Ligand binding kinetics of substance P and neurokinin A receptors stably expressed in Chinese hamster ovary cells and evidence for differential stimulation of inositol 1,4,5-trisphosphate and cyclic AMP second messenger responses

The Repurposing of Non-Peptide Neurokinin-1 Receptor Antagonists as Antitumor Drugs: An Urgent Challenge for Aprepitant

The substance P (SP)/neurokinin-1 receptor (NK-1R) system is involved in cancer progression. NK-1R, activated by SP, promotes tumor cell proliferation and migration, angiogenesis, the Warburg effect, and the prevention of apoptosis. Tumor cells overexpress NK-1R, which influences their viability. A typical specific anticancer strategy using NK-1R antagonists, irrespective of the tumor type, is possible because these antagonists block all the effects mentioned above mediated by SP on cancer cells. This review will update the information regarding using NK-1R antagonists, particularly Aprepitant, as an anticancer drug. Aprepitant shows a broad-spectrum anticancer effect against many tumor types. Aprepitant alone or in combination therapy with radiotherapy or chemotherapy could reduce the sequelae and increase the cure rate and quality of life of patients with cancer. Current data open the door to new cancer research aimed at antitumor therapeutic strategies using Aprepitant. To achieve this goal, reprofiling the antiemetic Aprepitant as an anticancer drug is urgently needed.

Substance P and Neurokinin-1 Receptor System in Thyroid Cancer: Potential Targets for New Molecular Therapies

In recent years, numerous approaches have been developed to comprehend the molecular alterations underlying thyroid cancer (TC) oncogenesis and explore novel therapeutic strategies for TC. It is now well established that the neurokinin-1 receptor (NK-1R) is overexpressed in cancer cells and that NK-1R is essential for the viability of cancer cells. The binding of substance P (SP) to NK-1R in neoplastic cells plays a pivotal role in cancer progression by promoting neoplastic cell growth, protecting tumor cells from apoptosis, triggering invasion and metastasis through the enhanced migration of cancer cells, and stimulating endothelial cell proliferation for tumor angiogenesis. Remarkably, all types of human TC (papillary, follicular, medullary, anaplastic), as well as metastatic lesions, exhibit the overexpression of SP and NK-1R compared to the normal thyroid gland. TC cells synthesize and release SP, which exerts its multiple functions through autocrine, paracrine, intracrine, and neuroendocrine processes, including the regulation of tumor burden. Consequently, the secretion of SP from TC results in increased SP levels in plasma, which are significantly higher in TC patients compared to controls. Additionally, NK-1R antagonists have demonstrated a dose-dependent antitumor action. They impair cancer cell proliferation on one side and induce apoptosis of tumor cells on the other side. Furthermore, it has been demonstrated that NK-1R antagonists inhibit neoplastic cell migration, thereby impairing both invasiveness and metastatic abilities, as well as angiogenesis. Given the consistent overexpression of NK-1R in all types of TC, targeting this receptor represents a promising therapeutic approach for TC. Therefore, NK-1R antagonists, such as the drug aprepitant, may represent novel drugs for TC treatment.

The Role of Substance P Within Traumatic Brain Injury and Implications for Therapy

This review examines the role of the neuropeptide substance P within the neuroinflammation that follows traumatic brain injury. It examines it in reference to its preferential receptor, the neurokinin-1 receptor, and explores the evidence for antagonism of this receptor in traumatic brain injury with therapeutic intent. Expression of substance P increases following traumatic brain injury. Subsequent binding to the neurokinin-1 receptor results in neurogenic inflammation, a cause of deleterious secondary effects that include an increased intracranial pressure and poor clinical outcome. In several animal models of TBI, neurokinin-1 receptor antagonism has been shown to reduce brain edema and the resultant rise in intracranial pressure. A brief overview of the history of substance P is presented, alongside an exploration into the chemistry of the neuropeptide with a relevance to its functions within the central nervous system. This review summarizes the scientific and clinical rationale for substance P antagonism as a promising therapy for human TBI.

The Neurokinin-1 Receptor Is Essential for the Viability of Human Glioma Cells: A Possible Target for Treating Glioblastoma

Background

Glioblastoma or glioma is the most common malignant brain tumor. Patients have a prognosis of approximately 15 months, despite the current aggressive treatment. Neurokinin-1 receptor (NK-1R) occurs naturally in human glioma, and it is necessary for the tumor development.

Objective

The purpose of the study was to increase the knowledge about the involvement of the substance P (SP)/NK-1R system in human glioma.

Methods

Cellular localization of NK-1R and SP was studied in GAMG and U-87 MG glioma cell lines by immunofluorescence. The contribution of both SP and NK-1R to the viability of these cells was also assessed after applying the tachykinin 1 receptor (TAC1R) or the tachykinin 1 (TAC1) small interfering RNA gene silencing method, respectively.

Results

Both SP and the NK-1R (full-length and truncated isoforms) were localized in the nucleus and cytoplasm of GAMG and U-87 MG glioma cells. The presence of full-length NK-1R isoform was mainly observed in the nucleus, while the level of truncated isoform was higher in the cytoplasm. Cell proliferation was decreased when glioma cells were transfected with TAC1R siRNA, but not with TAC1. U-87 MG cells were more sensitive to the effect of the TAC1R inhibition than GAMG cells. The decrease in the number of glioma cells after silencing of the TAC1R siRNA gene was due to apoptotic and necrotic mechanisms. In human primary fibroblast cultured cells, TAC1R silencing by siRNA did not produce any change in cell viability.

Conclusions

Our results show for the first time that the expression of the TAC1R gene (NK-1R) is essential for the viability of GAMG and U-87 MG glioma cells. On the contrary, the TAC1R gene is not essential for the viability of normal cells, confirming that NK-1R could be a promising and specific therapeutic target for the treatment of glioma.

What substance P might tell us about the prognosis and mechanism of Parkinson's disease?

The neuropeptide substance P (SP) plays an important role in neurodegenerative disorders, among which Parkinson's disease (PD). In the present work we have reviewed the involvement of SP and its preferred receptor (NK1-R) in motor and non-motor PD symptoms, in both PD animal models and patients. Despite PD is primarily a motor disorder, non-motor abnormalities, including olfactory deficits and gastrointestinal dysfunctions, can represent diagnostic PD predictors, according to the hypothesis that the olfactory and the enteric nervous system represent starting points of neurodegeneration, ascending to the brain via the sympathetic fibers and the vagus nerve. In PD patients, the α-synuclein aggregates in the olfactory bulb and the gastrointestinal tract, as well as in the dorsal motor nucleus of the vagus nerve often co-localize with SP, indicating SP-positive neurons as highly vulnerable sites of degeneration. Considering the involvement of the SP/NK1-R in both the periphery and specific brain areas, this system might represent a neuronal substrate for the symptom and disease progression, as well as a therapeutic target for PD.

Triple Negative Breast Cancer: How Neurokinin-1 Receptor Antagonists Could Be Used as a New Therapeutic Approach

Breast cancer (BC) is the most frequently diagnosed cancer and the leading cause of cancer death among females. BC cells not showing HER-2/Neu amplification and not expressing estrogen/ progesterone receptors are named triple-negative BC (TNBC) cells. TNBC represents 10-15% of all BC and is associated with an aggressive clinical course. TNBC patient prognosis, survival and response to current therapies are poor and for this reason, it is crucial to search for new therapeutic targets in TNBC to develop new therapeutic strategies. One of these targets is the neurokinin-1 receptor (NK-1R). It is well known that the substance P (SP)/NK-1R system is involved in cancer progression. TNBC cells overexpress the NK-1R and, after binding to this receptor, SP promotes the proliferation/ migration of TNBC cells. Non-peptide NK-1R antagonists (e.g., aprepitant) are known to exert, via the NK-1R, an antitumor action; TNBC cells die by apoptosis. In this review, we update the data on a promising therapeutic innovation: the use of NK-1R antagonists for the treatment of TNBC patients.

