Substance P analogues function as bombesin receptor antagonists and inhibit small cell lung cancer clonal growth

Bombesin receptor-targeted liposomes for enhanced delivery to lung cancer cells

Background: Gastrin-releasing peptide is a member of the bombesin family of peptides. Its cognate receptor, gastrin releasing peptide receptor (GRPR), is widely expressed in cancers of the lung, pancreas and ovaries. Gastrin releasing peptide (GRP) is an autocrine growth factor in small cell lung cancer, which has very poor patient outcomes. High affinity antagonist peptides have been developed for in vivo cancer imaging. In this report we decorated pegylated liposomes with a GRPR antagonist peptide and studied its interaction with, and accumulation within, lung cancer cells. Results: An N-terminally cysteine modified GRPR antagonist (termed cystabn) was synthesised and shown to inhibit cell growth in vitro. Cystabn was used to prepare a targeted 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE-PEG2000) lipid conjugate that was formulated into liposomes. The liposomes displayed desirable colloidal properties and good stability under storage conditions. Flow cytometric and microscopic studies showed that fluorescently labelled cystabn-decorated liposomes accumulated more extensively in GRPR over-expressing cells than matched liposomes that contained no cystabn targeting motif. Conclusion: The use of GRPR antagonistic peptides for nanoparticle targeting has potential for enhancing drug accumulation in resistant cancer cells.

Anticancer activity of BIM-46174, a new inhibitor of the heterotrimeric Galpha/Gbetagamma protein complex

A large number of hormones and local agonists activating guanine-binding protein-coupled receptors (GPCR) play a major role in cancer progression. Here, we characterize the new imidazo-pyrazine derivative BIM-46174, which acts as a selective inhibitor of heterotrimeric G-protein complex. BIM-46174 prevents the heterotrimeric G-protein signaling linked to several GPCRs mediating (a) cyclic AMP generation (Galphas), (b) calcium release (Galphaq), and (c) cancer cell invasion by Wnt-2 frizzled receptors and high-affinity neurotensin receptors (Galphao/i and Galphaq). BIM-46174 inhibits the growth of a large panel of human cancer cell lines, including anticancer drug-resistant cells. Exposure of cancer cells to BIM-46174 leads to caspase-3-dependent apoptosis and poly(ADP-ribose) polymerase cleavage. National Cancer Institute COMPARE analysis for BIM-46174 supports its novel pharmacologic profile compared with 12,000 anticancer agents. The growth rate of human tumor xenografts in athymic mice is significantly reduced after administration of BIM-46174 combined with either cisplatin, farnesyltransferase inhibitor, or topoisomerase inhibitors. Our data validate the feasibility of targeting heterotrimeric G-protein functions downstream the GPCRs to improve anticancer chemotherapy.

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

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

Bombesin-like peptides and associated receptors within the brain: distribution and behavioral implications

As we commemorate the 25th anniversary of the journal Peptides, it is timely to review the functional significance of the bombesin (BB)-like peptides and receptors in the CNS. Over two decades ago we published an article in the journal Peptides demonstrating that BB-like peptides are present in high densities in certain rat brain regions (such as the paraventricular nucleus of the hypothalamus). Subsequently, one of the mammalian forms of BB, gastrin-releasing peptide (GRP) containing cell bodies were found in the suprachiasmatic nucleus of the hypothalamus and nucleus of the solitary tract of the hindbrain. Another related peptide, namely neuromedin (NM)B, was detected in the olfactory bulb and dentate gyrus. BB and GRP bind with high affinity to BB(2) receptors, whereas NMB binds with high affinity to BB(1) receptors. The actions of BB or GRP are blocked by BB(2) receptor antagonists such as (Psi(13,14)-Leu(14))BB whereas PD168368 is a BB(1) receptor antagonist. Exogenous administration of BB into the rat brain causes hypothermia, hyperglycemia, grooming and satiety. BB-like peptides activate the sympathetic nervous system and appear to modulate stress, fear and anxiety responses. GRP and NMB modulate distinct biological processes through discrete brain regions or circuits, and globally these peptidergic systems may serve in an integrative or homeostatic function.

