Muscarinic receptor agonists and antagonists: effects on cancer

Cholinergic Machinery as Relevant Target in Acute Lymphoblastic T Leukemia

Various types of non-neuronal cells, including tumors, are able to produce acetylcholine (ACh), which acts as an autocrine/paracrine growth factor. T lymphocytes represent a key component of the non-neuronal cholinergic system. T cells-derived ACh is involved in a stimulation of their activation and proliferation, and acts as a regulator of immune response. The aim of the present work was to summarize the data about components of cholinergic machinery in T lymphocytes, with an emphasis on the comparison of healthy and leukemic T cells. Cell lines derived from acute lymphoblastic leukemias of T lineage (T-ALL) were found to produce a considerably higher amount of ACh than healthy T lymphocytes. Additionally, ACh produced by T-ALL is not efficiently hydrolyzed, because acetylcholinesterase (AChE) activity is drastically decreased in these cells. Up-regulation of muscarinic ACh receptors was also demonstrated at expression and functional level, whereas nicotinic ACh receptors seem to play a less important role and not form functional channels in cells derived from T-ALL. We hypothesized that ACh over-produced in T-ALL may act as an autocrine growth factor and play an important role in leukemic clonal expansion through shaping of intracellular Ca²⁺ signals. We suggest that cholinergic machinery may be attractive targets for new drugs against T-ALL. Specifically, testing of high affinity antagonists of muscarinic ACh receptors as well as antagomiRs, which interfere with miRNAs involved in the suppression of AChE expression, may be the first choice options.

Accelerated molecular dynamics simulations of ligand binding to a muscarinic G-protein-coupled receptor

Elucidating the detailed process of ligand binding to a receptor is pharmaceutically important for identifying druggable binding sites. With the ability to provide atomistic detail, computational methods are well poised to study these processes. Here, accelerated molecular dynamics (aMD) is proposed to simulate processes of ligand binding to a G-protein-coupled receptor (GPCR), in this case the M3 muscarinic receptor, which is a target for treating many human diseases, including cancer, diabetes and obesity. Long-timescale aMD simulations were performed to observe the binding of three chemically diverse ligand molecules: antagonist tiotropium (TTP), partial agonist arecoline (ARc) and full agonist acetylcholine (ACh). In comparison with earlier microsecond-timescale conventional MD simulations, aMD greatly accelerated the binding of ACh to the receptor orthosteric ligand-binding site and the binding of TTP to an extracellular vestibule. Further aMD simulations also captured binding of ARc to the receptor orthosteric site. Additionally, all three ligands were observed to bind in the extracellular vestibule during their binding pathways, suggesting that it is a metastable binding site. This study demonstrates the applicability of aMD to protein-ligand binding, especially the drug recognition of GPCRs.

Autonomic nervous infiltration positively correlates with pathological risk grading and poor prognosis in patients with lung adenocarcinoma

Background

Perineural invasion has been found in several types of human tumors, and is associated with poor prognosis; however, few studies have examined perineural invasion in lung cancer. We evaluated the relationship between autonomic nervous densities, pathological risk grading, and prognosis in patients with lung adenocarcinoma (LADC).

Methods

Neural fiber expression was examined by immunofluorescence in resected lung specimens in control patients (n = 30), and low‐risk (n = 22), and high‐risk LADC patients (n = 43). The nerve densities of normal lung tissue and abnormal lung tissues in the tumor and surrounding tissues were evaluated by a semi‐quantitative score method.

Results

Increased sympathetic fibers mainly infiltrated the paratumoral area, while increased parasympathetic fibers were largely restricted to the tumor (paratumor vs. tumor, P = 0.000 in high, P = 0.034 in low; each). In addition, high‐risk patients presented the highest density of neural fibers, followed by low‐risk and control patients (P = 0.000; each). In Kaplan–Meier survival analysis, the densities of sympathetic fibers in paratumoral tissue and parasympathetic fibers in the tumor, respectively, correlated with poor recurrence‐free survival in patients who were not treated with adjuvant therapy (P < 0.001; each). Further multivariate analysis showed that these two factors were associated with poor prognosis in all LADC patients (P = 0.024 sympathetic fibers; P = 0.037 parasympathetic fibers).

