Stromal Co-Cultivation for Modeling Breast Cancer Dormancy in the Bone Marrow

Abstract

Cancers metastasize to the bone marrow before primary tumors can be detected. Bone marrow micrometastases are resistant to therapy, and while they are able to remain dormant for decades, they recur steadily and result in incurable metastatic disease. The bone marrow microenvironment maintains the dormancy and chemoresistance of micrometastases through interactions with multiple cell types and through structural and soluble factors. Modeling dormancy in vitro can identify the mechanisms of these interactions. Modeling also identifies mechanisms able to disrupt these interactions or define novel interactions that promote the reawakening of dormant cells. The in vitro modeling of the interactions of cancer cells with various bone marrow elements can generate hypotheses on the mechanisms that control dormancy, treatment resistance and reawakening in vivo. These hypotheses can guide in vivo murine experiments that have high probabilities of succeeding in order to verify in vitro findings while minimizing the use of animals in experiments. This review outlines the existing data on predominant stromal cell types and their use in 2D co-cultures with cancer cells.

Fibroblasts as Turned Agents in Cancer Progression

“…Hence, cancer cells modify primary and bone marrow stroma with which they are in direct contact, as in turn, stroma modify the behavior of primary cancer cells and macro- and micrometastases. The 2D modular co-culture methods we have used can successfully query these interactions using a variety of available methods [ 22 , 134 , 138 ].…”

“…In turn, malignant cells modify normal fibroblasts (NFs), endothelial cells, macrophages, and immune cells that reside in the microenvironment, and recruit and modify additional cells from outside the tumor to promote inflammation, immune suppression, treatment resistance, angiogenesis, invasion, metastasis [ 15 , 16 , 17 ] and the immune microenvironment, which engenders exceptional plasticity in their mission to support cancer progression [ 18 , 19 , 20 , 21 ]. Co-evolution of the cancer with its supporting cellular structures involves coordinate modification of supporting cells by the cancer, by reciprocal effects of modified supporting cells on each other and in turn, their communal effects on cancer cells [ 22 ]. Non-orchestrated, multiple, diverse effects applied by transformed epithelial cells on stromal cells are fostered by the permissive bioenergetic and physical characteristics of solid tumors [ 23 ].…”

Awakening of Dormant Breast Cancer Cells in the Bone Marrow

“…Disseminated tumor cells (DTCs) in the BM interact with a wide array of cell types, proteins, proteoglycans, growth factors and cytokines endemic to the hematopoietic microenvironment, which, together with its biophysical and bioenergetic characteristics, regulate dormancy and participate in reawakening [37]. The BM hematopoietic microenvironment is made up of a complex network of cells consisting of mesenchymal cells of different lineages and degrees of stemness, osteogenic cells, chondrocytes, adipocytes, neuroglial cells, hematopoietic lineage cells, including megakaryocytes and macrophages, cells of the sympathetic nervous system and a network of endothelial cells that include cells lining the sinusoids, arterioles and transition zones [38].…”

“…Ultimately, the scarcity of micrometastases is the most likely reason why the cancer cells' attempts at modifying the niche to promote cancer growth are overwhelmed by the collective suppressive effects of the cellular, structural and soluble factors of the niche [82]. DTCs in the BM interact with a wide array of cell types, proteins, proteoglycans, growth factors and cytokines endemic to the hematopoietic microenvironment, which, together with their biophysical and bioenergetic characteristics, regulate dormancy and eventually participate in reawakening [37].…”

“…Stromal co-cultivation models can use a genetic model of induced senescence by the expression of p27 Kip1 , which is sufficient to recapitulate the senescent phenotype in human cells [284] and induce cancer cell reawakening [283]. In fact, a virtually unlimited number of variable interventions can be introduced in a 2D stromal co-culture to test hypotheses on the reactivation of cancer cells [37]. Stimulation of dormant cells with inflammatory cytokines after being released from FGF-2 stimulation results in the reactivation of dormant cells into growing cells with spindle-like morphology and downregulation of the mesenchymal gene expression pattern in an in vitro model [121].…”