A vasoactive intestinal peptide antagonist inhibits the growth of glioblastoma cells

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

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

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

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

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

Therapeutic advances in small cell lung cancer

Small cell lung cancer (SCLC) is characterised by neuroendocrine differentiation, early metastatic potential and initial responsiveness to cytotoxic therapy. Unfortunately, despite recent therapeutic advances, most patients relapse and the overall five-year survival rate is only 5%. Standard treatment of SCLC consists of platinum-based combination chemotherapy, with thoracic irradiation added for patients with limited-stage disease. Several newer chemotherapeutic drugs have recently been shown to have significant activity in patients with untreated or relapsed SCLC. These agents include: the topoisomerase I inhibitors, topotecan and irinotecan; the taxanes, paclitaxel and docetaxel; the pyrimidine analogue, gemcitabine; and the vinca alkaloid, vinorelbine. Recent advances in our understanding of the molecular events involved in the pathogenesis and progression of SCLC have led to the identification of a variety of potential targets for novel therapeutic interventions. Strategies aimed at inhibiting the myriad of growth factor pathways that control the proliferation of SCLC cells, include: broad spectrum neuropeptide antagonists (e.g., substance P analogues); growth factor/receptor-specific inhibitors (e.g., anti-GRP monoclonal antibodies, bradykinin antagonist dimers); and a variety of selective protein kinase inhibitors. The importance of cell death pathways in carcinogenesis and treatment-resistance has led to several novel strategies targeting apoptotic mediators, such as bcl-2, that are frequently dysregulated in SCLC (e.g., bcl-2 antisense). Our current challenges are to further refine these promising therapeutic strategies, efficiently evaluate their activity in the clinical setting and integrate them into more effective treatment regimens to improve the overall prognosis of patients with SCLC.

Synthesis of peptide and pseudopeptide amides inhibiting the proliferation of small cell and epithelial types of lung carcinoma cells

Small cell lung cancer (SCLC) cell lines produce and secrete various peptide hormones, e.g. bombesin (BN)/gastrin releasing peptide (GRP) like peptides that are proposed to function as their autocrine growth factors. To inhibit the proliferative effect of these hormones we have synthesized short chain BN[7-14]-analogues replacing the C-terminal peptide bond by a methylene-amino (-CH2NH-) unit and introducing D-Phe or D-Ser into position 12. As several substance P (SP) analogues were found to inhibit the growth of SCLC cells, some short chain SP-analogues have been synthesized. (Pseudo)octapeptides were synthesized in solution, by fragment condensation using the DCC/HOPfp method. Fragments and SP-analogues were synthesized stepwise using pentafluorophenyl esters. The resistance to hydrolysis of the reduced peptide bond made permitted exact quantification of the Leupsi(CH2NH)Leu pseudopeptide in hydrolysates. The binding ability of both types of peptides to BN-receptors on Swiss 3T3 mouse fibroblast cells and their antiproliferative effect on NCI-H69 human SCLC cell line have been tested and compared with a short chain SP-antagonist pHOPA-D-Trp-Phe-D-Trp-Leu-Leu-NH2 (R) previously described as a potent inhibitor of SCLC proliferation. While BN-analogues showed weak activity in inhibition of proliferation of SCLC cells, SP-analogues 6: D-MePhe-D-Trp-Phe-D-Trp-Leu(psi)(CH2NH)-Leu-NH2 and 7: D-MePhe-DTrp-Phe-D-Trp-Leu-MPA, in spite of greatly diminished affinity towards the BN-receptor, inhibited SCLC proliferation more effectively than R (6: IC50 = 2 microM, 7: IC50 = 5 microM and R: IC50 = 10 microM). Moreover, 6 inhibited the respiratory activity of SK-MES 1 epithelial type of lung carcinoma cells in proliferating but not in the quiescent state, suggesting that the antiproliferative effect of these compounds is not due to simple cytotoxicity. These short chain analogues of SP might be promising candidates as therapeutic agents in the treatment of SCLC.

