Objectives: To determine the antiproliferative and analgesic potential of demethylating drugs decitabine and zebularine in a mouse oral cancer model and translate the findings to patients.
Methods: A mouse model was created by inoculating an oral squamous cell carcinoma (SCC) cell line, into the hindpaw of BALB/c mice. Mice were divided into 4 treatment groups: 1) zebularine-only, 2) decitabine-only, 3) combination of both drugs, and 4) control. Mechanical allodynia (pain) and tumor size were measured at baseline and up to post-inoculation day (PID) 21. ANOVA and Holm-Sidak analyses were performed. To translate these findings to patients, cancer tissue and contralateral normal tissue were collected from patients with oral SCC. Methylation and mRNA quantification of OPRM1 (mu-opioid receptor gene) were performed in patient and mouse tissues.
Results: Mice developed visible tumors by PID 4. Mechanical allodynia increased significantly from baseline. Combination treatment with both drugs resulted in more significant decrease in proliferation and pain than either drug alone. Tumors and associated sensory neurons of treated but not control mice showed demethylation and increased expression of OPRM1. Endogenous opioid secretion was higher in cells expressing OPRM1. Methylation quantification of tissues from 19 oral SCC patients demonstrated methylation of OPRM1 in cancer and not normal tissue.
Conclusions: In this study we demonstrate the novel antiproliferative and analgesic effects of demethylating drugs in oral cancer. Analgesia is produced by increase in endogenous opioid and mu-opioid receptor expression on tumors and neurons. The oral cancer patients demonstrate aberrant methylation of OPRM1.These parallel findings in the mouse model and in patients implicate the potential antiproliferative and analgesic effect of demethylating drugs in oral cancer patients.
Keywords: Behavioral science, Carcinogenesis, Neoplasia and Pain