[D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P, a potent bombesin antagonist in murine Swiss 3T3 cells, inhibits the growth of human small cell lung cancer cells in vitro

Establishment of a Cell Line Stably Expressing the Growth Hormone Secretagogue Receptor to Identify Crocin as a Ghrelin Agonist

The growth hormone secretagogue receptor-1a (GHSR1a) is the endogenous receptor for ghrelin. Activation of GHSR1a participates in many physiological processes including energy homeostasis and eating behavior. Due to its transitory half-life, the efficacy of ghrelin treatment in patients is restricted; hence the development of new adjuvant therapy is an urgent need. This study aimed to establish a cell line stably expressing GHSR1a, which could be employed to screen potential ghrelin agonists from natural compounds. First, by means of lentiviral transduction, the genome of a human HEK293T cell was modified, and a cell platform stably overexpressing GHSR1a was successfully established. In this platform, GHSR1a was expressed as a fusion protein tagged with mCherry, which allowed the monitoring of the dynamic cellular distribution of GHSR1a by fluorescent microscopy. Subsequently, the authenticity of the GHSR1a mediated signaling was further characterized by using ghrelin and teaghrelin, two molecules known to stimulate GHSR1a. The results indicated that both ghrelin and teaghrelin readily activated GHSR1a mediated signaling pathways, presumably via increasing phosphorylation levels of ERK. The specific GHSR1a signaling was further validated by using SP-analog, an antagonist of GHSR1a as well as using a cell model with the knockdown expression of GHSR1a. Molecular modeling predicted that crocin might be a potential ghrelin agonist, and this prediction was further confirmed by the established platform.

Neurokinin-1 Receptor Antagonists as Anticancer Drugs

Background::

Human tumor cells lines and tumor samples overexpress the neurokinin-1 receptor (NK-1R). Substance P (SP), after binding to NK-1Rs, induces tumor cell proliferation, an antiapoptotic effect and promotes angiogenesis and the migration of cancer cells for invasion and metastasis.

Methods: :

In contrast, NK-1R antagonists block the previous pathophysiological actions mediated by SP. These antagonists promote the death of tumor cells by apoptosis. Peptide and non-peptide NK-1R antagonists have been reported.

Results: :

Peptide NK-1R antagonists show chemical modifications of the SP molecule (L-amino acids being replaced by D-amino acids), whereas non-peptide NK-1R antagonists include numerous compounds with different chemical compositions while showing similar stereochemical features (affinity for the NK- 1R). Currently, there are more than 300 NK-1R antagonists.

Conclusion::

In combination therapy with classic cytostatics, NK-1R antagonists have additive or synergic effects and minimize the side-effects of cytostatics. The effect of NK-1R antagonists as broad-spectrum anticancer drugs is reviewed and the use of these antagonists for the treatment of cancer is suggested.

Blocking constitutive activity of GHSR1a in the lateral amygdala facilitates acquisition of conditioned taste aversion

Ghrelin is a circulating peptide hormone promoting feeding and regulating energy metabolism in human and rodents. Ghrelin functions by binding to its receptor, the growth hormone secretagogue receptor 1a (GHSR1a), which are widely distributed throughout the brain including the amygdala, a brain region important for regulating valenced behavior, such as aversion. Interestingly, GHSR1a was once characterized by highly constitutive, ligand-independent activity. However, the physiological importance of such ligand-independent signaling on aversive memory processing has not been tested yet. Here, we applied [D-Arg¹, D-Phe⁵, D-Trp^7,9, Leu¹¹]-Substance P (D-SP), a full inverse agonist for GHSR1a, into the lateral amygdala (LA) and investigated the effect of blocking GHSR1a constitutive activity on conditioned taste aversion (CTA) in rats. We found that intra-LA infusion of a single low dose of D-SP (8ng/0.5μl/side) facilitates CTA acquisition. Moreover, pre-administration of a high dose of D-SP into the LA abolishes the suppressive effect of exogenous ghrelin on CTA acquisition. In contrast, pre-administration of the same dose of D-SP does not affect the suppression of substance P, a potent neurokinin-1 (NK1) receptor ligand, on CTA. Therefore, our data indicated that the spontaneous or basal activity of GHSR1a signaling in the LA might interfere with CTA memory formation. D-SP decreases the constitutive activity of GHSR1a and thus facilitates CTA. Altogether, our present findings along with previous results support the idea that ghrelin/GHSR1a signaling in the LA circuit blocks conditioned taste aversion.

Pentapeptides for the treatment of small cell lung cancer: Optimisation by Nind-alkyl modification of the tryptophan side chain

The pentapeptide, tert-Prenyl^4th-NH₂ (DMePhe-DTrp-Phe-DTrp(N-tert-prenyl)-Leu-NH₂), has recently been reported by our group to exhibit properties of substance P (SP) antagonist G against small cell lung cancer (SCLC). In this study, we undertook a systematic structure activity investigation to optimise this lead compound to improve its in vitro anti-tumour activity and biocompatibility. A series of d-tryptophan (D-Trp) derivatives were synthesised, with a range of aliphatic N-alkyl chains (methyl to pentyl) on the indole nitrogen (N^ind). These were incorporated into the pentapeptide sequence by substitution of the N^ind-tert-prenylated D-Trp 4th residue with the N^ind-alkylated D-Trp derivatives. These pentapeptides were significantly more potent than tert-Prenyl^4th-NH₂, with the N^ind-butyl modification generating the most cytotoxic peptides. Compared to tert-Prenyl^4th-NH₂, a single butyl modification on the 4th D-Trp residue (Butyl^4th-NH₂) showed a ∼3 fold enhancement in cytotoxicity in either the chemo-naive H69 or the DMS79 (originating from a patient treated with chemotherapeutics and radiation therapy) SCLC cell lines. In addition, the di-butylated sequence on the 2nd and 4th D-Trp residues (Butyl^2nd,4th-NH₂) gave ∼4.5 times higher cytotoxicity against the H69 cell line and a ∼2 fold increase against the DMS79 cell line, compared to tert-Prenyl^4th-NH₂. The favoured position for butyl modification was the 4th D-Trp residue, as the Butyl^2nd-NH₂ peptide gave lower cytotoxicity on both cell lines. Butylated peptide sequences, when exposed to neat mouse plasma for 24 h at 37 °C, were found to resist degradation with >80% remaining intact compared to ∼58% for tert-Prenyl^4th-NH₂. The degradation pathway in plasma occurs via de-amidation of the C-terminus, confirmed by mass spectrometry and RP-HPLC analysis. The butyl modification also conferred resistance to metabolism when tested using S9 liver fraction from mouse. The optimum analogue responsive against the DMS79 cell line was the Butyl^4th-NH₂ pentapeptide, which revealed a concentration dependent increase in apoptosis: the level of late apoptotic cells rose from ∼36% at 2 μM to ∼96% at 6 μM, as determined by flow cytometry, compared to the unmodified peptide that showed no such effect. Concluding, the butyl substitutions offered the best perspective for high cytotoxicity, induction of apoptosis and metabolic compatibility thereby comprising an improved broad spectrum SP antagonist candidate for treatment of SCLC.

N-tert-Prenylation of the indole ring improves the cytotoxicity of a short antagonist G analogue against small cell lung cancer

Natural prenylated indoles have been proposed as potential anticancer agents. To exploit this discovery for developing new peptide therapeutics, we report the first studies whereby incorporation of prenylated indoles into primary sequences has been achieved. We developed a route to synthesise Nα-Fmoc-protected tryptophan derivatives in which the prenyl group is linked to the N-indole core, using Pd(ii)-mediated C-H functionalisation of 2-methyl-2-butene. Based on the Substance P antagonist G (SPG), a well-known Small Cell Lung Cancer (SCLC) anticancer agent, we designed a new penta-peptide sequence to include a prenyl moiety on one of the tryptophan residues. The N-tert-prenylated tryptophan analogue was assembled into the pentameric peptide using standard solid phase peptide synthesis or liquid phase synthesis by fragment coupling. In vitro screening showed that the N-tert-prenylation of the indole ring on the tryptophan residue located near the C-terminal of the penta-peptide enhanced the cytotoxicity against H69 (IC50 = 2.84 ± 0.14 μM) and DMS79 (IC50 = 4.37 ± 0.44 μM) SCLC cell lines when compared with the unmodified penta-peptide (H69, IC50 = 30.74 ± 0.30 μM and DMS79, IC50 = 23.00 ± 2.07 μM) or the parent SPG sequence (IC50 > 30 μM, both cell lines). SCLC almost invariably relapses with therapy-resistant disease. The DMS79 cell line was established from a patient following treatment with a number of chemotherapeutics (cytoxan, vincristine and methotrexate) and radiation therapy. Treating DMS79 tumour-bearing nude mice provided a human xenograft model of drug resistance to test the efficacy of the prenylated peptide. A low dose (1.5 mg kg-1) of the prenylated peptide was found to reduce tumour growth by ∼30% (P < 0.05) at day 7, relative to the control group receiving vehicle only. We conclude that the availability of the Fmoc-Trp(N-tert-prenyl)-OH amino acid facilitates the synthesis of prenylated-tryptophan-containing peptides to explore their therapeutic potential.