Induction of apoptosis by a short-chain neuropeptide analog in small cell lung cancer

Small cell lung cancer (SCLC) cells express a variety of neuropeptides which act as autocrine growth factors. Although several neuropeptide analogs have been reported to antagonize SCLC proliferation, the development of these compounds has been limited by their low potency and the cytostatic nature of their effects. In the present study we evaluated the cytotoxic activity of four short-chain substance P analogs (NY3460, NY3238[-pHOPA], NY3238[Phe1], NY3238[Lys5]) against a panel of five SCLC cell lines. NY3460 was the most potent compound in all five SCLC cell lines (IC50 = 2.8-3.7 microM) as assessed by a MTT growth inhibitory assay. NY3238[Phe1] was also relatively active in all cell lines (IC50 = 3.5-11.2 microM), while NY3238[Lys5] and NY3238[-pHOPA] were substantially less active. NY3460 was the only agent to induce an increase in the percentage of cells with subdiploid DNA content suggestive of apoptosis by flow cytometric DNA content analysis. The induction of apoptosis was confirmed by fluorescent microscopy in NCI-H69, NCI-H82, NCI-H446, and NCI-H510 cells after exposure to 5.0 microM NY3460 for 48 h. These findings suggest that NY3460 is a relatively potent cytotoxic inhibitor of SCLC growth, and that short-chain neuropeptide analogs deserve further evaluation as anti-SCLC agents.

BW 1023U90: a new GRP receptor antagonist for small-cell lung cancer cells

Gastrin-releasing peptide (GRP) receptor antagonists were synthesized and their ability to interact with small-cell lung cancer (SCLC) cells determined. [125I] BW1023U90, bound with high affinity (Kd = 2 nM) to a single class of sites (Bmax = 55 fmol/mg protein) using SCLC cell line NCI-H345. [125I] BW1023U90 binding was time dependent and reversible even at 37 degrees C as the ligand was minimally internalized. Specific [125I] BW1023U90 binding was inhibited with high affinity by GRP as well as bombesin (BB) but not neuromedin B (NMB). BW1023U90 inhibited the ability of BB to elevate cytosolic Ca2+ and increase the growth of SCLC cells. A BW1023U90 analogue, BW2258U89 (10 micrograms/day, SC) slowed SCLC xenograft format on in nude mice and [125I] BW 1023U90 localized to SCLC tumors 1 h after injection into nude mice. BW2258U89 (4% by weight) was placed in microspheres and slowly released over a 3-week period in nude mice bearing SCLC xenografts. The microspheres containing BW2258U89 strongly inhibited SCLC growth in vivo. A radioimmunoassay was developed for the GRP receptor antagonists and the rabbit antiserum cross-reacted totally with BW2258U89 or BW1023U90. BW2258U89 immunoreactivity (5 nM) was detected in the plasma of nude mice containing the microspheres after 1 week. These data suggest that GRP receptor antagonists bind to receptors on SCLC tumors.

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.

New short-chain analogs of a substance-P antagonist inhibit proliferation of human small-cell lung-cancer cells in vitro and in vivo

Human small-cell lung-cancer cells (SCLC) produce and secrete gastrin-releasing peptide (GRP), the mammalian equivalent of bombesin (BN). There is some evidence to suggest that GRP is an autocrine regulator of SCLC cell growth. In the search for potent BN antagonists, several substance-P (SP) analogs were found to inhibit the growth of SCLC cells. We found that a known short-chain SP antagonist, pHOPA-DTrp-Phe-DTrp-Leu-Leu-NH2(NY3238), inhibits the binding of 125I-Tyr4-BN on Swiss 3T3 cell line expressing BN receptors, as well as the proliferation of NCI-H69 SCLC cells. In this study we tested several analogs of NY3238 and we found that NY3521 and NY3460 are more effective in inhibition of proliferation of SCLC cells but less potent in inhibition of binding of 125I-Tyr4-BN on Swiss 3T3 cells than NY3238. Furthermore, we detected specific binding of radiolabelled NY3238 even below 1 nM on NCI-H69 cells that could have been inhibited by SP and NY3460 rather than by BN. In addition to these in vitro studies, NY3460 proved to be effective in inhibiting the growth of NCI-H69 SCLC xenografts in nude mice in vivo. These analogs of NY3238 could be promising therapeutic agents in the treatment of SCLC.

