Neurotensin receptor expression in prostate cancer cell line and growth effect of NT at physiological concentrations

Chelator boosted tumor-retention and pharmacokinetic properties: development of 64Cu labeled radiopharmaceuticals targeting neurotensin receptor

PURPOSE

Accumulating evidence suggests that neurotensin (NTS) and neurotensin receptors (NTSRs) play key roles in lung cancer progression by triggering multiple oncogenic signaling pathways. This study aims to develop Cu-labeled neurotensin receptor 1 (NTSR1)-targeting agents with the potential for both imaging and therapeutic applications.

METHOD

A series of neurotensin receptor antagonists (NRAs) with variable propylamine (PA) linker length and different chelators were synthesized, including [64Cu]Cu-CB-TE2A-iPA-NRA ([64Cu]Cu-4a-c, i = 1, 2, 3), [64Cu]Cu-NOTA-2PA-NRA ([64Cu]Cu-4d), [64Cu]Cu-DOTA-2PA-NRA ([64Cu]Cu-4e, also known as [64Cu]Cu-3BP-227), and [64Cu]Cu-DOTA-VS-2PA-NRA ([64Cu]Cu-4f). The series of small animal PET/CT were conducted in H1299 lung cancer model. The expression profile of NTSR1 was also confirmed by IHC using patient tissue samples.

RESULTS

For most of the compounds studied, PET/CT showed prominent tumor uptake and high tumor-to-background contrast, but the tumor retention was strongly influenced by the chelators used. For previously reported 4e, [64Cu]Cu-labeled derivative showed initial high tumor uptake accompanied by rapid tumor washout at 24 h. The newly developed [64Cu]Cu-4d and [64Cu]Cu-4f demonstrated good tumor uptake and tumor-to-background contrast at early time points, but were less promising in tumor retention. In contrast, our lead compound [64Cu]Cu-4b demonstrated 9.57 ± 1.35, 9.44 ± 2.38 and 9.72 ± 4.89%ID/g tumor uptake at 4, 24, and 48 h p.i., respectively. Moderate liver uptake (11.97 ± 3.85, 9.80 ± 3.63, and 7.72 ± 4.68%ID/g at 4, 24, and 48 h p.i.) was observed with low uptake in most other organs. The PA linker was found to have a significant effect on drug distribution. Compared to [64Cu]Cu-4b, [64Cu]Cu-4a had a lower background, including a greatly reduced liver uptake, while the tumor uptake was only moderately reduced. Meanwhile, [64Cu]Cu-4c showed increased uptake in both the tumor and the liver. The clinical relevance of NTSR1 was also demonstrated by the elevated tumor expression in patient tissue samples.

CONCLUSIONS

Through the side-by-side comparison, [64Cu]Cu-4b was identified as the lead agent for further evaluation based on its high and sustained tumor uptake and moderate liver uptake. It can not only be used to efficiently detect NTSR1 expression in lung cancer (for diagnosis, patient screening, and treatment monitoring), but also has the great potential to treat NTSR-positive lesions once chelating to the beta emitter 67Cu.

Synthesis of 64Cu-, 55Co-, and 68Ga-Labeled Radiopharmaceuticals Targeting Neurotensin Receptor-1 for Theranostics: Adjusting In Vivo Distribution Using Multiamine Macrocycles

The development of theranostic radiotracers relies on their binding to specific molecular markers of a particular disease and the use of corresponding radiopharmaceutical pairs thereafter. This study reports the use of multiamine macrocyclic moieties (MAs), as linkers or chelators, in tracers targeting the neurotensin receptor-1 (NTSR-1). The goal is to achieve elevated tumor uptake, minimal background interference, and prolonged tumor retention in NTSR-1-positive tumors. Methods: We synthesized a series of neurotensin antagonists bearing MA linkers and metal chelators. The MA unit is hypothesized to establish a strong interaction with the cell membrane, and the addition of a second chelator may enhance water solubility, consequently reducing liver uptake. Small-animal PET/CT imaging of [64Cu]Cu-DOTA-SR-3MA, [64Cu]Cu-NT-CB-NOTA, [68Ga]Ga-NT-CB-NOTA, [64Cu]Cu-NT-CB-DOTA, and [64Cu]Cu-NT-Sarcage was acquired at 1, 4, 24, and 48 h after injection using H1299 tumor models. [55Co]Co-NT-CB-NOTA was also tested in HT29 (high NTSR-1 expression) and Caco2 (low NTSR-1 expression) colorectal adenocarcinoma tumor models. Saturation binding assay and internalization of [55Co]Co-NT-CB-NOTA were used to test tracer specificity and internalization in HT29 cells. Results: In vivo PET imaging with [64Cu]Cu-NT-CB-NOTA, [68Ga]Ga-NT-CB-NOTA, and [55Co]Co-NT-CB-NOTA revealed high tumor uptake, high tumor-to-background contrast, and sustained tumor retention (≤48 h after injection) in NTSR-1-positive tumors. Tumor uptake of [64Cu]Cu-NT-CB-NOTA remained at 76.9% at 48 h after injection compared with uptake 1 h after injection in H1299 tumor models, and [55Co]Co-NT-CB-NOTA was retained at 60.2% at 24 h compared with uptake 1 h after injection in HT29 tumor models. [64Cu]Cu-NT-Sarcage also showed high tumor uptake with low background and high tumor retention 48 h after injection Conclusion: Tumor uptake and pharmacokinetic properties of NTSR-1-targeting radiopharmaceuticals were greatly improved when attached with different nitrogen-containing macrocyclic moieties. The study results suggest that NT-CB-NOTA labeled with either 64Cu/67Cu, 55Co/58mCo, or 68Ga (effect of 177Lu in tumor to be determined in future studies) and NT-Sarcage labeled with 64Cu/67Cu or 55Co/58mCo may be excellent diagnostic and therapeutic radiopharmaceuticals targeting NTSR-1-positive cancers. Also, the introduction of MA units to other ligands is warranted in future studies to test the generality of this approach.

GPCR-Gα13 Involvement in Mitochondrial Function, Oxidative Stress, and Prostate Cancer

Gα13 and Gα12, encoded by the GNA13 and GNA12 genes, respectively, are members of the G12 family of Gα proteins that, along with their associated Gβγ subunits, mediate signaling from specific G protein-coupled receptors (GPCRs). Advanced prostate cancers have increased expression of GPCRs such as CXC Motif Chemokine Receptor 4 (CXCR4), lysophosphatidic acid receptor (LPAR), and protease activated receptor 1 (PAR-1). These GPCRs signal through either the G12 family, or through Gα13 exclusively, often in addition to other G proteins. The effect of Gα13 can be distinct from that of Gα12, and the role of Gα13 in prostate cancer initiation and progression is largely unexplored. The oncogenic effect of Gα13 on cell migration and invasion in prostate cancer has been characterized, but little is known about other biological processes such as mitochondrial function and oxidative stress. Current knowledge on the link between Gα13 and oxidative stress is based on animal studies in which GPCR-Gα13 signaling decreased superoxide levels, and the overexpression of constitutively active Gα13 promoted antioxidant gene activation. In human samples, mitochondrial superoxide dismutase 2 (SOD2) correlates with prostate cancer risk and prognostic Gleason grade. However, overexpression of SOD2 in prostate cancer cells yielded conflicting results on cell growth and survival under basal versus oxidative stress conditions. Hence, it is necessary to explore the effect of Gα13 on prostate cancer tumorigenesis, as well as the effect of Gα13 on SOD2 in prostate cancer cell growth under oxidative stress conditions.

