MRI Elastography Identifies Regions of Extracellular Matrix Reorganization Associated with Shorter Survival in Glioblastoma Patients

Background The biomechanical tissue properties of glioblastoma tumors are heterogeneous, but the molecular mechanisms involved and the biological implications are poorly understood. Here, we combine magnetic resonance elastography (MRE) measurement of tissue stiffness with RNA sequencing of tissue biopsies to explore the molecular characteristics of the stiffness signal. Methods MRE was performed preoperatively in 13 patients with glioblastoma. Navigated biopsies were harvested during surgery and later classified as ‘stiff’ or ‘soft’ according to MRE stiffness measurements (|G*| norm ). Twenty-two biopsies from eight patients were analysed by RNA sequencing. Results The mean whole-tumor stiffness was lower than in normal-appearing white matter. The surgeon’s biopsy stiffness evaluation did not correlate with the MRE measurements, which suggests that they measure different properties. Gene set enrichment analysis of the differentially expressed genes between ‘stiff’ and ‘soft’ biopsies showed that genes involved in extracellular matrix reorganization and cellular adhesion were overexpressed in ‘stiff’ biopsies. Supervised dimensionality reduction identified a gene expression signal separating ‘stiff ‘and ‘soft’ biopsies. Using the NIH Genomic Data Portal, 265 patients with glioblastoma were divided into patients with (n=63) and without (n=202) this gene expression signal. The median survival time of patients with tumors expressing the gene expression signal associated with ‘stiff’ biopsies was 100 days shorter than that of patients not expressing it (360 versus 460 days, hazard ratio: 1.45, P<0.05). Conclusion MRE imaging of glioblastoma can provide non-invasive information on intratumoral heterogeneity. Regions of extracellular matrix reorganization showed an expression signal correlated to shorter survival time in patients with glioblastoma. Importance of the study While the importance of biomechanical forces in glioblastoma is unquestioned, the underlying mechanisms are still not well understood, nor its clinical implications. Several methods exist to assess tissue stiffness, but MRE is unique in allowing measurements of stiffness in vivo and in situ . For the first time, we present molecular profiling of glioblastoma tissue correlated with in situ stiffness measurements. The transcriptomic profiles of ‘stiff’ and ‘soft’ biopsies showed that extracellular matrix reorganization was strongly associated with the ‘stiff’ biopsies, in particular collagen binding. Genes associated with innate immune processes were also upregulated in ‘stiff’ biopsies, indicating that these are active regions of the tumor. The association between gene expression in ‘stiff’ biopsies and survival is in concordance with previous reports of elevated extracellular matrix stiffness increasing glioblastoma aggression. Key Points - MR Elastography can provide unique information on intratumoral heterogeneity preoperatively. - MR Elastography identifies tumor regions of active extracellular reorganization - Gene expression signal associated with increased stiffness negatively correlates with survival