The Role of Peripheral Brain-Derived Neurotrophic Factor (BDNF) Signaling in Oral Cancer Pain

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Project Summary Numerous studies have indicated that pain is the top ranked symptom in head and neck cancer (HNC) patients. However, available treatments are limited and associated with severe side effects adding substantially to the burden of having cancer. Thus, there is a critical need for novel analgesics. However, there is a large gap in knowledge for oral cancer pain mechanisms and thus pain control is often incomplete. Because pain in oral cancer occurs even before a tumor becomes clinically apparent, this cardinal symptom indicates that cancer cells control the activities of surrounding nociceptors at the site of the tumor. The objective here is to study a novel mechanism for oral cancer pain by which tumor cells interact with sensory neurons at the orthotopic site. Our central hypothesis is that Brain-derived neurotrophic factor (BDNF) is released from oral squamous cell carcinoma (OSCC) cells and activates adjacent sensory fibers, contributing to OSCC-induced pain. This hypothesis is based on compelling preliminary data demonstrating that BDNF levels are elevated in oral tumor in mice and that antagonizing the BDNF receptor reverses pain-like behaviors in vivo. We will employ behavioral, biochemical, anatomical methods as well as electrophysiological analysis of lingual nerve fibers that allows studying tumor-nerve interactions in situ, to study the aims: Aim 1: Determine whether OSCC-released BDNF contributes to oral cancer pain. Using superfusion techniques, electrophysiology and behavioral assays, this aim will determine the release of BDNF from tongue tumor as well as test whether released BDNF regulate surrounding nerve fibers activities in the tongue and produce pain-like behaviors in vivo. Results from male and female mice will be compared to determine BDNF- induced sexually dimorphic effects. Aim 2: Determine whether TrkB and p75 receptors (p75R) play a role in BDNF mediated peripheral oral cancer pain. The effects of pharmacological and molecular inhibition on the TrkB and p75 receptors in sensory neurons will be determined with electrophysiologic recordings. Follow-up experiments will test the effect of application of recombinant human BDNF on sensory fiber activities in naïve animals. Sex-dependent differences will also be determined. Aim 3: Determine downstream BDNF signaling pathways in mediating oral cancer pain. Using male and female mice, this aim will employ anatomical and electrophysiological methods to identify the downstream pathways of TrkB and the p75 receptor that may play a role in BDNF-induced oral cancer pain. Collectively, experiments proposed herein provide critical and comprehensive tests of the central hypothesis. The translational significance of this project is strengthened by the use of human cancer cells and a clinically relevant orthotopic model that mimics patient symptoms as well as the novel electrophysiology method to study tumor-nerve interaction at the very site of tumor development. RELEVANCE: It is often very difficult to treat pain from oral cancer with available medications due to limited effectiveness or rapid development of tolerance. We propose a highly novel mechanism that will evaluate the peripheral role of BDNF signaling in oral cancer pain. The research project addresses a significant medical problem with an innovative hypothesis and newly developed experimental methods. Moreover, there is a strong rationale for the focus of this application, as BDNF signaling is known to trigger pain and contribute to tumor progression and chemoresistance in head and neck cancer.