Neuropeptides in Cancer: Friend and Foe?

Neuropeptides are small regulatory molecules found throughout the body, most notably in the nervous, cardiovascular, and gastrointestinal systems. They serve as neurotransmitters or hormones in the regulation of diverse physiological processes. Cancer cells escape normal growth control mechanisms by altering their expression of growth factors, receptors, or intracellular signals, and neuropeptides have recently been recognized as mitogens in cancer growth and development. Many neuropeptides and their receptors exist in multiple subtypes, coupling with different downstream signaling pathways and playing distinct roles in cancer progression. The consideration of neuropeptide/receptor systems as anticancer targets is already leading to new biological and diagnostic knowledge that has the potential to enhance the understanding and treatment of cancer. In this review, recent discoveries regarding neuropeptides in a wide range of cancers, emphasizing their mechanisms of action, signaling cascades, regulation, and therapeutic potential, are discussed. Current technologies used to manipulate and analyze neuropeptides/receptors are described. Applications of neuropeptide analogs and their receptor inhibitors in translational studies and radio-oncology are rapidly increasing, and the possibility for their integration into therapeutic trials and clinical treatment appears promising.

Positron Emission Tomography Imaging of Neurotensin Receptor-Positive Tumors with 68Ga-Labeled Antagonists: The Chelate Makes the Difference Again

Neurotensin receptor 1 (NTS₁) is involved in the development and progression of numerous cancers, which makes it an interesting target for the development of diagnostic and therapeutic agents. A small molecule NTS₁ antagonist, named [¹⁷⁷Lu]Lu-IPN01087, is currently evaluated in phase I/II clinical trials for the targeted therapy of neurotensin receptor-positive cancers. In this study, we synthesized seven compounds based on the structure of NTS₁ antagonists, bearing different chelating agents, and radiolabeled them with gallium-68 for PET imaging. These compounds were evaluated in vitro and in vivo in mice bearing a HT-29 xenograft. The compound [⁶⁸Ga]Ga-bisNODAGA-16 showed a promising biodistribution profile with mainly signal in tumor (4.917 ± 0.776%ID/g, 2 h post-injection). Its rapid clearance from healthy tissues led to high tumor-to-organ ratios, resulting in highly contrasted PET images. These results were confirmed on subcutaneous xenografts of AsPC-1 tumor cells, a model of NTS₁-positive human pancreatic adenocarcinoma.

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 neurotensin receptor 1 as potential biomarker for prostate cancer theranostic use

INTRODUCTION

Despite recent developments in the diagnosis and treatment of prostate cancer, the advanced stages still have poor survival rates. This warrants further exploration of related molecular targets for patient screening, detection of metastatic disease, and treatment/treatment monitoring. Recent studies have indicated that neurotensin receptors (NTSRs) and their ligand neurotensin (NTS) critically affect the progression of prostate cancers. In this study, we evaluated the expression of neurotensin receptor1 (NTSR1) in patient tissues and performed NTSR1 PET imaging in a prostate cancer animal model.

METHODS

The NTSR1 expression was evaluated in 97 cases of prostate cancer and 100 cases of benign prostatic hyperplasia (BPH) of clinical patients by immunohistochemistry staining. The expression profile of PSMA and GRPR was also performed for comparison. The mRNA expression of NTSR1 in LnCap and PC-3 cells was measured by PCR. NTSR1 PET, and biodistribution studies were performed in PC-3 xenografts using ¹⁸F-DEG-VS-NT.

RESULTS

NTSR1 showed high or moderate expression in 91.8% of prostate cancer tissue, compared with PSMA (86.7%) and GRPR (65.3%). All examined PSMA-negative tissues showed positive NTSR1 expression, suggesting the potential complementary role of NTSR1 targeted imaging or therapy. Only 8% of BPH shows strong or moderate expression of NTSR1, which is significantly lower than that in prostate cancer (91.8%). PCR results indicated LNCap (an androgen-dependent prostate cancer cell) showed negative NTSR1 expression while PC-3 demonstrated positive expression (an androgen-independent prostate cancer cell), which correlated well with previously reported western blot results. In a preclinical animal model, NTSR1 targeted PET probe ¹⁸F-DEG-VS-NT demonstrated prominent tumor accumulation and low background.

CONCLUSION

We have demonstrated that NTSR1 is a promising molecular marker for prostate cancer based on patient tissue staining. The NTSR targeted probe ¹⁸F-DEG-VS-NT demonstrated high tumor to background contrast in animal models, which could be valuable in selecting patients for therapies targeting NTSR1 as well as monitoring therapeutic efficacy during treatment accordingly.

Ru(ii)-Peptide bioconjugates with the cppH linker (cppH = 2-(2'-pyridyl)pyrimidine-4-carboxylic acid): synthesis, structural characterization, and different stereochemical features between organic and aqueous solvents

Three new Ru(ii) bioconjugates with the C-terminal hexapeptide sequence of neurotensin, RRPYIL, namely trans,cis-RuCl2(CO)2(cppH-RRPYIL-κNp) (7), [Ru([9]aneS3)(cppH-RRPYIL-κNp)(PTA)](Cl)2 (8), and [Ru([9]aneS3)Cl(cppH-RRPYIL-κNp)]Cl (11), where cppH is the asymmetric linker 2-(2'-pyridyl)pyrimidine-4-carboxylic acid, were prepared in pure form and structurally characterized in solution. The cppH linker is capable of forming stereoisomers (i.e. linkage isomers), depending on whether the nitrogen atom ortho (No) or para (Np) to the carboxylate on C4 in the pyrimidine ring binds the metal ion. Thus, one of the aims of this work was to obtain pairs of stereoisomeric conjugates and investigate their biological (anticancer, antibacterial) activity. A thorough NMR characterization clearly indicated that in all cases exclusively Np conjugates were obtained in pure form. In addition, the NMR studies showed that, whereas in DMSO-d6 each conjugate exists as a single species, in D2O two (7) or even three if not four (8 and 11) very similar stable species form (each one corresponding to an individual compound). Similar results were observed for the cppH-RRPYIL ligand alone. Overall, the NMR findings are consistent with the occurrence of a strong intramolecular stacking interaction between the phenol ring of tyrosine and the pyridyl ring of cppH. Such stacking interactions between aromatic rings are expected to be stronger in water. This interaction leads to two stereoisomeric species in the free cppH-RRPYIL ligand and in the bioconjugate 7, and is somehow modulated by the less symmetrical Ru coordination environments in 8 and 11, affording three to four very similar species.

