Muscarinic receptor M3 mediates cell proliferation induced by acetylcholine and contributes to apoptosis in gastric cancer

Nerve-tumor crosstalk in tumor microenvironment: From tumor initiation and progression to clinical implications

The autonomic nerve system (ANS) innervates organs and tissues throughout the body and maintains functional balance among various systems. Further investigations have shown that excessive activation of ANS not only causes disruption of homeostasis, but also may promote tumor formation. In addition, the dynamic interaction between nerve and tumor cells in the tumor microenvironment also regulate tumor progression. On the one hand, nerves are passively invaded by tumor cells, that is, perineural invasion (PNI). On the other hand, compared with normal tissues, tumor tissues are subject to more abundant innervation, and nerves can influence tumor progression through regulating tumor proliferation, metastasis and drug resistance. A large number of studies have shown that nerve-tumor crosstalk, including PNI and innervation, is closely related to the prognosis of patients, and contributes to the formation of cancer pain, which significantly deteriorates the quality of life for patients. These findings suggest that nerve-tumor crosstalk represents a potential target for anti-tumor therapies and the management of cancer pain in the future. In this review, we systematically describe the mechanism by which nerve-tumor crosstalk regulates tumorigenesis and progression.

circVAPA-rich small extracellular vesicles derived from gastric cancer promote neural invasion by inhibiting SLIT2 expression in neuronal cells

Gastric cancer (GC) is one of the most common cancer worldwide. Neural invasion (NI) is considered as the symbiotic interaction between nerves and cancers, which strongly affects the prognosis of GC patients. Small extracellular vesicles (sEVs) play a key role in intercellular communication. However, whether sEVs mediate GC-NI remains unexplored. In this study, sEVs release inhibitor reduces the NI potential of GC cells. Muscarinic receptor M3 on GC-derived sEVs regulates their absorption by neuronal cells. The enrichment of sEV-circVAPA in NI-positive patients' serum is validated by serum high throughput sEV-circRNA sequencing and clinical samples. sEV-circVAPA promotes GC-NI in vitro and in vivo. Mechanistically, sEV-circVAPA decreases SLIT2 transcription by miR-548p/TGIF2 and inhibits SLIT2 translation via binding to eIF4G1, thereby downregulates SLIT2 expression in neuronal cells and finally induces GC-NI. Together, this work identifies the preferential absorption mechanism of GC-derived sEVs by neuronal cells and demonstrates a previously undefined role of GC-derived sEV-circRNA in GC-NI, which provides new insight into sEV-circRNA based diagnostic and therapeutic strategies for NI-positive GC patients.

Cholinergic Mechanisms in Gastrointestinal Neoplasia

Acetylcholine-activated receptors are divided broadly into two major structurally distinct classes: ligand-gated ion channel nicotinic and G-protein-coupled muscarinic receptors. Each class encompasses several structurally related receptor subtypes with distinct patterns of tissue expression and post-receptor signal transduction mechanisms. The activation of both nicotinic and muscarinic cholinergic receptors has been associated with the induction and progression of gastrointestinal neoplasia. Herein, after briefly reviewing the classification of acetylcholine-activated receptors and the role that nicotinic and muscarinic cholinergic signaling plays in normal digestive function, we consider the mechanics of acetylcholine synthesis and release by neuronal and non-neuronal cells in the gastrointestinal microenvironment, and current methodology and challenges in measuring serum and tissue acetylcholine levels accurately. Then, we critically evaluate the evidence that constitutive and ligand-induced activation of acetylcholine-activated receptors plays a role in promoting gastrointestinal neoplasia. We focus primarily on adenocarcinomas of the stomach, pancreas, and colon, because these cancers are particularly common worldwide and, when diagnosed at an advanced stage, are associated with very high rates of morbidity and mortality. Throughout this comprehensive review, we concentrate on identifying novel ways to leverage these observations for prognostic and therapeutic purposes.

Changes in the Acetylcholinesterase Enzymatic Activity in Tumor Development and Progression

Acetylcholinesterase is a well-known protein because of the relevance of its enzymatic activity in the hydrolysis of acetylcholine in nerve transmission. In addition to the catalytic action, it exerts non-catalytic functions; one is associated with apoptosis, in which acetylcholinesterase could significantly impact the survival and aggressiveness observed in cancer. The participation of AChE as part of the apoptosome could explain the role in tumors, since a lower AChE content would increase cell survival due to poor apoptosome assembly. Likewise, the high Ach content caused by the reduction in enzymatic activity could induce cell survival mediated by the overactivation of acetylcholine receptors (AChR) that activate anti-apoptotic pathways. On the other hand, in tumors in which high enzymatic activity has been observed, AChE could be playing a different role in the aggressiveness of cancer; in this review, we propose that AChE could have a pro-inflammatory role, since the high enzyme content would cause a decrease in ACh, which has also been shown to have anti-inflammatory properties, as discussed in this review. In this review, we analyze the changes that the enzyme could display in different tumors and consider the different levels of regulation that the acetylcholinesterase undergoes in the control of epigenetic changes in the mRNA expression and changes in the enzymatic activity and its molecular forms. We focused on explaining the relationship between acetylcholinesterase expression and its activity in the biology of various tumors. We present up-to-date knowledge regarding this fascinating enzyme that is positioned as a remarkable target for cancer treatment.

