Oestrogen receptor positive breast cancer metastasis to bone: inhibition by targeting the bone microenvironment in vivo

Clin Exp Metastasis Oestrogen receptor positive breast cancer metastasis to bone: inhibition by targeting the bone microenvironment in vivo I. Holen 0 1 2 M. Walker 0 1 2 F. Nutter 0 1 2 A. Fowles 0 1 2 C. A. Evans 0 1 2 C. L. Eaton 0 1 2 P. D. Ottewell 0 1 2 0 Bone Biology, Department of Human Metabolism, Mellanby Centre for Bone Research, University of Sheffield , Sheffield S10 2RX , UK 1 Academic Unit of Clinical Oncology, Department of Oncology, Medical School, University of Sheffield , Beech Hill Road, Sheffield S10 2RX , UK 2 & P. D. Ottewell Clinical trials have shown that adjuvant Zoledronic acid (ZOL) reduces the development of bone metastases irrespective of ER status. However, postmenopausal patients show anti-tumour benefit with ZOL whereas pre-menopausal patients do not. Here we have developed in vivo models of spontaneous ER?ve breast cancer metastasis to bone and investigated the effects of ZOL and oestrogen on tumour cell dissemination and growth. ER?ve (MCF7, T47D) or ER-ve (MDA-MB-231) cells were administered by inter-mammary or inter-cardiac injection into female nude mice ± estradiol. Mice were administered saline or 100 lg/kg ZOL weekly. Tumour growth, dissemination of tumour cells in blood, bone and bone turnover were monitored by luciferase imaging, histology, flow cytometry, two-photon microscopy, micro-CT and TRAP/P1NP ELISA. Estradiol induced metastasis of ER?ve cells to bone in 80-100 % of animals whereas bone metastases from ER-ve cells were unaffected. Administration of ZOL had no effect on tumour growth in the fat pad but significantly inhibited dissemination of ER?ve tumour cells to bone and frequency of bone metastasis. Estradiol and ZOL increased bone volume via different mechanisms: Estradiol increased activity of bone forming osteoblasts whereas administration of ZOL to estradiol supplemented mice decreased osteoclast activity and returned osteoblast activity to levels comparable to that of saline treated mice. ER-ve cells require increased osteoclast activity to grow in bone whereas ER?ve cells do not. Zol does not affect ER?ve tumour growth in soft tissue, however, inhibition of bone turnover by ZOL reduced dissemination and growth of ER?ve breast cancer cells in bone. ER?ve; Breast cancer; Bone metastasis; Zoledronic acid; Estradiol Introduction Oestrogen receptor positive breast cancer accounts for approximately 70 % of primary breast malignancies. The development of targeted hormonal and biological therapies have resulted in significant increases in survival, however progression to metastasis remains a substantial clinical problem. Around 65–70 % of cancers that metastasise to bone are ER?ve and this condition remains incurable [ 1 ]. Due to the lack of clinically relevant models for ER?ve breast cancer bone metastasis the vast majority of preclinical studies have used hormone receptor negative cell lines to investigate breast cancer dissemination and growth in bone [reviewed in 2 and 3]. We have established in vivo models of spontaneous bone metastasis from ER?ve MCF7 and T47D cells grown in mouse mammary fat pads. These new models have enabled us, for the first time, to investigate some of the fundamental steps of bone metastasis following inoculation of cell lines into hind mammary fat pads, including growth at the primary site, tumour cell dissemination into the circulation and colonisation and growth in the bone microenvironment. We are now using these models to investigate the effects of bone targeted therapies on spontaneous bone metastasis of ER?ve xenografts. There is increasing clinical and pre-clinical evidence supporting anti-tumour effects of the anti-resorptive agent zoledronic acid (ZOL) in hormone receptor negative breast cancer, but the effects on ER?ve breast cancers remain to be elucidated. Recent clinical trials suggest that menopausal status, rather than the hormone receptor status of the tumour, determines the anti-cancer efficiency of ZOL. The AZURE (Does Adjuvant zoledronic acid reduce Recurrence in stage II/III breast cancer?) trial [ 4 ] study investigated the use of adjuvant ZOL alongside chemotherapy in women with high risk of breast cancer recurrence. 3360 women were randomised to receive either placebo or intensive treatment with ZOL, in addition to standard therapy. Approximately 78 % of patients in each group had ER?ve tumours [ 5 ] and there was no correlation between hormone receptor status, disease free survival (DFS) or risk of death (ROD). In contrast, women who were postmenopausal for at least 5-years before entering the trial had a significantly increased disease free survival (25 %) and reduced risk of death from any cause (26 %) [ 6 ]. These data were confirmed in the ABCSG-12 trial that showed increased DFS in women more than age 40 who received ZOL. However the ABCSC-12 study also presented evidence indicating that adjuvant use of ZOL improves the outcome of pre-menopausal patients with ER?ve tumours [ 7 ], a (...truncated)