Impact of the Sensory Neurons on Melanoma Growth In Vivo

From pain to tumor immunity: influence of peripheral sensory neurons in cancer

The nervous and immune systems are the primary sensory interfaces of the body, allowing it to recognize, process, and respond to various stimuli from both the external and internal environment. These systems work in concert through various mechanisms of neuro-immune crosstalk to detect threats, provide defense against pathogens, and maintain or restore homeostasis, but can also contribute to the development of diseases. Among peripheral sensory neurons (PSNs), nociceptive PSNs are of particular interest. They possess a remarkable capability to detect noxious stimuli in the periphery and transmit this information to the brain, resulting in the perception of pain and the activation of adaptive responses. Pain is an early symptom of cancer, often leading to its diagnosis, but it is also a major source of distress for patients as the disease progresses. In this review, we aim to provide an overview of the mechanisms within tumors that are likely to induce cancer pain, exploring a range of factors from etiological elements to cellular and molecular mediators. In addition to transmitting sensory information to the central nervous system, PSNs are also capable, when activated, to produce and release neuropeptides (e.g., CGRP and SP) from their peripheral terminals. These neuropeptides have been shown to modulate immunity in cases of inflammation, infection, and cancer. PSNs, often found within solid tumors, are likely to play a significant role in the tumor microenvironment, potentially influencing both tumor growth and anti-tumor immune responses. In this review, we discuss the current state of knowledge about the degree of sensory innervation in tumors. We also seek to understand whether and how PSNs may influence the tumor growth and associated anti-tumor immunity in different mouse models of cancer. Finally, we discuss the extent to which the tumor is able to influence the development and functions of the PSNs that innervate it.

Melanomas and mast cells: an ambiguous relationship

Mast cells (MCs) accumulate in a broad range of tumors, including melanomas. While MCs are potent initiators of immunity in infection, and in allergic inflammation, the function of MCs in anti-melanoma immunity is unclear. MCs have the potential to release tumoricidal cytokines and proteases, to activate antigen-presenting cells and to promote anti-tumor adaptive immunity. However, within the immunosuppressive tumor microenvironment (TME), MC activation may promote angiogenesis and contribute to tumor growth. In this review, the relationship between MCs and melanomas is discussed with a focus on the impact of the TME on MC activation.

The relationship between the tumor and its innervation: historical, methodical, morphological, and functional assessments - A minireview

The acceptance of the tumor as a non-isolated structure within the organism has opened a space for the study of a wide spectrum of potential direct and indirect interactions, not only between the tumor tissue and its vicinity, but also between the tumor and its macroenvironment, including the nervous system. Although several lines of evidence have implicated the nervous system in tumor growth and progression, for many years, researchers believed that tumors lacked innervation and the notion of indirect neuro-neoplastic interactions via other systems (e.g., immune, or endocrine) predominated. The original idea that tumors are supplied not only by blood and lymphatic vessels, but also autonomic and sensory nerves that may influence cancer progression, is not a recent phenomenon. Although in the past, mainly due to the insufficiently sensitive methodological approaches, opinions regarding the presence of nerves in tumors were inconsistent. However, data from the last decade have shown that tumors are able to stimulate the formation of their own innervation by processes called neo-neurogenesis and neo-axonogenesis. It has also been shown that tumor infiltrating nerves are not a passive, but active components of the tumor microenvironment and their presence in the tumor tissue is associated with an aggressive tumor phenotype and correlates with poor prognosis. The aim of the present review was to 1) summarize the available knowledge regarding the course of tumor innervation, 2) present the potential mechanisms and pathways for the possible induction of new nerve fibers into the tumor microenvironment, and 3) highlight the functional significance/consequences of the nerves infiltrating the tumors.

Crosstalk Between Peripheral Innervation and Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive lethal malignancy, characterized by late diagnosis, aggressive growth, and therapy resistance, leading to a poor overall prognosis. Emerging evidence shows that the peripheral nerve is an important non-tumor component in the tumor microenvironment that regulates tumor growth and immune escape. The crosstalk between the neuronal system and PDAC has become a hot research topic that may provide novel mechanisms underlying tumor progression and further uncover promising therapeutic targets. In this review, we highlight the mechanisms of perineural invasion and the role of various types of tumor innervation in the progression of PDAC, summarize the potential signaling pathways modulating the neuronal-cancer interaction, and discuss the current and future therapeutic possibilities for this condition.

