Neurotensin Receptor Antagonist Research Articles

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

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. 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. 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 24h. 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 48h 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 48h 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. 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.

Neurotensin receptor‐1 antagonist SR48692 modulation of high‐fat diet–induced pathogenesis of NAFLD in mice

AbstractThis study investigates the efficacy of the antagonist of neurotensin receptor‐1 (NTSR1) SR48692 in modulating the high‐fat diet (HFD)‐induced nonalcoholic fatty liver disease (NAFLD). HFD increases NTS secretion, which enhances fat absorption from the gastrointestinal tract (GIT) via receptors NTSR1/NTSR2/NTSR3. Absorbed fat from the GIT via hepatic‐portal system reaches the liver, where it gets accumulated to cause NAFLD. Swiss albino mice (8 weeks) were maintained in two batches fed standard diet (SD) and HFD for 4 weeks, then divided into six groups: Group I (SD) and Group II (HFD) administered intraperitoneally 0.9% saline (vehicle), Group III: low dose of antagonist (100 µg kg−1 bw: HFD+SR48692L), Group IV: high dose (400 µg kg−1 bw: HFD+SR48692H), Group V (SD+SR48692L), and Group VI (SD+SR48692H). SR48692L treatment in HFD‐fed mice showed partial efficacy in preventing lipid absorption and reducing oxidative stress, as reflected in histology and plasma transaminases. Contrarily, with SR48692H dose, the effects were detrimental. Involvement of other signaling pathways (NTS‐NTSR2, NTS‐NTSR3) in lipid absorption might be the reason of partial efficacy. The adverse effects with the SR48692H might be due to the differential dose–response effect of the antagonist.Practical Application: HFD‐induced hyperlipidemia and NAFLD are linked to enhanced NTS secretion. As NTS enhances fat absorption, blocking its receptors with antagonists might provide efficacy against HFD‐induced NAFLD. This study with NTSR1 antagonist SR48692 provides some evidence of its in preventing hyperlipidemia; further studies targeting other receptors (NTSR2, NTSR3) are essential for understanding the therapeutic efficacy of the NTS antagonists for NAFLD.

Abstract 6266: Neurotensin receptor 1 regulates dimerization of HER2-HER4 and proliferation of non-small cell lung cancer cells

Abstract The neurotensin receptor 1 (NTSR1) is a 418 amino acid type A G protein-coupled receptor which causes phosphatidylinositol turnover and proliferation of non-small cell lung cancer (NSCLC) cells (Moody et al., Peptides 2021; 137: 710480). Adding the agonist NTS to NSCLC cells increases transactivation of the receptor tyrosine kinases (RTK) EGFR, HER2 and HER3 (Moody et al., Biology 2023 12: 957). The RTK tyrosine phosphorylation and growth caused by NTS is impaired by SR48692, a small molecule NTSR1 antagonist. The effects of NTS were investigated on HER4 using NSCLC cells. By Western blot, cell lines NCI-H522 and H661 had high levels of NTSR1, HER 4 and neuregulin 1 (NRG1), a ligand for HER4 but not NTSR2, HER3 or NRG2. By RT-PCT, high levels of HER4 and its isoforms JM-a, CYT1 and CYT2 were present in NCI-H522 and H661 cells. Adding NTS (0.1 μM) or NRG1 (0.01 μg/ml) to NCI-H522 or H661 cells increased P-Tyr1284-HER4 and P-ERK 3-fold. Using immunoprecipitation techniques, adding NTS to NSCLC cells increased formation of HER4-HER2 heterodimers which leads to cancer proliferation (Lucas et al., Pharmacol Rev 2022; 74:18). The increase in PY1284-HER4 caused by NTS was impaired by SR48692, HER4 siRNA, NRG1 siRNA or ibrutinib (TKI). The NTSR1 regulation of HER4 transactivation is impaired by GM6001 (MMP inhibitor]), PP2 (Src inhibitor) or N-acetylcysteine (antioxidant). The clonal growth of NSCLC cells is increased by NTS or NRG1 but decreased by SR48692 or ibrutinib. The results indicate that NTS increases the formation of HER2/HER4 heterodimers leading to the proliferation of NSCLC cells. Citation Format: Terry W. Moody, Irene Ramos-Alvarez, Robert T. Jensen. Neurotensin receptor 1 regulates dimerization of HER2-HER4 and proliferation of non-small cell lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6266.