Hypothalamic regulation of body growth and appetite by ghrelin-derived peptides during balanced nutrition or undernutrition

Among the gastrointestinal hormones that regulate food intake and energy homeostasis, ghrelin plays a unique role as the first one identified to increases appetite and stimulate GH secretion. This review highlights the latest mechanism by which ghrelin modulates body growth, appetite and energy metabolism by exploring pharmacological actions of the hormone and consequences of genetic or pharmacological blockade of the ghrelin/GHS-R (Growth Hormone Secretagogue Receptor) system on physiological responses in specific nutritional situations. Within the hypothalamus, novel mechanisms of action of this hormone involve its interaction with other ghrelin-derived peptides, such as desacyl ghrelin and obestatin, which are thought to act as functional ghrelin antagonists, and possible modulation of the GHS-R with other G-protein coupled receptors. During chronic undernutrition such as anorexia nervosa, variations of ghrelin-derived peptides may be an adaptative metabolic response to maintain normal glycemic control. Interestingly, some of ghrelin's metabolic actions are thought to be relayed through modulation of GH, an anabolic and hyperglycemic agent.

Endostatin and irradiation modifies the activity of ADAM10 and neprilysin in breast cancer cells

Angiogenesis, the formation of new blood vessels, is regarded as a key cancer cell property. Endostatin (ES) is a potential antiangiogenic agent and it may be useful when implemented in combination with other cancer therapeutic strategies. The present study investigated the in vitro effects of ES, radiotherapy (RT) or combination therapy (ES + RT) on two important proteases, a disintegrin and metalloproteinase domain‑containing protein 10 (ADAM10) and neprilysin (NEP) in 4T1 mouse breast cancer cells and the more metastatic phenotype of 4THMpc breast cancer cells. 4T1 and 4THMpc cells were treated with recombinant murine ES (4 µg/ml) alone, RT (45 Gy) alone or with ES + RT. ADAM10 enzyme activity was determined using a tumor necrosis factor‑α converting enzyme (α‑secretase) activity assay kit, and NEP enzyme activity was measured with a fluorometric assay based on the generation of free dansyl‑D‑Ala‑Gly from N-dansyl-Ala-Gly-D-nitro-Phe-Gly, the substrate of NEP. Western blotting analysis was performed to determine whether the altered enzyme activity levels of the two cell lines occurred due to changes in expression level. These data indicate that ES independently potentiates the activity of ADAM10 and NEP enzymes in 4T1 and 4THMpc breast cancer cells.

Pharmacological characterization of the first in class clinical candidate PF-05190457: a selective ghrelin receptor competitive antagonist with inverse agonism that increases vagal afferent firing and glucose-dependent insulin secretion ex vivo

BACKGROUND AND PURPOSE

Ghrelin increases growth hormone secretion, gastric acid secretion, gastric motility and hunger but decreases glucose-dependent insulin secretion and insulin sensitivity in humans. Antagonizing the ghrelin receptor has potential as a therapeutic approach in the treatment of obesity and type 2 diabetes. Therefore, the aim was to pharmacologically characterize the novel small-molecule antagonist PF-05190457 and assess translational pharmacology ex vivo.

EXPERIMENTAL APPROACH

Radioligand binding in filter and scintillation proximity assay formats were used to evaluate affinity, and europium-labelled GTP to assess functional activity. Rat vagal afferent firing and calcium imaging in dispersed islets were used as native tissues underlying food intake and insulin secretion respectively.

KEY RESULTS

PF-05190457 was a potent and selective inverse agonist on constitutively active ghrelin receptors and acted as a competitive antagonist of ghrelin action, with a human Kd of 3 nM requiring 4 h to achieve equilibrium. Potency of PF-05190457 was similar across different species. PF-05190457 increased intracellular calcium within dispersed islets and increased vagal afferent firing in a concentration-dependent manner with similar potency but was threefold less potent as compared with the in vitro Ki in recombinant overexpressing cells. The effect of PF-05190457 on rodent islets was comparable with glibenclamide, but glucose-dependent and additive with the insulin secretagogue glucagon-like peptide-1.

CONCLUSIONS AND IMPLICATIONS

Together, these data provide the pharmacological in vitro and ex vivo characterization of the first ghrelin receptor inverse agonist, which has advanced into clinical trials to evaluate the therapeutic potential of blocking ghrelin receptors in obesity and type 2 diabetes.

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.

Pharmacological lineage analysis revealed the binding affinity of broad-spectrum substance P antagonists to receptors for gonadotropin-releasing peptide

A group of synthetic substance P (SP) antagonists, such as [Arg(6),D-Trp(7,9),N(Me)Phe(8)]-substance P(6-11) and [D-Arg(1),D-Phe(5),D-Trp(7,9),Leu(11)]-substance P, bind to a range of distinct G-protein-coupled receptor (GPCR) family members, including V1a vasopressin receptors, and they competitively inhibit agonist binding. This extended accessibility enabled us to identify a GPCR subset with a partially conserved binding site structure. By combining pharmacological data and amino acid sequence homology matrices, a pharmacological lineage of GPCRs that are sensitive to these two SP antagonists was constructed. We found that sensitivity to the SP antagonists was not limited to the Gq-protein-coupled V1a and V1b receptors; Gs-coupled V2 receptors and oxytocin receptors, which couple with both Gq and Gi, also demonstrated sensitivity. Unexpectedly, a dendrogram based on the amino acid sequences of 222 known GPCRs showed that a group of receptors sensitive to the SP antagonists are located in close proximity to vasopressin/oxytocin receptors. Gonadotropin-releasing peptide receptors, located near the vasopressin receptors in the dendrogram, were also sensitive to the SP analogs, whereas α1B adrenergic receptors, located more distantly from the vasopressin receptors, were not sensitive. Our finding suggests that pharmacological lineage analysis is useful in selecting subsets of candidate receptors that contain a conserved binding site for a ligand with broad-spectrum binding abilities. The knowledge that the binding site of the two broad-spectrum SP analogs partially overlaps with that of distinct peptide agonists is valuable for understanding the specificity/broadness of peptide ligands.

RC-3095, a gastrin-releasing peptide receptor antagonist, synergizes with gemcitabine to inhibit the growth of human pancreatic cancer CFPAC-1 in vitro and in vivo

OBJECTIVES

Pancreatic cancer remains a lethal disease. In this study, we investigated the efficacy of a combination of gastrin-releasing peptide receptor antagonist RC-3095 and gemcitabine on pancreatic cancer CFPAC-1.

METHODS

The antiproliferation effects of RC-3095, gemcitabine, or the combination on pancreatic cancer were monitored in vitro. Nude mice bearing xenografts of CFPAC-1 cell received injections of the vehicle (control), RC-3095 (20 μg, subcutaneously, daily), gemcitabine (15 mg/kg, intraperitoneally, every 3 days), or the combination of RC-3095 and gemcitabine for 4 weeks. The histological changes and protein expression were tested using immunohistochemistry and Western blotting.

RESULTS

Treatment with the combination in culture exhibited a powerful inhibition effect on CFPAC-1 cell proliferation. In xenograft mice model, RC-3095 or gemcitabine significantly reduced the volume and weight of tumors after 4 weeks of treatment, as compared with controls. The combination more potently inhibited the tumor growth than either agent used individually. Immunohistochemistry and Western blotting showed gastrin-releasing peptide receptor/bombesin receptor subtype-3 positive cells and protein expression in tumors decreased by treatment with RC-3095 or gemcitabine alone or greater in combination.

CONCLUSIONS

Our data suggested that the combination could be considered for the possible new approaches for treatment of pancreatic cancers.

Vasorelaxin: a novel arterial smooth muscle-relaxing eicosapeptide from the skin secretion of the Chinese piebald odorous frog (Odorrana schmackeri)

The defensive skin secretions of amphibians are a rich resource for the discovery of novel, bioactive peptides. Here we report the identification of a novel vascular smooth muscle-relaxing peptide, named vasorelaxin, from the skin secretion of the Chinese piebald odorous frog, Odorrana schmackeri. Vasorelaxin consists of 20 amino acid residues, SRVVKCSGFRPGSPDSREFC, with a disulfide-bridge between Cys-6 and Cys-20. The structure of its biosynthetic precursor was deduced from cloned skin cDNA and consists of 67 amino acid residues encoding a single copy of vasorelaxin (vasorelaxin, accession number: HE860494). Synthetic vasorelaxin caused a profound relaxation of rat arterial smooth muscle with an EC₅₀ of 6.76 nM.

