In this paper we compare two innovative models of movement-related pain: tumor-induced nociception following implantation of fibrosarcoma cells into bone and muscle inflammation-induced nociception following injection of the irritant carrageenan into muscle. Importantly, using the grip force test, an assay of movement-related hyperalgesia, both non-malignant and malignant pain are examined in parallel. Movement-related hyperalgesia, known clinically as a specific type of 'breakthrough pain', is a common feature of bone cancer and is thought to be a predictor of poor response to conventional analgesic pharmacotherapy (Bruera et al., 1995, J. Pain Symptom. Manage. 10 (1995) 348; Mercadaute et al., 1992, Pain 50 (1992) 151; Pain 81 (1999) 129). Implantation of NCTC 2472 sarcoma cells in both humeri or injection of carrageenan (4%) in both triceps of C3H/He mice produced apparent forelimb hyperalgesia that was not associated with mechanical hyperalgesia in the forepaw, whereas carrageenan at 6 and 8% did evoke significant cutaneous hyperalgesia of the forepaw as well. Control groups receiving implants of vehicle or no treatment at all did not manifest this forelimb hyperalgesia. B6C3/F1 mice implanted with non-lysis-inducing G3.26 melanoma cells or vehicle did not manifest significant hyperalgesia when compared to B6C3/F1 mice receiving fibrosarcoma cells, indicating a dependence on bone involvement for induction of hyperalgesia in this model. Histological examination at days 3, 7, and 10 post-implantation showed a clear correlation of tumor growth-induced bone destruction with behavioral hyperalgesia. Morphine was more potent in decreasing the maximal hyperalgesia induced by carrageenan than that induced by tumor implantation. Acutely administered morphine (3-100mg/kg, i.p.) attenuated peak hyperalgesia of carrageenan-injected mice (ED50 6.9mg/kg) and tumor-bearing mice (ED50 23.9mg/kg) in a dose-related manner with a difference in potency of 3.5. Tumor-implanted mice with a level of hyperalgesia comparable to that induced by carrageenan required almost three times more morphine (ED50 18.5mg/kg) for equivalent attenuation of forelimb hyperalgesia. These animal models of movement-related hyperalgesia may aid in discerning the peripheral and central mechanisms underlying pain that accompanies bone metastases and distinguishing it from the pain associated with muscular inflammation. Importantly, they may also aid in predicting differences in analgesic efficacy in different types of musculoskeletal pain.
Bibliographical noteFunding Information:
Cell cultures were maintained in the laboratory of Dr Denis Clohisy at the University of Minnesota Cancer Center. Ms Kristin Schreiber contributed to the final preparation of this manuscript. The authors would also like to thank Deb Lee for processing the tissue for histological examination, clinical pathologist Dr David Hayden for his help interpreting the histological results and Ms Laura Eikmeier for figure presentation. This research was supported by seed research funds provided by the University of Minnesota Academic Health Center, 1R01-CA84233-01A2, and P.W.W. was supported by NIDR training grant NIH/5T 32-DEO 7288-02.
- Cancer pain
- Movement-related hyperalgesia
- Musculoskeletal pain