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

Tumor-infiltrating nerves functionally alter brain circuits and modulate behavior in a mouse model of head-and-neck cancer

Cancer patients often experience changes in mental health, prompting an exploration into whether nerves infiltrating tumors contribute to these alterations by impacting brain functions. Using a mouse model for head and neck cancer and neuronal tracing, we show that tumor-infiltrating nerves connect to distinct brain areas. The activation of this neuronal circuitry altered behaviors (decreased nest-building, increased latency to eat a cookie, and reduced wheel running). Tumor-infiltrating nociceptor neurons exhibited heightened calcium activity and brain regions receiving these neural projections showed elevated Fos as well as increased calcium responses compared to non-tumor-bearing counterparts. The genetic elimination of nociceptor neurons decreased brain Fos expression and mitigated the behavioral alterations induced by the presence of the tumor. While analgesic treatment restored nesting and cookie test behaviors, it did not fully restore voluntary wheel running indicating that pain is not the exclusive driver of such behavioral shifts. Unraveling the interaction between the tumor, infiltrating nerves, and the brain is pivotal to developing targeted interventions to alleviate the mental health burdens associated with cancer.

Retrograde tracing of breast cancer-associated sensory neurons

Breast cancer is one of the leading causes of mortality among women. The tumour microenvironment, consisting of host cells and extracellular matrix, has been increasingly studied for its interplay with cancer cells, and the resulting effect on tumour progression. While the breast is one of the most innervated organs in the body, the role of neurons, and specifically sensory neurons, has been understudied, mostly for technical reasons. One of the reasons is the anatomy of sensory neurons: sensory neuron somas are located in the spine, and their axons can extend longer than a meter across the body to provide innervation in the breast. Next, neurons are challenging to culture, and there are no cell lines adequately representing the diversity of sensory neurons. Finally, sensory neurons are responsible for transporting several different types of signals to the brain, and there are many different subtypes of sensory neurons. The subtypes of sensory neurons, which innervate and interact with breast tumours, are unknown. To establish the tools for labelling and subtyping neurons that interact with breast cancer cells, we utilised two retrograde tracer's standards in neuroscience, wheat-germ agglutinin (WGA) and cholera toxin subunit B (CTB). In vitro, we employed primary sensory neurons isolated from mouse dorsal root ganglia, cultured in a custom-built microfluidic device DACIT, that mimics the anatomical compartmentalisation of the sensory neuron's soma and axons. In vivo, we utilised both syngeneic and transgenic mouse models of mammary carcinoma. We show that CTB and WGA trace different but overlapping sensory neuronal subpopulations: while WGA is more efficient in labelling CGRP+ neurons, CTB is superior in labelling the NF200+ neurons. Surprisingly, both tracers are also taken up by a significant population of breast cancer cells, both in vitro and in vivo. In summary, we have established methodologies for retrograde tracing of sensory neurons interacting with breast cancer cells. Our tools will be useful for future studies of breast tumour innervation, and development of therapies targeting breast cancer-associated neuron subpopulations of sensory neurons. Lay description: Breast cancer is an aggressive disease that affects both women and men throughout the world. While it has been reported that the increasing size of nerves in breast cancer correlates to bad prognosis in patients, the role of nerves, especially sensory nerves, in breast cancer progression, has remained largely understudied. Sensory nerves are responsible for delivering signals such as pain, mechanical forces (pressure, tension, stretch, touch) and temperature to the brain. The human body is densely innervated, and nerves extending into peripheral organs can be as long as a few meters. Nerve classification and function can be very complex, as they contain bundles of extensions (axons) originating in different neuronal bodies (soma). Maintaining neurons and growing axons in cell culture conditions in order to mimic innervation is technically challenging, as it involves multiple organs of the human body. Here, we focus on tracing sensory axons from the breast tumours back to the neuronal soma, located in the dorsal root ganglia, inside the spine. To do so, we are using two different 'retrograde' tracers, WGA and CTB, which are proteins with a natural ability to enter axons and travel in a retrograde fashion, arriving at the soma, even if it means to travel distances longer than a meter. Both tracers are fluorescently labelled, making them visible using high-resolution fluorescent microscopy. We show that both WGA and CTB can label sensory neurons in tumours, or in cell culture conditions. The two tracers differ in efficiency of tracing different sensory neurons subpopulations: while WGA is more efficient in tracing small C-fibres (CGRP-positive), CTB is more efficient in tracing A-fibres (NF200+) of sensory neurons. In summary, we have successfully established retrograde tracing techniques for sensory neurons towards studying and targeting breast cancer innervation.