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.

Neurotensin receptor 1 signaling promotes pancreatic cancer progression.

Pancreatic cancer is one of the cancers with the poorest prognosis, with a 5-year survival rate of approximately 5-10%. Thus, it is urgent to identify molecular targets for the treatment of pancreatic cancer. Using serial transplantations in a mouse pancreatic orthotopic inoculation model, we previously produced highly malignant pancreatic cancer sublines with increased tumor-forming abilities in vivo. Here, we used these sublines to screen molecular targets for the treatment of pancreatic cancer. Among the genes with increased expression levels in the sublines, we focused on those encoding cell surface receptors that may be involved in the interactions between cancer cells and the tumor microenvironment. Based on our previous RNA-sequence analysis, we found increased expression levels of neurotensin (NTS) receptor 1 (NTSR1) in highly malignant pancreatic cancer sublines. Furthermore, re-analysis of clinical databases revealed that the expression level of NTSR1 was increased in advanced pancreatic cancer and that high NTSR1 levels were correlated with a poor prognosis. Overexpression of NTSR1 in human pancreatic cancer cells Panc-1 and SUIT-2 accelerated their tumorigenic and metastatic abilities in vivo. In addition, RNA-sequence analysis showed that MAPK and NF-κB signaling pathways were activated upon NTS stimulation in highly malignant cancer sublines and also revealed many new target genes for NTS in pancreatic cancer cells. NTS stimulation increased the expression of MMP-9 and other pro-inflammatory cytokines and chemokines in pancreatic cancer cells. Moreover, the treatment with SR48692, a selective NTSR1 antagonist, suppressed the activation of the MAPK and NF-κB signaling pathways and induction of target genes in pancreatic cancer cells in vitro, while the administration of SR48692 attenuated the tumorigenicity of pancreatic cancer cells in vivo. These findings suggest that NTSR1 may be a prognostic marker and a molecular target for pancreatic cancer treatment.

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.

The low affinity neurotensin receptor antagonist levocabastine impairs brain nitric oxide synthesis and mitochondrial function by independent mechanisms.

Neurotensin is known to inhibit neuronal Na+ , K+ -ATPase, an effect that is rescued by nitric oxide (NO) synthase inhibition. However, whether the neurotensinergic and the nitrergic systems are independent pathways, or are mechanistically linked, remains unknown. Here, we addressed this issue and found that the administration of low affinity neurotensin receptor (NTS2) antagonist, levocabastine (50μg/kg, i.p.) inhibited NO synthase (NOS) activity by 74 and 42% after 18h in synaptosomal and mitochondrial fractions isolated from the Wistar rat cerebral cortex, respectively; these effects disappeared 36h after levocabastine treatment. Intriguingly, whereas neuronal NOS protein abundance decreased (by 56%) in synaptosomes membranes, it was enhanced (by 86%) in mitochondria 18h after levocabastine administration. Levocabastine enhanced the respiratory rate of synaptosomes in the presence of oligomycin, but it failed to alter the spare respiratory capacity; furthermore, the mitochondrial respiratory chain (MRC) complexes I-IV activities were severely diminished by levocabastine administration. The inhibition of NOS and MRC complexes activities were also observed after incubation of synaptosomes and mitochondria with levocabastine (1μM) invitro. These data indicate that the NTS2 antagonist levocabastine regulates NOS expression and activity at the synapse, suggesting an interrelationship between the neurotensinergic and the nitrergic systems. However, the bioenergetics effects of NTS2 activity inhibition are likely to be independent from the regulation of NO synthesis.

177Lu-3BP-227 for Neurotensin Receptor 1-Targeted Therapy of Metastatic Pancreatic Adenocarcinoma: First Clinical Results.

