Harley, Brendan A.C.

ABSTRACT Glioblastoma (GBM) is a highly aggressive brain tumor with a five-year survival rate of less than 5%. The current standard of care established 20 years ago includes maximal surgical resection and administration of alkylating agent temozolomide (TMZ). GBM is highly invasive, and GBM cells that evade surgical resection can become resistant to TMZ and develop new aggressive secondary tumors. Post-relapse there are few treatment options available to patients. Tissue engineering approaches suggest the opportunity to develop in vitro models of the GBM tumor microenvironment that may accelerate the discovery of novel therapies for GBM. Here, we report the adaptation of hydrogel microdroplets (microgels) to encapsulate GBM cells in a tailorable 3D matrix to assess patters of growth and to screen TMZ drug response using patient-derived xenograft (PDX) specimens. We exploit a unique aspect of the microgel system to account for the cellular heterogeneity within the tumor microenvironment (TME). We combine cell-laden microgels generated from TMZ-resistant and TMZ responsive variants of the same PDX specimens to create heterogeneous populations with varying levels of drug sensitivity. We demonstrate a range of drug resistance phenotypes as a function of the ratio of TMZ-responsive to resistance cells and identify the population required for TMZ-resistance to overtake take the response. We then investigate the influence of tumor mimetic shifts in hyaluronic acid bioavailability and hypoxia on patterns of TMZ resistance. We show exposure to matrix-bound hyaluronan increases TMZ resistance and the glioma stem cell population in both cell variants. Lastly, we report an increase in TMZ sensitivity but divergent changes in the GSC subfraction for TMZ resistant vs responsive GBM in the presence of hypoxia. Together, we demonstrate the versatility of cell-laden microgel approach to replicate heterogenous tumor populations, model shifts in the tumor microenvironment, and rapidly screen therapeutic response.

Abstract Radiation therapy (RT) has long been included in the treatment of glioblastoma (GBM). However, radioresistance in cancer cells as well as toxicity in normal tissues are major obstacles to clinical efficacy. Improved understanding of the mechanisms of tumor microenvironment-induced radioresistance during and after radiation therapy can provide fundamental insights to improve clinical outcomes in GBM. Here, using three-dimensional engineered hydrogel models in vitro, we report the influence of extracellular matrix, hypoxia, and adjacent neuronal cells in radiotherapeutic sensitivity. We find that mechanical cues and oxygen availability regulate cellular response to radiation, with softer matrices allowing for more DNA damage. Hyaluronan fragments from the extracellular matrix also modulate rapid metabolic response to radiation, especially in hypoxic environments. We show that neuronal networks influence tumor metabolic activity and the inflammatory response. Overall, we demonstrate here that alternative radiation strategies, such as low dose rate radiation therapy and microenvironmental regulation, have the potential to be more effective in a specific subset of radiosensitive GBM tumors.

Abstract Despite extensive advances in cancer research, glioblastoma (GBM) still remains a very locally invasive and thus challenging tumor to treat, with a poor median survival. Tumor cells remodel their microenvironment and utilize extracellular matrix to promote invasion and therapeutic resistance. It is aimed here to determine how GBM cells exploit hyaluronan (HA) to maintain proliferation using ligand‐receptor dependent and ligand‐receptor independent signaling. Tissue engineering approaches are used to recreate the 3D tumor microenvironment in vitro, then analyze shifts in metabolism, hyaluronan secretion, HA molecular weight distribution, as well as hyaluronan synthetic enzymes (HAS) and hyaluronidases (HYAL) activity in an array of patient‐derived xenograft GBM cells. It is revealed that endogenous HA plays a role in mitochondrial respiration and cell proliferation in a tumor subtype‐dependent manner. A tumor‐specific combination treatment of HYAL and HAS inhibitors is proposed to disrupt the HA stabilizing role in GBM cells. Taken together, these data shed light on the dual metabolic and ligand – dependent signaling roles of hyaluronan in glioblastoma.

