SR31747A is a sigma receptor ligand exhibiting antitumoural activity both in vitro and in vivo

SR31747A is a recently described sigma receptor ligand that binds SR31747A-binding protein 1 (SR-BP) and emopamil-binding protein (EBP) (also called the sigma 1 receptor and the human sterol isomerase (HSI), respectively), and has immunoregulatory and antiproliferative activities. To further investigate its antitumour activity and focusing on cancers, which are sensitive to the molecule, we measured the proliferation of different human epithelial breast or prostate cancer cell lines following in vitro and in vivo SR31747A treatment. Firstly, in vitro, we found that nanomolar concentrations of SR31747A dramatically inhibited cell proliferation in both hormono-responsive and -unresponsive cancer cell lines. Secondly, tumour development was significantly decreased in mice treated with SR31747A. In an attempt to decipher the SR31747A mode of action, we found that the two binding sites may not fully account for this activity. Indeed, while competitive experiments indicated that EBP prevails in mediating SR31747A antiproliferative activity, an analysis of the expression of both receptors indicated that the cellular sensitivity to SR31747A is not correlated with either EBP or SR-BP expression. These data suggest that additional binding sites may exist. Preliminary binding studies demonstrated that SR31747A also binds to sigma 2, a protein that has not yet been cloned, but which is considered as a potential marker of the proliferative status of tumour cells. Altogether, our data demonstrate the antitumoural activity of SR31747A both in vitro and in vivo in two different cancer models, broaden the spectrum of its binding proteins and enhance the potential for further therapeutic development of the molecule.

The neuroprotective agent SR 57746A abrogates experimental autoimmune encephalomyelitis and impairs associated blood-brain barrier disruption: implications for multiple sclerosis treatment

Experimental autoimmune encephalomyelitis (EAE) is a T cell autoimmune disorder that is a widely used animal model for multiple sclerosis (MS) and, as in MS, clinical signs of EAE are associated with blood-brain barrier (BBB) disruption. SR 57746A, a nonpeptide drug without classical immunosuppressive properties, efficiently protected the BBB and impaired intrathecal IgG synthesis (two conventional markers of MS exacerbation) and consequently suppressed EAE clinical signs. This compound inhibited EAE-induced spinal cord mononuclear cell invasion and normalized tumor necrosis factor alpha and IFN-gamma mRNA expression within the spinal cord. These data suggested that pharmacological intervention aimed at inhibiting proinflammatory cytokine expression within the central nervous system provided protection against BBB disruption, the first clinical sign of EAE and probably the key point of acute MS attacks. This finding could lead to the development of a new class of compounds for oral therapy of MS, as a supplement to immunosuppressive agents.

Purification and characterization of the human SR 31747A-binding protein. A nuclear membrane protein related to yeast sterol isomerase

SR 31747A, defined as a sigma ligand, is a novel immunosuppressive agent that blocks proliferation of human and mouse lymphocytes. Using a radiolabeled chemical probe, we here purified a target of SR 31747A and called it SR 31747A-binding protein (SR-BP). Purified SR-BP retained its binding properties and migrated on SDS-polyacrylamide gel as a Mr 28,000 protein. Cloning of the cDNA encoding human SR-BP shows an open reading frame for a 223-amino acid protein, which is homologous to the recently cloned sigma 1 receptor. Interestingly, the deduced amino acid sequence was found to be related to fungal C8-C7 sterol isomerase, encoded by the ERG2 gene. The ERG2 gene product has been identified recently as the molecular target of SR 31747A that mediates antiproliferative effects of the drug in yeast. Northern blot analysis of SR-BP gene expression revealed a single transcript of 2 kilobases which was widely expressed among organs, with the highest abundance in liver and the lowest abundance in brain. Subcellular localization analysis in various cells, using a specific monoclonal antibody raised against SR-BP, demonstrated that this protein was associated with the nuclear envelope. When studying the binding of SR 31747A on membranes from yeast expressing SR-BP, we found a pharmacological profile of sigma 1 receptors; binding was displaced by (+)-pentazocine, haloperidol, and (+)-SKF 10,047, with (+)-SKF 10, 047 being a more potent competitor than (-)-SKF 10,047. Scatchard plot analysis revealed Kd values of 7.1 nM and 0.15 nM for (+)-pentazocine and SR 31747A, respectively, indicating an affinity of SR-BP 50-fold higher for SR 31747A than for pentazocine. Additionally, we showed that pentazocine, a competitive inhibitor of SR 31747A binding, also prevents the immunosuppressive effect of SR 31747A. Taken together, these findings strongly suggest that SR-BP represents the molecular target for SR 31747A in mammalian tissues, which could be critical for T cell proliferation.

