Peripheral nerve injury and sensitization underlie pain associated with oral cancer perineural invasion

Tumor-associated Schwann cells as new therapeutic target in non-neurological cancers

Cancer neuroscience, a burgeoning field, investigates the complex interactions between cancer and the nervous system, emphasizing how cancer cells exploit neuronal components for growth and metastasis. Tumor-associated Schwann cells (TASc) have emerged as crucial players in the progression of highly innervated cancers, highlighting the intricate relationship between the tumor microenvironment (TME) and the nervous system. This review concludes how TASc, as the most abundant glial cell in the peripheral nervous system, contribute to tumor growth, metastasis, and the remodeling of the TME. Acting similarly to reactive astrocytes in the central nervous system, TASc are implicated in driving perineural invasion (PNI), a distinctive cancer progression pathway facilitating tumor infiltration and metastasis. These TASc not only contribute indirectly to pain but also promote tumor recurrence and poor prognosis. Intrinsic to their role, TASc exhibit unique gene expression profiles and phenotypic transformations, shifting from myelinating to non-myelinating states, thereby actively participating in metastasis and the remodeling of the tumor microenvironment. Targeting TASc represents a novel and promising therapeutic strategy in non-neurological cancers, offering new avenues for clinical intervention.

Cancer neuroscience in head and neck: interactions, modulation, and therapeutic strategies

Head and neck cancer (HNC) is an aggressive malignancy with significant effects on the innervation. Not only is it at the top of the cancer spectrum with a dismal prognosis, but it also imposes considerable stress on patients and society owing to frequent neurological symptoms. With progress in cancer neuroscience, the interactions between HNC and the nervous system, as well as the underlying mechanisms, have become increasingly clear. Compelling evidence suggests communication of information between cancer and nerve cells and devastation of the neurological system with tumor growth. However, the thorough grasp of HNC in cancer neuroscience has been severely constrained by the intricacy of HNC and fragmented research. This review comprehensively organizes and summarizes the latest research on the crosstalk between HNC and the nervous system. It aims to clarify various aspects of the neurological system in HNC, including the physiology, progression, and treatment of cancer. Furthermore, the opportunities and challenges of cancer neuroscience in HNC are discussed, which offers fresh perspectives on the neurological aspects of HNC diagnosis and management.

Pretreatment Pain as a Prognostic Predictor in Oral Tongue Squamous Cell Carcinoma: The Mediating Role of Perineural Invasion

BACKGROUND

The potential effects of pretreatment pain on prognosis of tongue squamous cell carcinoma (TSCC) and the role that perineural invasion (PNI) plays in this process remains unclear.

PURPOSE

The purposes of this study are to estimate the prognostic value of pretreatment pain and identify whether PNI is a mediating factor in the relationship between pretreatment pain and prognosis in TSCC.

STUDY DESIGN, SETTING, SAMPLE

This retrospective cohort study included TSCC patients who underwent first resections of primary lesions at the Beijing Stomatological Hospital of Capital Medical University between January 2009 and December 2019. Patients who had incomplete medical records and pathological data, received neoadjuvant radiotherapy and chemotherapy before surgery, and did not receive a TSCC diagnosis, were excluded.

PREDICTOR VARIABLE

The predictor variables are pretreatment pain and PNI. The visual analog scale (VAS) was used to assess pretreatment pain levels, and the PNI status was evaluated by pathological section.

MAIN OUTCOME VARIABLE(S)

The main outcome variables were the 3-year disease-specific survival (DSS) and disease-free survival (DFS).

COVARIATES

Covariates included age, sex, smoking history, alcohol history, growth pattern, and T-stage.

ANALYSES

The χ2 test was used to describe the baseline data. Kaplan-Meier analysis was used to estimate the 3-year DSS and DFS. The Cox regression model was adapted for univariate and multivariate analysis. The association between VAS score and PNI was analyzed using logistic regression analysis and mediation analysis. P value less than .05 indicated statistical significance.

RESULTS

The study included 307 subjects with a mean age of 52 (±12.1) years, and 164 (53.4%) were male. There were 65 (21.2%) with high VAS (>5) and 242 (78.8%) with low VAS (≤5). The DSS and DFS of high VAS were 64.6% (95% CI: 23.6 to 80.9%) and 52.3% (95% CI: 35.3 to 92.8%), of patients with PNI were 62.7% (95% CI: 19.6 to 64.5%) and 46.7% (95% CI: 25.9 to 66.9%), respectively. The group high VAS/with PNI had lower DSS and DFS than group high VAS/without PNI (55.3 and 40.4% vs 88.9 and 83.3%). The VAS and PNI were identified as independent factors associated with prognosis (P < .05). Mediation analysis revealed that the indirect effect of VAS on DFS was 0.071 (95% CI: 0.011 to 0.135, P = .024), while the total effect was 0.187 (95% CI: 0.074 to 0.296, P < .001), VAS score affected the DFS of TSCC through the mediating effect of PNI.

CONCLUSION AND RELEVANCE

Our findings confirmed that pretreatment pain is associated with worse outcomes in TSCC. Patients with TSCC and severe pretreatment pain are more likely to be diagnosed with PNI, which results in a worse prognosis.

Effects of Opioids in Cancer Pain: An Interplay Among Genetic Factors, Immune Response, and Clinical Outcomes-A Scoping Review

Background/Objectives: Managing cancer-related pain presents complex challenges involving the interplay between analgesic efficacy, immune system responses, and patient outcomes. Methods: Following the Scale for the Assessment of Narrative Review Articles (SANRA) criteria, we conducted a comprehensive literature search in Medline, Scopus, and Web of Science databases. The review synthesized evidence regarding opioid pain management modalities, genetic variations affecting pain perception, and associated drug metabolism. Results: The literature reveals significant associations between opioid administration and immune function, with potential implications for cancer progression and survival. Genetic polymorphisms in key genes influence individual responses to pain opioid metabolism and, finally, pain management strategies. The immunosuppressive effects of opioids emerge as a critical consideration in cancer pain management, potentially influencing disease progression and treatment outcomes. Conclusions: Genetic variants influence analgesic efficacy, while the interaction between opioid-induced immunosuppression and genetic factors impacts both pain control and survival outcomes. This emphasizes the need for personalized treatment approaches considering individual genetic profiles and immune function.

