Inhibition of growth of PC-82 human prostate cancer line xenografts in nude mice by bombesin antagonist RC-3095 or combination of agonist [D-Trp6]-luteinizing hormone-releasing hormone and somatostatin analog RC-160

Tumor targeting with 99m Tc radiolabeled peptides: Clinical application and recent development

Targeting overexpressed receptors on the cancer cells with radiolabeled peptides has become very important in nuclear oncology in the recent years. Peptides are small and have easy preparation and easy radiolabeling protocol with no side-effect and toxicity. These properties made them a valuable tool for tumor targeting. Based on the successful imaging of neuroendocrine tumors with ¹¹¹ In-octreotide, other receptor-targeting peptides such as bombesin (BBN), cholecystokinin/gastrin analogues, neurotensin analogues, glucagon-like peptide-1, and RGD peptides are currently under development or undergoing clinical trials. The most frequently used radionuclides for tumor imaging are ^99m Tc and ¹¹¹ In for single-photon emission computed tomography and ⁶⁸ Ga and ¹⁸ F for positron emission tomography imaging. This review presents some of the ^99m Tc-labeled peptides, with regard to their potential for radionuclide imaging of tumors in clinical and preclinical application.

From Bench to Bed: New Gastrin-Releasing Peptide Receptor-Directed Radioligands and Their Use in Prostate Cancer

Gastrin-releasing peptide receptors (GRPRs) are overexpressed in prostate and breast cancer, and are therefore attractive molecular targets for diagnosis and therapy with radiolabeled GRPR-directed peptide probes. The amphibian tetradecapeptide bombesin or the mammalian gastrin-releasing peptide and neuromedin C have been modified with a variety of chelators. As a result, labeling with radiometals attractive for SPECT or PET imaging and for radionuclide therapy has led to the development of peptide radioligands suitable for in vivo targeting of prostate cancer. A shift of paradigm from internalizing GRPR-agonists to antagonists has occurred owing to the higher biosafety and superior pharmacokinetics of radioantagonists.

Expression and function of gastrin-releasing peptide (GRP) in normal and cancerous urological tissues

Gastrin-releasing peptide (GRP) acts as an important regulatory peptide in several normal physiological processes and as a growth factor in certain cancers. In this review we provide a comprehensive overview of the current state of knowledge of GRP in urological tissues under both normal and cancerous conditions. GRP and its receptor, GRP-R, are expressed in the normal kidney and renal cancers. GRP can stimulate the growth of renal cancer cells. GRP and GRP-R are expressed in prostate cancer and GRP can stimulate the growth of prostate cancer cell lines. Importantly, GRP is a key neuroendocrine peptide, which may be involved in the progression of advanced prostate cancer and in the neuroendocrine differentiation of prostate cancer. Recent animal studies have shown that GRP and GRP-R are an integral part of male sexual function and play a crucial role in spinal control of erections and ejaculation.

A standardised study to compare prostate cancer targeting efficacy of five radiolabelled bombesin analogues

Purpose

Prostate-specific antigen (PSA)-based screening for prostate cancer (PC) has dramatically increased early diagnosis. Current imaging techniques are not optimal to stage early PC adequately. A promising alternative to PC imaging is peptide-based scintigraphy using radiolabelled bombesin (BN) analogues that bind to gastrin-releasing peptide receptors (GRPR) being overexpressed in PC. When labelled to appropriate radionuclides BN targeting of GRPRs may also provide applications for peptide radionuclide receptor therapy (PRRT). Assessment studies under identical experimental conditions allowing a reliable comparison of the potential of such analogues are lacking. This study was performed to evaluate and directly compare five promising radiolabelled BN analogues for their targeting efficacy for PC under standardised conditions.

Methods

The BN agonists [¹¹¹In]DOTA-PESIN, [¹¹¹In]AMBA, [¹¹¹In]MP2346 and [¹¹¹In]MP2653 and one antagonist [^99mTc]Demobesin-1 were evaluated in GRPR-overexpressing human PC-3 tumour-bearing mice to determine peptide stability in vivo, biodistribution and GRPR targeting potential by animal SPECT/CT imaging and ex vivo autoradiography.

Results

HPLC analysis of blood showed intact Demobesin-1 at 5 and 15 min after injection (64.1 ± 1.6% and 41.0 ± 01%, respectively) being much less for the other compounds. AMBA, the second most stable analogue, showed 36.1 ± 2.7% and 9.8 ± 1.1% intact peptide after 5 and 15 min. PC-3 tumour uptake at 1 h was comparable for Demobesin-1, AMBA, PESIN and MP2346 (3.0 ± 0.4, 2.7 ± 0.5, 2.3 ± 0.5 and 2.1 ± 0.9%ID/g, respectively), but very low for MP2653 (0.9 ± 0.2%ID/g). In addition, MP2346 showed undesirably high uptake in the kidneys (7.9 ± 1.9%ID/g) being significantly less for the other analogues. AMBA, MP2346 and PESIN revealed favourable increases in tumour to blood ratios over time while changes in tumour to kidney and pancreas ratios for Demobesin-1 from 1 to 24 h after injection were significantly better than for the other analogues. All analogues visualised PC-3 tumours by SPECT/CT and autoradiography.

Conclusion

In the present study the BN antagonist Demobesin-1 was the best performing analogue showing superior in vivo stability, highest tumour uptake and retention while pancreatic and renal clearance were rapid. PESIN and AMBA were the best GRP agonists with sufficient in vivo stabilities as well as high tumour uptake and retention. Based on these results all three analogues deserve further evaluation for clinical use in PC patients.

Action, localization and structure-function relationship of growth factors and their receptors in the prostate

Whereas the direct action of sex steroids, namely of androgens, on prostate cell division was questioned as early as in the 1970s, and remains so, the interest in prostatic growth factors (GFs) is rather recent but has expanded tremendously in the last five years. This lag period can be partly explained by the fact that, at the time, androgen receptors had just been discovered, and newly developed hormonal regimens or strategies to treat patients with prostate carcinoma (PCa) or epithelioma had generated great enthusiasm and hopes in the medical and scientific community. Another point to consider was the difficulty in maintaining prostate tissues in organ cultures and the relative novelty of culturing prostate epithelial cells in monolayers. Failures of sex steroids to elicit a direct positive response on prostate cell divisionin vitro, as seenin vivo, were interpreted as resulting from inappropriate models or culture conditions. However, the increasing number of reports confirming the lack of mitogenic activity of sex steroidsin vitro, coupled with the powerful mitogenic activity of GFs displayed in other systems, the discovery of GF receptors (GF-Rs), and the elucidation of their signalling pathways showing sex steroid receptors as potential substrates of GF-activated protein kinases gradually led to an increased interest in the putative role of GFs in prostate physiopathology. Of utmost importance was the recognition that hormone refractiveness was responsible for PCa progression, and for the poor outcome of patients with advanced disease under endocrine therapies. This problem remains a major issue and it raises several key questions that need to be solved at the fundamental and clinical levels.

