Location and characterization of the human GRP receptor expressed by gastrointestinal epithelial cells

Gastric Corpus Mucosal Hyperplasia and Neuroendocrine Cell Hyperplasia, but not Spasmolytic Polypeptide-Expressing Metaplasia, Is Prevented by a Gastrin Receptor Antagonist in H+/K+ATPase Beta Subunit Knockout Mice

Proton pump inhibitor use is associated with an increased risk of gastric cancer, which may be mediated by hypergastrinemia. Spasmolytic polypeptide-expression metaplasia (SPEM) has been proposed as a precursor of gastric cancer. We have examined the effects of the gastrin receptor antagonist netazepide (NTZ) or vehicle on the gastric corpus mucosa of H⁺/K⁺ATPase beta subunit knockout (KO) and wild-type (WT) mice. The gastric corpus was evaluated by histopathology, immunohistochemistry (IHC), in situ hybridization (ISH) and whole-genome gene expression analysis, focusing on markers of SPEM and neuroendocrine (NE) cells. KO mice had pronounced hypertrophy, intra- and submucosal cysts and extensive expression of SPEM and NE cell markers in the gastric corpus, but not in the antrum. Numerous SPEM-related genes were upregulated in KO mice compared to WT mice. NTZ reduced hypertrophia, cysts, inflammation and NE hyperplasia. However, NTZ neither affected expression of SPEM markers nor of SPEM-related genes. In conclusion, NTZ prevented mucosal hypertrophy, cyst formation and NE cell hyperplasia but did not affect SPEM. The presence of SPEM seems unrelated to the changes caused by hypergastrinemia in this animal model.

Distribution of the pig gastrin-releasing peptide receptor and the effect of GRP on porcine Leydig cells

Gastrin-releasing peptide (GRP) is a mammalian bombesin (BN)-like peptide which plays a role in a number of important physiological functions via its receptor (gastrin-releasing peptide receptor, GRPR) in most animals. However, little is known about the gene encoding GRPR and its functions (especially reproduction) in pigs. In this study, we first cloned and analyzed the pig GRPR cDNA. Then we systematically investigated the expression levels of GRPR mRNA by relative real-time PCR (RT-PCR), and analyzed the distribution of the GRPR protein in pig tissues via immunohistochemistry (IHC). Finally, we studied the effect of GRP on testosterone secretion and GRPR (mRNA and protein) expression in Leydig cells. Results showed that the pig GRPR cDNA cloned at 1487bp, including one open reading frame (ORF) of 1155bp and encodes 384 amino acids. Significantly, compared with other species, the cDNA sequence and amino acid sequence of the pig GRPR were highly homologous and conservative. The RT-PCR results showed that: in the central nervous system (CNS) and the pituitary, GRPR mRNA was found in the cerebellum, hypophysis, spinal cord and hypothalamus; in the peripheral tissues, GRPR mRNA was mainly expressed in the pancreas, esophagus, ovary, testis, spleen, thymus, jejunum lymph node, muscle and fat. Moreover, the IHC results showed that GRPR immunoreactivity was widely distributed in the pig tissues and organs, such as the pancreas, esophagus, testis, ovary, spleen, pituitary gland and adrenal gland. In addition, we found that GRP promotes testosterone secretion, and increases GRPR mRNA and protein expression in cultured Leydig cells in vitro. These molecular and morphological data not only describe the anatomical locations of GRPR in pigs, but also provide the theoretical foundation for further research into its possible physiological functions in pigs. These results suggest that the GRP/GRPR system may play an important role in regulating the reproductive system of the boar.

Exploiting cancer's phenotypic guise against itself: targeting ectopically expressed peptide G-protein coupled receptors for lung cancer therapy

Lung cancer, claiming millions of lives annually, has the highest mortality rate worldwide. This advocates the development of novel cancer therapies that are highly toxic for cancer cells but negligibly toxic for healthy cells. One of the effective treatments is targeting overexpressed surface receptors of cancer cells with receptor-specific drugs. The receptors-in-focus in the current review are the G-protein coupled receptors (GPCRs), which are often overexpressed in various types of tumors. The peptide subfamily of GPCRs is the pivot of the current article owing to the high affinity and specificity to and of their cognate peptide ligands, and the proven efficacy of peptide-based therapeutics. The article summarizes various ectopically expressed peptide GPCRs in lung cancer, namely, Cholecystokinin-B/Gastrin receptor, the Bombesin receptor family, Bradykinin B1 and B2 receptors, Arginine vasopressin receptors 1a, 1b and 2, and the Somatostatin receptor type 2. The autocrine growth and pro-proliferative pathways they mediate, and the distinct tumor-inhibitory effects of somatostatin receptors are then discussed. The next section covers how these pathways may be influenced or 'corrected' through therapeutics (involving agonists and antagonists) targeting the overexpressed peptide GPCRs. The review proceeds on to Nano-scaled delivery platforms, which enclose chemotherapeutic agents and are decorated with peptide ligands on their external surface, as an effective means of targeting cancer cells. We conclude that targeting these overexpressed peptide GPCRs is potentially evolving as a highly promising form of lung cancer therapy.

Insights into bombesin receptors and ligands: Highlighting recent advances

This following article is written for Prof. Abba Kastin's Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin's Handbook of Biological Active Peptides [137,138,331].

177Lu-labeled RGD-BBN heterodimeric peptide for targeting prostate carcinoma

INTRODUCTION

Radiolabeled Arg-Gly-Asp (RGD) and bombesin (BBN) heterodimers have been investigated for dual targeting of tumor integrin αvβ3 receptors and gastrin-releasing peptide receptors. The goal of this study was to evaluate the potential use of a Lu-labeled RGD-BBN heterodimer for targeted prostate cancer therapy.