Validation of Neurotensin Receptor 1 as a Therapeutic Target for Gastric Cancer

Gastric cancer is the fifth most common type of malignancy worldwide, and the survival rate of patients with advanced-stage gastric cancer is low, even after receiving chemotherapy. Here, we validated neurotensin receptor 1 (NTSR1) as a potential therapeutic target in gastric cancer. We compared NTSR1 expression levels in sixty different gastric cancer-tissue samples and cells, as well as in other cancer cells (lung, breast, pancreatic, and colon), by assessing NTSR1 expression via semi-quantitative real-time reverse transcription polymerase chain reaction, immunocytochemistry and western blot. Following neurotensin (NT) treatment, we analyzed the expression and activity of matrix metalloproteinase-9 (MMP-9) and further determined the effects on cell migration and invasion via wound-healing and transwell assays. Our results revealed that NTSR1 mRNA levels were higher in gastric cancer tissues than non-cancerous tissues. Both of NTSR1 mRNA levels and expression were higher in gastric cancer cell lines relative to levels observed in other cancer-cell lines. Moreover, NT treatment induced MMP-9 expression and activity in all cancer cell lines, which was significantly decreased following treatment with the NTSR1 antagonist SR48692 or small-interfering RNA targeting NTSR1. Furthermore, NT-mediated metastases was confirmed by observing epithelial-mesenchymal transition markers SNAIL and E-cadherin in gastric cancer cells. NT-mediated invasion and migration of gastric cancer cells were reduced by NTSR1 depletion through the Erk signaling. These findings strongly suggested that NTR1 constitutes a potential therapeutic target for the inhibition of gastric cancer invasion and metastasis.

Imaging Neurotensin Receptor in Prostate Cancer With 64Cu-Labeled Neurotensin Analogs

INTRODUCTION

Neurotensin receptor 1 (NTR-1) is expressed and activated in prostate cancer cells. In this study, we explore the NTR expression in normal mouse tissues and study the positron emission tomography (PET) imaging of NTR in prostate cancer models.

MATERIALS AND METHODS

Three ⁶⁴Cu chelators (1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid [DOTA], 1,4,7-triazacyclononane-N,N',N″-triacetic acid [NOTA], or AmBaSar) were conjugated to an NT analog. Neurotensin receptor binding affinity was evaluated using cell binding assay. The imaging profile of radiolabeled probes was compared in well-established NTR⁺ HT-29 tumor model. Stability of the probes was tested. The selected agents were further evaluated in human prostate cancer PC3 xenografts.

RESULTS

All 3 NT conjugates retained the majority of NTR binding affinity. In HT-29 tumor, all agents demonstrated prominent tumor uptake. Although comparable stability was observed, ⁶⁴Cu-NOTA-NT and ⁶⁴Cu-AmBaSar-NT demonstrated improved tumor to background contrast compared with ⁶⁴Cu-DOTA-NT. Positron emission tomography/computed tomography imaging of the NTR expression in PC-3 xenografts showed high tumor uptake of the probes, correlating with the in vitro Western blot results. Blocking experiments further confirmed receptor specificity.

CONCLUSIONS

Our results demonstrated that ⁶⁴Cu-labeled neurotensin analogs are promising imaging agents for NTR-positive tumors. These agents may help us identify NTR-positive lesions and predict which patients and individual tumors are likely to respond to novel interventions targeting NTR-1.

Activation of matrix metalloproteinase-9 (MMP-9) by neurotensin promotes cell invasion and migration through ERK pathway in gastric cancer

Neurotensin (NT) is distributed throughout the brain and gastrointestinal tract. Although the relationship between NT and matrix metalloproteinase-9 (MMP-9) activity in gastric cancer has not been reported, the elevation of MMP-9 and NT is reported in the breast, lung, prostate, and gastric cancer. The aim of our study is to investigate the relationship between NT and MMP-9 activity and the underlying signaling mechanism in gastric cancer cell lines. Commercial ELISA kits were used for estimation of NT and MMP-9 expression, and fluorescence resonance energy transfer (FRET) assay was used for measurement of MMP-9 activity. Cell migration and invasion were determined by wound healing and transwell assay. The expression of signaling proteins was measured by Western blotting. Our study reveals a positive correlation between increased plasma NT and MMP-9 activity in both of patient's serum and gastric cancer cell lines. A dose-dependent elevation of MMP-9 activity was observed by NT treatment in gastric cancer cells (MKN-1 and MKN-45) compared to untreated gastric cancer and normal epithelial cell (HFE-145). Moreover, NT-mediated migration and invasion were observed in gastric cancer cells unlike in normal cell. The signaling mechanism of NT in gastric cancer cells was confirmed in protein kinase C (PKC), extracellular-signal regulated kinase (ERK), and phosphatidylinositol 3-kinase (PI3K) pathway. In addition, pretreatment of gastric cancer cells with NTR1 inhibitor SR48692 was shown to significantly inhibit the NT-mediated MMP-9 activity, cell invasion, and migration. Our finding illustrated NTR1 could be a possible therapeutic target for gastric cancer.

Sortilin regulates progranulin action in castration-resistant prostate cancer cells

The growth factor progranulin is as an important regulator of transformation in several cellular systems. We have previously demonstrated that progranulin acts as an autocrine growth factor and stimulates motility, proliferation, and anchorage-independent growth of castration-resistant prostate cancer cells, supporting the hypothesis that progranulin may play a critical role in prostate cancer progression. However, the mechanisms regulating progranulin action in castration-resistant prostate cancer cells have not been characterized. Sortilin, a single-pass type I transmembrane protein of the vacuolar protein sorting 10 family, binds progranulin in neurons and negatively regulates progranulin signaling by mediating progranulin targeting for lysosomal degradation. However, whether sortilin is expressed in prostate cancer cells and plays any role in regulating progranulin action has not been established. Here, we show that sortilin is expressed at very low levels in castration-resistant PC3 and DU145 cells. Significantly, enhancing sortilin expression in PC3 and DU145 cells severely diminishes progranulin levels and inhibits motility, invasion, proliferation, and anchorage-independent growth. In addition, sortilin overexpression negatively modulates Akt (protein kinase B, PKB) stability. These results are recapitulated by depleting endogenous progranulin in PC3 and DU145 cells. On the contrary, targeting sortilin by short hairpin RNA approaches enhances progranulin levels and promotes motility, invasion, and anchorage-independent growth. We dissected the mechanisms of sortilin action and demonstrated that sortilin promotes progranulin endocytosis through a clathrin-dependent pathway, sorting into early endosomes and subsequent lysosomal degradation. Collectively, these results point out a critical role for sortilin in regulating progranulin action in castration-resistant prostate cancer cells, suggesting that sortilin loss may contribute to prostate cancer progression.

