(637h) A Biomimetic Hyaluronic Acid Hydrogel Models Mass Dormancy in Brain Metastatic Breast Cancer Spheroids

Approximately 90% of breast cancer related mortalities are due to metastasis to distant organ sites. Among breast cancer metastasis, breast cancer brain metastasis (BCBM) is highly aggressive with a survival period of only 4-16 months. At the metastatic site, breast cancer cells are capable of evading death by exhibiting either cellular or mass dormancy. However, the mechanisms involved in attaining the dormant phenotype at the metastatic site are not well understood. This is, in part, due to the lack of experimental models to study metastatic site-specific interactions, particularly in the context of BCBM.

To address this need, herein, we developed an in vitro hyaluronic acid (HA) hydrogel-based model to study mass dormancy in BCBM. We utilized HA hydrogels with a stiffness of ~0.4 kPa to mimic the brain extracellular matrix. 10,000 MDA-MB-231Br or BT474Br3 BCBM cells were used to prepare spheroids and were cultured on top of HA hydrogels or in suspension culture for 7 days. We found that the cross-sectional area of spheroids cultured on HA hydrogel remained constant throughout the culture period irrespective of cell type and the ratio of proliferating to dead cells (quantified via Ki67 and nuclear green DCS1 staining) was almost equal to 1 (for MDA-MB-231Br – 0.93 ± 0.05; BT474Br3 – 0.87 ± 0.08), indicative of a mass dormant state. In stark contrast, these spheroids exhibited growth in suspension cultures. We investigated the ratio of % extracellular signal - regulated kinase 1/2 (p-ERK) to % phosphorylated p38 (p-p38) positive cells as low ratio of p-ERK to p-p38 has been reported to be a characteristic of the dormant state. We found that the ratio of % p-ERK to % p-p38 positive cells was significantly lower in HA hydrogels compared to suspension cultures. Further, we demonstrated that HA hydrogel induced mass dormancy was reversible as the transfer of cell spheroids cultured on HA hydrogel for 7 days to suspension cultures resulted in a proliferative phenotype at the end of day 14. Overall, such hydrogel-based models provide useful tools to study microenvironmental regulation of dormancy in BCBM.