MATERIALS AND METHODS

A 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-conjugated RGD-BBN peptide (DO3A-RGD-BBN) was radiolabeled with Lu and purified by high-performance liquid chromatography. The in-vivo biodistribution study of Lu-DO3A-RGD-BBN was carried out in mice bearing human prostate cancer PC3 xenografts. The receptor-targeting specificity of the radiolabeled peptide was assayed by injecting the tracer with the unlabeled RGD-BBN peptide. Radiation absorbed doses in adult male patients, based on biodistribution data from mice, were also calculated.

RESULTS

DO3A-RGD-BBN peptides were successfully labeled with Lu, and high radiochemical purity (>95%) could be achieved after high-performance liquid chromatography purification. In human PC3 xenograft-bearing mice, the tumor accumulation of Lu-DO3A-RGD-BBN was 5.88±1.12, 2.77±0.30, 2.04±0.19, and 1.18±0.19%ID/g at 0.5, 2, 24, and 48 h, respectively. With rapid clearance from normal tissues, the radiolabeled probe displayed high tumor-to-blood and tumor-to-muscle ratios. On calculating the radiation absorbed doses for Lu-DO3A-RGD-BBN, we found that the prostate tumor and the pancreas were the organs receiving the highest radiation absorbed doses.

CONCLUSION

Dual integrin αvβ3 and GPRP-targeted agent Lu-DO3A-RGD-BBN shows excellent prostate cancer-targeting ability, and it is worthy of further evaluation for prostate cancer-targeted therapy.

Combination of gastrin-releasing peptide antagonist with cytotoxic agents produces synergistic inhibition of growth of human experimental colon cancers

We investigated the efficacy of a powerful antagonist of bombesin/gastrin-releasing peptide (BN/GRP) RC-3940-II administered as a single agent or in combination with cytotoxic agents on the growth of HT-29, HCT-116 and HCT-15 human colon cancer in vitro and in vivo. GRP-receptor mRNA and protein were found in all three cell lines tested. Exposure of HT-29 cells to 10 μM RC-3940-II led to an increase in the number of cells blocked in S phase and G 2/M and cells with lower G(0)/G(1) DNA content. Similar changes on the cell cycle traverse of HT-29 cells could also be seen at lower concentrations of RC-3940-II (1 μM) after pretreatment with 100 nM GRP (14-27), indicating a dose-dependent mechanism of action based on the blockage of BN/GRP induced proliferation of tumor cells at lower concentrations. Daily in vivo treatment with BN/GRP antagonist RC-3940-II decreased the volume of HT-29, HCT-116 and HCT-15 tumors xenografted into athymic nude mice by 25 to 67% (p < 0.005). Combined treatment with RC-3940-II and chemotherapeutic agents 5-FU and irinotecan resulted in a synergistic tumor growth suppression of HT-29, HCT-116 and HCT-15 xenografts by 43% to 78%. In HT-29 and HCT-116 xenografts the inhibition for the combinations of RC-3940-II and irinotecan vs. single substances (p < 0.05) was significantly greater. These findings support the use of RC-3940-II as an anticancer agent and may help to design clinical trials using RC-3940-II in combinations with cytotoxic agents.

In vitro binding evaluation of 177Lu-AMBA, a novel 177Lu-labeled GRP-R agonist for systemic radiotherapy in human tissues

Members of the gastrin-releasing peptide (GRP) family and its analogs bombesin (BBN) have been implicated in the biology of several human cancers including prostate, breast, colon and lung. To date, three mammalian GRP/BBN receptor subtypes have been cloned and characterized: the neuromedin B receptor (NMBR), the GRP receptor (GRPR) and the BBN-receptor subtype 3 (BB(3)). The fourth BBN receptor subtype, BB(4), has only been identified in amphibian and at present no mammalian equivalent of this receptor has been described. GRPR analogs have been used as carriers to deliver drugs, radionuclides and cytotoxins to target various cancer types that are GRPR positive. We investigated the in vitro binding properties of (177)Lu-AMBA, a novel radiolabelled BBN analog currently undergoing clinical trial as systemic radiotherapy for hormone refractory prostate cancer (HRPC) patients. Pharmacological analyses of the (177)Lu-AMBA was determined using in vitro binding studies using membrane target system containing specific receptor subtypes. We investigated the distribution of binding sites for (177)Lu-AMBA by receptor autoradiography on human neoplastic and non-neoplastic tissues. Pharmacological characterizations of (177)Lu-AMBA shows, high affinity towards NMB and GRP receptors, while little or no affinity towards BB(3) receptor. Among the 40 different types of non-neoplastic tissues tested seven of them showed limited but specific binding of (177)Lu-AMBA. Fourteen of 17 primary prostate cancers, six of 13 primary breast cancers expressed binding sites for (177)Lu-AMBA. Furthermore, no apparent differences in (177)Lu-AMBA-binding sites expression were observed between matched pairs (primary vs. secondary) of prostate and breast cancer tissues. These data represent the molecular basis for clinical applications of (177)Lu-AMBA for diagnosis and treatment of GRP-R and NMB-R positive tumors.

Requirement of the tissue-restricted homeodomain transcription factor Nkx6.3 in differentiation of gastrin-producing G cells in the stomach antrum

Many homeodomain transcription factors function in organogenesis and cell differentiation. The Nkx family illustrates these functions especially well, and the Nkx6 subfamily controls differentiation in the central nervous system and pancreas. Nkx6.3, a recent addition to this subfamily, overlaps Nkx6.1 and Nkx6.2 in expression in the hindbrain and stomach. Nkx6.3 transcripts localize in the epithelium of the most distal stomach region, the antrum and pylorus; expression in the adult intestine is lower and confined to the proximal duodenum. Nkx6.3(-)(/)(-) mice develop and grow normally, with a grossly intact stomach and duodenum. These mice show markedly reduced gastrin mRNA, many fewer gastrin-producing (G) cells in the stomach antrum, hypogastrinemia, and increased stomach luminal pH, with a corresponding increase in somatostatin mRNA levels and antral somatostatin-producing (D) cells. They express normal levels of other transcription factors required for gastric endocrine cell differentiation, Pdx1, Pax6, and Ngn3; conversely, Ngn3(-)(/)(-) mice, which also show reduced gastrin levels, express Nkx6.3 normally. These studies implicate Nkx6.3 as a selective regulator of G- and D-cell lineages, which are believed to derive from a common progenitor, and suggest that it operates in parallel with Ngn3.