The Neurokinin-1 Receptor Antagonist Aprepitant, a New Drug for the Treatment of Hematological Malignancies: Focus on Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy. To treat the disease successfully, new therapeutic strategies are urgently needed. One of these strategies can be the use of neurokinin-1 receptor (NK-1R) antagonists (e.g., aprepitant), because the substance P (SP)/NK-1R system is involved in cancer progression, including AML. AML patients show an up-regulation of the NK-1R mRNA expression; human AML cell lines show immunoreactivity for both SP and the NK-1R (it is overexpressed: the truncated isoform is more expressed than the full-length form) and, via this receptor, SP and NK-1R antagonists (aprepitant, in a concentration-dependent manner) respectively exert a proliferative action or an antileukemic effect (apoptotic mechanisms are triggered by promoting oxidative stress via mitochondrial Ca⁺⁺ overload). Aprepitant inhibits the formation of AML cell colonies and, in combination with chemotherapeutic drugs, is more effective in inducing cytotoxic effects and AML cell growth blockade. NK-1R antagonists also exert an antinociceptive effect in myeloid leukemia-induced bone pain. The antitumor effect of aprepitant is diminished when the NF-κB pathway is overactivated and the damage induced by aprepitant in cancer cells is higher than that exerted in non-cancer cells. Thus, the SP/NK-1R system is involved in AML, and aprepitant is a promising antitumor strategy against this hematological malignancy. In this review, the involvement of this system in solid and non-solid tumors (in particular in AML) is updated and the use of aprepitant as an anti-leukemic strategy for the treatment of AML is also mentioned (a dose of aprepitant (>20 mg/kg/day) for a period of time according to the response to treatment is suggested). Aprepitant is currently used in clinical practice as an anti-nausea medication.

The substance P and neurokinin-1 receptor system in human thyroid cancer: an immunohistochemical study

To develop a new therapeutic strategy against thyroid cancer (TC), the expression of both substance P (SP) and neurokinin-1 receptor (NK-1R) must be demonstrated in TC cells. This study aims to examine by immunohistochemistry, the localization of SP and the NK-1R in human TC samples (papillary, follicular, medullary, anaplastic), in metastasis and in healthy thyroid samples. SP and the NK-1R were expressed in all normal and TC samples. In healthy glands, SP was located in follicular cells (nucleus) and colloid and NK-1R in follicular cells (cytoplasm) and stroma. In TC samples, SP was visualized in follicular cells (nucleus and cytoplasm), stroma and colloid and NK-1R in follicular cells (cytoplasm), stroma and colloid. A semiquantitative scoring system (Allred Unit Scoring System) was applied. The expression (Allred total score) of SP and NK-1R was weaker in normal thyroid glands than in TC. In comparison with TC samples, a lower intensity/proportion of SP (nucleus and cytoplasm of follicular cells; stroma) was observed in normal samples. By contrast, in the colloid of TC samples the presence of SP was lower than in normal samples. In comparison with TC samples, the presence of the NK-1R in the cytoplasm of follicular cells and colloid was lower in normal thyroid samples, whereas the expression of this receptor in the stroma was higher. The results reported in this study suggest that the NK-1R could be a new target for the treatment of TC and use of the NK-1R antagonists could serve as a new anti-TC therapeutic strategy.

Glioma and Neurokinin-1 Receptor Antagonists: A New Therapeutic Approach

BACKGROUND

In adults, the most lethal and frequent primary brain tumor is glioblastoma. Despite multimodal aggressive therapies, the median survival time after diagnosis is around 15 months. In part, this is due to the blood-brain barrier that restricts common treatments (e.g., chemotherapy). Unfortunately, glioma recurs in 90% of patients. New therapeutic strategies against glioma are urgently required. Substance P (SP), through the neurokinin (NK)-1 receptor, controls cancer cell proliferation by activating c-myc, mitogenactivated protein kinases, activator protein 1 and extracellular signal-regulated kinases 1 and 2. Glioma cells overexpress NK-1 receptors when compared with normal cells. The NK-1 receptor/SP system regulates the proliferation/migration of glioma cells and stimulates angiogenesis, triggering inflammation which contributes to glioma progression. In glioma cells, SP favors glycogen breakdown, essential for glycolysis. By contrast, in glioma, NK-1 receptor antagonists block the proliferation of tumor cells and the breakdown of glycogen and also promote the death (apoptosis) of these cells. These antagonists also inhibit angiogenesis and exert antimetastatic and anti-inflammatory actions.

OBJECTIVE

This review updates the involvement of the NK-1 receptor/SP system in the development of glioma and the potential clinical application of NK-1 receptor antagonists as antiglioma agents.

CONCLUSION

The NK-1 receptor plays a crucial role in glioma and NK-1 receptor antagonists could be used as anti-glioma drugs.

Neurokinin-1 Receptor Antagonists against Hepatoblastoma

Hepatoblastoma (HB) is the most common malignant liver tumor that occurs during childhood. The prognosis of children with HB is favorable when a complete surgical resection of the tumor is possible, but for high-risk patients, the prognosis is much worse. New anti-HB strategies must be urgently developed. The undecapeptide substance P (SP) after binding to the neurokinin-1 receptor (NK-1R), regulates cancer cell proliferation, exerts an antiapoptotic effect, induces cell migration for invasion/metastasis, and triggers endothelial cell proliferation for neoangiogenesis. HB samples and cell lines overexpress NK-1R (the truncated form) and SP elicits HB cell proliferation. One of these strategies could be the use of non-peptide NK-1R antagonists. These antagonists exert, in a concentration-dependent manner, an antiproliferative action against HB cells (inhibit cell proliferation and induce the death of HB cells by apoptosis). NK-1R antagonists exerted a dual effect in HB: Decreased both tumor volume and angiogenic activity. Thus, the SP/NK-1R system is an important target in the HB treatment and NK-1R antagonists could act as specific drugs against HB cells. In this review, we update and discuss the use of NK-1R antagonists in the treatment of HB.

Substance P and fibrotic diseases

Substance P (SP) is an undecapeptide encoding the tachykinin 1 (TAC1) gene and belongs to the tachykinin family. SP is widely distributed in the central nervous system and the peripheral nervous system. SP is also produced by nonneuronal cells, such as inflammatory cells and endothelial cells. The biological activities of SP are mainly regulated through the high-affinity neurokinin 1 receptor (NK-1R). The SP/NK-1R system plays an important role in the molecular bases of many human pathophysiologic processes, such as pain, infectious and inflammatory diseases, and cancer. In addition, this system has been implicated in fibrotic diseases and processes such as wound healing, myocardial fibrosis, bowel fibrosis, myelofibrosis, renal fibrosis, and lung fibrosis. Recently, studies have shown that SP plays an important role in liver fibrosis and that NK-1R antagonists can inhibit the progression of fibrosis. NK-1R receptor antagonists could provide clinical solutions for fibrotic diseases. This review summarizes the structure and function of SP and its involvement in fibrotic diseases.

Affinity, potency, efficacy, and selectivity of neurokinin A analogs at human recombinant NK2 and NK1 receptors

A series of peptide NK2 receptor agonists was evaluated for affinity, potency, efficacy, and selectivity at human recombinant NK2 and NK1 receptors expressed in CHO cells to identify compounds with the greatest separation between NK2 and NK1 receptor agonist activity. Binding studies were performed using displacement of [¹²⁵I]-NKA binding to NK2 receptors and displacement of [³H]-Septide binding to NK1 receptors expressed in CHO cells. Functional studies examining the increase in intracellular calcium levels and cyclic AMP stimulation were performed using the same cell lines. A correlation was demonstrated between binding affinities (Ki) and potency to increase intracellular calcium (EC₅₀) for NK2 and NK1 receptors. Ranking compounds by their relative affinity (Ki) or potency (EC₅₀) at NK2 or NK1 receptors indicated that the most selective NK2 agonists tested were [Lys⁵,MeLeu⁹,Nle¹⁰]-NKA(4-10) (NK1/NK2 Ki ratio = 674; NK1/NK2 EC₅₀ ratio = 105) and [Arg⁵,MeLeu⁹,Nle¹⁰]-NKA(4-10) (NK1/NK2 Ki ratio = 561; NK1/NK2 EC₅₀ ratio = 70). The endogenous peptide, NKA, lacked selectivity with an NK1/NK2 Ki ratio = 20 and NK1/NK2 EC₅₀ ratio = 1. Of the compounds selected for evaluation in cyclic AMP stimulation assays, [β-Ala⁸]-NKA(4–10) had the greatest selectivity for activation of NK2 over NK1 receptors (NK1/NK2 EC₅₀ ratio = 244), followed by [Lys⁵,MeLeu⁹,Nle¹⁰]-NKA(4-10) (ratio = 74), and NKA exhibited marginal selectivity (ratio = 2.8).