Understanding and modeling nerve-cancer interactions

The peripheral nervous system plays an important role in cancer progression. Studies in multiple cancer types have shown that higher intratumoral nerve density is associated with poor outcomes. Peripheral nerves have been shown to directly regulate tumor cell properties, such as growth and metastasis, as well as affect the local environment by modulating angiogenesis and the immune system. In this Review, we discuss the identity of nerves in organs in the periphery where solid tumors grow, the known mechanisms by which nerve density increases in tumors, and the effects these nerves have on cancer progression. We also discuss the strengths and weaknesses of current in vitro and in vivo models used to study nerve-cancer interactions. Increased understanding of the mechanisms by which nerves impact tumor progression and the development of new approaches to study nerve-cancer interactions will facilitate the discovery of novel treatment strategies to treat cancer by targeting nerves.

Sensory nerves enhance triple-negative breast cancer invasion and metastasis via the axon guidance molecule PlexinB3

In breast cancer, nerve presence has been correlated with more invasive disease and worse prognosis, yet the mechanisms by which different types of peripheral nerves drive tumor progression remain poorly understood. In this study, we identified sensory nerves as more abundant in human triple-negative breast cancer (TNBC) tumors. Co-injection of sensory neurons isolated from the dorsal root ganglia (DRG) of adult female mice with human TNBC cells in immunocompromised mice increased the number of lung metastases. Direct in vitro co-culture of human TNBC cells with the dorsal root ganglia (DRG) of adult female mice revealed that TNBC cells adhere to sensory neuron fibers leading to an increase in migration speed. Species-specific RNA sequencing revealed that co-culture of TNBC cells with sensory nerves upregulates the expression of genes associated with cell migration and adhesion in cancer cells. We demonstrated that lack of the semaphorin receptor PlexinB3 in cancer cells attenuate their adhesion to and migration on sensory nerves. Together, our results identify a mechanism by which nerves contribute to breast cancer migration and metastasis by inducing a shift in TNBC cell gene expression and support the rationale for disrupting neuron-cancer cell interactions to target metastasis.

Stem Cell-Based Models for Studying the Effects of Cancer and Cancer Therapies on the Peripheral Nervous System

In recent years, the complexity of cancer and cancer therapies and their interactions with the peripheral nervous system have come into focus, but limitations in experimental models have remained a significant challenge in the field. As evidence, there are currently no therapies approved that target cancer-peripheral nervous system or cancer therapy-peripheral nervous system interactions as an anti-neoplastic or anti-neurotoxic agent, respectively. Human pluripotent stem cells offer an appealing model system that, unlike rodent models, is compatible with high throughput, high content applications; techniques that reflect modern drug discovery methodologies. Thus, utilizing the key advantages of stem cell-based models in tandem with the strengths of traditional animal models offers a complementary and interdisciplinary strategy to advance cancer and cancer therapy-peripheral nervous system research and drug discovery. In this review, the current status of the cancer-peripheral nervous system and cancer therapy-peripheral nervous system research is discussed, examples where stem cell-based models have been implemented are described, and avenues where stem cell-based models may further advance the field are proposed.

The Role of Neural Signaling in the Pancreatic Cancer Microenvironment

Simple Summary

Pancreatic cancer is a highly lethal malignant disease with a dense stroma, called the tumor microenvironment. Accumulating evidence indicates the important role of sympathetic, parasympathetic, and sensory nerves in the tumor microenvironment of various cancers, including pancreatic cancer. Cancer cells and neural cells interact with each other to form a complex network and cooperatively promote cancer growth and invasion. In this review article, we describe the current understanding of the role of nerves in the tumor microenvironment.

Abstract

Pancreatic cancer is one of the most lethal malignant diseases. Various cells in the tumor microenvironment interact with tumor cells and orchestrate to support tumor progression. Several kinds of nerves are found in the tumor microenvironment, and each plays an essential role in tumor biology. Recent studies have shown that sympathetic, parasympathetic, and sensory neurons are found in the pancreatic cancer microenvironment. Neural signaling not only targets neural cells, but tumor cells and immune cells via neural receptors expressed on these cells, through which tumor growth, inflammation, and anti-tumor immunity are affected. Thus, these broad-range effects of neural signaling in the pancreatic cancer microenvironment may represent novel therapeutic targets. The modulation of neural signaling may be a therapeutic strategy targeting the whole tumor microenvironment. In this review, we describe the current understanding of the role of nerves in the tumor microenvironment of various cancers, with an emphasis on pancreatic cancer. We also discuss the underlying mechanisms and the possibility of therapeutic applications.