Conclusion

These findings reveal a positive correlation between nervous infiltration and risk of poor prognosis in patients with LADC.

The insect repellent N,N-diethyl-m-toluamide (DEET) induces angiogenesis via allosteric modulation of the M3 muscarinic receptor in endothelial cells

The insect repellent N,N-diethyl-m-toluamide (DEET) has been reported to inhibit AChE (acetylcholinesterase) and to possess potential carcinogenic properties with excessive vascularization. In the present paper, we demonstrate that DEET specifically stimulates endothelial cells that promote angiogenesis which increases tumor growth. DEET activates cellular processes that lead to angiogenesis including proliferation, migration and adhesion. This is associated with an enhancement of NO production and VEGF expression in endothelial cells. M3 silencing or the use of a pharmacological M3 inhibitor abrogates all of these effects which reveals that DEET-induced angiogenesis is M3 sensitive. The experiments involving calcium signals in both endothelial and HEK cells overexpressing M3 receptors, as well as binding and docking studies demonstrate that DEET acts as an allosteric modulator of the M3 receptor. In addition, DEET inhibited AChE which increased acetylcholine bioavailability and binding to M3 receptors and also strengthened proangiogenic effects by an allosteric modulation.

Muscarinic receptor signaling and colon cancer progression

Due to the lack of effective treatments, advanced colorectal cancer (CRC) remains a leading cause of cancer death in the United States. Emerging evidence supports the observation that muscarinic receptor (MR) signaling plays a critical role in growth and progression of CRC. MR activation by acetylcholine and bile acids results in transactivation of epidermal growth factor receptors (EGFR) and post-EGFR signal transduction that enhances cell proliferation, migration, and invasion. Here, the authors review recent progress in understanding the molecular mechanisms underlying MR-mediated CRC progression and its therapeutic implications.

Targeted tumor delivery and controlled release of neuronal drugs with ferritin nanoparticles to regulate pancreatic cancer progression

Pancreatic cancer is a lethal malignancy whose progression is highly dependent on the nervous microenvironment. This study develops neural drug-loaded ferritin nanoparticles (Ft NPs) to regulate the nervous microenvironment, in order to control the pancreatic cancer progression. The drug-loaded Ft NPs can target pancreatic tumors via passive targeting of EPR effects of tumors and active targeting via transferrin receptor 1 (TfR1) binding on cancer cells, with a triggered drug release in acidic tumor environment. Two drugs, one activates neural activity (carbachol), the other impairs neural activity (atropine), are encapsulated into the Ft NPs to form two kinds of nano drugs, Nano-Cab NPs and Nano-Ato NPs, respectively. The activation of the nervous microenvironment by Nano-Cab NPs significantly promotes the pancreatic tumor progression, whereas the blockage of neural niche by Nano-Ato NPs remarkably impairs the neurogenesis in tumors and the progression of pancreatic cancer. The Ft-based nanoparticles thus comprise an effective and safe route of delivery of neural drugs for novel anti-cancer therapy.

Allosteric effects of sodium ion binding on activation of the m3 muscarinic g-protein-coupled receptor

G-protein-coupled receptors (GPCRs) are important membrane proteins that mediate cellular signaling and represent primary targets for about one-third of currently marketed drugs. Recent x-ray crystallographic studies identified distinct conformations of GPCRs in the active and inactive states. An allosteric sodium ion was found bound to a highly conserved D2.50 residue in inactive GPCRs, whereas the D2.50 allosteric pocket became collapsed in active GPCR structures. However, the dynamic mechanisms underlying these observations remain elusive. In this study, we aimed to understand the mechanistic effects of sodium ion binding on dynamic activation of the M3 muscarinic GPCR through long-timescale accelerated molecular dynamics (aMD) simulations. Results showed that with the D2.50 residue deprotonated, the M3 receptor is bound by an allosteric sodium ion and confined mostly in the inactive state with remarkably reduced flexibility. In contrast, the D2.50-protonated receptor does not exhibit sodium ion binding to the D2.50 allosteric site and samples a significantly larger conformational space. The receptor activation is captured and characterized by large-scale structural rearrangements of the transmembrane helices via dynamic hydrogen bond and salt bridge interactions. The residue motions are highly correlated during receptor activation. Further network analysis revealed that the allosteric signaling between residue D2.50 and key residues in the intracellular, extracellular, and orthosteric pockets is significantly weakened upon sodium ion binding.