Increased nuclear localization of substance P in human gastric tumor cells

Gastric cancer (GC) is an aggressive disease that remains the fourth most common type of cancer and is the second leading cause of cancer-related death worldwide. Treatment of advanced or metastatic GC has seen little progress and median overall survival in this group remains <1 year. It is urgent to investigate new mechanisms to understand GC progression. It is known that substance P (SP), after binding to the neurokinin-1 (NK-1) receptor, elicits GC proliferation; that GC cells and samples express NK-1 receptors; that NK-1 receptor antagonists, in a concentration dependent manner, inhibit the proliferation of GC cells and that these cells die by apoptosis. However, the presence of SP in GC and normal gastric cells is unknown. In order to know more on the involvement of the SP/NK-1 receptor system in GC, we studied in thirty human GC and normal gastric samples the immunolocalization of SP after using an immunohistochemical technique. SP was observed in the cytoplasm and in the nucleus of GC and normal gastric cells. The nuclear expression of SP was higher in GC cells than in normal cells. No significant difference was observed when the cytoplasmatic expression of SP in normal and GC cells was compared. The findings suggest that SP plays an important role in both nuclear function and GC.

Kinetic binding and activation profiles of endogenous tachykinins targeting the NK1 receptor

Ligand-receptor binding kinetics (i.e. association and dissociation rates) are emerging as important parameters for drug efficacy in vivo. Awareness of the kinetic behavior of endogenous ligands is pivotal, as drugs often have to compete with those. The binding kinetics of neurokinin 1 (NK1) receptor antagonists have been widely investigated while binding kinetics of endogenous tachykinins have hardly been reported, if at all. Therefore, the aim of this research was to investigate the binding kinetics of endogenous tachykinins and derivatives thereof and their role in the activation of the NK1 receptor. We determined the binding kinetics of seven tachykinins targeting the NK1 receptor. Dissociation rate constants (k_off) ranged from 0.026±0.0029min^-1 (Sar⁹,Met(O₂)¹¹-SP) to 0.21±0.015min^-1 (septide). Association rate constants (k_on) were more diverse: substance P (SP) associated the fastest with a k_on value of 0.24±0.046nM^-1min^-1 while neurokinin A (NKA) had the slowest association rate constant of 0.001±0.0002nM^-1min^-1. Kinetic binding parameters were highly correlated with potency and maximal response values determined in label-free impedance-based experiments on U-251 MG cells. Our research demonstrates large variations in binding kinetics of tachykinins which correlate to receptor activation. These findings provide new insights into the ligand-receptor interactions of tachykinins and underline the importance of measuring binding kinetics of both drug candidates and competing endogenous ligands.

Biological Characterization of Neurokinin Antagonists Discovered Through Screening of a Combinatorial Library

Recent advances in combinatorial chemistry have resulted in the rapid screening of libraries against biological targets. Another advance in biological screening is the ability to design and utilize novel, automated, nonradioactive assays for targets of pharmaceutical interest. Using encoding technology and europium time-resolved fluorescence, we have designed primary receptor binding assays to define active compounds against the neurokinin-1 and neurokinin-2 receptor subtypes. In addition, a secondary, cell-based, functional assay measuring intracellular calcium flux with calcium sensitive fluorophores was used to determine receptor agonist or antagonist activities. We adapted a cuvette based assay to a CCD camera and digital imaging system that allowed us to demonstrate functional receptor antagonist activity in all 96 wells of a microtiter plate simultaneously. The screening of a 20,000 member library using europium labeled neurokinin ligands resulted in the identification of 43 active compounds for neurokinin-1 and 27 for neurokinin-2. Through medicinal chemistry and structure-activity relationships, a compound was synthesized with balanced dual antagonist activity at both neurokinin receptors with greater than 100-fold less activity against the neurokinin-3 receptor subtype. The structure-activity relationships generated from this initial library can now be used to design a new focused library to improve on neurokinin-1/neurokinin-2 receptor potency and selectivity.

Neurokinin-1 receptor antagonists as antitumor drugs in gastrointestinal cancer: A new approach

Gastrointestinal (GI) cancer is the term for a group of cancers affecting the digestive system. After binding to the neurokinin-1 (NK-1) receptor, the undecapeptide substance P (SP) regulates GI cancer cell proliferation and migration for invasion and metastasis, and controls endothelial cell proliferation for angiogenesis. SP also exerts an antiapoptotic effect. Both SP and the NK-1 receptor are located in GI tumor cells, the NK-1 receptor being overexpressed. By contrast, after binding to the NK-1 receptor, NK-1 receptor antagonists elicit the inhibition (epidermal growth factor receptor inhibition) of the proliferation of GI cancer cells in a concentration-dependent manner, induce the death of GI cancer cells by apoptosis, counteract the Warburg effect, inhibit cancer cell migration (counteracting invasion and metastasis), and inhibit angiogenesis (vascular endothelial growth factor inhibition). NK-1 receptor antagonists are safe and well tolerated. Thus, the NK-1 receptor could be considered as a new target in GI cancer and NK-1 receptor antagonists (eg, aprepitant) could be a new promising approach for the treatment of GI cancer.

Antitumor action of temozolomide, ritonavir and aprepitant against human glioma cells

In the effort to find better treatments for glioblastoma we tested several currently marketed non-chemotherapy drugs for their ability to enhance the standard cytotoxic drug currently used to treat glioblastoma- temozolomide. We tested four antiviral drugs- acyclovir, cidofovir, maraviroc, ritonavir, and an anti-emetic, aprepitant. We found no cytotoxicity of cidofovir and discussed possible reasons for discrepancy from previous findings of others. We also found no cytotoxicity from acyclovir or maraviroc also in contradistinction to predictions. Cytotoxicity to glioma cell line GAMG for temozolomide alone was 14%, aprepitant alone 7%, ritonavir alone 14%, while temozolomide + aprepitant was 19%, temozolomide + ritonavir 34%, ritonavir + aprepitant 64 %, and all three, temozolomide + ritonavir + aprepitant 78%. We conclude that a remarkable synergy exists between aprepitant and ritonavir. Given the long clinical experience with these two well-tolerated drugs in treating non-cancer conditions, and the current median survival of glioblastoma of 2 years, a trial is warranted of adding these two simple drugs to current standard treatment with temozolomide.

Targeting NK-1 Receptors to Prevent and Treat Pancreatic Cancer: a New Therapeutic Approach

Pancreatic cancer (PC) is the fourth leading cause of cancer related-deaths in both men and women, and the 1- and 5-year relative survival rates are 25% and 6%, respectively. It is known that smoking, alcoholism and psychological stress are risk factors that can promote PC and increase PC progression. To date, the prevention of PC is crucial because there is no curative treatment. After binding to the neurokinin-1 (NK-1) receptor (a receptor coupled to the stimulatory G-protein Gαs that activates adenylate cyclase), the peptide substance P (SP)-at high concentrations-is involved in many pathophysiological functions, such as depression, smoking, alcoholism, chronic inflammation and cancer. It is known that PC cells and samples express NK-1 receptors; that the NK-1 receptor is overexpressed in PC cells in comparison with non-tumor cells, and that nanomolar concentrations of SP induce PC cell proliferation. By contrast, NK-1 receptor antagonists exert antidepressive, anxiolytic and anti-inflammatory effects and anti-alcohol addiction. These antagonists also exert An antitumor action since in vitro they inhibit PC cell proliferation (PC cells death by apoptosis), and in a xenograft PC mouse model they exert both antitumor and anti-angiogenic actions. NK-1 receptor antagonists could be used for the treatment of PC and hence the NK-1 receptor could be a new promising therapeutic target in PC.

Involvement of substance P and the NK-1 receptor in pancreatic cancer

Pancreatic cancer is the fourth leading cause of cancer related-death for both men and women and the 1- and 5-year relative survival rates are 25% and 6%, respectively. Thus, it is urgent to investigate new antitumor drugs to improve the survival of pancreatic cancer patients. The peptide substance P (SP) has a widespread distribution throughout the body. After binding to the neurokinin-1 (NK-1) receptor, SP regulates biological functions related to cancer, such as tumor cell proliferation, neoangiogenesis, the migration of tumor cells for invasion, infiltration and metastasis, and it exerts an antiapoptotic effects on tumor cells. It is known that the SP/NK-1 receptor system is involved in pancreatic cancer progression: (1) pancreatic cancer cells and samples express NK-1 receptors; (2) the NK-1 receptor is overexpressed in pancreatic cancer cells in comparison with non-tumor cells; (3) nanomolar concentrations of SP induce pancreatic cancer cell proliferation; (4) NK-1 receptor antagonists inhibit pancreatic cell proliferation in a concentration-dependent manner, at a certain concentration, these antagonists inhibit 100% of tumor cells; (5) this antitumor action is mediated through the NK-1 receptor, and tumor cells die by apoptosis; and (6) NK-1 receptor antagonists inhibit angiogenesis in pancreatic cancer xenografts. All these data suggest that the SP/NK-1 receptor system could play an important role in the development of pancreatic cancer; that the NK-1 receptor could be a new promising therapeutic target in pancreatic cancer, and that NK-1 receptor antagonists could improve the treatment of pancreatic cancer.

