In vitro Models of Breast Cancer Metastatic Dormancy

Abstract

Delayed relapses at distant sites are a common clinical observation for certain types of cancers after removal of primary tumor, such as breast and prostate cancer. This evidence has been explained by postulating a long period during which disseminated cancer cells (DCCs) survive in a foreign environment without developing into overt metastasis. Because of the asymptomatic nature of this phenomenon, isolation, and analysis of disseminated dormant cancer cells from clinically disease-free patients is ethically and technically highly problematic and currently these data are largely limited to the bone marrow. That said, detecting, profiling and treating indolent metastatic lesions before the onset of relapse is the imperative. To overcome this major limitation many laboratories developed in vitro models of the metastatic niche for different organs and different types of cancers. In this review we focus specifically on in vitro models designed to study metastatic dormancy of breast cancer cells (BCCs). We provide an overview of the BCCs employed in the different organotypic systems and address the components of the metastatic microenvironment that have been shown to impact on the dormant phenotype: tissue architecture, stromal cells, biochemical environment, oxygen levels, cell density. A brief description of the organ-specific in vitro models for bone, liver, and lung is provided. Finally, we discuss the strategies employed so far for the validation of the different systems.Keywords: cancer dormancy, metastatic dormancy, in vitro models cancer, cancer metastasis, breast cancer, metastasis biology METASTATIC DORMANCYDormancy is an old concept that describes a clinical phenomenon (Klein, 2011; Uhr and Pantel, 2011), i.e., the relapse of a cancer after surgical removal of the primary tumor in a patient considered clinically disease-free for a long time. This implies that cancer cells disseminated prior to surgery and persisted as Minimal Residual Disease (MRD) for a prolonged time (arbitrarily defined, but usually longer than 5 years) before switching to aggressive growth and overt metastasis. The recurrence can be at the primary site (primary tumor dormancy) or at a secondary site (metastatic dormancy). The mechanisms underlying the two types of dormancy are likely to be partially overlapping if involving cell intrinsic genetic/epigenetic mechanisms, or distinct, if dependent on the tissue microenvironment. Clinical dormancy is common for breast, prostate, melanoma, renal, and thyroid cancers, while it is rarely observed in lung and colon cancers (Uhr and Pantel, 2011). In breast cancers, estrogen receptor (ER) status seems to profoundly influence the rate of relapse: ER− patients tend to recur within the first 5 years following primary tumor diagnosis, while ER+ patients have increased risk between 5 and 20 years (Pan et al., 2017;Pantel and Hayes, 2018). While anti-estrogen therapy significantly improved patient outcomes, a significant fraction of them still

The Brain Microenvironment Induces DNMT1 Suppression and Indolence of Metastatic Cancer Cells

“…In some cases, brain metastasis is evident soon after detection of the primary tumor, whereas in other cases, there can be a long period of remission before cancer recurrence and the development of brain metastases, a phenomenon called cancer dormancy ( Sosa et al., 2014 ; Yeh and Ramaswamy, 2015 ). The causes of cancer dormancy and mechanisms of re-awakening are multi-factorial and can include differential interactions with components of the tumor microenvironment, such as endothelial cells and infiltrating leukocytes ( De Cock et al., 2016 ; Ghajar et al., 2013 ; Montagner and Sahai, 2020 ). In the case of brain metastasis, Kienast et al.…”

Technical Advancements for Studying Immune Regulation of Disseminated Dormant Cancer Cells

“…Cell intrinsic programs involve oncogenes and tumor suppressors, membrane proteins (integrins, receptors etc…), intracellular components (such as cytoskeletal proteins and mechanotransducers), signaling pathways and sensors that integrate genetic and microenvironmental inputs and translate them into cellular processes. Cell extrinsic programs include triggers from the niche, such as stromal cells, tissue architecture, biophysical and biochemical cues, as reviewed in ( 24 , 25 ). Intrinsic and extrinsic signals do not act on their own, rather they are nodes and connectors of a complex and dynamic network where extrinsic signals from TME (organ specific or shared) funnel into key intrinsic signaling hubs.…”

“…Another determinant of dormancy/growth signaling is the PI3K/Akt/mTOR axis, whose activation drives survival and exit from dormancy ( 33 – 37 ). Different integrin dimers, often in conjunction with Src, have been consistently linked with survival of DDCCs and/or metastatic outbreak ( 20 , 24 , 38 – 45 ). Several signaling pathways have also been linked so far with quiescence and metastatic fitness: TGFβ and BMP pathways ( 23 , 28 , 29 , 46 – 48 ), canonical and non-canonical Wnt pathway ( 21 , 49 – 51 ), YAP/TAZ ( 41 , 42 ), Notch ( 49 , 52 ), JAK/STAT ( 53 , 54 ).…”

“…Advances in biomaterial technologies, including 3D bioprinting, are fundamental to model TME in vitro ( 131 – 136 ). The use of complex multi-cultures to mimic and perturb metastatic dormancy in vitro has been rapidly expanding, as reviewed in ( 24 ). More recently, the advances in microfluidic technologies are also boosting the development of cancer-on-chip models to better recapitulate multiple parameters of the TME complexity in vitro ( 137 , 138 ) ( Figure 1 ).…”

“…Advancements in biomaterials allow to mimic the natural architecture of human tissues with scaffolds of tunable properties, either of natural (for example Matrigel) or synthetic origin (such as PCL, PLGA or PEG, polycaprolactone, polylactic-co-glycolic acid, polyethylene glycol, respectively) ( 132 , 134 ). 3D scaffolds have been used to study the effects of ECM components and physical tissue properties as well as to dissect interactions between disseminated cells and stromal cells, such as fibroblasts, endothelial cells and macrophages ( 24 , 134 ). Heterotopically implanted 3D hydrogels have been used to recreate artificial metastatic niches in vivo .…”