The synthesis of neurotensin antagonist SR 48692 for prostate cancer research

An improved synthesis of the molecule SR 48692 is presented and its use as a neurotensin antagonist biological probe for use in cancer research is described. The preparation includes an number of enhanced chemical conversions and strategies to overcome some of the limiting synthetic transformations in the original chemical route.

Synthesis and in vitro cytotoxicity of cis,cis,trans-diamminedichloridodisuccinatoplatinum(IV)-peptide bioconjugates

The synthesis and characterization of four Pt(IV)-peptide conjugates, containing one or two peptides in the axial position, designed for the purpose of targeted drug delivery to tumor cells, are described. The precursor cis,cis,trans-diamminedichloridodisuccinatoplatinum(IV) was coupled in the last step of standard solid-phase peptide synthesis (SSPS) with an analogue of neurotensin (pseudo-neurotensin = Lys-Lys-Pro-Tyr-Ile-Leu) and with octreotate (D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr-OH), an analogue of somatostatin, respectively. For all peptides, the SSPS reactions afforded both mono- and diconjugated Pt-peptide species, which were separated and purified by RP-HPLC. The two couples of conjugates, together with the precursor, were tested as cytotoxic agents towards different cancer cell lines. In general all conjugates are good inhibitors of cellular proliferation when compared to a nontargeting platinum(IV) parent compound, so that its relatively low cytotoxicity is greatly improved by addition of the peptides.

Neurotensin and its high affinity receptor 1 as a potential pharmacological target in cancer therapy

Cancer is a worldwide health problem. Personalized treatment represents a future advancement for cancer treatment, in part due to the development of targeted therapeutic drugs. These molecules are expected to be more effective than current treatments and less harmful to normal cells. The discovery and validation of new targets are the foundation and the source of these new therapies. The neurotensinergic system has been shown to enhance cancer progression in various cancers such as pancreatic, prostate, lung, breast, and colon cancer. It also triggers multiple oncogenic signaling pathways, such as the PKC/ERK and AKT pathways. In this review, we discuss the contribution of the neurotensinergic system to cancer progression, as well as the regulation and mechanisms of the system in order to highlight its potential as a therapeutic target, and its prospect for its use as a treatment in certain cancers.

Baculoviruses as gene therapy vectors for human prostate cancer

Prostate cancer is the most commonly diagnosed cancer in ageing men in the western world. While the primary cancers can be treated with androgen ablation, radiotherapy and surgery, recurrent castration resistant cancers have an extremely poor prognosis, hence promoting research that could lead to a better treatment. Targeted therapeutic gene therapy may provide an attractive option for these patients. By exploiting the natural ability of viruses to target and transfer their genes into cancer cells, either naturally or after genetic manipulation, new generations of biological control can be developed. In this review we present the advantages and practicalities of using baculovirus as a vector for prostate cancer gene therapy and provide evidence for the potential of the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) as a safer alternative vehicle for targeting cancer cells. Strategies to target baculovirus binding specifically to prostate cell surfaces are also presented. The large insertion capacity of baculoviruses also permits restricted, prostate-specific gene expression of therapeutic genes by cloning extended human transcriptional control sequences into the baculovirus genome.

Comparative analysis of the ERα/ERβ ratio and neurotensin and its high-affinity receptor in myometrium, uterine leiomyoma, atypical leiomyoma, and leiomyosarcoma

Deregulated steroids are involved in different hormone-dependent tumors, including benign and malignant uterine neoplasms. Leiomyomas (LM) are estrogen and progesterone-dependent benign tumors, whereas "bizarre or atypical LMs" (AL) are considered a subgroup of LM and clinically benign, although their malignant potential is suspect. Uterine leiomyosarcomas (LMS) are malignant smooth muscle tumors, and ovarian steroids may control their growth. Estrogen effects are mediated by 2 receptors, estrogen receptors (ER) α and β, and the ratio of both receptors seems to be a critical parameter in the estrogen-mediated carcinogenic process. Estradiol induces the expression of neurotensin (NTS), and the coupling of this peptide with its high-affinity receptor, NTS1, has been involved in the regulation of tumoral cell growth. Given the importance of these markers in tumor development, we aim to determine the status of ERα and ERβ in the myometrium and LM, AL, and LMS, concomitantly with the expression of NTS/NTS receptor 1 in these tumors. For that purpose, we use immunohistochemistry for all markers analyzed and in-situ hybridization to detect NTS mRNA. These data suggest that LMS are estrogen-dependent tumors, which may use NTS as an autocrine growth factor. In addition, the phenotype of AL with regard to ERα and ERβ status and NTS expression is closer to LMS than LM; thus, a potential malignization of this tumor is feasible.

Inhibition of neurotensin receptor 1 selectively sensitizes prostate cancer to ionizing radiation

Radiotherapy combined with androgen depletion is generally successful for treating locally advanced prostate cancer. However, radioresistance that contributes to recurrence remains a major therapeutic problem in many patients. In this study, we define the high-affinity neurotensin receptor 1 (NTR1) as a tractable new molecular target to radiosensitize prostate cancers. The selective NTR1 antagonist SR48692 sensitized prostate cancer cells in a dose- and time-dependent manner, increasing apoptotic cell death and decreasing clonogenic survival. The observed cancer selectivity for combinations of SR48692 and radiation reflected differential expression of NTR1, which is highly expressed in prostate cancer cells but not in normal prostate epithelial cells. Radiosensitization was not affected by androgen dependence or androgen receptor expression status. NTR1 inhibition in cancer cell-attenuated epidermal growth factor receptor activation and downstream signaling, whether induced by neurotensin or ionizing radiation, establish a molecular mechanism for sensitization. Most notably, SR48692 efficiently radiosensitized PC-3M orthotopic human tumor xenografts in mice, and significantly reduced tumor burden. Taken together, our findings offer preclinical proof of concept for targeting the NTR1 receptor as a strategy to improve efficacy and outcomes of prostate cancer treatments using radiotherapy.

