Novel animal models of acute and chronic cancer pain: a pivotal role for PAR2.

Targeted therapy to prevent the progression from acute to chronic pain in cancer patients remains elusive. We developed three novel cancer models in mice that together recapitulate the anatomical, temporal, and functional characteristics of acute and chronic head and neck cancer pain in humans. Using pharmacologic and genetic approaches in these novel cancer models, we identified the interaction between protease-activated receptor 2 (PAR2) and serine proteases to be of central importance. We show that serine proteases such as trypsin induce acute cancer pain in a PAR2-dependent manner. Chronic cancer pain is associated with elevated serine proteases in the cancer microenvironment and PAR2 upregulation in peripheral nerves. Serine protease inhibition greatly reduces the severity of persistent cancer pain in wild-type mice, but most strikingly, the development of chronic cancer pain is prevented in PAR2-deficient mice. Our results demonstrate a direct role for PAR2 in acute cancer pain and suggest that PAR2 upregulation may favor the development and maintenance of chronic cancer pain. Targeting the PAR2-serine protease interaction is a promising approach to the treatment of acute cancer pain and prevention of chronic cancer pain.