Understanding the role of nerves in head and neck cancers - a review

Worldwide, head and neck cancers (HNCs) account for approximately 900,000 cases and 500,000 deaths annually, with their incidence continuing to rise. Carcinogenesis is a complex, multidimensional molecular process leading to cancer development, and in recent years, the role of nerves in the pathogenesis of various malignancies has been increasingly recognized. Thanks to the abundant innervation of the head and neck region, peripheral nervous system has gained considerable interest for its possible role in the development and progression of HNCs. Intratumoral parasympathetic, sympathetic, and sensory nerve fibers are emerging as key players and potential targets for novel anti-cancer and pain-relieving medications in different tumors, including HNCs. This review explores nerve-cancer interactions, including perineural invasion (PNI), cancer-related axonogenesis, neurogenesis, and nerve reprogramming, with an emphasis on their molecular mechanisms, mediators and clinical implications. PNI, an adverse histopathologic feature, has been widely investigated in HNCs. However, its prognostic value remains debated due to inconsistent results when classified dichotomously (present/absent). Emerging evidence suggests that quantitative and qualitative descriptions of PNI may better reflect its clinical usefulness. The review also examines therapies targeting nerve-cancer crosstalk and highlights the influence of HPV status on tumor innervation. By synthesizing current knowledge, challenges, and future perspectives, this review offers insights into the molecular basis of nerve involvement in HNCs and the potential for novel therapeutic approaches.

NK1 receptor blockade disrupts microtumor growth and aggregation in a three-dimensional murine breast cancer model

Several data indicate that Substance P (SP) neurokinin type 1 receptor (NK1R) is at the center of the interaction between cancer cells and peripheral sensory neurons. Selecting the appropriate cancer cell line and its susceptibility to being modulated by NK1 antagonists are critical to studying this complex interaction. In the current study, we have focused on this selection by comparing several aspects of the triple-negative breast cancer (TNBC) cell line (MDA-MB-231LUC+) with a modified murine cell line (E0771LUC+), both expressing luciferase. This comparison was made using several methods, SP stimulation and 3D cell culture models, to better reproduce the heterogenous microenvironment of solid tumors observed in vivo. Furthermore, the susceptibility of the murine cell line (E0771LUC+) to NK1R antagonist (Aprepitant) was tested. Our results indicate that E0771LUC+ recapitulates several essential aspects of the human cell line, rendering this murine line ideal to be used on immune-competent animals during in vivo studies. We have also found that both cell lines are susceptible to SP stimulation, and their proliferation is disrupted by NK1R antagonists (Aprepitant). In vivo studies are required to verify and refine these findings.

Advanced cancer perineural invasion induces profound peripheral neuronal plasticity, pain, and somatosensory mechanical deactivation, unmitigated by the lack of TNFR1. Part 2. Biophysics and gene expression

Preclinical studies addressing the peripheral effects of cancer perineural invasion report severe neuronal availability and excitability changes. Oral cell squamous cell carcinoma perineural invasion (MOC2-PNI) shows similar effects, modulating the afferent's sensibility (tactile desensitization with concurrent nociceptive sensitization) and demyelination without inducing spontaneous activity (see Part 1.). The current study addresses the electrical status (normal or abnormal) of both active (low threshold mechano receptors (LT) and high threshold mechano receptors (HT)) and inactive (F-type and S-type) afferents. Concurrently, we have also evaluated changes in the genetic landscape that may help to understand the physiological dynamics behind MOC2-PNI-induced functional disruption of the peripheral sensory system. We have observed that the altered cell distribution and mechanical sensibility of the animal's somatosensory system cannot be explained by cellular electrical dysfunction or MOC2-PNI-induced apoptosis. Although PNI does modify the expression of several genes related to cellular hypersensitivity, these changes are insufficient to explain the MOC2-PNI-induced aberrant neuronal excitability state. Our results indicate that genetic markers provide limited information about the functional hyperexcitable state of the peripheral system. Importantly, our results also highlight the emerging role of plasma membrane Ca2+-ATPase activity (PMCA) in explaining several aspects of the observed gender-specific neuronal plasticity and the reported cellular distribution switch generated by MOC2-PNI.

Advanced cancer perineural invasion induces profound peripheral neuronal plasticity, pain, and somatosensory mechanical deactivation, unmitigated by the lack of TNFR1. Part. 1: Behavior and single-cell in vivo electrophysiology

Patients with cancer perineural invasion (PNI) report greater spontaneous pain and mechanical allodynia. Here, we examine the impact of the disease on the peripheral sensory system, the excitability changes induced by PNI at the dorsal root ganglia, and the potential protective role of the absence of Tumor Necrosis Factor-α Receptor 1 (TNFR1). To study these effects, we use a murine model generated by injecting mouse oral cancer squamous cell carcinoma (MOC2) into the sciatic nerve (MOC2-PNI) in both male and female mice. We found that MOC2-PNI induces a profound change in the somatosensory landscape by deactivating/blocking the peripheral inputs while modulating the afferent's sensibility (tactile desensitization with concurrent nociceptive sensitization) and demyelination without inducing spontaneous activity. All these changes caused by MOC2-PNI are unmitigated by the absence of TNFR1. We conclude that MOC2-PNI induces an aberrant neuronal excitability state and triggers extreme gender-specific neuronal plasticity. These data allow us to speculate on the role of such plasticity as a powerful defense mechanism to prevent terminal sensory dysfunction, the rise of chronic pain, and extend animals' survivability.

