Mechanisms of treatment of cancer pain with a topical Chinese herbal formula in rats

Background Pain has a substantial impact on patients' activities and overall quality of life, but current conventional drugs have debilitating side effects, including gastrointestinal disorders. Thus there is a pressing need for new therapies with fewer side effects to alleviate cancer pain. We recently developed a topical herbal formula Xiaotan Tongluo analgesic gel (XTTL gel) based on the principles of traditional Chinese herbalism, and we have received positive feedback from bone cancer pain patients. The aim of this study was to determine the analgesic effects and explore the mechanisms of XTTL gel in a rat model of bone cancer pain. Methods The rat model of bone cancer pain was established by inoculating Walker-256 rat carcinoma cells directly into the right tibial medullary cavity of Wistar rats. The rats were randomly assigned to three groups (n=10 per group): (1) sham bone cancer control (sham group): vehicle (PBS) inoculation without carcinoma cells plus topical administration of blank gel; (2) Sham treatment control (vehicle group): Walker-256 cell inoculation plus topical administration of blank gel; (3) XTTL gel treatment (treatment group): Walker-256 cell inoculation plus topical administration of XTTL gel. XTTL gel treatments were applied daily for 7 days starting on day 14 following inoculation. Outcomes were assessed 21 days after inoculation by mechanical allodynia, histological staining, and by measuring concentrations of type I collagen carboxy-terminal telopeptide (ICTP) and bone-specific alkaline phosphatase (BAP) in serum. Results Fourteen days after cancer cell incubation, significant mechanical allodynia in the ipsilateral hind paw and tumor growth in proximal end of the tibia were observed in the vehicle and treatment groups but not in the sham group. At day 21, mechanical withdrawal thresholds in treatment group rats were significantly higher ((4.8557 +/- 0.8336) g) compared with those of the vehicle group ((1.8630 +/- 1.4369) g, P <0.05). ICTP and BAP levels increased significantly in vehicle group rats ((101.5176 +/- 11.0694) U/L and (370.7838 +/- 12.8273) U/L, respectively) compared with those of the sham group ((11.7553 +/- 1.1885) U/L and (185.7338 +/- 3.6761) U/L, respectively; P <0.05). XTTL gel decreased the level of blood serum ICTP ((41.8998 +/- 6.4970) U/L, P <0.05) but had little effect on blood serum BAP ((365.5338 +/- 18.5361) U/L, P >0.05). Conclusion Topical use of XTTL gel may have an analgesic effect on bone cancer pain, an effect mediated by lowering of ICTP levels and inhibiting bone resorption. Chin Med J 2009;122(17):2027-2031