Vagus innervation in the gastrointestinal tumor: Current understanding and challenges

The vagus nerve (VN) is the main parasympathetic nerve of the autonomic nervous system. It is widely distributed in the gastrointestinal tract and maintains gastrointestinal homeostasis with the sympathetic nerve under physiological conditions. The VN communicates with various components of the tumor microenvironment to positively and dynamically affect the progression of gastrointestinal tumors (GITs). The intervention in vagus innervation delays GIT progression. Developments in adeno-associated virus vectors, nanotechnology, and in vivo neurobiological techniques have enabled the creation of precisely regulated "tumor neurotherapies". Furthermore, the combination of neurobiological techniques and single cell sequencing may reveal more insights into VN and GIT. The present review aimed to summarize the mechanisms of communication between the VN and the gastrointestinal TME and to explore the potential and challenges of VN-based tumor neurotherapy in GITs.

Blocking Muscarinic Receptor 3 Attenuates Tumor Growth and Decreases Immunosuppressive and Cholinergic Markers in an Orthotopic Mouse Model of Colorectal Cancer

Tumor cells have evolved to express immunosuppressive molecules allowing their evasion from the host's immune system. These molecules include programmed death ligands 1 and 2 (PD-L1 and PD-L2). Cancer cells can also produce acetylcholine (ACh), which plays a role in tumor development. Moreover, tumor innervation can stimulate vascularization leading to tumor growth and metastasis. The effects of atropine and muscarinic receptor 3 (M3R) blocker, 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide (4-DAMP), on cancer growth and spread were evaluated in vitro using murine colon cancer cell line, CT-26, and in vivo in an orthotopic mouse model of colorectal cancer. In the in vitro model, atropine and 4-DAMP significantly inhibited CT-26 cell proliferation in a dose dependent manner and induced apoptosis. Atropine attenuated immunosuppressive markers and M3R via inhibition of EGFR/AKT/ERK signaling pathways. However, 4-DAMP showed no effect on the expression of PD-L1, PD-L2, and choline acetyltransferase (ChAT) on CT-26 cells but attenuated M3R by suppressing the phosphorylation of AKT and ERK. Blocking of M3R in vivo decreased tumor growth and expression of immunosuppressive, cholinergic, and angiogenic markers through inhibition of AKT and ERK, leading to an improved immune response against cancer. The expression of immunosuppressive and cholinergic markers may hold potential in determining prognosis and treatment regimens for colorectal cancer patients. This study's results demonstrate that blocking M3R has pronounced antitumor effects via several mechanisms, including inhibition of immunosuppressive molecules, enhancement of antitumor immune response, and suppression of tumor angiogenesis via suppression of the AKT/ERK signaling pathway. These findings suggest a crosstalk between the cholinergic and immune systems during cancer development. In addition, the cholinergic system influences cancer evasion from the host's immunity.

Nerves in gastrointestinal cancer: from mechanism to modulations

Maintenance of gastrointestinal health is challenging as it requires balancing multifaceted processes within the highly complex and dynamic ecosystem of the gastrointestinal tract. Disturbances within this vibrant environment can have detrimental consequences, including the onset of gastrointestinal cancers. Globally, gastrointestinal cancers account for ~19% of all cancer cases and ~22.5% of all cancer-related deaths. Developing new ways to more readily detect and more efficiently target these malignancies are urgently needed. Whereas members of the tumour microenvironment, such as immune cells and fibroblasts, have already been in the spotlight as key players of cancer initiation and progression, the importance of the nervous system in gastrointestinal cancers has only been highlighted in the past few years. Although extrinsic innervations modulate gastrointestinal cancers, cells and signals from the gut's intrinsic innervation also have the ability to do so. Here, we shed light on this thriving field and discuss neural influences during gastrointestinal carcinogenesis. We focus on the interactions between neurons and components of the gastrointestinal tract and tumour microenvironment, on the neural signalling pathways involved, and how these factors affect the cancer hallmarks, and discuss the neural signatures in gastrointestinal cancers. Finally, we highlight neural-related therapies that have potential for the management of gastrointestinal cancers.

Neural Component of the Tumor Microenvironment in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive primary malignancy of the pancreas, with a dismal prognosis and limited treatment options. It possesses a unique tumor microenvironment (TME), generating dense stroma with complex elements cross-talking with each other to promote tumor growth and progression. Diversified neural components makes for not having a full understanding of their influence on its aggressive behavior. The aim of the study was to summarize and integrate the role of nerves in the pancreatic tumor microenvironment. The role of autonomic nerve fibers on PDAC development has been recently studied, which resulted in considering the targeting of sympathetic and parasympathetic pathways as a novel treatment opportunity. Perineural invasion (PNI) is commonly found in PDAC. As the severity of the PNI correlates with a poorer prognosis, new quantification of this phenomenon, distinguishing between perineural and endoneural invasion, could feature in routine pathological examination. The concepts of cancer-related neurogenesis and axonogenesis in PDAC are understudied; so, further research in this field may be warranted. A better understanding of the interdependence between the neural component and cancer cells in the PDAC microenvironment could bring new nerve-oriented treatment options into clinical practice and improve outcomes in patients with pancreatic cancer. In this review, we aim to summarize and integrate the current state of knowledge and future challenges concerning nerve-cancer interactions in PDAC.

Emerging Roles of the Nervous System in Gastrointestinal Cancer Development

Simple Summary

Nerve–cancer cross-talk has increasingly become a focus of the oncology field, particularly in gastrointestinal (GI) cancers. The indispensable roles of the nervous system in GI tumorigenesis and malignancy have been dissected by epidemiological, experimental animal and mechanistic data. Herein, we review and integrate recent discoveries linking the nervous system to GI cancer initiation and progression, and focus on the molecular mechanisms by which nerves and neural receptor pathways drive GI malignancy.

