Microenvironmental Cues That Regulate Cancer Cell Dormancy in Estrogen‐Receptor Positive and Triple‐Negative Breast Cancer Cell Lines

ABSTRACT The processes regulating cellular dormancy in tumor cells remain inadequately characterized. Further, there are very few models available that can recapitulate a dormancy‐like phenotype in vitro. In this study, we investigated the role of microenvironmental cues in inducing a dormancy‐like phenotype in estrogen receptor‐positive (MCF‐7) and triple‐negative (MDA‐MB‐231) breast cancer cell lines. We characterized an in vitro model in distinct conditions defined hierarchically by the following: (a) normoxia or true hypoxia, (b) dishes coated with fibronectin or laminin or none, and (c) presence or absence of 10 ng/mL basic fibroblast growth factor (FGF‐2) in the culture medium, added on day 0 of culture. Cells were cultured at clonogenic densities for 9 days (day −1, day 0, up to day +7). Cells were characterized for dormancy‐ like behavior using increased p‐p38 and decreased p‐ERK expression (dormant, p‐p38 High and p‐ERK Low expression), reduced Ki67 expression, elevated p21 and p27 levels by immunofluorescence, absence of senescence using β‐galactosidase staining and resistance to doxorubicin. Fibronectin or laminin were sufficient for the induction of a dormancy‐like phenotype in MCF‐7 cells under hypoxic conditions, whereas the addition of FGF‐2 to fibronectin (but not laminin) could induce a dormancy‐like phenotype under normoxic conditions. FGF‐2 was required with laminin to induce dormancy in MDA‐MB‐231 cells under hypoxic conditions (FGF‐2 plus fibronectin were unable to induce dormancy), whereas laminin or fibronectin alone were sufficient under normoxic conditions. Overall, we established culture conditions that recapitulate an in vitro breast cancer dormancy‐like phenotype and reveal subtype‐specific differences in dormancy regulation.