Development of a Synthetic, Injectable Hydrogel to Capture Residual Glioblastoma and Glioblastoma Stem-Like Cells with CXCL12-Mediated Chemotaxis.

Glioblastoma (GBM), characterized by high infiltrative capacity, is the most common and deadly type of primary brain tumor in adults. GBM cells, including therapy-resistant glioblastoma stem-like cells (GSCs), invade the healthy brain parenchyma to form secondary tumors even after patients undergo surgical resection and chemoradiotherapy. New techniques are therefore urgently needed to eradicate these residual tumor cells. A thiol-Michael addition injectable hydrogel for compatibility with GBM therapy is previously characterized and optimized. This study aims to develop the hydrogel further to capture GBM/GSCs through CXCL12-mediated chemotaxis. The release kinetics of hydrogel payloads are investigated, migration and invasion assays in response to chemoattractants are performed, and the GBM-hydrogel interactions in vitro are studied. With a novel dual-layer hydrogel platform, it is demonstrated that CXCL12 released from the synthetic hydrogel can induce the migration of U251 GBM cells and GSCs from the extracellular matrix microenvironment and promote invasion into the synthetic hydrogel via amoeboid migration. The survival of GBM cells entrapped deep into the synthetic hydrogel is limited, while live cells near the surface reinforce the hydrogel through fibronectin deposition. This synthetic hydrogel, therefore, demonstrates a promising method to attract and capture migratory GBM cells and GSCs responsive to CXCL12 chemotaxis.

Characterization and structure-property relationships of an injectable thiol-Michael addition hydrogel toward compatibility with glioblastoma therapy.

Glioblastoma multiforme (GBM) is an aggressive primary brain cancer and although patients undergo surgery and chemoradiotherapy, residual cancer cells still migrate to healthy brain tissue and lead to tumor relapse after treatment. New therapeutic strategies are therefore urgently needed to better mitigate this tumor recurrence. To address this need, we envision after surgical removal of the tumor, implantable biomaterials in the resection cavity can treat or collect residual GBM cells for their subsequent eradication. To this end, we systematically characterized a poly(ethylene glycol)-based injectable hydrogel crosslinked via a thiol-Michael addition reaction by tuning its hydration level and aqueous NaHCO3 concentration. The physical and chemical properties of the different formulations were investigated by assessing the strength and stability of the polymer networks and their swelling behavior. The hydrogel biocompatibility was assessed by performing in vitro cytotoxicity assays, immunoassays, and immunocytochemistry to monitor the reactivity of astrocytes cultured on the hydrogel surface over time. These characterization studies revealed key structure-property relationships. Furthermore, the results indicated hydrogels synthesized with 0.175 M NaHCO3 and 50 wt% water content swelled the least, possessed a storage modulus that can withstand high intracranial pressures while avoiding a mechanical mismatch, had a sufficiently crosslinked polymer network, and did not degrade rapidly. This formulation was not cytotoxic to astrocytes and produced minimal immunogenic responses in vitro. These properties suggest this hydrogel formulation is the most optimal for implantation in the resection cavity and compatible toward GBM therapy. STATEMENT OF SIGNIFICANCE: Survival times for glioblastoma patients have not improved significantly over the last several decades, as cancer cells remain after conventional therapies and form secondary tumors. We characterized a biodegradable, injectable hydrogel to reveal structure-property relationships that can be tuned to conform the hydrogel toward glioblastoma therapy. Nine formulations were systematically characterized to optimize the hydrogel based on physical, chemical, and biological compatibility with the glioblastoma microenvironment. This hydrogel can potentially be used for adjuvant therapy to glioblastoma treatment, such as by providing a source of molecular release for therapeutic agents, which will be investigated in future work. The optimized formulation will be developed further to capture and eradicate glioblastoma cells with chemical and physical stimuli in future research.

Bubble Cloud Behavior and Ablation Capacity for Histotripsy Generated from Intrinsic or Artificial Cavitation Nuclei.

The study described here examined the effects of cavitation nuclei characteristics on histotripsy. High-speed optical imaging was used to compare bubble cloud behavior and ablation capacity for histotripsy generated from intrinsic and artificial cavitation nuclei (gas-filled microbubbles, fluid-filled nanocones). Results showed a significant decrease in the cavitation threshold for microbubbles and nanocones compared with intrinsic-nuclei controls, with predictable and well-defined bubble clouds generated in all cases. Red blood cell experiments showed complete ablations for intrinsic and nanocone phantoms, but only partial ablation in microbubble phantoms. Results also revealed a lower rate of ablation in artificial-nuclei phantoms because of reduced bubble expansion (and corresponding decreases in stress and strain). Overall, this study demonstrates the potential of using artificial nuclei to reduce the histotripsy cavitation threshold while highlighting differences in the bubble cloud behavior and ablation capacity that need to be considered in the future development of these approaches.