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.

Novel 111In-labelled bombesin analogues for molecular imaging of prostate tumours

PURPOSE

It has been shown that some primary human tumours and their metastases, including prostate and breast tumours, overexpress gastrin-releasing peptide (GRP) receptors. Bombesin (BN) is a neuropeptide with a high affinity for these GRP receptors. We demonstrated successful scintigraphic visualisation of BN receptor-positive tumours in preclinical studies using the radiolabelled BN analogue [(111)In-DTPA-Pro(1),Tyr(4)]BN. However, the receptor affinity as well as the serum stability of this analogue leave room for improvement. Therefore new (111)In-labelled BN analogues were synthesised and evaluated in vitro and in vivo.

METHODS AND RESULTS

The receptor affinity of the new BN analogues was tested on human GRP receptor-expressing prostate tumour xenografts and rat colon sections. Analogues with high receptor affinity (low nM range) were selected for further evaluation. Incubation in vitro of GRP receptor-expressing rat CA20948 and human PC3 tumour cells with the (111)In-labelled analogues resulted in rapid receptor-mediated uptake and internalisation. The BN analogue with the best receptor affinity and in vitro internalisation characteristics, Cmp 3 ([(111)In-DTPA-ACMpip(5),Tha(6),betaAla(11),Tha(13),Nle(14)]BN(5-14)), was tested in vivo in biodistribution studies using rats bearing GRP receptor-expressing CA20948 tumours, and nude mice bearing human PC3 xenografts. Injection of (111)In-labelled Cmp 3 in these animals showed high, receptor-mediated uptake in receptor-positive organs and tumours which could be visualised using planar gamma camera and microSPECT/CT imaging.

CONCLUSION

With their enhanced receptor affinity and their rapid receptor-mediated internalisation in vitro and in vivo, the new BN analogues, and especially Cmp 3, are promising candidates for use in diagnostic molecular imaging and targeted radionuclide therapy of GRP receptor-expressing cancers.

Progastrin-releasing peptide and gastrin-releasing peptide receptor mRNA expression in non-tumor tissues of the human gastrointestinal tract

AIM: To investigate the expression of gastrin-releasing peptide (GRP) and GRP-receptor mRNA in non-tumor tissues of the human esophagus, gastrointestinal tract, pancreas and gallbladder using molecular biology techniques.

METHODS: Poly A⁺ mRNA was isolated from total RNA extracts using an automated nucleic acid extractor and, subsequently, converted into single-stranded cDNA (ss-cDNA). PCR amplifications were carried out using gene-specific GRP and GRP-receptor primers. The specificity of the PCR amplicons was further confirmed by Southern blot analyses using gene-specific GRP and GRP-receptor hybridization probes.

RESULTS: Expression of GRP and GRP-receptor mRNA was detected at various levels in nearly all segments of the non-tumor specimens analysed, except the gallbladder. In most of the biopsy specimens, co-expression of both GRP and GRP-receptor mRNA appeared to take place. However, expression of GRP mRNA was more prominent than was GRP-receptor mRNA.

CONCLUSION: GRP and GRP-receptor mRNAs are expressed throughout the gastrointestinal tract and provides information for the future mapping and determination of its physiological importance in normal and tumor cells.

Gastrin-releasing peptide and cancer

Over the past 20 years, abundant evidence has been collected to suggest that gastrin-releasing peptide (GRP) and its receptors play an important role in the development of a variety of cancers. In fact, the detection of GRP and the GRP receptor in small cell lung carcinoma (SCLC), and the demonstration that anti-GRP antibodies inhibited proliferation in SCLC cell lines, established GRP as the prototypical autocrine growth factor. All forms of GRP are generated by processing of a 125-amino acid prohormone; recent studies indicate that C-terminal amidation of GRP18-27 is not essential for bioactivity, and that peptides derived from residues 31 to 125 of the prohormone are present in normal tissue and in tumors. GRP receptors can be divided into four classes, all of which belong to the 7 transmembrane domain family and bind GRP and/or GRP analogues with affinities in the nM range. Over-expression of GRP and its receptors has been demonstrated at both the mRNA and protein level in many types of tumors including lung, prostate, breast, stomach, pancreas and colon. GRP has also been shown to act as a potent mitogen for cancer cells of diverse origin both in vitro and in animal models of carcinogenesis. Other actions of GRP relevant to carcinogenesis include effects on morphogenesis, angiogenesis, cell migration and cell adhesion. Future prospects for the use of radiolabelled and cytotoxic GRP analogues and antagonists for cancer diagnosis and therapy appear promising.

Bombesin and neurotensin reduce endotoxemia, intestinal oxidative stress, and apoptosis in experimental obstructive jaundice

OBJECTIVE

To evaluate the effect of bombesin (BBS) and neurotensin (NT) on intestinal histopathology, intestinal oxidative stress, and endotoxemia in experimental obstructive jaundice.

SUMMARY BACKGROUND DATA

Obstructive jaundice compromises gut barrier function, resulting in endotoxemia. BBS and NT, exerting various biologic actions on gastrointestinal tissues, preserve gut mucosal integrity in cases of injury or atrophy.