Involvement of substance P and the NK-1 receptor in cancer progression

Many data suggest the deep involvement of the substance P (SP)/neurokinin (NK)-1 receptor system in cancer: (1) Tumor cells express SP, NK-1 receptors and mRNA for the tachykinin NK-1 receptor; (2) Several isoforms of the NK-1 receptor are expressed in tumor cells; (3) the NK-1 receptor is involved in the viability of tumor cells; (4) NK-1 receptors are overexpressed in tumor cells in comparison with normal ones and malignant tissues express more NK-1 receptors than benign tissues; (5) Tumor cells expressing the most malignant phenotypes show an increased percentage of NK-1 receptor expression; (6) The expression of preprotachykinin A is increased in tumor cells in comparison with the levels found in normal cells; (7) SP induces the proliferation and migration of tumor cells and stimulates angiogenesis by increasing the proliferation of endothelial cells; (8) NK-1 receptor antagonists elicit the inhibition of tumor cell growth; (9) The specific antitumor action of NK-1 receptor antagonists on tumor cells occurs through the NK-1 receptor; (10) Tumor cell death is due to apoptosis; (11) NK-1 receptor antagonists inhibit the migration of tumor cells and neoangiogenesis. The NK-1 receptor is a therapeutic target in cancer and NK-1 receptor antagonists could be considered as broad-spectrum antitumor drugs for the treatment of cancer. It seems that a common mechanism for cancer cell proliferation mediated by SP and the NK-1 receptor is triggered, as well as a common mechanism exerted by NK-1 receptor antagonists on tumor cells, i.e. apoptosis.

NK-1 as a melanoma target

INTRODUCTION

Melanoma expresses both neurokinin-1 (NK-1) receptors and substance P (SP). After binding to the NK-1 receptor, SP induces tumor cell proliferation in melanoma cells, whereas after binding to the same NK-1 receptor, antagonists inhibit melanoma cell proliferation and cause tumor cell death by apoptosis. Thus, the NK-1 receptor could be a new and promising target in melanoma therapy.

AREAS COVERED

This review provides an overview of the underlying mechanism of action of the SP/NK-1 receptor system, and NK-1 receptor antagonists in human melanoma, over the last 7 years.

EXPERT OPINION

In stages III - IV, no effective treatment exists for melanoma and hence there is an urgent need to improve therapy in melanoma patients. The NK-1 receptor is a promising new target in human melanoma treatment, since preclinical assays (most of them in vitro assays) have reported that NK-1 receptor antagonists exert an antitumor action against melanoma. The NK-1 receptor antagonist aprepitant is used in clinical practice and exerts an antitumor action against human melanoma in vitro. In the future, such antitumor action should be tested in human clinical trials. This should be faster compared with less investigated NK-1 receptor antagonists, because a great part of the required safety and characterization studies for aprepitant have already been carried out.

PKCepsilon-dependent potentiation of TTX-resistant Nav1.8 current by neurokinin-1 receptor activation in rat dorsal root ganglion neurons

Background

Substance P (SP), which mainly exists in a subtype of small-diameter dorsal root ganglion (DRG) neurons, is an important signal molecule in pain processing in the spinal cord. Our previous results have proved the expression of SP receptor neurokinin-1 (NK-1) on DRG neurons and its interaction with transient receptor potential vanilloid 1 (TRPV1) receptor.

Results

In this study we investigated the effect of NK-1 receptor agonist on Na_v1.8, a tetrodotoxin (TTX)-resistant sodium channel, in rat small-diameter DRG neurons employing whole-cell patch clamp recordings. NK-1 agonist [Sar⁹, Met(O₂)¹¹]-substance P (Sar-SP) significantly enhanced the Na_v1.8 currents in a subgroup of small-diameter DRG neurons under both the normal and inflammatory situation, and the enhancement was blocked by NK-1 antagonist Win51708 and protein kinase C (PKC) inhibitor bisindolylmaleimide (BIM), but not the protein kinase A (PKA) inhibitor H89. In particular, the inhibitor of PKCε, a PKC isoform, completely blocked this effect. Under current clamp model, Sar-SP reduced the amount of current required to evoke action potentials and increased the firing rate in a subgroup of DRG neurons.

Conclusion

These data suggest that activation of NK-1 receptor potentiates Na_v1.8 sodium current via PKCε-dependent signaling pathway, probably participating in the generation of inflammatory hyperalgesia.

Effects of substance P in the amygdala, ventromedial hypothalamus, and periaqueductal gray on fear-potentiated startle

The neural pathways through which substance P (SP) influences fear and anxiety are poorly understood. However, the amygdala, a brain area repeatedly implicated in fear and anxiety processes, is known to contain large numbers of SP-containing neurons and SP receptors. Several studies have implicated SP neurotransmission within the amygdala in anxiety processes. In the present study, we evaluated the effects of site-specific infusions of an SP receptor antagonist, GR 82334, on conditioned fear responses using the fear-potentiated startle paradigm. GR 82334 infusion into the basolateral (BLA) or the medial (MeA) nuclei of the amygdala, but not into the central nucleus of the amygdala (CeA), dose dependently reduced fear-potentiated startle. Similar effects were obtained with GR 82334 infusion into the ventromedial nucleus of the hypothalamus (VMH), to which the MeA projects, and into the rostral dorsolateral periaqueductal gray (PAG), to which the VMH projects, but not into the deep layers of the superior colliculus/deep mesencephalic nucleus (dSC/DpMe), an output of the CeA previously shown to be important for fear-potentiated startle. Consistent with previous findings, infusion of the AMPA receptor antagonist, NBQX, into the dSC/DpMe, but not into the PAG, did disrupt fear-potentiated startle. These findings suggest that multiple outputs from the amygdala play a critical role in fear-potentiated startle and that SP plays a critical, probably modulatory role, in the MeA to VMH to PAG to the startle pathway based on these and data from others.

The role of peptides in central sensitization

Peptides released in the spinal cord from the central terminals of nociceptors contribute to the persistent hyperalgesia that defines the clinical experience of chronic pain. Using substance P (SP) and calcitonin gene-related peptide (CGRP) as examples, this review addresses the multiple mechanisms through which peptidergic neurotransmission contributes to the development and maintenance of chronic pain. Activation of CGRP receptors on terminals of primary afferent neurons facilitates transmitter release and receptors on spinal neurons increases glutamate activation of AMPA receptors. Both effects are mediated by cAMP-dependent mechanisms. Substance P activates neurokinin receptors (3 subtypes) which couple to phospholipase C and the generation of the intracellular messengers whose downstream effects include depolarizing the membrane and facilitating the function of AMPA and NMDA receptors. Activation of neurokinin-1 receptors also increases the synthesis of prostaglandins whereas activation of neurokinin-3 receptors increases the synthesis of nitric oxide. Both products act as retrograde messengers across synapses and facilitate nociceptive signaling in the spinal cord. Whereas these cellular effects of CGRP and SP at the level of the spinal cord contribute to the development of increased synaptic strength between nociceptors and spinal neurons in the pathway for pain, the different intracellular signaling pathways also activate different transcription factors. The activated transcription factors initiate changes in the expression of genes that contribute to long-term changes in the excitability of spinal and maintain hyperalgesia.

Mechanisms of relaxing response induced by rat/mouse hemokinin-1 in porcine coronary arteries: roles of potassium ion and nitric oxide

Rat and mouse hemokinin-1(r/m hemokinin-1) is a recently described member of the tachykinin family whose cardiovascular functions are not fully understood. In this study, we investigated the mechanisms of the relaxing response induced by r/m hemokinin-1 in isolated porcine coronary arteries by using a specific antagonist of tachykinin NK(1) receptor (SR140333), a nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (L-NNA), and 1H-[1,2,4] Oxadiazolo [4,3-a] quinoxalin-1-one (ODQ), a blocker of cGMP production. r/m Hemokinin-1 (10(-12)-10(-6 )M) evoked a marked endothelium-dependent vasodilatation (E(max)=121.12+/-10.6% and 91.79+/-2.39% in 10(-6) M PGF(2)alpha and 30 mM KCl precontracted arterial rings, respectively) of coronary arteries mediated by activation of endothelial tachykinin NK(1) receptors. Two components contributed to this r/m hemokinin-1-elicited vasodilatation, the first of which was endothelium-derived hyperpolarizing factor (EDHF), which played a major role. This EDHF was identified as a potassium current through certain kinds of potassium channels on the endothelial cell membrane of porcine coronary arteries. Specific antagonists of Ca(2+)-activated K(+) channels (dequalinium and clotrimazole) did not have an inhibitory effect on the r/m hemokinin-1-induced vasodilatation, whereas they did on the substance P-induced vasodilatation. When potassium ion efflux was impaired by a high K(+) concentration (30 mM) or removal of K(+) from the surroundings, NO synthesis was triggered by r/m hemokinin-1 to produce an equivalent EDHF (K(+))-independent vasorelaxation as a compensatory mechanism.

