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

Novel insight on GRP/GRPR axis in diseases

The gastrin-releasing peptide receptor (GRPR), a member of the G protein-coupled receptors (GPCRs), binds to ligands such as gastrin-releasing peptide (GRP) and plays a variety of biological roles. GRP/GRPR signalling is involved in the pathophysiological processes of many diseases, including inflammatory diseases, cardiovascular diseases, neurological diseases, and various cancers. In the immune system, the unique function of GRP/GRPR in neutrophil chemotaxis suggests that GRPR can be directly stimulated through GRP-mediated neutrophils to activate selective signalling pathways, such as PI3K, PKC, and MAPK, and participate in the occurrence and development of inflammation-related diseases. In the cardiovascular system, GRP increases intercellular adhesion molecule 1 (ICAM-1) and induces vascular cell adhesion molecule-1 (VCAM-1). GRP activates ERK1/2, MAPK, and AKT, leading to cardiovascular diseases, including myocardial infarction. Central nervous system signal transduction mediated by the GRP/GRPR axis plays a vital role in emotional responses, social interaction, and memory. The GRP/GRPR axis is elevated in various cancers, including lung, cervical, colorectal, renal cell, and head and neck squamous cell carcinomas. GRP is a mitogen in a variety of tumour cell lines. Its precursor, pro-gastrin-releasing peptide (ProGRP), may play an important role as an emerging tumour marker in early tumour diagnosis. GPCRs serve as therapeutic targets for drug development, but their function in each disease remains unclear, and their involvement in disease progression has not been well explored or summarised. This review lays out the above mentioned pathophysiological processes based on previous research conclusions. The GRP/GRPR axis may be a potential target for treating multiple diseases, and the study of this signalling axis is particularly important.

The V2 receptor antagonist tolvaptan counteracts proliferation and invasivity in human cancer cells

PURPOSE

Hyponatremia, the most frequent electrolyte alteration in clinical practice, has been associated with a worse prognosis in cancer patients. On the other hand, a better outcome has been related to serum sodium normalization. In vitro studies have shown that low extracellular sodium promotes cancer cells proliferation and invasiveness. Tolvaptan, a selective vasopressin receptor type 2 (V₂) antagonist, has been effectively used in the last decade for the treatment of hyponatremia secondary to the Syndrome of Inappropriate Antidiuresis. A few in vitro data suggested a direct role of tolvaptan in counteracting cancer progression, so far. The aim of this study was to evaluate the effect and the mechanism of action of tolvaptan in cell lines from different tumours [i.e. colon cancer (HCT-8), hepatocarcinoma (HepG2), neuroblastoma (SK-N-AS)].

METHODS AND RESULTS

First, we showed that these cell lines express the V₂ receptor. Tolvaptan significantly reduced cell proliferation with an IC₅₀ in the micromolar range. Accordingly, reduced levels of cAMP, of the catalytic α subunit of PKA, and a reduced pAKT/AKT ratio were observed. Tolvaptan effectively inhibited cell cycle progression, whereas it induced apoptotis. Furthermore, it reduced cell invasiveness. In particular, anchorage-independent growth and the activity of collagenases type IV were blunted in the three cell lines. Accordingly, tolvaptan counteracted the RhoA/ROCK1-2 pathway, which has a pivotal role in regulating cell movement.

CONCLUSIONS

Overall, these findings indicate that tolvaptan effectively inhibits tumour progression in vitro. Further studies should clarify whether the V₂ receptor might be considered a possible target in anti-cancer strategies in the future.

Targeting the vasopressin type-2 receptor for renal cell carcinoma therapy

Arginine vasopressin (AVP) and its type-2 receptor (V2R) play an essential role in the regulation of salt and water homeostasis by the kidneys. V2R activation also stimulates proliferation of renal cell carcinoma (RCC) cell lines in vitro. The current studies investigated V2R expression and activity in human RCC tumors, and its role in RCC tumor growth. Examination of the cancer genome atlas (TCGA) database, and analysis of human RCC tumor tissue microarrays, cDNA arrays and tumor biopsy samples demonstrated V2R expression and activity in clear cell RCC (ccRCC). In vitro, V2R antagonists OPC31260 and Tolvaptan, or V2R gene silencing reduced wound closure and cell viability of 786-O and Caki-1 human ccRCC cell lines. Similarly in mouse xenograft models, Tolvaptan and OPC31260 decreased RCC tumor growth by reducing cell proliferation and angiogenesis, while increasing apoptosis. In contrast, the V2R agonist dDAVP significantly increased tumor growth. High intracellular cAMP levels and ERK1/2 activation were observed in human ccRCC tumors. In mouse tumors and Caki-1 cells, V2R agonists reduced cAMP and ERK1/2 activation, while dDAVP treatment had the reverse effect. V2R gene silencing in Caki-1 cells also reduced cAMP and ERK1/2 activation. These results provide novel evidence for a pathogenic role of V2R signaling in ccRCC, and suggest that inhibitors of the AVP-V2R pathway, including the FDA-approved drug Tolvaptan, could be utilized as novel ccRCC therapeutics.

