Chi T. Viet

Re-expression of the methylated EDNRB gene in oral squamous cell carcinoma attenuates cancer-induced pain

Summary Epigenetic silencing by methylation is a novel mechanism regulating cancer‐induced pain. Re‐expression of the hypermethylated EDNRB gene produces an antinociceptive effect in a mouse model. Abstract Endothelin‐1 is a vasoactive peptide that activates both the endothelin A (ETA) and endothelin B (ETB) receptors, and is secreted in high concentrations in many different cancer environments. Although ETA receptor activation has an established nociceptive effect in cancer models, the role of ETB receptors on cancer pain is controversial. EDNRB, the gene encoding the ETB receptor, has been shown to be hypermethylated and transcriptionally silenced in many different cancers. In this study we demonstrate that EDNRB is heavily methylated in human oral squamous cell carcinoma lesions, which are painful, but not methylated in human oral dysplasia lesions, which are typically not painful. ETB mRNA expression is reduced in the human oral squamous cell carcinoma lesions as a consequence of EDNRB hypermethylation. Using a mouse cancer pain model, we show that ETB receptor re‐expression attenuates cancer‐induced pain. These findings identify EDNRB methylation as a novel regulatory mechanism in cancer‐induced pain and suggest that demethylation therapy targeted at the cancer microenvironment has the potential to thwart pain‐producing mechanisms at the source, thus freeing patients of systemic analgesic toxicity.

Biologic Mechanisms of Oral Cancer Pain and Implications for Clinical Therapy

Cancer pain is an ever-present public health concern. With innovations in treatment, cancer patients are surviving longer, but uncontrollable pain creates a poor quality of life for these patients. Oral cancer is unique in that it causes intense pain at the primary site and significantly impairs speech, swallowing, and masticatory functions. We propose that oral cancer pain has underlying biologic mechanisms that are generated within the cancer microenvironment. A comprehensive understanding of key mediators that control cross-talk between the cancer and peripheral nervous system, and possible interventions, underlies effective cancer pain management. The purpose of this review is to explore the current studies on oral cancer pain and their implications in clinical management for cancer pain in general. Furthermore, we will explore the endogenous opioid systems and novel cancer pain therapeutics that target these systems, which could solve the issue of opiate tolerance and improve quality of life in oral cancer patients.

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.

Oral mucosal injury caused by mammalian target of rapamycin inhibitors: emerging perspectives on pathobiology and impact on clinical practice

In recent years oral mucosal injury has been increasingly recognized as an important toxicity associated with mammalian target of rapamycin (mTOR) inhibitors, including in patients with breast cancer who are receiving everolimus. This review addresses the state‐of‐the‐science regarding mTOR inhibitor‐associated stomatitis (mIAS), and delineates its clinical characteristics and management. Given the clinically impactful pain associated with mIAS, this review also specifically highlights new research focusing on the study of the molecular basis of pain. The incidence of mIAS varies widely (2–78%). As reported across multiple mTOR inhibitor clinical trials, grade 3/4 toxicity occurs in up to 9% of patients. Managing mTOR‐associated oral lesions with topical oral, intralesional, and/or systemic steroids can be beneficial, in contrast to the lack of evidence supporting steroid treatment of oral mucositis caused by high‐dose chemotherapy or radiation. However, steroid management is not uniformly efficacious in all patients receiving mTOR inhibitors. Furthermore, technology does not presently exist to permit clinicians to predict a priori which of their patients will develop these lesions. There thus remains a strategic need to define the pathobiology of mIAS, the molecular basis of pain, and risk prediction relative to development of the clinical lesion. This knowledge could lead to novel future interventions designed to more effectively prevent mIAS and improve pain management if clinically significant mIAS lesions develop.

Analgesia targeting IB4-positive neurons in cancer-induced mechanical hypersensitivity

UNLABELLED Cancer patients often suffer from pain and most will be prescribed μ-opioids. μ-opioids are not satisfactory in treating cancer pain and are associated with multiple debilitating side effects. Recent studies show that μ and δ opioid receptors are separately expressed on IB4 (-) and IB4 (+) neurons, which control thermal and mechanical pain, respectively. In this study we investigated IB4 (+) and IB4 (-) neurons in mechanical and thermal hypersensitivity in an orthotopic mouse oral cancer model. We used a δ opioid receptor agonist and a P2X(3) antagonist to target IB4 (+) neurons and to demonstrate that this subset plays a key role in cancer-induced mechanical allodynia, but not in thermal hyperalgesia. Moreover, selective removal of IB4 (+) neurons using IB4-saporin impacts cancer-induced mechanical but not thermal hypersensitivity. Our results demonstrate that peripherally administered pharmacological agents targeting IB4 (+) neurons, such as a selective δ-opioid receptor agonist or P2X(3) antagonist, might be useful in treating oral cancer pain. PERSPECTIVE To clarify the mechanisms of oral cancer pain, we examined the differential role of IB4 (+) and IB4 (-) neurons. Characterization of these 2 subsets of putative nociceptors is important for further development of effective clinical cancer pain relief.

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

IntroductionCancer 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.ResultsWe 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.ConclusionsThese 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.

Decitabine rescues cisplatin resistance in head and neck squamous cell carcinoma.

