Beta-endorphin and neurotensin stimulate in vitro clonal growth of human SCLC cells

Neuropeptides in Cancer: Friend and Foe?

Neuropeptides are small regulatory molecules found throughout the body, most notably in the nervous, cardiovascular, and gastrointestinal systems. They serve as neurotransmitters or hormones in the regulation of diverse physiological processes. Cancer cells escape normal growth control mechanisms by altering their expression of growth factors, receptors, or intracellular signals, and neuropeptides have recently been recognized as mitogens in cancer growth and development. Many neuropeptides and their receptors exist in multiple subtypes, coupling with different downstream signaling pathways and playing distinct roles in cancer progression. The consideration of neuropeptide/receptor systems as anticancer targets is already leading to new biological and diagnostic knowledge that has the potential to enhance the understanding and treatment of cancer. In this review, recent discoveries regarding neuropeptides in a wide range of cancers, emphasizing their mechanisms of action, signaling cascades, regulation, and therapeutic potential, are discussed. Current technologies used to manipulate and analyze neuropeptides/receptors are described. Applications of neuropeptide analogs and their receptor inhibitors in translational studies and radio-oncology are rapidly increasing, and the possibility for their integration into therapeutic trials and clinical treatment appears promising.

Investigation of proNT/NMN secretion from small cell lung carcinoma cells using a mouse xenograft model

Proneurotensin/neuromedin N (proNT/NMN), the precursor of neurotensin (NT) and neuromedin N (NMN), is produced by cancer tissues derived from the pancreas and colon. NT stimulates tumor growth and proliferation through its receptors; however, little is known about the precursor molecule in cancer tissues. We previously demonstrated that proNT/NMN is secreted from small cell lung carcinoma (SCLC) cell lines in serum-free conditioned medium, but not from non-small cell lung carcinoma (NSCLC) cell lines. It was suggested that this precursor may serve as a tumor marker for SCLC. In this study, we established in vivo xenograft models to evaluate the possibility of proNT/NMN as a specific tumor marker. SBC3 cells, derived from human SCLC, were inoculated into mice, and the proNT/NMN levels in plasma and tumor tissues were detected using specific antibodies. In contrast to control mouse plasma, the proNT/NMN levels in tumor-bearing mice increased as the tumors grew, and the elevated plasma proNT/NMN levels were decreased by tumor resection. Moreover, proNT/NMN was expressed in SBC3 tumors, suggesting that proNT/NMN was secreted into blood from the tumor, and this secretion may be specific to SCLC.

Cancer, chemistry, and the cell: molecules that interact with the neurotensin receptors

The literature covering neurotensin (NT) and its signalling pathways, receptors, and biological profile is complicated by the fact that the discovery of three NT receptor subtypes has come to light only in recent years. Moreover, a lot of this literature explores NT in the context of the central nervous system and behavioral studies. However, there is now good evidence that the up-regulation of NT is intimately involved in cancer development and progression. This Review aims to summarize the isolation, cloning, localization, and binding properties of the accepted receptor subtypes (NTR1, NTR2, and NTR3) and the molecules known to bind at these receptors. The growing role these targets are playing in cancer research is also discussed. We hope this Review will provide a useful overview and a one-stop resource for new researchers engaged in this field at the chemistry-biology interface.

Neurotensin receptor binding and neurotensin-induced growth signaling in prostate cancer PC3 cells are sensitive to metabolic stress

Neurotensin (NT) stimulates the proliferation of prostate cancer PC3 cells, which express high levels of its G protein-coupled receptor NTS1. To shed light on mechanisms that might serve to coordinate mitogenic responses to metabolic status, we studied the effects of metabolic inhibitors on NTS1 function. We also related these effects to cellular ATP levels and to the activation of AMP-activated protein kinase (AMPK). Glycolytic and mitochondrial inhibitors, at concentrations that reduced cellular ATP levels, altered NT binding to the cells, inhibited NT-induced inositol phosphate formation, and inhibited NT-induced DNA synthesis. For eight of the nine inhibitors, the potencies to alter NT receptor function correlated to the potencies to decrease cellular ATP levels. In keeping with its known role to oppose metabolic stress, AMPK was activated by the metabolic inhibitors. Accordingly, the AMPK activator AICAR elevated cellular ATP levels and produced effects on NTS1 function that were opposite to those for the metabolic inhibitors. These results indicate that metabolic stress inhibited NTS1 function by a mechanism that involved a fall in cellular ATP levels and that was opposed by activation of AMPK. In a broader context, these findings are compatible with the idea that one means by which cells might coordinate mitogenic signaling to metabolic status could involve changes in growth factor receptor function.

Involvement of neurotensin in cancer growth: evidence, mechanisms and development of diagnostic tools

Focusing on the literature of the past 15 years, we evaluate the evidence that neurotensin and neurotensin receptors participate in cancer growth and we describe possible mechanisms. In addition, we review the progress achieved in the use of neurotensin analogs to image tumors in animals and humans. These exciting advances encourage us to pursue further research and stimulate us to consider novel ideas regarding the multiple inputs to cancer growth that neurotensin might influence.

