A cannabinoid 2 receptor agonist attenuates bone cancer-induced pain and bone loss

Aims: Cannabinoid CB₂ agonists have been shown to alleviate behavioral signs of inflammatory and neuropathic pain in animal models. AM1241, a CB₂ agonist, does not demonstrate central nervous system side effects seen with CB₁ agonists such as hypothermia and catalepsy. Metastatic bone cancer causes severe pain in patients and is treated with analgesics such as opiates. Recent reports suggest that sustained opiates can produce paradoxical hyperalgesic actions and enhance bone destruction in a murine model of bone cancer. In contrast, CB₂ selective agonists have been shown to reduce bone loss associated with a model of osteoporosis. Here we tested whether a CB₂ agonist administered over a 7day period inhibits bone cancer-induced pain as well as attenuates cancer-induced bone degradation. Main methods: A murine bone cancer model was used in which osteolytic sarcoma cells were injected into the intramedullary space of the distal end of the femur. Behavioral and radiographic image analysis was performed at days 7, 10 and 14 after injection of tumor cells into the femur. Key findings: Osteolytic sarcoma within the femur produced spontaneous and touch evoked behavioral signs of pain within the tumor-bearing limb. The systemic administration of AM1241 acutely or for 7. days significantly attenuated spontaneous and evoked pain in the inoculated limb. Sustained AM1241 significantly reduced bone loss and decreased the incidence of cancer-induced bone fractures. Significance: These findings suggest a novel therapy for cancer-induced bone pain, bone loss and bone fracture while lacking many unwanted side effects seen with current treatments for bone cancer pain.