Neuroendocrine regulations in tissue-specific immunity: From mechanism to applications in tumor

Immune responses in nonlymphoid tissues play a vital role in the maintenance of homeostasis. Lots of evidence supports that tissue-specific immune cells provide defense against tumor through the localization in different tissue throughout the body, and can be regulated by diverse factors. Accordingly, the distribution of nervous tissue is also tissue-specific which is essential in the growth of corresponding organs, and the occurrence and development of tumor. Although there have been many mature perspectives on the neuroendocrine regulation in tumor microenvironment, the neuroendocrine regulation of tissue-specific immune cells has not yet been summarized. In this review, we focus on how tissue immune responses are influenced by autonomic nervous system, sensory nerves, and various neuroendocrine factors and reversely how tissue-specific immune cells communicate with neuroendocrine system through releasing different factors. Furthermore, we pay attention to the potential mechanisms of neuroendocrine-tissue specific immunity axis involved in tumors. This may provide new insights for the immunotherapy of tumors in the future.

Sensory nerves impede the formation of tertiary lymphoid structures and development of protective anti-melanoma immune responses

Peripheral neurons comprise a critical component of the tumor microenvironment (TME). The role of the autonomic innervation in cancer has been firmly established. However, the effect of the afferent (sensory) neurons on tumor progression remains unclear. Utilizing surgical and chemical skin sensory denervation methods, we showed that afferent neurons supported the growth of melanoma tumors in vivo and demonstrated that sensory innervation limited the activation of effective anti-tumor immune responses. Specifically, sensory ablation led to improved leukocyte recruitment into tumors, with decreased presence of lymphoid and myeloid immunosuppressive cells and increased activation of T-effector cells within the TME. Cutaneous sensory nerves hindered maturation of intratumoral high endothelial venules (HEVs) and limited formation of mature tertiary lymphoid-like structures containing organized clusters of CD4+ T cells and B cells. Denervation further increased T-cell clonality and expanded the B-cell repertoire in the TME. Importantly, CD8a depletion prevented denervation-dependent anti-tumor effects. Finally, we observed that gene signatures of inflammation and the content of neuron-associated transcripts inversely correlated in human primary cutaneous melanomas, with the latter representing a negative prognostic marker of patient overall survival. Our results suggest that tumor-associated sensory neurons negatively regulate the development of protective anti-tumor immune responses within the TME, thereby defining a novel target for therapeutic intervention in the melanoma setting.

Model-Based Anticancer Effect of Botulinum Neurotoxin Type A1 on Syngeneic Melanoma Mice

In recent, Botulinum Neurotoxin A1 (BoNT/A1) has been suggested as a potential anticancer agent due to neuronal innervation in tumor cells. Although potential BoNT/A1's mechanism of action for the tumor suppression has been gradually revealed so far, there were no reports to figure out the exposure-response relationships because of the difficulty of its quantitation in the biological matrix. The main objectives of this study were to measure the anticancer effect of BoNT/A1 using a syngeneic mouse model transplanted with melanoma cells (B16-F10) and developed a kinetic-pharmacodynamic (K-PD) model for quantitative exposure-response evaluation. To overcome the lack of exposure information, the K-PD model was implemented by the virtual pharmacokinetic compartment link to the pharmacodynamic compartment of Simeoni's tumor growth inhibition model and evaluated using curve-fitting for the tumor growth-time profile after intratumoral injection of BoNT/A1. The final K-PD model was adequately explained for a pattern of tumor growth depending on represented exposure parameters and simulation studies were conducted to determine the optimal dose under various scenarios considering dose strength and frequency. The optimal dose range and regimen of ≥13.8 units kg^-1 once a week or once every 3 days was predicted using the final model in B16-F10 syngeneic model and it was demonstrated with an extra in-vivo experiment. In conclusion, the K-PD model of BoNT/A1 was well developed to optimize the dosing regimen for evaluation of anticancer effect and this approach could be expandable to figure out quantitative interpretation of BoNT/A1's efficacy in various xenograft and/or syngeneic models.