METHODS

Seventy male Wistar rats were randomly divided into 5 groups: I = controls, II = sham operated, III = bile duct ligation (BDL), IV = BDL + BBS (30 microg/kg/d), V = BDL + NT (300 microg/kg/d). By the end of the experiment, on day 10, endotoxin was measured in portal and aortic blood. Tissue sections of the terminal ileum were examined histologically, and villus density, mucosal thickness, mitotic activity and apoptosis in crypts were assessed. In addition, ileal mucosa was analyzed for DNA and protein content. To estimate intestinal oxidant/antioxidant equilibrium, lipid peroxidation, protein oxidation, and thiol redox state (reduced glutathione [GSH], oxidized glutathione [GSSG], total nonprotein mixed disulfides [NPSSR], protein thiols [PSH], and protein disulfides [PSSP]) were determined on tissue homogenates from the terminal ileum.

RESULTS

BBS or NT administration significantly reduced portal and systemic endotoxemia observed in obstructive jaundice. Both factors reversed obstructive jaundice-induced morphologic features of intestinal atrophy, increasing villus density and mucosal thickness. This effect was accompanied by induction of mitoses and reduction of apoptosis in intestinal crypts. Mucosal DNA and protein content were reduced, although not to significant levels, in BDL animals and restored to control levels after BBS or NT treatment. Moreover, BBS or NT administration protected the intestine in jaundiced rats against oxidative stress, as demonstrated by reduction of intestinal lipid peroxidation, increase of the antioxidant GSH, and decrease of the oxidized forms GSSG and NPSSR, while BBS additionally reduced protein oxidation as well.

CONCLUSIONS

Administration of BBS or NT in bile duct-ligated rats exerts beneficial effects on intestinal oxidative stress, cell proliferation, apoptosis, and endotoxemia. This observation might be of potential value in patients with extrahepatic cholestasis.

Gastrin releasing peptide receptor expression is decreased in patients with Crohn's disease but not in ulcerative colitis

BACKGROUND

Gastrin releasing peptide (GRP) and neuromedin B are bombesin (BN)-like peptides involved in regulating motility and inflammation in the gastrointestinal tract, which may be useful in treating inflammatory bowel disease (IBD). Three bombesin-like peptide receptors have been reported, but no studies have investigated their localisation in normal and inflamed human intestine.

AIM

To localise and characterise BN receptors in normal intestine and to see whether this is modified in IBD.

METHODS

Full thickness intestinal tissue samples were collected from 13 patients with Crohn's disease (CD), 11 with ulcerative colitis (UC), and 19 controls. BN receptor expression was characterised and quantified with storage phosphor autoradiography using BN, GRP, neuromedin B, and the synthetic analogue BN(6-14) as ligands.

RESULTS

Only BN receptor type 2 (high affinity for GRP) was present in intestinal tissue. Minimal BN binding was detected in the mucosa. In normal colonic smooth muscle, mean BN binding was 336 fmol/g tissue in longitudinal muscle, including the myenteric plexus, and 71 fmol/g in circular muscle. In CD, colonic smooth muscle BN binding was significantly decreased (longitudinal muscle, 106; circular muscle, 19 fmol/g), in contrast to UC (377 and 62 fmol/g, respectively). In CD, a small (not significant) decrease was seen in ileal muscle compared with controls (111 v 169 and 18 v 32 fmol/g tissue for longitudinal and circular muscle, respectively).

CONCLUSIONS

Only the GRP receptor is expressed in human intestine; expression is highest in longitudinal muscle and myenteric plexus of the colon. Expression is decreased in inflamed and non-inflamed colon of CD, but not in UC.

Developmental expression and biological activity of gastrin-releasing peptide and its receptors in the kidney

Mammalian gastrin-releasing peptide (GRP) has a widespread distribution and multiple stimulating effects on metabolism, release of regulatory peptides, gastrointestinal and pancreatic secretions, and behavior. GRP is a potent mitogen for a number of tumor types, including colon and lung. Although GRP is known to stimulate the growth of renal tumors, little is known of its synthesis, distribution, and receptors in the developing and mature kidney. Both Northern blot analysis and RT-PCR revealed the presence of GRP mRNA in ovine kidney from midgestation through to adulthood. GRP mRNA was detected in rat kidney from embryonic day 19 to postnatal day 30 by RT-PCR. Sequence-specific radioimmunoassay demonstrated the presence of substantial amounts of fully processed amidated GRP in the ovine renal cortex and medulla. The mRNA for the major receptor subtype, GRP-R, was present in fetal and adult sheep and rat kidneys. The mRNA for the low-affinity GRP receptor, bombesin receptor subtype-3 (BRS-3), was only detected in the rat kidney. In the ovine kidney, immunohistochemistry localized GRP predominantly to the thick ascending limb of the loop of Henle. mRNAs for GRP, GRP-R, and BRS-3 were detected in the human embryonic kidney cell line HEK293, and radioimmunoassay of cell extracts and conditioned media revealed the presence of proGRP but not the amidated form. However, amidated GRP did stimulate the proliferation of these cells. These studies demonstrate that the developing and mature kidney may be previously unidentified sites of autocrine or paracrine action for GRP.

Gastrin releasing peptide and gastrin releasing peptide receptor expression in gastrointestinal carcinoid tumours

AIMS

To establish whether gastrin releasing peptide (GRP) and the GRP receptor (GRPR) are expressed together in gastrointestinal carcinoid tumours.

METHODS

Twenty six carcinoid tumours from the stomach, small intestine, appendix, and colorectum were investigated by immunohistochemistry for GRP and GRPR.

RESULTS

GRP was detected in nine of 19 tumours and GRPR in 22 of 26. Coexpression of both the ligand and receptor was seen in six of 19 cases. GRPR but not GRP was more strongly expressed in appendix and colonic tumours.

