Hydrogels To Study Ecm-Oxygen Gradient Interactions For Sarcoma Cell Migration

Hypoxia is a critical factor in the progression and metastasis of many cancers, including soft tissue sarcomas. Frequently, oxygen (O2) gradients develop in tumors as they grow beyond their vascular supply, leading to heterogeneous areas of O2 depletion. Here, we report the impact of hypoxic O2 gradients and collagen fibers on sarcoma cell invasion and migration. We begun with O2 gradient measurements and found that large sarcoma mouse tumors (>300 mm3) contain a severely hypoxic core [≤0.1% partial pressure of O2 (pO2)] whereas smaller tumors possessed hypoxic gradients throughout the tumor mass (0.1–6% pO2). To analyze tumor invasion, we used O2-controllable hydrogels to recreate the physiopathological O2 levels in vitro. Small tumor grafts encapsulated in the hydrogels revealed increased invasion that was both faster and extended over a longer distance in the hypoxic hydrogels compared with nonhypoxic hydrogels. To model the effect of the O2 gradient accurately, we examined individual sarcoma cells embedded in the O2-controllable hydrogel. We observed that hypoxic gradients guide sarcoma cell motility and matrix remodeling through hypoxia-inducible factor-1α (HIF-1α) activation. We further found that in the hypoxic gradient, individual cells migrate more quickly, across longer distances, and in the direction of increasing O2 tension. Treatment with minoxidil, an inhibitor of hypoxia-induced sarcoma metastasis, abrogated cell migration and matrix remodeling in the hypoxic gradient. Next, we have developed hypoxic hydrogels where we can control collagen fiber density and cross-linking density independently from oxygen gradients. Using this new platform we show that an increase in fiber density in conjunction with the hypoxic oxygen gradient leads to an increase in sarcoma cell migration. This increase in migration speed was also correlated with quicker stress relaxation times of the collagen gel and larger pore size. Using these platforms we are able to create a novel 3D experimental system with control over mechanical properties (crosslinking density, binding sight density, fiber density, stress relaxation time, and stiffness) independently from oxygen concentration. Overall, we show that O2 acts as a 3D physicotactic agent during sarcoma tumor invasion and that this migration is modulated by collagen fiber density and pore size, in the surrounding matrix. We propose the O2-controllable hydrogels as a predictive system to study early stages of the metastatic process and therapeutic targets. Citation Format: Daniel M. Lewis, Sharon Gerecht, T. S. Karin Eisinger-Mathason. Hydrogels to study ECM-oxygen gradient interactions for sarcoma cell migration [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5477. doi:10.1158/1538-7445.AM2017-5477