Inhibition of akt/protein kinase B signaling by naltrindole in small cell lung cancer cells

The phosphatidylinositol 3-kinase-Akt/protein kinase B (PKB) survival signaling is very important for cancer cell survival and growth. Constitutively active phosphatidylinositol 3-kinase-Akt/PKB signaling in small cell lung cancer (SCLC) is a major factor for the survival of SCLC cells. Inhibitors of this signaling pathway would be potential antitumor agents, particularly for SCLC. Here we report that naltrindole, which has been used as a classic delta opioid antagonist, inhibited growth and induced apoptosis in the three characteristic SCLC cell lines, NCI-H69, NCI-H345, and NCI-H510. Naltrindole treatment reduced constitutive phosphorylation of Akt/PKB on serine 473 and threonine 308 in cells. We found that the levels of constitutive phosphorylation of Akt/PKB on serine 473 correlate with the sensitivity of the three cell lines to naltrindole treatment. Furthermore, naltrindole treatment not only reduced the phosphorylation of the Akt/PKB upstream kinase phosphoinositide-dependent kinase-1, but also its downstream effectors glycogen synthase kinase-3beta and the Forkhead transcription factors AFX and FKHR. DNA array analysis of 205 apoptosis-related genes indicated that some Akt/PKB-dependent genes were either up- or down-regulated by naltrindole. Flow cytometric and microscopic analyses clearly showed that naltrindole induced apoptosis in SCLC cells. RNA interference experiments confirmed that naltrindole-induced cell death was associated with the Akt/PKB survival pathway. Together, these results show that naltrindole is a new inhibitor of the Akt/PKB signaling pathway, suggesting that naltrindole could be a potential lead for the development of a new type of inhibitors that target the constitutively active Akt/PKB signaling-dependent SCLC cells.

Involvement of MAP-kinase, PI3-kinase and EGF-receptor in the stimulatory effect of Neurotensin on DNA synthesis in PC3 cells

The mechanism by which neurotensin (NT) promotes the growth of prostate cancer epithelial cells is not yet defined. Here, androgen-independent PC3 cells, which express high levels of the type 1 NT-receptor (NTR1), are used to examine the involvement of epidermal growth factor receptor (EGFR), mitogen-activated protein kinases (ERK, SAPK/JNK and p38), PI3 kinase and PKC in the mitogenic effect of NT. NT dose dependently (0.1-30 nM) enhanced phosphorylation of EGFR, ERK and Akt, reaching maximal levels within 3 min as measured by Western blotting. These effects were associated with an accumulation of EGF-like substance(s) in the medium (assayed by EGFR binding) and a 2-fold increase in DNA synthesis (assayed by [3H]thymidine incorporation). The DNA synthesis enhancement by NT was non-additive with that of EGF. The NT-induced stimulation of EGFR/ERK/Akt phosphorylation and DNA synthesis was inhibited by EGFR-tyrosine kinase inhibitors (AG1478, PD153035), metallo-endopeptidase inhibitor phosphoramidon and by heparin, but not by neutralizing anti-EGF antibody. Thus, transactivation of EGFR by NT involved heparin-binding EGF (HB-EGF or amphiregulin) rather than EGF. The effects of NT on EGFR/ERK/Akt activation and DNA synthesis were attenuated by PLC-inhibitor (U73122), PKC-inhibitors (bisindolylmaleimide, staurosporine, rottlerin), MEK inhibitor (U0126) and PI3 kinase inhibitors (wortmannin, LY 294002). We conclude that NT stimulated mitogenesis in PC3 cells by a PKC-dependent ligand-mediated transactivation of EGFR, which led to stimulation of the Raf-MEK-ERK pathway in a PI3 kinase-dependent manner.

Comparison of mice deficient in the high- or low-affinity neurotensin receptors, Ntsr1 or Ntsr2, reveals a novel function for Ntsr2 in thermal nociception

Neurotensin (NT) is a neuropeptide that induces a wide range of biological activities including hypothermia and analgesia. Such effects are mediated by the NT receptors Ntsr1, Ntsr2 and Ntsr3, although the involvement of each receptor in specific NT functions remains unknown. To address nociceptive function in vivo, we generated both Ntsr1-deficient and Ntsr2-deficient mice. In addition, histochemical analyses of both Ntsr1 and Ntsr2 mRNAs were performed in the mouse brain regions involved in NT-related nociception. The expression of Ntsr2 mRNA was greater than that of Ntsr1 in the periaqueductal gray (PAG) and the rostral ventral medulla (RVM). The mutant and control mice were subjected to the examination of thermal nociception, and in the hot plate test, a significant alteration in jump latency was observed in Ntsr2-deficient mice compared to Ntsr1-deficient or wild-type control mice. Latencies of tail flick and hind paw licking of the mutant mice were not affected compared to control mice. These results suggest that Ntsr2 has an important role in thermal nociception compared to Ntsr1, and that these mutant mice may represent a useful tool for the development of analgesic drugs.

Neurotensin causes tyrosine phosphorylation of focal adhesion kinase in lung cancer cells

The effects of neurotensin on focal adhesion kinase were investigated using lung cancer cells. Neurotensin bound with high affinity to large cell carcinoma cell line NCI-H1299 as did neurotensin-(8-13), but not neurotensin-(1-7) or levocabastine. Addition of 100 nM neurotensin to NCI-H1299 cells caused transient tyrosine phosphorylation of focal adhesion kinase which was maximal after 1-2.5 min. Also, neurotensin-(8-13), but not neurotensin-(1-8) or levocabastine, caused tyrosine phosphorylation of focal adhesion kinase after addition to NCI-H1299 cells. Focal adhesion kinase tyrosine phosphorylation caused by neurotensin was inhibited by the nonpeptide neurotensin receptor antagonist (2-(1-(7-chloroquinolin-4-yl)-5-(2,6-dimethoxyphenyl)-1H-pyrazole-3-carbonyl)amino)-adamantane-2-carboxylic acid) (SR48692). SR48692 inhibited the clonal growth of NCI-H1299 cells, whereas neurotensin-stimulated proliferation and levocabastine had no effect. These results indicate that lung cancer cells have functional neurotensin receptors which regulate focal adhesion kinase tyrosine phosphorylation. It remains to be determined if neurotensin receptors and focal adhesion kinase plays a role in lung cancer cellular adhesion and migration.