Neural regulations of the tumor microenvironment

The identification of nerves in the tumor microenvironment has ushered in a new area of research in cancer biology. Numerous studies demonstrate the presence of various types of peripheral nerves (sympathetic, parasympathetic, sensory) within the tumor microenvironment; moreover, an increased density of nerves in the tumor microenvironment correlates with worse prognosis. In this review, we address the current understanding of nerve-mediated alterations of the tumor microenvironment and how they impact disease through a variety of processes, including direct nerve-cancer cell communication, alteration of the infiltrative immune population, and alteration of stromal components.

Intra-Tumoral Nerve-Tracing in a Novel Syngeneic Model of High-Grade Serous Ovarian Carcinoma

Dense tumor innervation is associated with enhanced cancer progression and poor prognosis. We observed innervation in breast, prostate, pancreatic, lung, liver, ovarian, and colon cancers. Defining innervation in high-grade serous ovarian carcinoma (HGSOC) was a focus since sensory innervation was observed whereas the normal tissue contains predominantly sympathetic input. The origin, specific nerve type, and the mechanisms promoting innervation and driving nerve-cancer cell communications in ovarian cancer remain largely unknown. The technique of neuro-tracing enhances the study of tumor innervation by offering a means for identification and mapping of nerve sources that may directly and indirectly affect the tumor microenvironment. Here, we establish a murine model of HGSOC and utilize image-guided microinjections of retrograde neuro-tracer to label tumor-infiltrating peripheral neurons, mapping their source and circuitry. We show that regional sensory neurons innervate HGSOC tumors. Interestingly, the axons within the tumor trace back to local dorsal root ganglia as well as jugular-nodose ganglia. Further manipulations of these tumor projecting neurons may define the neuronal contributions in tumor growth, invasion, metastasis, and responses to therapeutics.

Cancer-Associated Neurogenesis and Nerve-Cancer Cross-talk

In this review, we highlight recent discoveries regarding mechanisms contributing to nerve-cancer cross-talk and the effects of nerve-cancer cross-talk on tumor progression and dissemination. High intratumoral nerve density correlates with poor prognosis and high recurrence across multiple solid tumor types. Recent research has shown that cancer cells express neurotrophic markers such as nerve growth factor, brain-derived neurotrophic factor, and glial cell-derived neurotrophic factor and release axon-guidance molecules such as ephrin B1 to promote axonogenesis. Tumor cells recruit new neural progenitors to the tumor milieu and facilitate their maturation into adrenergic infiltrating nerves. Tumors also rewire established nerves to adrenergic phenotypes via exosome-induced neural reprogramming by p53-deficient tumors. In turn, infiltrating sympathetic nerves facilitate cancer progression. Intratumoral adrenergic nerves release noradrenaline to stimulate angiogenesis via VEGF signaling and enhance the rate of tumor growth. Intratumoral parasympathetic nerves may have a dichotomous role in cancer progression and may induce Wnt-β-catenin signals that expand cancer stem cells. Importantly, infiltrating nerves not only influence the tumor cells themselves but also impact other cells of the tumor stroma. This leads to enhanced sympathetic signaling and glucocorticoid production, which influences neutrophil and macrophage differentiation, lymphocyte phenotype, and potentially lymphocyte function. Although much remains unexplored within this field, fundamental discoveries underscore the importance of nerve-cancer cross-talk to tumor progression and may provide the foundation for developing effective targets for the inhibition of tumor-induced neurogenesis and tumor progression.

Neuroimmune Regulation of Surgery-Associated Metastases

Surgery remains an essential therapeutic approach for most solid malignancies. Although for more than a century accumulating clinical and experimental data have indicated that surgical procedures themselves may promote the appearance and progression of recurrent and metastatic lesions, only in recent years has renewed interest been taken in the mechanism by which metastasizing of cancer occurs following operative procedures. It is well proven now that surgery constitutes a risk factor for the promotion of pre-existing, possibly dormant micrometastases and the acceleration of new metastases through several mechanisms, including the release of neuroendocrine and stress hormones and wound healing pathway-associated immunosuppression, neovascularization, and tissue remodeling. These postoperative consequences synergistically facilitate the establishment of new metastases and the development of pre-existing micrometastases. While only in recent years the role of the peripheral nervous system has been recognized as another contributor to cancer development and metastasis, little is known about the contribution of tumor-associated neuronal and neuroglial elements in the metastatic disease related to surgical trauma and wound healing. Specifically, although numerous clinical and experimental data suggest that biopsy- and surgery-induced wound healing can promote survival and metastatic spread of residual and dormant malignant cells, the involvement of the tumor-associated neuroglial cells in the formation of metastases following tissue injury has not been well understood. Understanding the clinical significance and underlying mechanisms of neuroimmune regulation of surgery-associated metastasis will not only advance the field of neuro–immuno–oncology and contribute to basic science and translational oncology research but will also produce a strong foundation for developing novel mechanism-based therapeutic approaches that may protect patients against the oncologically adverse effects of primary tumor biopsy and excision.