Neurotensin receptor 1 (NTR1) is overexpressed in ductal pancreatic adenocarcinoma, which is still one of the deadliest cancers, with a very poor prognosis. Eligible patients were offered salvage radiopharmaceutical therapy with the novel NTR1 antagonist 177Lu-3BP-227. Methods: Six patients with confirmed ductal pancreatic adenocarcinoma who had exhausted all other treatment options received 177Lu-3BP-227 for evaluation of NTR1 expression in vivo. Three patients received treatment activities of 5.1-7.5 GBq. Results: Administration of 177Lu-3BP-227 was well tolerated by all patients. The kidneys were identified as the dose-limiting organ. The most severe adverse event was reversible grade 2 anemia. One patient achieved a partial response and experienced significant improvement of symptoms and quality of life. This patient survived 13 mo from diagnosis and 11 mo from the start of 177Lu-3BP-227 therapy. Conclusion: This initial report provides clinical evidence of the feasibility of treatment of ductal pancreatic adenocarcinoma using 177Lu-3BP-227.

NTS/NTR1 co-expression enhances epithelial-to-mesenchymal transition and promotes tumor metastasis by activating the Wnt/β-catenin signaling pathway in hepatocellular carcinoma.

Neurotensin (NTS) is a neuropeptide distributed in central nervous and digestive systems. In this study, the significant association between ectopic NTS expression and tumor invasion was confirmed in hepatocellular carcinoma (HCC). In primary HCC tissues, the NTS and neurotensin receptor 1 (NTR1) co-expression (NTS+NTR1+) is a poor prognostic factor correlated with aggressive biological behaviors and poor clinical prognosis. Enhanced epithelial-to-mesenchymal transition (EMT) features, including decreased E-cadherin, increased β-catenin translocation and N-cadherin expression, were identified in NTS+NTR1+ HCC tissues. Varied NTS-responsible HCC cell lines were established using NTR1 genetically modified Hep3B and HepG2 cells which were used to elucidate the molecular mechanisms regulating NTS-induced EMT and tumor invasion in vitro. Results revealed that inducing exogenous NTS stimulation and enhancing NTR1 expression promoted tumor invasion rather than proliferation by accelerating EMT in HCC cells. The NTS-induced EMT was correlated with the remarkable increase in Wnt1, Wnt3, Wnt5, Axin, and p-GSK3β expression and was significantly reversed by blocking the NTS signaling via the NTR1 antagonist SR48692 or by inhibiting the activation of the Wnt/β-catenin pathway via specific inhibitors, such as TSW119 and DKK-1. SR48692 also inhibited the metastases of NTR1-overexpressing HCC xenografts in the lungs in vivo. This finding implied that NTS may be an important stimulus to promote HCC invasion and metastasis both in vitro and in vivo, and NTS signaling enhanced the tumor EMT and invasion potentials by activating the canonical Wnt/β-catenin signaling pathway. Therefore, NTS may be a valuable therapeutic target to prevent tumor progression in HCC.

Ventral tegmental area neurotensin signaling links the lateral hypothalamus to locomotor activity and striatal dopamine efflux in male mice.

Projections from the lateral hypothalamic area (LHA) innervate components of the mesolimbic dopamine (MLDA) system, including the ventral tegmental area (VTA) and nucleus accumbens (NAc), to modulate motivation appropriately for physiologic state. Neurotensin (NT)-containing LHA neurons respond to multiple homeostatic challenges and project to the VTA, suggesting that these neurons could link such signals to MLDA function. Indeed, we found that pharmacogenetic activation of LHA NT neurons promoted prolonged DA-dependent locomotor activity and NAc DA efflux, suggesting the importance of VTA neurotransmitter release by LHA NT neurons for the control of MLDA function. Using a microdialysis-mass spectrometry technique that we developed to detect endogenous NT in extracellular fluid in the mouse brain, we found that activation of LHA NT cells acutely increased the extracellular concentration of NT (a known activator of VTA DA cells) in the VTA. In contrast to the prolonged elevation of extracellular NAc DA, however, VTA NT concentrations rapidly returned to baseline. Intra-VTA infusion of NT receptor antagonist abrogated the ability of LHA NT cells to increase extracellular DA in the NAc, demonstrating that VTA NT promotes NAc DA release. Thus, transient LHA-derived NT release in the VTA couples LHA signaling to prolonged changes in DA efflux and MLDA function.

