Nerve growth factor links oral cancer progression, pain, and cachexia

Genetically predicted levels of circulating cytokines and prostate cancer risk: A Mendelian randomization study

Inflammation is considered to play a pivotal role in the pathogenesis of cancer, and observational studies have reported a relationship between circulating inflammation markers and the risk of prostate cancer. Using summary data of >140 000 individuals, two-sample Mendelian randomization (MR) analyses were performed to evaluate whether circulating levels of 27 cytokines and growth factors have a causal effect on the risk of developing prostate cancer. Genetically predicted elevated levels of monocyte chemotactic protein-1 (MCP-1) were associated with an increased risk of prostate cancer (odds ratio (OR) per 1 SD increase = 1.06, 95% confidence interval (CI): 1.04-1.09) at Bonferroni-adjusted level of significance (P < 1.85 × 10^-3). Results were stable across sensitivity analyses, and there was no evidence of directional pleiotropy. Under MR assumptions, our findings suggested a risk-increasing effect of circulating MCP-1 levels on prostate cancer. Whether targeting MCP-1 or its downstream effectors are useful in reducing prostate cancer incidence needs further investigation.

Perineural invasion in oral squamous cell carcinoma: Incidence, prognostic impact and molecular insight

BACKGROUND

The objective of this study was to characterise the incidence and prognostic correlation of perineural invasion (PNI) in oral squamous cell carcinoma and determine whether nerve growth factor and its receptor tyrosine Kinase A expression could be used as biological markers for PNI.

METHODS

A retrospective review of pathology reports of 430 patients with oral squamous cell carcinoma who were treated from 1992 to 2014 in Tayside, Scotland, was carried out. The expression of nerve growth factor and tyrosine kinase A was assessed with immunohistochemistry in 132 tissue sections of oral squamous cell carcinoma.

RESULTS

Perineural invasion was identified in 17.4% of oral squamous cell carcinomas. High expression of nerve growth factor and tyrosine kinase A was seen in 84% and 92% of oral squamous cell carcinoma, respectively. Tumours with PNI expressed nerve growth factor and tyrosine kinase A with a greater frequency than tumours without PNI. PNI and high expression of nerve growth factor were significantly associated with pain. PNI was significantly associated with stage IV tumours and poor disease-specific survival.

CONCLUSIONS

A higher level of expression of nerve growth factor and tyrosine kinase A may predict PNI and therefore may be considered as biological markers for PNI in oral squamous cell carcinoma. PNI and nerve growth factor overexpression may contribute to the pain generation in oral cancer patients. PNI and nerve growth factor expression can predict the aggressiveness and prognosis of oral squamous cell carcinoma patients.

Ameloblastomas Exhibit Stem Cell Potential, Possess Neurotrophic Properties, and Establish Connections with Trigeminal Neurons

Ameloblastomas are locally invasive and aggressive odontogenic tumors treated via surgical resection, which results in facial deformity and significant morbidity. Few studies have addressed the cellular and molecular events of ameloblastoma onset and progression, thus hampering the development of non-invasive therapeutic approaches. Tumorigenesis is driven by a plethora of factors, among which innervation has been long neglected. Recent findings have shown that innervation directly promotes tumor progression. On this basis, we investigated the molecular characteristics and neurotrophic properties of human ameloblastomas. Our results showed that ameloblastomas express dental epithelial stem cell markers, as well as components of the Notch signaling pathway, indicating persistence of stemness. We demonstrated that ameloblastomas express classical stem cell markers, exhibit stem cell potential, and form spheres. These tumors express also molecules of the Notch signaling pathway, fundamental for stem cells and their fate. Additionally, we showed that ameloblastomas express the neurotrophic factors NGF and BDNF, as well as their receptors TRKA, TRKB, and P75/NGFR, which are responsible for their innervation by trigeminal axons in vivo. In vitro studies using microfluidic devices showed that ameloblastoma cells attract and form connections with these nerves. Innervation of ameloblastomas might play a key role in the onset of this malignancy and might represent a promising target for non-invasive pharmacological interventions.

Nerve growth factor-induced migration in oral and salivary gland tumour cells utilises the PI3K/Akt signalling pathway: Is there a link to perineural invasion?

OBJECTIVES

The aims of this study were to investigate the role of nerve growth factor on perineural invasion in oral and salivary gland tumour cell lines and whether there is an involvement of PI3K/Akt pathway.

MATERIALS AND METHODS

Four cell lines were investigated: HSG and TYS (salivary gland tumours), SAS-H1 (oral squamous cell carcinoma) and HaCaT (human skin keratinocyte). Initially, Boyden chamber assay was done to examine the effect of different concentration of nerve growth factor on cell migration. Western blot/ immunofluorescence techniques were used to investigate the phosphorylation status of the Akt pathway within the cells in response to nerve growth factor. The effect of this growth factor and the addition of an Akt inhibitor on cell morphology and migration were also examined using scatter/scratch assays.

RESULTS

Nerve growth factor triggered the PI3K/Akt pathway in oral and salivary tumour cells and induced oral and salivary tumour cell scattering and migration. Inhibitor assays confirmed that oral and salivary gland tumour cell scattering and migration is Akt dependent.

CONCLUSIONS

Nerve growth factor can stimulate scattering and migration in cells derived from oral and salivary gland tumours, thereby potentially enhancing perineural invasion. Phosphorylated Akt controls cancer cell migration and scattering. Blocking the Akt pathway may inhibit cell migration and therefore perineural invasion and metastasis.

Oral Pain in the Cancer Patient

Oral pain due to cancer and associated treatments is common. The prevalence and severity of oral cancer is high. Painful oral mucositis develops in head and neck cancer patients following surgery and associated radiation therapy and/or chemotherapy. In addition, oral pain, including pain from mucositis, occurs in patients receiving chemotherapy for cancers of the hematopoietic system and cancers at other anatomic sites. Despite pain management practices that include high-dose opioid analgesics, patients rarely obtain relief from either head and neck cancer pain or mucositis pain. Because oral pain in cancer patients is likely due to both nociceptive and neuropathic mechanisms, effective management of pain requires treatments for both processes. As knowledge of the pathophysiology of oral pain in cancer patients increases, new approaches for the prevention and management are anticipated. This article focuses on the emerging evidence that supports the molecular mechanisms and the unique oral micro-neuroanatomy that in combination produce the severe oral pain experienced by cancer patients. In addition, this article summarizes the current state of clinical management of oral mucositis pain.

TRPA1 Channel as a Regulator of Neurogenic Inflammation and Pain: Structure, Function, Role in Pathophysiology, and Therapeutic Potential of Ligands

TRPA1 is a cation channel located on the plasma membrane of many types of human and animal cells, including skin sensory neurons and epithelial cells of the intestine, lungs, urinary bladder, etc. TRPA1 is the major chemosensor that also responds to thermal and mechanical stimuli. Substances that activate TRPA1, e.g., allyl isothiocyanates (pungent components of mustard, horseradish, and wasabi), cinnamaldehyde from cinnamon, organosulfur compounds from garlic and onion, tear gas, acrolein and crotonaldehyde from cigarette smoke, etc., cause burning, mechanical and thermal hypersensitivity, cough, eye irritation, sneezing, mucus secretion, and neurogenic inflammation. An increased activity of TRPA1 leads to the emergence of chronic pruritus and allergic dermatitis and is associated with episodic pain syndrome, a hereditary disease characterized by episodes of debilitating pain triggered by stress. TRPA1 is now considered as one of the targets for developing new anti-inflammatory and analgesic drugs. This review summarizes information on the structure, function, and physiological role of this channel, as well as describes known TRPA1 ligands and their significance as therapeutic agents in the treatment of inflammation-associated pain.