Abstract

Our understanding of the fascinating connection between nervous system and gastrointestinal (GI) tumorigenesis has expanded greatly in recent years. Recent studies revealed that neurogenesis plays an active part in GI tumor initiation and progression. Tumor-driven neurogenesis, as well as neurite outgrowth of the pre-existing peripheral nervous system (PNS), may fuel GI tumor progression via facilitating cancer cell proliferation, chemoresistance, invasion and immune escape. Neurotransmitters and neuropeptides drive the activation of various oncogenic pathways downstream of neural receptors within cancer cells, underscoring the importance of neural signaling pathways in GI tumor malignancy. In addition, neural infiltration also plays an integral role in tumor microenvironments, and contributes to an environment in favor of tumor angiogenesis, immune evasion and invasion. Blockade of tumor innervation via denervation or pharmacological agents may serve as a promising therapeutic strategy against GI tumors. In this review, we summarize recent findings linking the nervous system to GI tumor progression, set the spotlight on the molecular mechanisms by which neural signaling fuels cancer aggressiveness, and highlight the importance of targeting neural mechanisms in GI tumor therapy.

Differential Actions of Muscarinic Receptor Subtypes in Gastric, Pancreatic, and Colon Cancer

Cancers arising from gastrointestinal epithelial cells are common, aggressive, and difficult to treat. Progress in this area resulted from recognizing that the biological behavior of these cancers is highly dependent on bioactive molecules released by neurocrine, paracrine, and autocrine mechanisms within the tumor microenvironment. For many decades after its discovery as a neurotransmitter, acetylcholine was thought to be synthesized and released uniquely from neurons and considered the sole physiological ligand for muscarinic receptor subtypes, which were believed to have similar or redundant actions. In the intervening years, we learned this former dogma is not tenable. (1) Acetylcholine is not produced and released only by neurons. The cellular machinery required to synthesize and release acetylcholine is present in immune, cancer, and other cells, as well as in lower organisms (e.g., bacteria) that inhabit the gut. (2) Acetylcholine is not the sole physiological activator of muscarinic receptors. For example, selected bile acids can modulate muscarinic receptor function. (3) Muscarinic receptor subtypes anticipated to have overlapping functions based on similar G protein coupling and downstream signaling may have unexpectedly diverse actions. Here, we review the relevant research findings supporting these conclusions and discuss how the complexity of muscarinic receptor biology impacts health and disease, focusing on their role in the initiation and progression of gastric, pancreatic, and colon cancers.

Regulation of the Autonomic Nervous System on Intestine

Intestine is composed of various types of cells including absorptive epithelial cells, goblet cells, endocrine cells, Paneth cells, immunological cells, and so on, which play digestion, absorption, neuroendocrine, immunological function. Intestine is innervated with extrinsic autonomic nerves and intrinsic enteric nerves. The neurotransmitters and counterpart receptors are widely distributed in the different intestinal cells. Intestinal autonomic nerve system includes sympathetic and parasympathetic nervous systems, which regulate cellular proliferation and function in intestine under physiological and pathophysiological conditions. Presently, distribution and functional characteristics of autonomic nervous system in intestine were reviewed. How autonomic nervous system regulates intestinal cell proliferation was discussed. Function of autonomic nervous system on intestinal diseases was extensively reviewed. It might be helpful to properly manipulate autonomic nervous system during treating different intestinal diseases.

Interrupting Neuron-Tumor Interactions to Overcome Treatment Resistance

Neurons in the tumor microenvironment release neurotransmitters, neuroligins, chemokines, soluble growth factors, and membrane-bound growth factors that solid tumors leverage to drive their own survival and spread. Tumors express nerve-specific growth factors and microRNAs that support local neurons and guide neuronal growth into tumors. The development of feed-forward relationships between tumors and neurons allows tumors to use the perineural space as a sanctuary from therapy. Tumor denervation slows tumor growth in animal models, demonstrating the innervation dependence of growing tumors. Further in vitro and in vivo experiments have identified many of the secreted signaling molecules (e.g., acetylcholine, nerve growth factor) that are passed between neurons and cancer cells, as well as the major signaling pathways (e.g., MAPK/EGFR) involved in these trophic interactions. The molecules involved in these signaling pathways serve as potential biomarkers of disease. Additionally, new treatment strategies focus on using small molecules, receptor agonists, nerve-specific toxins, and surgical interventions to target tumors, neurons, and immune cells of the tumor microenvironment, thereby severing the interactions between tumors and surrounding neurons. This article discusses the mechanisms underlying the trophic relationships formed between neurons and tumors and explores the emerging therapies stemming from this work.

Functional Characterization of Cholinergic Receptors in Melanoma Cells

In the last two decades, the scientific community has come to terms with the importance of non-neural acetylcholine in light of its multiple biological and pathological functions within and outside the nervous system. Apart from its well-known physiological role both in the central and peripheral nervous systems, in the autonomic nervous system, and in the neuromuscular junction, the expression of the acetylcholine receptors has been detected in different peripheral organs. This evidence has contributed to highlight new roles for acetylcholine in various biological processes, (e.g., cell viability, proliferation, differentiation, migration, secretion). In addition, growing evidence in recent years has also demonstrated new roles for acetylcholine and its receptors in cancer, where they are involved in the modulation of cell proliferation, apoptosis, angiogenesis, and epithelial mesenchymal transition. In this review, we describe the functional characterization of acetylcholine receptors in different tumor types, placing attention on melanoma. The latest set of data accessible through literature, albeit limited, highlights how cholinergic receptors both of muscarinic and nicotinic type can play a relevant role in the migratory processes of melanoma cells, suggesting their possible involvement in invasion and metastasis.

