Abstract LB-156: A RANKL inhibitor but not a bisphosphonate, zoledronic acid, reduces mammary tumor formation in a carcinogen- and hormone-dependent mouse model
Authors: Jacob Allison P. , Branstetter Daniel G. , Jones Jon C. , Erwert Ryan , Miller Robert E. , Dougall William C. 
Published: February 2011

RANKL and its target receptor, RANK, are key factors in bone remodeling and pathologic bone destruction associated with bone metastasis. Denosumab, a fully human monoclonal antibody that specifically inhibits RANKL, inhibits osteoclastogenesis and osteoclast-mediated bone destruction. In clinical trials, denosumab robustly reduced bone loss due to postmenopausal osteoporosis and prevented skeletal-related events in patients with metastatic bone lesions. It is currently being studied for the prevention of bone metastasis and disease recurrence in early breast and prostate cancer.

RANKL and RANK not only have critical roles in bone resorption, but are also essential for the development of lobulo-alveolar structures in mouse mammary gland during pregnancy. RANKL expression in mouse mammary epithelia is regulated by progesterone, prolactin, and parathyroid hormone-related protein (PTHrP). Using a hormone (medroxyprogesterone, MPA)- and carcinogen (7,12-dimethylbenz[a]anthracene, DMBA)-induced model of mammary tumorigenesis, we have demonstrated that transgenic MMTV-RANK overexpression results in more rapid onset of preneoplastic lesions and mammary tumors relative to wild type (WT) mice. Using immunohistochemistry, we observed that RANKL expression in mammary epithelia increased after MPA treatment and was elevated in epithelial cells at the stage of early preneoplastic mammary intraepithelial neoplasia (MIN) lesions and in adenocarcinomas. RANK is highly expressed in the epithelial component of preneoplasias and adenocarcinoma.

Using the same MPA and DMBA-induced mammary tumor model in WT mice, treatment with RANK-Fc at the initiation of DMBA treatment delayed the time to mammary tumor formation vs. control-treated mice (P&lt;0.0001, log rank test). RANK-Fc treatment also decreased the incidence of palpable mammary tumors at 32 weeks post last DMBA (22% in RANK-Fc treated mice vs. 94% in control-treated mice, n&gt;19 mice per group). We also tested three different doses of the bisphosphonate zoledronic acid (ZA at 0.025, 0.2 and 0.5 mg/kg given weekly beginning at initiation of DMBA) in WT mice for anti-tumor activity. Zoledronic acid had no effect at any dose on time to tumor formation compared to control. In addition, ZA had no effect at any dose on mammary tumor incidence at 32 weeks post last DMBA (92%,100% and 95% mammary tumor incidence for 0.5 mg/kg, 0.2 mg/kg and 0.025 mg/kg ZA-treated groups respectively, n&gt;19 mice per group). Inhibition of bone resorption (as evident by increases in bone mineral density) was demonstrated in mice treated with either RANK-Fc or ZA (all doses). These data indicate that in this model, RANK-Fc reduces mammary tumorigenesis by inhibiting local RANKL in the normal mammary epithelial and/or preneoplasias and tumors and warrant further analysis of RANKL actions in tumor development, progression, and metastasis.

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 LB-156.