Exosomal Induction of Tumor Innervation

The naïve view of tumors as isolated islands of rogue cells has given way to a deeper understanding of cancer as being closer to a foreign organ. This "organ" contains immunologic, vascular, and neural connections to its host that provide not only mechanisms for disease progression but also opportunities for therapeutic intervention. The presence of nerves within tumor tissues has long been appreciated. However, a mechanistic understanding of how tumors recruit nerves has been slower to emerge. Tumor release of neurotrophic factors and axonal guidance molecules likely directs axons toward the tumor bed. Newly emerging data support a contribution of tumor-released exosomes in the induction of axonogenesis toward the tumor. Exosomes, small membrane-bound vesicles that carry a complex cargo (DNA, RNA, miRNA, lipids, and proteins), protect their cargo from the low pH of the tumor microenvironment. They also represent an efficient means of local and distal communication between the tumor and potentially innervating nerves. Likely, a combination of neurotrophins, guidance molecules, and exosomes work in concert to promote tumor innervation. As such, defining the critical components driving tumor innervation will identify new targets for intervention. Moreover, with a deepening understanding, tumor innervation may emerge as a new hallmark of cancer.

Depiction of Oral Tumor-Induced Trigeminal Afferent Responses Using Single-Fiber Electrophysiology

Considerable gap in knowledge exists about the mechanisms by which oral tumors regulate peripheral sensory fibers to produce pain and altered sensations. To address this gap, we used a murine model of oral squamous cell carcinoma (OSCC) of the tongue to investigate changes in response properties of trigeminal afferent neurons. Using this model, we developed an ex vivo method for single neuron recordings of the lingual nerve from isolated tongue tissue. Our data demonstrated that the tongue tumor produced increased spontaneous firing of lingual fibers compared to control as well as produced mechanical hypersensitivity and reduced von Frey thresholds of C- and A-slow-high-threshold mechanoreceptors (HTMR) fibers but had no effect on C-LTMR, A-slow-LTMR and A-fast lingual fibers. Mechanically-insensitive fibers were also detected in lingual afferents of the control group, that were significantly decreased in tumor-bearing preparations. Collectively, using single fiber electrophysiology of lingual sensory fibers, we show that human OSCC tumors sensitize peripheral trigeminal nerve terminals, providing a unique opportunity to study mechanisms of oral cancer pain.

Reciprocal interactions between cancer and Schwann cells contribute to oral cancer progression and pain

Pain associated with oral squamous cell carcinoma (oral SCC) decreases quality of life and survival. The interaction between cancer and the peripheral nerves is known to initiate and amplify pain and contribute to carcinogenesis. Schwann cells envelop peripheral nerves and are activated in response to neuronal damage. The contributions of Schwann cells to oral SCC progression and pain are unknown. Using a non-contact co-culture model, we demonstrate that Schwann cells (RSC-96) and oral SCC cells (HSC-3) reciprocally interact to promote proliferation, migration, and invasion. Schwann cell-oral SCC interaction leads to increased production of adenosine, which stimulates cell proliferation and migration of both cell types. The adenosine receptor A2B (ADORA2B) is expressed on RSC-96 cells. We show that supernatant from the RSC-96 cells co-cultured with HSC-3 cells induces increased mechanical hypersensitivity in mice compared to supernatant from control RSC-96 cells. Treatment with the ADORA2B antagonist PSB603 significantly inhibits co-culture interactions - proliferation and migration, and co-culture supernatant induced mechanical hypersensitivity. RSC-96 cells co-cultured with HSC-3 cells secrete increased amounts of the pronociceptive mediator, interleukin-6 (IL-6), which can be reduced by adding PSB603 into the co-culture. Our data support a reciprocal interaction between oral SCC and Schwann cells mediated by adenosine with potential to promote oral SCC progression and pain via increased secretion of IL-6.

Nerve growth factor continuously elevates in a rat rotator cuff tear model

BACKGROUND

Nerve growth factor (NGF) plays a key role in osteoarthritic pain and low back pain. Rotator cuff tear (RCT) is often associated with severe shoulder pain. However, the role of NGF in RCT remains to be fully understood.

METHODS

Rats were divided into sham and RCT groups. The rotator cuff was harvested from the sham and RCT groups on various days for reverse transcription-polymerase chain reaction analysis of Tnfa, Ngf, Il1b, and Cox2 expression. Rotator cuffs from the sham and RCT groups were also harvested at 1 and 14 days for enzyme-linked immunosorbent assay and immunohistochemistry to assess NGF protein levels and localization. Rotator cuff-derived cells were stimulated with rat recombinant tumor necrosis factor (TNF)-α to investigate the involvement of TNF-α in the regulation of NGF expression.

RESULTS

Tnfa and Ngf messenger RNA levels increased within 1 day in the RCT group. Notably, Tnfa and Ngf upregulation persisted for up to 56 days after the RCT surgery, while Il1b and Cox2 expression was significantly reduced. NGF levels in the RCT group were significantly higher than those in the sham operation group on days 1 and 14. Certain inflammatory cells and synovial-like cells lining the surface of the laminated tears were NGF-positive on days 1 and 14, respectively. Ngf messenger RNA levels increased significantly in rotator cuff-derived cells after TNF-α stimulation.

CONCLUSION

NGF levels are continuously elevated in RCT, which is mainly regulated by TNF-α. NGF may thus represent a potential target for therapies that modulate RCT pain.

Cancer pain: where are we now?

Increasing numbers of those living with and beyond cancer presents a clinical challenge for pain specialists. A large proportion of these patients experience pain secondary to their disease or its treatment, impeding rehabilitation and significantly impacting upon their quality of life. The successful management of this pain presents a considerable challenge. This review aims to outline current concepts and treatment options, while considering nuances within pain assessment and the use of large-scale data to help guide further advances.

Anti-nerve growth factor does not change physical activity in normal young or aging mice but does increase activity in mice with skeletal pain

Anti-nerve growth factor (anti-NGF) therapy has shown significant promise in attenuating several types of skeletal pain. However, whether anti-NGF therapy changes the level of physical activity in individuals with or without skeletal pain is largely unknown. Here, automated day/night activity boxes monitored the effects of anti-NGF treatment on physical activity in normal young (3 months old) and aging (18-23 months old) mice and mice with bone fracture pain. Although aging mice were clearly less active and showed loss of bone mass compared with young mice, anti-NGF treatment had no effect on any measure of day/night activity in either the young or aging mice. By contrast, in mice with femoral fracture pain, anti-NGF treatment produced a clear increase (10%-27%) in horizontal activity, vertical rearing, and velocity of travel compared with the Fracture + Vehicle group. These results suggest, just as in humans, mice titrate their level of physical activity to their level of skeletal pain. The level of skeletal pain may in part be determined by the level of free NGF that seems to rise after injury but not normal aging of the skeleton. In terms of bone healing, animals that received anti-NGF showed an increase in the size of calcified callus but no increase in the number of displaced fractures or time to cortical union. As physical activity is the best nondrug treatment for many patients with skeletal pain, anti-NGF may be useful in reducing pain and promoting activity in these patients.