Neurotensin receptor-1 inducible palmitoylation is required for efficient receptor-mediated mitogenic-signaling within structured membrane microdomains

Neurotensin receptor-1 (NTSR-1) is a G-protein coupled receptor (GPCR) that has been recently identified as a mediator of cancer progression. NTSR-1 and its endogenous ligand, neurotensin (NTS), are co-expressed in several breast cancer cell lines and breast cancer tumor samples. Based on our previously published study demonstrating that intact structured membrane microdomains (SMDs) are required for NTSR-1 mitogenic signaling, we hypothesized that regulated receptor palmitoylation is responsible for NTSR-1 localization and signaling within SMDs upon NTS stimulation. Site-directed mutagenesis and pharmacological strategies were utilized to assess NTRS-1 post-translational modifications in an over-expression cell model (HEK293T) as well as a native breast cancer cell model (MDA-MB-231). NTSR-1 palmitoylation was confirmed by multiple chemical and fluororadiographic methodologies. NTSR-1 glycosylation was confirmed by pharmacological (tunicamycin) and chemical (PGNaseF and O-type glycosidase) approaches. Physiological correlates including cell viability (MTS assay), apoptosis (caspase 3/7 assay) and ERK phosphorylation were utilized to assess the consequences of NTRS-1 palmitoylation. The interaction between palmitoylated NTRS-1 and Gαq/11 within SMDS was confirmed with immunopreciptation analysis of detergent-free isolated fractions of caveolin-rich microdomains. We identified dual-palmitoylation at Cys381 and Cys383 of endogenously-expressed NTSR-1 in MDA-MB-231 breast adeno-carcinomas as well as exogenously-expressed NTSR-1 in HEK293T cells (which do not normally express NTSR-1). Pharmacological inhibition of NTSR-1 palmitoylation in MDA-MB-231 cells as well as NTSR-1-expressing HEK293T cells diminished NTS-mediated ERK 1/2 phosphorylation. Additionally, NTSR-1 mutated at Cys381 and Cys383 showed diminished ERK1/2 stimulation and reduced ability to protect HEK293T cells against apoptosis induced by serum starvation. Mechanistically, mutated C381,383S-NTSR-1 showed reduced ability to interact with Gαq/11 and diminished localization to structured membrane microdomains (SMDs), where Gαq/11 preferentially resides. We also demonstrated that only glycosylated isoforms of NTRS-1 localize within SMDs by palmitotylation. Collectively, our data establish palmitoylation as a novel pharmacological target to inhibit NTSR-1 mitogenic signaling in breast cancer cells.

The potential use of the neurotensin high affinity receptor 1 as a biomarker for cancer progression and as a component of personalized medicine in selective cancers

A growing challenge in medicine today, is the need to improve the suitability of drug treatments for cancer patients. In this field, biomarkers have become the "flags" to provide additional information in tumor biology. They are a relay between the patient and practitioner and consequently, aid in the diagnosis, providing information for prognosis, or in some cases predicting the response to specific therapies. In addition to being markers, these tumor "flags" can also be major participants in the process of carcinogenesis. Neurotensin receptor 1 (NTSR1) was recently identified as a prognosis marker in breast, lung, and head and neck squamous carcinomas. Neurotensin (NTS) was also shown to exert numerous oncogenic effects involved in tumor growth and metastatic spread. These effects were mostly mediated by NTSR1, making the NTS/NTSR1 complex an actor in cancer progression. In this review, we gather information on the oncogenic effects of the NTS/NTSR1 complex and its associated signaling pathways in order to illuminate its significant role in tumor progression and its potential as a biomarker and a therapeutic target in some tumors.

Differential expression of new splice variants of the neurotensin receptor 1 gene in human prostate cancer cell lines

Neurotensin is a neuroendocrine peptide acting as a trophic factor in a variety of cells in vivo but it can also function as an autocrine growth factor in human prostate cancer cells in vitro. In addition, the high-affinity G protein-coupled NT receptor (NTS1) is overexpressed in prostate cancer cell lines. Increasing evidence argues for a direct correlation between specific alternative splice variants and cancer. We detected four splice variants of the NTS1 receptor in human prostate cancer cell lines. These isoforms include one or more exons skipping as well as an alternative 5' splice donor site and are expressed in the late-stage androgen independent prostate cancer cell lines PC3 and DU145, but not in the early-stage androgen-sensitive LNCaP or in normal prostate tissue, which only express the normal transcript. This result shows new splice variants of NTS1 for the first time. The differential expression observed among prostate cancer cell lines and normal prostate tissue opens the interesting possibility of a new role of NT/NTS1 pathway in prostate cancer.

Altered expression of neurotensin receptors is associated with the differentiation state of prostate cancer

In prostate cancer, traditional treatments such as androgen response manipulation often provide only temporary resolution of disease, with emergence of a more aggressive, androgen-independent tumor following initial therapy. To treat recurrent disease, cell surface proteins that are specifically overexpressed on malignant cells may be useful for generating targeted therapeutics. Recent evidence suggests that neurotensin receptors (NTR) are recruited in advanced prostate cancer as an alternative growth pathway in the absence of androgens. In this study, we assessed the potential use of these receptors as targets by analyzing NTR expression patterns in human prostate cell lines and primary prostate tumor cell cultures derived from patient samples. In primary tumor cell cultures, NTR1 was upregulated in cells with a basal phenotype (cytokeratin 1/5/10/14+), whereas NTR2 and NTR3 were upregulated in cells with luminal phenotype (cytokeratin 18+). Similar patterns of NTR expression occurred in benign prostate tissue sections, implicating differentiation state as a basis for the differences observed in tumor cell lines. Our findings support the use of NTRs as tools for therapeutic targeting in prostate cancers composed of both poorly differentiated and/or well-differentiated cells.

Cancer, chemistry, and the cell: molecules that interact with the neurotensin receptors

The literature covering neurotensin (NT) and its signalling pathways, receptors, and biological profile is complicated by the fact that the discovery of three NT receptor subtypes has come to light only in recent years. Moreover, a lot of this literature explores NT in the context of the central nervous system and behavioral studies. However, there is now good evidence that the up-regulation of NT is intimately involved in cancer development and progression. This Review aims to summarize the isolation, cloning, localization, and binding properties of the accepted receptor subtypes (NTR1, NTR2, and NTR3) and the molecules known to bind at these receptors. The growing role these targets are playing in cancer research is also discussed. We hope this Review will provide a useful overview and a one-stop resource for new researchers engaged in this field at the chemistry-biology interface.

Proneurotensin/neuromedin N secreted from small cell lung carcinoma cell lines as a potential tumor marker

Proteins secreted from specific cancer cells have a high potential for use as tumor markers. We identified secreted proteins produced by 15 different carcinoma cell lines grown in serum-free medium using MS/MS. Proneurotensin/neuromedin N (proNT/NMN) was found in conditioned medium from four of seven small cell lung carcinoma cell lines but not from eight nonsmall cell lung carcinoma cell lines. These results indicate proNT/NMN has potential as a specific tumor marker of small cell lung carcinoma.

Is there a role for platinum chemotherapy in the treatment of patients with hormone-refractory prostate cancer?

