Substance P-related antagonists inhibit vasopressin and bombesin but not 5'-3-O-(thio)triphosphate-stimulated inositol phosphate production in Swiss 3T3 cells

Biological evaluation and molecular docking studies of AA3052, a compound containing a μ-selective opioid peptide agonist DALDA and d-Phe-Phe-d-Phe-Leu-Leu-NH2, a substance P analogue

The design of novel drugs for pain relief with improved analgesic properties and diminished side effect induction profile still remains a challenging pursuit. Tolerance is one of the most burdensome phenomena that may hamper ongoing opioid therapy, especially in chronic pain patients. Therefore, a promising strategy of hybridizing two pharmacophores that target distinct binding sites involved in pain modulation and transmission was established. Previous studies have led to the development of opioid agonist/NK1 agonist hybrids that produce sufficient analgesia and also suppress opioid-induced tolerance development. In our present investigation we assessed the antinociceptive potency of a new AA3052 chimera comprised of a potent MOR selective dermorphin derivative (DALDA) and an NK1 agonist, a stabilized substance P analogue. We have shown that AA3052 significantly prolonged responses to both mechanical and noxious thermal stimuli in rats after intracerebroventricular administration. Additionally, AA3052 did not trigger the development of tolerance in a 6-day daily injection paradigm nor did it produce any sedative effects, as assessed in the rotarod performance test. However, the antinociceptive effect of AA3052 was independent of opioid receptor stimulation by the DALDA pharmacophore as shown in the agonist-stimulated G-protein assay. Altogether the current results confirm the antinociceptive effectiveness of a novel opioid/SP hybrid agonist, AA3052, and more importantly its ability to inhibit the development of tolerance.

The lipid-associated 3D structure of SPA, a broad-spectrum neuropeptide antagonist with anticancer properties

[D-Arg(1), D-Trp(5,7,9), Leu(11)] substance P (SPA) belongs to a family of peptides including antagonist G and SpD that act as broad-spectrum neuropeptide antagonists at several peripheral receptors. The lipid-induced structure of these peptides may be important for the receptor interactions of these analogs. Thus we describe the tertiary structure of SPA in the presence of sodium dodecylsulfate micelles at pH 5.0, and 25 degrees C as determined from two-dimensional (1)H-NMR data recorded at 500 MHz. The resulting three-dimensional structure can be generally described as two type IV nonstandard turns around Arg(1)*, Pro(2), Lys(3), and Pro(4) and Gln(6), Trp(7)*, Phe(8), and Trp(9)* residues, respectively, inserted into the interfacial region of the micelles (the asterisks denote D-form amino acid). These turns juxtapose the N- and C-termini of SPA and may form the basis of this peptide's unique ability to inhibit peptide receptor interactions at multiple receptor types.

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

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

Antagonist G-mediated targeting and cytotoxicity of liposomal doxorubicin in NCI-H82 variant small cell lung cancer

The aim of the present study was to characterize the interactions of antagonist G (H-Arg-D-Trp-N(me)Phe-D-Trp-Leu-Met-NH 2)-targeted sterically stabilized liposomes with the human variant small cell lung cancer (SCLC) H82 cell line and to evaluate the antiproliferative activity of encapsulated doxorubicin against this cell line. Variant SCLC tumors are known to be more resistant to chemotherapy than classic SCLC tumors. The cellular association of antagonist G-targeted (radiolabeled) liposomes was 20-30-fold higher than that of non-targeted liposomes. Our data suggest that a maximum of 12,000 antagonist G-targeted liposomes were internalized/cell during 1-h incubation at 37 masculine C. Confocal microscopy experiments using pyranine-containing liposomes further confirmed that receptor-mediated endocytosis occurred, specifically in the case of targeted liposomes. In any of the previously mentioned experiments, the binding and endocytosis of non-targeted liposomes have revealed to be negligible. The improved cellular association of antagonist G-targeted liposomes, relative to non-targeted liposomes, resulted in an enhanced nuclear delivery (evaluated by fluorimetry) and cytotoxicity of encapsulated doxorubicin for incubation periods as short as 2 h. For an incubation of 2 h, we report IC50 values for targeted and non-targeted liposomes containing doxorubicin of 5.7 +/- 3.7 and higher than 200 micro M doxorubicin, respectively. Based on the present data, we may infer that receptors for antagonist G were present in H82 tumor cells and could mediate the internalization of antagonist G-targeted liposomes and the intracellular delivery of their content. Antagonist G covalently coupled to liposomal drugs may be promising for the treatment of this aggressive and highly heterogeneous disease.