Tumor necrosis factor alpha secreted from oral squamous cell carcinoma contributes to cancer pain and associated inflammation

Patients with oral cancer report severe pain during function. Inflammation plays a role in the oral cancer microenvironment; however, the role of immune cells and associated secretion of inflammatory mediators in oral cancer pain has not been well defined. In this study, we used 2 oral cancer mouse models: a cell line supernatant injection model and the 4-nitroquinoline-1-oxide (4NQO) chemical carcinogenesis model. We used the 2 models to study changes in immune cell infiltrate and orofacial nociception associated with oral squamous cell carcinoma (oSCC). Oral cancer cell line supernatant inoculation and 4NQO-induced oSCC resulted in functional allodynia and neuronal sensitization of trigeminal tongue afferent neurons. Although the infiltration of immune cells is a prominent component of both oral cancer models, our use of immune-deficient mice demonstrated that oral cancer-induced nociception was not dependent on the inflammatory component. Furthermore, the inflammatory cytokine, tumor necrosis factor alpha (TNFα), was identified in high concentration in oral cancer cell line supernatant and in the tongue tissue of 4NQO-treated mice with oSCC. Inhibition of TNFα signaling abolished oral cancer cell line supernatant-evoked functional allodynia and disrupted T-cell infiltration. With these data, we identified TNFα as a prominent mediator in oral cancer-induced nociception and inflammation, highlighting the need for further investigation in neural-immune communication in cancer pain.

Systemic Depletion of Nerve Growth Factor Inhibits Disease Progression in a Genetically Engineered Model of Pancreatic Ductal Adenocarcinoma

OBJECTIVES

In patients with pancreatic ductal adenocarcinoma (PDAC), increased expression of proinflammatory neurotrophic growth factors (eg, nerve growth factor [NGF]) correlates with a poorer prognosis, perineural invasion, and, with regard to NGF, pain severity. We hypothesized that NGF sequestration would reduce inflammation and disease in the KPC mouse model of PDAC.

METHODS

Following biweekly injections of NGF antibody or control immunoglobulin G, beginning at 4 or 8 weeks of age, inflammation and disease stage were assessed using histological, protein expression, and quantitative polymerase chain reaction analyses.

RESULTS

In the 8-week anti-NGF group, indicators of neurogenic inflammation in the dorsal root ganglia (substance P and calcitonin gene-related peptide) and spinal cord (glial fibrillary acidic protein) were significantly reduced. In the 4-week anti-NGF group, TRPA1 mRNA in dorsal root ganglia and spinal phosphorylated ERK protein were elevated, but glial fibrillary acidic protein expression was unaffected. In the 8-week anti-NGF group, there was a 40% reduction in the proportion of mice with microscopic perineural invasion, and no macrometastases were observed.

CONCLUSIONS

Anti-NGF treatment beginning at 4 weeks may increase inflammation and negatively impact disease. Treatment starting at 8 weeks (after disease onset), however, reduces neural inflammation, neural invasion, and metastasis. These data indicate that NGF impacts PDAC progression and metastasis in a temporally dependent manner.

Anti-cancer and analgesic effects of resolvin D2 in oral squamous cell carcinoma

Oral cancer is often painful and lethal. Oral cancer progression and pain may result from shared pathways that involve unresolved inflammation and elevated levels of pro-inflammatory cytokines. Resolvin D-series (RvDs) are endogenous lipid mediators derived from omega-3 fatty acids that exhibit pro-resolution and anti-inflammatory actions. These mediators have recently emerged as a novel class of therapeutics for diseases that involve inflammation; the specific roles of RvDs in oral cancer and associated pain are not defined. The present study investigated the potential of RvDs (RvD1 and RvD2) to treat oral cancer and alleviate oral cancer pain. We found down-regulated mRNA levels of GPR18 and GPR32 (which code for receptors RvD1 and RvD2) in oral cancer cells. Both RvD1 and RvD2 inhibited oral cancer proliferation in vitro. Using two validated mouse oral squamous cell carcinoma xenograft models, we found that RvD2, the more potent anti-inflammatory lipid mediator, significantly reduced tumor size. The mechanism of this action might involve suppression of IL-6, C-X-C motif chemokine 10 (CXCL10), and reduction of tumor necrosis. RvD2 generated short-lasting analgesia in xenograft cancer models, which coincided with decreased neutrophil infiltration and myeloperoxidase activity. Using a cancer supernatant model, we demonstrated that RvD2 reduced cancer-derived cytokines/chemokines (TNF-α, IL-6, CXCL10, and MCP-1), cancer mediator-induced CD11b⁺Ly6G^- myeloid cells, and nociception. We infer from our results that manipulation of the endogenous pro-resolution pathway might provide a novel approach to improve oral cancer and cancer pain treatment.

Interactions of peripheral endothelin-1 and nerve growth factor as contributors to persistent cutaneous pain

Endothelin-1 (ET-1) and Nerve Growth Factor (NGF) are proteins, released from cancer-ridden tissues, which cause spontaneous pain and hypersensitivity to noxious stimuli. Here we examined the electrophysiological and behavioral effects of these two agents for evidence of their interactions. Individual small-medium cultured DRG sensory neurons responded to both ET-1 (50 nM, n=6) and NGF (100 ng/ml, n=4), with increased numbers of action potentials and decreased slow K(+) currents; pre-exposure to ET-1 potentiated NGF´s actions, but not vice versa. Behaviorally, single intraplantar (i.pl.) injection of low doses of ET-1 (20 pmol) or NGF (100 ng), did not increase hindpaw tactile or thermal sensitivity, but their simultaneous injections sensitized the paw to both modalities. Daily i.pl. injections of low ET-1 doses in male rats caused tactile sensitization after 21 days, and enabled further tactile and thermal sensitization from low dose NGF, in ipsilateral and contralateral hindpaws. Single injections of 100 ng NGF, without changing the paw's tactile sensitivity by itself, acutely sensitized the ipsilateral paw to subsequent injections of low ET-1. The sensitization from repeated low ET-1 dosing and the cross-sensitization between NGF and ET-1 were both significantly greater in female than in male rats. These findings reveal a synergistic interaction between cutaneously administered low doses of NGF and ET-1, which could contribute to cancer-related pain.

