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The nervous system regulates tissue stem and precursor populations throughout life. Parallel to roles in development, the nervous system is emerging as a critical regulator of cancer, from oncogenesis to malignant growth and metastatic spread. Various preclinical models in a range of malignancies have demonstrated that nervous system activity can control cancer initiation and powerfully influence cancer progression and metastasis. Just as the nervous system can regulate cancer progression, cancer also remodels and hijacks nervous system structure and function. Interactions between the nervous system and cancer occur both in the local tumour microenvironment and systemically. Neurons and glial cells communicate directly with malignant cells in the tumour microenvironment through paracrine factors and, in some cases, through neuron-to-cancer cell synapses. Additionally, indirect interactions occur at a distance through circulating signals and through influences on immune cell trafficking and function. Such cross-talk among the nervous system, immune system and cancer—both systemically and in the local tumour microenvironment—regulates pro-tumour inflammation and anti-cancer immunity. Elucidating the neuroscience of cancer, which calls for interdisciplinary collaboration among the fields of neuroscience, developmental biology, immunology and cancer biology, may advance effective therapies for many of the most difficult to treat malignancies. This Review examines the interplay between the nervous system and tumours, from cancer initiation to progression and metastasis.

Key Points Integrin signalling regulates diverse functions in tumour cells, including migration, invasion, proliferation and survival. In several tumour types, the expression of particular integrins correlates with increased disease progression and decreased patient survival. In addition to tumour cells, integrins are also found on tumour-associated host cells, such as the vascular endothelium, perivascular cells, fibroblasts, bone marrow-derived cells and platelets. Integrin signalling crucially regulates the contribution of these cell types to cancer progression. Therefore, integrin antagonists may inhibit tumour progression by blocking crucial signalling events in both the tumour microenvironment and the tumour cells themselves. Integrins have a profound influence on tumour cells, both in the ligated and unligated states, in which they regulate tumour cell survival and malignancy. Although integrins alone are not oncogenic, recent data have found that some oncogenes may require integrin signalling for their ability to initiate tumour growth and invasion. These effects may be due to the important contribution of integrin signalling in maintaining the cancer stem cell population in a given tumour. Crosstalk between integrins and growth factor or cytokine receptors on both tumour and host cell types is vital for many aspects of tumour progression. Mechanisms of crosstalk include both direct and indirect association of integrins with growth factor or cytokine receptors, which affects the expression, ligand affinity and signalling of the receptors. The important contribution of integrins to the biology of both tumour cells and tumour-associated cell types has made them appealing targets for the design of specific therapeutics. Of particular interest, the integrin αv inhibitor cilengitide is now in a Phase III clinical trial in glioblastoma, and because this is the first integrin antagonist to achieve this milestone it places anti-integrin therapy on the doorstep of clinical availability. In addition to their use as therapeutic targets, integrins can be imaging biomarkers for assessing the efficacy of anti-angiogenic and anti-tumour agents. Integrin-targeted nanoparticles with a diverse array of anti-tumour payloads also represent a particularly promising area of research that may decrease the toxicities associated with systemic delivery of radiation or chemotherapy. The integrins regulate a diverse array of cellular functions that are crucial to the initiation, progression and metastasis of solid tumours. This Review discusses the exciting developments in targeting integrins, including the recent initiation of a Phase III trial for an integrin antagonist in patients with glioblastoma. The integrin family of cell adhesion receptors regulates a diverse array of cellular functions crucial to the initiation, progression and metastasis of solid tumours. The importance of integrins in several cell types that affect tumour progression has made them an appealing target for cancer therapy. Integrin antagonists, including the αvβ3 and αvβ5 inhibitor cilengitide, have shown encouraging activity in Phase II clinical trials and cilengitide is currently being tested in a Phase III trial in patients with glioblastoma. These exciting clinical developments emphasize the need to identify how integrin antagonists influence the tumour and its microenvironment.