Docetaxel chemotherapy is the current standard of care for metastatic hormone-refractory prostate cancer (HRPC). Platinum chemotherapy drugs, such as cisplatin and carboplatin, have moderate single-agent activity in HRPC. Next-generation platinum drugs, including satraplatin and oxaliplatin, may have additional activity in the management of HRPC. Furthermore, neuroendocrine differentiation may play a role in disease progression, providing a rationale for platinum-based chemotherapy in the management of HRPC. The authors reviewed the MEDLINE database for reports related to platinum-based chemotherapy in patients with advanced prostate cancer and evaluated studies that reviewed the role of neuroendocrine differentiation in the progression of HRPC. Older studies from the 1970s and 1980s suggested a lack of activity of cisplatin and carboplatin; however, those studies were flawed at least in part by their methods of response assessment. More recent Phase II studies of carboplatin suggested a moderate level of clinical and palliative activity when it was used as a single agent. However, when carboplatin was combined with a taxane and estramustine, high response rates were observed in several recent clinical trials. In addition, a randomized trial suggested that satraplatin plus prednisone improved progression-free survival compared with prednisone alone. For patients who progressed after docetaxel, no standard options existed in the literature that was reviewed. Several preliminary reports suggested that carboplatin and oxaliplatin may have activity as second-line chemotherapy. Platinum chemotherapy drugs historically have been considered inactive in HRPC, although a review of the data suggested otherwise. Carboplatin, in particular, induced very high response rates when it was combined with estramustine and a taxane, but it also appeared to have activity in patients who progressed after docetaxel. Satraplatin plus prednisone is being investigated in a large Phase III trial as second-line chemotherapy for HRPC. Targeting neuroendocrine cells may provide a new therapeutic approach to HRPC.

A role for neurotensin in bicalutamide resistant prostate cancer cells

BACKGROUND

Anti-androgens are administered as a principal treatment for prostate cancer. Aggressive hormone refractory disease is characterized in some cases by the development of a neuroendocrine phenotype. However little attention has been paid to resistance pathways selected for by long-term treatment with non-steroidal anti-androgens.

METHODS

Using a resistant sub-line, LNCaP-Bic, we performed a comparative gene expression profiling using cDNA microarrays and target validation by qRT-PCR. Targets were then explored using cell proliferation, cell cycle analysis and in vitro invasion assays using siRNA technology.

RESULTS

Neurotensin/Neuromedin N (NTS) was upregulated in the LNCaP-Bic line at both the transcript and protein level. The resistant line was found to have an increased proliferation rate, more rapid cell cycle progression and increased invasiveness through Matrigel. Each phenotypic difference could be reduced using siRNA knockdown of NT.

CONCLUSION

Increased expression of NT in bicalutamide resistant prostate cancer cells induces cell proliferation and invasion suggesting that this peptide may contribute to the development of bicalutamide resistant prostate cancer.

Neurotensin receptor binding and neurotensin-induced growth signaling in prostate cancer PC3 cells are sensitive to metabolic stress

Neurotensin (NT) stimulates the proliferation of prostate cancer PC3 cells, which express high levels of its G protein-coupled receptor NTS1. To shed light on mechanisms that might serve to coordinate mitogenic responses to metabolic status, we studied the effects of metabolic inhibitors on NTS1 function. We also related these effects to cellular ATP levels and to the activation of AMP-activated protein kinase (AMPK). Glycolytic and mitochondrial inhibitors, at concentrations that reduced cellular ATP levels, altered NT binding to the cells, inhibited NT-induced inositol phosphate formation, and inhibited NT-induced DNA synthesis. For eight of the nine inhibitors, the potencies to alter NT receptor function correlated to the potencies to decrease cellular ATP levels. In keeping with its known role to oppose metabolic stress, AMPK was activated by the metabolic inhibitors. Accordingly, the AMPK activator AICAR elevated cellular ATP levels and produced effects on NTS1 function that were opposite to those for the metabolic inhibitors. These results indicate that metabolic stress inhibited NTS1 function by a mechanism that involved a fall in cellular ATP levels and that was opposed by activation of AMPK. In a broader context, these findings are compatible with the idea that one means by which cells might coordinate mitogenic signaling to metabolic status could involve changes in growth factor receptor function.

Clinical implications of neuroendocrine differentiation in prostate cancer

The cellular signaling pathways of the prostate play a central role in the induction, maintenance, and progression of prostate cancer (CaP). Neuroendocrine (NE) cells demonstrate attributes that suggest they are an integral part of these signaling cascades. We summarize what is known regarding NE cells in CaP focusing on NE cellular transdifferentiation. This significant event in CaP progression appears to be accelerated by androgen deprivation (AD) treatment. We examine biochemical pathways that may impact NE differentiation in a chronological manner focusing on AD therapy (ADT) as a central event in inducing androgen-independent CaP. Our analysis is limited to the common adenocarcinoma pattern of CaP and excludes small-cell and carcinoid prostatic variants. In conclusion, we speculate on the future of treatment and research in this area.

Internalization-dependent regulation of HT29 cell proliferation by neurotensin

In this study, we have investigated the involvement of the internalization process induced by neurotensin (NT) on MAP kinases Erk1/2 activation, inositol phosphates (IP) accumulation and cell growth in the human colonic cancer cell line HT29. Reversible blocking of NT/neurotensin receptor (NTR) complex endocytosis by hyperosmolar sucrose totally abolished both the phosphorylation of the MAP kinases Erk1/2 and the [3H]-thymidine incorporation induced by the peptide. By contrast, NT-evoked IP formation was not affected by sucrose treatment. These results therefore indicate that NT/NTR complex endocytosis triggers MAP kinase activation and subsequently the growth of HT29 cells. This property could be useful for the development of novel anticancer treatments.

Neurotensin and growth of normal and neoplastic tissues

Neurotensin (NT) is a brain-gut tridecapeptide that functions as a neurotransmitter/neuromodulator in the central nervous system (CNS) and as an endocrine agent in the periphery. NT has numerous physiologic effects on multiple organs. This review will focus on the effects of NT as a trophic factor for normal and neoplastic tissues. In this regard, NT may act as an endocrine agent or, in some instances, in a paracrine and/or autocrine fashion. These effects appear to be mediated predominantly through the G protein-coupled high-affinity NT receptor. However, some of the trophic effects may also be through the other two receptor subtypes, particularly the NT receptor type 3, which belongs to a recently identified family of sorting receptors. The signaling pathways mediating the effects of NT are multiple but most appear to activate the ERK signaling pathway, which then activates downstream transcription factors, ultimately leading to proliferation. NT may be a useful agent to enhance the growth of normal tissues such as the small bowel mucosa during periods of gut disuse or disease and, finally, the selective targeting of NT receptor subtypes on certain cancers may offer a novel strategy in the armamentarium of cancer chemotherapeutics.

Involvement of neurotensin in cancer growth: evidence, mechanisms and development of diagnostic tools

Focusing on the literature of the past 15 years, we evaluate the evidence that neurotensin and neurotensin receptors participate in cancer growth and we describe possible mechanisms. In addition, we review the progress achieved in the use of neurotensin analogs to image tumors in animals and humans. These exciting advances encourage us to pursue further research and stimulate us to consider novel ideas regarding the multiple inputs to cancer growth that neurotensin might influence.

Protein tyrosine phosphatase PTP1B is involved in neuroendocrine differentiation of prostate cancer

BACKGROUND

Prostate cancer (PC) contains a minor component of neuroendocrine (NE) cells that may stimulate androgen-independent growth of the tumor. The mechanism of neuroendocrine differentiation remains unknown.