Biased signaling of G protein coupled receptors (GPCRs): Molecular determinants of GPCR/transducer selectivity and therapeutic potential

G protein coupled receptors (GPCRs) convey signals across membranes via interaction with G proteins. Originally, an individual GPCR was thought to signal through one G protein family, comprising cognate G proteins that mediate canonical receptor signaling. However, several deviations from canonical signaling pathways for GPCRs have been described. It is now clear that GPCRs can engage with multiple G proteins and the line between cognate and non-cognate signaling is increasingly blurred. Furthermore, GPCRs couple to non-G protein transducers, including β-arrestins or other scaffold proteins, to initiate additional signaling cascades. Receptor/transducer selectivity is dictated by agonist-induced receptor conformations as well as by collateral factors. In particular, ligands stabilize distinct receptor conformations to preferentially activate certain pathways, designated 'biased signaling'. In this regard, receptor sequence alignment and mutagenesis have helped to identify key receptor domains for receptor/transducer specificity. Furthermore, molecular structures of GPCRs bound to different ligands or transducers have provided detailed insights into mechanisms of coupling selectivity. However, receptor dimerization, compartmentalization, and trafficking, receptor-transducer-effector stoichiometry, and ligand residence and exposure times can each affect GPCR coupling. Extrinsic factors including cell type or assay conditions can also influence receptor signaling. Understanding these factors may lead to the development of improved biased ligands with the potential to enhance therapeutic benefit, while minimizing adverse effects. In this review, evidence for ligand-specific GPCR signaling toward different transducers or pathways is elaborated. Furthermore, molecular determinants of biased signaling toward these pathways and relevant examples of the potential clinical benefits and pitfalls of biased ligands are discussed.

Pentapeptides for the treatment of small cell lung cancer: Optimisation by Nind-alkyl modification of the tryptophan side chain

The pentapeptide, tert-Prenyl^4th-NH₂ (DMePhe-DTrp-Phe-DTrp(N-tert-prenyl)-Leu-NH₂), has recently been reported by our group to exhibit properties of substance P (SP) antagonist G against small cell lung cancer (SCLC). In this study, we undertook a systematic structure activity investigation to optimise this lead compound to improve its in vitro anti-tumour activity and biocompatibility. A series of d-tryptophan (D-Trp) derivatives were synthesised, with a range of aliphatic N-alkyl chains (methyl to pentyl) on the indole nitrogen (N^ind). These were incorporated into the pentapeptide sequence by substitution of the N^ind-tert-prenylated D-Trp 4th residue with the N^ind-alkylated D-Trp derivatives. These pentapeptides were significantly more potent than tert-Prenyl^4th-NH₂, with the N^ind-butyl modification generating the most cytotoxic peptides. Compared to tert-Prenyl^4th-NH₂, a single butyl modification on the 4th D-Trp residue (Butyl^4th-NH₂) showed a ∼3 fold enhancement in cytotoxicity in either the chemo-naive H69 or the DMS79 (originating from a patient treated with chemotherapeutics and radiation therapy) SCLC cell lines. In addition, the di-butylated sequence on the 2nd and 4th D-Trp residues (Butyl^2nd,4th-NH₂) gave ∼4.5 times higher cytotoxicity against the H69 cell line and a ∼2 fold increase against the DMS79 cell line, compared to tert-Prenyl^4th-NH₂. The favoured position for butyl modification was the 4th D-Trp residue, as the Butyl^2nd-NH₂ peptide gave lower cytotoxicity on both cell lines. Butylated peptide sequences, when exposed to neat mouse plasma for 24 h at 37 °C, were found to resist degradation with >80% remaining intact compared to ∼58% for tert-Prenyl^4th-NH₂. The degradation pathway in plasma occurs via de-amidation of the C-terminus, confirmed by mass spectrometry and RP-HPLC analysis. The butyl modification also conferred resistance to metabolism when tested using S9 liver fraction from mouse. The optimum analogue responsive against the DMS79 cell line was the Butyl^4th-NH₂ pentapeptide, which revealed a concentration dependent increase in apoptosis: the level of late apoptotic cells rose from ∼36% at 2 μM to ∼96% at 6 μM, as determined by flow cytometry, compared to the unmodified peptide that showed no such effect. Concluding, the butyl substitutions offered the best perspective for high cytotoxicity, induction of apoptosis and metabolic compatibility thereby comprising an improved broad spectrum SP antagonist candidate for treatment of SCLC.

