Supplementary Figure S2. (a) Mechanical threshold of mice transduced with Ad-OPRM1 was significantly higher than the control, indicating lower mechanical allodynia (*p<0.05, ***p<0.001, with treatment as the main effect, see Supplementary Table S3 for statistical analysis). (b) Thermal threshold of mice transduced with Ad-OPRM1 was significant higher than control (***p<0.001, with treatment as the main effect). (c) Bar graph shows beta-endorphin concentration in supernatant from WM-164 transduced with either Ad-OPRM1 or Ad-GFP at 100 MOI. WM-164 cells transduced with Ad-OPRM1 secreted significantly more beta-endorphin than control cells (***p<0.001, Student's t test).
ARTICLE ABSTRACTPurpose: 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.