Production of recombinant large proneurotensin/neuromedin N-derived peptides and characterization of their binding and biological activity

Proneurotensin/neuromedin N (pro-NT/NN) is the common precursor of two biologically active related peptides, neuromedin N (NN) and neurotensin (NT). It undergoes a tissue-specific processing leading to the formation in some tissues and cancer cell lines of large peptides ending with the NT (large NT) or NN (large NN) sequence. In this study, we prepared and purified high amounts of recombinant large NT and large NN using the Drosophila S2 cell expression system. The binding and pharmacological properties of recombinant large peptides were characterized and compared to those of NT and NN using either COS cells transfected with the human subtype-1 NT receptor (hNTS1) or the human colon adenocarcinoma HT29 cell line that endogenously expresses hNTS1. Furthermore, the metabolic stability of the large peptides, when exposed to HT29 cells, was compared to that of NT and NN. Both large NT and large NN were able to bind to and activate hNTS1 with potencies that were approximately 10 times lower than that of their small counterpart. In addition, the large forms proved to be far less sensitive to degradation than the small peptides. Taken together, these data suggest that the large forms might represent endogenous, long-lasting activators of hNTS1 in a number of physiopathological situations.

Involvement of the neurotensin receptor subtype NTR3 in the growth effect of neurotensin on cancer cell lines

The expression of the 3 currently known neurotensin receptors was studied in human cancer cells of prostatic, colonic or pancreatic origin by means of RT-PCR analysis and binding experiments. All the cells selected for this work have been shown to exhibit a growth response to neurotensin. We found that the 7 transmembrane domain, levocabastine insensitive receptor (NTR1) is expressed in most but not all of the cells studied whereas the 7 transmembrane domain, levocabastine sensitive receptor (NTR2) is present in none of these cells. The 100 kDa-type I neurotensin receptor (NTR3) is expressed in all the cells assayed. Moreover, we demonstrated that neurotensin can stimulate the growth of CHO cells stably transfected with the NTR3. Taken together, our results strongly suggest that the NTR3 subtype could be involved in the growth response of human cancer cells to neurotensin.

SR48692 is a neurotensin receptor antagonist which inhibits the growth of small cell lung cancer cells

Neurotensin (NT) is an autocrine growth factor for some small cell lung cancer (SCLC) cells. In this communication, the effects of a non-peptide NT receptor antagonist, SR48692, were investigated using SCLC cells. (3)H-SR48692 bound with high affinity (IC(50) = 20 nM) to NCI-H209 cells. Also, NT and SR48692 inhibited specific (125)I-NT binding with high affinity (IC(50) values of 2 and 200 nM). In contrast, the NT(2) receptor agonist, levocabastine, had little effect on specific (125)I-NT binding, second messenger production and proliferation using NCI-H209 cells. SR48692 (5 microM) antagonized the ability of NT (10 nM) to cause elevated cytosolic Ca2+ in Fura-2 AM loaded NCI-H209 cells. SR48692 antagonized the ability of NT to cause elevation of c-fos mRNA in these cells. Using a MTT proliferation assay, SR48692 inhibited NCI-H209 and H345 proliferation in a concentration-dependent manner. Using a clonogenic assay, 1 microM SR48692, reduced NCI-H209 colony number. Also, SR48692 (0.4 mg/kg per day) inhibited NCI-H209 xenograft proliferation in nude mice. These results suggest that SR48692 is a NT(1) receptor antagonist which inhibits SCLC growth.

Synergistic effects of neurotensin and beta-adrenergic agonist on 3,5-cyclic adenosine monophosphate accumulation and DNA synthesis in prostate cancer PC3 cells

Since neurotensin is often co-stored with catecholamines and since it can excite the release of dopamine and norepinephrine, responses to this peptide might depend upon the activity of catecholaminergic systems. In this study, we used prostate cancer PC3 cells, which express neurotensin receptors and 12-adrenergic receptors, to demonstrate that neurotensin can potentiate the effects of isoproterenol on 3',5'-cyclic adenosine monophosphate (cAMP) formation and on inhibition of DNA synthesis. While neurotensin had only a slight effect on basal cAMP levels, it nearly doubled the response to isoproterenol even at maximal levels without altering potency. Neurotensin increased the rate of cAMP accumulation and the steady-state level achieved. Consistent with the known antimitogenic action of dibutyryl-cAMP in PC3 cells, isoproterenol was found to inhibit DNA synthesis concentration-dependently, measured using [3H]thymidine. Neurotensin enhanced DNA synthesis when given alone. However, it inhibited DNA synthesis when given with a threshold level of isoproterenol, which by itself had no significant effect. These results, demonstrating cross-talk in the neurotensin and beta-adrenergic signaling pathways, suggest that there may be other physiologic instances of similar interactions between neurotensin and catecholamines.

Neurotensin is metabolized by endogenous proteases in prostate cancer cell lines

The formation and processing of neurotensin (NT) by three prostate cancer cell lines was investigated. Neurotensin (NT) immunoreactivity was detected in conditioned media and extracts of LNCaP cells. Using HPLC techniques, the immunoreactivity extracted from LNCaP cells coeluted with synthetic NT standard. Metalloendopeptidase 3.4.24.15 activity was detected in PC-3, DU-145 and LNCaP cells, whereas high levels of neutral endopeptidase 3.4.24.1 1 activity was detected only in LNCaP cells. NT was relatively stable when incubated with PC-3 or D-145 cells but was rapidly degraded by LNCaP cells to NT1-11 and NT1-10. Phosphoramidon inhibited the metabolism of NT by LNCaP cells. These data suggest that NT is present in and metabolized by LNCaP cellular enzymes.