G Protein-Coupled Receptors in cancer: biochemical interactions and drug design

G Protein-Coupled Receptors (GPCRs) share the same topology made of seven-transmembrane segments and represent the largest family of membrane receptors. Initially associated with signal transduction in differentiated cells, GPCRs and heterotrimeric G proteins were shown to behave as proto-oncogenes whose overexpression or activating mutations confer transforming properties. The first part of this review focuses on the link between biochemical interactions of a GPCR with other receptors, such as dimerization or multiprotein complexes, and their oncogenic properties. Alteration of these interactions or deregulation of transduction cascades can promote uncontrolled cell proliferation or cell transformation that leads to tumorigenicity and malignancy. The second part concerns the design of drugs specifically targeting these complex interactions and their promise in cancer therapy.

The substance P/neurokinin-1 receptor system in lung cancer: focus on the antitumor action of neurokinin-1 receptor antagonists

The last decades have seen no significant progress in extending the survival of lung cancer patients and there is an urgent need to improve current therapies. The substance P (SP)/neurokinin-1 receptor (NK-1R) system plays an important role in the development of cancer: SP and NK-1R antagonists respectively induce cell proliferation and inhibition in human cancer cell lines. No study of the involvement of this system in non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) cells has been carried out in depth. Here, we demonstrate the involvement of the SP/NK-1R system in human H-69 (SCLC) and COR-L23 (NSCLC) cell lines: (1) they express isoforms of the NK-1R and mRNA for the NK-1R; (2) they overexpress the tachykinin 1 gene; (3) the NK-1R is involved in their viability; (4) SP induces their proliferation; (5) NK-1R antagonists (Aprepitant (Emend), L-733,060, L-732,138) inhibit the growth of both cell lines in a concentration-dependent manner; (6) the specific antitumor action of these antagonists against such cells occurs through the NK-1R; and (7) lung cancer cell death is due to apoptosis. We also demonstrate the presence of NK-1Rs and SP in all the human SCLC and NSCLC samples studied. Our findings indicate that the NK-1R may be a promising new target in the treatment of lung cancer and that NK-1R antagonists could be new candidate antitumor drugs in the treatment of SCLC and NSCLC.

The role of neurokinin-1 receptor in the microenvironment of inflammation and cancer

The recent years have witnessed an exponential increase in cancer research, leading to a considerable investment in the field. However, with few exceptions, this effort has not yet translated into a better overall prognosis for patients with cancer, and the search for new drug targets continues. After binding to the specific neurokinin-1 (NK-1) receptor, the peptide substance P (SP), which is widely distributed in both the central and peripheral nervous systems, triggers a wide variety of functions. Antagonists against the NK-1 receptor are safe clinical drugs that are known to have anti-inflammatory, analgesic, anxiolytic, antidepressant, and antiemetic effects. Recently, it has become apparent that SP can induce tumor cell proliferation, angiogenesis, and migration via the NK-1 receptor, and that the SP/NK-1 receptor complex is an integral part of the microenvironment of inflammation and cancer. Therefore, the use of NK-1 receptor antagonists as a novel and promising approach for treating patients with cancer is currently under intense investigation. In this paper, we evaluate the recent scientific developments regarding this receptor system, its role in the microenvironment of inflammation and cancer, and its potentials and pitfalls for the usage as part of modern anticancer strategies.

Physiological roles of preproghrelin-derived peptides in GH secretion and feeding

Among the factors playing a crucial role in the regulation of energy metabolism, gastro-intestinal peptides are essential signals to maintain energy homeostasis as they relay to the central nervous system the informations about the nutritional status of the body. Among these factors, preproghrelin is a unique prohormone as it encodes ghrelin, a powerful GH secretagogue and the only orexigenic signal from the gastrointestinal tract and obestatin, a proposed functional ghrelin antagonist. These preproghrelin-derived peptides may contribute to balance energy intake, metabolism and body composition by regulating the activity of the GH/IGF-1 axis and appetite. Whereas the contribution of ghrelin has been well characterized, the role of the more recently identified obestatin, in this regulatory process is still controversial. In this chapter, we describe the contribution of these different preproghrelin-derived peptides and their receptors in the regulation of GH secretion and feeding. Data obtained from pharmacological approaches, mutant models and evaluation of the hormones in animal and human models are discussed.

Targeting V1A-vasopressin receptors with [Arg6, D-Trp7,9, NmePhe8]-substance P (6-11) identifies a strategy to develop novel anti-cancer therapies

BACKGROUND AND PURPOSE

The anti-cancer agent [Arg(6), D-Trp(7,9), N(me)Phe(8)]-substance P (6-11) (SP-G) modulates gastrin releasing peptide (GRP) and arginine vasopressin signalling in small cell lung cancer cells leading to growth arrest and apoptosis. We have shown that SP-G acts as a biased agonist at GRP receptors. This work examines the hypothesis that SP-G acts as a biased agonist at the V(1A) vasopressin receptor.

EXPERIMENTAL APPROACH

The human V(1A) receptor was expressed in CHO-K1 cells. Extracellular regulated kinase (ERK) activation and intracellular Ca(2+) were measured using activation state-specific antibodies and Fura-2-AM respectively. The effect of SP-G on tumourigenicity was assessed by colony assay.

KEY RESULTS

In V(1A) receptor expressing cells, SP-G caused a sustained activation of ERK via a stimulation of V(1A) receptor coupling to G(i). Inhibition of G(i) with Pertussis toxin attenuated the inhibition by SP-G of the growth of CHO-K1 cells stably expressing the V(1A) receptor. Chimeric V(1A) receptors containing the second or third intracellular loop of the V(2) receptor were capable of binding vasopressin and SP-G but had altered ability to activate phospholipase C (PLC) and ERK. The second intracellular loop of the V(1A) receptor was essential for vasopressin-stimulated PLC and ERK activation but not for SP-G-induced ERK activation.

CONCLUSIONS AND IMPLICATIONS

This work provides mechanistic insight, for biased agonists at V(1A) receptors and highlights a potential role for such agents as anti-cancer agents.

Targeting growth factors in lung cancer

Lung cancer causes more deaths than any other malignancy in the developed world. Advances in surgical techniques and chemotherapy/radiotherapy regimes have produced only minimal improvements in long-term survival. New therapeutic interventions are urgently required. Research has indicated that growth factor signaling may be an important novel target in lung cancer therapy. Preclinical studies have demonstrated the role of extracellular growth factors in lung cancer cell proliferation, metastasis, and resistance to cytotoxic therapy, and have elucidated the key molecular components of growth factor-signaling cascades. This has enabled the development of selective growth factor inhibitors, which have been evaluated in clinical trials and are now an accepted component of advanced lung cancer treatment. Further research is underway to improve the efficacy of this growth factor-targeted therapy. This article will outline the important aspects of this translational research indicating the growth factor-signaling pathways identified in lung cancer, clinical trials of anti-growth factor therapy, and potential future research directions.

International Union of Pharmacology. LXVIII. Mammalian bombesin receptors: nomenclature, distribution, pharmacology, signaling, and functions in normal and disease states

The mammalian bombesin receptor family comprises three G protein-coupled heptahelical receptors: the neuromedin B (NMB) receptor (BB(1)), the gastrin-releasing peptide (GRP) receptor (BB(2)), and the orphan receptor bombesin receptor subtype 3 (BRS-3) (BB(3)). Each receptor is widely distributed, especially in the gastrointestinal (GI) tract and central nervous system (CNS), and the receptors have a large range of effects in both normal physiology and pathophysiological conditions. The mammalian bombesin peptides, GRP and NMB, demonstrate a broad spectrum of pharmacological/biological responses. GRP stimulates smooth muscle contraction and GI motility, release of numerous GI hormones/neurotransmitters, and secretion and/or hormone release from the pancreas, stomach, colon, and numerous endocrine organs and has potent effects on immune cells, potent growth effects on both normal tissues and tumors, potent CNS effects, including regulation of circadian rhythm, thermoregulation; anxiety/fear responses, food intake, and numerous CNS effects on the GI tract as well as the spinal transmission of chronic pruritus. NMB causes contraction of smooth muscle, has growth effects in various tissues, has CNS effects, including effects on feeding and thermoregulation, regulates thyroid-stimulating hormone release, stimulates various CNS neurons, has behavioral effects, and has effects on spinal sensory transmission. GRP, and to a lesser extent NMB, affects growth and/or differentiation of various human tumors, including colon, prostate, lung, and some gynecologic cancers. Knockout studies show that BB(3) has important effects in energy balance, glucose homeostasis, control of body weight, lung development and response to injury, tumor growth, and perhaps GI motility. This review summarizes advances in our understanding of the biology/pharmacology of these receptors, including their classification, structure, pharmacology, physiology, and role in pathophysiological conditions.

