摘要Background:Calpain,a calcium-dependent cysteine protease,has been demonstrated to regulate osteoclastogenesis,which is considered one of the major reasons for cancer-induced bone pain (CIBP).In the present study,calpain inhibitor was applied in a rat CIBP model to determine whether it could reduce CIBP through regulation of osteoclastogenesis activity.Methods:A rat CIBP model was established with intratibial injection of Walker 256 cells.Then,the efficacy of intraperitoneal administered calpain inhibitor Ⅲ (MDL28170,1 mg/kg) on mechanical withdrawal threshold (MWT) of bilateral hind paws was examined on postoperative days (PODs) 2,5,8,11,and 14.On POD 14,the calpain inhibitor's effect on tumor bone tartrate-resistant acid phosphatase (TRAP) stain and radiology was also carefully investigated.Results:Pain behavioral tests in rats showed that the calpain inhibitor effectively attenuated MWTs of both the surgical side and contralateral side hind paws on POD 5,8,and 11 (P ＜ 0.05).TRAP-positive cell count of the surgical side bone was significantly decreased in the calpain inhibitor group compared with the vehicle group (P ＜ 0.05).However,bone resorption and destruction measured by radiographs showed no difference between the two groups.Conclusions:Calpain inhibitor can effectively reduce CIBP of both the surgical side and nonsurgical side after tumor injection in a rat CIBP model.It may be due to the inhibition of receptor activator of nuclear factor-kappa B ligand-induced osteoclastogenesis.Whether a calpain inhibitor could be a novel therapeutic target to treat CIBP needs further investigation.