Neurotensin receptor expression in prostate cancer cell line and growth effect of NT at physiological concentrations

BACKGROUND

Neurotensin (NT), a neuroendocrine peptide, exerts trophic effects in vivo and stimulates growth of some tumor cells in vitro. Androgen-sensitive prostate cells derived from lymph node carcinoma of the prostate (LNCaP) secrete NT and exhibit growth responses to NT. This study examines NT secretion, NT receptor and NT-growth responses in androgen-independent prostatic carcinoma (PC3) cells derived from prostate adenocarcinoma metastatic to bone.

METHODS

Binding of 125I-NT to PC3 membranes was studied by filtration. NT was measured by RIA. Reverse transcriptase polymerase chain reaction (RT-PCR) was used for NT and NT receptor mRNA. Growth was measured as 3H-thymidine incorporation into DNA.

RESULTS

Scatchard analyses gave two binding components (Kd1 = 40 pM and Kd2 = 300 pM) in equal amounts (15-30 x 10(3) sites/cell). The bioactive region of NT was essential and the specific, non-peptide NT antagonist, SR48692, inhibited (IC50 = 3 nM). GTP analogs, sodium ion and SH-directed alkylating agents also inhibited. Glutaraldehyde crosslinking labeled two substances (M(r) of 23 and 46 kDa). RT-PCR indicated robust expression of authentic NT receptor but little for NT precursor. NT was stable in PC3 cultures but it was not found in cells or conditioned media. Incubated with PC3 cells, NT exhibited a mitogenic effect with bell-shaped dose-response and maximum at 100 pM NT.

CONCLUSIONS

PC3 cells expressed genuine NT receptors and generated growth responses to physiologic levels of NT which were blocked by SR48692. If NT contributes to the survival of prostate tumor cells upon androgen deprivation therapy, NT antagonists might be useful agents in further treatment.

Activation of mitogen-activated protein kinase couples neurotensin receptor stimulation to induction of the primary response gene Krox-24

Neurotensin (NT) is a neuropeptide that is important in a variety of biological processes such as signal transduction and cell growth. NT effects are mediated by a single class of cell-surface receptors, known as neurotensin receptors (NTRs), which exhibit structural features of the G-protein-coupled receptors superfamily. We investigated NTR signalling properties with Chinese hamster ovary (CHO) cells stably transformed with human NTR (hNTR). First, we showed that NTR stimulation by NT induced the activation of the mitogen-activated protein kinases (MAPKs) in time- and dose-dependent manners. Both p42 and p44 MAPK isoforms were retarded in gel-shift assays, which was consistent with their activation by phosphorylation. In addition we showed that NT caused a prolonged activation of MAPK as measured by in-gel kinase assay. Secondly, we demonstrated that NT induced the expression of the growth-related gene Krox-24 at the protein level, as assessed by Western-blot analysis, and at the transcriptional level, as demonstrated in CHO cells transfected with hNTR and a reporter gene for Krox-24. Activation of MAPK and induction of Krox-24 were both prevented by the NTR antagonist SR 48692, confirming the specific action on NTR. Furthermore we observed coupling of NTR to a mitogenic pathway and Krox-24 induction in the human adenocarcinoma cell line HT29, which naturally expresses NTRs. Considering coupling pathways between NTR stimulation and MAPK activation, we observed a partial inhibition by pertussis toxin (PTX) and a complete blockade by the protein kinase C (PKC) inhibitor GF 109203X. Taken together, these results suggest that (1) stimulation of NTR activates the MAPK pathway by mechanisms involving dual coupling to both PTX-sensitive and PTX-insensitive G-proteins as well as PKC activation, and (2) these effects are associated with the induction of Krox-24, which might be a target of MAPK effector.

Peptides and growth factors in non-small cell lung cancer

Numerous growth factors and receptors that alter proliferation have been identified in lung cancer. In non-small cell lung cancer (NSCLC) cell lines, high levels of vasoactive intestinal peptide (VIP) mRNA have been detected by Northern analysis, and immunoreactive VIP is present. VIP elevates intracellular cAMP and stimulates the clonal growth of NSCLC cells. Also, transforming growth factor alpha (TGF-alpha) mRNA is present in NSCLC cells and TGF-alpha is present in conditioned media exposed to NSCLC cells. TGF-alpha binds with high affinity to epidermal growth factor (EGF) receptors present on NSCLC cells. EGF stimulates tyrosine kinase activity and growth in NSCLC cells. Synthetic peptide antagonists and monoclonal antibodies have been identified that disrupt autocrine growth pathways and inhibit NSCLC growth. These data suggest that VIP and TGF-alpha are important autocrine growth factors for NSCLC.

Human small cell lung cancer cells express high affinity naloxone-insensitive [125I]-endorphin binding sites

Previous reports have demonstrated that beta-endorphin stimulates the clonal growth of human small cell lung carcinoma (SCLC) cell lines. In this study, the human SCLC lines, NCI-H69, NCI-H345, and NCI-N417, were observed to be highly-enriched in saturable, high-affinity binding sites which are labeled by [125I]beta-endorphin. In contrast to conventional opioid receptors, [125I]beta-endorphin SCLC binding was insensitive to naloxone and other mu, delta, or kappa opioid ligands. Further analysis of the NCI-H69 cells demonstrated that specific (naloxone-insensitive) binding was dependent on receptor concentration, reversible, sensitive to sodium ion, but insensitive to the GTP analogue, Gpp(NH)p. These results suggest a role for naloxone-insensitive beta-endorphin in modulating SCLC metabolism.