Anticancer activity of a peptide combination in gastrointestinal cancers targeting multiple neuropeptide receptors

A novel peptide combination consisting of four synthetic neuropeptide analogs of Vasoactive Intestinal Peptide (VIP), Bombesin, Substance P and Somatostatin has been found to have potent anticancer activity in vitro and in vivo. The receptors of these four neuropeptides are known to be over expressed in various cancers. We have found the presence of native neuropeptides in the culture supernatant of the primary tumor cells of human colon adenocarcinomas. It was further demonstrated by receptor-ligand assays that not only do these tumor cells synthesize and secrete four peptide hormones but also possess specific high affinity receptors on their surface. Screening a large panel of analogs to the four peptide hormones on tumor cell proliferation led to the identification of four cytotoxic analogs, the combination of which was code-named DRF7295. The design and synthesis of the peptide analogs have been described in this paper. In vitro anticancer activity of DRF7295 was studied in a large panel of human tumor cells. Gastrointestinal tumor cells of the colon, pancreas and duodenum were found to be most sensitive to DRF7295 with moderate activity seen in glioblastoma, prostate, leukemia and those of oral cancer cells. Efficacy studies in xenograft models of colon and duodenum resulted in T/C% of less than 40%, which is indicative of strong tumor regressing potential of DRF7295 in gastrointestinal cancers. Acute and long-term toxicity studies as well as safety pharmacology studies conducted indicate the safety of the drug upon systemic administration with no significant adverse pharmacological effects.

Substance P analogs containing alpha,alpha-dialkylated amino acids with potent anticancer activity

Six analogs (peptides 1-6) of the potent substance P (SP) derivative known as 'Antagonist D' were synthesized by substituting constrained amino acids Aib or Acp (cycloleucine, 1-amino cyclopentane carboxylic acid) at different positions in the Antagonist D sequence: D-Arg(1)-Pro(2)-Lys(3)-Pro(4)-D-Phe(5)-Gln(6)-D-Trp(7)-Phe(8)-D-Trp(9)-Leu(10)-Leu(11)-NH(2). In the preliminary in vitro antiproliferative screening of the analogs on different human cancer cell lines by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, peptide 1 was found to be the most active. Further, peptide 1 was butanoylated (analog 5) or octanoylated (analog 6) at the N-terminus. SP analogs 1, 5, and 6 were evaluated in vivo in a xenograft model of human primary colon tumor (PTC) cell line in athymic nude mice and were found to cause tumor regression. This study investigates if the use of the constrained amino acids Aib and Acp in the designed SP analogs can retain the in vitro and in vivo anticancer activities, which could be useful in cancer therapy and drug targeting. Further, the strategy of incorporation of Aib or Acp in biologically active peptides can be exploited in determining the receptor-bound conformation and in transforming these bioactive peptides into pharmacologically useful drugs.

NK-1 receptor antagonists induce apoptosis and counteract substance P-related mitogenesis in human laryngeal cancer cell line HEp-2

It has been demonstrated that substance P (SP) induces cell proliferation and neurokinin-1 (NK-1) receptor antagonists inhibit growth in several human cancer cell lines, but it is currently unknown whether such actions are exerted on human laryngeal carcinoma cell line HEp-2. In addition, the presence of NK-1 receptor has not been demonstrated in this cell line. We carried out an in vitro study of the growth inhibitory capacity of the NK-1 receptor antagonists L-733,060 and L-732,138 against human laryngeal carcinoma cell line HEp-2. Coulter counter was used to determine viable cell numbers followed by application of the tetrazolium compound MTS. Furthermore, an immunoblot analysis was used to determine the NK-1 receptor, and the 4',6-diamidino-2-phenylindole (DAPI) method was applied to demonstrate apoptosis of the laryngeal carcinoma cells. We observed the presence of several NK-1 receptors isoforms (34, 46, 58 and 75 kDa). Nanomolar concentrations of SP increased the growth rate of the cell line and micromolar concentrations of L-733,060 and L-732,138 inhibited the growth of the HEp-2 cells in a dose-dependent manner, with and without previous administration of SP. The 50% inhibition concentration values were 21.34 microM and 37.97 (48 h) respectively for HEp-2. NK-1 receptor presence on HEp-2 cells was confirmed by western blotting. DAPI staining revealed the presence of apoptosis following NK-1 receptor antagonists treatment. We demonstrated that NK-1 receptors were present in this laryngeal cancer cell line; these findings demonstrate that SP acts as a mitogen on the human laryngeal carcinoma cell line HEp-2 through the NK-1 receptor, and also indicate that both NK-1 receptors antagonists induced apoptosis of the tumour cells. This new action, reported here for the first time, suggests that the NK-1 receptor is a new and promising target in the treatment of human laryngeal carcinoma.

Delivering multiple anticancer peptides as a single prodrug using lysyl-lysine as a facile linker

A large 40-residue precursor peptide (propeptide 5) was synthesized by linking together four designed anticancer peptide analogs to the neuropeptides: vasoactive intestinal peptide, somatostatin, bombesin and substance P, using enzyme cleavable lysyl-lysine linkers. On incubation with the enzyme trypsin, propeptide 5 was cleaved in a sequence-specific manner at the lysyl-lysine residues in the linker to release the individual peptide fragments which were identified by LC-MS. Another precursor peptide (propeptide 5a), consisting of two of the peptide analogs linked through lysyl-lysine linker, was also preferentially cleaved at the Lys-Lys site on incubation with the enzyme trypsin. Propeptide 5 showed potent anticancer activity, both in vitro and in vivo, which was greater than that of the individual component peptides. The enhanced activity suggests that the propeptide is possibly cleaved in the biological system at the lysyl-lysine site to yield the individual peptide analogs, which together show a synergistic effect. On the basis of these experimental findings, it can be concluded that pairs of basic amino acids such as Lys-Lys can be used as facile linkers for delivering multiple biologically active peptides.

Recent Developments in Ghrelin Receptor Ligands

The 28-amino acid peptide ghrelin is a neuroendocrine hormone synthesized primarily in the stomach. It stimulates growth hormone secretion and appetite, thus promoting food intake and body-weight gain. The pharmacological properties of this peptide are mediated by the growth hormone secretagogue receptor type 1a (GHS-R1a). Given its wide spectrum of biological activities, it is evident that the discovery of ghrelin and its receptor has opened up many perspectives in the fields of neuroendocrine and metabolic research and has had an influence on such fields of internal medicine as gastroenterology, oncology, and cardiology. It is therefore increasingly likely that synthetic, peptidyl, and nonpeptidyl GHS-R1a ligands, acting as agonists, partial agonists, antagonists, or inverse agonists, could have both clinical and therapeutic potential. This review summarizes the various types of GHS-R1a ligands that have been described in the literature and discusses the recent progress made in this research area.

Heterogeneity of ghrelin/growth hormone secretagogue receptors. Toward the understanding of the molecular identity of novel ghrelin/GHS receptors

Ghrelin is a gastric polypeptide displaying strong GH-releasing activity by activation of the type 1a GH secretagogue receptor (GHS-R1a) located in the hypothalamus-pituitary axis. GHS-R1a is a G-protein-coupled receptor that, upon the binding of ghrelin or synthetic peptidyl and non-peptidyl ghrelin-mimetic agents known as GHS, preferentially couples to G(q), ultimately leading to increased intracellular calcium content. Beside the potent GH-releasing action, ghrelin and GHS influence food intake, gut motility, sleep, memory and behavior, glucose and lipid metabolism, cardiovascular performances, cell proliferation, immunological responses and reproduction. A growing body of evidence suggests that the cloned GHS-R1a alone cannot be the responsible for all these effects. The cloned GHS-R1b splice variant is apparently non-ghrelin/GHS-responsive, despite demonstration of expression in neoplastic tissues responsive to ghrelin not expressing GHS-R1a; GHS-R1a homologues sensitive to ghrelin are capable of interaction with GHS-R1b, forming heterodimeric species. Furthermore, GHS-R1a-deficient mice do not show evident abnormalities in growth and diet-induced obesity, suggesting the involvement of another receptor. Additional evidence of the existence of another receptor is that ghrelin and GHS do not always share the same biological activities and activate a variety of intracellular signalling systems besides G(q). The biological actions on the heart, adipose tissue, pancreas, cancer cells and brain shared by ghrelin and the non-acylated form of ghrelin (des-octanoyl ghrelin), which does not bind GHS-R1a, represent the best evidence for the existence of a still unknown, functionally active binding site for this family of molecules. Finally, located in the heart and blood vessels is the scavenger receptor CD36, involved in the endocytosis of the pro-atherogenic oxidized low-density lipoproteins, which is a pharmacologically and structurally distinct receptor for peptidyl GHS and not for ghrelin. This review highlights the most recently discovered features of GHS-R1a and the emerging evidence for a novel group of receptors that are not of the GHS1a type; these appear involved in the transduction of the multiple levels of information provided by GHS and ghrelin.