Sensitization of spinal cord nociceptive neurons with a conjugate of substance P and cholera toxin

Background

Several investigators have coupled toxins to neuropeptides for the purpose of lesioning specific neurons in the central nervous system. By producing deficits in function these toxin conjugates have yielded valuable information about the role of these cells. In an effort to specifically stimulate cells rather than kill them we have conjugated the neuropeptide substance P to the catalytic subunit of cholera toxin (SP-CTA). This conjugate should be taken up selectively by neurokinin receptor expressing neurons resulting in enhanced adenylate cyclase activity and neuronal firing.

Results

The conjugate SP-CTA stimulates adenylate cyclase in cultured cells that are transfected with either the NK1 or NK2 receptor, but not the NK3 receptor. We further demonstrate that intrathecal injection of SP-CTA in rats induces the phosphorylation of the transcription factor cyclic AMP response element binding protein (CREB) and also enhances the expression of the immediate early gene c-Fos. Behaviorally, low doses of SP-CTA (1 μg) injected intrathecally produce thermal hyperalgesia. At higher doses (10 μg) peripheral sensitivity is suppressed suggesting that descending inhibitory pathways may be activated by the SP-CTA induced sensitization of spinal cord neurons.

Conclusion

The finding that stimulation of adenylate cyclase in neurokinin receptor expressing neurons in the spinal cord produces thermal hyperalgesia is consistent with the known actions of these neurons. These data demonstrate that cholera toxin can be targeted to specific cell types by coupling the catalytic subunit to a peptide agonist for a g-protein coupled receptor. Furthermore, these results demonstrate that SP-CTA can be used as a tool to study sensitization of central neurons in vivo in the absence of an injury.

Relating protein pharmacology by ligand chemistry

The identification of protein function based on biological information is an area of intense research. Here we consider a complementary technique that quantitatively groups and relates proteins based on the chemical similarity of their ligands. We began with 65,000 ligands annotated into sets for hundreds of drug targets. The similarity score between each set was calculated using ligand topology. A statistical model was developed to rank the significance of the resulting similarity scores, which are expressed as a minimum spanning tree to map the sets together. Although these maps are connected solely by chemical similarity, biologically sensible clusters nevertheless emerged. Links among unexpected targets also emerged, among them that methadone, emetine and loperamide (Imodium) may antagonize muscarinic M3, alpha2 adrenergic and neurokinin NK2 receptors, respectively. These predictions were subsequently confirmed experimentally. Relating receptors by ligand chemistry organizes biology to reveal unexpected relationships that may be assayed using the ligands themselves.

Tachykinins and excitotoxicity in cerebellar granule cells

The tachykinins represent an important group of neuropeptides that are widely distributed both in the central and peripheral nervous system where they perform several functions connected with neuronal modulation, often in synergy with glutamate excitatory transmission. While a great deal of data is available on their distribution and many studies have been performed by molecular, biochemical, and immunohistochemical techniques, much less is known about their physiological role, in particular in the cerebellum. This review is an attempt to summarize the diverse evidence suggesting a role for tachykinins in cerebellar granule neurons.

The role of substance P in stress and anxiety responses

Substance P (SP) is one of the most abundant peptides in the central nervous system and has been implicated in a variety of physiological and pathophysiological processes including stress regulation, as well as affective and anxiety-related behaviour. Consistent with these functions, SP and its preferred neurokinin 1 (NK1) receptor has been found within brain areas known to be involved in the regulation of stress and anxiety responses. Aversive and stressful stimuli have been shown repeatedly to change SP brain tissue content, as well as NK1 receptor binding. More recently it has been demonstrated that emotional stressors increase SP efflux in specific limbic structures such as amygdala and septum and that the magnitude of this effect depends on the severity of the stressor. Depending on the brain area, an increase in intracerebral SP concentration (mimicked by SP microinjection) produces mainly anxiogenic-like responses in various behavioural tasks. Based on findings that SP transmission is stimulated under stressful or anxiety-provoking situations it was hypothesised that blockade of NK1 receptors may attenuate stress responses and exert anxiolytic-like effects. Preclinical and clinical studies have found evidence in favour of such an assumption. The status of this research is reviewed here.

G protein-coupled receptors in haematopoietic disruption

Haematopoiesis is the process by which blood and immune cells are replenished from a finite number of resident bone marrow (BM) haematopoietic stem cells (HSCs). Regulatory molecules within the BM microenvironment contribute developmental signals to an interactive network capable of ensuring ordered biological processes. Many bioactive molecules contribute to the network through G protein-coupled receptors (GPCRs). GPCRs are seven-transmembrane receptors that, following ligand binding, signal by activating coupled heterotrimeric G proteins. This review focuses on those bioactive molecules that regulate haematopoietic development through GPCRs. Chemokines (SDF-1alpha, MIP-1), opioids and tachykinins (SP, NK-A) are important G protein-coupled haematopoietic regulators. Their biology in normal and diseased haematopoiesis is discussed below, as well as their potential as therapeutic targets.

Neurokinin-1 receptor resensitization precedes receptor recycling

Following agonist binding, neurokinin-1 receptors undergo rapid desensitization followed by internalization and recycling. Desensitization requires receptor phosphorylation but does not require internalization, whereas resensitization is thought to require internalization and recycling. Our previous data, however, have suggested that, following activation and desensitization, the return of responsiveness to the neurokinin-1 agonist substance P (termed "resensitization") occurs hours before internalized receptors are recycled back to the plasma membrane. To further investigate this novel mechanism of neurokinin-1 receptor resensitization, we have studied the time courses of neurokinin-1 receptor responsiveness, recycling, and dephosphorylation by measuring cellular Ca(2+) responses, ligand-receptor binding, and receptor phosphorylation, respectively. Concentration-response curves and competition binding curves were obtained at various times following desensitization. The effects of the nonhydrolyzable GTP analog Gpp(NH)p on substance P binding were also studied to assess receptor-G protein coupling. After receptor activation and desensitization, Ca(2+) signaling in response to substance P occurred within 90 min, whereas the return of receptor binding required 240 min. Receptor dephosphorylation was greater than 90% complete 20 min after agonist washout. In addition, the return of substance P responsiveness coincided with a return in sensitivity of substance P binding to Gpp(NH)p, indicating a return in receptor-G protein coupling. These data show that the resensitization of responsiveness to substance P precedes receptor recycling. This may result from a conversion of nonfunctional neurokinin-1 receptors to functional receptors at the plasma membrane.

Sciatic inflammatory neuropathy in the rat: surgical procedures, induction of inflammation, and behavioral testing

Peripheral nerve damage involves inflammation, and is frequently causal to the development of neuropathic pain. However, inflammatory neuropathies often occur in the absence of trauma. We have recently developed an animal model of neuropathic pain where allodynia is induced by nerve inflammation rather than injury. This sciatic inflammatory neuropathy (SIN) model was developed to understand immunologic, neuropathic, and spinal mechanisms underlying allodynia in the territory of the sciatic nerve as well as in extraterritorial and contralateral ("mirror image") sites. A specially designed indwelling catheter system allows immune activators to be selectively injected around one healthy sciatic nerve in awake, behaving rats. Here, we provide detailed procedures on the construction and implantation of chronic indwelling perisciatic catheters used to create SIN. Detailed procedures for implantation of intrathecal catheters via a lumbar vertebra 5 and 6 approach in the same rat are also provided. Methods for testing allodynia and for data analysis are additionally described so to provide all the steps needed for behavioral experimentation.

A 25 year adventure in the field of tachykinins

Several aspects of our 25 year adventure in the field of tachykinins will be successively described. They concern: substance P (SP) synthesis and release in the basal ganglia, the identification and pharmacological characterization of central tachykinin NK(1), NK(2) and NK(3) binding sites and their topographical distribution, the description of some new biological tests for corresponding receptors, the identification of tachykinin NK(1) receptor subtypes or conformers sensitive to all endogenous tachykinins (substance P, neurokinin A (NKA), neurokinin B (NKB), neuropeptide gamma (NP gamma) and neuropeptide K (NPK)) and finally, the functional involvement of these receptors and their subtypes in tachykinin-induced regulations of dopamine and acetylcholine release in the striatum.

