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

Neurokinin-1 Receptor Antagonists as Anticancer Drugs

Background::

Human tumor cells lines and tumor samples overexpress the neurokinin-1 receptor (NK-1R). Substance P (SP), after binding to NK-1Rs, induces tumor cell proliferation, an antiapoptotic effect and promotes angiogenesis and the migration of cancer cells for invasion and metastasis.

Methods: :

In contrast, NK-1R antagonists block the previous pathophysiological actions mediated by SP. These antagonists promote the death of tumor cells by apoptosis. Peptide and non-peptide NK-1R antagonists have been reported.

Results: :

Peptide NK-1R antagonists show chemical modifications of the SP molecule (L-amino acids being replaced by D-amino acids), whereas non-peptide NK-1R antagonists include numerous compounds with different chemical compositions while showing similar stereochemical features (affinity for the NK- 1R). Currently, there are more than 300 NK-1R antagonists.

Conclusion::

In combination therapy with classic cytostatics, NK-1R antagonists have additive or synergic effects and minimize the side-effects of cytostatics. The effect of NK-1R antagonists as broad-spectrum anticancer drugs is reviewed and the use of these antagonists for the treatment of cancer is suggested.

Differential consequences of neurokinin receptor 1 and 2 antagonists in metastatic breast carcinoma cells; Effects independent of Substance P

INTRODUCTION

The biological action of Substance P (SP) is mediated mainly by NK-1 receptors (NK1R) followed by NK2 receptors (NK2R). Aberrant expression of NK1R and NK2R has been identified in various carcinomas. The role of Substance P and its receptors, especially NK2R in cancer progression is not entirely known and there are conflicting results in the literature demonstrating the need for further investigation. In the current study, we examined the effects of SP and antagonists selective for the NK1R and NK2R in breast carcinoma cells metastasize to vital organs.

METHODS

The effects of highly potent and selective non-peptide mouse NK1R and NK2R antagonists RP 67,580 and GR 159897, respectively, as well as SP and SP methyl ester, on both metastatic (4THM, 4TBM, 4TLM, 4T1) and non-metastatic (67NR) breast cancer cells were determined.

RESULTS

NK1R and NK2R were over expressed in metastatic breast cells compared to non-metastatic cells. The NK1R antagonist at a 30 μM dose inhibited cell growth and induced cell death in metastatic cells while enhancing phosphorylation of Akt, the latter response not observed in the non-metastatic 67NR cells. Blocking the action of SP at the NK2R (30 μM antagonist) suppressed cellular proliferation in all the cell lines examined, with a response less prominent than that of the NK1R antagonist. Differently, the NK2R antagonist increased phosphorylation of p38 and enhanced MIP-2 secretion. SP and the SP methyl ester neither altered cell proliferation nor the effects of NK1R and NK2R antagonists in the metastatic cell lines.

CONCLUSIONS

Increased sensitivity of metastatic breast carcinoma cells to NK1R and NK2R antagonists suggest potential therapeutic value of antagonists in metastatic disease. NK1R and NK2R in metastatic breast carcinoma cells react differently to agonists and antagonists. These findings together with previously published data demonstrate that differential consequences of receptor antagonists and SP may inhibit breast cancer growth and metastasis.

Critical role of G(alpha)12 and G(alpha)13 for human small cell lung cancer cell proliferation in vitro and tumor growth in vivo

PURPOSE

In small cell lung cancer cells (SCLC), various autocrine stimuli lead to the parallel activation of G(q/11) and G(12/13) proteins. Although the contribution of the G(q/11)-phospholipase C-beta cascade to mitogenic effects in SCLC cells is well established, the relevance of G(12/13) signaling is still elusive. In other tumor entities, G(12/13) activation promotes invasiveness without affecting cellular proliferation. Here, we investigate the role of G(12/13)-dependent signaling in SCLC.

EXPERIMENTAL DESIGN

We used small hairpin RNA-mediated targeting of G(alpha)(12), G(alpha)(13), or both in H69 and H209 cells and analyzed the effects of G(alpha)(12) and/or G(alpha)(13) knockdown on tumor cells in vitro, tumor growth in vivo, and mitogen-activated protein kinase (MAPK) activation.