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.

Targeting multiple signaling pathways as a strategy for managing prostate cancer: multifocal signal modulation therapy

The aberrant behavior of cancer reflects upregulation of certain oncogenic signaling pathways that promote proliferation, inhibit apoptosis, and enable the cancer to spread and evoke angiogenesis. Theoretically, it should be feasible to decrease the activity of these pathways-or increase the activity of pathways that oppose them-with noncytotoxic agents. Since multiple pathways are dysfunctional in most cancers, and cancers accumulate new oncogenic mutations as they progress, the greatest and most durable therapeutic benefit will likely be achieved with combination regimens that address several targets. Thus, a multifocal signal modulation therapy (MSMT) of cancer is proposed. This concept has already been documented by researchers who have shown that certain combinations of signal modulators-of limited utility when administered individually-can achieve dramatic suppression of tumor growth in rodent xenograft models. The present essay attempts to guide development of MSMTs for prostate cancer. Androgen ablation is a signal-modulating measure already in standard use in the management of delocalized prostate cancer. The additional molecular targets considered here include the type 1 insulin-like growth factor receptor, the epidermal growth factor receptor, mammalian target of rapamycin, NF-kappaB, hypoxia-inducible factor-1alpha, hsp90, cyclooxygenase-2, protein kinase A type I, vascular endothelial growth factor, 5-lipoxygenase, 12-lipoxygenase, angiotensin II receptor type 1, bradykinin receptor type 1, c-Src, interleukin-6, ras, MDM2, bcl-2/bclxL, vitamin D receptor, estrogen receptor-beta, and PPAR-. Various nutrients and phytochemicals suspected to have potential utility in prostate cancer prevention and therapy, but whose key molecular targets are still unknown, might reasonably be incorporated into MSMTs for prostate cancer; these include lycopene, selenium, green tea polyphenols, genistein, and silibinin. MSMTs can be developed systematically by testing various combinations of signal-modulating agents, in concentrations that can feasibly be achieved and maintained clinically, on human prostate cancer cell lines; combinations that appear promising can then be tested in xenograft models and, ultimately, in the clinic. Some signal modulators can increase response to cytotoxic drugs by upregulating effectors of apoptosis. When MSMTs fail to raise the spontaneous apoptosis rate sufficiently to achieve tumor stasis or regression, incorporation of appropriate cytotoxic agents into the regimen may improve the clinical outcome.

Receptor Imaging in Oncology by Means of Nuclear Medicine: Current Status

To date, our understanding of the role of receptors and their cognate ligands in cancer is being successfully translated into the design and development of an arsenal of new, less toxic, and more specific anticancer drugs. Because most of these novel drugs are cytostatic, objective response as measured by morphologic imaging modalities (eg, computed tomography or magnetic resonance imaging) cannot be used as a surrogate marker for drug development or for clinical decision making. Positron emission tomography (PET) can be used to image and quantify the in vivo distribution of positron-emitting radioisotopes such as oxygen-15, carbon-11, and fluorine-18 that can be substituted or added into biologically relevant and specific receptor radioligands. Similarly, single-photon emission computed tomography (SPECT) can be used to image and quantify the in vivo distribution of receptor targeting compounds labeled with indium-111, technetium-99m, and iodine-123. By virtue of their whole-body imaging capacity and the absence of errors of sampling and tissue manipulation as well as preparation, both techniques have the potential to address locoregional receptor status noninvasively and repetitively. This article reviews available data on the in vivo evaluation of receptor systems by means of PET or SPECT for identifying and monitoring patients with sufficient receptor overexpression for tailored therapeutic interventions, and also for depicting tumor tissue and determining the currently largely unknown heterogeneity in receptor expression among different tumor lesions within and between patients.

Human prostate cancer risk factors

Prostate cancer has the highest prevalence of any nonskin cancer in the human body, with similar likelihood of neoplastic foci found within the prostates of men around the world regardless of diet, occupation, lifestyle, or other factors. Essentially all men with circulating androgens will develop microscopic prostate cancer if they live long enough. This review is a contemporary and comprehensive, literature-based analysis of the putative risk factors for human prostate cancer, and the results were presented at a multidisciplinary consensus conference held in Crystal City, Virginia, in the fall of 2002. The objectives were to evaluate known environmental factors and mechanisms of prostatic carcinogenesis and to identify existing data gaps and future research needs. The review is divided into four sections, including 1) epidemiology (endogenous factors [family history, hormones, race, aging and oxidative stress] and exogenous factors [diet, environmental agents, occupation and other factors, including lifestyle factors]); 2) animal and cell culture models for prediction of human risk (rodent models, transgenic models, mouse reconstitution models, severe combined immunodeficiency syndrome mouse models, canine models, xenograft models, and cell culture models); 3) biomarkers in prostate cancer, most of which have been tested only as predictive factors for patient outcome after treatment rather than as risk factors; and 4) genotoxic and nongenotoxic mechanisms of carcinogenesis. The authors conclude that most of the data regarding risk relies, of necessity, on epidemiologic studies, but animal and cell culture models offer promise in confirming some important findings. The current understanding of biomarkers of disease and risk factors is limited. An understanding of the risk factors for prostate cancer has practical importance for public health research and policy, genetic and nutritional education and chemoprevention, and prevention strategies.

The diffuse endocrine system: from embryogenesis to carcinogenesis

In the present review we will summarise the current knowledge about the cells comprising the Diffuse Endocrine System (DES) in mammalian organs. We will describe the morphological, histochemical and functional traits of these cells in three major systems gastrointestinal, respiratory and prostatic. We will also focus on some aspects of their ontogeny and differentiation, as well as to their relevance in carcinogenesis, especially in neuroendocrine tumors. The first chapter describes the characteristics of DES cells and some of their specific biological and biochemical traits. The second chapter deals with DES in the gastrointestinal organs, with special reference to the new data on the differentiation mechanisms that leads to the appearance of endocrine cells from an undifferentiated stem cell. The third chapter is devoted to DES of the respiratory system and some aspects of its biological role, both, during development and adulthood. Neuroendocrine hyperplasia and neuroendocrine lung tumors are also addressed. Finally, the last chapter deals with the prostatic DES, discussing its probable functional role and its relevance in hormone-resistant prostatic carcinomas.

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.

Expression of gastrin-releasing peptide receptors in endometrial cancer

BACKGROUND

The Bombesin (BBS)-related peptide, gastrin-releasing peptide, and its cognate receptor are ectopically expressed by many cancers, in which they regulate tumor proliferation and metastasis. But, their role in endometrial cancers is unknown. The purpose of this study was to determine whether endometrial cancer cell lines express functional BBS receptors and to determine whether they were coupled to the regulation of vascular endothelial growth factor (VEGF-A) expression.