Stress hormones concentrations in the normal microenvironment predict risk for chemically induced cancer in rats

Evidence show that stress hormones can influence cancer progression, but its role in carcinogenesis is poorly understood. In this study, we used a new method based on oral carcinogenesis model in rats to test the hypothesis that physiological levels of stress hormones in the normal tissue microenvironment would have significant predictive value for chemically induced cancer occurrence. Male Wistar rats were submitted to a tongue biopsy for measuring not-stress induced levels of norepinephrine, corticosterone, adrenocorticotropic hormone (ACTH) and brain-derived neurotrophic factor (BDNF) in the tissue before carcinogenic induction. Rats were treated with the 4-nitroquinoline-1-oxide (4NQO) chemical carcinogen for twenty weeks and then euthanized for microscopic evaluation of the tongue lesions. Increased pre-carcinogen norepinephrine concentrations and reduced basal corticosterone levels in the normal tissue microenvironment were predictive for oral squamous cell carcinoma (OSCC) occurrence. Likewise, increased pre-carcinogen norepinephrine levels in the normal microenvironment were associated a lower expression of pCDKN2a-p16 in OSCCs. Post-carcinogen levels of corticosterone and BDNF in oral leukoplakia tissues (precursor lesion of OSCC) and post-carcinogen corticosterone concentrations in OSCCs were higher than basal levels in the normal mucosa. Increased norepinephrine concentrations in OSCCs were associated to a greater tumor volume and thickness. Furthermore, higher levels of norepinephrine, ACTH and BDNF in OSCCs were associated to a lesser intensity of the lymphoplasmocytic infiltrate. This study shows that pre-carcinogen stress hormones levels in the normal microenvironment may be predictive for chemically induced cancer in rats. Moreover, chemical carcinogenesis can promote stressor-like effects with hormonal changes in the tissue microenvironment, which may be associated to tumor progression.

Is Perineural Invasion of Head and Neck Squamous Cell Carcinomas Linked to Tobacco Consumption?

Perineural invasion (PNI) is an underrecognized path of cancer spread, and its causes and mechanisms are poorly understood. Recent research indicates a mutual attraction of neuronal and cancer cells, largely dependent on neurotrophic factors and their receptors. Interestingly, the release of neurotrophic factors occurs upon cigarette smoke/nicotine exposure in a dose-dependent manner, and serum levels correlate with current smoking, number of smoking years, and smoking severity. Among cell types capable of neurotrophic factors secretion are lung and oral fibroblasts. In our study of 178 patients with head and neck squamous cell carcinoma, tumors of current and former smokers showed PNI significantly more often than tumors of never smokers. Moreover, PNI was a marker for aggressive tumor growth. Surprisingly, PNI was more significant for survival than p16 status. Our study warrants further research on PNI in head and neck squamous cell carcinoma with special emphasis on the impact of tobacco consumption to identify suitable candidates for therapeutic interventions.

Yoga as an Integrative Approach for Prevention and Treatment of Oral Cancer

Despite tremendous advancements in medicine, the number of oral cancer cases continues to increase, and the need for integrating alternate medicine or adopting an integrative approach has become a compelling cost-effective requirement for the management and treatment of diseases. Conventional treatment of oral cancer involves surgery followed by radiotherapy with or without chemotherapy which causes several complications including poor quality of life and high chances of recurrence of cancer. Oral cancer is often linked with obesity which is major risk factors in other cancers. Apart from obesity, oral cancer is thought to have an inverse relation with neurodegenerative disorders presumably because cell death decreases in the former case and increases in the latter. Ancient mind-body techniques such as yoga have not been adequately tested as a tool to synergize the cellular equilibrium pertaining to the treatment of oral cancer. Nerve growth factor (NGF), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6) are among the early experimental cellular biomarkers that may be used to probe the modulation of oral cancer, obesity, and neurodegenerative disorders. Yoga has been reported to influence these molecules in healthy individuals but whether their expression can be altered in patients of oral cancer by yoga intervention is the subject of this research being discussed in this review article. Therefore, the present article not only reviews the current status of research studies in oral cancer, obesity, and neurodegenerative disorders but also how these are linked to each other and why the investigations of the putative NGF pathway, involving TNF-α and IL-6, could provide useful clues to understand the molecular effects brought about by yoga intervention in such patients.

A Novel Model of Cancer-Induced Peripheral Neuropathy and the Role of TRPA1 in Pain Transduction

Background

Models of cancer-induced neuropathy are designed by injecting cancer cells near the peripheral nerves. The interference of tissue-resident immune cells does not allow a direct contact with nerve fibres which affects the tumor microenvironment and the invasion process.

Methods

Anaplastic tumor-1 (AT-1) cells were inoculated within the sciatic nerves (SNs) of male Copenhagen rats. Lumbar dorsal root ganglia (DRGs) and the SNs were collected on days 3, 7, 14, and 21. SN tissues were examined for morphological changes and DRG tissues for immunofluorescence, electrophoretic tendency, and mRNA quantification. Hypersensitivities to cold, mechanical, and thermal stimuli were determined. HC-030031, a selective TRPA1 antagonist, was used to treat cold allodynia.

Results

Nociception thresholds were identified on day 6. Immunofluorescent micrographs showed overexpression of TRPA1 on days 7 and 14 and of CGRP on day 14 until day 21. Both TRPA1 and CGRP were coexpressed on the same cells. Immunoblots exhibited an increase in TRPA1 expression on day 14. TRPA1 mRNA underwent an increase on day 7 (normalized to 18S). Injection of HC-030031 transiently reversed the cold allodynia.

Conclusion

A novel and a promising model of cancer-induced neuropathy was established, and the role of TRPA1 and CGRP in pain transduction was examined.

Gallic acid modulates phenotypic behavior and gene expression in oral squamous cell carcinoma cells by interfering with leptin pathway

Gallic acid is a polyphenolic compost appointed to interfere with neoplastic cells behavior. Evidence suggests an important role of leptin in carcinogenesis pathways, inducing a proliferative phenotype. We investigated the potential of gallic acid to modulate leptin-induced cell proliferation and migration of oral squamous cell carcinoma cell lines. The gallic acid effect on leptin secretion by oral squamous cell carcinoma cells, as well as the underlying molecular mechanisms, was also assessed. For this, we performed proliferation, migration, immunocytochemical and qPCR assays. The expression levels of cell migration-related genes (MMP2, MMP9, Col1A1, and E-cadherin), angiogenesis (HIF-1α, mir210), leptin signaling (LepR, p44/42 MAPK), apoptosis (casp-3), and secreted leptin levels by oral squamous cell carcinoma cells were also measured. Gallic acid decreased proliferation and migration of leptin-treated oral squamous cell carcinoma cells, and reduced mRNA expression of MMP2, MMP9, Col1A1, mir210, but did not change HIF-1α. Gallic acid decreased levels of leptin secreted by oral squamous cell carcinoma cells, accordingly with downregulation of p44/42 MAPK expression. Thus, gallic acid appears to break down neoplastic phenotype of oral squamous cell carcinoma cells by interfering with leptin pathway.

Alterations in opioid inhibition cause widespread nociception but do not affect anxiety-like behavior in oral cancer mice

Widespread pain and anxiety are commonly reported in cancer patients. We hypothesize that cancer is accompanied by attenuation of endogenous opioid-mediated inhibition, which subsequently causes widespread pain and anxiety. To test this hypothesis we used a mouse model of oral squamous cell carcinoma (SCC) in the tongue. We found that mice with tongue SCC exhibited widespread nociceptive behaviors in addition to behaviors associated with local nociception that we reported previously. Tongue SCC mice exhibited a pattern of reduced opioid receptor expression in the spinal cord; intrathecal administration of respective mu (MOR), delta (DOR), and kappa (KOR) opioid receptor agonists reduced widespread nociception in mice, except for the fail flick assay following administration of the MOR agonist. We infer from these findings that opioid receptors contribute to widespread nociception in oral cancer mice. Despite significant nociception, mice with tongue SCC did not differ from sham mice in anxiety-like behaviors as measured by the open field assay and elevated maze. No significant differences in c-Fos staining were found in anxiety-associated brain regions in cancer relative to control mice. No correlation was found between nociceptive and anxiety-like behaviors. Moreover, opioid receptor agonists did not yield a statistically significant effect on behaviors measured in the open field and elevated maze in cancer mice. Lastly, we used an acute cancer pain model (injection of cancer supernatant into the mouse tongue) to test whether adaptation to chronic pain is responsible for the absence of greater anxiety-like behavior in cancer mice. No changes in anxiety-like behavior were observed in mice with acute cancer pain.

