It is well documented that the tumor microenvironment profoundly impacts the etiology and progression of
breast cancer, yet the contribution of the resident microbiome within breast tissue remains poorly understood.
Tumor microenvironmental conditions, such as
hypoxia and dense
tumor stroma, predispose progressive phenotypes and
therapy resistance, however the role of bacteria in this interplay remains uncharacterized. We hypothesized that the effect of individual bacterial secreted molecules on
breast cancer viability and proliferation would be modulated by these
tumor-relevant stressors differentially for cells at varying stages of progression. To test this, we incubated human breast
adenocarcinoma cells (MDA-MB-231, MCF-DCIS.com) and non-malignant breast epithelial cells (MCF-10A) with
N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL), a quorum-sensing molecule from Pseudomonas aeruginosa that regulates bacterial stress responses. This molecule was selected because Pseudomonas was recently characterized as a significant fraction of the breast tissue microbiome and OdDHL is documented to impact mammalian cell viability. After OdDHL treatment, we demonstrated the greatest decrease in viability with the more malignant MDA-MB-231 cells and an intermediate MCF-
DCIS.com (
ductal carcinoma in situ) response. The responses were also culture condition (i.e. microenvironment) dependent. These results contrast the MCF-10A response, which demonstrated no change in viability in any culture condition. We further determined that the observed trends in
breast cancer viability were due to modulation of proliferation for both cell types, as well as the induction of
necrosis for MDA-MB-231 cells in all conditions. Our results provide evidence that bacterial quorum-sensing molecules interact with the host tissue environment to modulate
breast cancer viability and proliferation, and that the effect of OdDHL is dependent on both cell type as well as microenvironment. Understanding the interactions between bacterial signaling molecules and the host tissue environment will allow for future studies that determine the contribution of bacteria to the onset, progression, and
therapy response of
breast cancer.