STUDY DESIGN

Endometrial cancer cell lines (HEC-1A, KLE, and AN3CA) were cultured according to the recommendations of the American Tissue Culture Collection. Ishikawa cells were maintained in Dulbecco's modified Eagle's medium plus 10% fetal bovine serum. Before BBS treatment, all cell lines were placed in serum-free, phenol-free media for 24 hours. BBS-stimulated increases in intracellular Ca(2+) ([Ca(2+)]i) were used to assess functional BBS receptor status. VEGF-A mRNA expression was determined by Northern blotting.

RESULTS

BBS (100 nM) stimulated an increase in [Ca(2+)]i in HEC-1A, Ishikawa, and KLE cells, indicating the presence of functional BBS receptors. This increase did not occur in AN3CA cells. BBS stimulated a time-dependent increase in VEGF-A mRNA expression in Ishikawa and KLE cells. Ishikawa cells exhibited a peak of VEGF-A mRNA expression between 8 and 12 hours with a partial decline by 24 hours. KLE cells showed a relatively small increase at 12 hours. In contrast, HEC-1A cells exhibited a high baseline level of VEGF-A mRNA expression and did not show a response to BBS.

CONCLUSIONS

These data demonstrate that endometrial cancer cell lines express functional BBS receptors. In Ishikawa, KLE, and HEC-1A cells, BBS receptors are coupled to the regulation of VEGF-A mRNA expression.

Neuropeptides bombesin and calcitonin inhibit apoptosis-related elemental changes in prostate carcinoma cell lines

BACKGROUND

Etoposide-induced apoptosis in prostate carcinoma cells is associated with changes in the elemental content of the cells. The authors previously reported that calcitonin and bombesin inhibited etoposide-induced apoptosis in these cells. In the current study, the authors investigated whether these neuropeptides block the etoposide-induced changes in elemental content.

METHODS

Cells from the PC-3 and Du 145 prostate carcinoma cell lines were grown either on solid substrates or on thin plastic films on titanium electron microscopy grids, and they were exposed to etoposide for 48 hours in the absence or presence of calcitonin and bombesin. After the exposure, the cells were frozen and freeze dried, and their elemental content was analyzed by energy-dispersive X-ray microanalysis in both in the scanning electron microscope and the scanning transmission electron microscope.

RESULTS

Etoposide treatment consistently induced an increase in the cellular Na concentration and a decrease in the cellular K concentration, resulting in a marked increase of the Na/K ratio and also an increase in the phosphorus:sulphur (P/S) ratio. Both bombesin and calcitonin inhibited the etoposide-induced changes in the cellular Na/K ratio, and calcitonin, but not bombesin, inhibited the changes in the P/S ratio. No significant elemental changes were found with bombesin or calcitonin alone.

CONCLUSIONS

The neuropeptides bombesin and calcitonin, which inhibited etoposide-induced apoptosis, also inhibited the etoposide-induced elemental changes in prostate carcinoma cells. This important fact strengthens the link between apoptosis and changes in the intracellular elemental content. This correlation provides an objective basis for the study of neuropeptide target points and may be helpful for alternative therapeutic protocols using neuropeptide inhibitors in the treatment of patients with advanced prostatic carcinoma.

Neuropeptide-induced androgen independence in prostate cancer cells: roles of nonreceptor tyrosine kinases Etk/Bmx, Src, and focal adhesion kinase

The bombesin/gastrin-releasing peptide (GRP) family of neuropeptides has been implicated in various in vitro and in vivo models of human malignancies including prostate cancers. It was previously shown that bombesin and/or neurotensin (NT) acts as a survival and migratory factor(s) for androgen-independent prostate cancers. However, a role in the transition from an androgen-dependent to -refractory state has not been addressed. In this study, we investigate the biological effects and signal pathways of bombesin and NT on LNCaP, a prostate cancer cell line which requires androgen for growth. We show that both neurotrophic factors can induce LNCaP growth in the absence of androgen. Concurrent transactivation of reporter genes driven by the prostate-specific antigen promoter or a promoter carrying an androgen-responsive element (ARE) indicate that growth stimulation is accompanied by androgen receptor (AR) activation. Furthermore, neurotrophic factor-induced gene activation was also present in PC3 cells transfected with the AR but not in the parental line which lacks the AR. Given that bombesin does not directly bind to the AR and is known to engage a G-protein-coupled receptor, we investigated downstream signaling events that could possibly interact with the AR pathway. We found that three nonreceptor tyrosine kinases, focal adhesion kinase (FAK), Src, and Etk/BMX play important parts in this process. Etk/Bmx activation requires FAK and Src and is critical for neurotrophic factor-induced growth, as LNCaP cells transfected with a dominant-negative Etk/BMX fail to respond to bombesin. Etk's activation requires FAK, Src, but not phosphatidylinositol 3-kinase. Likewise, bombesin-induced AR activation is inhibited by the dominant-negative mutant of either Src or FAK. Thus, in addition to defining a new G-protein pathway, this report makes the following points regarding prostate cancer. (i) Neurotrophic factors can activate the AR, thus circumventing the normal growth inhibition caused by androgen ablation. (ii) Tyrosine kinases are involved in neurotrophic factor-mediated AR activation and, as such, may serve as targets of future therapeutics, to be used in conjunction with current antihormone and antineuropeptide therapies.

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.

Expression of membrane-type 1 matrix metalloproteinase (MT1-MMP) on prostate cancer cell lines

Membrane-type metalloproteinase-1 (MT1-MMP) is a transmembrane metalloproteinase, which activates proMMP-2 and expressed on the cell surface in many invasive cancer cells. We investigated the expression of MT1-MMP in prostate cancer cell lines. MT1-MMP protein and mRNA were expressed in PC-3, DU-145 and TSU-pr1 cells (androgen-independent prostate cancer cell lines), but in LNCaP cells (androgen-dependent prostate cancer cell line). MT1-MMP protein was negative and mRNA was low to detect by RT-PCR. Cell lysate of PC-3 cleaved proMMP-2 to the active form. In addition, both hepatocyte growth factor (HGF) and gastrin-releasing peptide (GRP) increased Matrigel invasion and induced the expression of MT1-MMP protein in DU-145 prostate cancer cells. These results suggest that MT1-MMP is indeed the tumor-specific activator of proMMP-2 in androgen-independent prostate cancer cells and plays an important role in the invasive properties of prostate cancer cells.

Sex-specific expression of gastrin-releasing peptide receptor: relationship to smoking history and risk of lung cancer

BACKGROUND

Activation of gastrin-releasing peptide receptor (GRPR) in human airways has been associated with a proliferative response of bronchial cells to gastrin-releasing peptide and with long-term tobacco use. The GRPR gene is located on the X chromosome and escapes X-chromosome inactivation, which occurs in females. Increasing evidence demonstrates that women are more susceptible than men to tobacco carcinogenesis. We hypothesized that the susceptibility of women to the effects of tobacco may be associated with airway expression of GRPR.