Cholinergic Targets in Lung Cancer

Lung cancers express an autocrine cholinergic loop in which secreted acetylcholine can stimulate tumor growth through both nicotinic and muscarinic receptors. Because activation of mAChR and nAChR stimulates growth; tumor growth can be stimulated by both locally synthesized acetylcholine as well as acetylcholine from distal sources and from nicotine in the high percentage of lung cancer patients who are smokers. The stimulation of lung cancer growth by cholinergic agonists offers many potential new targets for lung cancer therapy. Cholinergic signaling can be targeted at the level of choline transport; acetylcholine synthesis, secretion and degradation; and nicotinic and muscarinic receptors. In addition, the newly describe family of ly-6 allosteric modulators of nicotinic signaling such as lynx1 and lynx2 offers yet another new approach to novel lung cancer therapeutics. Each of these targets has their potential advantages and disadvantages for the development of new lung cancer therapies which are discussed in this review.

Cytotoxic and genotoxic effects mediated by M2 muscarinic receptor activation in human glioblastoma cells

Glioblastomas are the most common brain tumors in humans. Previously, we demonstrated that the muscarinic receptor agonist, arecaidine propargyl ester, via M2 receptors, inhibits cell proliferation in a time and dose-dependent manner and induces a severe apoptosis in human U251 and U87 glioblastoma cell lines. In order to clarify the mechanisms causing apoptosis after arecaidine treatment, we analyzed the ability of arecaidine to induce oxidative stress. By dichloro-dihydro-fluorescein diacetate (DCFDA) staining, we demonstrated that arecaidine increased the intracellular ROS levels. ROS accumulation was completely counteracted by the ROS scavenger, N-acetyl-l-cysteine (NAC). Apoptotic cell death appeared directly correlated to ROS production since NAC was able to counteract this effect. Although there was an up-regulation of some detoxifying enzyme expression such as superoxide dismutase (MnSOD) and sirtuin-1 (SIRT1), the cytotoxic effect caused by arecaidine treatment caused DNA damage, as demonstrated by the increase of histone γ-H2AX positive cells, and chromosomal aberrations. These effects were mediated by M2 receptor activation; in fact after silencing of M2 receptors by siRNA, the increase of γ-H2AX positive cells was abolished. In conclusion, in addition to a cytostatic effect previously described, in the present study we have better characterized the mechanisms causing the cytotoxic effects and the apoptotic cell death in glioblastoma cells after M2 receptor activation. These data allow to consider this receptor a new interesting therapeutic tool for the glioblastoma treatment.

Unbalanced acetylcholinesterase activity in larynx squamous cell carcinoma

Previous reports have demonstrated that a non-neuronal cholinergic system is expressed aberrantly in airways. A proliferative effect is exerted directly by cholinergic agonists through the activation of nicotinic and muscarinic receptors. In cancer, particularly those related with smoking, the mechanism through which tumour cells respond to aberrantly activated cholinergic signalling is a key question. Fifty paired pieces of larynx squamous cell carcinoma and adjacent non-cancerous tissue were compared in terms of their acetylcholinesterase activity (AChE). The AChE activity in non-cancerous tissues (0.248 ± 0.030 milliunits per milligram of wet tissue; mU/mg) demonstrates that upper respiratory tissues express sufficient AChE activity for controlling the level of acetylcholine (ACh). In larynx carcinomas, the AChE activity decreased to 0.157 ± 0.024 mU/mg (p=0.009). Larynx cancer patients exhibiting low ACh-degrading enzymatic activity had a significantly shorter overall survival (p=0.031). Differences in the mRNA levels of alternatively spliced AChE isoforms and molecular compositions were noted between glottic and supraglottic cancers. Our results suggest that the low AChE activity observed in larynx squamous cell carcinoma may be useful for predicting the outcome of patients.

