Abstract A01: Mechanical properties of matrices strongly influence spontaneous tumor dormancy and responses to chemotherapy in a 3D model of metastasis

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 netwo