METHODS

We analyzed GRPR messenger RNA (mRNA) expression in lung tissues and cultured airway cells from 78 individuals (40 males and 38 females) and in lung fibroblasts exposed to nicotine in vitro. Nicotinic acetylcholine receptors in airway cells were assayed by use of radioactively labeled nicotine and nicotine antagonists. A polymorphism in exon 2 of the GRPR gene was used to detect allele-specific GRPR mRNA expression in some individuals. Statistical tests were two-sided.

RESULTS

GRPR mRNA expression was detected in airway cells and tissues of more female than male nonsmokers (55% versus 0%) and short-term smokers (1-25 pack-years [pack-years = number of packs of cigarettes smoked per day multiplied by the number of years of smoking]) (75% versus 20%) (P =.018 for nonsmoking and short-term smoking females versus nonsmoking and short-term smoking males). Female smokers exhibited expression of GRPR mRNA at a lower mean pack-year exposure than male smokers (37.4 pack-years versus 56.3 pack-years; P =.037). Lung fibroblasts and bronchial epithelial cells exhibited high-affinity, saturable nicotinic acetylcholine-binding sites. Expression of GRPR mRNA in lung fibroblasts was elevated following exposure to nicotine.

CONCLUSIONS

Our results suggest that the GRPR gene is expressed more frequently in women than in men in the absence of smoking and that expression of this gene is activated earlier in women in response to tobacco exposure. The presence of two expressed copies of the GRPR gene in females may be a factor in the increased susceptibility of women to tobacco-induced lung cancer.

The luteinizing hormone-releasing hormone receptor in human prostate cancer cells: messenger ribonucleic acid expression, molecular size, and signal transduction pathway

Evidence has accumulated indicating that LHRH might behave as an autocrine/paracrine growth inhibitory factor in some peripheral tumors. However, LHRH receptors in tumor cells have not been fully characterized, so far. The present experiments were performed to analyze: 1) the messenger RNA expression; 2) the molecular size; and 3) the signal transduction pathway of LHRH receptors in prostate cancer. For these studies, the human androgen-dependent LNCaP and androgen-independent DU 145 prostate cancer cell lines were used. 1) By RT-PCR, a complementary DNA product, which hybridized with a 32P-labeled oligonucleotide probe specific for the pituitary LHRH receptor complementary DNA, was found both in LNCaP and in DU 145 cells. 2) Western blot analysis, using a monoclonal antibody raised against the human pituitary LHRH receptor, revealed the presence of a protein band of approximately 64 kDa (corresponding to the molecular mass of the pituitary receptor) in both cell lines. 3) In LNCaP and DU 145 cells, pertussis toxin completely abrogated the antiproliferative action of a LHRH agonist (LHRH-A). Moreover, LHRH-A substantially antagonized the pertussis toxin-catalyzed ADP-ribosylation of a Galpha(i) protein. Finally, LHRH-A significantly counteracted the forskolin-induced increase of intracellular cAMP levels in both cell lines. These data demonstrate that the LHRH receptor, which is present in prostate cancer cells, independently of whether they are androgen-dependent or not, corresponds to the pituitary receptor, in terms of messenger RNA expression and protein molecular size. However, at variance with the receptor of the gonadotrophs, prostate cancer LHRH receptor seems to be coupled to the Galpha(i) protein-cAMP signal transduction pathway, rather than to the Galpha(q/11)-phospholipase C signaling system. This might be responsible for the different actions of LHRH in anterior pituitary and in prostate cancer.

Synthesis and biological evaluation of C-terminal hydroxamide analogues of bombesin

Bombesin pseudo-peptide analogues containing a hydroxamide function on the C-terminal part of the molecule, e.g. H-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOBzl 1 and H-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOH 2 were synthesized. These compounds were tested for their ability to recognize the bombesin receptor on rat pancreatic acini and on 3T3 cells, to stimulate (i) amylase secretion from rat pancreatic acini and (ii) accumulation of tritiated thymidine in 3T3 cells. Compounds 1 and 2 were able to recognize bombesin receptors on both models with high affinity (Ki = 7 +/- 2 and 5.8 +/- 0.9 nM on rat pancreatic acini, and Ki = 4.1 +/- 1.2 and 7.7 +/- 1.9 nM on 3T3 cells, respectively). Interestingly, compound 1 behaved as a potent agonist in stimulating amylase secretion from rat pancreatic acini and is able to stimulate thymidine accumulation in 3T3 cells, while compound 2 was able to potently antagonize bombesin-stimulated amylase secretion (Ki = 22 +/- 5 nM) in rat pancreatic acini and had no proper effect on 3T3 cells; however, it was able to inhibit bombesin-stimulated thymidine accumulation in 3T3 cells with high potency (Ki = 1.6 +/- 0.6 nM).

Syntheses and biological activities of potent bombesin receptor antagonists

Bombesin receptor antagonists are potential therapeutic agents due to their ability to act as inhibitors of cellular proliferation. On the basis of our hypothesis concerning the mechanism of action of gastrin associating an activating enzyme to the receptor and on the results reported in the literature, we have synthesized bombesin analogs which have been modified in the C-terminal part. Potent bombesin receptor antagonists were obtained by replacement of Leu-13 with a statyl residue or with a residue bearing an hydroxyl group in place of the carbonyl function of Leu-13. Several inhibitors were able to recognize the bombesin receptor on rat pancreatic acini and antagonized bombesin stimulated amylase secretion in the nanomolar range. These compounds were also able to recognize the bombesin receptor and to inhibit [3H] thymidine incorporation in 3T3 cells with the same potency.

Growth-inhibitory effects of luteinizing hormone-releasing hormone (LHRH) agonists on xenografts of the DU 145 human androgen-independent prostate cancer cell line in nude mice

Experiments have been performed to clarify whether LHRH agonists might decrease growth of hormone-unresponsive prostate cancer in vivo. Male nude mice were injected s.c. with the human androgen-independent prostate tumor DU 145 cells; osmotic minipumps releasing the LHRH agonist Zoladex (LHRH-A) for 14 days were simultaneously implanted under the skin. Treatment with LHRH-A induced a significant decrease in tumor growth up to the end of the treatment. In subsequent experiment, minipumps releasing LHRH-A were implanted in nude mice either 7 or 14 days after cell inoculation. When the treatment was started 7 days after inoculation of the cells, tumor growth was significantly decreased up to 28 days; thereafter, tumor volume remained lower than in controls, although not significantly. When LHRH-A was administered beginning 14 days after cell inoculation, tumor growth was not significantly affected at any time interval considered. LHRH-A did not appear to induce apoptosis in DU 145 cells, at least on the basis of the apoptotic index and immunohistochemical staining of the p53 protein. On the other hand, treatment with LHRH-A was accompanied by a significant decrease of the concentration of epidermal growth factor receptors in DU 145 prostate cancer specimens. Our results show that the LHRH agonist used significantly inhibits the growth of DU 145 androgen-independent prostate tumor xenografts in nude mice.