METHODS

The expression of PTP1B, a protein tyrosine phosphatase, was studied in LNCaP cells induced to show neuroendocrine phenotype by androgen withdrawal. Wild-type PTP1B and its dominant-negative mutant were transfected into LNCaP cells to study their effects on neuroendocrine differentiation. In vivo expression of PTP1B in human prostate cancer was studied by immunohistochemistry.

RESULTS

Androgen withdrawal of LNCaP cells led to increased expression of PTP1B with a corresponding increase in its tyrosine phosphatase activity. Overexpression of PTP1B in LNCaP cells led to neuroendocrine differentiation while expression of its dominant-negative mutant inhibited neuroendocrine differentiation. Immunohistochemical study showed that PTP1B was exclusively expressed in neuroendocrine cells of human prostate cancer tissue.

CONCLUSION

Our findings suggest that PTP1B plays an important role in neuroendocrine differentiation, and therefore, may possibly be involved in the progression of prostate cancer.

Neurotensin stimulates mitogenesis of prostate cancer cells through a novel c-Src/Stat5b pathway

Neuroendocrine (NE)-like cells are hypothesized to contribute to the progression of prostate cancer by producing factors that enhance the growth, survival or metastatic capabilities of surrounding tumor cells. Many of the factors known to be secreted by NE-like cells, such as neurotensin (NT), parathyroid hormone-related peptide, serotonin, bombesin, etc., are agonists for G-protein-coupled receptors, but the signaling pathways activated by these agonists in prostate tumor cells are not fully defined. Identification of such pathways could provide insights into novel methods of treating late-stage disease. Using conditioned culture medium (CM) from LNCaP-derived NE-like cells (as a source of these agonists) or NT (a prototypical component of CM) to treat PC3 cells, we found that the epidermal growth factor (EGF) receptor (EGFR) was transactivated and that such activation was required for maximal PC3 cell mitogenesis, as measured by 5-bromo-2'-deoxy-uridine incorporation or cell number. NT also induced a time-dependent increase in EGFR Tyr(845) phosphorylation and phosphorylation of c-Src and signal transducer and activator of transcription 5b (Stat5b) (a downstream effector of Tyr(845)), events that were blocked by specific inhibition of c-Src (which mediates Tyr(845) phosphorylation of EGFR) or of EGFR. Introduction of mutant forms of EGFR (Tyr(845)) or Stat5b in PC3 cells, or treatment with selective, catalytic inhibitors of EGFR, c-Src and matrix metalloproteinases (MMPs) resulted in the loss of NT-induced stimulation of DNA synthesis, relative to wild-type controls. These data indicate that the mitogenic effect of NT on prostate cancer cells requires transactivation of the EGFR by MMPs and a novel downstream pathway involving c-Src, phosphorylation of EGFR Tyr(845) and activation of Stat5b.

Regulation of neurotensin receptor function by the arachidonic acid-lipoxygenase pathway in prostate cancer PC3 cells

Neurotensin (NT) elevates leukotriene levels in animals and stimulates 5-HETE formation in prostate cancer PC3 cells. PC3 cell growth is stimulated by NT and inhibited by lipoxygenase (LOX) blockers. This led us to test LOX blockers (NDGA, MK886, ETYA, Rev5901, AA861 and others) for effects on NT binding and signaling. LOX blockers dramatically enhanced 125I-neurotensin binding to NT receptor NTR1 in PC3 cells, whereas they inhibited NT-induced inositol phosphate formation. These effects were indirect (binding to isolated membranes was unaffected), receptor-specific (binding to beta2-adrenergic, V1a-vasopressin, EGF and bombesin receptor was unaffected) and pathway-specific (cyclooxygenase inhibitors were inactive). NT receptor affinity was increased but receptor number and % internalization were unchanged. Also supporting the involvement of arachidonic acid metabolism in NTR1 regulation was the finding that inhibitors of PLA2 and DAG lipase enhanced NT binding. These findings suggest that NTR1 is regulated by specific feedback mechanism(s) involving lipid peroxidation and/or LOX-dependent processes.

Involvement of arachidonic acid metabolism and EGF receptor in neurotensin-induced prostate cancer PC3 cell growth

Dietary fats, which increase the risk of prostate cancer, stimulate release of intestinal neurotensin (NT), a growth-promoting peptide that enhances the formation of arachidonic acid metabolites in animal blood. This led us to use PC3 cells to examine the involvement of lipoxygenase (LOX) and cyclooxygenase (COX) in the growth effects of NT, including activation of EGF receptor (EGFR) and downstream kinases (ERK, AKT), and stimulation of DNA synthesis. NT and EGF enhanced [3H]-AA release, which was diminished by inhibitors of PLA2 (quinacrine), EGFR (AG1478) and MEK (U0126). NT and EGF phosphorylated EGFR, ERK and AKT, and stimulated DNA synthesis. These effects were diminished by PLA2 inhibitor (quinacrine), general LOX inhibitors (NDGA, ETYA), 5-LOX inhibitors (Rev 5901, AA861), 12-LOX inhibitor (baicalein) and FLAP inhibitor (MK886), while COX inhibitor (indomethacin) was without effect. Cells treated with NT and EGF showed an increase in 5-HETE levels by HPLC. PKC inhibitor (bisindolylmaleimide) blocked the stimulatory effects of NT, EGF and 5-HETE on DNA synthesis. We propose that 5-LOX activity is required for NT to stimulate growth via EGFR and its downstream kinases. The mechanism may involve an effect of 5-HETE on PKC, which is known to facilitate MEK-ERK activation. NT may enhance 5-HETE formation by Ca2+-mediated and ERK-mediated activation of DAG lipase and cPLA2. NT also upregulates cPLA2 and 5-LOX protein expression. Thus, the growth effects of NT and EGF involve a feed-forward system that requires cooperative interactions of the 5-LOX, ERK and AKT pathways.

Insulin-like growth factor (IGF) induced proliferation of human lung fibroblasts is enhanced by neurotensin

Fibroblasts are key cells in tissue repair and important contributors to the inflammatory response. Insulin-like growth factors (IGFs) have been shown to participate in growth, in immune responses and in tissue repair where they stimulate cell growth. Neurotensin (NT) has been suggested to participate in inflammation and in tissue repair and is an autocrine or paracrine growth factor for several cancer cell types. Here we show that IGF-induced proliferation of fibroblasts is enhanced by NT in a concentration and type 1 NT-receptor dependent manner. This action of NT was blocked by inhibitors of phospholipase C and protein kinase C but not by inhibitors of phosphoinositide-3-kinase. An inhibitor of MEK 1/2 significantly reduced the proliferative effects of the IGFs but NT's ability to enhance IGF-induced proliferation was not effected. The ability of NT to enhance IGF-induced proliferation did not involve an autocrine factor. These results suggest that interactions between NT and the IGFs may contribute to the regulation of fibroblasts in for example, inflamed or injured tissues.