The role of cancer cell-released extracellular vesicles: have we become closer to cancer pain treatment?

The effective management of cancer pain continues to be a challenge because of our limited understanding of cancer pain mechanisms and, in particular, how cancer cells interact with neurons to produce pain. In a study published in Pain, Inyang et al. used a mouse model of human papillomavirus (HPV1)-induced oropharyngeal squamous cell carcinoma to show a role for cancer cell-derived extracellular vesicles (cancer sEVs) in cancer pain. They found that inhibiting the release of sEVs reduced spontaneous and evoked pain behaviors, and that pain produced by sEVs is due to activation of TRPV1 channels. An innovative approach was the use of publicly available human RNA-sequencing data from unstimulated cultured human dorsal root ganglia (DRG) that were exposed to human head and neck squamous cell carcinoma (HNSCC)-derived sEVs to identify signaling pathways involved in the nascent translation associated with nociception. These studies further our understanding of functional interactions between cancer cells and neurons, and suggest an approach to identify novel targets for the treatment of cancer pain.

Animal models of neuropathic pain

Animal models continue to be crucial to developing our understanding of the molecular, cellular, and neurophysiological mechanisms that lead to neuropathic pain. The overwhelming majority of animal studies use rodent models, ranging from surgical and trauma-induced models to those induced by metabolic diseases, genetic mutations, viruses, neurotoxic drugs, and cancer. We discuss the clinical relevance of the available models and the pain behavior tests commonly used as outcome measures. Finally, we summarize the refinements that have been proposed to improve the ability of animal model studies to predict clinical efficacy.

Perineural Invasion Is Associated With Function-evoked Pain and Altered Extracellular Matrix in Patients With Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is painful, and perineural invasion (PNI) has been associated with the worst pain. Pain due to HNSCC is diverse and may vary based on clinicopathological factors. This study aims to characterize different pain patterns linked with PNI, its influence on daily functioning, and gain insights into molecular changes and pathways associated with PNI-related pain in HNSCC patients. We conducted a cross-sectional study across 3 medical centers (n = 114), assessing pain phenotypes and their impact on daily functioning using 2 self-reported pain questionnaires, given to patients prior to their cancer surgery. Furthermore, we conducted RNA-seq analysis utilizing the The Cancer Genome Atlas dataset of HNSCC tumor from patients (n = 192) to identify genes relevant to both PNI and pain. Upon adjusting for demographic and clinicopathological variables using linear regression models, we found that PNI independently predicted function-evoked pain according to the University of Calfornia San Francisco Oral Cancer Pain Questionnaire, as well as the worst pain intensity reported in the Brief Pain Inventory. Distinct pain patterns were observed to be associated with daily activities in varying manners. Our molecular analyses revealed significant disruptions in pathways associated with the extracellular matrix structure and organization. The top differentially expressed genes linked to the extracellular matrix are implicated in cancer development, pain, and neurodegenerative diseases. Our data underscore the importance of properly categorizing pain phenotypes in future studies aiming to uncover mechanistic underpinnings of pain. Additionally, we have compiled a list of genes of interest that could serve as targets for both cancer and cancer pain management. PERSPECTIVE: PNI independently predicts function-evoked pain. Different pain phenotypes affect daily activities differently. We identified a list of candidate genes involved in the extracellular matrix structure and function that can be targeted for both cancer and cancer pain control.

Neuroimmune cell interactions and chronic infections in oral cancers

Inflammation is a process that is associated with the activation of distal immunosuppressive pathways that have evolved to restore homeostasis and prevent excessive tissue destruction. However, long-term immunosuppression resulting from systemic and local inflammation that may stem from dysbiosis, infections, or aging poses a higher risk for cancers. Cancer incidence and progression dramatically increase with chronic infections including HIV infection. Thus, studies on pro-tumorigenic effects of microbial stimulants from resident microbiota and infections in the context of inflammation are needed and underway. Here, we discuss chronic infections and potential neuro-immune interactions that could establish immunomodulatory programs permissive for tumor growth and progression.

Sleep disorders and orofacial pain: insights for dental practice

In dental sleep medicine several sleep disorders commonly coexist with pain, contributing to complex clinical presentations which might affect the provision of appropriate and timely treatment. There are associations between sleep disorders and pain in general, as well as with specific orofacial pain conditions. As many as five of six patients with orofacial pain can present with sleep problems. The comorbidity of orofacial pain and sleep disorders overlays a complex web of altered neurobiological mechanisms that predispose to the chronification of orofacial pain. This review discusses the relationship between orofacial pain and sleep disorders and highlights their interactions and the neurobiological mechanisms underlying those relationships.

HPV+ head and neck cancer-derived small extracellular vesicles communicate with TRPV1+ neurons to mediate cancer pain

ABSTRACT

Severe pain is often experienced by patients with head and neck cancer and is associated with a poor prognosis. Despite its frequency and severity, current treatments fail to adequately control cancer-associated pain because of our lack of mechanistic understanding. Although recent works have shed some light of the biology underlying pain in HPV-negative oral cancers, the mechanisms mediating pain in HPV+ cancers remain unknown. Cancer-derived small extracellular vesicles (cancer-sEVs) are well positioned to function as mediators of communication between cancer cells and neurons. Inhibition of cancer-sEV release attenuated pain in tumor-bearing mice. Injection of purified cancer-sEVs is sufficient to induce pain hypersensitivity in naive mice that is prevented by QX-314 treatment and in Trpv1-/- mice. Cancer-sEVs triggered calcium influx in nociceptors, and inhibition or ablation of nociceptors protects against cancer pain. Interrogation of published sequencing data of human sensory neurons exposed to human cancer-sEVs suggested a stimulation of protein translation in neurons. Induction of translation by cancer-sEVs was validated in our mouse model, and its inhibition alleviated cancer pain in mice. In summary, our work reveals that HPV+ head and neck squamous cell carcinoma-derived sEVs alter TRPV1+ neurons by promoting nascent translation to mediate cancer pain and identified several promising therapeutic targets to interfere with this pathway.

