Background: Cancer-induced bone pain remains a serious public health concern, with a need for translational behavioural tests in order to assess nociception in preclinical models of this condition. Burrowing is an innate, ethologically relevant rodent behaviour that has been proven sensitive to chronic pain conditions. Herein, we studied for the first time whether burrowing performance is altered in preclinical models of cancer-induced bone pain. Materials and Methods: Mice and rats were inoculated with syngeneic breast cancer cells. Bone degradation was radiographically evaluated and nociception was assessed in limb-use and burrowing tests. Results: Cancer-bearing rodents showed reduced relative bone density and limb-use scores, confirming disease development. Burrowing performance decreased over time in both rodent models. Conclusion: Burrowing performance was reduced in both rodent models, indicating that the burrowing test is a relevant and reproducible behavioural test for assessing disease development in both mouse and rat models of cancerinduced bone pain.

The world health organization (WHO) has predicted a global amount of 19 million cancer cases by 2025. Breast, prostate and lung cancer are common cancer types and show metastasis in 60 to 84% of the cases, with 75 to 90% experiencing life-altering cancer-induced bone pain (CIBP), characterized by continuous, dull progressive pain with movement-induced incident peaks and random breakthrough spikes. Therefore, it is the most difficult pain condition to treat. CIBP is a unique type of pain with neuropathic and nociceptive components. Briefly, an invading tumor cell disturbs the healthy balance of the bone resulting in an acidic microenvironment, activating sensory fibers in the bone. The invaded tumor cell and adjacent stromal cells secrete mediators initiating an immune response with transcriptional signaling, resulting in increased cytokines and growth factors. Sensory nerve fibers are damaged and start to sprout, causing ectopic firing, and as tumors grow in size they activate mechanoreceptors. Aside from bisphosphonates and antibody therapy, CIBP is treated by a range of NSAIDs to strong opioids, but remains undertreated in one-third of cases. This chapter discusses the accompanying CIBP of bone tumors, the mechanism of action and current treatments.

Background and Purpose: Cancer-induced bone pain remains inadequately controlled, and current standard of care analgesics is accompanied by several side effects. Nociceptin/orphanin FQ peptide (NOP) receptor agonists have demonstrated broad analgesic properties in rodent neuropathic and inflammatory pain models.Here, we investigate the analgesic potential of NOP receptor activation in a rodent cancer-induced bone pain model. Experimental Approach: Model validation by intratibial inoculation in male SpragueDawley rats was performed with varying MRMT-1/Luc2 cell quantities (0.5-1.5 × 10 6 Áml −1 ) and a behavioural battery (>14 days post-surgery) including evoked and non-evoked readouts: paw pressure test, cold plate, von Frey, open field, and weight distribution. Anti-allodynic potential of the endogenous NOP receptor ligand nociceptin (i.t.) and NOP receptor agonist Ro65-6570 ( i.p.) was tested using von Frey filaments, followed by a combination experiment with Ro65-6570 and the NOP receptor antagonist J-113397 (i.p.). Plasma cytokine levels and NOP receptor gene expression in dorsal root ganglion (DRG, L4-L6) and bone marrow were examined.