Mini-review: Trophic interactions between cancer cells and primary afferent neurons

Cancer neurobiology is an emerging discipline that inevitably unfurls new perspectives in oncology. The role that nerves play in cancer progression resonates with the long-reported dependency of tumors on neuro-molecular mechanisms that remain insufficiently elucidated. Whereas interactions between neurotrophic growth factors and receptors have been heavily studied in the nervous system, their expression in cancers and their impact on tumor cell growth and metastasis through their corresponding signaling pathways has been undervalued. Accumulating evidence suggests that trophic factors released by nerves strongly influence tumor development and that this neural contribution appears to not only play a stimulatory role but also function as an essential part of the tumor's microenvironment. This bidirectional communication between proliferating cells and tumor-infiltrating nerves drives axonogenesis and tumor growth and migration. Acquiring a better understanding of the trophic interactions between primary afferent neurons and invading tumors will guide clinically actionable strategies to prevent tumor-associated axonogenesis, disrupting the chemical crosstalk between neurons and tumors and ultimately decreasing tumor growth and spread.

Head and neck cancer exosomes drive microRNA-mediated reprogramming of local neurons

Solid tumors are complex collections of cells surrounded by benign tissues that influence and are influenced by the tumor. These surrounding cells include vasculature, immune cells, neurons, and other cell types, and are collectively known as the tumor microenvironment. Tumors manipulate their microenvironment for the benefit of the tumor. Autonomic neurons innervate and drive malignant growth in a variety of solid tumors. However, the mechanisms underlying neuron-tumor relationships are not well understood. Recently, Amit et al. described that trophic relationships between oral cavity squamous cell carcinomas (OCSCCs) and nearby autonomic neurons arise through direct signaling between tumors and local neurons. An inducible tumor model in which 4NQO was introduced into the drinking water of Trp53 knockout mice was used to model OCSCC-microenvironment interactions. Using this model, this group discovered that loss of p53 expression in OCSCC tumors resulted in increased nerve density within these tumors. This neuritogenesis was controlled by tumor-derived microRNA-laden extracellular vesicles (EVs). Specifically, EV-delivered miR-34a inhibited neuritogenesis, whereas EV-delivered miR-21 and miR-324 increased neuritogenesis. The neurons innervating p53-deficient OCSCC tumors were predominantly adrenergic and arose through the transdifferentiation of trigeminal sensory nerve fibers to adrenergic nerve fibers. This transdifferentiation corresponded with increased expression of neuron-reprogramming transcription factors, including POU5F1, KLF4, and ASCL1, which were overexpressed in the p53-deficient samples, and are proposed targets of miR-34a-mediated regulation. Human OCSCC samples enriched in adrenergic neuron markers are associated strongly with poor outcomes, thus demonstrating the relevance of these findings to cancer patients.

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.

Ablation of sensory nerves favours melanoma progression

The tumour mass is composed not only of heterogeneous neoplastic cells, but also a variety of other components that may affect cancer cells behaviour. The lack of detailed knowledge about all the constituents of the tumour microenvironment restricts the design of effective treatments. Nerves have been reported to contribute to the growth and maintenance of numerous tissues. The effects of sensory innervations on tumour growth remain unclear. Here, by using state-of-the-art techniques, including Cre/loxP technologies, confocal microscopy, in vivo-tracing and chemical denervation, we revealed the presence of sensory nerves infiltrating within the melanoma microenvironment, and affecting cancer progression. Strikingly, melanoma growth in vivo was accelerated following genetic ablation or chemical denervation of sensory nerves. In humans, a retrospective analysis of melanoma patients revealed that increased expression of genes related to sensory nerves in tumours was associated with better clinical outcomes. These findings suggest that sensory innervations counteract melanoma progression. The emerging knowledge from this research provides a novel target in the tumour microenvironment for therapeutic benefit in cancer patients.

