Abstract A01: Mechanical properties of matrices strongly influence spontaneous tumor dormancy and responses to chemotherapy in a 3D model of metastasis
Authors: Clark Amanda M. , Wheeler Sarah E. , Young Carissa L. , Neiman Jaclyn Shepard , Pillai Venkateswaran , Stockdale Linda , Stolz Donna , Lauffenburger Douglas A. , Venkataramanan Raman , Griffith Linda G. , Wells Alan 
Published: March 2017

Abstract
Background: Distant metastasis is the major cause of breast cancer (BrCa)-related mortality with half of the disseminated disease emerging clinically after 5 or more years of seeming “cure” of the primary tumor. The lack of relevant accessible model systems for metastasis has hindered our understanding of the molecular basis of metastasis and the development of therapies against these lethal outgrowths. Furthermore, standard culture techniques employ rigid surfaces that are associated with driving even non-transformed cells towards aggressive phenotypes. To address this gap, we previously developed an innovative all-human 3D ex vivo hepatic microphysiological system (MPS) that faithfully reproduces human liver physiology. This MPS also enables spontaneous dormancy in subpopulations of, but not all, BrCa cells. In this study, we query this subpopulation effect by examining matrix stiffness on the occurrence of spontaneous tumor dormancy; we compared a conventional polystyrene material (~3 GPa) to a PEG-based hydrogel biomaterial (~100 kPa) that more closely approaches the malleable physiologic consistency of the liver (~600 Pa). We hypothesized that providing a more physiological environment would promote BrCa dormancy and provide increased protection from chemotherapy as observed in patients, enabling the study of this elusive but critical stage in cancer progression.
Methods: A hepatic all-human MPS was retrofitted with hydrogel scaffolding in place of the standard polystyrene. Hydrogel scaffolds were formed by micromolding with polydimethylsiloxane (PDMS) and UV-initiated free radical polymerization. Prior to polymerization, a SynKRGD peptide sequence was conjugated to PEGDa via Michael-type addition to aid in hepatocyte interaction with the hydrogel. The MPS incorporated de-identified excess primary human hepatocytes and non-parenchymal cells (NPCs) isolated from therapeutic patient liver resections. MDA-MB-231 BrCa cells (RFP labeled) were seeded on day 3 and allowed time to intercalate into the hepatic tissue prior to treatment with chemotherapies on day 7 for 72 h. Proliferation was determined by RFP quantification, Ki67 staining and EdU incorporation. Hepatic tissue function was monitored by protein catabolism (urea), metabolism (glucose, CYP P450) and injury markers (AST, ALT). Multiplex bead-based immunoassays of 77 analytes were used to assess physiologic tissue health, cancer markers and inflammatory signals as well as to discern signaling networks within the metastatic niche.
Results: The use of hydrogels in this system further fostered spontaneous BrCa quiescent dormancy, as indicated by a lower presence of BrCa cells and decreased proliferation. Hepatic tissue in hydrogel scaffolds secreted lower levels of pro-inflammatory analytes and NPCs were more responsive to inflammatory stimuli. As a result, high dose chemotherapy that targets proliferating cells was less effective against BrCa cells within tissues supported by hydrogel scaffolds. Interestingly, proliferation (emergence) of BrCa cells was observed following treatment with the lower doses of chemotherapy. The lower doses may be damaging the hepatic tissue, causing cellular stress and activation of the more responsive NPCs, which in turn secrete signals that promote the outgrowth and emergence of BrCa cells.
Conclusion: These data suggest that using hydrogel scaffolds to more closely align the physiologic and mechanical properties of the macro-environment imparts a healthier hepatic microenvironment. This allowed for interesting insights into the effect of different chemotherapeutic doses on dormant BrCa cells, and highlights this all-human hepatic model of metastasis fitted with hydrogel scaffolds as a critical tool in the assessment and development of therapeutic strategies to target dormant metastatic BrCa.
Citation Format: Amanda M. Clark, Sarah E. Wheeler, Carissa L. Young, Jaclyn Shepard Neiman, Venkateswaran Pillai, Linda Stockdale, Donna Stolz, Douglas A. Lauffenburger, Raman Venkataramanan, Linda G. Griffith, Alan Wells. Mechanical properties of matrices strongly influence spontaneous tumor dormancy and responses to chemotherapy in a 3D model of metastasis. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr A01.