Protein kinase C is involved in neurokinin receptor modulation of N- and L-type Ca2+ channels in DRG neurons of the adult rat

Whole cell patch-clamp techniques were used to examine neurokinin receptor modulation of Ca2+ channels in small to medium size dorsal root ganglia neurons (<40 pF) that express mainly N- and L-type Ca2+ currents. Low concentrations of substance P enhanced Ca2+ currents (5-40%, <0.2 microM), while higher concentrations applied cumulatively reversed these enhancements (5-28% reductions, >0.5 microM). This apparent inhibition by high concentrations of substance P was blocked by the administration of the NK3 antagonist SB 235,375 (0.2 microM). The NK1 agonist, [Sar9,Met11]-substance P (0.05 to 1.0 microM) did not alter Ca2+ currents; whereas the NK2 agonist, [betaAla8]-neurokinin A (4-10), enhanced Ca2+ currents (5-36% increase, 0.05-0.5 microM). The enhancement was reversed by the NK2 antagonist MEN 10,376 (0.2 microM) but unaffected by the NK3 antagonist SB 235,375 (0.2 microM). The NK3 agonist [MePhe7]-neurokinin B (0.5-1.0 microM) inhibited Ca2+ currents (6-24% decrease). This inhibition was not prevented by the NK2 antagonist MEN 10,376 (0.2 microM) but was blocked by the NK3 antagonist SB 235,375 (0.2 microM). Both the enhancement and inhibition of Ca2+ currents by neurokinin agonists were reversed by the protein kinase C inhibitor bisindolylmaleimide I HCl (0.2-0.5 microM). Following inhibition of Ca2+ channels by [MePhe7]-neurokinin the facilitatory effect of BayK 8644 (5 microM) was increased and the inhibitory effect of the N-type Ca2+ channel blocker w -conotoxin GVIA (1 microM) was diminished, suggesting that the NK3 agonist inhibits N-type Ca2+ channels. Similarly, block of all but N-type Ca2+ channels, revealed that [betaAla8]-neurokinin A (4-10) enhanced the currents while [MePhe7]-neurokinin B inhibited the currents. Inhibition of all but L-type Ca2+ channels, revealed that [betaAla8]-neurokinin A (4-10) enhanced the currents while [MePhe7]-neurokinin B had no effect. Activation of protein kinase C with low concentrations of phorbol-12,13-dibutyrate enhanced Ca2+ currents, but high concentrations inhibited N- and L-type Ca2+ currents. In summary, these data suggest that in adult rat dorsal root ganglia neurons, NK2 receptors enhance both L- and N-type Ca2+ channels and NK3 receptors inhibit N-type Ca2+ channels and that these effects are mediated by protein kinase C phosphorylation of Ca2+ channels.

Modulation of somatostatin receptors, somatostatin content and Gi proteins by substance P in the rat frontoparietal cortex and hippocampus

Substance P (SP) and somatostatin (SRIF) are widely spread throughout the CNS where they play a role as neurotransmitters and/or neuromodulators. A colocalization of both neuropeptides has been demonstrated in several rat brain areas and SP receptors have been detected in rat cortical and hippocampal somatostatinergic cells. The present study was thus undertaken to determine whether SP could modulate SRIF signaling pathways in the rat frontoparietal cortex and hippocampus. A single intraperitoneal injection of SP (50, 250 or 500 micro g/kg) induced an increase in the density of SRIF receptors in membranes from the rat frontoparietal cortex at 24 h of its administration, with no change in the hippocampus. The functionality of the SRIF receptors was next investigated. Western blot analysis of Gi proteins demonstrated a significant decrease in Gialpha1 levels in frontoparietal cortical membranes from rats treated acutely (24 h) with 250 micro g/kg of SP, which correlated with a decrease in functional Gi activity, as assessed by use of the non-hydrolyzable GTP analog 5'-guanylylimidodiphosphate. SRIF-mediated inhibition of basal or forskolin-stimulated adenylyl cyclase activity was also significantly lower in the frontoparietal cortex of the SP-treated group, with no alterations in the catalytic subunit of the enzyme. SRIF-like immunoreactivity content was increased in the frontoparietal cortex after acute (24 h) SP administration (250 or 500 micro g/kg) as well as in the hippocampus in response to 7 days of SP (250 micro g/kg) administration. All these SP-mediated effects were prevented by pretreatment with the NK1 receptor antagonist RP-67580. Although the physiologic significance of these results are unknown, the increase in SRIF receptor density together with the desensitization of the SRIF inhibitory signaling pathway might be a mechanism to potentiate the stimulatory pathway of SRIF, inducing a preferential coupling of the receptors to PLC.

A novel mechanism of neurokinin-1 receptor resensitization

Prolonged or repeated activation of many G protein-coupled receptors induces rapid desensitization followed by a period during which receptors are resensitized. In this study, concanavalin A (Con A) and monensin were used to investigate the mechanisms of desensitization and resensitization of the neurokinin-1 receptor. Con A inhibits internalization, whereas monensin prevents receptor recycling. The effects of Con A and monensin on desensitization, resensitization, receptor phosphorylation, endocytosis, and recycling of the neurokinin-1 receptor were assessed. Desensitization was defined as the decrease in the ability of substance P (SP) to elicit an intracellular Ca2+ response after a prolonged SP exposure. Resensitization was characterized as the return of SP responsiveness. Under control conditions, desensitization occurred after a 5-min exposure to agonist. Resensitization was evident 30 min after agonist washout. Neither monensin nor Con A prevented desensitization. Monensin completely inhibited resensitization, whereas Con A decreased but did not completely block resensitization. Receptor phosphorylation was increased after agonist activation and returned to basal levels after a recovery period. Neither Con A nor monensin altered the amount of agonist-specific receptor phosphorylation. Receptor binding analysis showed that plasma membrane receptors were internalized after a 5-min agonist exposure. Receptor recycling was not observed after a 1-h recovery period; however, resensitization was apparent. Taken together, these results suggest that rapid neurokinin-1 receptor desensitization can occur without receptor internalization and that resensitization occurs before receptor recycling.

The expression of neurokinin-1 receptor at striatal and pallidal levels in normal human brain

To further our knowledge of the site of action of substance P (SP) in the human basal ganglia, we applied single- and double-antigen localization methods to human postmortem tissue to compare the distribution of SP and its high affinity receptor neurokinin-1 (NK1R) at striatal and pallidal levels. The human striatum was found to harbor numerous heterogeneously distributed aspiny neurons that expressed NK1R. Most of them were of small size, but a moderate number of large-sized neurons and a small number of medium-sized neurons also expressed NK1R. The medium-sized NK1R-positive neurons coexpressed parvalbumin and appear to represent a hitherto unknown striatal interneuron. The three types of striatal NK1R-positive neurons were preferentially localized in the peripheral region of the striosomes, which were identified by their intense immunostaining for the limbic system-associated membrane protein. Numerous NK1R expressing neurons also occurred in both external (GPe) and internal (GPi) segments of the globus pallidus, as well as in the ventral pallidum (GPv). There was a marked decreasing rostrocaudal gradient in the number of these neurons in the GPe, but not in the GPi. A multitude of smooth and highly branched SP-immunoreactive fibers pervaded the entire pallidal complex and some of these fibers were in close contact with NK1R-positive neurons in the GPi, as well as in the rostral portion of the GPe. The latter result reveals that the so-called 'direct' striatofugal pathway provides SP-immunoreactive collaterals to the GPe, a finding that is at odd with the current model of basal ganglia organization.

Evidence for spatial proximity of two distinct receptor regions in the substance P (SP)*neurokinin-1 receptor (NK-1R) complex obtained by photolabeling the NK-1R with p-benzoylphenylalanine3-SP

Substance P (SP) belongs to the tachykinin family of bioactive peptides and exerts its many biological effects through functional interaction with its cell-surface, G protein-coupled neurokinin-1 receptor (NK-1R). Previous studies from our laboratory have shown that (125)I-Bolton-Hunter reagent-labeled p-benzoylphenylalanine(8)-SP (Bpa(8)SP) covalently attaches to Met(181), whereas (125)I-Bolton-Hunter reagent-labeled Bpa(4)SP covalently attaches to Met(174), both of which are located on the second extracellular loop (EC2) of the NK-1R. In this study, evidence has been obtained that at equilibrium, the photoreactive SP analogue (125)I-[D-Tyr(0)]Bpa(3)SP covalently labels residues in two distinct extracellular regions of the NK-1R. One site of (125)I-[D-Tyr(0)]Bpa(3)SP photoinsertion is located on EC2 within a segment of the receptor extending from residues 173 to 177; a second site of (125)I-[D-Tyr(0)]Bpa(3)SP photoinsertion is located on the extracellular N terminus within a segment of the receptor extending from residues 11 to 21, a sequence that contains both potential sites for N-linked glycosylation. Since competition binding data presented in this study do not suggest the existence of multiple peptide.NK-1R complexes, it is reasonable to assume that the receptor sequences within EC2 and N terminus identified by peptide mapping are in close proximity in the equilibrium complex.

