Abstract P2-05-19: Breast cancer dormancy, re-emergence, and treatment
Authors: Beckwitt C , Wheeler SE , Clark AM , Pillai VC , Young CL , Stolz DB , Lauffenburger DA , Venkataramanan R , Griffith LG , Wells A 
Published: May 2016

Abstract
Breast cancer (BrCa) mortality continues to result predominately from distant metastases that can emerge years after successful treatment of the primary disease. Metastatic resistance to agents that eradicate the primary mass is likely due to protection from the metastatic microenvironment and the quiescent state of dormant BrCa cells. Advancements for the treatment of metastatic tumors have been made, but significant progress has been hampered by the lack of relevant model systems, particularly for dormancy. We address this gap with an innovative all-human 3D liver microphysiological system (MPS). The liver is both a major site for BrCa metastasis (and other solid tumors) and the primary site of drug metabolism and limiting toxicities, an important consideration in evaluating cancer therapy efficacy and availability.
Primary hepatocytes and non-parenchymal cells (NPC) from human liver resections were seeded into the MPS. Following tissue formation on day 3, tagged BrCa cells were seeded and allowed a minimum of 4 days to integrate into the tissue before interventions were initiated. On day 7, chemotherapy treatment of micrometastases was initiated for 72h. Cultures were allowed 3 days to recover before the MPS was challenged with inflammatory factors (LPS/EGF) for 48h. BrCa cells were then re-treated with chemotherapy (either the same or alternate therapy) on day 21 for 72h. Hepatocyte function and injury were measured by urea, AST, ALT, A1AT, fibrinogen and CYP P450 assays. BC proliferation was monitored by quantification, Ki67 staining, and EdU incorporation. Communication networks within the metastatic microenvironment during different stages of metastatic BrCa progression were identified using Luminex assays (55 analytes).
The metastatically aggressive MDA-MB-231 BrCa cells demonstrated growth attenuation after 12d of culture in a subpopulation of cells (Ki67-/EdU-). Treatment of BrCa cells with doxorubicin for 72h eradicates the cycling cells, leaving behind a dormant cell population (Ki67-/EdU-) that can be subsequently stimulated to cycle by addition of inflammatory stimuli. A second dose of doxorubicin or cisplatin reduced the BrCa load but did not eradicate the BrCa. Luminex analysis of culture supernatants identified signaling molecules potentially involved in metastatic progression. In addition, we present the use of adjuvant therapy in the MPS to prevent this outgrowth of the dormant tumor cells.
In parallel, we have piloted hydrogel scaffolds that better support tissue formation and produce signals consistent with a healthier liver physiology. Hydrogels enhanced MDA-MB-231 cell entry into dormancy, resulting in reduced efficacy of doxorubicin treatment with greater persistence of tumor load.
The MPS provides a mechanism to close the gap in understanding metastatic dormancy. We demonstrate spontaneous dormancy for the first time in an all-human system and mimicked the dormancy and outgrowth observed in patients. Namely, that dormant BrCa are resistant to chemotherapy and can be stimulated to reemerge following an inflammatory insult. The completion of these studies will provide insights into the tumor biology of metastatic seeding, dormancy, and re-emergence and provide an accessible tool for testing therapeutics against metastatic BrCa in a metabolically competent system capable of evaluating dose-limiting toxicity.
Citation Format: Beckwitt C, Wheeler SE, Clark AM, Pillai VC, Young CL, Stolz DB, Lauffenburger DA, Venkataramanan R, Griffith LG, Wells A. Breast cancer dormancy, re-emergence, and treatment. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-05-19.