[Feasibility of establishment of rat model of bone cancer pain by using Walker 256 cells cultured in vitro or in vivo].

OBJECTIVE: To investigate the possibility of establishing rat model of bone cancer pain using cancer cells cultured in vitro or by ascites passaging and verify the reliability of this method.
METHODS: Syngeneic SD rat carcinoma cells of the line Walker 256 were cultured in vitro and inoculated into the peritoneal cavity of SD rats respectively. Two kinds of Walker 256 cell suspension were made. Thirty-two SD rats were randomly divided into 4 equal groups: Group N (undergoing injection of Hank's solution into cavitas medullaris of left tibia), Group K (undergoing injection of heat-killed Walker 256 cells), Group V (injected with Walker 256 cells cultured in vitro), and Group A (injected with Walker 256 cells passaged in ascites). After 6, 12, and 18 days, the rats underwent roentgenography. Radio nuclide emission computed tomography (ECT) was conducted 12 days later. And MRI was conducted 15 days later. Thermal withdrawal latency (TWL) and pressure withdrawal threshold (PWT) were measured. Von Frey threshold and weight bearing of left hind limb were examined. On the 18th day after the establishment of model the rats were killed with their left tibia taken out to undergo microscopy.
RESULTS: The rats of Groups A and V began to display decrease of left hint limb activity and roentgenography showed minute defect of bone trabecula in the proximal epiphysis by day 6. By day 12 roentgenography showed multiple defect of bone trabecula, ECT showed reactive bone formation. The rats of Groups A and V displayed signs of weight loss by day 14, and by day 18 roentgenography showed full thickness bicortical bone loss and formation of soft tissue tumor. Histological examination 18 days later revealed that the bones inoculated with live cells showed infiltration of bone marrow spaces by malignant tumor. The PWT values gradually decreased since day 6 to day 18, and the PWT values in this period of Groups A and V were all significantly lower than those of Groups K and N (all P < 0.01). The von Frey values gradually decreased since day 6 to day 18, and the von Frey values in this period of Groups A and V were all significantly lower than those of Groups K and N (all P < 0.01). The weight bearing value of left hind limb gradually decreased and the weight bearing difference between the 2 hind limbs gradually increased since day 6 to day 18, and the values of weight bearing difference between the 2 hind limbs of Groups A and V were significantly higher than those of Groups K and N (all P < 0.01). Sixteen rats underwent subcutaneous injection of morphine, and the PWT values increased 20, 30, and 40 min later in a dose-dependent manner (P < 0.01). Naloxone injected 1 h later antagonized the analgesic effect of morphine.
CONCLUSION: A SD rat model of bone cancer pain has been successfully established by using syngeneic rat bone carcinoma cells cultured in vitro or in vivo, and the latter being more convenient.