Inhibition of growth of MDA-MB-231 human breast cancer xenografts in nude mice by bombesin/gastrin-releasing peptide (GRP) antagonists RC-3940-II and RC-3095

Bombesin or gastrin-releasing peptide (GRP) may act as autocrine growth factors and play a role in the initiation and progression of breast cancer. We investigated the effect of bombesin/GRP antagonists RC-3095 and RC-3940-II on the growth of the MDA-MB-231 oestrogen-independent human breast cancer cell line xenografted into female nude mice. Bombesin/GRP antagonists, RC-3095 and RC-3940-II, were administered subcutaneously twice daily at a dose of 10 micrograms for 5 weeks. The growth of MDA-MB-231 tumours was inhibited during the treatment, as shown by a reduction in tumour volume. RC-3940-II and RC-3095 significantly decreased the final tumour volume by 72.4% and 57.7%, respectively, and greatly reduced tumour weights. RC-3940-II also significantly increased tumour doubling time and appeared to be more effective than RC-3095 in inhibiting the growth of MDA-MB-231 breast cancers. Serum gastrin and insulin-like growth factor-I (IGF-I) levels in animals treated with RC-3095 or RC-3940-II showed no significant changes as compared with controls. There was a significant decrease in the number of binding sites for epidermal growth factor (EGF), as well as bombesin, in tumour cells after chronic treatment with RC-3095 or RC-3940-II, which might be related to inhibition of tumour growth. Reverse transcription polymerase chain reaction, followed by Southern blot analysis, also showed a reduction in the expression of mRNA for EGF receptors in the group treated with RC-3940-II. Our findings suggest that bombesin/GRP antagonists such as RC-3095 or RC-3940-II could be considered for endocrine therapy for oestrogen-independent breast cancers, but further investigations are necessary.

In situ hybridization for gastrin-releasing peptide receptor (GRP receptor) expression in prostatic carcinoma

Bombesin-like peptides (BLPs), which have been implicated in the regulation of growth of prostatic carcinoma cells, are a product of neuroendocrine cells frequently found in prostate tissue and are postulated to play a role in the initiation or progression of prostatic carcinoma. In this report, we examined the expression, in human prostate tissue, of mRNA encoding the 3 known receptors that respond to BLPs in humans, i.e., gastrin-releasing peptide (GRP) receptor, neuromedin B (NMB) receptor and bombesin receptor subtype 3 (BRS-3). Competitive rt-PCR experiments demonstrated the widespread but variable expression of GRP receptor mRNA in fresh-frozen specimens of prostatic carcinoma (12 cases) and benign prostatic hypertrophy (6 cases). NMB receptor mRNA expression was also widespread, but its level was less variable than GRP receptor message. In contrast, we could not detect BRS-3 mRNA in most tissue samples by rt-PCR. To address which cells in the prostate express the GRP receptor, we used in situ hybridization methods to stain selectively GRP receptor mRNA. GRP receptor mRNA was expressed predominantly in the luminal and basal epithelial cells in both histologically normal and cancerous glands within sections of normal (3 cases) and diseased (37 cases) tissue. GRP receptor mRNA staining in cancerous tissue ranged widely from very intense to not detectable (about 30% of the cases), while normal tissue consistently displayed a low level of message staining. Taken together, our results demonstrate expression of the GRP receptor in a high percentage of basal and/or luminal epithelial cells of normal and diseased prostate tissues.

Mechanisms of electrolyte transport across the endometrium. II. Regulation by GRP and substance P

The purpose of this study was to investigate the regulation of electrolyte transport across the porcine endometrium by gastrin-releasing peptide (GRP) and substance P (SP). Luminal addition of GRP, neuromedin B (NMB), SP, or neurokinin A(NKA) to mucosal tissues mounted in Ussing chambers produced a multiphasic change in short-circuit current (Isc) characterized by an initial rapid increase and subsequent decrease in current. A similar response was obtained after addition of ionomycin or thapsigargin to the tissues. The Isc response to the peptides or Ca ionophore was inhibited by pretreatment of the tissues with luminal amiloride or benzamil. GRP and SP were more potent [50% effective concentration (EC50) of 3 nM] than NMB or NKA (EC50 values of 46 and 26 nM, respectively) in producing the decrease in Isc. Pretreatment with the GRP receptor antagonist 3-Phe-His-Trp-Ala-Val-D-Ala-His-D-Pro-psi Phe-NH2 blocked the Isc response to GRP and NMB but not to SP or NKA, whereas the NMB receptor antagonist D-Nal-[Cys-Try-D-Trp-Orn-Val-Cys]-Nal-NH2 was ineffective in inhibiting the Isc response to any of the peptides. In contrast, pretreatment of the tissue with the nonpeptide SP receptor antagonist CP-99,994 blocked the Isc response to SP and NKA but not to GRP or NMB. Experiments with amphotericin B-permeabilized tissues showed that GRP, SP, ionomycin, and thapsigargin increased current through an outwardly rectifying K conductance located on the apical membrane of the cells. The K-to-Na selectivity ratio of this conductance was calculated to be 2.5:1. These experiments showed that GRP and SP, acting through different receptors, produced an increase in K efflux through a Ca-dependent K conductance present in the apical membrane of surface endometrial epithelial cells. In addition, immunohistochemistry data showed that GRP-like immunoreactivity was localized to surface and glandular epithelial cells, whereas GRP receptor antibody labeling was observed in both epithelial and stromal cells. These results suggest that GRP functions as both an autocrine and paracrine regulatory peptide in the endometrium.

Characterization of intracellular calcium mobilization by bombesin-related neuropeptides in PC-3 human prostate cancer cells

BACKGROUND

The objective of this study was to characterize the calcium mobilizing activity of bombesin-related neuropeptides in PC-3 cells.

METHODS

Intracellular free Ca2+ concentration ([Ca2+]i) was measured following the administration of bombesin-related neuropeptides using spectrofluorometric monitoring of PC-3 cells loaded with Fura2/AM.

RESULTS

Individual neuropeptides induced a rapid rise in [Ca2+]i immediately after stimulation in similar fashion. When two different peptides were administered simultaneously, the [Ca2+]i changes were similar to that produced by each peptide alone. However, simultaneous addition of tyr4-bombesin 100 nM and 2% serum resulted in [Ca2+]i increase greater than either alone. Sequential stimulation by same or different peptides, was not able to induce another response. However, 6 hrs after the first stimulus, a second stimulus was able to induce a similar response.

CONCLUSIONS

The data indicate that all members of the bombesin-related family of neuropeptides are capable of triggering calcium mobilization in PC-3 cells via a similar signalling pathway. PC-3 cells become acutely desensitized to additional stimulation of neuropeptide. This desensitization is selective and reversible, requiring approximately 6 hrs for recovery.