Ghrelin Receptor Inverse Agonists: Identification of an Active Peptide Core and Its Interaction Epitopes on the Receptor

[D-Arg1,D-Phe5,D-Trp7,9,Leu11]Substance P functions as a low-potency antagonist but a high-potency full inverse agonist on the ghrelin receptor. Through a systematic deletion and substitution analysis of this peptide, the C-terminal carboxyamidated pentapeptide wFwLX was identified as the core structure, which itself displayed relatively low inverse agonist potency. Mutational analysis at 17 selected positions in the main ligand-binding crevice of the ghrelin receptor demonstrated that ghrelin apparently interacts only with residues in the middle part of the pocket [i.e., between transmembrane (TM)-III, TM-VI and TM-VII]. In contrast, the inverse agonist peptides bind in a pocket that extends all the way from the extracellular end of TM-II (AspII:20) across between TM-III and TM-VI/VII to TM-V and TM-IV. The potency of the main inverse agonist could be improved up to 20-fold by a number of space-generating mutants located relatively deep in the binding pocket at key positions in TM-III, TM-IV and TM-V. It is proposed that the inverse agonists prevent the spontaneous receptor activation by inserting relatively deeply across the main ligand-binding pocket and sterically blocking the movement of TM-VI and TM-VII into their inward-bend, active conformation. The combined structure-functional analysis of both the ligand and the receptor allowed for the design of a novel, N-terminally Lys-extended analog of wFwLL, which rescued the high-potency, selective inverse agonism that was dependent upon both AspII:20 and GluIII:09. The identified pharmacophore can possibly serve as the basis for targeted discovery of also nonpeptide inverse agonists for the ghrelin receptor.

Endogenous ghrelin regulates episodic growth hormone (GH) secretion by amplifying GH Pulse amplitude: evidence from antagonism of the GH secretagogue-R1a receptor

Ghrelin was purified from rat stomach as an endogenous ligand for the GH secretagogue (GHS) receptor. As a GHS, ghrelin stimulates GH release, but it also has additional activities, including stimulation of appetite and weight gain. Plasma GH and ghrelin secretory patterns appear unrelated, whereas many studies have correlated ghrelin variations with food intake episodes. To evaluate the role of endogenous ghrelin, GH secretion and food intake were monitored in male rats infused sc (6 mug/h during 10 h) or intracerebroventricularly (5 microg/h during 48 h) with BIM-28163, a full competitive antagonist of the GHS-R1a receptor. Subcutaneous BIM-28163 infusion significantly decreased GH area under the curve during a 6-h sampling period by 54% and peak amplitude by 46%. Twelve hours after the end of treatment these parameters returned to normal. Central treatment was similarly effective (-37 and -42% for area under the curve and -44 and -49% for peak amplitude on the first and second days of infusion, respectively). Neither peripheral nor central BIM-28163 injection modified GH peak number, GH nadir, or IGF-I levels. In this protocol, food intake is not strongly modified and water intake is unchanged. Subcutaneous infusion of BIM-28163 did not change plasma leptin and insulin levels evaluated at 1200 and 1600 h. On the contrary, central BIM-28163 infusion slightly increased leptin and significantly increased insulin concentrations. Thus, endogenous ghrelin, through GHS-R1a, acts as a strong endogenous amplifier of spontaneous GH peak amplitude. The mechanisms by which ghrelin modifies food intake remain to be defined and may involve a novel GHS receptor.

Pathogenesis of lung cancer: 100 year report

Over the past 100 years, our understanding of the pathogenesis of lung cancer has advanced impressively. Environmental carcinogens and a gene locus determining susceptibility have been identified. The pathology of lung cancer has been classified into categories with major clinical implications. The cellular and molecular genetic changes underlying lung cancer have become better understood over the past 25 years, but the stepwise progression of respiratory epithelium from normal to neoplastic is not yet well demarcated, limiting abilities to advance early detection and chemoprevention. The translation of improved understanding of dominant signal transduction pathways in lung cancer to rationally designed therapeutic strategies has had recent successes, demonstrating a proof of principle for targeted therapy in lung cancer. Improvement in overall patient outcomes has been stubbornly slow and will require concerted efforts.

The NK1 receptor is involved in the antitumoural action of L-733,060 and in the mitogenic action of substance P on neuroblastoma and glioma cell lines

We have carried out an in vitro study to investigate the ability of substance P to activate cell growth and the NK1 receptor antagonist L-733,060 to inhibit cell growth in the SKN-BE(2) neuroblastoma and GAMG glioma cell lines. A coulter counter was used to determine viable cell numbers, followed by application of the tetrazolium compound [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)2-(4-sulfophenyl)-2H-tetrazolium], inner salt, colorimetric method to evaluate cell viability in this cytotoxicity assay. Nanomolar concentrations of substance P increased, and micromolar concentrations of L-733,060 inhibited the growth of both cell lines studied, with and without previous administration of substance P. In addition, we have demonstrated by immunoblot analysis that NK1 receptors are present in both cancer cell lines studied here. Thus, this study demonstrates that substance P acts as a mitogen in the SKN-BE(2) neuroblastoma and GAMG glioma cell lines, and that the antitumoural action of L-733,060 on both human cell lines occurs through the NK1 receptor. This action suggests that the NK1 receptor is a new and promising target in the treatment of human neuroblastoma and glioma.

Expression of V1A and GRP receptors leads to cellular transformation and increased sensitivity to substance-P analogue-induced growth inhibition

Small-cell lung cancer (SCLC) is a particularly aggressive cancer, which metastasises early. Despite initial sensitivity to radio- and chemo-therapy, it invariably relapses, so that the 2-year survival remains less than 5%. Neuropeptides particularly arginine vasopressin (AVP) and gastrin-releasing peptide (GRP) act as autocrine and paracrine growth factors and the expression of these and their receptors are a hallmark of the disease. Substance-P analogues including [D-Arg1,D-Phe5,D-Trp7,9,Leu11]-substance-P (SP-D) and [Arg6,D-Trp7,9,NmePhe8]-substance-P (6-11) (SP-G) inhibit the growth of SCLC cells by modulating neuropeptide signalling. We show that GRP and V1A receptors expression leads to the development of a transformed phenotype. Addition of neuropeptide provides some protection from etoposide-induced cytotoxicity. Receptor expression also leads to an increased sensitivity to substance-P analogue-induced growth inhibition. We show that SP-D and SP-G act as biased agonists at GRP and V1A receptors causing blockade of Gq-mediated Ca2+ release while directing signalling to activate ERK via a pertussis toxin-sensitive pathway. This is the first description of biased agonism at V1A receptors. This unique pharmacology governs the antiproliferative properties of these agents and highlights their potential therapeutic potential for the treatment of SCLC and particularly in tumours, which have developed resistance to chemotherapy.

Comparative study of SP[6-11] and its analogs using simulated annealing

In this study we compared the steric structures of the bioactive part of substance P (SP[6-11]) and its analogs (NY3460 and pHOPA-SP5). The molecular dynamics-simulated annealing method was used to explore the conformational space, and the structural differences and similarities of these molecules were identified. For the three peptides, the conformational distributions were represented in Ramachandran density plots. The occurring secondary structural elements of the investigated molecules were identified, namely alpha-Helix, type III beta-Turn, gamma-Turn, and inverse gamma-Turn. For SP[6-11] and its two analogs, different intramolecular interactions (H-bonds between the main-chain atoms, aromatic-aromatic interactions, and amino-aromatic interactions) that can stabilize the various conformations of the three peptides were investigated. Detailed examination of these intramolecular interactions revealed that H-bonds between the main-chain atoms are relevant in the determination and stabilization of the conformer structures of the peptides, while the aromatic-aromatic interactions do not play an important stabilizing role. Furthermore, in the conformers of NY3460 and pHOPA-SP5, different types of amino-aromatic interactions were identified that contribute to the formation of the various structures of these peptides. For all three molecules, the orientations of the side chains were investigated and the rotamer populations were determined.

