Inhibition of ATR opposes glioblastoma invasion through disruption of cytoskeletal networks and integrin internalization via macropinocytosis

BACKGROUND

Glioblastomas have highly infiltrative growth patterns that contribute to recurrence and poor survival. Despite infiltration being a critical therapeutic target, no clinically useful therapies exist that counter glioblastoma invasion. Here, we report that inhibition of ataxia telangiectasia and Rad 3 related kinase (ATR) reduces invasion of glioblastoma cells through dysregulation of cytoskeletal networks and subsequent integrin trafficking.

METHODS

Glioblastoma motility and invasion were assessed in vitro and in vivo in response to ATR inhibition (ATRi) and ATR overexpression using time-lapse microscopy, two orthotopic glioblastoma models, and intravital imaging. Disruption to cytoskeleton networks and endocytic processing were investigated via high-throughput, super-resolution and intravital imaging.

RESULTS

High ATR expression was associated with significantly poorer survival in clinical datasets while histological, protein expression, and spatial transcriptomics using glioblastoma tumor specimens revealed higher ATR expression at infiltrative margins. Pharmacological inhibition with two different compounds and RNAi targeting of ATR opposed the invasion of glioblastoma, whereas overexpression of ATR drove migration. Subsequent investigation revealed that cytoskeletal dysregulation reduced macropinocytotic internalization of integrins at growth-cone-like structures, resulting in a tumor microtube retraction defect. The biological relevance and translational potential of these findings were confirmed using two orthotopic in vivo models of glioblastoma and intravital imaging.

CONCLUSIONS

We demonstrate a novel role for ATR in determining invasion in glioblastoma cells and propose that pharmacological targeting of ATR could have far-reaching clinical benefits beyond radiosensitization.

Glioblastoma extracellular vesicles influence glial cell hyaluronic acid deposition to promote invasiveness

Background

Infiltration of glioblastoma (GBM) throughout the brain leads to its inevitable recurrence following standard-of-care treatments, such as surgical resection, chemo-, and radiotherapy. A deeper understanding of the mechanisms invoked by GBM to infiltrate the brain is needed to develop approaches to contain the disease and reduce recurrence. The aim of this study was to discover mechanisms through which extracellular vesicles (EVs) released by GBM influence the brain microenvironment to facilitate infiltration, and to determine how altered extracellular matrix (ECM) deposition by glial cells might contribute to this.

Methods

CRISPR was used to delete genes, previously established to drive carcinoma invasiveness and EV production, from patient-derived primary and GBM cell lines. We purified and characterized EVs released by these cells, assessed their capacity to foster pro-migratory microenvironments in mouse brain slices, and evaluated the contribution made by astrocyte-derived ECM to this. Finally, we determined how CRISPR-mediated deletion of genes, which we had found to control EV-mediated communication between GBM cells and astrocytes, influenced GBM infiltration when orthotopically injected into CD1-nude mice.

Results

GBM cells expressing a p53 mutant (p53R273H) with established pro-invasive gain-of-function release EVs containing a sialomucin, podocalyxin (PODXL), which encourages astrocytes to deposit ECM with increased levels of hyaluronic acid (HA). This HA-rich ECM, in turn, promotes migration of GBM cells. Consistently, CRISPR-mediated deletion of PODXL opposes infiltration of GBM in vivo.

Conclusions

This work describes several key components of an EV-mediated mechanism though which GBM cells educate astrocytes to support infiltration of the surrounding healthy brain tissue.

Glioma Cell Invasion Is Dependent Upon the DNA Damage Response Kinase ATR

AIMS

Gliomas have high levels of DNA replication stress and clinical trials of inhibitors of the key replication stress response protein ATR (ataxia telangiectasia and rad 3 related protein) as radiosensitisers are planned. We aimed to investigate the effect of ATR inhibition on the ability of glioma cells to infiltrate and invade the brain.

METHOD

Live cell imaging in a panel of primary glioma cultures following siRNA or pharmacological inhibition of ATR. Invasion following treatment of murine orthotopic gliomas was determined by immunohistochemistry. Intravital imaging of GFP expressing murine orthotopic xenografts via an intracranial window model of glioma was undertaken.

RESULTS

Invading margins of human glioma samples demonstrated increased pATR expression relative to core. Live cell imaging demonstrated reduced cell velocity following ATR inhibition (Berzosertib/BAY1895344) or siRNA. Cytoplasmic vacuolation occurred following ATRi or siRNA which were single walled structures which engulf high molecular weight dextran, compatible with blockade of macropinosome processing. Live cell imaging with GFP-integrin α5 and integrin recycling assays showed sequestration of integrins within macropinosomes and reduced integrin cycling. Intravital in vivo imaging of murine xenograft tumours confirmed vacuolation and dextran uptake following ATRi, whilst a further in vivo study demonstrated a reduction in invading tumour cells.

CONCLUSION

We demonstrate a novel role for ATR in facilitating macropinocytic vesicle trafficking and integrin recycling in GBM cells which results in a profound motility defect in vitro and in vivo. ATR inhibitors are entering early phase trials as radiation sensitisers and we propose that therapeutic benefit will extend beyond DNA damage potentiation.