RESULTS

Lentiviral expression of small hairpin RNAs resulted in robust and specific G(alpha)(12) and G(alpha)(13) knockdown as well as markedly inhibited proliferation, colony formation, and bradykinin-promoted stimulation of cell growth. Analyzing the activation status of all three major MAPK families revealed nonredundant functions of G(alpha)(12) and G(alpha)(13) in SCLC and a marked p42/p44 activation upon G(alpha)(12)/G(alpha)(13) knockdown. In a s.c. tumor xenograft mouse model, G(alpha)(12) or G(alpha)(13) downregulation led to decreased tumor growth due to reduced tumor cell proliferation. More importantly, G(alpha)(12)/G(alpha)(13) double knockdown completely abolished H69 tumorigenicity in mice.

CONCLUSIONS

G(alpha)(12) and G(alpha)13) exert a complex pattern of nonredundant effects in SCLC, and in contrast to other tumor types, SCLC cell proliferation in vitro and tumorigenicity in vivo critically depend on G(12/13) signaling. Due to the complete abolishment of tumorgenicity in our study, RNAi-mediated double knockdown may provide a promising new avenue in SCLC treatment.

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

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

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.

[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.

Metabolism of the broad-spectrum neuropeptide growth factor antagonist: [D-Arg1, D-Phe5, D-Trp7,9, Leu11]-substance P

Broad-spectrum neuropeptide growth factor antagonists, such as [D-Arg1, D-Phe5, D-Trp7,9, Leu11]substance P (antagonist D) and [Arg6, D-Trp7,9, NmePhe8]substance P(6-11) (antagonist G), are currently being investigated as possible anti-tumour agents. These compounds are hoped to be effective against neuropeptide-driven cancers such as small-cell lung cancer. Antagonist D possesses a broader antagonistic spectrum than antagonist G and hence may be of greater therapeutic use. The in vitro metabolism of antagonist D has been characterised and the structures of two major metabolites have been elucidated by amino acid analysis and mass spectrometry. Metabolism was confined to the C-terminus where serine carboxypeptidase action produced [deamidated]-antagonist D (metabolite 1) and [des-Leu11]-antagonist D (metabolite 2) as the major metabolites. Biological characterisation of the metabolites demonstrated that these relatively minor changes in structure resulted in a loss of antagonist activity. These results provide some of the first structure-activity information on the factors that determine which neuropeptides these compounds inhibit and on the relative potency of that inhibition.

Interaction of substance P with epidermal growth factor and fibroblast growth factor in cyclooxygenase-dependent proliferation of human skin fibroblasts

Substance P (SP), fibroblast growth factor (FGF), and epidermal growth factor (EGF) are mitogens for fibroblasts. EGF acts as a progression factor, whereas FGF and SP have competence factor activity. The ability of eicosanoids to regulate proliferation of fibroblasts and the increased production of prostaglandins by fibroblasts in response to the growth factors, led us to investigate the involvement of cyclooxygenase-dependent arachidonic acid metabolites in the mitogenic response of serum-starved human skin fibroblasts to SP, FGF, and EGF. We tested the interaction of a submaximal concentration of SP(10(-9)M) with baFGF(40 micrograms/ml) and EGF(0.01 microgram/ml) both on fibroblast proliferation and release of arachidonic acid metabolites. A combination of SP and EGF synergistically stimulated fibroblast proliferation and prostaglandin E2 release, whereas addition of SP to FGF-containing cultures did not affect cell growth. Inhibition of cyclooxygenase by acetylsalicylic acid augmented the growth response of fibroblasts to all: SP, FGF, and EGF. In the presence of acetylsalicylic acid, SP combined with FGF enhanced fibroblasts proliferation, whereas a combination with EGF inhibited cellular growth with respect to growth induced by EGF alone. Thus, interactions of SP with FGF and EGF differently affected the mitogenic response depending on the formation of arachidonic acid metabolites. The findings indicate that eicosanoids may be important mediators of competence and progression factor activities that may determine the effects of substance P on fibroblast proliferation in a cytokine network.