Measurement of the Association of Pain with Clinical Characteristics in Oral Cancer Patients at Diagnosis and Prior to Cancer Treatment

Aim

Oral cancer patients suffer pain at the site of the cancer, which degrades quality of life (QoL). The University of California San Francisco Oral Cancer Pain Questionnaire (UCSFOCPQ), the only validated instrument specifically designed for measuring oral cancer pain, measures the intensity and nature of pain and the level of functional restriction due to pain.

Purpose

The aim of this study was to compare pain reported by untreated oral cancer patients on the UCSFOCPQ with pain they reported on the Brief Pain Inventory (BPI), an instrument widely used to evaluate cancer and non-cancer pain.

Patients and Methods

The correlation between pain measured by the two instruments and clinical characteristics were analyzed. Thirty newly diagnosed oral cancer patients completed the UCSFOCPQ and the BPI.

Results

Pain severity measurements made by the UCSFOCPQ and BPI were concordant; however, the widely used BPI average pain over 24 hours score appeared less sensitive to detect association of oral cancer pain with clinical characteristics of patients prior to treatment (nodal status, depth of invasion, DOI). A BPI average score that includes responses to questions that measure both pain severity and interference with function performs similarly to the UCSFOCPQ in detection of associations with nodal status, pathologic T stage (pT stage), stage and depth of invasion (DOI).

Conclusion

Pain assessment instruments that measure sensory and interference dimensions of oral cancer pain correlate with biologic features and clinical behavior.

Effects of systemic oxytocin administration on ultraviolet B-induced nociceptive hypersensitivity and tactile hyposensitivity in mice

Ultraviolet B (UVB) radiation induces cutaneous inflammation, leading to thermal and mechanical hypersensitivity. Here, we examine the mechanical properties and profile of tactile and nociceptive peripheral afferents functionally disrupted by this injury and the role of oxytocin (OXT) as a modulator of this disruption. We recorded intracellularly from L4 afferents innervating the irradiated area (5.1 J/cm2) in 4-6 old week male mice (C57BL/6J) after administering OXT intraperitoneally, 6 mg/Kg. The distribution of recorded neurons was shifted by UVB radiation to a pattern observed after acute and chronic injuries and reduced mechanical thresholds of A and C- high threshold mechanoreceptors while reducing tactile sensitivity. UVB radiation did not change somatic membrane electrical properties or fiber conduction velocity. OXT systemic administration rapidly reversed these peripheral changes toward normal in both low and high-threshold mechanoreceptors and shifted recorded neuron distribution toward normal. OXT and V1aR receptors were present on the terminals of myelinated and unmyelinated afferents innervating the skin. We conclude that UVB radiation, similar to local tissue surgical injury, cancer metastasis, and peripheral nerve injury, alters the distribution of low and high threshold mechanoreceptors afferents and sensitizes nociceptors while desensitizing tactile units. Acute systemic OXT administration partially returns all of those effects to normal.

Repurposing EGFR Inhibitors for Oral Cancer Pain and Opioid Tolerance

Oral cancer pain remains a significant public health concern. Despite the development of improved treatments, pain continues to be a debilitating clinical feature of the disease, leading to reduced oral mobility and diminished quality of life. Opioids are the gold standard treatment for moderate-to-severe oral cancer pain; however, chronic opioid administration leads to hyperalgesia, tolerance, and dependence. The aim of this review is to present accumulating evidence that epidermal growth factor receptor (EGFR) signaling, often dysregulated in cancer, is also an emerging signaling pathway critically involved in pain and opioid tolerance. We presented preclinical and clinical data to demonstrate how repurposing EGFR inhibitors typically used for cancer treatment could be an effective pharmacological strategy to treat oral cancer pain and to prevent or delay the development of opioid tolerance. We also propose that EGFR interaction with the µ-opioid receptor and glutamate N-methyl-D-aspartate receptor could be two novel downstream mechanisms contributing to pain and morphine tolerance. Most data presented here support that repurposing EGFR inhibitors as non-opioid analgesics in oral cancer pain is promising and warrants further research.

Perineural invasion: A potential driver of cancer-induced pain

Perineural invasion (PNI) is the process through which tumors invade and interact with nerves. The dynamic changes in the nerves caused by PNI may induce disturbing symptoms. PNI-related cancer pain in neuro-rich tumors has attracted much attention because the occurrence of tumor-induced pain is closely related to the invasion of nerves in the tumor microenvironment. PNI-related pain might indicate the occurrence of PNI, guide the improvement of treatment strategies, and predict the unresectability of tumors and the necessity of palliative care. Although many studies have investigated PNI, its relationship with tumor-induced pain and its common mechanisms have not been summarized thoroughly. Therefore, in this review, we evaluated the relationship between PNI and cancer-associated pain. We showed that PNI is a major cause of cancer-related pain and that this pain can predict the occurrence of PNI. We also elucidated the cellular and molecular mechanisms of PNI-induced pain. Finally, we analyzed the possible targets for alleviating PNI-related pain or combined antitumor and pain management. Our findings might provide new perspectives for improving the treatment of patients with malignant tumors.

Sex-dependent differences in the genomic profile of lingual sensory neurons in naïve and tongue-tumor bearing mice

Mechanisms of sex-dependent orofacial pain are widely understudied. A significant gap in knowledge exists about comprehensive regulation of tissue-specific trigeminal sensory neurons in diseased state of both sexes. Using RNA sequencing of FACS sorted retro-labeled sensory neurons innervating tongue tissue, we determined changes in transcriptomic profiles in males and female mice under naïve as well as tongue-tumor bearing conditions Our data revealed the following interesting findings: (1) FACS sorting obtained higher number of neurons from female trigeminal ganglia (TG) compared to males; (2) Naïve female neurons innervating the tongue expressed immune cell markers such as Csf1R, C1qa and others, that weren't expressed in males. This was validated by Immunohistochemistry. (3) Accordingly, immune cell markers such as Csf1 exclusively sensitized TRPV1 responses in female TG neurons. (4) Male neurons were more tightly regulated than female neurons upon tumor growth and very few differentially expressed genes (DEGs) overlapped between the sexes, (5) Male DEGs contained higher number of transcription factors whereas female DEGs contained higher number of enzymes, cytokines and chemokines. Collectively, this is the first study to characterize the effect of sex as well as of tongue-tumor on global gene expression, pathways and molecular function of tongue-innervating sensory neurons.