A sigma ligand, SR 31747A, potently modulates Staphylococcal enterotoxin B-induced cytokine production in mice

Sigma receptors originally described in distinct regions of the central nervous system are expressed on cells of the immune system. A sigma ligand, SR 31747A, was observed here to inhibit in vitro the Staphylococcal enterotoxin B (SEB)-driven lymphocyte proliferation. In mice, the drug confers a potent protection against the lethality induced by SEB, stimulates the SEB-induced serum release of interleukin (IL)-10 and inhibits at the same time the systemic release of IL-2, IL-4, granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-6 and tumour necrosis factor-alpha (TNF-alpha). The enhancement of IL-10 production by this compound is also effective in nude mice treated with SEB, indicating that IL-10 of T-cell origin is not involved in this process. The finding that a sigma ligand protects against the SEB-induced toxicity provides insights into the clinical use of this family of compounds, particularly in food poisoning and septic shock where Staphylococcal enterotoxins are involved. The observation that this compound stimulates IL-10 synthesis indicates that it could be a potent regulatory agent of chronic inflammatory diseases.

Signaling pathway associated with stimulation of CB2 peripheral cannabinoid receptor. Involvement of both mitogen-activated protein kinase and induction of Krox-24 expression

Cannabinoids, known for their psychoactive effects, also possess immunomodulatory properties. The recent isolation and cloning of the G-protein-coupled peripheral cannabinoid receptor (CB2), mainly expressed in immune tissues, have provided molecular tools to determine how cannabinoid compounds may mediate immunomodulation. We here investigated the CB2 signaling properties using stably transfected Chinese hamster ovary cells expressing human CB2. First, we showed that stimulation by a cannabinoid agonist activated mitogen-activated protein (MAP) kinase in time- and dose-dependent manners. The rank order of potency for MAP kinase activation of cannabinoid agonists correlated well with their binding capacities. Second, we demonstrated that, following MAP kinase activation, cannabinoids induced the expression of the growth-related gene Krox-24, also known as NGFI-A, zif/268, and egr-1. Pertussis toxin completely prevented both MAP kinase activation and Krox-24 induction, even more these responses appeared to be dependent of specific protein kinase C isoforms and independent of inhibition of adenylyl cyclase. A similar coupling of CB2 to a mitogenic pathway and to the regulation of Krox-24 expression was also observed in human promyelocytic cells HL60. Taken together, these findings provide evidence for a functional role of the CB2 receptor in gene induction mediated by the MAP kinase network.

Activation of mitogen-activated protein kinases by stimulation of the central cannabinoid receptor CB1

The G-protein-coupled central cannabinoid receptor (CB1) has been shown to be functionally associated with several biological responses including inhibition of adenylate cyclase, modulation of ion channels and induction of the immediate-early gene Krox-24. Using stably transfected Chinese Hamster Ovary cells expressing human CB1 we show here that cannabinoid treatment induces both phosphorylation and activation of mitogen-activated protein (MAP) kinases, and that these effects are inhibited by SR 141716A, a selective CB1 antagonist. The two p42 and p44 kDa MAP kinases are activated in a time- and dose-dependent manner. The rank order of potency for the activation of MAP kinases with various cannabinoid agonists is CP-55940 > delta 9-tetrahydrocannabinol > WIN 55212.2, in agreement with the pharmacological profile of CB1. The activation of MAP kinases is blocked by pertussis toxin but not by treatment with hydrolysis-resistant cyclic AMP analogues. This suggests that the signal transduction pathway between CB1 and MAP kinases involves a pertussis-toxin-sensitive GTP-binding protein and is independent of cyclic AMP metabolism. This coupling of CB1 subtype and mitogenic signal pathway, also observed in the human astrocytoma cell line U373 MG, may explain the mechanism of action underlying cannabinoid-induced Krox-24 induction.

Stimulation of cannabinoid receptor CB1 induces krox-24 expression in human astrocytoma cells

The recent isolation and cloning of the G protein-coupled central cannabinoid receptor (CB1) from brain tissue has provided a molecular basis to elucidate how cannabinoid compounds may mediate their psychoactive effects. Here we report the high expression of cannabinoid receptors in human astrocytoma tumors of different grades, in the astrocytoma cell lines U373 MG and GL-15, as well as in normal astrocytes. From an analysis of the coupling mechanisms of functional CB1 receptors in U373 MG, we show that, in addition to the inhibition of adenylyl cyclase, activation by the cannabinoid agonist CP-55940 induces the expression of the immediate-early gene krox-24, also known as NGFI-A, zif/268, egr-1, and TIS8. The amount of Krox-24 protein and the level of Krox-24 DNA binding activity, as measured by Western blot and electrophoretic mobility shift assay, respectively, were also increased by the addition of CP-55940. These effects were blocked by incubation with pertussis toxin but not by treatment with hydrolysis-resistant cAMP analogues, suggesting that the transduction pathway between the cannabinoid receptor and krox-24 involves a pertussis toxin-sensitive GTP-binding protein and is independent of cAMP metabolism. The specific involvement of CB1 in Krox-24 induction was demonstrated in Chinese hamster ovary cells transfected with the human CB1 receptor and also in experiments using the CB1-selective cannabinoid antagonist SR 141716A.