Recent advances in understanding and managing cancer pain

Cancer pain remains a significant clinical problem worldwide. Causes of cancer pain are multifactorial and complex and are likely to vary with an array of tumor-related and host-related factors and processes. Pathophysiology is poorly understood; however, new laboratory research points to cross-talk between cancer cells and host’s immune and neural systems as an important potential mechanism that may be broadly relevant to many cancer pain syndromes. Opioids remain the most effective pharmaceuticals used in the treatment of cancer pain. However, their role has been evolving due to emerging awareness of risks of chronic opioid therapy. Despite extensive research efforts, no new class of analgesics has been developed. However, many potential therapeutic targets that may lead to the establishment of new pharmaceuticals have been identified in recent years. It is also expected that the role of non-pharmacological modalities of treatment will grow in prominence. Specifically, neuromodulation, a rapidly expanding field, may play a major role in the treatment of neuropathic cancer pain provided that further technological progress permits the development of non-invasive and inexpensive neuromodulation techniques.

Leptin acts on neoplastic behavior and expression levels of genes related to hypoxia, angiogenesis, and invasiveness in oral squamous cell carcinoma

Leptin, one of the main hormones controlling energy homeostasis, has been associated with different cancer types. In oral cancer, its effect is not well understood. We investigated, through in vitro and in vivo assays, whether leptin can affect the neoplastic behavior of oral squamous cell carcinoma. Expression of genes possibly linked to the leptin pathway was assessed in leptin-treated oral squamous cell carcinoma cells and also in tissue samples of oral squamous cell carcinoma and oral mucosa, including leptin, leptin receptor, hypoxia-inducible factor 1-alpha, E-cadherin, matrix metalloproteinase-2, matrix metalloproteinase-9, Col1A1, Ki67, and mir-210. Leptin treatment favored higher rates of cell proliferation and migration, and reduced apoptosis. Accordingly, leptin-treated oral squamous cell carcinoma cells show decreased messenger RNA caspase-3 expression, and increased levels of E-cadherin, Col1A1, matrix metalloproteinase-2, matrix metalloproteinase-9, and mir-210. In tissue samples, hypoxia-inducible factor 1-alpha messenger RNA and protein expression of leptin and leptin receptor were high in oral squamous cell carcinoma cases. Serum leptin levels were increased in first clinical stages of the disease. In animal model, oral squamous cell carcinoma-induced mice show higher leptin receptor expression, and serum leptin level was increased in dysplasia group. Our findings suggest that leptin seems to exert an effect on oral squamous cell carcinoma cells behavior and also on molecular markers related to cell proliferation, migration, and tumor angiogenesis.

OPRM1 Methylation Contributes to Opioid Tolerance in Cancer Patients

Cancer patients in pain require high doses of opioids and quickly become opioid-tolerant. Previous studies have shown that chronic cancer pain as well as high-dose opioid use lead to mu-opioid receptor downregulation. In this study we explore downregulation of the mu-opioid receptor gene (OPRM1), as a mechanism for opioid tolerance in the setting of opioid use for cancer pain. We demonstrate in a cohort of 84 cancer patients that high-dose opioid use correlates with OPRM1 hypermethylation in peripheral leukocytes of these patients. We then reverse-translate our clinical findings by creating a mouse cancer pain model; we create opioid tolerance in the mouse cancer model to mimic opioid tolerance in the cancer patients. Using this model we determine the functional significance of OPRM1 methylation on cancer pain and opioid tolerance. We focus on 2 main cells within the cancer microenvironment: the cancer cell and the neuron. We show that targeted re-expression of mu-opioid receptor on cancer cells inhibits mechanical and thermal hypersensitivity, and prevents opioid tolerance, in the mouse model. The resultant analgesia and protection against opioid tolerance are likely due to preservation of mu-opioid receptor expression on the cancer-associated neurons.

PERSPECTIVE

We demonstrate that epigenetic regulation of OPRM1 contributes to opioid tolerance in cancer patients, and that targeted gene therapy could treat cancer-induced nociception and opioid tolerance in a mouse cancer model.

Cancer and orofacial pain

BACKGROUND

Cancer pain is a devastating condition. Pain in the orofacial region, may be present as the single symptom of cancer or as a symptom of cancer in its later stages. This manuscript revises in a comprehensive manner the content of the conference entitled "Orofacial Pain and Cancer" (Dolor Orofacial y Cancer) given at the VI Simposio International "Advances in Oral Cancer" on the 22 July, 2016 in San Sebastioan-Donostia, Spain.

MATERIAL AND METHODS

We have reviewed (pubmed-medline) from the most relevant literature including reviews, systematic reviews and clinical cases, the significant and evidence-based mechanisms and mediators of cancer-associated facial pain, the diverse types of cancers that can be present in the craniofacial region locally or from distant sites that can refer to the orofacial region, cancer therapy that may induce pain in the orofacial region as well as discussed some of the new advancements in cancer pain therapy.

RESULTS

There is still a lack of understanding of cancer pain pathophysiology since depends of the intrinsic heterogeneity, type and anatomic location that the cancer may present, making more challenging the creation of better therapeutic options. Orofacial pain can arise from regional or distant tumor effects or as a consequence of cancer therapy.

CONCLUSIONS

The clinician needs to be aware that the pain may present the characteristics of any other orofacial pain disorder so a careful differential diagnosis needs to be given. Cancer pain diagnosis is made by exclusion and only can be reached after a thorough medical history, and all the common etiologies have been carefully investigated and ruled out. The current management tools are not optimal but there is hope for new, safer and effective therapies coming in the next years.

Emerging factors in the progression of cancer-related pain

Most cancer patients experience severe pain during their disease course, and the management of cancer pain is a major challenge for patients and the healthcare team. Many diverse translational models of cancer pain in recent years have improved our understanding of cancer-related pain. Cancer and associated cells in the cancer microenvironment may release various peripheral mediators, including ATP, formaldehyde, protons, proteases, endothelin, bradykinin, TNF and NGF, that result in the activation and/or sensitization of peripheral and central neurons, that contribute to the clinical manifestations of cancer-related pain. Identification of these mediators and the peripheral and central mechanisms by which they contribute to cancer-related pain may provide novel therapeutic targets to alleviate cancer patient suffering.