Inhibitory cyclic analogues and chlorambucil derivatives of bombesin-like peptides

Analogues of the amphibian neuropeptide, bombesin, and of the mammalian homologue, gastrin-releasing peptide, have been synthesized and their biological activity studied in small cell lung carcinoma and rat pancreatic acinar cells. The compounds are truncated sequences of the active tetradecapeptide BN(1-14) or GRP(20-27). Peptides were cyclized between position 5 or 7 and the carboxyl end of the des-Met14 fragment with D and L Ala11 and Lys5 substitutions, as well as various N-terminal groups attached. The smallest cyclic peptide, BN(7-13), bound to SCLC membranes with microM potency and inhibited BN stimulation of intracellular Ca++ levels. The most potent inhibitor is N-chloroambucil-[His7,D-Ala11]BN(7-13)ethyl ester, which antagonized BN function in SCLC and acinar cells with nM potency and also inhibited clonal growth of carcinoma cell lines.

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.

Growth-regulatory effects of sensory neuropeptides, epidermal growth factor, insulin, and somatostatin on the non-transformed intestinal epithelial cell line IEC-6 and the colon cancer cell line HT 29

A non-transformed small-intestinal cell line from the rat (IEC-6) and a human colon cancer cell line (HT 29) were examined for their trophic response to sensory neuropeptides. Substance P, neurokinin A (NKA), calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP), and peptide YY (PYY) were tested. Epidermal growth factor (EGF), insulin, and somatostatin-14 were also used. Interaction studies were performed on IEC-6 cells by combining EGF or insulin with somatostatin-14. The sensory neuropeptides had no effect either on IEC-6 cell growth and DNA synthesis or on HT29 cell growth. EGF and insulin stimulated cell growth and DNA synthesis in IEC-6 cells and cell growth in HT 29 cells in a dose-dependent fashion. Somatostatin-14 had no effect either alone or in combination with EGF or insulin on IEC-6 cell growth and DNA synthesis. HT 29 cell growth was inhibited by somatostatin-14 only in the presence of serum with a maximal and significant response at 10(-7) M. Our observations suggest that the sensory neuropeptides do not exert a direct growth-regulatory effect either on IEC-6 cells or on HT 29 cells. Somatostatin, however, inhibits serum-induced HT 29 cell growth but does not interfere directly with the proliferative effect of serum, EGF, or insulin on IEC-6 cells in this model.

Unexpected effects of peptide and nonpeptide substance P receptor antagonists on basal prolactin and growth hormone release in vitro

The effect of peptide and nonpeptide substance P antagonists on prolactin (PRL) and growth hormone (GH) secretion was evaluated in three-dimensional rat anterior pituitary cell aggregates. [D-Arg1,D-Phe5,D-Trp7,9,Leu11]Substance P inhibited basal growth hormone (GH) release at a concentration range of 1-10 microM. At higher concentrations (50 microM), the analogue inhibited basal prolactin (PRL) release but provoked a tenfold stimulation of GH release. However, these latter two effects could neither be mimicked nor antagonized by the tachykinins substance P (10 microM), neurokinin A (10 microM), and neurokinin B (3.3 microM). The effects could also not be explained by agonism or antagonism at the level of other receptors (e.g., vasopressin, bombesin, angiotensin II, thyroid hormone-releasing hormone, vasoactive intestinal peptide, dopamine, adrenaline, acetylcholine). Remarkably the nonpeptide substance P antagonists R 30732 (10 microM), R 32602 (10 microM), and CP-96,345 (10 microM) showed a similar inhibition of PRL release and a stimulation of GH release. At a one hundredfold lower concentration, sufficient to block substance P receptors in other tissues. CP-96,345 did not affect PRL or GH release. It is concluded that substance P antagonists, when used at high concentrations, have profound intrinsic activities on PRL and GH release that are not mediated by substance P receptors. The failure of the more potent substance P antagonist, CP-96,345, to influence basal PRL or GH release when used at lower concentrations suggests that endogenous substance P in the anterior pituitary does not play a tonic paracrine role on GH or PRL secretion.