ATM is a key mediator of radiation response, and pharmacological inhibition of ATM is a rational strategy to radiosensitize tumors. AZD1390 is a brain-penetrant ATM inhibitor and a potent radiosensitizer. This study evaluated the spectrum of radiosensitizing effects and the impact of TP53 mutation status in a panel of IDH1 wild-type (WT) glioblastoma (GBM) patient-derived xenografts (PDXs). AZD1390 suppressed radiation-induced ATM signaling, abrogated G 0 -G 1 arrest, and promoted a proapoptotic response specifically in p53-mutant GBM in vitro. In a preclinical trial using 10 orthotopic GBM models, AZD1390/RT afforded benefit in a cohort of TP53 -mutant tumors but not in TP53 -WT PDXs. In mechanistic studies, increased endogenous DNA damage and constitutive ATM signaling were observed in TP53 -mutant, but not in TP53 -WT, PDXs. In plasmid-based reporter assays, GBM43 ( TP53 -mutant) showed elevated DNA repair capacity compared with that in GBM14 (p53-WT), whereas treatment with AZD1390 specifically suppressed homologous recombination (HR) efficiency, in part, by stalling RAD51 unloading. Furthermore, overexpression of a dominant-negative TP53 (p53DD) construct resulted in enhanced basal ATM signaling, HR activity, and AZD1390-mediated radiosensitization in GBM14. Analyzing RNA-seq data from TCGA showed up-regulation of HR pathway genes in TP53 -mutant human GBM. Together, our results imply that increased basal ATM signaling and enhanced dependence on HR represent a unique susceptibility of TP53 -mutant cells to ATM inhibitor–mediated radiosensitization.

AbstractGlioblastoma (GBM) tumor cells are found in the perivascular niche microenvironment and are believed to associate closely with the brain microvasculature. However, it is largely unknown how the resident cells of the perivascular niche, such as endothelial cells, pericytes, and astrocytes, influence GBM tumor cell behavior and disease progression. A 3D in vitro model of the brain perivascular niche developed by encapsulating brain‐derived endothelial cells, pericytes, and astrocytes in a gelatin hydrogel is described. It is shown that brain perivascular stromal cells, namely pericytes and astrocytes, contribute to vascular architecture and maturation. Cocultures of patient‐derived GBM tumor cells with brain microvascular cells are used to identify a role for pericytes and astrocytes in establishing a perivascular niche environment that modulates GBM cell invasion, proliferation, and therapeutic response. Engineered models provide unique insight regarding the spatial patterning of GBM cell phenotypes in response to a multicellular model of the perivascular niche. Critically, it is shown that engineered perivascular models provide an important resource to evaluate mechanisms by which intercellular interactions modulate GBM tumor cell behavior, drug response, and provide a framework to consider patient‐specific disease phenotypes.

Abstract Biomaterial-based ex vivo models of healthy and diseased brain tissue are among those tools that may help study the complexity of cerebral tissue to better diagnose, prevent, and treat brain diseases. We have established engineered brain tumor biomaterials based on methacrylamide-functionalized gelatin hydrogels and used microfluidic-forming techniques to generate platforms that combine transitions of biophysical and biomolecular properties found in the glioblastoma tumor microenvironment, from the core to the tumor margins (1). Moreover, this biomaterial approach is able to monitor the response of patient-derived xenograft (PDX) cell populations with different molecular signatures; in particular, we have analyzed the amplified and the constitutively activated vIII mutant EGF receptor. We have also characterized PDX response to targeted inhibitors, such as erlotinib, a tyrosine kinase inhibitor that specifically blocks EGFR (2). Patients with glioblastoma (GBM) exhibit poor survival rates, tied both to the significant intra and interpatient heterogeneity of the tumor as well as the complex signaling pathways underlying malignancy. Spatial and temporal gradients regulate cell proliferation, migration, and differentiation during cancer. Therefore, the use of a microfluidic approach to fabricate patterned biomaterials, have the ability to examine transitions between defined environments (e.g., glioma core, periphery and neural tissue). Cells within these structured materials can be fully analyzed by imaging, secretomic and gene expression analyses. Cell morphology evolved to a more spread shape from low to high crosslinking density of gelatin and hypoxic levels depended on cell concentration. Using patient derived GBM tumor samples we are able to generate a miniaturized tumor tissue analog to examine how the heterogeneities within the tumor microenvironment impact glioma malignant phenotype, growth, and therapeutic efficacy. The ability to manipulate tumor extracellular matrix (ECM) can improve therapeutic outcomes and restrict glioma infiltration. Our in vitro tumor model is able to analyze the relationship between HA and the invasive phenotype of GBM tumor cells. We show that cell growth, motility and proteomic responses of GBM cells within our platform were significantly altered by HA molecular weight in response to a tyrosine kinase inhibitor. These results provide additional insights regarding the importance of extracellular microenvironment in the invasive potential of GBM tumors. We have demonstrated that repeated dosing of erlotinib promotes expression of PDGFRb in EGFR vIII mutant cells and that extracellular HA plays a favorable role in the inhibition of EGFR, through STAT3 deactivation (3). (1) Pedron S et al. (2015), Adv. Mater., 27: 1567; (2) Pedron S. et al. (2017), Adv. Healthcare Mater., 6: 1700529; (3) Pedron S, et al. (2019), Biomaterials, 219: 119371. Citation Format: Sara Pedron, Jann N. Sarkaria, Brendan A.C. Harley. Engineered glioblastoma tumor models reveal extracellular matrix signals influence the efficacy of targeted inhibitors [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr PO035.