Sympathetic and parasympathetic innervation in cancer: therapeutic implications

PURPOSE

The autonomic nervous system, consisting of sympathetic and parasympathetic/vagal nerves, is known to control the functions of any organ, maintaining whole-body homeostasis under physiological conditions. Recently, there has been increasing evidence linking sympathetic and parasympathetic/vagal nerves to cancers. The present review aimed to summarize recent developments from studies addressing the relationship between sympathetic and parasympathetic/vagal nerves and cancer behavior.

METHODS

Literature review.

RESULTS

Human and animal studies have revealed that sympathetic and parasympathetic/vagal nerves innervate the cancer microenvironment and alter cancer behavior. The sympathetic nerves have cancer-promoting effects on prostate cancer, breast cancer, and melanoma. On the other hand, while the parasympathetic/vagal nerves have cancer-promoting effects on prostate, gastric, and colorectal cancers, they have cancer-suppressing effects on breast and pancreatic cancers. These neural effects may be mediated by β-adrenergic or muscarinic receptors and can be explained by changes in cancer cell behavior, angiogenesis, tumor-associated macrophages, and adaptive antitumor immunity.

CONCLUSIONS

Sympathetic nerves innervating the tumor microenvironment promote cancer progression and are related to stress-induced cancer behavior. The parasympathetic/vagal nerves have variable (promoting or suppressing) effects on different cancer types. Approaches directed toward the sympathetic and parasympathetic/vagal nerves can be developed as a new cancer therapy. In addition to existing pharmacological, surgical, and electrical approaches, a recently developed virus vector-based genetic local neuroengineering technology is a powerful approach that selectively manipulates specific types of nerve fibers innervating the cancer microenvironment and leads to the suppression of cancer progression. This technology will enable the creation of "cancer neural therapy" individually tailored to different cancer types.

The Combination of Two Bioactive Constituents, Lactoferrin and Linolenic Acid, Inhibits Mouse Xenograft Esophageal Tumor Growth by Downregulating Lithocholyltaurine and Inhibiting the JAK2/STAT3-Related Pathway

The addition of lactoferrin and three unsaturated fatty acids, oleic acid, docosahexaenoic acid (DHA), and linolenic acid, to dairy products was approved in recent years. Research into the biological activities of lactoferrin and these three unsaturated fatty acids has revealed anti-inflammatory, antiviral, antioxidant, antitumor, antiparasitic, and antibiotic effects. However, investigations and comparisons of lactoferrin + oleic acid/DHA/linolenic acid combinations in an esophageal cancer cell model and in xenograft tumor models have not been extensively reported, and the related mechanism of these combinations remains elusive. In the present study, the effects of lactoferrin and the three fatty acids on KYSE450 cell viability, migration, and invasion were investigated to choose the proper doses and effective combination in vitro. A tumor-bearing nude mouse model was established to investigate the role of selected combinations in inhibiting esophageal tumor formation in vivo. Metabonomics detection and data analysis were performed to screen special metabolites and related pathways, which were validated by western blotting. The results demonstrated that lactoferrin, the three unsaturated fatty acids, and their combinations inhibited the viability, migration, and invasion of KYSE450 cells and induced apoptosis and the lactoferrin + linolenic acid combination exhibited the strongest activity in suppressing KYSE450 tumor formation in vivo. The lactoferrin + linolenic acid combination inhibited phosphorylation in the JAK2/STAT3-related pathway by downregulating the special metabolite lithocholyltaurine, thereby suppressing formation of KYSE450 tumors.

Acetylcholine From Tuft Cells: The Updated Insights Beyond Its Immune and Chemosensory Functions

Tuft cells, rare solitary chemosensory cells, are distributed in mucosal epithelium throughout mammalian organs. Their nomenclatures are various in different organs and may be confused with other similar cells. Current studies mainly focus on their chemosensory ability and immune functions in type 2 inflammation. Several state-of-the-art reviews have already systematically discussed their role in immune responses. However, given that tuft cells are one of the crucial components of non-neuronal cholinergic system, the functions of tuft cell derived acetylcholine (ACh) and the underlying mechanisms remain intricate. Existing evidence demonstrated that tuft cell derived ACh participates in maintaining epithelial homeostasis, modulating airway remodeling, regulating reflexes, promoting muscle constriction, inducing neurogenic inflammation, initiating carcinogenesis and producing ATP. In this review, the ACh biosynthesis pathways and potential clinical applications of tuft cells have been proposed. More importantly, the main pathophysiological roles and the underlying mechanisms of tuft cell derived ACh are summarized and discussed.

Nervous system and gastric cancer

The nervous system has been recently shown to exert impact on gastric cancer directly and indirectly. Gastric cancer cells invade nerve fibers to induce outgrowth and branching of neural cells, and nerve fibers in turn infiltrate into tumor microenvironment to promote progression of gastric cancer. Additionally, the neuro-immune interaction also plays an important role in gastric cancer development. The interplay of nerves and gastric cancer is mediated by many nervous system-associated factors, which can not only be synthesized and released by both cancer cells and nerve terminals, but also participate in regulation of many aspects of gastric cancer such as cell proliferation, angiogenesis, metastasis and recurrence. Furthermore, clinical researches indicate that some of these factors are significant diagnosis and prognosis biomarkers for gastric cancer. Herein, we reviewed recent advances and future prospects of the interaction between nervous system and gastric cancer.