CONCLUSIONS

GRP and GRPR are produced by a large number of gastrointestinal carcinoid tumours. An autocrine/paracrine pathway may exist for GRP stimulated cell proliferation in some of these neoplasms, analogous to that seen in small cell anaplastic carcinoma of the lung.

Over-expression of gastrin-releasing peptide in human esophageal squamous cell carcinomas

Gastrin-releasing peptide (GRP) is known as an autocrine growth factor for a number of gastrointestinal cancers. There is, however, little information on the expression of GRP in the squamous epithelia and squamous cell carcinoma, particularly in the esophagus. With a differential display approach, up-regulated GRP was observed in human esophageal squamous cell carcinoma (ESCC) samples obtained from a high-risk area for esophageal cancer, Linzhou in northern China. Up-regulation of phosphoglycerate mutase and P311 HUM (3.1) and down-regulation of keratin 13, cystatin B, endoglin and annexin I were observed. Using a reverse transcription-polymerase chain reaction (RT-PCR) method, significant over-expression of GRP was observed in 10 out of 12 ESCC samples (83.3%) and all four ESCC cell lines. With in situ hybridization, GRP mRNA expression was detected in nine out of 21 (42.8%) samples with basal cell hyperplasia (BCH), five out of seven (71.4%) samples with dysplasia (DYS) and 17 out of 24 (70.9%) ESCC samples. In contrast, GRP was expressed only in three out of 16 (18.7%) normal epithelium. Digital image analysis revealed that the mean value of GRP expression index, determined by intensity and area ratio of staining, was 0.19 in normal epithelium, 1.23 in BCH, 2.94 in DYS and 2.38 in ESCC, showing a progressive increase. Studies on ESCC cell lines showed GRP increased cell growth in a dose-dependent pattern in GRP receptor-positive ESCC cells, but not in GRP receptor-negative ESCC cells. GRP (1 mM) also increased cyclooxygenase-2 protein expression by 3.4-fold. This is the first demonstration that GRP is over-expressed in ESCC, and its over-expression may play a role in ESCC development and growth.

Trypsin IV, a novel agonist of protease-activated receptors 2 and 4

Certain serine proteases signal to cells by cleaving protease-activated receptors (PARs) and thereby regulate hemostasis, inflammation, pain and healing. However, in many tissues the proteases that activate PARs are unknown. Although pancreatic trypsin may be a physiological agonist of PAR(2) and PAR(4) in the small intestine and pancreas, these receptors are expressed by cells not normally exposed pancreatic trypsin. We investigated whether extrapancreatic forms of trypsin are PAR agonists. Epithelial cells lines from prostate, colon, and airway and human colonic mucosa expressed mRNA encoding PAR(2), trypsinogen IV, and enteropeptidase, which activates the zymogen. Immunoreactive trypsinogen IV was detected in vesicles in these cells. Trypsinogen IV was cloned from PC-3 cells and expressed in CHO cells, where it was also localized to cytoplasmic vesicles. We expressed trypsinogen IV with an N-terminal Igkappa signal peptide to direct constitutive secretion and allow enzymatic characterization. Treatment of conditioned medium with enteropeptidase reduced the apparent molecular mass of trypsinogen IV from 36 to 30 kDa and generated enzymatic activity, consistent with formation of trypsin IV. In contrast to pancreatic trypsin, trypsin IV was completely resistant to inhibition by polypeptide inhibitors. Exposure of cell lines expressing PAR(2) and PAR(4) to trypsin IV increased [Ca(2+)](i) and strongly desensitized cells to PAR agonists, whereas there were no responses in cells lacking these receptors. Thus, trypsin IV is a potential agonist of PAR(2) and PAR(4) in epithelial tissues where its resistance to endogenous trypsin inhibitors may permit prolonged signaling.

Peptide receptors as molecular targets for cancer diagnosis and therapy

During the past decade, proof of the principle that peptide receptors can be used successfully for in vivo targeting of human cancers has been provided. The molecular basis for targeting rests on the in vitro observation that peptide receptors can be expressed in large quantities in certain tumors. The clinical impact is at the diagnostic level: in vivo receptor scintigraphy uses radiolabeled peptides for the localization of tumors and their metastases. It is also at the therapeutic level: peptide receptor radiotherapy of tumors emerges as a serious treatment option. Peptides linked to cytotoxic agents are also considered for therapeutic applications. The use of nonradiolabeled, noncytotoxic peptide analogs for long-term antiproliferative treatment of tumors appears promising for only a few tumor types, whereas the symptomatic treatment of neuroendocrine tumors by somatostatin analogs is clearly successful. The present review summarizes and critically evaluates the in vitro data on peptide and peptide receptor expression in human cancers. These data are considered to be the molecular basis for peptide receptor targeting of tumors. The paradigmatic peptide somatostatin and its receptors are extensively reviewed in the light of in vivo targeting of neuroendocrine tumors. The role of the more recently described targeting peptides vasoactive intestinal peptide, gastrin-releasing peptide, and cholecystokinin/gastrin is discussed. Other emerging and promising peptides and their respective receptors, including neurotensin, substance P, and neuropeptide Y, are introduced. This information relates to established and potential clinical applications in oncology.

Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV

Dipeptidyl-peptidase IV/CD26 (DPP IV) is a cell-surface protease belonging to the prolyloligopeptidase family. It selectively removes the N-terminal dipeptide from peptides with proline or alanine in the second position. Apart from its catalytic activity, it interacts with several proteins, for instance, adenosine deaminase, the HIV gp120 protein, fibronectin, collagen, the chemokine receptor CXCR4, and the tyrosine phosphatase CD45. DPP IV is expressed on a specific set of T lymphocytes, where it is up-regulated after activation. It is also expressed in a variety of tissues, primarily on endothelial and epithelial cells. A soluble form is present in plasma and other body fluids. DPP IV has been proposed as a diagnostic or prognostic marker for various tumors, hematological malignancies, immunological, inflammatory, psychoneuroendocrine disorders, and viral infections. DPP IV truncates many bioactive peptides of medical importance. It plays a role in glucose homeostasis through proteolytic inactivation of the incretins. DPP IV inhibitors improve glucose tolerance and pancreatic islet cell function in animal models of type 2 diabetes and in diabetic patients. The role of DPP IV/ CD26 within the immune system is a combination of its exopeptidase activity and its interactions with different molecules. This enables DPP IV/CD26 to serve as a co-stimulatory molecule to influence T cell activity and to modulate chemotaxis. DPP IV is also implicated in HIV-1 entry, malignant transformation, and tumor invasion.

Increased frequency of gastrin-releasing peptide receptor gene mutations during colon-adenocarcinoma progression

Epithelial cells lining the mature human colon do not normally express receptors for gastrin-releasing peptide (GRPR). In contrast, we have shown that when aberrantly expressed in functional form in colon cancer, this protein acted as a morphogen where it caused tumor cells to adopt a better-differentiated phenotype. Importantly, GRPR mRNA is ubiquitously mutated in human colon cancer cell lines, with inactivating mutations detected in all cell lines not expressing functional receptor. Since colon cancers are heterogeneously differentiated, we set out to determine if the GRPR gene was mutated as a function of tumor cell differentiation in archived human colon cancers. We used laser capture microscopy to dissect out 67 regions of defined differentiation from 20 human colon cancers randomly selected from the UIC GI Tumor Bank. Except for two polymorphisms, the GRPR gene was not mutated in nonmalignant epithelial cells. In contrast, 42 distinct mutations were identified in malignant cells. Overall mutation number inversely correlated with the degree of tumor cell differentiation. Within any cancer, all GRPR mutations found within better-differentiated cells were conserved in more poorly-differentiated cells; while all poorly-differentiated cells contained mutations resulting in GRPR pharmacological inactivation. These data suggest that accumulation of mutations within the GRPR gene ultimately resulting in the production of nonfunctional receptors may represent a previously unappreciated mechanism allowing for the dedifferentiation of tumor cells within any particular colon cancer; and that poorly-differentiated tumor cells within any individual cancer may arise clonally from their better-differentiated precursors.

Contribution of gastrin-releasing peptide and its receptor to villus development in the murine and human gastrointestinal tract

Recent studies have shown that aberrantly expressed gastrin-releasing peptide (GRP) and its receptor (GRP-R) critically regulate tumor cell differentiation in colon cancers developing in humans and mice. This finding suggested that the ability of GRP/GRP-R to promote a well-differentiated phenotype in colon cancer might reflect a re-capitulation of a normal role in regulating intestinal organogenesis. To determine if this was the case, we compared and contrasted intestinal development in GRPR-/- mice with their wild type littermates. GRP/GRP-R co-expression in wild type mice was only observed in villous enterocytes between N-1 and N-12. During this time frame villous growth was completely attenuated in GRPR-/- mice. The contribution of GRP/GRP-R to villous growth was due to their act in increasing enterocyte proliferation prior to N-8 but increasing enterocyte size thereafter. From N-12 onwards, small intestinal villous growth in GRPR-/- mice resumed such that no difference in this structure could be detected at adulthood between mice of either genotype. We next studied GRP/GRP-R expression in human abortuses. These proteins were co-expressed by villous enterocytes only between weeks 14 and 20 post-conception, a time frame analogous to when they are expressed in the murine intestine. Thus, this study shows for the first time that GRP/GRP-R play a transient and non-critical role in intestinal development, yet provides a rationale for their re-appearance in colon cancer.

The case for gastrin-releasing peptide acting as a morphogen when it and its receptor are aberrantly expressed in cancer

Gastrin-releasing peptide (GRP) and its receptor (GRP-R) are frequently expressed by cancers of the gastrointestinal tract, breast, lung, and prostate. Most studies have found that GRP and its amphibian homologue bombesin act to increase tumor cell proliferation, leading to the hypothesis that this peptide hormone is a mitogen important for the growth of various cancers. Yet GRP/GRP-R co-expression in cancer promotes the development of a well-differentiated phenotype; while multiple studies suggest that the presence of these 2 proteins confer a survival advantage. Along with recent reports showing that GRP and its receptor critically regulate aspects of colon and lung organogenesis, we argue that these proteins do not function primarily as mitogens when aberrantly expressed in cancer. Rather, we postulate that GRP/GRP-R are onco-fetal antigens that function as morphogens, with their effect on tumor cell proliferation being a component property of their ability to regulate differentiation. Thus aberrant GRP/GRP-R expression in cancer recapitulates, albeit in a dysfunctional manner, their normal role in development.

Is there a role for agonist gastrin-releasing peptide receptor radioligands in tumour imaging?

Gastrin-releasing peptide (GRP) has been shown to be a tumour growth stimulating agent for a number of normal and human cancer cell lines. The tumour growth effect is a direct result of GRP binding to membrane G-protein coupled GRP receptors (GRP-R) on the cell surface. Available data on the role of GRP and GRP-R in human lung, prostate, breast, colorectal and gastric carcinoma are reviewed and it is suggested that radiolabelled agonists are preferable to antagonists for imaging and therapy as they appear to be internalised, yielding a higher target/background ratio. The use of rhenium or indium radiolabels for therapy may provide a new approach to GRP/bombesin expressing tumours.

