Abstract 1322: Comparison of brain extracellular matrices in a blood brain barrier organ on a chip model
Authors: Apu Ehsanul Hoque , li Huing , Zhao Victor , Serhan Habib , Morikawa Aki , Lowenstein Pedro R. , Castro Maria G. , Merajver Sofia D. , Oliver Christopher Ryan 
Published: April 2023

Abstract
Recent advances in organ on a chip blood brain barriers (BBB) to study brain metastasis have revealed a critical understanding about the metastatic cascade. Most BBB models utilize collagen as brain parenchyma. While the exact role of the tumor microenvironment (TME) in brain metastasis is poorly understood, it has been observed to influence tumor growth. Therefore, the contents of this space must mimic the human brain composition. The extracellular matrix (ECM) occupies 10–20% of the brain volume to form its microenvironment (BME) and contains large quantities of hyaluronan/hyaluronic acid (HyA). Therefore, although collagen is widely used to mimic BME in vitro we propose that HyA is a more appropriate substrate. In this study using our published blood brain barrier niche on a chip (BBN), we use HyA matrix to evaluate brain metastasis. We compared cancer cell phenotypes, and TME remodeling to prior work using type I collagen. The BBN device has two chambers and a 5 µm microporous membrane sandwiched between them. Human brain microvascular endothelial cells (hCMECs) are seeded over the membrane in the upper chamber. The bottom chamber contains a brain stroma and normal human astrocytes (NHA)s. Cancer cells are added into top chamber and allowed to extravasate into the brain niche. We studied the phenotypic differences of human MDA-MB-231 breast cancer cells and their brain-seeking subclone MDA-MB-231-BRs in between 1:3 HyA:media mixture, and 2% collagen diluted in media for 9 days. Both migratory and phenotypic characteristics of cancer cell lines were measured by volume, shape, and positions in the brain stroma relative to the endothelial barrier. We analyzed sphericity and the distance from the barrier to the final positions on days 2 and 9. Comparing with cells extravasated between the collagen and 1:3 mixtures, all parameters showed marked differences, especially in day 9. In 1:3 samples, more cells were in a single plane near barrier than in the 2% collagen which might be result due to biophysical differences. To study the biophysical variations, matrix responses to oscillatory shear were measured using a rheometer. Briefly, the samples were subjected to a frequency sweep with a maximum strain of 1%. Both storage modulus (G’)/stiffness and loss modulus (G”) were measured in the linear viscoelastic region. We evaluated the stiffness of 1:1, 1:3 HyA:media mixtures, undiluted HyA and 2% collagen. Undiluted HyA was the stiffest, around 60 Pa, followed by 1:1 and 1:3 mixtures, about 5 Pa and 3.5 Pa, respectively. 2% collagen was the softest among the samples, much weaker than 0.01 Pa, shown liquid-like behaviors.In conclusion, due to biological and biophysical differences between matrices, marked variations were observed in cancer cell phenotypes. The data gathered can be used to cover the knowledge gaps about brain metastasis and may indicate the need to consider the efficacy of using the BME mimicking HyA for more realistic findings.
Citation Format: Ehsanul Hoque Apu, Huing li, Victor Zhao, Habib Serhan, Aki Morikawa, Pedro R. Lowenstein, Maria G. Castro, Sofia D. Merajver, Christopher Ryan Oliver. Comparison of brain extracellular matrices in a blood brain barrier organ on a chip model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1322.