Inflammatory breast cancer (IBC) is more aggressive and deadly than other breast cancers (K Rowan. JNCI. 2009;101(19):1302-1304). IBC cells secrete angiogenic and vasculogenic growth factors, such as VEGF, bFGF, IL-6 and IL-8, resulting in a cluster of tumor cells, termed anembolus. Through maintaining cell-cell interactions, the IBC emboli can become resistant to “anoikis”, a cell death process following the loss of contact from their neighboring cells. It is hypothesized that this resistance may allow IBC cells to survive the migration through lymphatic vessels and facilitate development of skin and lymph node metastasis. With current therapy, the disease-free survival for IBC patients is only about 35% (SD Merajver et al. J Clin Oncol. 1997;15(8):2873-81). Clearly better therapy is needed for patients with IBC and insights may be gained from exploration of and subsequent interventions in the roles these growth factors play in the biology of IBC. In this study, we investigated the role of IL-6 in activating the signal transducer and activator of transcription 3 (STAT3), conferring resistance to anoikis, and promoting cell proliferation in IBC SUM-149 tumor spheres. Moreover, we targeted JAK2, a transducer of IL-6 signaling to STAT3, by a small molecule JAK2 inhibitor, LY2784544, to inhibit the IL-6-Stat3 pathway and induce apoptosis in SUM-149 tumor spheres. In brief, SUM-149 cells were grown to form tumor spheres under low adherence culture conditions. IL-6 mediated-Stat3 activation and the induction of the cleavage of PARP were evaluated by Western Blotting. Anoikis and cell viability were measured by calcein-AM accumulation and the expression of IL-6 was examined by RT-PCR. We found that exogenous IL-6 activated STAT3, conferred resistance to anoikis and promoted the cell proliferation in SUM-149 cells under the low adherent culture condition. Furthermore, the expression of IL-6 was increased by 50-fold in IBC tumor spheres as measured by RT-PCR. The autocrine production of IL-6 activated STAT3 and inhibited anoikis- induced apoptosis in SUM-149 tumor spheres. Very importantly, we showed that targeting JAK2 by LY2784544 potently inhibited the phosphorylation of STAT3 in a dose dependent manner with an IC50 of 0.25 µM. Blockage of this signal pathway by LY2784544 resulted in potent induction of apoptosis (EC50=0.49 µM). Taken together, these studies suggest the IL-6-JAK-STAT3 pathway may serve as a molecular signature of IBC and as a potential therapeutic target. LY2784544 is currently in clinical studies for the treatment of myeloid proliferative neoplasm indications and the results reported here support clinical investigation for the treatment of IBC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2820. doi:10.1158/1538-7445.AM2011-2820