Internalization and trafficking of neurotensin via NTS3 receptors in HT29 cells

The neurotensin receptor-3, originally identified as sortilin, is unique among neuropeptide receptors in that it is a single trans-membrane domain, type I receptor. To gain insight into the functionality of neurotensin receptor-3, we examined the neurotensin-induced intracellular trafficking of this receptor in the human carcinoma cell line HT29, which expresses both neurotensin receptor-1 and -3 sub-types. At steady state, neurotensin receptor-3 was found by sub-cellular fractionation and electron microscopic techniques to be predominantly associated with intracellular elements. A small proportion (approximately 10%) was associated with the plasma membrane, but a significant amount (approximately 25%) was observed inside the nucleus. Following stimulation with neurotensin (NT), neurotensin/neurotensin receptor-3 complexes were internalized via the endosomal pathway. This internalization entailed no detectable loss of cell surface receptors, suggesting compensation through either recycling or intracellular receptor recruitment mechanisms. Internalized ligand and receptors were both sorted to the pericentriolar recycling endosome/Trans-Golgi Network (TGN), indicating that internalized neurotensin is sorted to this compartment via neurotensin receptor-3. Furthermore, within the Trans-Golgi Network, neurotensin was bound to a lower molecular form of the receptor than at the cell surface or in early endosomes, suggesting that signaling and transport functions of neurotensin receptor-3 may be mediated through different molecular forms of the protein. In conclusion, the present work suggests that the neurotensin receptor-3 exists in two distinct forms in HT29 cells: a high molecular weight, membrane-associated form responsible for neurotensin endocytosis from the cell surface and a lower molecular weight, intracellular form responsible for the sorting of internalized neurotensin to the Trans-Golgi Network.

Involvement of metabotropic glutamate receptor�1, a G protein coupled receptor, in melanoma development

Melanoma is the aberrant proliferation of melanocytes, the cells in the skin responsible for pigment production. In the United States the current lifetime risk of melanoma development is 1 in 57 in males and 1 in 81 in females. In its early stages melanoma can be surgically removed with great success; however, advanced stages of melanoma have a high mortality rate due to the lack of responsiveness to currently available therapies. The development of animal models to be used in the studies of melanoma will provide the means for developing improved and targeted treatments for this disease. This review focuses on the recent report of a mouse melanoma model, TG-3, which has implicated the ectopic expression of the metabotropic glutamate receptor 1 (Grm1), a G protein coupled receptor (GPCR), in melanomagenesis and metastasis. The involvement of other GPCRs in cellular transformation, particularly GPCRs in melanoma biology, and signaling of Grm1 are also discussed.

Involvement of MAP-kinase, PI3-kinase and EGF-receptor in the stimulatory effect of Neurotensin on DNA synthesis in PC3 cells

The mechanism by which neurotensin (NT) promotes the growth of prostate cancer epithelial cells is not yet defined. Here, androgen-independent PC3 cells, which express high levels of the type 1 NT-receptor (NTR1), are used to examine the involvement of epidermal growth factor receptor (EGFR), mitogen-activated protein kinases (ERK, SAPK/JNK and p38), PI3 kinase and PKC in the mitogenic effect of NT. NT dose dependently (0.1-30 nM) enhanced phosphorylation of EGFR, ERK and Akt, reaching maximal levels within 3 min as measured by Western blotting. These effects were associated with an accumulation of EGF-like substance(s) in the medium (assayed by EGFR binding) and a 2-fold increase in DNA synthesis (assayed by [3H]thymidine incorporation). The DNA synthesis enhancement by NT was non-additive with that of EGF. The NT-induced stimulation of EGFR/ERK/Akt phosphorylation and DNA synthesis was inhibited by EGFR-tyrosine kinase inhibitors (AG1478, PD153035), metallo-endopeptidase inhibitor phosphoramidon and by heparin, but not by neutralizing anti-EGF antibody. Thus, transactivation of EGFR by NT involved heparin-binding EGF (HB-EGF or amphiregulin) rather than EGF. The effects of NT on EGFR/ERK/Akt activation and DNA synthesis were attenuated by PLC-inhibitor (U73122), PKC-inhibitors (bisindolylmaleimide, staurosporine, rottlerin), MEK inhibitor (U0126) and PI3 kinase inhibitors (wortmannin, LY 294002). We conclude that NT stimulated mitogenesis in PC3 cells by a PKC-dependent ligand-mediated transactivation of EGFR, which led to stimulation of the Raf-MEK-ERK pathway in a PI3 kinase-dependent manner.

G Proteins in Cancer: The Prostate Cancer Paradigm

Signal transduction research investigating mechanisms of androgen-independent prostate cancer cell proliferation has historically focused on the role of androgen and peptide growth factor receptors. More recent work has raised the idea that intracellular signaling mechanisms triggered by extracellular hormonal factors acting through heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) can also mediate and sustain this pathologic process. Prostate cancer patients with advanced disease express elevated levels of GPCRs and GPCR ligands, suggesting that the GPCR system is activated in the cancerous gland and may contribute to tumor growth. Importantly, inhibition of G protein signaling attenuates prostate cancer cell growth in animal models. The nature of intracellular signaling pathways mediating mitogenic effects of GPCRs in prostate cancer is poorly defined, although the G protein-dependent activation of the Ras-to-mitogen-activated protein kinase pathway has emerged as a critical regulatory event. Activated GPCRs may also exert their mitogenic effects in the prostate by activating the androgen receptor.

Polyphenolic Antioxidants Mimic the Effects of 1,4-Dihydropyridines on Neurotensin Receptor Function in PC3 Cells

This study aimed to determine the mechanism(s) by which 1,4-dihydropyridine Ca2+ channel blockers (DHPs) enhance the binding of neurotensin (NT) to prostate cancer PC3 cells and inhibit NT-induced inositol phosphate formation. Earlier work indicated that these effects, which involved the G protein-coupled NT receptor NTR1, were indirect and required cellular metabolism or architecture. At the micromolar concentrations used, DHPs can block voltage-sensitive and store-operated Ca2+ channels, K+ channels, and Na+ channels, and can inhibit lipid peroxidation. By varying [Ca2+] and testing the effects of stimulators and inhibitors of Ca2+ influx and internal Ca2+ release, we determined that although DHPs may have inhibited inositol phosphate formation partly by blocking Ca2+ influx, the effect on NT binding was Ca2+-independent. By varying [K+] and [Na+], we showed that these ions did not contribute to either effect. For a series of DHPs, the activity order for effects on NTR1 function followed that for antioxidant ability. Antioxidant polyphenols (luteolin and resveratrol) mimicked the effects of DHPs and showed structural similarity to DHPs. Antioxidants with equal redox ability, but without structural similarity to DHPs (such as alpha-tocopherol, riboflavin, and N-acetyl-cysteine) were without effect. A flavoprotein oxidase inhibitor (diphenylene iodonium) and a hydroxy radical scavenger (butylated hydroxy anisole) also displayed the effects of DHPs. In conclusion, DHPs indirectly alter NTR1 function in live cells by a mechanism that depends on the drug's ability to donate hydrogen but does not simply involve sulfhydryl reduction.