Morphine-Sparing Effect by COX-1 Inhibitor Sustains Analgesic Function without Compromising Antigen-Specific Immunity and Antitumor Effect of Naked DNA Vaccine

Abstract

Morphine and ketorolac, two analgesics with different mechanisms, have been widely used in controlling cancer pain and postoperative pain in surgery. Our previous study revealed that morphine could suppress the anti-tumor effect of antigen-specific DNA vaccine. In this study, we further evaluated and compared another analgesic drug, ketorolac, with morphine for its analgesic functions and the antitumor immunities of antigen-specific DNA vaccine. We first observed that ketorolac-treated mice did not enhance tumorigenesis nor suppress the anti-tumor effects of antigen-specific (calreticulin linked to HPV16 E7) CRT/E7 DNA vaccine. We then demonstrated that ketorolac was less potent in inducing apoptosis of T lymphocytes and the generation of reactive oxygen species, in reducing mitochondrial membrane potentials, and leading to the activation of caspases 3 and 7 in T lymphocytes than morphine. When CRT/E7 DNA vaccinated mice treated with ketorolac, the declines of frequencies of E7-specific IFN-γ-secreting CD8⁺ T cell precursors were slower in the morphine-treated group. CRT/E7 DNA vaccinated mice, treated with a mixture of morphine and ketorolac, could maintain the analgesic function without experiencing a decrease in the anti-tumor effects. CRT/E7 DNA vaccine with the opioid-sparing effect of ketorolac could provide potent anti-tumor effects and good analgesic function.