Effect of matrix metalloproteinase‐mediated matrix degradation on glioblastoma cell behavior in 3D PEG‐based hydrogels

Abstract

Glioblastoma (GBM) is the most common and aggressive form of primary brain tumor with median survival of 12 months. To improve clinical outcomes, it is critical to develop in vitro models that support GBM proliferation and invasion for deciphering tumor progression and screening drug candidates. A key hallmark of GBM cells is their extreme invasiveness, a process mediated by matrix metalloproteinase (MMP)-mediated degradation of the extracellular matrix. We recently reported the development of a MMP-degradable, poly(ethylene-glycol)-based hydrogel platform for culturing GBM cells. In the present study, we modulated the percentage of MMP-degradable crosslinks in 3D hydrogels to analyze the effects of MMP-degradability on GBM fates. Using an immortalized GBM cell line (U87) as a model cell type, our results showed that MMP-degradability was not required for supporting GBM proliferation. All hydrogel formulations supported robust GBM proliferation, up to 10 fold after 14 days. However, MMP-degradability was essential for facilitating tumor spreading, and 50% MMP-degradable hydrogels were sufficient to enable both robust tumor cell proliferation and spreading in 3D. The findings of this study highlight the importance of modulating MMP-degradability in engineering 3D in vitro brain cancer models and may be applied for engineering in vitro models for other cancer types.

Shooting for the moon: using tissue-mimetic hydrogels to gain new insight on cancer biology and screen therapeutics

“…In a separate study using the same material platform, but with thiolated hyaluronic acid that can be chemically conjugated to the matrix, the gel stiffness was maintained between 1.2 and 2.0 kPa but the degradability of the matrix was adjusted by varying the ratio of MMP-degradable crosslinker peptide to PEG-di-thiol. [66] They observed that U87 cells in degradable matrices (50% or 100% degradable crosslinker) exhibited a spread morphology and actin-dense structures extending into the surrounding gel, while cells in the non-degradable gels maintained a round morphology. [66] Interestingly, cells in all gels exhibited increased expression of MMP-1 and MMP-9 as well as significantly increased expression of hyaluronic acid synthase 2 compared with pre-encapsulation levels, but the differences in MMP and hyaluronic acid synthase expression between gels of different levels of degradability were not significant.…”

“…[66] They observed that U87 cells in degradable matrices (50% or 100% degradable crosslinker) exhibited a spread morphology and actin-dense structures extending into the surrounding gel, while cells in the non-degradable gels maintained a round morphology. [66] Interestingly, cells in all gels exhibited increased expression of MMP-1 and MMP-9 as well as significantly increased expression of hyaluronic acid synthase 2 compared with pre-encapsulation levels, but the differences in MMP and hyaluronic acid synthase expression between gels of different levels of degradability were not significant. In addition, gene expression levels in these gels, normalized to pre-encapsulated gene expression, were similar to the soft gels of the previous study.…”

Integrating the Glioblastoma Microenvironment Into Engineered Experimental Models

“…Hydrogels are often photo-crosslinked through chain-growth polymerization of acrylates [ 44 , 45 ]. More recently, thiol–ene photoreactions (e.g., between thiol and norbonene groups) have gained popularity [ 163 , 166 ]. Thiol–ene reactions proceed by step-growth polymerization, which yield hydrogels with more defined networks and fewer defects than those produced by chain-growth polymerization [ 170 ].…”

“…To mimic the biochemical composition of the native brain and GBM tumor microenvironment, 3D hydrogel scaffolds have been fabricated from a variety of ECM-derived biopolymers, including HA [ 44–45 , 147 , 163–164 , 172 ], chitosan [ 158 , 165 ] and chondroitin sulfate [ 167 ] polysaccharides, and collagen/gelatin proteins [ 44–45 , 157 , 162 , 167 , 172 ]. As the ECM in the CNS contains high amounts of GAGs and few fibrous proteins like collagen I, many researchers have used HA-based hydrogels to mimic native brain.…”

“…Nonadhesive PEG [ 163 , 166 ] and alginate [ 82 , 165 ] hydrogels have been used as ‘blank slates’ to which bioactive molecules are added. As proteins and peptides naturally contain cysteines, they are often tethered to hydrogel backbones through thiol-based chemistries, such as Michael-type addition [ 158 , 163 , 176 ]. Using this method, a specified number of arms of branched PEG macromers can be modified with bioactive molecules, so that a defined number of arms are left to participate in hydrogel crosslinking [ 176 ].…”