Neurons have recently emerged as essential cellular constituents of the tumour microenvironment, and their activity has been shown to increase the growth of a diverse number of solid tumours 1 . Although the role of neurons in tumour progression has previously been demonstrated 2 , the importance of neuronal activity to tumour initiation is less clear—particularly in the setting of cancer predisposition syndromes. Fifteen per cent of individuals with the neurofibromatosis 1 (NF1) cancer predisposition syndrome (in which tumours arise in close association with nerves) develop low-grade neoplasms of the optic pathway (known as optic pathway gliomas (OPGs)) during early childhood 3 , 4 , raising  the possibility that postnatal light-induced activity of the optic nerve drives tumour initiation. Here we use an authenticated mouse model of OPG driven by mutations in the neurofibromatosis 1 tumour suppressor gene ( Nf1 ) 5 to demonstrate that stimulation of optic nerve activity increases optic glioma growth, and that decreasing visual experience via light deprivation prevents tumour formation and maintenance. We show that the initiation of Nf1- driven OPGs ( Nf1- OPGs) depends on visual experience during a developmental period in which Nf1 -mutant mice are susceptible to tumorigenesis. Germline Nf1 mutation in retinal neurons results in aberrantly increased shedding of neuroligin 3 (NLGN3) within the optic nerve in response to retinal neuronal activity. Moreover, genetic Nlgn3 loss or pharmacological inhibition of NLGN3 shedding blocks the formation and progression of Nf1- OPGs. Collectively, our studies establish an obligate role for neuronal activity in the development of some types of brain tumours, elucidate a therapeutic strategy to reduce OPG incidence or mitigate tumour progression, and underscore the role of Nf1 mutation-mediated dysregulation of neuronal signalling pathways in mouse models of the NF1 cancer predisposition syndrome. Mouse models of NF1-associated optic pathway glioma show that tumour initiation and growth are driven by aberrantly high levels of NLGN3 shedding in the optic nerve in response to retinal neuron activity.

Substitution of lysine 27 to methionine in histone H3 (H3K27M) defines an aggressive subtype of diffuse glioma. Previous studies have shown that a H3K27M-specific long peptide vaccine (H3K27M-vac) induces mutation-specific immune responses that control H3K27M + tumors in major histocompatibility complex-humanized mice. Here we describe a first-in-human treatment with H3K27M-vac of eight adult patients with progressive H3K27M + diffuse midline glioma on a compassionate use basis. Five patients received H3K27M-vac combined with anti-PD-1 treatment based on physician’s discretion. Repeat vaccinations with H3K27M-vac were safe and induced CD4 + T cell-dominated, mutation-specific immune responses in five of eight patients across multiple human leukocyte antigen types. Median progression-free survival after vaccination was 6.2 months and median overall survival was 12.8 months. One patient with a strong mutation-specific T cell response after H3K27M-vac showed pseudoprogression followed by sustained complete remission for >31 months. Our data demonstrate safety and immunogenicity of H3K27M-vac in patients with progressive H3K27M + diffuse midline glioma. In this compassionate use study, treatment of adult patients with H3K27M-mutant diffuse midline glioma with a long peptide vaccine targeting H3K27M led to vaccine-induced peripheral T cell immune responses and encouraging clinical efficacy in the majority of patients, including a durable complete response.

Experience sculpts brain structure and function. Activity-dependent modulation of the myelinated infrastructure of the nervous system has emerged as a dimension of adaptive change during childhood development and in adulthood. Myelination is a richly dynamic process, with neuronal activity regulating oligodendrocyte precursor cell proliferation, oligodendrogenesis and myelin structural changes in some axonal subtypes and in some regions of the nervous system. This myelin plasticity and consequent changes to conduction velocity and circuit dynamics can powerfully influence neurological functions, including learning and memory. Conversely, disruption of the mechanisms mediating adaptive myelination can contribute to cognitive impairment. The robust effects of neuronal activity on normal oligodendroglial precursor cells, a putative cellular origin for many forms of glioma, indicates that dysregulated or ‘hijacked’ mechanisms of myelin plasticity could similarly promote growth in this devastating group of brain cancers. Indeed, neuronal activity promotes the pathogenesis of many forms of glioma in preclinical models through activity-regulated paracrine factors and direct neuron-to-glioma synapses. This synaptic integration of glioma into neural circuits is central to tumour growth and invasion. Thus, not only do neuron–oligodendroglial interactions modulate neural circuit structure and function in the healthy brain, but neuron–glioma interactions also have important roles in the pathogenesis of glial malignancies.Neuron–oligodendroglial interactions modulate neural circuit structure and function in the healthy brain. In this Review, Taylor and Monje describe the accumulating evidence for how glial malignancies subvert and repurpose these powerful neuron–glial interactions to drive glioma pathophysiology.

