There is no doubt that there are increased benefits of hormonal therapy to breast cancer patients; however, current evidence suggests that estrogen receptor (ER) blockage using antiestrogens is associated with a small induction of invasiveness in vitro. The mechanism by which epithelial tumor cells escape from the primary tumor and colonize to a distant site is not entirely understood. This study investigates the effect of two selective antagonists of the ER, Fulvestrant (Fulv) and Tamoxifen (Tam), on the invasive ability of breast cancer cells. We found that 17β-estradiol (E2) demonstrated a protective role regarding cell migration and invasion. Fulv did not alter this effect while Tam stimulated active cell migration according to an increase in Snail and a decrease in E-cadherin protein expression. Furthermore, both tested agents increased expression of matrix metalloproteinases (MMPs) and enhanced invasive potential of breast cancer cells. These changes were in line with focal adhesion kinase (FAK) rearrangement. Our data indicate that the anti-estrogens counteracted the protective role of E2 concerning migration and invasion since their effect was not limited to antiproliferative events. Although Fulv caused a less aggressive result compared to Tam, the benefits of hormonal therapy concerning invasion and metastasis yet remain to be investigated.

Current evidence indicates that angiogenesis plays an important role in the pathogenesis of several malignancies, including breast cancer. Bevacizumab is a monoclonal antibody that targets the vascular endothelial growth factor (VEGF). Recent clinical data have demonstrated that the addition of bevacizumab to first-line chemotherapy improves the progression-free survival of patients with advanced breast cancer. This review presents an update on the role of bevacizumab, as well as other anti-angiogenic agents in the management of patients with breast carcinoma.

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Acquisition of resistance to endocrine therapies is a major limiting factor to their clinical effectiveness, resulting in disease relapse and poor prognosis. This may be due in part to the observations that acquired resistance to agents such as tamoxifen is accompanied by a gain in aggressive cellular features likely to promote disease spread and survival at metastatic sites. Bisphosphonates (BPs) are potent antiresorptive drugs used to treat osteoporosis and bone metastasis. Recent evidence also suggests that these agents may possess anti-tumour properties independently of their action on osteoclasts in a range of different tumours including breast cancers resulting in suppression of proliferation and migration and an induction of apoptosis. Here we have explored the potential of the bisphosphonate, zoledronic acid (ZOL) to suppress the aggressive phenotype of acquired endocrine-resistant breast cancer models versus their endocrine-sensitive counterparts. ER+, endocrine-sensitive MCF7 cells and their highly-proliferative, ER+, tamoxifen-resistant (‘TamR’) counterparts were exposed to increasing concentrations of ZOL (1-160μM) for 3 days and changes in growth determined by MTT assay and cell counting. Immunohistochemical analysis of Ki67 confirmed cell growth effects whilst cell cycle analysis was performed using FACS and propidium iodide. Changes in signalling pathways were investigated by Western blotting. The proliferative capacity of TamR cells was greatly suppressed by ZOL in a dose dependent manner in contrast to MCF7, where the effect was minimal (IC50 ± SD: 30 ± 4 μM (TamR) versus 150 ± 15 μM (MCF7); p<0.05). This was confirmed with Ki67 analysis which showed a reduction in Ki67 positivity of 40% (TamR) versus 25% (MCF7); p<0.05. ZOL treatment of TamR cells resulted in a significant loss of cells in G1 phase and an accumulation of the cells in S phase. ZOL treatment of TamR cells also resulted in loss of AKT activity, whilst AKT was unaffected in MCF7 cells. Our data suggests that acquisition of resistance to tamoxifen confers a sensitivity to BPs where treatment of resistant cells with agents such as zoledronic acid results in suppression of proliferation and modulation of AKT signalling. These data suggest that BPs may exert direct anti-tumour effects on breast cancers which have relapsed on endocrine treatment. Citation Format: Dionysia Lymperatou, Christopher Smith, Wen Guo Jiang, Bronwen Evans, Stephen Hiscox. Acquired tamoxifen resistance sensitises breast cancer cells to bisphosphonates. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2155.

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