Nerve input to tumours: Pathophysiological consequences of a dynamic relationship

It is well known that tumours arising in different organs are innervated and that 'perineural invasion' (cancer cells escaping from the tumour by following the nerve trunk) is a negative prognostic factor. More surprisingly, increasing evidence suggests that the nerves can provide active inputs to tumours and there is two-way communication between nerves and cancer cells within the tumour microenvironment. Cells of the immune system also interact with the nerves and cancer cells. Thus, the nerve connections can exert significant control over cancer progression and modulating these (physically or chemically) can affect significantly the cancer process. Nerve inputs to tumours are derived mainly from the sympathetic (adrenergic) and the parasympathetic (cholinergic) systems, which are interactive. An important component of the latter is the vagus nerve, the largest of the cranial nerves. Here, we present a two-part review of the nerve inputs to tumours and their effects on tumorigenesis. First, we review briefly some relevant general issues including ultrastructural aspects, stemness, interactions between neurones and primary tumours, and communication between neurones and metastasizing tumour cells. Ultrastructural characteristics include synaptic vesicles, tumour microtubes and gap junctions enabling formation of cellular networks. Second, we evaluate the pathophysiology of the nerve input to five major carcinomas: cancers of prostate, stomach, colon, lung and pancreas. For each cancer, we present (i) the nerve inputs normally present in the cancer organ and (ii) how these interact and influence the cancer process. The best clinical evidence for the role of nerves in promoting tumorigenesis comes from prostate cancer patients where metastatic progression has been shown to be suppressed significantly in cases of spinal cord injury. The balance of the sympathetic and parasympathetic contributions to early versus late tumorigenesis varies amongst the different cancers. Different branches of the vagus provide functional inputs to several of the carcinomas and, in two-way interaction with the sympathetic nervous system, affect different stages of the cancer process. Overall, the impact of the vagus nerve can be 'direct' or 'indirect'. Directly, the effect of the vagus is primarily to promote tumorigenesis and this is mediated through cholinergic receptor mechanisms. Indirectly, pro- and anti-tumour effects can occur by stimulation or inhibition of the sympathetic nervous system, respectively. Less well understood are the 'indirect' anti-tumour effect of the vagus nerve via immunomodulation/inflammation, and the role of sensory innervation. A frequent occurrence in the nerve-tumour interactions is the presence of positive feedback driven by agents like nerve growth factor. We conclude that the nerve inputs to tumours can actively and dynamically impact upon cancer progression and are open to clinical exploitation.

The Neuroimmune Axis in the Tumor Microenvironment

Cancer is a complex ecosystem and should be considered in the context of its cellular and molecular microenvironment, which includes the nerves. Peripheral nerves can modulate phenotype and behavior of the malignant cells and thus affect tumor growth and metastasis. Only recently has the role of neuroimmune cross-talk surfaced as a key contributor to cancer progression. However, little is known about the immunomodulatory role of the neuroglial cells in cancer progression and metastasis and the response to therapy. Schwann cells, the principal glial cells of the peripheral nervous system, are now considered to be important players in the tumor microenvironment. They can directly accelerate malignant cell migration and the formation of metastases. Better understanding of the neuroimmune circuits in the tumor milieu will be instrumental in the development of novel therapeutic approaches for the malignancies known to be associated with inflammation and dysregulated immune responses.

Schwann cells shape the neuro-immune environs and control cancer progression

At present, significant experimental and clinical data confirm the active involvement of the peripheral nervous system (PNS) in different phases of cancer development and progression. Most of the research effort focuses on the impact of distinct neuronal types, e.g., adrenergic, cholinergic, dopaminergic, etc. in carcinogenesis, generally ignoring neuroglia. The very fact that these cells far outnumber the other cellular types may also play an important role worthy of study in this context. The most prevalent neuroglia within the PNS consists of Schwann cells (SCs). These cells play a substantial role in maintaining homeostasis within the nervous system. They possess distinct immunomodulatory, inflammatory and regenerative capacities-also, one should consider their broad distribution throughout the body; this makes them a perfect target for malignant cells during the initial stages of cancer development and the very formation of the tumor microenvironment itself. We show that SCs in the tumor milieu attract different subsets of immune regulators and augment their ability to suppress effector T cells. SCs may also up-regulate invasiveness of tumor cells and support metastatic disease. We outline the interactive potential of SCs juxtaposed with cancerous cells, referring to data from various external sources alongside data of our own.