Abstract 3D biomaterial models have potential to explore the influence of the tumor microenvironment on aberrant signaling pathways and compensatory signals using patient‐derived cells. Glioblastoma (GBM) tumors are highly heterogeneous, with both cell composition and extracellular matrix biophysical factors seen as key regulators of malignant phenotype and treatment outcomes. Amplification, overexpression, and mutation of the epidermal growth factor receptor (EGFR) tyrosine kinase have been identified in 50% of GBM patients. Here, hyaluronic acid (HA) decorated methacrylamide‐functionalized gelatin (GelMA) hydrogels are used to examine the synergies between microenvironmental factors and a model EGFR tyrosine kinase inhibitor (TKI) using patient‐derived xenograft cells. The in vitro behavior of 3 patient‐derived xenografts that reflect a clinically relevant range of EGFR variants is characterized: GBM10 (EGFR, wild type), GBM12 (EGFR+), and GBM6 (EGFRvIII). GelMA hydrogels support xenograft culture; cells remain viable, active, respond to matrix‐immobilized HA, and upregulate genes associated with matrix remodeling and tumor growth. Interestingly, matrix‐immobilized HA alters the response of GBM cells to a model tyrosine kinase inhibitor, erlotinib. While constitutively activated EGFRvIII cells are sensitive to TKI in gelatin hydrogels, hyaluronic acid mediated adhesive signaling interacts with EGFRvIII signaling to increase cell metabolic activity, increase soluble hyaluronic acid synthesis, and modify response to erlotinib exposure.

Abstract Introduction Glioblastoma (GBM) is the most common and lethal form of brain cancer. Poor survival is linked to diffuse infiltration throughout the brain, suggesting the need to examine the effect of the tissue environment at the margins of the GBM tumor on processes of GBM invasion. Further, the presence of GBM cancer stem cells (GSCs) in primary tumor specimens is believe to play a significant role in GBM spreading, recurrence, and therapeutic resistance. While biophysical properties of the tumor microenvironment, such as spatial gradients in matrix stiffness and hyaluronic acid (HA) content as well as regional hypoxia, may affect GBM invasive phenotypes, limited tools are available to rigorously examine the relationship between tissue microenvironment and tumor growth, invasion, and therapeutic outcomes. This work focuses on the integration of HA-functionalized gelatin hydrogels with 3D cell invasion assays to investigate the impact of tissue microenvironment on GBM invasion and GSC population. Methods Hydrogels are generated from methacrylamide functionalized gelatin (GelMA) and methacrylated HA. Prepolymer mixture was crosslinked under UV light in the presence of a photoinitiator. GBM cells, either U87 cell lines or patient-derived xenografts (PDX), were mixed with prepolymer solution prior to polymerization and collected for up to 7 days in culture. To assess invasion, cells were seeded onto dextran beads overnight, with populational invasion metrics calculated after 3 and 7 days, while live cell tracing via confocal microscopy was employed for single cell invasion metrics. Samples were cultured with 5% CO2 and ~20% O2 (normoxia) or 1% O2(hypoxia). Results The invasion of U87 and U87viii (constitutively active EGFR) cells increased significantly in GelMA hydrogels lacking HA, consistent with our previous findings that compensatory secretion of soluble HA in the absence of matrix-bound HA was associated with upregulated invasion. Heightened U87 invasion was observed in the presence of hypoxia for all hydrogel compositions, and was associated with upregualted markers of invasion (gene expression: MMP-2, VEGF; protein expression: ERK1/2) while PI3K was downregulated, suggesting cells respond to hypoxia by alternating invasion and proliferation behaviors. We subsequently examined the effect of matrix biophysical properties and hypoxia on the expansion of GSC populations within PDX cells (a gift of Jann Sarkaria, Mayo Clinic). Here, the expansion of the GSC population in EGFRviii mutant GBM6 was a function of hypoxia as well as matrix-bound HA. Conclusions This work demonstrates that GBM cells respond dynamically to their matrix biophysical (Stiffness, HA content, hypoxia) properties. Using PDX cells, we provide evidence that the expansion of GSC is related with both metabolic environment (O2%) and matrix composition (+/- HA). Ongoing work seeks to understand how GSCs contribute to the invasive phenotype of GBM. Citation Format: Jee-wei E. Chen, Jan C. Lumibao, H Rex Gaskins, Jann N. Sarkaria, Brendan A. Harley. Extracellular matrix stimuli regulate cancer stem cell population and migratory potential in glioblastoma [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 931. doi:10.1158/1538-7445.AM2017-931