Characterization of a rat model of metastatic prostate cancer bone pain

PURPOSE: The objectives of this study were to establish and characterize a novel animal model of metastatic prostate cancer-induced bone pain. METHODS: Copenhagen rats were injected with 10(6) MATLyLu (MLL) prostate cancer cells or phosphate-buffered saline by per cutaneous intra femoral injections into the right hind leg distal epiphysis. Over 13 days, rats progressively developed a tumor within the distal femoral epiphysis. On days 3, 7, 10, and 13 post injection, rats were subjected to the incapacitance and Randall-Selitto behavioral tests as they are believed to be indirect reflections of tumor induced pain. Ipsilateral hind limbs were subjected to X-ray and computed tomography (CT) scans and histological sections were stained with hematoxylin and eosin (H&E). RESULTS: Intra femoral injections of MLL cells resulted in the progressive development of a tumor leading to bone destruction and nociceptive behaviors. Tumor development resulted in the redistribution of weight to the contralateral hind leg and significantly reduced the paw withdrawal threshold of the ipsilateral hind paw as observed via the incapacitance and Randall-Selitto tests, respectively. X-ray and computed tomography scans along with H&E stains indicated tumor-associated structural damage to the distal femur. This model was challenged with administration of meloxicam. Compared with vehicle-injected controls, the meloxicam-treated rats displayed smaller nociceptive responses as observed with the incapacitance and Randall-Selitto tests, suggesting that meloxicam was effective in reducing the pain-related symptoms displayed by model animals and that the model behaved in a predictable way to cyclooxygenase-2 treatment. CONCLUSIONS: This model is unique from other bone cancer models in that it is a comprehensive model utilizing a competent immune system with a syngeneic tumor. The model establishes a tool that will be useful to investigate mechanisms of cancer pain that are induced by cancer cells.