Antitumoral action of the neurokinin-1 receptor antagonist L-733 060 on human melanoma cell lines

Melanoma represents 1% of all cancers and accounts for approximately 65% of skin cancer deaths. At present, effective treatment does not exist. Substance P (SP) is a neuropeptide expressed in invasive malignant melanomas. We studied the in vitro growth inhibitory capacity of the potent and long-acting neurokinin-1 (NK1) receptor antagonist L-733 060 at concentration ranges of 2.5-20 microM, 10-30 microM and 20-50 microM in the melanoma cell lines COLO 858, MEL H0 and COLO 679, respectively. A Coulter counter was used to determine the number of viable cells, and the tetrazolium compound 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)2-(4-sulphophenyl)-2H-tetrazolium, inner salt (MTS) colorimetric method was used to evaluate cell proliferation. L-733 060 inhibited the growth of all three cell lines in a dose-dependent manner. The 50% inhibition concentration (IC(50)) was 8.7 microM at 48 h and 7.1 microM at 96 h for COLO 858, 27.5 microM at 24 h and 18.9 microM at 48 h for MEL H0, and 33.8 microM at 30 h and 31.5 microM at 72 h for COLO 679. These findings indicate that the NK1 receptor antagonist L-733 060 acts as an antitumoral agent. This action, shown here for the first time, suggests that the NK1 receptor antagonist L-733 060 could be a promising therapeutic drug in the treatment of the human melanoma.

A novel growth hormone secretagogue-1a receptor antagonist that blocks ghrelin-induced growth hormone secretion but induces increased body weight gain

Ghrelin, the natural ligand for the growth hormone secretagogue-1a (GHS-1a) receptor, has received a great deal of attention due to its ability to stimulate weight gain and the hope that an antagonist of the GHS-1a receptor could be a treatment for obesity. We have discovered an analog of full-length human ghrelin, BIM-28163, which fully antagonizes GHS-1a by binding to but not activating the receptor. We further demonstrate that BIM-28163 blocks ghrelin activation of the GHS-1a receptor, and inhibits ghrelin-induced GH secretion in vivo. Unexpectedly, however, BIM-28163 acts as an agonist with regard to stimulating weight gain. These results may suggest the presence of an unknown ghrelin receptor that modulates ghrelin actions on weight gain. In keeping with our results on growth hormone (GH) secretion, BIM-28163 acts as an antagonist of ghrelin-induced Fos protein immunoreactivity (Fos-IR) in the medial arcuate nucleus, an area involved in the ghrelin modulation of GH secretion. However, in the dorsal medial hypothalamus (DMH), a region associated with regulation of food intake, both ghrelin and BIM-28163 act as agonists to upregulate Fos-IR. The observation that ghrelin and BIM-28163 have different efficacies in inducing Fos-IR in the DMH, and that concomitant administration of ghrelin and an excess of BIM-28163 results in the same level of Fos-IR as BIM-28163 administered alone may demonstrate that in the DMH both ghrelin and BIM-28163 act via the same receptor. If so, it is unlikely that this receptor is GHS-1a. Collectively, our findings suggest that the action of ghrelin to stimulate increased weight gain may be mediated by a novel receptor other than GHS-1a, and further imply that GHS-1a may not be the appropriate target for anti-obesity strategies.

Dexamethasone regulation of gastrin-releasing peptide receptor in human lung cells

We investigated the effects of the glucocorticoid, dexamethasone (Dex), on expression of the gastrin-releasing peptide (GRP) receptor by human small cell lung carcinoma (SCLC) SHP77 cells. After 12h of 10nM Dex exposure, a six-fold increase in the peak of GRP receptor mRNA compared with untreated controls (10.5+/-4 versus 1.65+/-0.15 attomols/microg total RNA, respectively, P<0.05) occurred. GRP receptor mRNA levels fell to less than 0.5 attomols/microg total RNA after 24h; in Dex-treated cells, these levels rose to 1.2 compared with 0.12 attomols/microg total RNA in the absence of Dex after 7 days. A significant increase (P<0.05) in the GRP receptor-specific binding was also found. Stimulation of SHP77 cell proliferation (25-35% in the presence of 10-100 nM Dex; P<0.0001) was observed after 4-8 days of exposure; this stimulation was inhibited by GRP receptor antagonists. SHP77 cell content and concentration of bombesin-like peptides (BLP) in conditioned medium (approximately 4 nM) was unchanged by Dex. Stimulation of human SCLC SHP77 cell proliferation by Dex may, in part, occur via effects on the GRP autocrine system in these cells.

High constitutive signaling of the ghrelin receptor--identification of a potent inverse agonist

Ghrelin is a GH-releasing peptide that also has an important role as an orexigenic hormone-stimulating food intake. By measuring inositol phosphate turnover or by using a reporter assay for transcriptional activity controlled by cAMP-responsive elements, the ghrelin receptor showed strong, ligand-independent signaling in transfected COS-7 or human embryonic kidney 293 cells. Ghrelin and a number of the known nonpeptide GH secretagogues acted as agonists stimulating inositol phosphate turnover further. In contrast, the low potency ghrelin antagonist, [D-Arg1,D-Phe5,D-Trp7,9,Leu11]-substance P was surprisingly found to be a high potency (EC50 = 5.2 nm) full inverse agonist as it decreased the constitutive signaling of the ghrelin receptor down to that observed in untransfected cells. The homologous motilin receptor functioned as a negative control as it did not display any sign of constitutive activity; however, upon agonist stimulation the motilin receptor signaled as strongly as the unstimulated ghrelin receptor. It is concluded that the ghrelin receptor is highly constitutively active and that this activity could be of physiological importance in its role as a regulator of both GH secretion and appetite control. It is suggested that inverse agonists for the ghrelin receptor could be particularly interesting for the treatment of obesity.

Inhibition of proliferation of human small cell lung cancer cells expressing an autocrine system for gastrin releasing peptide by antisense oligodeoxynucleotides to gastrin releasing peptide receptor

The objectives of this study were to investigate the effect of antisense (AS) oligodeoxynucleotides (ODNs) directed against gastrin releasing peptide (GRP) receptor mRNA on proliferation of human small cell lung cancer (SCLC) NCI-H345 cells which express the autocrine system for GRP. The methods used were to expose human SCLC cell lines to antisense ODNs or sense ODNs and to measure their proliferation by spectrophotometric assay or viable cell counts. Our results demonstrated that the single or combined AS ODNs against GRP receptor inhibited proliferation of human SCLC NCI-H345 cells significantly by 37% (P<0.01), but did not inhibit proliferation of either human bronchial epithelial BEAS 2B cells or human SCLC NCI-N417 cells, neither of which express the GRP autocrine system. The sense controls did not significantly inhibit proliferation compared with no treatment controls. Specificity was also demonstrated by the observation that cells exposed to AS ODNs had a decrease in GRP receptor expression as measured by specific binding of 34% (P<0.01), and when all three AS ODNs were used, binding was decreased by 60% (P<0.03). Furthermore, AS ODNs decreased by 75% the maximum percentage of cells responding to GRP in an intracellular calcium release assay. Our conclusions are that antisense ODNs directed against a GRP receptor which is involved in an autocrine loop in human SCLC cells inhibited proliferation of these cells by their impact on reducing GRP receptor expression. Further development of means of increasing AS ODN specificity and effectiveness in human SCLC cell is warranted.

A vasoactive intestinal peptide antagonist inhibits the growth of glioblastoma cells

The effects of a vasoactive intestinal peptide (VIP) receptor antagonist (VIPhyb) on human glioblastoma cells were characterized. Pituitary adenylate cyclase activating polypeptide (125I-PACAP-27) bound with high affinity to U87, U118, and U373 cells. Specific 125I-PACAP-27 binding to U87 cells was inhibited, with high affinity, by PACAP but not VIP or VIPhyb (IC50 = 10, 1500, and 500 nM, respectively). By reverse transcriptase-polymerase chain reaction (RT-PCR), a major 305 bp band was observed indicative of PAC1 receptors. PACAP-27 caused cAMP elevation and the increase in cAMP caused by PACAP-27, was inhibited by the VIPhyb. Also, PACAP-27 caused cytosolic Ca2+ elevation in Fura-2AM loaded U87 cells and the VIPhyb inhibited this increase. Using the MTT growth assay, the VIPhyb was shown to inhibit glioblastoma growth in a concentration-dependent manner. Using a clonogenic assay in vitro, 10 microM VIPhyb significantly inhibited proliferation of U87, U118, and U373 cells. In vivo, 0.4 microg/kg VIPhyb inhibited U87 xenograft proliferation in nude mice. These results suggest that the VIPhyb antagonizes PAC1 receptors on glioblastoma cells and inhibits their proliferation.