Neuronal activity is emerging as a driver of central and peripheral nervous system cancers. Here, we examined neuronal physiology in mouse models of the tumor predisposition syndrome Neurofibromatosis-1 (NF1), with different propensities to develop nervous system cancers. We show that central and peripheral nervous system neurons from mice with tumor-causing Nf1 gene mutations exhibit hyperexcitability and increased secretion of activity-dependent tumor-promoting paracrine factors. We discovered a neurofibroma mitogen (COL1A2) produced by peripheral neurons in an activity-regulated manner, which increases NF1 -deficient Schwann cell proliferation, establishing that neurofibromas are regulated by neuronal activity. In contrast, mice with the Arg1809Cys Nf1 mutation, found in NF1 patients lacking neurofibromas or optic gliomas, do not exhibit neuronal hyperexcitability or develop these NF1-associated tumors. The hyperexcitability of tumor-prone Nf1 -mutant neurons results from reduced NF1 -regulated hyperpolarization-activated cyclic nucleotide-gated (HCN) channel function, such that neuronal excitability, activity-regulated paracrine factor production, and tumor progression are attenuated by HCN channel activation. Collectively, these findings reveal that NF1 mutations act at the level of neurons to modify tumor predisposition by increasing neuronal excitability and activity-regulated paracrine factor production. Neuronal activity is emerging as a driver of nervous system tumors. Here, the authors show in mouse models of Neurofibromatosis-1 (NF1) that Nf1  mutations differentially drive both central and peripheral nervous system tumor growth in mice through reduced hyperpolarization-activated cyclic nucleotide-gated (HCN) channel function.

Medulloblastoma (MB) comprises a biologically heterogeneous group of embryonal tumours of the cerebellum. Four subgroups of MB have been described (WNT, sonic hedgehog (SHH), Group 3 and Group 4), each of which is associated with different genetic alterations, age at onset and prognosis. These subgroups have broadly been incorporated into the WHO classification of central nervous system tumours but still need to be accounted for to appropriately tailor disease risk to therapy intensity and to target therapy to disease biology. In this Primer, the epidemiology (including MB predisposition), molecular pathogenesis and integrative diagnosis taking histomorphology, molecular genetics and imaging into account are reviewed. In addition, management strategies, which encompass surgical resection of the tumour, cranio-spinal irradiation and chemotherapy, are discussed, together with the possibility of focusing more on disease biology and robust molecularly driven patient stratification in future clinical trials. This Primer by Pfister and colleagues reviews the molecular genetics, diagnosis and management of medulloblastoma and touches upon the quality of life of patients and future outlooks.

Reactive astrocytes have been proposed to become incompetent bystanders in epilepsy as a result of cellular changes rendering them incapable of performing housekeeping tasks. This review discusses new research that suggests that reactive astrocytes may drive the disease process by impairing the inhibitory action of neuronal GABA receptors. Reactive astrocytes have been proposed to become incompetent bystanders in epilepsy as a result of cellular changes rendering them unable to perform important housekeeping functions. Indeed, successful surgical treatment of mesiotemporal lobe epilepsy hinges on the removal of the glial scar. New research now extends the role of astrocytes, suggesting that they may drive the disease process by impairing the inhibitory action of neuronal GABA receptors. Here we discuss studies that include hyperexcitability resulting from impaired supply of astrocytic glutamine for neuronal GABA synthesis, and epilepsy resulting from genetically induced astrogliosis or malignant transformation, both of which render the inhibitory neurotransmitter GABA excitatory. In these examples, glial cells alter the expression or function of neuronal proteins involved in excitability. Although epilepsy has traditionally been thought of as a disease caused by changes in neuronal properties exclusively, these new findings challenge us to consider the contribution of glial cells as drivers of epileptogenesis in acquired epilepsies.