Increased gastrin-releasing peptide (GRP) receptor expression in tumour cells confers sensitivity to [Arg6,D-Trp7,9,NmePhe8]-substance P (6-11)-induced growth inhibition

[Arg(6),D-Trp(7,9),N(me)Phe(8)]-substance P (6-11) (SP-G) is a novel anticancer agent that has recently completed phase I clinical trials. SP-G inhibits mitogenic neuropeptide signal transduction and small cell lung cancer (SCLC) cell growth in vitro and in vivo. Using the SCLC cell line series GLC14, 16 and 19, derived from a single patient during the clinical course of their disease and the development of chemoresistance, it is shown that there was an increase in responsiveness to neuropeptides. This was paralleled by an increased sensitivity to SP-G. In a selected panel of tumour cell lines (SCLC, non-SCLC, ovarian, colorectal and pancreatic), the expression of the mitogenic neuropeptide receptors for vasopressin, gastrin-releasing peptide (GRP), bradykinin and gastrin was examined, and their sensitivity to SP-G tested in vitro and in vivo. The tumour cell lines displayed a range of sensitivity to SP-G (IC(50) values from 10.5 to 119 microM). The expression of the GRP receptor measured by reverse transcriptase-polymerase chain reaction, correlated significantly with growth inhibition by SP-G. Moreover, introduction of the GRP receptor into rat-1A fibroblasts markedly increased their sensitivity to SP-G. The measurement of receptor expression from biopsy samples by polymerase chain reaction could provide a suitable diagnostic test to predict efficacy to SP-G clinically. This strategy would be of potential benefit in neuropeptide receptor-expressing tumours in addition to SCLC, and in tumours that are relatively resistant to conventional chemotherapy.

Targeting Stealth liposomes in a murine model of human small cell lung cancer

Tumor accumulation and therapeutic activity of Stealth liposomes loaded with doxorubicin (DXR) were examined in Balb/c nude mice xenografts inoculated subcutaneously with the human small cell lung cancer (SCLC) cell line, H69. Mice were treated with non-targeted liposomes (SL) or liposomes targeted with antagonist G coupled to the liposome surface (SLG). SLG showed 30-44-fold higher binding to H69 cells harvested from H69 xenografts than SL. At 48 and 72 h post injection, tumor accumulation of [(125)I]tyraminylinulin-containing liposomes was shown to be dependent on liposome size but independent of the presence of the targeting ligand. Maximum tumor uptake of either SLG or SL ranged from 2 to 4% of injected dose/g of tissue. In therapeutic studies, mice received three weekly injections of 3 or 6 mg free DXR/kg or 3 or 10 mg liposomal DXR/kg at initial tumor volumes of either 7 or 33 mm(3). The therapeutic efficacy of DXR-containing SL or SLG was significantly improved over free DXR, but SLG did not improve anti-tumor efficacy relative to SL. Stealth liposomes containing DXR have potential as a therapy against human SCLC tumors.

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

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

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

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

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

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

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

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

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

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

Preclinical studies on the broad-spectrum neuropeptide growth factor antagonist G

1. Antagonist G is a broad-spectrum neuropeptide growth factor antagonist that inhibits the growth of small cell lung cancer (SCLC) cells both in vitro and in vivo. 2. Antagonist G is metabolized in peripheral tissues by a chymotrypsin-like serine carboxypeptidase causing C-terminal deamidation and removal of the methionine residue. 3. The metabolites of Antagonist G retain neuropeptide antagonist properties and are thought to contribute to the parent peptide's antitumor activity. 4. Pharmacokinetic studies following systemic (IP) administration to nude mice revealed that the tissue distribution of Antagonist G is likely to be determined by vascular permeability. 5. Preclinical toxicology studies have been completed, and we have now started a phase I clinical trial.