N-tert-Prenylation of the indole ring improves the cytotoxicity of a short antagonist G analogue against small cell lung cancer

Natural prenylated indoles have been proposed as potential anticancer agents. To exploit this discovery for developing new peptide therapeutics, we report the first studies whereby incorporation of prenylated indoles into primary sequences has been achieved. We developed a route to synthesise Nα-Fmoc-protected tryptophan derivatives in which the prenyl group is linked to the N-indole core, using Pd(ii)-mediated C-H functionalisation of 2-methyl-2-butene. Based on the Substance P antagonist G (SPG), a well-known Small Cell Lung Cancer (SCLC) anticancer agent, we designed a new penta-peptide sequence to include a prenyl moiety on one of the tryptophan residues. The N-tert-prenylated tryptophan analogue was assembled into the pentameric peptide using standard solid phase peptide synthesis or liquid phase synthesis by fragment coupling. In vitro screening showed that the N-tert-prenylation of the indole ring on the tryptophan residue located near the C-terminal of the penta-peptide enhanced the cytotoxicity against H69 (IC50 = 2.84 ± 0.14 μM) and DMS79 (IC50 = 4.37 ± 0.44 μM) SCLC cell lines when compared with the unmodified penta-peptide (H69, IC50 = 30.74 ± 0.30 μM and DMS79, IC50 = 23.00 ± 2.07 μM) or the parent SPG sequence (IC50 > 30 μM, both cell lines). SCLC almost invariably relapses with therapy-resistant disease. The DMS79 cell line was established from a patient following treatment with a number of chemotherapeutics (cytoxan, vincristine and methotrexate) and radiation therapy. Treating DMS79 tumour-bearing nude mice provided a human xenograft model of drug resistance to test the efficacy of the prenylated peptide. A low dose (1.5 mg kg-1) of the prenylated peptide was found to reduce tumour growth by ∼30% (P < 0.05) at day 7, relative to the control group receiving vehicle only. We conclude that the availability of the Fmoc-Trp(N-tert-prenyl)-OH amino acid facilitates the synthesis of prenylated-tryptophan-containing peptides to explore their therapeutic potential.

Is the Canonical RAF/MEK/ERK Signaling Pathway a Therapeutic Target in SCLC?

The activity of the RAF/MEK/ERK signaling pathway is critical for the proliferation of normal and cancerous cells. Oncogenic mutations driving the development of lung adenocarcinoma often activate this signaling pathway. In contrast, pathway activity levels and their biological roles are not well established in small cell lung cancer (SCLC), a fast-growing neuroendocrine lung cancer subtype. Here we discuss the function of the RAF/MEK/ERK kinase pathway and the mechanisms leading to its activation in SCLC cells. In particular, we argue that activation of this pathway may be beneficial to the survival, proliferation, and spread of SCLC cells in response to multiple stimuli. We also consider evidence that high levels of RAF/MEK/ERK pathway activity may be detrimental to SCLC tumors, including in part by interfering with their neuroendocrine fate. On the basis of these observations, we examined when small molecules targeting kinases in the RAF/MEK/ERK pathway may be useful therapeutically in patients with SCLC, including in combination with other therapeutic agents.