Tumor-infiltrating nerves functionally alter brain circuits and modulate behavior in a male mouse model of head-and-neck cancer

Cancer patients often experience changes in mental health, prompting an exploration into whether nerves infiltrating tumors contribute to these alterations by impacting brain functions. Using a male mouse model for head and neck cancer, we utilized neuronal tracing techniques and show that tumor-infiltrating nerves indeed connect to distinct brain areas via the ipsilateral trigeminal ganglion. The activation of this neuronal circuitry led to behavioral alterations represented by decreased nest-building, increased latency to eat a cookie, and reduced wheel running. Tumor-infiltrating nociceptor neurons exhibited heightened activity, as indicated by increased calcium mobilization. Correspondingly, the specific brain regions receiving these neural projections showed elevated cFos and delta FosB expression in tumor-bearing mice, alongside markedly intensified calcium responses compared to non-tumor-bearing counterparts. The genetic elimination of nociceptor neurons in tumor-bearing mice led to decreased brain Fos expression and mitigated the behavioral alterations induced by the presence of the tumor. While analgesic treatment successfully restored behaviors involving oral movements to normalcy in tumor-bearing mice, it did not have a similar therapeutic effect on voluntary wheel running. This discrepancy points towards an intricate relationship, where pain is not the exclusive driver of such behavioral shifts. Unraveling the interaction between the tumor, infiltrating nerves, and the brain is pivotal to developing targeted interventions to alleviate the mental health burdens associated with cancer.

Retrograde tracing of breast cancer-associated sensory neurons

Breast cancer is one of the leading causes of mortality among women. The tumor microenvironment, consisting of host cells and extracellular matrix, has been increasingly studied for its interplay with cancer cells, and the resulting effect on tumor progression. While the breast is one of the most innervated organs in the body, the role of neurons, and specifically sensory neurons, has been understudied, mostly for technical reasons. One of the reasons is the anatomy of sensory neurons: sensory neuron somas are located in the spine, and their axons can extend longer than a meter across the body to provide innervation in the breast. Next, neurons are challenging to culture, and there are no cell lines adequately representing the diversity of sensory neurons. Finally, sensory neurons are responsible for transporting several different types of signals to the brain, and there are many different subtypes of sensory neurons. The subtypes of sensory neurons which innervate and interact with breast tumors are unknown. To establish the tools for labeling and subtyping neurons that interact with breast cancer cells, we utilized two retrograde tracer's standards in neuroscience, wheat-germ agglutinin (WGA) and cholera toxin subunit B (CTB). In vitro , we employed primary sensory neurons isolated from mouse dorsal root ganglia, cultured in a custom-built microfluidic device DACIT, that mimics the anatomical compartmentalization of the sensory neuron's soma and axons. In vivo , we utilized both syngeneic and transgenic mouse models of mammary carcinoma. We show that CTB and WGA trace different but overlapping sensory neuronal subpopulations: while WGA is more efficient in labeling CGRP+ neurons, CTB is superior in labeling the NF200+ neurons. Surprisingly, both tracers are also taken up by a significant population of breast cancer cells, both in vitro and in vivo . In summary, we have established methodologies for retrograde tracing of sensory neurons interacting with breast cancer cells. Our tools will be useful for future studies of breast tumor innervation, and development of therapies targeting breast cancer-associated neuron subpopulations of sensory neurons.

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.

The Ovary-Brain Connection

The brain and the ovaries are in a state of continuous communication [...].

NPFF stimulates human ovarian cancer cell invasion by upregulating MMP-9 via ERK1/2 signaling

Neuropeptide FF (NPFF) belongs to the RFamide peptide family. NPFF regulates a variety of physiological functions by binding to a G protein-coupled receptor, NPFFR2. Epithelial ovarian cancer (EOC) is a leading cause of death among gynecological malignancies. The pathogenesis of EOC can be regulated by many local factors, including neuropeptides, through an autocrine/paracrine manner. However, to date, the expression and/or function of NPFF/NPFFR2 in EOC is undetermined. In this study, we show that the upregulation of NPFFR2 mRNA was associated with poor overall survival in EOC. The TaqMan probe-based RT-qPCR showed that NPFF and NPFFR2 were expressed in three human EOC cells, CaOV3, OVCAR3, and SKOV3. In comparison, NPFF and NPFFR2 expression levels were higher in SKOV3 cells than in CaOV3 or OVCAR3 cells. Treatment of SKOV3 cells with NPFF did not affect cell viability and proliferation but stimulated cell invasion. NPFF treatment upregulates matrix metalloproteinase-9 (MMP-9) expression. Using the siRNA-mediated knockdown approach, we showed that the stimulatory effect of NPFF on MMP-9 expression was mediated by the NPFFR2. Our results also showed that ERK1/2 signaling was activated in SKOV3 cells in response to the NPFF treatment. In addition, blocking the activation of ERK1/2 signaling abolished the NPFF-induced MMP-9 expression and cell invasion. This study provides evidence that NPFF stimulates EOC cell invasion by upregulating MMP-9 expression through the NPFFR2-mediated ERK1/2 signaling pathway.

Functional neuronal circuits promote disease progression in cancer

The molecular and functional contributions of intratumoral nerves to disease remain largely unknown. We localized synaptic markers within tumors suggesting that these nerves form functional connections. Consistent with this, electrophysiological analysis shows that malignancies harbor significantly higher electrical activity than benign disease or normal tissues. We also demonstrate pharmacologic silencing of tumoral electrical activity. Tumors implanted in transgenic animals lacking nociceptor neurons show reduced electrical activity. These data suggest that intratumoral nerves remain functional at the tumor bed. Immunohistochemical staining demonstrates the presence of the neuropeptide, Substance P (SP), within the tumor space. We show that tumor cells express the SP receptor, NK1R, and that ligand/receptor engagement promotes cellular proliferation and migration. Our findings identify a mechanism whereby intratumoral nerves promote cancer progression.

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.