Further definition of the substance P (SP)/neurokinin-1 receptor complex. MET-174 is the site of photoinsertion p-benzoylphenylalanine4 SP

The covalent attachment site of a substance P (SP) analogue containing the photoreactive amino acid p-benzoyl-l-phenylalanine (Bpa) in position 8 of the C-terminal portion of the peptide was identified previously as Met-181 on the neurokinin-1 (NK-1) receptor. In this study, a second photoreactive SP analogue, Bpa(4)-SP, in which the Bpa residue is located in the N-terminal portion of the peptide, was used to define further the peptide-receptor interface. The NK-1 receptor expressed in Chinese hamster ovary cells was specifically and efficiently photolabeled with a radioiodinated derivative of Bpa(4)-SP. Fragmentation analysis of the photolabeled receptor restricted the site of photoincorporation of Bpa(4)-SP to an amino acid within the sequence Thr-173 to Arg-177 located on the N-terminal side of the E2 loop. To identify the specific amino acid in this sequence that serves as the covalent attachment site for Bpa(4)-SP, a small photolabeled receptor fragment was generated by chemical cleavage with cyanogen bromide. Matrix-assisted laser desorption/ionization time of flight mass spectrometric analysis of the purified fragment identified a single protonated molecular ion with a molecular mass of 1801.3 +/- 1.8, indicating that upon irradiation, the bound photoligand covalently attaches to the terminal methyl group of a methionine residue. This result, taken together with the results of the peptide mapping studies, establishes that the site of Bpa(4)-SP covalent attachment to the NK-1 receptor is Met-174.

The common C-terminal sequences of substance P and neurokinin A contact the same region of the NK-1 receptor

Although neurokinin A (NKA), a tachykinin peptide with sequence homology to substance P (SP), is a weak competitor of radiolabeled SP binding to the NK-1 receptor (NK-1R), more recent direct binding studies using radiolabeled NKA have demonstrated an unexpected high-affinity interaction with this receptor. To document the site of interaction between NKA and the NK-1R, we have used a photoreactive analogue of NKA containing p-benzoyl-L-phenylalanine (Bpa) substituted in position 7 of the peptide. Peptide mapping studies of the receptor photolabeled by (125)I-iodohistidyl(1)-Bpa(7)NKA have established that the site of photoinsertion is located within a segment of the receptor extending from residues 178 to 190 (VVCMIEWPEHPNR). We have previously shown that (125)I-BH-Bpa(8)SP, a photoreactive analogue of SP, covalently attaches to M(181) within this same receptor sequence. Importantly, both of these peptides ((125)I-iodohistidyl(1)-Bpa(7)NKA and (125)I-BH-Bpa(8)SP) have the photoreactive amino acid in an equivalent position within the conserved tachykinin carboxyl-terminal tail. In this report, we also show that site-directed mutagenesis of M(181) to A(181) in the NK-1R results in a complete loss of photolabeling of both peptides to this receptor site, indicating that the equivalent position of SP and NKA, when bound to the NK-1R, contact the same residue.

The tachykinin NK1 receptor in the brain: pharmacology and putative functions

After its discovery in 1931, substance P (SP) remained the only mammalian member of the family of tachykinin peptides for several decades. Tachykinins thus refer to peptides sharing the common C-terminal amino acid sequence Phe-X-Gly-Leu-Met x NH2. In recent years the family of mammalian tachykinins has grown with the isolation of two novel peptides from bovine and porcine central nervous system (CNS), neurokinin A and neurokinin B. In parallel with the identification of multiple endogenous tachykinins several classes of tachykinin receptors were discovered. The receptors described so far are named tachykinin NK1 receptor, tachykinin NK2 receptor and tachykinin NK1 receptor, respectively. The present review focuses on the pharmacology and putative function of tachykinin NK1 receptors in brain. The natural ligand with the highest affinity for the tachykinin NK1 receptor is SP itself. The C-terminal sequence is essential for activity, the minimum length of a fragment with reasonable affinity for the tachykinin NK1 receptor is the C-terminal hexapeptide. A rapid advance of knowledge was caused by development of non-peptidic tachykinin NK1 receptor antagonists. This area is under rapid development and a variety of different chemical classes of compounds are involved. Species-dependent affinities of tachykinin NK1 receptor antagonists reveal two clusters of compounds, targeting the tachykinin NK1 receptor subtype found in guinea pig, human or ferret or the one in rat or mouse, respectively. The most recently developed compounds are highly selective, enter the brain and are orally bioavailable. Distinct behavioural effects in experimental animals suggest the involvement of tachykinin NK1 receptors in nociceptive transmission, basal ganglia function or anxiety and depression. Recent clinical trials in man showed that tachykinin NK1 receptor antagonists are effective in treating depression and chemotherapy-induced emesis. Therefore, it is well possible that tachykinin NK1 receptor antagonists will be clinically used for treatment of specific CNS disorders within a short period of time.

Astroglial distribution of neurokinin-2 receptor immunoreactivity in the rat spinal cord

Two mouse monoclonal antibodies, 11H9.1 and 1G7.10, raised against the COOH-terminus peptide (359-390) of the rat neurokinin-2 receptor, were used to visualize by light and electron microscope immunocytochemistry the distribution of this receptor in adult rat spinal cord. At all spinal levels, immunoreactivity was mainly observed in two narrow crescentic zones bordering the gray matter of the dorsal and ventral horns, and around the central canal. In the light microscope, this labelling was the densest within the outer part of lamina I facing the dorsal column, where it took the form of minute dots and streaks scattered in the neuropil. In the electron microscope, such a localization was exclusively astrocytic and essentially involved astrocytic leaflets, as indicated by the size and irregular shape of the immunostained processes, their location between and around neuronal profiles, and their occasional display of glial filaments. The diaminobenzidine reaction product showed some predilection for the plasma membrane and was occasionally seen at gap junctions of these labelled processes. Many labelled astrocytic leaflets were observed in the immediate vicinity of axon terminals containing large dense-cored vesicles, and around fibres morphologically identifiable as primary afferent, unmyelinated C-fibres. These observations suggest that astrocytic neurokinin-2 receptors could define the effective sphere of neurokinin A neuromodulation in rat spinal cord, via alterations in the regulation of the extracellular environment and glutamate uptake by astrocytes and/or the release of putative astroglial mediators. The astrocyte neurokinin-2 receptors, activated by extrasynaptic neurokinin A, might thus co-operate with neurokinin-1 and neurokinin-3 neuronal receptors in the modulation of nociceptive information.

Human substance P receptor expressed in Chinese hamster ovary cells directly activates G(alpha q/11), G(alpha s), G(alpha o)

Substance P receptor (SPR) stably expressed in Chinese hamster ovary (CHO) cells stimulates at least three second messenger systems including phosphoinositide hydrolysis, cyclic AMP (cAMP) formation, and arachidonic acid release. Whether these second messenger systems are activated via single or multiple G proteins is not known. Therefore, in the present study we examined whether human SPR (hSPR) stably expressed in CHO cells activates multiple G proteins. This was achieved by photoaffinity labeling of G(alpha)-subunits with [32P]azidoanilido-GTP ([32P]AA-GTP) upon hSPR stimulation in CHO-hSPR membranes followed by immunoprecipitation of the labeled G(alpha)-subunits with antibodies specific for various G(alpha)-subunits. These experiments reveal that hSPR directly activates G(alpha q/11), G(alpha s) and G(alpha o). While hSPR is known to couple G(alpha q/11), the present study provides the first evidence that hSPR can also activate G(alpha s) and G(alpha o) in a mammalian system.