Characterization of gastrin-releasing peptide and its receptor aberrantly expressed by human colon cancer cell lines

Gastrin-releasing peptide (GRP) is a mitogen and morphogen important in the development of human colon cancers. Although epithelial cells lining the colon do not normally express GRP or its receptor (GRP-R), most human tumors express GRP-R mRNA. Yet functional protein has only been detected in 24 to 40% of colon cancers. To elucidate the reason for the difference between the expression of GRP/GRP-R mRNA and protein, we studied nine human colon cancer cell lines. Quantitative polymerase chain reaction revealed that all colon cancer cell lines expressed similar amounts of mRNA for both GRP as well as GRP-R. Yet binding studies using (125)I-Tyr(4)-bombesin detected functional receptors on only five of the nine cell lines studied. Conformational fragment-length polymorphism analysis indicated that although mRNA for the ligand GRP was never mutated, mRNA for the GRP-R was always mutated. Sequencing revealed that the message for GRP-R contained between two and seven separate mutations at the nucleotide level. This resulted in 14 separate coding mutations, 2 of which were observed in more than one cell line. Each mutation was individually recreated by site-directed mutagenesis and studied in transiently transfected Chinese hamster ovary-K1 cells. Alteration of Pro(145) into a tyrosine, of Val(317) into a glutamic acid, and insertion of a 32-nucleotide segment resulting in a frameshift distal to Asp(137) all resulted in GRP receptors incapable of binding ligand. Thus, these data indicate that human colon cancers commonly express GRP and GRP-R mRNA but that receptor mutations account for the failure of functional protein to be generated.

Signaling mechanisms regulating bombesin-mediated AP-1 gene induction in the human gastric cancer SIIA

The hormone bombesin (BBS) and its mammalian equivalent gastrin-releasing peptide (GRP) act through specific GRP receptors (GRP-R) to affect multiple cellular functions in the gastrointestinal tract; the intracellular signaling pathways leading to these effects are not clearly defined. Previously, we demonstrated that the human gastric cancer SIIA possesses GRP-R and that BBS stimulates activator protein-1 (AP-1) gene expression. The purpose of our present study was to determine the signaling pathways leading to AP-1 induction in SIIA cells. A rapid induction of c-jun and jun-B gene expression was noted after BBS treatment; this effect was blocked by specific GRP-R antagonists, indicating that BBS is acting through the GRP-R. The signaling pathways leading to increased AP-1 gene expression were delineated using phorbol 12-myristate 13-acetate (PMA), which stimulates protein kinase C (PKC)-dependent pathways, by forskolin (FSK), which stimulates protein kinase A (PKA)-dependent pathways, and by the use of various protein kinase inhibitors. Treatment with PMA stimulated AP-1 gene expression and DNA binding activity similar to the effects noted with BBS; FSK stimulated jun-B expression but produced only minimal increases of c-jun mRNA and AP-1 binding activity. Pretreatment of SIIA cells with either H-7 or H-8 (primarily PKC inhibitors) inhibited the induction of c-jun and jun-B mRNAs in response to BBS, whereas H-89 (PKA inhibitor) exhibited only minimal effects. Pretreatment with tyrphostin-25, a protein tyrosine kinase (PTK) inhibitor, attenuated the BBS-mediated induction of c-jun and jun-B, but the effect was not as pronounced as with H-7. Collectively, our results demonstrate that BBS acts through its receptor to produce a rapid induction of both c-jun and jun-B mRNA and AP-1 DNA binding activity in the SIIA human gastric cancer. Moreover, this induction of AP-1, in response to BBS, is mediated through both PKC- and PTK-dependent signal transduction pathways with only minimal involvement of PKA.

Quantitative immunohistochemistry by measuring cumulative signal strength using commercially available software photoshop and matlab

Currently available techniques for performing quantitative immunohistochemistry (Q-IHC) rely upon pixel-counting algorithms and therefore cannot provide information as to the absolute amount of chromogen present. We describe a novel algorithm for true Q-IHC based on calculating the cumulative signal strength, or energy, of the digital file representing any portion of an image. This algorithm involves subtracting the energy of the digital file encoding the control image (i.e., not exposed to antibody) from that of the experimental image (i.e., antibody-treated). In this manner, the absolute amount of antibody-specific chromogen per pixel can be determined for any cellular region or structure. (J Histochem Cytochem 48:303-311, 2000)

Bombesin family receptor and ligand gene expression in human colorectal cancer and normal mucosa

Bombesin-like peptides and their receptors are widely distributed throughout the gut and are potential mitogens for a number of gastrointestinal (GI) cancers. We have analysed the expression of bombesin-like peptides and their receptor subtypes in normal and neoplastic colorectal tissue. Expression was analysed by reverse transcription polymerase chain reaction (RT-PCR) using receptor and ligand subtype-specific primers and then expression localized by in situ hybridization (ISH) with riboprobes synthesized by in vitro transcription of cloned PCR product. Colorectal cancer tissue and matched normal mucosa from 23 patients were studied. Two of these patients had synchronous adenomatous polyps and two had synchronous hepatic metastases which were also studied. An additional two patients with adenomatous polyps were studied along with matched normal mucosa. Gastrin releasing peptide (GRP) receptor and ligand expression was present in all samples but with overall greater expression in the tumour samples. Neuromedin B (NMB) receptor expression was not detectable. NMB ligand was detected in all but one mucosal sample with overall overexpression in the tumour samples. Bombesin receptor subtype 3 (BRS-3) receptor expression was not detectable. These data support the possibility that GRP may be an autocrine growth factor in colorectal cancer.