A growth factor antagonist as a targeting agent for sterically stabilized liposomes in human small cell lung cancer

The ability of a growth factor antagonist, [D-Arg(6),D-Trp(7,9)-N(me)Phe(8)]-substance P(6-11), named antagonist G, to selectively target polyethylene glycol-grafted liposomes (known as sterically stabilized liposomes) to a human classical small cell lung cancer (SCLC) cell line, H69, was examined. Our results showed that radiolabeled antagonist G-targeted sterically stabilized liposomes (SLG) bound to H69 cells with higher avidity than free antagonist G and were internalized (reaching a maximum of 13000 SLG/cell), mainly through a receptor-mediated process, likely involving clathrin-coated pits. This interaction was confirmed by confocal microscopy to be peptide- and cell-specific. Moreover, it was shown that SLG significantly improved the nuclear delivery of encapsulated doxorubicin to the target cells, increasing the cytotoxic activity of the drug over non-targeted liposomes. In mice, [(125)I]tyraminylinulin-containing SLG were long circulating, with a half-life of 13 h. Use of peptides like antagonist G to promote binding and internalization of sterically stabilized liposomes, with their accompanying drug loads, i.e., anticancer drugs, genes or antisense oligonucleotides, into target cells has the potential to improve therapy of SCLC.

Bombesin and substance P analogues differentially regulate G-protein coupling to the bombesin receptor. Direct evidence for biased agonism

Substance P analogues including [d-Arg1,d-Phe5,d-Trp7,9,Leu11]substance P (SpD) act as "broad spectrum neuropeptide antagonists" and are potential anticancer agents that inhibit the growth of small cell lung cancer cells in vitro and in vivo. However, their mechanism of action is controversial and not fully understood. Although these compounds block bombesin-induced mitogenesis and signal transduction, they also have agonist activity. The mechanism underlying this agonist activity was examined. SpD binds to the ligand-binding site of the bombesin/gastrin-releasing peptide receptor and blocks the bombesin-stimulated increase in [Ca2+]i within the same concentration range that causes sustained activation of c-Jun N-terminal kinase and extracellular signal-regulated protein kinase (ERK). The activation of c-Jun N-terminal kinase by SpD and bombesin is blocked by dominant negative inhibition of G(alpha12). The ERK activation by SpD is pertussis toxin-sensitive in contrast to ERK activation by bombesin, which is pertussis toxin-insensitive but dependent on epidermal growth factor receptor phosphorylation. SpD does not simply act as a partial agonist but differentially modulates the activation of the G-proteins G(alpha12), G(i), and G(q) compared with bombesin. This unique ability allows the bombesin receptor to couple to G(i) and at the same time block receptor activation of G(q). Our results provide direct evidence that SpD is acting as a "biased agonist" and that this has physiological relevance in small cell lung cancer cells. This validation of the concept of biased agonism has important implications in the development of novel pharmacological agents to dissect receptor-mediated signal transduction and of highly selective drugs to treat human disease.

Autocrine and paracrine signaling through neuropeptide receptors in human cancer

Autocrine and paracrine signaling leading to stimulation of tumor cell growth is a common theme in human cancers. In addition to polypeptide growth factors such as EGF family members which signal through receptor tyrosine kinases, accumulating evidence supports the autocrine and paracrine involvement of specific neuropeptides with defined physiologic actions as neurotransmitters and gut hormones in lung, gastric, colorectal, pancreatic and prostatic cancers. These neuropeptides, including gastrin-releasing peptide, neuromedin B, neurotensin, gastrin, cholecystokinin and arginine vasopressin bind seven transmembrane-spanning receptors that couple to heterotrimeric G proteins. Studies with human small cell lung cancer (SCLC) cells support a requirement for balanced signaling through G(q) and G(12/13) proteins leading to intracellular Ca2+ mobilization, PKC activation and regulation of the ERK and JNK MAP kinase pathways. While specific neuropeptide antagonists offer promise for interrupting the single neuropeptide autocrine systems operating in pancreatic and prostatic cancers, SCLC is exemplified by multiple, redundant neuropeptide autocrine systems such that tumor growth cannot be inhibited with a single specific antagonist. However, a novel class of neuropeptide derivatives based on the substance P sequence have been defined that exhibit broad specificity for neuropeptide receptors and induce apoptosis in SCLC by functioning as biased agonists that stimulate discordant signal transduction. Thus, interruption of autocrine and paracrine neuropeptide signaling with specific antagonists or broad-spectrum biased agonists offer promising new therapeutic approaches to the treatment of human cancers.

A bombesin receptor subtype-3 peptide increases nuclear oncogene expression in a MEK-1 dependent manner in human lung cancer cells

A synthetic peptide, (D-Phe(6), beta-Ala(11), Phe(13), Nle(14))bombesin-(6-14) was used to investigate the signal transduction mechanisms of bombesin receptor subtype-3. Using NCI-1299#5 human lung cancer cells stably transfected with bombesin receptor subtype-3, 100 nM (D-Phe(6), beta-Ala(11), Phe(13), Nle(14))bombesin-(6-14) elevated the cytosolic Ca2+ from 150 to 250 nM within 10 s. Addition of (D-Phe(6), beta-Ala(11), Phe(13), Nle(14))bombesin-(6-14) caused phosphorylation of mitogen activated protein kinase in a time- and concentration-dependent manner. The mitogen activated protein kinase phosphorylation caused by (D-Phe(6), beta-Ala(11), Phe(13), Nle(14))bombesin-(6-14) was inhibited by 2'-amino-3'-methyoxyflavone (PD98059), a mitogen activated protein kinase kinase (MEK-1) inhibitor. Using a luciferase reporter gene construct, (D-Phe(6), beta-Ala(11), Phe(13), Nle(14))bombesin-(6-14) caused Elk-1 activation after 10 min and the increase in Elk-1 activation caused by (D-Phe(6), beta-Ala(11), Phe(13), Nle(14))bombesin-(6-14) was inhibited by PD98059 as well as a dominant-negative MEK-1. (D-Phe(6), beta-Ala(11), Phe(13), Nle(14))bombesin-(6-14) caused increased c-fos as well as c-jun mRNAs 1 h after addition to NCI-H1299#5 cells. The 47-fold increase in c-fos mRNA caused by 100 nM (D-Phe(6), beta-Ala(11), Phe(13), Nle(14))bombesin-(6-14) was inhibited by PD98059, a dominant-negative MEK-1 and a substance P antagonist but not (3-phenylpropanoyl-D-Ala(24), Pro(26), Psi(26,27), Phe(27))GRP-(20-27) (BW2258U89), a GRP receptor antagonist. These results indicate that (D-Phe(6), beta-Ala(11), Phe(13), Nle(14))bombesin-(6-14) caused increased nuclear oncogene expression and upstream events include mitogen activated protein kinase phosphorylation and Elk-1 activation.

Nonpeptide neuromedin B receptor antagonists inhibit the proliferation of C6 cells

The ability of nonpeptide antagonists to interact with neuromedin B receptors on C6 cells was investigated. 2-[3-(2, 6-Diisopropyl-phenyl)-ureido]3-(1H-indol-3-yl)-2-methyl-N-(1-pyridin- 2-yl-cyclohexylmethyl)-proprionate (PD165929), 3-(1H-indol-3-yl)-2-methyl-2-[3(4-nitro-phenyl)-ureido]-N-(1-pyridin- 2-yl-cyclohexylmethyl)-propionamide (PD168368) and 3-(1H-indol-3-yl)-N-[1-(5-methoxy-pyridin-2-yl)-cyclohexylmethyl]- 2-m ethyl-2-[3-(4-nitro-phenyl)-ureido]-propionamide (PD176252) inhibited (125I-Tyr0)neuromedin B binding with IC50 values of 2000, 40 and 50 nM, respectively. Because neuromedin B is a G-protein coupled serpentine receptor, the effects of neuromedin B antagonists on second messenger production and proliferation were investigated. PD168368 inhibited the ability of 10 nM neuromedin B to cause elevation of cytosolic Ca2+, whereas it had no effect on basal cytosolic Ca2+. PD168368 inhibited the ability of 100 nM neuromedin B to cause elevation of c-fos mRNA. Also, PD168368 in a dose-dependent manner inhibited the ability of 100 nM neuromedin B to cause phosphorylation of focal adhesion kinase. Using a [3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay, the order of antagonist potency to inhibit C6 proliferation was PD168368=PD176252>PD165929. Also, 1 microM PD168368 and PD176252 significantly inhibited colony number using a proliferation assay in vitro. PD168368 significantly inhibited C6 xenograft growth in nude mice in vivo. These results indicate that PD168368 is a C6 cell neuromedin B receptor antagonist, which inhibits proliferation.