Pretreatment pain predicts perineural invasion in patients with head and neck squamous cell carcinoma

OBJECTIVES

Perineural invasion (PNI) in head and neck cancer (HNC) is a distinct pathological feature used to indicate aggressive tumor behavior and drive treatment strategies. Our study examined the prevalence and predictors of PNI in HNC patients stratified by tumor site.

STUDY DESIGN AND METHODS

A retrospective analysis of head and neck squamous cell carcinoma (HNSCC) patients who underwent surgical resection at the University of Pittsburgh Medical Center between 2015 and 2018 was performed. Pretreatment pain was assessed at least 1 week before surgery using the Functional Assessment of Cancer Therapy-Head and Neck (FACT-H&N). Demographics, clinical characteristics, and concomitant medications were obtained from medical records. Patients with cancers at the oropharynx and non-oropharynx (i.e., cancer at oral cavity, mandible, larynx) sites were separately analyzed. Tumor blocks were obtained from 10 patients for histological evaluation of intertumoral nerve presence.

RESULTS

A total of 292 patients (202 males, median age = 60.94 ± 11.06) were assessed. Pain and PNI were significantly associated with higher T stage (p < 0.001) and tumor site (p < 0.001); patients with non-oropharynx tumors reported more pain and had a higher incidence of PNI compared to oropharynx tumors. However, multivariable analysis identified pain as a significant variable uniquely associated with PNI for both tumor sites. Evaluation of nerve presence in tumor tissue showed 5-fold higher nerve density in T2 oral cavity tumors compared to oropharyngeal tumors.

CONCLUSIONS

Our study finds that PNI is associated with pretreatment pain and tumor stage. These data support the need for additional research into the impact of tumor location when investigating targeted therapies of tumor regression.

Sex-dependent Differences in the Genomic Profile of Lingual Sensory Neurons in Naïve and Tongue-Tumor Bearing Mice

Mechanisms of sex-dependent orofacial pain are widely understudied. A significant gap in knowledge exists about comprehensive regulation of tissue-specific trigeminal sensory neurons in diseased state of both sexes. Using RNA sequencing of FACS sorted retro-labeled sensory neurons innervating tongue tissue, we determined changes in transcriptomic profiles in males and female mice under naïve as well as tongue-tumor bearing conditions Our data revealed the following interesting findings: 1) Tongue tissue of female mice was innervated with higher number of trigeminal neurons compared to males; 2) Naïve female neurons innervating the tongue exclusively expressed immune cell markers such as Csf1R, C1qa and others, that weren't expressed in males. This was validated by Immunohistochemistry. 4) Accordingly, immune cell markers such as Csf1 exclusively sensitized TRPV1 responses in female TG neurons. 3) Male neurons were more tightly regulated than female neurons upon tumor growth and very few differentially expressed genes (DEGs) overlapped between the sexes, 5) Male DEGs contained higher number of transcription factors whereas female DEGs contained higher number of enzymes, cytokines and chemokines. Collectively, this is the first study to characterize the effect of sex as well as of tongue-tumor on global gene expression, pathways and molecular function of tongue-innervating sensory neurons.

A pilot study to improve pain phenotyping in head and neck cancer patients

Pain associated with head and neck cancer (HNC) is difficult to manage and reduces quality of life. It has been increasingly recognized that HNC patients exhibit a wide range of pain symptoms. Here we developed an orofacial pain assessment questionnaire and conducted a pilot study to improve pain phenotyping in HNC patients at the diagnosis. The questionnaire captures the following pain characteristics: pain intensity, location, quality, duration, and frequency; the impact of pain on daily activities; changes in smell and food sensitivities. Twenty-five HNC patients completed the questionnaire. 88% patients reported pain at the site of tumor; 36% reported multiple pain sites. All patients with pain reported at least one neuropathic pain (NP) descriptor, 54.5% reported at least two NP descriptors. The most common descriptors were "burning" and "pins and needles". Most patients reported increased pain to sour or hot/spicy food/drinks, and to food with coarse/hard textures. Patients exhibited impaired oral function, especially chewing, talking, mouth/jaw opening, and eating. Tumor progression has a significant impact on pain. Nodal metastasis is linked to pain at multiple body sites. Patients with advanced tumor staging experience greater pain at the primary tumor site, when exposed to hot or spicy food/drinks or food with hard/coarse texture, or when eating or chewing. We conclude that HNC patients experience a wide range of pain symptoms with altered mechanical, chemical, and temperature sensation. Improved phenotyping and stratification of pain in HNC patients will help address the underlying etiology, which may enable personalized therapeutic approaches in the future.