In vivo inhibition of endotoxin-induced pro-inflammatory cytokines production by the sigma ligand SR 31747

In previous studies, the authors demonstrated that the new sigma ligand, cis-N-cyclohexyl-N-ethyl-3-(3-chloro-4-cyclohexyl-phenyl) propen-2-ylamine hydrochloride (SR 31747), elicited a suppressive effect on immune responses through the sigma receptor expressed on lymphocytes. Here the effect of SR 31747 on the proinflammatory cytokine production by endotoxin-activated macrophages is examined. In vivo, SR 31747 dramatically blocked lipopolysaccharide-induced production of interleukin (IL)-1, IL-6 and tumor necrosis factor-alpha in a dose-dependent manner (ED50, 2 mg/kg). Whereas SR 31747 suppression was not observed in vitro on lipopolysaccharide-induced IL-6 by macrophages, sera from SR 31747-treated animals displayed a strong inhibitory activity. It was shown that this effect could be completely reversed by the steroid receptor antagonist, mifepristone, which suggests that SR 31747 probably abrogated monokine production through an indirect mechanism that involves endogenous corticosteroids. This conclusion was supported by in vivo experiments that showed that 1) ablation of corticosteroids by use of mifepristone or adrenalectomy suppressed the effect of SR 31747 and 2) administration of SR 31747 induced an enhancement of the corticosterone level. It was also shown that this molecule improved the survival of animals with endotoxinic shock as a result of monokine inhibition. The combination of immunosuppression, previously described, along with anti-inflammatory properties makes SR 31747 a novel attractive molecule for therapeutic applications such as autoimmune diseases in which both immune and inflammatory disorders are involved.

Immunopharmacological profile of SR 31747: in vitro and in vivo studies on humoral and cellular responses

In our preceding paper, we demonstrated that both human and rat lymphocytes possess saturable high-affinity binding sites for the new sigma ligand SR 31747. Here we investigate the potential activity of this ligand on immune responses. In vitro, our study shows that SR 31747 exerts a concentration- and time-dependent inhibition of proliferative response to mitogens on mouse and human lymphocytes without affecting cell viability. This suppressive effect elicited by SR 31747 occurs over a concentration range which correlates with the pharmacological profile of the molecule in binding assays, strongly suggesting that SR 31747 acts through a receptor-mediated process. We showed that the SR 31747 effect, which was observed on purified T lymphocytes, affects a late event in the activation process which occurs after the G1 during the S phase of the cell cycle. Interestingly, no anti-proliferative effect was observed in a variety of tumor cell lines, supporting a specific effect limited to normal immune cells. In vivo, in mice, treatment with SR 31747 prevented both graft-versus-host disease and delayed-type hypersensitivity granuloma formation, while antibody response to sheep red blood cells was not affected. These results strongly suggest that the sigma-related receptor recognized by SR 31747 is very likely coupled to a biological function of lymphocytes.

Effect of a new, potent, non-peptide V1a vasopressin antagonist, SR 49059, on the binding and the mitogenic activity of vasopressin on Swiss 3T3 cells

The effects of SR 49059, a new non-peptide, selective arginine vasopressin (AVP), V1a antagonist, were investigated both on AVP's receptors and on the mitogenic effects of AVP on Swiss 3T3 fibroblasts. We characterized the AVP V1a receptors on Swiss 3T3 cell membranes using the new highly specific AVP V1a radioiodinated ligand, 125I-linear AVP antagonist. Specific binding of the 125I-linear AVP antagonist was saturable, time-dependent and reversible. A single class of high affinity binding sites was identified with an apparent Kd of 40 +/- 20 pM and a Bmax of 63 +/- 20 fmol/mg protein. 125I-Linear AVP antagonist binding to its receptors was potently inhibited in a concentration-dependent manner by AVP, by the peptide V1a antagonist d(CH2)5Tyr(Me)AVP and by the synthetic V1a antagonist, SR 49059 (IC50 in the nanomolar range) while OPC-21268, another non-peptide compound, was about 100-fold less potent. Both DDAVP, a selective V2 agonist, and oxytocin exhibited low affinity (IC50 > 1 microM) in agreement with the AVP V1a nature of the site identified on Swiss 3T3 cells. In addition, the broad-spectrum antiproliferative agent [Arg6, D-Trp7,9, MePhe8] substance P (6-11), was also able to interact at 3T3 AVP V1a receptors (IC50 = 395 +/- 170 nM). The mitogenic effects of AVP on quiescent Swiss 3T3 cells, assessed through [3H]thymidine incorporation, were selectively, stereospecifically and strongly inhibited by SR 40959 (IC50 = 14 +/- 2 nM) while OPC-21268 was inactive up to 220 nM. SR 49059 was even about six times more efficient than d(CH2)5Tyr(Me)AVP in inhibiting AVP-induced DNA synthesis. Moreover, SR 49059 fully inhibited Swiss 3T3 fibroblast proliferation since it completely blocked AVP-stimulated 3T3 cell growth from the G1/G0 into the S/G2M phase, as evidenced by cell cycle analysis using a cytofluorometer. In summary, SR 49059, through direct interaction at AVP V1a receptors, exerts the most potent antiproliferative effect yet described for any V1a antagonist on Swiss 3T3 cells.