Higher topoisomerase 2 alpha gene transcript levels predict better prognosis in GBM patients receiving temozolomide chemotherapy: identification of temozolomide as a TOP2A inhibitor

Abstract

The search for molecular markers which predict response to chemotherapy is an important aspect of current neuro-oncology research. MGMT promoter methylation is the only proved marker of glioblastoma. The purpose of this study was to assess the effect of topoisomerase expression on glioblastoma survival and study the mechanisms involved. The transcript levels of all isoforms of the topoisomerase family in all grades of diffuse astrocytoma were assessed. A prospective study of patients with glioblastoma treated by a uniform treatment procedure was performed with the objective of correlating outcome with gene expression. The ability of TOP2A enzyme to relax the super coiled plasmid DNA in the presence of temozolomide was evaluated to assess its effect on TOP2A. The temozolomide cyctotoxicity of TOP2A-silenced U251 cells was assessed. The transcript levels of TOP2A, TOP2B, and TOP3A are upregulated significantly in GBM in comparison with lower grades of astrocytoma and normal brain samples. mRNA levels of TOP2A correlated significantly with survival of the patients. Higher TOP2A transcript levels in GBM patients predicted better prognosis (P = 0.043; HR = 0.889). Interestingly, we noted that temozolomide inhibited TOP2A activity in in-vitro enzyme assays. We also noted that siRNA knock down of TOP2A rendered a glioma cell line resistant to temozolomide chemotherapy. We demonstrated for the first time that temozolomide is also a TOP2A inhibitor and established that TOP2A transcript levels determine the chemosensitivity of glioblastoma to temozolomide therapy. Very high levels of TOP2A are a good prognostic indicator in GBM patients receiving temozolomide chemotherapy.

Identification of potential key genes associated with glioblastoma based on the gene expression profile

“…In addition to its roles in DNA synthesis and transcription, and chromosomal segregation during mitosis, Tsavaris et al (43) has reported that TOP2A is also a sensitive and specific marker of actively proliferating cells. In the present study, TOP2A was found to be significantly involved in the prognosis of patients with glioblastoma, which was consistent with numerous previous studies (44–46). NEK2 encodes a serine/threonine-protein kinase, which is involved in mitotic regulation (47).…”

Progranulin reduces insoluble TDP-43 levels, slows down axonal degeneration and prolongs survival in mutant TDP-43 mice

“…Apart from effects on neuroinflammation, effects on DNA damage, which is an emerging disease mechanism in ALS-FTD [ 50 ], could be of interest. Top2a and GRN are upregulated in glioblastomas [ 51 , 52 ] and GRN overexpression was shown to protect against DNA damage induced by the Top2a inhibitor tomozolomide in glioblastoma cell lines [ 52 ].…”

A Fourteen Gene GBM Prognostic Signature Identifies Association of Immune Response Pathway and Mesenchymal Subtype with High Risk Group

“…We have recently demonstrated that temozolomide is a TOP2A inhibitor thus explaining the phenomenon of TOP2A overexpressing tumors being more sensitive to temozolomide chemotherapy with resultant longer survival of patients. Further, down regulation of TOP2A using RNA interference in glioma cells resulted in temozolomide chemosresistance [38]. Unlike these three genes, CALCRL ( Calc itonin r eceptor- l ike), has been shown to activate angiogenesis and was found to be expressed in endothelial cells of microvascular proliferations and in the neighbouring tumor cells of glial tumors [39], [40].…”