Calcium signaling in prostate cancer cells: evidence for multiple receptors and enhanced sensitivity to bombesin/GRP

BACKGROUND

Cellular calcium is an important second messenger for growth regulation. We sought to identify potentially important receptors on prostate tumor cells by screening over 20 agonists for their ability to increase intracellular free calcium ([Ca2+]i) in several human prostate tumor cell lines.

METHODS

Intracellular calcium mobilization was detected using fura-2.

RESULTS

We found bombesin, GRP, ATP/UTP, lysophosphatidic acid, thrombin, endothelin, histamine, and bradykinin increased [Ca2+]i in the advanced tumor cell lines DU-145, PC3, and PPC-1. Bombesin failed to elevate [Ca2+]i in an immortalized human prostate cell line. Rank-order of potency studies suggested the presence of P2U nucleotide receptors for ATP/UTP on prostate epithelial cells. Potency studies also revealed GRP > > bombesin > > neuromedin B at elevating [Ca2+]i in responding tumor cells.

CONCLUSIONS

These findings indicate that androgen independent prostate tumor cell lines express multiple receptors capable of elevating intracellular calcium, and suggest that GRP receptors may be selectively expressed and/or coupled to calcium signaling during prostate tumor progression. Calcium sensitive cellular events may therefore contribute to the progression of prostate cancer.

Design, synthesis, and in vitro evaluation of cytotoxic analogs of bombesin-like peptides containing doxorubicin or its intensely potent derivative, 2-pyrrolinodoxorubicin

Five peptide fragments, based on the C-terminal sequence of bombesin (BN)-(6-14) or BN-(7-14), were selected as carriers for radicals doxorubicin (DOX) and 2-pyrrolino-DOX to create hybrid cytotoxic analogs. All these compounds had a reduced peptide bond (CH2-NH or CH2-N) between positions 13 (Phe or Leu) and 14 (Phe, Leu, or Tac) (Tac = thiazolidine-4-carboxylic acid). Three pseudononapeptide carriers contained N-terminal D-Phe or D-Tpi at position 6 (Tpi = 2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid). Two pseudooctapeptides had Gln7 at the N terminus. The conjugation of N-(9-fluorenylmethoxycarbonyl) doxorubicin (N-Fmoc-DOX)-14-O-hemiglutarate to the peptide carriers at the N terminus resulted in cytotoxic hybrids of BN-like peptides containing DOX. These hybrids could then be converted to analogs with 2-pyrrolino-DOX by a reaction with 4-iodobutyraldehyde. The ability of the carriers and the conjugates to inhibit the binding of 125I-labeled [Tyr4]BN to receptors for BN/gastrin releasing peptide (GRP) on Swiss 3T3 cells was determined. Cytotoxic conjugates of pseudooctapeptide carrier analogs displayed the highest binding affinity (KD approximately 1 nM). The cytotoxic BN analogs and their corresponding cytotoxic radicals exerted similar inhibitory effects on the in vitro growth of CFPAC-1 human pancreatic cancer, DMS-53 human lung cancer, PC-3 human prostate cancer, and MKN-45 human gastric cancer cell lines that have receptors for BN/GRP. In DMS-53 cells, the activity of 2-pyrrolino-DOX and its conjugates was approximately 2500 times higher than that of DOX and its hybrids. These highly potent cytotoxic analogs of BN have been designed as targeted anti-tumor agents for the treatment of various cancers that possess receptors for BN/GRP.

Radiolabeled somatostatin analogs in prostate cancer

Vapreotide (RC-160), a somatostatin analog, was labeled with 99mTC by a direct method and also by using CPTA [1,4,8,11-tetraazacyclotetradecane] as a bifunctional chelating agent. The labeled compounds were evaluated in nude mice bearing experimental human prostate cancers. In these studies, 111In-DTPA-D-Phe-Octreotide (111In-DTPA-octreotide) served as a standard and 99mTc-oxytocin as a receptor-non-specific control. 99mTc-octreotide was also used. The 24 htumor uptake of 99mTc-RC-160 was nearly 400% higher, (p < 0.05), than that of 111In-DTPA-octreotide and diminished upon receptor blocking. In all tissues except the kidneys, the uptake of 99mTc-RC-160 was also higher than that of 111In-DTPA-octreotide. The uptake of 99mTc-RC-160 was influenced by the amount of peptide injected and the best tumor/muscle and tumor/blood ratios were obtained when only one micrograms of the peptide (200 Ci/mmol) was administered.

Androgen-repressed phenotype in human prostate cancer

An androgen-repressed human prostate cancer cell line, ARCaP, was established and characterized. This cell line was derived from the ascites fluid of a patient with advanced metastatic disease. In contrast to the behavior of androgen-dependent LNCaP and its androgen-independent C4-2 subline, androgen and estrogen suppress the growth of ARCaP cells in a dose-dependent manner in vivo and in vitro. ARCaP is tumorigenic and highly metastatic. It metastasizes to the lymph node, lung, pancreas, liver, kidney, and bone, and forms ascites fluid in athymic hosts. ARCaP cells express low levels of androgen receptor mRNA and prostate-specific antigen mRNA and protein. Immunohistochemical staining shows that ARCaP cells stain intensely for epidermal growth factor receptor, c-erb B2/neu, and c-erb B3. Staining is negative for chromogranin A and positive for bombesin, serotonin, neuron-specific enolase, and the c-met protooncogene (a hepatic growth factor/scatter factor receptor). ARCaP cells also secrete high levels of gelatinase A and B and some stromelysin, which suggests that this cell line may contain markers representing invasive adenocarcinoma with selective neuronendocrine phenotypes. Along with its repression of growth, androgen is also found to repress the expression of prostate-specific antigen in ARCaP cells as detected by a prostate-specific antigen promoter-beta-galactosidase reporter assay. Our results suggest that the androgen-repressed state may be central to prostate cancer progression and that advanced prostate cancer can progress from an androgen-independent to an androgen-repressed state.

Mechanisms of bombesin on growth of gastrinoma (PT) in vivo

The growth of the human gastrinoma model (PT) in athymic nude mice is stimulated by bombesin (BBS), an amphibian peptide homologous to both human gastrin-releasing peptide (GRP) and neuromedin B (NMB). The mechanism is not known, and a potent and specific GRP-R antagonist BIM26226, which has low affinity for NMB-R, was used in vivo in athymic nude mice bearing gastrinoma subcutaneously. Both the BBS and BIM26226 stimulated the growth of PT, and the growth stimulation was even greater when given together. RT-PCR study of gastrinoma revealed the presence of both GRP-R and NMB-R mRNA, but much more abundant NMB-R mRNA. We conclude that BBS-stimulated growth of gastrinoma involves both GRP-R and NMB-R, and our findings suggest that GRP-R mediates negative and NMB-R produces positive growth effects on gastrinoma.

