Project Summary/Abstract
Oral cancer patients suffer from severe pain that is treated with opioids. However, opioid tolerance develops
quickly. Currently, there are no other approaches to alleviate oral cancer pain or to forestall the development of
opioid tolerance. In exploring a potential role of the epidermal growth factor receptor (EGFR) in oral cancer
pain and opioid tolerance, we made an exciting discovery that one of the EGFR ligands, HB-EGF, is
upregulated in patients with severe pain, and that EGFR interacts with both the mu opioid receptor (MOR) and
the glutamate N-Methyl-D-aspartic acid receptor (NMDAR), two proteins important for chronic pain and opioid
tolerance. This led us to hypothesize that HB-EGF mediated signaling in trigeminal (TG) neurons would: a)
desensitize and down-regulate MOR and b) potentiate NMDAR-dependent synaptic transmission, contributing
to oral cancer pain and opioid tolerance. We will test our hypothesis in three specific aims. Aim 1 will discover
whether HB-EGF and trigeminal EGFR regulate pain, opioid tolerance, and NMDAR-mediated synaptic
transmission in oral cancer. We will use pharmacological and genetic approaches to determine if HB-EGF and
trigeminal EGFR are essential for oral cancer pain and opioid tolerance. Behaviors related to pain and opioid
tolerance will be measured using a battery of assays. NMDAR mediated synaptic transmission will be studied
using electrophysiological recordings in a newly developed brainstem preparation. We will quantify NMDAR
expression in the mouse TG and brainstems using western blot. Aim 2 will discover whether HB-EGF and
EGFR modulate MOR signaling and endocytosis. We will use BRET-based biosensors and super resolution
imaging in model cell lines and TG neurons to study the impact of HB-EGF and EGFR on MOR cAMP activity,
G-protein coupling, ßARR recruitment and trafficking to endosomes. We will determine the effect of EGFR
gene deletion and inhibition on MOR expression by qPCR, western blot, and fluorescence imaging in mouse
TG neurons. Aim 3 will validate HB-EGF and EGFR as potential targets for pain and opioid tolerance in three
oral cancer patient cohorts. First, we will model EGFR ligand expression in the tumor with self-reported pain,
quantitative sensory testing scores, and opioid intake and explore the cellular origin of EGFR ligands by single
cell RNA sequencing in tumor tissues. In the second cohort, we will model HB-EGF and EGFR expression in
tumor tissues using immunofluorescence staining as a function of self-reported pain and opioid intake using
data generated in a phase II anti-cancer trial examining the effect of an EGFR inhibitor erlotinib as an adjuvant
to standard chemotherapy for cancer regression. In the third cohort, we will model peripheral EGFR and
ligand(s) expression from self-reported pain. EGFR inhibitors are FDA-approved therapies for cancer
management. HB-EGF is an emerging cancer target and a pain mediator. Targeting HB-EGF and EGFR
therefore has the potential for rapid clinical translation to reduce oral cancer pain and opioid tolerance.