Processing of [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P in xenograft bearing Nu/Nu mice

[D-Arg1,D-Phe5,D-Trp7,9,Leu11]Substance P is a broad-spectrum neuropeptide growth factor antagonist that has exhibited in vitro activity against a range of human cancer cell lines. The fate of this compound in vivo following i.p. administration at 12 micrograms/g to nu/nu mice bearing the H69 small-cell lung cancer xenograft has been studied. Metabolism was confined to the C-terminus producing [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P acid and [D-Arg1,D-Phe5,D-Trp7,9]substance P(1-10). The peptide had a long half-life in plasma (45.9 min) and became widely distributed among the tissues studied with the highest accumulation observed in the liver (AUC 1102 micrograms/g x min) and the lowest in the brain (5 micrograms/g x min). Uptake into the tumor xenograft was poor (AUC 189 micrograms/g x min); however, uptake into the lungs was much greater (AUC 507 micrograms/g x min), offering encouragement that therapeutic concentrations may be targeted to primary lung tumors.

[D-Arg1,D-Trp5,7,9,Leu11]Substance P coordinately and reversibly inhibits bombesin- and vasopressin-induced signal transduction pathways in Swiss 3T3 cells

The novel substance P (SP) analogue, [D-Arg1,D-Trp5,7,9,Leu11]SP like [D-Arg1,D-Phe5,D-Trp7,9,Leu11]SP inhibited DNA synthesis induced by bombesin, vasopressin, and bradykinin, but did not interfere with the mitogenic response induced by other growth factors or pharmacological agents in Swiss 3T3 cells. [D-Arg1,D-Trp5, 7,9,Leu11]SP reversibly inhibited bombesin-induced DNA synthesis, causing a 6-fold greater rightward shift in the bombesin dose response than [D-Arg1,D-Phe5,D-Trp7,9,Leu11]SP at identical concentrations (10 microM). We found that the new, more potent, SP analogue coordinately and reversibly inhibited bombesin-induced Ca2+ mobilization and protein kinase C (PKC) and mitogen-activated protein (MAP) kinase activation. The dose-response curves for bombesin-induced Ca2+ mobilization and MAP kinase activation were similarly displaced (51- and 40-fold, respectively) by [D-Arg1, D-Trp5,7,9,Leu11]SP. In addition, [D-Arg1,D-Trp5,7,9,Leu11]SP reversibly inhibited bombesin-induced tyrosine phosphorylation of Mr 110,000-130,000 and 70,000-80,000 bands as well as p125 focal adhesion kinase. [D-Arg1,D-Trp5,7,9,Leu11]SP also reversibly and coordinately inhibited vasopressin-induced Ca2+ mobilization, PKC stimulation, MAP kinase activation, tyrosine phosphorylation, and DNA synthesis in Swiss 3T3 cells. Surprisingly, deletion of the terminal Leu of [D-Arg1,D-Phe5,D-Trp7,9,Leu11]SP to yield [D-Arg1, D-Phe5,D-Trp7,9]SP1-10 resulted in a selective loss of inhibitory activity of this analogue against bombesin- but not vasopressin-stimulated DNA synthesis, Ca2+ mobilization, and MAP kinase activation. Collectively, these results suggest that SP analogues act at the receptor level to coordinately and reversibly antagonize bombesin- or vasopressin-induced signal transduction in Swiss 3T3 cells.

Effect of tyrphostin combined with a substance P related antagonist on small cell lung cancer cell growth in vitro

The protein tyrosine kinase inhibitor [(3,4,5,-trihydroxyphenyl)-methylene]-propanedinitrile (tyrphostin) was originally designed to inhibit polypeptide growth factor receptor signalling, but was also found to inhibit neuropeptide stimulated tyrosine phosphorylation and mitogenesis in Swiss 3T3 cells [J Biol Chem 1993, 268, 9548-9554]. Here, we demonstrate that tyrphostin inhibits in vitro colony growth of the H-345 and H-69 small cell lung cancer (SCLC) cell lines stimulated by the neuropeptides, bombesin and bradykinin, respectively. This effect was dose-dependent and, at tyrphostin concentrations above 5 microM, both background and neuropeptide stimulated colony formation were reduced. In liquid culture, tyrphostin inhibited the growth of the H-345 and H-69 SCLC cell lines with an IC50 of 7 microM. Time course experiments in liquid culture revealed that tyrphostin delayed the rate of entry of both SCLC cell lines into rapid phase growth and reduced the number of cells reaching a plateau phase of growth compared with control cells. Furthermore, tyrphostin concentrations at or above 50 microM reduced the number of cells present over time compared with untreated cells. When combined with a substance P (SP) analogue, which inhibits the action of multiple neuropeptides and SCLC cell growth, both in semisolid media and liquid culture, tyrphostin additively inhibited the growth of the H-345 and H-69 SCLC cell lines in liquid culture.