Contemporary views on inflammatory pain mechanisms: TRPing over innate and microglial pathways

Tissue injury, whether by trauma, surgical intervention, metabolic dysfunction, ischemia, or infection, evokes a complex cellular response (inflammation) that is associated with painful hyperalgesic states. Although in the acute stages it is necessary for protective reflexes and wound healing, inflammation may persist well beyond the need for tissue repair or survival. Prolonged inflammation may well represent the greatest challenge mammalian organisms face, as it can lead to chronic painful conditions, organ dysfunction, morbidity, and death. The complexity of the inflammatory response reflects not only the inciting event (infection, trauma, surgery, cancer, or autoimmune) but also the involvement of heterogeneous cell types including neuronal (primary afferents, sensory ganglion, and spinal cord), non-neuronal (endothelial, keratinocytes, epithelial, and fibroblasts), and immune cells. In this commentary, we will examine 1.) the expression and regulation of two members of the transient receptor potential family in primary afferent nociceptors and their activation/regulation by products of inflammation, 2.) the role of innate immune pathways that drive inflammation, and 3.) the central nervous system’s response to injury with a focus on the activation of spinal microglia driving painful hyperalgesic states.

EXPRESS: BDNF Signaling Contributes to Oral Cancer Pain in a Preclinical Orthotopic Rodent Model

The majority of patients with oral cancer report intense pain that is only partially managed by current analgesics. Thus, there is a strong need to study mechanisms as well as develop novel analgesics for oral cancer pain. Current study employed an orthotopic tongue cancer model with molecular and non-reflexive behavioral assays to determine possible mechanisms of oral cancer pain. Human oral squamous cell carcinoma cells line, HSC2, was injected into the tongue of male athymic mice and tumor growth was observed by day 6. Immunohistological analyses revealed a well-differentiated tumor with a localized immune response and pronounced sensory and sympathetic innervation and vascularization. The tumor expressed TMPRSS2, a protein previously reported with oral squamous cell carcinoma. ATF3 expression in trigeminal ganglia was not altered by tumor growth. Molecular characterization of the model demonstrated altered expression of several pain-related genes, out of which up-regulation of BDNF was most striking. Moreover, BDNF protein expression in trigeminal ganglia neurons was increased and inhibition of BDNF signaling with a tyrosine kinase B antagonist, ANA-12, reversed pain-like behaviors induced by the oral tumor. Oral squamous cell carcinoma tumor growth was also associated with a reduction in feeding, mechanical hypersensitivity in the face, as well as spontaneous pain behaviors as measured by the conditioned place preference test, all of which were reversed by analgesics. Interestingly, injection of HSC2 into the hindpaw did not reproduce this spectrum of pain behaviors; nor did injection of a colonic cancer cell line into the tongue. Taken together, this orthotopic oral cancer pain model reproduces the spectrum of pain reported by oral cancer patients, including higher order cognitive changes, and demonstrates that BDNF signaling constitutes a novel mechanism by which oral squamous cell carcinoma induces pain. Identification of the key role of tyrosine kinase B signaling in oral cancer pain may serve as a novel target for drug development.

Nerve growth factor & TrkA as novel therapeutic targets in cancer

In the past 20years, nerve growth factor (NGF) and its receptors TrkA & p75NTR were recognized to be overexpressed in the overwhelming majority of human solid cancers. Recent studies discovered the presence of overactive TrkA signaling due to TrkA rearrangements or TrkA fusion products in frequent cancers like colorectal cancer, thyroid cancer, or acute myeloid leukemia. Thus, targeting TrkA/NGF via selective small-molecule-inhibitors or antibodies has gained enormous attention in the drug discovery sector. Clinical studies on the anti-cancer impact of NGF-blocking antibodies are likely to be accelerated after the recent removal of clinical holds on these agents by regulatory authorities. Based on these current developments, the present review provides not only a broad overview of the biological effects of NGF-TrkA-p75NTR on cancer cells and their microenvironment, but also explains why NGF and its receptors are going to evoke major interest as promising therapeutic anti-cancer targets in the coming decade.

Cancer and Referred Facial Pain

Orofacial pain may be a symptom of diverse types of cancers as a result of local or distant tumor effects. The pain can be presented with the same characteristics as any other orofacial pain disorder, and this should be recognized by the clinician. Orofacial pain also can arise as a consequence of cancer therapy. In the present article, we review the mechanisms of cancer-associated facial pain, its clinical presentation, and cancer therapy associated with orofacial pain.

The Neurobiology of Cancer Pain

Oral cancers are often severely painful and clinically difficult to manage. Few researchers have investigated the neurobiologic factors responsible for cancer pain; however, the study of oral cancer pain might inform us about the fundamental biology of cancer. The purpose of the present report was to summarize the clinical challenges inherent in oral cancer pain management, oral cancer pain mechanisms and mediators, and the convergence of the investigation of carcinogenesis and pain.

Proceedings of the American Association of Oral and Maxillofacial Surgeons 2015 Research Summit

The Fifth Biennial Research Summit of the American Association of Oral and Maxillofacial Surgeons and its Committee on Research Planning and Technology Assessment was held in Rosemont, Illinois on May 6 and 7, 2015. The goal of the symposium is to provide a forum for the most recent clinical and scientific advances to be brought to the specialty. The proceedings of the events of that summit are presented in this report.

What pain tells us about cancer

Cancer pain sends a message. It is frightening to the patient. It heralds progression or recurrence to the oncologist. It is a biological readout of the cancer-nerve interaction for the scientist. Nerves have been considered bystanders within the cancer microenvironment. However, emerging information suggests that nerves are recruited and participate in the carcinogenic process. These newly formed fibers respond to mediators secreted by constituents of the cancer microenvironment. In this manner, these nerves serve as bellwethers and sensors embedded within the cancer. When we rigorously assess patients' cancer pain, we gain insight into the action of cancer. An enhanced understanding of cancer pain offers biological questions that if answered might not only provide relief from cancer pain but might also improve survival.

Targeting cells of the myeloid lineage attenuates pain and disease progression in a prostate model of bone cancer

Tumor cells frequently metastasize to bone where they can generate cancer-induced bone pain (CIBP) that can be difficult to fully control using available therapies. Here, we explored whether PLX3397, a high-affinity small molecular antagonist that binds to and inhibits phosphorylation of colony-stimulating factor-1 receptor, the tyrosine-protein kinase c-Kit, and the FMS-like tyrosine kinase 3, can reduce CIBP. These 3 targets all regulate the proliferation and function of a subset of the myeloid cells including macrophages, osteoclasts, and mast cells. Preliminary experiments show that PLX3397 attenuated inflammatory pain after formalin injection into the hind paw of the rat. As there is an inflammatory component in CIBP, involving macrophages and osteoclasts, the effect of PLX3397 was explored in a prostate model of CIBP where skeletal pain, cancer cell proliferation, tumor metastasis, and bone remodeling could be monitored in the same animal. Administration of PLX3397 was initiated on day 14 after prostate cancer cell injection when the tumor was well established, and tumor-induced bone remodeling was first evident. Over the next 6 weeks, sustained administration of PLX3397 attenuated CIBP behaviors by approximately 50% and was equally efficacious in reducing tumor cell growth, formation of new tumor colonies in bone, and pathological tumor-induced bone remodeling. Developing a better understanding of potential effects that analgesic therapies have on the tumor itself may allow the development of therapies that not only better control the pain but also positively impact disease progression and overall survival in patients with bone cancer.

