Evaluation of Bone Cancer Pain Induced by Different Doses of Walker 256 Mammary Gland Carcinoma Cells.

Background: Cancer pain is a complex medical syndrome. Understanding its underlying mechanisms relies on the use of animal models which can mimic the human condition. A crucial component of this model is the quantity of tumor cells; however, the exact relationship between the doses of tumor cells on bone cancer pain is yet unknown. Objective: We explored the relationship of different doses of Walker 256 carcinoma cells using a bone cancer pain model in rats, and evaluated its success and stability. Study Design: Experimental animal study using a comparative design. Setting: Experimental Animal Center and Tumor Institute of Traditional Chinese Medicine. Methods: We constructed the bone cancer pain model by implanting Walker 256 carcinoma cells into the right tibia of Sprague-Dawley (SD) rats (150 - 170 g). Spontaneous pain, mechanical threshold, and paw withdrawal latency (PWL) were measured and x-ray, bone mineral density (BMD), histological, interleukin-1 beta (IL-1 beta) mRNA, carboxyterminal telopeptide of type I collagen (ICTP), and bone alkaline phosphatase (BAP) were analyzed for bone pain model evaluation. Results: The results showed that: (1) the 3 doses (3x10(5), 3.5x10(5), 4x10(5)) of Walker 256 carcinoma cells can induce bone cancer pain from day 7 to day 21 after implantation into the right tibia of SD rats; (2) compared to the control group, 3x10(5), 3.5x10(5), and 4x10(5) Walker 256 carcinoma cells produced different pain manifestations, where the 3.5x10(5) dose of Walker 256 carcinoma cells resulted in the greatest bone cancer pain response; (3) the 3.5x10(5) dose induced the lowest mortality rate in rats; (4) Walker 256 carcinoma cells (3x10(5), 3.5x10(5), and 4x10(5)) resulted in a significant decrease in the general condition and body weight of rats, where the 3.5x10(5) and 4x10(5) doses of carcinoma cells produced a greater effect than 3x10(5) dose of carcinoma cells; (5) progressive spontaneous pain, PWL, and mechanical threshold were exacerbated by 3.5x105 and 4x10(5) doses of carcinoma cells; (6) implantation of 3.5x10(5) and 4x10(5) doses of carcinoma cells induced progressive bone destruction and decrease in BMD; (7) ICTP and BAP were significantly increased following the implantation of 3.5x10(5) and 4x10(5) doses of carcinoma cells; (8) IL-1 beta mRNA was significantly up-regulated in the spinal cord of rats implanted with 3.5x10(5) and 4x10(5) doses of carcinoma cells. Limitations: One limitation of this study was the small sample size; therefore, additional research is needed to provide better validation. Another limitation is the unavailability of small animal Micro computed tomography (CT), which is a more advanced and precise technique in determining bone marrow density than the x-ray imaging system we used. In addition, ethology experiments during late-stage tumor progression can be more objective. Conclusion: This study provides evidence that implantation of 3.5x10(5) and 4x10(5) dose of Walker 256 carcinoma cells produced the greatest effects in relation to the bone cancer pain model in SD rats, and 3.5x10(5) dose induced the lowest mortality rate.