accumulation and SSTR2 is unknown. We conducted a correlative analysis of a range of [⁶⁸Ga]Ga-DOTA-TOC PET metric(s) as imaging surrogate(s) of the receptor binding in meningiomas by correlating the PET results with SSTR2 expression from surgical specimens. We additionally investigated possible influences of secondary biological factors such as vascularization, inflammation and proliferation.

METHODS

Fifteen patients with MRI-presumed or recurrent meningiomas underwent a 60-min dynamic [⁶⁸Ga]Ga-DOTA-TOC PET/CT before surgery. The PET data comprised maximum and mean standardized uptake values (SUV_max, SUV_mean) with and without normalization to reference regions, and quantitative measurements derived from kinetic modelling using a reversible two-tissue compartment model with the fractional blood volume (V_B). Expressions of SSTR2 and proliferation (Ki-67, phosphohistone-H3, proliferating cell nuclear antigen) were determined by immunohistochemistry and/or quantitative polymerase chain reaction (qPCR), while biomarkers of vascularization (vascular endothelial growth factor A (VEGFA), endothelial marker CD34) and inflammation (cytokine interleukin-18, microglia/macrophage-specific marker CD68) by qPCR.

RESULTS

Histopathology revealed 12 World Health Organization (WHO) grade I and three WHO grade II meningiomas showing no link to SSTR2. The majority of [⁶⁸Ga]Ga-DOTA-TOC PET metrics showed significant associations with SSTR2 protein, while all PET metrics were positively correlated with SSTR2 mRNA with the best results for mean tumour-to-blood ratio (TBR_mean) (r = 0.757, P = 0.001) and SUV_mean (r = 0.714, P = 0.003). Significant positive correlations were also found between [⁶⁸Ga]Ga-DOTA-TOC PET metrics, and VEGFA and V_B. SSTR2 mRNA was moderately correlated with VEGFA (r = 0.539, P = 0.038). Neither [⁶⁸Ga]Ga-DOTA-TOC PET metrics nor SSTR2 were correlated with proliferation or inflammation.

CONCLUSION

[⁶⁸Ga]Ga-DOTA-TOC accumulation in meningiomas is associated with SSTR2 binding and vascularization with TBR_mean being the best PET metric for assessing SSTR2.

Effects of somatostatin analog treatment on cardiovascular parameters in patients with acromegaly: A systematic review

Background:

There is a belief that in patients with acromegaly, first-generation somatostatin analogs (SSAs) might improve cardiovascular (CV) structure and function. However, most published clinical trials involved only a few patients and their results are rather variable. We aimed to conduct a systematic review on available studies on the impact of these drugs on CV parameters.

Materials and Methods:

A literature search was conducted in MEDLINE (OVID), EMBase, Cochrane, and ISI Web of Science for citations published until April 30 2018 to identify studies on our objective that considered changes in CV parameters. For this search, we established a Boolean search strategy using keywords related to “acromegaly,” “Somatostatin analog,” and “cardiovascular diseases and parameters.” All study types except for case reports or conference abstracts were included. Twenty-four studies (n = 558) fulfilled the inclusion criteria and were selected for final analysis.

Results:

In 12 studies (n = 350), decrease in heart rate (HR) and in 4 studies (n = 128), decrease in blood pressure (BP) was significant. In 15 studies (n = 320), left ventricular mass index (LVMi) changes were significant. In 9 studies (n = 202), the early diastole to peak velocity flow in late diastole (E/A ratio) was evaluated, and in 5 of them (n = 141), the improvement was significant. Eighteen studies (n = 366) examined changes in left ventricular ejection fraction (LVEF), 5 of which (n = 171) reported that these changes were significant. Decrease of left ventricular end-diastolic diameter was reported in only 2 studies (n = 27).

Conclusion:

We found that first-generation SSAs have a beneficial effect on cardiac parameters such as HR and LVMi. For other parameters such as LVEF, BP, LV diameter, and E/A ratio, we were not able to draw a firm conclusion.

PEGylated trimethylchitosan emulsomes conjugated to octreotide for targeted delivery of sorafenib to hepatocellular carcinoma cells of HepG2

The current study aimed to develop PEGylated trimethyl chitosan (TMC) coated emulsomes (EMs) conjugated with octreotide for targeted delivery of sorafenib to hepatocellular carcinoma cells (HCC) of HepG2. Sorafenib loaded TMC coated EMs were prepared by the emulsion evaporation method and characterized concerning particle size, zeta potential, drug encapsulation efficiency, and in vitro drug release. Synthesized EMs were then conjugated to octreotide. The cytotoxicity of the targeted and non-targeted EMs was determined by cellular uptake and MTT assay on HepG2 cell. Cell cycle assay was also studied using flow cytometry. The results showed the optimized EMs had the particle size of 127 nm, zeta potential of -5.41 mV, loading efficiency of 95%, and drug release efficiency of 62% within 52 h. Octreotide was attached efficiently to the surface of EMs as much as 71%. MTT assay and cellular uptake studies showed that targeted EMs had more cytotoxicity than free sorafenib and non-targeted EMs. Cell cycle analyses revealed that there was a significant more accumulation of targeted EMs treated HepG2 cells in the G1 phase than free sorafenib and non-targeted EMs. The results indicate that designed EMs may be promising for the treatment of hepatocellular carcinoma.

Boosting Antitumor Drug Efficacy with Chemically Engineered Multidomain Proteins

A facile chemical approach integrating supramolecular chemistry, site-selective protein chemistry, and molecular biology is described to engineer synthetic multidomain protein therapeutics that sensitize cancer cells selectively to significantly enhance antitumor efficacy of existing chemotherapeutics. The desired bioactive entities are assembled via supramolecular interactions at the nanoscale into structurally ordered multiprotein complexes comprising a) multiple copies of the chemically modified cyclic peptide hormone somatostatin for selective targeting and internalization into human A549 lung cancer cells expressing SST-2 receptors and b) a new cysteine mutant of the C3bot1 (C3) enzyme from Clostridium botulinum, a Rho protein inhibitor that affects and influences intracellular Rho-mediated processes like endothelial cell migration and blood vessel formation. The multidomain protein complex, SST3-Avi-C3, retargets C3 enzyme into non-small cell lung A549 cancer cells and exhibits exceptional tumor inhibition at a concentration ≈100-fold lower than the clinically approved antibody bevacizumab (Avastin) in vivo. Notably, SST3-Avi-C3 increases tumor sensitivity to a conventional chemotherapeutic (doxorubicin) in vivo. These findings show that the integrated approach holds vast promise to expand the current repertoire of multidomain protein complexes and can pave the way to important new developments in the area of targeted and combination cancer therapy.