Ectopic cushing's syndrome caused by an 8 mm lung carcinoid localized by scintigram with the somatostatin analog111in-pentetreotide

Small tumors producing adrenocorticophic hormone (ACTH) ectopically may be very difficult to locate. We describe a 57-year-old woman who presented with ectopic Cushing's syndrome as diagnosed by bilateral inferior petrosal sinus catheterization with corticotrophin-releasing hormone (CRH) test. Thoracic pentetreotide (a somatostatin analogue) revealed a small "hot spot" in the base of the left lung. This "hot spot" was constant throughout the procedure. A second thoracic CT scan with 3-mm cuts showed a small image in the area under suspicion, similar to vascular images found elsewhere in both lungs. At surgery, an 8-mm tumor was found and excised. Pathological examination revealed a carcinoid tumor immunoreactive for ACTH, beta-endorphin, bombesin, serotonin, and the α-subunit. One month after surgery, the patient was clinically well and had normal adrenal function. An¹¹¹ln-pentetreotide scintiscan clearly identified a small ACTH-producing neuroendocrine tumor of the lung undetectable by plain chest radiography or CT scan.

Serological tumor markers for small cell lung cancer and their therapeutic implications

Serological tumor markers may become widely used as inexpensive and non-invasive methods of cancer detection. Markers of current interest for small cell lung cancer (SCLC) comprise enzymes, peptides, proteins, and carbohydrates. None of the serological markers for SCLC have yet proven to be of diagnostic value and at present their use is limited to monitoring disease and indicating prognosis. However, whilst serological markers related to the metabolic state of SCLC cells, such as neuron-specific enolase, serum thymidine kinase and tissue polypeptide antigen, may only be used for monitoring patients and for estimating prognosis, the other serological markers under current investigation may be used to indicate new treatment forms. Several novel approaches, including interference in the autocrine growth-regulating loop of SCLC by either peptides or antibodies, have been tried, SCLC is a highly heterogeneous tumor with respect to antigen expression, regulation of growth, and differentiation state. It is therefore important that new interventions are directed against both antigen-positive and antigen-negative tumor cells. For instance, radioisotopes or enzymes coupled to antibodies may be effective by exerting toxicity at some distance from the target. Antigens expressed on SCLC cells, such as peptide receptors involved in growth regulation, carbohydrate antigens like Lewis antigens, carcinoembryonic antigen and the ganglioside fucosylGM1, provide potential targets for antibody-conjugated therapy.

A novel hypothesis: specific oncogenes and tumor suppression genes are involved in the expression of the proopiomelanocortin gene by small cell lung cancer

The endogenous opioid beta-endorphin, a derivative of proopiomelanocortin, stimulates the growth of cloned human small cell lung carcinoma. The present hypothesis states that mutations of the retinoblastoma gene (a tumor suppressor gene) associated to the malignant transformation of bronchial cells would trigger a cascade of biomolecular events leading to 'de novo' proopiomelanocortin expression in small cell lung carcinoma.

Neurotensin is an autocrine trophic factor stimulated by androgen withdrawal in human prostate cancer

After therapeutic hormone deprivation, prostate cancer cells often develop androgen-insensitive growth through mechanisms thus far undefined. Neuropeptides have been previously implicated as growth factors in some prostate cancers. Here, we demonstrate that androgen-sensitive LNCaP human prostate cancer cells produce and secrete neurotensin following androgen withdrawal. We show that while LNCaP cells express the neurotensin receptor, only androgen-deprived cells exhibit a growth response to exogenous neurotensin. We further demonstrate that androgen-stimulated cells may be refractory to exogenous neurotensin due to androgen induction of a metalloprotease active toward neurotensin. Thus, prostate cancer cells deprived of androgen develop an alternative autocrine growth mechanism involving neurotensin.

Protease inhibitors suppress in vitro growth of human small cell lung cancer

The effect of the protease inhibitors Bowman Birk inhibitor (BBI) and aprotinin on the in vitro clonal growth of two human small cell lung cancer (SCLC) cell lines was investigated. In addition, the effect of BBI on the growth factor processing of proGRP by SCLC cells and on mRNA levels for prohormone convertase 1 and 2 (PC1 and PC2) in SCLC cells was examined. The protease inhibitors BBI and aprotinin significantly decreased growth in both SCLC cell lines studied. In NCI-H345 cells, BBI appears to inhibit the processing of proGRP to GRP, as indicated by Western blot analysis. NCI-H345 cells, when treated with BBI (100 micrograms/ml), also showed highly significant decreases of mRNA for PC1 and PC2 of about 50%. These data suggest that proteases serve an important role in the growth regulation of SCLC and that inhibitors of these proteases may be potent suppressors of SCLC growth at the level of the gene.

The cellular and molecular basis of the ectopic ACTH syndrome

In recent years the techniques of molecular and cellular biology have made it possible to begin to dissect the origins and behaviour of the ACTH-secreting tumour cell. It is becoming apparent that these tumours represent undifferentiated neuroendocrine cells, and it may be that their peptide-secreting properties may have no more sinister oncological significance. However, an autocrine role for beta-endorphin may confer a selective growth advantage on the POMC-expressing cell. It is still not clear why glucocorticoids fail to inhibit the POMC gene in these extra-pituitary tumours despite the presence of glucocorticoid receptors. This may not be resolved until the mechanism for inhibition of POMC by glucocorticoids in the normal pituitary is understood, although it is tempting to speculate that a mutation in the glucocorticoid receptor or a tissue specific interaction is responsible for the resistance of POMC observed in the ectopic ACTH syndrome. In studying the peptides secreted by the extra-pituitary tumours responsible for the ectopic ACTH syndrome it would appear that direct measurement of ACTH precursors and comparison with the circulating concentrations of ACTH can give valuable information on the percentage of tumours which do not effectively process the ACTH precursors. However, far more data have to be collected on patients with occult tumours in order to identify whether this type of processing is tissue specific. Nevertheless, these studies provide useful insights into the mechanisms of intracellular signalling and regulation in such tumours which may identify unique pharmacological tools to inhibit ACTH secretion or more importantly tumour growth.