Pharmacological lineage analysis revealed the binding affinity of broad-spectrum substance P antagonists to receptors for gonadotropin-releasing peptide

A group of synthetic substance P (SP) antagonists, such as [Arg(6),D-Trp(7,9),N(Me)Phe(8)]-substance P(6-11) and [D-Arg(1),D-Phe(5),D-Trp(7,9),Leu(11)]-substance P, bind to a range of distinct G-protein-coupled receptor (GPCR) family members, including V1a vasopressin receptors, and they competitively inhibit agonist binding. This extended accessibility enabled us to identify a GPCR subset with a partially conserved binding site structure. By combining pharmacological data and amino acid sequence homology matrices, a pharmacological lineage of GPCRs that are sensitive to these two SP antagonists was constructed. We found that sensitivity to the SP antagonists was not limited to the Gq-protein-coupled V1a and V1b receptors; Gs-coupled V2 receptors and oxytocin receptors, which couple with both Gq and Gi, also demonstrated sensitivity. Unexpectedly, a dendrogram based on the amino acid sequences of 222 known GPCRs showed that a group of receptors sensitive to the SP antagonists are located in close proximity to vasopressin/oxytocin receptors. Gonadotropin-releasing peptide receptors, located near the vasopressin receptors in the dendrogram, were also sensitive to the SP analogs, whereas α1B adrenergic receptors, located more distantly from the vasopressin receptors, were not sensitive. Our finding suggests that pharmacological lineage analysis is useful in selecting subsets of candidate receptors that contain a conserved binding site for a ligand with broad-spectrum binding abilities. The knowledge that the binding site of the two broad-spectrum SP analogs partially overlaps with that of distinct peptide agonists is valuable for understanding the specificity/broadness of peptide ligands.

CD133+ cancer stem-like cells in small cell lung cancer are highly tumorigenic and chemoresistant but sensitive to a novel neuropeptide antagonist

Small cell lung cancer (SCLC) is a highly aggressive malignancy with poor survival rates, with initial responses nearly invariably followed by rapid recurrence of therapy-resistant disease. Drug resistance in SCLC may be attributable to the persistence of a subpopulation of cancer stem-like cells (CSC) that exhibit multiple drug resistance. In this study, we characterized the expression of CD133, one important marker of CSC in other cancers, in SCLC cancer cells. CD133 expression correlated with chemoresistance and increased tumorigenicity in vitro and in vivo accompanied by increased expression of Akt/PKB and Bcl-2. CD133 expression was increased in mouse and human SCLC after chemotherapy, an observation confirmed in clinical specimens isolated longitudinally from a patient receiving chemotherapy. We discovered in CD133(+) SCLC cells, an increased expression of the mitogenic neuropeptide receptors for gastrin-releasing peptide and arginine vasopressin. Notably, these cells exhibited increased sensitivity to the growth inhibitory and proapoptotic effects of a novel broad spectrum neuropeptide antagonist (related to SP-G), which has completed a phase I clinical trial for SCLC. Our results offer evidence that this agent can preferentially target chemoresistant CD133(+) cells with CSC character in SCLC, emphasizing its potential utility for improving therapy in this setting.

Quantifying biased β-arrestin signaling

It is now established that agonists do not uniformly activate pleiotropic signaling mechanisms initiated by receptors but rather can bias signals according to the unique receptor conformations they stabilize. One of the important emerging signaling systems where this can occur is through β-arrestin. This chapter discusses biased signaling where emphasis or de-emphasis of β-arrestin signaling is postulated (or been shown) to be beneficial. The chapter specifically focuses on methods to quantify biased effects; these methods furnish scales that can be used in the process of optimizing biased agonism (and antagonism) for therapeutic benefit. Specifically, methods to derive ΔΔLog(τ/K A) or ΔΔLog(Relative Activity) values are described to do this.

The potential for selective pharmacological therapies through biased receptor signaling

The discovery that not all agonists uniformly activate cellular signaling pathways (biased signaling) has greatly changed the drug discovery process for agonists and the strategy for treatment of disease with agonists. Technological advances have enabled complex receptor behaviors to be viewed independently and through these assays, the bias for an agonist can be quantified. It is predicted that therapeutic phenotypes will be linked, through translational studies, to quantified scales of bias to guide medicinal chemists in the drug discovery process.

Signalling bias in new drug discovery: detection, quantification and therapeutic impact

Agonists of seven-transmembrane receptors, also known as G protein-coupled receptors (GPCRs), do not uniformly activate all cellular signalling pathways linked to a given seven-transmembrane receptor (a phenomenon termed ligand or agonist bias); this discovery has changed how high-throughput screens are designed and how lead compounds are optimized for therapeutic activity. The ability to experimentally detect ligand bias has necessitated the development of methods for quantifying agonist bias in a way that can be used to guide structure-activity studies and the selection of drug candidates. Here, we provide a viewpoint on which methods are appropriate for quantifying bias, based on knowledge of how cellular and intracellular signalling proteins control the conformation of seven-transmembrane receptors. We also discuss possible predictions of how biased molecules may perform in vivo, and what potential therapeutic advantages they may provide.