Somatostatin receptor staining in FFPE sections using a ligand derivative dye as an alternative to immunostaining

The confirmation of target expression in tissues is a prerequisite for molecular-targeted therapy. However, difficulties are sometimes associated with the production of appropriate antibodies against receptors. We herein developed a ligand derivative dye for the staining of receptors. The somatostatin receptor (sstr) was selected as the target and FITC-octreotate as the detective agent. We performed a blot analysis to detect sstr in the transfer membrane. The sstr2 recombinant protein or cell lysate from a small cell lung carcinoma cell line (H69) was boiled and loaded onto SDS-PAGE, and the proteins were transferred to a membrane. Even after denaturing processes, FITC-octreotate still bound sstr on the membrane. Furthermore, FITC-octreotate depicted the expression of sstr in formalin-fixed and paraffin-embedded (FFPE) sections, a method that we named ligand derivative staining (LDS). The accuracies of immunostaining and LDS were compared at the points of the detection of sstr using FFPE sections of 30 neuroendocrine tumor specimens. The sensitivity of LDS was 81.8%, while those of immunostaining using anti-sstr2 and sstr5 antibodies were 72.7% and 63.6%, respectively. Thus, LDS appears to be superior to immunostaining. A ligand derivative may be used as a substitute for antibodies, and has the potential to support economical, simple, and accurate detection methods.

Octreotide therapy in meningiomas: in vitro study, clinical correlation, and literature review

OBJECTIVE Meningiomas express somatostatin receptor subtype 2 (SST2), which is targeted by the somatostatin analog octreotide. However, to date, using somatostatin analog therapy for the treatment of these tumors in clinical practice has been debated. This study aims to clarify the in vitro effects of octreotide on meningiomas for precise clinical applications. METHODS The effects of octreotide were analyzed in a large series of 80 meningiomas, including 31 World Health Organization (WHO) Grade II and 4 WHO Grade III tumors, using fresh primary cell cultures to study the impact on cell viability, apoptosis, and signal transduction pathways. RESULTS SST2 mRNA was detected in 100% of the tested meningiomas at levels similar to those observed in other SST2-expressing tumors, neuroendocrine tumors, or pituitary adenomas. Octreotide significantly decreased cell proliferation in 88% of meningiomas but did not induce cell death. On average, cell proliferation was more inhibited in the meningioma group expressing a high level of SST2 than in the low-SST2 group. Moreover, octreotide response was positively correlated to the level of merlin protein and inversely correlated to the level of phosphorylated p70-S6 kinase, a downstream effector of the PI3K/Akt/mammalian target of rapamycin (mTOR) pathway. Octreotide inhibited Akt phosphorylation and activated tyrosine phosphatase without impacting the extracellular regulated kinase (ERK) pathway. CONCLUSIONS Octreotide acts exclusively as an antiproliferative agent and does not promote apoptosis in meningioma in vitro. Therefore, in vivo, octreotide is likely to limit tumor growth rather than induce tumor shrinkage. A meta-analysis of the literature reveals an interest in octreotide for the treatment of WHO Grade I tumors, particularly those in the skull base for which the 6-month progression-free survival level reached 92%. Moreover, somatostatin analogs, which are well-tolerated drugs, could be of interest for use as co-targeting therapies for aggressive meningiomas.

Paclitaxel-loaded solid lipid nanoparticles modified with Tyr-3-octreotide for enhanced anti-angiogenic and anti-glioma therapy

Somatostatin receptors (SSTRs) especially subtype 2 (SSTR2) are overexpressed in glioma. By taking advantage of the specific expression of SSTR2 on both glioma neovasculature endothelial cells and glioma cells, we constructed Tyr-3-octreotide (TOC)-modified solid lipid nanoparticles (SLN) loaded with paclitaxel (PTX) to enable tumor neovasculature and tumor cells dual-targeting chemotherapy. In this work, a TOC-polyethylene glycol-lipid (TOC-PEG-lipid) was successfully synthesized and used as a targeting molecule to enhance anticancer efficacy of PTX loaded sterically stabilized lipid nanoparticles. The prepared PTX-loaded SLN modified with TOC (PSM) was characterized by standard methods. In rat C6 glioma cells, PSM improved PTX induced apoptosis. Both tube formation assay and CD31 staining of treated orthotopic glioma tissues confirmed that PSM significantly improved the antiangiogenic ability of PTX in vitro and in vivo, respectively. Radiolabelled PSM achieved a much higher and specific accumulation within the glioma as suggested by the biodistribution and imaging studies. Furthermore, PSM exhibited improved anti-glioma efficacy over unmodified nanoparticles and Taxol in both subcutaneous and orthotopic tumor models. These findings collectively indicate that PSM holds great potential in improving the efficacy of anti-glioma therapy.

STATEMENT OF SIGNIFICANCE

Somatostatin receptors (SSTRs) especially subtype 2 (SSTR2) are overexpressed in various mammalian cancer cells. Proliferating endothelial cells of neovasculature also express SSTR2. Tyr-3-octreotide (TOC) is a known ligand for SSTR2. We have successfully prepared paclitaxel-loaded solid lipid nanoparticles modified with TOC (PSM) having diameter less than 100nm. We found that PSM improved anti-cancer efficacy of paclitaxel in SSTR2 positive glioma of rats. This improved anti-glioma efficiency of PSM can be attributed to dual-targeting (i.e. tumor cell and neovasculature targeting) efficiency of PSM and promoted anti-cancer drug accumulation at tumor site due to TOC modification of solid lipid nanoparticles. This particular study aims at widening the scope of octreotide-derivative modified nanocarrier by exploring dual-targeting potential of PSM.

