Inhibition of bone metastasis from breast cancer with pamidronate resulting in reduction of urinary pyridinoline and deoxypyridinoline in a rat model

Abstract

Breast cancers frequently metastasize to bone, in a process in which osteoclasts play a major role. Bisphosphonate pamidronate, a specific inhibitor of osteoclasts, has been widely used in the treatment of bone metastasis (BM). In this study, using an animal model of BM, we examined the prophylactic and treatment effects of pamidronate against BM and clarified the relationships between BM, pamidronate and bone resorption markers such as urinary pyridinoline and deoxypyridinoline. Bone metastases were established by inoculating c-SST-2 (spontaneously developed rat mammary adenocarcinoma) cells into the thoracic aorta of 27 rats, which were then divided into three groups of rats: the untreated control group, the pre-treatment group, consisting of rats treated with pamidronate (10 mg/kg) injected subcutaneously a day before tumor inoculation, and the post-treatment group, in which rats were injected with pamidronate a week after tumor inoculation. Three weeks after tumor inoculation, blood and urine samples were collected. The subjects were then sacrificed to harvest the thoracic and lumbar vertebrae for histological examination, consisting of staining with hematoxylin and eosin and tartrate resistant acid phosphatase (TRACP). The incidence of BM was 70.0%, 44.4% and 37.5% in the control, pre-treatment and post-treatment groups, respectively. Although there was no significant difference among the groups, the rate of BM in the treated groups was lower than that of the control group and no bone destruction was observed in treated rats. The TRACP-stained specimens revealed that there were numerous osteoclasts contributing to the control group tumor burden. The urinary levels of pyridinoline and deoxypyridinoline were reduced by pamidronate. Our results suggest that pamidronate prevents the development of BM and the destruction of bone associated with BM. Maintaining the values of Pyr and Dpyr at low levels with pamidronate might lead to inhibition of the incidence and development of BM.