Functional selectivity and biased receptor signaling

With the emergence of information describing functional selectivity and biased agonists and antagonists has come a lack of confidence in "one size fits all" assays for detection of agonism. Seven-transmembrane receptors are pleiotropic with respect to the signaling protein to which they couple in a cell, and many conformations of the receptor can be formed; this leads to systems where ligands can stabilize unique conformations that go on to selectively activate signaling pathways. Thus, such "biased" ligands can produce cell-specific agonism that may require targeted assays to detect and quantify. It also predicts that ligands can have many different efficacies for the many behaviors that the receptor can exhibit (referred to as "pluridimensional efficacy"), leading to a breakdown in the common classifications of agonist and antagonist. This all poses unique challenges to the pharmacologic nomenclature of drugs, the detection and optimization of new drugs, and the association of phenotypic clinical profiles with pharmacological properties of drugs.

G protein coupled receptors as allosteric proteins and the role of allosteric modulators

Seven transmembrane receptors (7TMRs) are proteins that convey signals through changes in conformation. These conformations are stabilized by external molecules (i.e. agonists, antagonists, modulators) and act upon other bodies (termed 'guests') which can be other molecules in the extracellular space, or proteins along the plane of the membrane (receptor oligomerization) or signaling proteins in the cytosol (i.e. G protein, β-arrestin). These elements comprise allosteric systems and a great deal of 7TMR pharmacology can be considered in terms of allosteric behavior. Allosteric ligands acting on 7TMRs possess four unique behaviors that can be valuable therapeutically; (1) the ability to alter the interaction of very large proteins, (2) probe dependence, (3) saturable effect, and (4) induction of separate changes in affinity and efficacy of other ligands. Two of these behaviors (namely probe dependence for CCR5-based HIV-1 entry inhibitors and functional selectivity for biased agonism) will be highlighted with examples.

Seven transmembrane receptors as shapeshifting proteins: the impact of allosteric modulation and functional selectivity on new drug discovery

It is useful to consider seven transmembrane receptors (7TMRs) as disordered proteins able to allosterically respond to a number of binding partners. Considering 7TMRs as allosteric systems, affinity and efficacy can be thought of in terms of energy flow between a modulator, conduit (the receptor protein), and a number of guests. These guests can be other molecules, receptors, membrane-bound proteins, or signaling proteins in the cytosol. These vectorial flows of energy can yield standard canonical guest allostery (allosteric modification of drug effect), effects along the plane of the cell membrane (receptor oligomerization), or effects directed into the cytosol (differential signaling as functional selectivity). This review discusses these apparently diverse pharmacological effects in terms of molecular dynamics and protein ensemble theory, which tends to unify 7TMR behavior toward cells. Special consideration will be given to functional selectivity (biased agonism and biased antagonism) in terms of mechanism of action and potential therapeutic application. The explosion of technology that has enabled observation of diverse 7TMR behavior has also shown how drugs can have multiple (pluridimensional) efficacies and how this can cause paradoxical drug classification and nomenclatures.

Biased agonism

Seven-transmembrane receptors are commonly coupled to multiple signaling pathways in cells. The simple model describing agonists for these receptors as producing a common active state to induce uniform activation of the pathways linked to the receptor has been shown to be untenable in light of a large body of data that suggest that some agonists produce activation of some but not all available pathways. These agonists are referred to as ‘biased’ in that they select which signaling pathways become activated upon binding to the receptor. The data to support this mechanism as well as ideas on the possible therapeutic application of this effect will be discussed.

Targeting V1A-vasopressin receptors with [Arg6, D-Trp7,9, NmePhe8]-substance P (6-11) identifies a strategy to develop novel anti-cancer therapies

BACKGROUND AND PURPOSE

The anti-cancer agent [Arg(6), D-Trp(7,9), N(me)Phe(8)]-substance P (6-11) (SP-G) modulates gastrin releasing peptide (GRP) and arginine vasopressin signalling in small cell lung cancer cells leading to growth arrest and apoptosis. We have shown that SP-G acts as a biased agonist at GRP receptors. This work examines the hypothesis that SP-G acts as a biased agonist at the V(1A) vasopressin receptor.

EXPERIMENTAL APPROACH

The human V(1A) receptor was expressed in CHO-K1 cells. Extracellular regulated kinase (ERK) activation and intracellular Ca(2+) were measured using activation state-specific antibodies and Fura-2-AM respectively. The effect of SP-G on tumourigenicity was assessed by colony assay.