Delirium from the gliocentric perspective

Delirium is an acute state marked by disturbances in cognition, attention, memory, perception, and sleep-wake cycle which is common in elderly. Others have shown an association between delirium and increased mortality, length of hospitalization, cost, and discharge to extended stay facilities. Until recently it was not known that after an episode of delirium in elderly, there is a 63% probability of developing dementia at 48 months compared to 8% in patients without delirium. Currently there are no preventive therapies for delirium, thus elucidation of cellular and molecular underpinnings of this condition may lead to the development of early interventions and thus prevent permanent cognitive damage. In this article we make the case for the role of glia in the pathophysiology of delirium and describe an astrocyte-dependent central and peripheral cholinergic anti-inflammatory shield which may be disabled by astrocytic pathology, leading to neuroinflammation and delirium. We also touch on the role of glia in information processing and neuroimaging.

Dysregulated cholinergic network as a novel biomarker of poor prognostic in patients with head and neck squamous cell carcinoma

BACKGROUND

In airways, a proliferative effect is played directly by cholinergic agonists through nicotinic and muscarinic receptors activation. How tumors respond to aberrantly activated cholinergic signalling is a key question in smoking-related cancer. This research was addressed to explore a possible link of cholinergic signalling changes with cancer biology.

METHODS

Fifty-seven paired pieces of head and neck squamous cell carcinoma (HNSCC) and adjacent non-cancerous tissue (ANCT) were compared for their mRNA levels for ACh-related proteins and ACh-hydrolyzing activity.

RESULTS

The measurement in ANCT of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities (5.416 ± 0.501 mU/mg protein and 6.350 ± 0.599 mU/mg protein, respectively) demonstrated that upper respiratory tract is capable of controlling the availability of ACh. In HNSCC, AChE and BChE activities dropped to 3.584 ± 0.599 mU/mg protein (p = 0.002) and 3.965 ± 0.423 mU/mg protein (p < 0.001). Moreover, tumours with low AChE activity and high BChE activity were associated with shorter patient overall survival. ANCT and HNSCC differed in mRNA levels for AChE-T, α3, α5, α9 and β2 for nAChR subunits. Tobacco exposure had a great impact on the expression of both AChE-H and AChE-T mRNAs. Unaffected and cancerous pieces contained principal AChE dimers and BChE tetramers. The lack of nerve-born PRiMA-linked AChE agreed with pathological findings on nerve terminal remodelling and loss in HNSCC.

CONCLUSIONS

Our results suggest that the low AChE activity in HNSCC can be used to predict survival in patients with head and neck cancer. So, the ChE activity level can be used as a reliable prognostic marker.

Denervation suppresses gastric tumorigenesis

The nervous system plays an important role in the regulation of epithelial homeostasis and has also been postulated to play a role in tumorigenesis. We provide evidence that proper innervation is critical at all stages of gastric tumorigenesis. In three separate mouse models of gastric cancer, surgical or pharmacological denervation of the stomach (bilateral or unilateral truncal vagotomy, or local injection of botulinum toxin type A) markedly reduced tumor incidence and progression, but only in the denervated portion of the stomach. Vagotomy or botulinum toxin type A treatment also enhanced the therapeutic effects of systemic chemotherapy and prolonged survival. Denervation-induced suppression of tumorigenesis was associated with inhibition of Wnt signaling and suppression of stem cell expansion. In gastric organoid cultures, neurons stimulated growth in a Wnt-mediated fashion through cholinergic signaling. Furthermore, pharmacological inhibition or genetic knockout of the muscarinic acetylcholine M3 receptor suppressed gastric tumorigenesis. In gastric cancer patients, tumor stage correlated with neural density and activated Wnt signaling, whereas vagotomy reduced the risk of gastric cancer. Together, our findings suggest that vagal innervation contributes to gastric tumorigenesis via M3 receptor-mediated Wnt signaling in the stem cells, and that denervation might represent a feasible strategy for the control of gastric cancer.