Expression of Somatostatin Receptors 1-5 and Dopamine Receptor 2 in Lung Carcinoids: Implications for a Therapeutic Role

OBJECTIVE

The expression of somatostatin receptors (SSTRs) and dopamine receptor 2 (DR2) in neuroendocrine tumors is of clinical importance as somatostatin analogues and dopamine agonists can be used for their localization and/or treatment. The objective of this study is to examine the expression of the five SSTR subtypes and DR2 in lung carcinoids (LCs).

METHODS

We conducted a retrospective study of 119 LCs from 106 patients [typical carcinoids (TCs): n = 100, and atypical carcinoids (ACs): n = 19]. The expression of all five SSTR subtypes and DR2 was evaluated immunohistochemically and correlated to clinicopathological data. In a subgroup of cases, receptor expression was further analyzed using semiquantitative RT-PCR.

RESULTS

SSTR2A was the SSTR subtype most frequently expressed immunohistochemically (72%), followed by SSTR1 (63%), SSTR5 (40%), and SSTR3 (20%), whereas SSTR4 was negative. DR2 was expressed in 74% and co-expressed with SSTR1 in 56%, with SSTR2A in 59%, with SSTR3 in 19%, and with SSTR5 in 37% of the tumors. Receptor expression was not related to the histological subtype, tumor aggressiveness (disease extent/grading) or functionality; however, DR2 was expressed more frequently in ACs than TCs (95 vs. 70%, p = 0.017). In a subset of patients, RT-PCR findings highly suggested that the expression of SSTR2A, SSTR3, DR2, and to a lesser extent that of SSTR1 and SSTR5 is the outcome of increased gene transcription.

CONCLUSIONS

The high and variable immunohistochemical expression of the majority of SSTRs along with their co-expression with DR2 in LCs provides a rationale for their possible treatment with agents that target these receptors.

The GH-IGF-SST system in hepatocellular carcinoma: biological and molecular pathogenetic mechanisms and therapeutic targets

Hepatocellular carcinoma (HCC) is the sixth most common malignancy worldwide. Different signalling pathways have been identified to be implicated in the pathogenesis of HCC; among these, GH, IGF and somatostatin (SST) pathways have emerged as some of the major pathways implicated in the development of HCC. Physiologically, GH-IGF-SST system plays a crucial role in liver growth and development since GH induces IGF1 and IGF2 secretion and the expression of their receptors, involved in hepatocytes cell proliferation, differentiation and metabolism. On the other hand, somatostatin receptors (SSTRs) are exclusively present on the biliary tract. Importantly, the GH-IGF-SST system components have been indicated as regulators of hepatocarcinogenesis. Reduction of GH binding affinity to GH receptor, decreased serum IGF1 and increased serum IGF2 production, overexpression of IGF1 receptor, loss of function of IGF2 receptor and appearance of SSTRs are frequently observed in human HCC. In particular, recently, many studies have evaluated the correlation between increased levels of IGF1 receptors and liver diseases and the oncogenic role of IGF2 and its involvement in angiogenesis, migration and, consequently, in tumour progression. SST directly or indirectly influences tumour growth and development through the inhibition of cell proliferation and secretion and induction of apoptosis, even though SST role in hepatocarcinogenesis is still opened to argument. This review addresses the present evidences suggesting a role of the GH-IGF-SST system in the development and progression of HCC, and describes the therapeutic perspectives, based on the targeting of GH-IGF-SST system, which have been hypothesised and experimented in HCC.

Somatostatin analogues for receptor targeted photodynamic therapy

Photodynamic therapy (PDT) is an established treatment modality, used mainly for anticancer therapy that relies on the interaction of photosensitizer, light and oxygen. For the treatment of pathologies in certain anatomical sites, improved targeting of the photosensitizer is necessary to prevent damage to healthy tissue. We report on a novel dual approach of targeted PDT (vascular and cellular targeting) utilizing the expression of neuropeptide somatostatin receptor (sst₂) on tumor and neovascular-endothelial cells. We synthesized two conjugates containing the somatostatin analogue [Tyr3]-octreotate and Chlorin e6 (Ce6): Ce6-K₃-[Tyr3]-octreotate (1) and Ce6-[Tyr3]-octreotate-K₃-[Tyr3]-octreotate (2). Investigation of the uptake and photodynamic activity of conjugates in-vitro in human erythroleukemic K562 cells showed that conjugation of [Tyr3]-octreotate with Ce6 in conjugate 1 enhances uptake (by a factor 2) in cells over-expressing sst₂ compared to wild-type cells. Co-treatment with excess free Octreotide abrogated the phototoxicity of conjugate 1 indicative of a specific sst₂-mediated effect. In contrast conjugate 2 showed no receptor-mediated effect due to its high hydrophobicity. When compared with un-conjugated Ce6, the PDT activity of conjugate 1 was lower. However, it showed higher photostability which may compensate for its lower phototoxicity. Intra-vital fluorescence pharmacokinetic studies of conjugate 1 in rat skin-fold observation chambers transplanted with sst₂⁺ AR42J acinar pancreas tumors showed significantly different uptake profiles compared to free Ce6. Co-treatment with free Octreotide significantly reduced conjugate uptake in tumor tissue (by a factor 4) as well as in the chamber neo-vasculature. These results show that conjugate 1 might have potential as an in-vivo sst₂ targeting photosensitizer conjugate.

Feasibility of experimental BT4C glioma models for somatostatin receptor 2-targeted therapies

Somatostatin receptor subtype 2 (sstr2) is regarded as a potential target in malignant gliomas for new therapeutic approaches. Therefore, visualizing and quantifying tumor sstr2 expression in vivo would be highly relevant for the future development of sstr2-targeted therapies. The purpose of this study was to evaluate sstr2 status in experimental BT4C malignant gliomas.

METHODS

Rat BT4C malignant glioma cells were injected into BDIX rat brain or subcutaneously into nude mice. Tumor uptake of [(68)Ga]DOTA-(Tyr(3))-Octreotide ([(68)Ga]DOTATOC), a somatostatin analog binding to sstr2, was studied by positron emission tomography/computed tomography (PET/CT). Additionally, subcutaneous tumor-bearing mice underwent PET imaging with 5-deoxy-5-[(18)F]fluororibose-NOC ([(18)F]FDR-NOC), a novel glycosylated peptide tracer also targeting sstr2. Ex vivo tissue radioactivity measurements, autoradiography and immunohistochemistry were performed to study sstr2 expression.