Promotion by substance P of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effects of prolonged administration of neuropeptide substance P (SP) on gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and on the labeling index of gastric mucosa were investigated in Wistar rats. Rats received subcutaneous injections of 12 micrograms/kg body weight of SP every other day after 25 weeks of oral treatment with MNNG. Long-term administration of SP significantly increased the incidence of gastric cancers in week 52. However, it did not affect the histological type and depth of involvement of gastric cancers. SP also caused a significant increase in the labeling index of the antral and fundic epithelial cells in week 52. These findings indicate that SP promotes gastric carcinogenesis and suggest that this effect may be related to its stimulation of antral epithelial cell proliferation.

Substance P: a competence factor for human fibroblast proliferation that induces the release of growth-regulatory arachidonic acid metabolites

Substance P (SP) was recognized to stimulate cell growth. The mechanisms of growth control by SP are unknown. We, therefore, investigated mechanisms of the effect of SP on proliferation of human skin fibroblasts. SP did not stimulate proliferation of fibroblasts growth arrested by serum starvation over 48 hours. However, in the presence of acetylsalicylic acid SP potently stimulated fibroblast growth. A bell-shaped dose-response curve with maximal stimulation at picomolar concentrations was found. Specificity of the mitogenic effect was analyzed by use of synthetic SP analogs. Only neurokinin-1 receptor agonists were active, whereas a specific neurokinin-2 receptor analog did not exhibit mitogenicity. Analyzing the supernatants of growth-arrested fibroblasts treated with SP indicated that SP provokes release of the arachidonic acid metabolites, prostaglandin E2, and prostacyclin but not thromboxane B2 or leukotriene B4. Since similar response patterns in proliferation and arachidonic acid metabolite release have been described for several proinflammatory cytokines, some of which are known to act as competence factors in proliferation, we characterized the mitogenic effect of SP. Results established that SP stimulates fibroblast growth in a manner typical of competence factors. We conclude that arachidonic acid metabolites are involved in the cell cycle-dependent mitogenic action of SP on human skin fibroblasts.

[D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P inhibits the growth of human small cell lung cancer xenografts in vivo

We report the effect of substance P analogue, [D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P (D-Phe5SP), on the growth of human small cell lung cancer (SCLC) xenografts HC12 and ICR-SC112. Daily intraperitoneal (ip) administration (500 micrograms/day for 3 weeks) had no effect on HC12 growth rate. When administered by continuous 14-day subcutaneous (sc) infusion by osmotic minipump implanted adjacent to the tumour, D-Phe5SP 2.1 micrograms/day, caused significant inhibition (P < 0.05) of the growth of HC12 and ICR-SC112 on day 7 and day 14 compared with phosphate buffered saline (PBS)-treated controls. HC12 and ICR-SC112 tumour volume remained at 53-67% of control for 14-21 days postinfusion. D-Phe5SP 1 mg/day did not inhibit tumour growth, but dense fibrous capsules developed at the minipump outlet. Animals treated by sc infusion (but not ip) of PBS or D-Phe5SP failed to gain weight, and some groups lost weight. D-Phe5SP-treated animals had lower white blood counts than controls (not significant). These data suggest a potential clinical role for D-Phe5SP in the treatment of SCLC.

Parathyroid hormone-related peptide can regulate the growth of human lung cancer cells, and may form part of an autocrine TGF-alpha loop

Parathyroid hormone-related peptide (PTHrP) and transforming growth factor-alpha (TGF-alpha) were found to stimulate proliferation of human lung cancer cells (BEN-57). TGF-alpha stimulated PTHrP secretion from these cells. The polyclonal antisera raised against PTHrP significantly inhibited the growth of BEN-57 cells, and also the proliferation induced by TGF-alpha. Treatment of cells for up to 10 days with either a PTHrP receptor antagonist (PTHrP(7-34)) or PTHrP antiserum significantly inhibited the subsequent growth of these cells. We suggest that PTHrP may be a component of a complex autocrine loop involving TGF-alpha.