Positive reinforcing effect of neurotensin microinjection into the ventral pallidum in conditioned place preference test

The ventral pallidum (VP) is innervated by the mesolimbic dopaminergic system and it has a key role in motivation, reward, and memory processes. Neurotensin (NT) is an important neuromodulator which has been shown to modulate reinforcement in the ventral tegmental area, in the ventral mesencephalic region and in the central nucleus of amygdala. Neurotensin receptor 1 (NTR1) has already been detected in the VP in abundance, but its role in rewarding and reinforcing processes is not fully understood yet.In our present experiments, the effects of NT on positive reinforcement were investigated in the VP. In conditioned place preference (CPP) test, male Wistar rats were microinjected bilaterally with 100ng or 250ng NT in the volume of 0.4μl. In other groups of animals, 35ng NTR1 antagonist SR 48692 was applied by itself, or microinjected 15min before 100ng NT treatment.One hundred ng dose of NT induced CPP, whereas animals injected with 250ng NT did not exhibit significant differences from the vehicle group.Antagonist pretreatment inhibited the effect of NT, while the antagonist applied by itself had no effect. Our results show that NT injected into the VP is involved in positive reinforcement. This effect is specific to NTR1 receptors because the development of CPP can be prevented by specific antagonist.

Neurotensin receptor1 antagonist SR48692 reduces proliferation by inducing apoptosis and cell cycle arrest in melanoma cells

Malignant melanoma is highly aggressive, and always resistant to conventional chemo-radiotherapy, which results in poor prognosis. As a specific antagonist of neurotensin receptor 1 (NTSR1), emerging evidences confirmed that SR48692 can reverse the pro-growth effect of neurotensin (NTS) by interrupting the interaction between NTS and NTSR1. A375 melanoma cell line was used in this experiment, and SR48692 was employed as the inhibitor of NTS/NTSR1 pathway. We detected the expression of NTSR1 by NTSR1 immunofluorescence and Western blot. After SR48692 treatment, cell proliferation was determined by cell counting, MTT assay and BrdU incorporation study, the cell cycle and apoptosis were performed by flow cytometry. At last Soft Agar Clonogenic assay and xenograft cancer mice model in vivo were used to confirm our result. In this study, we showed that NTSR1 is commonly high expressed in melanoma cells, but low expressed in normal immortalized human keratinocyte line HaCaT. SR48692 not only reduced cell proliferation and self-renewal potential in vitro, but also inhibited the tumor growth derived from A375 cells in NOD/SCID mice in vivo. Further, we originally reported that SR48692 inhibited cell proliferation through cell cycle arrest and apoptosis. Considering the favorable toxicity profile in vitro and in vivo though targeting NTS/NTSR1, SR48692 is worthy of further study and exploitation in melanoma treatment.

Abstract C50: Down-regulation of Bcl2 sensitizes radiation resistance prostate cancer cells to ionizing radiation.

Abstract Radiation therapy (RT) is an important treatment for primary prostate cancer (PCa). However, intermediate and high risk patients can relapse and recurrent disease can be resistant to RT. Bcl2 is one of the critical regulators of apoptotic cell death. Previously, we selected from the DU145 cell line (DU) a subset of cells (DUIR) that survive fractionated high dose ionizing radiation (IR) in vitro. In the current work, we have identified Bcl2 as an important regulator that determines IR resistance and IR-induced aggressiveness in PrCa cells. DUIR has undergone epithelial-mesenchymal transition (EMT) as defined by reduced E-cadherin and enhanced vimentin expression. DUIR cells display higher levels of neurotensin receptor 1 (NTR1), neuron specific enolase (NSE) and chromogranin B, resembling a neuroendocrine (NE) phenotype. DUIR survives better than DU when exposed to IR (6-10 Gy) or to zinc-directed toxins, and DUIR grows faster in response graded levels of serum or NT. NTR1 antagonist (SR48692) blocks the response to NT. NT stimulation reduces apoptosis while SR486923 enhances apoptosis in DUIR cells exposed to IR. The expression level of Bcl2 is dramatically higher in DUIR than in DU. To assess the role of Bcl2 in the ability of cells to survive IR, we generated stable cell lines using lentivirus caring Bcl2 specific shRNA. Down-regulation of Bcl2 sensitized the cells to IR, as shown by decreased proliferation, decreased clonogenicity, increased apoptosis (cleaved PARP and caspase 3/7 activity), and increased DNA breakage (γ-H2AX foci), as compared to control cells. Our study indicates that PCa cells that survive high dose IR display an aggressive phenotype characterized by NE and EMT features with resistance to IR or drug induced cell death. The up-regulation of Bcl2 plays an important role in cell survival following IR. These findings define a mechanism of cellular resistance to IR therapy and they suggest that strategies aimed to limit the effects of Bcl2 could be beneficial. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C50. Citation Format: Tao Wang, Robert E. Carraway, Joshua Briggs, Huazhen Chen, Thomas J. FitzGerald. Down-regulation of Bcl2 sensitizes radiation resistance prostate cancer cells to ionizing radiation. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C50.

