Interleukin-6 is a Potential Therapeutic Target in Interleukin-6 Dependent Estrogen Receptor-alpha Positive Breast Cancer [cell lines]

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. Ten ERα-positive breast cancer cell lines, T47D, MDA-MB-134VI, BT474, BT-483, HCC1428, EFM-19, MCF-7, MDA-MB-175-VIIdsRed, MDA-MB-415 and ZR-751, were grown in TME-aligned 3D culture. After establishment, the cells were grown in triplicate for 6 days in the absence or presence of 10 ng/ml IL-6, which was added on day 1. Sampling was performed on days 4, 5, and 6. Five additional conditions were investigated in duplicate: (i) 10 ng/ml IL-6 added on day 0 + 50 μg/ml siltuximab added on day 1 (ii) 10 ng/ml IL-6 added on day 1 + 50 μg/ml siltuximab added on day 1 (iii) 50 μg/ml siltuximab added on day 0 (iv) human marrow stromal cell-conditioned media (hMSC-CM) (v) hMSC-CM + 50 μg/ml siltuximab.