Neurotensin regulates growth of human pancreatic cancer

OBJECTIVE

The effect of neurotensin (NT) on in vitro-growth of human pancreatic cancer cells (MIA PaCa-2) was examined. Furthermore, the intracellular signal-transduction pathways by which neurotensin regulates growth of MIA PaCa-2 cells were determined.

SUMMARY BACKGROUND DATA

NT is trophic for normal rat pancreas, but the effect of NT on growth of human pancreatic cancer is not known.

METHODS

Effects of NT (10(-12) to 10(-6) mol/l) on growth of MIA PaCa-2 cells were determined by both count of cell numbers and 3H-thymidine incorporation. Action of NT on phosphatidylinositol (PI) hydrolysis, cyclic AMP production, and intracellular calcium level were determined by conventional methods. The effects of 8-bromo-cyclic AMP and prostaglandin E2 on cell growth were determined.

RESULTS

Low concentrations of NT (10(-12) to 10(-9) mol/l) stimulated growth in a dose-dependent manner, but higher concentrations of NT (10(-8) to 10(-6) mol/l) did not stimulate growth of MIA PaCa-2 cells. NT (10(-12) to 10(-6) mol/l) stimulated PI hydrolysis and increased intracellular calcium levels in a dose-dependent manner. High concentrations of NT (10(-8) to 10(-6) mol/l) stimulated production of cyclic AMP in a dose-dependent manner. 8-bromo-cyclic AMP inhibited growth of MIA PaCa-2 cells; prostaglandin E2 did not affect growth of MIA PaCa-2 cells.

CONCLUSIONS

NT stimulates growth of MIA PaCa-2 cells through stimulation of PI hydrolysis and mobilization of calcium. Stimulation of the cyclic AMP pathway by high concentrations of NT abolishes the growth-stimulatory effect of NT that is mediated through PI hydrolysis or calcium mobilization.

Growth factor and peptide receptors in small cell lung cancer

In the past decade, over 1000 continuous human cell lines have been established from lung cancer biopsy specimens. Numerous growth factors and receptors have been identified in the small cell lung cancer (SCLC) cell lines. SCLC is a neuroendocrine tumor which contains numerous peptides, including bombesin/gastrin releasing peptide (BN/GRP), and receptors. High levels of GRP mRNA and immunoreactivity are present in SCLC cells. The secretion rate of GRP from SCLC cells is increased by vasoactive intestinal peptide (VIP), which elevates the intracellular cAMP. GRP binds to cell surface receptors, elevates cytosolic calcium and stimulates the growth of SCLC cells. Additional SCLC growth factors include insulin-like growth factor I (IGF-I) and transferrin. IGF-I mRNA and protein is present in SCLC. IGF-I binds with high affinity to SCLC cells and stimulates tyrosine kinase activity and growth. Transferrin is also present in SCLC cells. Transferrin binds with high affinity to SCLC cells and stimulates iron transport and growth. Synthetic peptide antagonists and monoclonal antibodies have been identified which disrupt autocrine growth pathways and inhibit SCLC growth.

Neurotensin expression and release in human colon cancers

Neurotensin (NT), a distal gut peptide released by intraluminal fats, is trophic for normal small bowel and colonic mucosa. In addition, NT stimulates growth of certain colon cancers; the mechanism for this effect is not known. The purpose of this study was to determine whether human colon cancers (HCC) (1) express the mRNA for NT/neuromedin N (N), (2) produce NT peptide, and (3) express the mRNA for a functional NT receptor (NTR). RNA was extracted from four HCC cell lines in culture, nine HCC lines established in athymic nude mice, and from six HCC and adjacent normal mucosa from freshly resected operative specimens; the RNA was analyzed for NT/N mRNA by Northern hybridization with a complementary DNA probe. Neurotensin peptide content, NTR expression, and intracellular Ca++ ([Ca++]i) mobilization in response to NT were evaluated in three HCC cell lines (LoVo, HT29, HCT116). Neurotensin/N mRNA transcripts were identified in all four of the HCC cell lines and in one of nine HCC in nude mice. Neurotensin expression was found in two of six freshly resected HCC and in none of the six corresponding samples of normal mucosa. Neurotensin peptide was identified by RIA in LoVo, HT29, and HCT116. In addition, NTR mRNA was found in HT29 and HCT116. Neurotensin stimulated [Ca++]i mobilization in HCT116 (without serum) and in LoVo (with 0.25% serum). These findings demonstrate the presence of NT/N mRNA and NT peptide and the presence of a functional NTR in certain HCC. Neurotensin, a potent trophic factor for normal gut mucosa, may function as an autocrine growth factor in certain human colon cancers.

Bromocriptine inhibits pro-opiomelanocortin mRNA and ACTH precursor secretion in small cell lung cancer cell lines

We have previously reported that a human small cell lung cancer (SCLC) cell line (COR L103) that expresses the proopiomelanocortin (POMC) gene and secretes ACTH precursor peptides is relatively resistant to glucocorticoid regulation. Using this model, we have now examined alternative regulatory mechanisms of the POMC gene and found that both the mRNA and ACTH precursor peptides were stimulated four- and two-fold, respectively, after 48 h incubation with db-cAMP. Next, we examined the dopamine agonist, bromocriptine, which acts predominantly through D2 receptors linked to adenyl cyclase to cause a reduction in intracellular cAMP. Bromocriptine suppressed cAMP levels and inhibited precursor peptide secretion within 24 h in a dose-dependent manner (0.15-15 microM). At the highest dose, peptide secretion was inhibited from 95 to 53 pmol/mg protein, and POMC mRNA was reduced by 50%, while beta-actin mRNA remained unchanged. This effect could not be mimicked by incubation of cells with the alpha-adrenergic antagonist, phenoxybenzamine, suggesting that the alpha-adrenergic effects of bromocriptine were not responsible for this observation. These cells also secrete estradiol, but the secretory rate was unaffected by bromocriptine, suggesting, with the beta-actin data, that the POMC inhibition was not a cytotoxic effect. No recovery in precursor peptide secretion was seen in a 48-h period after the removal of bromocriptine. However, when the postchallenge incubation was extended to 8 d, there was a recovery in secretory potential between day 3 and day 8 and normal growth kinetics in the 4 d after removal of the drug. In contrast to these findings, the mouse corticotroph cell line, AtT20, showed no response to bromocriptine, in keeping with reports that this agonist has no effect on anterior lobe corticotrophs. We conclude that bromocriptine effectively inhibits POMC expression in SCLC cells, and that this phenomenon might be of useful clinical application.

