P2-11-10: Low Toll-Like Receptor 9 Expression Is Required for the Aggressive Behavior of Triple Negative Breast Cancer Cells in Hypoxia.

Abstract

Abstract Toll-like receptor-9 (TLR9) is a cellular DNA-receptor and a member of the innate immune system which is widely expressed in breast cancers. Although synthetic TLR9-ligands stimulate breast cancer cell invasion in vitro, through down-regulation of tissue inhibitor of matrix metalloproteinase-3 (TIMP-3), the role of this protein in breast or other cancer pathophysiology is unclear. We discovered that low tumor TLR9 expression is associated with a significantly shortened breast cancer specific survival among patients with triple negative tumors, but not among those with ER+ tumors. We further discovered that hypoxia induces TLR9 expression in breast cancer cells in vitro and in vivo. Although the triple negative TLR9 siRNA MDA-MB-231 breast cancer cells (with lower TLR9 expression) were less invasive than control siRNA cells in normoxia, these cells became highly aggressive in hypoxia and they formed significantly larger tumors than corresponding control cells in an orthotopic model in vivo. Further in vitro experiments revealed that the removal of TLR9 expression through siRNA significantly potentiated the hypoxia-induced invasive capacity of the triple negative MDA-MB-231 cells, but not that of the ER+ T47-D cells. Low TLR9 expression in hypoxia resulted also in complete disappearance of TIMP-3 in the MDA-MB-231 cells, but not in the ER+ T47-D cells. Taken together, these studies suggest that low TLR9 expression has different effects on the behavior of triple negative and ER+ breast cancer cells in hypoxia; triple negative cells become more invasive under these conditions, possibly through loss of endogenous invasion inhibitors, such as TIMP-3. Furthermore, these studies suggest that low TLR9 expression in triple negative breast cancers may serve as a novel prognostic factor and help characterize the group of patients that are at a high risk of relapse. Finally, our results suggest that any treatments or factors that lower TLR9 expression or induce hypoxia in residual or metastatic triple negative breast cancer cells, might actually induce their spread. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-11-10.