A Rat Model Of Bone Cancer Pain Produced By Walker 256 Mammary Gland Carcinoma Cells Inoculation Of The Tibia

Excluding skin cancer, more than 10 million people are diagnosed with cancer every year and by 2020 it is estimated that this will have increased to 15 million new cases each year. In 2005, cancer caused 7.6 million deaths worldwide. In the United States, one in four deaths are cancer related and it is estimated that cancer has now eclipsed heart disease as the leading cause of death.As improvements in cancer detection and treatment have extended the life expectancy of cancer patients, more attention has been focused on improving the patients'quality of life. Approximately 30–50% of all cancer patients will experience moderate to severe pain. The common type of cancer pain was bone cancer pain that was difficult to treat. It was a serious clinical pain syndrome, which mostly occurred in patients with primary bone cancer or secondary bone metastasis from distant sites such as breast, prostate, and lung cancer. This type of pain was dull and constant, increased with time, and was exacerbated by the use of involved bone. As bone cancer progressed, breakthrough pain, which was an intermittent episode of extreme pain, occurred spontaneously or more commonly by weight bearing or movement of the affected bone.Skeletal metastasis results in significant bone pain, which cannot be well controlled because its underlying mechanisms are not clear. To clarify the mechanisms of bone cancer pain, a model has been developed recently by injecting osteolytic sarcoma cells into the femur of syngeneic C3H mice in 1999. Another model of bone cancer pain has been developed in female rats by injecting MRMT-1 rat mammary gland carcinoma cells into the tibia in 2002. Then a new model that closely mimics the bone cancer pain caused by prostate cancer has been established in the male rat in 2005. Cancer cells were injected into the bone, producing progressive bone destruction and sustained hyperalgesia and allodynia.In this article, we establish new rat bone cancer pain model produced by inoculating mammary gland carcinoma cells—Walker 256 cells into the tibia cavity of rats. Bone destruction and the time course of pain-related behavioral changes were evaluated. The following is results:1.The rate of tumou-growing in post-inoculating ratsFollowing inoculate Walker256 cells, the only of 67.3% rats suffer the growing of tumor. Because some of rats die in some post-operation days, the rate of really useful inoculating rats is only 53.8%.2. The general health and Body weight of post-inoculating ratsAll animals displayed general good health with no signs of distress and no marked weight loss during the 14-day observation period . The 85% rats show the signs of tumor growth by day 15-18, observed as swelling around the knee,while the 15% rats do by day 19-21. Different inoculating rat has different time of beginning of tumor-growing.The duration of pain in inoculation rats are different, 90% is 6-7 days, 10% is 8-11days.3.Radiological analysis of tumor development in the tibiaNo radiological change was found in control animals . 14 days after injection with Walker256 cells, the tibiae of the cancer rats showed signs of small radiolucent lesions in the proximal epiphysis . By day 17 after inoculation, some loss of medullary bone and destruction of cortical bone were observed . 26 days after inoculation, major cortical destruction of the proximal epiphysis was detected .4.Histochemical analysis of tumor development in the tibiaHE staining showed that tumor cells were densely packed in the marrow cavity and had induced the destruction of trabeculae. 5.Assessment of pain behavior of inoculation rats5.1 Time course of ambulatory painIn the sham group, rats showed no significant difference of hind limb use in comparison to normal rats. In contrast, all rats injected with Walker256 cells showed apparent limp on the injected hind limb over days following injection.5.2 Time course of thermal hyperalgesia and allodynia Before Walker256 cell injection, the overall mean baseline PWL to non-noxious heat stimuli was similar in all groups of rats and there was no significant difference in PWL between left and right hind paws.Following injection of tumor cells into the tibia bone cavity, hind paw PWL significantly and progressively decreased on days 15-18.5.3 Time course of mechanical hyperalgesiaBefore tumor cell injection, the overall mean baseline PWPT to mechanical pressure was similar in all groups of rats, and there was no significant difference in PWPT between left and right hind paws. Following injection of Walker256 cells into the cavity of the right tibia, right hind paw PWPT progressively decreased on days 15-18 and 20 compared to that of the contralateral hind paw and the hind paw of normal rats, which remained at the pre-injection level.6 . Activation of spinal astrocytesGFAP staining of the spinal cord showed increased staining in the ipsilateral spinal cord 18-20 days after tumor cell inoculation of the tibia .This enhanced staining appeared in all areas of the spinal grey matter, with the most prominent increase being in dorsal horn laminaeⅠ–Ⅱ. GFAP stained astrocytes were hypertrophied .In conclusion, the present study demonstrated that1. Walker256 mammary gland carcinoma cell is a good choice to build a rat bone cancer pain . 2. Because diference of individual immunity rat , The rate of tumou-growing in post-inoculating is different.This is reasonable.3. Radiological and histochemical analysis show that the pain progressively becomes heavy with tumor cells growth and bone destruction.4. The analytical results indicate that Walker256 cells in the tibia induced progressive and significant thermal hyperalgesia and allodynia.5. These results indicate that astrocytes on the inoculated side of the spinal cord were activated by inputs from the bone cancer area.