Chronic stress promotes gastric cancer progression and metastasis: an essential role for ADRB2

An increasing number of studies indicate that adrenergic signalling plays a fundamental role in chronic stress-induced tumour progression and metastasis. However, its function in gastric cancer (GC) and its potential mechanisms remain unknown. The expression levels of β-adrenergic receptor (ADRB) in GC cell lines were examined by using real-time polymerase chain reaction (RT-PCR) and western blotting. The effects of β2 adrenergic receptor (ADRB2) activation and blockade were investigated in vitro in GC cells by using proliferation, migration, invasion, cell cycle and apoptosis assays. Chronic restraint stress (CRS) increased the plasma levels of catecholamines and cortisol and also induced progression and metastasis of GC in vivo. Furthermore, immunohistochemical staining and a TUNEL assay were employed to observe the regulation of cell viability in vivo. The expression levels of ADRB2 in 100 human GC samples were measured by RT-PCR and immunohistochemistry. The stress hormones epinephrine and norepinephrine significantly accelerated GC cell proliferation, invasion and viability in culture, as well as tumour growth in vivo. These effects were reversed by the ADRB antagonists propranolol and ICI118,551 (an ADRB2-specific antagonist). Moreover, the selective ADRB1 antagonist atenolol had almost no effect on tumour cell proliferation and invasion in vitro and in vivo. ADRB2 antagonists suppressed proliferation, invasion and metastasis by inhibiting the ERK1/2-JNK-MAPK pathway and transcription factors, such as NF-κB, AP-1, CREB and STAT3. Analysis of xenograft models using GC cells revealed that ADRB2 antagonists significantly inhibited tumour growth and metastasis, and chronic stress antagonized these inhibitory effects. In addition, chronic stress increased the expression of VEGF, MMP-2, MMP-7 and MMP-9 in transplanted tumour tissue, and catecholamine hormones enhanced the expression of metastasis-related proteins. The expression of ADRB2 was upregulated in tumour tissues and positively correlated with tumour size, histological grade, lymph node metastasis and clinical stage in human GC samples. Stress hormone-induced activation of the ADRB2 signalling pathway plays a crucial role in GC progression and metastasis. These findings indicate that ADRB2 signalling regulates GC progression and suggest β2 blockade as a novel strategy to complement existing therapies for GC.

Acetylcholine receptors: Key players in cancer development

Acetylcholine (ACh) was first identified as a classic neuromodulator and transmit signals through two subgroups of receptors, namely muscarinic receptors (mAChRs) and nicotinic receptors (nAChRs). Apart from its well-established physiological role in central nervous system (CNS) and peripheral nervous system (PNS), autonomic nervous system and neuromuscular junction, the widely distributed expression of AChRs in different human organs suggests roles in other biological processes in addition to synaptic transmission. Accumulating evidence revealed that cancer cell processes such as proliferation, apoptosis, angiogenesis and even epithelial-mesenchymal transition (EMT) are mediated by overexpression of AChRs in different kinds of tumors. In breast cancer, α7-nAChR and α9-nAChR were reported to be oncogenic. On the other hand, research on the role of mAChRs in breast cancer tumorgenesis is limited and confined to M3 receptor only. Since AChRs distributed in both CNS and PNS even non-neuronal tissues, there is an urgent need for the development of subtype-specific AChR antagonist which inhibits cancer cell progression with minimal intervention on the normal acetylcholine-regulated system within human body.

Role of Muscarinic Acetylcholine Signaling in Gastrointestinal Cancers

In the tumor microenvironment, various stromal and immune cells accumulate and interact with cancer cells to contribute to tumor progression. Among stromal players, nerves have recently been recognized as key regulators of tumor growth. More neurotransmitters, such as catecholamines and acetylcholine (ACh), are present in tumors, as the cells that secrete neurotransmitters accumulate by the release of neurotrophic factors from cancer cells. In this short review, we focus on the role of nerve signaling in gastrointestinal (GI) cancers. Given that muscarinic acetylcholine receptor signaling seems to be a dominant regulator of GI stem cells and cancers, we review the function and mechanism of the muscarinic ACh pathway as a regulator of GI cancer progression. Accumulating evidence suggests that ACh, which is secreted from nerves and tuft cells, stimulates GI epithelial stem cells and contributes to cancer progression via muscarinic receptors.

Acacetin-induced cell apoptosis in head and neck squamous cell carcinoma cells: Evidence for the role of muscarinic M3 receptor

Aacacetin, a plant flavone has shown antitumor efficacy recently. However, its associated mechanisms are poorly known. We hypothesized that the muscarinic M3 receptor (M₃ R), which is highly expressed in some cancer tissue, is related to the antitumor effect of acacetin in head and neck squamous cell carcinoma (HNSCC) cells. Our results showed that 12.5- to 200-μM acacetin inhibited cell viability in dose- and time-dependent manners in HNSCC cells, but a relative higher concentration was needed for oral adenoid cystic carcinoma cells. M₃ R expression level was higher in HNSCC cells than that in adenoid cystic carcinoma cells. Flow cytometry and electron microscopy confirmed acacetin-induced cell apoptosis in 22B cells, a HNSCC cell line. Acacetin promoted mitochondrial cytochrome c release and caspase 9, 3 processing. Knocking down of M₃ R expression by specific siRNA significantly prevented the acacetin-induced cell viability damage, cell apoptosis, and caspase 3 activation. Besides, M₃ R was also involved in acacetin-induced elevation of reactive oxygen species and intracellular calcium ([Ca²⁺ ]_i ). These data indicate that acacetin-induced cell apoptosis in HNSCC cells may through M₃ R related calcium signaling and caspase 3 activation. Acacetin is a potent natural antitumor reagent especially for the tumor cells, which highly expressed M₃ R.

