Interleukin-6 is a Potential Therapeutic Target in Interleukin-6 Dependent Estrogen Receptor-alpha Positive Breast Cancer [patient tumor tissue]

Interleukin-6 (IL-6) is an important growth factor for estrogen receptor-alpha (ERα) positive breast cancer, and elevated serum IL-6 is associated with poor prognosis. We firstly demonstrated that pSTAT3 is the primary downstream IL-6 signaling pathway in ERα-positive breast cancer, using ten different breast cancer cell lines. Three-dimensional cultures of these cell lines were also used to develop a 17-gene IL-6 specific gene signature that could be used to identify IL-6 driven disease. This signature included a variety of genes involved in immune cell function and migration, cell growth and apoptosis, and the tumor microenvironment. To further validate this IL-6 signature, we obtained 36 human ERα-positive breast cancer tumor samples with matched serum for gene expression profiling and determination of an IL-6 pathway activation score (PAS). Patients with high IL-6 PAS were also enriched for elevated serum IL-6 (>=10 pg/ml). We then utilized a murine MCF-7 xenograft model to determine the role of IL-6 in ERα-positive breast cancer and potential anti-IL-6 therapy in vivo. When IL-6 was administered in vivo, MCF-7 cells engrafted without the need for estrogen supplementation. Subsequently, we prophylactically treated mice at MCF-7 engraftment with an anti-IL-6 antibody (siltuximab), fulvestrant or combination therapy. Siltuximab alone was able to blunt MCF-7 engraftment. Similarly, when tumors were allowed to grow to 125 mm3 before treatment, siltuximab alone demonstrated tumor regressions in 90% (9/10) of tumors. Given the established role for IL-6 in ERα+ breast cancer, this data demonstrates the potential for anti-IL-6 therapeutics. Matched formalin-fixed paraffin-embedded (FFPE) tissue and serum from 36 ERα-positive breast tumors were purchased from Asterand USA (Detroit, MI, USA).