Schwann cell-derived CXCL2 contributes to cancer pain by modulating macrophage infiltration in a mouse breast cancer model

Pain is one of the most severe complications affecting the quality of life of cancer patients. Although substantial progress has been made in the diagnosis and treatment of cancer, the neurobiological mechanism of cancer pain is still unclear. In the present study, we identified the critical role of CXC chemokine 2 (CXCL2), released by Schwann cells after being activated by cancer cells, in maintaining cancer-induced macrophage infiltration and the resulting mechanical hypersensitivity and persistent spontaneous nociception. In vitro, Schwann cells cocultured with breast cancer cells exhibited a significant increase in CXCL2 expression; in addition, conditioned medium from Schwann cells activated by breast cancer cells had a similar effect to recombinant CXCL2 in terms of inducing macrophage migration. Targeting CXCL2 signaling by both CXC chemokine receptor 2 (CXCR2) antagonist pharmacological blockade and anti-CXCL2 mAb immunological blockade robustly prevented conditioned medium-induced macrophage migration. In vivo, both application of recombinant CXCL2 and perineural breast cancer cell implantation resulted in mechanical hypersensitivity and persistent spontaneous nociception in mice, along with increased macrophage infiltration into the sciatic nerves. Similar to the in vitro results, inhibition of CXCL2/CXCR2 signaling or conditional knockdown of CXCL2 in sciatic nerve Schwann cells effectively attenuated breast cancer cell-induced mechanical hypersensitivity, persistent spontaneous nociception, and macrophage recruitment in the sciatic nerve. Mechanistically, we found that redox effector factor-1 (Ref-1) secreted by breast cancer cells activated hypoxia inducible factor-1α (HIF-1α) expression and inhibited reactive oxygen species (ROS) production in Schwann cells, ultimately inducing CXCL2 expression in Schwann cells. In brief, the present study expands new insights into cancer pain mechanisms from promising animal models to provide new strategies for the control of cancer pain.

The 3D's of Neural Phenotypes in Oral Cancer: Distance, Diameter, and Density

Squamous cell carcinoma of the oral cavity (OSCC) is the most common type of head and neck cancer; survival is poor, and response to treatment varies. Metastasis or recurrence in the regional lymph nodes is associated with poor survival. Consequently, overt or occult spread to the lymph nodes is used to identify patients who will receive adjuvant radiation therapy. Perineural invasion and the diameter of nerves exhibiting perineural invasion have also been suggested to be of prognostic significance. The explosion of interest in cancer neuroscience in the last two decades has led to novel biological insights into interactions between nerves and tumor cells. However, the criteria for defining perineural invasion have lagged behind current knowledge. It is important to re-evaluate the concept of perineural invasion and identify other neural phenotypes in OSCC that can impact treatment selection and prognosis. In addition to perineural invasion, neural phenotypes that are of potential relevance to tumor progression include nerve-tumor distance, nerve diameter, and nerve density. This manuscript discusses the translational significance of recent mechanistic studies on the progression of oral cancer.

Chronic pain and local pain in usually painless conditions including neuroma may be due to compressive proximal neural lesion

It has been unexplained why chronic pain does not invariably accompany chronic pain-prone disorders. This question-driven, hypothesis-based article suggests that the reason may be varying occurrence of concomitant peripheral compressive proximal neural lesion (cPNL), e.g., radiculopathy and entrapment plexopathies. Transition of acute to chronic pain may involve development or aggravation of cPNL. Nociceptive hypersensitivity induced and/or maintained by cPNL may be responsible for all types of general chronic pain as well as for pain in isolated tissue conditions that are usually painless, e.g., neuroma, scar, and Dupuytren's fibromatosis. Compressive PNL induces focal neuroinflammation, which can maintain dorsal root ganglion neuron (DRGn) hyperexcitability (i.e., peripheral sensitization) and thus fuel central sensitization (i.e., hyperexcitability of central nociceptive pathways) and a vicious cycle of chronic pain. DRGn hyperexcitability and cPNL may reciprocally maintain each other, because cPNL can result from reflexive myospasm-induced myofascial tension, muscle weakness, and consequent muscle imbalance- and/or pain-provoked compensatory overuse. Because of pain and motor fiber damage, cPNL can worsen the causative musculoskeletal dysfunction, which further accounts for the reciprocity between the latter two factors. Sensitization increases nerve vulnerability and thus catalyzes this cycle. Because of these mechanisms and relatively greater number of neurons involved, cPNL is more likely to maintain DRGn hyperexcitability in comparison to distal neural and non-neural lesions. Compressive PNL is associated with restricted neural mobility. Intermittent (dynamic) nature of cPNL may be essential in chronic pain, because healed (i.e., fibrotic) lesions are physiologically silent and, consequently, cannot provide nociceptive input. Not all patients may be equally susceptible to develop cPNL, because occurrence of cPNL may vary as vary patients' predisposition to musculoskeletal impairment. Sensitization is accompanied by pressure pain threshold decrease and consequent mechanical allodynia and hyperalgesia, which can cause unusual local pain via natural pressure exerted by space occupying lesions or by their examination. Worsening of local pain is similarly explainable. Neuroma pain may be due to cPNL-induced axonal mechanical sensitivity and hypersensitivity of the nociceptive nervi nervorum of the nerve trunk and its stump. Intermittence and symptomatic complexity of cPNL may be the cause of frequent misdiagnosis of chronic pain.

Sympathetic modulation of tumor necrosis factor alpha-induced nociception in the presence of oral squamous cell carcinoma

ABSTRACT

Head and neck squamous cell carcinoma (HNSCC) causes more severe pain and psychological stress than other types of cancer. Despite clinical evidence linking pain, stress, and cancer progression, the underlying relationship between pain and sympathetic neurotransmission in oral cancer is unknown. We found that human HNSCC tumors and mouse tumor tissue are innervated by peripheral sympathetic and sensory nerves. Moreover, β-adrenergic 1 and 2 receptors (β-ARs) are overexpressed in human oral cancer cell lines, and norepinephrine treatment increased β-AR2 protein expression as well as cancer cell proliferation in vitro. We have recently demonstrated that inhibition of tumor necrosis factor alpha (TNFα) signaling reduces oral cancer-induced nociceptive behavior. Norepinephrine-treated cancer cell lines secrete more TNFα which, when applied to tongue-innervating trigeminal neurons, evoked a larger Ca 2+ transient; TNF-TNFR inhibitor blocked the increase in the evoked Ca 2+ transient. Using an orthotopic xenograft oral cancer model, we found that mice demonstrated significantly less orofacial cancer-induced nociceptive behavior during systemic β-adrenergic inhibitory treatment with propranolol. Furthermore, chemical sympathectomy using guanethidine led to a significant reduction in tumor size and nociceptive behavior. We infer from these results that sympathetic signaling modulates oral cancer pain through TNFα secretion and tumorigenesis. Further investigation of the role of neurocancer communication in cancer progression and pain is warranted.