Cisplatin resistance in head and neck squamous cell carcinoma (HNSCC) reduces survival. In this study we hypothesized that methylation of key genes mediates cisplatin resistance. We determined whether a demethylating drug, decitabine, could augment the anti-proliferative and apoptotic effects of cisplatin on SCC-25/CP, a cisplatin-resistant tongue SCC cell line. We showed that decitabine treatment restored cisplatin sensitivity in SCC-25/CP and significantly reduced the cisplatin dose required to induce apoptosis. We then created a xenograft model with SCC-25/CP and determined that decitabine and cisplatin combination treatment resulted in significantly reduced tumor growth and mechanical allodynia compared to control. To establish a gene classifier we quantified methylation in cancer tissue of cisplatin-sensitive and cisplatin-resistant HNSCC patients. Cisplatin-sensitive and cisplatin-resistant patient tumors had distinct methylation profiles. When we quantified methylation and expression of genes in the classifier in HNSCC cells in vitro, we showed that decitabine treatment of cisplatin-resistant HNSCC cells reversed methylation and gene expression toward a cisplatin-sensitive profile. The study provides direct evidence that decitabine restores cisplatin sensitivity in in vitro and in vivo models of HNSCC. Combination treatment of cisplatin and decitabine significantly reduces HNSCC growth and HNSCC pain. Furthermore, gene methylation could be used as a biomarker of cisplatin-resistance.

Demethylating Drugs as Novel Analgesics for Cancer Pain

Purpose: In this study, we evaluated the analgesic potential of demethylating drugs on oral cancer pain. Although demethylating drugs could affect expression of many genes, we focused on the mu-opioid receptor (OPRM1) gene pathway, because of its role in pain processing. We determined the antinociceptive effect of OPRM1 re-expression in a mouse oral cancer model. Experimental Design: Using a mouse oral cancer model, we determined whether demethylating drugs produced antinociception through re-expression of OPRM1. We then re-expressed OPRM1 with adenoviral transduction and determined if, and by what mechanism, OPRM1 re-expression produced antinociception. To determine the clinical significance of OPRM1 on cancer pain, we quantified OPRM1 methylation in painful cancer tissues and nonpainful contralateral normal tissues of patients with oral cancer, and nonpainful dysplastic tissues of patients with oral dysplasia. Results: We demonstrated that OPRM1 was methylated in cancer tissue, but not normal tissue, of patients with oral cancer, and not in dysplastic tissues from patients with oral dysplasia. Treatment with demethylating drugs resulted in mechanical and thermal antinociception in the mouse cancer model. This behavioral change correlated with OPRM1 re-expression in the cancer and associated neurons. Similarly, adenoviral-mediated OPRM1 re-expression on cancer cells resulted in naloxone-reversible antinociception. OPRM1 re-expression on oral cancer cells in vitro increased β-endorphin secretion from the cancer, and decreased activation of neurons that were treated with cancer supernatant. Conclusion: Our study establishes the regulatory role of methylation in cancer pain. OPRM1 re-expression in cancer cells produces antinociception through cancer-mediated endogenous opioid secretion. Demethylating drugs have an analgesic effect that involves OPRM1. Clin Cancer Res; 20(18); 4882–93. ©2014 AACR.

Structural and functional interactions between six-transmembrane μ-opioid receptors and β2-adrenoreceptors modulate opioid signaling.

The primary molecular target for clinically used opioids is the μ-opioid receptor (MOR). Besides the major seven-transmembrane (7TM) receptors, the MOR gene codes for alternatively spliced six-transmembrane (6TM) isoforms, the biological and clinical significance of which remains unclear. Here, we show that the otherwise exclusively intracellular localized 6TM-MOR translocates to the plasma membrane upon coexpression with β2-adrenergic receptors (β2-ARs) through an interaction with the fifth and sixth helices of β2-AR. Coexpression of the two receptors in BE(2)-C neuroblastoma cells potentiates calcium responses to a 6TM-MOR ligand, and this calcium response is completely blocked by a selective β2-antagonist in BE(2)-C cells, and in trigeminal and dorsal root ganglia. Co-administration of 6TM-MOR and β2-AR ligands leads to substantial analgesic synergy and completely reverses opioid-induced hyperalgesia in rodent behavioral models. Together, our results provide evidence that the heterodimerization of 6TM-MOR with β2-AR underlies a molecular mechanism for 6TM cellular signaling, presenting a unique functional responses to opioids. This signaling pathway may contribute to the hyperalgesic effects of opioids that can be efficiently blocked by β2-AR antagonists, providing a new avenue for opioid therapy.

Differential Regulation of 6- and 7-Transmembrane Helix Variants of μ-Opioid Receptor in Response to Morphine Stimulation.

The pharmacological effect of opioids originates, at the cellular level, by their interaction with the μ-opioid receptor (mOR) resulting in the regulation of voltage-gated Ca2+ channels and inwardly rectifying K+ channels that ultimately modulate the synaptic transmission. Recently, an alternative six trans-membrane helix isoform of mOR, (6TM-mOR) has been identified, but its function and signaling are still largely unknown. Here, we present the structural and functional mechanisms of 6TM-mOR signaling activity upon binding to morphine. Our data suggest that despite the similarity of binding modes of the alternative 6TM-mOR and the dominant seven trans-membrane helix variant (7TM-mOR), the interaction with morphine generates different dynamic responses in the two receptors, thus, promoting the activation of different mOR-specific signaling pathways. We characterize a series of 6TM-mOR-specific cellular responses, and observed that they are significantly different from those for 7TM-mOR. Morphine stimulation of 6TM-mOR does not promote a cellular cAMP response, while it increases the intracellular Ca2+ concentration and reduces the cellular K+ conductance. Our findings indicate that 6TM-mOR has a unique contribution to the cellular opioid responses. Therefore, it should be considered as a relevant target for the development of novel pharmacological tools and medical protocols involving the use of opioids.