Treatment-associated DNA-binding domain missense mutations in the pathogenesis of secondary gliosarcoma.

BACKGROUND

Gliosarcoma is a rare variant of glioblastoma (GBM) that exhibits frequent mutations in and can develop in a secondary fashion after chemoradiation of a primary GBM. Whether temozolomide (TMZ)-induced mutagenesis of the DNA-binding domain (DBD) can drive the pathogenesis of gliosarcoma is unclear.

METHODS

We identified a case of a primary GBM that rapidly progressed into secondary gliosarcoma shortly after chemoradiation was initiated. Bulk tumor was collected and gliomasphere cultures derived from both the pre- and post-treatment tumors. We performed targeted DNA sequencing and transcriptome analyses of the specimens to understand their phylogenetic relationship and identify differentially expressed gene pathways. Gliomaspheres from the primary GBM were treated with TMZ and then analyzed to compare patterns of mutagenesis and .

RESULTS

The pre- and post-treatment tumors shared , , and mutations, but only the secondary gliosarcoma exhibited DBD missense mutations. Two mutations, R110C, and R175H, were identified, each in distinct clones. Both were base transitions characteristic of TMZ mutagenesis. Gene expression analysis identified increased JAK-STAT signaling in the gliosarcoma, together with reduced expression of microRNAs known to regulate epithelial-mesenchymal transition. treatment of the GBM spheres with TMZ generated numerous variants in cancer driver genes, including and , which were mutated in the post-treatment tumor.

CONCLUSIONS

TMZ-induced gain-of-function mutations can have a driving role in secondary gliosarcoma pathogenesis. Analysis of variants identified in TMZ-treated gliomaspheres may have utility in predicting GBM evolutionary trajectories during standard chemoradiation.