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Alpha7 nicotinic acetylcholine receptor agonist properties of tilorone and related tricyclic analogues.

ABSTRACT: BACKGROUND AND PURPOSE: The alpha7 nicotinic acetylcholine receptor (nAChR) has attracted considerable interest as a target for cognitive enhancement in schizophrenia and Alzheimer's Disease. However, most recently described alpha7 agonists are derived from the quinuclidine structural class. Alternatively, the present study identifies tilorone as a novel alpha7-selective agonist and characterizes analogues developed from this lead. EXPERIMENTAL APPROACH: Activity and selectivity were determined from rat brain alpha7 and alpha4beta2 nAChR binding, recombinant nAChR activation, and native alpha7 nAChR mediated stimulation of ERK1/2 phosphorylation in PC12 cells. KEY RESULTS: Tilorone bound alpha7 nAChR (IC(50) 110 nM) with high selectivity relative to alpha4beta2 (IC(50) 70 000 nM), activated human alpha7 nAChR with an EC(50) value of 2.5 microM and maximal response of 67% relative to acetylcholine, and showed little agonist effect at human alpha3beta4 or alpha4beta2 nAChRs. However, the rat alpha7 nAChR maximal response was only 34%. Lead optimization led to 2-(5-methyl-hexahydro-pyrrolo[3,4-c]pyrrol-2-yl)-xanthen-9-one (A-844606) with improved binding (alpha7 IC(50) 11 nM, alpha4beta2 IC(50)>30 000 nM) and activity at both human and rat alpha7 nAChR (EC(50)s 1.4 and 2.2 microM and apparent efficacies 61 and 63%, respectively). These compounds also activated native alpha7 nAChR, stimulating ERK1/2 phosphorylation in PC12 cells. CONCLUSIONS AND IMPLICATIONS: Tilorone, known as an interferon inducer, is a selective alpha7 nAChR agonist, suggesting utility of the fluorenone pharmacophore for the development of alpha7 nAChR selective agonists. Whether alpha7 stimulation mediates interferon induction, or whether interferon induction may influence the potential anti-inflammatory properties of alpha7 nAChR agonists remains to be elucidated.

SUBMITTER: Briggs CA

PROVIDER: S-EPMC2267268 | biostudies-other | 2008 Mar

REPOSITORIES: biostudies-other

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Project description:We and others have shown that one of the mechanisms of growth regulation of small cell lung cancer cell lines and cultured pulmonary neuroendocrine cells is by the binding of agonists to the alpha7 neuronal nicotinic acetylcholine receptor. In addition, we have shown that the nicotine-derived carcinogenic nitrosamine, 4(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is a high affinity agonist for the alpha7 nicotinic acetylcholine receptor. In the present study, our goal was to determine the extent of alpha7 mRNA and protein expression in the human lung.Experiments were done using reverse transcription polymerase chain reaction (RT-PCR), a nuclease protection assay and western blotting using membrane proteins.We detected mRNA for the neuronal nicotinic acetylcholine receptor alpha7 receptor in seven small cell lung cancer (SCLC) cell lines, in two pulmonary adenocarcinoma cell lines, in cultured normal human small airway epithelial cells (SAEC), one carcinoid cell line, three squamous cell lines and tissue samples from nine patients with various types of lung cancer. A nuclease protection assay showed prominent levels of alpha7 in the NCI-H82 SCLC cell line while alpha7 was not detected in SAEC, suggesting that alpha7 mRNA levels may be higher in SCLC compared to normal cells. Using a specific antibody to the alpha7 nicotinic receptor, protein expression of alpha7 was determined. All SCLC cell lines except NCI-H187 expressed protein for the alpha7 receptor. In the non-SCLC cells and normal cells that express the alpha7 nAChR mRNA, only in SAEC, A549 and NCI-H226 was expression of the alpha7 nicotinic receptor protein shown. When NCI-H69 SCLC cell line was exposed to 100 pm NNK, protein expression of the alpha7 receptor was increased at 60 and 150 min.Expression of mRNA for the neuronal nicotinic acetylcholine receptor alpha7 seems to be ubiquitously expressed in all human lung cancer cell lines tested (except for NCI-H441) as well as normal lung cells. The alpha7 nicotinic receptor protein is expressed in fewer cell lines, and the tobacco carcinogen NNK increases alpha7 nicotinic receptor protein levels.

Project description:ObjectiveThe central nervous system can regulate peripheral inflammation, but the efferent neuronal routes and the mediators remain poorly defined. One candidate is the cholinergic pathway, which releases acetylcholine (ACh). This neurotransmitter can bind to the alpha7 cholinergic receptor (alpha7R) expressed by nonneuronal cells and reduce inflammation. To test this possibility, we evaluated the expression of alpha7R and its potential role as a target in rheumatoid arthritis (RA).MethodsThe expression of alpha7R in human synovium and fibroblast-like synoviocytes (FLS) was determined using immunohistochemical, Western blot, and quantitative polymerase chain reaction (PCR) analyses. The effects of ACh in vitro were determined in interleukin-1 (IL-1)-stimulated FLS using immunoassays for protein, quantitative PCR for messenger RNA (mRNA), luciferase reporter constructs for IL-6 and NF-kappaB promoter activity, and electrophoretic mobility shift assays. Expression of alpha7R was knocked down with small interfering RNA (siRNA) or was inhibited with the selective alpha7R antagonist methyllycaconitine (MLA).ResultsProtein and mRNA for alpha7R were demonstrated in RA and osteoarthritis synovium and cultured synoviocytes. Expression in synovium was mainly in the intimal lining. ACh significantly reduced the production of IL-6, CXCL8, CCL2, CCL3, CCL5, and granulocyte colony-stimulating factor by IL-1-stimulated FLS. This effect was blocked by the alpha7R antagonist MLA or by using alpha7R siRNA to knock down receptor expression. The selective alpha7R agonist PNU-282,987 decreased the production of IL-6 by IL-1-stimulated FLS. ACh did not reduce IL-6 transcription, but it decreased IL-6 mRNA half-life and reduced IL-6 mRNA steady-state levels.ConclusionThe alpha7 receptor is expressed in the synovium and by synoviocytes. Receptor ligation inhibits cytokine expression in FLS through a posttranscriptional mechanism. Therefore, alpha7R is a potential therapeutic target for inflammatory diseases.

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Alpha7 nicotinic acetylcholine receptor agonist properties of tilorone and related tricyclic analogues.

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