Efficient Synthesis of Heterocyclic Neurotensin Receptor Ligands by Microwave-Assisted Aminocarbonylation

Marking the heterocyclic neurotensin receptor antagonist SR142948A as a lead compound, the development of an efficient and a practical synthetic route to heterocyclic aryl carboxamides is reported. Thus, a highly efficient and flexible access to these carboxamides was elaborated by taking advantage of microwave-assisted aminocarbonylation reaction mediated by Mo(CO)6, Herrmann’s palladacycle, [(t-Bu)3PH]BF4, and DBU.

Response of Neurotensin Basal Ganglia Systems during Extinction of Methamphetamine Self-Administration in Rat

Because of persistent social problems caused by methamphetamine (METH), new therapeutic strategies need to be developed. Thus, we investigated the response of central nervous system neurotensin (NT) systems to METH self-administration (SA) and their interaction with basal ganglia dopamine (DA) pathways. Neurotensin is a peptide associated with inhibitory feedback pathways to nigrostriatal DA projections. We observed that NT levels decreased in rats during extinction of METH SA when lever pressing resulted in intravenous infusions of saline rather than METH. Thus, 6 h after the first session of extinction, NT levels were 53, 42, and 49% of corresponding controls in the anterior dorsal striatum, posterior dorsal striatum, and globus pallidus, respectively. NT levels were also significantly reduced in corresponding yoked rats in the anterior dorsal striatum (64% of control), but not the other structures examined. The reductions in NT levels in the anterior dorsal striatum particularly correlated with the lever pressing during the first session of extinction (r =s; 0.745). These, and previously reported findings, suggest that the extinction-related reductions in NT levels were mediated by activation of D2 receptors. Finally, administration of the neurotensin receptor 1 (NTR1) agonist [PD149163 [Lys(CH2NH)Lys-Pro,Trp-tert-Leu-Leu-Oet]; 0.25 or 0.5 mg/kg] diminished lever pressing during the first extinction session, whereas the NTR1 antagonist [SR48692 [2-[(1-(7-chloro-4-quinolinyl)-5-(2,6-imethoxyphenyl)pyrazol-3-yl)carbonylamino]tricyclo(3.3.1.1.(3.7))decan-2-carboxylic acid]; 0.3 mg/kg per administration] attenuated the reduction of lever pressing during the second to fourth days of extinction. In summary, these findings support the hypothesis that some of the endogenous basal ganglia NT systems contribute to the elimination of contingent behavior during the early stages of the METH SA extinction process.

Neurotensin Co-Expressed in Orexin-Producing Neurons in the Lateral Hypothalamus Plays an Important Role in Regulation of Sleep/Wakefulness States

Both orexin and neurotensin are expressed in the lateral hypothalamic area (LHA) and have been implicated in the regulation of feeding, motor activity and the reward system. A double label immunofluorescence and in situ hybridization studies showed that neurotensin colocalizes with orexin in neurons of the LHA. Pharmacological studies suggested that neurotensin excites orexin-producing neurons (orexin neurons) through activation of neurotensin receptor-2 (NTSR-2) and non-selective cation channels. In situ hybridization study showed that most orexin neurons express neurotensin receptor-2 mRNA but not neurotensin receptor-1 (Ntsr-1) mRNA. Immunohistochemical studies showed that neurotensin-immunoreactive fibers make appositions to orexin neurons. A neurotensin receptor antagonist decreased Fos expression in orexin neurons and wakefulness time in wild type mice when administered intraperitoneally. However, the antagonist did not evoke any effect on these parameters in orexin neuron-ablated mice. These observations suggest the importance of neurotensin in maintaining activity of orexin neurons. The evidence presented here expands our understanding of the regulatory mechanism of orexin neurons.