Emergence of neural regulatory mechanisms in carcinogenesis

Emerging data indicate that the nervous system plays an important role in carcinogenesis. However, more studies are required to help further elucidate the mechanisms involved in the neural regulation of carcinogenesis. Some recent findings describing the neural regulatory mechanisms of action in prostate cancer, pancreatic cancer and hepatocellular carcinoma are discussed, with a focus on the sympathetic, parasympathetic, and sensory neuronal elements of the nervous system. Norepinephrine, which is released by the sympathetic nervous system and binds to the beta-adrenergic receptor, regulates cellular responses in both normal and tumor cells. It has also been shown that the destruction of sensory neurons can prevent or at least slow pancreatic cancer. Cortisol, the main stress hormone, is also discussed and how it could potentially be involved in hepatocellular carcinoma development. The importance of studying other signaling molecules in the nervous system, such as oxytocin and its receptor, the oxytocin receptor, and how they might be involved in carcinogenesis when aberrantly expressed is highlighted. This is an area of study which clearly needs further investigation. A clearer understanding of the detailed mechanisms of how the nervous system is involved in carcinogenesis could potentially aid in the identification of novel biomarkers and development of novel preventative and therapeutic strategies in various cancers.

Melanoma-Induced Reprogramming of Schwann Cell Signaling Aids Tumor Growth

The tumor microenvironment has been compared with a nonhealing wound involving a complex interaction between multiple cell types. Schwann cells, the key regulators of peripheral nerve repair, have recently been shown to directly affect nonneural wound healing. Their role in cancer progression, however, has been largely limited to neuropathic pain and perineural invasion. In this study, we showed that melanoma activated otherwise dormant functions of Schwann cells aimed at nerve regeneration and wound healing. Such reprogramming of Schwann cells into repair-like cells occurred during the destruction and displacement of neurons as the tumor expanded and via direct signaling from melanoma cells to Schwann cells, resulting in activation of the nerve injury response. Melanoma-activated Schwann cells significantly altered the microenvironment through their modulation of the immune system and the extracellular matrix in a way that promoted melanoma growth in vitro and in vivo. Local inhibition of Schwann cell activity following cutaneous sensory nerve transection in melanoma orthotopic models significantly decreased the rate of tumor growth. Tumor-associated Schwann cells, therefore, can have a significant protumorigenic effect and may present a novel target for cancer therapy. SIGNIFICANCE: These findings reveal a role of the nerve injury response, particularly through functions of activated Schwann cells, in promoting melanoma growth.

The ATP-Binding Cassette Gene ABCF1 Functions as an E2 Ubiquitin-Conjugating Enzyme Controlling Macrophage Polarization to Dampen Lethal Septic Shock

Sepsis is a bi-phasic inflammatory disease that threatens approximately 30 million lives and claims over 14 million annually, yet little is known regarding the molecular switches and pathways that regulate this disease. Here, we have described ABCF1, an ATP-Binding Cassette (ABC) family member protein, which possesses an E2 ubiquitin enzyme activity, through which it controls the Lipopolysaccharide (LPS)- Toll-like Receptor-4 (TLR4) mediated gram-negative insult by targeting key proteins for K63-polyubiquitination. Ubiquitination by ABCF1 shifts the inflammatory profile from an early phase MyD88-dependent to a late phase TRIF-dependent signaling pathway, thereby regulating TLR4 endocytosis and modulating macrophage polarization from M1 to M2 phase. Physiologically, ABCF1 regulates the shift from the inflammatory phase of sepsis to the endotoxin tolerance phase, and modulates cytokine storm and interferon-β (IFN-β)-dependent production by the immunotherapeutic mediator, SIRT1. Consequently, ABCF1 controls sepsis induced mortality by repressing hypotension-induced renal circulatory dysfunction.