KEY RESULTS

In V(1A) receptor expressing cells, SP-G caused a sustained activation of ERK via a stimulation of V(1A) receptor coupling to G(i). Inhibition of G(i) with Pertussis toxin attenuated the inhibition by SP-G of the growth of CHO-K1 cells stably expressing the V(1A) receptor. Chimeric V(1A) receptors containing the second or third intracellular loop of the V(2) receptor were capable of binding vasopressin and SP-G but had altered ability to activate phospholipase C (PLC) and ERK. The second intracellular loop of the V(1A) receptor was essential for vasopressin-stimulated PLC and ERK activation but not for SP-G-induced ERK activation.

CONCLUSIONS AND IMPLICATIONS

This work provides mechanistic insight, for biased agonists at V(1A) receptors and highlights a potential role for such agents as anti-cancer agents.

Targeting growth factors in lung cancer

Lung cancer causes more deaths than any other malignancy in the developed world. Advances in surgical techniques and chemotherapy/radiotherapy regimes have produced only minimal improvements in long-term survival. New therapeutic interventions are urgently required. Research has indicated that growth factor signaling may be an important novel target in lung cancer therapy. Preclinical studies have demonstrated the role of extracellular growth factors in lung cancer cell proliferation, metastasis, and resistance to cytotoxic therapy, and have elucidated the key molecular components of growth factor-signaling cascades. This has enabled the development of selective growth factor inhibitors, which have been evaluated in clinical trials and are now an accepted component of advanced lung cancer treatment. Further research is underway to improve the efficacy of this growth factor-targeted therapy. This article will outline the important aspects of this translational research indicating the growth factor-signaling pathways identified in lung cancer, clinical trials of anti-growth factor therapy, and potential future research directions.

Recent Developments in Ghrelin Receptor Ligands

The 28-amino acid peptide ghrelin is a neuroendocrine hormone synthesized primarily in the stomach. It stimulates growth hormone secretion and appetite, thus promoting food intake and body-weight gain. The pharmacological properties of this peptide are mediated by the growth hormone secretagogue receptor type 1a (GHS-R1a). Given its wide spectrum of biological activities, it is evident that the discovery of ghrelin and its receptor has opened up many perspectives in the fields of neuroendocrine and metabolic research and has had an influence on such fields of internal medicine as gastroenterology, oncology, and cardiology. It is therefore increasingly likely that synthetic, peptidyl, and nonpeptidyl GHS-R1a ligands, acting as agonists, partial agonists, antagonists, or inverse agonists, could have both clinical and therapeutic potential. This review summarizes the various types of GHS-R1a ligands that have been described in the literature and discusses the recent progress made in this research area.

Provasopressin expression by breast cancer cells: implications for growth and novel treatment strategies

The arginine vasopressin (AVP) gene is expressed in certain cancers such as breast cancer, where it is believed to act as an autocrine growth factor. However, little is known about the regulation of the AVP protein precursor (proAVP) or AVP-mediated signaling in breast cancer and this study was undertaken to address some of the basic issues. The cultured cell lines examined (Mcf7, Skbr3, BT474, ZR75, Mcf10a) and human breast cancer tissue extract were found to express proAVP mRNA. Western analysis revealed multiple forms of proAVP protein were present in cell lysates, corresponding to those detected in human hypothalamus extracts. Monoclonal antibodies directed against different regions of proAVP bound to intact live Mcf7 and Skbr3 cells. Dexamethasone increased the amount of proAVP-associated glycopeptide (VAG) secreted by Skbr3 cells and a combination of dexamethasone, IBMX and 8br-cAMP increased cellular levels of VAG. Exogenous AVP (1, 10, and 100 nM) elevated phospho-ERK1/2 levels, and increased cell proliferation was observed in the presence of 10 nM AVP. Concurrent treatment with the V1a receptor antagonist SR49059 reduced the effects of AVP on proliferation in Mcf7 cells, and abolished it in Skbr3 cells. Results here show that proAVP components are found at the surface of Skbr3 and Mcf7 cells and are also secreted from these cells. In addition, they show that AVP promotes cancer cell growth, apparently through a V1-type receptor-mediated pathway and subsequent ERK1/2 activation. Thus, strategies for targeting proAVP should be examined for their effectiveness in diagnosing and treating breast cancer.