A Machine‐Assisted Flow Synthesis of SR48692: A Probe for the Investigation of Neurotensin Receptor‐1

Here we report the direct comparison of a conventional batch mode synthesis of Meclinertant (SR48692, 1), a neurotensin receptor-1 antagonist, with its machine-assisted flow chemistry alternative. By using these enabling tools, combined with solid-supported reagents and scavengers, many process advantages were observed. Care, however, must be taken not to convert these techniques into expensive solutions to problems that do not exist.

Aggressive phenotype for prostate cancer cells that survive high-dose ionizing radiation.

236 Background: Radiation therapy (RT) is an important primary treatment for localized prostate cancer (PCa). However, certain patients can relapse and become resistant to RT. To identify the molecular mechanisms underlying RT resistance, we studied human PCa cells that survive fractionated high dose IR in vitro. Methods: DU145 (DU), a human cell line from PCa metastasized to brain, was exposed to fractionated ionizing radiation (IR) up to 40 Gy. The cancer biology of the surviving cells (DUIR) after 4 month in culture was studied. Cell growth and survival were assessed using cell counting, SRB and clonogenic assay. Invasiveness was measured using Boyden chambers. Caspase activity was determined for apoptosis. Activation of signaling molecules and expression of biomarkers was assessed using Immunoblot. Hormone binding to receptors was assayed using iodinated ligands. Results: Whereas DU was squamous in shape, DUIR displayed fibroblast-like morphology with long protrusions resembling cells undergoing epithelial-mesenchymal transition (EMT) confirmed by reduced E-cadherin and enhanced vimentin expression. DUIR cells showed higher level of neurotensin receptor 1 (NTR1) and chromogranin B resembling a neuroendocrine (NE) phenotype. DUIR has significantly higher survival than DU when exposed to IR (6–10 Gy) or zinc-directed toxins and grows significantly faster in response to serum or NT at a dose dependent manner. Addition of NTR1 antagonist SR486923 abolished the NT enhanced cell growth. DUIR had increased invasiveness through the matrigel-coated membrane. ERK and PKC, but not AKT, were constitutively active in DUIR. BCL2 level was upregulated in DUIR. NT stimulation reduced apoptosis while SR486923 enhanced apoptosis in DUIR cells upon IR. Conclusions: PCa cells that survive high dose IR display an aggressive phenotype characterized by NE and EMT features including invasion and resistance to IR/drug induced cell death. These changes could be due to constitutive activation of growth signaling pathways and upregulation of anti-apoptosis/necrosis molecules. Further study may provide insight into the mechanism of cellular resistance to therapy and establish strategies for novel therapeutic applications.

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 regulates cortical glutamate transmission by modulating N‐methyl‐D‐aspartate receptor functional activity: An in vivo microdialysis study

The aim of the present in vivo microdialysis study was to investigate whether the tridecapeptide neurotensin (NT) influences the N-methyl-D-aspartate (NMDA) receptor-mediated increase of cortical glutamate transmission in freely moving rats. Intracortical perfusion with NT influenced local extracellular glutamate levels in a bell-shaped, concentration-dependent manner. One hundred and three hundred nanomolar NT concentrations increased glutamate levels (151% ± 7% and 124% ± 3% of basal values, respectively). Higher (1,000 nM) and lower (10 nM) NT concentrations did not alter extracellular glutamate levels. The NT receptor antagonist SR48692 (100 nM) prevented the NT (100 nM)-induced increase in glutamate levels. NMDA (100 and 500 μM) perfusion induced a concentration-dependent increase in extracellular glutamate levels, the lower 10 μM NMDA concentration being ineffective. When NT (10 nM, a concentration by itself ineffective) was added in combination with NMDA (100 μM) to the perfusion medium, a significant greater increase in extracellular glutamate levels (169% ± 7%) was observed with respect to the increase induced by NMDA (100 μM) alone (139% ± 4%). SR48692 (100 nM) counteracted the increase in glutamate levels induced by the treatment with NT (10 nM) plus NMDA (100 μM). The enhancement of cortical glutamate levels induced by NMDA (100 and 500 μM) was partially antagonized by the presence of SR48692, at a concentration (100 nM) that by itself was ineffective in modulating glutamate release. These findings indicate that NT plays a relevant role in the regulation of cortical glutamatergic transmission, especially by modulating the functional activity of cortical NMDA receptors. A possible role in glutamate-mediated neurotoxicity is suggested.