Exposure to antimuscarinic medications for treatment of overactive bladder and risk of lung cancer and colon cancer

Introduction

One out of six adults has symptoms of overactive bladder (OAB). Antimuscarinic medication is the main pharmacological group used in the treatment of OAB. In preclinical studies, antimuscarinic compounds have been found to inhibit cell proliferation in lung cancer and colon cancer.

Objective

The aim of this study was to investigate the association between exposure to anti-muscarinic medication and the risk of lung cancer and colon cancer.

Methods

Individuals in Sweden who first filled a prescription for an antimuscarinic medication used to treat OAB (ie, oxybutynin, solifenacin, darifenacin, fesoterodine, or tolterodine) between July 1, 2006, and December 31, 2012, were identified and classified as exposed. Each exposed individual was individually matched with up to ten unexposed individuals from the Swedish general population, based on year of birth, sex, and county of residence. Cox proportional hazard models with follow-up time as the underlying time scale were used to estimate HRs with 95% CIs.

Results

In total, 164,000 exposed and 1,446,472 unexposed individuals were included in this study. The estimated HRs for lung cancer, in follow-up time intervals of <1 year, 1–4 years, and ≥4 years, were as follows: 0.86 (95% CI: 0.75–0.98), 0.63 (95% CI: 0.56–0.70), and 0.43 (0.34–0.55), respectively. The corresponding estimates for colon cancer were as follows: 0.91 (95% CI: 0.80–1.03), 0.81 (95% CI: 0.74–0.88), and 0.61 (95% CI: 0.51–0.73), respectively.

Conclusion

There was an inverse association between exposure to antimuscarinic medications, used in the treatment of OAB, and a diagnosis of colon cancer or lung cancer, which is in line with the findings in preclinical studies.

Role of Muscarinic Acetylcholine Receptors in Breast Cancer: Design of Metronomic Chemotherapy

BACKGROUND

muscarinic acetylcholine receptors (mAChRs) have attracted interest as targets for therapeutic interventions in different illnesses like Alzheimer´s disease, viral infections and different tumors. Regarding the latter, many authors have studied each subtype of mAChRs, which seem to be involved in the progression of distinct types of malignancies.

METHODS

We carefully revised research literature focused on mAChRs expression and signaling as well as in their involvement in cancer progression and treatment. The characteristics of screened papers were described using the mentioned conceptual framework.

RESULTS

Muscarinic antagonists and agonists have been assayed for the treatment of tumors established in lung, brain and breast with beneficial effects. We described an up-regulation of mAChRs in mammary tumors and the lack of expression in non-tumorigenic breast cells and normal mammary tissues. We and others demonstrated that muscarinic agonists can trigger anti-tumor actions in a dose-dependent manner on tumors originated in different organs like brain or breast. At pharmacological concentrations, they exert similar effects to traditional chemotherapeutic agents. Metronomic chemotherapy refers to the administration of anti-cancer drugs at low doses with short intervals among them, and it is a different regimen applied in cancer treatment reducing malignant growth and angiogenesis, and very low incidence of adverse effects.

CONCLUSION

The usage of subthreshold concentrations of muscarinic agonists combined with conventional chemotherapeutic agents could be a promising tool for breast cancer therapy.

Muscarinic acetylcholine receptor 3 mediates vagus nerve-induced gastric cancer

Increasing evidence shows that the vagus nerve plays an important role in tumourigenesis. However, the effects and underlying mechanisms of the vagus nerve on gastric cancer (GC) development have not been established. In this study, we performed a unilateral truncal vagotomy at the subdiaphragmatic level in a mouse xenograft GC model to study the effects of the vagus nerve on GC development. Gene microarray analysis was used to explore the mechanism underlying this process. Significantly altered genes and pathways were analysed by Kyoto Encyclopaedia of Genes and Genomes analysis tool. We also detected muscarinic acetylcholine receptor 3 (M3) mRNA and protein levels by quantitative real-time polymerase chain reaction and immunohistochemical staining in mouse stomach tissue. To further confirm the functional role of M3, an in vivo M3 selective antagonist (darifenacin) assay was applied. Finally, we determined the M3 protein levels in human GC tissues and paired non-cancerous gastric tissues by immunohistochemical staining. We found that the surgical vagotomy inhibited the development of GC in an orthotopic xenograft mouse model. Further analysis showed that multiple signalling pathways participated in this process and that M3 was a key factor in these pathways. We established that the M3 mRNA and protein levels decreased in the vagotomy group relative to the sham group. We also demonstrated that the M3 antagonist suppressed the development of GC. Finally, we revealed that M3 protein level was up-regulated in human GC tissues. In conclusions, we revealed the functional role of M3 on mediating the effects of the vagus nerve on GC. Our study contributes to understanding the mechanism underlying the interaction between GC and the vagus nerve and may help to identify new therapeutic targets for GC.