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.

In vitro effects of substance P analogue [D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P on human tumour and normal cell growth

Analogues of the neurotransmitter substance P (SP) can interact with neuropeptide receptors, and are reported to inhibit growth of small cell lung cancer cell lines (SCLC CLs). We found [D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P (D-Phe5SP) significantly inhibited DNA synthesis by 10/10 human tumour CLs; six SCLC, one N-SCLC (squamous), two ovarian and one squamous cervical carcinoma, with inhibition to 50% control levels (IC50) of 20-50 microM. There was dose dependent inhibition of colony forming efficiency (CFE) in 3/3 SCLC and 1/1 N-SCLC CL, IC50s of 0.5-6.5 microM in 5% serum. Exposure of SCLC CL HC12 to 100 microM D-Phe5SP for 1-4 h caused a progressive fall in viable cell number; surviving cells, grown in the absence of peptide, showed a decreased growth rate. During 1 week's exposure of two SCLC CLs to 20 microM D-Ph5SP, growth was slower than control cultures, while 50-100 microM completely inhibited growth. These inhibitory effects were partially reversed by increasing serum concentration from 5 to 20%, but not by SP, vasopressin, bombesin or insulin-like growth factor 1. There was some inhibition of CFE by 3/3 normal human bone marrows, IC50s of 30-80 microM, compared with 8 microM for HC12 in 20% FCS. Therefore D-Phe5SP appears to have more potent antiproliferative effects in tumour cells than normal cells, suggesting a role for this analogue in tumour treatment.

Vasopressin elevates cytosolic calcium in small cell lung cancer cells

The ability of vasopressin to elevate cytosolic Ca2+ in small cell lung cancer (SCLC) cells was investigated. Ten nanomolar vasopressin elevated the cytosolic Ca2+ in 6 of 8 SCLC cell lines that were loaded with Fura-2 AM. Using SCLC cell line NCI-H345, the effect of vasopressin was dose dependent, being maximal at 100 nM, where the cytosolic Ca2+ was elevated from 150 to 210 nM. Because addition of 1 mM EGTA had no effect on the vasopressin response, vasopressin released Ca2+ from intracellular pools. Also, oxytocin weakly elevated the cytosolic Ca2+. The response to vasopressin was strongly blocked by [(beta-mercapto-beta,beta-cyclopentamethylene propionic acid)1,O-MeTyr2,Arg8]vasopressin and weakly blocked by [(beta-mercapto-beta,beta-cyclopentamethylene propionic acid)1,O-MeTyr2,Orn8]vasotocin. These data suggest that V1 vasopressin receptors are present on SCLC cells.

Homodimeric forms of bombesin act as potent antagonists of bombesin on Swiss 3T3 cells

Two Lys3-bombesin dimers were prepared by crosslinking epsilon-amino groups Lys3-bombesin with noncleavable (glutaraldehyde) and cleavable [dimethyl-3,3'-dithiobispropionimidate (DTBP)] crosslinkers. The dimers were purified by HPLC ion-exchange chromatography and were shown to have retained immunoreactivity with an anti-bombesin monoclonal antibody directed against the C-terminal binding region of bombesin. The glutaraldehyde cross-linked bombesin dimer specifically inhibited binding of 125I-GRP to its receptor on Swiss 3T3 cells. Bombesin, at 0.6-60 nM induced mitogenesis in quiescent Swiss 3T3 cells, whereas, incubation of cells with the glutaraldehyde bombesin dimer at concentrations up to 124 nM did not. In competition assays, the bombesin dimer exhibited a dose dependent inhibition of bombesin-induced mitogenic activity and intracellular Ca++ mobilization. The bombesin dimer was 100 to 1000-fold more potent than D-Phe12Leu14-bombesin and D-Phe12bombesin, respectively, in inhibiting bombesin-induced mitogenesis on quiescent Swiss 3T3 cells. Similarly, the DTBP-bombesin dimer was not mitogenic to Swiss 3T3 cells, however, cleavage of the disulfide crosslinker with DTT of cell bound DTBP dimer restored mitogenic activity. Finally, the glutaraldehyde bombesin dimer also inhibited growth of bombesin receptor positive H345 SCLC cells in vitro. These findings suggest that the dimeric forms of bombesin are potent antagonists of bombesin.