RESULTS

Increased tumor uptake of [(68)Ga]DOTATOC was detected at autoradiography with mean tumor-to-brain ratio of 68 ± 30 and tumor-to-muscle ratio of 9.2 ± 3.8 for rat glioma. High tumor-to-muscle ratios were also observed in subcutaneous tumor-bearing mice after injection with [(68)Ga]DOTATOC and [(18)F]FDR-NOC with both autoradiography (6.7 ± 1.5 and 4.3 ± 0.8, respectively) and tissue radioactivity measurements (6.5 ± 0.8 and 4.8 ± 0.6, respectively). Furthermore, sstr2 immunohistochemistry showed positive staining in both tumor models. However, surprisingly low tumor signal compromised PET imaging. Mean SUVmax for rat gliomas was 0.64 ± 0.28 from 30 to 60 min after [(68)Ga]DOTATOC injection. The majority of subcutaneous tumors were not visualized by [(68)Ga]DOTATOC or [(18)F]FDR-NOC PET.

CONCLUSIONS

Experimental BT4C gliomas show high expression of sstr2. Weak signal in PET imaging, however, suggests only limited benefit of [(68)Ga]DOTATOC or [(18)F]FDR-NOC PET/CT in this tumor model for in vivo imaging of sstr2 status.

Vascular targeting to the SST2 receptor improves the therapeutic response to near-IR two-photon activated PDT for deep-tissue cancer treatment

BACKGROUND

Broader clinical acceptance of photodynamic therapy is currently hindered by (a) poor depth efficacy, and (b) predisposition towards establishment of an angiogenic environment during the treatment. Improved depth efficacy is being sought by exploiting the NIR tissue transparency window and by photo-activation using two-photon absorption (2PA). Here, we use two-photon activation of PDT sensitizers, untargeted and targeted to SST2 receptors or EGF receptors, to achieve deep tissue treatment.

METHODS

Human tumor lines, positive or negative for SST2r expression were used, as well as murine 3LL cells and bovine aortic endothelial cells. Expression of SST2 receptors on cancer cells and tumor vasculature was evaluated in vitro and frozen xenograft sections. PDT effects on tumor blood flow were followed using in vivo scanning after intravenous injection of FITC conjugated dextran 150K. Dependence of the PDT efficacy on the laser pulse duration was evaluated. Effectiveness of targeting to vascular SST2 receptors was compared to that of EGF receptors, or no targeting.

RESULTS

Tumor vasculature stained for SST2 receptors even in tumors from SST2 receptor negative cell lines, and SST2r targeted PDT led to tumor vascular shutdown. Stretching the pulse from ~120fs to ~3ps led to loss of the PDT efficacy especially at greater depth. PDT targeted to SST2 receptors was much more effective than untargeted PDT or PDT targeted to EGF receptors.

GENERAL SIGNIFICANCE

The use of octreotate to target SST2 receptors expressed on tumor vessels is an excellent approach to PDT with few recurrences and some long term cures.

Somatostatin subtype-2 receptor-targeted metal-based anticancer complexes

Conjugates of a dicarba analogue of octreotide, a potent somatostatin agonist whose receptors are overexpressed on tumor cells, with [PtCl(2)(dap)] (dap = 1-(carboxylic acid)-1,2-diaminoethane) (3), [(η(6)-bip)Os(4-CO(2)-pico)Cl] (bip = biphenyl, pico = picolinate) (4), [(η(6)-p-cym)RuCl(dap)](+) (p-cym = p-cymene) (5), and [(η(6)-p-cym)RuCl(imidazole-CO(2)H)(PPh(3))](+) (6), were synthesized by using a solid-phase approach. Conjugates 3-5 readily underwent hydrolysis and DNA binding, whereas conjugate 6 was inert to ligand substitution. NMR spectroscopy and molecular dynamics calculations showed that conjugate formation does not perturb the overall peptide structure. Only 6 exhibited antiproliferative activity in human tumor cells (IC(50) = 63 ± 2 μM in MCF-7 cells and IC(50) = 26 ± 3 μM in DU-145 cells) with active participation of somatostatin receptors in cellular uptake. Similar cytotoxic activity was found in a normal cell line (IC(50) = 45 ± 2.6 μM in CHO cells), which can be attributed to a similar level of expression of somatostatin subtype-2 receptor. These studies provide new insights into the effect of receptor-binding peptide conjugation on the activity of metal-based anticancer drugs, and demonstrate the potential of such hybrid compounds to target tumor cells specifically.

Large fat and skin necroses after deep subcutaneous injections of a slow-release somatostatin analogue in a woman with acromegaly

OBJECTIVE

Somatostatin analogues are the most commonly used drugs for treatment of acromegaly. Known side effects include gastrointestinal reactions, cholelithiasis, effects on glucose metabolism, and mild reactions at injection sites. We report a patient who developed fat and skin necroses after injections of a depot somatostatin analogue.

SUBJECT

A woman with active acromegaly was given deep subcutaneous injections of an extended release formulation of lanreotide at alternate sides of the buttocks on three occasions over a ten week period. The regimen was then discontinued due to gastrointestinal complaints. One month later indurated subcutaneous nodules appeared at both sites. After another two months, the patient presented 10×10 cm lesions on the buttocks, with central erythematous zones and, at the site of two injections, a necrotic 5×3 cm ulcer. There were no signs of infection or systemic diseases. MRI revealed bilateral fat necroses. A month later, an ulcer developed at the second site. The ulcers were managed conservatively until clear demarcations were obtained, where after surgical revisions were performed. Eight months after the last injection, the wounds could be closed.

CONCLUSION

The fat and skin necroses represent a side-effect not previously described after deep subcutaneous injections. Possibly, the patient had an exceptional susceptibility to develop an inflammatory, foreign-body like reaction that hypothetically was aggravated by a sustained anti-angiogenic effect of the compound.