The tachykinin NK1 receptor. Part I: ligands and mechanisms of cellular activation

The tachykinin NK1 receptor is widely expressed in the mammalian central and peripheral nervous system. Powerful pharmacological tools (agonists and antagonists) are now available to elucidate the physiological role of NK1 receptors at these levels, as well as to understand their role in diseases and establish the possible therapeutic usefulness of NK1 receptor antagonists for treatment of human diseases. The structure-activity studies that have led to the development of potent peptide and non-peptide ligands for the tachykinin NK1 receptor are here reviewed. Among the peptide agonists and antagonists, linear and cyclic sequences have been developed. The non peptide antagonists belong to different chemical classes, i.e. steroids, perhydroisoindolones, quinuclidines, piperidines and tryptophane derivatives. The first non peptide antagonists for NK1 receptors have been obtained by random screening of chemical compounds large collections. The resulting leads were optimized with 'classic' structure activity approaches, aiming at identifying 'common' motifs for interaction with the receptor by ligands of different chemical classes. The results derived from the recent application of molecular biology techniques were useful to drive the design of new ligands toward a precise structural definition of ligand-receptor bi-molecular interactions. Studies on mutant receptors have established that the sites of interaction of peptide agonists and non peptide antagonists with the tachykinin NK1 receptor are largely non overlapping. Moreover, data obtained from mutagenesis of the NK1 receptor further indicate that some amino acid residues in the NK1 receptor sequence are critical for determining the binding affinity of some but not all ligands. Therefore, different antagonists discovered from random screening may not possess common points of interaction or common structural and conformational characteristics for their interaction with the tachykinin NK1 receptor. The tachykinin NK1 receptor couples with G-proteins to determine its biological effects in target cells. Several G-proteins both sensitive (Go, Gi) and insensitive (Gq, G11) to pertussis toxin can mediate the action of NK1 receptors. Moreover, several second messanger signalling systems (elevation of intracellular calcium, stimulation of phosphoinositol turnover, arachidonic acid mobilization, cAMP accumulation) have to be activated following NK1 receptor signalling. Also a direct modulation of certain ion channels at membrane level has been proposed. The NK1 receptor undergoes prompt and significant tachyphylaxis upon exposure to the agonist: this has been shown to be linked with receptor internalization which also occurs physiologically when the NK1 receptor is stimulated by endogenous tachykinins.

Variations in levels of substance P-encoding beta-, gamma-preprotachykinin and substance P receptor NK-1 transcripts in the rat hypothalamus throughout the estrous cycle: a correlation between amounts of beta-preprotachykinin and NK-1 mRNA

Using a sensitive RNase protection assay, the simultaneous quantification of hypothalamic beta-, gamma-preprotachykinin (PPT) and SP receptor NK-1 transcripts was performed throughout the estrous cycle. The amounts of these 3 transcripts were up-regulated during diestrus II-proestrus night (2-, 1.5- and 1.3-fold, respectively). These levels returned to low values during the proestrous day in the case of gamma-PPT mRNA and during the estrus-diestrus I night in the cases of beta-PPT and NK-1 mRNAs. These results implicate a differential regulation in amounts of the two alternatively spliced PPT transcripts. The 160 hypothalami of this study had been previously assayed for amounts of substance P (SP) and neurokinin A (NKA) peptides [P. Duval, V. Lenoir, S. Moussaoui, C. Garret and B. Kerdelhué, Substance P and neurokinin A variations throughout the rat estrous cycle; comparison with ovariectomized and male rats: I. Plasma, hypothalamus, anterior and posterior pituitary, J. Neurosci. Res., 45 (1996) 598-609]. Variations in mRNA and peptide levels were compared by statistical analysis. Surprisingly, variations in SP level paralleled those in beta-PPT mRNA level and variations in NKA level paralleled those of gamma-PPT mRNA level, although beta- and gamma-PPT transcripts encode both SP and NKA. Furthermore, the level of NK-1 mRNA was positively correlated with the level of beta-PPT mRNA (r = 0.90, P < 10(-58)) and with the level of SP peptide (r = 0.30, P < 10(-3)) but not with the level of NKA peptide. This analysis suggests that SP receptor NK-1 mRNA could be physiologically regulated by SP peptide in the rat hypothalamus.

A substance P (neurokinin-1) receptor mutant carboxyl-terminally truncated to resemble a naturally occurring receptor isoform displays enhanced responsiveness and resistance to desensitization

Two isoforms of the substance P (SP) receptor, differing in the length of the cytoplasmic carboxyl-terminus by approximately 8 kDa, have been detected previously in rat salivary glands and other tissues. The binding and functional properties of these two isoforms have been investigated using full-length (407 amino acids) and carboxyl-terminally truncated (324 amino acids) rat SP receptors transfected stably into Chinese hamster ovary cells. Both the full-length and the truncated receptor bound radiolabeled SP with a similar Kd ( approximately 0.1 nM). The average number of high affinity SP binding sites per cell was 1.0 x 10(5) and 0.3 x 10(5) for the full-length and the truncated SP receptor, respectively. In both cell lines, SP induced a rapid but transient increase in cytosolic calcium concentration ([Ca2+]i), which consisted of the release of Ca2+ from intracellular stores and the influx of extracellular Ca2+. Both components are dependent on phospholipase C activation. Although the full-length and the truncated receptor utilize the same calcium pathways, they differ in their EC50 values (0.28 nM for the full-length; 0.07 nM for the truncated). These differences in responsiveness may be related to the observed differences in receptor desensitization. The truncated receptor, in contrast to the full-length receptor, does not undergo rapid and long-lasting desensitization. Cells possessing the short isoform of the SP receptor would thus be expected to exhibit a prolonged responsiveness.

Molecular characterization and functional expression of a substance P receptor from the sympathetic ganglion of Rana catesbeiana

Substance P is an important neuropeptide neurotransmitter in the central, autonomic and enteric nervous systems. In sympathetic ganglia, substance P is thought to play a role in modulating synaptic transmission. Release of substance P by neuronal stimulation or direct application of substance P to ganglionic neurons increases neuronal excitability. An amphibian substance P receptor complementary DNA has been cloned and characterized from bullfrog, Rana catesbeiana, sympathetic ganglion complementary DNA libraries. The deduced primary structure contains features indicative of a seven transmembrane domain G-protein-coupled receptor. The deduced protein sequence shows 69% identity to previously cloned mammalian substance P receptors. In situ hybridization analysis performed on bullfrog sympathetic ganglia using digoxigenin-labelled complementary RNA probe demonstrated that approximately 75% of the principal neurons displayed reaction product above background levels. Radioligand binding studies were performed on stably transfected cells with [(125)I]Tyr-1-substance P as the ligand. Substance P had an IC50 of 16 nM and the agonist potency profile was substance P>neurokinin A >> neurokinin B. The order of potency for three tachykinins to increase intracellular calcium when applied to a stably transfected clonal cell line was substance P>neurokinin A >> neurokinin B. This order of agonist potency also held for inhibition of the M-type potassium current in intact bullfrog sympathetic neurons. The non-peptide substance P antagonists CP-96345 and RP-67580 at concentrations that block mammalian substance P receptors had little or no effect on the responses to substance P at the bullfrog receptor. Overall, these results demonstrate that the cloned sequence has the features consistent with and characteristic of a substance P receptor. The results are discussed with reference to the established pharmacology of the bullfrog substance P receptor and known structure activity relationships of mammalian tachykinin receptors.

Functional expression of a novel human neurokinin-3 receptor homolog that binds [3H]senktide and [125I-MePhe7]neurokinin B, and is responsive to tachykinin peptide agonists

In 1992, Xie et al. identified a cDNA sequence in the expression cloning search for the kappa opioid receptor. When the cDNA was expressed in Cos-7 cells, binding of opioid compounds was observed to be of low affinity and without kappa, mu, or delta selectivity [Xie, G.-X., Miyajima, A. and Goldstein, A. (1992) Proc. Natl. Acad. Sci. USA 89, 4124-4128]. This cDNA was highly homologous to the human neurokinin-3 (NK-3) receptor sequence, and displayed lower homology to NK-1 and NK-2 sequences. This sequence was stably expressed in Chinese hamster ovary cells, which do not express neurokinin receptors naturally, and ligand binding and second messenger characteristics were compared with a human NK-3 receptor. The NK-3 receptor homolog bound [3H] senktide with a Kd of 39 nM, similar to that of the NK-3 receptor. The rank order of tachykinin peptides competing for [3H]senktide binding at the NK-3 receptor homolog was [MePhe7]neurokinin B > senktide > substance P = neurokinin A > neurokinin B. This cell line also bound [125I-MePhe7]neurokinin B; however, neurokinin B was an effective competitor. Tachykinin peptides stimulated both inositol phospholipid hydrolysis and arachidonic acid release at NK-3 and NK-3 receptor homolog cell lines, with similar rank orders of potency of [MePhe7] neurokinin B = neurokinin B = senktide > NKA = substance P. These results indicate that expression of the NK-3 receptor homolog cDNA in the Chinese hamster ovary cell system induces the expression of a receptor site with many similarities but certain key differences from that of the human NK-3 receptor. The results are discussed with reference to the existence of a novel human tachykinin receptor.