Regulation of Carcinogenesis by Sensory Neurons and Neuromediators

Interactions between the immune system and the nervous system are crucial in maintaining homeostasis, and disturbances of these neuro-immune interactions may participate in carcinogenesis and metastasis. Nerve endings have been identified within solid tumors in humans and experimental animals. Although the involvement of the efferent sympathetic and parasympathetic innervation in carcinogenesis has been extensively investigated, the role of the afferent sensory neurons and the neuropeptides in tumor development, growth, and progression is recently appreciated. Similarly, current findings point to the significant role of Schwann cells as part of neuro-immune interactions. Hence, in this review, we mainly focus on local and systemic effects of sensory nerve activity as well as Schwann cells in carcinogenesis and metastasis. Specific denervation of vagal sensory nerve fibers, or vagotomy, in animal models, has been reported to markedly increase lung metastases of breast carcinoma as well as pancreatic and gastric tumor growth, with the formation of liver metastases demonstrating the protective role of vagal sensory fibers against cancer. Clinical studies have revealed that patients with gastric ulcers who have undergone a vagotomy have a greater risk of stomach, colorectal, biliary tract, and lung cancers. Protective effects of vagal activity have also been documented by epidemiological studies demonstrating that high vagal activity predicts longer survival rates in patients with colon, non-small cell lung, prostate, and breast cancers. However, several studies have reported that inhibition of sensory neuronal activity reduces the development of solid tumors, including prostate, gastric, pancreatic, head and neck, cervical, ovarian, and skin cancers. These contradictory findings are likely to be due to the post-nerve injury-induced activation of systemic sensory fibers, the level of aggressiveness of the tumor model used, and the local heterogeneity of sensory fibers. As the aggressiveness of the tumor model and the level of the inflammatory response increase, the protective role of sensory nerve fibers is apparent and might be mostly due to systemic alterations in the neuro-immune response. Hence, more insights into inductive and permissive mechanisms, such as systemic, cellular neuro-immunological mechanisms of carcinogenesis and metastasis formation, are needed to understand the role of sensory neurons in tumor growth and spread.

Advances in Head and Neck Cancer Pain

Head and neck cancer (HNC) affects over 890,000 people annually worldwide and has a mortality rate of 50%. Aside from poor survival, HNC pain impairs eating, drinking, and talking in patients, severely reducing quality of life. Different pain phenotype in patients (allodynia, hyperalgesia, and spontaneous pain) results from a combination of anatomical, histopathological, and molecular differences between cancers. Poor pathologic features (e.g., perineural invasion, lymph node metastasis) are associated with increased pain. The use of syngeneic/immunocompetent animal models, as well as a new mouse model of perineural invasion, provides novel insights into the pathobiology of HNC pain. Glial and immune modulation of the tumor microenvironment affect not only cancer progression but also pain signaling. For example, Schwann cells promote cancer cell proliferation, migration, and secretion of nociceptive mediators, whereas neutrophils are implicated in sex differences in pain in animal models of HNC. Emerging evidence supports the existence of a functional loop of cross-activation between the tumor microenvironment and peripheral nerves, mediated by a molecular exchange of bioactive contents (pronociceptive and protumorigenic) via paracrine and autocrine signaling. Brain-derived neurotrophic factor, tumor necrosis factor α, legumain, cathepsin S, and A disintegrin and metalloprotease 17 expressed in the HNC microenvironment have recently been shown to promote HNC pain, further highlighting the importance of proinflammatory cytokines, neurotrophic factors, and proteases in mediating HNC-associated pain. Pronociceptive mediators, together with nerve injury, cause nociceptor hypersensitivity. Oncogenic, pronociceptive mediators packaged in cancer cell-derived exosomes also induce nociception in mice. In addition to increased production of pronociceptive mediators, HNC is accompanied by a dampened endogenous antinociception system (e.g., downregulation of resolvins and µ-opioid receptor expression). Resolvin treatment or gene delivery of µ-opioid receptors provides pain relief in preclinical HNC models. Collectively, recent studies suggest that pain and HNC progression share converging mechanisms that can be targeted for cancer treatment and pain management.

Targeting tumor innervation: premises, promises, and challenges

A high intratumoral nerve density is correlated with poor survival, high metastasis, and high recurrence across multiple solid tumor types. Recent research has revealed that cancer cells release diverse neurotrophic factors and exosomes to promote tumor innervation, in addition, infiltrating nerves can also mediate multiple tumor biological processes via exosomes and neurotransmitters. In this review, through seminal studies establishing tumor innervation, we discuss the communication between peripheral nerves and tumor cells in the tumor microenvironment (TME), and revealed the nerve-tumor regulation mechanisms on oncogenic process, angiogenesis, lymphangiogenesis, and immunity. Finally, we discussed the promising directions of ‘old drugs newly used’ to target TME communication and clarified a new line to prevent tumor malignant capacity.

Oral carcinogenesis triggers a nociceptive behavior and c-Fos expression in rats' trigeminal pathway

OBJECTIVE

To recognize changes that occur along the trigeminal pathway in oral cancer in order to establish an effective approach to pain control.

METHODS

Wistar rats were divided into control and 4-NQO-groups for 8, 12, 16, or 20 weeks. 4-NQO suspension was administered on the animals` tongues. Mechanical hyperalgesia, assessment of facial expressions and an open field test were performed. After euthanasia, the animals' tongues were removed for macro and microscopic analysis. c-Fos expression was analyzed in the trigeminal pathway structures.

