Introduction: Inflammatory breast cancer (IBC) is aggressive, as approximately one third of patients present with distant metastases. Bisphosphonates are often administered to breast cancer patients for cancer-induced osteolysis. Recent evidence suggests bisphophanates may also have anti-tumor properties. This study examined the effects of the bisphosphonate, zoledronate (ZA), on the proliferation and invasive capabilities of highly aggressive IBC cell lines.

Methods: The IBC cell line SUM149 was cultured utilizing both adherent and serum-free, non-adherent cancer stem cell enriching conditions. An MTT assay was used to quantify proliferation and mammosphere formation of cells. Adherent cell growth was measured at days 1-4 following 0, 0.1, 1, 5, 10, 50 and 100uM zelodronate treatment. Mammosphere formation was measured at 10 days following 0, 0.01, 0.1, 1, 10, and 100uM ZA treatment. Modified Boyden chambers were employed to assess the ability of both adherent and non-adherent cells to invade to SDF-1 (100ng/mL) following 24 hour 1uM ZA treatment. Protein expression was assessed using immunofluorescent staining, protein arrays and Western blotting.

Results: ZA treatment with <5uM did not inhibit SUM149 adherent cell growth at any of the measured time points. ZA concentrations ≥10uM significantly inhibited SUM149 adherent cell growth at day 4 (p≤0.05). SUM 149 mammosphere formation was significantly inhibited following 10uM ZA treatment (p≤0.001). However, significantly more SUM149 non-adherent cells invaded to SDF-1 compared to adherent cells (p≤0.001). SUM 149 non-adherent cell invasion was inhibited by 24 hour 1uM ZA treatment (p≤0.001). SUM 149 non-adherent cells expressed significantly increased levels of the epithelial-mesenchymal transition (EMT) associated proteins smooth muscle actin (SMA), fibronectin, and N-Cadherin. The increased expression of SMA, fibronectin, and N-Cadherin observed in non-adherent cells returned to levels comparable to adherent cells following 24 hour 1uM ZA treatment.

Conclusions: ZA inhibited the growth of IBC cells grown under adherent and non-adherent conditions. SUM 149 non-adherent cells had much greater invasive potential than adherent cells did, and their invasive capability was inhibited following low dose ZA treatment. Interestingly, ZA inhibited up-regulation of EMT associated proteins SMA, fibronectin, and N-Cadherin in SUM 149 non-adherent cells. These results indicate that some IBC cells grown under cancer stem cell enriching conditions have the potential to undergo EMT and invade. ZA may also inhibit metastases through novel mechanisms.

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 1461.