Expression of PD-L1 in tumor-associated nerves correlates with reduced CD8+ tumor-associated lymphocytes and poor prognosis in prostate cancer

To investigate immune profile consisting of stromal PD-L1 expression, inhibitory or non-T-cell inflamed tumor microenvironment that may predict response to anti-PD-L1/PD-1 immunotherapy in prostate cancer, we validated the specificity of a PD-L1 monoclonal antibody (E1L3N) and identified PD-L1 specific expression in prostatic stromal nerve cells. PD-L1 expression was analyzed in 73 primary prostate cancers and 7 castration-resistant prostate cancers (CRPC) by immunohistochemistry (IHC) and resulting data from primary prostate cancers were correlated with tumor-associated lymphocytes (TALs), clinicopathological characteristics and clinical outcome. PD-L1 was expressed in the tumor cells in only one primary prostate cancer case and none of the CRPC. However, PD-L1 was frequently observed in the nerve branches in the tumor-associated stroma (69 of 73 cases, 94.5%), supported by colocalization with axonal marker PGP9.5. FoxP3-, CD3- and CD8-positive T lymphocytes were observed in 74.6% (47/63), 98.4% (62/63) and 100% (61/61) of the cases, respectively. The density of PD-L1⁺ tumor-associated nerves (TANs) was inversely correlated with that of CD8⁺ TALs. Higher density of PD-L1⁺ TANs was significantly associated with biochemical recurrence (BCR) in Kaplan-Meier survival analysis (p = 0.016). In both univariate and multivariate Cox analysis, the density of PD-L1⁺ TANs was independently prognostic of BCR. In conclusion, PD-L1 expression is rare in prostate tumor cells but prevalent in TANs and negatively correlated with CD8⁺ TALs. Neuro-immunological interaction may be a contribution to immune-suppressive microenvironment. Combinatorial treatment regimen designs to neural PD-L1 and TALs should be warranted in future clinical application of anti-PD-L1/PD-1 immunotherapy in prostate cancer.

Schwann Cells Augment Cell Spreading and Metastasis of Lung Cancer

Although lungs are densely innervated by the peripheral nervous system (PNS), the role of the PNS in the progression of lung cancer is unknown. In this study, we report that mouse adult Schwann cells (SC), the principal glial cells of the PNS, can regulate the motility of lung cancer cells in vitro and the formation of metastases in vivo SCs promoted epithelial-to-mesenchymal transition (EMT) and the motility of two lung cancer cell lines by increasing expression of Snail and Twist in tumor cells; blocking of Snail and Twist expression abolished SC-induced motility of tumor cells. SC-derived CXCL5 was responsible for EMT in lung cancer cells, as the inhibition of CXCL5 or its receptor CXCR2 reduced SC-induced expression of Snail and Twist and reduced motility in tumor cells. CXCL5/CXCR2 binding activated the PI3K/AKT/GSK-3β/Snail-Twist signaling pathway in lung cancer cells, and the PI3K inhibitor blocked CXCL5-dependent phosphorylation of AKT and GSK-3β, reduced expression of Snail/Twist, and limited tumor cell invasiveness. SC conditioning of tumor cells prior to their injection into mice significantly increased the formation of metastases in the regional lymph nodes. In summary, SCs can regulate the CXCL5/CXCR2/PI3K/AKT/GSK-3β/Snail-Twist pathway to promote EMT, invasiveness, and metastatic potential of lung cancer cells. Our results reveal a new role of the PNS in the functional organization of the tumor microenvironment and tumor progression.Significance: This study increases our understanding of how nerves and, in particular, specific glial cells, Schwann cells, in the peripheral nervous system, may help promote tumor growth and metastasis. Cancer Res; 78(20); 5927-39. ©2018 AACR.

Schwann cells: a new player in the tumor microenvironment

Cancerous cells must cooperate with the surrounding stroma and non-malignant cells within the microenvironment to support the growth and invasion of the tumor. The nervous system is a component of every organ system of the body, and therefore, is invariably at the front line of the tumor invasion. Due to the complexity of the nervous system physiology, this review separately discusses the contributions of the central and peripheral nervous systems to the tumorigenesis and tumor progression. We further focus the discussion on the evidence that Schwann cells aid in tumor growth and invasion. Schwann cells, a largely unexplored element of the tumor microenvironment, may participate in the creation of tumor-favorable conditions through both bi-directional interaction with cancer cells and the facilitation of the immune-suppressive microenvironment through the mechanism of neural repair and immunomodulation.