A direct effect of the autonomic nervous system on somatic stem cell proliferation?

Regulation of somatic stem cell proliferation is critical for the maintenance of tissue and organ function throughout the body. Modulators of this process include nutrients and peptides, but the role of an autonomic neural influence on stem cell proliferation has been neglected. This article describes the literature in support of autonomic nervous system (ANS) influence on somatic stem cells, with emphasis on intestinal epithelial stem cells (IESCs) as a representative somatic stem cell. Based on the current available data, models for the direct influence of both branches of the ANS (the sympathetic and parasympathetic nervous systems) on IESCs are outlined. Finally, the prospect of treatments derived from ANS influence on somatic stem cells is explored.

Acetylcholine induces stem cell properties of gastric cancer cells of diffuse type

Gastric cancer is the third leading cause of cancer-related death worldwide, but the mechanisms of gastric carcinogenesis are not completely understood. Recently, the role of cholinergic neuronal pathways in promoting this process has been demonstrated. Our aim was to extend these studies and to evaluate, using an in vitro model of tumorspheres, the effect of acetylcholine on human gastric cancer cells, and the role of acetylcholine receptors and of the nitric oxide pathway, in this effect. The gastric cancer cell line MKN-45 of the diffuse type of gastric cancer was cultured in the presence of acetylcholine, or different agonists or inhibitors of muscarinic and nicotinic acetylcholine receptors, or nitric oxide donor or inhibitor of the nitric oxide pathway, and the number and size of tumorspheres were assessed. The expression of cancer stem cell markers (CD44 and aldehyde dehydrogenase) was also evaluated by immunofluorescence and quantitative reverse transcription polymerase chain reaction. We showed that acetylcholine increased both the number and size of tumorspheres and that this effect was reproduced with both muscarinic and nicotinic acetylcholine receptors agonists and was inhibited by both receptor antagonists. The nitric oxide donor stimulated the tumorsphere formation, while the nitric oxide synthesis inhibitor inhibited the stimulatory effect of acetylcholine. Moreover, acetylcholine increased the expression of stem cell markers on gastric cancer cells. These results indicate that acetylcholine induces the stem cell properties of gastric cancer cells and both muscarinic and nicotinic receptors and a nitrergic pathway might be involved in this effect.

Aclidinium bromide inhibits the growth and metastasis of gastric cancer MKN‑28 cells via the PI3K signaling pathway

The present study investigated the effect and underling mechanisms of aclidinium bromide, a novel, inhaled long‑acting muscarinic antagonist, on the development of gastric cancer. Human gastric cancer MKN‑28 cells, as a model in vitro, were treated with aclidinium bromide and dimethyl sulfoxide. Cell Counting Kit‑8 assay, transwell assay and flow cytometry were used to assess cell proliferation, invasion/migration and apoptosis, respectively. In addition, western blotting was performed to determine the relative expression of proteins associated with apoptosis and the phosphatidylinositol‑3‑kinase (PI3K) signaling pathway. Optical density values of MKN‑28 cells were decreased in a time‑ and dose‑dependent manner in the aclidinium bromide treated group. Matrigel invasion analysis demonstrated the number of invasive cells were significantly decreased in the aclidinium bromide‑treated group when compared with the control group. Furthermore, aclidinium bromide led to the marked reduction of the number of MKN‑28 cells passing though the microwells of the transwell chamber. The expression levels of the anti‑apoptotic protein B‑cell lymphoma 2 (Bcl‑2) decreased, and the expression of pro‑apoptotic proteins active Caspase3 and Bcl‑2‑associated X protein increased concurrently following aclidinium bromide stimulation using western blotting. The phosphorylation of protein kinase B and mechanistic target of rapamycin were significantly inhibited in MKN‑28 cells treated with aclidinium bromide; and the activity of the downstream proteins such as p70S6K and Cyclin D1 were also significantly decreased. In conclusion, aclidinium bromide could inhibit gastric cancer cell proliferation and metastasis, which may be associated with the enhancement of apoptosis induced by the PI3K signaling pathway.

Mir-34a-5p Mediates Cross-Talk between M2 Muscarinic Receptors and Notch-1/EGFR Pathways in U87MG Glioblastoma Cells: Implication in Cell Proliferation

Glioblastoma (GBM) is the most aggressive human brain tumor. The high growth potential and decreased susceptibility to apoptosis of the glioma cells is mainly dependent on genetic amplifications or mutations of oncogenic or pro-apoptotic genes, respectively. We have previously shown that the activation of the M2 acetylcholine muscarinic receptors inhibited cell proliferation and induced apoptosis in two GBM cell lines and cancer stem cells. The aim of this study was to delve into the molecular mechanisms underlying the M2-mediated cell proliferation arrest. Exploiting U87MG and U251MG cell lines as model systems, we evaluated the ability of M2 receptors to interfere with Notch-1 and EGFR pathways, whose activation promotes GBM proliferation. We demonstrated that the activation of M2 receptors, by agonist treatment, counteracted Notch and EGFR signaling, through different regulatory cascades depending, at least in part, on p53 status. Only in U87MG cells, which mimic p53-wild type GBMs, did M2 activation trigger a molecular circuitry involving p53, Notch-1, and the tumor suppressor mir-34a-5p. This regulatory module negatively controls Notch-1, which affects cell proliferation mainly through the Notch-1/EGFR axis. Our data highlighted, for the first time, a molecular circuitry that is deregulated in the p53 wild type GBM, based on the cross-talk between M2 receptor and the Notch-1/EGFR pathways, mediated by mir-34a-5p.