Ontogenesis and binding properties of high-affinity neurotensin receptors in human brain

The ontogenesis of neurotensin binding sites was studied in human brain of subjects deceased from Sudden Infant Death Syndrome. Monoiodo-Tyr3 neurotensin specifically recognized 2 distinct classes of binding sites in human brain homogenate. The high affinity sites were already present at birth and increased to a maximal level of 240 fmol/mg protein 1 month after birth. Thereafter, the density of these sites decreased to reach a value of 8 fmol/mg protein in 15-month-old brain, a value similar to that found in adult brain. The dissociation constant of the high-affinity sites (about 0.3 nM) did not vary from birth to adulthood. The high-affinity binding sites were sensitive to GTP which decreased their affinity for neurotensin by a factor of 3, indicating that these sites are functional receptors coupled to GTP-binding proteins. By contrast, the low-affinity sites were insensitive to GTP and could be partly blocked by the antihistaminic drug levocabastine. These sites were absent in human brain during the first post-natal year and could be detected only in brain homogenate of 15-month-old infants. The transient increase in high-affinity neurotensin binding sites after birth suggests that neurotensin could act as a regulatory peptide during brain development.

Neurotensin stimulates growth of colon cancer

Neurotensin (NT), a peptide from the distal gut that is released by fat ingestion, stimulates the growth of normal small bowel and colonic mucosa. The purpose of this study was to determine whether chronic administration of NT would affect the growth of a mouse colon cancer (MC-26) and a human colon cancer (LoVo) in vivo. In experiment 1, male Balb/c mice were inoculated with MC-26 cells (5 x 10(4)) and then randomized to four treatment groups receiving either saline (control) or NT (150, 300 or 600 micrograms kg-1) administered subcutaneously (s.c.) every 8 h for 21 days. In experiment 2, 60 mice with MC-26 tumours were randomized to receive saline (control) or NT (300 or 600 micrograms kg-1) for 28 days, and survival was then assessed. In experiment 3, 16 athymic nude mice with LoVo tumour xenografts were randomized to receive either saline (control) or NT (600 micrograms kg-1). We found that administration of NT (300 and 600 micrograms kg-1) significantly stimulated mean tumour area, weight and DNA, RNA and protein content of MC-26 tumours. In addition, the survival rate of mice bearing MC-26 tumours and treated with either dose of NT was significantly decreased compared with the control group given saline injections. Similarly, NT (600 micrograms kg-1) stimulated growth (tumour area, weight and nucleic acid contents) of the human colon cancer, LoVo. We conclude that NT acts as a tropic factor for the colon cancer cell lines MC-26 and LoVo in vivo. NT may play an important role in growth regulation of certain colon cancers.

Expression of neurotensin messenger RNA in a human carcinoid tumor

Neurotensin (NT), a distal gut peptide, has important regulatory and trophic effects throughout the gut; however the intracellular mechanisms that regulate the gene expression and release of human NT are not known. The purpose of this endeavor was to study a functioning human pancreatic carcinoid cell line (called BON) in vitro that expresses the NT gene, and to study the effect of the cyclic adenosine monophosphate (cAMP) signal-transduction pathway on the expression and release of human NT. RNA was prepared from BON cell line (which has been established in this laboratory); the RNA was analyzed for NT mRNA expression by Northern hybridization with a complementary DNA probe. RNA blot analysis demonstrated that the NT gene is expressed in BON and is transcribed to two mRNAs of 1.0- and 1.5-kb sizes. In the second part of this study, BON cells were treated with either forskolin (FSK), which increases intracellular levels of cAMP, or with serotonin (5-HT), which reduces cAMP in BON cells. Forskolin produced a dose-dependent increase in NT peptide release and, furthermore, FSK (10(-6) mol/L) rapidly increased NT mRNA abundance 1 hour after addition; conversely, 5-HT (10(-5) mol/L) decreased NT mRNA at 1 hour. Neurotensin mRNA levels returned to control values by 3 hours after either FSK or 5-HT, which suggests that the transcript half-life for NT is relatively short. These findings show that the expression and peptide release of human NT is mediated, in part, by the cAMP signal-transduction pathway. Our human carcinoid cell line will provide a useful model to study the in vitro regulation of NT gene expression and peptide release.