The role of angiogenesis in neuroendocrine tumors

The first studies to assess in vitro angiogenesis in neuroendocrine tumors used animal-based assays to study the antiangiogenic properties of somatostatin analogs. Current technologies enable investigators to directly appraise the in vitro angiogenic response of an individual's neuroendocrine tumor with and without potential antiangiogenic reagents. This article describes the evolution of methods to assess in vitro angiogenesis in neuroendocrine tumors and describes some of the clinical data.

Neuroendocrine tumors: a critical appraisal of management strategies

OBJECTIVES

This supplement represents the proceedings of a panel of investigators whose goal was to assess the quality of evidence pertaining to current therapeutic approaches in the management of neuroendocrine tumors (NETs). It will examine the differences in opinions between expert faculty and community physicians.

METHODS

The Neuroendocrine Tumors Summit convened in December 2009 to address 6 statements prepared by panel members that reflect important questions in the management of NETs.

RESULTS

Panel members were polled on their acceptance of each statement, and those results were compared with community-based oncologists, gastroenterologists, and endocrinologists.

CONCLUSIONS

More education regarding the treatment of NETs, including pertinent studies, is needed for physicians. Additional multicenter, prospective, placebo-controlled trials are necessary to demonstrate the benefits of somatostatin analogs, including their ability to control symptoms and affect tumor growth, and their synergistic effect with other therapies. New trials should be reported consistently and include time to tumor progression and progression-free survival as primary or secondary end points.

Differential efficacy of SSTR1, -2, and -5 agonists in the inhibition of C6 glioma growth in nude mice

Somatostatin receptors (SSTR1-5) mediate antiproliferative effects. In C6 rat glioma cells, somatostatin is cytostatic in vitro via phosphotyrosine phosphatase-dependent inhibition of ERK1/2 activity mediated by SSTR1, -2, and -5. Here we analyzed the effects of SSTR activation on C6 glioma growth in vivo and the intracellular mechanisms involved, comparing somatostatin effects with selective agonists for SSTR1, -2, and -5 (BIM-23745, BIM-23120, BIM-23206) or receptor biselective compounds (SSTR1 and -2, BIM-23704; and SSTR2 and -5, BIM-23190). Nude mice subcutaneously xenografted with C6 cells were treated with somatostatin, SSTR agonists (50 μg, twice/day), or vehicle. Tumor growth was evaluated every 3 days for 19 days. The intracellular pathways responsible of SSTR effects in vivo were evaluated measuring Ki-67, phospho-ERK1/2, and p27(kip1) expression by immunohistochemistry in sections from explanted tumors. Somatostatin and SSTR1, -2, and -5 agonists strongly inhibited in vivo C6 tumor growth, intratumoral neovessel formation, Ki-67 expression, and ERK1/2 phosphorylation and induced upregulation of p27(Kip1), whereas only a modest activation of caspase-3 was observed. Somatostatin (acting on SSTR1, -2, and -5) displayed the highest efficacy; SSTR5 selective agonist showed a stronger effect than SSTR1 agonist, and SSTR2 agonist was less effective. On the other hand, SSTR1 and -2 agonists maximally reduced tumor neovascularization. The combined activation of SSTR1 and -2 showed a synergistic activity, reaching a higher efficacy than BIM-23206, whereas the simultaneous activation of SSTR2 and -5 resulted in a response resembling SSTR5 effects. Thus the simultaneous activation of different SSTRs inhibits glioma cell proliferation in vivo through both direct cytotostatic and antiangiogenic effects.

Targeted chemotherapy using a cytotoxic somatostatin conjugate to inhibit tumor growth and metastasis in nude mice

The major problems of traditional chemotherapy are non-selectivity and non-specificity, resulting in severe toxic side effects. Peptides are a new-generation of drug-delivery vector to increase efficacy of this therapy and avoid the resulting damage. The cytotoxic somatostatin (SST) conjugate JF-10-81 was developed by coupling camptothecin (CPT) to the N-terminus of a SST analog (JF-07-69) using an activated carbamate linker. This conjugate selectively targets somatostatin receptor subtype 2 (SSTR2) and also retains high binding affinity and rapid internalization as well as anti-proliferative activity towards various tumor cells. JF-10-81 was tested for its inhibitory activity against the growth of human tumors which included neuroblastoma (IMR32), pancreatic cancer (CFPAC-1), leukemia (MOLT-4), pancreatic carcinoid (BON) and prostate cancer (PC-3). Both SSTR2 mRNAs and proteins were detected in all these tumor cell lines. The conjugate displayed potent in vivo inhibitory activity, although some of the potency measured in in vitro experiments was lost. JF-10-81 was found to significantly inhibit growth of these SSTR-positive tumors, resulting in 87% tumor reduction in neuroblastoma IMR32 and 97% in leukemia MOLT-4 bearing animals, even inducing regression of CFPAC-1 tumors. SSTR-overexpressing BON tumors were unfortunately relatively CPT-insensitive in vitro, however, JF-10-81 again exhibited in vivo potency presumably by specifically increasing CPT concentrations inside the tumor cells so that the inhibition rate for JF-10-81 was 85%. Also, JF-10-81 was used to treat highly invasive PC-3 tumors where s.c. injections inhibited both tumor growth (almost 60% reduction) and tumor metastasis (over 70%). This conjugate demonstrated its broad and excellent anti-tumor activity by targeting SSTR2-specific tumor tissues, supporting that short peptides and their analogs may be applied as ideal drug-delivery carriers to improve the traditional chemotherapy.

Antitumor effects of somatostatin

Since its discovery three decades ago as an inhibitor of GH release from the pituitary gland, somatostatin has attracted much attention because of its functional role in the regulation of a wide variety of physiological functions in the brain, pituitary, pancreas, gastrointestinal tract, adrenals, thyroid, kidney and immune system. In addition to its negative role in the control of endocrine and exocrine secretions, somatostatin and analogs also exert inhibitory effects on the proliferation and survival of normal and tumor cells. Over the past 15 years, studies have begun to reveal some of the molecular mechanisms underlying the antitumor activity of somatostatin. This review covers the present knowledge in the antitumor effect of somatostatin and analogs and discusses the perspectives of novel clinical strategies based on somatostatin receptor sst2 gene transfer therapy.

