One of the limited options in obtaining molecular data defining the behavior of these cells is by development of models, initially with a limited number of key components that define the in vivo system. Such models can be expanded subsequently to include additional key components in order to determine their effects on the model and validate the data obtained. Towards understanding basic elements of dormancy, we developed an in vitro model incorporating

three key elements affecting breast cancer cell dormancy in the bone marrow microenvironment [3]. The components of our system consist of estrogen-dependent human breast cancer cell this website lines MCF-7 and T-47D, fibronectin and basic fibroblast growth factor (FGF-2) 10 ng/ml. Estrogen-dependent breast cancer cell lines model estrogen-dependent human tumors, which are likely to remain dormant for extended periods and are least likely to have distant

metastatic recurrences [4–6]. In the clinical setting, recurrent estrogen receptor positive cells continue to be estrogen sensitive and susceptible to hormonal blockade [7, 8]. The second element of our system is fibronectin, a structural protein of the bone marrow microenvironment in physical contact with the dormant cells. Fibronectin is found throughout the bone marrow and particularly in the endosteum where buy C59 wnt homing hematopoietic stem cells have a high affinity [9]. Casein kinase 1 Fibronectin is VX-680 concentration produced in high amounts with a characteristic cellular matrix formation in an extensive network [10] by two types of bone marrow stromal cells, the subendosteal reticulocytes and osteoblasts [11]. Both have functional roles in hematopoiesis, with the latter inducing low

proliferation and high maintenance of early haemopoietic progenitors, while reticulocytes promote proliferation and differentiation in an in vitro co-culture model [11]. Evidence suggests that metastatic breast cancer cells usurp the hematopoietic niche and respond to signals from the stromal elements [12]. Fibronectin is upregulated in this pre-metastatic niche primed to receive metastatic cancer cells [12]. In an in vitro co-culture system, tumor cells binding to bone marrow stromal cells exclusively depended on the fibronectin receptor integrin α5β1 [10]. The third element of our model is basic fibroblast growth factor (FGF-2). FGF-2 is a morphogenic differentiation factor in mammary epithelial cells [13]. It inhibits the proliferation of estrogen-dependent breast cancer cells [14] and promotes their partial re-differentiation [15]. This includes a diminished malignant potential in vitro, including decreased motility and invasion [15, 16] and anchorage independent growth [17] and decreased tumor growth in murine xenografts [16]. Breast cancer cells transfected with FGF-2 also form branching duct-like stuctures in Matrigel [15].