Macrophages Induce Tamoxifen Resistance in Breast Cancer

ANDRES CASTELLARO, HUGO CEJAS, BEATRIZ L. CAPUTTO, OSCAR PUCCI AND GERMAN A. GIL; CECILIA RODRÍGUEZ; GIL GERMAN

Washigton

Congreso; AACR; 2017

AACR

AbstractBackground: Anti-estrogen adjuvant treatments are the first line of treatment for the management of more than two-thirds of breast cancer patients whose tumors are estrogen receptor positive. Notwithstanding, such strategies need improvement since a significant proportion of patients are initially refractory to anti-estrogen treatments, and most tumors eventually acquire resistance. The tumor microenvironment plays vital roles in cancer but the molecular basis underlying these tumor-promoting effects and the endocrine resistance is not yet fully understood.Methods: Macrophages cells lines coincubated with breast cancer cell lines were used as a model to mimic the inflammatory microenvironment. Tamoxifen resistance in breast cancer cells line was evaluated by proliferation, migration and colony assay. Mouse xenograft model was utilized to confirm these results. To explore the molecular mechanisms involved, cytokine profiles of conditioned media from breast cancer cells lines, Macrophages and the coculture were characterized by an antibody cytokine array. To explore deeper the molecular mechanism implicated, Western Blot, ELISA, ChIP, siRNA and Real Time qPCR assays were utilized. Results:  Our data shows that tumor associated macrophages promote proliferation, migration, invasiveness, and tumor growth of breast cancer cells and render estrogen-dependent breast cancer cells resistant to estrogen withdrawal or treatment with tamoxifen. Macrophages co-cultured with breast cancer cells induce a sustained release of proinflamatory cytokines TNF-α and IL-6 from both cell types, leading to the activation of NF-kB, STAT3 and ERK in the breast cells. Furthermore, this crosstalk between both cell types induces hyperphosphorylation of the estrogen receptor (ER) that render it constitutively active. The formation of a novel NF-kB/STAT3/phospho-ER complex at the Cyclin D1 gene is associated with increased proliferation regardless of the ER ligand status, demonstrating that the tumor microenvironment can rapidly activate proliferative and proinflammatory signaling pathways implicated in endocrine resistance.Conclusions: Our results indicate that the microenvironment formed by macrophages and breast cancer cells profoundly altered both endocrine and inflammatory signaling pathways in breast tumor cells. This microenvironment inducing the continuous release of TNF-α and IL-6 from both cell types, leading to tamoxifen-resistance in breast cancer cells.Keywords: Macrophages, Breast Cancer, Tamoxifen resistance, Endocrine resistance, TNF, IL-6, Estrogen Receptor, NFkB,