Bone metastases still present an unmet need for effective treatment. One preclinical study has suggested a beneficial effect with sequential treatment of doxorubicin (DOX) and zoledronic acid (ZOL). Furthermore, bisphosphonates are used as adjuvant therapy, but controversy of their anti-tumor effects remains. We tested clinically relevant doses of DOX, ZOL and their sequential combination in a treatment setting in a widely used nude mouse model of breast cancer bone metastasis.

GFP-transfected MDA-MB-231(SA) human breast cancer cells were inoculated into five-week-old female nude mice via left cardiac ventricle. Subsequent tumor growth and development of osteolytic bone lesions were quantitated by fluorescence imaging and radiography, respectively, on days 14 and 25. The mice were randomized to four groups (n=8/group) on day 14 according to body weight and the presence of osteolytic lesions. Starting on day 15, groups received either weekly dose of vehicle (control group), DOX 2.5 mg/kg i.p. weekly, ZOL 0.1 mg/kg s.c. on day 15 and vehicle weekly, or weekly dose of DOX and a single injection of ZOL 24 hrs after the first dose of DOX (combination group). Bone resorption marker tartrate-resistant acid phosphatase 5b (TRACP 5b) was determined in serum samples collected on days 1, 9, 17 and 24. Bone samples were collected on day 25, and tumor area, trabecular bone area and apoptotic index (TUNEL and apoptotic morphology) were quantitated by histomorphometry. Statistical analysis was performed using One-way ANOVA followed by Dunnett's test or Kruskal-Wallis test followed by Mann-Whitney U-test.

All animals in the control and DOX groups had lesions at sacrifice, whereas 12.5% of the mice in the ZOL group and 42.9% in the combination group had lesions. Osteolytic lesion area at sacrifice was significantly lower in both groups treated with ZOL compared to the control group, with no increase from day 14. Lesion area in the DOX-treated group was not different from control. Whole body tumor burden or the tumor area in hind limbs did not differ between the groups, indicating no inhibition on tumor growth. Apoptotic index was increased in groups treated with DOX. ZOL inhibited the increase in serum TRACP 5b, although less effectively in the combination group. Taken together, clinically relevant doses of DOX, ZOL or a sequential combination treatment of these two were not able to inhibit tumor growth in the established disease in this aggressive model of breast cancer bone metastasis. However, DOX increased the apoptosis of cancer cells and ZOL potently inhibited cancer-induced osteolysis, but the sequential treatment did not have additive affects on either tumor growth or osteolytic lesion area.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5394.