[Arg(6), D-Trp(7,9), N(me)Phe(8)]-substance P (6-11) (antagonist G) induces AP-1 transcription and sensitizes cells to chemotherapy

[Arg(6), D-Trp(7,9), N(me)Phe(8)]-substance P (6-11) (antagonist G) inhibits small cell lung cancer (SCLC) growth and is entering Phase II clinical investigation for the treatment of SCLC. As well as acting as a neuropeptide receptor antagonist, antagonist G stimulates c-jun-N-terminal kinase (JNK) activity and apoptosis in SCLC cells. We extend these findings and show that the stimulation of JNK and apoptosis by antagonist G is dependent upon the generation of reactive oxygen species (ROS) being inhibited either by anoxia or the presence of N-acetyl cysteine (n-AC). Antagonist G is not intrinsically a free radical oxygen donor but stimulates free radical generation specifically within SCLC cells (6.2-fold) and increases the activity of the redox-sensitive transcription factor AP-1 by 61%. In keeping with this, antagonist G reduces cellular glutathione (GSH) levels (38% reduction) and stimulates ceramide production and lipid peroxidation (112% increase). At plasma concentrations achieved clinically in the phase I studies, antagonist G augments, more than additively, growth inhibition induced by etoposide. Our results suggest that antagonist G may be particularly effective as an additional treatment with standard chemotherapy in SCLC. These novel findings will be important for the clinical application of this new and exciting compound and for the future drug development of new agents to treat this aggressive cancer.

[D-Arg(1),D-Trp(5,7,9),Leu(11)]Substance P inhibits bombesin-induced mitogenic signal transduction mediated by both G(q) and G(12) in Swiss 3T3cells

Substance P (SP) analogues including [d-Arg(1),d-Trp(5,7,9), Leu(11)]SP are broad spectrum neuropeptide antagonists and potential anticancer agents, but their mechanism of action is not fully understood. Here, we examined the mechanism of action of [d-Arg(1), d-Trp(5,7,9),Leu(11)]SP as an inhibitor of G protein-coupled receptor (GPCR)-mediated signal transduction and cellular DNA synthesis in Swiss 3T3 cells. Addition of [d-Arg(1),d-Trp(5,7,9), Leu(11)]SP, at 10 micrometer, caused a striking rightward shift in the dose-response curves of DNA synthesis induced by bombesin, bradykinin, or vasopressin and markedly inhibited the activation of p42(mapk) (ERK-2) and p44(mapk) (ERK-1) induced by these GPCR agonists. In addition, this SP analogue also prevented the protein kinase C-dependent activation of protein kinase D induced by these agonists. [d-Arg(1),d-Trp(5,7,9),Leu(11)]SP, at a concentration (10 micrometer) that inhibited these G(q)-mediated events, also prevented GPCR agonist-induced responses mediated through the G proteins of the G(12) subfamily. These include bombesin-induced assembly of focal adhesions, formation of parallel arrays of actin stress fibers, increase in the tyrosine phosphorylation of focal adhesion kinase (FAK), p130(Cas), and paxillin, and formation of a complex between FAK and Src. We conclude that [d-Arg(1),d-Trp(5,7,9),Leu(11)]SP acts as a mitogenic antagonist of neuropeptide GPCRs blocking signal transduction via both G(q) and G(12).

The metabolism of BW2258U89, a GRP receptor antagonist

BW2258U89 is a gastrin releasing peptide (GRP) receptor antagonist which inhibits the proliferation of the neuroendocrine tumor small cell lung cancer (SCLC). Here the biological activity of BW2258U89 and its metabolite were investigated. Using mass spectroscopy (LC-ESI/MS) techniques, three major peaks for BW2258U89 were observed with mass/charge (m/z) ratios of 1081.6, 541.4 and 361.4. After metabolism by mouse plasma enzymes, the major product had a m/z ratio of 1082.5, 541.9 and 361.8 suggesting that BW2258U89 was deamidated. Deamidated (Da) BW2258U89 was synthesized and it inhibited ((125)I-Tyr(4)) BB binding to NCI-H345 SCLC cells with an IC(50)value of 450 nM; BW2258U89 had an IC(50)value of 17 nM. BW2258U89 (1 microM) antagonized the ability of 50 nM BB to elevate cytosolic Ca(2+)in NCI-H345 cells, whereas 1 microM (Da) BW2258U89 did not. One micromolar BW2258U89 antagonized the increase in NCI-H345 c-fos mRNA caused by 10 nM BB, whereas 1 microM (Da) BW2258U89 had little effect. One microM BW2258U89 inhibited NCI-H345 clonal growth significantly whereas 1 microM (Da) BW2258U89 did not. These data suggest that an amidated C-terminal is important for antagonism of SCLC GRP receptors by BW2258U89.

Presence of receptors for bombesin/gastrin-releasing peptide and mRNA for three receptor subtypes in human prostate cancers

BACKGROUND

Bombesin-like peptides can function as autocrine or paracrine growth factors and stimulate the growth of some cancer cells, including human prostate cancer. Three bombesin receptor subtypes, termed gastrin-releasing peptide receptor (GRPR), neuromedin B receptor (NMBR), and bombesin receptor subtype 3 (BRS-3), have been identified in rodents and humans.

METHODS

We investigated the presence and characteristics of the functional receptors for bombesin/GRP in human prostate adenocarcinoma specimens by radio-receptor assay and the mRNA expression of the three bombesin receptor subtypes by RT-PCR.

RESULTS

Of the 80 specimens of primary prostate cancer examined by receptor binding assays, 50 ( approximately 63%) showed high-affinity, low-capacity binding sites for bombesin/GRP, and 12 of these 50 receptor-positive specimens also showed a second binding site. Of the 22 prostate cancer specimens analyzed by RT-PCR, 20 (91%) expressed GRPR mRNA, 3 (14%) showed NMBR mRNA, and 2 ( approximately 9%) revealed BRS-3 mRNA. No correlation was observed between receptor expression and patients' age or pathological data.

CONCLUSIONS

The detection of a wide distribution of bombesin/GRP receptors in human prostate carcinomas supports the view that they may be involved in modulation of tumor progression and suggests that approaches based on binding of bombesin receptor antagonists or new targeted cytotoxic bombesin analogs to prostate cancers could be considered for the therapy.

[Arg6,D-Trp7,9,NmePhe8]-substance P (6-11) activates JNK and induces apoptosis in small cell lung cancer cells via an oxidant-dependent mechanism

[Arg6,D-Trp7,9,NmePhe8]-substance P (6-11) (antagonist G) is a novel class of anti-cancer agent that inhibits small-cell lung cancer (SCLC) cell growth in vitro and in vivo and is entering phase II clinical investigation for the treatment of SCLC. Although antagonist G blocks SCLC cell growth (IC50 = 24.5 +/- 1.5 and 38.5 +/- 1.5 microM for the H69 and H510 cell lines respectively), its exact mechanism of action is unclear. This study shows that antagonist G stimulates apoptosis as assessed by morphology (EC50 = 5.9 +/- 0.1 and 15.2 +/- 2.7 microM for the H69 and H510 cell lines respectively) and stimulates c-jun-N-terminal kinase (JNK) activity in SCLC cells (EC50 = 3.2 +/- 0.1 and 15.2 +/- 2.7 microM). This activity is neuropeptide-independent, but dependent on the generation of reactive oxygen species (ROS) and is inhibited by the free radical scavenger n-acetyl cysteine. Furthermore, antagonist G itself induces inflammation (59% increase in oedema volume compared to control) and potentiates (by 35-40%) bradykinin-induced oedema formation in vivo. In view of these results we show that, as well as acting as a 'broad-spectrum' neuropeptide antagonist, antagonist G stimulates basal G-protein activity in SCLC cell membranes (81 +/- 12% stimulation at 10 microM), thereby displaying a unique ability to stimulate certain signal transduction pathways by activating G-proteins. This novel activity may be instrumental for full anti-cancer activity in SCLC cells and may also account for antagonist G activity in non-neuropeptide-dependent cancers.

Bombesin activates MAP kinase in non-small cell lung cancer cells

The effects of bombesin (BB) on mitogen activated protein (MAP) kinase were investigated using non-small cell lung cancer (NSCLC) cells. By Western blot, both 42 and 44 kDalton forms of MAP kinase were present in NCI-H1299 and NCI-H838 cells. Addition of BB to NCI-H1299 cells resulted in phosphorylation of the MAP kinase substrate myelin basic protein (MBP). Phosphorylation of MBP was maximal 6 min after the addition of 10 nM BB to NCI-H1299 cells. Addition of gastrin releasing peptide (GRP) or GRP14-27 but not GRP1-16 to NCI-H 1299 cells caused MBP phosphorylation. The effects of BB were inhibited by BW2258U89, a BB receptor antagonist, and PD98059, a MAP kinase kinase inhibitor. Also, PD98059 inhibited the clonal growth of NCI-H1299 cells. These data suggest that MAP kinase may be an important regulatory enzyme in NSCLC.