Neurotensin may function as a regulatory peptide in small cell lung cancer

Neurotensin (NT) has been postulated to act as a modulatory agent in the central nervous system. Besides its presence in mammalian brain, NT is produced by small cell carcinoma of the lung (SCLC) and cell lines derived from these tumors. Receptors have also been characterized in some SCLC cell lines leading to the suggestion that NT could regulate the growth of SCLC in an autocrine fashion similar to bombesin/GRP. Previously, we had reported that a 10 nM dose of NT and NT(8-13), but not NT(1-8), elevated cytosolic Ca2+, indicating that SCLC NT receptors may use Ca2+ as a second messenger. Using intact SCLC cells we report that time-course incubations with NT lead to the formation of the amino-terminal fragment NT(1-8) and small amounts of the C-terminal fragment NT(9-13). These fragments are formed by metalloendopeptidase 3.4.24.15 cleaving enzyme at the Arg8-Arg9 bond of NT. Significant levels of soluble 3.4.24.15 (10-17 nmoles/mg Pr-/min) are present in SCLC cell lines. Using the in vitro clonogenic assay we tested the effect of 0.5, 5.0 and 10.0 nM doses of NT, NT(1-8) and NT(8-13) on SCLC clonal growth. NT and the C-terminal fragment NT(8-13) stimulated colony formation whereas the N-terminal fragment did not. In summary, NT may function as a regulatory peptide in SCLC through the formation of peptide fragments.

Neurotensin high affinity binding sites and endopeptidase 24.11 are present respectively in the meningothelial and in the fibroblastic components of human meningiomas

The presence of neurotensin receptors and endopeptidase 24.11 (E-24.11) in 16 human meningioma specimens, obtained at surgery, was assessed by measuring the binding of 125I-[tyrosyl3]neurotensin(1-13) (125I-NT) and the inhibitor 3H-N(2RS)-3-hydroxyaminocarbonyl-2-benzyl-1-oxopropyl)glycine (3H-HACBO-Gly), for the receptor and enzyme, respectively. E-24.11 activity was also measured. Autoradiography, on the 16 meningiomas, showed that specific 125I-NT labeling (nonspecific labeling was assessed in the presence of excess NT) was exclusively located in the meningothelial regions. In contrast, specific 3H-HACBO-Gly labeling (nonspecific labeling was assessed in the presence of an excess of the E-24.11 inhibitor thiorphan) was exclusively found in fibroblastic regions. No specific labeling of either ligand was found on collagen or blood vessels. In vitro binding assays were performed on membranes of 10 of the 16 meningiomas. In the 4 meningiomas rich in meningothelial cells, 125I-NT specifically bound to one population of sites with Bmax ranging from 57 to 405 fmol/mg protein and Kd around 0.3 nM. These sites share common properties with the brain NT receptor, since the carboxy terminal acetyl NT(8-13) fragment bound to the same sites but with a higher affinity. The carboxy terminal analogue of NT, neuromedin N, also bound to the same sites with a 10-fold lower affinity and the sites were bradykinin and levocabastine insensitive. In the 4 meningiomas rich in fibroblastic cells, 3H-HACBO-Gly specifically bound to one population of sites with Bmax ranging from 251 to 739 fmol/mg protein and Kd around 2.8 nM.(ABSTRACT TRUNCATED AT 250 WORDS)

CCK antagonists interact with CCK-B receptors on human small cell lung cancer cells

The ability of cholecystokinin (CCK) receptor antagonists to interact with CCK receptors in small cell lung cancer (SCLC) cells was investigated. L-365,260, CCK-8, L-364,718, CBZ-CCK(27-32)-NH2 and proglumide analogue 10 inhibited specific 125I-CCK-8 binding to SCLC cells with IC50 values of 0.2, 2, 500, 100,000 and 500,000 nM, respectively. Gastrin-I and CCK-8 elevated the cytosolic Ca2+ when SCLC cells were loaded with Fura 2-AM. L-365,260 inhibited the cytosolic Ca2+ increase caused by 10 nM CCK-8 in a dose-dependent manner. The effects of 10 nM L-365,260 were reversed by high concentrations of CCK-8. These data indicate that L-365,260 functions as a reversible CCK-8 antagonist using SCLC cells.

Cholecystokinin elevates cytosolic calcium in small cell lung cancer cells

The ability of cholecystokinin (CCK) to elevate intracellular Ca2+ levels in small cell lung cancer cells was investigated using the fluorescent Ca2+ indicator Fura 2. CCK-8 elevated the cytosolic Ca2+ levels in cell line NCI-H345 in a dose dependent manner. Nanomolar concentration of CCK-8 elevated cytosolic Ca2+ levels in the absence or presence of extracellular Ca2+. Potent CCK agonists such as gastrin-1 and nonsulfated CCK-8 but not inactive compounds such as CCK-27-32-NH2 elevated cytosolic Ca2+ levels. These data suggest that CCK receptors may regulate the release of Ca2+ from intracellular organelles in small cell lung cancer cells.

The effect of mycoplasma on the autocrine stimulation of human small cell lung cancer in vitro by bombesin and beta-endorphin

The tumor stem cell clonogenic assay was utilized to investigate the autocrine growth response of small cell lung cancer (SCLC) to bombesin (BN) and beta-endorphin (beta-E). Mycoplasma contamination was detected in the human SCLC cell line NCl-H345 by a nucleic acid hybridization assay which detects mycoplasma ribosomal RNA. Clonogenic assays of mycoplasma (+) cells were compared to assays of the same cell line following treatment for mycoplasma. Concentrations of beta-E ranging from 0.1nM to 25nM or BN (0.1nM-100nM) were added to cells, media and agarose and applied to prepared base layers. Following incubation for 12-14 days at 37 degrees C, the degree of clonal growth stimulation was determined by colony counts greater than or equal to 42 mu. The non-infected cell population grew in the presence of 25nM BN up to 69% over control growth. The infected cells, however, did not grow more than 27% above control. In the presence of 10nM beta-E, colony counts of non-infected cells exceeded the control values by up to 187% whereas the mycoplasma (+) colonies did not grow more than 20% over the control values. These results indicate a marked reduction in the response of SCLC cell lines to the peptides BN and beta-E when infected with mycoplasma. Since infecting mycoplasma typically adhere to cellular membranes, these adherent mycoplasma may interfere with membrane receptors or alter signal transduction, thus, inhibiting the development of the autocrine response.