Aberrant expression of gastrin-releasing peptide and its receptor by well-differentiated colon cancers in humans

Epithelial cells lining the adult human colon do not normally express gastrin-releasing peptide (GRP) or its receptor (GRPR). In contrast, approximately one-third of human colon cancers and cancer cell lines have been shown to express GRP-binding sites. Because GRPR activation causes the proliferation of many cancer cell lines, GRP has been presumed to act as a clinically significant growth factor. Yet GRP has not been shown to be expressed by colon cancers in humans nor has the effect of GRP and/or GRPR coexpression on tumor behavior been investigated. We therefore determined GRP and GRPR expression by immunohistochemistry in 50 randomly selected colon cancers resected between 1980 and 1997, all 37 associated lymph node and liver metastases, and 20 polyps. Tumor sections studied were those that contained the margin and adjacent nonmalignant epithelium. Overall, 84% of cancers aberrantly expressed GRP or GRPR, with 62% expressing both ligand and receptor, whereas expression was not observed in adjacent normal epithelium. Consistent with the previously established mitogenic capabilities of GRP, tissues coexpressing GRP and GRPR were more likely to express proliferating cell nuclear antigen than tissues not expressing both ligand and receptor. Yet GRP/GRPR coexpression was seen with equal frequency in stage A as in stage D cancers and was only detected in 1 in 37 metastases. Furthermore, Kaplan-Meier analysis did not reveal any difference in patient survival between those whose tumors did or did not express GRP/GRPR. In contrast, GRP/GRPR coexpression was found in all well-differentiated tumor regions, whereas poorly differentiated tissues never coexpressed GRP/GRPR. Overall, these data indicate that, although GRP is a mitogen, it is not a clinically significant growth factor in human colon cancers. Rather, the strong association of GRP/GRPR coexpression with tumor differentiation raises the possibility that these proteins primarily act in vivo as morphogens.

Characterization of gastrin-releasing peptide receptors aberrantly expressed by non-antral gastric adenocarcinomas

Epithelial cells lining the GI tract except in the gastric antrum do not normally express gastrin-releasing peptide receptors (GRP-R). Because GRP-R activation causes the proliferation of many GI cancer cell lines, aberrant expression has been presumed to negatively influence patient survival. We therefore determined the incidence and quality of GRP-R aberrantly expressed by non-antral gastric adenocarcinomas, and evaluated the impact of receptor expression on patient survival. We studied RNA isolated from 20 consecutive non-antral gastric adenocarcinomas, and determined that 8 (40%) aberrantly expressed GRP-R. Of these, 6 (75%) were found to be mutated. Pharmacologically, the effect of these mutations ranged from rendering the GRP-R non-functional to constitutively active. Contrary to expectations, however, survival of patients whose tumor expressed functional GRP-R (18.5 +/- 9.8 months) was not statistically different from those that did not (8.3 +/- 1.8 months; p = 0.24). Thus our data indicate that mutated isoforms of GRP-R are commonly expressed by non-antral gastric adenocarcinomas. However, expression of functional GRP-R does not alter patient survival, suggesting that this receptor may not be clinically important to the growth of gastric cancers.

Galanin causes Cl- secretion in the human colon. Potential significance of inflammation-associated NF-kappa B activation on galanin-1 receptor expression and function

Galanin is widely distributed in enteric nerves and nerve terminals throughout the gastrointestinal (GI) tract. Within the GI tract galanin is best known for its ability to alter smooth muscle contractility and regulate intestinal motility. However, recent studies also indicate that galanin can modulate epithelial ion transport. We previously showed that epithelial cells lining the human GI tract, including those of colonic origin, express Gal1 galanin receptors (Gal1-R). We herein demonstrate that epithelial cells lining the human colon only express Gal1-R receptors and do not express other galanin receptor subtypes. We previously showed that Gal1-R expression was transcriptionally regulated by the transcription factor NF-kappa B. Consistent with this transcription factor being activated in a number of inflammatory conditions, we show increased colonic Gal1-R expression in patients with colitis due to a variety of causes. To further evaluate the physiology of Gal1-R activation, we studied this receptor expressed by the human colon epithelial cell line T84. Gal1-R activation resulted in a dose-dependent increase in Cl- secretion; whereas infection of T84 cells with pathogens known to activate NF-kappa B augmented Gal1-R expression and Cl- secretion. Thus, galanin acts as a secretagogue in epithelial cells lining the human colon, with alterations in Gal1-R expression possibly playing an important role in the diarrhea associated with various inflammatory processes affecting the GI tract.

Constitutive activation of the gastrin-releasing peptide receptor expressed by the nonmalignant human colon epithelial cell line NCM460

Gastrin-releasing peptide (GRP) causes multiple effects in humans by activating a specific heptaspanning receptor. Within the gastrointestinal tract, GRP receptors (GRP-R) are not normally expressed by mucosal epithelial cells except for those lining the gastric antrum. In contrast, recent studies have shown that up to 40% of resected colon cancers aberrantly express this receptor. This is important because the GRP-R can cause the proliferation of many, but not all, tissues in which it is expressed. Since GRP and other agonists are not known to exist in the colonic lumen, it has not been clear how or even if GRP-R expression in colon cancer contributes to cell proliferation. To evaluate the functional consequence of GRP-R expression on colonic epithelium, we transfected the recently isolated nonmalignant human colon epithelial cell line NCM460 with the cDNA for this receptor. All NCM460 cell lines expressing varying numbers of GRP-R bound selected agonists and antagonists indistinguishably from receptors expressed by other human tissues. Furthermore GRP-R-expressing transfected cell lines, but not wild-type NCM460 cells, proliferated independently of serum or other growth factors. Further evaluation revealed that GRP-R in these cells tonically stimulated G alpha q/11, resulting in increased phospholipase C activation. Since transfected cells do not secrete GRP, nor is their growth influenced by exposure to receptor-specific antagonists, these data indicate that GRP-R ectopically expressed by NCM460 cells are constitutively active. This report provides the first evidence of mutation-independent heptaspanning receptor constitutive activation resulting in cell proliferation, and identifies a potential mechanism whereby the GRP-R may act as an oncogene in human colon cancer.