Abstract P5-04-08: Modeling breast cancer dormancy
Authors: Wheeler SE , Taylor DP , Clark AM , Borenstein JT , Ebrahimkhani MR , Inman W , Nguyen T , Pillai VC , Prantil-Baun R , Ulrich TA , Venkataramanan R , Lauffenburger DA , Griffith L , Stolz DB , Wells A 
Published: August 2014

Abstract
Most cancer mortality results from distant metastases. The metastatic microenvironment protects ectopic tumors, these nodules are often resistant to agents that eradicate the primary mass. Although significant interventional progress has been made on primary tumors, the lack of relevant accessible model in vitro systems in which to study metastases has plagued metastatic therapeutic development – particularly among micrometastases. One third of women diagnosed with breast cancer (BC) will have metastatic disease which often presents years after a seeming cure from the primary malignancy. An in silico model of micrometastases strongly suggests that these disseminated cells are quiescent, or ‘dormant’, for long periods of time. Current models fail to recapitulate metastatic dormancy, in vivo due to issues of spontaneous metastases and rodent lifespan and in vitro due to the nascent state of organotypic organs or microphysiological systems (MPS). We hypothesize that even the most developed MPS do not allow tumors to attain dormancy due to continued stress signaling from stiff matrices and an artificial microenvironment. We use an innovative all human three dimensional liver MPS to faithfully reproduce human physiology and pathology. In the initial iteration, the liver cells are isolated from therapeutic partial hepatectomies, but as this source may be limiting, we are examining induced pluripotent stem cells (iPSC). Currently these iPSC-derived hepatocyte-like cells demonstrate cyp p450 activity and production of fibrinogen and urea through 15 days in our MPS, albeit at levels below fresh human hepatocytes; optimization protocols are underway.
In the first phase of this work we optimized the flow rate and seeding of hepatocytes with non-parenchymal cells (NPCs) from fresh human liver resections. We found that higher flow rates produced poorer tissue formation and increased stress fibers/actin filaments. We maintained functioning hepatocytes in the MPS through 15 days. Hepatocyte function and injury was measured by urea, lactate, AST, ALT, A1AT, fibrinogen and cyp p450 assays. NPCs survived through the 15 day endpoint with immunofluorescent microscopy visualizing leukocytes, endothelial cells and macrophages. The proliferative MDA MB 231 BC cell line showed preliminary evidence of growth attenuation after 12 days of culture in a subpopulation of cells in our MPS. Luminex cancer panel studies are underway with systems biology modeling to describe a communication network in the early microenvironment of micrometastases.
In parallel we are piloting hydrogel scaffolds that support tissue formation but provide a more physiologic rheology; stiff supporting materials yield an inflammatory phenotype in the NPC which forces even well-differentiated BC cells towards a mesenchymal phenotype. We found that hydrogels support hepatocytes through 15 days and incorporate cancer cells. Micropumps are also being developed by Draper Laboratories to allow for physiologic diurnal variations of hormones and nutrients to liver tissues to accurately assess dormancy and chemotherapy response. The completion of these studies will provide insights into the tumor biology of dormant micrometastases and an accessible tool for testing of therapeutics against metastatic BC in a metabolically competent system.
Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-04-08.