Correlation between the effects of bombesin antagonists on cell proliferation and intracellular calcium concentration in Swiss 3T3 and HT-29 cell lines

Bombesin (BN) acts as an autocrine mitogen in various human cancers. Several pseudononapeptide BN-(6-14) analogs with a reduced peptide bond between positions 13 and 14 have been shown to suppress the mitogenic activity of BN or gastrin-releasing peptide (GRP) when assessed by radioreceptor or proliferation assays and may have significant clinical applications. The search for potent and safe BN antagonists requires the evaluation of a large series of analogs in radioreceptor and proliferation assays. In this paper, we report that the ability of BN analogs to inhibit BN-induced calcium transients in Swiss 3T3 cells shows a high correlation with their inhibitory potency as evaluated by classical proliferation tests. The assay of calcium transients allows a rapid characterization of new BN analogs (in terms of minutes rather than days) and can be adapted as a labor and cost-effective screening step in the selection of potentially relevant BN antagonists for further characterization in cell proliferation systems. We also observed that results from the assay of calcium transients in Swiss 3T3 cells can be correlated with the results of the proliferative response in HT-29 cells, a cell line that does not seem to use the same early transmembrane ionic signal system. This result suggests that the calcium pathway is not mandatory for triggering cell division by the BN receptor.

Bombesin receptor structure and expression in human lung carcinoma cell lines

Mammalian bombesin-like peptides gastrin-releasing peptide (GRP) and neuromedin B (NMB) are regulatory neuropeptides involved in numerous physiologic processes, and have been implicated as autocrine and/or paracrine growth factors in human lung carcinoma. Three structurally and pharmacologically distinct bombesin receptor subtypes have been isolated and characterized: the gastrin releasing peptide receptor (GRP-R), the neuromedin B receptor (NMB-R), and bombesin receptor subtype-3 (BRS-3). The three receptors are structurally related, sharing about 50% amino acid identity. They are members of the G-protein coupled receptor superfamily with a seven predicted transmembrane segment topology characteristic of receptors in this family. The signal transduction pathway for GRP-R and NMB-R involves coupling to a pertussis-toxin insensitive G-protein, activation of phospholipase C (PLC), generation of inositol trisphosphate (IP3), release of intracellular calcium, and activation of protein kinase C. While all three bombesin receptors are activated by bombesin agonists, GRP-R, NMB-R, and BRS-3 have very different affinities for the mammalian bombesin-like peptides GRP and NMB, as well as bombesin receptor antagonists. The three bombesin receptor subtypes are expressed in an overlapping subset of human lung carcinoma cell lines. Any therapeutic strategy based on modulation of bombesin growth responses in human lung carcinoma would be well served to take into account the pharmacologic heterogeneity of the relevant receptors.

Cellular signalling as a target in cancer chemotherapy. Phospholipid analogues as inhibitors of mitogenic signal transduction

Mitogenic signalling mechanisms emerged as novel targets for tumor chemotherapy. Current strategies for pharmacological interventions are briefly discussed. Phospholipid analogues are treated in greater detail. It is shown here that this new class of antitumor agents acts as inhibitors of mitogenic signal transduction. The common target of all phospholipid analogues studied so far is the phosphatidylinositol (PI)-specific phospholipase C (PLC). This results in an attenuated formation of inositol-1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). The reduction in IP3-levels leads to a depressed release of Ca2+ from internal stores, and the reduced formation of DAG interferes with the growth factor-induced activation of protein-kinase C (PKC). In addition to the effect on PI-specific PLC, most phospholipid analogues inhibit PKC directly by interacting with the regulatory domain of the enzyme. This effect, however, is not observed with all phospholipid analogues. Some potent growth inhibitory representatives from this group like hexadecylphosphoserine or hexadecylphosphonoserine do not affect PKC in cell-free extracts. It is concluded, therefore, that the direct inhibition of PKC is not required for the growth-inhibitory activity of these agents. The ability of phospholipid analogues to interact with PKC was also not found to be correlated the occurrence of unwanted side effects. Phospholipid analogues have also been found to act as inhibitors of phospholipase D (PLD). However, in this case the correlation to the growth inhibitory potency of various phospholipid analogues was less clear, so that the contribution of the PLD inhibition to the growth inhibitory effect of these agents still remains to be established. The inhibition of the thrombin-induced rise in cytosolic free Ca2+ by phospholipid analogues is reversible by washing the cells in phospholipid-free medium. These findings suggest that phospholipid analogues do not cause persistent membrane damage and may act as cytostatic rather than cytotoxic agents.

GRP receptors are present in non small cell lung cancer cells

Previously, GRP receptors were characterized in small cell lung cancer cells and here non-small cell lung cancer (NSCLC) cells were investigated: (125I-Tyr4) bombesin (BN) or 125I-GRP bound with high affinity to NCI-H720 (lung carcinoid) and NCI-H1299 (large cell carcinoma) cells. Binding was specific, time dependent, and saturable. Specific (125I-Tyr4)BN binding to NCI-H1299 cells was inhibited with high affinity by GRP, BN, GRP14-27, (D-Phe6)BN6-13methyl ester, moderate affinity by NMB, and low affinity by GRP1-16. BN (10 nM) transiently elevated cytosolic calcium in a dose dependent manner. BN caused translocation of protein kinase C from the cytosol to the membrane and the translocation caused by BN was reversed by (D-Phe6)BN6-13methylester. BN stimulated arachidonic acid release and the increase caused by BN was reversed by (D-Phe6)BN6-13methylester. Using a clonogenic assay, BN stimulated the growth of NCI-H720 cells, and the number of colonies was reduced using (D-Phe6)BN6-13methylester. These data suggest that GRP receptors that are present in lung carcinoid and NSCLC cells may regulate proliferation.

Somatostatin receptors in prostate tissues and derived cell cultures, and the in vitro growth inhibitory effect of BIM-23014 analog

We investigated somatostatin receptors (SSTRs) in surgical specimens of prostate cancer and benign prostate hyperplasia (BPH), a normal immortalized epithelial cell line (PNT1), epithelial cancer cell lines, and stromal cells in short-term culture derived from normal and BPH biopsies. Cross-linking studies with 125I-Tyr11-SRIF-14 (125I-SRIF) and the SRIF analog 125I-BIM-23104 identified one major 57-kDa band both in surgical specimens and in epithelial and stromal cells cultures. In membrane-enriched fractions and whole stromal cells from a normal prostate and from one BPH, a single type of SSTR was characterized (Kd = 6.10(-9) and 10(-8) M, respectively, Bmax = 1.6 pmol per mg of proteins). mRNA for SSTR1 was detected in all epithelial and stromal cells tested except for PNT1, while SSTR2 mRNA was detected in one BPH stromal cell culture. BIM-23104 had no effect on the in vitro growth of the epithelial cells tested. Conversely, 10(-10) M BIM-23104 induced >50% growth inhibition of stromal cells after 6 days in culture. These results may have implications for therapeutic strategies using SRIF analogs in BPH and prostate cancer.

