Abstract 3189: Characterization of secretory cues that promote brain metastasis using a microfluidic blood brain niche (BBN) device
Authors: Oliver Christopher Ryan , Westerhof Trisha M. , Yang Benjamin A. , Merrill Nathan M. , Yates Joel A. , Russell Liam , Miller Anna J. , Ulintz Peter J. , Aguilar Carlos A. , Morikawa Aki , Castro Maria G. , Merajver Sofia M. 
Published: June 2022

Abstract
Brain metastases occur in ~ 20% of cancers and are one of the most lethal progression events. The dynamic processes underpinning cancer/tumor microenvironment (TME) interactions are poorly understood. We examined the TME remodeling in response to secretory cues provided by the brain niche components that attract metastatic cancer cells. We identified individual secretions by cell type in the niche. Dkk1 was regulated in response to the brain niche cells exposure to cancer cells; thus, we delineated how Dkk1 modulates the remodeling of the niche and migratory behavior of the cancer cells. We utilized two in vitro microfluidic devices: 1) a blood brain niche (BBN) chip that recapitulates the BBB and brain TME; 2) a migration chip that assesses linear cell migration.
The BBN chip consists of two-chambers separated by a porous membrane. The bottom is filled with human astrocytes or their secretions in collagen to recapitulate the pre-metastatic niche. Endothelial cells (hCMEC/D3) form a barrier on the membrane separating the two chambers. MDA-231-BR extravasate into BBN chips containing astrocytes within 2-Days, develop into micro-metastases after 9-Days, and establish cancer – astrocyte contacts. Providing astrocytic secretions in BBN chips produced similar results. Increased interaction was found between brain seeking clones of MDA-MB-231 and JIMT-1 cells and astrocytes compared to parental cells. Analysis of astrocytic and endothelial secretions detected, amongst others, Dkk-1, that is preferentially elevated in astrocytes when stimulated with MDA-231-BR compared to MDA-231.
The migration chip was utilized to assess the impact of Dkk-1 on cancer cell migration. Dkk-1 gradients are established using passive diffusion, then migration is monitored. Neither 231-BR or 231 increase migration towards a Dkk-1 gradient. Instead, both increase migration when directly stimulated with Dkk-1 and then exposed to an external chemotactic gradient of FBS, indicating cancer exposure to Dkk-1 produced within the BBN may promote cancer cell migration. Strikingly, Dkk-1 neutralization in BBN chips with astrocytes reduces 231-BR extravasation across the BBB, decreases migration within the brain niche space, and disrupts cancer–astrocyte contacts, suggesting Dkk-1 is a critical cytokine that promotes brain metastasis.
Thirty genes were significantly differentially expressed with Dkk-1 stimulation. The top 3, MDA-231-BR expressed genes FGF-13, PLCB1, and MYC are involved in important oncological pathways: Ras, PI3K, MAPK, Wnt suggesting the plasticity of metastatic cancer permits the cells to adapt to the brain TME. An FGF-13 knockdown of the cells showed Dkk1 effects are partially reduced migration in the brain tropic cells in Dkk1 stimulated conditions. We conclude that the cancer response to Dkk-1 is one critical interaction amenable to therapeutics.
Citation Format: Christopher Ryan Oliver, Trisha M. Westerhof, Benjamin A. Yang, Nathan M. Merrill, Joel A. Yates, Liam Russell, Anna J. Miller, Peter J. Ulintz, Carlos A. Aguilar, Aki Morikawa, Maria G. Castro, Sofia M. Merajver. Characterization of secretory cues that promote brain metastasis using a microfluidic blood brain niche (BBN) device [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3189.