Oral Squamous Cell Carcinoma Induces Nerve Injury and Adrenergic Receptor Plasticity, Resulting in Sympathetic-Sensory Coupled Pain

Head and neck squamous cell carcinoma (HNSCC) causes severe pain and stress, which exceeds other cancers. We hypothesize that oral tumor growth drives sensory and sympathetic nerve injury, resulting in sympathetic-sensory coupled signaling comprised of nociceptive adrenergic sensitivity, spontaneous pain, and increased sympathetic tone. Using an aggressive syngeneic orthotopic transplant mouse model, tongue tumor-innervating nerves were identified using retrograde tracers. Nerve injury (i.e. ATF3 expression) was assessed in trigeminal (TG) and superior cervical ganglia (SCG) using immunohistochemistry. Spontaneous pain behavior was assessed by a novel automated grimace assay. Calcium imaging and pharmacology evaluated neuronal adrenergic receptor (ADR) isoform functionality. Alpha1-ADR protein expression was quantified in acute culture using prazosin-BODIPY. There was a 4-fold increase in tongue-innervating ATF3+ SCG and TG neurons from tumor-bearing mice compared to sham. Grimace scores were assessed during tumor progression and plotted to calculate area under the curve; at post-inoculation day 14 there was a 100% increase in grimace behaviors in tumor-bearing mice compared to baseline. Sympathetic neurotransmitter, norepinephrine (NE) evoked a larger (350%) Ca2+transient in more tongue afferents from cancer mice (91%) compared to sham (9%); a pan-alpha1-ADR antagonist blocked the NE-evoked transient. We also found that the application of a pan-alpha1-ADR agonist evoked Ca2+ transients similar to NE in tumor-bearing mice, while a pan-alpha2-ADR agonist did not. Lastly, there was 15% more alpha1-ADR expression in tongue afferents from tumor-bearing mice compared to sham. These results suggest tumor-induced nerve injury may drive sympathetic-sensory nerve coupling, resulting in a significant sympathetic component of oral cancer pain.