Released lipids regulate transient receptor potential channel (TRP)-dependent oral cancer pain

Background

Pain in the head neck area is an early symptom in oral cancer, supporting the hypothesis that cancer cells control the activities of surrounding nociceptors at the site of the tumor. Several reports implicate TRPV1 and TRPA1 in cancer pain, although there is a large gap in knowledge since the mechanisms for tumor-induced activation of these TRP receptors are unknown. Interestingly, TRP-active lipids such as linoleic acid, arachidonic acid, hydroxyoctadecadienoic acid and hydroxyeicosatetraenoic acid are significantly elevated in the saliva of oral cancer patients compared to normal patients, supporting a possible linkage between these lipids and oral cancer pain. We therefore hypothesize that oral squamous cell carcinomas release certain lipids that activate TRPV1 and/or TRPA1 on sensory neurons, contributing to the development of oral cancer pain.

Methods

Lipid extracts were made from conditioned media of three human oral squamous cell carcinoma (OSCC) cell lines as well as one normal human oral keratinocytes cell line. These were then injected intraplantarly into rat hindpaws to measure spontaneous nocifensive behavior, as well as thermal and mechanical allodynia. For interventional experiments, the animals were pretreated with AMG517 (TRPV1 antagonist) or HC030031 (TRPA1 antagonist) prior to extract injection.

Results

These studies demonstrate that lipids released from the three OSCC cell lines, but not the normal cell line, were capable of producing significant spontaneous nocifensive behaviors, as well as thermal and mechanical allodynia. Notably each of the cell lines produced a different magnitude of response for each of three behavioral assays. Importantly, pre-treatment with a TRPVI antagonist blocked lipid-mediated nocifensive and thermal hypersensitivity, but not mechanical hypersensitivity. In addition, pre-treatment with a TRPA1 antagonist only reversed thermal hypersensitivity without affecting lipid-induced nocifensive behavior or mechanical allodynia.

Conclusions

These data reveal a novel mechanism for cancer pain and provide strong direction for future studies evaluating the cellular mechanism regulating the TRP-active lipids by OSCC tumors.

Role of nerve growth factor in pain

Nerve growth factor (NGF) was first identified as a substance that is essential for the development of nociceptive primary neurons and later found to have a role in inflammatory hyperalgesia in adults. Involvement of NGF in conditions with no apparent inflammatory signs has also been demonstrated. In this review we look at the hyperalgesic effects of exogenously injected NGF into different tissues, both human and animal, with special emphasis on the time course of these effects. The roles of NGF in inflammatory and neuropathic conditions as well as cancer pain are then reviewed. The role of NGF in delayed onset muscle soreness is described in more detail than its other roles based on the authors' recent observations. Acute effects are considered to be peripherally mediated, and accordingly, sensitization of nociceptors by NGF to heat and mechanical stimulation has been reported. Changes in the conductive properties of axons have also been reported. The intracellular mechanisms so far proposed for heat sensitization are direct phosphorylation and membrane trafficking of TRPV1 by TrkA. Little investigation has been done on the mechanism of mechanical sensitization, and it is still unclear whether mechanisms similar to those for heat sensitization work in mechanical sensitization. Long-lasting sensitizing effects are mediated both by changed expression of neuropeptides and ion channels (Na channels, ASIC, TRPV1) in primary afferents and by spinal NMDA receptors. Therapeutic perspectives are briefly discussed at the end of the chapter.

Intradermal Injection with Nerve Growth Factor: A Reproducible Model to Induce Experimental Allodynia and Hyperalgesia

BACKGROUND

Nerve growth factor (NGF) plays a pivotal role in survival, growth, and differentiation of the nervous system. Increased levels of NGF have been reported in human pain disorders. Experimental injection of NGF in humans is known to evoke long-lasting mechanical sensitization and subsequent allodynia and hyperalgesia.

METHODS

Reproducibility of intradermal injection of NGF was investigated. Twenty healthy male volunteers were included (mean age 24 years, range 19 to 31). The experiment consisted of 3 identical treatment periods with period 1 stimulating the right arm, period 2 the left arm, and period 3 stimulating the right arm again (period one and three were separated by at least 21 days). Pain intensity was assessed in response to several phasic stimuli in 3 adjacent sites of the volar forearm: pressure; pinprick; brush; and heat before and after NGF injection. Additionally, areas of allodynia and secondary hyperalgesia were assessed. Rekindling with pressure was performed 1 hour and 24 hours after injection. Reproducibility was assessed with intraclass correlation coefficient (ICC 3,1).

RESULTS

ICC values > 0.6 for all phasic stimuli and for the area of hyperalgesia. After NGF injection, pressure pain (P < 0.001) and heat pain (P < 0.01) sensitivity increased significantly. After rekindling, the area of hyperalgesia (von Frey 26 g) was significantly increased (P = 0.03) and sensitivity to pinprick was increased (P < 0.02).

CONCLUSION

Intradermal NGF injection is capable of inducing reproducible allodynia and hyperalgesia, and the model is recommended for future experimental and pharmacological pain studies.

Perineural growth in head and neck squamous cell carcinoma: a review

Perineural growth is a unique route of tumor metastasis that is associated with poor prognosis in several solid malignancies. It is diagnosed by the presence of tumor cells inside the neural space seen on histological or imaging evaluations. Little is known about molecular mechanisms involved in the growth and spread of tumor cells in neural spaces. The poor prognosis associated with perineural growth and lack of targeted approaches necessitates the study of molecular factors involved in communication between tumor and neural cells. Perineural growth rates, shown to be as high as 63% in head and neck squamous cell carcinoma (HNSCC), correlate with increased local recurrence and decreased disease-free survival. Here we describe the literature on perineural growth in HNSCC. In addition, we discuss factors implicated in perineural growth of cancer. These factors include brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin-3 and -4, glial cell-line derived neurotrophic factor (GDNF), the neural cell adhesion molecule (NCAM), substance P (SP), and chemokines. We also explore the literature on membrane receptors, including the Trk family and the low-affinity nerve growth factor receptor. This review highlights areas for further study of the mechanisms of perineural invasion which may facilitate the identification of therapeutic targets in HNSCC.

NGF blockade at early times during bone cancer development attenuates bone destruction and increases limb use

Studies in animals and humans show that blockade of nerve growth factor (NGF) attenuates both malignant and nonmalignant skeletal pain. While reduction of pain is important, a largely unanswered question is what other benefits NGF blockade might confer in patients with bone cancer. Using a mouse graft model of bone sarcoma, we demonstrate that early treatment with an NGF antibody reduced tumor-induced bone destruction, delayed time to bone fracture, and increased the use of the tumor-bearing limb. Consistent with animal studies in osteoarthritis and head and neck cancer, early blockade of NGF reduced weight loss in mice with bone sarcoma. In terms of the extent and time course of pain relief, NGF blockade also reduced pain 40% to 70%, depending on the metric assessed. Importantly, this analgesic effect was maintained even in animals with late-stage disease. Our results suggest that NGF blockade immediately upon detection of tumor metastasis to bone may help preserve the integrity and use, delay the time to tumor-induced bone fracture, and maintain body weight.

