Inhibition of bone resorption, rather than direct cytotoxicity, mediates the anti-tumour actions of ibandronate and osteoprotegerin in a murine model of breast cancer bone metastasis

• Published in: Bone (New York, N.Y.) N.Y.), 2007-02, Vol.40 (2), p.471-478
• Main Authors: Zheng, Yu, Zhou, Hong, Brennan, Karen, Blair, Julie M, Modzelewski, James R.K, Seibel, Markus J, Dunstan, Colin R
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; Biological and medical sciences; Bone Density Conservation Agents - administration & dosage; Bone Density Conservation Agents - therapeutic use; Bone metastasis; Bone Neoplasms - drug therapy; Bone Neoplasms - secondary; Bone resorption; Bone Resorption - drug therapy; Breast cancer; Breast Neoplasms - drug therapy; Breast Neoplasms - pathology; Cell Line, Tumor; Cell Proliferation - drug effects; Diphosphonates - administration & dosage; Diphosphonates - therapeutic use; Diseases of the osteoarticular system; Drug Therapy, Combination; Female; Fundamental and applied biological sciences. Psychology; Gynecology. Andrology. Obstetrics; Ibandronate; Mammary gland diseases; Medical sciences; Mice; Mice, Inbred BALB C; Mice, Nude; Orthopedics; Osteoprotegerin; Osteoprotegerin - administration & dosage; Osteoprotegerin - therapeutic use; Skeleton and joints; Tibia - drug effects; Tibia - pathology; Tumors; Tumors of striated muscle and skeleton; Vertebrates: osteoarticular system, musculoskeletal system; Xenograft Model Antitumor Assays
• ISSN: 8756-3282; 1873-2763
• DOI: 10.1016/j.bone.2006.09.016

Abstract Inhibition of bone resorption either by bisphosphonate (BP) treatment or by blocking RANKL signalling with osteoprotegerin (OPG) has been shown to reduce tumour burden in bone and inhibit bone destruction in murine xenograft models of breast cancer. However, whether the anti-tumour effect of OPG or BP in bone is mediated by inhibition of bone resorption or by direct effects on tumour cells is uncertain. The current study is designed to investigate anti-tumour effects of OPG and ibandronate (IBN), dosed alone or in combination, on tumour growth to determine if there is experimental support for combination treatments and to provide evidence for the presence of direct anti-tumour effects. To this aim, 10 μl (5 × 106  cells/ml) of the bone-seeking MDA-MB-231 (Tx-SA) cell line was injected intra-tibially into nude mice. After 10 days, when the tumours were evident radiologically, mice were treated with vehicle, OPG (1 mg/kg/day), ibandronate (IBN) (160 μg/kg/day) or IBN and OPG at the same doses (IBN + OPG) for a week, and the effects of each treatment on lytic lesions, tumour cell growth, cell apoptosis and proliferation were measured by radiography, immunohistochemistry and histomorphometry. Compared to vehicle controls, in vivo treatment with OPG, IBN, or IBN + OPG, each prevented the expansion of osteolytic bone lesions (increase in lytic lesion area day 10 to day 17: OPG − 3.2%, IBN 6.6%, IBN + OPG 3.6%, Vehicle 232.5%; p < 0.01). Treatment with OPG, IBN or IBN + OPG each produced similar reductions in tumour area relative to vehicle-treated mice (OPG 52%, IBN 54%, IBNp and OPG 48%, p < 0.01 vs. vehicle) OPG and IBN alone and in combination each produced a similar increase in cancer cell apoptosis (OPG 330%, IBN 342%, IBN and OPG 347%, p < 0.01 vs. vehicle) and a decrease in cancer cell proliferation (OPG 59%, IBN 62%, IBN and OPG 58%, p < 0.05 vs. vehicle). Our findings indicate that (i) combined treatment with OPG and a bisphosphonate is not significantly more effective than either agent alone; and that (ii) inhibition of bone resorption, rather than direct anti-tumour action, mediates the effects of these agents on tumour growth in this in vivo model.