Participation of non-neuronal muscarinic receptors in the effect of carbachol with paclitaxel on human breast adenocarcinoma cells. Roles of nitric oxide synthase and arginase

Breast cancer is the most common type of cancer in women and represents a major issue in public health. The most frequent methods to treat these tumors are surgery and/or chemotherapy. The latter can exert not only beneficial effects by reducing tumor growth and metastasis, but also toxic actions on normal tissues. Metronomic therapy involves the use of low doses of cytotoxic drugs alone or in combination to improve efficacy and to reduce adverse effects. We have previously reported that breast tumors highly express functional muscarinic acetylcholine receptors (mAChRs) that regulate tumor progression. For this reason, mAChRs could be considered as therapeutic targets in breast cancer. In this paper, we investigated the ability of a combination of the cytotoxic drug paclitaxel plus carbachol, a cholinergic agonist, at low doses, to induce death in breast tumor MCF-7 cells, via mAChR activation, and the role of nitric oxide synthase (NOS) and arginase in this effect. We observed that the combination of carbachol plus paclitaxel at subthreshold doses significantly increased cytotoxicity in tumor cells without affecting MCF-10A cells, derived from human normal mammary gland. This effect was reduced in the presence of the muscarinic antagonist atropine. The combination also increased nitric oxide production by NOS1 and NOS3 via mAChR activation, concomitantly with an up-regulation of NOS3 expression. The latter effects were accompanied by a reduction in arginase II activity. In conclusion, our work demonstrates that mAChRs expressed in breast tumor cells could be considered as candidates to become targets for metronomic therapy in cancer treatment.

The effect of deficient muscarinic signaling on commonly reported biochemical effects in schizophrenia and convergence with genetic susceptibility loci in explaining symptom dimensions of psychosis

With the advent of DSM 5 criticism has generally centered on a lack of biological validity of the diagnostic criteria. Part of the problem in describing a nosology of psychosis is the tacit assumption of multiple genetic causes each with an incremental loading on the clinical picture that fails to differentiate a clear underlying pathophysiology of high impact. The aim of this paper is to consolidate a primary theory of deficient muscarinic signaling underlying key clinical features of schizophrenia and its regulation by several important genetic associations including neuregulin, DISC and dysbindin. Secondary reductions in markers for GABAergic function and changes in the levels of interneuron calcium binding proteins parvalbumin and calbindin can be attributed to dysfunctional muscarinic transduction. A parallel association exists for cytokine production. The convergent pathway hypothesis is likewise used to model dopaminergic and glutamatergic theories of schizophrenia. The negative symptom dimension is correlated with dysfunction of Akt and ERK transduction, a major point of convergence. The present paradigm predicts the importance of a recent finding of a deletion in a copy number variant of PLCB1 and its potential use if replicated, as one of the first testable biological markers differentiating schizophrenia from bipolar disorder and further subtyping of schizophrenia into deficit and non-deficit. Potential limitations of PLCB1 as a prospective marker are also discussed.

Muscarinic acetylcholine receptors: novel opportunities for drug development

The muscarinic acetylcholine receptors are a subfamily of G protein-coupled receptors that regulate numerous fundamental functions of the central and peripheral nervous system. The past few years have witnessed unprecedented new insights into muscarinic receptor physiology, pharmacology and structure. These advances include the first structural views of muscarinic receptors in both inactive and active conformations, as well as a better understanding of the molecular underpinnings of muscarinic receptor regulation by allosteric modulators. These recent findings should facilitate the development of new muscarinic receptor subtype-selective ligands that could prove to be useful for the treatment of many severe pathophysiological conditions.

Muscarinic receptor subtype mRNA expression in the human prostate: association with age, pathological diagnosis, prostate size, or potentially interfering medications?