miR-424-5p promotes proliferation of gastric cancer by targeting Smad3 through TGF-β signaling pathway

MiRNAs have been reported to regulate gene expression and be associated with cancer progression. Recently, miR-424-5p was reported to play important role in a variety of tumors. However, the role and molecular mechanisms of miR-424-5p in GC (gastric cancer) remains largely unknown. In this study, we aimed to explore the role of miR-424-5p in GC. QRT-PCR was used to determine the expression levels of miR-424-5p and Smad3. CCK8 assay, plate clone assay and cell cycle assay were used to measure the effects of miR-424-5p on GC cell proliferation. Luciferase reporter assay and western blotting were used to prove that Smad3 was one of the direct targets of miR-424-5p. Tumorigenesis assay was used to investigate the role of miR-424-5p in tumor growth of GC cells in vivo. We found that miR-424-5p was up-regulated in GC tissues and cells. Over-expression of miR-424-5p could promote the proliferation of GC cells. In addition, luciferase reporter assay and western blotting assay revealed that Smad3 was a direct target of miR-424-5p. Over-expression of Smad3 could partially reverse the effects of miR-424-5p on GC cell proliferation. Our study further revealed that miR-424-5p could inhibit TGF-β signaling pathway by Smad3.

Acetylcholine acts through M3 muscarinic receptor to activate the EGFR signaling and promotes gastric cancer cell proliferation

Acetylcholine (ACh), known as a neurotransmitter, regulates the functions of numerous fundamental central and peripheral nervous system. Recently, emerging evidences indicate that ACh also plays an important role in tumorigenesis. However, little is known about the role of ACh in gastric cancer. Here, we reported that ACh could be auto-synthesized and released from MKN45 and BGC823 gastric cancer cells. Exogenous ACh promoted cell proliferation in a does-dependent manner. The M3R antagonist 4-DAMP, but not M1R antagonist trihexyphenidyl and M2/4 R antagonist AFDX-116, could reverse the ACh-induced cell proliferation. Moreover, ACh, via M3R, activated the EGFR signaling to induce the phosphorylation of ERK1/2 and AKT, and blocking EGFR pathway by specific inhibitor AG1478 suppressed the ACh induced cell proliferation. Furthermore, the M3R antagonist 4-DAMP and darifenacin could markedly inhibit gastric tumor formation in vivo. 4-DAMP could also significantly enhance the cytotoxic activity of 5-Fu against the MKN45 and BGC823 cells, and induce the expression of apoptosis-related proteins such as Bax and Caspase-3. Together, these findings indicated that the autocrine ACh could act through M3R and the EGFR signaling to promote gastric cancer cells proliferation, targeting M3R or EGFR may provide us a potential therapeutic strategy for gastric cancer treatment.

MACC1 mediates acetylcholine-induced invasion and migration by human gastric cancer cells

The neurotransmitter acetylcholine (ACh) promotes the growth and metastasis of several cancers via its M3 muscarinic receptor (M3R). Metastasis-associated in colon cancer-1 (MACC1) is an oncogene that is overexpressed in gastric cancer (GC) and plays an important role in GC progression, though it is unclear how MACC1 activity is regulated in GC. In this study, we demonstrated that ACh acts via M3Rs to promote GC cell invasion and migration as well as expression of several markers of epithelial-mesenchymal transition (EMT). The M3R antagonist darifenacin inhibited GC cell activity in both the presence and absence of exogenous ACh, suggesting GC cells secrete endogenous ACh, which then acts in an autocrine fashion to promote GC cell migration/invasion. ACh up-regulated MACC1 in GC cells, and MACC1 knockdown using siRNA attenuated the effects of ACh on GC cells. AMP-activated protein kinase (AMPK) served as an intermediate signal between ACh and MACC1. These findings suggest that ACh acts via a M3R/AMPK/MACC1 signaling pathway to promote GC cell invasion/migration, which provides insight into the mechanisms underlying GC growth and metastasis and may shed light on new targets for GC treatment.

High expression of muscarinic acetylcholine receptor 3 predicts poor prognosis in patients with pancreatic ductal adenocarcinoma

Aims

Recent studies showed that muscarinic acetylcholine receptor 3 (M3), as a muscarinic acetylcholine receptor family member that plays an important role in normal physiological function, is engaged in cancer progression. However, the role of M3 in pancreatic ductal adenocarcinoma (PDAC) is not known. The aim of this study is to investigate the expression and prognostic value of M3 in patients with PDAC.

Materials and methods

The localization and expression of M3 in PDAC were examined by immunohistochemistry. VAChT was employed to detect parasympathetic nerve fibers in the corresponding M3 PDAC tissues. The correlation between M3 expression and patients’ survival was assessed by Kaplan–Meier analysis.

Results

M3 was discovered predominantly localized in the cell cytoplasm and expressed in all specimens of PDAC patients. Significant correlation was noted between increased M3 intensity and high grade of PDAC (P<0.01), more lymph node metastasis (P<0.01) as well as shorter patient overall survival (P<0.01). Morphologically, cells with high M3 expression were more frequently located at the invasive tumor front/tumor budding cells, metastatic lymph nodes and parasympathetic nerve fibers.

Conclusion

High expression of M3 is a prognostic marker for PDAC.