Neurotrophins, endocannabinoids and thermo-transient receptor potential: a threesome in pain signalling

Because of the social and economic costs of chronic pain, there is a growing interest in unveiling the cellular and molecular mechanisms underlying it with the aim of developing more effective medications. Pain signalling is a multicomponent process that involves the peripheral and central nervous systems. At the periphery, nociceptor sensitisation by pro-inflammatory mediators is a primary step in pain transduction. Although pain is multifactorial at cellular and molecular levels, it is widely accepted that neurotrophin (TrkA, p75NTR, Ret and GFRs), cannabinoid (CB1 and CB2), and thermo-transient receptor potential (TRPs; TRPV1, TRPA1 and TRPM8) receptors play a pivotal role. They form a threesome for which endocannabinoids appear to be a first line of defence against pain, while neurotrophins and thermoTRPs are the major generators of painful signals. However, endocannabinoids may exhibit nociceptive activity while some neurotrophins may display anti-nociception. Accordingly, a clear-cut knowledge of the modulation and context-dependent function of these signalling cascades, along with the molecular and dynamic details of their crosstalk, is critical for understanding and controlling pain transduction. Here, the recent progress in this fascinating topic, as well as the tantalizing questions that remain unanswered, will be discussed. Furthermore, we will underline the need for using a systems biology approach (referred to as systems pain) to uncover the dynamics and interplay of these intricate signalling cascades, taking into consideration the molecular complexity and cellular heterogeneity of nociceptor populations. Nonetheless, the available information confirms that pharmacological modulation of this signalling triad is a highly valuable therapeutic strategy for effectively treating pain syndromes.

Nanotechnology-based drug delivery systems for treatment of oral cancer: a review

Oral cancer (oral cavity and oropharynx) is a common and aggressive cancer that invades local tissue, can cause metastasis, and has a high mortality rate. Conventional treatment strategies, such as surgery and chemoradiotherapy, have improved over the past few decades; however, they remain far from optimal. Currently, cancer research is focused on improving cancer diagnosis and treatment methods (oral cavity and oropharynx) nanotechnology, which involves the design, characterization, production, and application of nanoscale drug delivery systems. In medicine, nanotechnologies, such as polymeric nanoparticles, solid lipid nanoparticles, nanostructured lipid carriers, gold nanoparticles, hydrogels, cyclodextrin complexes, and liquid crystals, are promising tools for diagnostic probes and therapeutic devices. The objective of this study is to present a systematic review of nanotechnology-based drug delivery systems for oral cancers.

Simultaneous inferior alveolar nerve regeneration and osseointegration with a nerve growth factor-supplying implant: a preliminary study

PURPOSE

Although nerve growth factor (NGF) has been proved to enhance inferior alveolar nerve (IAN) regeneration, its clinical application remains a challenging issue. This study investigated the functional regeneration of IAN injury by supplying NGF using an NGF-supplying implant and its effect on the osseointegration.

MATERIALS AND METHODS

In canine IAN transection-and-repair models (n = 9), NGF-supplying implants connected to osmotic pumps were installed just above the transection site. In the right IAN, NGF 300 μg in phosphate buffered saline (PBS) 2 mL was loaded in the pump and pure PBS 2 mL was loaded in the left IAN. The gross clinical finding was evaluated by wound healing, inflammation, implant exposure, and loss of fixture. To evaluate IAN regeneration, electrophysiologic (amplitude, latency, conduction velocity, and peak voltage) and histomorphometric (axon count and density, myelin thickness, and ratio of axon diameter to fiber diameter) analyses were performed. Implant stability quotient, bone-to-implant contact ratio, and new bone area were measured to assess the osseointegration of the NGF-supplying implant.

RESULTS

The conduction velocity (2.675 m/second) and peak voltage (1.940 μV) of the NGF group at 6 weeks were considerably higher than those of the PBS group (1.892 m/second and 1.300 μV, respectively). The same results were observed for axon count (NGF vs PBS, 4,576.107 ± 270.413 vs 3,606.972 ± 242.876), axon density (10,707.458 ± 638.835 vs 7,899.781 ± 1,063.625/mm(2)), and myelin thickness (1.670 ± 0.555 vs 1.173 ± 0.388 μm). There were no meaningful differences for the other parameters.

CONCLUSIONS

Supplying NGF with specially designed dental implants can be a new therapeutic approach to enable IAN regeneration and osseointegration simultaneously.

Review of preclinical studies on treatment of mucositis and associated pain

Oral mucositis is a significant problem in cancer patients treated with radiation or chemotherapy, often hindering definitive cancer treatment. For patients with oral mucositis, pain is the most distressing symptom, leading to loss of orofacial function and poor quality of life. While oral mucositis has been well-described, its pathophysiology is poorly understood. Oral health professionals treating patients with mucositis have almost no effective therapies to treat or prevent oral mucositis. The purpose of this review is to (1) describe the current preclinical models of oral mucositis and their contribution to the understanding of mucositis pathophysiology, (2) explore preclinical studies on therapies targeting mucositis and discuss the clinical trials that have resulted from these preclinical studies, and (3) describe the proposed pathophysiology of oral mucositis pain and preclinical modeling of oral mucositis pain.

Adenosine triphosphate drives head and neck cancer pain through P2X2/3 heterotrimers

Introduction

Cancer pain creates a poor quality of life and decreases survival. The basic neurobiology of cancer pain is poorly understood. Adenosine triphosphate (ATP) and the ATP ionotropic receptor subunits, P2X2 and P2X3, mediate cancer pain in animal models; however, it is unknown whether this mechanism operates in human, and if so, what the relative contribution of P2X2- and P2X3-containing trimeric channels to cancer pain is. Here, we studied head and neck squamous cell carcinoma (HNSCC), which causes the highest level of function-induced pain relative to other types of cancer.

Results

We show that the human HNSCC tissues contain significantly increased levels of ATP compared to the matched normal tissues. The high levels of ATP are secreted by the cancer and positively correlate with self-reported function-induced pain in patients. The human HNSCC microenvironment is densely innervated by nerve fibers expressing both P2X2 and P2X3 subunits. In animal models of HNSCC we showed that ATP in the cancer microenvironment likely heightens pain perception through the P2X2/3 trimeric receptors. Nerve growth factor (NGF), another cancer-derived pain mediator found in both human and mouse HNSCC, induces P2X2 and P2X3 hypersensitivity and increases subunit expression in murine trigeminal ganglion (TG) neurons.

Conclusions

These data identify a key peripheral mechanism in cancer pain and highlight the clinical potential of specifically targeting nociceptors expressing both P2X2 and P2X3 subunits (e.g., P2X2/3 heterotrimers) to alleviate cancer pain.

Electronic supplementary material

The online version of this article (doi:10.1186/2051-5960-2-62) contains supplementary material, which is available to authorized users.

The neurobiology of cancer pain

The global burden of cancer pain is enormous and opioids, despite their side effects, remain the primary therapeutic approach. The cause of cancer pain is unknown. Mechanisms driving cancer pain differ from those mechanisms responsible for inflammatory and neuropathic pain. The prevailing hypothesis put forward to explain cancer pain posits that cancers generate and secrete mediators which sensitize and activate primary afferent nociceptors in the cancer microenvironment. Moreover, cancers induce neurochemical reorganization of the spinal cord, which contributes to spontaneous activity and enhanced responsiveness. The purpose of this review, which covers clinical and preclinical studies, is to highlight those peripheral and central mechanisms responsible for cancer pain. The challenges facing neuroscientists and clinicians studying and ultimately treating cancer pain are discussed.