Analgesic effects of a soy-containing diet in three murine bone cancer pain models

Bone is a common metastatic site for prostate and breast cancer, and bone cancer is usually associated with severe pain. Traditional treatments for cancer pain can sometimes be ineffective or associated with side effects. Thus an increasing number of patients seek alternative therapies. In this study we investigated the analgesic effects of a soy diet on 3 experimental models of bone cancer pain. Mice were fed a diet in which the protein source was either soy or casein. After 1 week on the diet, sarcoma cells (NCTC 2472) were injected into the medullary cavity of the humeri, femur, or calcaneus. Experimenters blinded to diet of the animal assessed the pain behavior in these animals, forelimb grip force in the humerus model and paw withdrawal frequency to mechanical stimuli in the calcaneus and femur models. The effect of morphine on cancer-induced pain behavior was investigated in calcaneus and femur models. In addition, in the femur model, the effects of soy on tumor size and bone destruction were studied. The soy diet reduced secondary mechanical hyperalgesia in the femur model but had no effect on primary mechanical hyperalgesia in the calcaneus model or on movement-related hyperalgesia in the humerus model. No dietary impact was discerned in measurements of tumor size, bone destruction, and body weight in the femur model, suggesting that the soy diet had no effect on cancer growth. Morphine dose-dependently reduced hyperalgesia with no diet-based difference. These results suggest that a soy diet might provide analgesia in certain forms of hyperalgesia associated with bone cancer. Perspective The study raises the possibility of dietary supplements influencing aspects of cancer pain. Further research will help determine if use of nutritional supplements, such as soy proteins, can reduce opioid analgesic use in chronic pain states and help minimize the side effects associated with long term use of opioids.