Growth inhibition of human prostate tumor cells by an agonist of gonadotrophin-releasing hormone

The effect of [D-Leu6,des-Gly-NH2(10),Proethylamide9]-GnRH, leuprolide, was determined for the human primary prostate tumor cell line ALVA-31 by in vitro mitogenic assays. Prostate tumor cell proliferation was inhibited up to 50% by leuprolide. Inhibition was not observed in parallel cultures treated with other low molecular weight bioactive peptides. The incorporation and metabolic reduction of testosterone was not affected by concentrations of leuprolide that were inhibitory in the mitogenic assay. Specific high-affinity binding of 125I-labeled leuprolide was also demonstrated on intact tumor cells with an estimated effective median dose (ED50) of < 1 x 10(-9)M. Inhibition of prostate tumor growth was further demonstrated in Balb/c athymic intact and castrate male mice bearing ALVA-31 tumor xenografts following chronic administration of leuprolide. These data clearly demonstrate that leuprolide can inhibit the growth of a human prostate carcinoma cell line. Studies conducted in castrate animals further suggest an alternative mechanism of growth inhibition that appears to be independent of the suppression of steroid hormone biosynthesis by LHRH analogues.

Neuroendocrine cells in the normal, hyperplastic and neoplastic prostate

Neuroendocrine cells can be demonstrated in normal, hyperplastic and neoplastic prostatic tissues. The products secreted by these cells can be used as tissue and/or serum markers but may also have biological effects. Neuroendocrine cells in prostate cancer most probably do not contain the androgen receptor and are therefore primarily androgen independent. Some of the neuropeptides secreted by the neuroendocrine cells may act as growth factor by activation of membrane receptors in an autocrine-paracrine fashion or by ligand-independent activation of the androgen receptor in neighboring non-neuroendocrine cells. Evidence is accumulating from experiments with tumor models that neuropeptides indeed can influence the growth of prostatic tumor cells. Future research on neuroendocrine differentiation may answer some questions concerning the biological behavior of clinical prostatic tumors.

BW2258U89: a GRP receptor antagonist which inhibits small cell lung cancer growth

The ability of reduced peptide bond analogues of gastrin releasing peptide (GRP) to antagonize small cell lung cancer (SCLC) GRP receptors was investigated. BW462U89, BW1023U90, BW2123U89 and BW2258U89 inhibited binding of (125I-Tyr4) BN to NCI-H345 cells with IC50 values of 5, 6, 140 and 10 nM respectively. The GRP analogues had no effect on basal cytosolic Ca2+ but inhibited the increase caused by 10 nM BN. BW462U89 reversibly blocked the increase in cytosolic Ca2+ caused by BN. The GRP analogues (1 microM) inhibited NCI-H345 colony formation in the absence or presence of 10 nM BN. Also, BW2258U89 (0.4 mg/kg, s.c. daily) inhibited xenograft growth in nude mice. These data indicate that BW2258U89 inhibits SCLC growth in vitro and in vivo.

Potent bombesin antagonists with C-terminal Leu-psi(CH2-N)-Tac-NH2 or its derivatives

Various pseudononapeptide bombesin (BN)-(6-14) antagonists with a reduced peptide bond (CH2-NH) between positions 13 and 14 can suppress the mitogenic activity of BN or gastrin-releasing peptide in 3T3 fibroblast cells and small cell lung carcinoma. In the search for more potent BN antagonists, 10 modified nonapeptide BN antagonists containing N-terminal D-Phe, D-Cpa, and D- or L-Tpi and C-terminal Leu-psi(CH2-N)-Tac-NH2, Leu-psi(CH2-N)-MeTac-NH2, or Leu-psi(CH2-N)-Me2Tac-NH2 have been synthesized by incubating [13 psi 14,CH2-NH,Cys14]BN-(6-14) or [13 psi 14-CH2-NH,Pen14]BN-(6-14) with formaldehyde or acetaldehyde (Cpa = 4-chlorophenylalanine, Tac = thiazolidine-4-carboxylic acid, Tpi = 2,3,4,9-tetrahydro-1H- pyrido[3,4-b]indol-3-carboxylic acid, and Pen = penicillamine). The biological activities of these compounds were then evaluated. [D-Phe6,13 psi 14,CH2-N,Tac14]BN-(6-14) (RC-3950-II) and [D-Phe6,13 psi 14,CH2-N,Me2Tac14]BN-(6-14) (RC-3985-II) exhibited greater potency in inhibition of 125I-labeled [Tyr4]BN binding to Swiss 3T3 cells than their parent compounds [D-Phe6,13 psi 14,CH2-NH,Cys14]BN-(6-14) (RC-3950-I) and [D-Phe6,13 psi 14,CH2-NH,Pen14]BN-(6-14) (RC-3985-I). The order of binding affinities of these compounds was as follows: [13 psi 14,CH2-N,Tac14]BN-(6-14) > [13 psi 14,CH2-N,Me2Tac14]BN-(6-14) > [13 psi 14,CH2-N,MeTac14]BN-(6-14). In most cases, the analogs with C-terminal Leu-psi(CH2-N)-Tac-NH2 were also more potent growth inhibitors of 3T3 cells than compounds containing C-terminal Leu-psi(CH2-N)-Me2Tac-NH2 or Leu-psi(CH2-N)-MeTac-NH2. The best BN antagonists of this series, RC-3950-II and [D-Cpa6,13 psi 14,CH2-N,Tac14]BN- (6-14) (RC-3925-II), inhibited gastrin-releasing peptide-stimulated growth of Swiss 3T3 cells with IC50 values of 1 nM and 6 nM, respectively. Since antagonists of this class inhibit growth of various tumors in animal cancer models, some of them may have clinical applications.

Bombesin receptor gene expression during mammalian development

Mammalian bombesin-like peptides (gastrin-releasing peptide [GRP] and neuromedin B [NMB]) and their receptors (GRP-R and NMB-R) can stimulate growth of cultured cells, and have been shown to be part of an autocrine growth regulatory network in some human small cell lung carcinoma cells. Given the connection between bombesin receptor expression and bombesin-mediated growth regulation in cultured cells, we were interested in investigating the possibility that bombesin peptides and their receptors might be important for normal growth and differentiation during development. As a first step, we examined the distribution of expression of GRP-R and NMB-R mRNA during rat embryonic development to identify changing spatio-temporal patterns of gene expression. In situ hybridization studies show that GRP-R mRNA is expressed at early embryonic stages in various locations of the nervous, urogenital, respiratory, and gastrointestinal systems. In contrast, the distribution of expression of NMB-R mRNA is more limited (upper gastrointestinal tract, bladder, and central nervous system) and is observed at later embryonic stages. In most locations, receptor mRNA levels increased steadily throughout development after onset of expression. However, transient GRP-R mRNA expression is observed in the posterior pituitary where expression increases from embryonic day 12 to 20, and abruptly disappears at birth. These studies suggest that appropriate development of several organ systems, in particular the posterior pituitary, may involve GRP-R-mediated signaling. We plan to test this hypothesis using gene targeting to inactivate the GRP-R gene in the mouse.