Diagnostic targeting of colon cancer using a novel fluorescent somatostatin conjugate in a mouse xenograft model

Colorectal carcinoma is one of the more prevalent, highly malignant human tumors, occurring in about 7% of the population. However, if diagnosed and treated in its early stages, colon cancer is curable. In our study, we used a mouse xenograft model to investigate the capability of a fluorescent conjugate of a novel synthetic somatostatin (SST) analog to improve detection of human colorectal tumors that are characterized by over-expressed SST receptors. Human HT-29 colon carcinomas were induced in nude mice. After administration of the fluorescent SST conjugate, in vivo low- and high-magnification fluorescence microscopy, as well as high-resolution spectrally resolved imaging were performed, and the time-dependent biodistribution was determined quantitatively (using fiber-optic spectroscopy). Administration of the conjugate (at concentrations of 6 mg/kg body weight) enabled targeting small (1-5 mm diameter) tumors with high sensitivity and selectivity. Toxicity studies at dosages up to 1,000 mg/kg body weight did not reveal any drug related abnormalities. In conclusion, the SST conjugate significantly enhanced the detection of HT-29 colon tumors by fluorescence imaging because of a 5- to 8-fold increase in the contrast between malignant and normal tissues.

Nonclassic endogenous novel [corrected] regulators of angiogenesis

Angiogenesis, the process through which new blood vessels arise from preexisting ones, is regulated by several "classic" factors, among which the most studied are vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2). In recent years, investigations showed that, in addition to the classic factors, numerous endogenous peptides play a relevant regulatory role in angiogenesis. Such regulatory peptides, each of which exerts well-known specific biological activities, are present, along with their receptors, in the blood vessels and may take part in the control of the "angiogenic switch." An in vivo and in vitro proangiogenic effect has been demonstrated for erythropoietin, angiotensin II (ANG-II), endothelins (ETs), adrenomedullin (AM), proadrenomedullin N-terminal 20 peptide (PAMP), urotensin-II, leptin, adiponectin, resistin, neuropeptide-Y, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), and substance P. There is evidence that the angiogenic action of some of these peptides is at least partly mediated by their stimulating effect on VEGF (ANG-II, ETs, PAMP, resistin, VIP and PACAP) and/or FGF-2 systems (PAMP and leptin). AM raises the expression of VEGF in endothelial cells, but VEGF blockade does not affect the proangiogenic action of AM. Other endogenous peptides have been reported to exert an in vivo and in vitro antiangiogenic action. These include somatostatin and natriuretic peptides, which suppress the VEGF system, and ghrelin, that antagonizes FGF-2 effects. Investigations on "nonclassic" regulators of angiogenesis could open new perspectives in the therapy of diseases coupled to dysregulation of angiogenesis.

A conjugate of camptothecin and a somatostatin analog against prostate cancer cell invasion via a possible signaling pathway involving PI3K/Akt, αVβ3/αVβ5 and MMP-2/-9

Camptothecin (CPT) was conjugated to the N-terminal of a somatostatin analog (SSA) directly via a carbamate group and a basic N-terminal linking motif, D-Lys-D-Tyr-Lys-D-Tyr-D-Lys. This new CPT-SSA conjugate termed JF-10-81 was evaluated as a receptor-specific delivery system for its anti-invasive and anti-angiogenic activities. It was found that, in addition to blocking migration and invasion of highly invasive prostate cancer PC-3 cells, this conjugate also inhibited in vitro capillary-like tube formation of endothelial cells and in vivo angiogenesis in C57B1/6N female mice. JF-10-81 was found to block PC-3 cell attachment to various extracellular matrix components, mainly to vitronectin, the ligand of cell surface receptors integrin alphaVbeta3 and alphaVbeta5. Additionally, JF-10-81 reduced expression of integrins alphaVbeta3 and alphaVbeta5 on PC-3 cell surfaces, without effects on beta1 or any alphabeta1 heterodimers. This conjugate also inactivated phosphorylation of protein kinase B (PKB/Akt), down-regulated the expression of latent matrix metalloproteinase (MMP) -2 and MMP-9, but had little effect on MMP-3/-10. Meanwhile, membrane type-1 matrix metalloproteinase (MT1-MMP) and the tissue inhibitor of matrix metalloproteinase-2 (TIMP-2) were not detectable in PC-3 cells. alphaVbeta3/alphaVbeta5 and MMP-2/-9 are known to be highly expressed in many tumor cells and play an important role in tumor progression. Our results support that this conjugate could possibly inhibit prostate cancer PC-3 cell invasion through a signaling pathway involving PI3K/Akt, alphaVbeta3/alphaVbeta5 and MMP-2/-9, and this SSA could be used as an efficient vector to deliver CPT or other cytotoxic agents to target sites for cancer therapy.

Expression pattern of somatostatin receptor subtypes 1-5 in human skin: an immunohistochemical study of healthy subjects and patients with psoriasis or atopic dermatitis

In psoriasis and atopic dermatitis, the inflammatory events have neurogenic components and the neuropeptides modify the functions of immuno-active cells in the skin. Somatostatin is a neuropeptide with several neuroendocrine and immunomodulating properties and mediates its actions by five distinct subtypes of G-protein-coupled receptors (SSTR1-5). This study describes the distribution of SSTR1-5, analysed with immunohistochemistry, in psoriasis, atopic dermatitis and controls. Normal human skin and lesional skin from patients with psoriasis or atopic dermatitis showed many similarities, but also some differences, as regards SSTR expression. SSTR1-3 were strongly expressed in the epidermis of healthy skin, and in the skin of patients with psoriasis or atopic dermatitis. It is noteworthy that SSTR4 and 5 were strongly expressed in the epidermis of psoriasis patients, but weakly expressed in the epidermis of those with atopic dermatitis and normal skin. The intensity of the staining also varied considerably between the different layers of the epidermis, especially in psoriasis patients. In all cases, the dendritic cells, found mostly in the papillary and upper reticular dermis, showed a strong expression of SSTR1-4, but a weak expression of SSTR5. SSTR1-5 were strongly expressed in the sweat glands in all skin biopsies. Hair follicles and sebaceous glands expressed all five subtypes. Striated muscle fibres showed an intense positive expression of SSTR1-4, but a weak or negative expression of SSTR5. The wide distribution and expression pattern of all five SSTRs in human skin suggest that somatostatin is involved in the interactions between the nervous system and the skin.