As the prostate abundantly expresses muscarinic receptors and antagonists for such receptors are increasingly used in the treatment of men with voiding function and large prostates, we have explored an association of the mRNA expression of human M1, M2, M3, M4, and M5 receptors in human prostate with patient age, prostate size, prostate-specific antigen level, pathological diagnosis, and concomitant medication. mRNA was isolated from prostate chips of 110 consecutive patients undergoing transurethral resection of the prostate for the treatment of benign prostatic hyperplasia or prostate cancer. Expression of each of the five muscarinic receptor subtype transcripts was assessed by real-time PCR and association with patient age, prostate size, prostate-specific antigen level, pathological diagnosis, and concomitant medication were explored. M1 and M4 receptors were the most and least prevalently expressed subtypes in the human prostate, respectively. M1 receptor mRNA expression was weakly but significantly associated with prostate size (r = 0.2494, p = 0.0451), but mRNA expression of none of the five subtypes was significantly associated with age, prostate-specific antigen level, pathological diagnosis (benign prostatic hyperplasia vs. prostate cancer), or concomitant medication (5α-reductase inhibitors, α1- or β-adrenoceptor antagonists). We conclude that human prostate muscarinic receptor subtype transcripts apparently undergo only a very limited regulation by a variety of physiological, pathophysiological, or treatment factors. In light of the growing use of muscarinic receptor antagonists in men with voiding dysfunction including those with large prostates, the functional role of the weak association between M1 receptor mRNA expression and prostate size merits further investigation.

Acetylcholine-induced AMP-activated protein kinase activation attenuates vasoconstriction through an LKB1-dependent mechanism in rat aorta

Numerous studies of acetylcholine (ACh)-induced endothelium-dependent relaxation in arteries have been reported since the original description by Furchgott and Zawadzki (1980). ACh also produces endothelium-independent relaxation. However, it is still unknown whether ACh-induced AMP-activated protein kinase (AMPK) activation can attenuate vasoconstriction in endothelium-denuded rat aorta. Here, we investigated whether ACh may exert a regulatory effect for vascular tone via AMPK activation and its underlying mechanism in vascular smooth muscle cells (VSMCs). Western blotting showed that ACh dose- and time-dependently increased LKB1 and AMPK phosphorylation in VSMCs. The ACh-induced activation of AMPK required muscarinic receptors in VSMCs. LKB1 and AMPK activation by ACh inhibited myosin light-chain kinase (MLCK) and phosphorylated myosin light chain (p-MLC) expression in VSMCs. In addition, a tension study showed the inhibitory effect of ACh-induced AMPK activation on phenylephrine-mediated contraction in endothelium-denuded rat aorta. These data suggest that the ACh-induced activation of AMPK may attenuate vasoconstriction via LKB1-AMPK-dependent mechanism in endothelium-denuded rat aorta.

Different muscarinic receptor subtypes modulate proliferation of primary human detrusor smooth muscle cells via Akt/PI3K and map kinases

While acetylcholine (ACh) and muscarinic receptors in the bladder are mainly known for their role in the regulation of smooth muscle contractility, in other tissues they are involved in tissue remodelling and promote cell growth and proliferation. In the present study we have used primary cultures of human detrusor smooth muscle cells (HDSMCs), in order to investigate the role of muscarinic receptors in HDSMC proliferation. Samples were obtained as discarded tissue from men >65 years undergoing radical cystectomy for bladder cancer and cut in pieces that were either immediately frozen or placed in culture medium for the cell culture establishment. HDSMCs were isolated from samples, propagated and maintained in culture. [(3)H]-QNB radioligand binding on biopsies revealed the presence of muscarinic receptors, with a Kd of 0.10±0.02nM and a Bmax of 72.8±0.1fmol/mg protein. The relative expression of muscarinic receptor subtypes, based on Q-RT-PCR, was similar in biopsies and HDSMC with a rank order of M2≥M3>M1>M4>M5. The cholinergic agonist carbachol (CCh, 1-100μM) concentration-dependently increased [(3)H]-thymidine incorporation (up to 46±4%). This was concentration-dependently inhibited by the general muscarinic receptor antagonist atropine and by subtype-preferring antagonists with an order of potency of darifenacin >4-DAMP>AF-DX 116. The CCh-induced cell proliferation was blocked by selective PI-3 kinase and ERK activation inhibitors, strongly suggesting that these intracellular pathways mediate, at least in part, the muscarinic receptor-mediated cell proliferation. This work shows that M2 and M3 receptors can mediate not only HDSM contraction but also proliferation; they may also contribute bladder remodelling including detrusor hypertrophy.