Suzanne Baker and colleagues sequenced the whole genomes of seven pediatric brainstem glioblastomas and matched normal tissue. They found that 78% of diffuse intrinsic pontine gliomas and 22% of non-brainstem pediatric glioblastomas contained a mutation in H3F3A , encoding histone H3.3, or in the related HIST1H3B , encoding histone H3.1, causing a p.Lys27Met amino acid substitution in each protein. To identify somatic mutations in pediatric diffuse intrinsic pontine glioma (DIPG), we performed whole-genome sequencing of DNA from seven DIPGs and matched germline tissue and targeted sequencing of an additional 43 DIPGs and 36 non-brainstem pediatric glioblastomas (non-BS-PGs). We found that 78% of DIPGs and 22% of non-BS-PGs contained a mutation in H3F3A , encoding histone H3.3, or in the related HIST1H3B , encoding histone H3.1, that caused a p.Lys27Met amino acid substitution in each protein. An additional 14% of non-BS-PGs had somatic mutations in H3F3A causing a p.Gly34Arg alteration.

Key Points Neuroblastomas in younger children have a higher propensity to undergo spontaneous regression than any other human malignancy, but only genetic subtype 1 tumours with numerical chromosome aberrations are prone to spontaneous regression Although spontaneous regression of neuroblastoma is strongly associated with stage 4S disease, mass-screening studies suggest that genetic subtype 1 tumours of any stage in infants <18 months can undergo spontaneous regression The TrkA/NGF pathway might have a major role in causing spontaneous regression, but alternative mechanisms might involve cellular or humoral immune responses, telomere shortening, or epigenetic modifications Inhibition of the TrkA pathway represents the most-promising approach to initiate regression in infants with favourable tumours; other approaches involving immune modulation or epigenetic regulation are being investigated Recent studies of neuroblastoma have shed light on the dramatic heterogeneity in its clinical behaviour, which spans from spontaneous regression or differentiation to relentless disease progression. This Review describes the different mechanisms of spontaneous neuroblastoma regression—including neurotrophin deprivation, humoral or cellular immunity, loss of telomerase activity and alterations in epigenetic regulation—and the consequent therapeutic approaches, as a better understanding of these mechanisms might help to identify optimal therapies. Recent genomic and biological studies of neuroblastoma have shed light on the dramatic heterogeneity in the clinical behaviour of this disease, which spans from spontaneous regression or differentiation in some patients, to relentless disease progression in others, despite intensive multimodality therapy. This evidence also suggests several possible mechanisms to explain the phenomena of spontaneous regression in neuroblastomas, including neurotrophin deprivation, humoral or cellular immunity, loss of telomerase activity and alterations in epigenetic regulation. A better understanding of the mechanisms of spontaneous regression might help to identify optimal therapeutic approaches for patients with these tumours. Currently, the most druggable mechanism is the delayed activation of developmentally programmed cell death regulated by the tropomyosin receptor kinase A pathway. Indeed, targeted therapy aimed at inhibiting neurotrophin receptors might be used in lieu of conventional chemotherapy or radiation in infants with biologically favourable tumours that require treatment. Alternative approaches consist of breaking immune tolerance to tumour antigens or activating neurotrophin receptor pathways to induce neuronal differentiation. These approaches are likely to be most effective against biologically favourable tumours, but they might also provide insights into treatment of biologically unfavourable tumours. We describe the different mechanisms of spontaneous neuroblastoma regression and the consequent therapeutic approaches.