Medical treatment of diabetic retinopathy with somatostatin analogues

Traditional management strategies for retinal neovascularisation accompanying proliferative diabetic retinopathy include photocoagulation laser therapy. The development of preventative pharmacological treatments aimed at replacing or delaying this acute intervention has been an active research area and somatostatin analogues have shown promise in reducing the progression of retinal vascular pathologies. This review summarises the present knowledge on the molecular and cellular mechanisms of neovascularisation, and the rationale for the therapeutic use of somatostatin analogues as well as the results of two key recent clinical trials using octreotide. The potential use of octreotide and other somatostatin analogues in reducing the risk of severe visual impairment in proliferative diabetic retinopathy is discussed and pharmacological treatment regimens are proposed as an additional strategy or a less invasive alternative to laser therapy.

Endocrine tumours of the gastrointestinal tract. Somatostatin receptors as tools for diagnosis and therapy: molecular aspects

Somatostatin is a neuropeptide that acts as an endogenous inhibitor of various cellular functions including endocrine and exocrine secretions and the proliferation of normal and tumour cells. Its action is mediated by a family of G-protein-coupled receptors (sst1-sst5) that are widely distributed in normal and tumour cells. Gastroenteropancreatic endocrine tumours express multiple somatostatin receptors, sst2 being clearly predominant. These receptors represent the molecular basis for the clinical use of somatostatin analogues in the treatment of endocrine tumours and their in vivo localisation. This review covers current knowledge in somatostatin receptor biology and signalling.

Somatostatin receptors 2 and 5 are preferentially expressed in proliferating endothelium

Angiogenesis is characterised by activation, migration and proliferation of endothelial cells and is central to the pathology of cancer, cardiovascular disease and chronic inflammation. Somatostatin is an inhibitory polypeptide that acts through five receptors (sst 1, 2, 3, 4, 5). Sst has previously been reported in endothelium, but their role remains obscure. Here, we report the expression of sst in human umbilical vein endothelial cells (HUVECs) in vitro, during proliferation and quiescence. A protocol for culturing proliferating and quiescent HUVECs was established, and verified by analysing cell cycle distribution in propidium-iodide-stained samples using flow cytometry. Sst mRNA was then quantified in nine proliferating and quiescent HUVEC lines using quantitative reverse transcriptase–polymerase chain reaction. Sst 2 and 5 were preferentially expressed in proliferating HUVECs. All samples were negative for sst 4. Sst 1 and 3 expression and cell cycle progression were unrelated. Immunostaining for sst 2 and 5 showed positivity in proliferating but not quiescent cells, confirming sst 2 and 5 protein expression. Inhibition of proliferating cells with somatostatin analogues Octreotide and SOM230, which have sst 5 activity, was found (Octreotide 10⁻¹⁰–10⁻⁶ M: 48.5–70.2% inhibition; SOM230 10⁻⁹–10⁻⁶ M: 44.9–65.4% inhibition) in a dose-dependent manner, suggesting that sst 5 may have functional activity in proliferation. Dynamic changes in sst 2 and 5 expression during the cell cycle and the inhibition of proliferation with specific analogues suggest that these receptors may have a role in angiogenesis.

STUDY OF INHIBITORY EFFECTS OF AN ANTIANGIOGENIC SOMATOSTATIN-CAMPTOTHECIN CONJUGATE ON LASER-INDUCED CHOROIDAL NEOVASCULARIZATION IN RATS

PURPOSE

To evaluate the ocular toxicity and efficacy of intravitreal camptothecin-somatostatin conjugate (JF-10-81), a somatostatin type 2 receptor-directed, antiangiogenic compound.

METHODS

Part 1: New Zealand albino rabbits (except for controls) were injected intravitreally with conjugate at various concentrations. Preoperative and postoperative ocular examinations and electroretinography were performed until animals were killed for histology. Part 2: Long-Evans pigmented rats had choroidal neovascularization (CNV) induced by argon laser. One eye per animal was injected with concentration 10M (safe dose), whereas the other eyes were controls and received 30 microL of sterile water at different time intervals after laser application. Fluorescein angiography was performed at various time points to evaluate the lesions and confirm presence of CNV. Animals were euthanized. The eyes were immediately enucleated and prepared for histologic examination.

RESULTS

Part 1: No clinical changes were seen in groups receiving 10(-8)M, 10(-7)M, 10(-6)M, and 10(-5) M of conjugate. Electroretinography showed decreasing b-wave amplitude in groups receiving 10(-4) M and 10(-3) M; cataracts also developed in these eyes. Part 2: Fluorescein angiography revealed that intravitreal injection of somatostatin conjugate JF-10-81 favorably affected the development of CNV when the treatment was performed at least 1 week after the laser application. These results were statistically significant. Histologic analysis results of eyes treated 2 weeks after laser application also showed significant benefit.

CONCLUSIONS

Part 1: Camptothecin-somatostatin conjugate injected intravitreally appeared safe at concentrations of 10(-5)M or less. Part 2: Conjugate JF-10-81 at a concentration of 10(-5)M administered intravitreally 1 to 3 weeks after laser demonstrated statistically significant efficacy in the treatment of choroidal neovascularization.

TNF-alpha decreases expression of somatostatin, somatostatin receptors, and cortistatin in human coronary endothelial cells

BACKGROUND

The objective of this study was to determine the expression of somatostatin (SST) and its receptors (SSTRs) and their regulation by TNF-alpha as well as cell proliferation in response to SST in human endothelial cells.

MATERIALS AND METHODS

Human coronary artery endothelial cells (HCAECs) were cultured without or with TNF-alpha (0.1, 1, or 10 ng/ml) for 24 h. The mRNA levels of SST, SSTR-1-5, as well as a housekeeping gene (beta-actin) were determined by real-time RT-PCR. Expression of SSTR-2 was also demonstrated by immunofluorescence staining. Cell proliferation in response to SST treatment (0.04, 0.2, or 1 ng/ml) was performed by [3H]thymidine incorporation.

