Spatial Transcriptomics Characterisation of Radionecrotic Changes in Glioblastoma Patients

Background

IDH-wildtype Glioblastoma (GB) is the most prevalent primary CNS tumour in adults. The standard treatment involves radiotherapy, which can cause radionecrotic changes. Progressive GB and radionecrotic changes can be challenging to differentiate, as they present with similar symptoms and appear alike on MRI. Histopathological examination remains the gold standard of diagnostics. To this date, little is known about the biological mechanisms underlying radionecrotic changes.

Methods

The cohort comprised ten samples from nine patients diagnosed with GB, who underwent first-line standard treatment including surgery, radio- and chemotherapy with temozolomide. Subsequent radiological examination identified tumour progression in all patients, necessitating a second surgery. Based on histopathological examination of the material collected from the second surgery, four patients were diagnosed with tumour recurrence, four manifested with radionecrotic changes, and one patient demonstrated both. The spatial single cell transcriptomics profiling of the samples was conducted using the Xenium platform.

Results

We generated a comprehensive spatial single cell transcriptomics atlas of progressive GB and brain tissue with radionecrotic changes. Tumour cells were detected in samples from both groups. Progressive GB samples contained OPC/NPC-like and proliferating tumour cells with high EGFR expression. In radionecrotic samples, tumour cells exhibited lower EGFR expression even in the presence of gene amplification and did not show proliferation markers. Border-associated macrophages infiltrated the tissue and might have promoted gliosis in radionecrotic samples.

Conclusions

This study delineates a complex spatial architecture of brain tissue with post-treatment changes and its discrepancies from progressive GB, facilitating future research into novel treatment strategies.

Key Points

• A spatial transcriptomics atlas enables comparison of GB and radionecrotic changes.

• GB contains progenitor and proliferating tumour cells with high EGFR expression.

• Radionecrotic changes are linked to infiltrating BAMs and tumour cells with low EGFR levels.

Importance of the Study

Radionecrosis is a delayed treatment effect in patients with GB undergoing radiotherapy. Despite its frequent occurrence, very little is known about the underlying biology and cells involved in the process. This study presents the first spatially-resolved single cell atlas of histologically diagnosed radionecrotic changes compared to progressive GB consisting of 1,189,460 cells across ten samples from nine patients. Most importantly, we detect a high number of tumour cells in samples with radionecrotic changes. However, in contrast to progressive GB, these cells have lower EGFR expression even in the presence of genetic amplification and do not proliferate. Furthermore, tumour cells colocalise with BAMs that release cytokines, which may promote the formation of gliosis in patients with radionecrotic changes of brain tissue. Our study gives valuable insights into cell-cell interactions in radiation necrosis, which can inform future studies aimed at improving treatment strategies for GB patients.