Growth factors in lung cancer: possible etiologic role and clinical target

Growth factors play an important role in the pathogenesis and progression of all histologic types of lung cancer. Ideas for the exploitation of growth factors in lung cancer management are growing. The inhibition of the interaction between growth factors and their receptors, utilization of negative growth factors, interruption of the signal transduction pathways, or effecting decreased growth factor and/or receptor expression, could result in cell death, and all seem logical possibilities for new and specific treatment approaches. There can be no question that observations of the abnormal expression of growth factors have made a startling impact in every aspect of cancer research. The elucidation of their role in cell proliferation, coupled with our growing knowledge of the functions of oncogenes, has given birth to a unifying concept for the etiology of malignant transformation, which hopefully will translate into new, less toxic, more effective, and desperately needed lung cancer treatment.

[Des-Met14]bombesin analogues function as small cell lung cancer bombesin receptor antagonists

A series of bombesin (BN) analogues lacking the C-terminal methionine at the 14 position were evaluated as BN receptor antagonists. [D-Phe6]BN(6-13)amide inhibited specific 125I-GRP binding to lung cancer cell line NCI-H720 with an IC50 value of 12 nM. In contrast, [D-Phe6]BN(6-13)propylamide, butylamide and methylester were more potent with IC50 values of 3, 5 and 5 nM whereas [D-Phe6,Sta13]BN(6-13)amide was less potent with an IC50 value of 180 nM. [D-Phe6]BN(6-13)propylamide antagonized the ability of BN to elevate cytosolic Ca2+, whereas [D-Phe6]BN(6-13)butylamide was a partial agonist. In a small cell lung cancer (SCLC) growth assay, [D-Phe6]BN(6-13)propylamide inhibited colony formation. In summary, BN analogues which lack a C-terminal methionine may function as useful SCLC BN receptor antagonists.

Inhibitory effect of galanin on basal and pentagastrin-stimulated gastric acid secretion in rats

The dose-dependent effects of galanin on basal and pentagastrin-stimulated gastric acid secretion in pentobarbital-anesthetized rats were examined. Intravenous infusion of galanin at doses of 0.31, 0.62, 1.25, 1.87, 3.11, and 6.22 nmol/kg-1/h-1 into pentagastrin-stimulated rats produced a diminution in gastric acid secretion which was maximal (54.7%) at the level of the 1.87 nmol/kg-1/h-1 dose. Furthermore, the effect was biphasic, since both lower and higher doses of peptide were less effective. At the optimum concentration of 1.87 nmol/kg-1/h-1 galanin also inhibited basal gastric acid secretion. We conclude that endogenous galanin might be involved in the physiologic regulation of gastric acid secretion.

Neurotensin elevates cytosolic calcium in small cell lung cancer cells

The ability of neurotensin (NT) to elevate cytosolic Ca2+ in small cell lung cancer (SCLC) cells was investigated using the fluorescent Ca2+ indicator Fura 2-AM. Using SCLC cell line NCI-H345, NT elevated cytosolic Ca2+ levels in a concentration-dependent manner. Using a 10 nM dose, NT and C-terminal fragments such as NT(8-13) but not N-terminal fragments such as NT(1-8) elevated the cytosolic Ca2+ levels. Because EGTA (5 mM) did not affect the NT response, NT may cause release of Ca2+ from intracellular stores. These data indicate that SCLC NT receptors may use Ca2+ as a second messenger.