RESULTS

4-NQO induced time-dependent macroscopic lesions that were compatible with neoplastic tumors. Histopathological analysis confirmed oral squamous cell carcinoma in 50% of the animals on the 20th week. There was a significant nociceptive threshold reduction during the first two weeks, followed by a threshold return to the baseline levels, decreasing again from the 12th week. Facial nociceptive expression scores were observed on the 20th week, while increased grooming and exploratory activity were observed on the 8th week. Trigeminal ganglion showed an increased c-Fos immunoexpression on the 20th week and in the trigeminal subnucleus caudalis, it occurred on the 16th and 20th. The long-term carcinogenic exposure caused changes in the nociceptive behavior and c-Fos expression in the rats' trigeminal pathway.

Glia and Orofacial Pain: Progress and Future Directions

Orofacial pain is a universal predicament, afflicting millions of individuals worldwide. Research on the molecular mechanisms of orofacial pain has predominately focused on the role of neurons underlying nociception. However, aside from neural mechanisms, non-neuronal cells, such as Schwann cells and satellite ganglion cells in the peripheral nervous system, and microglia and astrocytes in the central nervous system, are important players in both peripheral and central processing of pain in the orofacial region. This review highlights recent molecular and cellular findings of the glia involvement and glia–neuron interactions in four common orofacial pain conditions such as headache, dental pulp injury, temporomandibular joint dysfunction/inflammation, and head and neck cancer. We will discuss the remaining questions and future directions on glial involvement in these four orofacial pain conditions.

A Novel Syngeneic Immunocompetent Mouse Model of Head and Neck Cancer Pain Independent of Interleukin-1 Signaling

BACKGROUND

Pain is one of the first presenting symptoms in patients with head and neck cancer, who often develop chronic and debilitating pain as the disease progresses. Pain is also an important prognostic marker for survival. Unfortunately, patients rarely receive effective pain treatment due to our limited knowledge of the mechanisms underlying head and neck cancer pain (HNCP). Pain is often associated with neuroinflammation and particularly interleukin (IL)-1 signaling. The purpose of this study is to develop a novel syngeneic model of HNCP in immunocompetent mice to examine the contribution of IL-1 signaling.

METHODS

Male C57BL/6 mice were injected with a murine model of human papillomavirus (HPV+)-induced oropharyngeal squamous cell carcinoma in their right hindlimb to induce tumor growth. Pain sensitivity was measured via von Frey filaments. Spontaneous pain was assessed via the facial grimace scale. IL-1β was measured by quantifying gene expression via quantitative polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA).

RESULTS

Pain hypersensitivity and spontaneous pain develop quickly after the implantation of tumor cells, a time when tumor volume is still insignificant. Spinal and circulating IL-1β levels are significantly elevated in tumor-bearing mice. Blocking IL-1 signaling either by intrathecal administration of interleukin-1 receptor antagonist (IL-1ra) or by genetic deletion (interleukin-1 receptor knockout [Il1r1-/-]) does not alleviate HNCP.

CONCLUSIONS

We established the first syngeneic model of HNCP in immunocompetent mice. Unlike inflammatory or nerve-injured pain, HNCP is independent of IL-1 signaling. These findings challenge the common belief that pain results from tissue compression or IL-1 signaling in patients with head and neck cancer.

TNFα promotes oral cancer growth, pain, and Schwann cell activation

Oral cancer is very painful and impairs a patient's ability to eat, talk, and drink. Mediators secreted from oral cancer can excite and sensitize sensory neurons inducing pain. Cancer mediators can also activate Schwann cells, the peripheral glia that regulates neuronal function and repair. The contribution of Schwann cells to oral cancer pain is unclear. We hypothesize that the oral cancer mediator TNFα activates Schwann cells, which further promotes cancer progression and pain. We demonstrate that TNFα is overexpressed in human oral cancer tissues and correlates with increased self-reported pain in patients. Antagonizing TNFα reduces oral cancer proliferation, cytokine production, and nociception in mice with oral cancer. Oral cancer or TNFα alone increases Schwann cell activation (measured by Schwann cell proliferation, migration, and activation markers), which can be inhibited by neutralizing TNFα. Cancer- or TNFα-activated Schwann cells release pro-nociceptive mediators such as TNFα and nerve growth factor (NGF). Activated Schwann cells induce nociceptive behaviors in mice, which is alleviated by blocking TNFα. Our study suggests that TNFα promotes cancer proliferation, progression, and nociception at least partially by activating Schwann cells. Inhibiting TNFα or Schwann cell activation might serve as therapeutic approaches for the treatment of oral cancer and associated pain.

Animal Models of Cancer-Related Pain: Current Perspectives in Translation

The incidence of pain in cancer patients during diagnosis and treatment is exceedingly high. Although advances in cancer detection and therapy have improved patient prognosis, cancer and its treatment-associated pain have gained clinical prominence. The biological mechanisms involved in cancer-related pain are multifactorial; different processes for pain may be responsible depending on the type and anatomic location of cancer. Animal models of cancer-related pain have provided mechanistic insights into the development and process of pain under a dynamic molecular environment. However, while cancer-evoked nociceptive responses in animals reflect some of the patients’ symptoms, the current models have failed to address the complexity of interactions within the natural disease state. Although there has been a recent convergence of the investigation of carcinogenesis and pain neurobiology, identification of new targets for novel therapies to treat cancer-related pain requires standardization of methodologies within the cancer pain field as well as across disciplines. Limited success of translation from preclinical studies to the clinic may be due to our poor understanding of the crosstalk between cancer cells and their microenvironment (e.g., sensory neurons, infiltrating immune cells, stromal cells etc.). This relatively new line of inquiry also highlights the broader limitations in translatability and interpretation of basic cancer pain research. The goal of this review is to summarize recent findings in cancer pain based on preclinical animal models, discuss the translational benefit of these discoveries, and propose considerations for future translational models of cancer pain.