RESULTS

Without TNF-alpha treatment, HCAECs showed mRNA expression of SST, SSTR-1, SSTR-2, and SSTR-5. The mRNA of SSTR-2 was expressed at a higher level than that of SSTR-1 and SSTR-5. However, SSTR-3 and SSTR-4 were not expressed or were minimally expressed. After treatment with TNF-alpha, the mRNA levels of SST, SSTR-1, SSTR-2, and SSTR-5 were significantly reduced in a dose-dependent fashion. TNF-alpha (1 ng/ml) reduced SST, SSTR-1, SSTR-2, and SSTR-5 by 93, 51, 85, and 99%, respectively, compared to controls (P < 0.001, t test). The immunoreactivity of SSTR-2 was also reduced after TNF-alpha treatment. SST-treated cells showed a significant reduction in [3H]thymidine incorporation in a dose-dependent manner. TNF-alpha treatment decreased SST inhibitory potential in cell proliferation.

CONCLUSIONS

HCAECs express SST, SSTR-1, SSTR-2, and SSTR-5, which are all decreased by TNF-alpha treatment. Furthermore, treatment with exogenous SST significantly reduces cell proliferation, and this inhibitory effect is also decreased by TNF-alpha.

Effects of camptothecin conjugated to a somatostatin analog vector on growth of tumor cell lines in culture and related tumors in rodents

Two CPT-SSA conjugates, JF-10-71 and JF-10-81, containing a chemically adjustable release-rate carbamate linker, have been reported previously by us to potently inhibit growth of human neuroblastoma IMR32 cells overexpressing somatostatin receptor type II (SSTR2) but are stable under buffer incubation conditions or in rat plasma. Further experiments now reveal that the conjugates performed well against many additional cell lines, particularly somatostatin receptor containing rat pancreatic CA20948 cells that were actually more sensitive to the conjugates than free camptothecin itself. JF-10-71 and JF-10-81 also were examined for their inhibitory effects on the growth of this and several other tumors transplanted into rats (CA20948) or nude mice. CA20948 tumors, known to overexpress SSTR2 and grown in Lewis rats, were treated, respectively, with nontoxic 400 nmol/kg intraperitoneal (i.p.) doses of JF-10-71 or JF-10-81. Also, SSTR2-positive human SCLC NCI-H69 tumors transplanted in nude mice were treated in a similar fashion. Human prostate PC-3 tumors, which do not contain high concentrations of SSTR2, also were grown in nude mice and treated with a 400 nmol/kg ip dose of JF-10-71. Both cytotoxic conjugates significantly inhibited growth of SSTR2-specific pancreatic and SCLC tumors, but JF-10-81 did not significantly affect PC-3 tumor growth. These experimental results suggested that CPT-SSA conjugates can effectively target and kill tumor cells growing in vivo and that the effect is mediated by somatostatin receptors resulting in either release of camptothecin at the cell surface or, more likely, after receptor-mediated cellular internalization.

Somatostatin inhibits IGF-1 mediated induction of VEGF in human retinal pigment epithelial cells

Neovascularization stimulated by IGF-1 mediated induction of vascular endothelial growth factor (VEGF) is one of the leading causes of blindness in humans. It plays a central role in the pathogenesis of proliferative diabetic retinopathy (DR), neovascular glaucoma, exudative age-related macular degeneration (AMD) and retinopathy of prematurity. Neovascularization is a multi-step process that involves complex interactions of a variety of mitogenic factors such as VEGF and IGF-I which are produced locally in the human eye by a variety of cells including retinal pigment epithelial (RPE) cells, retinal capillary pericytes, endothelial cells, Mueller cells and ganglion cells. We hypothesized that somatostatin would inhibit the IGF-1 signal transduction pathway in RPE cells, resulting in decreased VEGF production. We have observed expression of somatostatin receptor protein in retinal pigment epithelial (RPE) cells of the human eye using immunohistochemistry and have confirmed expression of somatostatin receptors in cultured human RPE cells using reverse transcriptase-PCR. IGF-1 induced a dose dependent increase in IGF-1R phosphorylation and in VEGF mRNA levels in cultured human RPE cells. Somatostatin and octreotide, a somatostatin analogue, inhibited IGF-1 receptor (IGF-1R) phosphorylation and decreased VEGF production. Both IGF-1R phosphorylation and accumulation of VEGF mRNA were inhibited by physiological levels of somatostatin and octreotide (1 nM). These results demonstrate somatostatin and octreotide mediated attenuation of both IGF-1R signal transduction and VEGF mRNA accumulation via somatostatin receptor type 2 (sst2). Furthermore, these data suggest a rationale for the use of octreotide as a prophylactic and therapeutic option in disease states that cause ocular neovascularization.

Inhibition of endothelial proliferation by the somatostatin analogue SOM230

OBJECTIVE

Somatostatin (SST) modulates exocrine and endocrine secretion, proliferation and apoptosis via five G protein-linked receptors (SSTRs 1-5). Long-acting SST analogues such as Octreotide, and the new analogue SOM230, have been developed for the treatment of neuroendocrine tumours. Octreotide has previously been reported to inhibit endothelial proliferation. We wished to determine if SOM230 is a more potent inhibitor of endothelial cell proliferation than Octreotide.

DESIGN

We have determined the expression of SSTRs in proliferating human umbilical vein endothelial cells (HUVECs) in vitro, and determined their response to the somatostatin analogues SOM230 and Octreotide, following vascular endothelial growth factor (VEGF) stimulation.

MEASUREMENTS

Quantitative RT-PCR and western blotting were used to determine the expression of SSTRs 1-5 in proliferating HUVECs. These cells were grown in media containing 200 pg/ml VEGF and treated with 10(-11) to 10(-6) M Octreotide or SOM230. The WST-1 assay was then used to determine the effects of these analogues on HUVEC proliferation.

RESULTS

Using quantitative RT-PCR and western blotting, HUVECs were found to express SSTRs 1, 2 and 5. SSTRs 3 and 4 were not detected. Using the WST-1 assay, SOM230 was found to significantly inhibit proliferation by up to 46.0% +/- 9.4% (10(-6)-10(-7) M; P < 0.05), whereas in parallel studies Octreotide failed to inhibit HUVEC proliferation.

CONCLUSIONS

The pan SST analogue SOM230 inhibits proliferation of HUVECs, which are unaffected by Octreotide. SOM230 may thus represent a suitable candidate drug for antiangiogenic therapy.